This dissertation has been microfilmed exactly as received Mic e 1-908
FRITZ, Robert Charles. CERAMIC TECH NOLOGY: A TECHNOLOGICAL RESEARCH AND CURRICULUM ANALYSIS, WITH IMPLICATIONS FOR INDUSTRIAL EDUCA TION.
The Ohio State University, Ph.D., 1960 Education, theory and practice University Microfilms, Inc., Ann Arbor, Michigan CERAMIC TECHNOLOGY
A Technological Research and Curriculum Analysis, with Implications for Industrial Education
DISSERTATION resented ■'n Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
B y
ROBERT CHARLES FRTTZ, A.3., M.A
The 0hJo St^te University I960
Approved by
Department of Education ACKNOWLEDGMENT
The writer Is pleased to express his sincere
appreciation for the counseling and guidance of his
adviser, Dr. Robert M. Reese, and the other members
of h^s committee, Dr. Earl W. Anderson and Dr. Robert
W. Haws, for their constructive aid during the study.
The writer is most grateful to Dr. Ralston Russell, Jr.
for his review of the ceramic technological research
for the study and to the staff of the Ceramic Division
of Battelle Memorial Institute for their constant en
couragement and interest in the study. CONTENTS
PART T
INTRODUCTION
Chapter Page
I. NATURE OF THE DISSERTATION ...... 1
Statement of the Problem ...... C. Assumptions ...... 4 Limitations ...... 6 Methods and Techniques ...... 8 Terminology ...... 10
II. THE FUNCTION OF INDUSTRIAL EDUCATION . . . . 14
General Education ...... 16 Industrial Education...... 17
III. HISTORICAL DEVELOPMENT OF CERAMICS ...... 31
Genesis of Industrial Processes ...... 31 Technological Advancements ...... 40
PART tj
INVESTIGATION OF CERAMIC TECHNOLOGY
TV. THE AMERICAN CERAMIC TECHNOLOGY ...... 45 The Nature of Ceramics...... ^5 Scope of the Industry - Growth ...... 46 Nature of the Ceramic Industry ...... 57
V. ANALYSIS OF THE CERAMTC TECHNOLOGY ...... 70
Ceramic Minerals Analysis ...... 70 Origin and Occurrence of Ceramic Minerals . 83 Properties of Ceramic Materials ...... 92 Rheologlcal Phenomena ...... 100 Physio-Chemical Reaction between Ceramic Materials ...... 105 Classification of Ceramic Materials . . . . 112 11 i 1v
CONTENTS (Continued)
Chapter Page
VT. ANALYSTS OF MANUFACTURING AND PROCESSING. . . . 126
Preparation of Raw Materials...... 126 Composition and Calculation of Ceramic Products...... 129 Preparation of Ceramic Bodies ...... 146
VII. ANALYSTS OF PRODUCTION PROCESSES ...... 177
Forming Methods ...... 177 Drying Products ...... 195 Design Development ...... 199 Decorative Processes ...... 200 Firing and Settings...... 204 Thermal Chemical Reactions...... 221
PART ITT
ORGANIZATION OF THE SUBJECT MATTER
VTTT. CURRICULAR ELEMENTS ...... 243
Scientific Research ...... 245 Analysis of Ceramic Material and Classifications ...... 251 Composition and Preparation of Ceramic Materials...... 254 Ceramic Processes ...... 257 Tests of Ceramic Material and Products . . . 266
PART TV
APPLICATION AND CONCLUSIONS
IX. APPLICATION OF CERAMTC TECHNOLOGY TO INDUSTRIAL EDUCATION...... 279
Implications for Industrial Education .... 28l The Problem: Slip c a s t i n g ...... 283 Recommendations...... 290 CONTENTS (Continued)
Chapter Page
X. SUMMARY AND CONCLUSIONS...... 293
Summary...... 293 Conclusions...... 295
BIBLIOGRAPHY...... 300
AUTOBIOGRAPHY...... 310 LIST OF TABLES
Table Page
I. Statistical Summary of Ceramic Manufacturing in 1956 ...... 53
IT. General Statistics, 1957 55
TIT. Mendeleef's Periodic Table ...... 76
TV. Optical, Crystallographic, and Thermal Properties of Some Clay Minerals ...... 8l
V. World-Wide Composite Analysis of Igneous Rocks. 85
VT. Chemical Composition of Some C l a y s ...... 90
VIT. Classification of Clays as to O r i g i n ...... 113
VTTT. Classification of Clays as to U s e ...... 115
TX. Chemical Analysis of Several F X. Standards for British and American Sieves , . . 130 LIST OF FIGURES Figure Page 1. Comparison of Antique Glass and a Comtemporary Commercially Used Window Glass...... 36 2. Ceramic Product Classification ...... 47 3. Indexes of the Physical Volume of Mineral Production and Population Rise, 1925 to 1958...... 51 4. Upper Operating Temperatures of Commercial Ceramics and Melting Points of Pure Compounds...... 66 5. Analyses of Thermal Curves...... 82 6 . Viscosity: Effect of Pressure on Flow of Liquid and Plastic Paste...... 106 7. Analysis of a Washed North Carolina Residual Kaol 8 . Chemical Analysis of Tennessee Ball Clay. . . . 117 9. Graphical Representation of the Molecular Formulas of Ceramic Glazes...... 142 10. Illustration of Triaxial Blending for Three Glaze Batches...... 145 11. Blending Glaze Slips ...... 147 12. Representative Chemical Analysis of Albany s u p ...... 153 13. Effect of Water Content on Properties of Plaster...... I85 14. Viscosity Curves for a Whiteware Slip Solid Castings are Made at (A) and Drain Castings at ( B ) ...... 189 15. Range of Temperature Instruments...... 209 yi 1 viii LIST OP FIGURES (Continued) Figure Page 16. Single-Component Equilibrium Diagram...... 227 17. Two-Component Equilibrium Diagram ...... 227 18. Equilibrium Diagram of the System A1203 • Si 0 2 ...... 229 19. Standard Method for Testing for Water of Plasticity...... 238 20. Standard Method for Testing Fired Properties of Clay Products...... 239 PART T INTRODUCTION CHAPTER I NATURE OP THE DISSERTATION This dissertation is a technological research and curriculum analysis focused upon the ceramic phase of American technology. It has general reference to tech nology's impact upon man and society, and special refer ence to curriculum development for Industrial Education. Scientific research has changed with explosive force the complex economic system of the United States, particularly in occupations. Technological advancements, giving impetus to the need for technical occupations, have produced changes in the requirements for the training and education of the working force. Consequently, industrial education programs for the technical level have been de veloped in most states to train persons for highly skilled occupations. in recent years, the ceramic industry, with the development of new raw materials, new fabricating processes, and new products, has become one of the major industries 1 In the United States. Through scientific research, man has developed and advanced ceramics toward new horizons. Ceramic materials have become Important to such areas as agriculture, science, transportation, the domestic scene, medicine, electricity and electronics, and national de fense developments. It is evident that as a major industry ceramics should be represented In industrial education. Statement of the Problem Industrial education is dedicated to the postulate that the curriculum Bhould reflect that part of the culture which is technological. Curriculum research for industrial education is needed to keep abreaBt of the technological advances. The curriculum, therefore, should be derived from and be reflective of technology through the utilization of the materials, processes, and tools of industry that are applicable to curriculum development. The ceramic in dustry has inherent within it a wealth of subject matter for curriculum organization. This study Is based upon a working hypothesis derived from the above stated postulate and involves a technological investigation of ceramics and the development of a subject matter outline pertinent to industrial education. The subject matter Is organized so as to be applicable primarily to the secondary and 3 technical levels of educational institutions and to reflect both philosophies represented within industrial education: general education (industrial arts) and vocational edu cation (trade or technical). Quldlng principles are needed to provide a plan for presentation, Tt Is expected that the following principles for the dissertation are clearly Justified by the material gathered and presented within the text of this study: 1. The presentation of a basic philosophical foundation for industrial education should Illustrate Its position in education: general and vocational. 2. The presentation of an investigation of the historical significance of ceramics, Its nature, and techno logical development from 12000 B.C. to the twentieth cen tury should illustrate the role ceramics has played in past civilizations. 3. The presentation of information to Illustrate the relationship between ceramics, a major industry, and the economy of the United States should show the diversity and size of the industry. 4. The presentation of an investigation of techno logical resource material on ceramics In the United States should represent the relationship of the sciences to the ceramic Industry. 4 5. The presentation of curricular elements derived from the technological investigation and interpreted in outline form should facilitate comprehension of the scope of the subject matter. 6 . The presentation of an illustrative instruc tional unit in ceramic technology should be derived from the subject matter outline of selected curricular elements in order to establish a basis for curriculum analysis. The unit should be applicable to industrial education at the technical level through research, experimentation, and the industrial processes of the industry. Assumptions It is assumed throughout the study that the ceramic industry has a definite influence upon the economy and the people; that ceramic technology is advanced by methods of scientific research; and, that there exists within the ceramic technology curricular elements which are applicable to various educational levels. Most of the major industries are represented at the secondary and technical levels; therefore, it is as sumed that, as one of the major industries in the United States, ceramic technology should be represented in the curriculum in a form other then fine arts or engineering. 5 It is assumed that there has developed in the Wilted States a definite need for more highly trained workers. The trend instituted by technological advances and automation has Increased the training requirements for skilled and technical workers with a corresponding de crease in the need for unskilled workers. This trend may be further emphasized by the recent growth of the so-called technical institutes and vocational technical programs of post-high school level. These are definite, organized educational programs for technician training. It is assumed that the schools are institutions organized to disseminate the culture of the society to the young people of the Nation. The education of the indi vidual should include those objectives of general education which pertain to the intangible areas of social living and individual attitudes. The education of the individual should include those areas of individual development neces sary to maintain an equal and participating role In the society. An area assumed to be under the Jurisdiction of the educational institution Is industrial education: in dustrial arts to disseminate knowledge about that part of our culture which is basically technological in the realm of general education; trade or technical, more specific forms of educational service designed to prepare youth and adults for a vocation. 6 Limitations This study is limited to an investigation of se lected scientific and practical elements of ceramic tech nology that are recorded as resource references. The selected curricular elements represent a breadth rather than depth of concentration of the elements of science re lated to ceramics. Ihe elements also represent the mani pulative skills! requisite to the processing of ceramic materials in areas such as forming and preparation of raw materials, which are applicable to that phase of education termed industrial education. An Important limitation is the use of literature In the field of ceramics as a primary source of material for the study. There are many technical books on ceramics at the engineering level, and also hobby or how-to-do-it literature; however, there Is a paucity of material written specifically for technical level programs of train ing. Consequently, the material presented Is limited to ideas discovered through discussion in personal contacts with many ceramic scientists and engineers in the industry, and to those Ideas derived by logical processes from the technological Investigation. Probably the most important limitation for the in vestigation of ceramic technology Is that it has been re stricted to special emphasis on mineral technology, glasses, 7 and coatings (glazes* and vitreous enamels). This is necessary because of the magnitude of the ceramic Industry and the required condensation of the technological research for the dissertation. Although the limitation was neces sary, the technical aspects emphasized for the Investi gation are extensively presented, m a number of instances* however* statements are made as unequivocal which are usually correct although some do have shades of meaning through exceptions. The writer has attempted to qualify such statements* but It was occasionally unavoidable be cause of the need for brevity. The organization of the subject matter, presented in outline form to exemplify ceramic technology, Is limited to the technological investigation and to the presentation of selected curricular elements. The elements of the out line are restricted to specific sub-headings that were de veloped, In sequential order, from the basic fundamental knowledges to the culminating process of testing the properties of ceramic materials and finished products. The study Is further limited to the delineation of the curricular elements into one Illustrative unit of In struction* slip casting* which is applicable to the techni cal level; however* there are implications for other edu cational levels. The instructional unit is extracted from and restricted to, the subject matter outline of the 8 curricular elements and is presented to demonstrate how units may be developed. The unit Is presented as a re search problem in which the student becomes involved in research, in experimentation, and through use of procedures arrives at a solution to the unit problem. The study Is limited to industrial education theories for curriculum development. The technique of Job analysis for the determination of curriculum content for industrial education has been employed in vocational trade and industrial programs. Consideration has been given in this study to the underlying theories of direction and control of the educational processes in determining the content In technical programs through a technological investigation. Methods and Techniques This technological research is not a compilation of factual statistics, but rather it is data selected from bibliographical references: technical, literary, scientific books, periodicals, and scientific writings. An endeavor was made to examine critically the selected data pertaining to ceramic technology and technical In struction. The statements expressed or Implied were ex tracted from the literature and condensed so as to be ap plicable to the scope or limitations of the study. 9 The technical information was written as an over view of selected areas of ceramics; quotations were inter polated to substantiate or express the technical, scien tific, and educational factors. Much of the technical information was obtained from a bibliographical research. The process of classifying and organizing the subject matter components into an outline of curricular elements reduced their number and permitted a more con venient method for interpretation and analysis. Based on the philosophy of industrial education and the selected bibliographical data, an attempt was made to present an organized unit of instruction for the techni cal level. The unit was derived from elements of the sub ject matter, and synthesized into a sequential problematic solution of a unit of instruction utilizing bibliographical research techniques, laboratory experimentation, and ac ceptable standard procedures. The bibliographical data for the study were ob tained primarily from the library facilities of the Battelle Memorial Institute, the American Ceramic Society, and the following libraries of The Ohio State University: Metal lurgy and Ceramic Engineering, Education, Commerce, In dustrial Engineering, and the Main Library. Other publi cations were obtained through Battelle's bulletin distri bution system. 10 Terminology TndustrlalArts Industrial arts is the study of industrial tools, materials, processes, products, and occupations pursued for general education purposes in shops, laboratories, and drafting rooms. Technician Technician is the general term applied to an indi vidual who assists with technical details in a trade or profession. He uses tools, instruments, and/or special devices to design, illustrate, fabricate, maintain, oper ate, and test objects, materials, or equipment. He per forms mathematical and scientific operations reporting on and/or carrying out a prescribed action in relation to them. He examines and evaluates plans, designs, and data; determines action to be taken on the basis of analysis; and assists In determining or interpreting work procedures and maintaining harmonious relations among groups of workers. Vocational Education Vocational education Is specific occupational training. The purpose of the program Is to prepare men and 11 women to earn a livelihood In a socially recognized occu pational field, and 1b usually sponsored cooperatively by the federal, state, and local governments. Trade and Industrial Vocational Education Trade and Industrial education provides Instruction for the development of basic manipulative skills, safety Judgment, technical knowledge, and related occupational information for the purpose of fitting persons for useful employment in trade and industrial pursuits. It Is designed to aid youth and adults to make satisfactory adjustments in their economic and social life. Technical Education Technical education prepares Individuals to enter gainful employment at the technical level, and is extracted from industry, science, and commerce, synthesized and oriented within a curriculum. The content of the currlculm is based on analyses of occupational responsibilities of the technical areas and divided into four major subject matter fields: (l) basic sciences and mathematics; (2) communicative; (3 ) manipulative; and (4) supervisory skills. Technical education Is usually at a post-high school level and of such scope and duration as to suf ficiently qualify individuals for technical employment 12 as defined by Industrial, scientific, and commercial Interests. Industrial Education Industrial education Is the generic term applied to all types of education related to industry, including gener al industrial education (industrial arts), vocational indus trial education (trade and Industrial), and technical edu cation. Ceramics Ceramics are products having a stony, crystalline or glassy character made essentially of clays, rocks, or minerals which are rendered useful by usually firing at high temperatures. Ceramic Technology Ceramic technology is (l) the organization and verification of knowledge which might be applied to the manufacture of ceramic products. (2) The application of scientific principles to the study and manufacture of cerami cs . Ceramic Engineering Ceramic engineering is that field of engineering concerned with industrial ceramic processes; the mining and processing of the nonmetallic minerals and rocks, ex cept fuels and ores as such; the manufacture and appli cation of products made therefrom; and the design and con struction of the necessary structures and equipment for the manufacture of such products. Ceramic Art Ceramic art is the expression of beauty through a ceramic medium by the appropriate choice of line, color, and surface texture for articles intended for use or orna mentation. CHAPTER II THE FUNCTION OF INDUSTRIAL EDUCATION The scientific discoveries of the nineteenth and twentieth centuries, produced in one direction the indus trial Revolution, and in another a deeper insight into the activities and possibilities of the human mind. New views were acquired as to the value and power of education. It was no coincidence that the realization of a need for an educative system to perpetuate a changing culture had originated and kept pace with the growth of the indus trial development which undermined the foundations of the old social and economic order. The Industrial Revolution brought with it the demand for Increased knowledge on the part of those workers whose duty it was to control the new forces ap plied to industry and the changes Introduced into the conditions of labor. The earning of a living by Increased mechanization meant the decreased importance of independent work. Every addition of labor-saving devices confirmed Adam Smiths assertion pertaining to the mental, moral and physical effects of the progress of the division of labor 14 15 upon the majority of the population* About this progress Ware (125, p. 5 ) quotes Smith as saying, The employment of the far greater part of those who live by labour, that is, of the great body of the people, comes to be confined to a very few simple operations; frequently one or two . . . • The man whose whole life is spent in performing a few simple operations, of which the effects too are perhaps always the same, or very nearly the same, has no occasion to exert his understanding, or to exercise his invention, in finding out expedients for removing difficulties which never occur. Every individual should be educated to see himself in relation to his potential in order that he may con tribute to contemporary culture. It may be said that the growth of a national system of education during the nine teenth century was due to two main causes. "On the one hand," Ware states that, "the new conditions of labor threatened the destruction of that *selfdependent power* which may be regarded as one of the chief sources of a nation*s strength." This cause has implications for the general education of all classes of the people. Ware con tinues, "... the application of the new discoveries of science to industry necessitated greater intelligence and wider knowledge than had hitherto sufficed for those at the head of industrial undertakings." This second cause has obvious implications for the special education of those who are to be educated for a trade or profession. 16 General Education General education Is the term that has come to be accepted for the phases of nonspeclallzed and nonvocatlonal learning which should be experienced by all. The knowledge and understanding which general education encompasses are the means to a better personal life and a stronger, freer society; they are not regarded as ends In themselves. A discussion of general education inevitably raises the question, general education for what? Just as inevitably the answer is given that general education should prepare students for life in a free society. It is not general in the meaning of things in general; that is, general edu cation does not take in all encompassed learning but rather restricts itself to certain disciplines and certain fields of knowledge. It is not general in the sense of not being specific; respectable systems of general education do not endeavor simply to inculcate vague generalities. The superior general education system endeavors to lead the students to habits of right reason by showing him the methods for sound judgments and by introducing him to literature and the skills of definite intellectual disci pline. Approaches to general education are in existence which attempt to develop balanced educational programs. It is proposed that general education should contribute to 17 vocational competencies of students by providing the breadth of view and perspective that makes the individual a more effective worker and a more intelligent member of a free society. Industrial Education industrial education is not of recent origin but rather it has an ancestry of many thousands of years. The fifteenth and sixteenth centuries comprised a period in history that resulted in the industrial revolution and the ultimate need for a new type of training and educational program. Up to thiB period the apprenticeship system was adequate and appeared to be the means of providing indus try with capable workers. V’ith the substitution of machine workers rather than craftBmen, it became evident that the apprenticeship system was inadequate to meet the demands of an Industrial nation. The development of the factory system was a major factor in breaking down apprenticeship training and was the strengthening force in perpetuating industrial education. As the general public gradually became aware of the need for technical information and training, manual training became accepted as a function of the school sys tem and as a part of the general education curriculum. As this type of program grew in popularity, there was a 18 tendency to increase the range of courses in order to serve a greater number of students. This tendency to en rich the manual training courses in secondary schools had an important influence on their development, Bennett (6 ) states that it brought about important changes in two directions: the acceptance of manual training within the regular or academic high school; and the development of an enriched technical curriculum resulting in what was called a technical high school. Industrial Arts The influence of industry brought about a new de velopment in education in 1906-1910 which Richard3, Russel and Bonser referred to as "industrial arts," This term implied that all of the old that was good should be re tained but that the point of reference should now be oriented toward industrial processes. Proponents of in dustrial arts were emphasizing general rather than vo cational education. This was advocated by Dewey (31, p. 33) as "learning by doing" in general education through the industrial arts role of disseminating the technical phase of the culture: This means that these occupations in the school shall not be mere practical devices or modes of employment, the gaining of better technical skill as cooks, seamstresses, or carpenters, but active centers of insight into natural materials and 19 processes and points of departure whence children shall be led into a realization of the development of man. The industrial arts approach to education was one of diversification rather than specialization of skills. Many more materials and experiences in basic techniques employed in industry were incorporated into the industrial arts curriculum; in addition the philosophical emphasis was placed upon the transmission of that phase of the culture which is primarily technological in the realm of general education. In his widely quoted definition of industrial arts, Bonser (14, p. 5) emphasized this cul tural phase: The industrial arts are those occupations by which changes are made in the forms of materials to increase their value for human usage. As a subject for educative purposes, industrial arts is a study of the changes made by man in the forms of materials to increase their values, and of the problems of life related to these changes. The late director of industrial Arts at San Jose State College, Heber Sotzin (110) states that the function of industrial arts in the total school program Is an Inte gral part of general education: "it occupies the same re lationship to the schoolfs curriculum as the areas which comprise social studies, health activities, language studies, the fine arts, etc. It does not attempt to de velop skills to earn a livelihood or to train a pupil for a Job!' 20 The effect of Bonser's definition wes national in scope upon the philosophical question of the position of industrial arts in the educational system. Industrial arts is considered and recognized as an Integral part of general education by the majority of educators in the United States, Contemporary programs of industrial arts are characterized as interpreting the complexity of tech nology end the importance of power and its control. With the rapid growth of technology and the subsequent techno logical changes, a change was effected in philosophical emphasis Initiated by William E, Warner and others in 19^7, at the Columbus, Ohio meeting of the American Industrial Arts Association; "The New Industrial Arts Curriculum" was presented. The concepts for this presentation were interpreted from previous statements and publications outlined by Warner and others both in A Prospectus for Industrial Arts In Ohio (77)» published In 193^ and the Federal bulletin, Industrial. Arts: Its Interpretation in American Schools (120), published in 1937. ihe definition was a proposal to identify the principal functions of industrial arts, to Indicate how they should apply at various levels, to de scribe the type of subject matter, to suggest the variety of methods, and to recommend the kind of physical settings needed. 21 The years between 1900 to World War T were years of controversy between those who wanted to Institute "real vocational education" for manual training. The evolution of industrial arts philosophy and Its present position in the educational system of the United States has been stated above. The purpose of the following section is to define that area of industrial education known as "trade and in dustrial, " or vocational training, and to show its develop ment. Trade and Industrial Education An attempt to define trade and industrial edu cation was not officially made until 1937. Two terms, trade and industrial education, and trade and industrial pursuits were used in the SmJth-Hughes Act. The principal provision of the Act related to trade and industrial edu cation was stated by Hawkins et al, (42, p. 3^6), as "the controlling purpose of such education shall be to fit for useful employment," and it "shall be designed to meet the needs of persons over fourteen years of age who are pre paring for a trade and industrial pursuit or who have entered upon the work of a trade and industrial pursuit." The Vocational Education Bulletin No. 1 was revised in 1937. The revision, aB reported by Hawkins et al. was 22 the first official attempt to define the term: "trade and industrial": By 'trade and industrial pursuits' is meant: (1) any occupation which directly functions in the designing, producing, processing, assembling, maintaining, servicing or repairing of any manu factured product; and (2) any public or other service trades or occupations which are not classi fied as agricultural, commercial, professional or homemaking. The vocational aim is to serve the needs of two distinct groups by programs conducted under provisions of the two Acts (l) those who have entered upon and (2) those who are preparing to enter upon the work of various occu pations, These aims have persisted with the original aims as Btated in 1917 to the present day. The major objectives of trade and industrial edu cation are more clearly defined today than originally stated in Smith-Hughes Act, The two major objectives for trade and industrial programs ere stated in Vocational and Practical Arts Education, by Roberts (91» P. 285) as follows: 1, To provide instruction of an extension or supplemental type for the further development of performance skills, technical knowledge, re lated industrial education, safety, and Job Judge ment for persons already employed in trade and in dustrial pursuits. 2. To provide instruction of a preparatory type in the development of basic manipulative skills, safety Judgement, technical knowledge and related industrial information for the purpose of fitting persons for useful employment in trade and indus trial pursuits. 23 Tn order to accomplish these objectives, various programs have been established to serve specific purposes: full-time preparatory, part-time cooperative, pre-employ ment training, apprecticeship instruction, and trade ex tension. Tn general, the purposes of these classified programs are described below. Full-time training is a day school program for in-school youth who have selected a specific occupation. Its purpose is to prepare students for useful employment in a selected occupation and provide an opportunity to continue a general education. The training is given in government approved programs either in trade, industrial or technical type programs usually In the last two years in high school. Part-time cooperative education is designed to provide training in an occupational choice in which the student is employed part-time. During the remaining part of the day the student spends part-time studying related information and the completion of his general education. The program is provided for students In their last one or two years in high school; it is generally not considered apprenticeship training. Pre-employment training is designed for out-of school youth or adults as a short, intensive program. The purpose is for intensive training for entrance into 2k employment In a specific industrial Job, or the retraining of workers for a new position. Apprenticeship training is designed for persons employed as apprentices in trade or industrial occupations. Tts purpose is to provide instruction related to the Job experience for an alloted period of time. Trade extension is designed to provide supplemental instruction and train ing to the respective employment experience for advancement or increased knowledge in a craft or occupation. It is organized for adult workers, including supervisory person nel employed in trade and industrial pursuits. In each type of program there is reflected the re lationship that exists between trade and industrial programs and industrial pursuits. It has been commonly accepted that to meet the objectives of these programs it is necessary that the instruction should be based on an analysis of an occupation or of a particular phase of the occupation. All instructional material should be based on an occupational analysis. The analysis should include an investigation and organization of the occupation and the reducing or dividing of the information into its manipu lative skills and technological details. These skills and details are arranged Into a logical order to satisfy the particular objectives for the course of instruction. 25 A relationship should exist between industrial arts and trade and industrial education. Tt becomes ap parent that an effective industrial arts program is contri butory to a successful trade and industrial program. The first two years of high school in which trade and industrial education usually cannot be taken, permits the students to enroll in industrial arts courses to provide the means for students to discover their abilities, aptitudes and interest and thereby to make a more intelligent selection of their vocation. The section which follows presents the position of the third phase of industrial education— technical edu cation. The discussion is to illustrate the relationship of technical education with the other occupatlons--pro- fessional and trade and industrial. Technical Education The recent technological and industrial develop ment points directly to the need for improved programs of technical education beyond the high school level. Ad vances in such fields as electronics, chemistry* and astro physics are creating shortages of scientists, engineers, technicians, and skilled craftsmen. Tt is estimated that in ten years the number of persons employed in professional and sub-professional technical positions may increase about 40 per cent, and the number employed in managerial 26 and highly skilled Jobs will increase by 25 per cent or more. At the same time, despite an increase in the total labor force, the number of openings for laborers and un skilled workers will continue to decline (11). An analysis of Job description by the Consulting Committee on Vocational-Technical Training (123, p. 22) re vealed that those occupations for which technical training was required could be divided into four classifications. There exists a multitude of Jobs within each of the follow ing groups and many times the training needs are different: 1. Engineering aides and science aides, such as drafting specialists and laboratory technicians, requiring a year or two of preemployment training. 2. The technical specialists or limited tech nicians, such as certain specialized instrument repair men and certain types of inspectors, who can be trained in relatively short preemployment or pre- production courses. 3. The technical production and maintenance supervisors, who must have a background of indus trial or trade experience, plus supplementary technical and foremanship training. 4. The sem4technica1 men, such as salesmen... who must have some technical knowledge of the things they sell; and such as the factory accountant, . . . who must have some technical knowledge of the plant and its products. . . . A seminar group under Robert M. Reese, Director of Trade and Industrial Education Services at The Ohio State University, defined technical education as follows: Technical education prepares individuals to enter gainful employment at the technical level, and is extracted from industry, science, and commerce, synthesized and oriented within a cur riculum. The content of the curriculum shall be 27 based on analyses of occupational responsibilities of the technical areas and divided into four major subject-matter fields: (l) basic sciences and mathematics; (2) communicative; (3) manipulative; and (4) supervisory skills. Technical education shall be at a post-high school level and of such scope end duration as to sufficiently qualify indi viduals for technical employment as defined by Industrial, scientific and commercial Interests. Because of the difficulty of defining technical education adequately, and In order for technical education to expand and develop, some attempt was made to clarify a basic philosophy. Clarification was attempted by the consideration of a number of characteristics of programs as they have been developed to date and are listed in a paper presented by Robert Jacoby (47) at the American Vocational Association Convention in 1957: 1. Technical education must be different from trade education. Trade education is a curriculum designed to prepare for earning a living in a skilled trade. . . . Technical education differs from trade education by emphasizing definite in dustrial applications of laws of science .... 2. Technical education functions most effectively as a program of non-college grade. . . . The place or institution in which technical education is offered is of limited importance as long as the established objectives, principles are not altered .... 3. The nature of the method of instruction in most technical courses must be directed toward de veloping original thinking and diagnosis rather than trial and error application. This neces sitates the laboratory method of teaching rather than the Job or project type or demonstration- analysis or laboratory workbook method .... 4. Technical education offered on a service area basis is sufficiently large to operate efficiently 28 and economically as well as provide a broad and varied curricular program . . . . 5. The technical program can operate as a part of a comprehensive vocational education program en compassing a broad curricular program of technical trade and operational levels • • • the states muBt assume greater responsibility and vision in the development of plans for meeting the needs of all youth and adults for trade and technical education. 6 . More attention must be directed to training in technical occupations for girls and women .... 7* Technical education must be for the able student. One of the most important obligations is to actively recruit and properly guide youth into technical education who can profit from the in struction .... To understand fully the need for technical edu cation, one must be aware of the changes which have evolved in the industrial economy. There has been tremendous industrial growth and continuous increased use of mecha nization, thus requiring labor with technical knowledge to maintain it. In numerous instances, established trades and occupations have disappeared and new and more highly skilled technical fields have emerged. This constant advancement of industrial technology with accompanying new industries, new methods, and new end more complex equipment is placing greater demands upon skilled mechanics and technicians. The economy is based upon a complex and constantly evolving technology; it cannot function without an adequate supply of skilled workers and technicians to keep abreast of the new scientific advances. Therefore, 29 the curriculum planners of post-high school education should be cognizant of the significant facts concerning (l) current occupational, social and educational con ditions and needs of the people of the nation, and (2 ) facilities existing within the nation for serving these needs• This chapter was concerned with the derivation of a statement of position for industrial education as a foundation for the development of a sound educational philosophy. The evolution of industrial education with a discussion of philosophy, objectives, definitions, positioi, and methods was presented. The relationships among the three areas of industrial education: industrial arts, trade and industrial, and technical education were recog nized and stated. Tt is shown that there exists a depen dence of one area upon the other; consequently, trade and industrial education benefits from industrial arts through guidance in that students become acquainted with the same tools, materials and processes. The technical level of training is dependent upon trade and industrial education because there still exists a demand for skilled craftsmen and machine operators to facilitate the technician^ Job. The following chapter is an historical develop ment of ceramics to illustrate the position it has maintained in past civilizations. The study is re stricted primarily to the technology of ceramics and the effect of inventions and discoveries upon its development. CHAPTER TXT HISTORICAL DEVELOPMENT OF CERAMICS The evolutionary and revolutionary implications are presented in order to illustrate the historical im portance of ceramics, and its technological effects upon other industries. The techniques of modem mechanization and developments in research are described chronologically beginning with the basic processes of wheel-work and glass-blowing. Genesis of Industrial Processes Clay and other ceramic materials are made im pervious by fire; thus, early ceramic history is chrono logically based on archeological discoveries of numerous well-preserved clay tablets, jewelry, and pottery. Many times an event was recorded upon them or a way of life depicted pertaining to that particular era of history. The first ceramic materials used in pre-historic times consisted of natural materials indigeneous to the region. It was surmised by Phillips (82, p. 3) that glass was the first natural material used by man, for "glass" is as old as the earth. 31 32 Long before man was able to manufacture glass artificially, he shaped objects by hand from the glasses formed by nature* The commonest of these, obsidian, is of volcanic origin • • • • Objects made from this hard, glassy material have been found all over the world, from Greece to Patagonia, Obsidian became an article of conmerce as early as the Bronze Age and it continued to be used for thousands of years. Morey substantiates Phillip's statement for he also contends that archeological records show that glass has been used by man from the earliest times. Glass, obsidian, apparently was almost a universal natural material located over most of the earth's crust and was used extensively for utensils, weapons, and ultimately works of art. Worked objects of obsidian, Morey reports (70 ), have been found almost everywhere the mineral occurs. Baskets lined with clay were one of man's earliest constructive efforts, according to Carlton Atherton (82 ); this is generally considered to be the first production of ceramic articles. It can only be surmised as to when the first "fired" ceramic article was produced and in what form it existed. The beginning and ultimately the evolution of the ceramic industry has been a rather slow process. Usually, Improvement in materials and processes have been dis covered by the method of trial and error, sometimes ac cidentally attained. While the birth of ceramics Is lost 33 in unrecorded history, it appears to be the oldest recorded major industry. Archeologists acknowledge the probability that civilized history began in the Mediteranean region. The location of the beginning of ceramics can only be surmised because of the incomplete data discovered to date. While claims have been made for Persia and the Near East, Egypt, which is generally recognized as the origin of civilization, may be the birthplace of ceramics. Although the other areas mentioned appear to have been influential in the early history of ceramics, the discovery of glazed stone beads in Egypt believed to date from 12000 B.C. seems to vali date this claim (70). Tt 13 3till questionable, however, as to the exact date in history for the beginning of the production of ceramic articles. New archeological dis coveries often change the calendar of time and place. The quest for answers to the unknown are constantly in progress. Tt was announced in the May 15, I960, issue of the "New York Times," that an expedition to study ancient glassmaking at the site of Sardis in Turkey was to be started this summer. "Among the subjects to be studied," it reported, "are ancient methods of glass production, the components of ancient glass and the phenomenon of irri- descence for which ancient glass is famous." Tt is through 3^ archeological expeditions such as this that the history of civilization is pieced together. The precise dating of ceramic developments is difficult to accomplish because of the paucity of factual information and the apparent independent developments of a similar general nature in diverse cultures. Ceramic developments even in modem times are often disputed as to the date of, and credit for, discoveries and in ventions . Many archeological discoveries, especially in Egypt, give a fairly accurate evolutionary account of the development of early ceramic processes. Unquestion ably, these processes were transported to other civili zations and technically advanced. Glazes are believed to have been used first as a covering on stone beads, and later beads of glass were developed. Preceding these glass beads werefhience beads (neither glass nor stone) which were made of a clay paste fashioned over an axis of thread or other material. The stone beads are those discovered by archeologlsts in Egypt, as stated previously, and are reported to be the first attempt at glazing and the use of glass. Beads made in many sizes, shapes, and kinds of material were reported, according to Lucas (58* P. 33)j to have been found in an Egyptian tomb dating from 1500 B.C., "in the 35 Eighteenth Dynasty tomb of Tut-ankhamun there were thousands of beads of different kinds, calcite, camelian, coloured faience, gold, green, feldspar, opaque coloured glass, lapis lazuli • • ., dark red resin . • , and gilt wood." There Is existing evidence, however, that glazing of small objects began at an earlier date. Glass is defined by D. B. Harden (103, p. 311), as those objects manufactured from molten glass by the various forming processes; he contends that "the manufacture of free-standing glass objects is thought to have begun about 2500 B.C. both In Egypt and in Mesopotamia." Lead and alkaline base glaze recipes are recorded In use as early as the 1700 B.C. Glasses of the period were basic ally lime-soda-slllca type commonly used today. Tn Figure 1, as reported by Morey (70), is a comparison between an analysis of an Egyptian glass from about 1200 B.C. and a modem commercial glass formula for window glass. Tt can be seen that little difference exists between the two glasses. Only in recent years have glasses other than the lime-soda-slllca type been developed, such as borosilicate and lead silicate. The first attempt at mechanization is believed to have been the potters* wheel, although at first it was probably only a pivoted turntable; this is in evidence in paintingB from Egyptian tombs, pieces of turntable, and 36 "thrown" marks on pottery. Evidence of thrown pieces have also been found in other civilizations, such as Antiaue Window G Si02 61.20 72.14 Na20 17.63 12.60 KgO 1.58 MgO 5.14 2.62 CaO 10.05 11.24 A120^ 2.45 1.06 Fe203 0.72 0.15 Mn2C>3 0.47 CuO 0.32 Pig. 1 Comparison of Antique Glass and a Contemporary Commercially Used Window Glass China, India and Japan. Scott (102, p. 389) contends that no archeological evidence has been uncovered as to the ac tual type of wheel construction: We must reconcile ourselves to the fact that, in the absence of archeological finds, we can learn little of the construction and operation of ancient potters' wheels. We can only judge the economy re sulting from the rapid throwing of vessels on the wheel from the elaboration of shapes in the pottery, and from the quantity produced. The methods of 37 throwing in antiquity were, so far as we can Judge from the product, the same as those now used. The discovery and development of glass blowing (about the first century B.C.) was an invention that revo lutionized the glass industry. This development coincided with new technical methods of forming which came after the sand-core technique lost popularity and, as D. B. Harden (103, p. 322) describes this coincidence, was "a major turning-point in the history of glass." His description of the new forming techniques developed is that "There arose new technical methods which combined mould pressing and cold-cutting (tailpiece), and also introduced the 'cane1 technique for elaborate inlay designs and bowls with mosaic patterns." Historically, technical advancements were slow to evolve; ceramic technology was no exception. There was a span of approximately 1500 years from the record of the first glass objects and vessels to the dis covery of the glass-blowing technique, which has remained a basic technique since Roman civilization. The clay processes had slowly evolved from those done by hand, to the use of the potters' wheel, to the production process of terra cotta mold-making which was used by the Greeks between 700-300 B.C. The preparation of clay remained the same for only natural clays were uti lized; however, new decorative techniques and forms were developed by the Greeks during this period. "The seventh 38 century in Greek Art" states Richter (103, p. 259)» "is generally called by archeologists the period of oriental influence, because, after the geometric patterns prevalent in the preceding age, the decoration, in its stylized plant-forms and animal friezes, shows borrowings from Asia Minor, Egypt, and Mesopotamia." Few examples of enameling are known before the Greek enamels of about the sixth or fifth centuries B.C. All enameling was fired on the base metals of gold, silver, copper, bronze; iron end other metals were not enameled until modem times. The composition of early enamel as reported by Maryon (103, p. 458), was generally a soft glass compound of flint or sand (50 per cent), red lead (35 per cent), and soda or potash (15 per cent). It is surmised that in the early days of enameling it is likely that the goldsmith and glassblower worked together to develop the process. In Enamels. Andrews (3) states, "The enamels developed in this period are classified Into two groups, cloisonn^ and champlev£, depending on their method of fabrication." Tt was during the fifth century B.C., at the end of the Greek domination and the beginning of the Roman Empire, that various developments in ceramic processes were also taking place. Construction and design princi ples of dryers and kilns were becoming recognized, saggers 39 were conceived, stilts for glazed pieces were uti lized. During the time of the Roman Empire, processed building materials came into use after the first century B.C. One of the most important products was a volcanic earth which when mixed with lime formed a useful cement. This cement, called "pozzolana," sets hard in water and has fire-resistant qualities (103), "Prom the first century B.C. onwards," Briggs states (103, p. 410), "the commonest building material in Rome was concrete, not only for walling and foundations but for the vaults and domes which formed the finest achievement of later Roman architecture." It was also during this period that fired bricks and tiles were used rather than sun-dried bricks. Porcelain, possibly the most important ceramic development credited to the Chinese, occurred in approxi mately the second century B.C. The Chinese attained a state of artistic perfection in porcelain and glazes, which in some instances cannot be reproduced today. It was the Chinese porcelain which stimulated the search to produce whitewares in Europe and eventually led to the application of vitreous whitewares both in the home and in Industry. Pew advancements were made during the so-called Dark Ages— approximately 476 A.D.-1450 A.D.; however, 40 there existed a period of continued production of glass in the near and pottery in the Par East, Eventually, the glass Industry found its way to Venice and it developed into a major center for glass manufacture, Morey (70, p, 20) describes the Venetian glass development as follows: Probably as an indirect result of the Crusades and of the fall of the Eastern Empire, glass manu facture in Venice entered a period of development about the beginning of the eleventh century which soon made that city the center of the glass in dustry, which dominant position it maintained for at least four centuries. Technological Advancements New developments in ceramics started with the re awakening of Europe and the beginning of the Industrial Revolution, The discovery of porcelain in Germany, the production of purer raw materials, a better understanding of the chemistry of ceramics, all were influential in the development of mass production techniques, such as the technique of mold-making, and utilization of plaster of Paris. In the glass industry, optical glass was dis covered and grinding methods perfected in the early eighteenth century. Sheet glass evolved from crown glass (a blowing and flattening process) to the casting and grinding of plate glass. 4l The development of ceramics In the late nineteenth and early twentieth centuries in the United States Is typical of the technological advances of the Industrial Revolution. The accumulation of scientific knowledge, the discoveries of new sources of energy, and the invention of machinery led to new horizons for ceramic technology. The changes In the ceramic industry were caused by new de mands upon the industry as well as changes in materials and production techniques. Ceramics became important to other areas of manufacturing, such as the chemical, elec trical and metallurgical industries. The major changes that occurred can be briefly described as an extension of the use of ceramics: an improvement in the quality and quantity of existing manufactures; a new range of products; and the new, improved methods of manufacture. The dependence of one industry upon another can be illustrated with the advancements made in the enameling industry. Andrews (3, p. 7) describes this relationship as, "The chemical industry began to appreciate the market the enameler offered, and catered to his requirements. The steel industry made great strides in the development of better enameling irons." Greater demands upon the enamel ing industry were made as better application and diversifi cation of products were developed. Andrews reports that various improvements were initiated to meet the needs of 42 the enameling Industry, "The technique of sand blasting, cleaning, pickling, application, and firing was greatly Improved. The continuous enameling furnace, automatic control, continuous conveyors, and mass production re sulted from the increased demand." Although the glass industry before 1900 was not appreciably different from that of the preceding 1500 years; in the early 1900*s, the old methods were beginning to be replaced by chemical control and mechanical methods of manufacture. Today, the glass industry Is almost en tirely mechanized. Morey (70, p. 26) mentions that World War T gave Impetus to developments In the glass Industry especially in optical glass which led to improvements In technical processes and methods, and an Increase in fundamental scientific knowledge of glass technology. He elaborates further on the latter development as follows: Partly as the result of war-time necessity, and partly as the result of the appreciation by the glass manufacturers that the soundest foundation for a strong industry is the understanding of its funda mental scientific principles, there have been pub lished extensive and thorough studies of the relation between the composition and physical properties of all kinds of glass. Studies of phase equilibrium relations in glass-forming systems have given us an understanding of why glass can be manufactured and worked, and of what the chemical relationships are that set limits to the composition of matter ob tainable as glass. The above statement has implications for a ll phases of ceramics; in particular, increased scientific knowledge and the dissemination of this knowledge has effected tremendous advancements in glass technology. With the increased scien tific knowledge, new developments in design and construction of machinery were needed. Phillips (82) mentions several mechanical processes de veloped for continuous production in such areas as sheet glass, bottle manufacture, light bulbs, pressed glassware. Probably the greatest demand made upon the ceramic industry has been in the field of refractories. It limits many developments in ceramics as well as other In dustries because all high-temperature industries are dependent upon refractory material in one form or another. Emery, a natural occurring abrasive, was the only grinding material available for centuries. This industry was revolutionized by the discovery in the late nineteenth century of silicon carbide, a man-made abrasive. Silicon carbide and succeeding developments and discoveries of other abrasives are controlled processes in the manu facture of a material approaching the degree of hardness of a diamond. New discoveries, improvements of existing pro cesses, and the accumulation of scientific knowledge expe dite the advancement of ceramics in many new fields, such 44 as nuclear refractories* Scientific researches In the ceramic industiy have been focused upon the nature of the raw materials used, the factors of control In manufactur ing, and the development of methods of measurement. Although ceramics has been an Important part of past civilizations. It was not until the beginning of the twentieth century that great technological advancements were made in the ceramic Industry. The reasons for this relatively slow technical progress may be briefly sum marized: (l) The study of thermo-chemical reactions is comparatively difficult without adequate means of measure ment and controls, as a result, the methods and knowledge have been slow to evolve. (2) The development of knowl edge has been limited in the fields of colloidal and physi cal chemistry. (3 ) The physico-chemical systems involved are complex and many factors Influence the end results. (4) Changes from old processing methods to modernization were not rapidly effected. The following chapter is an investigation of the contemporary ceramic Industry in the United States. The scope of the industry, the size, and implications for the future, as well as uses for ceramics in industry, the home, national defense, and science are presented. PART TX INVESTIGATION OP CERAMIC TECHNOLOGY CHAPTER IV THE AMERICAN CERAMIC TECHNOLOGY When one considers that Ceramic Technology Is a subject that pertains to several closely integrated sciences and applied sciences, It can readily be seen that research in the field could Include the sciences of chemistry, physics, mineralogy, and geology; and In the field of applied science— ceramics, engineering, and agriculture. A consideration of structure, physical properties, origin, and occurrence of ceramic minerals is essential to an understanding of the technology. The Nature of Ceramics Ceramic products are of very ancient origin and are comprised of a great variety of products for indus trial and domestic application. The products may be purely artistic or functional in character, or they may Incorporate both attributes. Since the meaning of "ce ramics" is so poorly understood, and possibly meaning less to many, it Is appropriate that the definitions in 45 Chapter I be reviewed. Generally speaking, ceramic products are manufactured from nonmetalllc, inorganic raw materials during which process high temperature treatment is usually Involved. The field of ceramics offers a diversity of oppor tunity for exploration, and it is stimulating enough to maintain a continual attraction by the very fact that crude minerals can be transformed by ceramic manufacturing pro cesses into products of permanence, utility and beauty. The variety of mineral combinations, the many feasible methods of processing, and the diverse current and possi ble future applications for ceramic products, Insures a continuing interest whether it is in research, development, education, product design, equipment, raw material process ing, purchasing, production control, testing, distribution, sales, or management. The diversity is comprehensible when the scope of the industry and its classification of products are observed in Figure 2 and the following section on the scope of the industry is reviewed. Scope of the Industry - Growth Ceramic products have been loosely classified as regards raw materials, fabrication methods, character of product, and ware utility. Although it is difficult if not impossible to avoid some overlapping in classifying Structural Ceramics Glass Brick - paving, common Household and art glass, structural Tile - facing, structural, drain, Lighting, electrical, optical, photo roof, wall, floor sensitive Terra Cotta Fiber, mechanical, chemical Insulation - acoustical, thermal Container (bottles) Structural - glass, porcelain enamel Ceramic glazes Flue lining Vitreous enamels Refractories Agricultural frits Fireclays Abrasives and Ceramic Tools and Dies Refractory mortars Silicon carbide Silica, aluminous, chromite, magnesia, Aluminous zirconla, mullite, kyanite & Silica and porcelain sellimanite Insulating Cements. Lime, and Gypsum Portland cement Cermets Calcium alumlnate cement Refractory ceramic coating Magnesia, silicate, dental cements Special oxide, carbide, nitride, etc. Special cements Carbon and graphite Building, agricultural, and chemical lime Whltewares Calcined gypsum products Porcelain, chine, semi-vltreous ware, Miscellaneous earthenware, stoneware, etc. Cermets Nuclear ceramics Cerganlcs Semi-conductors and resistors Slag and rock wool Electrical insulation and dielectrics Chemical wares Mineral-glass composites Filtering media Asbestos products Synthetic gems Vitreous Enamels Household Sanitary, medical, chemical, electrical Refractory coatings Structural, advertising ware and signs 4=- Source: Derived from Wilson, Ceramics: Clay Technology. Fig. 2 Ceramic Product Classification 48 products, the modification of Wilson's (130# P» 2) classi- flcatlon as presented in Figure 2 should he satisfactory for the purpose of this research. Hie figure clearly indi cates the extensive scope and diversity of the ceramic field. It is of further interest to review seven of the general methods of manufacture: 1. Those products which are molded in the aqueous plastic condition and which derive their strength from the partial fusion of silicate at high temperatures: structural, whlteware, and refractory. 2. Those products which are heated until they become fluid and are molded in the viscous liquid state. The final strength obtained from cooling: glass. 3. Those pulverized products in which raw materials acquire a latent cementitious property by heating the addition of water: cements, plasters, and limes. 4. Those raw materials which, sometimes after fusion of sintering and crystallization, are crushed or pulverized and graded into specified grain sizes: abrasives. 5. Those minerals which, after mining in massive form, are cut, machined, or shaped Into useful products: insulation and dlatomaceous earth. 6. Those raw materials or compositions which are applied as coatings to ceramic or metal articles and heated to fuse or sinter the coat ings: glazes and vitrified enamels. 7. Those large crystals which are grown from an aqueous solution, from fused powder, by solid state reaction, or by other me^ns: synthetic gems, mica, and other crystals. 49 It Is impossible to define accurately the size of the ceramic industry in the United States. The difficulty is in assembling complete factual data because of the dis agreement as to which borderline products are ceramic. For the purposes of a statistical analysis, it is evident that the first requirement is a set of well-defined limits for inclusion and exclusion of various branches for collecting data on only ceramic industries. After a survey of the literature it was found that the Research Committee of the American Ceramic Society (87, P. 536) adopted a definition previously reported in 1920, by the Committee on Definition of the Term "Ceramics": In general, the usage of the term by the Greeks may be said to involve two characteristic elements. First and primarily, a product in whose manufacture a high-temperature treatment is involved; and second and secondarily, a product customarily manufactured entirely or chiefly from raw materials of an earthy (as dis tinguished from metallic, organic, and so forth) nature. Tt is also clear that it is these very elements which characterize the significance of the term "ceramics" as it has come to be employed by the American Ceramic Society. In accordance with this definition, ceramics in dustries may be properly defined and described as those industries which manufacture products by the action of heat on raw materials, most of which are of an earthy nature, while the constituents of these raw materials, the chemical element silicon together with its oxide and the compounds occupies a predominant position. The importance of the ceramic industry to everyday living, as well as to other areas of industry, becomes in creasingly obvious after surveying the role ceramic products 50 have played in the economy of the United States, In ad dition to the number of ceramic products observed in the home and used daily, it is learned that all metal pro ducts are made possible because of ceramic refractories; and, that the distribution and consumption of electricity for lighting, power, heat end the tremendous electronic applications are possible because of porcelain electrical insulators. The operation of the internal combustion engine in the automobile and Jet engines in aircraft re quires the use of ceramic insulation of the spark plug and ceramic metal coatings. Many of the highways and buildings are constricted primarily with cement, bricks, glass, and other ceramic structural materials. Through a presentation of e statistical survey, it can be seen that the ceramic industry is an influential segment of the economy in the United States. A number of interesting statistics for ceramic and other industries are included in the accompanying tables and figures. For example, Figure 3 is r composite of the indexes from the Bureau of Mines between 1925 and 1958, of all minerals, non-minerals, metals, and the population index from a Deem and Sullivan (26) publication for approximately the same years. Economists use the indexes for estimating future population growth in relation to projected production and consumption of products. Total mineral production in 1957 200 200 160 (20 120 J-— /930 f9SS M O M M S S /ISO HSO MSS' Source: U. S._. Department_ . of __Commerce, - Commerce, Statistical. Abstract of the United States, 1959 Fig, 3 Indexes of the Physical Volume of Mineral Production and Population Rise, 1925 to 1958 52 was 18.1 billion dollars, as compared to 10.6 billion in 1949, and 13.4 billion in 1952. Table I, derived from a statistical survey by S. M. Swain _gt al. (114), has been assembled to show the size and scope of the ceramic industry. According to the survey, the listed ceramic industries constitute a value of shipped products of approximately six and one-half billion dollars. Excluded from the survey are data on raw materials, concrete, cut stone and asbestos products which are related to the ce ramic industry but not to the manufacture of products. Several other groups, although connected with the industry but not with manufacturing, were not included— such as de sign, administration, sales, and research. Disregarding allied products which may or may not be termed "ceramic" there were in 1956 approximately 4,768 ceramic plants which employed three or more people each, with a total of 442,114 employees. Glass manufacturing is the largest segment of the ceramic industry, involving approximately 38 per cent of the total products shipped. It may be noted that Table IT, derived from statis tics by the United States Bureau of Census, lists the total for Stone, Clay, and Glass Products at approximately 4.8 billions. Although there appears to be a difference between the total value of products shipped for ceramic manufacture as shown in Tables I and II, there exists the factor of TABLE T STATISTICAL SUMMARY OP CERAMIC MANUFACTURING IN 1236 All Production Value of Product* Industry Establishments Employees Workers Shipped CERAMIC ABRASIVES Ceramic Abrasives 219 17,385 11,973 $ 306,666,000 CERAMIC MINERAL PREPARATION Minerals, Ground & Treated 353 8,59^ 7,183 194,891,000 GIASS Glass Containers 85 51,754 46,256 758,092,000 Flat Glass 32 26,628 23,332 467,275,000 Pressed & Blown Glass, n.e.c. 287 45,006 37,677 476,446,000 Products of Purchased Glass 859 24,215 20,157 449,169,000 Mineral Wool 85 11,645 9,113 197,606,000 Totals 1,348 159,248 136,535 2,348,588,000 LIME, CEMENT, AND GYPSUM Cement, Hydraulic 162 41,429 35,809 997,007,000 Gypsum Products 90 12,388 10,419 324,983,000 Lime 145 8.344 LJ 1 3 S 150,169,000 Totals 397 62,161 53,367 1,472,159,000 REFRACTORIES Clay Refractories 177 17,810 15,436 232,780,000 Nonclay Refractories 77 10,770 9,129 210,692,000 Asbestos Heat Insulation 71 3,976 3,056 49,961,000 Misc. Refractory Materials 53 2,078 _ 1,729 26.872.000 Totals 378 34,634 29,350 520,305,000 TABIB I (Continued) Industry Establishments All Production Value of Products Employees Workers Shipped STRUCTURAL CLAY PRODUCTS Brick and Hollow Tile 610 35,288 31,670 $ 284,482,000 Sewer Pipe 66 9,904 8,765;, 90,874,000 Struc. Clay Prod, n.e.c. 151 5.022 4,2962 53,2*5,00° Totals 827 50,214 M , 7 3 1 428,701,000 VITREOUS ENAMELED WARE Plumbing Fixtures 151 14,270 11,884 225,280,000 Enameled Products 51 7,168 5,946 73,507,000 Stove Parts 42 3,643 2,709 61,575,000 Refrigerator Parts 15 3,519 2,684 52,938,0002 Washing Machine Parts 4 1,862 1,456 52,234,000 Elect. Appliance Parts 14 2,185 1, 7.75 _ 37,949,000 Totals 277 32,647 26,454 503,483,000 WHITE WARES Earthenware Food Utensils 47 12,470 11,502 69,307,000 Porcelain Electrical Supplies 45 10,347 8,813 99,403,000 Vitreous Plumbing Fixtures 37 11,365 9,822 162,978,000 Carbon and Graphite Products 9,999 7,989 178,388,000 Vitreous China Food Utensils 8,306 7,308 49,214,000 Floor and Wall Tile 49f 13,129 11,248 126,518,000 Pottery Products, n.e.c. 654 11,118 9 ,958. 68,455,000 China Decorating for the Trade 50 497 ... A37s 3j 779j OO° Totals 969 77,231 67,077 758,042,000 GRAND TOTALS FOR THE UNITED STATES 4,768 442,114 376,670 $ 6,532,835,000 ^Figures are for 1954. Source: Swain, et al., "Scope and Size of Ceramic Production in the United States" 55 TABIZ II GENERAL STATISTICS, 1957 Value added All employees by manufac United States Totals ture $1,000 unadlusted* 1. Transportation equipment 1,900,319 18,235,153 2. Food and kindred products 1 ,688,228 16,021,535 3. Machinery, except electrical 1,707,459 15,442,481 4. Primary metal industries 1,271,940 13,063,386 5. Chemicals and products 763,934 12,085,764 6. Electrical machinery 1,084,367 9,398,165 7. Fabricated metal products 1,113,534 9,329,236 8. Printing and publishing 867,485 7,723,217 9. Apparel and related products 1,264,308 5,968,807 10. Pulp, paper and products 565,874 5,642,384 11. Textile mill products 988,951 5,180,623 12. Stone, clay. & xlass products 525,597 4,810,104 13. Misc. manufactures 665,067 4,637,704 14. Lumber and wood products 645,792 3,295,567 15. Petroleum and coal products 185,562 3,008,896 16. Instruments & related products 307,207 2,725,636 17. Furniture and fixtures 374,850 2,466,644 18. Rubber products 259,894 2,380,204 19. Leather & leather goods 361,945 1,869,630 20. Tobacco manufacturers 88,086 1,233,184 17,104,655 144,518,305 ♦Unadjusted value added by manufacture represents value of product shipped (excluding resales) during the year less the cost of materials, supplies, fuel, electric energy, and contract work. Source: U.S. Dept, of Commerce, Bureau of Census. classification of products under each title for each table. The classification in Table XT does not reflect the total ceramic industries as the industry defines It; consequently, the total product figure is deceiving. Table X Is more realistic In representing the breadth of the industry's products shipped at approximately 6.5 billion for the year 1956. The classification of products was derived from an interpretation of the definition of ceramics as proposed by the American Ceramic Society. As broad as this classifi cation is defined, there are ceramic products that are not represented In the totals. The diversified uses for ce ramics materials makeB It very difficult to consider all uses of "raw" ceramic materials In the production of pro ducts In unrelated industries. in Table XT, General Statistics, It may be seen that the ceramic industry, represented by the classification of Stone, Clay, and Glass Products, Is in twelfth place when compared to the value of products shipped by other classi fied manufacturing. Therefore, it may be interpreted that ceramics is one of the major industries In the United States and is of greater economic importance than shown in the statistical survey. This is also apparent in Chapters III and IV, where the importance of ceramics is discussed as to the relationship of refractory materials such as pure 57 metallic oxides of alumina and titanium to the other manu facturing areas; these are not included In the statistical analysis. The statistical data presented, reflects the role of the ceramic industry in the United States. The scope of ceramics along with a definition were presented as to the industries classified as "ceramic." The size of the indus try was represented by tables in a survey of the industries. There can be little doubt that the ceramic industry is con tributing greatly to the economy of the United States. Tlie following section pertains to the industry and its place in the economy aB a discussion rather than the presentation of statistics. Nature of the Ceramic Industry The reason ceramics has continued to advance in many areas lies partly in the inherent properties of ceramic materials and partly in their increased exploitation through an accelerated research program. Research activities are continually expanding the accumulation of basic data essen tial for future developments, increased production of es tablished products, and the development of new products and processes. A. B. Kinzel (63), Vice-president in Charge of Research for the Alloys Group of Union Carbide and Carbon 58 Corporation, stated his predictions for ceramics as follows: Ceramics, long outstanding with respect to temperature and corrosion resistance, are coming into wide use as their strength and toughness are improved. Much remains to be done, but the scien tific approach has already resulted in such new ceramics as silicon nitride and various metal sili- cldes, borides, and carbides, not to mention metal ceramics. Potentialities in the field are impressive, and the new ceramics promise better furnaces, better chemical plantB, better cutting tools, and better jet engines, to mention just a few of the items making for better living. The most striking developments have occurred in glass, ceramic coatings, ceramics for electronic uses, and refractories. Much of the progress has resulted from funda mental studies concerning the nature of ceramic materials; investigations of fine structures of matter, nucleation; research based on crystal structure studies, a new abrasive material; and, investigation of the phenomenon of sintering has led to the developments of new materials. Scientific research has developed new materials as well as new uses for older known materials. Through better application of their properties, long established ceramic products ere finding new uses. Glass, in some instances, is being used as a lubricant in the forging and extrusion of metals. Finally, old processes are being improved and new ones are being developed and evaluated. To establish a greater relationship between ceramics and various areas of the economy, the following discussion is presented 59 as a brief survey of the development of new uses in Indus try, National Defense, science, In the domestic scene, and the possibilities for future development. Industrial Uses The numerous ceramic materials and products applied to Industry Is extensive. Many industrial areas could not subsist without ceramic refractory materials. Refractory materials, Important to the metal industries, have become paramount In the development of missiles, satellites, and nuclear advances through constant research In ceramics. Refractories are also necessary in the processing of ce ments, limes, and other ceramic materials, as well as for linings of boilers and furnaces. These and other require ments, make it understandable why refractory ceramic ma terials are so essential to modem industry. Electronic ceramics Is the fastest growing Industry In the United States according to Deem and Sullivan (26); It includes transltors in communications and other elec tronic controls and operations, and the ferrites in the field of computers. Ceramic parts composed of aluminas meet many of the demands of high-powered, high-frequency, and high-temperature electronic equipment. There appears to be no limit to the size and shape in which alumina can be fabricated. Many parts are produced to precise tolerances such as vacuum tube envelopes, coll forms and other high- frequency products. The list of glass products for Industrial use is almost endless. In every field of science and industry, glass has an important role. In regard to new developments in glass products, H. E. Simpson (101, p. 17*0, of Alfred University, comments as follows: Continued research with photo-chemical glass has produced a new process of chemical machining .... Pieces can be produced by this process which are so intricate that their manufacture by mechanical means would be impossible. New glasses are being developed that will transmit or retard radiations of specific frequencies. Olasses of improved faculties for the absorption of infrared and ultraviolet rays have been produced as well as glasses capable of absorbing slow neutrons. . . . There is apparently no limit to the horizons for the uses of glass. In the whiteware products, industry is concerned with electrical insulators, chemical ware, and parts of television sets. Other functions of whiteware in industry are such products as the proximity fuse, the Jet igniter plug, the television transformer core, and a great variety of products under this classification. The final machining of bearings, shafts, and other highly finished products by abrasive tools has attained new dimensions never thought possible with the use of metal tools. Many other major industrial operations vital to manufacturing are performed with the use of artificial abrasives. Although fifty years ago the only hard abrasive available was emery— a natural form of impure alumina— today, there exists many manufactured grinding materials possessing great hardness. One of the more recent developments has been the ceramic-tipped tools that are replacing all-metal tools. National Defense Because of the properties of ceramic materials, the United States Government has become interested in promoting ceramic research to aid programs in rocketry, missiles, and nuclear energy. Peaceful interests are usually adopted when they are applicable. One defense use is in the ceramic covers for radar equipment (radomes) and missile noses to reflect the intense heat of friction as they travel through the atmosphere into outer space and back again. In many instances, the point of development of heat engines where available metals melt or lose their strength has been reached. The alternatives are provided through adequate surface protection and insulation by means of a coating applied to existing metals, or through development of new materials with properties to meet the higher temperature requirements. Coatings of ceramic materials have shown exceptional promise in the following applications: nozzles; 62 motor tube linings; termal barriers in rockets; and in guided missiles— vanes, skin protection, and motor compo nents. Unquestionably, there are many additional uses applied to National Defense, however, due to the necessity for security measures, these are restricted and classified Information. Science In science, glass plays a major role* Doctors rely on glass equipment to facilitate research, reagents are stored in glass containers, precision glass lenses reveal that which is otherwise invisible. Glass makes it possible to examine the world of microbes and bacteria; and somewhat paradoxically, it makes possible the examination of the great expanse of the universe. Intricate electronic equipment In Industry, on the seas, in the air, in the hospitals, function accurately because many glass parts are used. Ceramic whitewares are an essential part of laboratory equipment. Dental ware and fast and hard drying cements have revolutionized that area of medicine. Domestic - Ceramics virtually touches everyone*s life during a day. Most people are not familiar with what constitutes 63 the ceramic industry, but rather think of it only as art pot tery or predominantly a whiteware industry. They are usually amazed to discover that items of glass, bricks, tiles, kitchen appliance coverings, bathroom fixtures, are all considered ceramics. There seems to be no end to glass products. Glass automobiles, glass boats, glass buildings*and furniture are a few developments perfected in recent years. Products de rived from new techniques have been developed for domestic use, such as foam glass, fiber glass, laminated glass and glass bricks. The art of applying glass to metal has developed beyond a decorative technique. Today, there are many in dustrial applications involving the different appliances used daily in the home: enameled stoves, refrigerators, sinks, and other appliances. It has been only recently that porcelain enamel has assumed its important position in the field of ceramics. Applications to new areas have been developed such as architecture, enameled steel sheets in modem building, both interior and exterior paneling, and farm silos. The Columbus Dispatch, Sunday, May 22, I960, reported that a research house was to be built in Cleveland to "explore methods of adapting residential housing components to the techniques of mass production as well as serving as a proving ground for advances in 64 plumbing, heating, and wiring systems." The house Is to be constructed and finished in porcelain enamel in a variety of colors and textures. Future The following projection of the future for ceramics Is covered more extensively than the other areas. The writer believes that consideration should be given to the other areas, because these processes are already controlled and are in production. It is essential to understand the existing processes In order to build upon this knowledge. It Is, however, In the realm of higher temperature that control of reactions more basic to pure science are en countered; therefore, the following emphasis Is on the future of ceramics and more specifically, refractories. The changing nuclear and electronic fields demand the development of new techniques for developing materials and processes. One such development has been the recent process of applying a ceramic coating to copper wire. Significant advances in nuclear energy experiments have been accompanied by, or followed by, new developments In the uses of ceramics. Ceramic products should increase in Importance as the trend continues toward high-temperature applications for electrical and electronic currents. 65 Edward Teller (18), a leading scientist in the development of the hydrogen bomb, had the following to Bay about the future use of ceramics In the nuclear field: Hlgh-temperature resistance ceramics are playing an Increasingly important role in the planning of the nuclear reactors of the future. A thorough under standing of these materials will be needed in order to engineer the energy supply for the coming decades. Hydrogen fuBlon may become a source of low cost power through the A.E.C. Project Matterhorn. Alumina, be cause of its properties of density and strength is to be used as the ceramic material for the reactor changer. Other uses for Alumina are being developed. Wayne A. Deringer (109, p. 66), A. 0. Smith Corporation, predicted to the American Industrial Chemical Engineering Association in a Philadelphia meeting that, In the future it is expected that there will be refinement In equipment and design and lines of product. With the developing trend to processing at higher temperatures and pressures, there will be more security built Into porcelain piping .... More Is being done in the research laboratory with high alumina bodies which give promise of raising the strength of commercial high-grade porcelain by two or three times. Such bodies can probably be operated at far higher temperatures and sustain more severe thermal shock conditions than is true with chemical porcelain bodies today. Melting points have become a major factor con sidered for the future development potential of new materials in high refractory processes. The temperature chart, Figure illustrates how the utilization of pure compounds, many very scarce materials, make it practical to Temperature, F Compound Tempuro. term, F Compound 66 4*00 ■ b4c 7*00 — Z r O i , 5 i0 2 — UC2 4tOO 7200 -Majnes/ffc brick , grapKit* —TaC "SiC t Jetf-bondicl silicon carbide 3 4 0 0 6400 — BtgC (decomposes) Graphite 3600 — Alg Oj 6600 — B«0 » Fused alumina. — M o S l z — "noz 3 3 0 0 6300 — ZrC alumina , c^'v'M-majnrJ/f'9 f — ThOi 2700 5700 — TiC ■ Hf0 - BN (jufel imtt) 2-400 “ “ P Y r« cloy fcnifh 5400 -HfO •uo2 2100 5(00 -M ,0 — WC teoo 4800 ZrOi y Ceg0j — CaO Smg0j , Ge/2Gj , BeC 1500 45 00 Source: Snyder, "Ceramic Materials for Higb-Temperature Applications in the Chemical Process Industries Fig. *f Upper Operating Temperatures of Commercial Ceramics and Melting Points of Pure Compounds 67 use higher temperature materials as compared to present- day commercial refractories. Presently, the only practi cal possibility of achieving temperatures above 5000°F. is with graphite in a controlled atmosphere. M. Jack Snyder (109), Project Engineer, Battelle Memorial Institute has the following to say about the future of refractories: Although new high-melting compounds undoubtedly will be discovered. It is highly unlikely that they will be composed of the more abundant elements, and accordingly these new compounds also are likely to be unavoidable in the quantities needed for refractory application even at a high price . . . It is likely that some expedient such as cooling the walls, use of the reactants as the container, or levitation would be employed In developing the process and be adapted to commercial operation. The development of new high-temperature chemical processes requires an associated development of new ma terials. Snyder proposes a number of new Ideas that re quires new materials such as processing ozone from oxygen, direct synthesis of cyanogen from carbon and nitrogen, and additional production of products by thermal decompo sition of gases. Snyder (109) continues with needs of adequate refractory materials by stating: . . . some processes undoubtedly will be de veloped that will operate at temperature and under conditions where present day commercial ceramic materials are perfectly satisfactory. Others will be developed where the temperature will be a little too severe for present day materials, and a ceramic material will be tailormade for the process by modifying those that are now available. Still others will be developed where the temperatures are so high or the corrosive nature of the re actants or products such that none of the 68 present-day commercial ceramics come even close to being usable • • • there will still be the problem of developing higher melting, more stable, and more chemical resistant materials than we now have. As to the future developments In the glass Indus- try* there should be greater conversion to adapt the combination of gas and electric heating for melting furnaces. It has been reported by ceramists that the output of furnaces already In use should, when converted, increase production from 30 to 50 per cent. A few of the predictions in glass research are for the future development of a large mirror to produce a tem perature of 5000°F from the sun*s rays; malleable glass that can be worked like plastic, but still resistant to heat; light-weight glass for construction; glass cements; and glass-coated bearings for engines. Research in electronics has already advanced this Industry to one of the fastest growing industries today. The development of the transistor, solid-state devices, has replaced certain vacuum tubes and electron tubes for amplification, signal regeneration and rapid switching operations, invented in 1948, the growth has been tre mendous. Deem and Sullivan (26) report about 47 million transistor units were manufactured in 1958. The ferrites have made possible the computers and other electronic "memory" machines. 69 Equally diversified predictions are forecast in the ceramic areas of abrasives, the laboratory development of a man-made material more hard than the diamond; cements, plaster, limes, extending the longevity of concrete by new developments in cements; insulation, using newly developed theories, ad infinitum. The data presented in Chapter XV, reflects the scope and size of the ceramic industry in the United States. The nonmetallic minerals mostly contained in ceramic products have extensive use in other industries. The role that they play in the economy and the future contributions to technological advancement to promote economic growth is vitally important. The statistical data presented shows that the ceramic industry is one of the major industries in the United States. The classification of products illustrates the diversity in the scope of the industry and defines the areas of ceramics for inclusion of only ceramic products. The discussion is a review of the important role ceramics plays in industry, in the home, in science, and in National Defense. The role that ceramics is to play in the future through increased basic research and experimentation, and the collecting of data of high-temperature reactions was discussed and predictions presented. CHAPTER V ANALYSTS OP THE CERAMIC TECHNOLOGY This chapter will be primarily concerned with selected fundamental information pertaining to the mine rals and materials of the ceramic industry. Selected basic knowledge in geology and mineralogy is discussed concerning the possible origin and mineralogical composition of ceramic materials. Selected chemical and physical reactions are discussed concerning crystal chemistry and physical state reactions. Also included is a discussion on a number of scientific phenomena that affect the preparation and processing of ceramic materials. Ceramic Minerals Analysis The ceramic industries ere mineral industries, therefore, an understanding of mineralogy is an essential prerequisite to a study in this field. It is not necessary to become a mineralogist, but a working knowledge of mineralogical terms and definitions in addition to an ac quaintance with the minerals of ceramics is important. The subject of mineralogy is concerned with the study of that class of substances designated as minerals. The term "mineral" has a specific meaning. According to 70 71 Webster's New World Dictionary (127), a mineral is defined as follows: . . . an inorganic substance occurring naturally in the earth and having a consistent and distinctive set of physical properties (e.g., color, hardness, and crystalline structure) and a composition that can be expressed by a chemical formula. In Fundamentals of Ceramics. McNamara and Dulberg (62, p. 6), offer the following as their definition of a mineral: "A mineral is a naturally occurring homogeneous inorganic crystalline solid having a definite chemical composition, definite crystal form, and characteristic physical properties." The authors' contend however, that the definition Is too broad, covering practically all the substances of the earth's crust; therefore, they developed the following detailed examination of their definition: The first requirement of the definition states that a mineral must be naturally occurring: that is, it must not be the product of any process designed or controlled by man .... The second requirement of a mineral is homo geneity. A certain rock . . . may appear to con sist of a single substance but upon complete Investi gation with a microscope, It is found to contain a mixture of several homogeneous substances . . . a mixture of minerals. Third, a mineral must be of inorganic chemical nature. The chemist classifies chemical substances either as organic or Inorganic. The organic compounds consisting mainly of carbon, hydrogen and oxygen. All living matter, both animal and vegetable, its products and derivatives, consists of organic compounds. Thus wood and coal are not minerals even though they may fulfill the other requirements. 72 Fourth, a mineral must he a crystalline solid. All crystalline materials are solids hut not all solids are crystalline* Obsidian, a naturally oc curring glass, Is a good example of a non-crystalline solid. Tt Is an amorphous glassy solid and, conse quently, Is not classed as a mineral. A naturally occurring liquid, Buch as petroleum. Is ruled out because It Is not a solid; however, water and liquid mercury are exceptions to this requirement and are classed as minerals. The fifth requirement of a mineral is that It has a definite chemical composition. Most minerals contain varying amounts of Impurities as they occur naturally, hut for the most part the chemical composition may he expressed hy a definite molecular formula. Sixth, a mineral muBt have a definite crystal form according to the crystalographlc classification. There are 32 classes of crystals to which a mineral may be long and, In addition, each mineral usually has peculiar characteristics of its own. Seventh, a mineral has definite physical charac teristics. such as hardness, color, density, optical properties, cleavage and internal arrangements of atoms (62, p. 7). The process of crystallization from a saturated so lution is one of the most Important methods of mineral for mation. The earth*s crust was considered originally to consist of molten rock-forming liquids. As these liquids cooled, during the earth*s crust formation, the solvent liquids became saturated. As cooling continued, the mineral compounds crystallized from the liquid, forming the igneous rocks of the earth*s crust. In general, the compounds sepa rated in the order of their solubility in the liquid, the least soluble separating first and the most soluble last. 73 Finally, when the temperature became low enough, the solvent Itself crystallized. As Bowen has Btated (15, P. 285 ), the igneous rocks of the earth are the "original primary rocks and the source of all matter, living or dead," Some of the minerals from igneous rocks, are of little particular value to the ce ramic industry, but after weathering and other natural and man-produced processes of alteration, they form feldspar, clays, and many other minerals which are of great importance to ceramics. As stated above, minerals are crystalline solids and each mineral has its own particular crystal form. For this reason a basic knowledge of crystal forms is necessary for an understanding of the properties of crystalline materials. The crystal form may be any one of the 32 classes set up by mineralogists and outlined by V. E. Ford in Dana's Text book of Mineralogy (37). Classification of Minerals Although there are a large number of possible forms that crystals may take, McNamara and Dulberg believe it is possible to classify all of them in six groups. Each of these groups is known as a crystal system. By referring the faces of a crystal to imaginary lines within the crystal called axes, it is possible to designate the system to which 74 the particular crystal belongs. Therefore, the arrangement of the faces with respect to the axes Is the determining factor in the classification of the crystal. One of the fundamental laws of crystallography Is that the angles formed by the Intersection of two crystal faces are constant for the crystals of any one substance; this offers an important means of identifying crystals. The mterfaclal angleB for most of the common minerals may be found in any good textbook on mineralogy. The regularity of the crystal form of a substance is due to the regular arrangement that the atom or molecules of a substance always assume on crystallization. This theory was first predicted and proven by Von Laue, In 1910, with the use of X-ray photography. The study of crystals by the X-ray method led to the conclusion that a crystal is made of a large number of Identical geometric forms each of which has all the properties of the entire crystal. Elements of Crystal Chemistry Although there is still much to be done in the in vestigation of crystalline structure, researchers now have a good insight into crystallography. The following is a brief explanation of crystal chemistry as applied to the silicates and clay minerals. 75 Every chemical element has a symbol of one or two letters which are the abbreviations used in all Chemical equations, and has associated with It an atomic weight which is the theoretical weight for the element. Taking chemical elements in the order of increasing atomic weight gives the atomic number. For example, it may be seen in Mendeleef's Periodic Table (Table TTT), that the elements are arranged according to the atomic number— hydrogen, as the lightest (atomic weight) has one electron and an atomic number of one; uranium, with a total of 92 electrons is numbered 92. An interesting phenomenon brought to light by modern atomic technology, as described by Day (24, p. 39), shows that . . . all but 21 of our chemical elements as found in nature are actually mixtures of two or more isotopes of equal chemical behavior but different mass. A large number of additional isotopes of our familiar chemical elements have again been added in the form of radioactive "nuclides" which is the name given the new radioactive fission products of nuclear disintegrations many of which are currently finding experimental application as "tracer" elements. When atoms are located in a regular position in a crystalline material, there has to be certain forces that hold them in place. These forces are termed bonds and generally represent a condition of attracting or repelling forces; this is explained by Norton in his book, Elements of Ceramics (76, p. 1) as follows: "The atom may be con sidered to consist of a nucleus having a net positive charge MENDELEEF'5 PERIODIC TABLE TABLE M 7y ft «f HyalriW* RH RH RH, RH* RHj RH, RH Typm 4 Qxt Sb ■ f e «. 4 j * <* * fc so Si 32 „ 1 132.U Em TM ns.e (8020 193.12 196.31 110.2 113.1 115.23 Cs KM flZMtA/TJ Hf Os lr Pi 3V ST sx 37-7/ » 73 76 T7 * ...... - . 5 117.2 zoo. Cl 204.31 207.21 201. g> Au h9 Ti Pb Vo At 77 80 * 9/ 92 47 99 226.05 ACTINIOC 6 jnun AT Rf* */* tff-» Ra w - Eartk r».i2 140.13 140.12 44.27 147.0 1150.43 152.0 156,1 151.2 162.46 (34.44 137,2 161.4 173.04 |75.0 Elcmcwts Ce a Eu S3 64 6T _ ,P> > J v > > Actimidt 232.(2 231 239.07 SFRifS ^ ,A PU A ™ vCw I * 77 equal to the atomic number* surrounded by shells of electrons which total up to an equal negative charge." He states that one of the most Important bonding forces in crystals is the Ionic bond which refers to an atom that has lost or gained one or more electrons (ions). Tonic bonded crystals are brittle and have medium to high melting points. Norton (76, p. 3) continues by listing three other bonding forces: Another type of bonding force Is the covalent bond, where a pair of electrons Is shared by two atoms. Elements such as C,Si, N, P, and 0 often have the covalent bond. This type of bonding gives hard, strong materials with high melting points. There Is a third type of bond, called the metallic bond, in crystals composed only of posi tive Ions. Here the closely packed atoms are pictured as surrounded by an electron cloud which holds them together. This bond gives more plas tic materials with a wide range of melting points. A fourth type of bond, which can hardly be called chemical bonding, is the Van der Waals force. In general, it is weak In character and gives ready cleavage. Tn any one crystal It cannot be assumed that the bonding force is exclusively one of those mentioned above; it is more generally a combination of them. ThlB is certainly true in many of the silicates. The use of Mendeleef's Periodic Table as a source of atomic weight information Is particularly recommended because the elements in every vertical column have been found to be similar in their chemical behavior. Andrews, in Enamels (3, P- 22), states that it is interesting and instructive to note the similarity of reaction between 78 materials at high temperature with thoBe at low temperature. He states also that the use of the periodic table Is Important in the substitution of minerals in the calculation of ceramic bodies and coverings: The periodic arrangement of the elements Is Just as useful at high temperatures as It Is at low temperatures. It is interesting that the elements, cobalt and nickel, which give to a sheet Iron ground coat Its great adherence to Iron, occur together with iron in the periodic table. Potassium and sCdlum, which are almost Interchangeable in some enamels, occur together. Aluminum occurB between the bases and silicon, the same position as It holds In enamels. Magnesium, calcium, strontium, and barium occur in the same group near sodium and potassium, and they react similarly in an enamel. Tin, antimony, and zirconium are closely associated in the table, and in enamels they are again grouped together as opacifiers. In this way it Is possible to point out many charac teristics which make a familiarity with the periodic table a great aid to the enamel chemist. Although it la recognized that there are some Irregularities In the periodic table, it is recommended that it be kept in mind as It gives a systematic background for thought. Although Andrewfs reference Is primarily to enamels, the systematic use of the periodic table may be adapted to the areas of glasses and glazes as well. Each atom must fulfill certain rules In regard to bonding with other atoms for in most crystals, with fixed relative mrnbers of the various atoms, there is only one possible arrangement that will produce a stable structure of minimum energy. It is easy to predict, especially for simple structures where the ions act as rigid "spheres," the type of bonding in the crystal and the resulting 79 substance. For example, a specific ceramic compound such as silica (SiOg) may occur In several different forms of crystals. Tn each form the Ions and the ratio of the number of cations and anions Is the same, but the arrange ment differs. Some forms are stable In one temperature range and some in others* These different crystalline forms of the same material known as polymorphic forms, are of great Interest to ce ramists because of the possible future development of new products and processes. Pyroceram Is a recent development of nucleatlon, recrystallization control, by research scien tists at C o m i n g Glass Co. The company characterizes its development as "new materials made from glass, so radically different that they aren*t even glass any more;" they explain as follows: The basic internal pattern of glass is always that of a liquid. To make this new material, the glass molecules are rearranged by special heat treatment until they fall into a crystalline pattern, and the glass turns into a new solid. The result--Pyroceram— is a close-grained, super-hard crystalline material, of a kind never seen in the universe before. It has been made In well over 1,000 varieties, each with a special combination of carefully controlled proper ties, and all capable of being mass-produced in any shape glass can assume. Pyroceram was created In answer to modern science and industry^ demand for materials that can withstand ever-higher speeds and temperatures. Pyroceram is now used in the radomes (nose cones) of supersonic missiles, . . . its extremely fine crystalline structure enables It to resist acceleration temperatures up to 2200°F. When copper melts and steel sags, Pyroceram retains its full strength. Different types of Pyroceram will 80 expand, shrink, or remain exactly the same size under heat. One type stands up to acid solutions that destroy steel, copper, and aluminum. Some types have electrical insulating properties superior to most ceramics. Some will withstand stresses of 26,000 pounds per square inch. Still others are harder than hardened steel, flint, or granite (2 2 , P. ^3). Clay minerals are difficult to identify because of their small size, variable composition, and possibly im perfect crystallization. They require the use of various methods such as optical, electron microscope, X-ray, and thermal analysis for positive identification. Some of the more definite optical, crystallograph!c and thermal proper ties of clay minerals are given in Table TV. The use of X-ray has been covered previously under Classification of Minerals. The first three methods are for the identifi cation of the crystal, whereas the thermal analysis is of the chemical or physical change that occurs through temper ature change. Norton states (76, p. 15), that in thermal analysis, each clay mineral more or less writes its own signature, as shown in Figure 5; he describes this method as follows: . . . a sample of the mineral Is heated at a steady rate together with a neutral material such as calcined alumina. As the temperature increases, the difference In temperature between the two materials is recorded. The clay minerals at certain temperatures absorb heat (endothermlc reaction) and at other tem peratures give off heat (exothermic reaction). Norton names a number of other less Important methods of identifying clay minerals, such as weight loss 81 TABIZ TV OPTICAL, CRYSTALLOQRAFHIC, AND THERMAL PROPERTIES OF SOME CLAY MINERALS Musco Properties MontmorilIonite Kaolinite Olbbslte vite Np 1.560 1.532 1.567 1.552 Ng 1.566 1.557 1.589 1.558 Ng-Np 0.006 0.025 0,022 0.036 mono- mono- Crystal Class Mono- — clinic clinic clinic a 5.14# 5.10# 5.064# 5.2# b 8 .90# 8 .83# 8.620# 9.0# c 14.51# 10 .# 9.699# 20# M 100°12 * ---- 85°29' 89°54' Endothermic 450°C Effect 100°,600°,850°ct 250°C small Exothermic — Effect 98o°c 700°-800° small Specific Gravity 2 .0-2 .5 2 .0 -2.5 2 .3-2 .4 Z!.76-3.00 Np z least Index of refraction. Ng * greatest Index of refraction. Ng-Np = birefrigence. a,b,c s dimensions of the unit cell along the x-,y-, and z-axes respectively. = angle of the c-axis with the a-axis. Source: Norton, Elements of Ceramics. Fig. 5 Analysis of Thermal Curves Thermal of Analysis 5 Fig. THERMAL EFFECT Source: Norton, Elements gf Ceramics gf Elements Norton, Source: — + i'— + + ♦ 11 M 0 IL R O M T N O M 1AS /T£ T / R O F S 01 A # z B 83 determinations on heating, base exchange capacity, and infrared reflection. Origin and Occurrence of Ceramic Minerals It Is an exception to the general rule when deposits of pure minerals are found in nature; usually, minerals occur in rocks composed of a mixture of minerals. Granites, the most abundant of rock formations occurring in the earth*s crust, are composed of quartz, feldspars, mica, and horn blende . The transported or sedimentary rocks are more com plex as they contain mineral fragments, in all degrees of alteration, washed from a large area of land. In the beginning, as has been previously stated, all rocks were igneous, that is, those which formed as the earth cooled. Many minerals were composed during the earth*s forming, while many others were formed later by the action of water. Elements when cold and dry do not readily react, It Is necessary to have either a high temperature or the solvent action of water to promote activity. Probably the first activity toward disintegration of Igneous rock was through the chemical action of water. Charles P. Binns (7» P. 2), in his lectures on ceramics at Alfred University, describes this action: . . . The first of these were chemical. Certain parts of the rocks and minerals were attacked more easily than other parts, and so when the warm dew made inroads on the surface and slowly penetrated the solid crust the alkaline salts, soda and potash were 84 removed in solution. . . . The condensed water with Its dissolved burden flowed to the lower levels and became the ocean. That is why sea water is salt. The removal of the alkalies left a residue of in soluble material and in this residue clays are found* The second reaction toward disintegration or break ing up of solid masses was physical through the action of natural elements; heat, freezing, wind, water, and thawing. Sedimentary clays were formed when the disintegrated masses were transported and then deposited according to grain size and weight. The most abundant elements occurring in the earth's crust (92 are considered in this writing) are not free elements but are combined with oxygen as oxides or as a combination of oxides. In a geological survey and study of the earth's crust as reported by McNamara and Dulberg (62 , p. 2 9 )j it was estimated that the composition of the earth to a depth of ten miles was about 95 per cent igneous and 5 per cent sedimentary rock. It 1s from the above mentioned oxides and mixtures that most raw ceramic materials are selected. A world-wide composite chemical analysis of igneous rocks reveals the elements and their abundance, as shown in Table V. Silica (SiOg) constitutes nearly 60 per cent of the total, and alumina (AI2O3 ) accounts for another 15 per cent; they are by far the most important constituents of ceramic compositicn a s well as being plentiful and relatively inexpensive. 85 TABUS V WORLD-WIDE COMPOSITE ANALYSIS OP IGNEOUS ROCKS Constituent Per cent Si02 Silica 59.12 AlgO^ Alumina 15.34 PegO^ Ferric Oxide 3.88 PeO Ferrous Oxide 3.80 MgO Magnesium Oxide 3.^9 CaO Calcium Oxide 5.08 Na20 Sodium Oxide 3.84 k 2o Potassium Oxide 3.13 h 2o Water 1.15 t i o 2 Titanium Oxide 1.05 All Others 0.92 Source: Newcomb, Ceramic Whitewares. Ceramic Geology and Minerals In the early days, ceramic bodies were made of natural clays, which were depended upon to cari^r with them all the necessary Ingredients needed for durable ceramic body. However, the technical improvement of the industry since that time 3s well exemplified by the variety of raw materials now being used in the formulation of ceramic 86 bodies. This trend is important, not only as a result of the inherent improvement in ceramic processes developed by increased knowledge of the reactions involved, but also because it has brought about a wider geographical distri bution of ceramic manufacturing plants. Regarding the industry in the United States, Newcomb (75* P* ^8 ) made the following comment: until almost the end of the 19th century, a ce ramic plant was located as closely as possible to a source of good potting clay; for this reason, plants were bunched in eastern Ohio, New Jersey, and other areas where local clays were adequate and of proven quality. Today those areas, while still ceramic centers of importance, have no competitive advantage other than the greater availability of skilled labor. Every important ceramic plant produces ware made of a mixture of raw materials, blended to its own fonnula. These materials are usually shipped 3ome distance from their source. Through new techniques, machinery, and knowledge in the field of geology, many new deposits of minerals have been located. The economical extraction of minerals of low-grade quality has been made possible by the develop ment of new methods for processing minerals. Ceramic minerals are located in many sections of the United States and occur mostly in solid forms; however, pastes, slips, colloids and other mineral forms are found occasionally. The following are brief descriptions of each form mentioned above. Solids. Ceramic materials occur in nature almost entirely in the solid state. Ihe two important classes of solids are crystalline and amorphous. Solid substances are 87 bodies of a rigid, compact nature; each piece of a solid has a definite measurable length, width, and thickness. Pastes. Some clays occur in nature in a paste form which is a mixture of one or more solids and liquids. The mobility of the paste is determined by the proportion of liquid and solids. Pastes are intermediate between solids and viscous liquids. The colloidal matter in clay pastes is in the "gel" state. Slips. Some clays occur as a mixture of solid and liquid in which the liquid predominates; this is known as a slip. The mixture may be regarded as a suspension of a solid material in a liquid. The colloidal state of the suspended material is the determinant factor in the proper ties of clay; slips are considered to be in the ’’sol" state. Colloids. Colloids are more than Just a mixture of solid and liquid. Substances in the colloidal state may be either solids, liquids, or gases, and may contain substances in two of the states simultaneously. The colloidal phe nomenon is a complex of physical and chemical actions, al though in ceramic materials they influence the physical properties possibly more than the chemical ones. Formation of Clays Clays cannot always be defined in a definite mineralogical or chemical term or formula and be understood 88 by everyone, because in some instances it has a popular as well as a number of technical definitions. Tn the popular idea, clay is a fine-grained material which becomes sticky when wet. Potters and others working in ceramics apply the tern "plastic" to substances which become a workable mass by suitable treatment and by the addition of water. Chemists and physicists tend to define clay In chemical or physical terms, such as McNamara and Dulberg*s (62, p. 30) defi nition of clay: A clay is an earthy material resulting from the decomposition of rocks, chiefly feldspar I(Na2 0, KgO). AlgOo • 6Si0o] rocks, and containing hydrated alumina- silicates. xt usually becomes plastic when wet and will form a hard rock-like mass when heated to a high temperature. Since it is the decomposition product of a rock it contains a mixture of the residual minerals which occurred in the parent rock, and also the new minerals formed during decomposition. Most clays contain a rather large percentage of particles small enough to have colloidal properties. The exact mineral compo sition of the extremely fine grains is still open to question because of the difficulties involved in identification. Clays may be divided into two classifications: residual or primary clays, those clays which are an alter ation product of the parent rock and remains in piece; sedimentary or secondary clays, those residual clays which have been exposed on the surface and transported and de posited in a new location. 89 Residual clays are formed by the disintegration of rocks by weathering (physical) and chemical action of natural environmental solutions. The physical forces In clude sun, frost, wind, vegetation, water freezing in rock fissures, climatic changes causing expansion and contraction eventually causing the disintegration of the rock. The chemical processes which change the mineral, composition are classified by McNamara and Dulberg as, oxidation, hydroly sis, dehydration, hydration, carbonation and desjllcation (62, P. 31). Sedimentary clays usually are impure In that most of them are mixed with sand and other clays and minerals as they are transported to new locations. The conditions under which the clays are deposited have an effect on the properties of the resultant clay. Rles (90) divides transported clays into the following classes: marine clays, estaurine clays, swamp and lake clays, flood-plain and terrace clays, and delta clays. Chemical Constitution of Clay Minerals McNamara and Dulberg (62, p. 36) give the theo retical composition of clay as that of the mineral kaoli- nlte, Al2 0 3 *2S1 0 2 *2H2 0 , or 46.5 per cent Si02 > 39.5 per cent AI2 O3 * 14 per cent H2 O; however, they go on to state that this rarely occurs naturally in clay. Table VI gives TABLE VI CHEMICAL COMPOSITION OP SOME CLAYS 1 2 3 4 5 6 7 8 9 10 SIOp 46.5 46.95 46.87 48.99 51.92 34.62 57.10 71.50 51.10 48.20 A 120, 39.5 36.75 38.00 32.11 31.64 48.03 21.29 13.86 15.40 17.80 Fe20-i 0.80 0.89 2.34 1.13 1.09 7.31 4.78 4.50 2.09 CaO 0.15 trace 0.43 0.03 0.25 0.29 0.56 5.20 10.84 MgO 0.20 0.35 0.22 0,44 0.56 1.53 0.11 3.80 3.13 k 2o 0.24 1.22 3.31 0.40 0.44 3.44 2.29 1.50 Na20 0.61 0.81 TiOo 0.18 1.16 2.28 1.44 7.93 C m (co2) h 2o 14.0 14.95 13.58 9.63 13.49 13.30 7.30 4.61 17.10 8.91 1. Theoretical Clay 6* Diaspore Clay 2 . Washed Florida Kaolin 7. Sewer Pipe Clay Zellitz Kaolin 8. Brick Clay I: English Ball Clay 9. Bentonite 5. Flint Fire Clay 10. Fullerfs Earth (Note: Numbers 2 and 3 approach the composition of pure kaolinite. All other clays except No. 6 show excess silica. No. 6 has an excess of alumina. Iron oxide, lime, magnesia, alkalies and titania are common impurities.) Source: McNamara and Dulberg, Fundamentals of Ceramics. vo o 91 the chemical composition of several types of clay. They further list the more important clay mineral groups and subdivisions of the basic hydrous alumina silicate minerals according to their composition. 1. The Kaolinite group consisting of Kaolinite Dickite Al20 3 *2Si0 2 *2H20 Nacrite Halloysite Al20'>,2Si02 *xH20 Anauxlte Al20-a,xS102 *2H20 Allophane Alp0o*xS102 *xH20 Endelllte 2. The MontmorilIonite group consisting of MontmorilIonite (Mg, Ca JO •AljjO? *5S102 *xHpO Beldelllte (Al,Pe)20 2 *5SI0p*xH20 Pyrophylllte Al20-*4Sid2 *xH20 Talc, Nontronite, Saponite, Hectorite, Sauconite 3. The Aluminous group consisting of Diaspore Al20o*Hp0 Bauxite Al20^*2HoO(actually a mixture) Oibbsite A 12°3 *3H2° 4. The Micaceous group consisting of Muscovite Biotite and others of lesser importance The clay substance consists of the finest portion and particles of the above minerals, which have colloidal properties. It is this clay substance which gives a clay its plasticity, its ability to remain in suspension, its dry strength, and its shrinkage. It may be observed in Table VT, a comparison of a theoretical clay with the other clay analyses, that these 92 clays Include many Impurities. The molecular arrangement and distribution of Impurities in the clay Influences the properties of a clay. It Is Impossible, therefore, to be able to predict all the properties of a clay from its chemical copposition. Through chemical analysis, It may appear that many fonns of the same minerals exist; however, because of the structural arrangement of the atoms the chemical reaction of the mineral cannot always be determined. These reactions are controlled by the same basic laws of chemistry that apply to low temperature reactions; however, these same lave of chemical reactions when applied to high-temperature in organic chemistry normally take place only at relatively high temperatures and, therefore, are more difficult to observe. Searle (98 , p. vii) mentions the following chemi cal difficulties to be overcome: The difficulties experienced in obtaining perfectly pure substances, the general insolubility and apparent Inertness of most ceramic minerals at temperatures below a dull-red heat, and the impossibility of obtain ing many of them in some readily recognizable form— such as crystals of convenient size— have hindered re search, but as these difficulties are overcome, and more and more information regarding the constitution and properties of these materials and products is ob tained, great technical advances will be made. Properties of Ceramic Materials Clays and many of the allied materials conveniently termed "ceramic materials" are extremely complex, both in 93 their chemical constitution and in their physical struc ture. Some of their properties are difficult to investi gate and any attempt to study them should begin at the beginning, and the more obvious characteristics of their physical structure should be considered first. Crystalline substances consist of units of a defi nite geometrical form or fragments of such units. In this form they are readily distinguished from amorphous sub stances, either by the unaided eye or by means of a micro scope or other optical instrument. Amorphous solid sub stances have no definite shape or geometric internal struc ture. Searle (98, p. 6) divides amorphous substances into (a) glassy or vitreous substances; (b) colloidal substances or gels; (c) substances of a cellular structure; and (d) substances wh-*ch have no definitely recognizable structure and can only be described as amorphous. The physical state of ceramic materials has a definite effect upon the processes required to prepare the material for production. One of the Important phases In the field of ceramics is the investigation of the physical properties of the materials and how these properties effect the reaction and function during the processing of a ce ramic body. An investigation of selected properties that are common to all clays is presented below. Some of the properties selected are combinations of physical, chemical, 94 and electrical characteristics of a clay; others are the more desirable characteristics of the properties of ce ramic materials directly dependent upon their structure. Texture The shape, the size, and the sizing of the grains are the determinants of the texture of a ceramic material. This consideration has a very important influence on many material properties such as shrinkage, porosity, fusibility, and plasticity. The grain sizes in both raw and fired ce ramic materials may vary according to the purpose for which it is designed. The grain of a material should be shaped so as to contribute to the maximum strength and to the requisite porosity, permeability, and a smooth surface. Coarse grained materials usually produce a less porous mass, but insures greater permeability, refractoriness, and re sistance to thermal shock. Some of the more undesirable properties of grain structure and size are a more open textured mass, a reduction of strength, and a rougher sur face . Tn the grading of material It is desirable to have two or more sizes represented in the mass. The term "graded" is applied to any material composed of grains of various sizes, the proportion of grains of each size being such that the mixture has acquired certain physical 95 properties. The common reasons for using several sizes of grains in a material is to obtain close texture and maxi mum strength; where a single uniform grain size Is employed, the voids (interstices) are quite large which produces coarse texture and less strength. Homogeneity A uniform texture is requisite for most purposes for which ceramic materials are used. Grain particle arrangement should be distributed uniformly throughout the mass; however, coarse textured articles, such as building bricks, do not require such a high degree of homogeneity. This uniformity becomes very desirable and essential in refractory articles, because a material which is not homo geneous is likely to crack or spall. Homogeneity in raw materials is obtained by con stancy in the control of physical and chemical composition of the material, thorough mixing, and uniform distribution of moisture. Some of the methods of producing a homogeneo\s mass in the latter two controls are wedging, mixing, pugging^ tempering, and blunging. These methods are described in Chapter VT. Searle (98 , p. 7 8 ) contends that this property is a requisite for successful manufacture of clay articles; he states that: "The aim of all these methods of preparation 96 is that a perfectly structureless material of absolutely even composition may be produced. Defective mixing, where by, complete homogeneity is not obtained, results in de fective goods, and it has been proved repeatedly that if the mixture be imperfect no later treatment can possibly remedy defects in the earlier stages of manufacture." Porosity RieB (90, p. 240) defines porosity in unfired articles as "the volume of the porespace between the clay particles, expressed in percentages of the total volume of the clay, and depends on the shape and size of the par ticles making up the mass." A clay body possesses these pores to permit the passage and escape of the "water of plasticity" and as a determinant for fired properties. It is sometimes found that articles made from a very fine- textured plastic clay will warp considerably more than less plastic clay either in drying or firing, because the trapped moisture and combined water cannot escape and exerts pressure upon the clay form. According to Searle (9 8 , p. 8 0 ), porosity in fired articles may be measured as "true porosity" and "apparent porosity" by the following methods: The true porosity is the relation between the volume of the article and the total volume absorbed by the pores when the article is soaked in water 97 or other suitable liquid, plus the volume of the pores which are normally closed or are sealed by vitrified matter and so are not filled by the liquid. . . . The apparent porosity Is the relation between the volume (or weight) of a mass and the volume or weight of the water or other liquid absorbed on Immersion in it. This figure is the one gener ally used as a measure of the porosity, . . . Both the true and the apparent porosity may be expressed as (a) percentage by weight, and (b) percentage by volume. The permeability of raw clay material depends upon its plasticity or water content. Plasticity of dry clay remains dormant but Is permeable to water; however, the same clay when wetted and a state of plasticity obtained, Is Impermeable to water. Searle (9 8 * P. 106) defines permeability for fired clay bodies as . . . the readiness with which a substance permits a fluid to flow through it as Is measured by the rate at which a standard fluid such as water, air, or other gases flows through a mass of unit area and unit thickness. The permeability is due to the pores which either run completely through the material or are connected with other pores and form a series which extend through It. The fluid which fills the pores without passing through them Is not included in measurements of permeability. Permeability differs from porosity in that the latter is a measure of the total volume of pores or voids, and permeability depends on the extent to which they pene trate throughout the mass. Therefore, while a highly porous mass Is often permeable, there is no absolute re lationship between the porosity and permeability of a material. Strength and A llied Properties Strength Is a vague term used in various ways; the most frequent use of the term when applied to ceramic materials Is to indicate the resistance of a mass or object to a change of Bhape when a mechanical force is applied to It under different conditions. The strength of a material Is due to the cohesion of the particles In the material and the resistance of the Individual grains to pressure. The following allied properties are related to the strength of ceramic materials. The strength of any material Is dependent on a complicated series of qualities of which no single factor could possibly represent the strength of an article in every respect. When a material disintegrates or fractures after a sharp blow, it Is said to be brittle; If it Is easily and gradually crushed, It is friable, but If under a number of blows a different shape is formed It is termed malleable. If the shape is alterable by pulling through an aperture, It Is said to be ductile; however, If It shows resistance to such treatment, it is regarded as tough. Other proper ties of strength of materials consist of being elastic, 99 resilient, flexible, and deformable. Durability introduces the element of time, such as the length of time maintained for the required property. Another property, cohesion, which is the force that holds the particles of a mass together, may be regarded as the force of attraction between the atoms or molecules of a material. According to the intensity of the force, a mass may be rigid, fluid, or it may possess various intermediate characteristics such as malleability and plasticity. Co hesion is measured by the force required to separate the particles from each other, and, according to the purpose for which the material or article is to be used, its co hesion is Judged from its tensile strength, crushing strength, and other physical tests. Many other factors affect the strength of ceramic materials. Searle (98, p. 171) lists the following im portant ones in groups under the following heads: a) The chemical composition of the material b) The physical properties of the material c) The mode of preparation of the material d) The mode of manufacture of the article e) The conditions of drying f) The conditions of burning g) The temperature at which the article or material is used, or at which its strength is determined 100 h) Other conditions to which the articles or material Is or has been subjected, Including weathering, sudden changes of temperature, prolonged heating, etc. The strength of the raw clay will depend chiefly on factors (a), (b), and (h), and chiefly on the second; the strength of a dried clay will depend on factors (a) to (ej; the strength of freshly burned products on (a) to (g), .... Rheologlcal Phenomena Clay when disintegrated and wet can be molded and shaped; It may be dried and Its shape retained; It can be fired and made hard and permanent, these properties make clay a valuable raw material. Clay always contains water, either that amount which It already contains as chemically combined water, or that amount of water added which affects the degree of plasticity. Plasticity In the presence of water Is a typical characteristic of all materials which contain clay-substances. It Ib dependent not only on the amount of clay-substance present in the material but also on the physical properties, clay structure and clay crystal size, of the clay-substance Itself. Plasticity Is produced by small grain sizes peculiar not only to clays. All minerals acquire a degree of plasticity by very fine grinding. The state of aggregation of clay particles when mixed with water Is known as flocculation and deflocculation. Flocculation exists when the individual clay structures are 101 coagulated Into large masses producing sedimentation. De- flocculation Is a process of dispersing the coagulated masses into smaller ones causing particle suspension. Electrolytes are used to provide the necessary forces to cause sedimentation and particle suspension. McNamara and Dulberg (62, p. ^5) H a t the factors upon which the reaction of a clay with an electrolyte Is dependent: a. the percentage of grains fine enough to exhibit colloidal properties (colloldallty being not a specific physical property of a definite type of substance, but actually representing a possible state of matter). b. the amount and kind of salts already present in the clay c. the nature of the electrolyte used d. the mineral nature of the clay substance. Many pastes and slips owe some of their properties to the colloids £hey contain, these colloids are somewhat different from a mixture of a solid and liquid. One of the chief characteristics of colloids is that certain liquids behave quite differently from solutions of crystalline substances because one liquid (colloidal) would not pass through a membrane having water on the other side of it, while crystalline substances in solution passed through the membrane (90). Since this colloidal research by Thomas Graham In 1861, It has been found that most substances can be obtained in the colloidal state in the presence of a liquid in which they are insoluble. 102 Substances in the colloidal state may be either solids, liquids, or gases and may contain substances in two of these states simultaneously. Many familiar obJectB are not generally recognized as being In the colloidal state: smoke Is a solid gas colloidal system, a porous brick Is sometimes regarded as a gas (air) - solid colloidal system, and most Jellies are liquid-solid colloidal systems. Elements of Colloidal Chemistry The word "colloid"comes from the Greek word, kolla, meaning "glue." The term Is used to describe a condition of a substance whjch is in a very finely divided aggre gate. Norton in Elements of Ceramics (76, p. 86) defines the nature of colloids as follows: A colloid is any type of material so finely divided that Its surface effects become important when compared with the bulk effects. The upper limit for colloidal materials may be on the order of 5 microns, and the lower limit approaches mole cular size. Colloidal particles may be lyophoblc (shunning water) or lyocratic (attracting water). Clays and nearly all other ceramic materials are in the latter class. The colloidal state of matter is of great value in the ceramic industries, as the binding quality of solid particles often depends upon the presence of colloidal matters. The plasticity of clay appears to be due mainly to such materials as described previously. 103 Many non-plastic refractory materials, such as alumina which cannot be reduced to the colloidal state* may be made plastic by the addition of a colloidal material. Colloidal reactions have both a physical and a chemical aspect to the rheological phenomena. Certain colloids have a special affinity for each other which is not entirely chemical, but may follow the physical laws of adsorption. The two conditions or physical stages of colloidal precipitation are (1) the reversal of sign by the addition of an acid, and (2) flocculation by a colloid of opposite sign. The subject of colloidal phenomena is a complex of physical and chemical actions. The influence of the action on ceramic materials is more obviously a physical one rather than chemical. Fundamentals of Plasticity Plasticity may be defined as that property of a material by means of which It may be deformed or changed in shape and yet retain that shape when the deforming force is removed. Norton (76, p. 72) defines plasticity as, "A vital characteristic of clays and of most ceramic bodies is the nebulous quality known as plasticity. This is the quality that permits the forming of the piece, often in very intricate shapes, and then keeps the forces of gravity 104 or the shocks inherent in manufacture from deforming it.* Many materials are plastic, however, clays are unique in that their plasticity is destroyed although their shape is retained by the removal of water that appears to be essential to plasticity. The most widely accepted expla nation for the cause or causes of plasticity of clays, according to Searle (98, P. 27 5 ), is that plasticity is due to . . . the particles of clay retaining a super ficial film of liquid of such a thickness as to enable the particle to cohere and the mass to re tain its shape until they are disturbed by a de forming force. During the application of the force, the cohesion is sufficiently great to prevent dis integration of the masB, yet not great enough to prevent a change of shape. When the liquid which formB the film of lubricant is removed by drying the particles are brought sufficiently close to gether, by the shrinkage which occurs, to enable the molecular forces between them (aided by any colloidal matter present) to produce a strong co herent mass. In Fundamentals of Ceramics. McNamara and Dulberg list the following as the most logical theories, to explain the plasticity of clays: water of hydration, fineness of grain, plate, interlocking grain, colloid, molecular at traction, and stretched membrane (62). Many authorities on clays have come to the conclusion that no single theory explains plasticity in all clays, but rather it requires a combination of the factors listed above. 105 Pastes are intermediate between solids and viscous liquids. Searle (98, p. 10) defines the Intermediate action of plastic clay In that, "on the application of a steadily Increasing pressure It appears to be Immobile until a criti cal pressure Is applied, after which It behaves like a liquid and flows with a velocity proportional to the excess pressure." The chart in Figure 6 clearly shows the effect of pressure on the flow of a viscous liquid (oil) and a plastic paste (clay). The "plastic flow" and "plasticity" of a clay-paste appear to be related but are not Identical; plastic flow contributes to the cohesion between the solid and liquid constituents, and the liquid acts as a lubricant for the mass as well as a restraining influence. Tn recent years, It has been ascertained that most insoluble sub stances, if sufficiently finely ground, would develop a de gree of plasticity. However, the mixture Is not a true paste If no colloidal matter Is present. Physio-Chemical Reaction Between Ceramic Materials The reaction of substances when combined to form other substances of different chemical properties Is called chemical action. Elements combine In certain definite pro portions and certain chemical combinations; when this oc curs, heat Is either emitted or absorbed. Tn the former there Is a temperature rise, in the latter a temperature felL Fig. 6 Viscosity: Effect of Pressure on Flow of Liquid of Flow on Pressure of Effect Viscosity: 6 Fig. Source: Searle, Cheat Cheat a Physic Searle, a jug try Source: VELOCITY OF FLOW n Patc Paste Plastic and Ceraalc Materials. Ceraalc PRESSURE ------v; g£ Cas*d Other *nd Clays - 106 107 A number of the laws of chemistry— chemical action and the classification of substances into acids, bases, salts, and neutral substances— which occur In and between ceramic materials, are not the result of a purely chemical phenomenon. They are controlled and modified by various physical changes, A study of chemical reaction would be incomplete If the various physical changes were not con sidered. A chemical reaction involves the destruction of the original substance and the formation of a new one; physical changes involve an alteration in the properties of a substance, but not a new formation. Physical changes ereieually caused by the effect of pressure, heat, or other physical forces; chemical changes appear to be caused by a force called chemical affinity. The extent of reactions will depend greatly upon their physical state— liquids react more readily then solids, and gases more readily than liqulds--pluB the relationship of temperatures. The chemical reaction of these substances always proceeds toward the formation of the most stable compound possible under the existing conditions. When several substances are involved, those which have the greatest affinity for each other react until a state of equilibrium is reached. The reactions, therefore, may 108 occur between matter in the font of either solids, liquids, or gases. According to Searle (9 8 )» the reactions between substances in the varlouB forms may occur in a number of types of chemical actions such as the following five major kinds t 1. Direct combination. This type of action Is very common in ceramic processes, especially during the burning of goods. 2. Displacement of an element or group of elements. Reactions involving displacement are not very common in ceramic processes but are largely used In some metallurgical operation. 3. Mutual exchange or double decomposition. In all such reactions, the acid radicle or Ion of one base leaves It and becomes combined with another base, the acid radicle or Ion previously combined with the latter then combining with the first base. 4. A rearrangement Is said to occur when the atoms In a compound are recombined in a different manner. 5. Dissociation Is said to occur when a substance Is decomposed Into Its constituents. The factors which Influence chemical reactions are many and should be carefully considered if the reactions are to be understood. The number of these factors, the difficulties In distinguishing the influences of each, and the fact that most ceramic reactions occur at high temper atures, Is the reason for the lack of definite knowledge concerning reactions of clays and other ceramic materials. The principal factors which affect chemical reactions 109 between ceramic materials and form the bases for the indus try are temperature, time, and pressure. Other factors of less importance such as surface tension, viscosity, solu b ility also affect chemical reactions to a lesser degree but need to be considered in chemical analysis. Changes Effected by Water-Hydratlon Many of the properties of plastic clays are closely allied to those of water because of the number of Impurities in the water such as alkalies, calcium, sulphates. Water occurs In several different forms in clays, but the terms used often overlap. A number of water forms are listed by Searle (98* p. 254) as, 1. Moisture or hygroscopic water. This Is de rived from the atmosphere or from natural conditions to which the clay has been exposed. 2. Colloidal water— that present in the colloidal matter or adherent thereto by adsorption; it may have been derived from the same sources as the moisture, or have been added purposely. . . . When only the "colloi dal water" (sometimes termed the "water of plasticity") Is removed, the plasticity of the material may be re stored by mixing it with a suitable quantity of water and allowing it to stand or sour until that water Is uniformly distributed. . . . 3. Water of formation"-that added to a clay or clay-mixture in order to convert It Into a plastic or stiff-plastic paste. 4. Pore-water (less accurately termed capillary water) Is held In the pores. Hie term "lmblbltlonal moisture capacity" 1b used to Indicate the maximum amount of water which can be absorbed by a mass of clay without becoming sticky. 110 5. Combined water (including the water of crystal lizationwidtnewater of constitution). 6 . F r e e water Is that which Is not combined In any way. F. H. Norton, In "Clay-water Pastes,** states further that there Is evidence that the water in clay pastes Is not entirely of the same nature as free water, but may be al tered by the strong adsorption forces of the clay particles (49). He believes there Is still much to be studied about the effects of water-hydration as it Is an important factor connected with the clay-water system. Chemical Components of Ceramic Materials Knowledge of elementary chemistry Is necessary In order to understand termB such as element, electron, atom, molecule, compound, mixture, atomic and combining weights, valency, and the ordinary use of chemical formulae and equations. A knowledge of the usual conception of acids, bases, and salts, and some acquaintance with the theory of ionization or the dissociation of substances into ions are also important considerations. When stydying inorganic chemistry, simple compounds receive the greatest attention. However, in the branch of chemistry that deals with ceramic materials, complex compounds must be regarded as simple compounds because complex elements uniting with each other are similar in reftctlon to those of simple compounds. Ill Ceramic materials are chiefly of a mineral structure with very few organic substances being used* Primarily, they consist of such minerals as silica, alumina, lime, magnesia, iron oxide, soda, potash, and compounds of zlrconla and carborundum* Various other oxides are used to Impart color either to the clay body, to the glaze, or to glass, and vitreous enamels. The dividing line between mixtures, solid so lutions, and chemical compounds is often slight; each may appear to pass Imperceptibly into another. Chemical com pounds are divided into two classes: atomic and molecular compounds, the former Is much better known. Searle (98, p. 3^2 ) distinguishes the two as follows: Atomic compounds are formed by the Interaction of atoms and are usually very stable and strongly combined. Thus, silica is produced by the combi nation of atoms of silicon and oxygen, and is very resistant to dissociation or decomposition, other well-known atomic compounds used in the ceramic indus tries are water, alumina, the various iron oxides and other oxides, chloride, simple silicates, etc. Molecular compounds are those in which molecules (or atomic compounds) appear to combine with each other. The affinity of molecules for each other is much less than that of atoms for each other, and, consequently, molecular compounds are somewhat analogous to solid solutions, and some solid so lutions may be molecular compounds. Some names of minerals are confused with those of a definite chemical compound, because several minerals are known by the same name, however, they do not consist of exactly the same elements in the same proportions. An 112 example of this would be the term "feldspar*" the term Is applied to a group of substances of similar* but not Iden tical composition* Some substances may yield Identical results upon analysis* and appear to possess exactly the same composition In that they contain the same elements in the same proportions, however, when evaluated by their other properties they are entirely different substances. Classification of Ceramic Materials A classification of material usually depends on the point-of-vlew of the classifier; if he were a geologist* then a classification as to the origin might seem logical. A producer of clayware might be Interested in a classifi cation based on the properties of ceramic materials. These properties would be classified in terms of thermal, mechani cal* thermodynamic* as well as the uses of materials. The following listing will be classified into two divisions: plastic materials and non-plastic materials. Plastic Materials Most of the materials Involved in this classifi cation will be clays. Norton charts clays into two classi fications one as to origin, and the second as to use. Table VXT charts clays as to origin; Table VTTT is a classification of clays as to use. TABLE VII CLASSIFICATION OF CLAYS AS TO ORIGIN Residual Matter Products From crys Impure residual clay of talline ordinary rocks Primary kaolin weathering From sedi impure residual clay No mentary movement rocks Kaollnitlc clay during formation Same as From above with crystalline Bauxite additional rocks chemical action From sedimentary Bauxite rocks Dlaspore 00 TABLE VII (Continued) Transported Matter Productb of Argillaceous shale ordinary Argillaceous silt Deposit ted in weathering still water, Same as above Sedimentary kaolin little or no with Ball clay current action, additional Some bauxite seas, lakes, intensive Coal formation clay bogs, etc. chemical action Dlaspore Deposited by Products of slowly moving grinding with Siliceous shale waters, streams, some weathering Siliceous silt estauries, etc. Products of abrasion with slight Deposited by weathering Qlacial clay or till glacial Products of action abrasion with slight weathering Deposited by Loess winds Source: Norton, Elements of Ceramics. 115 TABLE VTTT CLASSIFICATION OP CLAYS AS TO USE A. White burning clays (used In whlteware) 1. Kaolins a. reBldual b. sedimentary 2. Ball clays B. Refractory clays (having a fusion point above 1600°C but not necessarily white burning) 1. Kaolins (sedimentary) 2. PIre clays a . flint b. plastic 3. High alumina clays a. glbbslte b. dlaspore C. Heavy clay-products clays (of low plasticity but containing fluxes) 1. Paving brick clays and shales 2. Sewer-plpe clays and shales 3. Brick and hollow tile clays and shales D. Stoneware clays (plastic, containing fluxes) E.. Brick clays (plastic, containing Iron oxide) 1. Terra-cotta clays 2 . Pace and common brick P. Slip clays (containing more Iron oxide) Source: Norton, Elements of Ceramics. 116 For ceramic production, a number of properties of the materials are of Interest; Newcomb (75* P. ^9) lists the most Important of these as 1. Firing behavior - shrinkage, range of vitri fication and tendency to warp In the kiln. 2. Drying behavior - drying shrinkage (per cent), tendency to warp or crack in drying. 3. Working properties - plasticity, dry strength, amount of abrasive wear on equipment. 4. Properties after firing - color, per cent ab sorption, ability of finish to take decoration, hard ness, refractoriness. On the basis of the properties listed for the classification of clays, the following is an analysis of clays from the classification table according to uses. Whlteware Clays. Materials used in the manu facture of whlteware must be of a type that bums white or nearly so. Most clays used in whlteware bodies are kaolins and ball clays. Kaolin is the most refractory of all clays because of its purity from contamination of carbonaceous matter. It is prepared for market by washing and removing the sand. The washed kaolin as represented in Figure 7 approaches theoretical kaolinite in composition (AlgO^ • 2Si02 • ZH20). Ball clays are very plastic, nearly white-burning sedimentary clays with an exceedingly fine-grain and high body strength when dry. An important property is their floating power. Ball clays are usually added to enamel and 117 Silica 45.78 per cent Alumina 36.46 Ferric Oxide 0.28 Ferrous Oxide 1.08 Lime .50 Magnesia 0.04 Alkalies 0.25 Titanium Water 13.40 Moisture 2.,05 99.84 Source: McNamara and Dulberg, Fundamentals of Ceramics. Pig. 7 Analysis of a Washed North Carolina Residual Kaolin glaze slips to help keep non-plastic materials in suspension. Figure 8 Is a chemical analysis of the popular Tennessee Ball Clay. Silica 4 6 .85 Alumina 33.15 Iron Oxide 2.04 Lime 0.33 Magnesia 0.40 Alkalies 0.71 Titanium Loss in Ignition 16.48 Source: McNamara and Dulbers. Fundamentals of Ceramics. Fig. 8 Chemical Analysis of Tennessee Ball Clay 118 Refractory Clays. McNamara and Dulberg state that no clay can be classified as a refractory clay If Its fusion temperature is below 2760°F (1515°C) or Cone 19* The fusion temperature being that temperature at which a liquid phase starts to form. Table IX Is an analysis of three types of refractory material: siliceous, kaollnltlc, and aluminous. TABLE IX CHEMICAL ANALYSIS OF SEVERAL FIRE CLAYS Silica 43.10 per cent 76.24 per cent 34.62 percent Alumina 39.40 15.76 48.02 Iron Oxide 1.35 0.52 1.09 Titania 2.01 1.68 2.28 Lime 0.13 0.26 0.25 Magnesia 0.08 0.29 0.56 Alkal!es 0.20 0.23 0.44 Ignition loss 13.63 5.60 13.30 Fusion -Cones 33-34 30 above 33 Degrees F 3146 3038 3128 Degrees C 1730 1670 1720 Note: 2 - Pennsylvania flint clay - kaollnltlc 7 - New Jersey plastic clay - siliceous 8 - Missouri burley dlaspore clay - aluminous Source: McNamara and Dulberg, Fundamentals of Ceramics. 119 Stoneware Clays. Stoneware clays are refractory or semi-refractory clays with the chief requirement of high plasticity and low vitrification. These clays are used in stoneware manufacture and also for blending when making other bodies such as earthenware and art ware. Vitrifying Clays. Paving bricks, sewer pipe and roofing tile require nearly the same degree of vitrification as stoneware. Shales are often used as the raw material for these products. Pace brick clay, brick clays, and common bricks usually fire red and have a very unstable chemical composition. Slip Clays. Slip clays are clays high in fluxes which cause them to melt at a low temperature to form a glass. Slip clays are used as a natural glaze on stone ware and electrical porcelain. Bentonite. This is a natural inorganic material composed chiefly of montmorlllonite (AlgO^ . ^S102 . 9H20 ) and Is usually derived from volcanic ash. The chief value of bentonite is in its extreme plasticity. Non-plastic Materials This classification consists of those materials which in normal processing of the raw material produces a non-plastic material. The following Is a brief discussion of the more commonly used materials. 120 Silica. Silica (S102) Is one of the most Im portant compounds used in ceramics. It Is both abundant and widespread over the world, and It Is one of the purest materials found. McNamara and Dulberg (62, p. 102) list eight forms of silica and state that the physical stability of these forms depends upon the temperature and structure of the crystal. Newcomb (75> P. 32) lists the normal stable forms of silica at various temperatures as, Stable form Temperature range Alpha - quartz up to 573°C Beta - quartz 573° to 870°C Tridymite 870° to 1^70°C Cristobalite 1^70° to 1713°C Silica glass 1713° up As a ceramic raw material, silica is important in that practically all ceramic products are silicates and uncorabined silica is the principal source. Tt is the major ingredient in silica brick, glasses, enamels, and in most abrasive products. Commercial forms of silica are obtained in such materials as sand, sandstones, quartzite, and diato- maceous earths. Alumina. Alumina (AlgO^) the only oxide of alumi num, Is second to silica in ceramic importance. The pure 121 compound Is highly refractory and a very stable substance, in this stage It is being used as a protective covering, thinly applied, through a flame-spray application. Although the compound is widely distributed, there are no known large deposits of pure alumina exist ing. At present the commercial source of pure alumina are the minerals corundum (AI2O3 ) and the hydrated minerals glbbsite (AI2O3 . 3H2O), bauxite ( A ^ O ^ • 2H2O), and diaspore (AI2O3 . H2 O). Feldspars. Feldspar is a broad term used to identify a group of alkali-alumino-silicate compounds con taining one or more of the bases of potash, soda, or lime. McNamara and Dulberg (62) divide feldspars into two groups (1) potash feldspars and (2) soda-lime feldspars. They list them as follows: 1. Potash Feldspars: Orthoclase Potash spar v n n r e ^ Microcline Potash spar K2° * A^C^SiC^ 2 . Soda-lime Feldspars (Plagioclase series) Albite Soda spar Oligoclase Soda-lime spar Andesine Soda-lime spar Labradorite Lime-soda spar Bytownite Lime-soda spar Anorthite Lime spar CaO • A^O^ • 2310^ Feldspars are used in whiteware bodies as a fluxing agent for dissolving flint and clay and assisting in the bonding of unfused particles. They are also a means of 122 adding alkali fluxes to a glaze, glasses, and enamels In an insoluble condition. Nephellne Syenite. (KgO'SNagO^AlgO^^SlOg) is closely related to feldspars. It Is an igneous rock com posed chiefly of nephellne (Na20'A^O^^SIC^), potash feldspar (microcllne), and soda feldspar (alblte). Nephe llne syenite Is used extensively in the glass industry as a source of alumina and In a more recent development of a low-flre vitrified body. Refractories. The refractory materials listed are used primarily in the refractory phase of ceramic indus tries because of their high softening point and their stability in contact with many slags. Magnesite, (MgCO^), is often associated with calcite, (CaCO^), to form a basic rock dolomite. In a rather recent development since World War II, magnesia is recovered from sea water. The princi pal use of magnesite is for refractories, with pure MgO considered as a super-refractory material with a melting point of 2800°C and up. Lime. Calcium oxide or lime, (CaO) is the unstable form of calcium and has wide uses in many industrial processes. Lime is used in Portland cements, plasters, and slaked limes. It Is one of the main ingredients of glasses and widely used in whlteware bodies in the form of Whiting (CaCO^). 123 Qypsum. Gypsum Is a calcium compound having the formula CaSOij. . 2H20. When gypsum Is heat treated part of the water hydration Is removed to form plaster-of-Paris or calcined gypsum. The action will reverse itself at room temperatures in the presence of water forming gypsum. Chromite. Chrome ores are spinels (CrgFeO^). They are used to form chromic oxide and other compounds used as colors or stain. Chromite, however, is used in ceramics primarily as a refractory in the form of burned bricks. Talc. Talc in recent years has become very im portant chiefly in the production of electrical insulation material known as steatite. Pure talc is a hydrated mag nesium silicate with the formula (3MgO • 4Si02 • H20). When talc is heated above 1500°F, it decomposes and in the presence of excess silica forms the hard compound cristo- balite or tridymlte. Fluorine Minerals. Fluorite (Calcium fluoride) has the chemical formula CaF^ which occurs in the rock fluorspar. Cryolite (Na^AlFg) is used principally as a flux in the electrolytic refining of metallic aluminum. Alkali Minerals. The monovalent metallic elements lithium, sodium, potassium, rubidium, and caesium are known as the alkali metals. Most of the alkalies are located in the salt deposits of dried up lakes. The principal use of 124 the compounds in ceramics Is as a flux In the melting of glasses, enamels, and glazes. Boron Minerals. Boron In the form of boric acid (H3BO3 ) or borax (NagE^O-^ . lOHg) Is used In glasses, enamels, and fritted glazes. Boron as a glass former greatly reduces the melting and softening temperatures of glasses and at the same time increases the durability and resistance of glass. In the search for more refractory materials, Investi gation has disclosed the discovery of newer materials. Data (16) have been tabulated on elevated-temperature character istics of refractory materials melting above 2500°P. These materials consist of carbides, nitrides, oxides, slllcldes, sulfides, beryllldes, alumlnldes, other lntermetallics, phosphates, and uranates. The minerals and materials used in the ceramic Industry were presented. The ceramic minerals were analyzed and crystallography established. The elements of crystal chemistry and factors that determine physical and chemical reactions were discussed. The controlling properties for ceramic materials were presented with an explanation of various phenomena which are Important in manufacturing and processing ceramic materials. These controls are further 125 discussed in the following chapter as important factors in the application to, and formulation of, ceramics m a terials, preparation of materials and bodies or coat ings. CHAPTER VT ANALYSTS OF MANUFACTURING AND PROCESSING This chapter will be concerned with the preparation, composition, calculation, and batching of ceramic materials into enamels, bodies, and coatings. The calculation of most ceramic bodies and coatings involve similar steps and methods of expressing formulas and recipes. The raw ma terials used are similar except In the degree of refine ments, therefore, the same consideration Is given to their classification. Preparation of Raw Materials The Important preliminary steps in the production of ceramic articles are the mining and treatment of raw materials. These operations, although an industry within itself, many times are the determining factors in the properties of ceramic products. The raw materials used are carefully processed at the producer's plant, arriving at the ceramic plants ready for use. Tn a few cases, costs or other factors may induce a ceramic manufacturer to purchase or mine clays or other materials In an unre fined condition; however, this procedure is usually not very successful because they lack adequate refining 126 127 equipment. The manufacturer performs certain necessary tests to assure that the Incoming raw materials are ac ceptable before releasing It to the production department. Such tests vary with the type of material but usually in volve purity, moisture content, fusion points, particle size, and chemical analysis. Mining Methods The mining operation is divided into a number of progressive steps: prospecting, stripping of overburden, mining, crushing, and refinement. Prospecting involves a careful appraisal of a deposit to determine the fitness of the material for use. Naturally occurring clays vary in many essential properties such as particle size, color, and particularly in their rheologlcal behavior. Such variations may exist not only between deposits of differ ent locations, but often within Individual deposits. Ac cording to the Huber Corporation (46, p. 25), laboratory evaluation of crude samples constitutes an important phase of prospecting, for such tests cover: "1 . the inherent brightness of the crude, 2 . the extent and nature of its coarse impurities, 3 . an evaluation of that particle fraction acceptable for industrial purposes, 4. an evalu ation in the final product." 128 Modem large scale operations require high powered equipment for removal of overburden and mining of clay; stripping the dirt Is accomplished by high powered mechani cal equipment. Dirt Is removed and the clay Is mined in the open pits and transported to the plant for processing. At the plant the crude form of the material is reduced to small lumps by roll crushers or similar devices and stored. The raw materials as they are found have to be broken and disintegrated so that the resultant particles meet specifications demanded In ceramic processes. This disintegration of raw material can be accomplished by weathering, calcination, and mechanical grinding and crushing. McNamara and Dulberg (62, p. 139) state that the properties of all ceramic products depend to some extent upon the particle sizes of the raw materials used and that, In heavy clay products, the workability of the raw clay, strength, shrinkage, density, hardness, texture and even color of the product are affected by the fineness of grinding of the clays and shales. The strength, thermal conductivity and resistance to abrasion, slagging and spalling are some of the properties of refractories which are partially de pendent upon grain size. All porcelain and china- ware require exceedingly fine-grained raw materials. Portland cement will be good or it will fail, de pending upon the degree of grinding both before and after clinkering. The crushing operation is generally accomplished in stages; the rock material is broken down by several 129 machines until the required degree of fineness has been obtained. Screening or size classification Is another important step in the preparation of raw materials. Sizing may be accomplished by several processes depending upon the condition of the material: wet or dry. Screens of various size apertures, frequently made of woven bronze wire, are usually used in series. See Table X for the Tyler Standard Screen Scale with intermediate sieves, m order to provide adequate screening, a mesh must be vibrated in some way to insure a constant flow of material passing over the screen. The material may be screened wet or dry; generally, wet screening of very fine sizes assures a more efficient ciasai fication. Dry, finely ground material may be sized by air or water classifiers. New developments in improving the methods of treat ment of raw materials have been made to produce a more pure and uniform product. The washing of kaolins and flotation refining of ground feldspars are examples of improvements. Another area of development is the purification of lower grade deposits as the supplies of better grade materials are exhausted. Composition and Calculation of Ceramic Products in ceramic calculations for bodies, glazes and other batches, the constituent oxides are considered as the 130 TABLE X STANDARDS FOR BRITISH AND AMERICAN SIEVES Relation of Aperture to thickness of wire and mesh-number N u m b e r ______Size of Aperture (side of Bguare)______of B.E.S .A « j A.S.T*M*2 Sieve inches inches Old Inches New inches 0.1320 0.1000 0.1026 0.1107 0.1320 0.0949 0.1110 0.0810 0.0937 0.0630 0.0620 0.0660 0.0787 0.0500 0.0513 0.0553 0.0661 0.0417 0.0414 0.0474 0.05 5 0.0395 0.04 0.0313 0.0316 O.O336 0,039? 0.0331 0.0250 0.0250 0.0275 O .0236 0.0280 0.0197 0.0232 0.0167 0.01701 0.0197 0.0166 0.0165 0.0125 0.01243 0.0139 0.0138 0.0117 0.0100 0.00987 0.0116 0.0099 0.0098 O.OO83 0.00828 0.0083 0.0071 0.00724 O.OO83 0.0070 0.0063 0.00630 0.0070 O.OO55 0.00549 0.0060 0.0059 0.0050 0.00485 0.0049 0.0049 0.0041 0.00414 0.0041 0.0041 0.0033 0.00335 O.OO35 0.0035 0.0030 0.0029 0.0025 0.00255 0.0026 iBrltlsh Engineering Standards Association. American Society for Testing Materials, made by the ?er Co. ^Institute of Mining and Metallurgy, made by N. Greening & Son, England. Source: Searle, Chemistry and Physics of Clays and Other Ceramic Materials. 131 fundamental units rather than the elements that go to make up oxides. Although chemical calculations use the elements, It is much more convenient and Informative to use the oxides from a ceramic standpoint. Similarly, the molecular weights of the various oxides are used as the numerical chemical units. Most of the ceramic materials are complex chemical compounds, usually silicates, but their constitution is such that the composition can be expressed in terms of simple oxides. The oxide method of expression makes It easier to understand the effects which any given material may have on the batch as a whole, and greatly simplifies the calcu lations needed when one material is substituted for another. Because the oxide method of representing materials is used in ceramics. It is Important for one to become familiar with the chemistry of the oxides. The oxides may be divided into three main chemical groups for purposes of this discussion. Andrews (2 , p. 51) describes this grouping as follows: Chemically, the oxides, In nature, may be classi fied in three groups: the oxides of the metallic elements; the oxides of the non-metallic elements; and the oxides of the elements that react either as metals or as non-metals (amphoteric elements). The oxides of the metals are called the basic oxides, or the bases; and the oxides of the non-metals are called the acid oxides, or the acids. The amphoteric- element oxides are called the neutral oxides, for in the presence of both acid and basic oxides they are likely to react neutral. 132 It Is common practice In glaze calculations to use three designations for the oxides. The letter "R" Is substl tuted to represent the element other than oxygen, thus, the bases should have the general formula RO or RgO; RgO^ for the neutrals; and ROg for the acids. It Is the custom in ceramics to call the basic oxides the RO group, even though It Includes the R2O oxides; the neutral oxides the RgO-^ group, and the acid oxides the ROg group In a formula. The following list gives some of the more common oxides accord ing to the three groups: Bases______Neutrals Acids RO R2O R2O3 RO2 CaO Na20 Alg°3 S102 MgO K20 b2o3 tio2 BaO Li20 Pe2°3 Zr02 PeO SbgO^ PbO CrgO^ ZnO CdO MnO As an explanation of the use of oxides, McNamara (61, p* 274) states The use of oxides as units in ceramics has arisen from the fact that the chemical analysis of a ceramic raw material or a fired product will reveal enough oxygen to completely satisfy all of the other 133 constituent elements. It has become the practice not to analyze for oxygen or as the oxides but to calculate all results to the oxide basis and report them as such. If this is not done it w ill be found that the total weights on a percentage basis w ill not add up to 100 per cent or anywhere near it. The use of empirical formulas, formula weights, equivalent weights, and formula batch weights is an im portant implement for calculations by a ceramist. In working with glazes and similar materials, which are not chemical compounds, it is a misnomer to use the term mole cular weight; formula weight is preferred. The formula weight, however, is calculated in the same manner as the molecular weight, the sum of the atomic weights of the atoms in a molecule of a compound. The equivalent weight of a material depends upon the part of the material for which it is to be used. Glazes, glasses, and enamels require the RO group to be in unity, if a clay body is to be formulated, the R2°3 group is determined as unity. Empirical Formula In ceramics the percentage composition is changed to what is known as empirical formula. An empirical formula is the same as a molecular formula except that it does not represent a molecule. It is a convenient method of repre senting chemical composition graphically. McNamara (61, p. 268 ) offers the following description: 134 in writing the formula of a feldspar or a clay it is customary to use the oxide form such as KgO . A I 2O3 . 6S12 or A12 03 . 2S102 . 2H20. By writing the formula in this manner the ceramist can estimate the properties of a compound or mineral by observing the number of molecules of the various oxides present and comparing it with other compounds of a similar nature with which he has had experience. A modification of this practice is used in calculating glaze and body formulas. The glaze or body is con sidered as if it were a chemical compound and its formula is calculated on a molecular basis and written in a way similar to the oxide formula of a feldspar or similar compound. This formula is known as an empirical formula since the substance it represents is not a true compound. The analysis of a feldspar as stated above by McNamara is the same practice that may be used to calculate the formulae of ceramic bodies and glazes. The method of doing the analysis may be learned by studying an example (61, p. 2 7 6 ) of a formula based on the feldspar analysis: CANADIAN FELDSPAR Oxide Per cent Mol. Wt Number of Eauivalents • 60 SI02 66 • 50 “ 1.11 -1. a i 2o 3 17.40 • 102 0.17 • CaO 0.15 • 56 0.003 • k 2 o 13.00 • 94 0.14 Na20 2.00 • 62 • 0.03 99.05 The oxides shown in the analysis are only those present in pure feldspar; Iron, titanium, organic matter 135 and volatiles are also present in limited amount. For this reason the total weight of oxides shown Is less than 100 per cent. Therefore, the formula that Is calculated from this analysis Is empirical and is not an exact dupli cate of the molecular ratios of a pure compound. McNamara (61, p. 276) continues his analysis of the formulation procedure: Calculating the empirical formulas of glazes, glasses, enamels, feldspars and other glassy ma terials the RO group of oxides Is always considered as unity, that is the formula is written so that the number of equivalents of the RpO and RO oxides equals one. In body calculations the Al 2 0 o or RoOq is considered as unity. The number of equivalents of the other groups are then calculated from this basis according to their amounts as indicated by the chemical analysis. This Is accomplished In the following calculations: Total number of RO equivalents CaO 0.003 K20 0.14 Na20 0.03 Total 0Tl73 If the above were a ceramic body, each equivalent would be divided by the number of equivalents of alumina (0.17) instead of the number of equivalents of RO, there fore, reducing the alumina to unity rather than the RO. Total number of RO equivalents: CaO 0.003 K2 0 0.14 Na20 0.03 Total 0.173 136 Divide the number of each equivalent by this total: Si02 1.11 -r 0,173 5 6.42 A12 03 0.17 -r 0.173 - 0.98 CaO 0.003 4- 0.173 " °*02 K2 O 0.14 4- 0.173 = 0.81 = 1.00 Na20 0.03 4- 0.173 * 0.17 The empirical formula is then written according to the following arrangement: 1.0 R0*X R2 03 *Y R02 The empirical formula for the feldspar is written: 0.02 CaO 0.81 KgO 0.98 Al203*6.42 S102 0.17 Na20 The empirical formula of a glaze, and bodies may be calculated from its chemical composition in the manner as described above. The reverse calculation, that of the calculation of the chemical composition of a glaze or body from its empirical formula, may be accomplished by re versing the calculations as described above and as demon strated by McNamara (61, p. 272): Given the empirical formula of a glaze: 0.107 k2o 0.672 CaO *1.00 Al203 *10.0 Si02 0.221 MgO 137 Calculate the percentage composition of the glaze. Oxide Equivalents Molecular Weight Weight of Oxide m KgO 0.107 X 94 10.1 CaO 0.672 X 56 m 37.6 MgO 0.221 X 40 8.84 AI2O3 1.00 X 102 — 10 2 . sio2 10.0 X 60 600 Total 758.54 The total weight of the oxides present Is known as the formula weight of the glaze. It corresponds to the molecular weight of a compound and the calculation is the same as is used to calculate the molecular weight of a complex compound from Its chemical compo sition. The percentage of each oxide in the mixture (or compound In the case of a true chemical compound) is obtained by dividing the Individual oxide weights by the formula weight (molecular weight when a com pound) and multiplying the Individual results by 10 0 . The calculation may be simplified by dividing the formula weight Into 100 and multiplying the result by the individual oxide weights. Formula weight * 758.5 = 0.1318 (factor) Oxide Weight Factor Weight per cent K20 10.1 X 0.1318 1.33 CaO 37.6 X 0.1318 4.95 MgO 8.84 X 0.1318 1.17 A lgO^ 1 0 2 . X 0.1318 13.44 sio2 6 0 0 . X 0.1318 79.1 99.99 Equivalent Weight The equivalent weight of a compound or mixture may be defined as the weight of the material necessary to provide 138 one molecular weight or one formula weight of the substance, m ceramic mixtures most elements tend to form the oxide highest in oxygen; therefore, that oxide Is the one upon which to base the equivalent weight. McNamara (61, p. 280) explains the use of the rule of equivalent weights as follows: The general rule for finding the equivalent weight of a compound or mixture with respect to any of its constituents Is to divide the molecular or formula weight by the number of equivalents of the constituent contained in the compound or mixture. Andrews (2, p. 61) summarizes equivalent weight as The equivalent weight may be greater than, equal to, or less than the molecular or formula weight; but In any case it Is dependent on the part of the material about which the interest Is centered. To avoid further confusion In calculations the term "batch formula weight" is used to distinguish between "formula weight" described above, and "equivalent weight." This distinction Is made to differentiate between the formula weight of a body consisting only of non-volatile oxides, and the formula weight of a raw batch which when fired will produce the finished body. McNamara (61, p. 28l) offers the following example for calculating the "batch formula weight": The batch formula weight is the equivalent weight of the batch with respect to the fired ma teriel, that is, one equivalent of batch will produce one equivalent of finished body. The calculation of a batch formula weight of a glaze 1b given below. It is merely the total of 139 the individual raw materials necessary to produce one equivalent of the finished body glaze or other ceramic product. „ . * , Batch or Recipe Raw Materials in weight units Canadian Feldspar 66.6 Whiting (CaC03) 67.0 MgC03 1 8 .6 EngliBh Chine Clay 2 3 8 . Potters* flint (Si02) 440. Batch formula wt. = 830.2 Batch Calculation-Compounding The empirical formula is the universal method of representing the composition of glazes and bodies. It is also desirable to be able to have calculated the raw batch required to produce the body and also the empirical formula of a fired material produced from a batch of a known compo sition. The following is an illustration of a glaze calcu lation formulated from an empirical formula. The points are listed by Andrews (2 , p. 69) as a procedure of calcu lating the recipe from the formula of a raw glaze, body, or enamel: 1. Arrange the constituent oxides of the formula in a horizontal line. 2. Observe the glaze composition, to note whether there are alkalies present or not. If potassium or Bodium i s p resen t, I t should be added as feldBpar, in which case this is the starting point for compounding the glaze. 140 3. Subtract the equivalents of feldspar from the glaze formula, to take care of the alkalies. 4. Subtract the equivalents of materials that contribute to only one permanent oxide* other than silica* of the glaze. 5. Subtract the equivalents of materials that contribute two permanent oxides of the glaze* but In such order that the alumina and the silica re main last unsatisfied. 6. Finally, satisfy the alumina and the silica in such a way as not to contribute to any of the other permanent oxides of the glaze. The calculation of the formula from the recipe of the glaze is Just the reverse of calculating the recipe from the formula. Andrews (2* p. 73) lists the procedures as follows: 1. Divide the amount of each constituent in the recipe by the equivalent weight of the constitu ent. 2. Construct a table and place the amount of each oxide contained In each constituent in the proper column. 3. Add the equivalent of each oxide. 4. Add the equivalent of all the RO oxides to gether. 5. Arrange in the conventional form of the empirical formula R0*R20^*R02 . Generalizations have been made for the development of glaze construction. As previously stated, the RO group is always in unity in the construction of a glaze and other glassy materials. Binns (7, p. 18) states that the alumina value does not closely follow any rule though there is a 141 definite limit or range for lower temperature glazes; his generalization Is RO • .05-*15 AI2O3 . SIO2 - 3 A^Og plus 1. Holscher and Watts proposed another generalization In the form of a graphical representation of ceramic glaze formu las as shown in Figure 9* Substitution. It Is often necessary to make certain changes in a ceramic composition by substituting one material for another. However, if too many changes are involved, a new calculation would be in order. In making a substitution, it must not be assumed that the new mixture produced is the same product. Ceramic products made from different materials may have decidedly different properties. The following illustrations from Andrews (2, p. 65) represents a simple (l) and a complex (2) substitution: Example 1 - In the following glaze, substitute white lead for red lead. Recipe No. 1: Potash feldspar 55*6 Whiting 30.0 Ball clay 7.7 Flint 32.4 Zinc oxide 8.1 Red lead 114.2 Since 258.5 parts of white lead are equivalent to 228,5 parts of red lead, we have the following pro portion: 258.5:228.5::x:ll4.2 X - 129.2 142 Pig. 9 Graphical Representation of the Molecular Formulas of Ceramic Olazee Source: Permelee, Ceramic Glazes Line a-A^Qr wrfritted « iu w to be mmI mNA time fatted. tjiazms. _ __PjQj wieS fr o n t 25 & 150 egtfimtott g y y - F t T * 1 LEAD PORCELAIN — FRITTED -♦'BRISTOL* U m lt- £ .0 5 unit '•PbO or ZnO O a m t Na u Q n t-tt n BaO^SrOyfrp B01 5 Cone /OJO ///O //00 m o m s Degrees C 144 129,2 parte of white lead must, therefore, be used to replace 114.2 parts of red lead • • • • Example 2 - Suppose in the above glaze No. 1 we wished to replace the potash spar by soda spar. If both were pure spars, we could substitute one for the other In proportion to their equivalent weights, which would be soda spar 524 parts to potash spar 556 parts. The calculation would be: 524 : 556 :: X : 55.6 X * 52.4, or 52.4 parts of soda spar Trlaxlal Diagram m many Investigations It Is desirable to have plotted and blended three-variable systems. This is not fundamentally different from the plotting of two-variable systems, except that the diagram Is an equilateral tri angle, each apex of which represents 100 per cent of one of the materials. Figure 10 was developed by the writer in an investigation of blending three glaze batches. In blending three materials the trlaxlal method is useful, for it is possible to make a controlled investi gation. The trlaxlal diagram is a means of graphically representing the properties resulting from a combination of three variables, and such properties can often be better coordinated with the compositions by the use of diagrams. Another means of blending Is the utilization of equilibrium diagrams for plotting the results of blends as A 1 V5G 2 75 25 0 3 75 0 25 b 50 50 0 5 50 25 25 6 50 0 50 7 25 75 0 a 25 50 25 9 25 25 50 10 25 0 75 i i 0 100 0 12 0 75 25 13 0 50 50 lb 0 25 75 15 0 0 100 Pig. 10 Illustration of Trlaxlal Blanding for Three Olase Batches 146 well as plotting the actual analysis of the resultant fired product to determine the actual chemical formation. Through the use of equilibrium or phase diagrams, the crystalli zation and melting relationship of specific oxides and their combinations have been plotted and are valuable tools for determining reactions at high temperatures. Blending m order that complete information may be obtained about a clay body or glaze, It is often necessary to make a series of compositions or blends. Much work can often be saved through the use of blended batches. A test of the four extreme compositions as shown m Figure 11 will give a sampling of the possibilities of the blend. 'Kiese glazes can be blended in varying proportions for tests of all the intermediate compositions. Preparation of Ceramic Bodies The forming of ceramic clay products requires the preparation of a wetted homogeneous mixture of the raw con stituents. This requirement is determined by the various molding processes which basically controls the method of clay preparation and the physical characteristics of a ce ramic body. Ceramic bodies vaiy in consistency from a rela tively dry mixture with no flow-abillty to highly fluid QLA2E NUMBER 0.50 1 2 3 4 5 6 0.45 7 6 9 to n 12 o 0.40 /J 14 15 16 17 18 & $ 'vj 0.35 19 20 2/ 22 23 24 5 0.30 25 26 27 26 29 30 8 0.25 3/ 32 33 34 35 36 O.IO 0.15 0.20 0.25 0.30 0.35 EQUIVALENTS K±0 Source: Newcomb, Ceramic Whitcwares Pig. 11 Blending Olaze Sllpa 148 suspensions. The variation generally operates between 2-15 Per cent water for the former, and the latter, de pending on the degree of deflocculatlon, from 20 to more than 50 per cent water (46, p. 134)* Generally, the vari ation for Intermediate plastic stages is 15 to 40 per cent. The wide variation in the physical character of ceramic bodies precludes the use of any single mechanism for their preparation. The following Is a discussion of the formulation of clay bodies, glazes, glasses, and vitreous enamels and Includes the preparation of these materials. Each area covers the application of a formula as It pertains to vari ous physical and chemical properties. Clay; In a well prepared clay body, Blnns (7) lists three properties that are necessary to produce a balanced material: plasticity, porosity, and density. The first two are properties of the raw clay, and the last In the fired product. The porosity of the clay In this Instance has reference to the apertures or passages through which the water of plasticity may escape. This avoids distortion or bursting of the clay product in drying. Porosity Is the reverse of plasticity and these two properties are balanced 149 properly according to the requirements demanded by the product. Some natural clays have these properties in their own substance. However, natural clays are almost always red or other colors; there Is no known natural white clay body available. Glazes Glazes are essentially glasses, some having compo sitions very similar to commercial glasses; however, glazes usually have a. higher alumina content. The term glaze as it is used in the ceramic industry indicates a thin glassy coating adhered to the surface of a clay body for the purpose of producing a ceramic product that is impervious to moisture or for the purpose of appearance and decoration. There are a number of different classifications pertaining to the characteristics of glazes; they may be transparent or opaque, colored or colorless, non-crystalline or crystalline, lead or leadless, raw or fritted. Glazes may be divided into three general groups according to their composition and method of preparation: salt glazes, raw or earthy glazes (lead or leadless), and fritted glazes. Salt Glaze. A salt glaze is a vitreous coating formed on the surface of clay ware by subjecting them to the action of common salt fumes at a high temperature 150 during the kiln firing, approximately 2000°F. In the presence of moisture the salt vapors react with the water to form NaOH and HC1. The NaOH vapors which come Into contact with the clay articles react with the silicates or alumina present forming sodium aluminum silicate liquids which upon cooling form a glaze. The salt glaze Is almost transparent allowing the clay body color and texture to show quite clearly. Salt glazing is usually confined almost entirely to heavy clay products, sewer pipes and other structural clay products. The best results are produced on these clays because they are usually higher in silica content than are other finer clays. The color obtained from salt glazing depends upon the condition of the kiln atmosphere and the nature of the clay body. With an oxidizing fire the colors are usually much lighter than with a reduction atmosphere. Parmelee (8 1 , p. 1 7 9 ) summarizes the relationship of the clay and salt glazing colors as follows: White to tan, if ferric oxide content Is not above 1J6 and the silica Is low; or up to 2 .19# ferric oxide If the silica is high. (The ferric oxide content Is calculated on the basis of cal cined clay) Light Brown. If the silica is low and the ferric oxide does not exceed 3 1/2#; or with ferric oxide 2.19 to 3 *5#* if the silica is high. Brown, if the iron oxide lies between 3.5 to 4.755^ 151 Mahogany. if the iron oxide exceeds 4.75# but is less than 8.2#. Black, if the content of iron oxide is greater than 8.2#. Raw Qlazes. Raw glazes are glazes which are com pounded of insoluble raw materials, and fused after they have been applied to the body. The raw materials must be insoluble because the glaze is usually prepared with water as a vehicle of suspension and any soluble substance would be lost by solution or absorption into the clay body. Consequently, such materials as soda ash, borax, and potassium carbonate have to be eliminated from raw glaze compositions. Glazes compounded from raw materials are also classified into leadless glazes and lead glazes. Lead glazes are those glazes utilizing lead oxide as a part or all of the RO group. Lead oxide is one of the most widely used fluxes for low and intermediate range glazes. Tt re acts easily with silica to form low melting lead silicates which form a stable glass without additional oxides. One of the main characteristics of lead glazes is that they have an extended firing range; also, they are less sensi tive to slight changes in the chemical composition which might result from poor preparation. Lead in a glaze is present as PbO but may be introduced as Fb^O^ (red lead), 152 litharge (PbO) or as the basic carbonate of lead [2PbC03 . Pb(0H)2K Colored lead glazes are available In an extensive variety of colors that may be produced by the Introduction of the proper oxides and many Interesting variations may be obtained by altering the amount and kind of the colorless base used. Lead glazes have broad application; they are applied on bodies in the leather-hard, bone-dry, and bisque condition and on many kinds of ware such as art pottery, structural clay products, cooking ware, and sanitary ware. Such glazes have been used for many years because lead minerals are distributed over much of the earth*s surface, the compounds are cheap and easy to recover and can be used in a variety of proportions with the resultant glaze at tractive and pleasant in appearance. Parmelee (8l) gives limits for practical use in the variation of the PbO as approximately 0.7 and 0.4 equivalents. Leadless glazes usually have feldspar introduced to supply the alkalies. In this state the alkalies are in soluble and blended within the raw material. Two other types of leadless glazes than the feldspathic are Bristol glazes and crystalline glazes. The color selection for leadless glazes is much more limited than glazes in the lower firing range. However, a product with more delicate and earthy appearance and texture is obtained. 153 Along with leadless glazes It would be apropos to mention those loam or earth glazes that occur In nature. The most widely known slip glaze In the United States Is called Albany slip obtained along the Hudson Valley In the State of Mew York. Albany slip has a number of unusual properties as a glaze. Parmelee (8l, p. l8l) refers to their reputation to never craze and that they have a very long heat range of 1170°C to 1290°C which affects the color, in Figure 12, Parmelee lists a representative chemical analysis of Albany slip. Silica 56.75 Alumina 15.^7 Ferric Oxide 5.73 Lime 5.78 Magnesia 3.23 Titania (l.00 ca.) Alkalies % 3-25 Unreported are moisture, Ignition loss, etc. Source: Parmelee, Ceramic Glazes. Fig. 12 Representative Chemical Analysis of Albany Slip 154 Fritted Glaze. Tn the discussion of raw glazes, it was stated that the materials to be used in a raw glaze must be insoluble in water or the soluble materials in the batch would be separated through the process of water grinding. This condition limits the resources available in the RO group; these soluble oxides would Include im portant materials in glass and glaze forming such as borax, boric acid, soda and potash. It is possible to use soluble materials in a smelt ing operation known as fritting, which is a preliminary fusicn of certain parts of a glaze batch before it is applied to the body. The two main objectives of fritting are to render soluble substances Insoluble, and to render infusible sub stances fusible. Other advantages gained by fritting are that volatile materials are driven off; shrinkage is re duced; thus rendering of a closer bond between ingredients is accomplished; and the toxic action of lead oxide is re moved • The materials to be used in the frit composition are weighed and thoroughly mixed. The mixture is then placed in a crucible and melted into a glassy fluid either in a tunnel type kiln or in a special furnace. The usual practice is to remove the crucible after the mixture has melted, and drain the molten content into a container of water. The shock to the cooling glass causes it to fracture, 155 which facilitates grinding of the material into a fine powder. The frit mixture contains all of the soluble ma terial and some of the silica. Tt also must contain a greater pert of the insoluble alkaline materials, such as lime and magnesia, because without these the resultant melt (frit) would not be insoluble in water. Certain rules should be applied to make certain the frit materials are compounded within certain limits that insure a successful frit. Andrews (2, p. 80) lists five rules, however, he feels they may have to be compromised on occasion because obeying one rule may result in a violation of another. These rules and how they are to be applied are listed as follows: 1. The ratio of the acid molecules to the basic molecules of a frit should never be less than 1 to 1 and never more than 3 to 1. This rule is designed to keep the frit within the limits of easy fusion .... 2. The ratio of the alkalies to the boric oxide in a frit should be the same as the ratio of the alkalies to the boric oxide in the glaze. Since the alkalies and the boric oxide in a glaze are the soluble constituents, this rule merely states that all of the boric oxide and the alkalies should be put in the frit .... 3. The ratio of the alkalies to the other RO oxides of a frit should never be more than 1 to 1. This is to insure an insoluble frit by sufficiently crossing the alkalies by at least an equal amount of the less soluble RO oxides. 4. The acid element of a frit should always contain silica, and, if boric oxide is present, the 156 ratio of the silica to the boric oxide should be at least 2 to 1 . . . . 5. The alumina in a frit must not greatly exceed 0,2 equivalent. If the alumina is too high it tends to form a very viscous frit, in addition to increasing the refractoriness .... A fritted glaze is calculated in the same manner as a raw glaze or body. If only part of the composition is to be fritted, and this is usually the procedure, the frit is calculated alone and its empirical formula de termined. After smelting and grinding, the frit is in corporated into a glaze batch containing other raw ma terials to satisfy a base glaze formula, when the empiri cal formula of the frit is known, it is treated exactly the same as a feldspar in the calculation of a batch. An alternate use would be through blending procedure utiliz ing the triaxial method as shown in Figure 10. Glasses Glass has been described as a fusion of silica, an amorphous substance, and as an undercooled solution. Norton (76) states glass has been defined in simple terms as an undercooled liquid of very high viscosity. Morey (70, p. 3^)t ranked by ceramists as an authority on glass, defines it as, "A glass is an inorganic substance in a condition which is continuous with, and analogous to, the liquid state of that substance, but which, as the result of 157 having been cooled from a fused condition, has attained so high a degree of viscosity as to be for all practical purposes rigid." The most common commercial glasses are the lime- soda-sllica type used in the manufacture of containers and most other types of inexpensive glassware. These three basic ingredients are inexpensive and available in great quantities, as well as producing a glass to meet the re quired standards. Morey (70, p. 75) defines these require ments as follows: The essential requirements of a commercial glass composition are that It be fluid enough at an indus trially accessible temperature to be melted on a commercial scale; viscous enough to be worked above its freezing point, so that devitrification cannot take place; so viscous at Its freezing po&nt that it will not devltrify; and that the resulting glass have physical properties and chemical durability suitable for the purpose for which it is intended. Morey refers to the number of elements, salts and mixtures that will form glass through controlled manu facture. However, most of the ingredients used to produce commercial glass are rather limited in number. The other compositions are interesting and unquestionably aid in further research of new techniques and new glass compo sitions. Analyses of ancient glass show similarities to modem compositions used in the common glasses. Prom the contemporary point of view, however, commercial glass 158 compositions must meet certain basic requirements of production as previously quoted from Morey, Phillips (82) classifies commercial glass compositions as vitreous silica, alkali silicates, lime glasses, lead glasses, boroslllcate glasses, and special glasses. Vitreous silica glass may be formed by melting a variety of silica minerals, primarily quartz. Coming Glass (22), however, lists the manufacture of silica from a special process of re-treatlng boroslllcate glass. Boro- silicate glass is highly refractory and possesses many desirable properties for chemical, as well as commercial ware under the trade name of "pyrex." Vycon is a trade name for a glass containing 96 per cent silica produced by a special process from pyrex. Special glasses have been developed to possess many unusual properties end in a number of Instances produced as commercial products. Referring again to Coming Glass, they have developed a photosensitive glass that can retain photographic Images through a process utilizing ultra violet light; the image extends throughout its thickness. Coming has also developed glass, "Fotoform," that can be etched into photographically accurate patterns often re ferred to as chemical machining. Another of their develop ments is "Pyrocerara" which was originally developed for rocket nose cones, but more recently, because of its 159 thermal resistance, has been produced as a new commercial line of ovenware. Pyroceram in itself is not a true glass but rather a crystalline refractory material pro duced by the process of devitrification of glass. Glass fibers are another form of special glass used as insu lation, to reinforce plastics, for textiles, and many other uses. Silicones, a form of soluble silica compound have been developed as a new form of lubricant. Phillips also lists colored glasses as a special glass because it involves many problems in chemical compo sitions. The coloring agents are classified by Phillips (82, p. 46) into three types: (1) the color is produced by absorption of certain characteristic frequencies of the incident light by substances in the glass; or (2) the color is produced by particles of Bub- microscopic size precipitated within an originally colorless glass by appropriate heat treatment; or (3) the color may be produced by larger particles, which may either be colored themselves as in aventurine glasses, or colorless as in opals. Phillips continues by stating that it is interesting to observe in the periodic table (See Table ITT) that all coloring agents in (1) above are elements of the first transition group with atomic numbers twenty-two to twenty- nine inclusive on the table. These include the elements titanium, vanadium, chromium, manganese, iron, cobalt, nickel, and copper, "in general," Phillips says (82, p. 46), 160 "these are used to produce the colors in the purple, blue, green portions of the spectrum, but there are exceptions to this," Although colors are basically determined by the colorants employed, glass composition, temperature, and atmospheric furnace conditions are also determinant factors. Because glass Is a non-crystalline material, diffi culty arises as to analysis of composition and structure* Glass maintains no specific structure unity but rather Is classified as a structureless material. It Is the In stability of glass as an undercooled solution that limits the composition range of practical glass. Crystallization, more often termed devitrification, takes place readily outside of the short compositions analyzed through the use of equilibrium diagrams, Morey states that the phase equilibrium relationships are the only factors which de fine the exact temperature and precise composition in the determination of the melting and crystallizing process of glass mixtures containing several materials. He states (70, p. 35) specifically that equilibrium diagrams "offer a means of expressing in compact and graphic form a large amount of information of a type which Is fundamental to the comprehension of many factors vital to ceramic engineer ing and glass technology." 161 Vitreous Enamels Although many considerations given to glasses and glazes also apply to enamels, various processes exist that are peculiar only to enamels. Basically, enamels are fused glass adhered to various metals. It Is this basic consider ation that makes procedures of production different. The chemical composition for enamels is deter mined as described in the section for the calculation and utilization of Identical materials. The batch is developed from the empirical formula. Research in enamels, however, has concluded that certain materials promote a greater bond ing force between the glass and metal. This force was found to correlate with the atomic number group In the periodic table. Those metal oxides within the same group with Iron promoted the greatest adherence; therefore, cobalt, manga nese, and nickel were necessary to create commercial enameled ware through the application of a ground covering or coat containing two or more of these oxides. Ground coats are usually dark blue in color; cover coats of various colors are then applied on the surface. Enamels are smelted or fritted after batching. The process Is the seme as described under fritting; the batch is melted and when it is completely melted, poured Into cold water to fracture the melt as it cools rapidly. The 162 batch Is thoroughly dried, weighed, additions added, and then ground. Mill additions and the required grain size are im portant in enamel slip suspensions. Ball clays up to about 7 per cent are added for this purpose, plus, the addition of an electrolyte. Andrews (3» P. 2 5 5 ) describes an enamel slip as a complex system consisting of a sus pension of several solid phases In one liquid phase. The solids consist of frit, clays, opaciflers, and color oxides; the liquid phase usually consists of a water solution, and may contain gums, dextrin or syrup and possibly electro lytes. The control of the slip involves the balance of the slip materials to provide an enamel with the required physical properties. The control of the specific gravity of the slip is important to enamel application. Enamels may be applied to the metal in various ways depending on the requirements and conditions of the individual materials. Sheet iron and cast iron enamel coats are generally applied by dipping, slushing, or spraying. The enamel has to be thoroughly dried after application. The firing of the enamel is necessary to melt it into a continuous glassy layer. The two major consideraticns for this process is temperature and time. Andrews (3, p. 29*0 163 lists various factors that affect time and temperature; they include the following: , • • the thickness and uniformity of the metal stock, the thickness of the enamel coating, the fineness of the enamel, the resulting product de sired, the ratio of the amount of ware to the re serve heat in the furnace, the weight and construction of the burning (firing) tools, the position and shape of the ware, the amount of preheating, and the radiating properties of the furnace. The preparation of metal surfaces becomes rather complicated because of the numerous metals that are enameled including both ferrous and non-ferrous metals. Diversity is needed in the cleaning operations as well as the develop ment of enamels for these metals. The preparation of sheet iron and steel may vary with the different types of ware, but the object of cleaning remains the same; that is, to produce a clean, polished surface. Andrews (3, p. 76) lists the following methods for cleaning sheet metal sur faces: Annealing is a heating operation, following the shaping of the Iron, to remove any strains in the metal, and, since the metal is heated to redness, the oil is burned off. Most ware does not require an annealing operation; therefore, it is not as common as the other methods. Scaling consists of heating the stock in the presence of acid or sulphur fumes, primarily to clean the ware, although annealing is a secondary function. An oxide scale is, thereby, formed on the surface of the metal, the scale and dirt being consequently re moved together in the pickling operation which follows. Chemical cleaning is a washing operation to re move oil and dirt from the surface of the ware. The 164 chemical cleaner is an alkali and soap solution, the alkali saponifying the soluble oils and the soap aiding in the emulsifiestlon of the oils and the removal of the dirt. Pickling is an operation in which acid solutions are used to remove rust and scale from the metal sur face. The pickle solutions, which are sulphuric or hydrochloric (muriatic) acid, attack the rust and the iron under the scale. The formation of hydrogen gas at the metal surface loosens the scale, forcing it from the iron. The metal surface becomes slightly roughened because of the selective solution of the iron and the surface is left in a suitable condition for enameling. Sheet metal is sand blasted when large pieces of heavy gauge stock are used. Sand blasting is not common, however, as most sheet iron is warped by the force of the sandblast. Improperly cleaned metal surfaces seriously affect the enameling process. It is necessary, therefore, to take careful precautions through the use of one or more of the methods to insure a properly prepared surface. Methods of Preparation The following processes of preparation are employed by industry to control raw materials during the processing of prepared ceramic materials. Wedging. Wedging is the oldest known method for getting clay into a workable condition. This is an essen tial step in preparing it for use by making the clay uniform in texture, removing the air pockets and making it a more pliable mass. The wedging process is accomplished by work ing the clay by hand, cutting the clay mass into halves, 165 and then smacking and slapping the pieces together until freedom from air bubbles and complete uniformity of texture throughout the mass Is achieved. Pugging. The pug mill is mechanization applied to wedging. As the dry clay Is forced through the pug mill, rotating blades turn and knead the clay blending in the water as It is added. The pug mill operation is designed to temper the clay by a continuous process. Some of the difficulties encountered, however, are the poor distri bution of water throughout the clay, and the considerable amount of air introduced Into the clay. The air entrappment causes defects In the extrusion process of forming If it Is not removed. The greatest aid to pugged clay has been the development of the de-airing attachment to the auger machine. De-airing. Clay material that has been prepared with water either by filter-pressing or pugging needs to be de-aired. Usually the auger and the de-airlng machine are attached directly to the pug mill. De-airing, as it is applied to clay products, is the process of removing by vacuum the entrapped and adsorbed air from a wet clay mixture. As the clay enters the vacuum chamber, rotating blades break up the clay mass allowing entrapped air to es cape. The pugged clay under vacuum is compressed and welded by an auger as the clay is extruded In the form of a solid cylinder. 166 Blunging. The blunging operation is the wet mixing of raw materials Into a homogeneous mass. Blungers or agitators are used to prepare the fluid suspension, more commonly known as Blips. Blungers are of varying deBlgn; however, the stirring is generally accomplished by rotating paddles mounted on one or more vertical Bhafts. The clays and water are usually added first and thoroughly mixed. The non-plastic materials are then added and the entire batch Is "blunged" resulting in a smooth fluid slip. The slip is kept constantly in motion to avoid causing the non-plastic material to settle to the bottom, thus forming a hard deposit which is difficult to remove. The slip is screened after complete blunging to remove unmixed lumps or foreign matter. The slip is then pumped into large storage tanks or agitators where it is stored until needed. The storage of slip usually improves the blending process, and removes considerable entrapped air that has been beaten into the slip in the blunger. Ball milling of ceramic bodies that require an extremely homogeneous mass is practiced by some plants in the production of hotel china. This milling operation, either wet or dry, may replace the blunging operation, or the material may be blunged a short time after ball milling. 167 Grinding. The most convenient and efficient method used for glaze grinding is called "ball milling"; so-called because the grinding Is accomplished by a number of small flint or porcelain pebbles that roll continuously inside the mill as It is rotated. The efficiency of the ball mill depends upon certain factors: the volume or weight of the pebbles; the volume or weight of the- batch to be ground; the amount of water used; and the speed of rotation. Ac cording to both Andrews and Parmelee, the greatest effici ency Is attained If the mills are one-half full of various size balls and the charge of materials added on top of the balls should fill the mill three-fourths full. The required amount of water should be added last. The con dition of the slip affects wet milling; a slip may be too thin or too thick to permit efficient milling. A thick slip does not flow properly and retards the action of the balls. A slip too thin allows the material to run off the balls and does not come in contact between them. It has been discovered that control of the speed of the mill is a major factor in efficient milling. When the mill Is rotated too slowly, the balls merely slide and roll over the inner surface. If the mill is rotated at too high a speed, the centrifugal force distributes the charge of balls over the inner surface without any grinding action. Optimum grinding Is accomplished when the rotating mill 1s 168 at a sufficient speed to cause a churning of the balls throughout the entire charge with the maximum effect of bringing the greatest number of moving surfaces into action. The theories regarding the operation of ball mills have received considerable Investigation which has made It possible to standardize ball mill practice. The studies have resulted In the development of reliable methods of operation and control. Filter Pressing. An excess amount of water Is used In the blunger to facilitate the disintegration of clay. In preparing the body for casting, plastic or dry-press processes, this excess water must be removed. The filter press is so designed that It contains a series of metal plates shaped 30 that when they are placed next to each other on a rack, shallow chambers are formed between them. Similarly shaped canvas cloths are fitted between the plates so that when the plates are clamped together the cloth forms a sack into which slip can be continuously pumped through a central opening. As pressure is increased by a slip pump, the water is forced through the canvas and out through holes provided in the bottom of the plates. The clay is retained by the canvas until eventually a solid cake of clay body is formed between the plates. The filter cakes with a final water content of 18 to 25 per cent are removed. 169 The steps in the wet process in body preparation are identical for each of the chief methodB of ware forming: casting, Jlggering, and pressing. Following the filter pressing operation, however, they have to be processed differently. Tf the ware is to be cast, the filter cake must be made into a slip by the addition of water. Tf it is to be Jiggered, the clay cakes need only to be processed through a de-airing machine, as they already contain about the proper water content. If it is to be pressed, they must be dried still more, and pulverized. Dry Mixing. Dry mixing is a recently developed method for preparing ceramic batches. This method consists of blending dry materials of proper purity and particle size and, after a short period of blending, the necessary water added. The dry mixing method is best suited to the prepa ration of bodies for ware formed on presses, such as steatite, tile, and electrical porcelain, because the de sired amount of moisture can be directly controlled at the mixer, Newcomb predicts that the dry mixing method of body preparation may become standard procedure in the whiteware Industry. He lists (75> P* 88) the following six factors in favor of dry mixing: (1) more efficient utilization of factory scrap is possible, (2) moisture content can be more accu rately controlled, (3) changes from one batch formu lation to another can be made much more easily and quickly, (4) power and labor costs are greatly re duced, (5) much less factory space is needed, 170 (6) when a new plant Is built, the Initial In vestment is considerably smaller. Magnetic Separating. There are a number of types of separators in use today. Whatever the design, the purpose Is to remove by magnetic attraction small particles of Iron or Iron minerals that might contaminate the clay body. It is, of course, necessary to ®*ind the mineral fine enough to unlock the magnetic grains. However, If the mineral Is too finely ground the material may not pass through the separator easily because of caking and uneven flow. Chemical Treatment. Ceramic raw materials, except for chemicals used In glazes or special refractories, are seldom chemically treated. Two other exceptions are mag nesite obtained from sea water, and various clays used In paper processing which are bleached with zinc hyposulphite in order to obtain a pure white material. Flocculating. When a substance such as clay Is in a state of suspension its particles repel each other be cause of identical electrical charges. By Introducing a substance to neutralize the electrical charge, the clay particles coagulate into larger groups and precipitate. This method of precipitation when applied to clay sus pension is known as flocculation. Calcium chloride or aluminum chloride are often used as a flocculant for clay slips. 171 Flocculation is utilized in slips which may contain large percentages of non-plastic materials. If the clay and other materials are mixed thoroughly in a slip and then a flocculating agent added to the water, the flocks of clay formed prevent the non-plastic materials from settling separately from the clay. Although the flocculated clay settles slowly, it may be easily refloated by stirring. Glaze and enamel slips are often treated in this manner to prevent the ingredients from separating from each other and settling, Deflocculatlng. It becomes evident upon exami nation of the requirements of clay slips that most proper ties relate to rheologlcal factors, Rheological control, therefore, is of great importance in slip casting. Al though several theories and mathematical formulas have been proposed to analyze the rheological phenomena, pre dictions through equations are not always successful. Viscosity control is possible for a limited application; specific gravity also has limited application for similar reasons. It is known, however, that the addition of alka lies at low concentration causes dispersion of the clay particles producing deflocculation. If the concentration is increased the effect is reversed and flocculation takes place. Sodium carbonate, or sodium silicate, or a combi nation of the two are the most common reagents used for de flocculation of clays. 172 The proportion of water In a slip should be as little as possible to avoid excessive shrinkage of the cast ware. In order to use the smallest proportion of water possible a suitable electrolyte Is used because clays as they are deflocculated become more fluid. If no electrolyte Is used, most dry clays require almost the same percentage of water as clay used to produce a slip of cast ing consistency. With a deflocculant, however, slips may usually be produced that contain approximately 15“25 per cent of water. Usually, non-plastic materials other than clays may be made into dense slips through the use of an adequate deflocculant. To obtain the best results in casting, it is often necessary to use suitable combinations of materials to produce a moderately plastic material of sufficient binding power. Slightly plastic materials are usually preferable to highly plastic ones in casting, because they require less electrolyte to maintain a suitable fluidity and the articles can be more easily removed from the molds. De flocculation, however, reduces the plasticity of clays, while flocculation increases it. Consequently, it is possible to decrease the plasticity of a dry-mix clay by mixing It with a small quantity of a dilute solution of alkali instead of plain water. 173 Searle (98, p. 308) categorizes electrolytes Into five kinds: Acids, which cause flocculation of clays and electro-negative colloids. Bases, which cause deflocculation of clays and electro-negative colloids. Salts, which dissociate into acids and basic ions and many cause either flocculation or deflocculation. Amphoteric electrolytes, which may cause either flocculation or deflocculation, according to circum stances, as aluminum and tin hydrates, which are soluble in both acids and alkalies. Pseudo-acids and pseudo-bases, which are neither acids nor bases, but can become so by intramolecular rearrangement. When electrolytes are added to a slip or suspension of clay in water, they have the effect of either floccu lating or deflocculating in the same manner as colloidal sols and gels. Therefore, the effect of electrolytes on a clay is often unpredictable; for example, the addition of sodium chloride decreases the shrinkage on drying, but the addition of sodium sulphate increases it. Color. Norton states that there are two general methods of measuring color: the Munsell system which is a comparison method with a series of standard samples. The second method is more scientific by the measurement of the transmission or reflection of each wave length in the spectrum by the means of a spectrophotometer. 174 There are qualities of a color that can be measured: hue, chroma, ^nd brilliance. However, there are others that are intangible factors connected with color for which there are no methods of measurement. This is particularly true In ceramics, where translucency or transparency denotes a depth to color. Norton points out (76, p. 191) this variable by stating that, It Is quite possible to find a Munsell color sample of ink on paper to match the color of a thick celadon glaze on an old Chinese vase, but the glaze has a depth that Is quite absent from the ink. The range of colors obtained In glazes usually de pend upon glaze composition, firing temperature, firing condition and coloring oxides. Colors are exhibited In various ways, so that an object may show different colors under different conditions. There also exists, as Norton describes above, the appearance of special types of color. Parmelee and Searle list other glaze qualities such as: opalescence, a pearly or milky appearance; irridescence, an unequal, multi-colored effect; fluorescence, a change of different colors which usually occur on some transparent minerals. Luster is another property of color; it is due to light that Is reflected usually from a metallic glaze surface. Color is more true in an opaque material than in a transparent one, because of the affect of Impurities or 175 body upon the color. Color, however, is usually of a minor consideration in a raw material. In finished products it often becomes an important factor, one which contributes greatly to the beauty of the article. The color of the raw material is not an indication as to its color when burned. A clay that is grey or yellow when in the raw state may turn a deep red color upon firing in a kiln. This is largely due to the organic natural colors that are destroyed when the clay is heated. On oc casion, some iron compounds in clays are a pale color, but develop into a red color when the clay is fired. The ce ramic industry quite often makes use of carbonaceous color ing matter which burns out of the clay by mixing special bodies and pastes with a strong aniline dye. While in the raw state, the materials are strongly colored and remain easy to identify until fired. The use of metallic oxides and other materials to produce color in ceramic products may vary when heated to different temperatures. To obtain the desired color when special agents are used, it is important that the temperature range should be reached but not exceeded. Excessively high temperatures may cause volatilization of the color. Often interesting effects of coloring may be obtained through a variation in the state of the atmosphere in the kiln. Copper oxide, which most often gives a green 176 color in an oxidizing kiln atmosphere, produces a red color in a reducing atmosphere. Other colors are affected in this manner with such materials as Iron oxide or cobalt. Another important factor affecting color 1b the glaze composition. For example, copper oxide in a leaded base glaze produces a strong green color; however, in a leadless glaze, copper oxide produces a bluish-green or turquoise. The preparation of raw materials as presented, illustrates the importance of processing to ceramic products. The methods of calculation and preparation of ceramic product compositions have been discussed in detail as well as the methods for preparing ceramic bodies and coverings. In Chapter VTT the methods of fabricating these bodies are presented with a description of the effects of heat upon the characteristics of drying and the firing processes. CHAPTER VTT ANALYSTS OF PRODUCTTON PROCESSES This chapter is primarily concerned with the various methods of forming ceramic materials, methods of drying, decorative techniques, and thermo-chemical re actions that occur during the firing process. There Is also a discussion of a number of properties and tests that are utilized by the ceramic industry. Forming Methods New fabricating processes have been required to keep pace with the developments of new ceramic raw ma terials } in addition, improvements have been necessary for those processes already in use. Kingery (49, p. 1) believes that the "... development of ceramics having new and better properties for specific applications subsequently leads to new uses for these ceramics and the demand for further improvements." However, the major problem in improving fabricating techniques 1s to develop first an uniformity of materials. For example, investigation of controls of materials has led to efficient production through the utilization of automation and mechanization by such processes as: extrusion, slip casting, plastic forming and jiggering. 177 178 The principles involved in ceramic fabrication processes, according to Kingery (49, p. l) are varied; he describes them as follows: The process of slip casting Is based on the ability to form stable suspensions, the rheology of suspensions, and the absorption of water by plaster molds to form hollow or solid ware. Pressing processes depend on developing suitable methods, compositions, and die designs to make uniform ware economically. Plastic forming processes are baBed on the deformation properties of soft or stiff clay or nonclay pastes. All these processes depend to a great extent on the particle size and shape and particle size distribution of the starting materials. In addition, several new processes have been developed for ceramic fabrication which depend on deformation properties at elevated temperatures, nucleation and crystal growth phenomena, chemical reactions, and other variables. In the beginning, the forming of ceramic articles was done by hand; a method utilized today by art potters and designers. Mechanization, to produce faster, with less skilled labor, and to duplicate products, caused the adoption of molds and dies in the ceramic industry. Concomitantly, the composition of clay and other ceramic materials had to be controlled and developed for the in creased automation of fabricating processes. Increased production and efficiency, and process control for uni formity of product has advanced in ceramics as in other industries. The selection of the method of forming adopted for a particular article to be processed Is determined by 179 such factors as geometric design and size, tolerances, quality of material in the product, and efficiency or economy. Plastic Forming The forming of plastic clay bodies is probably the oldest and most identifiable ceramic fabrication processes. The process of hand forming as slabs or coils may be Identified throughout history as the first forming process. The potter's wheel was to hand forming, as auto matic Jiggers are to wheel throwing today. The potter's wheel was for many years the mechanization of ceramic production; today, the potter's wheel is used primarily by designers of ceramic whiteware products and artist potters. Other forming methods of plastic materials are the mechanical extrusion of plastic clay under pressure through a die; jiggering clay, the forming of one side by means of a plaster form and the other side formed by a template as the mold with the flattened clay is rotated; and plastic pressing, using various shaped dies in a hy draulic presB. The plasticity or workability of the clay mass is the primary determinant for efficiency and mecha nization of plastic fabricating processes. Kingery (^9, p. 79) states that, "Our technical understanding of the 180 basis (clay plasticity) for these processes has been the subject of much misunderstanding and still Is not entirely clear." Extrusion. Extrusion is one process of pressure forming ceramic shapes* such as bricks* tiles* tubes* rods* and many other shapes which are fabricated by forcing a plastic mass* under pressure, through a die followed by cutting into required lengths. 'There apparently Is a great variety of cross sections available that can be extruded successfully from a properly designed die under controlled conditions. These conditions would be focused upon the uniformity and constancy of the materials ex truded. Extrusion machines are of two types, one, a piston operated extrusion which Is an intermittent process used In forming sewer tiles. The other and more versatile machine is the auger extruder which forms a continuous column by a feed screw forcing the material through a die and the sections cut the required length. W. 0. Williamson ((49) in his discussion* "Particle Orientation in Clays and Whitewares and Its Relation to Forming Processes," reported his observations in a system atical study of the orientation phenomena of the inquidi- raensional particles by forming processes* primarily ex trusion. Such microscopic observations revealed information l8l pertaining to the particle arrangement effected by the design of the die and other contributing factors that lead to harmful strains and stresses on extruded materials. These observations assisted in the research to alleviate these factors by Improving the strength, shrinkage control, and control of particle orientation of extruded products. The use of nonplastic materials mixed with small percentages of plasticizers has developed rapidly through extrusion or injection molding processes. One fabricating process utilizes a thermosetting or thermoplastic resin as a plastlclzer. After extrusion, the articles are processed by heat treatment to remove the organic material to prepare the article for firing. This method is used for forming small Bhapes using a nonplastic material, such as alumina for spark plug cores. Plastlcizers, however, make up a certain bulk of the material lowering the bulk density of extruded material. A study of various plastlcizers and materials reported by Collin Hyde (49, p. 108), "Vertical Extrusion of Nonclay Compositions," stated the problem as follows "Basically, the plastlclzer should impart to the mass being extruded properties such as are possessed by a clay body. Experi mental work Is required to arrive at the proper plastl- cizer for use with each individual composition to be ex truded." Hyde reported that the problem In using 182 plastlcizers Is In maintaining the limits controlled by the requirements of the properties of the extruded material. Hyde states that, "The hlgh-denslty requirement complicates the over-all problem because many suggestions recorded by previous investigators, If adopted, result in a decrease in the sintered density." The basic problem is the dis covery and use of a plastlclzer that will not lower the bulk density of the material. This property Is exceedingly important in the high temperatures encountered in rocketry and Jet engines. Jlggerlng. The Jigger machine Is a modification of the potter*s wheel. Although there exists many types or variations of the Jigger machine, fundamentally they are the same in design and accomplish similar or Identi cal operations. The Jlggerlng process is used almost en tirely in the whlteware industry in the forming of plates and a variety of hollow ware. The automatic Jigger is a modification of the hand Jigger and in most large ceramic Industries has superseded the hand method. The automatic Jigger is one of a large and varied group of automatic machines which are working with diversified materials and have become an integral part of American manufacturing techniques. Norton de scribes (76, p. 99) the steps in the automatic operation as follows: 183 A round column of de-aired plastic body is fed to the machine, where It is cut off in correct length and dropped on the Jigger mold* This mold is then pressed up against a heated die that spreads it on the plaster mold almost to Its final size. The die Is heated so that the resulting film of steam will prevent sticking of the body. The mold and formed body are then placed on the Jigger head where they are held by vacuum. The Jlggerlng operation takes off little clay, but produces a smooth finish as the surface Is sprayed with a water mist. The Jlggerlng speed Is much higher than in hand operation, 500 to 1200 rpm. A common feature of all automatic machines Is that certain characteristics of the raw material must be of a uniform quality with variables within certain limits. For successful automatic Jlggerlng the major factor Is a standard level in the plasticity or workability of the body. R. E. Gould and John Lux (49, P. 99) state that the difficulty of controlling these limits arise because, "definitions of plasticity are somewhat theoretical and no Instrument Is available that Is adequate for satis factory measurements." Casting Process Nearly all artware and whlteware are formed In or on plaster molds. Preparation of a mold from the original model through the steps of blocking and casing are im portant processes in ceramic industries. Original models are made by hand or on the potter1s wheel from either sketches or by designing directly in clay or plaster. 184 Plaster molds. The process of forming clay bodies by slip casting Is based on the material plaster of Paris or calcined gypsum. Plaster of Paris Is made from the mineral, gypsum (CaSO^ . 2H20), which when calcined at a temperature between 350°F. and 390°F., affects the follow ing reaction: CaSOjj. . 2H20 --- ► CaSOi* . l/SHgO + 1 I/2H2O (61). The hemihydrlde compound which contains l/2H20 is known as plaster of Paris or calcined gypsum. When the hemihydrlde is mixed with water there occurs a partial solution and a recrystallization of gypsum Into a hard mass with some evolution of heat. The properties of the set material are influenced to a considerable extent by the amount of water added, as shown in Figure 13. McNamara (61, p. 106) describes the use of the chart and the plaster of ParlB-water relationship as follows: The physical properties of the finished plaster depend to a large extent upon the amount of water used In mixing. In general, the more water used the less dense the finished plaster will be and conse quently it will have a higher water absorption and a weaker structure. . • • shows the relation between the water content of the plaster mix and the strength and absorption of the finished plaster. . • • However, a plaster which is mixed with 90 pints of water per 100 pounds of plaster will be classed as a soft porous plaster, and will not give long life when used in molds. A plaster containing approximately 60 pints of water per 100 pounds of plaster will be hard and durable while at the same time its water absorption will be decreased only about 25 per cent. 185 s t s t t t t I -H -26 £ -2t £ -20 C -X -32 -21 -31 -ZZ >s - 36 * -38 5 -25 - 10 i I - 24 i -12 1 1 -H ^ t? -16 -K X -16 4 4! -M5 * -SO CtMiitmy t f Mlv too to. ^luftr J To 3> /B To $ 35 CtMilttny • AmJi t f \f ik t t r f r tOO tf. Phittr Source i Melaaara, C«rMl 9 t» CllX Product! m J Whltawaraa Fig. 13 Xffoot of Wator Contant on Propartlas of Plaator 186 Plaster of Paris plays a very Important part in the ceramic industry and considerable research In mold making has standardized many of the bases In the operation. Prom the economic point of view, general requirements of a working Jigger or slip mold are that It accurately repre sent the product, produce saleable ware with uniform density, and provide long service. C. M. I*ambe (49, p. 35) In his report, "Preparation and Use of Plaster Molds," lists a number of specific requirements for a working mold as follows: (l) Low normal consistency so that slurries for the densest molds may be easily mixed and poured without pinholes or loss of detail. (2) Moderate but uniform expansion so that, while the working mold will free Itself from the case mold easily, It will (a) not bind or warp, (b) fit the Jigger ring, and (c) attain an accurate predetermined size and shape. (3) Sufficiently long and uniform period of plasticity to enable the moldmaker to complete pourings without haste and to plan work with the assurance that the length of the plastic period will not change from mix to mix. (4) Suf ficient regularity in physical properties of the calcined gypsum so that thousands of molds may be made over a period of years without significant strength to resist ordinary abuse. Slip Casting. The development of mechanization in the casting process requires additional refinements of control from those listed for plaster of Paris molds. The condition of the slip and the raw materials used for casting are Important factors bearing on the rate and quality of ware produced. The fluidity of a slip is one of Its most important properties; this is determined by 187 the water content of the Blip, the nature of the solids, and by certain chemical compounds which may be added to the slip. The use of deflocculents to control fluidity of casting slips is almost universal; however, some clays contain enough soluble salts, or possess enough colloidal properties to cause sufficient fluidity in the slip without further additions. Control requirements may be divided into control of sllpmaklng procedures, and testing of viscosity and specific gravity of the slip. H. S. Magid (49, p. 42), in "Controls Required and Problems Encountered in Production Slip Casting" lists the following as general control tests for slip making procedures: 1. A fixed order of successive addition to the batch, e.g., water, electrolyte, barium carbonate, ball clayB, china clays, flint, spars. 2. Control of the mixing or blunging time duration. 3. Control of viscosity and specific gravity. 4. Barium and electrolyte adjustments. Sulfate determination. 5. Control of temperatures at all stages from initial blunging to finished storage. 6 . Application of casting rate, thixotrophy, and "feel tests • The deflocculation of a slip is usually achieved by preparing a series of slips with varying specific 188 gravities, varying amounts of deflocculant, and using varying percentages of sodium Bilicate and sodium car bonate, After the clay slips have aged and agitated to equilibrium, each of the samples made are tested for apparent viscosity and charted aB shown in Figure 14. The deflocculant is kept at a minimum to produce the most economical slip, Norton lists a drain casting slip located at B, and a solid casting Blip possibly at A. There are a number of other factors that describe characteristics required of a casting slip, Norton (76, p, 91) assesses these requirements as follows: 1. A low enough viscosity to flow Into the mold readily* 2. A low rate of settling out on standing. 3. Ability to drain cleanly (in drain casting). 4. Giving sound casts in solid casting. 5. Stability of properties when stored. 6 . Quick release from mold. 7. Proper casting rate for each operation. 8 . Low drying shrinkage after casting. 9. High dry strength after casting. 10. High extensibility when partly dried. 11. Freedom from trapped air. 12. Freedom from scumming. There are various factors involved in the casting process which are not dependent entirely upon the nature APPARENT VISCOSITY IN POISES i. 1 VsoiyCre o htwr Slip. Vhitewars a for Curves Viscosity l1* Fig. 8ource: Norton, Elements of Ceramics of Elements Norton, 8ource: too 0 0. 04 .0 0 1 0 . 0 2 .0 0 01 0 0 E G T E CN O DEFLOCCULENT OF CENT PER WEIGHT ri atns t (B) at Castings Drain oi atns r ae t A and (A) at aade are Castings Solid G. SG s.G. - - s.G. - - 67 .6 1 m 189 190 of the casting slip. Searle (98, p. 330) lists these factors as follows: 1. The time required to give the required thick ness of deposit. 2. Alteration of the nature of the slip dtkrlng casting. 3. The proportion of water in the cast clay on the mold after casting. 4. The porosity of the mold. 5. The degree of saturation of the mold. 6 . The resistance of cast clay to the passage of water. Casting. The casting process consists of pouring a slip of suitable composition into a plaster of Paris mold, in which It remains a sufficient time to enable the mold to absorb water or other vehicle until a desired thick ness of clay or other material has coated the inBide of the mold. The superfluous slip is poured out of the mold if hollow drain casting, or the excess slip is left in the mold for solid casting. Pressure Forming Pressure forming has developed into one of the most important forming methods for special electrical and magnetic ceramic pieces of small dimension. The ware is formed with little or no liquid content, rapid and precise forming of simple shapes is achieved, and a variety of pressing methods and die designs can he used for different shapes and compositions. The accuracy required of an electrical part of a dimensional precision ceramic material depends on many factors such as shrinkage within the composition, the particle size and Its distribution, the density of the article before firing (green density), and the firing cycle and maximum temperature for maximum fired density. A defi nition of pressure forming, In this Instance dry pressing, Is proposed by Hans T h u m a u e r (49, p. 63)1 as follows: Dry pressing, as applied to the production of technical ceramics, comprises the compacting of a dry, granulated ceramic powder In a metallic die under high pressure. The moisture content of the granulated powder may be varied between 0# and 4#, but rarely more. The granules are free-flowing, but relatively nonplastic. They are merely crushed and densely packed under pressure, to form a co herent compact. Control of materials In pressure forming as in other methods, Is paramount to automation In the ceramic Industries. The granular nonplastic material can not retain its form after pressing because it lacks plas ticity and colloidal properties. Binders have been de veloped to use in pressing that hold the granular parti cles In the pressed shape and b u m out In the firing stage. Hans Thumauer (49, p. 6 6 ) states that the choice of binder and granular distribution affect the pressing operation: Because of the fact that the procedure of granu lation and the choice of binders have probably the 192 greatest effect on fired shrinkage and control of dimensions. It Is imperative that manufacturing conditions be kept constant as possible. Forming dieB are designed for certain percentages of shrinkage, and a change in the method of granu lation or binder may make a die obsolete. A constant difficulty with the pressing methods above, Is the pressure differential caused by wall friction and differential shrinkage, nonuniformity, and warping tendencies In the finished ware. Hydrostatic molding Is a recent development used to overcome difficulties caused by differential pressures. In this process a rubber mold Is filled with a dry powder, inserted In a liquid, and high pressure applied equally through the liquid In all di rections on the mold. Application of hydrostatic molding to production methods involves a number of problems associated with economical production. These difficulties of production and product control were overcome by researchers at Champion Spark Plug Company. Feasibility was accomplished by the use of heavy-walled rubber molds, sufficiently elastic to act as a fluid, with fluid pressure applied with the die enclosure and the rubber mold. Kingery (49, p. 73) re ported In "Hydrostatic Molding," a number of advantages In hydrostatic forming as follows: There are several advantages to the hydrostatic molding method, the primary one being that it makes possible the production of high length-diameter radio articles without the use of wet methods or excessive amounts of plasticlzers. Ware formed Is 193 of uniform density and shrinkage, has no drying shrinkage, and lower firing shrinkage than that produced with other forming methods. For these reasons, the process is also being used for pro ducing equidlmensional ware. Ware produced by hydrostatic molding is probably the most uniform and highest quality ceramic ware being produced in large-scale production. Glass Forming Glass products are mostly formed in the melted or viscous state; therefore, the fabricating processes and principles are different than those for clay or non-plastic forming. Glass processing has become so highly mechanized that the glass industry consists of approximately 38 Per cent of the entire ceramic products shipped as shown in Table I in Chapter TV. Research and development of new products has assisted in the growth. Glass production without mechanization is pro duction by various hand processes. Tt is recognized, how ever, that the early discovery of the blow-plpe was revo lutionary to the primitive methods used. Blowing glass is still used in some plants in the forming of art ware on an individualized basis; for example, Steuben Glass at the Coming Glass Works. Besides blowing, "off-hand" forming by the use of hand tools is also in use. Other hand methods utilize blowing into molds as a form of mass pro duction because the mold controls the form. Phillips (82) divides molds for glass forming into three types--iron, 194 paste, and press molds; the names were derived from the method of using the mold not the Iron of which they are all made. The distinction Is that Iron molds are heated and the temperature maintained; the paste mold Is cooled Intermittently, however, a paste Is used to prevent the glass and mold sticking. The two molds above are used by blowing the glass Into the molds. In the third mold, or press mold, the ware Is formed as the glass Is pressed between two molds: an outside mold and a plunger shaped inside mold. Uhtll recently, mechanization of forming processes was comprised of the ancient methods of hand forming with machine application. The complexity of forming glass articles by machines are many. The machine must be de signed to complete the forming process before the glass changes from a syrupy consistency to a solid. Phillips classifies glass forming machines into five types: blow ing, pressing, drawing, rolling, and casting. Some of these methods are used in combination such as press-and- blow machines, drawing and rolling. The development of Coming's ribbon machine and the use of the blowing and mold combination now produce up to two thousand forms per minute (22, p. 24). Tubing is now drawn at high speeds through the perfection of glass with the required properties. 195 Flat glass is either drawn or drawn and rolled depending on the forming process, m the Colburn process, the glass Is drawn horizontally over a series of rollers into the annealing oven. In the Fourcault Process the glass is drawn vertically through a series of rollers which are enclosed to form the lehr. Other production processes used are the grinding of the glass surfaces to produce plate glass, the lami nation of safety glass, and the manufacture of fiber glass. Glass also requires special handling after the forming process such s b annealing which is a heat treatment or gradual cooling of the glass to remove excessive strains. Edges are either ground with a fine abrasive and polished or fire polished. Fire polishing is the heating of the edges causing it to melt slightly and finish the edges. Although lamp-working might not be considered a glass forming process, it does involve the conversion of raw material by heat from ready-made tubing and cane into glass menageries. Intricate custom built chemical appa ratus is also constructed through the lamp-working method of fabrication. Drying Products The efficiency of automatic equipment is often dependent upon, and determined by, the efficiency of the 196 drying procedure* Efficient drying Is accomplished through control of the drying rate and control of the circulating air. To achieve maximum economy in the manufacturing operation, these two factors of drying determine the amount of salable product and the cost. Drying..,.Hate The drying of clay and other materials containing more than 10 per cent water Is accompanied by a shrinkage in volume caused by the particles moving closer together upon the removal of water. When shrinkage occurs it compli cates the drying process by introducing factors other than the simple removal of water. The shrinkage of clay is achieved by stages depending on the moisture content of the clay. Free or surface water is first removed by evapo ration and controlled by the air flow and its moisture content. The first stage, therefore, is the removal of moisture by evaporation. The rate of evaporation is de pendent upon factors effecting the condition of the drying air such as velocity, direction, relative humidity, and temperature. Tt is during the first stage of drying that most of the clay shrinkage occurs because during this time the v/ater separating the particles evaporates permitting closer contact of the particles. 197 The air flow is responsible for heating the ware and carrying off the moisture evaporated from the drying ware. The heated air and ware decreases the viscosity of the water, thus increasing the rate of water flow in the material permitting the pore water an easier exit without rupturing the ware. The second stage of drying is the internal vapor ization of moisture through capillary action. Porosity of unfired materials is a factor determining shrinkage, warpage, strains and cracking of ware. Finely ground and dense bodies have a much slower rate of drying, because of the lack of open pores, than has a material of a non plastic nature, A common method of correcting excessive shrinkage is by the addition of non-plastic or more coarsely ground materials. Consideration of the factors common to shrinkage are listed by Norton (76, p. 107) as follows: ", . . it 1s evident that to increase the rate of water flow in a given material we have the choice of increasing the permeability, increasing the moisture gradient, or de creasing the viscosity of the water." Drying Systems There are three basic drying systems in operation today, with the possibility of the infrared radiation method being considered a fourth. The utilization of infrared has 198 the advantage of heat transfer within the ware, therefore, decreasing the drying time tremendously and permitting the re-use of Jigger molds many times a day without their be coming saturated. However, the overall expense of Infra red heat has been the major deterent for widespread use. The three basic systems used for drying ware are controlled systems of temperature, velocity and relative humidity; they are listed by McNamara (61, p. 130) as follows: First, those in which the ware is subjected to a high temperature and a low percentage of humidity throughout the entire drying period. Second, those in which the percentage humidity is kept low during the whole drying time, while the temperature Is raised to a maximum at the end. Third, those In which the temperature is raised during the drying but the moisture content of the drying air Is kept near saturation in the early part of the operation and then lowered m the latter part. The maximum economy in drying clay wares may be achieved If proper control is maintained. The atmospheric conditions within the dryer need to be advantageous for absorbing additional moisture and of sufficient temper ature to raise the Interior temperature to an optimum rate. Air flow, also, is an important factor in controlling the drying of ware. There exists many different designs of driers; however, the system of drying utilizes one of the above as its basic principle. 199 Design Development Designers in industry, and more specifically of industrial processes, need to be cognizant of many factors that appear to be unrelated to design development or the product. Well-designed products Bhould be the responsi bility of the industry; however, the industry should "feel the pulse" of the consumers to improve design ideas in products. Six rules were proposed by William Goldsmith (39, p. 272) as a method of achieving optimum results from a design program in industry; however, he states that indus try is reluctant to accept the idea along with the change. In his article, "The Power of Positive Progress. • . . Six Rules for Creative Use of Research and Design," Goldsmith listed the rules as follows: First— Make the product or the service satisfy people— the consumer and his way of life--not things or a situation or a pat formula of pricing or production efficiency. Second. Take a broad look at many markets— the collective demands of all consumers--not just the market you are dealing in; look at the marketing framework, its long-range potential as well as its past, present, and even immediate future. Third. Keep an eye on your competitor, but donft let this omnipresent factor exert too much influence; donft allow "me-too-ism" to replace creative manage ment and research leadership. Fourth, Stop searching out all the reasons a design or research program proposed can*t be an 200 action plan; spend your energies finding how It can achieve reality. Fifth, Extend design and research functions farther into the future; don*t restrict them to a technical service • • • • Sixth, Establish within your organization the attitudes and organizational structure that are able to utilize and complement the results of creative study in any area. Product design is controlled by technical consider ations and the designer's knowledge of material gained from research or through practical use, "Every designer whether on paper or of model parts," states Bernard Leach (52, p, 21) "should have first-hand experience not only of the processes of manufacture but also of the limitations no less than the potentialities of his materials,11 He con tinues by stating that fresh design can only be achieved through closer contact between industry and the designer. Consideration must be given to the fabricating processes as well as good design. Each process has Its special problem relating to the mold or die and the ma terial and product. All considerations need to be kept in mind for a successful conclusion of design development. Decorative Processes Most processes established by industry are limited to a number of standardized methods. The process usually is of a type adaptable to mechanization although 201 considerable hand decoration is still used. Dinner-ware striping is applied by hand; Steuben ware is hand ground and etched; these hand processes naturally increase the cost. Decorative processes have been researched through various studies, and numerous books have been written. Brief descriptions are given of selected processes that the writer believes are exemplary of industry. Basically, decoration may be applied at four different stages on whiteware and art pottery: the plastic state, greenware, bisqueware, and glost ware. Corresponding to those states of condition are modeling, slip painting (including engobe) underglaze, and overglaze. Decalcomanlas, produced through a lithographic process, consist of a printing process utilizing underglaze or overglaze colors rather than ink. Norton (76) describes their application through the process of wetting the paper carrying the design and transferring the design to the ware. This process is used extensively in the whitewares indus try; in fact, many of the larger ceramic plants operate their own decalcomania printing operation. The silk screen process of design transfer lends itself to some mechani zation which increases production appreciably. Tn this process rather intricate designs may be reproduced. Other processes are utilized such as those listed by Newcomb: 202 stencil, embossing, stamping. One other rather interesting process reported by Norton is the photographic method of photo-etching through an applied gelatine. Decorative processes applied to glass involve such methods as etching, cutting, copper-wheel engraving. These methods are used at the Steuben Glass Works at Corning Glass Co., Coming, New York where the "glass in action" exhibit is established to allow visitors to observe these processes. Other techniques consist of applying lusterB or a noble metal and firing at a low temperature to form and overglaze. Today, sandblasting and acid etching are little used in the industry. Silvering, or the manufacture of mirrors, should be considered as a special form of decoration. As previously stated, one rather unique process recently developed by Coming Glass Co. is photosensitized glass in which a colored picture may be developed. The picture becomes a permanent part of the glass. There have been many other processes developed through the centuries which are described in books for those interested. Two studies by Herbert H Sanders, a Master's thesis and a Ph.D. dissertation at The Ohio State University are excellent investigations of decorative processes• Glaze Application Each method of applying glaze has ita own advantages. Spraying is generally considered the best way to apply an all-over glaze to a product. The other three methods, each of which also may be used in combination with another, are sometimes faster and more economical: pouring solves the problem of glazing the inside of small-mouthed pieces; brushing requires the least amount of glaze; and, dipping is particularly adaptable for fast glazing of smaller clay pieces. Although glazes may be applied by one of the above mentioned methods, spraying gives a more accurate control. "When mechanized," states Newcomb, "this process is by far the most efficient way of applying glaze." He continues by referring to the relationship of size and spraying, "When the ware is too large to be handled in dip tubs, or when the glaze is to be applied only to certain parts of the ware, spraying is the satisfactory method." Fully auto matic spray equipment has been used in production to achieve excellent results in labor saving and increased production. A number of types of spray equipment is manu factured; however, the controlling factor for efficient spraying is uniformity of the glaze formula. Viscosity is checked regularly to maintain a proper specific gravity for the glaze slip. 204 Dipping, as a glazing process, is controlled as In spraying by the viscosity of the glaze slip and the type of ceramic body to be glazed* The more porous the body the greater the glaze absorption; consequently, the glaze deposited may be too thick. This being the case the glaze needs to have a lower viscosity. Tf the ceramic body were fairly non-absorbent, the reverse exists and the glaze slip needs to have a higher viscosity. Hand brushing and pouring have a restricted use in the ceramic industry. Brushing is limited to brush deco rating. Pouring is usually limited to applying glaze to the inside of narrow necked products. Further information about the numerous decorative processes are available for review in the literature. This area has become another specialized field within the ceramic industry, especially in the whiteware industries. Firing and Settings Firing The effect of heat on ceramic materials is a final and determining factor in the production of ceramic products. Heat, when applied to ceramic materials, converts the raw material into a solid, hard material with valuable and distinct properties. Ceramic technology is based on the re action of non-metallic minerals under the influence of heat. 205 Tt ia the changes that take place under theBe conditions of temperature change that determine many properties of ceramic materials and products. Heat and Temperature These terms are often used interchangeably to denote a deviation in atmospheric conditions in a kiln or dryer. They are, however, different In that heat, as defined by Searle (98, p. 563)* 11. . . is a form of energy which Im parts an increase of motion to the ultimate particles (mole cules) of which all matter is composed," He continues by describing the method of transfer, "and it may be trans ferred from one body to another, either by direct contact or through a third body." Temperature, as differentiated by Searle, is de pendent upon the amount of heat, the mass and volume of the substance, and the nature of the substance. Heat measurement is termed "calorimetry"; temperature measure ment is termed "thermometry" or "pyrometry". With an understanding of the thermal factors— heat expressed in calories and temperature in thermo or pyro units— measure ments can be made. The two major scales for measuring temperature are Fahrenheit and Centigrade. The major heat measurement unit is expressed in an English measure termed "British Thermal 206 Uhit, ” abbreviated B.T.U. Sears (99, P. 565)/ in Mechanics. Heat and Sound, defines the unit as, "One B.T.U. Is the quantity of heat which must be supplied to one pound of water to raise its temperature through one fahrenhelt de gree." Heat values may be converted Into a variety of energy values: mechanical equivalent (Joule), watt-hours, and calories. Conversion tables with predetermined values have been developed. Factors of thermal conductivity important in kiln design are refractories, and economy of firing In volving heat transmission which Is accomplished by conduction convection, and radiation. All of the changes effected by heat or temperature are subject to formulas and equations b o that efficiency of operation may be calculated as well as the physical changes occurring in the material when sub jected to heat or temperature. Temperature Measurement and Controls Much of the science of ceramic technology occurs at this period In the processing of ceramic materials. There fore, continuing research and progress Is determined by the accurate measurement of temperature as well as the methods of control and recording devices. A concept of heat and temperature was presented in the above section, "Heat and Temperature," in which they were given as units of measure ment. The measurement of temperature was termed thermometry 207 for the lower range temperatures between about -30°C to 300°C. The high-temperature measurement Is called pyrometry. To be of further aid in the study of temperature controls, the fundamental concept of temperature measurement must be understood. McNamara and Dulberg (62, p. 171) state that the body temperature may be defined as "the property of a body which determines the sensation of warmth and coldness received from It." More exactly, they define the temper ature of a body as "the thermal state considered with refer ence to its ability to communicate heat to other bodies." The development of pyrometry was receded by the use of sight Judgment to determine temperatures; however, with the de mand for increased production, a dependable means of rapid temperature measurement and control was necessary. Auto mation and mechanization in ceramic processes also demand uniformity of ware through the use of automatic recorders and controls. Tt Is relatively simple to construct an arrangement of instruments for a specific experiment to measure the temperature. This may be accomplished by various methods such as building an instrument to measure the temperature of a thermocouple Junction, the average temperature of a volume of mercury or alcohol, or to measure the total radi ation from a specific source. Because of the importance 208 placed upon temperature measurement# the subject should be covered as thoroughly as possible. Day# In Qlass Re search Methods, classified measuring devices# which are available for use, into types# application# use, accuracy# and limitations, A graphic illustration In the use of temperature measurement devices may be observed In Figure 15# as well as the various commonly used combinations. McNamara and Dulberg (62# p. 172) state that pyrometric Instruments are constructed with many substances that are measurable. They list the following as those properties of the most Importance# together with an example of each: 1. Increase in dimensions. Mercury In glass thermometer, 2. increase In pressure# If confined. The gas thermometer, 3. Change in electromotive force developed when in contact with some other substance. Thermocouples. 4. Change in electrical resistance. Resistance thermometers, 5. increase in the amount of radiation from the surface of the body. Optical and total radiation pyrometers. 6. Change in color of the body. Temper colors observed in some heat treating operations. 7. Change In state. Melting points of pure elements and compounds# and pyrometric cones. 209 Opt/eo! Ay -omo te r H>qh Rangi A %ot/oma1/e Range fig i/o m e t^ dp. Ptl Thtr odometer ►- C o~ C o n ti m ta n T h a rnocaapf* Ft * C o n ifb/* tan 7 her mo too/ok ^brotnot A/vmof 7 hormotovpM IJobta Mi to / Thormi'topple Mi MU Tbtrmomtty 9« i fittaoL Thtrmomt tor VW, y fjth ct Thermometer ¥• i i i I XX I_I ±-L i i i i X XXX ‘III -450 •00 1000 1500 l06C 2500 3000 7500 TCMPERATURC.lT) So urea: McNamara and Dulbarg, Fundaaantala of Caraalea Fig. 15 Banga of Taaparatura Instnwanta 210 Temperature control Is accomplished by various means depending on the other measurable factors Involved, To control the temperature of equipment generally means some device or method of maintaining a constant temper ature. Day states that "Constancy of temperature can theoretically be most perfectly achieved by holding the heating rate constant and keeping all of the heat losses constant." However, changes in air temperature, humidity and other natural conditions as well as defective operation of a kiln cause variations in temperature. Potentiometers, millivoltmeters, and galvanometers are various instruments used In the construction of methods of temperature measurement and temperature control. Po tentiometers can also be modified in design to convert them into recorders. Used in conjunction with the above Instru ments are controllers which perform the operation of con trolling the fuel supply whether gas or electrical fuel. Controls of temperature In industry has become an involved and elaborate operation. Usually one control panel operates and controls all of the factors mentioned above: temper ature, kiln atmosphere, air velocity, fuel supply, and ex haust supply. The previously described devices are more recent means of temperature measurement developed for quick and accurate measurement. These existing devices, however, do 211 not give an indication of the actual condition of the kiln and to what effect the conditions are affecting the ceramic material, Pyrometric cones have been designed and used because they react similarly as the ceramic bodies in vitrification. The cones are composed of various ceramic materials and designed to melt and sag within a specific temperature range and time; they are arranged in graduated series of cones 022 to 42, with an average temperature interval of approximately 35°P. Cones are used primarily to indicate the final conditions of ceramic materials in selected locations within the kiln. There are certain conditions within the kiln during the firing period that cause the cones to be inaccurate such as kiln atmosphere which is the principal cause of the cone failure. Cones react most satisfactory when there is a neutral or oxidizing atmosphere in the kiln. This atmos pheric condition, however, is difficult to maintain in gas or coal fired kilns which produce conditions such as carbon izing (reduction) and sulphuring. These conditions cause abnormal functioning of the cones. Cold air from kiln cracks and open peepholes, temperature fluctuation, fire flashing, and dust of fluxing materials are some other reasons for cone failure. Besides these disadvantages in the use of pyrometric cones, McNamara and Dulberg (62, p. 2 1 8 ) mention that there are 212 . . . some serious disadvantages which limit their use to only one form of heat treating operation, namely heating to some temperature above red heat. The cones are of no use whatever in drying, in heating ware to 1112 F (600 C), or in the cooling operation, in many products these stages of the firing operation are Just as important as the maturing temperature of the material and In some cases, • • • are even more Important. Cones cannot be used for any heat treatment involving a necessary fluctuation of the temperature or where it Is desirable to hold a furnace at a cer tain temperature for a long time. In general, it is recommended that cones be used In conjunction with other types of measuring devices. The cones indicate the actual firing cycle, pyrometers give quick and accurate temperature measurement, and controllers and recorders control the constancy of temperature and a permanent record of the firing operation for reference to the properties of the product. TypeB of Kilns The following presentation is limited to a brief discussion of the classification of kilns, kiln design principles, typeB of fuels, and a listing of a few physical changes that occur in the ware during firing. Each of the above mentioned items is a complete research problem for the ceramic industry. Therefore, only the basic principles are discussed in this section; additional information is available from the references. 213 Kilns are described as to whether the ceramic products within it are subjected to open fire or the ware Is enclosed either by the use of saggers, fire clay boxes, or by a closed kiln chamber referred to as a muffle. Muffles and saggers, a form of protection for the ware to prevent direct contact with flames and combustion gases, are necessary for the control of most ceramic colors and decoration. Kilns are described further as to the kind of fuel utilized, the method of introducing the fuel, the type of ware to be produced, and the temperature range required. Descriptions of kiln classifications involve further de~ tails such as fuels: gas, oil, electricity, coal; methods of introducing fuel: blower, updraft, downdraft; type of ware: insulation, fire brick, salt glaze, in industry, kilns have still another classification: periodic and continuous. A periodic kiln is fired intermittently by loading and beginning the heating from cold to hot, to body maturing temperature, and slowly cooled. A tunnel kiln Is a continuous kiln, either straight or circular, which has a constant kiln temperature maintained while the ware is passed through on a conveyor. Other types of products such as glass are melted in furnaces which are similar to kilns except that they are designed and constructed differently because of their 214 special use. The same general principles of kiln design are applicable to furnaces because of the basic refractory materials required. Kiln Design Principles Kilns are designed to utilize the most economical fuel available and constructed to achieve the greatest efficiency. The most economical fuel utilization is based on such factors as complete combustion, air flow, and heat transfer. The design factors include the combustion con siderations in kiln construction as well as the size of the fire box, height and size of the stack, and forced or natural air flow. All of these factors are measurable and a balancing of equations usually determines kiln fuel efficiency. The construction involves such principles as type of refractory materials and type of ware to be fired. These considerations are important when one takes into account the durability of the kiln. Glass, for example, is almost a universal solvent and usually chemically at tacks any refractory material. Other considerations are given to various firing conditions such as type, size, and the finishing of ware. The various considerations that are necessary for the use of refractory materials are listed by Phillips (82, p. 143) as follows: 215 The porosity, thennal expansion, thermal con ductivity, and mechanical strength are all important, in varying degree, depending upon the application. The kind and quality of refractory most suitable in any particular case depends upon many factors, among them the followings (l) temperature, (2) continuity of operation, (3) rapidity and range of temperature changes, (4) kind of fuel, (5) abrasion, and (6) character of glass, gases, etc., in contact with the refractories. Design factors also muBt be considered: (l) type of construction, (2) dimensions of walls, arches, etc., (3) load Imposed, (4J conditions of heating— from one side or both, (5 ) function of the refractories— whether heat to be confined or trans mitted, (6) impinging flames or hot spots, and (7) ventilation. Ceramic industries are converting to continuous rather than periodic kilns because of the thermal effici ency and more accurate control systems. Continuous kilns are not cooled to permit the removal of the fired ware and the stacking of ware and refiring, but rather are maintained at a controlled constant temperature. The recirculation of hot air to preheat the ware and the kiln removes excessive strains and stresses caused by periodically changing temper atures. An intricate temperature measurement and control system for tunnel kilns is established by a series of thermo couples which are connected to a bank of panels and permits the control of the kiln by one man in a centralized locatiai. Already mentioned in this section was the use of saggers to protect the ware from the open flame; other types of kiln furniture are manufactured to support shelves, and to keep the glazed ware from direct contact with the shelves. Shelves, saggers and shelf supports are made of 216 various refractory materials, usually a mixture of silicon carbide, that should not deteriorate in the firing. The firing or efficiency of firing is also affected by the quantity of settings, because these supports absorb a considerable quantity of heat. Prom the point of view of economy, it is desirable to reduce the number and weight of the refractories to as few as possible. One major change occurring in the ceramic industry has been the exclusion of saggers in preference to the muffle or chamber kiln con struction. Proper settings mean less warpage due to strains and stresses produced in the ware, which ultimately means increased production. Production is also increased by efficient utilization of space; the greatest amount of ware is stacked in the kiln space. Physical and chemical changes and defects occur during firing. The following section presents a few of the common defects which heat effects in clays, glazes, glasses, and vitreous enamels. Firing Change_g_ and_ Defects in Clays The following are a few of the defects in clays: Sulphuring. Sulphur from combustion gases causes bloating of the clay body. Non-plastic material will aid in reducing bloating as well as a kiln adjustment from a reducing to oxidizing kiln atmosphere. 217 Changes in color. Many of the characteristics of s clay may be determined by the color changes during the firing process. Wilson (130* P* 158) states that, "Firing is a qualitative and rough quantatlve method for determin ing the iron content of clays." Other metallic oxides w hich may con tam in ate a clay body also affect the color c h a n g e s• Hardness. With the completion of the firing process, . a durable degree of hardness has occurred by the sintering and vitrification reaction. Moh*s hardness scale is the comparative test usually applied. Wilson states that hard ness depends on the density, tensile strength, and shear strength of the material, "and has been defined," he con tinues, "as resistance to permanent deformation." Strength. Strength of fired ceramic materials is achieved through the sintering (interlocking of crystals), or to the degree of fusion in the vitrification process. Waroage. Warpage is a change of shape closely allied to shrinkage and porosity. Wilson (130) states that warpage during firing may be caused by three factors: first, the continuation or relief of Btrains in the body Bet up during the forming or drying operation or by segre gation as a result of improper mixing; second, sagging from weight after the body has reached a plastic condition during vitrification; third, irregular shrinkage of the piece caused by non-uniform application of heat. 218 % Shrinkage. Shrinkage or the change in volume and the progressive change in shrinkage during firing are major considerations in testing clays for use. A high shrinkage usually indicates a dense body with considerable strength. A small shrinkage indicates the presence of a large quantity of non-plaBtlc material which has not become vitrified, or that the clay had passed beyond the maturing temperature. Through the balance of various materials, shrinkage may be controlled to meet required specifications. Firing Changes and Defects In Glazes The following are a few of the defects in glazes. Crazing. Minute cracks within the glaze may appear during firing or as the piece cools. While crackled glazes are used for certain decorative effects for artware, unintentional crackling is usually undesirable in utilitarian ware. The coefficient of expansion of the glaze 1b too high relative to that of the clay body. Newcomb (75, p. 2 0 5 ) lists various wayB for curing crazing through altering glaze composition: 1. By altering the glaze composition: (a) Raise the maturing point by adding flint or feldspar. (b) Increase B2 O3 at the expense of S 102* (c) increase the firing temperature by one or two cones. 219 (<3) Hold at highest temperature for a longer period. (e) increase CaO at expense of KgO. 2. By altering the body composition: (a) increase the flint content, decrease clay. (b) Fire body to a higher temperature. (c) Grind the flint finer. Shivering. This Is the reverse of crazing and is caused by Improper glaze fit. Corrections are the reverse for crazing, usually requiring a decrease of flint in either the glaze or the body. Shivering is the flaking off of the glaze from edges and curved surfaces. Crawling. Crawling Is the gathering of glaze In bunches or raised sections and other portions of the ware Is left bare. A common cause for crawling is dust or grease on the bisque ware; less handling and cleanliness helps to eliminate it. Other causes might be an underfired body, a too finely ground glaze material, and too thick glaze application. Plnhollng. Pinholes or minute circular pits in the glaze are usually caused by gas bubbling resulting from the reaction of glaze materials and temperature. A longer firing period usually eliminates this defect. 220 Firing Changes and Defects in Vitreous Enamela The defects for vitreous enamels are listed below. Blistering. Blistering is similar to pinholes in glazes in that the enamel has not been given sufficient time to smooth over a gas bubble or the gas has not escaped. Improperly cleaned metal and underfiring of the enamel is a cause for blistering. Chipping. Chipping, as in glaze shivering, is the cracking off of pieces of enamel. Causes may be extended to dirty metal or less thermal expansion than the metal. Flshscale. Fishscale Is probably the most trouble some defect occurring in enamels because the causes are so diversified. This makes the correction a long process of elimination for It becomes necessary to check the control of the enamel throughout the entire process. Firing Changes and Defects in OlaBS The following are a few of the defects in glass. Stones. Stones are the most difficult defect to eliminate. They develop either through imbedded bits of furnace refractory, a piece of undlssolved or crystallized silica, or crystals due to devitrification. Usually it re quires the cooling of the furnace and possible dismantling and rebuilding the pot. 221 Cords. Cords are caused by the lack of homogenlety of the glass due to differences in composition or unequal cooling. They may be Identified as narrow, stringy bandB having an Index of refraction different from the glass body. Seeds and Blisters. Both are caused by air or gas bubbles In the glass melt and are different only in size. They are broken blisters which develop sharp cutting edges, therefore producing unuseable material. There are many reactions that develop during the firing period that have to be taken into consideration so that the product has the required physical and chemical properties. These are presented and discussed in the following section on thermo-chemical reactions. Thermal Chemical Reactions The effects of heat on ceramic materials is the final and determining factor of properties of ceramic products. The Industry Is based on the action of heat to produce reaction In materials, for It Is the thermal chemi cal reaction that takes place during the temperature change that determines many properties of ceramic materials. Rles (90, p. 269) states that, "When clays are subjected to a rising temperature a number of changes of a physical or chemical nature may take place." He Includes such changes as loss of volatile constituents, vitrification, and 222 changes In volume, color, porosity, hardness, and specific gravity, Wilson (130, p. 145), in CeranHcs; Clay Tech nology. lists changes which correspond to Rles*, but more explicitly divides the firing of clay ware into three periods: 1. Dehydration a. Mechanical dehydration or water smoking, 20 to 150°C. b. Chemical dehydration or Chemical water- smoking, 150 to 600C. 2. Oxidation, 350 to 950°C, 3. Vitrification, 900° to plus, followed by fusion, Binns (7, p. 5), in his lecture at Alfred Uni versity, makes a distinction between the terms vitrifi cation and denslfication. He differentiates the two as follows: A vitrified ware is quite dense or glass-like, which Is the true meaning of the word. Under the influence of a high-temperature, a clay body will proceed towardB vitrification but the progress is arrested at the point required and predetermined. The word "denslfication" has been coined as ex plaining the process undergone by nearly all ce ramic wares. It may be observed from the statements above that clay and other ceramic materials undergo a dehydration period: by the removal of water in its various forms; by the removal of organic and other volatile constituents during the oxidation period; and, by the termination or 223 completion of vitrification. Also, vitrification to some ceramic materials means overfiring that may cause such defects as distortion or bloating. Thermal behavior of ceramic materials Is a chemical or physical reaction or both, in which equilibrium of the reaction is maintained. J. Willard Gibbs (40, p. 94), in Ceramics: A Symposium, proposes a method of studying this state: In studying the behavior of materials at high as at low temperatures we are concerned with find ing the answers to two main questions: (1 ) what Is the equilibrium state to which the material is tend ing under the conditions to which It Is subjected, and (2 ) at what rate does It tend towards the equi librium state, under these conditions Equilibrium Diagrams To find the answers to Gibbs' questions in the above quote, It is necessary to know the foundation of ceramic science: high-temperature silicate chemistry with an understanding of the interpretation and control of changes through reactions. A study of chemical re actions of low-temperature differs from high-temperature only in technology, the fundamental laws of chemistry apply equally to all of Its branches. Tn the hlgh-temper- ature range new chemical techniques had to be developed so that chemical laws could be applied. 224 m a study of the conditions which affect the equilibrium of ceramic materials at high-temperatures, a mixture or compound must first be cooled to room temper- ature. Many materials poBe problems because of the In version process In which crystallization In the material takes place* Silicate liquids, however, are viscous and form stable glassy materials upon rapid cooling by quenching. The stable condition of the glassy materials permits study of them to determine the termination point of the reaction, and In what phase the quantity of liquid formed at hlgh-temperature• It Is through the use of the quenching process and the application of Gibbs■ rule, that the study of ceramic reactions has been perfected to a high degree; they have contributed to the accumulation of considerable information regarding the silicate chemistry. Equilibrium stages of observation have been developed graphically into diagrams. McNamara and Dulberg (62, p. 309) define equilibrium diagrams as "a graph or suitable figure upon which are marked the fields of stability of the phases of one or more elements or compounds.” Because of the complexity of ceramic reactions, systems of more than three components are not attempted; however, it Is possible to produce a part of such a system and work out a diagram. 225 The phase rule, as applied above, was proposed with in certain llmltB or rules by Gibbs. The theory of the phase rule Is applied to a series of tests of a combination of materials in which they are heated to a specific temper ature and the reaction suspended with the results examined to determine the state of equilibrium. Norton(76) co n siders It to be one of the great contributions to science for on it is based the physical chemistry of the ceramic f i e l d . The most comprehensive study and collection of phase diagrams Is that complied by Levin, McMurdie and Hall. Their presentation, printed in 1956, is a collection of the many researches made of reactions under the phase rule. This important work (55, p. 6 ) defines phase rules as "The diagram known variously as phase diagram, equilibri um diagram, and so forth, is essentially a graphical ex pression of the phase rule." The usual mathematical form of the phase rule is represented by them as follows: P+F-C+2. Tn this equation, C, represents the number of components of the system; JP represents the number of phases present at equilibrium; and F represents the degrees of freedom (variance) of the system. The interpretation of the equilibrium diagrams can best be accomplished through the application of a single phase, such as water, which is described and represented in 226 Figure 16. Norton (76, p. 117) describes the system as, . . . "a single-component diagram with pressure as the ordinate and temperature as the abscissa. At point a, for example, there are three phases, crystal A, liquid and vapor." The application of the phase rule is equated as: P + V = C + 2; 3 + V = l + 2;V**0. ThuB, in Figure 16, a. is an invariant point with no degrees of freedom. Along the line ab. there are two components, crystal A and vapor, so here there would be one degree of freedom, either pressure or temperature. Norton (76, p. 117) continues in his description and illustration of the phase rule by applying it to a two-component system. Norton*s representation of the two- component system is represented in Figure 17 and described as follows: . . • there 1s shown a two-component diagram with one compound AB and two eutectics. In the same way as for the previous diagram it may be shown that the eutectic points a. and b have three phases, liquid and two solids, consequently, if a composition AB cools, it will completely crystallize at point c. and the solid phase will cool in this form. However, if a compo sition at d is cooled, the first crystals will come out at the liquidus curve, and the amount of crystals will increase as the temperature falls until the solidus line is reached. There the last of the liquid phase dis appears . The relative amounts of crystal and glass in a field may be determined graphically as follows. Take, for example, point h and draw a horizontal line inter secting the liquidus boundary. The ratio of solid to liquid is then hf/hg. by the so-called lever principle. LIQ.UID CRYSTAL CL i CRYSTAL 5 2 c£ VAPOR TEMPERATURE" ---- *- Sourcat Norton, Blaaanta of Caramlca Pig. 16 Single-Component Equilibrium Diagram A + L l B+L s & g AB COMPOSITION Source* Norton, Elementa of Caramlca Plgo 17 Two-Component Bquillbriua Diagram 228 It should be re-emphasized that the phase rule and the application of the rule in the ceramic industry is an Important development. Furthermore, the collection of the researched equilibrium phases under one cover in Levin, McMurdie and Hall^ book has made the information available to most people concerned with research. The diagram in Figure 18, and the following de scription Is an Illustration of an equilibrium diagram applied to a two-component system SiC^'AlgC^ by Bowen and Greig (62, p. 334). This diagram is included for the pur poses of illustrating the phase relations of the system, and that this system Is probably the most helpful and Is used most frequently in the firing of all clay products including refractories. As shown in the diagram Figure 18, the curved line on the left shows that pure silica melts at 3l42°F., and reaches a eutectic point at 2820°F with the addition of alumina. This point Is reached by a balanced ratio of material containing 94.5 per cent SiC>2 and 5-5 per cent AlgO^. Following the curved line from the eutectic point to the right, it can be seen that as the alumina content is increased the final melting temperature increases al though some liquid Is always present above 2820°F. The final stage of the phase begins at the point where corundum and mullite are formed (55 per cent AI2O3 and 45 per cent 229 WEIGHT PFR CENT Slflfe 100 70 60 50 40 JO 20 10 MElTWfc POINT Of SILICA (cRISTOBAUTt), I726'C, J M2‘F MfLTINC POINT OF ALUMINA ftORUNDUM),20500.7/22'F 3 8 0 0 I 5 2050 o 7 6 0 0 __ 2000 LIQUID Is 3RUND4/M + IIQUID- m o o 7 4 0 0 " 1 "o t «*F I 1800 3 2 0 0 _Ik .. CORUNDl/M 7/42. Fig* 18 Equilibrium Diagram of tbe System Al203*Sio2 230 Si02 ).at 3326°F. As the temperature is increased the corundum melts leaving mulllte the only stable compound of silica and alumina at high temperatures. Today, there are in existence diagrams of many compounds which have been developed and published. The quenching method in establishing the equilibrium is the accepted procedure, A study of a particular diagram con taining those compounds studied may assist in determining what ceramic materials may be used, what per cent of each, and what temperature is necessary to acquire the desired product properties. This is one of the major developments in ceramic research; it has advanced the ceramic industry in effecting the improvement and development of new products. Eutectics and Related Phenomena The most common method of detemining or pre determining a eutectic is through a study of desirable systems of equilibrium diagrams. Eutectics ere important in the process of fusion in glaze, glass, and other covering^ as well as many clay products. "An eutectic," as defined by Parmelee, "is the lowest melting mixture of the constitu ents actually making up the same system." (8l, p. 90) The eutectic may be a melting point lower than that of a number of constituents individually; there can exist also more than one eutectic in the same system. "The eutectic 231 temperature," says Parmelee, "is a definite and repro ducible characteristic of the system." This again can be studied through the numerous systems that have been dia gramed. Liquid, solid, and liquid-solid states exist under the same conditions, and identical reactions. A review of equilibrium diagrams discloses that eutectics are not always possible by mixing any two or more constituents and that more than one eutectic may be possible in a system. Other phenomena related to a knowledge of equilibrium diagrams and eutectics are discussed in the preceding section. Liquid and/or Solid State Reaction Sintering in the presence of a liquid is as old as ceramic technology (^9). This process exists when fluxes or impurities within the ceramic body react to temperature by melting and forming a glassy matrix to bond the less fusible materials together. Most often the term vitrifi cation is used to denote this phase of reaction. Binns (7) states that the liquid phase could be a point of re action which is terminated at a predetermined temperature before true vitrification. This reaction was graphically represented in Figure 18 in a two-component equilibrium diagram. A more recent development of sintering in ceramics has been that of bonding of pure elements without a liquid 232 phase represented. The technique of recrystallizatlon was already in use to process spinel colors for coloring glazes and bodies. A more recent development, however, involves the pure elements of alumina, calcium fluoride, ferrite, and others. This phenomenon as used In ceramics Is a phase change in the solid state without a glassy matrix. Burke defines sintering as the consolidation of an aggregate of fine particles upon heating (49). Sintering is one form of recrystallizatlon that applies to changes in microstructure that occur In crystalline or largely crystalline bodies when atoms move to a position of greater stability. Most of the solid-state sintering investigations have been initiated due to the interest of powder metal lurgists with problems of sintering without a liquid phase, and the interest in obtaining ceramic compositions for various desirable electrical, magnetic, or refractory properties. The liquid, and liquid-solid systems of the compositions can be established through the investigation of phase diagrams. Various studies have been made to establish theories concerning the particle formation during the sintering process by Burke and Kingery (49). Many times the process and procedure for obtaining the desired results are known, but the proving of correct theories as to how It happens remains unknown. However, the increased 233 knowledge of basic theory has developed a more exacting ceramic science. Vitrification. Porosity and Absorption During the firing period and until its termination certain chemical reactions occur in clay bodies ultimately leading to "freezing" the material or complete fusion to the point of vitrification. Previously in this chapter, the thermal reactions were discussed; the three periods of dehydration, oxidation, and vitrification, eutectic points were established; and diagrams of solid and liquid state systems were determined. Newcomb (75» P* 1^6) stateB that during this period up to vitrification the ware proceeds through phases of certain thermal lags and accelerations due to "endothermic (heat-absorbing) and exothermic (heat- producing) reactions, inversions, fusion, crystallization, dissociation, and combination." The vitrification period usually begins at about 900°C for most clay wares and extends upward toward the highest temperature attainable without distorting the ware. Usually at the beginning of vitrification period a certain amount of shrinkage and increased strength developes which is believed to be caused by sintering. As the temperature increases, the recrystallizatlon rate increases and new 234 crystal forms are developed. Newcomb (75, P* 148) defines the degree of vitrification as follows: The degree of vitrification of the ware, In sum, Is dependent primarily upon the amount and fluidity of the molten glass and upon the amount and character of the pore space to be filled. Tf the molten portion of the body Is large and is very fluid, the temperature range that may be used for firing will be narrow. Con versely, a body that develops a viscous glass will have a long firing range. For this reason, studies on the viscosity of glass have been of considerable practical benefit to the whltewares Industry. The molten glass referred to by Newcomb develops to a greater degree at the higher temperature end of the vitri fication range. The remaining solid particles become coated with the molten glass which generally does not crystallize upon cooling but remains as a glass and binds together the crystalline particles. The development of strength in a material through vitrification Is dependent upon the extent of glassy formation partially controlled by the temperature and the composition of the body, particularly the amount of fluxing material. Porosity and absorption are related to the process of physical properties of fired products. Absorption can determine porosity through the control of various materials In a composition. The determination of a number of physi cal properties and changes that occur during the firing period are Important to the ceramic Industry,* many times they determine the usefulness of the fired articles. The 235 properties of porosity, and its relation to absorption are determined by the weight differential between a dry ceramic article and the amount of liquid absorbed in the pores of the article. The testing methods are presented in the following section, "Properties and Tests of Ceramic Ma terials." Properties and Tests of Ceramic Material The testing of specific properties of ceramic ma terials Is a detailed and systematic procedure. Specific procedures have been initiated for testing standard proper ties by such organizations as the American Ceramic Society and the American Society for Testing Material. Tt is possi ble to prove or disapprove a theory through a series of accurately controlled experiments and tests, or to deter mine the property of a material through the proper selection of testing procedures. Although many testing procedures have been standard ized as to method, the human equation as an unknown factor for error always exists. Steps may be taken, however, that assists in minimizing or even alleviating this factor. Day (24) proposes that testing and experimentation are dependent on a realistic analysis which must follow a "rigorous rou tine" of procedures for accurate comparative measurements 236 in order to produce the most effective work. Day continues by stating that every measurement made in research to technology should follow this routine. He concludes (24, p. 11) his statement, Tf, for instance, the weight of several objects is to be determined, they will be weighed most accu rately if the same balance and the same weighing procedure is uBed and, of course, the set of weights used in the balance has already been compared ac cording to a most rigorous procedure, ultimately to standard weights at the Bureau of Standards in Washington. Careful measurements and procedures are demanded in technology bo that a series of tests or experiments can be made systematically and accurately* Variables must remain constant to be effective; therefore, it becomes necessary to follow procedures that are predetermined or standardized or those that are preferred by specialist groups. Discussing methods of decreasing the human factor, Day (24, p. 11) states the following: When you measure a temperature with a thermocouple, you must use exactly the same procedure or one proven to be equally as good as the procedure used in cali brating the thermocouple. Tn measuring a length with a scale, you must look at the divisions from a di rection perpendicular to the direction of the scale to avoid parallax Just as was done in making and cali brating the scale. Most measurements are comparative and the technologist who forms habits of identical procedure about details as well as the other major objectives will get more accurate and meaningful data. Hillebrand and Lundell (44, p. 2) present procedures or steps for inorganic analysis which they believe represent 237 standards for basic principles. The proposed steps do not determine the actual analysis but only the initial consider ations: The analyses that were proposed are as follows: "The principal operations in applied inorganic analysis are those of (l) taking the original sample; (2) preparing the laboratory sample; (3) preparing the sample for weighing; (4) weighing the sample; (5) choosing or developing the method of analysis; and (6) preparing the solution for the determination." in the ceramic field it becomes apparent that properties and tests are divided or grouped into two classes: those properties and tests for unfired ceramic materials; those properties and tests for fired material. McNamara (61) acknowledges this difference by differentiating be tween testing clays and testing clay products. He included such clay testing standard methods as obtaining a repre sentative sampling of material and subsequent treatment for test preparation; the formation of clay trials using standard size molds; and the forming and handling of clay test pieces including methods of drying. Other standards for testing clays are listed by McNamara, Selected test standards are briefly presented as samples for both testing clays and clay products: Figure 19 is a test for clay plasticity, and Figure 20 a test for the fired properties of a clay product. These examples are among the many possi ble testing procedures that may be applied to ceramic 238 Test Pieces: The test pieces shall be made approxi mately 30 by 30 by 45 mm. (l 1/2x1 1/8 x 1 7/8 inches). It is apparent that the dry dimensions will vary with different clays. Plastic Weight: The edges and comerB of three test pieces shall be rubbed lightly with the finger to prevent loss in handling. They shall then be weighed on a balance to an accuracy of 0.1 gram. Drying: After the plastic weight is obtained the test pieces Bhall be allowed to dry at room temperature until air dry. They shall then be dried at between 64°C. and 76°C. for at least five hours and finally at 110°C. until approximately constant in weight. Dry Weight: The dried test pieces shall be cooled to room temperature in a desiccator and then weighed with the same accuracy as before. Calculation: The water of plasticity shall be calculated as a percentage of the weight of the dry clay bar, by the following formula: T - x 100 Wd in which T - per cent water of plasticity Wp * weight of the plastic test piece Wd * weight of the dry test piece Report: The average of the three values obtained shall be reported as the per cent water of plasticity. Source: McNamara, Ceramics: Clay Products and Whltewares. Pig. 19 Standard Method for Testing for Water of Plasticity 239 Apparent Porosity. The apparent porosity shall be calcu lated by means of the following formula: P = g^~Wf x 100 in which P = the per cent apparent porosity Sf * weight of the saturated fired test piece in grams Wf * weight of the fired piece in grams Vf = volume of the fired test piece in cubic centimeters Volume Change. The volume change shall be determined by the relation bi = * 1 0 0 in which bj =■ per cent volume change Vd = volume of the dry test piece in cubic centi meters . Apparent Specific Gravity. Apparent specific gravity is the specific gravity of the water-impermeable portion of the specimen, that is, solid material plus sealed pores of cavi ties. Apparent specific gravity is then the weight per unit of volume of water-impermeable portion of the specimen. The apparent specific gravity shall be determined by the formula n - Wf u “ Vf-(Sf-Wf) in which G =■ the apparent specific gravity. Hardness. Changes in the hardness are determined by cutting the trials with a knife blade or noting the relative hard ness of the trials as compared with steel. Absorption. Absorption shall be reported as a percentage of the weight of the dry sample, and shall be obtained by dividing the weight of water absorbed, in grams, by the weight of the dry test piece, in grams. 2^0 Plotting Results. When the results are plotted in graphi- cal form (and this is advisable) heat treatment is prefer ably expressed in cone numbers. Under each cone number at which a trial is drawn, the reading of the temperature measuring instrument In degrees Centigrade shall be given. Equal distances on the abscissa and ordinate shall repre sent 2 cones and 5# porosity respectively. The same value of coordinates shall be used In expressing volume changes. Sources McNamara, Ceramics: Clay Products and White ware s. Pig. 20 Standard Method for Testing Fired Properties of Clay Products materials. The writer did not believe It necessary to re cord or even outline the many procedures listed by The American Ceramic Society and the American Society for Test ing Materials for these references are readily available to anyone. An extensive listing would be difficult to maintain for new tests are constantly being adopted, as well as re visions of those already in use. It was also believed that a sampling of the procedures would suggest the necessary type of material and equipment that is needed for testing procedures. Th reviewing this chapter, and Part III in general, It becomes apparent that research procedures, recording and reporting, are stressed throughout the discussion. It must be emphasized that successful operations In ceramic tech nology are dependent on the accuracy of systematic research and experimentation. Accuracy in reporting the procedures 241 and the results most often gives validity to researches and experimentations in that the variables to be measured may be controlled to maintain a constant or changed variable more pertinent to existing conditions. Day (24, p. 13) maintains that records written in detail about vari ables are the fundamentals of scientific research and that, Conversely, an adopted written procedure must fix all the variables which matter. Non-reproduc ible results always have their cause in unrecognized variables or variables which are not sufficiently controlled in the procedure. It happens entirely too often that a whole series of experiments is nullified or a published research paper proves to be of little value because important conditions of the experiments were not recorded. Tn the preceding chapter an analysis of production processes was presented with the final stages of production climaxed by the thermo-chemical reactions of ceramic ma terials. Various selected techniques were established as test procedures for ceramic materials as well as ceramic products. The material presented in Part TTT was a selected analysis representative of ceramic technology. The research of the technological material and its presentation required decisions that were difficult to make; therefore, the se lections presented were only those the writer believed to be pertinent to the study. Unquestionably, many of the areas discussed could involve major experimentation and re search by specialists; this was not the purpose for Part TIT. 242 Tf additional knowledge is needed, the many bibliographical references are available. Undoubtedly, additional refer ences are always needed to expand research and experimen tation in the ceramic field. \ PART TTT ORGANIZATION OP THE SUBJECT MATTER CHAPTER VIII CURRICULAR ELEMENTS This part of the study is an analysis of the technological resource material presented in Part IT* Prom the analysis, a selection of basic curricular elements was organized into a compilation of pertinent subject matter. The subject matter Is in no way a specific curriculum proposal foi4 a level of training, but rather a selection of basic learning elements discernible to the writer that may be applicable to the various educational levels. However, a specific proposal for one unit of instruction derived from the following curricular elements is presented in Part TV for the technical level. Although scientific knowledge has accumulated throughout the centuries to lay the foundation for modem research techniques, it has only been in the last half century that new applications have been discovered as well as new atomic theories developed. Through scientific re search, dynamic changes have been initiated in the ceramic industry. 2^3 244 The field of research in ceramic technology is so large that It has taken many years to understand and sub stantiate the basic principles involved. The major problem has been the difficulties experienced In obtaining pure sub stances, the general insolubility and apparent inertness of most ceramic materials at temperatures below a dull-red heat, and the need for the development of testing and recording the constitution and properties of materials and products. At present, many important fundamental principles need further investigation In areas such as colloidal phenomena, distribution of water in drying products, and the effects of temperature on ceramic materials. There has been a substantial accumulation of research recorded which has caused changes to take place in many phases of the ceramic Industry in manufacturing processes. The following outlines are concerned with an Intro duction to research techniques and procedures, and appli cation of the techniques and procedures as they apply to selected areas In ceramics. The subject matter, repre sented in the outlines, is divided Into the following sequential elements of the technological research: Scien tific Research, Analysis of Ceramic Material and Classifi cations, Composition and Preparation of Ceramic Materials, Ceramic Processes, and Tests of Ceramic Materials and Products. 2^5 Scientific Research This section is organized to represent an orien tation to ceramic technology and Its place in the American economy. Introduction to research techniques and a selected listing of various basic working laws as they apply to the ceramic technology are presented in the outline. The physi cal and chemical reactions that are inherent in ceramic materials and the method of measurement and control of them are also suggested. The basic fundamental knowledge requi site to technological research are presented as suggested elements throughout the curricular outlines. I. Nature of Ceramics A. Orientation to Ceramic Technology 1. Terminology 2. Etymology of "Ceramic" 3. Scope of the Industry B. Orientation to Occupational Field 1. Technical 2. Supervisory 3. Sales 4. Designing IT. Introduction to Research A. Language of Research —c 1. Centigrade vs. Fahrenheit 246 2* inches vs • Centimeters 3. C.g.s. — Centimeter, grams, seconds B. BaBic Working Laws 1. Electricity and Electronics a. Ohm's law b. Power law * c. Current * d. Voltage e. Resistance f . Calculation for small furnaces g. Calculation for wiring devices Optics. a . Snell's Law of Refraction b. Laws of Reflection c. Focal Length Law d. Size of Object and image e. Optical systems 1) Human eye 2) Magnifier 3) Microscope 4) Telescope 5) Inference bands 3. Physical Chemistry a. Four Gas Laws 1) Avogadros Law of Equal Molecular Volumes 2) Actual Weights of Equal Volumes of Oases are Pro portional to Their Mole cular Weights 3) Boyle1s Law 4) Charles' Law b. Understanding Atomic Weights, Isotopes, and the Periodic Table c. Understanding Molecular Weights, Valence, and Equations d. Study of Vapor Pressures, Bolling Points, and Preezlng Points e. Ions, Electromotive Series, and Corrosion f. understanding of Oxidation and Reduction Methods and Devices 1. Temperature Measurements a. Methods 1) Thermometers 2) Bimetal 3) Thermocouples - Types 4) Contact Thermocouples 5) Resistance Thermometer 6) Optical Pyrometer 7) Bolometer 8) Suction Pyrometer 248 2. Temperature Control a. Understanding Principles 1) Heat Capacity 2) Control of Heat Input 3) Control of Heat Loss b. Automatic Temperature Control 1) On-Off Regulation 2) High-Low Regulation 3) Proportioning Control c. Controllers and Time-Temperature Schedules d. Resistances 3. Potentiometers and Bridge Circuits and General Principles D, Construction of Experimental Furnaces ITT. Development of Scientific Procedures A. Procedures in Experiments 1, Standardization with Controlled Variables 2, Experimental B. Record Keeping 1. Procedure Change 2. Up-To-Date vs. Obsolete Procedures 3. Process Specifications 4. Reporting C. Measurements D. Investigation of Published Research 1. Bulletins and Journals of the American Ceramic Society 2. Scientific Reports and Bulletins 3. industrial Publications Application to Ceramic Technology A. Elements of Crystal Chemistry 1. Properties of Atoms 2, Classification 3* Crystal Structure 4. Polymorphism 5. Mineral Structures a. Silicates b. Kaolinite c. Montmorlllonite d. Micaceous e. Hydrated Aluminous 6. Identification of Minerals a. Optical b. Microscopic c . X-Ray d . Thermal 7. Crystalline Bonds 8. Atomic Structure B. Rheological Phenomena 1. Properties of Solid-Liquid Systems a. Plasticity b. Viscosity c. Plow Rate 2• Ton Exchange a. Cation Exchange Capacity b. Mechanisms c. Clay Mineral Structures d. Adsorption e. Flocculation and Deflocculation 3, Colloids a. Effect of Particle size b. Particle Aggregation c. investigation of Colloidal Theories Chemical Constitution of Ceramic Minerals 1. Acids, Bases, and Salts 2. Molecular Structure of Solids 3. Chemical Constitution of Materials Crystalline and Glassy State of Matter 1. Crystalline Bonds 2. Atomic Structure 3. Glass Structure and Composition k. Phase Rule and Equilibrium Diagrams Physico-Chemical Reactions 1. Factors Influencing Chemical Reaction 251 a. Heat, Time, Pressure b. Speed of Reaction 2. Phase Condition a. Eutectics b. Phase Rule Analysis of Ceramic Material and Classifications The fundamental curricular elements pertinent to research techniques have been presented. Concomitantly, the assimilation of sufficient knowledge of the ceramic technology is necessary in the area of physical and chemical properties of raw materials and finished products. Such a technical investigation illustrates the importance of raw material control to mechanization. This section 1b an outline of an analysis of sub ject matter of the properties of ,,ra w ,, materials as to their identification and methods of preparation. The classi fication of products is also presented to characterize and Identify ceramic products. T. Ceramic Materials A. Definition B. Origin and Occurence of Clays and Ceramic Materials 1. Ceramic Geology 2. Classification 3. Characteristics 252 C. Mineraloglcal Composition 1. Formation of Minerals 2. Crystallography 3. Examination D. Physical Structure 1. Texture 2. Homogeneity 3. Porosity 4. Permeability E. Identification 1. Descriptive mineralogy F. Physical State 1. Solids 2. Pastes 3. Slips 4. Colloids 5. State of Aggregation 6. Alteration 7* Plasticity G. Properties of Ceramic Materials 1. Color 2. Hardness 3. Strength 4. Determination of Strength 5. Hydraulic 6. Elasticity 7. Porosity 8. Firing Properties 9. Plasticity IT. Classification of Ceramic Products A. Characteristics, Identification, and Properties 1. Structural 2. Refractories 3. Whitewares 4. Glasses, Coverings, and Vitreous Enamels 5. Cements, Plaster, and Limes 6. Abrasive 7. Cermets, Ceroganics, Asbestos, and Synthetic Gems III. Preparation of Raw Materials A . Mining Methods B. Disintegration 1. Crushing 2. Grinding C. Size Classification 1. Screening 2. Milling D* Treatment 1• Washing 25^ 2. Blunging E. Controls of Uniformity Composition and Preparation of Ceramic Materials The physical and chemical properties of raw and pre pared materials have been presented; therefore, this secticn is to cover the composition and calculation of ceramic bodies and coverings which constitute the next important phase of ceramic technology. The determining factors of the proper ties of ceramic products are formulated at this time. The numerous theories and phenomena included in the technology are considered as they are applied to technical formulas. The section includes those elements involved in the formu lation, batching, and processing of ceramic materials as they apply to ceramic bodies and coatings. T. Composition and Calculation of Bodies and Coatings A. Constitution 1. Bases 2. Neutrals 3. Acids B. Methods of Expressing Composition 1. Molecular Weights 2. Empirical Formula 3. Formula Weight 4. Equivalent Weights 5. Batch Formula Weight 6. Raw Batches 7. Fritted Batches Formulation of Ceramic Bodies and Coatings 1. Phase Equilibrium Diagrams 2• Charts 3* Trlaxlal 4. Substitution 5. Blending 6. Analysis 7. Fundamentals of Color Formation 8. Theory of Adherence 9. Theory of Opacity Classification of Ceramic Bodies and Coatings 1. Salt Olaze 2. Raw - lead or leadless 3. Bristol 4. Feldspathic 5. Plastic 6. Non-plastic 7. Fritted 8. Earthenware, Stoneware, Porcelain 9. Transparent, Opaque, Matt, Gloss, Color 10. Ground and Cover Coats E. Physical Properties 1. Thermal Expansion 2. Density 3. Elasticity 4. Tensile Strength 5. Hardness 6. Thermal Conductivity 7* Compressive Strength 8. Impact Strength 9. Viscosity 10. Coefficient of Ex^fihsion n . Adherence 12. Surface Factors Preparation of Ceramic Materials A. Clay Bodies - Structural B. Glazes, Glasses, Vitreous Enamels C. Processes 1. Wedging 2. Blunging 3. Pugging - De-Airing 4. Milling 5. Filter Pressing 6. Magnetic Separating 7. Screening 8. Mixing 257 9. Chemical Treatment - Bleaching 10. Coloring 11. Grinding 12. Deflocculating 13. Fritting 14. Flocculating 15. Calcining D. Product Control E. Product Preparation 1. Chemical Cleaning of Metal 2. Pickling 3* Acid Washes Ceramic Processes The preceding sections Include a presentation In sequential order of the fundamental considerations of ce ramic materials and their preparation* The preparation and control of materials are the major determinants for the requisite method of fabrication; therefore, this section constitutes those elements of processing methods and their Implications for production techniques. Elements of drying and decoration are presented with related techniques appli cable to the forming, decorating, and drying of ceramic products. These curricular elements lead to the completion of processing raw materials Into finished products; this 258 culmination of the ceramic processes is represented as selected elements of firing and setting, including the elements of measurement and control of thermo-chemical reactions. As a result of extensive research into various phenomena and control of materials and fabricating processes^ the ceramic industry has adopted new methods of automation and mechanization. I. Processing Methods A. Plastic Forming 1. Hand Molding - - pinch, coil, slab 2. Wheel Throwing 3. Jiggering 4. Pressure Forming a . Die b. Hot c . Ram 5. Extrusion a. Pug Mill b. Auger c. Hydraulic d. Injection B. Casting 1. Slip Casting a. Solid b . Drain 259 2. Fusion Casting Pressure Die Forming 1. Dry Pressing 2. Damp Pressing 3. Sinter Pressing 4. Hot Molding (Resin) Special Forming 1. Grinding 2. Turning 3. Repressing 4. Drop Molding 5. Vibrating 6. Fluid Pressure 7. Coating Glass Forming Processes 1 . Rolling 2. Molding 3. Drawing 4. Cesting 3. Mechanical Glassworklng 6 . Pressing 7. Blowing 8. Hand Shaping 9. Lamp Working Manipulative Skills 1, Operation of Production Machines 2» understanding the Principles of Machine Operation 3, Working with the Media Application of Production Techniques 1. Plaster Molds a. Method of Mixing b# Production Techniques 2. Preparation of Casting Slips a. Plastic Materials 1) Electrolytes 2) Blending Materials 3) Controls b. Non-Plastic Material lj Methods of Deflocculating 2) Control 3. Understanding Binders and Lubricants a. Binders and Plasticlzers 1) Resins 2) Organic b. Preparation of Materials for Processing 4. Special Processes a. Cementitious Bonding b. Nucleation c. Cermets Equipment Design 1. Grinders 2. Crushers 3. Mills Sieves 5. Forming Equipment a. Potter's Wheel b. Jigger c. Pug Mill d. De-Airing Auger e. Die Designs f. Driers Elements of Drying 1. Surface evaporation 2 * Drying Shrinkage 3. Dry Strength 4. Vaporization 5. Defects in Drying a . Warpage b. Cracks c. Checking Application of Drying Method 1. Drying Systems 2. Classification a. Intermittent 1) Lofts and Hot Floors 2) Compartment or Cabinets 3) Humidity Cabinets b. Continuous 1) Tunnel 2) Mangles 3) Rotary 4) Drum 3* Controls a. Humidity b. Air Velocity c. Temperature Elements of Ceramic Design A. Controlling Factors 1. Ceramic Materials 2. Temperature 3. Decorating Materials 4. Firing Conditions 5. Composition a. Bodies b. Coverings c. Glasses B. Decorative Processes 1. Selected processes for Greenware 2* " " " Bisqueware 3. Selected processes for Glazes 4. " Glazing Techniques a. Glaze Application b. Decalcomanlas c. Silk Screening d. Stencils e. Stamping 5. Selected Processes for Glass a. Cutting b. Grinding c. Etching - acid, glue d. Sandblasting e . Fired Decoration f. Slivering g. Photography h. Colorants 1. Polishing Color Formation 1. Stains a. Silicates b. Spinels 2. Overglaze 3. Underglaze 4. Lusters 5. Oxides of Metal 264 a. Colloids b. Crystals D. Die Design E. Defects 1. Crazing 2. Crawling 3• Pinholing 4. Fish Scale 5. Sulphuring TXT. Elements of Firing and Setting A. Thermochemical Reactions and Changes 1. Thermodynamics of Reactions 2. Equilibrium Diagrams - Interpretation 3. Solid State Reactions 4. Pyrochemical Measurements 5. Chemical Change Inversions 6. Thermal Behavior of Ceramic Material 7. Sintering and Recrystallizatlon 8. Nucleatlon 9. Devitrification of Glass 10. Vitrification, Porosity, and Adsorption a. Densiflcatlon 11. Eutectics and Related Phenomena 12. Physical Changes a. Change in Weight b. Shrinkage c. Porosity d. Strength e. Hardness f * Warpage g. Dehydration 13. Effects of Heat, Temperature, Combi nation and Radiation a. Temperature Changes b. Thermal Conductivity c. Heats of Reaction d. Effect of Time e. Radiation and Refractoriness f. Tempering and Annealing g. Cooling h. Melting B. Fundamentals of Kiln Design and Construction 1. Principles of Design a. Periodic b. Continuous - tunnel c• Updraft, downdraft 2. Temperature Measurement a. Thermometers b. Thermoelectric c. Millivoltmeter d. Potentiometer 266 e. Optical Pyrometers f. Radiation Pyrometers g. Pyroaetrlc Cones 3* Controllers and Devices 4. Fuels a. Classification b. Combustion Theory c. Calculations C. Setting 1. Equipment Design 2. Principles 3* Methods Tests of Ceramic Material and Products Tt is through the study of the preceding outlines that this section is possible because through research, experimentation, and scientific reporting, standard procedures have been established. The establishment of these standard procedures has resulted in advanced research, standardization of products, and a standardized nomenclature for communi cation purposes. The following subject matter is concerned with the testing procedures that have been accepted as standards by the ceramic Industries. Test samples are prepared, formed, dried, and fired within the standards so that variables for 2 6 7 testing may be held constant. This Is essential, for one test or standard Is dependent on the preceding sample. Just as raw materials are essential to finished products, adequate testing procedures used concomitantly throughout all processing are necessary If standards are to be main tained . One of the many challenges to the researcher, es pecially when it Is out of the realm of standard procedures and into the field of creative thinking, is the area of ceramic technology for design and construction of special ized equipment requisite to experimentation and research. T, Determination of Test Procedures A. Clay Materials 1. Collection of Representative Samples 2. Forming Clay Trials a. Specified Mold Sizes b. Preparation of Plastic Clay Bodies 3. Slaking Test 4. Water of Plasticity Test 5. Shrinkage and Pore Water 6• Drying Shrinkage 7. Determining Dry Strength 8. Pyrometric Cone Equivalent 9. Testing for Particle Size of Ground Refractory material 268 a . Wet Sieve b. Dry Sieve 10. Method for True Specific Gravity 11. Method for Behavior In Firing a. Fired Properties 1) Apparent Porosity 2) Volume Change 3) Apparent Specific Gravity 4) Bulk Specific Gravity 5) Hardness 6) Absorption 1 2 . Methods for Strength Tests a. Tensile b. Compressive c. Modulus of Rupture d. impact 13. Absorption Test 14. Abrasive 15. Effect of Heat a. Resistance to Thermal Shock b. Mechanical Strength c. Porosity d. Water Absorption e. Pore Volume f. Resistance to impact 16. Method of Chemical Analysis a. General Consideration b. Solutions Required c • Methods 1) Moisture 2) Loss of Ignition d. Procedure in Reporting Tests 17* Heavy Liquid Glasses 1. Chemical Properties a. Durability 1) Powder Test 2) Surface Haze Test 2. Mechanical a. Tensile Strength - modules of rupture b. Flexure Testing c. Thermal Shock d. impact e. Modulus of Elasticity f. Abrasive Tests E • Stress-Optical Coefficient Optical Properties a. Refractive index -Snell's Law b. Dispersion l) Measurement c. Bl-refringence, Stress and Strain £• Crystals e« Polarized Light f. Color and Light Transmission g. Surface Reflections h. Transmission - Thickness 1. Reflection Losses J. Visual Color k* Optical Homogeniety 4. Electrical Properties a. Alternating Current Technology 1) Insulator 2) Dielectric 3) Basic Laws b. Electrical Volume Conductivity 5. Thermal Properties a. Coefficient Expansion b. Effect of Heat Treatment c. Heat Capacity 6. Hlgh-Temperature Glass Properties a. Viscosity b. Time-Temperature Effects c. Annealing d. Softening Point Method e. Plow Point Method Enamels Thermal Properties a. Fusibility and Fluidity 1) Cone Fusion Test 2) Button Cylinder Test 3) Fusion Block Test 4) Bead Test 5) interferometer Test 6) Trial Burn Test b. Thermal Expansion and Contraction 1) interferometer Test 2) Extensometer Test 3) Dllatometric Method 4) Enameling Test 5) Water Drop Test 6) Quench Test c. Optical Properties 1) Spectrophotometer 2) Reflectometer 3) X-ray Methods d. Physical and Mechanical 1) Adherence - Deformation Tests 2) Hardness - Mohfs Hardness Test 3) Elasticity 4) Compressive Strength 5) Tensile Strength 272 6) Abrasion 7) Density e. Chemical Properties 1) Acid Tests 2) Alkali Tests 3) Autoclave Tests 4) Weathering D. Refractories 1. Physical and Mechanical Properties a. Melting or Softening Point b. Load-Bearing Capacity c . Thermal Conductivity d. Shrinkage and Expansion e. Spalling Tests f . Physical Slag Resistance IT, Application of Equipment and instruments A. Chemical Laboratory Ware 1. Condensers 2. Funnels 3. Flasks 4. Dishes 5* Drawn Ware B. Standard and Analytical Scales 1. Weighing Materials 2. Measuring Density Test, Porosity, etc. Tyler Standard Sieve Series Specification for a Sieving Test 1. Apparatus a. Enumeration of Sieves to be Used b. Auxiliary Apparatus — Note: These are required for collection and reduction of gross sample, sample containers, and apparatus other than the sieves used in making the tests. 2. Sampling a. Unit of sampling b. Method of collecting representative gross sample c. Size of gross sample d. Caution to be taken in handling sample to prevent contamination or change e. Reduction of gross sample 3. Preparation of the Sample for Testing a . Drying b. Mixing c. Special Treatment, if any is neces sary d. Selection of Test Portion e. Size of Test Portion 4. Procedure a . Dry Screening 1) Order in which the sieves are to be used 2) Detailed description of method of shaking 3) End Point b. Wet Screening 1) Liquid to be used 2) Description of any preliminary separation by classification or other means 3) Order in which screens are to be used 4) Detailed description of procedure including amount and method of adding liquid, method of stirring or other agitation. 5) End point 5. Method of Reporting Results 6. Allowable Variations Between Duplicate Tests on the Same Material Specialized Equipment 1. Mills - Ball, pug 2. Mixer 3. Presses Microscope 5. Pumps Measuring Devices 1. Pyrometers 2. Controller 3. Converters 4. Testers 5. Potentiometers 0. Ceramic Equipment 1. Kilns 2. Driers 3- Furnaces ^ . Ovens ITT. Determination of Test Controls A. Investigation of Literature 1. American Standards on Tests and Measurement 2. American Ceramic Society Journal 3. Scientific Literature in Books, and other Published Research B. Hypothesis of Experiment 1. Theory 2. Variables 3. Measurements C. Procedure 1. Variable Constants and Changes 2. Measuring Devices 3. Anticipated Results Equipment Design D. Recording 1. Record of Hypothesis 2. Rocord of Procedure 3. Record of Variable 4. Record of Equipment 5. End Results XV. Development of Adaptable Methoda and Devices A. Temperature Measurements 1. Method a. Thermometers b. Thermocouples c. Cold Junction d. Calibration 2. Devices a. Pyrometers b. Potentiometers B. Controls 1. Basic Principles a. Large Heat Capacity b. Control of Heat input c. Control of Heat Output 2. Method of Automatic Control a. On-Off Regulation b. High-Low Regulation c. Proportional Control 3. Controllers a. Resistance b. Time-Temperature Timers c. Auto-transformers d. Servo-Thermocouple 277 V. Design and Construction of Specialized Equipment A, Experimental Kilns 1. Construction Principles a . Fuel b. Refractory Material c. Size 2. Special Features a. Anticipated Atmosphere b. induction or Regular 3. Measurement and Control a. Method b. Recording Instruments c. Controller B. Specialized Equipment — Note: Each experiment requires the construction of some special equipment, which IsuBually not purchasable, along with standard equipment such as chemi cal glass ware, measuring devices, and controllers. The experiment controls the type and method of construction. The outline as presented Is by no means intended to be a complete study of ceramic technology for changes are constantly being affected. Research in manufacturing processes, according to Kingery (49, p. 1) has caused many changes in the ceramic industry. He lists a number of fac tors that have been important in effecting these changes: First of all, there has been a substantial in crease In ceramic research and its general dissemination. 278 Secondly, users of special ceramic materials have become sufficiently concerned with special properties to undertake ceramic research .... Thirdly, rapidly growing electrical, electronic, aeronautical, atomic energy, and other industries have found that developing ceramics with Improved properties Is essential to technical progress. Fourthly, Increased automation and mechanization have been necessary to maintain economic production— and this has required better control of processes. Finally, increased realization that statistical quality control can be applied to ceramic processes with substantial advantages has led to a desire for better control of ceramic processes. In general, as theoretical understanding of the factors affecting ceramic processes becomes available, Improved utilization of automation and statistical quality control can be achieved— which leads to further study of the principles underlying actual processes. In summary, the organization of the subject matter in the form of an outline of curricular elements has been presented. These elements were extracted from the resource material gathered and presented in Part IT from which selected elements can be organized and presented at various edu cational levels. The following chapter Is the presentation of an example of a unit of Instruction derived from the curricular elements as outlined In this chapter and includes recommendations for additional research of the ceramic technology in industrial education. PART TV APPLICATION AND CONCLUSIONS CHAPTER DC APPLICATION OP CERAMIC TECHNOLOGY TO INDUSTRIAL EDUCATION A systematic presentation and analysis of American ceramic technology was developed In Part II. Specifically, an Investigation was presented, as a technological re search, of the highly complex nature of the principal divisions in ceramic technology. Part ITT contains an organizational treatment of the subject matter, presented in outline form that was derived from an analysis of the technological research. The organization of the subject matter Is not proposed as a curriculum outline for a spe cific program, but rather as a prototype for future use of this method for curriculum development by extracting the basic curricular components for arrangement In a course of study applicable to the objectives of specific educational program. The introduction in Part I included a review of the nature and foundations of the American educational system, with special reference to Industrial Education: 279 industrial arts, trade, and technical. The curricular unit (problem) is limited to the technical aspects of ceramic technology and the Implications for enrichment of industrial education curricula, with an illustration of a curricular unit derived and extracted from components of the subject matter outline. Just as resource studies are requisite to the development of curriculum guides, so are the guides (outlines) essential to sound application of the curricular elements to the educational level. The approach to the problem, ceramic technology, should be one that stimulates and challenges the creative capacities or potentialities of the students. It Is through the Individual's own experiences that real learning takes place. The objectives Involved In the application of ceramic technology to Industrial education are to encourage the student to think creatively; to stimulate his interest In the subject by research of literature which pertainB to the new learning areas; to require his experimentation with the possible methods for solving the problem; to re quire his reporting of the results of the problem In a systematic and scientific manner; and finally, to require an evaluation of his results based upon his written pro cedures and final product. 281 Implications for Industrial Education The following unit of Instruction in ceramic technology, slip casting, and the method of presentation are selected from Chapter VIIT, Curricular Elements, to demonstrate how units may be derived from the curricular elements into a teaching unit with breadth and depth. The unit Is a prototype for the technical level of vocational education; however, similar units may be derived appro priate to the various educational levels. Selected units may be made comprehensible to the secondary or elementary levels, or enriched with "theory" to the level of ceramic engineers, lhe unit should be designed to fulfill the ob jectives requisite to the specific level for which the proposal is made. The unit of instruction, slip casting, was selected because It Is a basic forming process in the ce ramic Industry by which many shapes and sizes can be mass produced. The process of slip casting Includes so many areas of the ceramic technology that study of this one unit alone could touch on a majority of the sciences involved in the subject matter. In addition, the evolution of the process is typical of the historical developments In ce ramic processes. * The primary purpose for the outline in Chapter VTTT Is that it makes it possible for the instructor to be cognizant of the scope of the ceramic technology when he determines which elements to use in the specific units of instruction. Furthermore, the outline serves as a readily understood source for the units of instruction inherent in the ceramic technology. To Illustrate the possibilities for the use of the outline, a consideration of the approach to the first manipulative procedure listed for the problem, "to design a ceramic article for production,M might require bibliographical research and laboratory experimentation by the students In such areas as follows: bibliographical research would include Investigation as to product use, design and decorative processes; laboratory experimentation would include such areas as model consideration by sketching and planning; and determining the method of application for the decorative process. The unit of instruction was organized to add breadth and depth of knowledge about slip casting in the ceramic technology. The emphasis Is upon individual research and experimentation in determining a solution for the problem through the use of techniques such as investigation of literature, experimentation in scientific procedures, application of the investigation and experimentation in solving the problem, and an evaluation of the problem through accurate recording and reporting. The writer be lieves that the length of time assigned to any one problem 283 is determined by the scope of the problem. However, a single unit may be organized In such a manner as to involve as much time for research as two or more problems would re quire. The following proposed unit Is an example of the application of the techniques described in the previous paragraph and encompasses In many respects the numerous basic scientific laws that apply to ceramics, as well as the more difficult high-temperature application of scientific measurement and control. The Problem: Slip Casting To investigate the technique of slip casting as a production process through the utilization of basic princi ples involving design, calculations, compounding, material preparation, measurements, controls, construction, testing, and production of a ceramic product. Manipulative Procedures The procedure should facilitate the development of a challenging, problem solving learning situation. Since the purpose of the problem is to develop the student's experience and knowledge in ceramic technology, the in structor's role should be to advise and counsel; to require individual review of the literature; to suggest new research 284 sources pertaining to the problem; to assist in interpret ing the results of the experiment; to encourage further experimentation. The instructor should make Judicious use of such methods as: demonstration and discussion; visi tation— to industry and museums; and teaching aids— films, slides, displays, mock-ups, charts, and diagrams. Each of the following selected procedures involves research or experimentation in order to successfully complete the unit. Many of the points listed are dependent upon the student's results from his investigation for the preceding point. 1. To design a ceramic article for production. 2. To construct a model. 3. To construct a case and block mold. 4. To construct a casting mold. 5. To calculate, batch, and prepare a casting slip body. 6. To make necessary tests for properties of the body and make necessary adjustments. 7. To cast and dry ceramic product. 8. To make necessary tests to determine quality of the unfired product. 9. To bisque fire product and make necessary tests to determine fired properties of product. 10. To calculate, batch, and prepare glaze. 11. To test fire glaze on body. 12. To apply glaze and/or decoration to product. 285 13. To gloet fire the ceramic product. 14. To test finished product and evaluate findings. 15. To report recorded results. Bibliographical Research The successful conclusion of the problem is often dependent upon the student'b accumulated knowledge acquired from the various research techniques. Today, there are many reports, bulletins, and scientific writings published on most phases of the ceramic industry. A review of the literature aids in developing the student's background in the new learning area requisite to experimentation with the materials. The following are selected research areas of slip casting: Product investigation— purpose: home, industrial Decorative process investigation— plastic, green ware, underglaze, overglaze. Body composition— materials, plastic, non-plastic, temperature range, classification properties. Rheological phenomena--colloid, base exchange, plasticity, suspension, electrolytes, viscosity, specific gravity. Glaze composition— temperature range, classification, properties, gloss, matt, transparent, opaque, color, fritted, leaded, alkali, Bristol, leadless. Plaster of Paris— density, strength, absorption, water-plaster ratio, burning, saturation. Property tests (unfired)— porosity, shrinkage, warpage, adjustments. 286 Drying of ceramic bodies— elements of drying, methods, infrared, humidity control, air velocity, temperature. Testing raw materials— grain, size, contamination, calcination. Fired qualities of ceramic bodies and coverings— thermal behavior, eutectics, phase diagrams, densifi- cation, vitrification, porosity, absorption, Investigation of defects— pinholes, crazing, spelling, cracking, crawling and others. Measurements and controls— thermocouples, thermometers, potentiometers, mllllameter. Investigation of recording techniques and reporting. Laboratory Experimentation Because record keeping and reporting are of key im portance to technicians, it should be stressed throughout the unit that it is necessary for the student to maintain accu rate and complete records; otherwise, a true evaluation of his problem is not possible. This section on experimentation includes the resolving of solutions from the research that are applicable to the manipulative procedures. Calculation of ceramic body--earthenware, stoneware, porcelain, terra cotta, non-plastic. Compound slip— viscosity, electrolyte, specific gravity, release, flocculation, deflocculation. Form test pieces— dry, test shrinkage, warpage, porosity. Test fire— temperature range, absorption, shrinkage, thermal analysis, density, vitrification. Plaster— water ratio, strength, density, absorption. 287 Calculate and batch glaze— substitution, blending, opacity, color, milling time, liquid contents, fritting, testing, specific gravity, viscosity. Glaze application— effects of method, thickness, effects of application. Properties and uniformity of raw materials— sieving, grinding, milling, calcining. Method of clay preparation— blunging, screening, properties, effects of method. Thermal behavior of ceramic materials— thermal analysis (thermograms, temperature measurement and control, microscopic examination. Effect of water and electrolyte on plaster of Paris molds— saturation, drying, sulphatlng, calcium de posits. Controls of production determined by records. Record keeping and reporting. Materials Ceramic raw materials include many complex compounds that are practically in unlimited supply. However, reactions involving these materials are often difficult to predict because complex compounds do not remain constant at high temperatures. Analyses and research of these ceramic material reactions are available for reference, as well as Information on product properties that are helpful in solving other ceramic problems. The following is a list of materials that may be used for this problem; however, there are 288 available many other materials and combinations of materials that a student may want to consider: Clays Metal Oxides Feldspars Calcium Silica Zinc Alkalies Tin Fluorspars Lead Borax and Borates Manganese Plaster of Paris Barium Electrolytes Chromi urn Bentonite Cobalt Kaolin Copper Sizing Ferric Nepheline Syenite Magnesium Tools and Equipment Tt may be seen from the 1.1st below, that technical ceramics involves many specialized tools and equipment; those listed are standard manufactured equipment. There are many occasions, however, in which they are used in combination with one another; at other times, they are adapted to the specific problem and additional equipment and tools are designed and constructed. Some problems require the use of a special kiln, oven, or method of measurement and temperature control in order to solve 289 the problem. The following list is only suggestive of the type needed for this problem: Blunger Scales Chemical Filter Press Viscosimeter Univac voltage control Blender Recorder Controller Grinder Servo unit Microscope Mill Potentiometer Drier or Oven Mixer Thermocouple Thermometer Pug Mill Sieves Assorted hand tools Auger Millimeter Individual research and the application of basic scientific knowledge are the essential factors in the study of ceramic technology. This basic technique once developed may be applied to most areas of ceramic research. The problem, slip casting, a ba3ic ceramic forming process, was presented to illustrate the procedure for selecting curricular elements from the subject matter out line and organizing them into an instructional unit for industrial education. Although the unit was designed for the technical level, similar units may be derived that are appropriate for, and comprehensible to, other educational programs. The selected unit is delimited by the objectives representative of a particular program. The inclusion of research and experimentation extends the problem beyond the usual project approach of curriculum organization; it 290 could include a theoretical problem implemented and solved on paper. With the wealth of subject matter presented in the outline, an enriched technical or general program can be developed. Recommendations Needless to say, the recommendation that further studies or continuing studies be made is self-evident. In his published dissertation, Technology and Industrial Arts. Delmar Olson proposed that the subject matter in Industrial Education, industrial arts in particular, be derived from technology. He recommended that further studies be made to develop proposed curricula by analyzing the curricular com ponents of the particular technology through use of resource research. In his dissertation, A Resource Research on Elec tricity. William Deck recommended that a companion study be made for electronics. The philosophy of Industrial Education does not materially differ in this proposal for the determination of curriculum content. The techniques of job analysis for skilled trades has been employed in curriculum development for trade and industrial programs for many years. Similar procedures are applied in determining the content for techni cal programs, except that in the technician occupations the "technical" aspects take precedence over the "manipulative" 291 skills and the analysis becomes broad in scope. The basic difference between the analyses— an industrial arts analysis as proposed in the above mentioned dissertations and the Job or occupational analysis of vocational education— is the emphasis placed upon the final objectives. Industrial arts, as proposed by Olson and Deck, is concerned with such ob jectives as consumer literacy, recreational interests, and orientation to industry; whereas, vocational trade and technical are concerned with specific occupational training. The primary recommendation in this study of ceramic technology is to encourage subsequent studies to strengthen the subject area, and to develop new techniques for accumu lating curricular elements to exemplify technology. The writer makes the following specific recommendations for ceramic technology: 1. The development of additional units requisite to a proposal for a complete "technicalfl program of ceramics, designed to fulfill the educational objectives in that area between the artist potter and the ceramic engineer. 2. The development of ceramic programs designed to reflect technology at the various educational levels; elementary, secondary, collegiate. This may be accomplished through additional research of the curricular components. 292 3. The extraction of Information from the technological research to be used In published articles in order to develop Interest 'tin the Initiation of orien tation programs about ceramic technology as a part of general education— industrial arts. if. The development of creative teaching tech niques for ceramic technology based upon the objectives previously stated in this chapter. The introduction (Part I), investigation (Part Tl), and organization (Part ITT) of the dissertation have been presented and application to the problem developed. Recom mendations have been stated as to the need for further development of the investigation and new techniques. The following chapter is a summary for the disser tation, reviewed by chapters; conclusions regarding the re search are stated by the writer as they apply to education and ceramic technology. CHAPTER X SUMMARY AND CONCLUSIONS This <3issertation has been concerned with de veloping a curriculum analysis based on certain well- defined postulates within the area of industrial education. The postulates are definable trends in the contemporary society of the United States. Summary In Chapter I, the purpose of the study was stated and assumptions made regarding Its implications for the educational system. Methods and techniques for the re search were discussed and terminology defined to clarify the semantics of the study. The development of the educational system in the United States, and specifically the evolution of indus trial education, was postulated in Chapter IT. The re lationships among the three areas of industrial education: industrial arts, vocational trade and ^ndustr'al, and vo cational technical education were recognized and stated. The historical development of the ceramic indus try is discussed in Chapter ITT and the importance of its role to all civilizations reported. It may be seen that 293 294 as man acquired technical knowledge and discovered new methods of product?on, he was able to control and trans form natural materials into new objects that were functional, artistic, and eventually scientifically ima ginative. The nature of ceramics and its scope as an industry were presented in Chapter TV. An analysis of its size was statistically presented with a comparison made of the size of the Industry to other selected industries. The study illustrates the diversity of an expansion in the industry, in the last half century, which has implications for new "technical" occupational opportunities. The technological research of the ceramic tech nology is presented in Chapters V, VT, and VTT. An analy sis is made of those elements of science that are appli cable to ceramic materials and manufacturing processes, including preparation and classification of ceramic bodies and coatings. Methods of formulating ceramic bodies and coatings are also covered extensively. The analysis of production processes is presented to show the methods of fabricating ceramic products with a brief discussion of decorative techniques employed, and the effects drying has on ceramic products. Also presented is an explanation of the chemical and physical changes that occur during the thermal chemical reactions of firing. Selected properties 295 and testa of ceramic materials and products are presented with a descriptive narrative and the formula equation for each measurement. An outline of curricular elements derived from an analysis of the technological research is presented in Chapter VTII. The process of classifying and grouping the subject matter components into an outline of curricular elements reduced their number and permitted a more con venient method for interpretation and organization. In Chapter IX, a teaching unit on "slip casting" has been developed as an illustration of the application of subject matter to the technical level. The process of selecting curricular elements to support the objectives of a program has implications for teaching units, derived from technology, for most educational areas such as in dustrial arts--to reflect the objectives of general edu- cation--as consumer literacy, recreational interests and orientation to industry; and vocational trade or technical areas as specific occupational training. Conclusions Considerable interest has been generated in the need for improvement of curriculum development in the United States, especially since the advent of the atomic age and "Sputnik," Numerous studies have been made to 296 determine curriculum content and to ascertain the status of Industrial education in the United States. This study was a departure from the usual research In curriculum development In that It was an attempt to obtain curricular components from a technological research and project It Into an outline of organized subject matter. The conclusions are based on the postulate that the contemporary society In the United States has developed into one that is basically technological, and that education al institutions should reflect this technology through the objectives of the various programs. The conclusions, there fore, reflect upon the dynamic technological advancements and a need to develop a curriculum to reflect these changes in industrial education programs. The postulates for Industrial education are well served by the subject matter inherent in ceramic technology. The divisions of Industrial education can be his torically developed and defined through a review of liter ature, and their relationships to the educational system and to one another determined. Some overlapping exists between the areas because similar basic tools, processes, and materials are utilized as the vehicles for instruction; consequently, there is a need for further study and con tinual defining of the objectives for the areas. 297 Ceramics has been a manufacturing process for many centuries and maintained an Important position in past civilizations. Some baBlc processes In ceramics had their Inception as early as 12000 B.C.; however, It was not until the twentieth century that technological advancements and the development of new processes revo lutionized the ceramic industry. Statistical figures as to the size of the indus try rank ceramics as a major Industry with approximately six and one-half billion dollars of shipped products during one year. The scope of the Industry includes many materials upon which other major industries are dependent: refractories in the steel Industry, and abrasives in tool ing and machining. The investigation of technological resource ma terial for ceramics in the United States demonstrates that ceramic materials are plentiful and exist over the earth's crust In great quantities. An analysis of the technology Illustrates the numerous scientific disciplines applicable to Inorganic materials. Areas of chemistry, physics, mathematics, and physical chemistry have increased man's knowledge of ceramic reactions and materials to make possi ble the advancement m many fields such as rocketry, Jet propulsion, electronics and others. The uncertainty in high-temperature reactions and the diversity of materials 298 and compounding processes make formulation of ceramic bodies and coatings difficult. Automation and mechani zation of fabrication processes have been facilitated by the Improvements made in processing of raw materials and the establishment and standardization of property tests and measurements for materials and products. The subject matter outline derived from the technological research Illustrates that the curricular elements are diversified and numerous with a wealth of material for potential units of Instruction. The outlining of the subject matter facilitated the Identification of the representative elements as authentic and definable. An analysis of the outline discloses that the curricular elements may be applied to various levels of education, controlled by the objectives of the program. The curricular elements in the unit of instruction are delimited by the philosophical objectives representatiw of the various educational levels, but the inclusion of re search and experimentation extends the unit problem beyond the usual project approach of curriculum organization, m addition, the unit of Instruction may be designed as a theo retical problem in which all research, experimentation, and procedures are presented as solutions to the problem and worked out on paper without manipulative activity. BIBLIOGRAPHY 299 BIBLIOGRAPHY 1. American Industrial Arts Association. The New Indus trial Arts Curriculum. Newark, New Jersey: Araeri- can Industrial Art Association, 1947. 2. Andrews, Andrew I. Ceramic Tests and Calculations. New York: John Wiley and Sons, Inc., 192b. 3. ______• Enamels The Preparation, Application^ gnd Properties of Vitreous Enamels. Champaign, Illinois The Garrard ^ress, 1935 • 4. Ansley, Arthur C. Manufacturing Methods and Processes. Philadelphia: Chilton Company, 1957. 5. Bennett, Charles Alpheus. History of Manual and indus trial Education Up to 1870. Peoria, Illinois: The Manual Arts Press, 1926. 6. . History of Manual and Industrial Education 1876 to 1917. Peoria, 111inois: The Manual Arts Press, 193*/. 7. Binns, Charles P. Lectures On Ceramics. Alfred, New York: The Box of Books, 1946. 8. . The Potter's Craft. New York: D. Van if os t rand Co., Inc., 19^7. 9. Bode, Boyd H. Modem Educational Theories. New York: The Macmillan Co., 1930. 10. Bodine, Merle W. ’’The Areas of Training Needs of Highly Skilled Technicians in Twenty-Three Selected Kansas Industries." Unpublished Master's thesis, Kansas State Teachers College, Emporia, Kansas, 1959. 11. Bogue, Jesse P. (Editor). American Junior Colleges. Fourth Edition, American Council on iducationT 1956. 12. Bogue, Robert Herman. The ChemlBtrv of Portland Cement. New York: Reinhold Publishing Corporation, 19^7. 13. Bonser, Frederick Gordon. 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Conant, James Bryant, The American High School Today. New York: McGraw-Hill Book Company7 Inc., 1959. 2 2 . Coming Glass Center. The. Coming, New York: Coming Glass Works, 1958. 23. Cottrell, Donald P. (ed.). Teacher Education for a Free Society. Oneonta, New York: The American Assoc, of Colleges for Teacher Education, 1956. 24. Day, Ralph K. Glass Research Methods. Chicago, Til.: Industrial Publications, Inc., 1953. 25. Deck, William L. A Resource Research in Electricity. Doctor's dissertation, Columbus, The Ohio State University, 1955. 2 6 . Deem, Betty and John D. Sullivan. "Ceramic Statistics'.' The American Ceramic Society Bulletin. Vol. 39, 2, I960. 27. Deringer, Wayne. "Ceramic Materials for Corrosion Re sistance,11 Chemical Engineering Progress. Vol. 54, 11, 1958. 302 28. DeSager, Walter. Making Pottery. New York: The Studio Publications, 193*. 29. Dewhuret, J. Frederic and Associates.^ America’s Needs aiand Resou^^s...... New York: The “Twentieth ‘ Century 30. ______. 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"The Power of Positive Progress," American Ceramic Society Bulletin. Vol. 39# 5# 40. Qreen, H. T. and Gerald H. Stewart. Ceramics: A Symposium. Stoke-On-Trent, The British Ceramic SoclSty, 1953. 41. Harper, Robert Francis. The Code of Hammurabi. King of Bala"Babylon. Chicago: The University of Chicago Press, 19011904. 303 42. Hawkins, Layton, Charles Prosser and John Wright. Development of Vocational Education. Chicago: American Technical Society, 1951. 43. Hetherlngton, A. L., Chinese Ceramic Glazes. South Fasedena, California!P. D. and Tone Perkins, 1948. 44. Hillebrand, W. P. and 0. E. P. Lundell. Applied Inorganic A nalysis. New York: John Wiley and SonB, In c ., 1929- 45. Honey, W. B. The Art of the Potter. London: Paber and Paber, 1945! 46. Huber Corporation. Kaolin Clays and Their Industrial Uses. New York: J. M. Huber Corp., 1955- 47. Jacoby, Robert. "An Overview of Technician Training Through Public Education and Expansion Possibilities Under Federal and State Policies." 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New York: The World Publishing Company, 1957. 128. Wilber, Gordon 0. Industrial Arts In General Edu cation. Scranton, Pennsylvania: International Textbook Co., 1948. 129. Wilds, Elmer Harrison. The Foundations of Modern Education. New York: Rinehart and Co., Inc., 1950. 130. Wilson, Hewitt. Ceramics: Clay Technology. New York: McGraw-Hill Book, Inc., 1927. 131. Winslow, Charles H. Industrial Education. Washing ton, D. C.: U. S. Government Printing Office, 1912. AUTOBIOGRAPHY I, Robert Charles Fritz, was b o m in Toledo, Ohio, on November 15# 1920. I received my public-school edu cation in the Cleveland area. My undergraduate training was obtained in San Jose State College, San Jose, California, from which I graduated with honors and a bachelor of arts degree in industrial arts education in 1951. T also received the Master of Arts degree in indus trial arts education with a thesis written in fine arts (ceramics) from the 3ame institution in 1956. While at San Jose State I was employed as a ceramic laboratory assistant for two years. I served in the united States Maritime Service as an Able Bodied Seaman and Diesel Oiler from August 19^3 to August 1945. I was granted Journeyman Auto Mechanic status in 19^5. I served as a Sergeant in the United States Army in Virginia and California from March, 19^6, until October, 19^7. T performed duties in the Quartermaster Corps as cadre and in the Military Police in criminal investigation. I taught secondary-school industrial arts for f^ve years in California from 1952 to 1957. In 1957# I was granted a Life General Secondary Credential for California on the recommendation of my Superintendent and the Board 310 of Education of the San Rafael City Schools. I was employed as an instructor in the industrial arts area of The Ohio State University from July, 1957# to September, I960. I was admitted to candidacy for the doctor of philo sophy degree in the Winter Quarter of 1959.