I I LLINOI S UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
PRODUCTION NOTE
University of Illinois at Urbana-Champaign Library Large-scale Digitization Project, 2007.
The Properties of Feldspars and Their Use in Whitewares
by
Joseph C. Kyonka
FORMERLY RESEARCH ASSOCIATE IN CERAMIC ENGINEERING
Ralph L. Cook
PROFESSOR OF CERAMIC ENGINEERING
ENGINEERING EXPERIMENT STATION BULLETIN NO. 422 UNIVERSITY 0 5050--1-54--53757 ,.eRss , CONTENTS
I. INTRODUCTION 5 1. Definition 5 2. Mode of Occurrence 5 3. Geographic Occurrence 5 4. Commercial Use 5 5. Acknowledgments 5 II. FUNDAMENTAL PROPERTIES 6 6. Chemical Composition 6 7. Mineralogical Composition 7 8. Structure 7 9. Thermal Properties 9 10. Solubility in Water 12 III. USE IN WHITEWARE COMPOSITIONS 13 11. Physico-Chemical Behavior 13 12. Purpose and Scope of Experimental Investigation 14 13. Properties of Feldspars Used 14 14. Semi-Vitreous Ware 15 15. Hotel China 20 16. Electrical Porcelain 21 17. Sanitary Ware 24 18. Floor Tile 26 IV. SUMMARY OF RESULTS 28 APPENDIX- DETAILED TEST PROCEDURE 29 19. Raw Materials Used in Experimental Bodies 29 20. Details of Body Preparation 29 21. Specimen Formation 29 22. Test Procedures 31 BIBLIOGRAPHY 33 FIGURES
1. Spacing of (201) Planes in a Series of Alkali Feldspars Crystallized at 900 deg C and 300 kg/cm2 Pressure of Water 7 2. Relation Between Refractive Index and Anorthite Content of Natural Plagioclase 8 3. The Alkali Feldspar Join, Showing the Probable Sub-Solidus Relations 9 4. Equilibrium Diagram for the Plagioclase Feldspars 9 5. Portions of the Equilibrium Diagrams, Soda-Alumina-Silica and Potash-Alumina-Silica 11 6. Fired Properties of Semi-Vitreous Bodies 17 7. Properties of Semi-Vitreous Bodies at Maturity (10 percent Porosity) 18 8. Linear Thermal Expansions of Series I and II Semi-Vitreous Bodies Fired to Cone 9 20 9. Linear Thermal Expansions of Semi-Vitreous Bodies Containing Tremolitic Talc and Fired to Cone 9 20 10. Fired Properties of Hotel China Bodies 22 11. Fired Properties of Electrical Porcelain 23 12. Fired Properties of Sanitary Ware Bodies 25 13. Fired Properties of Floor Tile Bodies 27
TABLES
1. Theoretical Compositions of Pure Feldspars 6 2. Range of Compositions of Commercial Feldspars 6 3. Properties of Feldspars Studied 14 4. Compositions of Semi-Vitreous Bodies 15 5. Comparison of Fired Properties of Semi-Vitreous Bodies as Obtained from Laboratory and Commercial Firings (2240 deg F) 16 6. Cristobalite Content of Fired Semi-Vitreous Bodies 19 7. Thermal Shock Resistance of Semi-Vitreous Bodies from 480 deg F to Room Temperature (70 ± 2 deg F) 20 8. Compositions of Hotel China Bodies 21 9. Compositions of Electrical Porcelain Bodies 23 10. Dielectric Properties of Electrical Porcelain Bodies 23 11. Compositions of Sanitary Ware Bodies 24 12. Casting Characteristics of Sanitary Ware Bodies 24 13. Composition of Floor Tile Bodies 26 14. Chemical Analyses of Raw Materials Used in Experimental Bodies I. INTRODUCTION 1. Definition rado, Virginia and South Dakota. In Canada, peg- Feldspars are the most common constituents in matites containing commercial feldspar are found crystalline rocks and make up about 60 percent of in the provinces from Nova Scotia and Labrador to the earth's crust. They may be technically defined Manitoba, and through the Rocky Mountain area. as aluminosilicates of sodium, potassium, calcium In Europe, Sweden and Norway are the most and barium; most commonly, the feldspars are con- important sources of feldspar; the Norwegian de- sidered as solid solutions of three limiting com- posits are noted for their high purity. Great Britain pounds, NaAlSi 8Os, KAISi3O,, and CaA12Si208, does not have any appreciable amounts of pure which are respectively known as soda feldspar, feldspar although British potteries use a feldspathic potash feldspar and lime feldspar. Natural deposits material known as "Cornish Stone" which is a type of feldspar are generally solid solutions of either of decomposed granite containing feldspar and the soda and potash feldspars or the soda and lime quartz with varying amounts of kaolin, muscovite, feldspars. fluorspar, and topaz. Other feldspar deposits in Europe are found in Czechoslovakia, Germany, 2. Mode of Occurrence France, Italy, Rumania, Russia, and Finland. Else- As the main constituent of the igneous rocks where in the world, pegmatite deposits are located making up the earth's surface, feldspars are abun- in China, India, Japan, Australia, New Zealand, dantly distributed; the chief commercial sources Egypt, South Africa, and Argentina. are found in pegmatite dikes associated with other pegmatite minerals such as quartz and the various 4. Commercial Use micas as well as minor amounts of tourmaline, The chief commercial value of the feldspars is in beryl, garnet, spodumene, pyrite and magnesite. their use by the ceramic industries for the manu- Although pegmatite deposits are widely distributed facture of glass, whiteware, and porcelain enamel geographically, feldspars sufficiently free from im- products. Their fundamental characteristics and purities and occurring in large mineable quantities their behavior in the presence of other constituents are not commonly found. For many years it has are important considerations in the formulation of been the practice to separate the feldspar minerals ceramic compositions. The following discussions will from the associated impurities by a method of hand attempt to describe the basic features of feldspars selection, but recent technological developments and to show their behavior and influence when used have led to flotation methods for the separation of as fluxing agents in whiteware bodies. quartz and mica. The flotation process has proved to be an effective method of producing large quan- 5. Acknowledgments tities of feldspar relatively free of undesirable Funds for this project were furnished under a impurities. cooperative arrangement with the Engineering Ex- 3. Geographic Occurrence periment Station by the Consolidated Feldspar Cor- Commercial sources of feldspar are found in all poration, which became the Consolidated Feldspar the states of the Appalachian Region from Georgia Department of International Minerals and Chem- to New York and in the New England States. South ical Company. This work has been carried out Dakota, Colorado, Minnesota, Arizona, California, under the general administrative direction of Dean Nevada, New Mexico and Texas also contain de- W. L. Everitt, Director of the Engineering Experi- posits. In recent years, North Carolina has been the ment Station and Professor A. I. Andrews, Head chief feldspar-producing state, followed by Colo- of the Department of Ceramic Engineering. II. FUNDAMENTAL PROPERTIES 6. Chemical Composition tions of feldspar composition; however, recent in- In a consideration of the properties of feldspars, strumental procedures have been introduced for the the chemical composition is of primary importance. analyses of silicates and have proven to be more The chemical analysis is an important key to the rapid than the older methods and to give results of behavior of the material under various conditions highly reproducible accuracy. Two of the instru- mental methods particularly applicable for the and is the criterion most often used in evaluating analysis of feldspars are colorimetry and flame the use of a particular feldspar in a whiteware photometry. Colorimetric methods may be em- body. The theoretical chemical compositions for the ployed for the complete feldspar analysis with ex- three major feldspars in their pure state are shown cellent reproducibility. 1 * Flame photometry has in Table 1. been used mostly for the determination of the alkali Table I 23 4 and alkaline earth metals, ', 5) although com- Theoretical Compositiions of Pure Feldspars* plete silicate analysis methods are proposed. K 20 NasO CaO AlsO1 Potash Feldspar Several proposals have been made for the clas- K 20 Ah03-6SiO0 16.9 18.3 Soda Feldspar sification of commercial feldspars on the basis of Na2O Al20 3 6Si0 2 11.8 19.4 Lime Feldspar their chemical composition, physical properties and CaO Al03 2Si0 2 20.2 36.6 * Weight percent. fineness of grind. An early basis for their classifica- tion and standardization was the alkali content and Since deposits of pure feldspar are rare or non- fusion temperature. ( 6 ) Another system for commer- existent, the naturally occurring minerals will have cial standards of quality was introduced by the compositions which deviate somewhat from those Bureau of Standards to cover the specifications of shown in the table. The range of chemical compo- ground feldspar used in ceramic processes. ( 7 ) This sitions of typical commercial feldspars in the method of classification was based on the particle United States is shown in Table 2. The most sig- size, chemical composition and end use of the nificant variations in composition are found to be in material. the contents of Si0 2, Al 20 3, NaO2 and KO2 ; there- Table 2 fore, it may be expected that these oxides will con- Range of Compositions of Commercial Feldspars* Oxide Range in percent by weight tribute to the variability of behavior of different NasO 2.0 - 9.0 K0O 0.5 -13.5 feldspars. Although the amounts of CaO, MgO and CaO 0.1 - 2.5 MgO tr - 0.5 FeO,3 are small in relation to the other constituents, FeOs3 0.02- 0.4 A1203s 15 - 21 their effects on the thermal behavior are quite SiOs 65 - 75 pronounced. * For use in whiteware compositions. The chemical compositions of feldspars and Although the proposed methods of feldspar clas- other body materials have been used to estimate sification were steps forward in the standardization the quantities of ceramic bond in fired bodies and of materials, their utilization was not fully realized. to differentiate the various phase constituents This lack of realization was no doubt largely due formed in the firing process. This method proposes to the advent of feldspar blending. The introduction to refer the chemical composition of the body to of blending and chemical control resulted in pro- appropriate equilibrium diagrams and to relate the moting standardization of composition and enabled calculated phases to the fired physical properties the producers to supply large quantities of uniform of the body. material. The conventional wet methods of chemical anal- SParenthesized superscripts refer to correspondingly numbered entries ysis are still widely employed for the determina- in the Bibliography. Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
While feldspar blending is chiefly based on the simplified and a mathematical expression has been uniform control of chemical composition, the mode proposed which describes the relation in the ranges of occurrence and the inherent nature of each feld- of 0-30 percent and 64-100 percent anorthite. This spar are also important considerations in judging is shown in Fig. 2. (11) (8) the feasibility of blending. 8. Structure 7. Mineralogical Composition As the most important group of rock minerals, The mineralogical compositions of feldspars may the geology and mineralogy of feldspars have long often be determined by calculation from the chem- been the subjects of extensive study. Although there ical analysis to an accuracy suitable for certain is probably more information regarding feldspars applications such as those concerned with the free than any other group of minerals, they are not silica content. Since commercial feldspars consist essentially of microcline, albite and anorthite mix- tures with some associated quartz, muscovite and kaolinite, the mineral composition may be calcu- lated on a 6-component basis. This method has been simplified to such an extent that mathematical IC~ formulae are available for direct computation of the mineral content. Formulae for the calculation are shown below. (9) Percent Albite = 8.458E Percent Microcline = 15.442A - 5.459C + 9.923D + 8.977E + Potash &6 d480 Soda 11.815F Feldspor Weight Percent Feldspar Fig. 1. Spacing of (201) Planes in a Series of Alkali Feldspars Percent Anorthite = 4.960D 2 Crystallized at 9000 C and 300 kg/cm Pressure of Water Percent Muscovite = 7.813C - 22.097A - (Reprinted from The Journal of Geology, Vol. 58, p. 493, 1950) 14.201D - completely understood. Optical methods have been 12.847E - 8.455F developed for their characterization, but the rela- Percent Quartz = B + 1.178C - tionships between optical properties and chemical - - 6.666A 4.284D composition are yet to be definitely determined. 7.751E - 5.101F Some of the optical properties are understood on where: the basis of crystal structure, and certain funda- B =percent A= percent H20; SiO 2 ; C= mental features have been established, even though percent A1 0l ; D=percent CaO; E=per- 2 a detailed knowledge of the complete structure is cent Na20; F = percent K 0, obtained from 2 yet unknown. chemical analysis. All feldspars consist of a three-dimensional net- The mineralogical compositions of feldspars may work of [Si0 4 ] and [A10 4] tetrahedra in which all be determined by direct methods such as optical the tetrahedra share their oxygen atoms with their and X-ray analyses, but the complex nature of neighbors. (12) The fundamental units of [Si04] and feldspathic crystallization makes a review of the [AlO] are linked together in a four-ring framework optical and X-ray methods beyond the scope of consisting of tetragons and collapsed octagons as this discussion. Nevertheless, recent studies have viewed along the crystallographic a-axis. Positively greatly simplified these methods and are note- charged ions of sodium, potassium or calcium are worthy of mention. In the soda-potash feldspar situated in the octagonal interstices of the nega- series a linear relationship has been found between tively charged framework. (l3) The fundamental the spacing of the (201) planes and the weight structure of these tetrahedra is elastic to some composition of the end members in solid solution. (10 ) degree and can adjust itself to the sizes of the This relationship is illustrated by Fig. 1. The cations in the octagonal openings. The crystal relations between the refractive indices and the symmetry of the feldspars is dependent upon the anorthite content of plagioclases have also been size of these cations; relatively large cations such ILLINOIS ENGINEERING EXPERIMENT STATION as K + give a symmetry which is monoclinic or NaAlSiOs form a continuous series of solid solu- nearly monoclinic while the small cations, such as tions at high temperatures, but at temperatures Na+ and Ca +, cause a slight distortion of the struc- below 600 deg C there is a gap in the isomorphic ture and triclinic symmetry results.( 14 series. At these lower temperatures, the solid solu- Commercial feldspars are considered on the tions between potash and soda feldspars are meta- basis of a three-component system, the end stable and under conditions of slow cooling show members of which are KAISiOs,, NaAlSi3Os and CaAl 2SiO08, or potash, soda and lime feldspars, I I I I respectively. The extent of solid solution between For O
QI 7'
KA/Si,0, 20 40 60 80 NaA/Si 0, Potash Weight Percent Soda _= Feldspar Feldspar I clu ur realpoar
Fig. 3. The Alkali Feldspar Join, Showing the Fig. 4. Equilibrium Diagram for the Probable Sub-Solidus Relations Plagioclase Feldspars (Reprinted from The Journal of Geology, Vol. 58, p. 501, 1950) (Reprinted from The Journal of Geology, Vol. 58, p. 582, 1950) series. This system, known as the plagioclase series, indicate a perfect isomorphism in the plagioclases, has been customarily designated as mixtures of and unmixing may take place during the cooling different albite and anorthite ratios as follows: of the magmatic crystals and result in a mixture of highly Mineral Name Molecular Ratio ordered end members at room tem- peratures. Percent Percent Albite Anorthite 9. Thermal Properties Albite 90-100 0-10 The melting characteristics of the soda, potash Oligoclase 70-90 10-30 and lime feldspars have been determined for the Andesine 50-70 30-50 pure materials and for their mixtures. It should be Labradorite 30-50 50-70 noted that the melting temperatures of feldspars Bytownite 10-30 70-90 are extremely difficult to obtain since the melting Anorthite 0-10 90-100 phenomena are very sluggish. The melting begins Plagioclases crystallized at high temperatures at the surfaces of crystals and proceeds so slowly exhibit the perfect solid solution characteristics that much of the crystal can exist in the presence attributed to this system; however, there is evidence of the melt for long periods of time even though that in natural plagioclases there is a considerable the temperature is somewhat above that of the miscibility gap between 30 and 70 mole percent melting point. The melting point is considered as anorthite. This gap is apparently affected by an the temperature at which the crystal and the melt albite inversion at about 700 deg C as shown in may exist in equilibrium and is determined by Fig. 4.' 16 ) Thus, although all appearances would locating the temperature above which crystals show ILLINOIS ENGINEERING EXPERIMENT STATION melting tendencies and below which the crystals The data obtained to date has been concerned with tend to grow. The exact temperature of this the completion of melting; however, determinations equilibrium is not easily determined and it has been are being made for the beginning of liquid forma- necessary to express feldspar melting points in tion. terms of temperature ranges. The melting behaviors which have been dis- Soda feldspar has been found to melt con- cussed above are those of the pure feldspars and gruently to a very viscous liquid at a temperature their mixtures under equilibrium conditions; the of 1118 ± 3 deg C. 17, 18) From the phase equi- thermal relations of commercial feldspars, such as librium diagram of the system NaO0-A120 3-SiO 2, as those used for the manufacture of whitewares, may shown in Fig. 5a, a binary mixture of pure soda be expected to be somewhat different due to the feldspar and silica is found to have a minimum influence of impurities. In ceramic processes, equi- melting temperature of 1062 ± 3 deg C (I); this librium states are seldom achieved although the mixture is equivalent to 68.5 percent soda feldspar reactions taking place tend to approach those and 31.5 percent silica. A ternary mixture of 66.0 states; therefore, the rates at which the reactions percent soda feldspar, 33.3 percent silica and 0.7 proceed toward equilibrium must be considered. percent alumina is shown to form an eutectic at It has been stated that feldspar melts approach 1050 + 10 deg C (M). equilibrium conditions very sluggishly due to their Potash feldspar has been established as melting high viscosities. These viscosities of melts have been incongruently at 1150 + 20 deg C to form crystals the basis of evaluating the thermal behavior of of leucite (K,0-A1203-4SiO2 ) and a viscous liquid feldspars for ceramic use; it is a common practice (12.5 percent KO, 13.5 percent A120 3, 74.0 percent to express this behavior in terms of fusibility or (19) SiO 2) which is more siliceous than the feldspar. the plastic deformation of a feldspar cone when With potash feldspar there is a long temperature heated at a specified rate (i.e. 20 deg C per hr). interval during which leucite and the liquid may When the feldspar cone deformation is compared coexist at equilibrium; above temperatures of 1530 to the deformation of standard pyrometric cones deg C the leucite crystals disappear. As a com- heated at the same rate, the fusibility is generally pound in the system K 20-Al103sSiO, (Fig. 5b), expressed in terms of pyrometric cone equivalents potash feldspar theoretically forms a binary eutec- (p.c.e.). tic with silica at 990 + 20 deg C (I) when the At equivalent temperatures, the viscosities of composition is 58.0 percent potash feldspar and soda feldspar melts have been found to be lower 42.0 percent silica; a ternary mixture of 56.2 per- than the viscosities of potash feldspar melts; the cent potash feldspar, 43.2 percent silica and 0.6 mixtures of these alkali feldspars having inter- percent of alumina forms a theoretical eutectic at mediate values. 24 ) Accordingly, the p.c.e. ranges of 985 ± 20 deg C (M). typical feldspars used in whiteware compositions The melting relations of binary mixtures of the are: (25) feldspars have also been determined. In the soda Cone 4-5(1165-1180 deg C) for high soda feldspar-potash feldspar binary system as shown in feldspars Fig. 3 a minimum melting temperature of 1063 -t Cone 5-8(1180-1225 deg C) for intermediate 30 deg C is obtained at three compositions (60, 65 alkali feldspars and 70 percent of soda feldspar), but the compo- Cone 8-10(1225-1260 deg C) for high potash sition of 65 percent soda feldspar and 35 percent feldspars potash feldspar is generally considered as the low Binary mixtures of 65 parts soda feldspar and (22) melting mixture. 35 parts potash feldspar have been found to de- In the plagioclase series (Fig. 4), the soda and form at temperatures slightly below the deforma- lime feldspars form a series of solid solutions with tion temperature of the soda feldspar.(2 6) Ternary a continuous rise in the liquidus and solidus tem- mixtures consisting of 70 parts soda feldspar, 25 peratures from pure soda feldspar to pure lime parts potash feldspar and 5 parts lime feldspar feldspar. give a lower deformation temperature than any A recent study has been made to determine the other feldspar mixture.(27) nature of the liquidus surface of the ternary sys- Viscosity studies have shown that the presence (23 ) tem soda feldspar-potash feldspar-lime feldspar. of uncombined SiO 2 will increase the viscosity of Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
E=767 1 3° F= II/8 3 = G 740 ± 5° = H 867 1 30 I = 1062 3 J r 1470 /0° K = 1545 L = 1470 /00 M = /050 /0° N /1104f 3j 0 1108 30 P = /063 5° = 0 068t 5° T 732 t 50
Weight Percent
A'= /3/5 /0° H 867 3° I 990 20° J /417010/ L 1470/4 /10 M 985 ±20° N= 1/40 t200 0 1//50 20 P = 710 -20° = 0 725 1 50 R /81O 5° f S 695 50 W /530 5S
Fig. 5. Portions of the Equilibrium Diagrams, Soda-Alumina-Silica and Potash-Alumina-Silica ILLINOIS ENGINEERING EXPERIMENT STATION a feldspar melt and also deter the drop in viscosity The density of feldspar is reduced when it with increasing temperatures;28) accordingly, the changes from the crystalline to the fused state. A presence of free SiO 2 increases the p.c.e. value of high soda feldspar with a density of 2.635 in its feldspars. This effect is most pronounced in high raw state will fuse to a density of 2.37, and as a soda feldspars; the presence of 10 percent of un- result will occupy a 12 percent greater volume. combined SiO, in a soda feldspar is sufficient to Similarly a high potash feldspar of 2.572 density increase its refractoriness, whereas a high potash will fuse to a density of 2.37 with a volume in- 25) feldspar may tolerate up to 20 percent of free SiO 2 crease of 9 percent./ 29) before the p.c.e. is materially increased.' The thermal properties of feldspars have been Amounts of Fe2Os in the order of 0.3 percent are the subject of considerable study in the past and sufficient to lower the viscosity of a feldspar melt will doubtless be the object of many future investi- and thereby lower its p.c.e. value. The addition of gations. Several factors have been established as the oxides of Ca, Mg, Ba and Zr in amounts of 2 significant for the thermal behavior of feldspars to 5 percent have also been found to lower the and may be summarized as: viscosities of feldspars melts and reduce the de- 28, 30 (a) chemical composition, which determines ) formation temperatures.( the ultimate equilibrium condition for any Studies of binary systems of feldspars and specified temperature clay have not revealed any deformation eutectics; (b) mineralogical composition, which deter- however, it has been established that as a feldspar mines the initial point from which reactions will melts it takes the decomposition products of clay proceed and the nature of melting (i.e. con- into solution at a rate dependent upon the tempera- gruent or incongruent) ture and the surface areas. In general, it has been shown that clay is more soluble in soda feldspar (c) particle size of the mineral constituents, 31, 32 which determines the extent than in potash feldspar.( ) of surface area and the rate at The relative solubilities of clay and quartz in which melting will take place feldspar melts have not been definitely established; (d) viscosity of the melt formed, which however, it is known the presence of both materials ultimately determines the rate at which re- affects their mutual solubility; as the quartz con- actions will proceed toward the equilibrium tent is increased the solubility of clay in the feld- state(36) spar melt is diminished. (33) 10. Solubility in Water The thermal expansion coefficients of feldspar In addition to the thermal behavior of feldspars, glasses may be predicted from the expansion fac- the solubility of feldspars in water is of interest tors proposed by Hall (34) if the free quartz content in ceramic processes. No definite conclusion has is not in excess of 4 percent. (35) In the crystalline been made as to whether a high soda or a high state soda feldspars have a higher coefficient of potash feldspar is more soluble in water. It is well expansion than potash feldspars; in the fused state known that when finer ground fractions of feld- the thermal expansion of the fused potash feldspar spar are placed in water, decomposition takes place is considerably greater than that of fused soda and alkalies are extracted from the feldspar. The feldspar chiefly due to the formation of leucite in alkalinity of the water is immediately increased the potash feldspar melt. The thermal expansion and continues to increase with time although the of fused potash feldspar is effectively reduced by rate of increase gradually becomes smaller with the presence of free SiOz or soda feldspar due to a longer exposure.(7) greater solution of the leucite. III. USE IN WHITEWARE COMPOSITIONS
11. Physico-Chemical Behavior pated by the fusion behavior of the feldspar alone The function of feldspar in whiteware bodies is or combinations of the feldspar with one of the that of a flux and as such it takes part in physico- other body ingredients. Each body composition is chemical reactions with other crystalline phases. an individual system and its thermal reactions are The old conception that the feldspar serves as a dependent on all of the components collectively. bond for the crystalline phases is being rejected and It might be expected that a body containing a high current theories consider that the bonding of grains soda feldspar of low p.c.e. value would reach and formation of a dense mass is due to a deep maturity at a temperature considerably lower than inter-diffusion of phases. (38 ) a similar body containing a high potash feldspar of During the firing of a whiteware body composed high p.c.e. value; actually, the difference in the of feldspar, clay and flint, the first glassy phase to maturing temperatures of the two bodies may be of form is due to a ternary eutectic. With pure mate- small magnitude (i.e. 10 deg C) in contrast to the rials and equilibrium conditions the temperature difference in fusion temperatures (i.e. 70 deg C) of of the eutectic formation would be 990 ± 20 deg C the individual feldspars. It has been shown that with a pure potash feldspar or 1050 ± 10 deg C bodies containing potash feldspar may even mature with a pure soda feldspar, and the amount of melt before those containing equivalent amounts of soda formed would vary with the amount of feldspar feldspar if free calcia is present in the compo- present. In bodies which contain somewhat impure sitions. (3) materials, the eutectic temperatures may be some- It has been generally accepted that finer particle what lower. Commercial bodies are fired at a rate sizes of feldspar and flint lower the maturing tem- which is necessarily much too rapid for the achieve- peratures of feldspar-flint-clay bodies and that ment of equilibrium conditions; and while some only the finest particles of feldspar form a glassy eutectic formation may occur at the theoretical matrix. The larger feldspar particles fuse and be- temperature, the amount of glass formed at that come isotropic but do not lose their original shape point will be very minute. The eutectic formation to any great degree. (4 0, 41) The advantage of finer may be more readily detected at somewhat higher particle size is most effectively realized with con- temperatures. Partial fusion has been observed at trolled firing procedures; a more gradual heating 1075 - 1085 deg C in bodies fired at a rate of 10 rate or longer soaking time at the maturing tem- deg C per minute.('" As the temperature is in- perature will effect a more representative saturation creased more liquid melt is formed which begins to of the glassy phase. ( 42) A body which achieves a draw particles together by surface tension and pro- porosity of zero percent in 10 min at 1250 deg C gressive solution takes place. Mullite, which was may reach the same degree of vitrification at 1200 formed from the decomposition of clay, may diffuse deg C in a longer time period. (43) into the melt or the crystals may continue to grow In addition to the effect of finer particle size on at higher temperatures and increased time of heat the maturing temperature of bodies, the fineness treatment. Mullite is also formed by recrystalliza- also governs the degree of firing shrinkage, strength, tion as the melt becomes saturated or when the thermal expansion and warpage. Finer grinds of temperature is lowered. Above the normal vitrifica- feldspar tend to increase the firing shrinkage and tion range, air, which had been entrapped within strength; however, greater warpage and lower the pores of the body by the melt, will build up thermal expansion result. (44) The warpage of bodies sufficient pressure to expand against the viscous is a function of the viscosity and the proportion glass and cause bloating or blistering. of glassy phase formed at elevated temperatures. The fluxing influence of a feldspar used in a Greatest warpage is obtained in bodies of high body does not necessarily follow the order antici- flint and high feldspar contents; increasing clay ILLINOIS ENGINEERING EXPERIMENT STATION
content at the expense of flint effectively reduces 2 to 1. These feldspars may be expected to give 4 5 46) warpage.' Soda feldspars which form less somewhat similar firing properties in typical viscous glasses have been found to cause more feldspar-flint-clay bodies due to their high potash body warpage than potash feldspars. The thermal content. A-3 and F-4 feldspars have KO to NazO expansion of fired bodies is largely dependent upon ratios of 1.53 and 1.07 respectively, so that they the amount of uncombined quartz and will there- fore decrease with higher firing temperatures."( 4 Table 3 Properties In general, higher thermal expansions have been of Feldspars Studied 25) a. Chemical Analyses obtained in bodies containing soda feldspars.( Weight Percent Buckingham Custer A-3 F-4 SiOJ 66.7 67.5 71.1 65.6 12. Purpose and Scope of Experimental Investigation A120o 18.4 17.8 16.4 20.3 Fe2Oa 0.05 0.08 0.07 0.04 A laboratory investigation was conducted to CaO 0.1 0.1 0.5 2.2 MgO tr tr tr tr determine the comparative effects of high potash Na2O 3.0 3.0 4.5 5.7 KzO 11.4 10.8 6.9 6.1 and intermediate soda-potash feldspars on the fired Ignition Loss 0.3 0.3 0.3 0.2 properties of various types of whiteware bodies. b. Mineralogical Analyses (calculated weight percent) Albite 25.4 25.4 38.1 48.2 The need for this study has been accentuated by Microcline 66.8 63.0 42.0 37.3 Anorthite 0.5 0.5 2.5 10.9 the rapid depletion of readily available supplies of Free Quartz 4.6 7.7 16.5 3.5 Muscovite high grade potash feldspar. In the past, feldspars Kaolinite and Assoc. of highest potash content have been sought as the Minerals 2.7 3.4 0.9 0.1 best type for use in ceramic whitewares, but c. Particle Size Distribution by Sedimentation Analyses (weight percent) recent Less than 30 microns 71 69 65 78 studies have shown that feldspars of considerable Less than 20 microns 58 58 54 66 Less than 15 microns 48 50 45 56 soda content may be used advantageously Less than 10 microns 33 38 34 42 as re- Less than 5 microns 16 21 17 21 placements for very high potash feldspars with Less than 2 microns 11 7 5 5 d. Fusibility little or no significant changes in the fired proper- p.c.e. (heating rate 3 ties of whiteware bodies.' 481 50 deg F per hr) 103 10 91 83 e. Solubility in Water (milliequivalent per liter*) Four commercial feldspars were used in the NasO 0.12 0.10 0.15 0.19 K 2 O 0.39 0.28 0.17 0.16 studies of bodies. The body compositions selected Total KNaO 0.51 0.38 0.32 0.35 * After 24 hrs of exposure; 1 part by weight of feldspar to 25 parts by for the investigation were those which are typical weight of distilled water; determined by flame photometer. of: semi-vitreous dinnerware are classified as intermediate soda-potash feldspars. hotel china Actually, F-4 may be considered as a plagioclase- sanitary ware potash feldspar due to its appreciable anorthite electrical porcelain content. It also should be noted that A-3 contains a floor tile considerable amount of free quartz and therefore Compositions were formulated to study the effects the actual feldspathic content per unit weight is of different types of feldspars, variable feldspar somewhat reduced. F-4 is a flotation-processed content and the effect of auxiliary fluxes in com- feldspar which is relatively free of the associated bination with the feldspars. minerals such as muscovite. Bodies were prepared and formed into test The chemical analyses of the feldspars are specimens according to commercial processing those furnished by the Consolidated Feldspar De- methods. The details of body preparation, specimen partment of the International Minerals and Chem- formation, firing and testing procedures are de- ical Corporation. The mineralogical compositions scribed in the Appendix. were calculated from these analyses according to the methods outlined by Koenig. 9) 13. Properties of Feldspars Used The particle size distribution was determined The properties of the four commercial feldspars by the Andreasen Pipette method as proposed by were determined and are shown in Table 3. The Loomis' 4' 9 and Russell and Weisz,"5o) and is pre- feldspars Buckingham and Custer are of the high sented in tabular form. potash type with KO to NaO ratios of more than Fusibilities of the individual feldspars were de- 3 to 1 and microcline to albite ratios greater than termined by firing several small slender trihedral Bul. 422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
pyramids of each at a heating rate of approxi- A typical semi-vitreous body which was known mately 50 deg F per hr in an electric furnace and to achieve a porosity of approximately 10 percent observing their deformation in relation to the de- at cone 10 was selected for a base composition. formation of standard pyrometric cones which were This composition contained: fired simultaneously. The reported values of fusi- 33.5 percent of flint bility are expressed in terms of p.c.e. and represent 36.0 percent of mixed Tennessee and Kentucky the pyrometric cone equivalent at the temperature ball clays when each feldspar specimen had deformed such 21.0 percent of mixed Georgia and North Caro- that the tip of the specimen was level with the lina kaolins supporting plaque. 13.5 percent feldspar The relative solubilities of the feldspars in Bodies of Series I (Table 4) were of this composi- water were obtained using particle sizes between tion; succeeding series of bodies represent variations 44 and 53 microns. Ten grams of each feldspar, in the base composition such as increased feldspar collected between Nos. 270 and 325 mesh sieves, content, addition of auxiliary flux, or both. The were placed in 300 ml pyrex bottles containing 250 deviations from the base composition were, for the ml of double distilled water. The bottles were most part, compensated for by appropriate altera- sealed and tumbled end over end for 24 hr; after tions in the kaolin content. the agitation period the feldspar water mixtures Four commercial feldspars were used for the were centrifuged and the supernatant liquid drawn compositions of Series I; the body in which each off for solubility tests. Ninety ml of each liquid was contained may be readily identified by the were added to 10 ml of a standard Li solution. code letter following the body composition number. These solutions were examined with a Perkin- Thus, bodies SV1B and SV1C respectively con- Elmer Flame Photometer for Na20 and KO con- tained Buckingham and Custer feldspars, which tent. The values expressed in the table of solubili- are of the high potash type; bodies SV1A and ties represent the milliequivalents of NaO and KO SV1F contained A-3 and F-4 feldspars respectively. per liter taken into solution from each feldspar These feldspars may be considered as intermediate after 24 hr of exposure in water. soda-potash types. The analyses arid properties of the feldspars used have been shown in the previous 14. Semi-Vitreous Ware section. The Custer (C) and F-4 (F) feldspars Composition were selected as representative of the high potash Four series of compositions were formulated for and intermediate soda-potash type feldspars and the purpose of studying the fired characteristics of were used for comparative purposes. typical semi-vitreous dinnerware bodies as in- Bodies of Series II represent increases in the fluenced by high potash and intermediate soda- feldspar content over that of the base composition. potash type feldspars, varying feldspar content, and Increases to 15.0 and 16.5 percent feldspar were combination of feldspar with small amounts of made at the expense of Pioneer kaolin. Series III auxiliary fluxes. A total of 21 bodies was studied; was composed of bodies in which 2.0 percent addi- the compositions are shown in Table 4. tions of various fluxes were added to the base
Table 4 Compositions of Semi-Vitreous Bodies Series I Series II Series III Series IV Body No. 1A 1B 1C 1F 2C 2F 3C 3F 40 4F 5C 5F 6C 6F 70 7F 8F 9F 10F 11F 12F Feldspar A 13.5 Feldspar B 13.5 Feldspar C 16.5 13.5 13.5 13.5 Feldspar F 16.5 13.5 13.5 13.5 16.5 13.5 15.0 16.5 C & C Ball Clay 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 6.5 7.0 6.5 6.0 Imperial Ball Clay 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Tenn. No. 5 Ball Clay 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 6.5 7.0 6.5 6.0 Old Mine No. 4 Ball Clay 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 6.5 6.5 6.0 6.0 Pioneer Kaolin 9.0 9.0 10.0 10.0 10.0 10.0 10.0 10.0 9.0 9.0 9.0 9.0 Kamec Kaolin 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 9.0 E.P.K. 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 5.5 5.5 5.5 5.0 Ottawa Flint 33.5 33.5 33.5 33.5 33.5 33.5 33.5 33.5 33.5 33.5 33.5 33.5 Whiting 2.0 2.0 Low Lime Tale 2.0 2.0 Tremolitic Talc 2.0 2.0 2.0 2.0 4.0 4.0 4.0 Magnesite 2.0 2.0 ILLINOIS ENGINEERING EXPERIMENT STATION
compositions. The fluxes used were whiting, low perature scale and the other physical property lime talc, tremolitic talc and magnesite. curves determine the maturing temperature and In Series IV only F-4 feldspar was used in the physical properties at that temperature. The results body compositions for the purpose of determining thus obtained with all bodies are shown as bar the effects of varying combinations of feldspar with graphs in Fig. 7. tremolitic talc. These compositions contained 15.0 In compositions of Series I, it was observed that and 16.5 percent F-4 feldspar in combination with the bodies containing high potash feldspars (SV1B 2.0 percent tremolitic talc, and combinations of and SV1C) matured at about the same tempera- 13.5, 15.0 and 16.5 percent F-4 feldspar with 4.0 ture with similar strengths and shrinkages. The percent tremolitic talc. soda-potash feldspar bodies (SV1A and SV1F) Processing and Firing matured at slightly higher temperatures with less The semi-vitreous dinnerware bodies were pre- Table 5 pared by blunging and filter pressing. Test speci- Comparison of Fired Properties of Semi-Vitreous Bodies as Obtained mens consisted of extruded 7/% in. diam rods. Sets from Laboratory and Commercial Firings (2240 deg F) of 15 specimens of each body composition were Body No. Percent Porosity Modulus of Rupture (psi) Lab. (cone 91) Comm. (cone 93) Lab. (cone 91) Comm. (cone 98) fired to temperatures of 2140 deg F, 2200 deg F, 1C 16.43 17.95 5814 5714 IF 17.45 18.07 5583 5549 2230 deg F, 2280 deg F and 2340 deg F in an 4C 12.21 13.40 6010 5658 4F 13.27 14.01 5780 5936 electrically heated kiln. These temperatures cor- 5C 11.96 12.62 6234 6231 5F 12.56 13.10 6523 6335 responded to cone equivalents of 56*, 76, 86, 96, and 6C 11.88 12.48 6520 6425 6F 12.21 12.95 6413 6513 116. The temperature rise was controlled at approxi- 7C 8.93 10.14 6541 6574 7F 7.87 8.75 6605 6513 mately 100 deg F per hr up to 2000 deg F and 50 Note: Laboratory firing in electric kiln with 100 deg F temperature rise; deg F per hr thereafter until the peak temperature commercial firing in gas fired tunnel with 29-hr total cycle. was reached and held for 11/ hr. In addition to the strength than the potash feldspar bodies. The laboratory firings, several bodies were fired in a shrinkage of SV1F was similar to the shrinkage of commercial tunnel kiln to cone 93 (See Table 5). SV1B and SV1C, while SV1A showed less shrink- Tests were conducted on the fired specimens to age, possibly due to the high free quartz content obtain the fired porosity, modulus of rupture and of A-3 feldspar. volume shrinkage. The thermal expansion and Increasing feldspar content lowered the matur- crystalline nature of bodies fired to cone 96 were ing temperature of the bodies somewhat as would also determined.t be expected; however, it was observed that while Results body SV1F matured at a slightly higher tempera- Physical Properties. The physical properties of ture than SVIC, the two bodies, SV2F and SV2C, the fired semi-vitreous dinnerware bodies are pre- matured simultaneously, and SV3F matured earlier sented in Fig. 6. The data in this form are con- than SV3C. The increased feldspar contents caused venient for examining the relations between the no appreciable change in the strengths of the firing temperatures and the changes in the proper- .matured bodies. The shrinkages of bodies made ties of each body; however, a comparison of the with high potash feldspar were essentially un- properties of all bodies at some common condition changed when the feldspar content was increased such as maturity is more desirable. For convenience, from 13.5 to 16.5 percent; however, in the soda- therefore, the authors have arbitrarily assumed potash bodies an increase in shrinkage was noted maturity in the semi-vitreous bodies to be that when the feldspar content was raised from 13.5 to condition at which the body has a fired porosity of 15.0 percent. 10 percent. In order to obtain the body properties From the results of physical properties obtained at the point of 10 percent porosity, the following with the first two series of compositions, it may be procedure was followed: A vertical line is drawn concluded that direct weight substitutions of soda- through the 10 percent point on the porosity curve; potash feldspar may be made for high potash the intersections of the vertical line with the tem- feldspar in a semi-vitreous type body with (a) little or no change in maturing temperature, (b) slightly *The superscript refers to the degree of bending of the cone tip corresponding to the numerals on a clock face between 1 and 6. less transverse strength, and (c) little or no in- tFor detailed description of the equipment and procedures employed in the processing and testing of bodies, see Appendix. crease in shrinkage. Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
0
04
Deg i ii i i ii i -- F 2/50 2200 2250 2300 2150 2200 2250 2300 Firing Temperature
Fig. 6. Fired Properties of Semi-Vitreous Bodies 18 ILLINOIS ENGINEERING EXPERIMENT STATION
254 25.4
::::i::: :_::----- 24.2 -i':------23 . 020" .... •JQ 23.6 :-:::: .::::·-: ~··I··I :: :: ::;::i::: 228 i::iii :::::::::: l142 22.4 225 2- :::::::::: 22.2 pq : ::::::-' :: : ::: 22.L l I . 220 91·iiii 2/.4 :::::::i~z :::·::::::- --::--:":::' -:-- I 202 ri iii:- -:::i:-: 1 20 :,:i::· ~II 20 /9.8 -:- ::-:::: 19.2 :~::; :;-_::: ::-ii-- :::::-I:·i: i~·iii :ii:, /8- i···:· -::::s~i -ii~ni -:is:s~ :::: ::" :::::::" -'- --'-" I -:_--:-i ·:::i::·::· i·-i ::a::- ilLii :::::~·i:::i:::·:~ ::::::::" ;:::·1::j::::~ :·· ii_-:ii--i "':: ·::;:::· :;-:::::;_ ::i:::::::·~ _i-ii:--1 ;·::::::i:· 16 3 i L iE-·l ~iiiiiiil ;:::;:·
Body IA /B IC IF 2C 2F 3C 3F 4C 4F 5C 5F 6C 6F 7C 7F 8F 9F IOF IIF 12F % Feldspar 13.5 /3.5 /35 135 /5.0 /5.0 /65 /6.5 /35 13.5 135 /3.5 /3.5 /3.5 /3.5 /3.5 5.0 /6.5 /35 5.0 16.5 %Auxi/iory 0 0 0 0 0 0 0 0 o 20 20 0 0 2.0 20 4.0 4.0 4.0 Flux Whiling Low Lime Tremolific Magnesite Tremo/itic Tolc Talc Talc
Fig. 7. Properties of Semi-Vitreous Bodies at Maturity (10 percent Porosity) Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
The addition of 2 percent whiting to the base showed a slight amount of cristobalite present but composition was effective in reducing the maturing not in excess of 5 percent. Increasing feldspar con- temperature of the potash feldspar body (SV4C) to tent was found to decrease the amount of free about one cone below that of the base body. The quartz and to increase the mullite formation. effect of a like whiting addition to the soda-potash The addition of whiting also decreased the body (SV4F) was not quite as pronounced. The quartz content and slightly increased the mullite whiting addition to the potash feldspar body re- formation. A small degree of cristobalite formation sulted in reduced strength at maturity. Little was noted in the soda-potash body. In those bodies change of matured shrinkage was noted. containing 2 percent of talc, the amount of free The effect of 2 percent low lime talc with the quartz was considerably reduced and some cristo- potash feldspar was very similar to that obtained balite development was noted in the potash feldspar with whiting; with soda-potash feldspar slightly bodies; while in the soda-potash bodies consider- more fluxing was obtained but with little change able cristobalite development occurred. Magnesite in the matured properties. The addition of 2 per- was found to cause extensive cristobalite formation cent tremolitic talc to the base composition was with the soda-potash feldspars and to a lesser only slightly more effective in its fluxing action degree with high potash feldspars. The quantitative than the whiting or low lime talc; however, some- determination of cristobalite for several fired bodies what greater shrinkage resulted. is shown in Table 6. Bodies SV7C and SV7F contained 2 percent additions of magnesite. The maturing temperature Table 6 of SV7C was about 2 cones lower than the base Cristobalite Content of Fired Semi-Vitreous Bodies Body No. Percent Percent Percent Cristobalite body SV1C, while SV7F matured about 3 cones Feldspar Tremolitic (± 2 percent) After6 Talc Firing to Cone 9 lower than the base body SV1F. These marked IC 13.5 C IF 13.5 ... tr. reductions in maturing temperature were accom- 6C 13.5 C 2.0 tr. 6F 13.5 F 2.0 12 panied by increases in volume shrinkages but no 8F 15.OF 2.0 11 9F 16.5 F 2.0 10 appreciable changes in strength. 10F 13.5 F 4.0 16 11F 15.0 F 4.0 15 Combined increases in feldspar content and talc 12F 16.5 F 4.0 12 additions reduced the maturing temperature very markedly. A 3 percent increase in feldspar content The compositions which showed high cristobalite and an addition of 4 percent of talc reduced the formation were fired in an X-ray furnace to -deter- maturing temperature by 5 cones. At the lower mine the temperature at which the cristobalite maturing temperatures, slightly less strength and formed. The formation was found to occur during reduced shrinkages were obtained. the cooling cycle at temperatures between 1100 A comparison of the results obtained from a deg C and 1000 deg C. The cristobalite was formed commercial firing and a laboratory kiln firing are by the process of separation with crystal deposition shown in Table 5. It is noted that in all bodies the of SiO, or devitrification. fired porosities obtained with the laboratory kiln Thermal Expansion. The linear thermal expan- were lower than those obtained from the commer- sion curves for bodies of Series I and II fired to cial firing. This difference may be attributed to the cone 96, are shown in Fig. 8. The expansions ob- difference in firing rates, the commercial rate being served with the soda-potash feldspar bodies were almost twice as rapid as the laboratory cycle. The slightly higher than those noted in bodies contain- values of strength obtained from the two firings ing potash feldspar. The high expansion of body were in close agreement. SV1A is undoubtedly due to the high free quartz Crystalline Content. The crystalline nature of content of A-3 feldspar. An increase of feldspar the specimens fired to cone 96 were determined by causes more crystalline silica to dissolve, thus de- X-ray analysis.* The only crystal phases identified creasing the expansion. in the bodies were quartz, mullite, and in some The combination of auxiliary fluxes and potash cases, cristobalite. The crystalline content of Series feldspar caused a reduction in the thermal expan- I bodies made with potash feldspar was entirely 6 quartz and mullite; the soda-potash feldspar bodies sion of bodies fired to cone 9 . In bodies containing soda-potash feldspar, the addition of auxiliary
* See Appendix for description of X-ray unit and techniques employed. fluxes which contained considerable percentages of ILLINOIS ENGINEERING EXPERIMENT STATION
bodies containing extensive cristobalite develop- ment were found to have a reduced thermal shock resistance although their crazing resistance was improved. Such bodies are likely to dunt in the kilns unless special precautions for cooling are S 0.5 observed.
15. Hotel China 0.4 Composition /,4 · Two series of hotel china compositions were formulated as shown in Table 8. A typical compo- o F\ /.ff /llll\l sition containing 21 percent feldspar was selected 0.2 as a base composition and four bodies of this type IF were made to show the influence of the four com- mercial feldspars, A-3, Buckingham, Custer and F-4, when each is used as the total flux content. These bodies are represented by compositions from 2A to 2F in Series I. All other bodies contain either Temperature, C Custer or F-4 feldspars. Fig. 8. Linear Thermal Expansions of Series I and II Semi-Vitreous Bodies Fired to Cone 9
MgO were found to cause a hump in the thermal expansion curves between 150 - 250 deg C, indi- cating the presence of cristobalite. The expansion data obtained with bodies containing the soda- potash feldspar and tremolitic talc are shown in cz Fig. 9. The most pronounced cristobalite inversion 13.5 was noted in body SV10F which contained A percent of F-4 feldspar and 4 percent tremolitic B talc. This data agrees favorably with the X-ray analysis since body SV10F was found to have the greatest cristobalite development among those bodies containing tremolitic talc as an auxiliary flux. Thermal Shock. The influence of cristobalite on 0 IoU zooiuu Uo U OU/u SUU Temperature, C the thermal shock properties of the bodies was Fig. 9. Linear Thermal Expansions of Semi-Vitreous Bodies studied using glazed 6-in. coupe plates. Five plates Containing Tremolitic Talc and Fired to Cone 9 of each of the compositions were heated to 480 deg F in an electric oven and quenched in a dye solu- In Series I, the feldspar content is varied from tion at 70 _ 2 deg F; the number of cycles re- 18 to 25 percent at the expense of kaolin. In series quired to cause a body or glaze defect was recorded. II additions of auxiliary flux are made to bodies Table 7 shows selected results of the test. The containing Custer and F-4 feldspars.
Table 7 Processing and Firing Thermal Shock Resistance of Semi-Vitreous Bodies from The hotel china bodies were prepared by a 480 deg F to Room Temperature (70 ± 2 deg F) process of ball milling and filter pressing. After one Body No. Percent Percent Trial Feldspar Tremolitic I II III week of aging, the bodies were formed into 7/-in. Talc c* c c1 13.5 C ... 4 5 4 diam rods by extrusion. Specimens were fired in an 5 5C IF 13.5 F ... 4Cc c 6C 13.5 C 2.0 4 C 5 5cE D electrically-heated kiln at a rate of approximately 6F 13.5 F 2.0 5 4ED 3D 10F 13.5 F 4.0 3ED 3D 4 75-80 deg F per hr up to 2000 deg F and 50 deg F * Number indicates the cycltheuring which the defect was noted: C- per hr thereafter crazed; ED-edge dunt; D-dunted. to temperatures of 2180, 2220, Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
2250, 2280, 2310, 2350, 2400, and 2450 deg F. A 11/2 vitrification, thus lowering the maturing tempera- hr soak at these temperatures was used to deform ture. An addition of 2 percent talc to the Custer standard pyrometric cones to 73, 83, 93, 103, 113, 122, feldspar body promoted vitrification at cone 11I 133, and 136 respectively. which was one cone lower than the maturing tem- perature with no talc present. In a similar Results body containing F-4 feldspar, a 2 percent talc addition The physical properties obtained with the fired reduced the vitrification temperature from cone 123 specimens of hotel china bodies are shown in Fig. to about cone 106. The bodies containing 2 percent 10. In the bodies which contain 18 percent of either talc began to overfire at cone 126. An increase in Custer or F-4 feldspar, vitrification was observed the talc addition to 4 percent was effective in to occur at a temperature of approximately cone promoting the vitrification of the Custer body at 126, where the bodies developed zero porosity and cone 103 and the F-4 body at about cone 96. Over- a transverse strength in excess of 10,000 psi. The firing took place at cone 123. The bodies of in- volume shrinkages of the two bodies were found to creased feldspar content with 2 percent talc addi- be similar with a value of approximately 30 per- tions vitrified at cone 103 and overfired at cone 126. cent at vitrification. Maximum values of strength In general it was observed that when talc was and shrinkage were observed at cone 133; the body added, the rate of fluxing was more rapid in F-4 containing Custer feldspar had slightly greater ulti- feldspar bodies than in corresponding Custer feld- mate strength than the corresponding F-4 feldspar spar bodies, and as a result had shorter firing body. ranges. With 21 percent feldspar (2A-2F), the firing The fluxing effect of whiting with Custer and behavior of bodies containing A-3, Buckingham, F-4 feldspars was observed in bodies 6C and 6F. Custer and F-4 feldspars may be compared. The Two percent additions to bodies containing 21 per- body containing A-3 feldspar was vitrified at cone cent of feldspar effected vitrification after firing to 126, while the bodies containing Buckingham, cone 123; overfiring was noted at cone 133. The Custer or F-4 feldspar vitrified at a half cone whiting was found to be a more efficient flux with lower, cone 121. The potash feldspars promoted Custer feldspar than with F-4 feldspar. slightly more strength and somewhat less shrinkage A qualitative analysis of the crystalline phases than the soda-potash feldspars. The A-3 feldspar present in the matured hotel china bodies investi- composition did not show evidence of overfiring at gated showed evidence of some cristobalite develop- cone 136, while the potash feldspars bodies indi- ment in all bodies which contained F-4 feldspar, cated overfiring at this temperature. The body con- while little or no cristobalite was noted in Custer taining F-4 feldspar was found to begin overfiring feldspar bodies. at cone 133. Bodies which contained 25 percent of either 16. Electrical Porcelain Custer or F-4 feldspar were found to vitrify be- Composition tween cones 11" to 123 with evidences of overfiring One series of electrical porcelain-type bodies at cone 133. The F-4 composition approached vitri- was investigated. The composition of this series of fication at a more rapid rate than the Custer feld- bodies is shown in Table 9; the only variation in spar body and also showed a little more shrinkage. the compositions of the four bodies is the type of The additions of talc to the hotel china bodies feldspar used. As in previous studies, the four containing 21 percent feldspar increased the rate of commercial feldspars, A-3, Buckingham, Custer
Table 8 Compositions of Hotel China Bodies Series I Series II Body No. 1C IF 2A 2B 2C 2F 3C 3F 4C 4F 5C 5F 6C 6F 7C 7F A-3 Feldspar 21 Buckingham Feldspar Custer Feldspar 18 21 21 F-4 Feldspar Ottawa Flint 35 35 35 35 35 Old Mine No. 4 Ball Clay 8.5 8.5 8.5 8.5 8.5 Kamec Kaolin 15 14 14 14 14 Pioneer Kaolin 13.5 12.5 12.5 12.5 11.5 Florida Kaolin 10 9 9 9 8 Tremolitic Talc No. 1 Whiting 2 2 ILLINOIS ENGINEERING EXPERIMENT STATION
'' '"'
CMn
Deg Firing Temper ature Fig. 10. Fired Propertiees of Hotel China Bodies and F-4 are employed as the total feldspathic con- shrinkage, porosity and modulus of rupture deter- tents, and the bodies in which they are contained minations were formed by extrusion. The test may be identified by the code letters following the specimens consisted of 7/-in. diam rods. Samples composition designations. for the determination of dielectric properties were formed by plastic pressing in a plaster mold; these Processing and Firing samples were made in the shape of a 6%-in. diam The electrical porcelain bodies were prepared disc 56 in. thick, the surfaces of which were by blunging and filter pressing. Test specimens for ground approximately parallel after drying. Bul. 422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
Test specimens were fired in an electrically heated kiln at a heating rate of approximately 80 deg F per hr to temperatures of 2230, 2260, 2300, 2340, 2375, and 2410 deg F and held at these tem- peratures for 2 hr. Cone plaques set among the .
Table 9 Composi tions of Electrical Porcelain Bodies Body No. EP1A EP1B EPIC EPlF L< A-3 Feldspar 30 Buckingham Feldspar 30 Custer Feldspar F-4 Feldspar 30 Ottawa Flint 20 20 20 Victoria Ball Clay 10 10 10 H.T.P. Ball Clay 12 12 12 Kentucky Old Mine No. 4 Ball Clay Pioneer Kaolin Kamec Kaolin E.P.K. Florida Kaolin
specimens in each burn indicated the above firings 6 to be respectively equivalent to cones 8 , 96, 112, 123, 126, and 131. The dielectric test samples were fired to the vitrification temperatures determined for each body composition. Results / The physical properties determined for the elec- trical porcelain bodies are shown in Fig. 11. Body EP1A, which contained A-3 feldspar was found to mature later than any of the other bodies showing highest values of porosity and lowest volume shrinkage throughout the firing range. As shown in other type bodies, this behavior was probably due C IC to the high free quartz content of A-3 feldspar. 7 The vitrification of body EP1A was shown to occur /1 at a temperature between cones 126 and 133. 8I 96 // /2 s /26' /3S The two potash feldspar bodies, EP1B and Deg F 2200 2250 2300 2350 2400 EP1C, had similar fired physical characteristics Firing Temperature Fig. II. Fired Properties of Electrical Porcelain Table 10 Dielectric Properties of Electrical Porcelain Bodies* The modulus of rupture values obtained with Body Range of Storage Dielectric Loss Dielectric No. Capacitance Factor Constant Factor Strength this series of bodies indicated the F-4 feldspar (uuf) (percent) (volts per mil) bodies gave higher strengths than the potash feld- EP1A 71-85 111.1 5.08 4.57 289.0 EPIB 77-90 117.0 5.40 4.62 284.3 spar bodies at equivalent firing temperatures. The EP1C 77-94 118.0 5.37 4.55 307.3 firing shrinkage of the F-4 feldspar body EP1F 80-86 106.0 5.60 5.28 207.7 was * Measured by Locke Department, General Electric Corporation. These greater than any of the other bodies in this series are the average of values obtained on 6 specimens. The specimens were circular discs approximately 6 in. in diam by .20 in. in thickness. throughout the firing range. The results of the electrical tests conducted on throughout the firing range studied. The vitrifica- the dielectric samples are shown in Table 10. The tion of both of these bodies was complete at cone measurements were made by the Locke Department 123-126. of the General Electric Company. The electrical The body showing the earliest vitrification in properties which were of chief concern in evaluating this series of electrical porcelain bodies was EP1F these bodies were the dielectric strength and loss which contained the flotation feldspar, F-4. This factors. The dielectric strengths of conventional body was shown to achieve complete vitrification high voltage porcelains range between 250 and 300 at temperatures between cone 112 to 123. volts per mil; all of the bodies tested show favor- ILLINOIS ENGINEERING EXPERIMENT STATION
Table 11 Compositions of Sanitary Ware Bodies Series I Series II Series III Series IV Body No. SIA S1B SiC S1F S2A S2B S2C S2F S3A S3B S3C S3F S4C S4F S5C S5F A-3 Feldspar 32 32 Buckingham Feldspar 32 Custer Feldspar F-4 Feldspar Martin No. 5 Ball Clay 15 15 C & C Ball Clay 7.5 7.5 Royal Ball Clay 7.5 7.5 Pioneer Kaolin 9 9 Kamec Kaolin 9 9 Ottawa Flint 20 20 Tremolitic Talc No. 1
Table 12 Casting Characteristics of Sanitary Ware Bodies Percent Percent Specific Flow Test Wet Wt Dry Wt Percent Drainage Type Sodium Sodium Gravity sec per of Cast of Cast Water Cast Carbonate Silicate 100cc Retention A. Body S1A 0.05 0.05 1.795 282.2 239.8 17.70 Good Soft 0.05 0.075 1.801 280.9 240.3 16.85 Good Good 0.05 0.100 1.797 264.8 227.2 16.60 Excellent Good 0.05 0.125 1.800 255.3 219.6 16.25 Excellent Very Good 0.05 0.150 1.801 245.6 211.9 15.90 Excellent Very Good 0.05 0.175 1.800 245.2 211.7 15.85 Excellent Very Good B. Body SIB 0.05 0.05 1.800 291.3 240.1 17.6 Fair Soft 0.05 0.075 1.801 266.3 221.7 17.1 Good Soft 0.05 0.100 1.797 250.0 208.6 16.5 Good Good 0.05 0.125 1.798 243.5 203.6 16.4 Excellent Good 0.05 0.150 1.800 235.7 196.8 16.5 Excellent Excellent 0.05 0.175 1.798 233.7 195.5 16.4 Excellent Excellent C. Body SIC 0.05 0.05 1.798 289.6 239.6 17.5 Fair Soft 0.05 0.075 1.801 256.8 216.2 17.0 Fair Soft 0.05 0.100 1.802 245.0 204.8 16.4 Good Good 0.05 0.125 1.800 241.4 201.6 16.5 Good Good 0.05 0.150 1.798 236.3 197.1 16.6 Excellent Excellent 0.05 0.175 1.797 235.0 196.5 16.4 Excellent Excellent D. Body S1F 0.05 0.05 1.797 277.4 236.1 17.5 Fair Soft 0.05 0.075 1.804 249.6 213.5 16.9 Good Soft 0.05 0.100 1.796 246.3 211.7 16.4 Good Good 0.05 0.125 1.798 239.5 205.6 16.5 Good Good 0.05 0.150 1.801 237.3 203.5 16.6 Excellent Excellent 0.05 0.175 1.797 236.1 202.2 16.75 Excellent Excellent able dielectric strengths: the highest breakdown were compensated for by appropriate alterations strength was shown by the Custer feldspar body in the kaolin content. and the lowest breakdown strength in the F-4 feld- Processing, Casting and Firing spar samples. .The F-4 feldspar body also had the The sanitary ware bodies were prepared by highest loss factor of the series. blunging and filter pressing. After one week of aging, the casting characteristics of the various 17. Sanitary Ware body compositions were determined at six electro- Composition lyte levels. These casting trials were determined In the study of sanitary ware bodies, four series with slip batches containing 1000 grams of dry of compositions were formulated as shown in Table body. The sodium carbonate content was held con- 11. A typical sanitary ware composition containing stant at 0.05 percent in all trial slips but the sodium 32 percent of feldspar was selected for the first silicate content was varied from 0.05 to 0.175 per- series of compositions. This series consisted of cent in increments of 0.025 percent.* four bodies, each of which was made with a differ- The results of the casting trials indicated that electrolyte additions of 0.05 percent sodium car- ent commercial feldspar - A-3, Buckingham, Cus- bonate and 0.10 percent sodium silicate ("N" ter and F-4. In Series II, 2 percent of tremolitic Brand) were suitable for all body compositions. talc was added to each of the above bodies. The Approximately 10 gal of slip were prepared from talc addition was increased to 4 percent in series each body composition with this addition of electro- III. In Series IV, bodies containing Custer and F-4 lyte. The slips were adjusted to 1.80 specific feldspars were made at a reduced feldspar level gravity and de-aired in a vacuum mixer. (28 percent) with and without a 2 percent talc Details of procedures used in conducting the initial casting trials may addition. All variations from the base composition be found in the Appendix. Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
Test specimens were formed by casting 7 in. Custer and Buckingham feldspars may be used lengths of % in. diam rods in plaster molds. Sets interchangeably with very little change in the cast- of 15 specimens were fired to six temperatures in ing characteristics of the body slip. The use of F-4 an electrically-heated kiln at a firing rate of 75 feldspar as a replacement for a potash feldspar deg F per hr to 2000 deg F and 50 deg F thereafter would cause slightly more rapid casting rates at an until the desired temperatures were reached; a 2- equivalent electrolyte level. The best casting slips hr soak was maintained at the peak temperatures. of the series were found to be those containing A-3 No cooling control was attempted. feldspar. Results Figure 12 presents the results obtained from the The results of casting trials made with Series I physical tests on fired specimens of sanitary ware sanitary ware bodies given in Table 12 show that bodies. In Series I, the data show that the body
(a) Bodies Containing Potash Feldspar (bl Bodies Confaining Intermediate Alkali Feldspar
8 ___ _\N 6 \ ------V------%.\ •'-. . 4 ^ ^\^ _____ 2\ k
-_I.~~~ 1I ___ i
Q !Y
i I I I I I ; Deg F 2/50 2200 2250 2300 2350 2/50 2200 2250 2300 2350 Firing Temperature Fig. 12. Fired Properties of Sanitary Ware Bodies ILLINOIS ENGINEERING EXPERIMENT STATION containing F-4 feldspar achieved maturity in the spar with no auxiliary flux additions. The reduced range of cone 93 to 96. Bodies containing Custer amount of feldspar was observed to yield bodies or Buckingham feldspar matured at a slightly of slightly lower ultimate strength but of similar higher temperature, between cone 96 and cone 103. shrinkage. The body containing A-3 feldspar was found to mature in the range of cone 103 to cone 106. The 18. Floor Tile maximum moduli of rupture in this series were Composition found at temperatures slightly above the point at Four bodies of a representative floor tile compo- which zero porosity was indicated. sition were prepared using the four commercial The tests indicated that more shrinkage may feldspars A-3, Buckingham, Custer and F-4 as total be anticipated with F-4 feldspar than with equiva- flux contents. The specific compositions are shown lent amounts of high potash feldspars such as in Table 13. Buckingham or Custer. The ultimate transverse Table 13 strengths of the potash feldspar bodies were some- Connposition of Floor Tile Bodies what greater than those obtained with F-4 feldspar Body No. FT1A FT1B FT1C FTIF A-3 Feldspar 55 bodies, although F-4 feldspar bodies showed higher Buckingham Feldspar 55 55 Custer Feldspar 55 strengths at equivalent firing temperatures up to F-4 Feldspar Victoria Ball Clay the point of overfiring. It should be noted, however, Kamec Kaolin E.P.K. Florida Kaolin that at equivalent firing temperatures the porosity Tremolitic Talc No. 1 of the F-4 feldspar body was lower. Ottawa Flint Results obtained with Series II and Series III bodies illustrated the effective fluxing action in- Processing and Firing prepared by dry mix- duced by small additions of tremolitic talc. In The floor tile bodies were The mixed materials compositions containing 32 percent A-3 feldspar, a ing with 8 percent of water. through a 10- 2 percent talc addition reduced the maturing tem- were aged for 24 hr and granulated perature range from cone 103-106 to cone 93-9', mesh screen, after which specimens were formed of 1 in. while a 4 percent addition of talc effected maturity by pressing at 2000 psi. Specimens consisted in the range of cone 76-83. In a like manner, 2 per- square bars 6 in. in length. Firings were made in an cent talc, added to similar bodies containing Buck- electric kiln at a temperature rate of 100 deg F ingham or Custer feldspars, reduced the maturing per hr to 2120, 2150, 2170, 2200, and 2230 deg F. ranges from cone 96-103 to cone 86-93, and 4 percent These temperatures represented pyrometric cone talc caused maturity at cone 76-83. The maturing equivalents of 46, 56, 65, 76, and 86. ranges of F-4 feldspar bodies were reduced from Results cone 9-9cone93 tone 86-93 and cone 73-76 by additions The results obtained from tests on the floor tile of 2 and 4 percent tremolitic talc. The addition of bodies are shown in Fig. 13. The data show a rapid auxiliary flux material apparently had little effect drop in the porosities of all bodies in the tempera- on the ultimate transverse strength of the bodies ture range of cone 4 to cone 8. The body containing investigated but caused a slight increase in shrink- F-4 feldspar reached vitrification at a temperature age. slightly above cone 76. The potash feldspar bodies Bodies of reduced feldspar content (reduced achieved vitrification at cone 86, while the A-3 from 32 to 28 percent) indicated that the 4 percent feldspar body was still incompletely vitrified at reduction raised the maturing temperature by that temperature. slightly more than one cone. A 2 percent talc addi- The shrinkages obtained with all bodies were tion to bodies containing 28 percent feldspar approximately of the same magnitude; this was affected maturity in about the same temperature also observed to be the case with the modulus of range as those bodies containing 32 percent feld- rupture values. Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES
SI T 1 I 1
2 \2K. FTIA \". \ FrIR % ...... -
__FT/F F 8• B6-- 4
2
n ------^ -'*
b i
5
4
3
Cone
Deg F 2 '00 2150 2200 Firing Temperature
Fig. 13. Fired Properties of Floor Tile Bodies IV. SUMMARY OF RESULTS
The results of this extensive study on the use 6. Whiting is a more active flux in bodies con- of high potash and intermediate alkali feldspars in taining high potash feldspars than in similar bodies a wide range of whiteware bodies may be summa- containing intermediate alkali feldspars. rized as follows: 7. Talc is a more active flux in bodies contain- 1. Intermediate alkali feldspars may be used ing intermediate alkali feldspars than in similar interchangeably with high potash feldspars in all bodies made with high potash feldspars. types of whiteware bodies with minor changes in 8. The over-all fluxing action of talc was found the firing characteristics and properties. to be more effective than equivalent amounts of 2. In whiteware bodies of low feldspar content, whiting in bodies containing either type of feldspar. such as semi-vitreous bodies, intermediate alkali 9. Magnesite was found to be a powerful flux feldspars with low free quartz content may be when added in amounts of 2 percent, but caused interchanged with high potash type feldspars with appreciable increases in the fired shrinkage. little or no change in the firing characteristics or 10. The addition of auxiliary fluxes was found fired properties if no other fluxes are present. to shorten the firing range of bodies in which they 3. In whiteware bodies of moderate and high were used. feldspar contents, such as electrical porcelain, sani- 11. Considerable cristobalite formation was ob- tary ware and floor tile, an intermediate alkali served in semi-vitreous bodies containing inter- feldspar such as F-4 may be substituted for potash mediate alkali feldspars and MgO-bearing fluxes feldspars to effect maturity at a lower temperature such as talc and magnesite. Little or no cristobalite with only a slight reduction in strength and a small was found in similar bodies made with high potash increase in shrinkage. feldspars. 4. Feldspars of high potash content may be used 12. Some cristobalite formation was found in interchangeably at all levels with small differences all whiteware bodies containing intermediate alkali- in the firing characteristics of bodies. feldspars. 5. Whiting and talc are beneficial in reducing 13. X-ray studies revealed that the formation the maturing temperatures of whiteware bodies of cristobalite took place during the cooling cycle when added in amounts of 2 to 4 percent. with crystal deposition of SiO, or devitrification. APPENDIX
19. Raw Materials Used in Experimental Bodies mixed an additional 15 min. The water addition The chemical analyses of the feldspars used in made was approximately 8 percent of the dry the experimental bodies are shown in Table 14. The weight of the body. The mixed material was placed analyses of other materials used in making various in sealed jars and aged for 24 hr, after which it body compositions are also given in Table 14. was granulated through a 10-mesh screen and re- placed in the storage jars until ready for use in 20. Details of Body Preparation pressing. Blunging Blunging was used for the blending of raw Filter Pressing and Pugging materials in preparation of semi-vitreous, electrical All of the bodies prepared by blunging or ball porcelain and sanitary ware bodies. The blunging milling were filter pressed and subsequently pugged. equipment consisted of a 20-gal tank with two sets The processed slips of each body were pumped from of paddles which were rotated in opposite directions the smooth blungers and filter pressed to a pressure to create turbulent counterflow blunging. Approxi- of 140 psi for 45 min; the resultant filter cakes mately 12 gal of water was used for the blunging contained approximately 20 percent of water. The of bodies; 120 lb of dry weight of each body com- filter cakes of each body composition were pugged position was slowly added to the water with the into slugs 3 in. in diam by 12 in. long and placed paddles rotating. The materials of each batch were in sealed damp jars for one week of aging. The added in the order of decreasing plasticity; the ball pugging operation was used to assure a uniform clays were added first, followed by the kaolins and moisture distribution within each body and also to then the non-plastic materials. Sufficient time was facilitate the storage during the aging period. allotted between the various additions to allow the 21. Specimen Formation slip to become smooth. After all materials had been Extrusion added, the slip was allowed to blunge for approxi- Specimens for the testing of semi-vitreous, elec- mately 1 hr and then passed through a 120-mesh trical porcelain and hotel china bodies were pre- lawn and over a set of magnets to remove any pared by vacuum extrusion with an International particles of iron. The processed slip was stored in Vac-aire De-airing Extrusion Machine. Specimens smooth blungers for filter pressing. were extruded as round rods 7 in. in diam; then Ball Milling 80 rods cut 7 in. in length and 40 rods cut 3% in. Ball milling was used to prepare the hotel china in length for each body composition. The specimens bodies. A 35-gal Patterson direct motor-driven ball were allowed to air dry in V-shaped troughs and mill was used. The mill charge consisted of 120 lb then placed in an oven at 220 deg F to complete of dry batch and 10 gal of water. Each batch was the drying. milled for a period of 4 hr after which it was Casting passed through a 120-mesh lawn and over magnets. Test specimens of sanitary ware bodies were The ball-milled batches were placed in smooth made by casting in plaster of Paris molds. Previous blungers for storage until ready for filter pressing. to the preparation of the casting slips of each body, Dry Mixing six small slip batches were prepared from each Dry mixing was employed for the blending of body composition to determine the casting char- raw materials in the preparation of floor tile bodies. acteristics. Each trial slip batch was prepared from Twenty-five lb of dry batch was added to a No. O slugs which had been aged for one week. The water Simpson Muller-mixer and allowed to mix for 5 content of each body slug was determined by the min, after which 1 qt of water was added and difference in weight before and after thorough dry- ILLINOIS ENGINEERING EXPERIMENT STATION ing of 100 grams of plastic slug. The percent mois- and allowing each slip to "set up" for 40 min after ture content based on the weight of dry solids was which time the molds were inverted and allowed to obtained as follows: drain for 5 min. The molds were opened after the % Moisture (dry basis) end of the draining period and the cast specimens removed; the nature of drainage and type of cast Plastic Weight - Dry Weight 100 ------T^ -- vr -* T" ------X Dry Weight 1UU was noted and a 7 in. length of each cast bar was cut and immediately weighed to obtain the wet cast The weight of plastic material equivalent to 1000 weight. The cast specimens were dried completely grams of dry body was calculated as follows: and reweighed to obtain the dry cast weight. The % percent water retention of the cast specimens was 1000 (i + ' 1 ) grams 1000(1)÷ m calculated as follows: It was desired to prepare slips with a specific grav- Percent Water Retention ity of approximately 1.80; by experiment it was SWet Cast Weight - Dry Cast Weight found that when the solid to water ratio was ap- Wet Cast Weight proximately 72 to 28 a specific gravity of slightly The molds used for the casting trials and all other more than 1.80 was obtained. Slips were prepared casting were prepared from a mixture of 65 per- with this solid to water ratio. The electrolyte con- cent gypsum plaster and 35 percent water. tents of the trial slips were based on the dry From the casting trials described above, it was weight of solids and were as follows: found that an electrolyte addition of 0.05 percent Percent sodium carbonate + 0.10 percent of "N" Brand Percent Sodium Silicate sodium silicate, based on the dry weight of the Sodium Carbonate ("N" Brand) body, was suitable for the casting of all body com- 0.05 + 0.05 positions. Using this electrolyte content, the plastic 0.05 + 0.075 bodies were made into slips of 1.80 specific gravity 0.05 + 0.100 Table 14 0.05 + 0.125 Chemical Analyses of Raw Materials Used in Experimental Bodies
0.05 + 0.150 SiO2 A120l Fe2Oa CaO MgO KNaO TiOs Ing. Loss 0.05 + 0.175 Tremolitic Tale No. 1* 56.72 0.70 0.18 4.80 30.81 0.50 5.95 Sierramic Low The electrolytes were added to the water re- Lime Talet 59.62 2.05 0.94 0.91 29.91 0.49 5.98 Wash. Dead quired for each body slip and thoroughly dispersed Burned Magnesitel 6.7 1.8 3.5 5.0 82.7 0.5 before adding any of the plastic body. A small E.P.K. Fla. motor-driven propeller type mixer was used for Kaolin¶ 46.75 36.75 0.80 0.80 0.20 0.24 14.95 Kamec mixing the plastic body into the electrolyte solu- Kaolin§ 46.18 38.38 0.57 0.37 0.42 0.68 0.04 13.28 Pioneer tion. The trial slips were mixed to a smooth con- Kaolin** 45.34 37.29 0.61 0.25 0.22 0.45 1.54 14.39 Tenn. No. 5 sistency, passed through a 120-mesh screen and Ball Claytt 46.85 36.15 2.04 0.50 0.40 0.71 16.48 Old Mine No. 4 adjusted to a specific gravity of 1.80. The slips were Ball Claytt 51.65 31.24 1.17 0.20 0.50 0.94 1. 72 12.13 then transferred to Mason jars which were placed H.T.P. Ball Claytt 50.15 34.17 1.06 0.12 0.08 1.33 1.21 11.85 in a vacuum chamber for de-airing of the slip. After Martin No. 5 Ball Claytt 60.72 25.53 0.74 0.08 tr 2.12 1.39 9.35 de-airing, the jars of slip were set in a tumbling Champion- end for Challenger apparatus and slowly tumbled end over Ball Claylt 54.08 28.90 1.06 0.14 0.20 0.49 1.74 13.25 48 hr. Victoria Ball Clay¶¶ 58.44 25.89 0.84 0.36 0.15 0.51 1.60 11.98 At the end of the tumbling period, the specific Imperial Ball ClayI¶ 54.24 26.84 0.86 0.53 0.42 0.65 1.70 14.90 gravity of each slip was determined by weighing Royal Ball 100 cc of slip. The flow properties of each were Clay¶¶ 56.06 27.61 1.12 0.33 0.56 1.58 1.62 11.10 Ottawa determined by the time required for 100 cc of slip Flint§§ 99.6 0.10 0.017 0.02 0.02 0.1 * W. H. Loomis Talc Corp., Gouverneur, N.Y. to flow through a % in. diam orifice of a Mariotte t Sierra Tale Co., Los Angeles, Calif. SHarbison-alker Refractories Co., Pittsburgh, Pa. flow tube. Three determinations were made with Edgar Plastic Kaolin Co., Metuchen, N.J. § Harris Clay Co., Spruce Pine, No. Car. each slip sample. ** Georgia Kaolin Co., Elizabeth, N.J. Kentuckyi Tennessee Clay Co., Mayfield, Ky. The relative casting rates of the various slips Spinks Clay Co., Paris, Tenn. ¶I United Clay Mines Corp., Trenton, N.J. were determined by casting two 1 in. square bars § Ottawa Silica Co., Ottawa, Ill. Bul.422. PROPERTIES OF FELDSPARS AND THEIR USE IN WHITEWARES using the same type calculations as described for Percent Volume Shrinkage= 100 [( --1l)-1], the casting trials. The slips were mixed for 4 hr and allowed to age in stoneware jars for 24 hr, where a equals the percent linear shrinkage. after which they were remixed for 30 min and Fired Modulus of Rupture passed through a 120-mesh lawn. De-airing of the The modulus of rupture values reported were slips was accomplished in a vacuum mixer. obtained as the average of a minimum of 12 speci- Specimens were cast into rods % in. in diam and mens. Specimens were stored in dessicators imme- 7 in. in length. Plaster of Paris molds were used diately after firing to prevent any moisture and the specimens were allowed to cast solid. Upon absorption. A Dillon Dynamometer with a 5 in. removal from the molds, eighty 7 in. lengths and span between knife edges was employed for the forty 31/2 in. lengths were cut and allowed to air determination of the cross-breaking load. dry for 3 days; drying was completed at 200 deg If P is the cross-breaking load in lbs, 1 is the F in an oven dryer. span between knife edges in in. and d is the diam Dry Pressing of a round specimen at the point of fracture; then Floor tile specimens were prepared by dry the modulus of rupture (M) is calculated as: pressing using a Denison "Hydroilic" press. 8P1 Seventy-five bars 1 in. square by 6 in. long were M - ps' pressed from each body composition at a pressure (for specimens of round cross of 2000 psi. section) 22. Test Procedures For square bars, such as the floor tile specimens, Volume Shrinkage 3P1 p1 M = 3 2 p s The firing volume shrinkages of all bodies ex- M 2b d cept those of floor tile were obtained with the 3% (where b and d are the breadth in. length specimens. Prior to firing, the dry and depth of the square bar at volumes of these specimens were obtained from the the point of fracture) saturated and suspended weights in kerosene. Each piece was placed in kerosene until saturated; dry Fired Porosity volume was calculated as shown below: The fired porosities were determined on the Dry Volume fractured portions of modulus of rupture specimens. The fractured portions were thoroughly dried in an Saturated Weight - Suspended Weight Specific Gravity of Kerosene oven at 220 deg F and allowed to cool to room temperature in a dessicator. The weights of the After firing, the fired volumes were obtained in dry pieces were determined after which the pieces a similar manner using the saturated and suspended were placed in water which was brought to a boil weights in water. The volume shrinkage was de- and allowed to boil for 8 hr. After cooling to room termined as follows: temperature, the specimens were removed from the Percent Volume Shrinkage water, wiped with a damp cloth to remove any Dry Volume - Fired Volume excess moisture and weighed. The suspended Dry Volume weights of the saturated pieces were also deter- The reported values of volume shrinkage are the mined. The porosity was calculated as follows: average of five specimens. Percent Porosity = The volume shrinkages of floor tile bodies were Fired Saturated Weight-Fired Dry Weight calculated from linear shrinkage determinations. Fired Saturated Weight - Fired Suspended Weight Linear shrinkage was calculated from the equa- X 100 tion: X-Ray Analysis Percent Linear Shrinkage The powder diffraction method was used for Dry Length - Fired Length X 100 qualitative ------T -- T - n ----- ^ 100 and quantitative analyses of the crys- Dry Length talline content of fired specimens. This study re- The conversion from linear to volume shrinkage is quired a Norelco Geiger-Counter X-ray Spectrom- determined as follows. eter with automatic recorder. ILLINOIS ENGINEERING EXPERIMENT STATION
The method of sample mount was that proposed Quantitative analyses were made according to by McCreery. (51 The sample holder consisted of methods described by Tuttle and Cook (5 2 ) in which an alloyed aluminum cell, 1% in. x 1 in. x % in. the ratio of the height of a peak to the height of with a %6 in. hole at the center. the internal standard peak (calcium fluoride) was Samples for X-ray analysis were obtained by compared to the calibration ratio curve obtained cutting a % in. x 1/2 in. section from the centers of with standard mixtures. Peak intensities were also specimens. These segments were crushed and ground determined by the counting method and also by in an agate mortar to pass a 325-mesh screen. Iron measurement of peak heights on the recorder chart impurities were removed by passing a permanent operating at 10 (2 theta) per min. Using the chart magnet through the finely ground material. Samples method, three runs for each of three mixings of designated for quantitative analysis were thor- each sample were made. oughly dried after grinding and 1.000 gram of each The major quartz and mullite peaks at d = was mixed with chemically-precipitated calcium 3.35 and 3.43 respectively could not be used due to fluoride in an agate mortar with 5 ml of methyl their juxtaposition and the tendency of each to alcohol. The alcohol was removed by evaporation reinforce the other. In most cases the mullite peak and the samples were mixed dry for an additional could not be separated from the more intense 10 min. quartz peak. The peaks used in the analyses were Standard samples for the determination of cali- those found at d-values of 4.24 for quartz, 4.05 for bration curves were prepared from Ottawa flint, cristobalite and 2.70 for mullite. electric furnace mullite, prepared cristobalite and Both copper and iron radiation were used for calcium fluoride with fused F-4 feldspar glass as a the X-ray analyses, but iron radiation was found diluent. Considerable difficulty was encountered in to give more resolution and also shifted the peak analyzing the mullite content because of its tend- locations to higher angles on the goniometer arc ency toward preferred orientation. where the background interferences were lower. BIBLIOGRAPHY
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