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University Microfilms, Inc., Ann Arbor, Michigan 70- 14,038 HOEKSTRA, Karl Egmond, 19 35- CRYSTAL CHEMICAL CONSIDERATIONS OF THE SPINEL STRUCTURAL GROUP. '’’h e Ohio State University, Ph.D., 1969 Chemistry, inorganic University Microfilms, Inc., Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED CRYSTAL CHEMICAL CONSIDERATIONS OP THE SPINEL STRUCTURAL GROUP DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Karl Egmond Hoekstra, B.A., M.S. ****** The Ohio State University 1969 Approved by V Adviser Department of Mineralogy ACKNOWLEDGMENTS The author wishes to express his appreciation to Dr. Henry E. Wenden, under whose advisorship this work was done, for his helpful suggestions and criticism during the course of the study. The writer also wishes to thank Drs. Rodney T. Tettenhorst and Dan McLachlan, Jr. for advice and careful reading of the manuscript. Thanks are also due Dr. Wilfred R. Foster, Chairman of the Department of Mineralogy, Mr. George D. Brush of Harrop Ceramic Service Co. and Dr. Robert A. Schoenlaub, formerly of Harrop, for their assistance, encouragement and understanding while pursuing this degree. ii VITA October 9, 1935 Born - Battle Creek, Michigan 1958 ........ B.A. in Geology, Miami University, Oxford, Ohio 1958-1963 . Research Engineer, Ferro Corporation, Cleveland, Ohio 1965 ........ M.S. in Mineralogy, Miami University, Oxford, Ohio 1964-1967 . Manager, Materials Testing Laboratory, Harrop Precision Furnace Company, Columbus, Ohio 1967-Present Director, Harrop Laboratories, Columbus, Ohio PUBLICATIONS With R. A. Schoenlaub and W. E. Troyer, "Burnout Rates on a Shale Body," Ceramic Bulletin, 45> No. 3, pp. 257-59, 1966. "Horizontal Tube, Vertical Tube and Rod Dilatometers,11 Proceedings of the 1968 Symposium on Thermal Expansion of Solids, to be published FIELDS OF STUDY Major Field: Mineralogy Studies in X-ray Crystallography. Drs. H. E. Wenden and D. McLachlan, Jr. Studies in Crystallochemical Mineralogy. Drs. H. E. Wenden and R. T. Tettenhorst Studies in Phase Equilibria and Crystal Growth. Drs. W. R. Foster, D. McLachlan and E. Ehlers iii TABLE OF CONTENTS Page ACKNOWLEDGMENTS....................................... ii VITA .................................................. ill LIST OF T A B L E S ...................................... v LIST OF F I G U R E S .................................... iv INTRODUCTION ........................................ 1 HISTORY ............................................ 4 CRYSTAL CHEMISTRY OF SPINELS ............ 8 Chemistry of Spinels Structure of Spinels Distribution of Cations over Tetrahedral and Octahedral Sites Departures from Cubic Symmetry STATEMENT OF THE PROBLEM............................ 40 SEMANTICS PROBLEMS .................................. 41 STOICHIOMETRY-ELECTRONEUTRALITY .................... 46 RESIDUAL CHARGE PRINCIPLE .................... 59 CONCLUSIONS........................................ 78 BIBLIOGRAPHY ........................................ 80 iv LIST OF TABLES Table Page 1. Cations Occurring in Spinels .................. 8 2. Common Spinel Types . .......................... 9 3. u Parameters for Various S p i n e l s .............. 18 4. Octahedral Crystal-Field Stabilization Energies for Ions with One to Five d-Electrons........ 27 5. Stabilization Energies Expected in Octahedral and Tetrahedral Environments for the First Series of the Transition Elements ............ 29 6. Octahedral Site Preference Energy for Various Cations .............................. 31 7’. Comparison of "Normal and "Inverse" with "Homologic" and "Heterologic" Distribution . 44 8. Mixed-Cation, Common-Anion Spinel Valence T y p e s ........................................ 51 9. Common-Cation, Mixed-Anion Spinel Valence T y p e s ........................................ 52 10. Lacunary Spinel Valency Types .................. 53 11. Residual Charges for Various Mixed-Cation, Common-Anion Valence Types ............. 65 12. Residual Charges for Various Common-Cation, Mixed-Anion Valence Types .................... 67 13. Cation Distribution in Existing Spinels ......... 69 v LIST OF FIGURES Figure Page 1. Projection and Packing Drawing of the Spinel Structure ............................ 13 2. Two Octants of the Spinel Structure............ 14 3. Basic Spinel Building Block .................... 16 4. Exploded View of Basic Spinel Building Block . 17 5. Graphic Representation of the Five d-Electron O r b i t a l s .................................... 25 6. Energy Splitting in an Octahedral Field ........ 26 7. Energy Splitting in a Tetrahedral Field ........ 28 8. X-Ray Peak Splitting in Cubic and Tetragonal Modifications in CuFe20]1 .................... 35 9. Polyhedral Structure Drawings of a Portion of the Spinel Structure— Showing Tetragonal Modifications ................................ 36 10. Tetragonal Modifications (Elongation) in a Tetrahedral Field ............................ 38 11. Tetragonal Modifications (Shortening) in a Tetrahedral Field .... .................... 38 vi INTRODUCTION The structure of the mineral spinel was first des­ cribed independently by Bragg and Nishikawa in the same year, 1915. Since that time a score or more minerals and over one hundred synthetic compounds have been found to crystallize with the same structure. Thus, the term "spinel" has come to mean the entire group of compounds possessing this structure as well as the mineral spinel itself. The group has great chemical variety. It includes compounds of many anions, such as oxides, sulfides, fluorides, selenides, tellurides, nitrides and cyanides and at least thirty cations of valencies one through six are found as components of spinels. The spinels have received a great deal of attention from mineralogists, geologists, geophysicists, gemmologists, academicians and a host of industrially oriented scientists and engineers. Magnetite is second among ores of iron in economic importance and chromite is the chief source of chromium. Spinel group minerals are widely distributed throughout the earth’s crust as accessory minerals in igneous rocks, as constituents of metamorphic rocks, and in placers. A polymorph of magnesium silicate having the spinel structure may be the major constituent of the mantle of the earth. Colored spinels have long been known as gem- stones, and red spinels were not distinguished from rubies until 1783. Among the Crown Jewels of England, the "Black Prince's Ruby" is a spinel. Synthetic spinels are of in­ dustrial importance as semiprecious gemstones, pigments, refractories, catalysts and ferromagnets. The spinels have also undergone a great deal of ex­ posure in the literature. This is due, not only to the large number and ubiquity of the spinels, but also because the spinels have been used as a testing ground for many crystal chemical theories. This group presents a structure r well suited for this application since it allows great variations in composition, valence and even structure. The crystal chemistry of the entire spinel group is, however, still not well understood. The great amount of literature on the spinels, along with their great variety, has apparently discouraged attempts at a comprehensive treatment of spinels. The treatment of spinels by the standard crystal chemistry texts is very elementary and does not discuss adequately the many chemical, valence and structural variations and their crystal chemical causes. Some technical papers have given good but not comprehensive treatments because they have placed emphasis on one peculiarity or physical property of particular relevance to their area of interest. The primary purpose of this dissertation is to organize existing crystal chemical information about the spinels and to clear the way for the understanding of spinels as a diverse but coherent struc­ tural group. A comprehensive treatment of the state of the art of spinel crystal chemistry follows after a brief historical orientation. HISTORY The origin of the name spinel is unknown. The word spinella was used by Roman authors, perhaps as a diminutive of the Latin spina, a thorn, but probably not with refer­ ence to the mineral called spinel today. The form splnellus was used in the 16^7 edition of Boetius De Boodt's Lapidum Gemmarum Et Lapidum Historia, but spinel was not distinguished from ruby corundum. The distinction between red spinel and red gem corundum was first made by Rome'De L'Isle in 1783 on the basis of the difference in crystal habit. The first chemical analysis of spinel was made in 1789 by Klaproth, who, on this occasion, found no magnesia. Dis­ satisfied with his first analysis, Klaproth repeated it in 1797 and this time found 8.25# MgO, 74.5# A1203 and 15-5# S102 . Vauquelin, who analyzed spinel in 1800, found no silica, but still reported only 8.5# MgO, as he was unable to make a clean separation of MgO from A^O^. The correct composition was finally established by Abich (Dissert. Chem. de Spinello, Berol., 1831) as 28# MgO, 72# A1203. Wallerius had noted in 1772, that red spinel, when fused with borax, yielded an emerald-green glass. Vauquelin, in 1800, also detected the chromium present in ruby spinel. Thus, chemical variation and the effect of vicarious constituents was observed very early. In addition ferroan spinel was described as a new species ceylonite by Dela- metherie in 1793. Gahnite, ZnAl2Oj^, was first recognized and described by Ekeberg in 1806. The mineral franklinite, ZnFe20jj was first found in 1819 at Franklin Furnace,
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