Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1986 An integrated study of the ceramic processing of yttria James Alan Voigt Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Chemical Engineering Commons Recommended Citation Voigt, James Alan, "An integrated study of the ceramic processing of yttria " (1986). Retrospective Theses and Dissertations. 8045. https://lib.dr.iastate.edu/rtd/8045 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This reproduction was made from a copy of a manuscript sent to us for publication and microfilming. 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Other University Microfilms international An integrated study of the ceramic processing of yttria by James Alan Voigt A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Major: Chemical Engineering Approved: Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. For the Major Department Signature was redacted for privacy. Iowa State University Ames, Iowa 1986 ii TABLE OF CONTENTS Page DEDICATION v INTRODUCTION 1 POWDER PROCESSING 7 Sintering 7 Powder Preparation 11 THE YTTRIUM NITRATE - HYDROXIDE - OXIDE SYSTEM 16 PRECIPITATION 22 Nucleation 23 Growth 27 Colloidal Interactions 29 Interparticle forces 30 Colloid stability 35 Zeta-potential 37 Perikinetic agglomeration 38 Orthokinetic agglomeration 39 Agglomerate Break-up 43 Morphology 44 Hydrous Oxide - Water Systems 45 PRECIPITATION MODEL 47 Crystallite Balance 47 Aggregate Balance 49 Floe Balance 52 Properties of the Population Density Functions 55 Overall Balances 57 Nucleation Kinetics 59 EXPERIMENTAL EQUIPMENT AND PROCEDURES 61 iii Continuous Precipitation System 61 Experimental Procedures 67 Batch precipitations 67 Continuous precipitations 67 Precipitate devatering and drying 71 Calcination, compaction, and sintering 72 Characterization Methods 72 Filtrate analysis 73 Zeta-potential and specific conductance determination 73 Suspension density measurements 74 Particle size distributions 74 Particle morphology 76 Surface area and apparent powder density 77 Powder tap density 77 Precipitate composition and structure 77 Pellet characterization 79 RESULTS AND DISCUSSION 81 Precipitation Reaction 81 Batch precipitations 81 Yttrium solubility - 87 Crystallites 87 Morphology 87 Composition 91 Structure 94 Agglomerated Particles 101 Zeta-potential Measurements on Yttrium 108 Hydroxynitrate Suspensions Potential determining ions 112 Effect of crystal growth 116 Precipitation Kinetics 119 Crystal growth and nucleation 120 Agglomerated particles 137 Assumption of total floe break-up 155 Precipitate Processing 157 Precipitate dewatering and drying 159 iv Calcination 177 Compaction and sintering 184 CONCLUSIONS 207 Precipitation Process 207 Precipitation Kinetics 209 Precipitate Processing 210 REFERENCES 212 ACKNOWLEDGEMENTS 224 APPENDIX A: SAMPLE COULTER RUN PROGRAM OUTPUT 225 Samples of Run Program Computer Output for Run 5 226 Coulter constants and run conditions 226 Seunple 5A-2 data, 9.07 T into run 227 Sample 5A-5 data, 15.7 T into run 228 Sample 5A-8 data, 21.3 T into run, sampled directly 229 from precipitator 200 vm aperture summary 230 50 wm aperture summairy 231 FDD plot of sample 5A-2 shoving counting consistency 232 for 50 ym aperture FDD plot of sample 5A-2 showing counting consistency 233 for 200 ym aperture FDD plot of sample 5A-8 showing counting consistency 234 for 50 ym aperture FDD plot of sample 5A-8 showing counting consistency 235 for 200 ym aperture FDD plot showing approach to steady-state for 50 ym 236 aperture FDD plot showing approach to steady-state for 200 ym 237 aperture Run lA FDD Plot Showing Approach to Steady-state for 238 50 ym Aperture Run lA Steady-state FDD for 50 ym Aperture 239 APPENDIX B: FDD DETERMINATION 240 APPENDIX C: MODEL PARAMETER DETERMINATION 255 APPENDIX D: PROCESSING DATA 270 V DEDICATION This work is dedicated to the author's parents, Mr. and Mrs. Robert Voigt, who have been constant sources of encouragement and support in the author's education. 1 INTRODUCTION Ceramics play a vital role in today's high technology industries. Their hardness and resistance to chemical attack make them useful as structural materials for corrosive environments. However, the ability to maintain these properties at high temperatures is their most unique advantage. In advanced energy conversion systems, the use of structural ceramics allows higher operating temperatures to be used, with a corresponding increase in thermodynamic efficiency. Currently available metallic superalloys usually cannot be used above about 1100 °C, but some of the new ceramic materials have already been tested successfully at temperatures up to 1400 °C. Even higher temperatures appear to be feasible. Their hardness also reduces wear in rotating machinery and erosion by entrained particulates in high velocity fluids. Because they do not soften at high temperatures, these new ceramics have found a ready market as bearing materials and as cutting tools. Their early success in these areas has come because bearings and cutting tools have simple geometric shapes. Thus, the need to fabricate and densify large, irregularly-shaped forms - a difficult problem with some of the new non- oxide ceramics - does not arise in such applications. Besides having desirable high temperature properties, structural ceramics are generally lighter than their metallic counterparts, sometimes weighing 40% less. This makes them attractive in aerospace applications where reduced weight conserves fuel, and in turbine applications where reduced inertia improves the response to load changes. Ceramics may also have a wide range of electrical properties; they 2 can be conductors, semi-conductors, or insulators. The electronics industry is a major consumer of ceramic materials. They are used in capacitors, thermistors, varistors, piezoelectric devices, magnetostictive devices, magnetic cores, and other components. World-wide sales of high-technology ceramics vas 4.1 billion dollars in 1980, seventy percent of that being sales to the electronics industry. Boven (7) estimates that the total figure will be about 19 billion dollars by 1995, with about forty percent being sales of electronic ceramics. Thus, although sales to the electronics industry now dominate the field, and are expected to show a substantial growth, the growth of structural ceramics may be even more spectacular. Host types of ceramics are made from readily available raw materials and do not require the use of strategic metals from geopolitically