Ceramic Processing Ceramic Processing Mohamed N. Rahaman University of Missouri-Rolla, USA Boca Raton London New York CRC is an imprint of the Taylor & Francis Group, an informa business CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2007 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 International Standard Book Number-10: 0-8493-7285-2 (Hardcover) International Standard Book Number-13: 978-0-8493-7285-8 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. 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Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Rahaman, M. N. 1950- Ceramic processing / Mohamed Rahaman. p. cm. Includes bibliographical references and index. ISBN 0-8493-7285-2 (acid-free paper) 1. Ceramics. 2. Ceramic engineering. 3. Polycrystals. 4. Sintering. I. Title. TP807.R278 2006 666--dc22 2006043889 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com T&F_LOC_B_Master.indd 1 6/19/06 8:41:01 AM 7285_book.fm Page xi Friday, June 9, 2006 10:28 AM Contents Chapter 1 Ceramic Fabrication Processes: An Introductory Overview.......................................1 1.1 Introduction...............................................................................................................................1 1.2 Ceramic Fabrication Processes.................................................................................................2 1.2.1 Gas-Phase Reactions....................................................................................................2 1.2.1.1 Chemical Vapor Deposition..........................................................................4 1.2.1.2 Directed Metal Oxidation.............................................................................7 1.2.1.3 Reaction Bonding..........................................................................................8 1.2.1.4 Silicon Nitride...............................................................................................9 1.2.1.5 Oxides..........................................................................................................10 1.2.1.6 Silicon Carbide............................................................................................11 1.2.2 Liquid Precursor Methods..........................................................................................12 1.2.2.1 Sol–Gel Processing.....................................................................................12 1.2.2.2 Polymer Pyrolysis.......................................................................................15 1.2.2.3 Silicon Carbide............................................................................................15 1.2.2.4 Silicon Nitride.............................................................................................17 1.2.2.5 Boron Nitride and Boron Carbide..............................................................18 1.2.3 Fabrication from Powders..........................................................................................19 1.2.3.1 Melt Casting................................................................................................19 1.2.3.2 Sintering of Compacted Powders...............................................................20 1.3 Production of Polycrystalline Ceramics from Powders: An Overview.................................21 1.3.1 Powder Synthesis and Powder Characterization........................................................21 1.3.2 Powder Consolidation................................................................................................22 1.3.3 The Sintering Process.................................................................................................22 1.3.4 Ceramic Microstructures............................................................................................25 1.4 Case Study in Processing: Fabrication of TiO from Powders.............................................28 2 1.5 Concluding Remarks..............................................................................................................30 Problems...........................................................................................................................................30 References........................................................................................................................................32 Chapter 2 Synthesis of Powders.................................................................................................37 2.1 Introduction.............................................................................................................................37 2.2 Powder Characteristics...........................................................................................................37 2.3 Powder Synthesis Methods....................................................................................................38 2.4 Powder Preparation by Mechanical Methods........................................................................39 2.4.1 Comminution..............................................................................................................39 2.4.1.1 High Compression Roller Mills..................................................................40 2.4.1.2 Jet Mills.......................................................................................................41 2.4.1.3 Ball Mills.....................................................................................................41 2.4.2 Mechanochemical Synthesis......................................................................................45 2.5 Powder Synthesis by Chemical Methods...............................................................................46 2.5.1 Solid-State Reactions..................................................................................................46 2.5.1.1 Decomposition.............................................................................................47 2.5.1.2 Chemical Reaction between Solids............................................................53 7285_book.fm Page xii Friday, June 9, 2006 10:28 AM 2.5.1.3 Reduction....................................................................................................57 2.5.2 Liquid Solutions.........................................................................................................58 2.5.2.1 Precipitation from Solution.........................................................................58 2.5.2.2 Evaporation of the Liquid...........................................................................74 2.5.2.3 Gel Route....................................................................................................79 2.5.2.4 Nonaqueous Liquid Reaction......................................................................81 2.5.3 Vapor-Phase Reactions...............................................................................................81 2.5.3.1 Gas–Solid Reaction.....................................................................................82 2.5.3.2 Reaction between a Liquid and a Gas........................................................84 2.5.3.3 Reaction between Gases.............................................................................84 2.6 Special Topic: Synthesis of Nanoscale Ceramic Powders.....................................................87 2.6.1 Liquid Solution Techniques.......................................................................................87 2.6.2 Vapor-Phase Techniques.............................................................................................88 2.7 Concluding Remarks..............................................................................................................89 Problems...........................................................................................................................................89 References........................................................................................................................................91 Chapter 3 Powder Characterization.............................................................................................97 3.1 Introduction.............................................................................................................................97 3.2 Physical Characterization.......................................................................................................97 3.2.1 Types of Particles.......................................................................................................98 3.2.1.1 Primary Particles.........................................................................................98 3.2.1.2 Agglomerates...............................................................................................98 3.2.1.3 Particles.......................................................................................................98 3.2.1.4 Granules.......................................................................................................99 3.2.1.5 Flocs............................................................................................................99 3.2.1.6 Colloids.......................................................................................................99 3.2.1.7 Aggregates...................................................................................................99 3.2.2 Particle Size and Particle Size Distribution...............................................................99 3.2.2.1 Definition of Particle Size.........................................................................100 3.2.2.2 Average Particle Size................................................................................101 3.2.2.3 Representation of Particle Size Data........................................................102 3.2.3 Particle Shape...........................................................................................................106 3.2.4 Measurement of Particle Size and Size Distribution...............................................106 3.2.4.1 Microscopy................................................................................................106 3.2.4.2 Sieving.......................................................................................................107 3.2.4.3 Sedimentation............................................................................................109 3.2.4.4 Electrical Sensing Zone Techniques (the Coulter Counter).....................110 3.2.4.5 Light Scattering.........................................................................................111 3.2.4.6 X-Ray Line Broadening............................................................................113 3.2.5 Surface Area.............................................................................................................113 3.2.6 Porosity of Particles.................................................................................................116 3.2.6.1 Gas Adsorption..........................................................................................116 3.2.6.2 Mercury Porosimetry................................................................................119 3.2.6.3 Pycnometry................................................................................................121 3.3 Chemical Composition.........................................................................................................122 3.3.1 Optical Atomic Spectroscopy: Atomic Absorption and Atomic Emission..............122 3.3.2 X-Ray Fluorescence Spectroscopy...........................................................................124 3.4 Crystal Structure and Phase Composition...........................................................................125 7285_book.fm Page xiii Friday, June 9, 2006 10:28 AM 3.5 Surface Characterization......................................................................................................127 3.5.1 Surface Structure......................................................................................................129 3.5.2 Surface Chemistry....................................................................................................130 3.5.2.1 Auger Electron Spectroscopy (AES)........................................................130 3.5.2.2 X-Ray Photoelectron Spectroscopy (XPS)...............................................132 3.5.2.3 Secondary Ion Mass Spectrometry (SIMS)..............................................133 3.6 Concluding Remarks............................................................................................................136 Problems.........................................................................................................................................136 References......................................................................................................................................138 Chapter 4 Science of Colloidal Processing...............................................................................141 4.1 Introduction...........................................................................................................................141 4.2 Types of Colloids.................................................................................................................142 4.3 Attractive Surface Forces.....................................................................................................142 4.3.1 van der Waals Forces between Atoms and Molecules............................................142 4.3.2 van der Waals Forces between Macroscopic Bodies...............................................144 4.3.3 The Hamaker Constant.............................................................................................146 4.3.4 Effect of the Intervening Medium...........................................................................148 4.4 Stabilization of Colloidal Suspensions................................................................................148 4.5 Electrostatic Stabilization.....................................................................................................149 4.5.1 The Development of Charges on Oxide Particles in Water....................................149 4.5.1.1 Isomorphic Substitution............................................................................150 4.5.1.2 Adsorption of Ions from Solution............................................................150 4.5.2 Origins of the Electrical Double Layer...................................................................153 4.5.3 Isolated Double Layer..............................................................................................154 4.5.4 Surface Charge.........................................................................................................157 4.5.5 Repulsion between Two Double Layers..................................................................158 4.5.6 Stability of Electrostatically Stabilized Colloids.....................................................160 4.5.7 Kinetics of Flocculation...........................................................................................161 4.5.8 Electrokinetic Phenomena........................................................................................162 4.5.8.1 Microelectrophoretic Technique...............................................................163 4.5.8.2 Significance of the ζ Potential..................................................................164 4.6 Steric Stabilization................................................................................................................164 4.6.1 Adsorption of Polymers from Solution....................................................................165 4.6.2 Origins of Steric Stabilization..................................................................................167 4.6.3 Effects of Solvent and Temperature.........................................................................168 4.6.4 Stability of Sterically Stabilized Suspensions.........................................................170 4.6.5 Stabilization by Polymers in Free Solution.............................................................171 4.7 Electrosteric Stabilization.....................................................................................................172 4.7.1 Dissociation of Polyelectrolytes in Solution............................................................172 4.7.2 Adsorption of Polyelectrolytes from Solution.........................................................174 4.7.3 Stability of Electrosterically Stabilized Suspensions..............................................175 4.8 Structure of Consolidated Colloids......................................................................................176 4.9 Rheology of Colloidal Suspensions.....................................................................................178 4.9.1 Rheological Properties..............................................................................................178 4.9.2 Factors Influencing the Rheology of Colloidal Suspensions..................................180 4.9.2.1 Influence of Interparticle Forces...............................................................180 4.9.2.2 Influence of Particle Interactions on the Viscosity...................................183 4.9.2.3 Influence of Particle Characteristics.........................................................185 4.10 Concluding Remarks............................................................................................................187 7285_book.fm Page xiv Friday, June 9, 2006 10:28 AM Problems.........................................................................................................................................187 References......................................................................................................................................189 Chapter 5 Sol–Gel Processing...................................................................................................193 5.1 Introduction...........................................................................................................................193 5.2 Types of Gels........................................................................................................................194 5.2.1 Particulate Gels.........................................................................................................194 5.2.2 Polymeric Gels.........................................................................................................195 5.3 Sol–Gel Processing of Aqueous Silicates............................................................................197 5.3.1 Effect of pH..............................................................................................................198 5.3.1.1 Polymerization in the pH range of 2 to 7................................................198 5.3.1.2 Polymerization above pH ≈ 7...................................................................200 5.3.1.3 Polymerization below pH ≈ 2...................................................................200 5.4 Metal Alkoxides....................................................................................................................201 5.4.1 Preparation of Metal Alkoxides...............................................................................201 5.4.1.1 Reactions between Metals and Alcohols..................................................201 5.4.1.2 Reactions Involving Metal Chlorides.......................................................202 5.4.1.3 Miscellaneous Methods.............................................................................202 5.4.2 Basic Properties........................................................................................................204 5.4.2.1 Physical Properties....................................................................................204 5.4.2.2 Chemical Properties..................................................................................205 5.5 Sol–Gel Processing of Silicon Alkoxides............................................................................206 5.5.1 Precursors.................................................................................................................206 5.5.2 Hydrolysis and Condensation..................................................................................207 5.5.2.1 Acid-Catalyzed Conditions.......................................................................208 5.5.2.2 Base-Catalyzed Conditions.......................................................................209 5.5.3 Polymer Growth.......................................................................................................209 5.5.3.1 Polymer Growth Models...........................................................................210 5.5.3.2 Structural Evolution of Sol–Gel Silicates................................................212 5.5.3.3 Rheological Measurements.......................................................................212 5.5.4 Gelation.....................................................................................................................215 5.5.5 Aging of Gels...........................................................................................................216 5.5.6 Drying of Gels..........................................................................................................216 5.5.6.1 Conventional Drying.................................................................................217 5.5.6.2 Supercritical Drying..................................................................................227 5.5.6.3 Structural Changes during Drying............................................................229 5.5.7 Gel Densification during Sintering..........................................................................230 5.6 Sol–Gel Preparation Techniques..........................................................................................234 5.6.1 Preparation of Particulate Gels................................................................................234 5.6.1.1 Single-Component Gels............................................................................234 5.6.1.2 Multicomponent Gels................................................................................236 5.6.2 Preparation of Polymeric Gels.................................................................................237 5.6.2.1 Use of Double Alkoxides..........................................................................237 5.6.2.2 Partial Hydrolysis of the Slowest Reacting Alkoxide..............................238 5.6.2.3 Use of a Mixture of Alkoxides and Metal Salts......................................239 5.6.2.4 Slow Addition of Small Amounts of Water..............................................240 5.6.2.5 Matched Hydrolysis Rates........................................................................241 5.7 Applications of Sol–Gel Processing....................................................................................241 5.7.1 Thin Films and Coatings..........................................................................................242 5.7.1.1 Dip Coating...............................................................................................242 7285_book.fm Page xv Friday, June 9, 2006 10:28 AM 5.7.1.2 Spin Coating..............................................................................................244 5.7.1.3 Structural Evolution in Films...................................................................245 5.7.1.4 Applications of Films................................................................................245 5.7.2 Fibers........................................................................................................................245 5.7.3 Monoliths..................................................................................................................246 5.7.4 Porous Materials.......................................................................................................247 5.8 Concluding Remarks............................................................................................................247 Problems.........................................................................................................................................247 References......................................................................................................................................249 Chapter 6 Mixing and Packing of Powders..............................................................................253 6.1 Introduction...........................................................................................................................253 6.2 Mixing of Particulate Solids................................................................................................254 6.2.1 Types of Mixtures.....................................................................................................254 6.2.2 Mixing and Segregation Mechanisms......................................................................254 6.2.3 Mixture Composition and Quality...........................................................................257 6.2.3.1 Statistical Methods....................................................................................257 6.2.3.2 Measurement Techniques..........................................................................259 6.2.4 Mixing Technology...................................................................................................260 6.3 Packing of Particles..............................................................................................................262 6.3.1 Regular Packing of Monosized Spheres..................................................................263 6.3.2 Random Packing of Particles...................................................................................264 6.3.2.1 Monosized Particles..................................................................................265 6.3.2.2 Bimodal Mixtures of Spheres...................................................................266 6.3.2.3 Binary Mixtures of Nonspherical Particles..............................................269 6.3.2.4 Ternary and Multiple Mixtures.................................................................270 6.3.2.5 Continuous Particle Size Distributions.....................................................271 6.4 Concluding Remarks............................................................................................................274 Problems.........................................................................................................................................274 References......................................................................................................................................276 Chapter 7 Forming of Ceramics................................................................................................279 7.1 Introduction...........................................................................................................................279 7.2 Additives in Ceramic Forming.............................................................................................280 7.2.1 Solvents.....................................................................................................................280 7.2.2 Dispersants................................................................................................................282 7.2.2.1 Inorganic Acid Salts..................................................................................283 7.2.2.2 Surfactants.................................................................................................284 7.2.2.3 Low- to Medium-Molecular-Weight Polymers........................................286 7.2.3 Binders......................................................................................................................287 7.2.4 Plasticizers................................................................................................................290 7.2.5 Other Additives.........................................................................................................292 7.3 Forming of Ceramics............................................................................................................292 7.3.1 Dry and Semidry Pressing.......................................................................................292 7.3.1.1 Die Compaction........................................................................................292 7.3.1.2 Isostatic Compaction.................................................................................301 7.3.2 Casting Methods.......................................................................................................302 7.3.2.1 Slip Casting...............................................................................................302 7.3.2.2 Pressure Casting........................................................................................306