Edited by Ralf Riedel and I-Wei Chen

Ceramics Science and TechnologyVolume 3

Synthesis and Processing

www.wiley-vch.de

Although ceramics have been known to mankind literally for millen-nia, research has never ceased. Apart from the classic uses as a bulk material in pottery, construction, and decoration, the latter half of the twentieth century saw an explosive growth of application fi elds, such as electrical and thermal insulators, wear-resistant bearings, surface coat-ings, lightweight armour, or aerospace materials. In addition to plain, hard solids, modern ceramics come in many new guises such as fabrics, ultrathin fi lms, microstructures and hybrid composites. Built on the solid foundations laid down by the 20-volume series Materials Science and Technology, Ceramics Science and Technology picks out this exciting material class and illuminates it from all sides. Materials scientists, engineers, chemists, biochemists, physicists and medical researchers alike will fi nd this work a treasure trove for a wide range of ceramics knowledge from theory and fundamentals to practical approaches and problem solutions.

Ralf Riedel has been a professor at the Institute of Materials Science at the Darmstadt Univer-sity of Technology in Darmstadt since 1993. He received a Diploma degree in chemistry in 1984 and he fi nished his dissertation in Inorganic Chemistry in 1986 at the University of Stuttgart. After postdoctoral research at the Max-Planck-Institute for Metals Research and the Institute of Inorganic Chemistry at the University of Stuttgart he completed his habilitation in the fi eld of Inorganic Chemistry in 1992. Prof. Riedel is Fellow of the American Ceramic Society and was awarded with the Dionyz Stur Gold Medal for merits in natural sciences. He is a member of the World Academy of Ceramics and Guest Professor at the Jiangsu University in Zhenjiang, China. In 2006 he received an honorary doctorate from the Slovak Academy of Sciences, Bratislava, Slo-vakia. In 2009 he was awarded with an honorary professorship at the Tianjin University in China. He published more than 300 papers and patents and he is widely known for his research in the fi eld of polymer derived ceramics and on ultra high pressure synthesis of new materials.

I-Wei Chen has been Skirkanich Professor of Materials Innovation at the University of Pennsyl-vania since 1997, where he also gained his master‘s degree in 1975. He received his bachelor‘s degree in physics from Tsinghua University, Taiwan, in 1972, and earned his doctorate in metal-lurgy from the Massachusetts Institute of Technology in 1980. He taught at the University of Michigan (Materials) during 1986 – 1997 and MIT (Nuclear Engineering ; Materials) during 1980 – 1986. He began ceramic research studying martensitic transformations in zirconia nano crystals, which led to work on transformation plasticity, superplasticity, fatigue, grain growth and sintering in various oxides and nitrides. He is currently interested in solid oxide fuel cells, nanotechnology of resistance memory and ferroelectrics, and nanoparticle-based medical imag-ing and drug delivery. A Fellow of American Ceramic Society (1991) and recipient of its Ross Coffi n Purdy Award (1994), Edward C. Henry Award (1999) and Sosman Award (2006), he authored over 90 papers in the Journal of the American Ceramic Society (1986 – 2006). He also received Humboldt Research Award for Senior U.S. Scientists (1997).

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eramics Science

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Edited by

Ralf Riedel and I-Wei Chen

Ceramics Science and

Technology

Related Titles

Riedel, R. / Chen, I-W. (eds.)

Ceramics Science andTechnologyVolume 2: Materials and Properties

2010

ISBN: 978-3-527-31156-9

Heimann, R. B.

Classic and Advanced CeramicsFrom Fundamentals to Applications

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Aldinger, Fritz / Weberruss, Volker A.

An Introduction to Structures,Properties, Technologies,Methods2010

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Ghosh, S. K. (ed.)

Self-healing MaterialsFundamentals, Design Strategies,

and Applications

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Riedel, R., Chen, I-W. (eds.)

Ceramics Science andTechnologyVolume 1: Structures

2008

ISBN: 978-3-527-31155-2

Krenkel, W. (ed.)

Ceramic Matrix CompositesFiber Reinforced Ceramics and

their Applications

2008

ISBN: 978-3-527-31361-7

Öchsner, A., Murch, G. E., de Lemos,M. J. S. (eds.)

Cellular and Porous MaterialsThermal Properties Simulation and

Prediction

2008

ISBN: 978-3-527-31938-1

Edited byRalf Riedel and I-Wei Chen

Ceramics Science andTechnology

The Editors

Prof. Dr. Ralf RiedelTU DarmstadtInstitut für MaterialwissenschaftPetersenstr. 3264287 DarmstadtGermany

Prof. Dr. I-Wei ChenUniversity of PennsylvaniaSchool of Engineering3231 Walnut StreetPhiladelphia, PA 19104-6272USA

All books published by Wiley-VCH are carefullyproduced. Nevertheless, authors, editors, andpublisher do not warrant the information containedin these books, including this book, to be free oferrors. Readers are advised to keep in mind thatstatements, data, illustrations, procedural details orother items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from theBritish Library.

Bibliographic information published bythe Deutsche NationalbibliothekThe Deutsche Nationalbibliothek lists this publica-tion in the Deutsche Nationalbibliografie; detailedbibliographic data are available on the Internet athttp://dnb.d-nb.de.

# 2012 Wiley-VCH Verlag & Co. KGaA,Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translationinto other languages). No part of this book may bereproduced in any form – by photoprinting,microfilm, or any other means – nor transmitted ortranslated into a machine language without writtenpermission from the publishers. Registered names,trademarks, etc. used in this book, even when notspecifically marked as such, are not to be consideredunprotected by law.

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Printed in the Federal Republic of GermanyPrinted on acid-free paper

Print ISBN: 978-3-527-31157-6ePDF ISBN: 978-3-527-63196-4oBook ISBN: 978-3-527-63195-7

Contents

Preface XVList of Contributors XVII

Part I Powders 1

1 Powder Compaction by Dry Pressing 3Rainer Oberacker

1.1 Introduction 31.2 Fundamental Aspects of Dry Pressing 31.2.1 Die or Mold Filling Behavior of Powders 41.2.1.1 Particle Packing: A Static View 51.2.1.2 Practical Aspects of Die Filling With Granulates 71.2.2 Compaction Behavior 81.2.2.1 Compaction of Monolithic Powders 81.2.2.2 Compaction of Granulated Powders 101.2.2.3 Understanding Powder Compaction by Advanced Modeling 141.3 Practice of Uniaxial Compaction 191.3.1 Die Filling 191.3.2 Tooling Principles and Pressing Tools 211.3.3 Powder Compaction Presses 231.4 Practice of Isostatic Compaction 251.4.1 Wet-Bag Isostatic Pressing 251.4.2 Dry-Bag Isostatic Pressing 281.5 Granulation of Ceramic Powders 291.5.1 Spray-Drying 301.5.2 Alternative Spray Granulation Methods 331.5.3 Characterization of Ceramic Granulates 34

References 34

2 Tape Casting 39Andreas Roosen

2.1 Use of the Tape Casting Process 392.2 Process Variations 41

V

2.3 Tape Casting Process 422.4 Components of the Slurry 442.4.1 Inorganic Raw Materials 452.4.2 Solvents 462.4.3 Organic Raw Materials 472.4.3.1 Dispersing Agents 472.4.3.2 Binder and Plasticizer 482.4.3.3 Other Additives 492.4.4 Interaction between Slurry Components 502.5 Preparation of the Slurry and its Properties 512.6 Tape Casting 522.6.1 Drying and Characteristics of the Green Tape 542.7 Machining, Metallization, and Lamination 552.8 Binder Burnout 562.9 Firing 562.10 Summary 58

References 58

3 Hydrothermal Routes to Advanced Ceramic Powdersand Materials 63Wojciech L. Suchanek and Richard E. Riman

3.1 Introduction to Hydrothermal Synthesis 633.1.1 Fundamental Definitions 633.1.2 Process Development and Industrial Production 653.1.3 Hydrothermal Hybrid Techniques 673.1.4 Physical and Chemical Advantages of Hydrothermal Solutions 683.2 Engineering Ceramic Synthesis in Hydrothermal Solution 693.2.1 Phase Partitioning in Hydrothermal Systems 693.2.2 A Rational Approach for Engineering Hydrothermal Synthesis

Methods 693.2.3 Thermodynamic Modeling 703.2.4 Examples of Synthesis Engineering 723.3 Materials Chemistry of Hydrothermal Ceramic Powders 743.3.1 Control of Chemical Composition 743.3.2 Physical Characteristics and their Control 773.4 Ceramics Processed from Hydrothermally Synthesized

Powders 803.4.1 Synthesis of Modified Powders for Enhanced Sinterability 803.4.2 Powders for Sintered Dense Ceramics with Fine Grain Size 813.4.3 Sintered Porous Ceramics from Hydrothermally Synthesized

Powders 853.4.4 Fabrication of Textured Ceramics from Hydrothermal Powders 863.4.5 In-Situ Hydrothermal Conversion and Hydrothermal Sintering 873.5 Summary 88

References 88

VI Contents

4 Liquid Feed-Flame Spray Pyrolysis (LF-FSP) in the Synthesisof Single- and Mixed-Metal Oxide Nanopowders 97Richard M. Laine

4.1 Introduction 974.2 Basic Concepts of Nanopowder Formation During LF-FSP 1004.2.1 Particle Size Distributions 1014.2.2 Phase Formation 1024.2.3 Phase Characterization 1034.3 Can Nanoparticles Be Prepared That Consist of Mixed Phases? 1044.3.1 The TiO2/Al2O3 System 1044.3.2 Changing Band Gaps 1074.4 Which Particle Morphologies Can be Accessed? 1074.5 Can Nanopowders Be Doped? 1104.5.1 Sinter-Resistant Materials 1104.5.2 Laser Paints 111

References 116

5 Sol–Gel Processing of Ceramics 121Nicola Hüsing

5.1 Introduction 1215.2 Principles of Sol–Gel Processing 1225.3 Porous Materials 1265.4 Hybrid Materials 1305.5 Bioactive Sol–Gel Materials 1335.5.1 In-Situ Encapsulation of Biomolecules 1335.5.2 Bioactive Materials 136

References 137

Part II Densification and Beyond 141

6 Sintering 143Suk-Joong L. Kang

6.1 Sintering Phenomena 1436.2 Solid-State Sintering 1446.2.1 Sintering Models and Kinetics with No Grain Growth 1446.2.1.1 Initial Stage Model and Kinetics 1456.2.1.2 Intermediate and Final Stage Models and Kinetics 1486.2.1.3 Grain Boundary Structure and Densification Kinetics 1506.2.2 Grain Growth 1506.2.2.1 Normal Grain Growth 1516.2.2.2 Grain Growth in the Presence of Second-Phase Particles 1526.2.2.3 Grain Growth with Boundary Segregation 1526.2.2.4 Grain Growth Behavior with Boundary Structure 1546.2.3 Microstructure Development 1556.3 Liquid-Phase Sintering 156

Contents VII

6.3.1 Densification Models and Theories 1576.3.1.1 Contact Flattening 1596.3.1.2 Pore Filling 1596.3.2 Grain Growth 1616.3.3 Microstructure Development 1636.4 Summary 164

References 165

7 Hot Isostatic Pressing and Gas-Pressure Sintering 171Michael J. Hoffmann, Stefan Fünfschilling, and Deniz Kahraman

7.1 Introduction 1717.2 Sintering Mechanisms with Applied Pressure 1727.3 Silicon Nitride Ceramics: Comparison of Capsule HIP

and Sinter-HIP Technology 1757.3.1 Capsule HIP 1767.3.2 Sinter-HIP 1777.3.3 Differences between Capsule-HIP and Sinter-HIP 1817.4 Other Applications 1827.4.1 Structural Ceramics 1827.4.2 Post-HIPing of Oxide Ceramics for Optical

Applications 182References 185

8 Hot Pressing and Spark Plasma Sintering 189Mats Nygren and Zhijian Shen

8.1 Introduction 1898.2 Advantages of Sintering Under a Uniaxial Pressure 1908.3 Conventional Hot Presses 1938.4 SPS Set-Up 1948.5 Unique Features and Advantages of the SPS Process 1968.6 The Role of High Pressure 1978.7 The Role of Rapid and Effective Heating 1998.8 The Role of Pulsed Direct Current 2028.9 Microstructural Prototyping by SPS 2038.9.1 Nanoceramics and Ceramics Nanocomposites 2038.9.2 Self-Reinforced Ceramics 2058.9.3 Superplasticity and Textured Ceramics 2068.9.4 Non-Equilibrium Ceramic Composites 2088.9.5 Ceramics with Macro- and Micro- Graded

Structures 2108.9.6 Hard-to-Make Ceramics 2118.9.7 Defect-Engineered Ceramics 2128.10 Potential Industrial Applications 213

References 213

VIII Contents

9 Fundamentals and Methods of Ceramic Joining 215K. Scott Weil

9.1 Introduction 2159.2 Basic Phenomena in Ceramic Joining 2169.2.1 Mechanics 2169.2.1.1 The Strength of Ceramics 2169.2.1.2 Contact Stress 2179.2.1.3 Residual Stress 2179.2.1.4 Elastic Modulus Effects 2199.2.1.5 Other Effects 2209.2.1.6 Strength of Bonded Joints 2209.2.2 Adhesion and Wetting 2219.2.3 Diffusion 2249.2.4 Chemical Reaction 2259.3 Methods of Joining 2279.3.1 Mechanical Joining 2279.3.2 Direct Bonding 2319.3.2.1 Solid-State Direct-Bonding Processes 2319.3.2.2 Liquid-State Direct-Bonding Processes 2349.3.3 Interlayer Bonding 2359.3.3.1 Solid-State Interlayer Bonding Processes 2359.3.3.2 Liquid-State Interlayer Bonding Processes 2379.4 Conclusions 243

References 243

10 Machining and Finishing of Ceramics 247Eckart Uhlmann, Gregor Hasper, Thomas Hoghé, Christoph Hübert,Vanja Mihotovic, and Christoph Sammler

10.1 Introduction 24710.2 Face and Profile Grinding 24810.2.1 Process Description 24810.2.2 Machining of Ceramics 25010.3 Current Status and Future Prospects 25110.4 Double-Face Grinding with Planetary

Kinematics 25210.4.1 Process Description 25210.4.2 Machining of Ceramics 25410.4.3 Current Status and Future Prospects 25510.5 Ultrasonic-Assisted Grinding 25610.5.1 Process Description 25610.5.2 Machining of Ceramics 25610.5.3 Current Status and Future Prospects 25810.6 Abrasive Flow Machining 26110.6.1 Process Description 26110.6.2 Machining of Ceramics 263

Contents IX

10.6.3 Current Status and Future Prospects 26310.7 Outlook 264

References 265

Part III Films and Coatings 267

11 Vapor-Phase Deposition of Oxides 269Lambert Alff, Andreas Klein, Philipp Komissinskiy,and Jose Kurian

11.1 Introduction 26911.1.1 Sputter Deposition 27011.1.2 Pulsed-Laser Deposition 27511.1.3 Oxide Molecular Beam Epitaxy 28211.2 Summary 289

References 289

12 Metal–Organic Chemical Vapor Deposition of Metal OxideFilms and Nanostructures 291Sanjay Mathur, Aadesh Pratap Singh, Ralf Müller, Tessa Leuning,Thomas Lehnen, and Hao Shen

12.1 Introduction 29112.2 Metal Oxide Film Deposition 30012.2.1 Physical and Chemical Vapor Deposition Techniques 30012.2.2 Chemical Vapor Deposition 30212.2.2.1 Thermally Activated CVD (TA-CVD) 30212.2.2.2 Plasma-Enhanced CVD (PE-CVD) 30312.2.2.3 Molecule-Based CVD (MB-CVD) 30412.2.3 Atomic Layer Deposition 30412.2.4 Growth Dynamics 30812.2.4.1 Amorphous Growth 30912.2.4.2 Epitaxial Growth 30912.2.4.3 Polycrystalline Growth 30912.2.5 Mechanistic Aspects of CVD 31012.3 The Precursor Concept in CVD 31312.3.1 Precursor Requisites 31312.3.2 Precursor–Material Relationship 31412.3.3 Influence of Precursor Flow Rate on Microstructure

and Growth 32012.4 Metal Oxide Coatings 32112.4.1 Monometallic Precursor (MOx) Systems 32112.4.2 Bimetallic Precursor (MMOx) Systems 32412.4.3 Composites (MOx/MOy) Systems 32612.5 Summary 327

References 330

X Contents

Part IV Manufacturing Technology 337

13 Powder Characterization 339Wolfgang Sigmund, Vasana Maneeratana, and Shu-Hau Hsu

13.1 Introduction 33913.1.1 Accuracy Versus Precision and Instrument Resolution 34013.1.2 Sampling 34113.2 Chemical Composition and Surface Characterization 34313.2.1 Bulk Elemental Identification 34413.2.1.1 Optical Absorption Spectroscopy 34413.2.1.2 Electron and X-Ray Microanalysis 34613.2.1.3 Infrared Spectroscopy 34713.2.1.4 Raman Spectroscopy 34813.2.1.5 Nuclear Magnetic Resonance Spectroscopy 34813.2.1.6 Detailed Depth Profiling of Elemental Distribution within a

Particle 34813.2.2 Surface Characterization 34913.2.2.1 Surface Chemistry Analysis 34913.2.2.2 Vacuum Techniques 35013.2.2.3 Specific Surface Area of Particles 35113.2.2.4 Electrokinetic Potential or Zeta-Potential 35313.2.3 Crystallographic Identification 35313.3 Particle Sizing and Data Interpretation 35413.3.1 Particles Types 35413.3.2 Particle Shapes 35513.3.3 General Methods 35613.3.4 Light Scattering Techniques 35713.3.5 Sedimentation Analysis 35813.3.6 Coulter Counter 36013.3.7 Image-Based Analysis 36113.3.8 Sieve Analysis 36213.3.8.1 Dry Sieving 36313.3.8.2 Wet Sieving 36313.4 Physical Properties 36313.4.1 Particle Density 36313.4.1.1 Particle Density Definition 36413.4.1.2 Particle Density Measurement 36513.4.2 Powder Porosity 36613.5 Summary 367

References 367

14 Process Defects 369Keizo Uematsu

14.1 Introduction 36914.2 Bulk Examination Methods 370

Contents XI

14.3 Characterization Methods for Green Compact 37114.3.1 Specimen Preparation 37114.3.1.1 Ceramics 37114.3.1.2 Green Compact 37114.3.2 Observation with an Optical Microscope 37314.3.2.1 Transmission Optical Microscopy 37314.3.2.2 Polarized Light Microscopy 37314.3.2.3 Infrared Transmission Microscopy 37414.3.2.4 Confocal Fluorescent Scanning Laser Microscopy (CFSLM) 37414.4 Process Defects in Ceramics 37514.4.1 Short-Range Defects 37514.4.1.1 Circumferential Cracks at the Granular Boundaries 37714.4.1.2 Dimple Defects at the Centers of Granules 37814.4.1.3 Coarse Particles/Aggregates 38114.4.1.4 Defects Due to Inhomogeneous Distribution of Binder 38314.4.2 Long-Range Defects 38714.4.2.1 Particle Size Variation 38714.4.2.2 Density Variation 38714.4.2.3 Orientation of Particles 38814.4.2.4 Anisotropic Packing 39214.4.2.5 Long-Range Distribution of Additives 392

References 393

15 Nonconventional Polymers in Ceramic Processing:Thermoplastics and Monomers 395John W. Halloran

15.1 Introduction: Ceramic Green Bodies as Filled Polymers 39515.2 Thermoplastics in Ceramic Processing 39615.3 A Brief Review of Thermoplastics Used in Ceramic Forming 39715.4 Melt Spinning of Fibers 39715.5 Single-Component Extrusion and ‘‘Plastics Processing’’ 39815.6 Thermoplastic Green Machining 40015.7 Thermoplastic Coextrusion 40115.8 Crystallinity in Thermoplastics 40315.9 Compounding Thermoplastic Blends 40415.10 Volumetric Changes in Thermoplastic–Ceramic Compounds 40515.11 Polymer Formation by Polymerization of Suspensions

in Monomers 40715.12 Summary 410

References 411

16 Manufacturing Technology: Rapid Prototyping 415James D. McGuffin-Cawley

16.1 Introduction 41516.2 Outline of Ceramic Processing 418

XII Contents

16.3 Solid Freeform Fabrication 42216.4 Additive Prototyping Processes 42216.4.1 Stereolithography-Based Methods 42216.4.2 Flowable Powder Methods 42316.4.3 Ink Jet Methods 42616.4.4 Extrusion Methods 42616.5 Sheet-Based Processes 42716.6 Formative Prototyping Methods 42716.7 Casting Methods 42816.8 Plastic-Forming Methods 42816.9 Subtractive Methods 42916.9.1 Green (and Bisque) Machining 42916.10 Examples of SFF 42916.11 Summary 432

References 432

Part V Alternative Strategies to Ceramics 439

17 Sintering of Nanograin Ceramics 441I.-Wei Chen and Xiaohui Wang

17.1 Introduction 44117.2 Background: What Went Wrong With Conventional Thinking? 44217.3 Two-Step Sintering of Y2O3 44517.4 Two-Step Sintering of Other Ceramics 45117.5 Conclusions 453

References 454

18 Polymer-Derived Ceramics 457Emanuel Ionescu

18.1 Introduction 45718.2 Preceramic Polymers 45718.3 Polymer-to-Ceramic Transformation 45918.4 Processing Techniques for PDCs 46218.4.1 Polymer-Derived Ceramic Monoliths: Filler-Controlled

Pyrolysis 46218.4.2 Polymer-Derived Ceramic Coatings 46418.4.3 Polymer-Derived Ceramic Fibers 46618.4.3.1 Silicon Carbonitride 46718.4.3.2 Silicon Borocarbonitride 46718.4.4 Polymer-Derived Ceramic Foams 46818.4.4.1 Direct-Foaming Techniques 46818.4.4.2 Infiltration of Porous Performs 46918.4.4.3 Sacrificial Fillers 46918.5 High-Temperature Behavior of PDCs 47018.5.1 Microstructure of PDCs 470

Contents XIII

18.5.2 Energetics in SiOC and SiCN Systems 47218.5.3 High-Temperature Stability of PDCs: Decomposition and

Crystallization Processes 47418.5.4 Oxidation Behavior of PDCs 47618.6 Electrical Properties of PDCs 47818.6.1 Electrical Properties of SiOC-Based Ceramics 47918.6.2 Electrical Properties of SiCN-Based Ceramics 47918.7 Magnetic Properties of PDCs 48118.8 Polymer-Derived Ceramic Membranes 48318.9 Microfabrication of PDC-Based Components for MEMS

Applications 48518.9.1 Direct Lithographic Methods 48718.9.2 Micromolding Techniques 48918.10 Summary and Outlook 491

References 492

19 High-Pressure Routes to Ceramics 501Dmytro A. Dzivenko and Ralf Riedel

19.1 Introduction 50119.2 Static High-Pressure Techniques 50219.2.1 Laser-Heated Diamond Anvil Cell (DAC) 50319.2.2 Multianvil Apparatus 50619.3 Shock-Wave Techniques 50819.4 Synthesis of Cubic Silicon Nitride 511

References 513

Index 519

XIV Contents

Preface

Volume 3 of this series is devoted to ceramic processing – a critical field in ceramicscience and technology. The importance of this field is witnessed by the continuingactivities in the areas of basic and applied research, and also in the development ofnew processing equipment for both production and experimentation. Steps inprocessing – from start to finish – have immediate impacts on the performance ofthe final ceramics. Notably, the more stringent the requirements for ceramicperformance, the stronger the connection between processing and performance.In other words – ceramics are ‘‘unforgiving’’ to processing mistakes.

Ceramic processing usually starts from powders that neither melt nor plasticallydeform, but must be densified by diffusion during firing. As finished ceramics donot plastically deform either, any remaining defects in the fired ceramic – as well asany new defects introduced during finishing –may become the fatal flaws that leadto mechanical and electrical failures. During firing, the diffusion distance is inti-mately related to the way in which the processing is conducted prior to firing. Thepowders characteristics and the packing mechanics determine the size and popula-tion of structural inhomogeneities in the green body. It is not only the size of thepowder (which is often small), but also the size of the largest inhomogeneity (whichsometimes is large) that determines the diffusion distance. Justifiably, great empha-sis has been placed on the powder characteristics that can promote a uniformpacking while minimizing the diffusion distance. The production and use ofsuch powders are, without question, critical stages in ensuring successful ceramicprocessing. Nonetheless, the detection of processing defects that remain aftersintering – and their removal by machining and finishing – are necessary, albeitexpensive, steps to ensure a good performance of the ceramic components in manyapplications.

When designing a powder processing scheme, the chemistry of the liquid and ofthe polymer more often than not represents an integral part of the system. Forexample, potters slips (which are ceramic powders mixed with water, and some-times with conditioners) exhibit a magical formability that is not associated withpowders. Consequently, with help from organics and polymers, contemporaryceramic technologists can routinely cast and stack together hundreds of large-area, micrometer-thick tapes, and then fire them into a multilayered dense bodywith an intricate inner architecture. Ceramic powders and polymers also make good

XV

company in such technologies as rapid prototyping. It is even possible to obtainceramics directly from polymers, through a pyrolytic transformation that removesthe weak elements (such as H) while retaining their stronger counterparts (such asSi, B, C, and N).Today, however, there is yet another way in which ceramics may be processed,

allowing technologically important ceramic films, ranging from optical coatings tothin-film electronics, to be processed without the use of powders. Whilst suchpowderless processing avoids the problems of powder packing, firing and flatnessrepresent issues that still must be resolved. Moreover, as films and coatings arealways deposited onto another material, compatibility between the componentsmust also be considered. This pertains not only to the material selection but alsoto the processing steps; for example, a low deposition temperature or a low firingtemperaturemay be required tomaintain the integrity of thematerial beneath and toavoid the build-up of large thermal stresses.Last – but not least – the evolution of microstructure as a constant, recurring

theme in materials science and technology is of equal concern in ceramic proces-sing. The latter procedure can be compared to physical metallurgy, which is the artand science of renderingmetals and alloys into forms with a desiredmicrostructure.Yet, because ceramics cannot plastically deform, the die – that is, the microstructure– is cast when the firing is complete. The fact that a microstructure can be controlledat all in firing is surprising: its driving force, the capillarity, is orders of magnitudesmaller than is available (mostly plastic work) in metal forming. To overcome thisdeficiency, however, an additional mechanical driving force can be introduced;examples include hot pressing and the so-called ‘‘spark plasma synthesis,’’ both ofwhich provide a degree of control over the microstructure. As this is an exceptionrather than a rule, however, a major discourse in the pressureless sintering theoryrelates to the density-grain size trajectory. Today, by carefully controlling the firingschedule, it is possible to achieve densification without coarsening, paving the way tothe fabrication of nanograin ceramics.We, the editors, wish to thank all of the contributing authors for their great

enthusiasm, and for writing excellent manuscripts in their respective areas ofexpertise. As in previous volumes, the Wiley-VCH editors are indispensable to theproduction of the volume: indeed, the long, arduous and worthwhile endeavor ofproducing such a volume would be impossible without the attention, encourage-ment and stewardship of the Wiley-VCH editors, Gudrun Walter, BernadetteGmeiner, and Martin Preuss. We thank you for your continuous support.

Philadelphia and Darmstadt I.-Wei ChenJuly 2011 Ralf Riedel

XVI Preface

List of Contributors

XVII

Lambert AlffTechnical University DarmstadtInstitute of Materials SciencePetersenstraße 3264287 DarmstadtGermany

I-Wei ChenUniversity of PennsylvaniaSchool of EngineeringDepartment of Materials Science andEngineering3231 Walnut StreetPhiladelphia, PA 19104-6272USA

Dmytro A. DzivenkoTechnical University DarmstadtInstitute for Materials SciencePetersenstraße 3264287 DarmstadtGermany

Stefan FünfschillingKarlsruhe Institute of Technology (KIT)Institute for Applied Materials –Ceramics in Mechanical EngineeringHaid und Neu Straße 776131 KarlsruheGermany

John W. HalloranUniversity of MichiganDepartment of Materials Science andEngineering2300 Hayward StreetAnn Arbor, MI 48109-2136USA

Gregor HasperTechnische Universität BerlinInstitut für Werkzeugmaschinen undFabrikbetrieb (IWF)PTZ1Pascalstraße 8–910587 BerlinGermany

Michael J. HoffmannKarlsruhe Institute of Technology (KIT)Institute for Applied Materials –Ceramics in Mechanical EngineeringHaid und Neu Straße 776131 KarlsruheGermany

Thomas HoghéTechnische Universität BerlinInstitut für Werkzeugmaschinen undFabrikbetrieb (IWF)PTZ1Pascalstraße 8–910587 BerlinGermany

Shu-Hau HsuUniversity of FloridaDepartment of Materials Science andEngineering100 Rhines Hall, P.O. Box 116400Gainesville, FL 32611-6400USA

Christoph HübertTechnische Universität BerlinInstitut für Werkzeugmaschinen undFabrikbetrieb (IWF)PTZ1Pascalstraße 8–910587 BerlinGermany

Nicola HüsingUniversität UlmAnorganische Chemie IAlbert-Einstein-Allee 1189081 UlmGermany

Emanuel IonescuTechnical University DarmstadtInstitute for Materials ScienceDepartment of Dispersive SolidsPetersenstraße 3264287 DarmstadtGermany

Deniz KahramanKarlsruhe Institute of Technology (KIT)Institute for Applied Materials –Ceramics in Mechanical EngineeringHaid und Neu Straße 776131 KarlsruheGermany

Suk-Joong L. KangKorea Advanced Institute of Science andTechnologyDepartment of Materials Science andEngineering291 Daehak-ro, Yuseong-guDaejeon 305-701Republic of Korea

Andreas KleinTechnical University DarmstadtInstitute of Materials SciencePetersenstraße 3264287 DarmstadtGermany

Philipp KomissinskiyTechnical University DarmstadtInstitute of Materials SciencePetersenstraße 3264287 DarmstadtGermany

Jose KurianTechnical University DarmstadtInstitute of Materials SciencePetersenstraße 3264287 DarmstadtGermany

Richard M. LaineUniversity of MichiganDepartment of Materials Science andEngineeringMacromolecular Science andEngineering Center2300 Hayward StreetAnn Arbor, MI 48109-2136USA

XVIII List of Contributors

Thomas LehnenUniversity of CologneInstitute of Inorganic ChemistryGreinstraße 650939 CologneGermany

Tessa LeuningUniversity of CologneInstitute of Inorganic ChemistryGreinstraße 650939 CologneGermany

Vasana ManeeratanaUniversity of FloridaDepartment of Materials Science andEngineering100 Rhines Hall, P.O. Box 116400Gainesville, FL 32611-6400USA

Sanjay MathurUniversity of CologneInstitute of Inorganic ChemistryGreinstraße 650939 CologneGermany

James D. McGuffin-CawleyCase Western Reserve UniversityDepartment of Materials Science andEngineering10900 Euclid AvenueCleveland, OH 44106-3207USA

Vanja MihotovicTechnische Universität BerlinInstitut für Werkzeugmaschinen undFabrikbetrieb (IWF)PTZ1Pascalstraße 8–910587 BerlinGermany

Ralf MüllerUniversity of CologneInstitute of Inorganic ChemistryGreinstraße 650939 CologneGermany

Mats NygrenStockholm UniversityDepartment of Materials andEnvironmental ChemistrySvante Arrhenius väg 16C Frescati106 91 StockholmSweden

Rainer OberackerKarlsruhe Institute of Technology (KIT)Institute for Applied Materials –Ceramics in Mechanical EngineeringHaid und Neu Straße 776706 KarlsruheGermany

Ralf RiedelTechnical University DarmstadtInstitute for Materials SciencePetersenstraße 3264287 DarmstadtGermany

List of Contributors XIX

Richard E. RimanRutgers UniversityDepartment of Materials Science andEngineeringCeramic and Composite MaterialsCenter607 Taylor RoadPiscataway, NJ 08854USA

Andreas RoosenUniversity of Erlangen-NurembergDepartment of Materials ScienceInstitute of Glass and CeramicsMartensstraße 591058 ErlangenGermany

Christoph SammlerTechnische Universität BerlinInstitut für Werkzeugmaschinen undFabrikbetrieb (IWF)PTZ1Pascalstraße 8–910587 BerlinGermany

Hao ShenUniversity of CologneInstitute of Inorganic ChemistryGreinstraße 650939 CologneGermany

Zhijian ShenStockholm UniversityDepartment of Materials andEnvironmental ChemistrySvante Arrhenius väg 16CFrescati106 91 StockholmSweden

Wolfgang SigmundUniversity of FloridaDepartment of Materials Science andEngineering100 Rhines Hall, P.O. Box 116400Gainesville, FL 32611-6400USA

and

Hanyang UniversityWCU Department of EnergyEngineering17 Haengdang-dong, Seongdong-gu,Seoul 133-791Republic of Korea

Aadesh Pratap SinghUniversity of CologneInstitute of Inorganic ChemistryGreinstraße 650939 CologneGermany

Wojciech L. SuchanekSawyer Technical Materials, LLC35400 Lakeland BoulevardEastlake, OH 44095USA

Keizo UematsuNagaoka University of TechnologyFaculty of EngineeringDepartment of Materials Science andTechnology1603-1 KamitomiokaNagaoka, Niigata 940-0845Japan

XX List of Contributors

Eckart UhlmannTechnische Universität BerlinInstitut für Werkzeugmaschinen undFabrikbetrieb (IWF)PTZ1Pascalstraße 8–910587 BerlinGermany

Xiaohui WangTsinghua UniversityState Key Laboratory of New Ceramicsand Fine ProcessingDepartment of Materials Science andEngineeringBeijing 100084China

K. Scott WeilPacific Northwest National Laboratory902 Battelle BoulevardRichland, WA 99352USA

List of Contributors XXI

Part IPowders

Ceramics Science and Technology: Volume3: Synthesis and Processing, First Edition.Edited by Ralf Riedel and I-Wei Chen� 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.

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1Powder Compaction by Dry PressingRainer Oberacker

1.1Introduction

Powder compaction by dry pressing is industrys preferred and most widely usedformingmethod for ceramic parts. This can be explained by the high efficiency of theprocess, which has two variants: uniaxial die pressing; and isostatic pressing. Bothmethods can be automated to a high degree and are used in the mass production ofparts such as ceramic cutting tools (via uniaxial pressing) or spark plug insulators(via isostatic pressing). Uniaxial die pressing produces shapes with accurate dimen-sions in large quantities, in the shortest cycle times. Compared to injectionmolding,dry pressing requires a relatively small amount of additives (�2%), and thus allowsfor less expensive additive removal operations. However, as fine powders lack theflowability required for the process, in general they must be transformed into a free-flowing press granulate, by employing a granulation process. A second problemresults from the nonuniform pressure transmission, leading to nonuniform particlearrangements and density variations in the compacts, which is a well-known sourceof nonuniform grain growth and other sintering defects [1]. This chapter provides abrief but current review of the fundamental aspects of dry pressing, the practice ofuniaxial die and isostatic pressing, and the granulation of fine ceramic powders togranulates. Further details can be found in a number of monographs and referencebooks (e.g. Refs [2–10]).

1.2Fundamental Aspects of Dry Pressing

The aim of the process is to transform loose powders into a green compact with adesired shape and a maximal overall density. Close geometrical tolerances, minimalvariations of density, packing homogeneity, and sufficient strengths and integrity towithstand the stresses occurring during the subsequent handling, debindering andsintering treatment are further properties required of the green compact. These

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Ceramics Science and Technology: Volume3: Synthesis and Processing, First Edition.Edited by Ralf Riedel and I-Wei Chen� 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.

properties are determined by the behavior of the powders during the pressingprocess. The unit operations of this process are filling of the die ormold, compactionof the powder under a particular state of stress and, in the case of uniaxial diepressing, ejection of the green compact from the die.

1.2.1Die or Mold Filling Behavior of Powders

Free-flowing powders are a precondition for automated pressing operations, and forachieving reproducible filling densities during the filling step. Free-flowing behaviorrequires particle sizes above a critical diameter dc, which is explained by forceconsiderations (Figure 1.1) [3]. The friction forces Ff are proportional to the cohesiveforces Fa, which result from van der Waals and electrostatic forces or capillarybridges [11]. They scale linearly with the particle diameter. These must be overcomeby the inertial force Fi that is proportional to the particle mass, and which scales withthe third power of the particle diameter dp. At high Ff/Fi, the powders becomecohesive and do not flow. The tapping density is independent of particle diameterbeyond dc, but decreases with decreasing particle diameter below dc which, forceramic powders, is in the range of several tens of microns.

Most ceramic powders are in the micrometer or submicrometer range, and thusare cohesive. Such powders can be made free-flowing by size enlargement viacontrolled agglomeration (granulation). Ideally, agglomerates of a spherical shapewith a homogeneous packing of the primary particles and a defined porosity andagglomerate size distribution should result from the granulation process. Suitablegranule diameters range between 20 and 200 mm. Pressing aids such as binders andplasticizers can be easily incorporated into the granules. Ready-to-press granulatesprovide flowability, but they also prevent dusting and particle intrusion into the gapsbetween punches and die, which would result in catastrophic tooling wear.

Figure 1.1 Effects of particle diameter on the forces of friction Ff and inertia Fi between particles [3].

4j 1 Powder Compaction by Dry Pressing

1.2.1.1 Particle Packing: A Static ViewAn important characteristic of the granulates is the packing structure they achieve asthey fill the die. A reproducible and sufficiently high apparent packing density isessential for avoiding defects during the subsequent compaction step. Geometricalaspects of particle (granulate) packing have been treated in detail [12] and subse-quently reviewed [13]. The models developed in these texts are based on sphericalparticles with monomodal, bimodal, and polymodal size distributions.

Monosize spheres can, in principle, be arranged in regular three-dimensional(3-D) patterns with a maximal packing density of �74% for (hexagonal hcp or face-centered fcc) close-packed structures. This can be regarded as an upper limit.The simple cubic structure (sc) exhibits a packing density of �52%, but is acutelyunstable and tends towards the hcp or fcc structure under a mechanical disturbance.

Regular packing arrangements are achieved in practice only over very smalldomains. Much more of practical relevance are random packings; that is, disorderedcollections of particles in contact with amaximumdensity close to 64% formonosizedspheres [12–15]. Referred to as randomdense packing (RDP) or random close packing(RCP), these are experimentally achieved by pouring uniform balls into a vessel andvibrating this arrangement. The system achieved without vibration is termed randomloose packing (RLP), with experimentally observed densities of about 58–60%.Computer simulations [16–18] and advanced characterization methods such ascomputer tomography [15] have led to a better understanding of such randomstructures. Randompackings would be better referred to as random jammed states;jammed packings exist, in theory, over the density range of 53.6 to 63.4%. Dependingon the friction coefficient between the particles, in the jammed state only a certainnumber (Z) of the particle contacts is mechanically loaded. For frictionless particlesZ¼ 6,whileZ¼ 4 for infinitely roughparticles. As illustratedby thephasediagram forjammedmatter (Figure 1.2), a packing of monosize spheres with Z¼ 5 can exist onlyfor densities between 59.1 (DRLP(Z¼ 5)) and63.4% (DRCP). All states belowDRCP tendto increase the density during vibration, until DRCP is reached.

Figure 1.2 Phase diagram of jammed matter [18]. Reprinted with permission from MacmillanPublishers Ltd: [Nature]; � 2008.

1.2 Fundamental Aspects of Dry Pressing j5

Interestingly, the density of random packing of slightly deformed spheres canreach about 70%, significantly more than the DRCP of spheres; for higher aspectratios, however, the density begins to decrease [14]. The packing density is alsoenhanced by size-polydispersity. Bimodal spheres pack more densely than uniformspheres, as illustrated in Figure 1.3, where the smaller spheres fill the intersticesbetween random dense-packed larger spheres. The density increases until theinterstices are completely occupied, which occurs when the fraction of small spheresreaches about 27% of the total volume of the spheres. If large spheres are placed intoa RDP of small spheres, each large sphere increases the local density fromD¼DRCPto D¼ 100%, which is true up to 73 vol.% of large spheres. Simple analytical rulesof mixture were derived for these filling and replacement operations, assuming aninfinite size ratio (dL/dS) ! 1 [12]. Experimental observations for mixtures withfinite size ratios follow these upper bounds at lower density levels, as shownschematically in Figure 1.3. Computer simulations for a finite size ratio confirmthese correlations [19]. Size ratios (dL/dS)> 7 are required for a substantial densityincrease, a fact which can be explained qualitatively by the interstice size ofthe packing, since small particles have to pass through a critical pore entrancediameter de with a dimension of 0.154�dL for both fcc and hcp packings. This is closeto (dL/dS)� 7, where packing enhancement by smaller particles approaches itsoptimum.

In principle, the interstices between the smaller spheres can be filled by athird population of even smaller particles, and so on. In this way, about 95% and97% packing density can be achieved in ternary and quaternary mixtures, respec-tively [13]. However, the required size ratio becomes impractical: ternarymixtures become effective only with size ratios >102, and quaternary mixtures withsize ratios>104. In practice, the suitable size ratio of industrial granulates is limitedto about 10.

Figure 1.3 Packing density of binary mixtures of spheres according to the analytical solution inRef. [12].

6j 1 Powder Compaction by Dry Pressing