General introduction ........................................... XV
1. Crystal Chemistry of Mullite and Related Phases .............. 1
1.1. The Mullite-type Family of Crystal Structures ........... 1
R.X. Fischer, H. Schneider
1.1.1. Introductory Remarks ............................. 1
1.1.2. The Derivation of Mullite-type Crystal
Structures ....................................... 4
1.1.3. Members of the Mullite-type Family of Crystal
Structures ...................................... 12
1.1.3.1. Introduction ........................... 12
1.1.3.2. MUL-II.l, P42/mhc: Schafarzikite
Group .................................. 13
1.1.3.3. MUL-VI.ll, P42/mhc: Apuanite Group ..... 15
1.1.3.4. MUL-IV.12, Pbam: Bi2M4O9 Group ......... 16
1.1.3.5. MUL-VIII.12, Pbam: Versiliaite Group ... 18
1.1.3.6. MUL-VIH.2, Pbnm: Grandidierite Group ... 19
1.1.3.7. MUL-H.3, Pbam: Mullite Group ........... 20
1.1.3.8. MUL-IV.31, Pnnm: Andalusite Group ...... 33
1.1.3.9. MUL-VIII.31, P21/nll: Olivenite
Group .................................. 35
1.1.3.10.MUL-IV32, Pbnm: Sillimanite Group ...... 35
1.1.3.11.MUL-VIII.33, A21am: A9B2 Boron
Aluminates ............................. 37
1.1.3.12.MUL-IV34, P21212: Al5Ge0.972
Pb0.2O9.71 Phase ......................... 40
1.1.3.13.MUL-VIII.34, P212121: Mozartite
Group .................................. 40
1.1.3.14.MUL-XVI.351, A112/m: Boralsilite
Group .................................. 42
1.1.3.15.MUL-XXXII.352, P 1: Werdingite Group ... 46
1.2. The Real Structure of Mullite .......................... 46
S. Rahman, S. Freimann
1.2.1. Introduction .................................... 46
1.2.2. High-resolution Electron Microscopy ............. 47
1.2.3. X-ray Investigation ............................. 54
1.2.4. Real-structure Determination Using
Videographic Reconstruction and Simulation
Techniques ...................................... 56
1.2 4.1. The Videographic Method ................ 57
1.2.4.2. Structure Variants of Mullite .......... 60
1.2.4.3. Two-dimensional Videographic
Reconstructions ........................ 62
1.2.4.4. Three-dimensional Videographic
Simulations for 2/1-and 3/2-mullite .... 64
1.2.4.5. Conclusions ............................ 68
1.3. Foreign Cation Incorporation in Mullite ................ 70
H. Schneider
1.3.1. Transition Metal Incorporation .................. 70
1.3.1.1. Titanium Incorporation ................. 74
1.3.1.2. Vanadium Incorporation ................. 76
1.3.1.3. Chromium Incorporation ................. 77
1.3.1.4. Manganese Incorporation ................ 81
1.3.1.5. Iron Incorporation ..................... 83
1.3.1.6. Cobalt Incorporation ................... 89
1.3.1.7. General Remarks on Transition Metal
Incorporation .......................... 89
1.3.2. Other Foreign Cation Incorporation .............. 90
1.4. Mullite-type Gels and Glasses .......................... 93
M. Schmucker, H. Schneider
1.4.1. Type I (Single Phase) Mullite Precursors and
Glasses ......................................... 94
1.4.1.1. Preparation of Type I Mullite
Precursors and Glasses ................. 94
1.4.1.2. Temperature-induced Structural
Evolution of Type I Mullite
Precursors and Glasses ................. 97
1.4.1.3. Mechanisms of Mullite formation From
Type I Precursors and Glasses ......... 103
1.4.2. Type II (Diphasic) Mullite Precursors .......... 105
1.4.2.1. Synthesis of Type II Mullite
Precursors ............................ 105
1.4.2.2. Temperature-induced Structural
Evolution of Type II Mullite
Precursors ............................ 106
1.4.3. Type III (Single Phase/Diphasic) Mullite
Precursors ..................................... 114
1.4.3.1. Synthesis of Type III Mullite
Precursors ............................ 115
1.4.3.2. Temperature-induced Structural
Evolution of Type III Mullite
Precursors ............................ 115
1.4.3.3. Mechanisms of Mullite Formation
From Type III Mullite Precursors ...... 117
1.4.4. General Remarks on the Structure and
Crystallization Behavior of Mullite
Precursors and Glasses ......................... 117
1.4.4.1. Mullite Precursors: Similarities
and Differences ....................... 117
1.4.4.2. The Coordination of Aluminum in
Mullite Precursors and Glasses ........ 120
1.4.4.3. The Origins of Mullite
Crystallization ....................... 125
References ................................................. 128
2. Basic Properties of Mullite ................................ 141
2.1. Mechanical Properties of Mullite ...................... 141
H. Schneider
2.1.1. Strength, Toughness and Creep .................. 141
2.1.2. Elastic Moduli and Compressibility ............. 142
2.1.3. Microhardness of Mullite ....................... 146
2.1.4. Mechanical Response to Dynamic Stress .......... 149
2.2. Thermal Properties of Mullite ......................... 149
H. Schneider
2.2.1. Thermochemical Data ............................ 149
2.2.1.1. Enthalpy, Gibbs Energy and Entropy .... 149
2.2.1.2. Heat Capacity ......................... 152
2.2.2. Thermal Expansion .............................. 152
2.2.3. Thermal Conductivity ........................... 155
2.2.4. Atomic Diffusion ............................... 156
2.2.4.1. Oxygen Diffusion ...................... 156
2.2.4.2. Silicon Diffusion ..................... 158
2.2.4.3. Aluminum Diffusion .................... 159
2.2.5. Grain Growth ................................... 160
2.2.6. Wetting Behavior ............................... 162
2.3. Miscellaneous Properties .............................. 164
H. Schneider
2.3.1. Optical and Infrared Properties ................ 164
2.3.2. Electrical Properties .......................... 165
2.4. Structure-controlled Formation and Decomposition
of Mullite ............................................ 167
H. Schneider, M. Schmücker
2.4.1. Temperature-induced Formation .................. 167
2.4.1.1. Formation from Kaolinite and
Related Minerals ...................... 167
2.4.1.2. Formation from Andalusite and
Sillimanite ........................... 172
2.4.1.3. Formation from X-sialon ............... 178
2.4.1.4. General Remarks ....................... 178
2.4.2. Pressure-induced Decomposition ................. 179
2.4.2.1. Decomposition to Sillimanite .......... 179
2.4.2.2. Decomposition to y-Alumina plus
silica ................................ 180
2.5. Mullite-mullite Phase Transformations ................. 180
H. Schneider, M. Schmücker
2.5.1. Compositional Transformations .................. 180
2.5.2. Structural Transformations ..................... 186
2.5.2.1. Transformation at about 450 °C ........ 186
2.5.2.2. Transformation above 1000 °C .......... 186
2.6. Spectroscopy of Mullite and Compounds with Mullite-
related Structures .................................... 189
K.J.D. MacKenzie
2.6.1. Solid-state Nuclear Magnetic Resonance (NMR)
Spectroscopy ................................... 190
2.6.1.1. Brief Principles of Solid-state NMR
Spectroscopy .......................... 190
2.6.1.2. NMR Spectroscopic Structural
Studies of Aluminosilicate Mullite .... 191
2.6.1.3. NMR Spectroscopic Studies of
Amorphous Materials of Mullite
Composition ........................... 195
2.6.1.4. NMR Spectroscopic Studies of
Mullite Formation from Minerals ....... 198
2.6.1.5. NMR Spectroscopic Studies of Other
Compounds with Mullite Structure ...... 199
2.6.2. Electron Paramagnetic Resonance (EPR)
Spectroscopy ................................... 204
2.6.3. Infrared (IR), Fourier-transform Infrared
(FTIR) and Raman Spectroscopy .................. 207
2.6.3.1. The IR Spectrum of Mullite ............ 207
2.6.3.2. IR Spectroscopic Studies of Mullite
Formation ............................. 208
2.6.4. Mossbauer Spectroscopy ......................... 210
References ................................................. 215
3. Phase Equilibria and Stability of Mullite .................. 227
3.1. The Al2O3-SiO2 Phase Diagram .......................... 227
J.A. Pask, H. Schneider
3.1.1. Experimental Observations ...................... 227
3.1.2. Processing Parameters and Reaction
Mechanisms ..................................... 230
3.1.3. Solid-solution Range of Mullite ................ 234
3.1.4. Melting Behavior of Mullite .................... 234
3.1.5. Simulations of the Al203-Si02 Phase Diagram .... 234
3.1.6. General remarks ................................ 235
3.2. Influence of Environmental Conditions on the
Stability of Mullite .................................. 235
H. Schneider
3.2.1. Interactions with Reducing Environments ........ 236
3.2.2. Interaction with Water Vapor-rich
Environments ................................... 239
3.2.3. Interactions with Molten Sodium Salts .......... 241
3.2.4. Interactions with Fluorine Salt Environments ... 242
3.3. Ternary X-Al2O3-SiO2 Phase-equilibrium Diagrams ....... 243
H. Schneider
3.3.1. Alkaline Oxide-Al2O3-SiO2 ...................... 243
3.3.2. Iron Oxide-Al2O3-SiO2 .......................... 244
3.3.3. Alkaline Earth Oxide-Al2O3-SiO2 ................ 245
3.3.4. MnO-Al2O3-SiO2 ................................. 245
3.3.5. TiO2-Al2O3-SiO2 ................................ 245
3.4. Multicomponent Systems ................................ 246
H. Schneider
References ................................................. 246
4. Mullite Synthesis and Processing ........................... 251
4.1. Mullite Synthesis ..................................... 251
S. Komarneni, H. Schneider, K. Okada
4.1.1. Solid-state-derived Mullite .................... 251
4.1.1.1. Formation from Kaolinite and
Related Phases ........................ 251
4.1.1.2. Formation from Kyanite, Andalusite
and Sillimanite ....................... 252
4.1.1.3. Formation from Staurolite and Topaz ... 252
4.1.1.4. Reaction Sintering of Alumina and
Silica ................................ 253
4.1.1.5. Effects of Mineralizers, Reaction
Atmosphere and Structural Defects ..... 254
4.1.1.6. Commercial Production (Sinter-
mullite) .............................. 256
4.1.2. Liquid-state-derived Mullite ................... 259
4.1.2.1. Crystal Growth Techniques ............. 259
4.1.2.2. Commercial Production (Fused-
mullite) .............................. 260
4.1.3. Solution-sol-gel-derived Mullite ............... 262
4.1.3.1. Solution-plus-solution Process ........ 263
4.1.3.2. Solution-plus-sol Process ............. 272
4.1.3.3. Sol-plus-sol Process .................. 275
4.1.4. Spray Pyrolysis Approach ....................... 277
4.1.5. Hydrothermally Produced Mullite ................ 281
4.1.6. Vapor-state-derived Mullite .................... 283
4.1.7. Mullite Produced by Miscellaneous Methods ...... 283
4.1.8. General Remarks on the Different Chemical
Synthesis Methods of Mullite ................... 284
4.2. Processing of Mullite Ceramics ........................ 286
S. Komarneni, H. Schneider
4.2.1. General Sintering Characteristics .............. 286
4.2.2. Sintering of Powder Compacts ................... 288
4.2.3. Reaction Sintering of Alumina and Silica ....... 291
4.2.4. Reaction Bonding from Different Starting
Materials ...................................... 298
4.2.5. Reaction Sintering of Chemically Produced
Mullite Precursors ............................. 299
4.2.6. Transient Viscous Sintering of Composite
Powders ........................................ 306
4.3. Mechanical Properties of Mullite Ceramics ............. 307
K. Okada, H. Schneider
4.3.1. Mechanical Strength and Fracture Toughness ..... 308
4.3.1.1. Mechanical Strength and Fracture
Toughness at Room Temperature ......... 308
4.3.1.2. Mechanical Strength and Fracture
Toughness at High Temperatures ........ 310
4.3.2. Elastic Modulus ................................ 312
4.3.3. Hardness ....................................... 314
4.3.4. Thermal Shock Resistance ....................... 315
4.3.5. Wear Resistance ................................ 316
4.3.6. Fatigue Behavior ............................... 316
4.3.7. Creep Resistance ............................... 317
4.4. Thermal Properties of Mullite Ceramics ................ 321
K. Okada, H. Schneider
4.4.1. Thermal Conductivity ........................... 322
4.4.2. Thermal Expansion .............................. 322
4.5. Miscellaneous Properties of Mullite Ceramics .......... 323
K. Okada, H. Schneider
4.5.1. Electrical Properties .......................... 323
4.5.2. Optical Properties ............................. 324
4.5.3. Chemical Corrosion Behavior .................... 324
4.6. Application of Mullite Ceramics ....................... 327
K. Okada, H. Schneider
4.6.1. Engineering Materials .......................... 327
4.6.1.1. Refractory Materials .................. 327
4.6.4.2. High Temperature Engineering
Materials ............................. 328
4.6.1.3. Materials for Heat Exchangers ......... 329
4.6.1.4. Structural Materials .................. 331
4.6.2. Electronic Packaging Materials ................. 331
4.6.3. Optical Materials .............................. 333
4.6.4. Tribological Materials ......................... 334
4.6.5. Porous Materials for Filters and Catalyst
Supports ....................................... 335
4.6.6. Materials for Miscellaneous Applications ....... 336
References ................................................. 337
5. Mullite Coatings ........................................... 349
5.1. Chemical Vapor-deposited Coatings (CVD Coatings) ...... 350
S. Basu, V.K. Sarin
5.1.1. Thermodynamics of Chemical Vapor-deposited
Coatings ....................................... 350
5.1.2. Growth Kinetics of Chemical Vapor-deposited
Coatings ....................................... 352
5.1.3. Microstructure of Chemical Vapor-deposited
Coatings ....................................... 353
5.1.4. The Structure of Chemical Vapor-deposited
А12O3-rich Mullite .............................. 358
5.1.5. High Temperature Phase Transformations in
Chemically Chemical Vapor-deposited Mullite .... 359
5.1.6. Oxidation, Hot Corrosion and Recession
Protection of Chemical Vapor-deposited
Mullite ........................................ 364
5.2. Plasma- and Flame-sprayed Coatings .................... 367
S. Basu, V K. Sarin
5.2.1. Microstructural Characteristics and
Stability of Coatings .......................... 367
5.2.2. Plasma-sprayed Environmental Barrier
Coatings (EBCs) ................................ 370
5.2.3. Plasma-sprayed Thermal Barrier Coatings
(TBCs) ......................................... 372
5.3. Deposition of Mullite Coatings by Miscellaneous
Techniques ............................................ 373
S. Basu, V.K. Sarin
References ................................................. 374
6. Mullite Fibers ............................................. 377
6.1. Mullite Whiskers ...................................... 377
H. Schneider
6.1.1. Whisker Formation From Melts ................... 377
6.1.2. Whisker Formation via Gas-transport
Reactions ...................................... 378
6.2. Sol-gel-derived Continuous Mullite Fibers ............. 381
H. Schneider
6.2.1. Laboratory Produced Fibers ..................... 381
6.2.2. Commercially Produced Fibers ................... 384
6.2.2.1. Altex Fibers (Sumitomo Chemicals,
Japan) ................................ 384
6.2.2.2. Nivity Fibers (Denka-Nivity, Japan) ... 385
6.2.2.3. Nextel Fibers (3M Company, U.S.A.) .... 385
6.3. Continuous Melt-grown Mullite Fibers .................. 391
H. Schneider
6.4. Application of Mullite Fibers ......................... 393
H. Schneider
References ................................................. 394
7. Mullite Matrix Composites .................................. 397
7.1. Whisker-reinforced Mullite Matrix Composites .......... 398
H. Schneider
7.1.1. Fabrication Routes ............................. 399
7.1.2. Mechanical Properties .......................... 399
7.1.3. Thermal Properties ............................. 402
7.1.4. Miscellaneous Properties ....................... 403
7.2. Continuous Fiber-reinforced Mullite Matrix
Composites ............................................ 403
H. Schneider
7.2.1. Fabrication Routes ............................. 403
7.2.1.1. Non-oxide Fiber-reinforced
Composites ............................ 407
7.2.1.2. Oxide Fiber-reinforced Composites ..... 409
7.2.2. Mechanical Properties .......................... 421
7.2.2.1. Non-oxide Fiber-reinforced
Composites ............................ 423
7.2.2.2. Oxide Fiber-reinforced Composites ..... 425
7.2.3. Thermal Properties ............................. 434
7.2.3.1. Thermal Expansion ..................... 434
7.2.3.2. Thermal Conductivity .................. 435
7.2.4. Miscellaneous Properties ....................... 435
7.2.5. The Role of the Fiber/Matrix Interphase ........ 436
7.2.5.1. Easy-cleavage Interphases ............. 437
7.2.5.2. Low-toughness Interphases ............. 438
7.2.5.3. Porous or Gap-producing Interphases ... 438
7.2.6. Applications ................................... 440
7.2.6.1. Spacecraft Applications ............... 440
7.2.6.2. Aircraft Engine and Powerplant
Applications .......................... 440
7.2.6.3. Other Industrial Applications ......... 442
7.3. Platelet- and Particle-reinforced Mullite Matrix
Composites ............................................ 443
H. Schneider, K. Okada
7.3.1. Basic Principles ............................... 443
7.3.1.1. Transformation Toughening ............. 443
7.3.1.2. Crack-deflection Toughening ........... 444
7.3.1.3. Toughening by Modulus Load Transfer ... 444
7.3.1.4. Nanoparticle Toughening ............... 445
7.3.2. Zirconia Particle-reinforced Composites ........ 445
7.3.2.1. Fabrication Routes .................... 445
7.3.2.2. Mechanical Properties ................. 453
7.3.2.3. Thermal Properties .................... 455
7.3.3. Silicon Carbide Platelet- or Particle-
reinforced Composites .......................... 455
7.3.3.1. Fabrication Routes .................... 456
7.3.3.2. Mechanical Properties ................. 459
7.3.4. Miscellaneous Oxide Particle-reinforced
Composites ..................................... 461
7.4. Metal-reinforced Mullite Matrix Composites ............ 463
H. Schneider
7.4.1. Aluminum Metal-reinforced Composites ........... 463
7.4.2. Molybdenum Metal-reinforced Composites ......... 466
References .................................................... 467
Index ......................................................... 477
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