3. 1 Techniques of Comminution 35 3. 2 Solid-Solid Reactions 42 3. 2. 1 Mixing and Calcination 42 3. 2. 2 Modem Techniques 45 3. 3 Solution Techniques 46 3. 3. 1 Precipitation and Co-precipitation 46 Forced Hydrolysis 3. 3. 2 49 3. 3. 3 Hydrotbennal Synthesis 51 The Sol-Gel Process 3. 3. 4 53 3. 3. 5 Hydrolysis of Metal-Organics 56 The Emulsion Process 3. 3. 6 56 Solvent Vaporization 3. 4 59 3. 4. 1 Simple Evaporation 59 3. 4. 2 Spray Drying 60 3. 4. 3 Spray Pyrolysis 64 3. 4. 4 Freeze Drying 66 3. 5 Vapour-Phase Techniques 68 3. 5. 1 Vaporization-Condensation 68 3. 5. 2 Vapour-Vapour Reaction 68 3. 5. 3 Vapour-Liquid Reaction 70 3. 5. 4 Vapour-Solid Reaction 71 3. 6 Precursor Decomposition 72 3. 6. 1 Salt Decomposition 72 3. 6. 2 Polymer Pyrolysis 73 4. Synthetic Powders : Options in Preparation 75 4. 0 Introduction 75 4. 1 Single and Multiple Oxide Powders 75 4. 1. 1 Aluminium Oxide 75 4. 1. 2 Zirconium Oxide 85 4. 1. 3 Titanium Oxide 96 4. 1. 4 Magnesium Oxide 99 4. 1. 5 Silicon Dioxide 101 4. 1. 6 Rare Earth Oxides 105 Yttrium Oxide 105 Cerium Oxide 106 4. 1. 7 Zinc Oxide 107 [vi] 4. 1. 8 Mullite 110 4. 1. 9 Magnesium Aluminate Spinel 114 4. 1.