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TITLE
DEDICATION
CERTIFICATE
DECLARATION
CONTENTS
ACKNOWLEDGEMENT
List of Publications
LIST OF FIGURES
LIST OF TABLES
I. INTRODUCTION
1.1 High Temperature Inorganic Materials and General Methods of Synthesis
Table 1.1 A general classification of ceramics based on function
1.1.1 General Methods of Preparation of High Temperature Oxides
1.2 Introduction to Mullite Ceramics
1.2.1 Properties of Mullite
1.2.2 Crystal Structure of Mullite
Fig. 1.1 Projection of the ideal orthorhombic mullite unit cell along the [001 ] direction
1.3 Synthesis and Formation of Mullite A brief literature review
Table 1.2 Typical properties of mullite ceramics
1.3.1 Synthesis from Al2O3-SiO2 Powders
1.3.2 Sol-Gel Processing of Mullite
1.4 Nucleating Seeds in Ceramic Systems
1.5 Definition of the Present Problem
II. EXPERIMENTAL PROCEDURE & INSTRUMENTATION TECHNIQUES
2.1 Materials used in the Present Investigation
2.2 Experimental Methods
2.2.1 Preparation of Bohemia Soy
2.2.2 Estimation of Alumina in the Boehmite Sol
2.2.3 Preparation of Mullite Seed Suspension
2.2.4 Preparation of α and γ-Al2O3 Seed Suspension
2.2.5 Preparation of Mullite Precursor gel
Fig. 2.1 A general flow chart for the preparation of mullite ceramic
Fig. 2.2 Synthesis of mullite under various pH conditions
2.2.6 Preparation of Seeded mullite gels
2.2.7 Density Measurement
2.3 Characterisation Techniques
2.3.1 X-Ray Diffraction
2.3.2 Thermal Analysis
2.3.3 Electron Microscopy
III. FORMATION CHARACTERISTICS AND IDENTIFICATION BEHAVIOUR OF MULLITE GELS UNDER VARIOUS pH CONDITIONS
3.1 TEOS Addition to Boehmite at Different pH (Route I)
3.1.1 Gelation and Phase formation Characteristics
Fig. 3.1 Optical photographs of mullite precursor gels
Fig. 3.2 TGA curves of mullite precursor samples
Fig. 3.3 DTA curves of mullite precursor samples
Fig. 3.4 XRD patterns of mullite precursor heated to 1225°C
Fig. 3.5 XRD patterns of mullite samples
Fig. 3.6 Dilatometric curve of mullite precursors
Fig. 3.7 SEM photographs of the sintered mullite samples (1400°C)
3.1.2 Densification Features
Fig. 3.8 Effect of calcination temperature on sintered density with pH (1400°C)
Table 3.1 Effect of calcination temperature on sintered density of mullite (1400°C)
Fig. 3.9 Effect of calcination temperature on sintered density with pH (1500°C)
Table 3.2 Effect of calcination temperature on sintered density of mullite (1500°C)
3.2 TEOS-Boehmite Mixture at Different pH (Route II)
3.2.1 Formation of Mullite
Fig. 3.10 DTA patterns of mullite samples
Fig. 3.11 XRD patterns of the heat treated mullite precursor
Fig. 3.12 XRD patterns of mullite samples at 1500°C
3.2.2 Densification Features
Fig. 3.13 Effect of pH on sintered densities (at 1400°C) of mullite at different calcination temperature
Fig. 3.14 SEM photographs of sintered mullite samples
Fig.3.14 SEM photograph of sintered mullite sample (c) pH 7.5
Table 3.3 Effect of pH on phase formation and density of mullite synthesised through different routes
IV. EFFECT OF SEEDS ON SOL - GEL MULLITE
4.1 The Concept of Seeding
4.2 Phase Transformation in Seeded Mullite Gels
4.2.1 Differential Thermal Analysis of Seeded Gels
Table 4.1 DTA exotherm temperature of mullitization in seeded / unseeded samples
Fig. 4.1A DTA pattern of unseeded mullite sample
Fig. 4.1B DTA patterns of α-alumina seeded samples
Fig. 4.1 C DTA patterns of γ-alumina seeded samples
Fig. 4.1D DTA patterns of mullite seeded samples
Fig. 4.1E DTA patterns of mixed seeded samples
4.2.2 X-ray Diffraction Analysis of Seeded Mullite Samples
Table 4.2 Phases formed at various temperatures in seeded / unseeded mullite samples
Fig. 4.2A XRD patterns of mullite precursors heat treated at 1200°C
Fig. 4.2B XRD patterns of mullite precursors heat treated at 1225°C
Fig. 4.2C XRD patterns of mixed seeded precursors heat treated at 1150°C
4.2.3 Discussion of XRD and DTA Results
Fig. 4.2D XRD pattern of mixed seeded precursors heat treated at 1200°C
4.3 Densifcation Features
Table 4.2 Sintered densities of mullite samples prepared from gel calcined at 500°C
Table 4.3 Sintered densities of mullite samples prepared from gel calcined at 900°C
Fig. 4.3 SEM fractographs of mullite samples (1350°C)
Fig. 4.4 DTA patterns of the mullite samples synthesised from different precursors
Fig. 4.5 XRD patterns of mullite precursor samples prepared from transitional alumina and TEOS mixtures
REFERENCES
V. MULLITE-SILICON CARBIDE NANOCOMPOSITES FROM SOL- GEL COATED POWDERS
5.1 introduction
5.1.1 Ceramic Nanocomposites
Table 5.1 A general summary of several classes of synthetic nanocomposites together with some examples
Fig. 5.1 The classification of ceramic nanocomposites
5.1.2 Synthesis of Ceramic Nanocomposites
5.1.3 Mullite-Matrix Composites
Fig.5.2 Schematic illustration of the process steps used to produce nanocomposites by reaction sintering
Fig. 5.3 Schematic diagram of the effect of coated particles on densification for two phase composite
Fig. 5.4 A general flow chart for the preparation of composite from coated powder
5.2 Experimental Procedure
5.2.1 Activation of SiC Powder
5.2.2 Preparation of Boehmite Sol
5.2.3 Preparation of Mullite Coated SiC Nanocomposite Precursor
5.3 Results and Discussion
5.3.1 Characterisation of Coating
Fig. 5.5 XRD patterns of mullite-SiC nanocomposite precursors
Fig. 5.6 TEM photogrphs of mullite-SiC nanocomposite precursors
Fig. 5.6 (b) TEM photograph of mullite - 15 vol. % Sic nanocompositeprecursor calcined at 600°C.
Fig. 5.6 (c) TEM photograph of mullite - 15 vol. % Sic nanocompositeprecursor calcined at 600°C (at a higher magnification)
5.3.2 Densification Features
Fig. 5.7 Dilatometric curve of mullite-SiC nanocomposite precursors
Fig. 5.7 Dilatometric curve of mullite-Sic nanocomposite precursors
5.3.3 Micro structural Features
Table 5.2 Relative densities of mullite-SiC samples sintered at various temperatures.
Fig. 5.8 SEM fractographs of mullite - SiC nanocomposites (1700°C)
Fig. 5.8 (c) Fractograph of mul1ite - 5 vol. % SiC composite indicating possibleinhibition of mullite grain growth interspaced between tcvo SICparticles.
5.4 References
VI. CONCLUSION
1. Effect of pH
2. Effect of nucleating seeds
3. Effect of Precursor Coating