L. Mariappan et al. / Materials Chemistry and Physics 75(2002)284-29 3. Results and discussion being natural minerals after the reaction, the sic content will be 33 vol. for Sillimanite. 49% for Kaolin and 38% The results were obtained by the carbothermal reduc- for Zircon. Since it had been decided to make a ZTA-SiC tion of mixtures of Kaolin. Sillimanite and Zircon taken composite, a minimum of 15% ZrO2 had to be taken with various proportions. The formation of the product phases 85% Al2O3 to form the matrix. When this ratio was taken in with respect to variations in temperature and variations composition has been analysed with the help of XRd while percentage works out to be 35%. For comparison by varying their morphology was analysed using SEM. The conditions SiC,40% compositions were also made. This also explains favouring the formation of tetragonal zirconia without the the reason why two sources of aluminosilicates were used addition of stabilisers is also enumerated for the experiments 3.1. Role of variation in composition 3.2. Formation of tetragonal zirconia As given in Table 2, seven compositions were made Three ratios of alumina zirconia was taken for these ex get various ratios of Al2O3+ZrO2+SiCw. The precursors periments. It is now known by the work of Lange [9], that ZAC 00090000 2540 2040 00 1540 0000 1535 35404550 O→a-Al2O3;V→β-SiC;◇→mZrO2寥→t-zrO2 Fig 3. Product phases obtained at 1650C for different compositions with AC. (O)a-Al2O3, (V) B-SiC, (o)m-ZrO and(4)t-zrO2L. Mariappan et al. / Materials Chemistry and Physics 75 (2002) 284–290 287 3. Results and discussion The results were obtained by the carbothermal reduc￾tion of mixtures of Kaolin, Sillimanite and Zircon taken in various proportions. The formation of the product phases with respect to variations in temperature and variations in composition has been analysed with the help of XRD while their morphology was analysed using SEM. The conditions favouring the formation of tetragonal zirconia without the addition of stabilisers is also enumerated. 3.1. Role of variation in composition As given in Table 2, seven compositions were made to get various ratios of Al2O3 + ZrO2 + SiCW. The precursors Fig. 3. Product phases obtained at 1650 ◦C for different compositions with AC. (
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-Al2O3, () -SiC, () m-ZrO2 and ( ) t-ZrO2. being natural minerals after the reaction, the SiC content will be 33 vol.% for Sillimanite, 49% for Kaolin and 38% for Zircon. Since it had been decided to make a ZTA–SiC composite, a minimum of 15% ZrO2 had to be taken with 85% Al2O3 to form the matrix. When this ratio was taken in natural mineral form the minimum content of SiC by volume percentage works out to be 35%. For comparison by varying SiC, 40% compositions were also made. This also explains the reason why two sources of aluminosilicates were used for the experiments. 3.2. Formation of tetragonal zirconia Three ratios of alumina:zirconia was taken for these ex￾periments. It is now known by the work of Lange [9], that