Mariappan et al. /Materials Chemistry and Physics 75(2002)284-290 Table 2 ZrO2)+35 vol. SiCw from starting composition Starting materials Weight Product phases in weight AlO zrO, SiC 44.07 17.28 16.8 (a Sample code ratIo 15 Zircon Zircon Carbon 1540 Fig 2 SEM pictures of the two types of carbon sources: (a)AC(Activated 2040 Charcoal) and(b)CB(Carbon Black). using an agate pestle and mortar. The alcohol evaporated Sillimanite after good physical blending and the resulting lumps were Zircon again crushed in the same pestle and mortar. The powder mix was sieved through a 100 mesh sieve to obtain -100 ZAC/ZCB Zircon mesh-free flowing powders. This powder was finally Carbon 36.25 in an air oven at 110C over night. These mixed powders were loaded into graphite crucibles. The furnace was heated in a programmed manner from room temperature to 1250C 1500.C to final temperature(1550, 1650 and 1700C)at expected product weight percentage are given in labe oy at 15. from 1250 to 1500.C at 10.C min-l and is given in Table 2. The quantities of starting materials 5Cmin. Soaking at the selected final temperature for Their eventual conversion to volume percentage is shown in I h, after which the furnace with the samples was cooled to Table 4 room temperature. The reacted powders were decarburised by heating in air at 700oC for 2 h to eliminate the excess carbon Table 4 Seven compositions were made to form various ratios Typical conversion table from weight percentage to volume percentage of silicon carbide, zirconia and alumina in the final prod- for the products ucts of the carbothermal reaction. The starting composi- Product Volume(cm) Volume (% tions were constituted according to the formula ((1-x) 52.59a Al2O3+(r)ZrO2)(l-y)+ SiC(y) to generate the product ZrOz phases as desired. As an example, the sample coded 2035 24.54 orresponds to ((0. 8)Al2O3 +(.2)ZrO2 J0.65+(0.35)SiCw a volume ratio of Al O3: ZrO2=80.39: 19.61286 L. Mariappan et al. / Materials Chemistry and Physics 75 (2002) 284–290 Fig. 2. SEM pictures of the two types of carbon sources: (a) AC (Activated Charcoal) and (b) CB (Carbon Black). materials and the carbon source were mixed in ethyl alcohol using an agate pestle and mortar. The alcohol evaporated after good physical blending and the resulting lumps were again crushed in the same pestle and mortar. The powder mix was sieved through a 100 mesh sieve to obtain −100 mesh-free flowing powders. This powder was finally dried in an air oven at 110 ◦C over night. These mixed powders were loaded into graphite crucibles. The furnace was heated in a programmed manner from room temperature to 1250 ◦C at 15 ◦C min−1, from 1250 to 1500 ◦C at 10 ◦C min−1 and 1500 ◦C to final temperature (1550, 1650 and 1700 ◦C) at 5 ◦C min−1. Soaking at the selected final temperature was for 1 h, after which the furnace with the samples was cooled to room temperature. The reacted powders were decarburised by heating in air at 700 ◦C for 2 h to eliminate the excess carbon. Seven compositions were made to form various ratios of silicon carbide, zirconia and alumina in the final prod￾ucts of the carbothermal reaction. The starting composi￾tions were constituted according to the formula {(1 − x) Al2O3 + (x)ZrO2}(1−y) + SiC(y) to generate the product phases as desired. As an example, the sample coded 2035 corresponds to {(0.8)Al2O3 + (0.2)ZrO2}0.65 + (0.35)SiCw Table 2 Typical calculation to arrive at the product 65 vol.% (80:20, Al2O3: ZrO2) + 35 vol.% SiCw from starting composition Starting materials Weight Product phases in weight Al2O3 ZrO2 SiC Sillimanite 70 44.07 – 17.28 Kaolin 5 2.297 – 1.80 Zircon 25 – 16.8 5.46 Table 3 Composition/formulation for obtaining the product {(1 − x)Al2O3 + (x)ZrO2}(1−y) + SiC(y) Sample code Precursor Weight ratio x y 1535 Sillimanite 77.00 15 35 Kaolin 05.00 Zircon 18.00 Carbon 40.41 2035 Sillimanite 70.00 20 35 Kaolin 05.00 Zircon 25.00 Carbon 40.09 2535 Sillimanite 55.00 25 35 Zircon 45.00 Carbon 38.65 1540 Sillimanite 52.00 15 40 Kaolin 30.00 Zircon 18.00 Carbon 43.02 2040 Sillimanite 46.00 20 40 Kaolin 30.00 Zircon 24.00 Carbon 42.74 2540 Sillimanite 40.00 25 40 Kaolin 30.00 Zircon 30.00 Carbon 42.46 ZAC/ZCB Zircon 100.00 100 38 Carbon 36.25 is given in Table 2. The quantities of starting materials and expected product weight percentage are given in Table 3. Their eventual conversion to volume percentage is shown in Table 4. Table 4 Typical conversion table from weight percentage to volume percentage for the products Product Weight Volume (cm3) Volume (%) Al2O3 46.36 11.8 52.59a ZrO2 16.8 2.8 12.38a SiC 24.54 7.9 34.94 a Volume ratio of Al2O3:ZrO2 = 80.39:19.61