Studies on Cordierite-Mullite Body - Part;;II: Effect of Sillimanite Sand in a Cordierite Composition

摘要

Beach sand sillimanite was substituted for china clay and fireclay grog in a standard cordierite body mix containing 60 percent china clay, 20 percent fireclay grog (IS-6 grade) and 20 percent talc. The specimens were fired at different temperatures ranged from 1200 deg to 1340 deg C with 2 h dwelling time at respective peak temperatures. The addition of 40 wt percent sillimanite in the standard composition was found to improve the mechanical properties and to reduce the coefficient of thermal expansion from 25.7 X 10~(-7) to 20.43 X 10~(-7) at 500 deg C and 25.20 X 10~(-7) to 21.34 X 10~(-7) AT 1000 deg C. The reduction in the coefficient of thermal expansion value of the body mix containing 40 wt percent sillimanite was due to the presence of cordierite and mullite and /or sillimanite phases in the composition. The final body also showed enhanced fired strength from 147.67 kg.cm~(-2) to 241.90 kg.cm~(-2) after firing at 1340 deg C. The thermal shock resistance of the developed body mix containing 40 wt percent sillimanite, measured in terms of percent loss of MOE after repeated thermal shock at gradually enhanced temperatures in water quenching, was found to be more than two times higher than that of the standard cordierite composition.