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

Abstract

Beach sand sillimanite was substituted for china clay and fireclay grog in a standard cordierite body mix containing 60% china clay, 20% fireclay grog (IS-6 grade) and 20% talc. The specimens were fired at different temperatures ranged from 1200 to 1340°C with 2 h dwelling time at respective peak temperatures. The addition of 40 wt% sillimanite in the standard composition was found to improve the mechanical properties and to reduce the coefficient of thermal expansion from 25.7 × 10−7 to 20.43 × 10−7 at 500°C and 25.20 × 10−7 to 21.34 × 10−7 at 1000 C. The reduction in the coefficient of thermal expansion value of the body mix containing 40 wt% 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 C. The thermal shock resistance of the developed body mix containing 40 wt% 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.