Studies on Cordierite-Mullite Body -- Part-III: Effect of Alumina in a Sillimanite Based Cordierite Composition

摘要

The present study aims to improve the mechanical strength, high temperature load bearing capacity and thermal shock resistance of a sillimanite based cordierite-mullite body, developed earlier and having a composition : china clay 40 percent, sillimanite sand 40 percent and talc 20 percent, through gradual incorporation of alumina powder in replacement of sillimanite sand. The specimens were fired at different test temperatures ranging from 1200 deg to 1400 deg C with 2 h dwelling time at the respective peak temperatures. An addition of 10 wt percent calcined alumina in the standard body mix was found to increase the mechanical strength of the specimens from 241.90 to 262.10 kg.cm~(-2) after firing at 1340 deg C. The specimens of standard body mix showed a tendency towards melting at the firing temperature in excess of 1340 deg C; but the specimens of the developed body mix showed no such indications even beyond 1400 deg C. The mechanical strength of developed body mix also increased to 297.14 kg.cm~(-2) in the specimens fired at 1400 deg C. The thermal shock resistance of the optimal body mix containing 10 wt percent calcined alumina, measured in terms of loss of MOE after repeated thermal shocks at different gradually enhanced temperatures in water quenching, was found to be improved marginally in comparison to that of the standard cordierite composition. The original MOE value of the final body mix increased from 30.12 GPa to 37.24 GPa. The thermal expansion coefficient, however, marginally increased from 20.70 X 10~(-7) to 29.65 X 10~(-7) at 500 deg C and 21.34 X 10~(-7) to 32.16 X 10~(-7) at 1000 deg C.