| 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%, sillimanite sand 40%
and talc 20%, through gradual incorporation of alumina powder
in replacement of sillimanite sand. The specimens were fired at
different test temperatures ranging from 1200° to 1400°C with 2
h dwelling time at the respective peak temperatures. An addition
of 10 wt"lo 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°C. The specimens of standard
body mix showed a tendency towards melting at the firing
temperature in excess of 1340°C; but the specimens of the
developed body mix showed no such indications even beyond
1400°C. The mechanical strength of developed body mix also
increased to 297.14 kg.cm·2 in the specimens fired at 1400°C.
The thermal shock resistance of the optimal body mix containing
10 wt% 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 soooc and 21.34 x 10"7 to 32.16 x 10"7 at 1000°C |
