1980 Volume 88 Issue 1024 Pages 703-712
In order to study a densification mechanism in kaolin-limestone mixtures, the phase and microstructural changes, and melt formation, which are related with the body densification during firing process, were in detail examined. The result obtained are as follows.
Densification of the kaolin-limestone mixtures during firing process occurs at 900°-950°C and above 1250°C separately. At 900°-950°C, active CaO reacts rapidly with metakaolin to form gehlenite, which always appears prior to anorthite and wollastonite, that results in the rapid shrinkage. At the intermediate temperatures, the reaction of calcia and metakaolin proceeds to attain equilibrium in the solid state and build up the three solid phases without sintering or vitrification. Above 1250°C, the onset of vitrification occurs depending upon the melt formation by eutectic reaction of the three solid phases, it follows that the mixtures containing 25-40wt% CaO results in the reduction of vitrification-range due to the excess amount of initial eutectic melt. Consequently, the experimental results for the vitrification process and the relation between calcia content and the vitrification temperature agreed well with the estimation from the pseud-binary system CaO-Al2O3⋅2SiO2 constructed from the CaO-Al2O3-SiO2 phase equilibrium diagram.
