REACTION AND SINTERING FOR THE MIXTURE OF KAOLIN AND CALCIUM-CARBONATE BELOW 1000-DEGREES-C

Reaction and sintering characteristics of kaolin and CaCO3 mixtures we re investigated using New Zealand kaolin and finely ground calcite pow ders as starting materials. Depending on the content of CaCO3, dense c eramics consisting of single phase of anorthite or composite of gehlen ite, wollastonite and anorthite were obtained by firing below 1000 deg rees C. With the heat processing, CaO reacted with decomposed kaolin f rom 800 to 850 degrees C and formed metastable amorphous materials. Th us formed active amorphous materials sintered rapidly between 850 and 950 degrees C by the viscous dow to form glass-like dense ceramics. Ac cording to the increase in amount of CaO, the sintering temperature lo wered from 950 to 900 degrees C. With the further heat processing, geh lenite, anorthite and wollastonite instantly crystallized, and the den se polycrystals were obtained. Their thermal expansions could be contr olled between 4.5 and 6.5 x 10(-6)/degrees C and the bending strengths were about 200 MPa. Thus obtained alkaline-free silicate ceramics cou ld be utilized as the electrical insulators or the multilayered cerami c substrates.