Low thermal expansion refractory composites based on CaAl 4O 7

Abstract

Following the previously reported elaboration of low thermal expansion refractory composites based on CaAl 4O 7, further compositions of this type are presented. They are principally based on combinations of CaAl 4O 7 with MgAl 2O 4; also, complementary data relating to those with CaZrO 3 are given. Specially adjusted bimodal particle size distributions were applied: granular fractions (0.09–0.5 mm) of the spinel and the zirconate embedded in fine (under 0.06) calcium dialuminate matrices. It could be shown that composites with up to more than 50% volume content of MgAl 2O 4 and CaZrO 3 grains will retain the merit of low expansion coefficients imposed by the matrix in spite of the much higher values of this property characteristic of both the granular constituents. A peculiar phenomenon of expansion even lower than that of CaAl 4O 7 itself was observed, too. The rather complex relations between the thermal expansion and composition/microstructure features are discussed and some relevant definitions are proposed. The added two minerals contributing to the favourable behaviour of the composites as a whole are fully compatible at high temperatures with the dialuminate. Interpretation of SEM and EPMA data for two representative compositions (with ca. one half of spinel and zirconate volume content) is presented; also, some technological implications are indicated.