Microstructure and mechanical properties of tabular alumina composites with geopolymer binder at elevated temperatures

摘要

Alumina/geopolymer refractory composite was prepared using tabular alumina aggregates and metakaolin with micro silica and potassium hydroxide. The effect of different sized tabular alumina particles on the castables microstructure and mechanical properties has been evaluated. The composition was with 75 vol% tabular alumina and 25 vol% geopolymer as binder exhibited high mechanical strength at ambient temperature. By increasing temperatures, significant change happens in microstructure, strength and observation of dislocations in the composite. Liquid sintering initiated collapse of pores, strong bonds among particles and densification of the composites which are up to 1000 degrees C. The crystallization of leucite was observed in samples which are heated in 1200 degrees C. However, the residual stresses in the specimens due to the mismatch of thermal expansion of components (liquid phase, leucite and tabular alumina) diminished the strength at 1200 degrees C and transgranular fracture observed in some aggregates.