Calcium hexaaluminate synthesis and its influence on the properties of CA2-Al2O3-based refractories

The investigations of low thermal expansion coefficient refractories, made of calcium dialuminate (CA2) and corundum, have been presented. Classifying them into a group of reactive materials means that there is a chemical reaction at the contact area of CA2 and Al2O3 grains, accompanied by a formation another compound CaAl12O19 (CA6) during firing. The conversion degree of the reaction as a function of temperature and time has been determined, including the formulation of kinetic equations, the assessment of apparent activation energy and a presumable mechanism of CA6 formation has been proposed. It has been proved that the formation of plate-shaped CA6 crystals at the contact area of Al2O3 grains with the surrounding CA2 matrix changes pore size distribution and total porosity of the materials. It is also related with local changes of thermal expansion coefficients, which in turn influences total expansion of the tested samples.