Thermal expansion of CaAl4O7-based refractory compositions containing MgO and CaO additions

Various compositions of recently developed CaAl4O7-based ceramics are mentioned with special reference to those called “nonexpansive refractories” (=NER). The observed effect of deep depression of their thermal expansion is mainly ascribed to the creation of a specific microstructure resulting from high temperature reactions of CaAl4O7 with MgO or CaO additives yielding a CaAl2O4-based liquid. Some details characterizing the phase composition of the reaction zone are given. The effect of the calculated approximate content of CaAl2O4 in the specimens is interpreted graphically. Basing on the results of changes in the CaAl4O7 single crystal dimensions presented in comparison with some other expansion data, the presumable nature of the specific behavior of NER bodies on heating up to 500 °C is discussed. The NER products fired at 1620 °C are characterized by high strength and low open porosity.