Mechanical properties of co-precipitated MgO-Al2O3 refractories as related to their phase composition and microstructure

The aim of this work is to study the densification, mechanical properties, phase composition and microstructure of four co-precipitated spinel-bearing grains after firing up to 1700 degrees C. The cold mechanical properties of the fired grains were assessed by means of microhardness and modulus of elasticity with relation to their phase composition, microstructure and densification parameters. The densification parameters in terms of bulk density and apparent porosity were determined using the water displacement method. XRD was used for quantitative determination of phase composition, while SEM techniques were applied to study the microstructure. Microhardness and the modulus of elasticity were assessed using the indentation method with a Vickers diamond. The results reveal that grains containing a maximum of direct bonded MgAl2O4-spinel solid solution phase show the highest densification as well as microhardness and elastic modulus. On the other hand periclase-spinel as well as spinel-corundum grains exhibit relatively lower densification and mechanical properties. The presence of considerable amounts of periclase in the former grains and relatively higher impurities in the latter contributes to lowering their densification and mechanical properties.