Enhancement of the densification and thermal properties of Ca2Mg2Al28O46 ceramic by MnO addition

Abstract Ca2Mg2Al28O46 consists of platelet or platelet-like structural features derived from CaAl12O19. However, its application in dense structural materials is limited due to its poor sinterability and loose structure. In this work, Ca2Mg2Al28O46 ceramic was fabricated by solid-state reaction sintering, and the effects of MnO addition on the densification and thermal properties were investigated at 1600-1750 °C. The results showed that the Mn2+ solid dissolved into the Ca2Mg2Al28O46 lattice by the isovalent substitution of Mg2+ at 1650 °C, causing the grain morphology to change from hexagonal to equiaxed and resulting in a distorted magnetoplumbite structure. At 1700 °C, the solid solution reaction accelerated the densification, with the apparent porosity decreasing from 32.5% to 8.4% when 3 wt% MnO is added, promoted grain growth and pore discharge by increasing the number of lattice defects, grain boundary migration rate and in-situ stress. The enhanced thermal expansion coefficient and thermal conduction were mainly due to lattice expansion and grain coarsening. Moreover, the formation of trace amount of the secondary phase Mg1-xMnxAl2O4 also contributed to the improvement in the thermal properties.