Low-temperature densification and shrinkage-induced microstructural evolution in MgO–LiF ceramics

This study investigated the densification and microstructural evolution of magnesium oxide (MgO)-based ceramics containing lithium fluoride (LiF) as a sintering additive, processed at 950 °C. Compositions containing 1, 2, 4, and 6 wt% LiF were prepared by powder mixing, mechanical homogenization, uniaxial pressing, and sintering for 6 h. After processing, the samples were subjected to physical and microstructural characterization by determining relative density and linear shrinkage, as well as by X-ray diffraction (XRD), scanning electron microscopy (SEM), and semiquantitative image analysis. The results showed that the composition containing 1 wt% LiF exhibited the best performance, combining high densification and controlled shrinkage, with a relative density of 98.86% and linear shrinkage of 18.72%. In contrast, the addition of 2 wt% LiF resulted in the lowest relative density, reaching 90.31%. Increasing the LiF content to 4 and 6 wt% promoted a partial recovery in densification, resulting in relative densities of 94.18% and 95.31%, respectively. However, these compositions exhibited greater linear shrinkage and evidence of microstructural heterogeneity. XRD analyses confirmed MgO as the predominant crystalline phase, with no detection of secondary crystalline phases associated with LiF. SEM micrographs revealed densified regions, particle coalescence, and cracks attributed to differential shrinkage during sintering. The results indicate that the addition of 1 wt% LiF is the most suitable condition for promoting MgO densification at 950 °C, providing the best balance among densification, linear shrinkage, and microstructural integrity.