Low-temperature and single-step synthesis of fully-dense MgAl₂O₄ by reaction spark plasma sintering Al₂O₃ and MgO nano-oxides

The availability of commercial nano-powders and the rapidly maturing powder metallurgy technology have enabled researchers to develop advanced ceramics, with tailored microstructure and improved properties. However, a major challenge in the production of MgAl₂O₄, from Al₂O₃ and MgO, is the relatively high-volume expansion (5–8%) accompanying spinellization. This study demonstrates the possibility to prepare fully-dense and single-phase magnesium aluminate spinel, at low temperature and in short time, without the use of a sintering aid. This is achieved by sonication of magnesia and alumina followed by reaction spark plasma sintering. X-ray powder diffraction and scanning electron microscopy methods were used to characterize the starting nano-powders, sonicated powder mixture, spinel formation, and fractured specimens. The values of HV, K_1c, and G_IC were obtained from indentation measurements. The chemical composition, the SEM images, and the X-ray maps of magnesium and aluminum, confirmed the stoichiometry and homogeneity, at nano scale, of the densified specimens. The fully dense spinel, obtained at 1300 °C and 30 min, had average grain size of 40.92 nm, HV of 17.29 ± 0.185 GPa, K_1c of 2.129 ± 0.106 MPa mm^1/2, and G_IC of 15.488 J/m².