Abstract: Transparent magnesium alumina spinel ceramics have both good optical and mechanical properties, and have broad practical and potential application prospects in the military and civilian fields. Due to its low densification rate, sintering aids are often introduced during the sintering process. Rare earth sesquioxides have high melting point and are not easily volatile at high temperatures. In recent years, some of them are used to promote the densification rate of magnesium aluminate spinel ceramics, but the sintering mechanism is still unclear. In this work, transparent magnesium aluminate spinel ceramics were prepared through pressureless sintering followed by hot isostatic pressing treatment, using high-purity commercial magnesium alumina spinel powders as the raw materials, and La₂O₃ as the sintering aid. XRD, SEM, UV-visible spectrophotometer and universal testing machine were employed to investigate the effect of La₂O₃ on the sintering and densification process of transparent magnesium aluminate spinel ceramics. The results show that La₂O₃ can result in lattice distortion through reaction with spinel or forming the solid solution at the high temperature, which promotes the densification process of spinel, and reduces the presintering temperature about 40 ℃. For samples subjected to hot isostatic pressing at 1 500 ℃/3 h at 190 MPa, La₂O₃ doping increases the transmittance in the ultraviolet region. At the same time, La segregates to the grain surface and inhibits the grain growth, which improves the mechanical strength of the sample. Compared with the undoped sample, the transmittance of 0.05% (mass fraction) La₂O₃ doped sample at 400 nm increases from 63% to 81%, its bending strength increases from 263.7 MPa to 319.0 MPa, and its fracture toughness increases from 1.69 MPa·m^1/2 to 1.82 MPa·m^1/2.

Key words: transparent ceramics, La₂O₃, magnesium aluminate spinel, sintering aid, densification, grain refinement