Preparation of high-quality transparent Al-rich spinel ceramics by reactive sintering

Transparent Al-rich spinel ceramics (MgO·nAl2O3, n = 1.05–2.5) were prepared by reactive sintering in air followed by the hot isostatic press (HIP). Commercial MgO and γ-Al2O3 powders were used as the raw materials, and the effects of composition and HIP temperature on the transmittance and microstructure of resulting samples were investigated. To obtain the high optical quality, extra alumina (n ≥ 1.1) was used to help eliminate residual pores and suppress abnormal grain growth during the sintering process. The appropriate HIP temperature was also critical to realize the single-phase formation and prevent the generation of second-phase precipitates. The resulting samples with n = 1.1 and 1.3 exhibited excellent optical quality and fine grains below 5 µm after HIPed at 1550 °C.