Abstract: In this paper, transparent MgO·nAl₂O₃ (n=0.98, 1, 1.1, 1.2, 1.3) spinel ceramics were prepared from high pure and ultra fine powder by hot pressing (HP) and hot isostatic press (HIP). Haze is very common in transparent ceramics, its presence greatly reduces transmittance and affects mechanical properties of ceramics. In order to obtain MgO·nAl₂O₃ spinel with high optical quality and suitable mechanical properties, the haze in spinel was measured and the haze formation was analyzed. It is found that many circular particles at the grain boundaries in the translucent Mg-rich samples with dense haze by SEM. The composition of the circular particles was measured to be n=0.41 by EDS. The second phase MgO is readily precipitated due to the extra magnesium, that will seriously reduce the grain boundary strength and affect the mechanical properties of ceramics. The residual MgO phase has different refractive index with spinel phase, which can cause serious light scattering and reduce the transmittance of the sample. The composition of the particles at the grain boundary was measured to be n=1.33 in another sample, the flexure strength of this Al-rich sample was measured is much higher than that of stoichiometric and Mg-rich samples.

Key words: MgO·nAl₂O₃, spinel, haze, flexure strength, transparent ceramics, hot isostatic press