Effect of grain boundary microcracking on the light transmittance of sintered transparent MgAl2O4

Optically transparent polycrystalline magnesium aluminate spinel (MgAl2O4) has been fabricated by hot-pressing followed by hot isostatic pressing (HIPing). The effect of microstructure on the light transmittance of the sintered MgAl2O4 is discussed. The sintered MgAl2O4 with a thickness of 2 mm has a maximum light transmittance of ∼60 and ∼70% in the UV–visible and near-IR wavelength regions, respectively, although it contains microcracking along its grain boundaries. Light transmittance losses in the sintered MgAl2O4 are explained in terms of light scattering at these microcracked grain boundaries: the light transmittance was determined to decrease with increase in the microcracked grain boundary surface area due to pronounced scattering. The light transmittance is well correlated with microcracked grain boundary surface area per unit volume.