Improvements on the fabrication of transparent MgAl2O4 prepared by hot pressing

In a previous work transparent MgAl2O4 spinel has been prepared by hot pressing (HP) of stoichiometric Al2O3-MgO powder mixtures obtaining transparencies up to 70% in the visible range. [1] Mixtures of powders has been preferred to the direct pressing of spinel for the readily availability of pure Al2O3 and MgO powders and to exploit the thermodynamic driving force of the spinel formation. Since hot pressing can be used for the production of flat components with large dimensions and good planarity, it has been preferred to other assessed techniques as hot isostatic pressing or spark plasma sintering. LiF has been used as sintering additive. In the present work the improvements obtained using the same experimental process but through the optimization of the sintering steps will be presented. The SEM microstructure of the sintered materials, in particular the mean grain size, undesired residual porosity and secondary phases, will be analysed and related to the transmittance and mechanical properties. The obtained values of 4-pt flexural strength, hardness, Young's Modulus and nanoindentation measurements will be compared to data available in the literature on this system. 1.L. Esposito, A. Piancastelli and S. Martelli, "Production and characterization of transparent MgAl2O4 prepared by hot pressing ", in press in the J. Eur.Ceram.Soc., 2012.