Development of optically transparent alumina and spinel ceramics with fine microstructure

This thesis deals with the elaboration and study of the physical properties of optically transparent and luminescent alumina-based ceramics for which applications are foreseen in the field of ionizing radiation resistant materials. The challenge of this work was to obtain a material that simultaneously has a high density and grain size at the nanoscale in order to give the ceramic transparency properties and resistance to ionizing radiation by capturing and recombination of induced charges at the grain boundaries. Ceramics of composition Al2O3 and MgAl2O4 were consolidated by Spark Plasma Sintering (SPS) from ultra-porous aluminas (UPA) on the one hand, and by reactive sintering of a mixture of Al2O3: MgO precursor in a ratio of 1 : 1 on the other hand. The UPAs were developed using an original process implemented at the LSPM. They were then impregnated with a solution of magnesium nitrate and then calcined at low temperature to obtain the "Nanostructured Precursor" (NP) for the spinel phase MgAl2O4. The synthesized NPs, like the UPAs, were then consolidated by SPS. The sintering parameters have been optimized to obtain ceramics with the desired microstructural and physical properties. The effect of Ta2O5 as a grain growth inhibitor has been tested on the microstructure of elaborated ceramics. The transmittance and luminescence properties, before and after irradiation, of the most promising materials were measured and correlated with their structural characteristics.