Transparent YAG and composite ceramic materials in the system Alumina-YAG-Zirconia

In this PhD study, Yttrium aluminum garnet (Y3 Al5 O12 , YAG) powder was synthesised with several methods, i.e. spray drying, reaction synthe- sis and co-precipitation. The most promising synthesis method, i.e. co- precipitation, was optimized to obtain a pure phase, highly sinterable pow- der. The appropriate pre-sintering processing, i.e. calcination treatment, efficient dispersion, homogeneous drying, were performed. YAG powder was dispersed with several methods, prior to sintering to transparency. Through Spark Plasma Sintering (SPS) a very fast assessment of the influence of the various treatments was performed. It was found that, for the synthesised powder, the dispersion method is crucial to obtain a high transparency. Due to the high sinterability of the powder and to the appro- priate pre-sintering treatment, a low temperature SPS cycle was performed, and a fine-grained material was obtained. X-ray Photoelectron Spectroscopy (XPS) measurements were performed on YAG powder and on the sintered material, and several differences were evidenced. Some hypothesis were made to explain the observed differences, and some additional proofs to verify them were put forward. A composite Alumina-YAG-Zirconia powder was synthesized, starting from a commercial alumina powder, which was functionalised with Yttrium and Zirconium chlorides. The appropriate pre-sintering treatments were performed, comprising a low temperature calcination and a ”fast” calcina- tion, to favour the germination of small crystallites. Two shaping methods, i.e. slip casting and pressing, were performed. It was found that slip cast- ing allows the production of much more homogeneous ceramic materials. A preliminary mechanical characterization of the composite was performed. A spectroscopic characterization of Alumina-YAG powders, heat-treated at low and high temperatures, was performed. It was evidenced that the hydration state of the powders changes with chlorides functionalization. The presence of Y sites on the surface of the composite powders was evidenced by X-ray Photoelectron Spectroscopy and from the difference spectra of powdered samples subjected to various CO pressures.