Synthesis and sintering of translucent yttrium aluminium garnet

Abstract

The prime objective of this investigation is the optimization of powder synthesis process and evaluation of their sintering behavior for futuristic laser host material. Selection of precursor and process variables for the large scale synthesis of yttrium aluminum garnet (YAG) nanopowder emphasizes in the first part of the dissertation. Co-precipitation of aluminum nitrate, yttrium nitrate and ammonium bicarbonate precursors below room temperature and their subsequent rapid calcination at 900oC develops high crystalline, 40nm pure YAG nanoparticles in comparison with other six powder synthesis processes. Particles have near spherical morphology with consist of high surface area of 34m2/gm. Batch size upto 250gm powder synthesis process has a high degree of reproducibility. Second part illustrates five different consolidation and sintering techniques of optimized YAG nanopowders known as uniaxial pressing – atmospheric sintering (UAS), cold isostatic pressing – atmospheric sintering (CAS), hot pressing (HP), uniaxial pressing – atmospheric sintering – hot isostatic pressing (UAS-HIP) and spark plasma sintering (SPS). Low degree of heating rate during conventional atmospheric sintering provides uniform equiaxed microstructure and better densification in presence of the optimum amount of silica content. Combination of UAS – HIP exhibits highest densification which is just above the spark plasma sintering process. Hot isostatic pressed disc (Ø ~15mm and thickness ~1.5mm) shows 99.6% relative density with average grain size of 2.5 micron. The transmittance of disc is around 60% in the visible region as well as near infra-red region of 550nm and 1100nm, respectively. This translucency behaviour is further needed to improve for laser host transparent ceramics.