Preparation of YAG nanopowder by different routes and evaluation of their characteristics including transparency after sintering

Yttrium aluminium garnet (YAG) nanopowder has been synthesized by five different routes: three of them are co-precipitation with different combinations of aluminium and yttrium sources as well as the precipitating agents, and the rest are by solid state synthesis with certain variation. They are designated as: process-1 (Al-nitrate, yttria, HNO3, NH4HCO3), process-2 (Al-nitrate, Y-nitrate, NH4HCO3), process-3 (Al-nitrate, Y-nitrate, NH4OH,), process-4 (Al-nitrate and Y-nitrate heated to 1000 degrees C), and process-5 (alpha-alumina and yttria heated to 1100 degrees C). Of them, process-2 develops the highest surface area (31 m(2)/g), soft agglomerated and near spherical crystalline YAG nanopowders through minimum mass loss, and excellent cation homogeneity. Pseudo solid state reaction between aluminium nitrate/yttrium nitrate (process-4) and solid state reaction of alumina/yttria (process-5) requires high-calcination temperature and results in hard agglomerates. In most cases, highly crystalline YAG is formed together with the formation of an intermediate metastable phase of YAP. Powder prepared by process-2 leads to 99.6% dense and 60% transparent YAG ceramics on hot isostatic pressing.