Despite numerous advances in the preparation and use of GaN, and many leading-edge applications in lighting technologies, the preparation of high-quality GaN powder remains a challenge. Ammonolytic preparations of polycrystalline GaN have been studied using various precursors, but all were time-consuming and required high temperatures. In this study, an efficient and low-temperature method to synthesize high-purity hexagonal GaN powder is developed using sub-micron Ga₂O₃ powder as a starting material. The sub-micron Ga₂O₃ powder was prepared by an ultrasonic spray pyrolysis process. The GaN powder is synthesized from the sub-micron Ga₂O₃ powder through a nitridation treatment in an NH₃ flow at 800°C. The characteristics of the synthesized powder are systematically examined by X-ray diffraction, scanning and transmission electron microscopy, and UV-vis spectrophotometer.

The GaN-powder scrap generated in the manufacturing process of LED contains significant amounts of gallium. This waste can be an important resource for gallium through recycling of scraps. In the present study, the influence of annealing temperatures on the structural properties of GaN powder was investigated when the waste was recycled through the mechanochemical oxidation process. The annealing temperature varied from 200°C to 1100°C and the changes in crystal structure and microstructure were studied. The annealed powder was characterized using various analytical tools such as TGA, XRD, SEM, and XRF. The results indicate that GaN structure was fully changed to Ga₂O₃ structure when annealed above 900°C for 2 h. And, as the annealing temperature increased, crystallinity and particle size were enhanced. The increase in particle size of gallium oxide was possibly promoted by powder-sintering which merged particles to larger than 50 nm.

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• High-temperature thermo-mechanical behavior of functionally graded materials produced by plasma sprayed coating: Experimental and modeling results
  Kang Hyun Choi, Hyun-Su Kim, Chang Hyun Park, Gon-Ho Kim, Kyoung Ho Baik, Sung Ho Lee, Taehyung Kim, Hyoung Seop Kim
  Metals and Materials International.2016; 22(5): 817.     CrossRef