Development and Characterization of Photocatalytic GaN Coatings by Cold Spray Process

For the first time, the low-pressure cold spray (LPCS) process was used to manufacture gallium nitride (GaN) films to enhance its photocatalytic properties and decrease its manufacturing cost. The deposition behavior of the GaN powder on stainless steel substrates was investigated. Several specimens, with sparsely deposited agglomerated GaN particles, were prepared under different spray conditions. Quantitative analysis of the evolution of the coverage area, deposited particle count, and average sectional area shows that, upon impact, agglomerated GaN particles disintegrate, leading to large deposition of small particles. By analyzing the cross-sectional area of the deposited particle, no discernible permanent deformation of the substrate was observed. In addition, x-ray diffraction analysis of the coatings and powder indicated that no phase transformation occurred during the process. Based on Williamson–Hall analysis, the broader peaks of the coatings were mainly attributed to the distortions in the GaN lattice rather than changes in the crystallite size. At 400°C and 0.6 MPa, the deposition efficiency reached 5.3%, and the photocatalytic activities of the coating were about 33% (+9% compared to the powder). It is attributed to the higher specific surface area and roughness that the coatings exhibit after the breakage of the particles during the cold spray.