Effect of Powder Calcination on the Cold Spray Titanium Dioxide Coating

抄録

The agglomeration of nanoparticles is usually undesirable in the formation of powder. However, a coating process using the cold spray method only allows the usage of micrometer-sized feedstock powder in a regular powder feeder. In this study, TiO₂ coatings on ceramic tiles were prepared by a cold spray process using agglomerated TiO₂ powders synthesized via a simple hydrolysis method. XRD analysis showed that TiO₂ powders, composed of anatase phase and calcination at 200℃ to 400℃, resulted in enhanced crystallinity and crystallite size of the anatase TiO₂ powders. SEM micrographs revealed that the obtained powders were in spherical-like agglomerates with the tertiary particles having diameters of 5–20 µm. TEM image revealed that the obtained TiO₂ powders were composed of nanometer primary particles. XPS analyses showed that TiO₂ powders without calcination and calcined at different temperatures were formed through the Ti-O bonds. The influences of post treatment at low calcination temperatures of the as-synthesized TiO₂ powders were studied on powder deposition. The results of this study indicated that a post treatment on TiO₂ powder improved powder deposition on ceramic tile substrate via the cold spray method. The cross-section of the obtained coating which was observed using SEM showed that nanoparticles TiO₂ powders in the agglomerated form were able to be deposited on the substrate and formed a thick coating. A stacking of agglomerated TiO₂ powders was found on the cross-section observation which is due to the breaking up of ceramic particles which was induced by porosity in the powder and is believed to be responsible for the formation of the coating.