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K. Shima
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Proceedings Papers
ITSC 2011, Thermal Spray 2011: Proceedings from the International Thermal Spray Conference, 1121-1125, September 27–29, 2011,
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Titanium dioxide (TiO 2 ) is a unique material that can be used as an excellent photocatalyst, hence it will be very useful to solve the current world pollution problem. For photocatalytic application, the cold spray process, which uses supersonic high velocity technique at moderate temperature is considered to be a suitable technique as it will inhibit the phase transformation of TiO 2 . It is known that obtaining a thick coating of TiO 2 is difficult as it is a hard ceramic material. However, we have successfully synthesised TiO 2 powders that can be cold sprayed. Our synthesis technique is a simple hydrolysis method of titanyl sulphate (TiOSO 4 ) in distilled water. It was discovered that the cold sprayability of TiO 2 powders is depended on the powder morphology and using our synthesis method, powder morphology can be easily altered. Addition of (NH 4 ) 2 SO 4 during hydrolysis and post synthesis hydrothermal treatment result in a unique oriented aggregated nanostructure of TiO 2 . Only TiO 2 with this nanostructure can be cold sprayed.
Proceedings Papers
ITSC 2011, Thermal Spray 2011: Proceedings from the International Thermal Spray Conference, 308-313, September 27–29, 2011,
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Cold-spraying has been developed as a high-quality metallic coating process. Recently, it became possible to fabricate a brittle ceramic coating using a particular nano-structured powder. In order to improve and control the process, the bonding mechanism should be understood. In this study, the bonding mechanism between cold-sprayed TiO 2 particle and stainless steel substrate was investigated by cross-section observation and quantitative adhesion strength measurement for the individual particles. The adhesion strength was measured by the combination using of scanning probe microscope (SPM) imaging and nano scratch test. The result clearly revealed a correlation in adhesion strength with splat diameter. The smaller splat diameter exhibited higher adhesion strength, though it is generally difficult to penetrate the cold-sprayed small particles through a shock wave formed in front of the substrate. The cross-section microstructure of the splats prepared by focused ion beam (FIB) showed the particular deposition behavior of the TiO 2 particle. The collided particle didn’t deform the substrate surface and deformed the particle itself. The bottom center of the splat is densified by the deformation and the other parts maintain the porous structure or broke up. Hence the higher adhesion strength of smaller splat was caused by this typical TiO 2 deposition behavior.
Proceedings Papers
ITSC 2011, Thermal Spray 2011: Proceedings from the International Thermal Spray Conference, 515-520, September 27–29, 2011,
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We have shown the fabrication of ceramics titanium dioxide (TiO 2 ) coating via cold spray process. Cold spraying of any hard ceramics coating is considered to be difficult, including TiO 2 . However, we could obtain a coating with thickness greater than 100 µm. The adhesion mechanism of this cold sprayed TiO 2 coating needs to be clarified. The effects of process gas parameters and substrate materials on coating's adhesion strength were studied. It was found that adhesion strength did not vary significantly with the change of process gas parameters, indicating that mechanical embedment is not the sole factor of coating¡¦s adhesion. The study of changing substrate materials reveals the degradation of adhesion strength due to surface oxide layer and that TiO 2 shows better adhesion on bare metal surface. Hence, by altering the surface chemistry, the adhesion of TiO 2 is varied, indicating the possibility of physical or chemical bonding between cold sprayed TiO 2 and substrate.
Proceedings Papers
ITSC 2010, Thermal Spray 2010: Proceedings from the International Thermal Spray Conference, 172-176, May 3–5, 2010,
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Cold spraying has been developed as a high-quality coating process. However, the deposition materials were limited as metallic materials. In this paper, titanium dioxide (TiO 2 ) ceramic particles are deposited on several substrate materials and formed thick coatings, making this approach suitable for a wide range of photocatalytic applications. In order to understand the adhesion mechanism of solid ceramic particles, the structures of feedstock particles are carefully observed with a scanning electron microscope (SEM) and a high-resolution transmission electron microscope (TEM). We find a porous structure which is agglomerated with nano-scaled primary particles. It is assumed that the break down phenomenon occurs due to the cold spray process and influences the adhesion of ceramic particles. The primary particles are bonded within a single crystal. This particular structure is the main factor to make adhesion between the particle and the substrate. SEM and TEM analysis clearly reveals adhesion mechanisms related to the impact of spraying ceramic particles toward the substrate.