Papers by Author: Hiroyuki Yoshida

Abstract: Photocatalyst coatings had been successfully fabricated by molten salt treatment at 673 K for 3 h for titanium (Ti) coatings, which coated on alumina (Al₂O₃) balls by mechanical coating technique with Ti powder. The influence of molten salt treatment on the formed compounds, surface morphology and photocatalytic activity under visible light irradiation on degradation of MB solution and suppression of Microcystis aeruginosa of photocatalyst coatings was investigated. XRD results show that potassium titanate (K₂Ti₆O₁₃) forms on the surface of Ti coatings during molten salt treatment. The visible light photocatalytic activity of photocatalyst coatings has been effectively enhanced by molten salt treatment.

Abstract: Photocatalyst coatings on alumina (Al₂O₃) balls had been successfully fabricated by mechanical coating technique, with titanium carbide (TiC) powder and subsequent heat treatment in carbon powder. The effect of heat treatment conditions in carbon powder on the formed compounds, surface morphology and photocatalytic activity of photocatalyst coatings was investigated. XRD results show that the formed compounds change with increasing the heat treatment temperature in carbon powder, and rutile TiO₂ on the surface of TiC coatings at 1073 K and 1173 K. The generated oxygen vacancies confirmed by XPS measurement, are in favor of narrowing band gap to enhance the visible-light photocatalytic activity of photocatalyst coatings. The photocatalytic activity of photocatalyst coatings has been effectively enhanced, and the samples fabricated at 1073 K and 1173 K for 2 h show higher activity. The fabrication strategy provides us a facile preparation procedure of visible-light responsive photocatalyst coatings.

Abstract: The photocatalyst coatings on alumina (Al₂O₃) balls had been prepared by mechanical coating technique (MCT) and subsequent oxidation process with Ti powder and Cr powder, and the influence of oxidation temperature on the photocatalyst composite coatings (Cr-TiO₂) were investigated. The contrast experiments of the oxidation temperature and the usage of Cr powder had been carried out. The crystal structure and microstructure of the coatings were investigated. Photocatalytic activity of the coatings was evaluated and discussed. The XRD results showed that the mixed-phase of anatase (A) and rutile (R), and mass fraction of rutile (X_R) had been increased with adding Cr, especially under 973 K. The SEM images indicated that the needle-like oxide was formed at the temperature of 973 K. The photocatalytic activity is relatively higher at 973 K under both of ultraviolet (UV) and visible light (VL). At the same time, the influence on photocatalytic activity of the photocatalyst coatings under UV or VL by adding Cr would guide the direction for the improvement of photocatalytic activity.

Abstract: Ti coatings on alumina (Al₂O₃) balls had been prepared by mechanical coating technique (MCT), and the influence of the rotation speed on the coating formation process were investigated. The crystal structure and microstructure of the Ti coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The formation process of Ti coatings was examined and discussed. The results showed that the rotation speed had great influence on the coating formation process. With increasing the rotation speed, the speed of coating formation had been accelerated and the surface became to be uneven. It was considered that the formation of metal coatings consists of 4 stages: nucleation, formation and coalescence of the discrete islands, formation of the continuous coating, and exfoliation.

Abstract: Titanium (Ti) coatings on alumina (Al₂O₃) balls fabricated by mechanical coating technique (MCT) were oxidized at relatively low temperatures. Crystal structure and microstructure of the coatings were investigated. Photocatalytic activity of the coatings was evaluated and discussed. The results showed that TiO₂ films on Ti or Ti/TiO₂ coatings were fabricated by the MCT and subsequent heat oxidation. The TiO₂ is anatase phase if the heat oxidation temperature is under 773 K. The TiO₂ is the mixed phases of anatase and rutile if the heat oxidation temperature is in the range of 673–973 K. Besides, rutile TiO₂ is formed if the heat oxidation temperature is beyond 1073 K. Photocatalytic activity of anatase TiO₂ is higher than rutile TiO₂.

Abstract: Photocatalytic TiO₂–Copper oxides composite coatings were prepared by the mechanical coating technique (MCT) and subsequent heat oxidation. The results showed that Cu particles were mainly adhered to the surfaces of the Ti–Cu composite coatings. After heat oxidation,the Ti coatings were partly oxidized to rutile TiO₂ and a Ti–TiO₂–Cu₂O–CuO composite microstructure was formed. These composite coatings had relative high photocatalytic activity because of the formation of the TiO₂–Ti composite microstructure and TiO₂–Cu₂O–CuO p–n heterojunctions.

Abstract: In the present study, the TiO₂-Ti compacts with Magneli phases Ti_nO_2n-1 were fabricated using the mixed powder of TiO₂ powder and addition Ti powder by spark plasma sintering (SPS). The composition and the crystal types of Magneli phases Ti_nO_2n-1 were examined. The results showed that various Magneli phases Ti_nO_2n-1 (single or multi Magneli phases) with the composition of Ti_1+yO_2-x were obtained. The Magneli phases Ti_nO_2n-1 were formed in the transformation from the mother phase rutile TiO₂ to TiO with increase in Ti addition fraction. In addition, the thermoelectric properties of the sintered compacts were also measured. The electrical resistivity of the sintered compacts decreased with increase in Ti addition fraction. The thermoelectric performance of the sintered compacts was improved by the formation of Magneli phases Ti_nO_2n-1 with the composition of Ti_1+yO_2-x.