Hirofumi Kikkawa

The photoelectrochemical properties of Nb-doped TiO2 semiconducting ceramic membrane

Abstract Photoelectrochemical properties of TiO2 membranes were investigated for samples which were prepared from several colloidal suspensions and supported on F-doped SnO2-coated glass. The effects of firing temperature, membrane thickness and Nb-doping level on quantum efficiency were examined in the range of 400-700°C, 0.1–1.1 μm and 0–10 mol % respectively. The conductivity, surface area and crystallinity of these membranes was also investigated as a part of this study. The colloidal suspensions were formed by hydrolysis of a titanium tetra-isopropoxide and niobium pentachloride solution. The photocurrent was found to be a function of firing temperature and membrane thickness. For undoped membranes, optimum photocurrent occurred at a thickness of ~0.3 μm for 600°C and 700°C, and 0.5 μm for 500°C. By doping Nb into the TiO2 membrane, the conductivity and photocurrent of the membrane could be affected, and an optimum value in photocurrent versus Nb-doping level was determined. The surface area and crystallinity of TiO2 were also influenced by Nb-doping level. The difference in crystallinity between supported and unsupported membranes was investigated as well.

Effect of adsorption characteristics of dispersant on flow and storage properties of coal-water mixtures

Abstract The flow and storage properties of coal—water mixtures (CWM) have been studied with respect to adsorption of anionic dispersants. The amount of adsorbed dispersants increased slightly for several days after the formulation of the CWM and then reached equilibrium, but was further increased by agitation. The adsorption of the dispersants increased as the surface property of coals became more hydrophobic and increased with the apparent surface area for a given coal. The adsorption also increased with the molecular weight of dispersants. The apparent viscosities of CWM depended on the amount of adsorbed dispersant and the viscosity of the carrier liquid. The yield stress at a given viscosity became larger as the adsorption of the dispersant increased, while the viscosity index decreased. There was a good relationship between the rheological behavior and the flow property and static stability. The optimum yield stress and viscosity index were found to be 1 – 5 Pa.s and 0.7 – 0.8, respectively.