Yoshiaki Kurata

Hydrothermal synthesis of potassium niobate photocatalysts under subcritical and supercritical water conditions

Hydrothermal synthesis of potassium niobate powders was carried out under various subcritical and supercritical water conditions using crystalline Nb2O5 powder as a starting material. A single phase of K4Nb6O17 was formed under subcritical water conditions, while mixed phases of K4Nb6O17 and KNbO3 were obtained under supercritical water conditions where KNbO3 was predominant over K4Nb6O17 as the heating duration was increased. Characterization of these hydrothermally synthesized potassium niobates by XRD, SEM, and TG-DTA analyses revealed that fine hydrated powders can be obtained under subcritical and supercritical water conditions. The hydrothermally synthesized potassium niobate powders were used for photocatalytic hydrogen evolution from water decomposition. The crystallinity is responsible for the high photocatalytic performance of the hydrothermally synthesized potassium niobate powders. The maximal hydrogen evolution rate was achieved for the potassium niobate hydrothermally synthesized at 400 °C for 4 hours. Besides, the hydrogen evolution rate was enhanced more than 10-fold by Ni loading for the hydrothermally synthesized potassium niobate powder which was much higher in comparison with the Ni loaded solid-state synthesized photocatalyst.

Corrosion Behavior of Nickel-Based Alloys and Type 316 Stainless Steel in Slightly Oxidizing or Reducing Supercritical Water

Abstract The objectives of this study were to evaluate the corrosion behavior of candidate corrosion-resistant alloys in slightly oxidizing or reducing supercritical water (SCW) environments contai...

The Effects of Velocity and Pressure Vibration on Erosion—Corrosion of Mild Steel in Water

Abstract The effects of velocity and pressure vibration on erosion—corrosion behavior of a mild steel (SS41) in tap water were studied with an impingement jet flow apparatus and a water bath. Obtained results were as follows: (1) The mass loss of the steel increased with the velocity in the range of 0 to 0.5 m/s, and decreased with the velocity above 0.5 m/s. The mass loss ranging from 1.5 to 6.0 m/s became as small as that at 0 m/s. (2) The mass loss occurring in the flow was proportional to the area of damaged surface, which consisted of pits. (3) The oxidation number of the iron oxide of the corrosion products was smaller in the flow field than in the static field. (4) The mass loss was larger in a vibrating pressure field than in a static field, and the damage pattern was nonuniform compared with that in the static field.

Phase behavior of Xe confined in porous vycor glass probed by 129Xe NMR chemical shift

129 Xe NMR spectroscopy is applied for direct observation of Xe confined in the porous Vycor glass. The chemical shifts of bulk and confined Xe are obtained simultaneously in a wide range of density from the gas phase to the liquid phase, including the supercritical region. The temperature and pressure dependences of the chemical shift of confined Xe are different from those of bulk Xe, which are approximately expressed by a linear function of bulk density. The phase transition of confined Xe is detected by the chemical shift, of which the pressure dependence along isotherms shows hysteresis loops.

The effects of jet velocity and pressure vibration on erosion-corrosion of mild steel in water.

An investigation of erosion-corrosion was carried out using an impingement jet apparatus and vibratory water bath. Obtained results were as follows: (1). The mass loss of the damaged material increased with the jet velocity in the range of V=0-0.5m/s, and got the largest at the velocity V=0.5m/s. Then the loss at V=1.5-6.0m/s became as small as that at V=0m/s. The mall loss was proportional to the area of damaged surface. (2) Pitting occurred in the surface of the target material number impingement jet flow. The diameter of a produced pit decreased with increasing the jet velocity, but the depth of the pit was independent on the velocity, (3) The oxidation number of the iron oxide of the corrosion products in the flow was relatively low. (4) The mass loss in pressure vibrating field is larger than that in a static field, and the damage pattern is unumiform compared with that in the static field.