Shin-ichi Sumi

Fabrication of Intermetallic Compounds by Spark Plasma Sintering

The characteristics of spark plasma sintering, a new method of powder processing, were investigated. Four systems of intermetallic compounds—Ti-Al, Ti-Al-Cr, Mo-Si, and Mo-Si-Nb—were fabricated, and the formation process of compounds, the formed phases, and the microstructure of samples were observed. During the sintering of all the compositions of mixed powders, most of the compounds were formed by combustion reaction which occurred at almost the same temperature as the conventional combustion reaction temperature. The fabricated samples were well densified, however, the relative densities of the Mo-Si samples were lower than the Ti-Al samples. Ultrasonic images show that no internal defects were found in any sample and the grain size became finer with the increase in the Cr content in the Ti-Al system and Nb content in the Mo-Si system. The formed phases of Ti:Al=1:1 composition samples were TiAl and Ti3Al phases, and Ti-Al added Cr samples consisted of TiAl, Ti3Al, Cr2Al, and Cr9Al17 phases. The sample synthesized with Mo:Si=1:2 mixed powders had only MoSi2 phases, and Mo-Si samples with added Nb consisted of four phases: MoSi2 with a small amount of Mo5Si3 phases in the matrix and Nb5Si3 with unreacted Nb for dispersed phases.

Double‐diffusive natural convection in a porous medium under constant heat and mass fluxes

Double-diffusive natural convection in a rectangular fluid-saturated porous medium has been studied analytically and numerically. The analysis reveals that there is a range of buoyancy ratios N in which one obtains two types of solutions or oscillating convection. In the case of 0.4 < N < 1.0, there exist two analytical solutions when Rc = 100 and Le = 30. In that case, two solutions, temperature-dominated and concentration-dominated solutions, are calculated when the aspect ratio is small. It is found that the oscillation is due to a temporal formation of a two-roll flow pattern in the cavity when the aspect ratio is sufficiently large. The oscillation of time-dependent Nusselt number and flow patterns are shown.

Titanium Oxide Removal from Clays by High Gradient Magnetic Separation Method

Titanium oxide (TiO2) removal by high gradient magnetic separation (HGMS) method on 16 clays collected from 8 localities was investigated. Effects of the operation conditions on the TiO2 removal, identification of TiO2 mineral and its micromorphology were studied. Following results are discussed.(1) TiO2 removal from clays varied from 15 to 100% under the conditions of 14.5 kG magnetic field strength and 38.4 m/hr linear velocity in the canister. According to the degree of the TiO2 removal, clays are divided into three types as follows:a) TiO2 removal>80%; 5 clays such as Ohtoge kaolins and Itaya clays, b) TiO2 removal=50-72%; 8 clays such as Ohtoge sericite, Sendatsu clays, Kuji clays, etc., c) TiO2 removal=l5-38%; 3 clays such as Murakami sericites and Aokiba clay.(2) Good results for TiO2 removal were obtained at the high magnetic field strength (9.7-14.5 kG) and at considerably lower linear velocity (22.1-38.4 m/hr).(3) Only anatase was identified as TiO2 contained mineral by the x-ray diffraction method. The 101 peak intensity of anatase is dependent on the TiO2 content of the clay.(4) In Ohtoge kaolin, anatase is occasionally found as pillar-like or plate-like euhedral crystal. Their particle sizes are relatively large and almost around 10-30 μm.(5) At the most suitable condition for TiO2 removal (14.5 kG, 38.4 m/hr with matrix FW), the contents of TiO2 and Fe2O3 of Ohtoge kaolin B decreased from 0.26 wt% to 0.05 wt% (TiO2 removal=81%) and from 0.43 wt% to 0.31 wt% (Fe2O3 removal=28%), respectively. The yield of nonmagnetics was 93%. Nonmagnetics separated from Itaya clay A contain 0.01 wt% TiO2 (TiO2 removal=80%) and 0.54 wt% (Fe2O3 removal=62%).