Ryosuke O. Suzuki

A new concept for producing Ti sponge: Calciothermic reduction

This article presents a new cell concept for the calciothermic reduction of titanium dioxide and an ongoing test program for its experimental verification. The thermochemical background of this concept is focused and a new cell design is described. This system consists of a single cell, where both the reduction reaction and the electrolytic reaction for recovery of reducing agent coexist in the same molten calcium-chloride bath. The theoretical electric energy requirement for this cell is about half of that for the magnesium electrolytic cell in the Kroll process.

Calcium-deoxidation of niobium and titanium in Ca-saturated CaCl2 molten salt

Niobium was deoxidized under Ca(liquid)–CaO(solid) equilibrium at 1273 K to a level below the lower limit of quantitative chemical analysis, 50 mass ppm oxygen. Because Ca does not react with Nb, it is easy to remove the excess Ca and the byproduct CaO, and no reaction layer remains such as for Ti external gettering. Due to direct contact with Ca liquid, however, Nb was contaminated by carbon and nitrogen. When Ca was supplied as vapor into a CaO-saturated CaCl2 melt, Ca could saturate in the CaCl2 melt, and the carbon and nitrogen impurities in Nb were minimized. The oxygen concentration in Ti was the same as that under Ca–CaO equilibrium, and that in Nb was below 50 ppm. By Ca-halide flux deoxidation using the Ca-saturated but CaO-unsaturated CaCl2 melt, the residual resistivity ratio, RRR, of Nb exceeded that of the starting commercial Nb wire by 500. The oxygen content in Nb was estimated to be smaller than a single ppm. The activity of CaO in the salt was also evaluated at 1273 K using the equilibrium oxygen concentration in Ti.

MoSi2 coating on molybdenum using molten salt

Abstract For obtaining oxidation resistance of molybdenum in air, molybdenum silicide was non-electrolytically coated in the molten salt, where a disproportion reaction occurs between the salt composed of NaCl–KCl–NaF–Na 2 SiF 6 –SiO 2 and the Si powder. Hexagonal MoSi 2 was formed as single phase with homogeneous thickness of tens of μm above 1073 K, while the tetragonal MoSi 2 phase was additionally formed at 973 K. The growth rate of the MoSi 2 layer and its morphology at the sample corner were affected by this phase formation. The protective layer on the siliconized sample proved to be effective for preventing oxidation that occurs for pure molybdenum at low temperatures. During the oxidation at the high temperature, Mo 5 Si 3 was formed at the interface between the Mo substrate and the MoSi 2 layer.

Mathematical simulation of thermoelectric power generation with the multi-panels

Electric power was estimated in case of the large-scale flat thermoelectric panels exposed to two thermal fluids. The output powers of the proposed 15 systems were analytically deduced from heat transfer theory, and written by non-dimensional functions to reflect the characteristics of system design. The maximum output was the largest in the ideal isothermal systems. In the other realistic systems, it was the largest for the system of the counter flow with one panel. The multiplication of thermoelectric panels can shorten significantly the device area, although the output from the multi-panels decreases a few percent. The worse heat conductivity, λ of thermoelectric materials and the better heat transfer at the surfaces are desired for these fluid systems, in addition to the better figure of merit, Z.

NbSi2 coating on niobium using molten salt

Abstract For obtaining better oxidation resistance of niobium in air, a niobium silicide was non-electrolytically deposited onto niobium from the molten salt, where a disproportional reaction occurs between Na2SiF6, SiO2, and Si. A single phase of NbSi2 was formed with a homogeneous thickness of about 10 μm above 1073 K. The oxidation resistance of pure niobium with this coating layer was improved. During the oxidation at the high temperatures, Nb5Si3 was formed at the interface between the Nb substrate and the NbSi2 layer. Due to this intermediate layer formation, the oxidation resistance became better than for pure NbSi2.

Formation and crystallization of Al-Fe-Si amorphous alloys

Rapid solidification experiments of Al-based Al-Fe-Si ternary alloys have been performed both by the gun and single roller methods. Glass forming tendency is found to be largest near theβ-phase (Al9Fe2Si2) composition, where the amorphous state is obtained both by the gun and single roller methods. Crystallization behaviour of amorphous AlFe13.0Si17.4 alloy, nearβ-phase composition, followed the course of (i) the appearance of fineα-Al particles and (ii) the transformation of the matrix intoβ-phase. The ratio of crystallization temperature and the melting point,Tx/Tm, for AlFe13.0Si217.4 amorphous alloy is smaller than 0.5 indicating the difficulty of glass formation of these alloys.

Rapid fabrication of self-ordered porous alumina with 10-/sub-10-nm-scale nanostructures by selenic acid anodizing

Anodic porous alumina has been widely investigated and used as a nanostructure template in various nanoapplications. The porous structure consists of numerous hexagonal cells perpendicular to the aluminum substrate and each cell has several tens or hundreds of nanoscale pores at its center. Because the nanomorphology of anodic porous alumina is limited by the electrolyte during anodizing, the discovery of additional electrolytes would expand the applicability of porous alumina. In this study, we report a new self-ordered nanoporous alumina formed by selenic acid (H2SeO4) anodizing. By optimizing the anodizing conditions, anodic alumina possessing 10-nm-scale pores was rapidly assembled (within 1 h) during selenic acid anodizing without any special electrochemical equipment. Novel sub-10-nm-scale spacing can also be achieved by selenic acid anodizing and metal sputter deposition. Our new nanoporous alumina can be used as a nanotemplate for various nanostructures in 10-/sub-10-nm-scale manufacturing.

Thermodynamic description of the Pb-O system

The phase relations and thermodynamic properties of the Pb-O system are reviewed and assessed. The transformation temperature between PbO and Pb3O4 was also experimentally reinvestigated. A model description of the Pb-O system is then proposed and thermodynamic parameters are optimized. The values calculated from the resulting consistent set of Gibbs energy functions are compared with experimental data and discussed.

Conversion of unused heat energy to electricity by means of thermoelectric generation in condenser

Thermoelectric power generation has the potential to recover a large amount of energy loss at the vapor condensers in the steam-based power plants. A suitable arrangement of thermoelectric modules was designed from the heat transfer theory in the cylindrical heat exchanger. Even under the practical operation limits, 150 kW can be generated by the thermoelectric conversion.

Mathematic simulation on thermoelectric power generation with cylindrical multi-tubes

Abstract Analytical expression of electric power was deduced in case of the large-scale cylindrical thermoelectric tubes exposed to two thermal fluids. The output powers of the proposed six geometrical arrangements were mathematically solved from heat transfer theory, and compared with the flat panel systems. The maximum output was the largest in the ideally cooled systems. In the other realistic systems, it was the largest for the system of the counter flow with a single thermoelectric tube. The multiplication of thermoelectric panels can shorten significantly the device length, although the output from the multi-tubes decreases only a little. For example, the double helical tubes (T2CH system) can generate 96% output by 35% length, compared with the single tube in the counter flow (T1C system).