Takeshi Yoshikawa

A fundamental approach for the measurement of solid-liquid interfacial energy

Solid-liquid interfacial energies in alloys are important properties for the process design of materials production such as casting and crystal growth. Inadequate information exists on solid-liquid interfacial energies. Our aim for this study was thus to establish a method to measure solid-liquid interfacial energies in alloys from equilibrium interfacial shapes of solid-liquid-gas phases. Experiments were carried out on Cu-B and Ag-Bi systems where copper and silver were treated as solid phases, respectively. Since the determined values for solid-liquid interfacial tensions for both systems agreed with reported values or estimated values, it was clarified that solid-liquid interfacial energies can be measured by observing the interfacial shape.

Fundamental study for solvent growth of silicon carbide utilizing Fe-Si melt

Fe-Si melt is a candidate for use as an alloy solvent for rapid liquid phase growth of SiC because of the high solubility of carbon in molten iron. In this work, the equilibrium phase relationship between SiC and the liquid phase of the Fe-Si-C system was investigated at 1523 K by the phase equilibration technique, and was further studied with the thermodynamic calculation. It was found that Fe- 36 mol% Si melt equilibrates with SiC at the temperature and possesses the higher carbon solubility than silicon-based melt. The first trial of the SiC crystal growth experiment was then carried out with Fe- 36 mol% Si melt by means of temperature difference method, and formation of SiC layer was obtained on the graphite substrate. Accordingly, it was found possibility for rapid growth of SiC by the solvent growth method with Fe- 36 mol% Si melt.

Hydrothermal metallurgy for recycling of slag and glass

The authors have applied hydrothermal reactions to develop recycling processing of slag or glass. As an example, under hydrothermal conditions such as 200 300°C and 30 40MPa with H2O, powders made of glass can be sintered to become solidified glass materials containing about 10mass% H2O. When the glass containing H2O is heated again under normal pressure, the glass expands releasing H2O to make porous microstructure. H2O starts to emit just above the glass transition temperature. Therefore, when we have a glass with low glass transition temperature, we can make low temperature foaming glass. The SiO2-Na2O-B2O3 glass is a candidate to be such a foaming glass. In this paper, we describe our recent trial on the fabrication of the low temperature foaming glass by using hydrothermal reaction.

Unusual Wetting Behavior of Liquid Metals on Porous Layer Formed at Surface of Iron Substrate Prepared by Oxidation-Reduction Process

Unusual wetting behavior of liquid Cu was found on a surface-oxidized iron substrate in reducing atmosphere. Liquid Cu wetted and spread very widely on the iron substrate when a droplet was attached with the substrate in Ar-10%H2 after the surface oxidation of the substrate. The oxidationreduction process fabricates a porous layer at the surface of the iron substrate. The pores in the porous iron layer are 3-dimensionally interconnected. Thus, liquid metals, which are contacted with the reduced iron samples, penetrate into these pores by capillary force to cause the unusual wetting behavior. It has been already confirmed that liquid Ag, Sn, In and Bi show this phenomenon onto surface-porous iron samples as well as liquid Cu. This unusual wetting behavior of a liquid metal has been correlated to the normal contact angle of the liquid metal on a flat iron substrate.