Papers by Keyword: Zone Refining

Abstract: Vanadium alloys are highly promising as structural materials of fusion reactor blanket, owing to their excellent high-temperature strength, and good compatibility with liquid metal lithium, which functions as both a coolant and a fuel tritium breeder material. Chemical composition of V-4Cr-4Ti has been selected as the primary candidate after systematic investigations into its neutron irradiation properties. Since V and Cr do not produce long-lived radioactive isotopes emitting high-energy gamma rays even under intense neutron irradiation conditions, low-activation characteristics are primarily governed by Ti and detrimental high-activation impurities, such as Co, Cu, Fe, Mo, Nb, and Ni. Very early material recycling, such as remote recycling within ten years, and re-use even in the same fusion reactor is achievable through effective impurity removal and minimization of Ti concentration. This paper discusses the progress in and mechanisms of vanadium metal refining. Additionally, the present paper reviews recent results and current status of redesign efforts for the Cr and Ti concentration balance to identify a new high-Cr and low-Ti composition, maintaining various attractive properties of the V-4Cr-4Ti alloy.

Abstract: As the silicon melting point is very high (1414 °C), the temperature in the solid fraction, near the interface solid/liquid during solidification is also high and this can provoke a solute redistribution in the solidified portion. This phenomena is called back diffusion. So, it is important to estimate the potential of back diffusion during the solidification processes. This calculation is complex and there is commercial software, such as DICTRA, to do this in binary alloys. For zone melting, a simple method to predict the extension of the back diffusion is not available. In this study, it was developed a simple method to evaluate the back diffusion during zone melting, which does not require computational calculation.

Abstract: It has been generally known that the refining efficiency in zone refining process depends on travel rate, number of pass and distribution coefficient of impurity. In the present study, the effect of distribution coefficient on copper purification was investigated by zone refining process. A numerical model capable of predicting the solute redistribution at any stage of zone refining was proposed. The composition profiles of each segment at the given condition were compared with the results of micro hardness profiles. After zone refining, metallic elements were analyzed by GDOS (Glow Discharge Optical Spectroscopy) and GDMS (Glow Discharge Mass Spectrometry). The impurities Ag, Pb, S and Ti, whose distribution coefficients are below 0.5, were concentrated at the finishing position. Cr, Mn, Si and Zn, whose distribution coefficients are between 0.5 and 1, were distributed irregularly. Fe and Ni, whose distribution coefficients are greater than 1, moved to the starting position. It was found that zone refining process was actually effective to remove impurities whose distribution coefficients are below 0.5. The experimental results agreed well with the simulation result.