Tomoharu Fukazawa

Measurements of diffusion coefficients of metallic melt under microgravity?current status of the development of shear cell technique towards JEM on ISS

The microgravity condition is one of the ideal conditions for the measurements of diffusion coefficients in high temperature melts because of the absence of convection in the liquid sample. Many kinds of experimental techniques, such as the long capillary method and the shear cell method, have been devised in ground based researches for the measurement of diffusion coefficient in such high temperature melts. Recently, the shear cell technique coupled with the microgravity condition was applied to the measurements of high temperature metallic melts. This technique enables us to measure the diffusion coefficient with high precision. In this paper, a brief discussion is given about the trends of previous diffusion experiments in space performed particularly by Japanese researchers. Recently, the Japanese space agency, JAXA, has developed the shear cell technique for future space experiments in JEM. The current status of the development of our shear cell technique is summarized and new results are presented as typical experiments on the ground by using test samples, for example, liquid silver–gold alloys.

X-ray observation of shear cell experiments for impurity diffusion of Au in liquid Ag

The most effective way to obtain liquid diffusion measurements is the shear cell technique. In this method, a diffusion couple is only joined at a target temperature, to avoid diffusion during heating and cooling and to avoid solidification effects. Numerical simulations confirm that the misalignment of a diffusion couple hinders precise diffusion experiments. Hence, the sample should be observed during the shear cell experiments to confirm the correct alignment. A direct X-ray observation system was thus specifically developed and the impurity diffusion of Au in liquid Ag was successfully measured using this apparatus.