The measurement of precise solute diffusion coefficients in molten metals and semiconductors

The measurement of precise solute diffusion coefficients in molten metals and semiconductors is of fundamental importance when studying and modeling metallurgical and crystal growth processes. Unfortunately, buoyancy-driven convection influences terrestrial experimentation so precise solute diffusion data cannot be generated without the use of a microgravity environment. In order to perform diffusion experiments in space, existing experimental techniques must be modified.; The long capillary and the shear cell techniques have been adopted for our planned liquid diffusion experiments in microgravity conditions. Experimental parameters, such as the sample dimensions and diffusion time have been determined and are fully discussed in this report. The cast-coating technique for long capillary diffusion couple preparation has been refined. A modified shear cell has been developed, which can be used to measure the diffusion coefficient of the liquids with high vapor pressure and also provide for safe operation in a manned space vehicle.; Comparative experiments have shown that buoyancy-driven convection exists in the liquid during ground-based diffusion experiments even when used in a vertical orientation in a small temperature gradient to reduce convection. It was found that the diffusion coefficients of antimony in lead obtained terrestrially are remarkably similar to the values obtained in space. This suggests that radial temperature gradients in the diffusion samples cause buoyancy-driven convection, which enhances solute transport and increases the measured diffusion coefficient value. However, if the density of the solute is significantly less than that of the solvent, then the radial-temperature-gradient-induced flow will be minimized. The significance of this effect may be gauged from the fact that, while the solute antimony gave 1 g results close to the microgravity values, it was present only in a small section of 1% alloy at the upper end of the diffusion couple at the start of the diffusion period.