Measurement of solutal and thermal diffusion in systems subjected to rapid cooling under microgravity during parabolic flight

In the process of crystal growth from solution under normal gravity, double diffusive convection occurs due to thermal and solute gradients. This natural convection disturbs the pure thermal and solutal diffusion field around a crystal, and phase change phenomena during the diffusion process cannot be seen directly. Microgravity environments, generated by parabolic flight, were used during experiments in order to suppress the double diffusive convection. In-situ measurements of the diffusion fields were carried out using a real-time phase-shift interferometer. The saturated solution around a seed crystal of NaClO₃ was subjected to rapid cooling during the duration of microgravity by Peltier elements in the test cell. A number of temperature profiles were applied during the microgravity experiments. In particular, the diffusion phenomena measured for a system subjected to rapid cooling to -17°C cannot be explained in terms of a conventional diffusion process nor by the kinetics of crystal growth.