PHYSICAL VAPOR TRANSPORT OF MERCUROUS CHLORIDE CRYSTALS - DESIGN OF AMICROGRAVITY EXPERIMENT

Flow field characteristics predicted from a computational model show t hat the dynamical state of the flow, for practical crystal growth cond itions of mercurous chloride, can range from steady to unsteady. Evide nce that the flow field can be strongly dominated by convection for,gr ound-based conditions is provided by the prediction of asymmetric velo city profiles by the model which show reasonable agreement with laser Doppler velocimetry experiments in both magnitude and planform. Unstea dy flow is shown to be correlated with a degradation of crystal qualit y as quantified by light scattering pattern measurements. A microgravi ty experiment is designed to show that an experiment performed with pa rameters which yield an unsteady Bow becomes steady (diffusive-advecti ve) in a microgravity environment of 10(-3)g(0) as predicted by the mo del; and hence yields crystals with optimal quality.