Modelling the growth of triglycine sulphate crystals in Spacelab 3

摘要

Two triglycine sulphate crystals were grown from an aqueous solution in Spacelab 3 aboard a Space Shuttle. Using a diffusion coefficient of 0.00002 sq cm/s, a computerized simulation gave reasonable agreement between experimental and theoretical crystal sizes and interferometric lines in the solution near the growing crystal. This diffusion coefficient is larger than most measured values, possibly due to fluctuating accelerations on the order of .001 g (Earth's gravity). The average acceleration was estimated to be less than .000001 g. At this level, buoyancy driven convection is predicted to add approx. 20 percent to the steady state growth rate. Only very slight distortion of the interferometric lines was observed at the end of a 33 hr run. It is suggested that the time to reach steady state convective transport may be inversely proportional to g at low g, so that the full effect of convection was not realized in these experiments.