Gravity driven disturbances during Bridgman crystal growth in space

The purpose of this paper is to analyse the crystal growth experiments perf ormed under microgravity conditions in order to learn, with the help of the existing theory, the degree to which residual convective level acts on che mical segregation. A survey of the existing bibliography on chemical segreg ation in crystal growth experiments in space is performed and the results a re analysed with the help of the existing order of magnitude analysis. It a ppears that useful data is restricted to the axial segregation in the cryst als and that little attention has been paid to quantitative analysis of rad ial or micro segregation under controlled growth conditions. Restricting the analysis to the axial segregation results, they show a good agreement with the theoretical prediction of the threshold between diffusi on and convection dominated transport in the liquid. From the convection do minated experiments, generally obtained onboard the space shuttle, it appea rs that the effective gravity level acting on the fluid was or the order of 10(-5)g(0). Considering this validation of the theoretical results, it is concluded tha t the experimental parameters to apply in order to get diffusive transport conditions during crystal growth from the melt in space can now be easily a nd reliably computed. (C) 2000 Elsevier Science Ltd. All rights reserved.