Convection and segregation during vertical Bridgman growth with centrifugation

• Published in: Journal of crystal growth Vol. 187; no. 3; pp. 543 - 558
• Main Authors: Wilcox, W.R., Regel, L.L., Arnold, W.A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-05-1998; Elsevier
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Growth from melts; zone melting and refining; Materials science; Methods of crystal growth; physics of crystal growth; Physics; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Segregation; Centrifugation; Digital simulation; Theoretical study; Experimental study; Convection; Bridgman method; Crystal growth from melts
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/S0022-0248(97)00885-3

Both experiments and numerical simulations have shown that centrifugation can have a large influence on convection and segregation during vertical Bridgman growth. The buoyancy-driven flow pattern differs dramatically from that observed without centrifugation. The Coriolis force introduces an azimuthal circulation that cannot be seen via the usual side view of the ampoule. The flow pattern and intensity depend on the rotation rate, centrifuge arm length, and interface shape. Several experiments and numerical simulations exhibited a minimum in axial convection or segregation at a particular rotation rate. A correlation for these results indicate that the minimum in convection occurs at a rotation rate that is independent of the centrifuge arm length, proportional to the square root of the depth of the concave interface, and inversely proportional to the ampoule radius. In attempts to better understand this minimum, three simple models have been proposed, here called “buoyancy-Coriolis balance”, “flow transition”, and “thermal stability”. The thermal stability model is developed here. Unfortunately, none of these models agree with the correlation to the published experimental and numerical results. Numerical simulations show that rotation of a vertical ampoule about its own axis at a constant rate may be a better method to control convection.