Convection in a Czochralski crucible - Part 1: non-rotating crystal

A Czochralski melt is simulated in a model experiment and by numerical anal ysis. We use a transparent fluid (0.65 cSt silicone oil with Pr=6.8) which is contained in a transparent sapphire crucible (40 mm inner diameter, 40 m m height, crystalline material). A copper rod (e.g. 14 mm diameter) is used to simulate the growing crystal. An imposed temperature difference between the crucible and the crystal dummy gives rise to convective flow in the fl uid. Forced convection by crystal rotation has also been applied but will b e treated in part 2 of this paper. Our experiment models to a good degree t he growth of oxide and fluoride crystals from noble metal crucibles. Flow v isualization and flow velocity measurements are performed. We report the fl ow patterns observed in the fluid for different parameters (temperature dif ference, fluid depth, meniscus, free surface cooling). We observe a separat ed surface tension driven convection roll at the free surface and a "cold j et" beneath the crystal dummy. The Row is strongly affected by thermocapill ary forces. The experimental results can be used as benchmarks to test nume rical simulation programs for Czochralski growth. Numerical simulations are performed (2D, steady, axisymmetric). The simulation results compare favor ably with the experimental data. In a parametric numerical study the relati ve importance of thermocapillary and buoyant forces is investigated. (C) 20 01 Elsevier Science B.V. All rights reserved.