Role of Vibration-Induced Streaming in Float-Zone Crystal Growth

The streaming induced in a short vertical liquid column by the vibration of one of the supporting end walls has been utilized in this novel study. Vibration essentially drives a surface flow in the zone away from the vibrating wall, with the return flow in the bulk towards the wall. Preliminary measurements of the surface streaming velocity show that it increases with the frequency and amplitude of vibration and the zone length, and decreases with the viscosity of the zone liquid. This controlled surface streaming has been employed to balance a opposing, steady thermocapillary flow in model half-zones of silicone oil and Sodium Nitrate. In addition, in a float-zone solidification experiment with Sodium Nitrate - Barium Nitrate eutectic as the study material, we have demonstrated that streaming-based balancing of thermocapillary flow promotes a planar solid/liquid interface and a uniform microstructure.