Interface control by rotating submerged heater/baffle in vertical Bridgman configuration

Abstract

Toroidal flow was used to control the shape of the solid-liquid interface, while growing NaNO3 crystals in vertical Bridgman configuration. The flow was driven by a disk-shaped rotating Submerged Heater/baffle (SH). The flow in the inner melt, below the rotating SH/baffle, closely resembles the flow in Czochralski melts. The experiments were conducted in a transparent furnace which allowed side view to the solid-liquid interface. Without baffle rotation, interface was concave. For zero growth rate, convex interface was obtained typically at 15 rpm. The degree of convexity increased with rotation rate. While growing NaNO3 at 3.5 mm/h and 5.5 mm/h, convex interface was maintained at 45 rpm.Detailed 3D CFD numerical simulations are in solid agreement with the NaNO3 experiments. The rotating baffle process is particularly useful for growing crystals of low thermal conductivity because flow, generated by baffle rotation, carries heat radially out bypassing slow conduction through the crystal.