Chemical vapor transport and thermal behavior of the GeSe-GeI4 system for different inclinations with respect to the gravity vector; Comparison with theoretical and microgravity data

Abstract

The diffusive and convective mass flux in closed tube chemical vapor transport of the GeSe-GeI4 system has been investigated as a function of inclination of the temperature gradient with respect to the gravity vector. A strong effect of inclination on the degree of convective contribution to mass transport was observed. Computed streaming-diffusive transport rates of this system are compared with experimental data observed for the vertical, stabilizing configuration and for microgravity conditions. At low to medium pressures, good agreement between experimental and predicted results is obtained, at higher pressures experimental transport rates are about 40% greater than predicted. Microgravity flux data of this system are about 300% greater at the highest pressure compared to experimental (vertical, stabilizing) rates on earth and about 400% greater relative to those predicted by diffusion. Transport rates for other ampoule orientations reveal progressively increasing convective contributions with increasing inclination relative to the vertical, stabilizing orientation, reaching in general the highest rates for the vertical, destabilizing orientation. Studies of the thermal behavior inside closed transport ampoules indicated changes of the temperature profile owing to natural convection. In addition, small amplitude (~ ±1°C) temperature oscillations were observed inside transport ampoules under both horizontal and vertical, stabilizing conditions. These could possibly be related to gas phase reactions. Very large oscillations (±25°C) observed under vertical, destabilizing conditions and at 1.5 atm pressure are caused by natural convection.