The mechanism of heat transfer from an RF plasma to a sintering sample and to the torch wall during plasma sintering at low pressures (1 to 50 torr) was investigated in this thesis. The investigation emphasized the influence of plasma pressure on the heat transfer rate to the surface of the sintering sample. The investigation was conducted through modeling and experimental work. A computer model of plasma sintering has been established in this study. The model employs the SIMPLER algorithm to solve the mass continuity and momentum equations, the electron and heavy particle energy equations, and the electromagnetic vector potential equation. It assumes a chemical equilibrium, 2-T plasma in steady state. It also considers the influence of the Knudsen number and magnetic field on the thermal conductivity of the plasma. The modeling results show that for a constant input power and pressures below 20 torr the heat transfer to the sintering sample increases if the plasma pressure decreases. The influence of the pressure is significant at pressures below 10 torr, and it becomes less pronounced in the pressure range between 20 and 50 torr. The RF plasma sintering model was verified through experiments. The experiments indirectly measured the heat transfer rate from the plasma to the sintering sample at various plasma pressures and power levels. The heat transfer measurements were performed by using a calorimetric technique. The experimental results show a fairly good agreement with the modeling results, although there are some discrepancies in the high power range. At plasma pressures below 5 torr, the chemical equilibrium assumption becomes less accurate and the sintering model under-estimates the heat transfer to the sample.
- Pub Date:
- January 1994