Behaviour of cavity formation and convection in FeOx-SiO₂ melts under plasma arc

The behaviour of oxides melted by plasma arc has been studied. Oxides of FeOx and FeOx-SiO₂ were melted by argon plasma arc. A direct-current-transferred-type plasma generator was employed. Observations of the sample surface revealed that a cavity formed in the region where the plasma arc was directed and that surface flow was operative in the direction from the centre toward the edge of the melt. The depth of the cavity was governed by the balance between the hydrostatic pressure and the sum of the pressures caused by the arc and the argon gas flow. The main driving force of convection on the sample surface was the aerodynamic drag force. The temperature distribution was dependent on both the argon gas flow rate and the viscosity of the sample, because the heat from the plasma arc was mostly transported by convection on the sample surface.