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In this paper the melting mechanism of granular raw powders by argon-oxygen induction thermal plasma (ITP) for vitrification has been described from both numerical and experimental point of views. A 2-dimensional LTE (local thermodynamic equilibrium) model for argon-oxygen induction thermal plasma has been developed to simulate the flow and temperature fields within the plasma torch for various flow conditions of carrier gas taking into account the effects of species diffusion. The model included a metal tube inserted into the torch for powder and carrier gas injection. Simulated results revealed that the higher the flow-rate of carrier gas, the lower the temperature profiles around the centerline of the torch, and the higher the axial plasma velocity. The average particle size of quenched powders became smaller and the softening temperature decreased with higher flow-rate of carrier gas, because of shorter relaxation time and lower temperature respectively. The numerical results well explained the experimental findings and provided a roadmap for the parameter optimization in the melting process.