The thermal state of a small spherical body in an air plasma

Heat exchange between an air plasma and a low-heat-capacity spherical body made from a refractory (tungsten) or fusible (aluminum) material is studied under conditions when the body exhibits the properties typical of either a thermally thin or thermally thick body. The problem is solved for an unperturbed plasma temperature of 5000–20000 K, a pressure of up to 1 atm, and a body (particle) size of 10 μm to 1 cm. The model developed accounts for the possible phase transitions at melting and boiling. It is shown that, under proper physical conditions, a refractory particle can relax to a steady thermal state (in various aggregate states). This property can be used in plasma sputtering of refractory coatings, which requires the preparation of a spatially homogeneous thermal state of the sputtered macroparticles that underwent a metal-liquid phase transition.