Abstract
In a previous work, the authors determined that different mechanisms control in-flight particle oxidation in the core of a plasma jet and in its plume. In the core, convective movements within the liquid particle govern the oxidation kinetics if the plasma-to-liquid particle kinematic viscosities ratio is greater than 55 and the particle Reynolds number (Re) is more than 20. Convective movements entrain the oxide and dissolved oxygen from the particle surface towards its interior forming oxide nodules, and the fresh liquid metal is continuously renewed at the surface. Higher particle reactivity can be achieved in the plasma core. Convective movements cease in the plasma plume and the mass transfer from particle surface to its interior ends. Only classical surface oxidation continues, and the formed oxide covers the surface of the particles. The reaction kinetics are diffusion controlled and the oxidation rate decreases. In this present study, two austenitic stainless steel powders were air plasma sprayed using a dc plasma gun (PTF4 type) and were collected in an argon atmosphere. This paper reviews the influence of plasma spraying parameters on the oxide content in the collected particles. The studied parameters were plasma current intensity, hydrogen gas content in the plasma gas, and sprayed particle size. From the results, it can be concluded that plasma spray conditions favoring higher plasma to particle kinematic viscosities ratio and particle Re results in higher convective oxidation of particles in the plasma core.
