Heating and acceleration processes of high melting point ceramic particles in pulsed plasma

Abstract Plasma spraying is gradually becoming an important technique in the materials processing field, its primary feature being the ease by which the area or thickness of the deposited film can be controlled. High‐temperature plasmas to heat ceramic particles with a high melting point have in the past been generated by dc power sources. Applying a pulsed plasma using a high current of the order of tens of kA is proposed for the plasma spraying of refractory materials. Numerical analysis of the short‐time heating and acceleration of the particles showed that alumina particles 20 μ in diameter reach the complete melting state after a residence time of 83 and 9.6 μs and a flying distance of 5.8 and 0.5 mm, when the temperature of the pulsed plasma is assumed to be 10,000 and 20,000, respectively, with a constant plasma velocity of 200 m/s. Experiments are then performed using a specially developed plasma torch with a pulsed discharged current of 24 kA peak and a duration of 400 μs. This current is provided from a capacitor with a maximum stored energy of 14 kJ. The simultaneous, in‐flight measurements of the temperature, velocity, and size were taken for alumina particles injected into the pulsed plasma. Results show that the surface temperature of the alumina particles reached values as high as 2700 to 3300 K, which was considerably higher than the melting point. Particle velocity was found to be around 200 m/s, which is comparable to that of dc plasma. The experimental results confirmed the applicability of pulsed plasma for the spraying of refractory materials.