Characterization of plasma jet at low pressure

Low pressure plasma spraying has been attracted attention due to special properties of the expanded plasma jet which may probably deposit specific and unique structure coatings. The formation of the coatings is affected by plasma generation and working conditions. The operating parameters such as arc power, plasma gas flow rate, and chamber pressure have influences on enthalpy, temperature and velocity of plasma jet. In this paper, an enthalpy probe was applied to measure the enthalpy of argon-hydrogen plasma jet generated at chamber pressure of 3 kPa. Attempts were also made to measure the pressure of plasma jet by U-tube fixed on the enthalpy probe. The temperature and velocity of plasma jet were calculated by measuring the enthalpy and pressure at different axial distances of the plasma jet. The results showed that the temperature of plasma jet reaches to 11 000 K at 25 mm from nozzle exit, and then dropped slowly to 7 000 K at 400 mm. The velocity of plasma jet reaches the maximum value of 2 024 m/s from the nozzle exit about 25 mm. The Knudsen number of the plasma jet is about 1.0, so the heating capacity of the plasma jet is significantly reduced.