CHARACTERISATION OF AL₂O₃ PLASMA SPRAYING BY ATOMIC EMISSION SPECTROSCOPY AND NEAR INFRARED PYROMETRY

Plasma temperature measurement and 2D light intensity mapping of an industrial plasma spraying equipment developed by 2PS (14 - 45 kW, Ar/H₂ plasma, AL₂O₃ powder) is performed based on atomic emission spectroscopy and near infrared pyrometry. The influence of the process parameter variations onto the plasma electron density with and without AL₂O₃ powder has been identified.
Plasma temperature and electron density are determined by Atomic Emission Spectroscopy (a monochromator with focal length of 320 mm is used, allowing spectra acquisitions on a wide spectral range up to 70 nm) based on the H-beta line broadening in the assumption of plasma equilibrium. A 2D pyrometer (vision zone 10 × 10 mm²) with the 0.860 µm spectral band has been applied to obtain the radiative intensity mapping of the jet. A 1 spot monochromatic pyrometer (in the 1.5 µm spectral range) sighted to the impact area has been used to control in real time the substrate brightness temperature versus process parameters.
The following variations of operational conditions were studied: hydrogen flow rate (0-15 l/min), powder flow rate (10-20 g/min) and current (500 - 700 A), argon flow rate was fixed (70 l/min). It has been found that along the jet axis (up to 40 mm from the nozzle) the temperature and the electron density vary in the range 13 000 - 11 000 K and 1.4 10¹⁷ - 4 10¹⁶ cm⁻³ respectively. The 2D radiation intensity fields are rather sensitive to the variation of current and H₂ flow rate and visualise the plasma flow pattern.