Probe Temperature Measurements and Optical Emission Spectroscopy in Vacuum Plasma Spraying Process Control

Abstract

The investigations on a vacuum plasma spray process under different H2/Ar working gas flow without and with powder
injection were carried out. The tungsten probe was placed inside the vacuum chamber and it’s temperature was evaluated
by means of the optical pyrometer. The factorial orthogonal central composite experimental plan design allowed us to
get an empirical equation of the probe temperature distribution in the plasma torch for 25 l/min – 31 l/min and 4 l/min –
8 l/min interval of Ar and H2 gas flow respectively. To study the processes occurring in vacuum plasma spraying the
optical emission spectroscopy has been employed as well. The optical emission spectrum consisted of hydrogen Balmer
series and excited argon lines before the powder injection into the plasma. After injection of YSZ, NiO powder mixture
into the plasma, the sharp peaks appeared in the wavelength range of 380 nm – 480 nm. The correlation between the
deposition rate of the vacuum plasma spray process and the integrated intensity in the wavelength range of 380 nm –
480 nm of optical emission spectrum was examined in the present work.