A particle image shape imaging (PSI) investigation of particles in a plasma jet

A necessary condition for the optimisation of plasma spraying processes is the capability to measure plasma jet, particle and coating parameters. Of special interest is the measurement of particle parameters such as number density, velocity, temperature, shape and size because these parameters influence the coating quality. In the following paper, recent developments of the innovative particle shape imaging (PSI) diagnostic [T. Streibl, Entwicklung eines bildgebenden Partikeldiagnostikverfahrens zur Untersuchung Thermischer Spritzprozesse, Dissertation, Universitنt der Bundeswehr, München, 2002] are presented. As far as possible, the PSI results are compared to these of a laser Doppler anemometry (LDA). he particle shape imaging (PSI) diagnostic the shape, size and velocity of particles can be determined. PSI is a laser based shadow image technique. The measurement volume is formed by the superposition of two laser beams generated by a beam splitter. A particle, being in the measurement volume, produces shadows in both laser beams. By a long distance microscope the shadows are imaged on an intensified CCD camera. Using a mirror and a photodiode array, the CCD camera is triggered with an adjustable delay time in order to determine the particle velocity. With the developed image processing software shape, size and velocity are calculated. The results are saved in a computer data bank for further statistical evaluation. The superposition of the two laser beams in the PSI system gives the opportunity to be used by an integrated standard LDA system. For different powder and plasma parameters, the behaviour of particles has been investigated in the area between the powder injector and substrate.