Injection of hot particles in the plasma flame

This study deals with experimental and theoretical investigations of prehea ting of the particles injected into a flame during the process of atmospher ic plasma spraying (APS). Prior to the injection in the flame, the particle s, delivered from the powder feeder, were heated in a carrier gas. The expe rimental devices to preheat the carrier gas, based on a principle of linear , superficial, and volume heating are discussed. The particle velocity and temperature in the pipeline connected to a preheating device were estimated theoretically using a simple analytical model. Two types of preheating dev ices were submitted to preliminary tests. The temperature of the carrier ga s was measured using a thermocouple for a volumetric device working with a gliding are discharge. The microstructure and properties of chromium oxide coatings plasma sprayed with the aid of a superficial preheating device are also presented and discussed.