Pulsed electrothermal powder spray

Abstract

A pulsed electrothermal powder spray apparatus and method increases coating particle velocities to the 2,000-4000 m/sec range. The apparatus includes a containment tube, which may be a reverse shock tube, having a capillary chamber section and a short barrel section. The tube is initially filled with an inert gas and powder is deposited in the barrel just downstream from the barrel's connection to the confined capillary discharge chamber. On receipt of a trigger signal, the muzzle shutter of the barrel section quickly opens, causing the inert gas to flow towards the open end of the barrel. A rarefaction wave propagates back up the barrel, towards the capillary chamber. Once the rarefaction wave reaches an electrode positioned at the front end of the capillary chamber, an arc discharge is triggered in the capillary, resulting in a quick rise in capillary temperature and pressure. Preferably, formation of the confined capillary arc discharge is triggered by a high voltage pulse generator which allows a lower, but still high, voltage pulse forming network to establish a main arc discharge between electrodes at each end of the capillary chamber. The increase in pressure and temperature resulting from the rapid electrothermal heating of the gas heats the powder deposited in the barrel and accelerates the powder down the barrel, through the muzzle opening and onto a target substrate. Control subsystems, gas delivery assemblies and cooling assemblies are included with the containment tube to form a highly efficient, easily controllable.