NANOMATERIAL DEPOSITS FORMED BY DC PLASMA SPRAYING OF LIQUID FEEDSTOCKS

An experimental system consisting of an axial feed plasma gun, a varia ble-rate liquid delivery system, a liquid atomizer-feeder, and a subst rate movement and control system was designed and assembled for prepar ing nanograined ceramic deposits. Sprayed deposits were produced with different spray and sol feed parameters and investigated in both the a s-sprayed and heat-treated conditions. As-sprayed deposits were predom inately hydroxide phases and were strongly adherent to the substrates. Postspray heat treatment at 873 K led to conversion of the alumina an d zirconia deposits to gamma-alumina and tetragonal zirconia phases, r espectively. Subsequent heat treatment at 1273 K resulted in densifica tion of the deposits and formation of high-temperature phases. A small increase in the grain size was observed with heat treatment, but the specimens still retained nanosized grains.