A shrouded-plasma spray process is described for the production of a metastable powder, deposit or preform. A high enthalpy atmospheric DC arc-plasma torch is used as heat source and a solution precursor as feed material. An aerosol-or liquid-jet of solution precursor is delivered to a steady-state reaction zone within the shrouded-plasma flame, where rapid and controlled precursor decomposition occurs. Depending on the operating conditions, the precursor material is pyrolyzed, melted or vaporized, prior to quenching to form a metastable nano-sized powder. This method is capable of processing a host of metastable materials, including the difficult-to-process refractory metals, oxide and non-oxide ceramics, as well as their composites. In this paper, we will discuss our results on multi-component oxide systems.

Cold Gas Dynamic Spray (CGDS), is a relatively new coating process in which small powder particles are accelerated to form coatings. Ductile metal powders are injected into a supersonic jet to achieve speeds of up-to approximately 1000m/s. Upon impact the powder particles dissipate their kinetic energy and form a coating without melting of the powder and unwanted heating of the substrate. In this process high deposition rates, at atmospheric conditions, of a wide range of ductile powders without phase change, grain growth or high residual stresses is possible. CGDS is ideal for production of coatings with bioactive materials, where it is desirable to maintain the chemical integrity of the powder in the coating. A twin powder feeder, that can feed two different materials in a cold gas dynamic spray system has been developed. The layered coatings of copper and aluminum are produced by this method are described.

A four inch external diameter copper reaction synthesis tube for attachment to an air plasma spray gun has been designed and constructed. This tube enables the entire hot plasma zone to be enclosed by flowing gas. The tube is water cooled, and enables control of the reaction/melting conditions for the materials that are injected into the plasma as dry powder, slurry or solutions. A supersonic nozzle is also incorporated into the design to promote powder production. Provision for capturing the reaction products in water is made and separation gives the final ceramic powders.