A reactor and process are described that allow the variation of the plasma deposition conditions such that a wide range of coating properties can be obtained. The reactor consists of three plasma torches mounted such that the deposition precursors can be injected centrally into the merging jets. This reactor has been used to deposit the different layers of a solid oxide fuel cell, including the very dense (99.5% density) zirconia electrolyte layer. Investigation of the zirconia layer showed a microstructure which has characteristics of both plasma sprayed coatings and vapor deposited coatings. The region of particle heating and acceleration has been characterized with enthalpy probes resulting in velocity and temperature fields. Calculations have been performed to describe the particle heating histories. The results show that a significant fraction of the particles evaporate and condense at the surface thus contributing to the formation of the dense layer. This hybrid process combines the possibility of obtaining high density coatings as with a PVD process with the rapid deposition rate of a plasma spray process.

Plasma sprayed tungsten and tungsten-copper coatings are being developed for potential application as plasma facing materials for fusion reactors. Initial spray tests indicated difficulties in tungsten melting and in-flight oxidation. Numerical modeling was performed to help explain these issues. A complex study of the process and its products was performed, including: in-flight diagnostics, characterization of isolated splats, and structure, composition, thermal and mechanical properties of the coatings. Based on these results, the process was optimized, with respect to powder size and various spraying parameters, to improve melting of the particles, reduce oxidation and increase the deposition efficiency.