Three-dimensional, transient simulations of the plasma flow inside different plasma spray torches have been performed using a local thermodynamic equilibrium model solved by a multiscale finite element method. The model describes the dynamics of the arc without any further assumption on the reattachment process except for the use of an artificially high electrical conductivity near the electrodes. Simulations of an F4-MB torch from Sulzer-Metco and two configurations of the SG-100 torch from Praxair are presented. The simulations show that, when straight or swirl injection is used, the arc is dragged by the flow and then jumps to form a new attachment, preferably at the opposite side of the original attachment, as has been observed experimentally. Although the predicted reattachment frequencies are at present higher than the experimental ones, the model is suitable as a design tool.

In the hypersonic plasma particle deposition process, vapor phase reactants are injected into a plasma and rapidly quenched in a supersonic nozzle, leading to nucleation of nanosize particles. These particles impact a substrate at high velocity, forming a coating with grain sizes of 10 to 40 nm. As previously reported, coatings of a variety of materials have been obtained, including silicon, silicon carbide, titanium carbide and nitride, and composites of these, all deposited at very high rates. Recent studies have shown that slight modifications of the process can result in nanosize structures consisting of single crystal silicon nanowires covered with nanoparticles. These nanowires are believed to grow in a vapor deposition process, catalyzed by the presence of titanium in the underlying nanoparticle film. However, simultaneously nanoparticles are nucleated in the nozzle and deposited on the nanowires, leading to structures that are the result of a plasma CVD process combined with a nanoparticle spray process. The combination of these two process paths opens new dimensions in nanophase materials processing.