Supersonic Thermal Plasma Expansion Process for Nanoparticle Synthesis : An Experimental and Numerical Study

Thermal arc plasma is one of the most preferred processing medium for synthesis of nanocrystalline materials in bulk quantities. The extremely high temperature, good crystallinity, sharp heating/cooling rates, relatively compact reactor size, appearance of non equilibrium phases in extremely fine particles are the highlights of this method. In this experiment, a segmented plasma torch, a special variety of non-transferred plasma torch is used, which produces highly stable plasma and constricts the flame better to produce higher ion density ensuring good reaction kinetics. A novel thermal plasma assisted technique i.e. supersonic thermal plasma expansion process is used for synthesis ceramic materials, in the form of crystalline nanoparticles. The reactants in gas phase are injected into plasma jet, which then expands to supersonic velocity, while moving through a converging nozzle, into a sample collection chamber maintained at lower pressure. The expansion produces a one-dimensional temperature gradient along the flow and negligible boundary layer irregularities, ensuring particle condensation in gas phase with narrow size dispersion.