RF Ar-H2 plasma spraying of metallurgical grade silicon particles (80-125 µm) was used in order to combine the purification and the deposition process of silicon particles with a high deposition rate (300 - 600 µm). The hydrogen and oxygen content of the plasma gas turned out to be of a great importance to purify metallurgical silicon powders. The whole process was investigated through ex-situ characterisation of the deposits and on-line diagnostics of the plasma which results matched quite well with the mathematical modelling. The deposits were characterised using SEM, EDX analysis, SIMS, XPS in order to explain the composition and overall properties of the layers in view of their use in photovoltaic applications. Characterisation of silicon deposits was completed by the hydrogen rate analysis using exodiffusion method. Hydrogen trapping in plasma sprayed deposits was found in order of 1019 at/cm3. The oxygen contained in the original powders (30%) was decreased down to 3 - 5% in the deposits. Finally, the on-line diagnostics of the plasma used was : Laser Doppler Anemometry (LDA), Laser Doppler Granulometry (LDG) and Optical Emission Spectroscopy (OES). The mean velocity and surface temperature of particles was found to be in agreement with modelling results.