Optical Emission Spectroscopy Study of Plasma-Precursor Interactions in TiO2 Suspension Plasma Spray

The influence of plasma power on liquid precursor decomposition in suspension plasma spray (SPS) is studied with optical emission spectroscopy (OES). The precursors consist in a suspension of titania nanoparticles (TiO2) in water. The precursor decomposition was observed through the emission of the titanium element and of the TiO molecule, from which temperature and density maps were plotted. The resulting coating phase and microstructure were determined with X-ray diffraction and scanning electron microscopy, respectively. OES results have been corelated to the microstructure and phase composition of the TiO2 coatings at three different powers. The aim of this study is to bring a new understanding of the precursor decomposition inside the plasma and to fathom the effect of the power on microstructure and phase. Results show that OES temperature maps alone are insufficient to understand the SPS process; atomic and molecular species densities maps are of prime importance.