An automated plasma spray apparatus was designed to investigate experimentally the formation of splats (spread and solidified melted particles) by fully controlling key physical parameters (the velocity, temperature and size of the molten droplets impacting a substrate, and the temperature and surface condition of the substrate). The plasma spray apparatus made it possible to obtain a representative set of yttria-stabilized zirconia (YSZ) splats deposited on polished metal substrates (stainless steel or polished CoNiCrAlY sub-layers sprayed on nickel alloy substrates by low pressure plasma spraying) with full control of key physical parameters. The set of splats allowed verification of the theoretical characterization of metal oxide splat formation. Even without introducing empirical coefficients to the theoretical equations, quite good agreement between the calculated and experimental diameters and thicknesses of YSZ-splats was obtained over a wide range of various values of the key physical parameters. The results obtained will be first of all interest for optimizing the deposition of thermal barrier coatings and also for optimizing the deposition of the first monolayer of coatings of metal oxides sprayed onto metal substrates.
Methods for controlling the synthesis of the submicron (including nanosized) powder of titanium dioxide (titania, TiO 2 ) in a setup with a plasmachemical flow reactor were investigated. The synthesis of titania particles from gaseous titanium tetrachloride (TiCl 4 ) in the plasmachemical reactor by the chloride method was experimentally studied. The processes of formation and growth of particles depending on the type of the plasmaforming gas, flow rates of TiCl 4 ; and the quenching gas (air), reactor length, and mean-mass temperature in the reaction zone were considered. When using nitrogen as heat-carrying gas, a new approach of titania powder synthesis based on combining of reaction zone and quenching zone has been applied. Under these nonequilibrium conditions and substantial temperature gradients, this method enabled us to synthesize reproducibly ultrafine titania powders (30-50 nm) with a high content (80-87%) of metastable anatase crystal lattice. The results reveal that the powder properties can be efficiently controlled, i.e., one setup can produce titania with a required particle size and a type of the crystal lattice: anatase (A) or rutile (R). The experimental data are found to agree well with the results of numerical calculations.
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