The influence of alumina additive from 1 to 5 wt. % upon the microstructure and ionic conductivity of ZrO2-8 mol % Y2O3 (YSZ) ceramics, deposited by means of plasma spray technology, was investigated. Plasma sprayed films have been analysed using scanning electron microscopy (SEM) and X-ray analysis (XRD). The microstructural examination reveals that alumina addition decreases the porosity and microcracks of plasma sprayed YSZ. Analysis of SEM micrographs shows that the amount of 5 wt. % alumina substantially improves the microstructure of plasma sprayed zirconia. The crystal structure of all plasma sprayed samples consists of cubic zirconia and α-alumina. By the data of ionic conductivity measurements, no significant influence of annealing at 1073 K for 10 h was noticed on characteristic temperature dependences of σ for plasma sprayed YSZ. Alumina doping from 2 to 5 wt. % considerably increases the ionic conductivity of plasma sprayed zirconia. The higher values of ionic conductivity were obtained when 5 wt. % of Al2O3 powder was added to YSZ.

The paper describes a process for preparation of yttria stabilized zirconia (YSZ) coatings by plasma spray technique employing non-equilibrium plasma spray technology at atmospheric pressure. Yttria-stabilized zirconia (10-15 wt. % Y2O3) powders (10-105 µm in diameter) have been used. Plasma sprayed coatings have been characterized using scanning electron microscope (SEM) and X-ray diffractometer (XRD) for the microstructural study and phase analysis as a part of a process optimisation study. The dependence of microstructure of coatings on initial powder characteristics and the influence of deposition temperature in the range of 3000-3350• C on the structural characteristics of plasma sprayed coatings were investigated. By the data of XRD analysis, all samples were obtained with cubic crystal orientation. It has been found that crystallite size has tendency to decrease with increasing the deposition temperature. YSZ deposited at 3150-3350• C are found to have a nanocrystalline structure with average crystallite size of 75 nm. The samples sprayed using coarse-grained powder feed are characterized by larger grain size and crystallite size. The main parameters influencing the coating formation are the properties of the initial powder and the plasma process temperature. The SEM analysis showed that the best temperature region for the deposition of YSZ coatings was about 3200-3350• C.

Interaction of plasma jet with hard ceramic particles was numerically investigated by means of "Jets&Poudres" software improved and applied to model a specific plasma jet. The data on free plasma jet, with injected dispersed particles, its temperature and velocity distribution, as well as particles' melting state are presented. It was found that dispersed particles achieve higher temperature and velocity values than plasma gas at dimensionless distance x/d = 8-12 from exhaust nozzle. Numerical investigations were compared with experimental data. The results show that applied numerical model of two-phase high temperature jet calculation is in good agreement with experimental data and could be used to determine the optimal plasma spray parameters for coatings with desirable characteristics.

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