Ceramics-Silikáty 45, (1) 1 - 8 (2001)

Different trajectories of powder particles in the plasma jet during spraying result in different states of the particles/molten droplets on impact, resulting in the variation of microstructure and homogeneity of the deposits. The distribution of trajectories in the jet is related to the overall spray setup, i.e. to the spray parameters such as number and geometry of powder injectors, flow rate and type of the powder feeding gas, powder size distribution and its chemical and mechanical properties, etc. This paper studies the deposits microstructure and properties (density, porosity, phase composition, etc.) and relates them to the distribution of particles in the plasma jet during spraying. Free-standing tubes are selected then as an example of the industrially important application and their microstructure is compared with microstructures of flat samples documenting microstructure variation related to different particle trajectories in the jet.The two materials studied are Alumina (Al₂O₃ + 3wt.% TiO₂) and natural ZrSiO₄. Significant microstructure variation related to particle trajectories were found for alumina deposits; for example, the alpha phase content varied between about 5 and 50 %, the porosity volume varied between about 3.8 and 8 % (about 2x), and the pore surface area varied between about 1.5 × 10⁴ to about 6.5 × 10⁴ cm² cm⁻³ (about 4x). Also the microstructure anisotropy documented by small-angle neutron scattering varied significantly. Variation in the microstructure of the ZrSiO₄ seemed to be less significant.