The paper aims at the development of coating having a gradient of crystal grain size. Thick, inner layer was plasma sprayed using coarse TiO 2 powder. This layer has the thickness ranging from 30 to 50 µm. Thin, outer layer of thickness smaller than 10 µm, was plasma sprayed using different aqueous suspensions of fine powders of TiO 2 . The morphology of coarse and fine powders was characterized using scanning electron microscope (SEM) X-ray diffraction (XRD). Electronic emission was tested using home made setup. X-ray diffraction enabled to find out an interesting result which is formation of a mixture of rutile and anatase in suspension sprayed coatings. This was also confirmed by Raman spectroscopy investigations. The technology of suspensions plasma spraying was optimized to obtain homogeneous and dense deposits. The sizes were in the range of tenth to one hundred nanometers in initial powders and get clearly smaller in the coatings sprayed using coarse powder but remained quite similar in suspension sprayed films. X-ray photoelectric spectroscopy (XPS) was used to analyze quantitatively TiO 2 powders and coatings. Electronic emission was correlated with phase composition of the coating and their grain size.

The powders of Bi 2 O 3 and Bi 2 WO 6 were prepared by calcination, sintering and crushing. Their sizes were screened out to be in the range from 50 to 150 µm. The initial spray parameters were optimised using numerical codes simulating the behaviour of powders in plasma jet. Spray experiments onto metallic substrates were carried out using commercial plasma torch SG-100, equipped in an external powder injector. The spraying of coatings was carried out by varying electric power input to plasma, distance of spraying and the geometry of injector. The morphology of sprayed coatings was investigated using scanning electron microscope (SEM). X-ray Diffraction (XRD) of Bi 2 O 3 coatings revealed the α-Bi 2 O 3 phase, present in the initial powder, and also β-Bi 2 O 3 in some of the samples. Reduction of oxide into metallic Bi at spraying process was not discovered using XRD and Differential Thermal Analysis (DTA). Bi 2 WO 6 powder was crystallized in an orthorhombic phase that transformed into tetragonal one at spraying. Finally, the X-ray Photoelectric Spectroscopy (XPS) investigations revealed a possible presence of Bi(OH)3 phase in the coatings sprayed using Bi 2 O 3 powder.