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 alloys Al 2 O 3 +13wt.%TiO 2 and Al 2 O 3 +40wt.% TiO 2 were plasma sprayed onto aluminum rolls coated initially with Ni20Cr bond deposits. The coatings were subsequently ground, polished and submitted to laser engraving. The engraving, similar to that applied for anilox rolls manufacturing, enabled production of three different patterns with the line densities of 60, 100 and 200 1/cm and depths of about 80, 50 and 10 µm correspondingly. The patterns were engraved under angle of 60° that corresponds to a honeycomb geometry of cells. Emission current, for the electric fields up to 150 V/µm, was in the range of 10-7-10-4A for coatings containing 13 wt.% of titania and, in the range 10-11–10-9 A for that of 40 wt.% of titania. The SEM observations of engraved coating morphology was made in order to find the electron emission spots.