Abstract Materials researchers discovered a series of promising oxide ceramic materials to serve for example in the field of solid oxide fuel cells (SOFC). This paper investigates the potential of the chemical vapor deposition (Thermal Plasma Chemical Vapor Deposition) supported by thermal high-frequency plasma for the deposition of Sr-doped La-Mn-Perovskite cathodes and Yttria-doped zirconia (YSZ) to demonstrate electrolytes of the SOFC. Aqueous solutions that evaporate completely in the plasma are used as starting materials. The microstructure of the layers produced depends on the position in the plasma jet at which the critical supersaturation of the precursor vapor is exceeded. Globular or stalky layers with growth rates of up to 30 micrometer/min are deposited. The homogeneity of the dopand distribution and the phase purity of the layers are excellent in the case of the YSZ. However, they have to be further improved for the perovskite layers through process modifications. Paper includes a German-language abstract.

Abstract Bond coats based on bioinert ceramic materials such as titania and zirconia were developed to increase the adhesion strength of the coating system hydroxyapatite/bond coat to Ti6A14V alloy surfaces used for hip endoprostheses and dental root implants. The bond coats improved the adhesion strength, measured by a modified ASTM D3167-76 peel test, by 50 to 100% and also the resorption resistance as determined by in vitro leaching in simulated body fluid (Hank's Balanced Salt Solution, HBSS) for up to 28 days.

Abstract Suspensions of cobalt spinel (Co3O4) powders were rf plasma sprayed to form electrocatalytically active anode layers. Stable cobalt oxide suspensions of low viscosity exceeding 50 wt% solid phase have been processed. A spheroidization study revealed the formation of large spherical powder particles (- 30 + 80 µm). Cobalt oxide coatings were produced by rf suspension plasma spraying. The porosity was controlled by optimizing spray distance and reactor pressure. The main disadvantage of the thermal plasma processing of cobalt spinel is that the decomposition of the spinel phase into CoO could not be prevented, not even with the application of an 80% oxygen plasma. However, with a relatively low power oxygen plasma post-treatment, the deposited CoO layers can be oxidized to Co3O4, greatly improving the electrochemical performance of the anode layers.

Abstract Oxide-bonded silicon nitride (OBSN) powders have been developed to address thermal spray problems associated with high temperatures. This paper examines how such powders perform when applied via detonation gun (DGS) and atmospheric plasma spraying (APS) with axial powder injection. All coatings were characterized using optical microscopy and X-ray diffraction with additional tests being performed on DGS coatings. For the first time, relatively dense Si3N4-rich coatings with an oxide binder phase were produced, and some of the DGS coatings were found to be sufficiently wear resistance for industrial use.

Abstract Fine (median size 6 μm and 0.3 μm) cobalt spinel (Co 3 O 4 ) powders were processed suspended in a suitable liquid phase. Suspensions exceeding 50 wt.% solid phase content were successfully injected into an inductively coupled plasma. Spheroidized powders with large particle size (up to 80 μm) were prepared, and cobalt oxide coatings were produced by this novel RF-SPS method. The microstructural features of the coatings can be controlled by parameter optimization similarly to plasma spraying of dry powders. Numerous variations of the physical and chemical conditions of the process were performed in an attempt to overcome the main disadvantage of the process, i.e. the decomposition of the spinel phase to CoO. So far, the spinel phase could be reestablished only by a post-treatment of the deposited coatings with atomic oxygen in the RF plasma.

Abstract Thermal spraying of silicon nitride has been considered impossible because the high temperatures involved lead inevitably to decomposition/oxidation of the material. To address these issues, improved silicon nitride-based powders were developed, two of which have been tested as reported in this paper. The powders were applied using low pressure plasma spraying (LPPS) and the resulting coatings characterized based on microhardness, adhesion, and cohesion strength. Phase transformations of the powders during spraying were also investigated and preliminary optimization strategies by statistical variation of plasma spray parameters were tested.