High temperature fuel cells of SOFC type as direct converter of chemical into electrical energy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced light-weight planar cells for electricity supply systems in cars and other mobile systems. Such cells, in one current design, consist mainly of metallic parts, e.g. of ferrite steels. These cells shall operate in the temperature range of 700 to 800 °C where oxidation and diffusion processes can be of detrimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of Cr-species from the inter-connect or the casing into the electrolyte/cathode interface forming insulating phases and the mutual diffusion of substrate and anode material, e.g. iron and chromium from the ferrite into the anode and nickel from the anode into the ferrite which in both cases reduces performance and system lifetime. Protecting intermediate layers, can reduce such effects considerably if they are dense, stable and of high electronic conductivity. Perovskite-type layers (e.g. doped LaCrO 3 ) applied with high-velocity Direct Current-Vacuum Plasma Spraying (DCVPS) promise to solve reliably such problems.

Plasma jets for thermal spraying are strongly affected in a negative sense by the interaction with the relatively static surrounding atmosphere, particularly at atmospheric spray conditions. Turbulences at the jet fringes arise resulting in entrained cold gas, in slowing and cooling down of the jet and in causing eventually its disintegration. All means suppressing or delaying this phenomenon, called cold gas entrainment, help to improve the interaction of plasma and spray material and hence lead to better product quality and higher deposition efficiency of the process. To observe the cold gas entrainment, to investigate the thermal and kinetic properties of DC plasma jets at different operating conditions and to study the effect of plasma source and powder injection modifications a diagnostic equipment with Schlieren optics, enthalpy probe and mass spectrometry was installed. By modification of the internal and external anode nozzle contours and also by application of a shroud nozzle around the plasma jet exit encouraging results with reduced penetration of cold ambient air into the jet could be obtained.

The vacuum plasma spraying process has to be optimized for each task in order to obtain the required mechanical and electrical properties for the desired coatings. This paper deals with the characterization of plasma and powder spray jets at deposition conditions for Solid Oxide Fuel Cells layers. First, DC plasma jets under soft vacuum conditions are characterized by using an enthalpy probe system and a Schlieren optic installation. The influence of the inner contour of the plasma spray torch anode on the temperature and velocity profiles as well on the shape of the plasma jets are investigated. Second, Laser Doppler Anemometry (LDA) measurements were performed for (8 mol %) yttria stabilized zirconia (YSZ) powder (-20+5 µm) spray jets for two chamber pressures, different argon carrier gas flow rates and injection modes. The results show that a M3 Laval nozzle and a F4V nozzle with conical inner profile allow to obtain a larger plasma volume and a more uniform plasma than with a standard F4 anode nozzle resulting in a better treatment of solid particles in the plasma. LDA measurements, using a M3 anode nozzle, show that the penetration and the acceleration of particles in the core of the plasma jet have their optimum at 10 kPa with an inclined injection with respect to the plasma jet axis for a 3.75 slpm carrier gas flow rate.

By means of Schlieren photography, enthalpy probe, mass spectrometry and the particle measuring system DPV 2000 the influence of the internal and external anode nozzle and torch geometry, on plasma jet quality for atmospheric plasma spraying was investigated. It turned out that there is a strong geometrical effect of the inner contour and that with a proper expansion of the hot core of the plasma jet a considerable improvement of the melting and deposition quality can be obtained. Also the outer torch contour is of influence on the spray process because it controls the formation and the intensity of turbulence and the interaction of the plasma jet with its surrounding and hence the cold gas entrainment.

In this paper a process based on both Thermal Plasma Chemical Vapor Deposition (TPCVD) and Suspension Plasma Spraying (SPS) is applied on r.f. induction thermal plasma for α/β-SiC ceramic synthesis and deposition. The starting materials are low-cost liquid disilanes. The resulting coatings are investigated by means of SEM and XRD. Results on the influence of the processing parameters (i.e. pressure, spray distance, substrate temperature, plasma gas nature and composition, precursor composition, atomization parameters) on the coating phase and microstructure are shown. Control of the microstructure (or nanostructure) as well as of the phase content, namely the ratio α/β can be achieved. A processing route presenting the elementary steps of SiC TPCVD is also proposed.