Microstructural study of plasma sprayed chromia coatings sealed with aluminum phosphate, was carried out for determining strengthening mechanisms of the sealant. Characterization was accomplished by X-ray diffractometry, scanning electron microscopy, and analytical transmission electron microscopy. The main phase in the coating is the eskolaite type α-Cr 2 O 3 . The overall structure of the coating is lamellar with columnar grains parallel to the lamella thickness. Amorphous aluminum phosphate sealant has penetrated into the coating filling the structural defects such as cracks, gaps and pores between the lamellas. The average composition of the sealant in the coating is 25 at% aluminum and 75 at% phosphorus giving the molar ratio P/Al of 3, that corresponds to metaphosphates Al(PO 3 ) 3 . The aluminum phosphate sealing in the chromium oxide coatings is based on adhesive binding due to the attractive forces between the condensed phosphates and the coating. There were no indications about chemical binding due to reactions between the sealant and the coating in the sealing treatment for chromia coatings.

Sufficient electrical insulation must be ensured between the individual connection plates made of the ODS alloy in planar high-temperature fuel cells. In this paper, APS coatings and coating systems consisting of zirconium dioxide or zirconium dioxide/aluminum oxide are sprayed onto structured plates made of ODS-chromium alloy, qualified and implemented. The electrical insulation of both the coatings and the sealing glass composites is determined at 850 deg C and 950 deg C. The gas resistance of the coated sealing glass composite samples to air, hydrogen and hydrogen/water is determined experimentally. The coating technology is developed for small series production and successfully implemented on a large joined multi-cell unit with basic dimensions of 260 x 260 millimeter square. The paper demonstrates that this coating technology is sufficiently developed for industrial applications. Paper includes a German-language abstract.

In order to improve the properties profile of thermally sprayed coats (in particular, the corrosion resistance), the coats are, amongst other items, posttreated with organic and/or inorganic posttreatment media. The coat combinations used are Al 2 O 3 /TiO 2 (87/12), APS-sprayed, and WC-Co (88/12), HVOF-sprayed. Commercially available sealants and two products from other areas of application were used for sealing purposes. The main contribution of the sealing agents to the anti-corrosion protection lies in the fact that they seal open, (inter)connected pores and/or cracks and thus prevent corrosive media from penetrating into the sprayed coat and from reaching the substrate. In this respect, the best results are achieved with sealing agents which form a dense film extending into the pores of the coat. The component underneath can be protected optimally by the combination of the sprayed coat and the sealing agents. Paper text in German.