In this paper, plasma layers sealed by aluminum phosphate and orthophosphoric acid are analyzed analytically by means of electron microscopy. Aluminum phosphate seals are used as thermal insulation layers for aluminum oxide and chromium oxide layers as well as for yttria stabilized zirconia thermal insulation layers based on zirconium oxide. 22 magnesium oxide-zirconium dioxide thermal barrier coatings are sealed with normal orthophosphoric acid. The microstructure of thermal barrier coatings based on zirconium oxide is extensively investigated. In yttria stabilized zirconia layers, the conversion-free tetragonal t'-zirconium oxide is found as the main phase in the lamellae. Seals created with the help of orthophosphoric acid are in amorphous form in the layer. The investigations of the sealing layer interface show a chemical reaction between the phosphate seal and the layer surface. From this, it follows that the sealing of the layer lamellas takes place through chemical reactions. Paper includes a German-language abstract.

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