SECONDARY-ION MASS-SPECTROMETRY AND MULTIREFLECTION INFRARED ANALYSESOF CONVERSION COATINGS ON FE-CR-AL STAINLESS-STEELS FOR CATALYSIS - STUDY OF THERMAL-STABILITY

The thermal stability of three stainless steel conversion coatings for high temperature applications (e.g. photothermal conversion catalysis ) are investigated. The thermal oxidation in air up to 1000-degrees-C of Fe-17Cr, Fe-18Cr-1.3Al, and Fe-22Cr-5 Al coatings (all wt-%) are co mpared. This study has revealed a critical temperature below which the coating thickness is preserved; the critical temperature increases an d the thermal oxidation of the conversion coating decreases with highe r chromium and aluminium content. This is attributed to the difference in the substitution ratio of gamma lacunar phase (additionally oxidis ed substituted magnetite), which is the main component of the conversi on coatings. The thermal stability of this phase is higher when it is richer in chromium or aluminium. Higher contents of these elements rai se the temperature of formation of chromite (FeCr2O4) and alumina, the occurrence of which causes thickening of the coating during thermal t reatment.