THERMAL-OXIDATION OF SOLAR SELECTIVE SURF ACES BASED ON FE-CR-AL OXIDES

Thermal oxidation of solar selective surfaces based on Fe-Cr-Al oxides . The thermal behaviour of selective optical coatings in the air was s tudied up to 900-degrees-C by optical methods, electro-chemical impeda nce spectrometry, SIMS, ESCA/XPS and RHEED. Up to 700-degrees-C, these coatings obtained from refractory steel containing aluminium present stable thermoptical properties. The thickness and the texture remain a pproximately the same. The diffusion of oxygen is restricted to the co ating. The chromium-aluminium substituted magnetite which is the main component of the coating and the hematite which appears beyond 200-deg rees-C present substitution rates increasing with the temperature. Aro und 600-degrees-C, iron titanate appears. Beyond 700-degrees-C, the em issivity increases. The thickening of the coating and the strong modif ication of the texture and composition are linked to substrate oxidati on.