On the Structure of Thin Spectral-Selective Thermal Oxide Coatings on the Surface of X18N10T Steel

The structure of spectral-selective solar radiation absorber coatings fabricated by thermal oxidation of high-chromium X18N10T steel at 400–800° C has been investigated. The structure of the films was controlled by electron microscopy with an X-ray probe and IR spectroscopy. It has been shown that thin thermal oxide layers (400–500 Å) formed during oxidation of steel at 500–600°C had an oxide–oxide composite structure and were characterized by high absorption capacity and a pronounced photoelectric response in the spectral regions of visible solar radiation. The efficiency of the spectral-selective solar radiation absorber coatings prepared by thermal oxidation of high-chromium X18N10T steel at 500–600°C is determined by the thermodynamically conditioned formation of a composite layer of FeCr2O4 granules on the steel surface in the matrix of excess iron oxide and spinel of variable composition in the matrix of the external layer of magnetite.