Preparing selective surfaces for solar collectors by dry oxidation and selective surfaces so obtained

摘要

Selective surfaces for photothermal solar collectors consisting of a nickel support, preferably commercial nickel of 99.5% purity, a layer of a porous nickel oxide of about 0.2 mu m covering the metallic support, the layer of porous nickel oxide being covered with asperities in the form of a network of nickel oxide discs in which the major portions are oriented at an angle with respect to the vertical. The network of discs has a thickness of about 2 mu m. The preparation of these selective surfaces is carried out in the following manner. Thin nickel plates are subjected to a heat treatment by heating and oxidizing in an oxidant gas during a short period of time at a temperature varying between about 1000 DEG C. and 1100 DEG C. The oxidized nickel plates are reduced at a temperature of about 1100 DEG C. in the presence of a reducing gas until the metallic state is obtained. The surrounding temperature is thereafter lowered between 810 DEG and 830 DEG C. and an oxidizing gas is circulated around the plates, at a rate of flow which is sufficient to flush away the reducing gas. The plates are rapidly cooled down to room temperature to give the intended selective surfaces.