Light absorption by metals with porous surface layer formed by oxidizationreduction treatment

Abstract

Metals with fine surface asperity show higher efficiency of sunlight absorption than those with flat surfaces. In the present study, ultravioletvisibleinfrared light absorption by metals with porous surface layers was examined. A three-dimensionally interconnected porous structure was formed on the surface of copper and iron substrates by oxidizing and then reducing. Pore size and layer thickness were dependent on oxidization and reduction temperatures and times. It was found that metals with porous surface layers exhibited higher efficiencies of light absorption over a wide wavelength range than those with mirror-polished surfaces. High light absorption efficiencies were obtained for metal substrates with fine porous structures. In particular, a very fine porous structure was formed on the surface of iron substrate by oxidizing and reducing it at low temperatures, and its light absorption reached 7580% over a wide wavelength range corresponding to ultravioletvisibleinfrared light. This light absorption index is much higher than light absorption by conventional metal substrates with flat surface. © 2012 The Japan Institute of Metals.