Preparation of Needle-Shaped Crystals on the Surface of Slag Compact to Control Its Light Absorption Properties

It has been found that metals and semiconductors with high surface asperity readily absorb sunlight. In our previous work, iron and copper substrates with porous surface layers were prepared by redox treatment. The metal substrates with porous surface layers absorbed more light of ultraviolet-visible-infrared wavelength than those with flat surfaces. In the present study, we attempt to enhance the light absorption properties of ceramic materials made from blast furnace slag, using needle-shaped hydrate crystals formed on the surface of the slag compact by hydrothermal reaction. Under the hydrothermal conditions used, blast furnace slag particles react with highly pressurized water to form a hydrate glass phase containing H2O, and form needle- or plate-shaped hydrate crystals such as Tobermorite (5CaO center dot 6SiO(2) center dot 5H(2)O) between original slag particles and on the surface of the slag compact. The slag compact with needle-like crystals on its surface absorbed ultraviolet-visible-infrared light more poorly than that with a flat surface. However, after the surface of slag compact was coated with metal, the sample with needle- or plate-shaped hydrate crystals on its surface absorbed light significantly better than that with a flat surface, exceeding 90% over ultraviolet-visible-infrared wavelengths.