Solar energy absorbing article and method of making same

A solar energy absorbing article comprising:

• an aluminum-silicon alloy base having predominantly aluminum and from small amounts up to 18% by weight of silicon;
• an aluminum oxide matrix layer grown from, a part of and extending internally of an original surface of said base and forming a physical and chemical bond with said base;
• a plurality of silicon dioxide crystals firmly embedded in and having a portion projecting from a surface of the aluminum-oxide matrix layer, the longitudinal axis of a plurality of said crystals being substantially perpendicular to the surface of said matrix layer to conduct solar energy to the alloy base;
• the surface of aluminum oxide matrix layer and silicon dioxide crystals having less than about 1% reflectivity from about 0.35 to about 15 microns wavelength;
• said aluminum oxide matrix layer and plurality of silicon dioxide crystals having a specific gravity of about 2.5 to 3.0, a dielectric constant of about 8.4 to 9.6, a dielectric strength of about 400 to 600 volts per mil, a melting point of about 2678.degree. to 3722 F.degree., a specific heat of about 0.16 to 0.20, a coefficient thermal expansion of about 4.0-6.7 .times. 10.sup.-.sup.6 in/in/F.degree., thermal conductivity of about 13.0-15.0 BTU/hr.sup.. ft.sup.2. F.degree./ft, surface hardness of about 8 to 9 Mohs, modulus elasticity of about 50-55 .times. 10.sup.6 lb/in.sup.2, and tensile strength of about 109-144 .times. 10.sup.3 lb/in.sup.2.

A method of making a solar energy absorbing article consisting essentially of the steps of:

• providing an aluminum-silicon alloy base having predominantly aluminum and from trace amounts up to 18% by weight silicon;
• treating a surface of the base with a solution that selectively etches aluminum from the surface to provide etched aluminum surfaces and exposes silicon surfaces between the etched aluminum surfaces that protrude above the etched aluminum surfaces;
• and
• anodizing the exposed protruding silicon surfaces and etched aluminum surfaces to grow silicon dioxide crystals and an aluminum oxide supporting matrix layer from the etched aluminum surface so that the silicon dioxide crystals are embedded in, protrude from a surface of said matrix layer and are substantially perpendicular to said matrix layer to conduct solar energy to said alloy base and said aluminum oxide matrix layer forms a physical and chemical bond with the original surface of said alloy base treated by said solution.