Spectral selectivity of composite enamel coatings on 321 stainless steel

Composite porcelain-enamel coatings consisting of spinel-type transition-metal-oxide pigments embedded in a borosilicate-glass matrix were deposited on 321 stainless steel using screen-printing techniques and characterized using total reflectance over the spectral range of 200 nm to 25 μm. The composite coatings exhibited moderate spectral selectivity and excellent thermal stability at 450 °C. Solar absorptance (α) ranged from 0.82 to 0.90 and calculated thermal emittance at 500 °C (ε) ranged from 0.46 to 0.79. Both depended on coating thickness and pigment volume concentrations. As an example, the highest solar selectivity was measured in a 0.9 μm coating with α and ε (500 °C) being 0.82 and 0.46, respectively.