The Impact of Annealing Temperature on the Optical Performance of Cr-Cr2O3 Produced by Plasma Spraying as Solar Energy Selective Absorber Coating

A series of selective solar absorber coatings of Cr-Cr2O3 were deposited in different content on stainless steel by plasma spraying. The samples were annealed at different temperatures. The optical performance (both the solar absorptance and the thermal emittance) were studied by spectrophotometry. The surface morphology, the structure and the surface roughness were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and roughmeter respectively. The results show that, as the content of Cr increased, the solar absorptance (a) decreased greatly, from 0.91 to 0.84. Meanwhile, the thermal emittance (epsilon) decreased more greatly, from 0.86 to about 0.64. The ratio between the solar absorptance and the thermal emittance increased from 1.06 to 1.31. Annealing had a great impact on the optical performance. Annealing temperature is an important element. But its influence was a little complex. To pure Cr coating, annealing at 500 degrees C was a perfect chosen, where the ratio between the solar absorptance and the thermal emittance was highest of 1.46.