Photothermal performance of three chromia-forming refractory alloys for high-temperature solar absorber applications

Spectral hemispherical emissivity is a crucial material characteristic that determines radiation heat transfer. In high-temperature solar thermal applications, it affects not only the efficiency of the solar energy absorption but also the heat losses caused by thermal radiation and the radiative heat transfer within the receiver. Due to the limitations of the working temperature of existing solar absorber coatings, the spectral hemispherical emissivity of the oxidized surface is a key performance indicator for evaluating the potential of a candidate refractory alloy for high-temperature (> 1000 degrees C) solar receiver/reactor designs. In this work, we systematically studied the photothermal performances of the oxidized surfaces of three widely used high-performance commercial chromia-forming alloys (Haynes 230, Hastelloy X, and SS 253MA) by analyzing the spectral hemispherical reflectance in the band 0.25-25 mu m. The stability of the optical properties of the formed oxide layers have also been studied by exposing the three alloys at 1150 degrees C in air for three different exposure periods (10 h, 100 h, and 200 h). The results show that the solar absorptivity of all the samples is in the range of 0.800-0.855, with SS 253MA showing the best performances in offering both high and stable solar absorptivity in the range of 0.837-0.855. The evaluation of the photothermal performances suggest the potential of these three alloys in solar-thermal applications.