The spectral emittance and long-term thermal stability of coatings for thermophotovoltaic (TPV) radiator applications

Vacuum plasma spray coatings (ZrO2+18% TiO2+10% Y2O3, ZrC, Fe2TiO5, ZrTiO4, ZrO2+8% Y2O3+2% HfO2, and Al2O3+TiO2) have been developed to improve the emissivity of material surfaces under consideration for TPV radiator applications. These coated surfaces have been shown to be thermally stable at temperatures up to 1200 °C for as much as 8000 h and have produced a desired increase in the surface emissivity of molybdenum and niobium radiators. The spectral emissivity of these surfaces is measured before and after long-term vacuum anneals to determine the power density that would be provided to a TPV cell. The thermal stability of the coatings is further evaluated by characterization after long-term vacuum annealing. A kinetic model of the volatility of oxide phases is used to describe the excellent thermal stability of the coatings that possess the highest post-anneal emittance values (ZrO2+18% TiO2+10% Y2O3, ZrC, and Al2O3+TiO2).