Optical absorption of lanthanide disilicate environmental barrier coating materials

• Advanced gas turbines are beginning to use SiC components in their hottest regions. • Environmental barrier coatings must be used to protect SiC parts in these engines. • The coatings function as both environmental and thermal barrier coatings. • Widely used Yb 2 Si 2 O 7 (YbDS) coatings are semi-transparent to engine radiation. • Binary YbTmDS and YbErDS reduce transmission by more than 70%. Gas turbine engine combustion environments transfer heat to their structures by convective and radiative mechanisms. While low thermal conductivity environmental barrier coatings (EBCs) provide thermal and environmental protection of the silicon-based composite components, their wide optical band gaps enable radiative heat transfer to the surfaces of coating protected components, resulting in substantial heating and acceleration of failure mechanisms. The most widely used EBC; ytterbium disilicate (Yb 2 Si 2 O 7 : YbDS) fortunately exhibits a relatively strong absorption band centered at a wavelength of 940 nm, near the peak in the black body spectrum. However, radiation of other wavelengths penetrates the coating. We investigate the spectral absorptivity of six unary, and numerous equi-atomic binary, ternary, quaternary, and quinary lanthanide disilicate materials of potentially low thermal conductivity, and assess their use for reduction of radiative thermal transport between wavelengths of 0.4 to 2.5 μm. Using a Dieke diagram to assign the 4f electronic transition origin of their optical absorption bands, unary TmDS, binary YbTmDS and YbErDS, and a ternary YbTmErDS EBC material are shown to provide broad band absorption while retaining the low CTE C2/m space group, β-phase structure necessary for CTE compatibility with composites.