High-temperature interactions of desert sand CMAS glass with yttrium disilicate environmental barrier coating material

Abstract A calcium-magnesium aluminosilicate (CMAS) glass was prepared by melting a sample of desert sand to evaluate the high-temperature interactions between molten CMAS and yttrium disilicate (Y 2 Si 2 O 7 ), an environmental barrier coating (EBC) candidate material. Cold-pressed pellets of 80 wt% Y 2 Si 2 O 7 powder and 20 wt% CMAS glass powder were heat treated at 1200 °C, 1300 °C, 1400 °C and 1500 °C for 20 h in air. The resulting phases were evaluated using powder X-ray diffraction. In the second set of experiments, free standing hot-pressed Y 2 Si 2 O 7 substrates with cylindrical wells were filled with CMAS powder to a loading of ~35 mg/cm 2 and heat treated in air at 1200 °C, 1300 °C, 1400 °C and 1500 °C for 20 h. Scanning electron microscopy, energy-dispersive spectroscopy and electron microprobe analysis were used to evaluate the microstructure and phase compositions of specimens after heat treatment. An oxyapatite silicate (Ca 2 Y 8 (SiO 4 ) 6 O 2 ) phase was identified in all specimens after CMAS exposure regardless of heat treatment temperature. Apatite appeared to form by dissolution of Y 2 Si 2 O 7 into molten CMAS, reacting with CaO in the melt according to the reaction 4Y 2 Si 2 O 7 + 2CaO → Ca 2 Y 8 (SiO 4 ) 6 O 2 + 2SiO 2 , and followed by precipitation of the apatite phase.