Exploration of YPO₄ as a potential environmental barrier coating

A non-silicate material, yttrium phosphate (YPO₄), is developed for the application as environmental barrier coatings. The key issues of environmental durability, phase stability, chemical compatibility, and coefficient of thermal expansion (CTE) are considered for the selection of YPO₄. The water corrosion behaviors for the sol-gel prepared YPO₄ were investigated in an atmosphere of 50% H₂O-50% O₂ water vapor at 1350 °C. The hot corrosion study of YPO₄ was carried out at 900 °C with Na₂SO₄ melt. The results demonstrate that YPO₄ has excellent environmental durability. During these tests, YPO₄ had no phase change and decomposition. Moreover, the reactions between YPO₄ and silica at high temperatures were not detected, indicating the good chemical compatibility of YPO₄. The measured CTE of YPO₄ is close to that of SiC. The suitable CTE, good environmental durability and chemical compatibility, and excellent phase stability of YPO₄ indicate that it is a potential environmental barrier coating material.