Burner Rig Evaluation of Ceramic Coatings With Vanadium-Contaminated Fuels

The performance of yttria-stabilized zirconia (YSZ), ceria-stabilized zirconia (CSZ), and magnesia-stabilized zirconia (MSZ) coatings was evaluated using an atmospheric burner rig; test environment contained compounds of vanadium, sodium, and sulfur. The coatings were deposited by plasma spraying and electron beam physical vapor deposition (EB-PVD); sputtered sealant layers of hafnia, alumina, and platinum were deposited on the YSZ coating. The tests were performed for up to 500 hours at 1650°F and 1300°F. The tests were designed to simulate the deposit chemistry and sulfur trioxide partial pressures expected in a marine gas turbine engine operating on contaminated fuel. YSZ, CSZ, and MSZ coatings all underwent reaction in the burner rig environment; the reaction products and their effects on spallation were varied. MSZ was by far the most reactive, readily forming MgSO₄ in both 1650°F and 1300°F tests. The observed reaction products provided a measure of “protection” for the bond coat by preventing molten salt infiltration for the duration of the test. The mechanism of ceramic spallation is discussed. Sputtered overlayers of platinum, hafnia, and alumina did not prevent salt infiltration and reaction with the underlying ceramic, although no reaction product between the overlayer and the salt was observed.