Vanadate-Sulfate Melt Thermochemistry Relating to Hot Corrosion of Thermal Barrier Coatings.
NAVAL RESEARCH LAB WASHINGTON DC SURFACE CHEMISTRY BRANCH
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The gas turbine industry is moving strongly toward the use of ZrO2-based thermal barrier coatings TBCs on hot section vanesblades to increase engine efficiency and durability. In some applications e.g., ship propulsion or electricity generation, such TBCs may be corroded by molten vanadate-sulfate deposits from fuel impurities. This Report provides a synopsis of vanadate-sulfate thermochemistry relating to TBC hot corrosion, and summarizes research conducted on this topic at the Naval Research Laboratory. The interactions of Na2O, V2O5 and SO3, the melt components which determine the composition of the vanadate-sulfate deposits, were examined and clarified. Vanadate-sulfate melts were shown to be nonideal rather than ideal a point of some contention in the past literature and, for melts of NaV 1, to have a V205 activity coefficient gamma that ranges from 5 x 10exp -4 up to essentially 1, depending on the S03 overpressure. Different NaVO3Na2SO4 mixtures gave a detectable but small change in gammaV2O5, suggesting that the NaV ratio is relatively unimportant, for melts equilibrated with SO3, in determining gammaV2O5. The reactions of several candidate ZrO2 stabilizers MgO, CeO2, Sc2O3, In2O3, SnO2 with vanadate-sulfate melts are categorized and discussed.
- Inorganic Chemistry
- Physical Chemistry
- Coatings, Colorants and Finishes