Performance of dicalcium silicate coatings in hot-corrosive environment

Thermally sprayed dicalcium silicate coatings have been developed for increased stability in highly corrosive environments at temperatures up to 900°C. In this study, the performance of dicalcium silicate based coatings was compared to yttria partially stabilized zirconia (Y-PSZ) coatings. The coatings were exposed to a V2O5-15 wt. % Na2SO4 slag at 700 and 900°C. At 700°C, gaseous sulfidation was stimulated by an addition of 0.5 vol.% sulfur dioxide in air. The results demonstrated that dicalcium silicate coatings exhibited superior endurance against hot corrosion induced by the V2O5-Na2SO4 slag. The mechanism of protection was related to stable calcium vanadate compounds, which formed on the surface and prevented the corrosive species from immediate penetration into the coating microstructure. In the presence of an SO2/air atmosphere, a CaSO4 reaction layer formed. Diffusion of SO2 further facilitated sulfidation within the coatings. However, the dicalcium silicate materials withstood combined attack by gaseous SO2 and V2O5-Na2SO4 slag without debonding. In this case, the zirconia coating deteriorated and spalled.