Nanostructured Environmental Barrier Coatings for Corrosion Resistance in Recovery Boilers

Corrosion of components in a recovery boiler is a major problem faced by the pulp and paper industry. The superheater tubes get severely corroded due to the presence of hot sulphidic gases in the boiler as well as the hot molten salts which get deposited on the surface of the tubes. As a result, the boiler has to be shut down for expensive maintenance and repairs. This thesis examines the possibility of using air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) environmental barrier coatings (EBC) to protect against molten salt corrosion of superheater tubes. Conventional YSZ and nanostructured YSZ samples were prepared and exposed to different environments to check their resistance to corrosion. The performances of both types of coatings were evaluated and a comparative study was made. It was found that the nanostructured YSZ samples protected the stainless steel substrate better than the its conventional counterpart. This superior performance was attributed to the presence of semi-molten nano agglomerates present in the coating microstructure which act as collection bags for the penetrating molten salts.