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Ceria films were deposited by electroless method on a nickel-based superalloy, Superni 75, to improve its performance at high temperatures. Ceria was produced from cerium acetate using triethanolamine as the reducing agent. The films were produced at three concentrations -0.1, 0.2 and 0.3 M of cerium acetate, to study the effect of increasing cerium concentration. For comparative study, the coated and bare substrates were oxidized at 1173 K for 100 h in air. The morphology and the chemistry of the oxide scale formed were analysed using FEG-SEM/EDS and XRD. It has been observed that increasing the cerium concentration in the film increases the oxidation resistance of the substrate which is evident from the calculated parabolic rate constant. It was also observed that the morphology of the scale improves with the increase in the concentration of cerium in the film. The scale formed on the ceria-coated substrate at 0.3 M concentration is dense and more uniform.

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The present work was aimed at analysing the oxidation behaviour of three nickel-based superalloys-Superni 718, Superni 75 and Superni 750, by conducting in-situ study in the secondary chamber of a medical waste incinerator at 800-850°C for 1000 h. It was observed that among the three superalloys, Superni 75 is best suited for such an environment. This was concluded by comparing the weight change after 100 h for total 1000 h, constituting 10 thermal cycles. The morphology of the oxide scale formed on the substrate was analysed using FE-SEM. The elemental composition was obtained by EDS. The depth profiling of the scale was done using the XPS technique. The chemical composition was also examined by the XRD analysis. The superior oxidation property of Superni 75 is due to the higher Ni-Cr content. The oxidation resistance of the nickel-based superalloys in the aggressive environment of medical waste incinerator is attributed to the presence of chromia oxide-Cr 2 O 3 and spinel NiCr 2 O 4 .