Optimization of pre-oxidation time for corrosion resistance of cobalt based coating alloy in mixed sulphates

Abstract

Purpose This study aims to optimise the effect of pre-oxidation on hot corrosion behaviour of Tribaloy T-900 at 900 °C in mixed Na2SO4 and K2SO4. Design/methodology/approach Prior to hot corrosion experiment, pre-oxidation treatments were carried in ambient air at 900 °C for 1, 5 and 10 h, respectively. The hot corrosion experiments were performed in a box type furnace at 900 °C. Both surfaces of specimens were brushed with saturated salt solution of 75 wt.% Na2SO4 + 25 wt.% K2SO4. After brushing, the salt-coated specimens were placed in electric stove to ensure drying of salt. After drying, presence of 3 mg/cm2 salt on specimen’s surface was ensured through weighting. Findings The 1-h pre-oxidation treatment prior to hot corrosion showed superior hot corrosion resistance against molten salt attack. An optimum pre-oxidation time of 1 h helped timely formation of protective Cr2O3 layer and inhibited the formation of less stable and porous surface oxides of Ni and Mo during hot corrosion. Originality/value Pre-oxidation effect on hot corrosion behaviour of refractory metal (such as Mo in investigated alloy) containing alloy has never been reported previously. Refractory metals oxide (e.g. MoO3) could transform the corrosion phenomena to catastrophic failure through acidic fluxing.

Aging behavior difference between aqueous coatings and solvent coatings in sulfuric acid environment

“…The failure mechanism of the coating system has been studied and explained by a large number of scholars (Li et al, 2023;Rehman et al, 2021). Some researchers have found that the failure process of the coating/metal system consists of three steps: (1) the coating system is in the corrosive medium and good isolation protects the metal substrate from corrosion; (2) the external corrosive medium penetrates from the microscopic defects of the coating, constantly reducing the protective effect of the coating; and (3) when the corrosive medium reaches the metal substrate, the metal corrosion occurs under the coating, which caused the metal and the coating stripping off.…”

“…The failure mechanism of the coating system has been studied and explained by a large number of scholars (Li et al. , 2023; Rehman et al. , 2021).…”