Pitting Corrosion Behavior of CUSTOM 450 Stainless Steel Using Electrochemical Characterization

In this study, the electrochemical polarization tests were performed on tensioned and non-tensioned CUSTOM 450 specimens in a 3.5 wt% NaCl solution to investigate pitting potential and stable pit initiation time. A potentiodynamic test was conducted to determine the exact amount of pitting potentials. According to the potentiostatic tests, a relation between applied potential and the stable pit initiation time was obtained. Concerning this relation, stable pitting time can be predicted without experimental works. Optical microscopy was used to evaluate the shape of the pits. Tensile stress led the pit to experience the “pit to crack” step. The corrosion rate of samples was studied by the determination of mass loss. Mass loss measurements and current density–time curve in potentiostatic tests demonstrated the rate of pitting corrosion decreased as time passed. Finally, the depth of the pits was measured by the eddy current technique. The results showed that tensile stress facilitated deeper pit development

Simulation of pitting corrosion behavior of CUSTOM 450 stainless steel by COMSOL software and DIC method

The CUSTOM 450 gas turbine compressor blades are corroded in chlorine environments. The initiation and growth of pits and cracks lead to failure. In this paper, prediction of the pitting corrosion behavior of the alloy is studied. In this regard, in the laboratory section, two-point bending specimen is first subjected to different potentials in a 3.5 wt.% sodium chloride solution to cause pitting corrosion and finally leads to failure at the maximum bending region. According to different potentiostatic tests, an equation is proposed to predict the pitting and life time of stressed sample at different potentials. In the numerical section, the strain in the grown pits is calculated by using digital image correlation method and also the COMSOL Multiphysics software. The location of the localized maximum strain obtained from these two methods is in good agreement with growth of the corrosion pits in the electrochemical experiments. Thus, without needs of experiments, the growth direction of the pit can be simulated

On the Potential of a Poly(vinylidenefluoride-<i>co</i>-hexafluoropropylene) Polymer Inclusion Membrane Containing Aliquat^® 336 and Dibutyl Phthalate for V(V) Extraction from Sulfate Solutions

A polymer inclusion membrane (PIM) composed of 50 wt% base polymer poly(vinylidenefluoride-co-hexafluoropropylene), 40 wt% extractant Aliquat® 336, and 10 wt% dibutyl phthalate as plasticizer/modifier provided the efficient extraction of vanadium(V) (initial concentration 50 mg L−1) from 0.1 M sulfate solutions (pH 2.5). The average mass and thickness of the PIMs (diameter 3.5 cm) were 0.057 g and 46 μm, respectively. It was suggested that V(V) was extracted as VO2SO4− via an anion exchange mechanism. The maximum PIM capacity was estimated to be ~56 mg of V(V)/g for the PIM. Quantitative back-extraction was achieved with a 50 mL solution of 6 M H2SO4/1 v/v% of H2O2. It was assumed that the back-extraction process involved the oxidation of VO2+ to VO(O2)+ by H2O2. The newly developed PIM, with the optimized composition mentioned above, exhibited an excellent selectivity for V(V) in the presence of metallic species present in digests of spent alumina hydrodesulfurization catalysts. Co-extraction of Mo(VI) with V(V) was eliminated by its selective extraction at pH 1.1. Characterization of the optimized PIM was performed by contact angle measurements, atomic-force microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis/derivatives thermogravimetric analysis and stress–strain measurements. Replacement of dibutyl phthalate with 2-nitrophenyloctyl ether improved the stability of the studied PIMs