The principles of Stress Corrosion Cracking (SCC) are supported in the behavior of the oxide film formed into a crack; in fact the active dissolution of metal atoms after a film rupture and until fill repassivation is the base of slip dissolution model which is a good model to justified the crack tip advance in stainless steels (SS) used in vessel internal components for the nuclear industry. This paper shows the analyzed made at the oxide film formed on samples of 304L SS sensitized and non sensitized, under autoclave conditions (288°C, 8MPa) with and without crevice geometric formation, using SEM, XRD and Raman Spectra.The crevice and no crevice condition allow establish the difference of an oxide formed on a free surface (no crevice) and the oxide formed on the wall in a crack (crevice); the chemical and physical properties of oxide film can alter the mechanism and kinetics of SCC process, so the difference between these two conditions will give more information about the behavior of the oxide film.
Stress Corrosion Cracking (SCC) in a general term describing stressed alloy fracture that occurs by crack propagation in specifically environments, and has the appearance of brittle fracture, yet it can occur in ductile materials like AISI 304L used in internal components of Boiling Water Reactors (BWR). The high levels of oxygen and hydrogen peroxide generated during an operational Normal Water Condition (NWC) promotes an Electrochemical Corrosion Potential (ECP), enough to generate SCC in susceptible materials. Changes in water chemistry have been some of the main solutions for mitigate this degradation mechanism, and one of these changes is reducing the ECP by the injection of Hydrogen in the feed water of the reactor; this addition moves the ECP below a threshold value, under which the SCC is mitigated (-230mV vs SHE). This paper shows the characterization by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Raman Spectroscopy of the oxide film formed in to a crack propagated during a Rising Displacement Test method (RDT), on Hydrogen Water Chemistry (HWC) conditions: 20 ppb O2, 125 ppb H2, P=8MPa, T=288°C, using a CT specimen of austenitic stainless steel AISI 304L sensitized. The characterization allowed identifying the magnetite formation since an incipient way, until very good formed magnetite crystals.
Carbon steel has gained wide applications as a structural material due to its combination of strength, ductility, and low cost; in fact, this material has been studied as one of the proposals for the manufacture of radioactive waste containers in countries such as Japan, France, and the United States. One of the biggest problems of carbon steel is its susceptibility to general corrosion, while copper and its alloys, despite not having high mechanical resistance, are materials with good corrosion resistance properties. This work evaluates the reliability of protective films developed from copper nanoparticles to improve the corrosion resistance of carbon steel plates. The nanoparticles were synthesized by a chemical reduction method using copper sulphate (CuSO4) as a precursor, sodium borohydride (NaBH4) as a reducing agent, and citric acid as an antioxidant. These nanoparticles were characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), as well as by Dynamic Light Scattering (DLS) before and after being treated with citric acid. Finally, they were deposited on the carbon steel surface by Electrophoretic Deposition using a current of 0.5 mA/cm2. The protective capacity of the films developed from copper nanoparticles was evaluated by means of Electrochemical Impedance Spectroscopy and Linear Polarization Resistance techniques in 0.1 M HCl solution.
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