Crevice Surface Research Articles

Effect of Dissolved Oxygen on the Corrosion Behavior at the Crevice Surface in High Temperature Water under Gamma-ray Irradiation

Effect of Dissolved Oxygen on the Corrosion Behavior at the Crevice Surface in High Temperature Water under Gamma-ray Irradiation

An investigation of plasma electrolytic oxidation coatings on crevice surface of AZ31 magnesium alloy

In an attempt to investigate the formation rule and corrosion resistance of the plasma electrolytic oxidation (PEO) coating on crevice surface of AZ31 magnesium alloy, the crevice coatings were fabricated on the samples of irregular shapes with different values of crevice width. The value of crevice width was varied from 200 to 350 μm for investigating the effect of crevice width on the surface and cross-sectional morphology, phase composition, corrosion resistance of crevice coatings. The results indicated that the crevice coating differs markedly in morphology and corrosion resistance when the value of crevice width reaches 350 μm, in spite of all coated samples have similar phase compositions. The effect of current density and ultrasound treatment on crevice coatings thickness were also studied systematically. Studies have shown that the increase of current density and the introduction of ultrasound treatment are both favorable for the crevice coatings.

Inverse Crevice Corrosion of Carbon Steel: Effect of Solution Volume to Surface Area

Crevice corrosion of carbon steel was investigated in different exposure environments by performing coupon exposure and electrochemical tests. The extent of corrosion on the bold surface of a carbon steel crevice coupon was more severe at 80°C than at 21°C, in aerated rather than dearated solutions, and with γ-radiation present. In contrast to normal crevice corrosion, we observed ‘inverse crevice corrosion’ behavior, the phenomenon where it is the corrosion on the bold surface that is accelerated when coupled, rather than that on the crevice surface. The coupling current measured between a crevice and a bold electrode in an electrochemical cell was also negative. This inverse crevice corrosion behavior is attributed to a significantly lower metal cation dissolution capacity of the small occluded water volume in the crevice, compared to that of the bulk water volume over the bold surface. The reduction in dissolution capacity results in faster and earlier formation of a protective oxide layer. Corrosion of the bold and crevice surfaces evolves at different rates, leading to galvanically accelerated corrosion of the bold surface. The effect of γ-radiation on corrosion evolution in different solution environments leading to inverse crevice corrosion is discussed.

Computational study of platinum nanoparticle deposition on the surfaces of crevices

A well-known issue in boiling water reactors (BWR), which can threaten their structural integrity, is stress corrosion cracking (SCC) of reactor internals and recirculation pipes due to the accumulation of oxidizing radiolysis products of water. Currently, many operators of BWRs use combined platinum particle and hydrogen injection into the reactor water to mitigate SCC by lowering the electrochemical corrosion potential. It is essential for efficient mitigation that Pt particles reach all water-wetted surfaces, including crevices and cracks, which are also reached by the oxidizing species.In this study, a set of crevices with different widths and orientations with respect to the fluid flow are investigated using numerical simulation tools and compared against experimental findings. The Reynolds-Averaged Navier–Stokes models are used to compute the mean turbulent flow quantities in three-dimensional crevices, and the discrete random walk model is used to evaluate the effect of velocity fluctuations on particle movement. The Lagrangian particle tracking analysis is performed and the average concentration of deposited particles on the surface of crevices is evaluated and compared with experimental results. The results show that Reynolds stress model combined with enhanced wall treatment provides a more accurate prediction of particle concentration and distribution on the surface of crevices than SST k–ω turbulence model, which was expected, owing to the anisotropic nature of the Reynolds stress model. Furthermore, analyses on the particle deposition shows that three different mechanisms play important roles in enhancing deposition on the surface of crevice, that is, flow penetration, interception and turbulent eddy entrainment.

Spherical agglomeration of telmisartan by quasi emulsion solvent diffusion technique to improve the solubility and dissolution rate

Spherical agglomerates of telmisartan (TEL) were prepared with and without the polymers viz. Polxamer F68, Gelucire 50/13, hydroxylpropyl methylcellulose (HPMC E15) and polyvinylpyrrolidone (PVP K90) at different concentrations by quasi emulsion solvent diffusion (QESD) technique, using the solvent system consisting of N,N dimethyl formamide, water and chloroform as good, poor solvent and bridging liquid respectively. All the prepared agglomerates were characterized for yield, particle size, flow properties, drug content, solubility, in vitro dissolution release, fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Results of physical evaluation indicates that, all the prepared agglomerates showed improvement in flowability, compactability, solubility and dissolution rate of TEL compared with pure TEL. Agglomerates prepared using polymers showed further improvement in solubility and dissolution rate compared to agglomerates with no drug, which in turn depends on type and concentration of polymer used. Spherical agglomerates containing 0.05 % Poloxamer F68 was considered optimum as it showed 9.96 and 4.48 folds improvement in solubility and dissolution rate respectively, compared with pure drug. FTIR spectrums of agglomerates indicated no incompatibility between the drug and solvents/ polymers used. PXRD patterns showed the agglomerates retained their crystal characteristics with reduced crystallanity or partial amorphization of TEL. SEM images confirm the spherical shape of agglomerates and their micro porous, rough and crevice surface. Thus, spherically agglomeration of TEL with polymers is a successful approach for improving the micromeritic, solid state and physicochemical properties.

Localized Corrosion of Carbon Steel in the Presence of Gamma Radiation

Canada’s long-term plan for used nuclear fuel includes permanent disposal in a deep geological repository (DGR) using a multiple-barrier system with a key barrier being the used fuel container (UFC). The UFC design consists of an inner vessel of carbon steel (CS), which provides the structural strength to withstand repository loads, and an outer layer of copper, which functions as an external corrosion barrier. The inner vessel of the current UFC design is composed of a pressure grade CS hemispherical head and pressure grade CS piping as a body, the two parts to be laser welded on-site. One of potential issues with this design is the effect of g-radiation on corrosion of the crevice near the weld region. The environment inside the sealed UFC would be humid air. Gamma-irradiation of humid air produces NOx and HNO3, and these species could accelerate the formation and condensation of water droplets in crevices (which might also have surface roughness features that act as preferential condensation sites). The chemical environment in such acidic condensed water, coupled with the presence of oxidizing water radiolysis products, could be very aggressive. Corrosion within the crevice between the head and the body of the container assembly or in the stressed regions near the welds could lead to a localized build-up of corrosion products (oxide deposits and H2gas). The effect of g-radiolysis on crevice corrosion of CS is being investigated using a combination of corrosion exposure tests and electrochemical measurements. These measurements are augmented by post-test analysis of oxide surface using SEM, XPS and Raman spectroscopy. In the corrosion tests reported here, a prepared CS crevice was wetted by adding a couple of water droplets to the mouth of the crevice. The test sample was then exposed to a desired environment in a sealed container for 20 h. Optical images of the corroded surfaces show that the corrosion of the wet bold surface progresses more extensively in air than in Ar, more at 80 oC than at 25 oC and more in the presence rather than in the absence of radiation. The composition of the oxide formed on the wet bold surface (as determined by Raman spectroscopy) shows the oxidation leads to formation of a mixed FeII/FeIII oxide/hydroxide in Ar, and to the formation of FeIII oxyhydroxide and FeIII oxide in addition to the FeII/FeIII oxide in air. Increasing temperature increases the ratio of oxide to hydroxide or oxyhydroxide but does not affect the metal oxidation states. More corrosion products are formed in the presence than absence of radiation. In contrast to the bold surface the interior surface of crevice remained smooth. The XPS analysis of the crevice surface indicates that the oxides formed there are thin (< ~ 9 nm) and that a larger fraction of the oxide is FeIII oxide/hydroxide rather than FeII/FeIII oxide. The thickness of the oxide formed at 80 oC is slightly higher than that formed at 25 oC. Radiation slightly decreases the oxide thickness at 25 oC while it increases the oxide thickness at 80 oC. The different corrosion behaviours of the crevice and bold surfaces raise the possibility of galvanic coupling between the two surfaces. This galvanic effect was investigated by monitoring the coupling current between two electrodes, one electrode representing the bold surface and the other representing the crevice surface, in the electrochemical coupling tests. To aid in interpretation of the galvanic coupling experiments, the corrosion potential and linear polarization measurements were made on each electrode separately. The post-test surfaces from these tests were examined by SEM and XPS. The observed effects of temperature and g-radiation on the corrosion potentials are consistent with the different oxide formation and growth observed in the coupon exposure study. The corrosion potential on the crevice electrode is always slightly higher than that of a bold electrode with the difference depending on temperature and radiation environment. A galvanic coupling current observed between the two electrodes shows that the crevice electrode is the net cathode. The measured coupling currents are consistent with the results from the dynamic polarization tests performed on each electrode. A CS crevice corrosion mechanism that can explain both the crevice corrosion tests and the electrochemical results is discussed.

Effects of local radiolysis and geometric parameters on intergranular attack caused by crevice corrosion

Effects of γ-ray irradiation upon crevice corrosion (CC) of type 316L stainless steel (316L SS) as an initiation site of stress corrosion cracking in a boiling water reactor environment have been studied using a material corrosion test loop which could be irradiated with a 60Co γ-ray source during testing. The CC tests were conducted using crevice specimens with various sizes of crevice gaps. Many of the examined specimen surfaces exhibited a selective grain boundary dissolution; that is, intergranular attack (IGA) as a result of the CC when the crevice gap size was lower than a certain value. The IGA initiation time was shortened by the γ-ray irradiation. The IGA occurred mostly near the crevice mouth at a distance of less than 2 mm from the mouth edge. When γ-ray exposure had occurred, it was found that the number of IGA sites deeper in the crevice increased compared with the IGA site distribution under the no-irradiation condition. Since the electrochemical corrosion potential inside crevice specimens must be low under the conditions for which IGA could occur, it was assumed that γ-ray irradiation accelerated the corrosion rate of 316L SS by decreasing the Fe2+ surface activity inside the crevice or increasing the cathodic current of radiolytic oxidants on the crevice surface. It was concluded that γ-ray irradiation affects the IGA occurrence not only temporally but also spatially.

환원제염조건에서 가압경수로 구조재료의 틈부식 특성

Crevice corrosion tests were conducted to examine the corrosion properties of HYBRID (HYdrazine Base Reductive metal Ion Decontamination) which was developed to decontaminate the PWR primary coolant system. To compare the corrosion properties of HYBRID with commonly existing decontamination agents, oxalic acid (OA) and citric oxalic acid (CITROX) were also examined. Type 304 Stainless Steel (304 SS) and Alloy 600 which are major components of the primary coolant system in Pressurized Water Reactor (PWR) were evaluated. Crevice corrosion tests were conducted under very aggressive conditions to confirm quickly the corrosion properties of primary coolant system structure components which have high corrosion resistance. Pitting and IGA were occurred in crevice surface under OA and CITROX conditions. But localized corrosion was not observed under HYBRID condition. Very low corrosion rate of less than 1.3×10-3 μm/h was observed under HYBRID condition for both materials. On the other hand, under OA condition, Alloy 600 indicated comparatively uniform corrosion rate of 4.0×10-2 μm/h but 304 SS indicated rapid accelerated corrosion in lower case than pH 2.0. In case of HYBRID condition, general corrosion and crevice corrosion were scarcely occurred. Therefore, material integrity of HYBRID in decontamination of primary coolant system in pressurized water reactor (PWR) reactor was conformed.

Chemical and structural analyses of subsurface crevices formed during spontaneous deposition of cerium-based conversion coatings

Abstract Subsurface crevices formed during the deposition of cerium-based conversion coatings were analyzed in cross-section to assess the effect of deposition and post-treatment on the structure and chemistry of phases present. An Al–O containing phase, believed to be amorphous Al(OH)3, was formed in crevices during coating deposition. Analysis by energy dispersive X-ray spectroscopy revealed the presence of up to 1.6 at.% chlorine within the Al–O phase, which was likely a product of soluble chlorides that were present in the coating solution. Cerium was not detected within crevices. After post-treatment in an 85 °C aqueous phosphate solution, the chloride concentration was reduced to ≤ 0.30 at.% and electron diffraction of the Al–O phase produced ring patterns, indicating it had crystallized. Some diffraction patterns could be indexed to gibbsite (Al(OH)3), but others are believed to be a combination of hydrated aluminum hydroxides and/or oxides. Aluminum phosphate was not identified. Separately from its effect on cerium-based conversion coatings, phosphate post-treatment improved the corrosion resistance of Al 2024-T3 substrates by acting to crystallize Al(OH)3 present on interior surfaces of crevices and by reducing the chloride concentration in this phase.

Water Chemistry in a Crack Tip under Irradiation, (II)

Under neutron and gamma-ray irradiations, radiolytic species are generated directly in the crack tip, which causes higher oxidant concentrations and subsequently influences crack propagation rate. A crevice radiolysis model was proposed to estimate the oxidant concentrations in the crack tip water under gamma-ray irradiation. Direct generation of radiolytic species in the crevice water, and their secondary generation and disappearance caused by their interaction with the crevice surface as well as species in the crevice water were included in the model. The diffusion of the radiolytic species through the narrow gap from the bulk water to the crack tip and vice versa were also considered. Calculation results confirmed that the concentrations of H2O2, one of the most important oxidants in BWR environments, in both bulk water and crack tip water under irradiation (energy deposition rate: 0.1 W/cm) were high enough to show high local ECP in both regions under NWC, but were high in the bulk water and low in the crack tip water under HWC. A high H2 diffusion rate from the bulk to the crack tip enhanced the recombination reaction of H2O2 and H2.

Numerical simulation of crevice corrosion: The effect of the crevice gap profile

A new mathematical model, recently developed for the numerical simulation of the incubation period of crevice corrosion, has been applied to a study of the effect of the crevice gap profile. Use of the crevice surface profile in the modelling of the ionic migration and diffusion processes leads to a much more realistic simulation of the crevice corrosion process. The crevice gap profile is demonstrated to be critical in the process of crevice corrosion. While the rest of the crevice remains completely passive, narrow micro-crevices within the overall crevice can achieve active corrosion, whether they are found at the tip, middle or mouth of the crevice.

On the mechanism of crevice corrosion of stainless Cr steels

The mechanism of crevice corrosion of stainless Cr steels in neutral 3%NaCl solution has been studied in a cell constructed for this purpose. Immediately after the start of an experiment, both pH and potential of the steel surface increase as a result of alkali formation (O 2 reduction) during corrosion of the steel in the passive state and thickening of the air-formed oxide film. After the oxygen available within the crevice has been consumed, the cathode process is concentrated to the outer surface whereas on the crevice surface only metal dissolution takes place. By hydrolysis of metal ions (Fe 2+ and Cr 3+) the crevice solution is now acidified. After having passed a maximum value of about 10, the pH in the crevice is lowered to a steady state value of about 4. The crevice surface is first activated locally (pitting) and finally in its entire extent and e crev. and e out. are both lowered. At the anode (crevice) surface, the Flade potential is raised whereas it is lowered on the outer surface where the pH is raised due to the cathode reaction. The crevice must therefore be active and the outer surface passive even if their potential difference is quite small (150 mV for 13%Cr, 50 mV for 17%Cr).