Noble Potential Research Articles

Corrosion degradation of AISI type 304L stainless steel for application in nuclear reprocessing plant

The degradation of materials involving corrosion in handling nitric acid in the spent fuel nuclear reprocessing plant is a serious issue. In the present work, the corrosion resistance of American Iron and Steel Institute (AISI) type 304L stainless steel (SS) and nitric acid grade (NAG) type 310L SS in 1 to 11.5 M HNO3 and boiling 15.65 M HNO3 was evaluated. In both the alloy steels, the open circuit potential and corrosion potential are shifted to more noble potential with increasing concentrations. However, the passive current density was not affected, and the transpassive potential was shifted to higher potential with increasing concentrations. The corrosion rate measured in boiling 15.65 M HNO3 after 240 h shows a much lower corrosion rate in type 310L SS (∼0.06 ± 0.012 mm/y) then type 304L SS (∼0.18 ± 0.02–0.2 ± 0.001 mm/y). These observations are corroborated with the scanning electron microscope (SEM) morphologies that show severe intergranular corrosion (IGC) attack in type 304L SS then in type 310L SS. The X-ray photoelectron spectroscopy (XPS) study of the passive oxide films of both alloy steels shows the presence of Cr2O3 and SiO2, and the depth profile indicated predominant Si enrichment.

Microstructure, mechanical and corrosion properties of Mg–Nd–Zn–Sr–Zr alloy as a biodegradable material

The Mg–2·5Nd–0·3Zn–0·1Sr–0·4Zr (wt-%) alloy was prepared by gravity casting. Solution treatment and extrusion were conducted. The microstructure, mechanical properties, and corrosion behaviour of the alloy under as cast, T4-treated, and as extruded conditions were evaluated using scanning electron microscope, tensile test, microhardometre, immersion test, and electrochemical test. The results show that the as extruded alloy exhibits the highest ultimate tensile strength (231 MPa), elongation (36·6%), and microhardness (57·8 HV). The as cast alloy shows the best corrosion resistance because the relative continuously distributed eutectic phase with noble corrosion potential acts as a corrosion barrier. The as extruded Mg–Nd–Zn–Sr–Zr alloy with high ductility and good corrosion resistance is desirable for preparing biodegradable implants.

Corrosion performance and surface analysis of Ti–Ni–Pd–Ru–Cr alloy in nitric acid solution

The corrosion resistance of Ti–0.4Ni–0.015Pd–0.025Ru–0.14Cr (AKOT Ti) and commercially pure titanium (CP Ti) has been studied in different concentrations of 6, 9 and 11.5M HNO3, and boiling 15.65M HNO3. In both CP Ti and AKOT Ti alloy, the open circuit potential and corrosion potential are shifted to more noble potential with increasing concentrations. However, passive current density decreases with increasing concentration. Lower corrosion rate was observed in AKOT Ti (∼0.075mm/y) compared to CP Ti (∼0.22mm/y) in boiling 15.65M HNO3 after 240h. The mechanisms by which dissolved titanium ions affect the corrosion are also discussed.

Tribocorrosion behavior and ions release of CoCrMo alloy coated with a TiAlVCN/CNx multilayer in simulated body fluid plus bovine serum albumin

While the CoCrMo biomaterial is currently employed in artificial joints, there are medical concerns regarding its metal ion release and material loss caused by tribocorrosion. In this work, a TiAlVCN/CNx multilayer coating has been employed to improve the tribocorrosion-resistance of the CoCrMo substrate. During the tribocorrosion test, with the sample immersed in a simulated body fluid containing bovine serum albumin, open-circuit potential measurements showed more noble potential as well as a reduction of both the friction coefficient and wear-rate during the sliding phase. Inductive coupled plasma results demonstrate that the multilayer coating effectively blocked the emigration of metallic ions.

Corrosion behaviour of ferrite and austenite phases on super duplex stainless steel in a modified green-death solution

Corrosion behaviour of super duplex stainless steel (SDSS) in acidic chloride solution was investigated electrochemically. Potentiostatic polarisations of SDSS at −0.377 and −0.447 VSHE resulted in selective dissolution of γ- and α-phases, respectively, and were utilized for fabricating single-phase electrodes. Potentiodynamic polarisation curve of SDSS could be calculated from those of single-phase electrodes. The higher corrosion current density and less noble corrosion potential of α-phase characterised by galvanic connection with γ-phase indicated that α- and γ-phases were functioned as the anode and the cathode, respectively, in the corrosion of SDSS.

Electroless iron plating on pure magnesium for biomedical applications

Electroless nickel plating is usually adopted to protect magnesium and its alloys from corrosion and abrasion. While in biomedical application, electroless nickel platting is not a good choice in consideration of the toxicity of nickel ion. In the present study, biocompatible and biodegradable iron coatings were directly electroless plated on pure magnesium in the alkaline plating solutions containing three different reducing agents: KBH4, NH2–NH2 and NaH2PO2. The electroless plated coatings consisting of crystalline α-Fe are tightly bonded to magnesium substrates. The surface morphology of the iron coatings differed with the reducing agents. When using KBH4, NH2–NH2 and NaH2PO2 as reducing agents, the plating rates were 5.2μm/h, 1.1μm/h and 1.1μm/h, respectively. All coated sample showed more noble potential than the magnesium substrate.

The role of silicon alloying addition on the pitting corrosion resistance of an Al-12 wt.%Si alloy

The electrochemical behavior of Al-12wt.%Si in neutral and slightly alkaline solutions was compared to that of pure Al in order to explore the effect of Si on the properties of the passive film. The film growth kinetics for the Al-Si alloy was slower than that corresponding to pure Al and XPS depth profile suggested that the oxide film was thinner. Potentiodynamic polarization measurements in borate solution with addition of 0.01M NaCl revealed that Si has a beneficial effect on the pitting resistance of the passive film. The Mott-Schottky analysis indicated an n-type semiconductor behavior and that less noble flat-band potential for the alloy corresponded with higher pitting potential. XPS results suggested that the barrier layer on the alloy contains SiO2 particles distributed within the Al2O3/AlOOH film. The protectivity of the Al-12%Si alloy was attributed in part to its ability to retard the adsorption of chloride ion, and also because silicon oxide helps to block entry sites and restricts the transport of chloride ions through the passive film.

Electrochemical Study on Anodic Dissolution Mechanisms of Copper and Copper-Alloys in Fresh Water

Analyses of dissolution mechanisms of copper and copper-alloys are important to obtain the fundamental knowledge concerning corrosion and etching. Various electrochemical measurements were performed to investigate the electrochemical properties of copper and copper-alloys with a channel double flow electrode (CFDE). CFDE is one of hydrodynamic technique whose principle is similar to a rotating ring disk electrode. The mass transfer in the electrolyte solution can be controlled by the solution flow in the channel. Therefore, the measurement with CFDE allows direct information concerning dissolution rate and the species by monitoring the emitted ions from the working electrode at detecting electrode. For example, the in-situ detections of cuprous and cupric ions were carried out with measuring of polarization curves of copper, brass and bronze. The polarization curve of brass showed two potential regions for different dissolution mechanisms and the dezincing was serious in less noble potential region.An electrochemical impedance spectroscopy (EIS) was used in order to discuss the detailed dissolution mechanisms because the EIS enables us to discriminate the time constants of elementary steps in the dissolution process. In addition, the formation of porous structure of brass surface due to dezincing was investigated with the equivalent circuit involving transmission line model (TLM).

Investigation on the corrosion behaviour and microstructure of 2024-T3 Al alloy treated via plasma electrolytic oxidation

Plasma electrolytic oxidation treatment was performed on 2024-T3 aluminium alloy in a simple and inexpensive electrolyte. It was found that treatment time of 30min resulted in the most noble corrosion potential and lowest corrosion current density. The surface and cross-sectional morphology indicated that the coating has a dense structure without any cracking. Furthermore, the result of X-ray diffraction analysis indicated that the coating was formed mainly from α-Al2O3, γ-Al2O3, Al3.21Si0.47 and small amounts of amorphous phases. The presence of glycerine in the electrolyte composition resulted in not only stabilising the solution but also improving the corrosion resistance.

Effect of Sn2+ on Anodic Dissolution of Ni in Perchloric Acid

The effect of Sn2+ on the anodic dissolution of nickel was investigated in deaerated 0.2 M HClO4 solution containing Sn2+ at room temperature. It has been found that the addition of 10−3 M Sn2+ inhibits completely the anodic dissolution of Ni. In contrast, tin itself is not passivated in 0.2 M HClO4 irrespective of the addition of 10−3 M Sn2+. Besides, the anodic dissolution of Ni is not inhibited by the surface coating with Sn (IV) colloid which mainly consistis of hydrous or amorphous nano-crystalline SnO2. X-ray photoelectron spectroscopy (XPS) analysis used to supplement our recent X-ray absorption spectroscopy (XAS) results has indicated that the inhibition effect of Sn2+ on anodic dissolution of Ni is associated with the underpotential deposition (UPD) of Sn on Ni. The metallic bond between Sn and Ni in the Sn-UPD layer on Ni is a prerequisite to the formation of Sn residue adhered to the Ni substrate at the more noble potential that brings the inhibition effect on anodic dissolution of Ni. Moreover, the difference between inhibition effects of Sn2+ and Pb2+ on anodic dissolution of Ni was discussed on the basis of the difference between Sn- and Pb-UPD on Ni.

The surface characterization and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr ODS steels for nuclear fuel reprocessing application

In spent fuel nuclear reprocessing plant, nitric acid is the main medium used in PUREX method. The passive film compositions and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr oxide dispersion strengthened steels in different nitric acid concentrations were studied. The open circuit potential is shifted toward more noble potential as the concentrations increased from 1 M HNO3 to 9 M HNO3 in all the investigated alloy steels. The results of the potentiodynamic polarization plots also exhibited a shift in corrosion potential as the concentrations increased from 1 M to 9 M HNO3. This shift is undesirable because of risk of overshooting the potential beyond passive region and may result into transpassive corrosion. The X-ray photoelectron spectroscopy results of the passive film analysis are composed mostly of Fe2O3, Cr2O3, and Y2O3, and the depth profile of Fe and Cr concentrations vary depending upon the nitric acid concentration. The surface morphology after the corrosion test does not show intergranular corrosion attack at the nitric acid concentrations studied. It is desirable that materials for use in nitric acid service are resistant to such corrosion induced degradation.

Microstructure, mechanical properties and corrosion performance of 7075 Al matrix ceramic particle reinforced composite coatings produced by the cold gas dynamic spraying process

In this study, microstructural evolutions, mechanical properties and corrosion performance of coatings made of 7075 Al matrix with B4C or SiC reinforcement deposited on T6 6061 Al alloy using the cold gas dynamic spraying process were investigated. Microstructural surveys have shown that coatings with no discontinuity at the interface as well as with fine grains were obtained and the addition of ceramic particles enhanced the coating density for a prescribed set of spray parameters and nozzle configuration. The presence of ceramic particles in the 7075 Al matrix improved the coatings hardness and wear resistance when compared to unreinforced 7075 Al coatings. Although coatings hardness increased with increasing ceramic particle content, the effect on the coatings wear performance is not that significant. B4C reinforced composite coatings exhibited slightly better wear performance compared to SiC reinforced composite coatings. The cold sprayed coatings showed more noble corrosion potentials but higher corrosion current densities than those of the T6 6061 Al substrate. The addition of ceramic particles into 7075 Al matrix led to increased corrosion current densities when compared to that of unreinforced 7075 Al coating.

Effect of Galvanostatic Condition on Growth Behavior and Repassivation Potential of Crevice Corrosion of Duplex Stainless Steels

The purpose of this study is to clarify effect of galvanostatic condition on growth behavior and repassivation potential (E R.CREV) of crevice corrosion of duplex stainless steels. E R.CREV measurements, microscopic observation of corroded area, and solution pH measurements inside crevice were carried out. Under the condition of large holding current in propagation step of E R.CREV measurements, the crevice corrosion grew from the bottom to the edge of crevice. Then, it grew towards depth direction, and the sharp corroded area formed near the edge of crevice. Solution pH inside crevice lowered easily under the condition of large holding current in repassivation step, and it induced the repassivation of corroding crevice at noble potential. It was suggested that the sharp corroded area formed near the edge of crevice under the large holding current condition contributed to lowering corrosivity of solution inside corroding crevice and the repassivation of corroding crevice at the noble potential.

Noble metals potential of sulfide-saturated melts from the subcontinental lithosphere

The origin of vast accumulations of nickel and platinum in some continental magmatic rocks is still enigmatic, but ultimately linked to silicate-sulfide liquid immiscibility. The exact composition of pristine sulfide melts has proved extremely difficult to document and understand, largely because of the ephemeral, reactive qualities and small quantities of such melts. Here we report the discovery of Fe-Ni sulfide melt globules highly enriched in noble metals (Pt, Pd, Au; 120 ppm total platinum group elements [PGE]) within an unusual high-Mg andesitic glass (8.2 wt% MgO, 57.3 wt% SiO2) dredged from the southern Mid-Atlantic Ridge, near the Bouvet triple junction. The composition of this glass indicates derivation of its parental silicate melt from a garnet pyroxenite mantle source with pronounced “continental” isotopic (Pb, Sr, Nd, Hf, Os, O) signatures. We infer that the chemical properties of this high-temperature (1250 °C) melt, notably high SiO2 and Ni (310 ppm) contents, promoted sulfide saturation at low pressures in a purely oceanic setting, and propose that this unique example, with its likely origin in the continental lithospheric mantle, may be a useful analogue for incipient Ni-PGE-sulfide melt generation and magmatic PGE enrichment.

Nitriding of 4140 Annealed Low Alloy Steel in RF Plasma

The annealed low alloy 4140 steel samples have been nitrided for di erent treatment periods (1 6 h) in an RF inductive plasma discharge with very low bias voltage (≈ 400 V). The resulting nitrided layer has been observed by means of an optical microscope whereas the nitride phases have been characterised by X-ray analysis. The corrosion response, assessed by the potentiodynamic tests in the 3.5% NaCl solution, presents both higher noble potential values and lower corrosion rates when compared with the untreated sample. The Vickers microhardness tests values show an appreciable increment compared to that of the untreated sample. The process is characterized by a high overall e ciency because similar average Vickers tests values were obtained, no matter for how long the treatment was extended. Likewise, the scanning electron micrographs con rmed no appreciable size evolution of the compound layer microstructure at di erent times of treatment.

Corrosion Resistance of 9% Cr Oxide Dispersion-Strengthened Steel in Different Electrolytic Media

The corrosion resistance and passive film compositions of 9% Cr oxide dispersion-strengthened steel in different acidified and chloride media was evaluated. The results presented below show that with increasing concentrations of 1 M to 11.5 M nitric acid (HNO3), the open-circuit potential reveals a more noble potential, while in chloride-containing media, a less noble potential was observed. The potentiodynamic polarization plots exhibited higher breakdown/transpassive potentials in acidic media with 0.5 M sulfuric acid (H2SO4) and 1 M to 11.5 M HNO3, and there was a shift in the corrosion potential toward the transpassive region as the HNO3 concentration increased from 1 M to 11.5 M. However, no intergranular corrosion attack was observed at the HNO3 concentrations studied. In acidic-chloride media (0.5 M H2SO4 with 0.1 M and 0.5 M sodium chloride [NaCl]) and in chloride only media (0.1 M NaCl and 0.5 M NaCl) poor pitting corrosion resistance was attributable to the microstructural inhomogeneity and inclusions in the steel. The x-ray photoelectron spectroscopy analysis indicated that the passive film has iron(III) oxide (Fe2O3) and chromium(III) oxide (Cr2O3), along with yttrium oxide (Y2O3). The scanning electron microscopy (SEM) examinations showed that the pits on the specimen were hemispherical and formed lace-like patterns. The corrosion properties affected by the dispersed oxide are also discussed in the paper.

Effect of the Degree of Crystallinity on the Electrochemical Behavior of Mg65Cu25Y10 and Mg70Zn25Ca5 Bulk Metallic Glasses

The effect of varying the percent crystallinity on the electrochemical behavior of Mg65Cu25Y10 and Mg70Zn25Ca5 bulk metallic glasses was studied. The alloys were heat-treated to achieve desired microstructures ranging from fully amorphous to fully crystalline, providing a systematic basis for subsequent testing. Potentiodynamic experiments in 0.01 M sodium chloride (NaCl) were used, whereby both the amorphous and partially crystallized samples were observed to have more noble corrosion potentials and lower anodic kinetics. However, this was accompanied by more rapid cathodic kinetics relative to their fully crystalline counterparts, meaning that corrosion rates were not significantly lower in the amorphous state. To describe the electrochemical response as a function of the degree of crystallinity, differential scanning calorimetry (DSC), scanning electron microscopy, x-ray diffraction (XRD), and electrical conductivity measurements were undertaken, where it was found that crystallinity alone is not necessarily the controlling factor and microchemistry that evolves upon devitrification, plays a key role in the electrochemical response of these materials.

Evaluating the performance of sulfonated Kraft lignin agent as corrosion inhibitor for iron-based materials in water distribution systems

The effectiveness of sulfonated Kraft lignin (LS) as corrosion inhibition material of steel bar grade 60 (ASTM A615) in water distribution systems was studied using potentiodynamic polarization and electrochemical impedance methods. LS were evaluated primarily for iron-based materials in water distribution systems. The experiments were performed on different solutions which simulated internal conditions of water distribution pipelines without or with different corrosion inhibitors. Potentiodynamic polarization and electrochemical impedance were used to evaluate the iron-based material's corrosion resistance under these conditions, and linear polarization resistance (LPR) tests were used to compare the efficiency of the corrosion inhibitor. The potentiodynamic polarization studies showed a reduction in the pitting potential to more noble potential for protected corrosion cell. Consistently, the electrochemical impedance spectroscopy tests showed an increase in the corrosion resistance for iron-based material treated by sulfonated lignin. Based on the potentiodynamic polarization studies and electrochemical impedance spectroscopy tests, the LS optimal dosage was found to be 0.3–0.4mg/L. The conducted polarization resistance tests showed a decrease in corrosion rates of LS treated iron. This study showed that LS provided increased protection for iron-based materials in water distribution pipelines by inhibiting corrosion.

Assessing the Accuracy of SAPT(DFT) Interaction Energies by Comparison with Experimentally Derived Noble Gas Potentials and Molecular Crystal Lattice Energies

The density functional version of symmetry-adapted perturbation theory, SAPT(DFT), is a computationally efficient method for calculating intermolecular interaction energies. We evaluate its accuracy by comparison with experimentally determined noble gas interaction potentials and sublimation enthalpies, most of which have not been previously calculated using this method. In order to compare the results with wavefunction methods, we also calculate these quantities using MP2 and, for noble gas dimers, using CCSD(T). For the crystal lattice energy calculations, we include corrections to the dispersion, electrostatic, and induction energies that account for the finite interaction distance cutoff and higher-order induction contributions. Overall, the energy values extrapolated to the complete basis set limit show that SAPT(DFT) achieves significantly better agreement with experiment than MP2.

Corrosion behaviour and bioactivity of electrophoretically deposited hydroxyapatite on titanium in physiological media (Hanks’ solution)

Hydroxyapatite (HA) coatings were developed on titanium by electrophoretic deposition at various deposition potentials from 30 to 60 V and at a constant deposition time of 5 minutes using the synthetic HA (Ca10(PO4)6(OH)2,) powder in a suspension of dimethyleformamide (DMF, HCON(CH3)2). The electrochemical corrosion behavior of the HA coatings in simulated body fluid (SBF Hanks’ solution) at 37 °C and pH 7.4 was investigated by means of open-circuit potential (OCP) measurement and potentiodynamic polarization tests. The OCP test showed that the values OCP for the coated samples shifted to more noble potential than for uncoated titanium, especially after addition of dispersants. The polarization test revealed that all HA coated specimens had a corrosion resistance higher than that of the substrate, especially after addition of dispersants such as polyvinyl butyral (PVB), polyethylene glycol (PEG) and triethanolamine (TEA) to the suspension. The coating morphology after polarization, characterized by scanning electron microscopy (SEM), showed penetration of electrolyte into the HA coats. Bone bioactivity of the coatings was also studied by immersion of coated specimens in Hanks’ solution for 3 and 7 days. Apatite granules growth on the surface of the HA layers was observed.