Primary Corrosion Research Articles

Effects of Yttrium on the Microstructure and Corrosion Behavior of Pb-39Mg-10Al-1B-Y Alloys

Pb-39Mg-10Al-1B-Y alloys with Y = 0, 0.2, 0.4, 0.6, 0.8, and 1.0 (wt.%) were fabricated by melting and casting. The microstructure and electrochemical corrosion behavior of the Pb-39Mg-10Al-1B-Y alloys in a 3.5 wt.% NaCl solution were investigated using x-ray diffraction, electron probe microanalysis, and scanning electron microscopy, polarization curve tests, electrochemical impedance spectroscopy (EIS), and electrochemical noise (EN). Mg2Pb + Pb eutectic gains are refined, and the distribution of Mg17Al12 + Mg eutectic gains becomes continuous by with the addition of Y. The polarization curves, EIS results and EN results show that the corrosion resistance of the alloys with various Y concentrations is in the order 0.8 > 1 > 0.6 > 0.4 > 0.2 > 0. The primary corrosion behaviors of Pb-39Mg-10Al-1B-Y alloys when Y ≤ 0.4 wt.% and Y > 0.4 wt.% are general corrosion and localized corrosion, respectively. There is a Mg-Mg2Pb galvanic cell present with Mg2Pb as the cathode and Mg as the anode. Moreover, Cl− can accelerate the corrosion of the Mg phase.

Sampling and Analysis of PWR Primary Cooling System Corrosion Products Using an EPMA

Chalk River Unidentified Deposit (CRUD) specimens were sampled and analyzed using an electron probe micro analyzer (EPMA; JEOL JXA-8230R) with a bundle of spent nuclear fuel (actual burnup 49 655 MWd/tonne U) from a Korean nuclear power plant. CRUD collection in the reactor refueling cavity was carried out using the following two methods. The first method used an Al2O3 scraper to scrape a specific area of the fuel cladding and then a paper filter to draw the suspended pieces around it. The second method removed CRUD deposited outside the cladding by vibrating the fuel bundle with an ultrasonic wave. In the first method, scraping some parts of the fuel rods with the Al2O3 scraper made it difficult to obtain an analytical sample because of the very small sample collection. However, the results of the analysis of the identified CRUD samples accurately confirmed the shape and composition of the CRUD in the specific area of the fuel rods desired by the user. In contrast, the second method using the ultrasonic cleaner made it very difficult to analyze samples because of the excessive amount of collected CRUD. In this study, we will discuss two methods for collecting corrosion products existing in the primary cooling system of a pressurized water reactor and the results of an analysis using a shielded EPMA. In addition, we will confirm the value of the Ni/Fe ratio.

Spontaneous Symmetry-Breaking in the Corrosion Transformation of Ancient Bronzes

In general, during long-term museum conservation, ancient bronzes will generate new corrosion products also called the “secondary corrosion” on the surface of the unearthed “primary corrosion” products due to various environmental conditions. In this paper, the corrosion stages of several ancient Chinese bronzes are characterized by using optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and Raman spectrometer (Raman). It is found that there exist phase transformation relationships in between the “primary corrosion” and the “secondary corrosion” stages (i.e., (1) the crystal lattice type tends to transform from a high symmetry system to a low symmetry system; (2) in case of the same crystal lattice type, the corrosions exhibit an inter-transformation or symbiosis). It is interesting to note that these transformation rules are very consistent with the well-known physical law of “spontaneous symmetry-breaking”, which won the 2008 Nobel Prize in Physics and also has been considered to be general law of nature, in addition to the principle of Gibbs free energy reduction. The significance of this discovery allows us to achieve the predictability and controllability of the bronze corrosion products (i.e., to predict the corrosive trends in advance and control the “second corrosion” by adjusting the conservation conditions. This research provides a novel conservation concept of ancient bronzes.

Inhibition effect of natural polysaccharide composite on hydrogen evolution and P110 steel corrosion in 3.5 wt% NaCl solution saturated with CO2: Combination of experimental and surface analysis

For the analysis of corrosion and hydrogen production inhibition, we have synthesized Guar gum and methylmethacrylate (GG-MMA) composite. The synthesized composite was used as an eco-friendly corrosion inhibitor for P110 steel in 3.5% NaCl solution saturated with carbon dioxide at 50 °C. The primary corrosion techniques like weight loss, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) was used to analyze the corrosion inhibition process. EIS study reveals the kinetically controlled corrosion inhibition process. The results of PDP proposed that GG-MMA composite is the cathodic type of inhibitor. The corrosion inhibition performance of GG-MMA alone is 90% at 400 mg/L, and that of formulation with KI (5 mM) + GG-MMA (300 mg/L) is 96.8%. The adsorption of GG-MMA over P110 steel is spontaneous and mixed type i.e., both physical and chemical. The conformation of GG-MMA molecule adsorption was done using a scanning electron microscope (SEM), Contact angle measurement, Atomic force microscopy (AFM), Scanning Electrochemical Microscopy (SECM) and X-ray photoelectron spectroscopy studies.

Controllable Corrosion and Electrochemical Nanoimprint

When the contact potential field between the metal catalyst and semiconductor were exposure to the electrolyte environment, a primary corrosion cell would be formed. The corrosion processes are controllble and going strictly along the metal/semiconductor/electroyte three-phase boundaries. Once the metal were seperated from the semiconductor with the corrosion going on, the corrosion would be ceased. In this way, the corrosion processes are well controlled in the scale of Debye-length of the space charge at the metal/semiconductor boundaries. Baseed on this corrosion principle, electrochemical nanoimprint was developed as a very competitive nanoimprint method to fabricate the functional micro-/nano-structures on semiconductor wafers such as Si, GaAs and other III-V semiconductors. Electrochemical nanoinprint are free of thermalplastic or photocuring resists, mold-filling and demolding processes. It can make micro-/nano-structures directly on semiconductor wafers with high efficiency and low cost. Furthermore, the machining processes can be accelerated by the external physical fields, such as electric filed, light field and force field. In this talk, we will give a comphrehensive report on our recent advances in electrochemical nanoimprint.

Experimental Study on Corrosion Fatigue Performance of High-Strength Steel Wire with Initial Defect for Bridge Cable

The durability problem in high-strength steel wire used for bridge cable is becoming more and more severe due to chlorine salt erosion, with the primary corrosion morphology of steel wire surfaces being pit corrosion. To simplify the pitting formation process, a machine-cut notch was used to represent a corrosion pit caused by electrochemical non-uniformity, and then the fatigue performance and corrosion fatigue performance of steel wire with initial defects were studied experimentally. A new type of test device was designed to carry out synchronous pulsating fatigue loading on multiple wires. A series of S-N curves of steel wire with initial defects under various loading conditions was obtained, and the effects of the concentration and pH value of the corrosive solution, and the shape and dimension of the initial defect on the fatigue corrosion performance of steel wire for bridge cables were investigated. The results show that the test device designed in this paper can effectively perform the life test under the combined action of corrosive medium and fatigue load, and can considerably shorten the duration of the fatigue test. Under the combined action of corrosive medium and fatigue load, the life of steel wire with an initial defect is significantly lower than that without consideration of the corrosion effect. The corrosion fatigue performance of steel wire decreases with the increase of acidity of the corrosive solution, rather than the increase of solution concentration. The life of steel wire with a narrow deep notch is much lower than that with a wide shallow notch. The stress concentration leads to a sharp reduction in wire life.

Hot corrosion behavior of NdYbZr2O7 exposed to V2O5 and Na2SO4 + V2O5 molten salts

In order to evaluate the application prospects of NdYbZr2O7 as a novel TBC material, NdYbZr2O7 ceramic was synthesized via a solid-state reaction sintering method, and its hot corrosion behavior exposed to V2O5 and Na2SO4 + V2O5 molten salts at 900 °C, 1000 °C, and 1100 °C was comparatively investigated. For the V2O5 salt, the primary corrosion products were granular (Nd,Yb)VO4 as well as cube-like m-ZrO2. The corrosion layer consisted of two distinct layers, one of which was Zr-rich layer and another was V-rich layer. In the case of Na2SO4 + V2O5, NaVO3, as an intermediate product, played an important role in dissolving the NdYbZr2O7 ceramic. Herein, the (Nd,Yb)VO4 exhibited a rod/plate-like morphology, which could be attributed to the synergistic effect of low driving force and low nucleation rate. Since the molten salt infiltration rate was superior to the pore filling rate throughout the hot corrosion, the thickness of corrosion layer increased with the rise of temperature. The hot corrosion mechanisms of NdYbZr2O7 ceramic in various molten salts were discussed based on the phase diagram, Lewis acid-base rule and chemical thermodynamics. On this basis, the NdYbZr2O7 coating was prepared by atmospheric plasma spray (APS) and it exhibits a higher corrosion resistance compared to YSZ coating.

Corrosion behavior of HVOF sprayed WC-10Co4Cr coatings in the simulated seawater drilling fluid under the high pressure

Two kinds of WC-10Co4Cr composite coatings with conventional (micron-sized WC particles) and bimodal (a mixture of nano-sized and micron-sized WC particles) structures were successfully prepared on 35CrMo steel (ANSI/ASTM 4135) substrate by high velocity oxygen fuel (HVOF) technology. Scanning electron microscope (SEM) equipped with the energy dispersive spectroscopy (EDS), mechanical testing machine, microhardness tester were used to analyze the characteristics of the coatings. The coatings were immersed in the simulated seawater drilling fluid under the high pressure to simulate the deep-sea environment, and then electrochemical impedance spectroscopy (EIS), potentiodynamic polarization were carried out to investigate the electrochemical properties of the coatings and substrate. The results show the WC-10Co4Cr coating has excellent corrosion resistance and can effectively protect the substrate under the high pressure. Besides, compared with the conventional coating (CC), the bimodal coating (BC) has a denser microstructure, superior mechanical properties, lower porosity, and better corrosion resistance. The corrosion mechanism of the coatings in the simulated seawater drilling fluid under high the pressure is as follows: The micro-galvanic corrosion between the WC phase and the CoCr binder phase is the primary corrosion mechanism. Besides, the electrolyte under the high pressure is more penetrable, so the crevice corrosion also exists.

Evaluation of Carica papaya leaf extract as a bio-corrosion inhibitor for mild steel applications in a marine environment

In this work, the weight loss technique was used to investigate the use of Carica papaya leaf extract as a bio-corrosion inhibitor for mild steel applications in a marine environment. The tested mild steel was prepared according to the recommended methods, and it consists of the as-received, cold-worked, and annealed samples. Similarly, the biomass extract was prepared according to the recommended techniques, while the authors rely on its physiochemical and phytochemical constituent analysis carried out elsewhere. Before the preparation of the bio-corrosion media, the physio-chemical analysis of the collected marine water sample was analyzed according to a standard method (APHA, 2005). Then, the bio-corrosion medium was prepared by dissolving the solid residue of the Carica papaya leaf extracts in the marine water filtrate solvent at a concentration of 10 grams per liter in a two-liter glass bottles at room temperature. During the incubation period of the experiments, the weight loss of the samples and the pH of the media were measured simultaneously at the interval of seven (7) days for forty-nine (49) days for uninhibited and inhibited conditions. The results showed that the Carica papaya leaf extract is active for the control of bio-corrosion of both untreated and treated mild steel in a marine environment. However, the annealed sample exhibited the most significant resistant to bio-corrosion activities for both conditions. Therefore, the authors strongly recommend that annealing should be carried out as a primary corrosion control measure with biomass inhibition as a secondary measure in the material treatment of mild steel for marine environment applications.

Study on corrosion mechanism of shielding line of copper clad aluminum cable in substation terminal box

By means of scanning electron microscope, energy spectrometer and X-ray diffraction method, the chemical element analysis and phase analysis of the cross section, corrosion products, fire resistance mud and shielding line of the copper clad aluminum cable under the special service environment in the terminal box of the substation were analyzed and the corrosion mechanism was studied. Salt Mist corrosion test was carried out on the shielding line with dilute HCl solution, NaCl solution and NaOH solution. The results showed that there are Cl elements and AlCl3, CuCl and other substances in the corrosive products, and a large number of Cl elements are found in the corrosion resistance mud and shielding line outsourcing materials. The salt mist test showed that the dilute HCl solution makes the corrosion rate of copper clad aluminum wire the fastest, and the cause of corrosion fracture of copper clad aluminum wire is the result of chemical corrosion of acidic atmosphere, corrosion of primary battery and corrosion of electrolytic pool.

Influence of coexisting ions on the electron efficiency of sulfidated zerovalent iron toward Se(VI) removal

Recently, sulfidation of zerovalent iron (ZVI) has gained increasing attention due to its merits to enhance both the reactivity and electron efficiency (EE) of ZVI. While few studies have been conducted to elucidate the influence of coexisting ions on EE of sulfidated ZVI, which is important for up-scaling such a decontamination strategy. In this study, taking Se(VI) as a probe, the influence of coexisting ions, including Cl−, SO42−, PO43−, Ca2+, and Mg2+, on the removal capacity and EE of ZVI under aerobic conditions was investigated. Results revealed that, compared to unamended ZVI, sulfidated ZVI synthesized by ball-milling with elemental sulfur (S-ZVIbm) could enhance EE of ZVI toward Se(VI). However, this enhancing effect is not very effective and the maximum of EE value obtained in this work is only 8.8%. Chloride with concentration range of 1–20 mM was found to exert little influence on EE of ZVI. While for SO42− and PO43−, relative to 10 mM NaCl, their presence could depress EE of S-ZVIbm, and this inhibiting effect became more pronounced as their concentration elevated. In contrast, Ca2+ or Mg2+ hardness ions (0.05–2 mM) increased the EE values of S-ZVIbm by 19.2–83.3%. X-ray absorption fine structure analysis revealed that all of Fe0 in S-ZVIbm was exhausted within 24 h with lepidocrocite and magnetite being the primary corrosion products. This suggested that it was the amounts of electrons accepted by Se(VI) rather than that donated by S-ZVIbm accounted for the variation of EE. In general, these co-solutes may impose their influence on EE through affecting Se(VI) adsorption and the subsequent electron transfer from Fe0 core to Se(VI) at the water-particle interface.

The effect of an MgO intermediate layer on a nanostructured HA coating fabricated by HVOF on an Mg alloy

Lightweight magnesium alloys are currently being investigated as implants due to their biodegradability and mechanical properties. However, their clinical applications are limited by their high corrosion rate in the physiological environment. Coating Mg-based alloys is an approach that is used to delay primary corrosion and increase their lifetime. Therefore, hydroxyapatite was coated on anodized and non-anodized magnesium substrates using high-velocity oxy-fuel spraying. This study aimed to evaluate the effect of the MgO intermediate layer between the hydroxyapatite coating and Mg alloy substrate. The microstructure and corrosion behaviour of the coated samples are the main focuses of this study. X-ray diffraction spectroscopy was used to analyse the phases. Electrochemical impedance spectroscopy was performed in simulated body fluid. The results revealed that the presence of an anodized layer increased corrosion resistance.

A Novel Environmentally Friendly Synergistic Mixture for Steel Corrosion Inhibition in 0.51 M NaCl

The ubiquitous use of plain and low-alloy steels in neutral, chloride bearing environments presents an everyday challenge for corrosion protection professionals. This paper explores the possibility of developing a non-toxic and environmentally friendly synergistic inhibitor mixture made of propolis, tannin, sodium benzoate, PEG400 and starch that could be applied into the solution to induce the formation of a persistent protective layer on steel. Components of the mixture were chosen based on the references giving their characteristics relevant to their possible action in the solution and/or at the surface of the steel. The efficiency of the protective layer formed under the influence of the inhibitor mixture, and then measured by the LPR probe in the inhibitor-free solution, was the lowest under quiescent conditions (75%) and the highest (95%) under flow conditions. Both, LPR and EIS data indicate that the inhibitor modified layer presents a barrier for diffusion of oxygen that acts as a primary corrosion reaction depolarizer in the investigated neutral chloride solution. The demonstrated persistence of the inhibitor modified layer is of primary interest as it gives possibility batch application.

Corrosion of stainless steel 316L in molten LiCl-Li2O-Li

Exposure testing of Stainless Steel 316L was performed in LiCl-Li2O-Li solutions at 650 °C for periods of 500 and 1000 h to investigate the effect of metallic Li on corrosion of materials used to contain the LiCl-Li2O electrolyte for the electrolytic reduction of used nuclear fuel. Melt compositions studied consisted of LiCl containing 1 or 2 wt% Li2O and 0, 0.3, 0.6, or 1 wt% Li. Post exposure surface analysis was performed using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Focused ion beam and mechanical cross sections of the samples and gravimetric analyses were performed to determine the time-averaged corrosion rate for each sample. Lithium metal induced attack rates were found to be as high as 2.91 mm/y. In the absence of solvated Li in the LiCl-Li2O system, LiCrO2, Li2CrO4, and NiFexCr2-xO4 were observed to be the primary corrosion products. When Li was present in the melt, the oxidized alloying elements were only detectable via X-ray photoelectron spectroscopy, and the surface was primarily comprised of bare metal.

Experimental Study on Corrosion of Anchored Rock Mass for Half‐Through Intermittent Joints

Make crackled mortar test block to simulate jointed rock mass reinforced by anchor bars. Computational model of corrosion penetration at different load times can be obtained by corrosion acceleration through electrochemistry. Through observation of anchor bar after corrosion, it is found that primary corrosion is mainly pitting; however, with the development of corrosion, corrosion moves along etch pit to the upper and lower surfaces so as to form partial corrosion. Meanwhile, computational formula of pitting ratio is put forward on the basis of mass loss rate. It is found that, through the pulling out experiment of anchor bar corrosion, corrosion has remarkable influence on anchoring performance of anchor bar; meanwhile, different pitting ratios have different influences on trends of ultimate bond strength, for example, when pitting ratio is bigger (between 9% and 30%), the biggest decreasing rate of bond strength is obviously lower than that under lower pitting ratio (from 1.5% to 5%). According to linear fitting of experimental data, the relationship curve of K, ultimate bond strength ratio, and pitting ratio can be obtained so as to provide basis for judgement of anchoring performance loss in practical engineering.

МЕТОДИЧЕСКИЙ ПОДХОД К ОБЕСПЕЧЕНИЮ РАБОТОСПОСОБНОСТИ МЕТАЛЛОКОНСТРУКЦИЙ В УСЛОВИЯХ КОРРОЗИОННОЙ ОПАСНОСТИ

The process has been analyzed of monitoring of structure and installation process safety under corrosion hazard of building facilities. A high level of wear and service limits of structures of buildings and installations are the real threat, which increases probability of a loss. The principles are analyzed of assurance of process safety of structures and installations as an integral structural component of the enterprise safety. It is shown that the development of measures of the reliability assurance program comprises the qualimetric monitoring and risk diagnostics of the determining parameters of structural corrosion state. As used here, a methodology is proposed for assessing serviceability of corrosive structures taking into account the requirements of the process approach to quality and safety management based on the principles of DMAIC (Define, Measure, Analyze, Improve and Control). Classified are the signs of serviceability based on the safety class of systems of structure corrosion protection to justify efficiency of measures for structure maintenance based on their actual state. Methods are theoretically and experimentally justified of redundancy of means of primary and secondary corrosion protection of structural steel. A practical example is presented of setting and solving the direct and inverse problems of the design calculation of structure survivability under corrosion hazard.

Effect of Electric Current Pulse on Microstructure and Corrosion Resistance of Hypereutectic High Chromium Cast Iron.

The effect of electric current pulse on the microstructure and corrosion resistance of hypereutectic high chromium cast iron was explored. The morphology of carbides in solidification microstructure was observed by an optical microscope and a scanning electron microscope and the composition was determined by an electron probe micro-analyzer. The microhardness of primary carbides and corrosion resistance of samples were also compared. Under the active of electric current pulse, the microstructure of hypereutectic high chromium cast iron was homogenized and its performance improved accordingly. On treatment by electric current, the morphology of primary carbides changed from thick long rods to hexagonal blocks or granular structures. The interlayer spacing of eutectic carbide decreased from ~26.3 μm to ~17.8 μm. Size statistics showed that the average diameter of primary carbide decreased from ~220 μm to ~60 μm. As a result, microhardness increased from 1412 HV to 1511 HV. No obvious microcrack propagation was found at the microindentation sites. The average length of microcracks decreased from ~20.7 μm to ~5.7 μm. Furthermore, corrosion resistance was remarkably enhanced. The average corrosion rate decreased from 2.65 mg/cm2·h to 1.74 mg/cm2·h after pulse current treatment.

Insight into the mechanism of alloying elements (Sn, Be) effect on copper corrosion during long-term degradation in harsh marine environment

Pure copper, tin copper and beryllium copper were exposed to a harsh marine environment, and the effects of tin and beryllium addition on copper corrosion were systematically investigated and compared. The corrosion rate for pure copper was similar with that for tin copper, but significantly higher than that for beryllium copper, indicating an improvement in corrosion resistance due to the addition of beryllium. Pitting corrosion occurred in all investigated materials and the extent of pitting damage was in the order of pure copper > tin copper > beryllium copper. Flaking corrosion was prominent on tin copper plate after long-term exposure and the primary corrosion products in all materials were Cu2O, CuCl and Cu2Cl(OH)3. The tin content in the inner corrosion layer was higher than in the outer layer for tin copper, whereas beryllium accumulated at the outer layer of beryllium copper, confirmed by auger electron spectroscopy, and related corrosion mechanisms were proposed.

Long-Term Corrosion Testing of Inconel Alloy 625 in Molten LiCl-Li2O-Li

Introduction In order to incorporate oxide based nuclear fuels from the current light water reactor fleet into a pyrometallurgical based fuel cycle, it is necessary to reduce the oxide fuel to a metallic form. This process is typically conducted electrolytically in a LiCl-Li2O electrolyte at 650°C. Due to the close reduction potentials of UO2 and Li2O, metallic Li is generated at the cathode and subsequently dissolves into the electrolyte, forming a tertiary LiCl-Li2O-Li solution. This study examines the long term corrosion behavior of Inconel 625 when exposed to LiCl-Li2O-Li solutions for 500 and 1000hr. Experimental Similar to our previous work on SS316, exposure testing was performed in LiCl with 1 or 2 wt%Li2O and 0, 0.3, 0.6 and 1.0wt%Li at 650°C for 500 and 1000 hours. I625 samples were polished to a 0.05μm surface finish prior to exposure. The salt solutions were replaced every 96 hours to make up for evaporation and reaction of Li and/or Li2O to ensure consistent solution chemistry. Following exposure, the samples were rinsed with methanol and analyzed using Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and micro-Vickers hardness testing. Results The primary corrosion products detected via Raman spectroscopy, XPS, and EDS on samples exposed to LiCl-Li2O solutions in the absence of Li were lithium chromite, nickel-iron-chromium spinel oxides, and lithium chromate. XRD confirmed the presence of lithium chromite on these samples. In the presence of Li, these surface layers were destabilized and the surface of the samples were free of any significant oxide film, while titanium oxynitride films of nm thickness were observed via XPS. The surface morphology of the samples was observed via SEM to undergo increased degradation with higher concentrations of Li. Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) under contracts DE-NE0008262 and DE-NE0008236, and the US Nuclear Regulatory Commission (NRC) under contracts NRCHQ-11-G-38-0039 and NRC-HQ-13-G-38-0027. W.P. acknowledges the Fellowship Award from the NRC. Dr. Kenny Osborne serves as the program manager for the DOE award and Ms. Nancy Hebron-Isreal serves as the grants program officer for the NRC awards.

Corrosion of stainless steel 316 in eutectic molten salts for thermal energy storage

Stainless steel 316 was examined for compatibility with the eutectic mixtures of NaCl + Na2CO3 and NaCl + Na2SO4 at 700 °C and Li2CO3 + K2CO3 + Na2CO3 at 450 °C in air for thermal energy storage. Electrochemical measurements combined with advanced microscopy and microanalysis techniques were employed. NaCl + Na2CO3 was found as the most aggressive salt at 700 °C. The attack morphology on the surface was uniform corrosion with no localized degradation at 450 °C. Microscopy observations showed grain boundary oxidative attack as the primary corrosion mechanism at 700 °C with depletion of alloying elements from grain boundaries.