Near-neutral pH Solution Research Articles

Enhanced degradation of Rhodamine B via α-Fe2O3 microspheres induced persulfate to generate reactive oxidizing species.

The porous α-Fe2O3 microspheres (MS-Fe2O3) were obtained through in-situ ion exchange-calcination method and then utilized to activate persulfate (PS) for Rhodamine B (Rh B) degradation. The influences of some important operational parameters were investigated for the MS-Fe2O3/PS system. Additionally, the physicochemical properties of the as-fabricated MS-Fe2O3 were revealed with the assistance of some analytical instruments (i.e., X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectra (XPS), Brunauer-Emmett-Teller (BET) and vibrating sample magnetometer (VSM)). The results showed that the physicochemical properties of MS-Fe2O3 played an important role in the activation of PS, which promoted MS-Fe2O3 to effectively induce PS to generate reactive oxidizing species, thus Rh B could be nearly 100% degraded within 30 min under near-neutral pH solution. Noticeably, the as-prepared MS-Fe2O3 revealed magnetism and could be separated conveniently through external magnetic, which was beneficial to reuse the catalyst. Finally, the reactive oxidizing species (SO4- and OH) participating in the oxidation process were illustrated by electron paramagnetic resonance (EPR) and radical quenching studies, and then a rational mechanism was proposed to better understand the catalytic oxidation degradation of organic pollutants.

Galvanic Corrosion Processes of Aluminum Coupled to Iron in Chloride Solutions at Near-Neutral pH

Multimaterial structures are effective for weight reduction of automobiles, which contributes to the prevention of global warming and the decrease in CO2 emission. Steel-aluminum joints have many advantages such as low cost, high strength, and high corrosion resistance. However, galvanic corrosion was expected to occur because the corrosion potential of aluminum alloys is usually different from those of iron and steels. Considering the galvanic corrosion processes in chloride-containing near-neutral pH solutions, the existence of surface oxides is an important factor affecting the initiation of corrosion. In this research, the galvanic corrosion behavior of aluminum alloy coupled to iron and the steel in near-neutral pH solutions was investigated. Pure iron, AISI 1045 carbon steel, pure aluminum, and A5083-O(Al-Mg alloy) were used as the specimens in this research. The surfaces of pure iron and AISI 1045 were polished down to 1 µm. Pure aluminum and A5083-O were polished down to 0.25 µm with a diamond paste and cleaned ultrasonically in ethanol before electrochemical measurements. The electrode area was ca. 1 cm2. Ag/AgCl (3.33 M KCl) was used as the reference electrode. In diluted synthetic seawater (200mg/L [Cl-], pH 8.2, naturally aerated, galvanic current was measured for 20 h using zero resistance ammeter technique. The distance between two electrodes was 1 cm. Fig. 1(a) shows the time variation of the galvanic current and electrode potential of pure aluminum coupled to pure iron. From the beginning of the immersion to 30 ks, many current transients were generated. However, after 30 ks, the galvanic current became a constant value of approximately 0.15 µA cm-2. The potential gradually decreased with time. The pH of the electrolyte decreased from 8.2 to 6.7 by galvanic corrosion. Fig. 1(b) and 1(c) shows the electrode surfaces of pure iron and pure aluminum after galvanic current measurements. Rust was observed on pure iron, and filiform corrosion was generated on pure aluminum. Anodic polarization curves were measured in diluted synthetic seawater (200mg/L [Cl-], deaerated), and the pH was adjusted to 8.2, 6.7, 5.2, 3.7, and 2.2 with NaOH or H2SO4. Potentiodynamic polarization was started from corrosion potential, and the scanning rate was 23 mV min-1. The electrode potential of pure aluminum under galvanic coupling conditions was found to be lower than the pitting potentials of pure aluminum. But, corrosion was initiated on the aluminum surface (see Fig. 1(b, c)). The galvanic corrosion behavior of pure aluminum and aluminum alloy AA5083 were discussed in terms of the surface properties of the specimens and solution chemistry. Figure 1

Nanoporous platinum-copper flowers for non-enzymatic sensitive detection of hydrogen peroxide and glucose at near-neutral pH values.

Multimodal nanoporous PtCu flowers(np-PtCu) were prepared via a two-step dealloying strategy under mild conditions. The np-PtCu alloy possesses an interconnected flower-like network skeleton with multiscale pore distribution. This material was placed on a glassy carbon electrode where it shows outstanding detection performance towards hydrogen peroxide and glucose in near-neutral pH solutions. It can be attributed to the specific structure in terms of interconnected nanoscaled ligaments, rich pore openings and a synergistic alloying effect. Figures of merit for detection H2O2 assay include (a) a working voltage of 0.7V (vs. the reversible hydrogen electrode); (b) a wide linear response range (from 0.01 to 1.7mM), and (c) a low detection limit (0.1μM). The respective data for the glucose assay are (a) 0.4V, (b) 0.01-2.0mM, and (c) 0.1μM. The method is not interfered in the presence of common concentrations of dopamine, acetaminophen and ascorbic acid. Graphical abstract Multimodal nanoporous (np) PtCu alloy was prepared via a two-step dealloying strategy under mild conditions. Np-PtCu exhibits superior electrocatalytic activity. The assay is highly sensitive, selective, and it allows for along-term detection of H2O2 and glucose.

Surface modification of NiCo2Te4 nanoclusters: a highly efficient electrocatalyst for overall water-splitting in neutral solution

In this paper, we for the first time report the catalytic activity and durability of nickel cobaltite telluride (NiCo2Te4) nanocluster bifunctional catalysts can be significantly boosted by surface modification with perylene-tetracarboxylic-dianhydride for overall water-splitting in neutral solution. We reveal that tuning energy distribution of nanoclusters via a simple surface ligand can drastically increase the catalytic activity towards efficient hydrogen and oxygen evolution reaction simultaneously. A two-electrode based water electrolysis cell using this newly developed nanocluster catalyst operates at a low bias voltage of 1.55 V to achieve a current density of 10 mA·cm−2 in near-neutral pH solution for overall water-splitting. This, to the best of our knowledge, represents the most efficient mixed-transition-metal-based electrode that has so far been reported for electrochemical water splitting.

Stress corrosion cracking of pipeline steels in near-neutral pH solutions: the role of mechanochemical and chemomechanical effects

The review presents brief theoretical foundations of the mechanochemical and chemomechanical surface effects (MCE and CME) associated with corrosion-mechanical destruction of metals, considers the results of various scientific publications that studied the mechanochemical behavior of steels in near-neutral pH media, and analyzes the application of the results of such studies with the purpose of their practical use in the stress corrosion cracking (SCC) prevention. The article attempts to summarize the results of modern experimental studies and numerical modeling of mechanochemical and chemomechanical processes occurring on the surface of pipe steels and at the tip of the crack under the simultaneous effects of stresses/strains and corrosion media. The influence of these processes on the mechanism and kinetics of corrosion cracking of pipe steels in near-neutral aqueous solutions is discussed. The criteria for the quantitative assessment of the influence of MCE and CME on the SCC of pipeline steels are considered. The analysis of research methods for the study of MCE and CME, was carried out with the aim of further developing a unified methodological approach to assessment and quantification in predicting SCC in neutral media.

Influence of inclusions on initiation of pitting corrosion and stress corrosion cracking of X70 steel in near-neutral pH environment

In-situ 2D and 3D microscopic technologies are used to analyze the influence of inclusions on pitting and stress corrosion cracking initiation of X70 steel in near-neutral pH solution. The chemical dissolution of complex oxide inclusions or part of them induces corrosion pits. Circular protected region forms around Ds inclusions due to dissolution of CaS. The Si-enriched inclusions remain intact, but interstice forms at the inclusion/matrix interface due to the dissolution of the matrix. Both complex oxide inclusions and Si-enriched inclusions can induce initiation of SCC micro-cracks, but most of the micro-cracks are generated inside the ferrite grains.

Constraints on Conceptual and Quantitative Modeling of Early Diagenetic Sediment-Hosted Stratiform Copper Mineralization

Early diagenetic sediment-hosted stratiform copper (eSSC) mineralization results from low-temperature cuprous chloride complexes carried by saline aqueous solution circulating through footwall aquifers. Favorable copper solubilities are attained in moderately oxidizing, near-neutral pH solutions. That specific oxidation level is not determined by co-existence with hematite, with its near-indiscriminant control over Eh. Instead, redbed footwall aquifers are signatures of diagenetic oxidation. Relentless in-situ oxidation of ferrous minerals in redbeds produces pore waters too reduced to transport copper, thus eliminating compaction waters as ore solutions. Continuous early influxes of descending oxygen-rich meteoric waters which have assimilated evaporitic salts may redden aquifers and still retain oxidation levels capable of carrying copper to form downstream eSSCs.

Degradation of organic pollutants in near-neutral pH solution by Fe-C micro-electrolysis system

The degradation of organic pollutants in the simulated and realistic wastewaters was investigated by Fe-C micro-electrolysis system. Effects of initial pH, Fe/C mass ratio, gas bubbling type (air or N2) and the type of anions on degradation and mineralization of Sunset Yellow (SY) were studied. The degradation and mineralization efficiencies of 500mg·L−1 SY were approximately 99.0% and 77.5% after 90min treatment, when the initial pH, Fe/C ratio and air bubbling flow rate were 6.0, 1:1 and 45L·h−1, respectively. Besides, the type of anions had a significant influence on the Fe-C micro-electrolysis process. The results of kinetics study indicated that Fe-C micro-electrolysis process followed second-order-kinetics well. The degradation pathway and mechanism for SY were proposed based on FTIR and LC–MS analyses of treated wastewater. Additionally, the Fe-C micro-electrolysis process could dispose linear alkyl chain and benzene ring compounds efficiently under the optimal conditions, and the mineralization efficiencies were in the range of 94–96% and approximately 80%, respectively. The degradation feasibility of a realistic wastewater by the Fe-C micro-electrolysis system was investigated with landfill leachate. In conclusion, Fe-C micro-electrolysis system is an effective and promising technology for organic wastewater treatment in near-neutral pH condition.

Formation and Evolution of Oxide/Oxyhydroxide Corrosion Products on Low-Alloy Steel During Exposure to Near-Neutral pH Solutions Containing Oxygen and Nitrate

The evolution of corrosion product and the transient behavior of corrosion during the first 24 h of low-alloy steel exposure to near-neutral pH solutions containing O2 and are investigated in this work through periodic electrochemical polarization, spectroscopy, and characterization techniques. The formation of porous FeOOH products occurs a few hours following immersion, with morphologies distinctly dependent on O2 concentration. O2 diffusion is less in the FeOOH tubercle formations formed in 20 ppm O2 conditions, whereas the presence of Fe2O3 is exclusive to corrosion products of 6 ppm O2 environments. Charge transfer on the compounds involved governs corrosion protectiveness trends of the overall multi-layered product and reaction kinetics at sub-tubercle surface sites. Atypical 0.005 M and 0.015 M presence in the environment minimizes the cathodic potential range of O2 reduction and intensifies the corrosion of the low-alloy steel specimen. The chronology of corrosion product evolution is corroborated...

Effect of Stress on Corrosion at Crack Tip on Pipeline Steel in a Near-Neutral pH Solution

In this work, the local corrosion at crack tip on an API 5L X46 pipeline steel specimens was investigated under various applied loads in a near-neutral pH solution. Electrochemical measurements, including potentiodynamic polarization and electrochemical impedance spectroscopy, combined with micro-electrochemical technique and surface characterization, were conducted to investigate the effect of stress on local anodic solution of the steel at the crack tip. The stress corrosion cracking of the steel was dominated by an anodic dissolution mechanism, while the effect of hydrogen was negligible. The applied load (stress) increased the corrosion rate at the crack tip, contributing to crack propagation. The deposit of corrosion products at the crack tip could protect somewhat from further corrosion. At sufficiently large applied loads such as 740 N in the work, it was possible to generate separated cathode and anode, further accelerating the crack growth.

Stress enhanced corrosion at the tip of near-neutral pH stress corrosion cracks on pipelines

In this work, corrosion at the tip of stress corrosion cracks on an X65 pipeline steel was investigated under various stress levels in a near-neutral pH solution. Electrochemical and micro-electroc...

Hydrogen Evolution and Absorption in an API X100 Line Pipe Steel Exposed to Near-Neutral pH Solutions

Hydrogen evolution kinetics and hydrogen absorption in an API X100 line pipe steel exposed to near-neutral pH solutions is studied in this work. At the corrosion potential, dissolved CO2 in the solution accelerates the hydrogen evolution kinetics through the carbonic acid discharge reaction. At potentials more negative than the corrosion potential, hydrogen evolution due to bicarbonate discharge dominates the other cathodic reactions occurring at the ocp. The hydrogen diffusivity in the API X100 steel is found to be approximately 4.4×10−7cm2/s. A measurable amount of diffusible hydrogen of approximately 1 appm is detected in the steel at the freely corroding condition using an electrochemical hydrogen permeation technique. Higher concentration of diffusible hydrogen is observed at more negative applied potentials as well as at higher CO2 partial pressures. The results in this paper support the attribution of stress corrosion cracking of pipelines in near-neutral pH trapped water environments to hydrogen embrittlement.

Effect of hydrogen-induced plasticity on the stress corrosion cracking of X70 pipeline steel in simulated soil environments

The susceptibility to stress corrosion cracking (SCC) of X70 pipeline steel under cathodic protection in near-neutral pH and acidic solutions was investigated by slow-strain-rate tensile test, circumferential-notch tensile (CNT) test, and three-point-bending (TPB) test. Results confirmed the existence of a hydrogen-induced plasticity (HIP) effect within a particular range of cathodic potentials. HIP effect lowered the SCC risk of X70 steel by releasing stress concentration at crack-initiation spots and then decreasing the stress intensity. Crack-growth behavior examined by CNT and TPB tests proved the existence of an HIP effect.

Crack propagation of pipeline steel exposed to a near-neutral pH environment under variable pressure fluctuations

This investigation attempts to understand the corrosion fatigue crack propagation behavior of pipeline steels exposed to near-neutral pH environments. The fatigue loading was designed to simulate the underload-type variable amplitude pressure fluctuations found during pipeline operation. The effects of amplitudes (R ratios) of underload and minor cycles were investigated. It has been found from this investigation that the crack growth rate is enhanced significantly through load interaction of the variable amplitude fatigue. The acceleration factor is found to be up to 2.7 and 5.3 for tests in air and in the near-neutral pH solution, respectively. The crack growth rate decreases with R ratios of underload and minor cycles for tests both in air and in near-neutral pH environments. The latter could enhance crack propagation by a factor of up to 11, as compared with the crack growth rate in air. The critical R ratio of minor cycles at which the minor cycles do not contribute to crack propagation through load interaction was determined to be as high as 0.982, which is much lower than the threshold determined by constant amplitude fatigue. This critical R ratio could be utilized to demarcate stress corrosion cracking and corrosion fatigue, and should be incorporated as one of the design principles for components/structures subjected to variable amplitude cyclic loading.

Study on the Crack Propagation Behavior of ×80 Pipeline Steel Under AC Application in High pH Solution

The crack propagation behavior of pipeline steels with or without AC application was studied in high pH solution using the crack propagation experiment (cyclic load). The results show that there is a significant difference in the crack propagation behavior of steels with or without AC interference. The crack growth rate (CGR) of steel under superimposed AC is considerably greater than that without AC. AC could cause an obvious effect on the crack propagation behavior, and enhance the CGR. The crack propagation behavior of steel under AC application in high pH solution is analogous to that in near-neutral pH solution.

Effect of pH Value on the Crack Growth Behavior of X70 Pipeline Steel in the Dilute Bicarbonate Solutions

In this work, the crack growth behavior of X70 pipeline steel in the near-neutral pH and acidic solutions was investigated using in-situ crack length measurement, microscopic observation and polarization curves. The results showed that the decrease of the solution pH promoted the anodic and cathodic reactions simultaneously and accelerate the corrosion rate of X70 steel. This resulted in the blunt crack tip of X70 steel in the acidic environment. The crack growth rate of X70 steel in the acidic solution was lower than that in the near-neutral pH environment, which was attributed to the higher corrosion rate and the weaker couple effect around the crack tip. [doi:10.2320/matertrans.M2015096]

Corrosion Inhibition of Aluminum Alloy 2024-T3 by Praseodymium Chloride

The mechanism of inhibition of AA2024-T3 (UNS A92024) by praseodymium chloride (PrCl) at varying pH was investigated using electrochemical, microscopic, and spectroscopic techniques. Polarization curves in naturally aerated solutions showed that praseodymium (Pr) provides cathodic inhibition in near-neutral pH solution. Corrosion inhibition of AA2024-T3 by Pr involves the formation of an insoluble film composed of praseodymium carbonate hydroxide (PrCO3·OH) over the intermetallic particles in response to an increase in the pH at the metal/electrolyte interface. As the cathodes on the surface become blocked by a thick oxide, new sites are activated, resulting in the formation of a thick film across the whole surface. The hydroxycarbonate protective layer formed in aerated solution was essential for the protection of the alloy, indicating that carbon dioxide (CO2) played an important role in the inhibition mechanism by Pr. In low and high pH solutions, Pr provided poor inhibition. In the latter case, Pr for...

Corrosion Inhibition of Aluminum Alloy 2024-T3 by Sodium Molybdate

The mechanism of corrosion inhibition of AA2024-T3 by sodium molybdate was investigated using various electrochemical, microscopic and spectroscopic techniques. Polarization curves in naturally-aerated solution showed that molybdate provided mixed inhibition in near-neutral pH solution and at a threshold concentration of 0.1 M. The largest effect was a 250 mV increase in the breakdown potential associated with pitting and a 350 mV decrease in the open-circuit potential (OCP). In addition, electrochemical impedance indicated that the corrosion inhibition mechanism is oxygen-dependent owing to the protection afforded by Mo(VI) species. It is proposed that the corrosion inhibition of AA2024-T3 by molybdate may occur following a two-step process whereby molybdate is rapidly reduced to MoO·(OH)2 over the intermetallic particles and is subsequently oxidized to intermediate molybdenum oxides (e.g. Mo4O11) in the presence of oxygen.

Development of a finite element model for simulation and prediction of mechanoelectrochemical effect of pipeline corrosion

In this work, a finite element model was developed to study mechanoelectrochemical effect of pipeline corrosion through a multiphysics field coupling technique. The modeling results, i.e., corrosion potential and corrosion current density, are well consistent with experimental measurements on pipeline steel in a near-neutral pH solution. It is demonstrated that, while a tensile strain enhances stress uniformly through pipe wall, an increasing depth of corrosion defect results in a concentrated stress at the defect center only. When the corrosion defect is under an elastic deformation, there is no apparent effect of mechanical–electrochemical interaction on corrosion. However, when the applied tensile strain or the geometry of corrosion defect is sufficient to cause a plastic deformation at the defect, the local corrosion activity is increased remarkably. Corrosion at the defect is composed of a series of local galvanic cells, where the region with a higher stress, such as the defect bottom, serves as anode, and that under lower stress, such as the defect sides, as cathode. The locally accelerated corrosion at the defect center can be further enhanced as the corrosion defect deepens.

An experimental investigation of corrosion of X100 pipeline steel under uniaxial elastic stress in a near-neutral pH solution

In this work, the effect of uniaxial elastic stress on corrosion of X100 pipeline steel in a near-neutral pH solution was investigated by localized electrochemical impedance spectroscopy (LEIS), corrosion potential and electrochemical impedance measurements, surface analysis techniques as well as finite element analysis. No effect of the static elastic stress on electrochemical corrosion potential of the steel is detected. The critical failure strain of corrosion scale formed on the steel surface is calculated to be 0.00357–0.00417, which is higher than the maximum strain of 0.0029 generated on the specimen. Thus, corrosion scale does not fracture during loading. No difference in the steady-state corrosion potential could be detected upon application of an elastic tensile or compressive stress. If the scale is pre-formed on the steel surface, the applied dynamic elastic load would “weaken” the scale by expanding its pores, and thus, increase the steel corrosion. While a dynamic tensile stress enhances the steel corrosion, the dynamic compressive stress would inhibit corrosion of the steel. This work provides important recommendations for pipeline safety design, where the corrosion enhancement due to the dynamic elastic stress should be considered.