Anodic Region Research Articles

Thermal fluctuations on the corrosion behaviour of 17-4PH stainless steel alloys fabricated via material extrusion additive manufacturing technique

Herein, the influence of fluctuating thermal conditions on the corrosion behaviour of 17-4PH stainless steel alloys manufactured via fused filament fabrication is reported. The printed samples were sintered and then exposed to different temperature-fluctuating conditions to simulate the application environment of such alloys. The first set of samples (A) was studied as-sintered, the second set of samples (B) was aged at 480°C for 3 h followed by quenching in water, the third set (C) was exposed to conditions of B followed by aging at 360°C for 3 h and quenching in water and the final set of samples (D) was exposed to conditions of C followed by aging at 200°C for 3 h, quenching in water, aging at 400°C for 3 h, and finally quenching in water. The surface roughness evolved with the temperature conditions. The optical microscopy revealed that sample B had a fine and homogenous distribution of precipitates. Sample B had the highest microhardness values followed by C, D, and A in that order. XRD analysis revealed the presence of retained FCC austenitic phases within the microstructure whose peaks became stronger with the increased thermal fluctuations. The potentiodynamic polarisation studies revealed a distinct linear Tafel region on the cathodic region and a dual-slope inflection point on the anodic region of the polarisation curves. Sample D exhibited the highest corrosion rate whereas sample B revealed the lowest. As such, exposing fused filament fabricated 17-4 PH SS to fluctuating temperature conditions leads to degradation of mechanical strength and corrosion resistance.

Dual-mode iodine sensing: Colorimetric and electrochemical detection methods using functionalized gold nanoparticles

Iodine in natural and treated waters exists mainly as iodide, iodate, and molecular iodine (I2). I2 is a highly volatile and reactive species impacting biological and chemical systems. Iodine, a vital micronutrient, is essential for human and animal growth and metabolism. It also plays a crucial role in synthesising artificial adrenaline within the metabolic processes of humans and animals. It is also widely used as an antiseptic, disinfectant, and for emergency water disinfection. Moreover, iodine deficiency can result in various diseases, especially hypothyroidism and goitre. Given its critical functions, it is imperative to have a straightforward, dependable, and efficient method for monitoring iodine levels. This study introduces a simple and innovative I2 detection system based on its reactivity, toxicity, and role as an indicator of oxidative conditions in water. It operates in terms of based on optical and electrochemical signal changes, utilising the anti-aggregation mechanism of gold nanoparticles (AuNPs) and 6-mercaptohexanol (MHA) for sensitive and selective detection under mild conditions. I2 determination is achieved by observing the colour change in AuNPs, which is influenced by competitive interactions between MHA, I2, and AuNPs. The optical detection system, with its low detection limit (LOD=260 nM), is based on the straightforward observation of colour changes. On the other hand, the electrochemical detection method utilises changing redox peaks observed in anodic region, providing selective and sensitive I2 detection (LOD=100 nM). The probe effectively detects the presence of I2 in real water samples as a practical application. Moreover, the proposed method revolutionises I2 detection by incorporating a smartphone for signal reading, eliminating the need for specialised equipment and significantly reducing the detection cost. This cost-effective approach carries the potential to expedite on-site and naked-eye I2 detection, opening up new possibilities for research and application.

Corrosion inhibition assessment of a sustainable inhibitor from the weed plant (Pouzolzia zeylanica L.) on SS-410 surface in 0.5 M HCl acidic medium

BackgroundThe research has looked into the potential of plant extracts as natural corrosion inhibitors as an alternative to synthetic ones. The study aims to investigate the ability of the weed plant Pouzolzia zeylanica L. extract (PZE) to prevent corrosion of stainless steel-410 in a 0.5 M HCl acidic medium. MethodIn this work, the leaf extract of PZE is prepared in water, and the functional activity of the prepared PZ water extract (PZE)is evaluated using various techniques. Both electrochemical and gravimetric techniques are employed in this study. The inhibitor from PZ inhibits the anodic region on the SS-410 surface active sites through straightforward adsorption. Experimental techniques such as UV–visible spectroscopy, FTIR, LC-MS, SEM, AFM, EDX, EIS, and computational studies demonstrate the formation of protective layers under inhibiting conditions. The gravimetric data confirms monolayer adsorption, following the Langmuir adsorption isotherm. Significant findingsThe data obtained demonstrate that when SS-410 is immersed directly in a corrosive solution containing dissolved inhibitor molecules, it effectively prevents corrosion. Therefore, increasing the concentration of this chemical improves its inhibitory efficiency. Indeed, the PZ inhibitor achieved a favourable experimental outcome with an efficacy of 95 % at 400 mg/L in 0.5 M HCl. Based on polarization analysis, the corrosion inhibitor exhibits anodic nature for SS-410 in 0.5 M HCl.

Deposition of Fe2O3:Sn semiconducting thin films by reactive pulsed HiPIMS + ECWR co-sputtering from Fe and Sn targets

Semiconducting Fe2O3 thin films were deposited on SnO2:F (FTO) and Pt substrates by reactive high-power impulse magnetron sputtering combined with electron cyclotron wave resonance plasma (HiPIMS + ECWR). Fe2O3 films were fabricated either by sputtering from a single Fe target or by co-sputtering from an additional Sn target. Plasma parameters during co-sputtering were measured by an RF probe system enabling the comparison between HiPIMS + ECWR and only HiPIMS conditions used for the film deposition. As deposited Fe2O3 films were post-annealed in air at 450 °C and 650 °C, respectively. It was shown that as deposited Fe2O3 films were amorphous but became crystalline after post-annealing at 450 °C. Further increase of annealing temperature to 650 °C did not improve significantly the crystalline structure of the Fe2O3 film. All post-annealed Fe2O3 films exhibited photocurrents in the anodic region; generally, hematite films annealed at 650 °C exhibited higher photocurrents than those annealed at 450 °C. Films doped by Sn co-sputtering had higher photocurrents than films only doped by Sn diffusion during post-annealing from the FTO substrate. Hematite films on Pt substrate doped by Sn co-sputtering and post-annealed at 650 °C exhibited the highest photocurrents. It was verified by XPS analysis with ion sputtering depth profiling that Pt atoms also diffuse from the Pt substrate into the Fe2O3 film during the post-annealing at 650 °C and can, similar to Sn in the case of an FTO substrate, act as a dopant.

Electrochemical behavior of aluminum in 1-ethyl-3-methylimidazolium chloroaluminate ionic liquids

The mechanism of electrochemical oxidation and reduction of aluminum in 1-ethyl-3-methylimidazolium-based (EMImCl) chloroaluminate ionic liquids is studied across the concentration range of N = 1.1–2.0 (N the molar ratio of AlCl3 to EMImCl) at temperatures between 303 K and 418 К. Anodic stationary polarization curves (SPCs) indicate that the process of anodic dissolution of aluminum is complicated by passivation. The current density in the passive region and the passivation potential decrease with a higher concentration of Al2Cl7– ion in the melt. To elucidate the processes taking place at the aluminum electrode, the relationship between the concentration of the ions in the vicinity of the electrode and the potential applied in the cathodic and anodic region was analyzed by in-situ Raman spectroscopy for the concentrations of N = 1.1 and 2.0. The resulting dependences of relative peak intensity vs. potential correlate with the cathodic and anodic polarization curves. In the anodic region the content of Al2Cl7– grows with the potential, while the concentration of AlCl4– ion decreases. In the cathodic region the opposite process is observed: the concentration of Al2Cl7– decreases and that of AlCl4–increases with growing potential. It is shown that a precipitate of AlCl3 forms on the electrode surface in the region of passive aluminum dissolution, which is responsible for the electrode passivation. Based on the results obtained, we propose a model for the process of aluminum oxidation/reduction preceded and followed by a chemical reaction of aluminum chloride formation for the cathodic and anodic process, respectively. Temperature dependences of diffusion coefficients are studied by chronopotentiometry. The results indicate that diffusion coefficients are not affected by the concentration across the temperature range studied. The activation energy for diffusion was found to be 13.65 kJ∙mol−1. Impedance spectroscopy was used to investigate the concentration and temperature dependences of exchange current density. The exchange currents increase with increasing aluminum chloride content in the melt. The transfer coefficient and electrochemical reaction rate constant were found to be α = 0.17 ± 0.04, ks = (1.7 ± 0.4)∙10−6 cm∙s−1, respectively. The activation energy for the electrochemical reaction rate constant does not depend on the concentration and was found to be 33.5 kJ∙mol−1.

In Situ Utilization of Electron-Enhanced Degradation of Azo Dyes in a Constructed Wetland–Microbial Fuel Cell Coupling System

In this study, a constructed wetland was coupled with a microbial fuel cell to establish a coupled system known as the constructed wetland–microbial fuel cell (CW–MFC), utilized for the treatment of X-3B azo dye wastewater at varying concentrations. Experimental results indicated that the anodic region made the primary contributions to the discoloration of azo dyes and COD removal, with a contribution rate of 60.9–75.8% for COD removal and 57.8–83.0% for the effectiveness of discoloration. Additionally, the role of plants in the constructed wetland area could achieve the removal of small molecular substances and further discoloration. In comparison to open-circuit conditions, under closed-circuit conditions the CW–MFC effectively degraded X-3B azo dye wastewater. Under an external resistance of 2000 Ω, a maximum COD removal rate of 60.0% and a maximum discoloration rate of 85.8% were achieved for X-3B azo dye at a concentration of 100 mg/L. Improvements in the treatment efficiency of X-3B dye wastewater were achieved by altering the external resistance. Under an external resistance of 100 Ω and an influent concentration of X-3B of 800 mg/L, the COD removal rate reached 78.6%, and the decolorization rate reached 85.2%. At this point, the CW–MFC exhibited a maximum power density of 0.024 W/m3 and an internal resistance of 99.5 Ω. Spectral analysis and GC–MS results demonstrated the effective degradation of azo dyes within the system, indicating azo bond cleavage and the generation of numerous small molecular substances. Microbial analysis revealed the enrichment of electrogenic microorganisms under low external resistance conditions, where Geobacter and Trichococcus were dominant bacterial genera under an external resistance of 100 Ω, playing crucial roles in power generation and azo dye degradation within the system.

Effect of submerged and floating cathodes on sustainable bioelectricity generation and benthic nutrient removal in sediment microbial fuel cells

Sediment microbial fuel cells (SMFC) are a potential alternative for benthic sediment remediation in bioelectricity generation. The cathodic oxygen reduction rate is an important limiting factor in SMFC. This study aims to evaluate the effects of submerged and floating cathodes on bioelectricity generation and benthic nutrient removal in SMFC. Based on the generated current density, SMFC with a wick-air cathode, 10 cm from the top sediment surface and partially submerged in water and exposed to air (SMFC-CW) was found to be superior to those with bottom cathode, 1 cm from the top sediment surface (SMFC-C1), a middle cathode, 5 cm from the top sediment surface (SMFC-C5), and a floating cathode, 10 cm from the top sediment surface and placed under the overlying surface water (SMFC-C10). In the polarization test, SMFC-CW contributed to the lowest concentration loss with a maximum current density of 236.4 mA/m2. The overshoot phenomenon in SMFC-C1 is not a good indicator of the SMFC system, despite the generation of a high maximum power density. This study has shown that a large pH difference between the anodic and cathodic regions in SMFC-CW is important for bioelectricity generation as it was observed that the internal resistance of SMFCs changes. SMFC-CW showed the largest reduction in phosphate concentration, from 0.61 mg/L to 0.14 mg/L. These results provide a simple strategy for sustainable bioelectricity generation in SMFC systems while remediating benthic sediments.

Galvanic Corrosion of E690 Offshore Platform Steel in a Simulated Marine Thermocline

Marked changes in temperature, pH, dissolved oxygen (DO) content, and nutrient content typically occur in marine thermoclines, which are key factors that affect the corrosion of metals. Offshore platforms require marine metals to be exposed to deep-sea environments and thus increase their penetration into the marine thermocline. This study investigates the galvanic corrosion of E690 steel in a marine thermocline using a simulated marine thermocline (SMT). Specifically, the corrosion of E690 steel was analyzed using the wire beam electrode (WBE) technique, linear polarization (LP), corrosion morphology, and weight loss measurement. Results indicated that the SMT had a stable multilayer structure, and the variations in temperature, DO, pH, and nutrient concentration in the SMT were similar to those in the natural marine thermocline. There were two forms of E690 steel corrosion in the SMT: galvanic corrosion and seawater corrosion. The corrosion rate of seawater corrosion was influenced by the DO concentration. Galvanic corrosion occurred after the intrusion of E690 steel into the marine thermocline. The driver of galvanic corrosion was the difference values for Ecorrs of E690 steel at various depths of the marine thermocline. The Ecorr of E690 steel was influenced by the temperature, pH, and DO of the seawater, in the following order: DO >> T > pH. The continuous reduction in Ecorr with depth contributed to large-scale galvanic corrosion, and the oscillation variation in Ecorr with depth was the reason for small-scale galvanic corrosion. The primary anodic regions of galvanic corrosion were located in the area with the fastest temperature variation in the thermocline, and the position of the anodic regions rose with time. The anodic regions gradually expanded with time. The proportion of galvanic corrosion in the average corrosion rate could increase up to approximately 80% in the stable anodic region. There were many hemispherical corrosion pits on the surface of the single electrodes that were at the depths of 75 cm, 105 cm, and 135 cm. These single electrodes comprised a long-term, sustainable anodic region of galvanic corrosion.

Phase-field chemo-mechanical modelling of corrosion-induced cracking in reinforced concrete subjected to non-uniform chloride-induced corrosion

A model for corrosion-induced cracking of reinforced concrete subjected to non-uniform chloride-induced corrosion is presented. The gradual corrosion initiation of the steel surface is investigated by simulating chloride transport considering binding. The transport of iron from the steel surface, its subsequent precipitation into rust, and the associated precipitation-induced pressure are explicitly modelled. Model results, obtained through finite element simulations, agree very well with experimental data, showing significantly improved accuracy over uniform corrosion modelling. The results obtained from case studies reveal that crack-facilitated transport of chlorides cannot be neglected, that the size of the anodic region must be considered, and that precipitate accumulation in pores can take years.

Impact of some inorganic anions on the corrosion of nickel in a solution containing Na2SO4 and NaClO4

Potentiodynamic study was carried out on nickel in Na2SO4 solution in the presence of ClO4–, WO42–, MoO42–, NO2– and NO3– ions. The anodic excursion spans of the metal nickel in a solution of Na2SO4 are marked by the appearance of clearly defined anodic peak, passive region, and transpassive shoulder. According to the data, the anodic peak current density (IPAI) rise from 1.82 to 8.12 mA cm–2 as the concentration of the Na2SO4 solution rises from 0.2 to 1.0 M. It is clear that as scan rate increases, the IPAI rises reaching to 11.8 mA cm–2. The apparent activation energy of nickel corrosion in Na2SO4 is 33.25 kJ mol–1. ClO4– anion addition speeds up nickel’s active dissolution, as well tends to break down the passive layer, and causes pitting penetration. It was found that, the pitting potential (Epit) of nickel in solutions containing the two anions ClO4– and SO42– shifts to the positive direction by addition of WO42–, MoO42–, NO2– anions and shifts to the negative direction by addition NO3- anion. Epit increased by 0.67, 0.37 and 0.15 V in the presence of WO42–, MoO42– and NO2–, respectively. WO42– > MoO42– > NO2– was the order in which the inhibitors were most effective.

Refining microbial potentiometric sensor performance with unique cathodic catalytic properties for targeted application scenarios

Traditional microbial electrochemical sensors encounter challenges due to their inherent complexity. In response to these challenges, the microbial potentiometric sensor (MPS) technology was introduced, featuring a straightforward high-impedance measurement circuit tailored for environmental monitoring. Nonetheless, the practical implementation of conventional MPS is constrained by issues such as the exposure of the reference electrode to the monitored water and the absence of methodologies to stimulate microbial metabolism. In this study, our objective was to enhance MPS performance by imbuing it with unique cathodic catalytic properties, specifically tailored for distinct application scenarios. Notably, the anodic region served as the sensing element, with both the cathodic region and reference electrode physically isolated from the analyzed water sample. In the realm of organic monitoring, the sensor without Pt/C coated in the cathodic region exhibited a faster response time (1 h) and lower detection limits (1 mg L−1 BOD, 1 mM acetic acid). Conversely, when monitoring toxic substances, the sensor with Pt/C showcased a lower detection limit (0.004% formaldehyde), while the Pt/C-free sensor demonstrated superior reusability. The sensor with Pt/C displayed a heightened anode biofilm thickness and coverage, predominantly composed of Rhodococcus. In conclusion, this study introduces simple, cost-effective, and tailorable biosensors holding substantial promise for water quality monitoring.

Hyphenation of lipophilic ruthenium(II)-diphosphine core with 5-fluorouracil: an effective metallodrug against glioblastoma brain cancer cells.

Glioblastoma multiforme (GBM) is the most common highly aggressive malignant brain tumor, with a very limited chance for survival post-diagnosis and post-treatment. Despite significant advancement in GBM genomics implicated in molecularly targeted chemotherapies, the prognosis remains poor and requires new drug discovery approaches. We used fluoropyrimidine 5-fluorouracil (5-FU), an antimetabolite anticancer drug conjugated or 'caged' within a lipophilic Ru(II)-diphosphine (dppe) core formulated as [RuII(dppe)2(5-FU)]PF6 (Ru-DPPE-5FU), where dppe = 1,2-bis(diphenylphosphino)ethane, and evaluated its in vitro cytotoxicity in depth with aggressive GBM cells (LN229). The hydrophilic nature of 5-FU limits its passage through the blood-brain barrier (BBB), which prevents its effective accumulation and efficacy for GBM tumors. Herein, we attempted to modulate the lipophilicity of 5-FU by inserting it within a well-designed lipophilic {Ru(dppe)2}-core with anticipated higher efficiency towards GBM. The physicochemical properties of [RuII(dppe)2(5-FU)]PF6 (Ru-DPPE-5FU) were studied using various spectroscopic and analytical techniques. The molecular structure was determined using X-ray crystallography, showing a distorted {RuP4NO} octahedral geometry with bidentate (N, O) binding of 5-FU and its aromatization in the Ru(II)-bound form. The 31P-NMR spectra of Ru-DPPE-5FU showed four closely spaced distinct 31P-signals, indicating four unique chemical environments around P, and the strong coupling constants between them make it a second-order spectrum. The RuII/RuIII redox potential in Ru-DPPE-5FU shifted by ∼0.91 V towards the anodic region as compared to its precursor complex cis-[Ru(dppe)2Cl2] (Ru-DPPE-Cl). DFT-based theoretical calculations have been performed to correlate the experimental electronic absorption spectra and redox behaviours of the complexes. The electrostatic potential (ESP) plots indicate the delocalization of the charge density on the O-/F-atom from the 5-FU ligand towards Ru(II) upon its complexation. The antioxidant properties of all the compounds were quantified by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay. The hyphenation of the 5-fluorouracil (5-FU) ligand to the lipophilic {Ru(dppe)2}-core endowed lipophilicity to Ru-DPPE-5FU with higher in vitro cytotoxicity (IC50 = 2.37 μM) against the LN229 GBM cells as compared to the hydrophilic 5-FU, suggesting efficient cellular uptake. Further biological assays indicated that the complex is highly potent in inhibiting significant proliferation and spheroid formation and restricting the migratory potentials of the GBM cells. Increased caspase 3/7 activity and the presence of apoptotic bodies at the center of 3-D GBM spheroids as revealed by AO/EB dual staining indicated a deeper penetration of the lipophilic complex. The Ru-DPPE-5FU complex displayed lower cytotoxicity in HaCaT normal cells (IC50 = 7.27 μM) in comparison to LN229 cancer cells with a selectivity index (S.I.) of ≥3. Overall, the synergism and caging of 5-FU within the hydrophobic {Ru(dppe)2}-core improves the pharmacokinetic profile of Ru-DPPE-5FU as a potent anticancer agent for glioblastoma.

Electricity generation and oxidoreductase potential during dye discoloration by laccase-producing Ganoderma gibbosum in fungal fuel cell

Color chemicals contaminate pure water constantly discharged from different points and non-point sources. Physical and chemical techniques have certain limitations and complexities for bioenergy production, which motivated the search for a novel sustainable production approaches during dye wastewater treatment. The emerging environmental problem of dye decolorization has attracted scientist's attention to a new, cheap, and economical way to treat dye wastewater and power production via fungal fuel cells. Ganoderma gibbosum was fitted in the cathodic region with laccase secretion in the fuel cell. At the same time, dye water was placed in the anodic region to move electrons and produce power. This study treated wastewater using the oxidoreductase enzymes released extracellularly from Ganoderma gibbosum for dye Remazol Brilliant Blue R (RBBR) degradation via fungal-based fuel cell. The maximum power density of 14.18 mW/m2 and the maximum current density of 35 mA/m2 were shown by the concentration of 5 ppm during maximum laccase activity and decolorization of RBBR. The laccase catalysts have gained considerable attention because of eco-friendly and alternative easy handling approaches to chemical methods. Fungal Fuel Cells (FFCs) are efficiently used in dye treatment and electricity production. This article also highlighted the construction of fungal catalytic cells and the enzymatic performance of fungal species in energy production during dye water treatment.

In-situ measurement of electrochemical activity related to filiform corrosion in organic coated steel by scanning vibrating electrode technique and scanning micropotentiometry

A new approach to studying the mechanism of filiform corrosion in organic coated steel based on the scanning vibrating electrode technique (SVET) and micropotentiometry (potentiometric SECM) is presented. The electrochemical activity of the process under the coating is evaluated by mapping the ionic current densities emanating from some artificial defects made in specific locations of the filament identifiable thanks to the transparency of the coating. In addition, antimony tips are employed to investigate the pH changes associated to the different corrosion reactions at the metal-paint interface. Local pH levels associated to anodic and cathodic regions are determined along the filament.

Corrosion Performance Analysis of Tubing Materials with Different Cr Contents in the CO2 Flooding Injection–Production Environment

In order to clarify the difference in corrosion performance between low Cr-containing (3Cr, 5Cr, and 9Cr) tubing material and carbon steel N80 in the Carbon dioxide (CO2) flooding injection and production environment and the range of adaptation, corrosion tests and analysis were carried out in simulated working conditions. In this paper, the electrochemical potentiodynamic testing technology and the weight loss method were used to comparatively analyze the corrosion performance and variation law of three types of tubing materials with different Cr contents in a simulated CO2 flooding-produced water environment under different partial pressure conditions. Additionally, scanning electron microscopy and Energy Dispersive Spectrometer (EDS) analysis were conducted to examine the surface corrosion morphology characteristics and elemental composition of material films under various conditions. The results indicate that the open circuit potentials of 3Cr, 5Cr, and carbon steel N80 were similar under the same experimental conditions. However, the open circuit potentials of 9Cr were relatively high and there was an obvious passivation zone in anodic polarization. Nevertheless, compared to that of 13Cr, the passivation state was unstable, and pitting corrosion continued to expand once it formed. This demonstrates that the corrosion resistance of the material can be effectively enhanced and a stable passivation state can be achieved in the anodic polarization region when the Cr content of the material reaches at least 13%. The service life of materials can be predicted based on their corrosion rate under high temperature and pressure simulation environments. We found that 9Cr materials exhibited good adaptability while 3Cr and 5Cr materials showed poor adaptability. Therefore, it was not recommended to use 3Cr and 5Cr materials. Therefore, 3Cr, 5Cr, and N80 materials will be used at lower partial pressure levels of CO2 (<0.2 MPa).

Effect of the Degree of Li3PO4 Vapor Dissociation on the Ionic Conductivity of LiPON Thin Films.

Thin films of solid-state lithium-ion electrolytes show promise for use in small-sized autonomous power sources for micro- and nanoelectronic elements. The high rate of vacuum-plasma synthesis (~0.5 μm/h) of lithium phosphor-oxynitride (LiPON) films with an ionic conductivity of ~2·10-6 S/cm is achieved through anodic evaporation of Li3PO4 in a low-pressure arc. The microstructure and ionic conductivity of LiPON films are influenced by the proportion of free lithium in the vapor flow. This paper presents the results of a study on the plasma composition during anodic evaporation of Li3PO4 in a discharge with a self-heating hollow cathode and a crucible anode. A method is proposed for adjusting the free lithium concentration in the gas-vapor (Li3PO4 + N2/Ar) discharge plasma based on changing the frequency of collisions of electrons with Li3PO4 vapor in the anodic region of the discharge. It is demonstrated that an increase in the proportion of free lithium in the flow of deposited particles leads to an enhancement in the concentration and mobility of lithium ions in the deposited films and, subsequently, an improvement in the ionic conductivity of LiPON films.

New Approaches to Comprehensive Electrochemical Processing of Sulfate-Chloride High-Mineralized Wastewater Treatment Residues

Abstract The results of electrochemical processing of spent acidic, neutral, and alkaline sulfate-chloride-containing regenerative solutions in two- and three-chamber electrolyzers are presented. It has been determined that the highest current efficiency for the products of electrodialysis can be achieved in the presence of hardness ions when processing acidic sulfate-containing solutions using three-chamber electrolyzers. It has been established that during electrodialysis of alkaline solutions after regeneration of anionites containing chloride ions, accumulation of alkali occurs in the cathodic region, and in the anodic region, chloride ions accumulate due to diffusion through the anion exchange membrane during the first stage, followed by preferential oxidation of chloride ions with liberation of free chlorine during the second stage. It has been shown that electrodialysis can effectively solve the problem of comprehensive processing of neutral, alkaline, and acidic regenerative sulfate-chloride-containing solutions, with the production of alkali and acid at concentrations suitable for reuse in regeneration processes.

Model development methodology for localized corrosion of copper

A 2-D axisymmetric time-dependent model for the corrosion of copper under an Evans droplet was developed using the finite-element method. Some unique features of the model are inclusion of 6 heterogeneous and 15 homogeneous reactions, implicit calculation of nm-scale films, and treatment of the influence of films on surface concentrations and potentials. Cathodic and anodic regions are not pre-defined on the electrode surface but are determined by values of local concentrations and potentials. The model shows time-dependent radial distributions for current density and surface coverage of films. The present work describes the methodology for the development of this mechanistic model.

Subtle introduction of membrane polarization-catalyzed H2O dissociation actuates highly efficient electrocoagulation for hardness ion removal

Electrocoagulation represents a promising process for hardness removal from cooling water. Nevertheless, the slow hydrolysis reaction severely restricted the floc formation, inhibiting the hardness co-precipitation and simultaneously causing secondary pollution from dissolved Al3+. Inspired by the detrimental membrane fouling phenomenon in conventional electrodialysis, we reported a rational strategy to substantially enhance the hardness removal efficiency in electrocoagulation by introducing a special membrane polarization-catalyzed H2O dissociation herein. Leveraging the electron transfer between functional groups (–SO3− and –N(CH3)3+) of ion exchange membrane (IEM) and surface-adsorbed H2O under the electric field-induced ion depletion scenario, H2O dissociation could be effectively catalyzed, with this catalytic activity more intensive in –SO3− than in –N(CH3)3+. Such a special H2O dissociation beneficially created a widely distributed and well-simulated alkalinity zone around the anodic region of IEM, which promoted the conversion of dissolved Al3+ to floc Al, thereby enhancing floc formation and circumventing secondary pollution. All these features enabled the resulting membrane-enhanced electrocoagulation (MEEC) to achieve a super-prominent hardness removal rate of 318.9 g h−1 m−2 with an ultra-low specific energy consumption of 3.8 kWh kg−1 CaCO3, considerably outperforming those of other conventional hardness removal processes reported to date. Additionally, in conjunction with a facile air-scoured washing method, MEEC exhibited excellent stability and universal applicability in various reaction conditions.

Anticorrosion and Antimicrobial Evaluation of Sol-Gel Hybrid Coatings Containing Clitoria ternatea Modified Clay.

In this study, Clitoria ternatea (CT) was incorporated into the structure of sodium montmorillonite (Na+-MMT), then these new nanoparticles (CT-MMT) were added to sol-gel-based hybrid silanol coatings (SGC). The results of the CT-MMT investigation using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM) confirmed the presence of CT in the structure. The results of polarization and electrochemical impedance spectroscopy (EIS) tests showed that the presence of CT-MMT in the matrix improves corrosion resistance. The EIS results showed that the coating resistance (Rf) of the sample containing 3 wt.% CT-MMT after immersion was 687 Ω·cm2, while this value was 218 Ω·cm2 for pure coating. CT and MMT compounds improve corrosion resistance by blocking anodic and cathodic regions, respectively. Additionally, the presence of CT in the structure created antimicrobial properties. CT contains phenolic compounds that have the ability to suppress by membrane perturbation, reduction of host ligands adhesion, and neutralizing bacterial toxins. Therefore, CT-MMT showed inhibitory effects and killing of Staphylococcus aureus (gram-positive bacteria) and Salmonella paratyphi-A serotype (gram-negative bacteria), and also improved corrosion resistance.