Anodic Dissolution Rate Research Articles

Electropolishing Behaviour of 73 Brass in a 70 vol % H3PO4 Solution by Using a Rotating Cylinder Electrode (RCE)

The electropolishing behaviour of 73 brass was studied by means of a rotating cylinder electrode (RCE) in a 70 vol % H3PO4 solution at 27 °C. Owing to the formation of a blue Cu2+-rich layer on the brass-RCE, an obvious transition peak was detected from kinetic- to diffusion-controlled dissolution in the anodic polarisation curve. Electropolishing was conducted at the potentials located at the transition peak, the start, the middle, and the end positions in the limiting-current plateau corresponding to the anodic polarisation curve of the brass-RCE. A well-polished surface can be obtained after potentiostatic electropolishing at the middle position in the limiting-current plateau. During potentiostatic etching in the limiting-current plateau, a blue Cu2+-rich layer was formed on the brass-RCE, reducing its anodic dissolution rate and obtaining a levelled and brightened brass-RCE. Moreover, a rod climbing phenomenon of the blue Cu2+-rich layer was observed on the rotating brass-RCE. This enhances the coverage of the Cu2+-rich layer on the brass-RCE and improves its electropolishing effect obviously.

Effect of Chloride on Anodic Dissolution of Aluminum in 4 M NaOH Solution for Aluminum-Air Battery

Aluminum air battery is a chemical cell that provides high theoretical energy density. However, the anodic dissolution rate of aluminum in 4 M NaOH solution is limited by the film formed on aluminum surface. Electrochemical measurements and scanning electron microscope (SEM) images after potentiostatic polarization were used to analyze the surface structure, ionic reactions, and anodic dissolution of aluminum in 4 M NaOH with chloride solution. The anodic dissolution is mainly affected by aluminum oxide layer. Chloride suppresses the anodic dissolution below the breakdown potential. However, above the breakdown potential, chloride breaks down the oxide layer, which improves the discharge performance of aluminum anode.

A Direct Measurement of the Activation Potential of Stainless Steels in Nitric Acid

The rate of anodic dissolution and the associated activation potential that characterizes the passive-active transition of stainless steels have been measured directly for the first time in nitric acid. The anodic dissolution current under cathodic polarization in pure nitric acid, in absence of chlorides, is masked by intense cathodic hydrogen reduction. In this work, atomic emission spectroelectrochemistry (AESEC) was used to record simultaneously the dissolution rate of the individual alloying elements of stainless steels as well as the overall cathodic current. This methodology has been used to quantify the influence of several parameters on the activation potential: nitric acid concentration, temperature, and the addition of silicon in the steel composition.

Effect of Chloride on Anodic Dissolution of Aluminum in 4 M NaOH Solution for Aluminum-Air Battery

Aluminum-air battery is a chemical cell that provides high theoretical energy density. However, the anodic dissolution rate of aluminum in 4 M NaOH solution is limited by the film formed on aluminum surface. Electrochemical measurements and scanning electron microscope (SEM) images after potentiostatic polarization were used to analyze the surface structure, ionic reactions, and anodic dissolution of aluminum in 4 M NaOH with chloride solution. The anodic dissolution is mainly affected by aluminum oxide layer. Chloride suppresses slightly the anodic dissolution below the breakdown potential. However, above the breakdown potential, chloride breaks down the oxide layer.

Technical Note: Synergistic Effect of Chloride Ions and Magnetite on the Corrosion of Alloy 690 in Alkaline Solutions

The effects of chloride ions and magnetite on the corrosion of Alloy 690 were investigated using electrochemical techniques in deaerated alkaline solutions at 60°C. Independently, the effect of chloride ions and galvanic coupling to magnetite produce a small influence on the corrosion rate of Alloy 690. However, the anodic dissolution rate of Alloy 690 is drastically accelerated when the effects of chloride ions and magnetite are combined. This acceleration is because the coupled potential between Alloy 690 and magnetite is shifted from the stable passive region of Alloy 690 to the active-passive transition region by the addition of 1 M NaCl.

Effect of Chloride Anion on Anodic Dissolution of Aluminum in 4 M NaOH Solution

Aluminum air battery is a chemical cell that provides theoretical high energy density. However the anodic dissolution rate of aluminum in 4 M NaOH solution is limited by the film formed on aluminum surface. Electrochemical measurements and scanning electron microscope (SEM) images after electrostatic polarization were used to analyze the surface structure, ionic reactions, and anodic dissolution of aluminum in 4 M NaOH. The anodic dissolution is mainly affected by aluminum oxide layer. Chloride anion suppresses the anodic dissolution below the breakdown potential. However, over the breakdown potential, chloride anion breaks down the oxide layer, and accelerates the anodic dissolution of aluminum.

Impact of Galvanic Anode Dissolution on Metal Trace Element Concentrations in Marine Waters

Submerged harbor steel structures often employ cathodic protection using galvanic anodes to guard against corrosion. A laboratory experiment, with three different cathodic protection config-urations by galvanic aluminum-based anodes, was performed to evaluate the potential metal trans-fer from the anodic alloy dissolution into the surrounding marine water. The anode dissolution rate is proportional to the imposed current demands and induced a significant Al, In, and Zn trans-fer in the dissolved and particulate fractions of the corrosion product layers covering the anode surface. These layers were poorly adherent, even under low hydrodynamic conditions. Conse-quently, at the anode vicinity, the suspended particle matter and dissolved fraction of surrounding marine waters showed strong enrichments in Al and Zn, respectively, the values of which could potentially affect the adjacent biota. After the anode activation period, however, the metal inputs from galvanic anode dissolution are rapidly diluted by seawater renewal. At regional scale, these metal fluxes should be negligible compared to river and wastewater fluxes. These results also showed that it is difficult to assess the impact of the anode dissolution on the concentrations of metals in the natural environment, especially for metals included in trace amounts in the anode alloy (i.e., Cu, Fe, In, Mn, and Si) in the aquatic compartment.

Electrochemical way of molybdenum extraction from the Bimetallic systems of Mo-W

Electrochemical dissolution of molybdenum and tungsten was investigated in water- dimethylsulfoxide (DMSO) media at different concentrations of lithium chloride and magnesium perchlorate. The terms of efficient extraction of molybdenum from bimetallic systems of Mo-W have been determined. The polarization curves of the electrooxidation of molybdenum in the solution of 0.25 M LiCl in the DMSO at the different rates of rotations and the scan rate equal to 50 mV/s were obtained. In the presence of the addition of water at the potential of 0.1-0.75 V the small area of polarizability occurs, then with increasing potentials above 1.5 V there is a sharp increase of the oxidation current. Comparison of the current values of anodic dissolution of molybdenum and tungsten showed that the rate of anodic dissolution of molybdenum significantly exceeds the rate of anodic dissolution of tungsten. In the case of molybdenum, the dissolution process is limited by diffusion, in the case of tungsten - by the passive film formation on the electrode surface.

A New Understanding of Stress Corrosion Cracking Mechanism of X80 Pipeline Steel at Passive Potential in High-pH Solutions

Susceptibilities to stress corrosion cracking (SCC) of X80 pipeline steel in relatively concentrated carbonate/bicarbonate solutions with different chloride ion concentrations or pH value at a passive potential of −200 mV vs SCE were investigated by slow strain rate tensile test. In order to explore the SCC mechanism and the evaluation criterion for the SCC susceptibility of the steel in passive state, electrochemical measurements were taken. Potentiodynamic polarization curves were obtained at different potential sweep rates, and electrochemical impedance spectroscopy measurements were taken after fast polarization to the passive potential. The effects of chloride ion and pH on SCC behaviors of X80 steel at the passive potential were also discussed. The results showed that the SCC mechanism of X80 pipeline steel was greatly influenced by the passive film formed in these solutions. The SCC behaviors followed the film suppressed anodic dissolution mechanism in these circumstances, because the filming process accounted for a considerable proportion of the overall electrode process. The criteria for evaluating the SCC susceptibility of the steel at passive potential were proposed and validated. Decreasing in the concentration of chloride ion or increasing in pH value resulted in the reduction in SCC susceptibility. The existence of chloride ion greatly lowered the passivation tendency and the film stability, while its concentration determined the dissolution rate of the steel matrix. Higher pH value was responsible for the stable and tenacious passive films and the high repassivation capability. It was also inclined to lower the anodic dissolution rate at crack tips by retarding the cathodic oxygen reduction.

Electro-dissolution of metal scrap anodes for nickel ion removal from metal finishing effluent

This contribution reports a novel and cost efficient strategy for nickel ion removal from metal finishing effluents by electro-dissolution of scrap aluminium and iron sacrificial anodes. Electro-coagulation of effluent was carried out at 30 mA/cm2 current density for 60 min. The nickel ion concentration of electroplating effluent was analysed by Atomic Absorption Spectroscopy. SEM images of iron and aluminium scrap anodes were critically analysed. Parameters such as heavy metal removal, anode dissolution rate with respect to heavy metal removal, reaction kinetics and cost estimation have been elaborately studied. Electro-coagulation at 30 mA/cm2 for 60 min using iron and aluminium scrap anodes resulted in 95.9 and 94.1 % nickel ion reduction, respectively, with 0.0094 and 0.0053 g/ppm dissolution rates. The energy consumption for scrap aluminium and iron anodes was 0.0547 kWh/L. Loose internal bonding and spongy surface morphology of used metal scrap render high porosity and active surface area, enhancing reaction rate. Low cost and ready availability of waste scrap makes the process of electro-coagulation economically viable. Thus, the findings from this contribution point decisively at the superiority of waste metal scrap-based anodes for economic and environmentally sustainable heavy metal ion removal from metal finishing effluent.

The influence of tensile stress on the electrochemical behavior of X80 steel in a simulated acid soil solution

Purpose – The aim of this paper was to clarify the influence of tensile stress on the electrochemical behavior of X80 steel in a simulated acid soil solution and attempt to understand mechanistic aspects of the corrosion behaviors of X80 under these conditions. Design/methodology/approach – The electrochemical behavior of X80 steel at various tensile stresses was investigated in a simulated acid soil solution using electrochemical impedance spectroscopy, potentiodynamic scan measurements and surface analysis techniques. Findings – The results show that as tensile stress was increased, the open-circuit potential decreased, the reaction activity increase, the reaction resistance (Rct)value became smaller by degrees, the corrosion product film resistance (Rf) first decreased and then increased and polarization current densities changed conversely. The corrosion product film was compact and continuous under the low stress, whereas it was relatively loose under high-stress conditions. Tensile stress promotes the movement of dislocations, which become active points when they move to the steel surface. The increase in the number of active points enhances the anodic dissolution rate and promotes the formation of corrosion product film whose blocking effect can decrease the dissolution rate. The corrosion rate of the specimen is determined by these two effects. Originality/value – This research provides an essential insight into the mechanism of the electrochemical behavior of X80 steel in acid soil environments.

Effect of thermal treatment of copper anodes on electrorefining process

The aim of this paper is to study the effect of thermal treatment of the conventional copper anodes on the dissolution behavior and passivation of anodes during electrorefining process. Four similar impure copper anode samples were heated to 800°C with holding time of 1800s followed by quenching in different media to achieve different cooling rates such as brine 10%, water, machine oil and/or still air. Each anode sample was centered in an electrolytic cell together with two stainless steel permanent cathode sheets and all was immersed in an acidified electrolyte containing 0.040kg/l of Cu2+ and 0.170kg/l of H2SO4 with some bath organic additives like bone glue and thiourea. The process was carried out at a constant electrolyte temperature of 65°C, an electrolyte stirring rate of 350rpm and a constant cathodic current density of 350A/m2. Polarization curves for the different copper anodes using a potentiodynamic technique with a scanning rate of 0.5mV/s were conducted to examine the dissolution rate and passivation of different anodes. The obtained results indicated that, the best anodic dissolution rate and anodic passivation time are obtained with anodes quenched in water (2.685∗10−6kg/s & 450s), while that of untreated anode is only 2.023∗10−6kg/s and 348s. Thermal treatment of copper anodes has a good effect on the specific energy required for the electrorefining process where it is about 0.329kWh/kg when quenched anode in water is electrolyzed, while it is about 0.491kWh/kg when untreated anode was electrorefined.

Effect of Thiosulfate on Pitting Corrosion of 316SS: I. Critical Pitting Temperature and Pit Chemistry

In this research, the effect of thiosulfate ion on pitting corrosion behavior of 316 stainless steel was studied. Part I of this work deals with the influence of thiosulfate on the critical pitting temperature of 316 SS in 0.1 M chloride solution and studies the effect of this ion on the pit chemistry. Electrochemical experiments performed in absence and presence of 0.01 M thiosulfate ion revealed that thiosulfate deteriorates the CPT. Pencil electrode studies showed that thiosulfate addition decreases both saturation concentration of metal cations necessary to metal salt precipitate at the pit bottom (CS) (the value of diffusion controlled limiting current density (iLim) was decreased) and the ratio of C*/CS (where C* is the critical concentration of metal cations in pit solution essential for a pit to remain stable) while it increases the anodic dissolution rate in a simulated pit solution. Furthermore, scanning electron microscopy showed that the lacy cover formed over the pits mouth has coarser pore structure in the presence of thiosulfate ion.

Effect of stress on electrochemical characteristics of pre-cracked ultrahigh strength stainless steel in acid sodium sulphate solution

The electrochemical behaviors of ultrahigh strength stainless steel Cr12Ni5MoCo14 at crack tip under applied stress were studied by micro-electrochemical measurements as well as finite element analysis. The non-uniform distribution of the stress and strain induces a higher electrochemical activity at crack tip and promotes the anodic dissolution rate. The corrosion rate increases with increasing applied stress. In the elastic stress range, the effect of the applied stress on the electrochemical behaviors of Cr12Ni4Mo2Co14 steel is small. In the plastic stress range, the plastic deformation has a dramatic effect on the mechanical–electrochemical interaction and enhances the anodic activity.

Examination of the electropolishing behaviour of 73 brass in a 70% H3PO4 solution using a rotating disc electrode

The electropolishing behaviour of 73 brass in a 70% H3PO4 solution was studied using a rotating disc electrode (RDE). Based on the results of an anodic polarisation test, a transition peak from kinetic-controlled to diffusion-controlled dissolution was detected when a blue Cu2+-rich layer was developed on the RDE. The blue Cu2+-rich layer impedes the anodic dissolution rate of the brass-RDE and is essential for levelling during electropolishing. Potentiostatic polishing at different locations on the limiting-current plateau was studied. By polishing at the transition-peak potential, grain boundaries were preferentially etched. In contrast, a well-polished surface with a nanosized surface roughness (Ra) was achieved after electropolishing in the middle of the limiting-current plateau. By polishing at the end of the limiting-current plateau at a relatively low rotational speed, nipple-like and flow-streak features were observed. The formation of these features is attributed to the evolution of oxygen bubbles on the RDE surface. Mechanisms for the formation of the above-mentioned features were proposed.

Effects of Stress Intensity Factor on Electrochemical Corrosion Potential at Crack Tip of Nickel-Based Alloys in High Temperature Water Environments

Abstract Stress will enhance the local anodic dissolution rate of nickel-based alloys at crack tip and accelerate the crack propagation in high temperature water environments. The relationship between stress and corrosion was studied by the elastic plastic finite element method. The effects of stress intensity factor on the surface electrochemical corrosion potential (ECP) at the crack tip of alloys 600 with a 1T-CT specimen in simulated boiling water reactor environment were analyzed. The effects of plastic deformation and elastic deformation on the changes of the electro-chemical corrosion potential around the crack tip were also discussed. The results indicate that the effects of stress intensity factors on ECP changes of the crack tip surface have the maximum values in the front of the crock propagation, and they decrease gradually towards the sides of the crack. The values of ECP changes increase with the increase of stress intensity factor. The effect of plastic deformation is more obvious than that of elastic deformation.

Intensification of the rate of electropolishing and diffusion controlled electrochemical machining by workpiece oscillation

The effect of electrode oscillation on the rate of diffusion-controlled anodic processes such as electropolishing and electrochemical machining was studied by measuring the limiting current of the anodic dissolution of a vertical copper cylinder in phosphoric acid. Parameters studied were frequency and amplitude of oscillation, and phosphoric acid concentration. Within the present range of conditions, electrode oscillation was found to enhance the rate of anodic dissolution up to a maximum of 7.17 depending on the operating conditions. The mass transfer coefficient of the dissolution of the oscillating vertical copper cylinder in H3PO4 was correlated to other parameters by the equation: Sh=0.316Sc0.33Rev0.64.The importance of the present study for increasing the rate of production in electropolishing and electrochemical machining, and other electrometallurgical processes limited by anode passivity due to salt formation such as electrorefining of metals was highlighted.

The effect of thallium ions on the gold dissolution rate in thiosulfate electrolytes

The effect of TlNO3 additions in the concentration (c 1) range from 5 × 10−6 to 1 × 10−4 M on the anodic dissolution of gold in sodium thiosulfate solutions with the concentration (c 2) from 0.005 to 0.2 M is studied by voltammetry on the electrode surface renewed by cutting off a thin metal layer immediately in solution and also by the quartz-crystal microbalance method. For c 2 = 0.2 M, as c 1 increases from 5 × 10−6 to 1 × 10−4 M, the gold anodic dissolution rate is observed to increase from 0.02 (in the absence of TlNO3) to 0.75 mA/cm2 for c 1 = 7.5 × 10−5 M according to a nearly linear law. The dissolution accelerates because the effective values of the transfer coefficient and the exchange current density increase from 0.2 and 4 μA/cm2 (in the absence of TlNO3 admixtures) to 0.47 and 35 μA/cm2 (for c 1 = 1 × 10−4), respectively. Experiments with the renewal of the electrode surface in the course of electrolysis suggest that the gold dissolution is catalyzed in the presence of thallium ions by the adsorption mechanism and also as the result of the mixed kinetics of their adsorption on the electrode surface.

Formation of high purity Si nanofiber from metallurgical grade Si by molten salt electrorefining

We studied the purification of metallurgical grade Si from solutions of K2SiF6 in fluoride melts using a molten salt electrorefining process at 700 °C. Electrorefining close to the deposition potential gave dense, coherent, and well-adherent deposits. It was shown that the deposition rate and microstructure of Si strongly depend on the process temperature. Deposited polycrystalline silicon has a well defined rod shape and crooked structure that varies with current density. The anodic dissolution rate is affected by the initial concentrations of K2SiF6 and the applied current density. The results of an inductively coupled plasma (ICP) analysis indicated that recovered silicon fiber deposits with purities greater than 99.98% can be obtained using the developed technique. The morphology of the electrodeposited silicon on silver substrates is discussed in the context of a cathodic reaction on the electrode surface, and a comprehensive explanation of the purification mechanism with salt removal is provided.

Coupling of electrochemical techniques to study copper corrosion inhibition in 0.5 mol L−1 NaCl by 1-pyrrolidine dithiocarbamate

In this work, as for the preliminary step to the protection of Al 2xxx alloys, the anticorrosion effect of environmentally friendly 1-pyrrolidine dithiocarbamate (PDTC) on Cu was investigated by combining various electrochemical methods in addition to SEM-EDS analyses and gravimetric measurements. The Cu/PDTC system was used as a model to simulate the inhibition of Cu-rich particles contained in Al 2xxx alloys. The corrosion test solution was 0.5molL−1 NaCl in the presence of 10−4, 10−3, or 10−2molL−1 PDTC. The immersion time of the copper electrode was extended generally up to 24h. By EQCM measurements, a marked protective effect of PDTC was observed for the highest PDTC used, and corroborated by voltammetry and EIS measurements. The cathodic reduction under constant current allowed determining the corrosion products remaining on the copper surface in terms of electrical charge. The protective effect of PDTC was explained by the formation of highly stable compounds on the copper surface, which decreases the rate of both anodic dissolution and oxygen reduction reaction.