Dissolution Rate Of Zinc Research Articles

Galvanic Corrosion Behavior of Zn and Al Couples in NaCl Solution

Multi-materialization is being promoted in automotive structural materials, and fuel economy is being improved by replacing steel with aluminum and other lightweight metallic materials. Automotive steel is often galvanized for corrosion protection, and galvanic corrosion of aluminum and zinc in an atmospheric environment is a very important issue in evaluating automotive durability. Zinc is usually considered to be an anode when combined with aluminum, but its galvanic corrosion behavior can be complicated by environmental conditions because the corrosion potentials of the two are relatively close. Therefore, the objective of this study is to investigate the galvanic corrosion behavior of the couples consisting of zinc and aluminum under corrosive environmental conditions.The galvanic couple used in this study was fabricated from AA1050 Al and zinc plates. The width and length of both plates are 10 mm and 15 mm, respectively. After connecting lead wires to each plate, both plates were embedded in epoxy resin. To fabricate coplanar galvanic couples in this study, both plates were placed separately along the surface from a gap size of 500 um. The surfaces of the galvanic pairs were polished with SiC paper to JIS 2000 grit and cleaned with EtOH. The test solutions used in this study were aqueous NaCl solutions of various concentrations from 0.01 to 2 M, prepared with Milli-Q water and reagent grade chemicals. Galvanic currents and corrosion potentials were measured to investigate the galvanic corrosion behavior of the couples after 72 hours of galvanic corrosion experiments in the test solutions.The results of the galvanic corrosion test showed that the immersion potentials of the galvanic couples were lower at higher NaCl concentrations. The galvanic current decreased with immersion time, finally reaching about 1 uA in all NaCl solutions. The results of the electrochemical impedance measurements for galvanic couples in various NaCl concentrations showed that the impedance gradually increased with immersion time. It was also found that the impedance can be expressed as an electrical equivalent circuit consisting of two time constants, and that the impedance increases at intermediate frequencies between 0.1 and 1 Hz, which is thought to correspond to the dissolution reaction of Zn. This was the same trend as the behavior of the galvanic current. These results suggest that prolonged immersion reduces the galvanic current and the dissolution rate of zinc due to the passivation of the A1050 surface and the suppression of cathodic reactions.

Мырыш электродын өндірістік айнымалы токпен натрий хлориді ерітіндісінде поляризациялау арқылы мырыш оксидін алу

The purpose of the work is to dissolve the zinc electrode during polarization with an alternating current with a frequency of 50 Hz and to obtain zinc oxide. It is shown that the pre-recorded anode-cathode cyclic potentiodynamic polarization curves allow to predict to a certain extent the processes occuriing on the zinc electrode during alternating current polarization. It has been established that when two zinc electrodes are polarized in sodium chloride with an alternating current with a frequency of 50 Hz, they do not dissolve, but when one electrode is replaced with a titanium one, zinc dissolves intensively with the production of zinc hydroxide. It is shown that the rate of zinc dissolution directly depends on the current density at the titanium electrode. When the values of the current density on the titanium electrode change in the range of 5-10 kA/m2, the zinc dissolution current efficiency exceeds 100%. Based on the results of the research, it was established that zinc (II) hydroxide is produced during electrolysis, and zinc oxide can be obtained by dehydration. The composition of the resulting compound was identified by X-ray phase and elemental analyses

Engineering a zinc-rich ethyl silicate coating based on nickel oxide nanoparticles for improving anticorrosion performance

In this research, nickel oxide (NiO) nanoparticles with different concentrations of 1, 2, 3, and 4 wt% were added to a zinc-rich ethyl silicate (ZRES) coating containing 90 wt% zinc dust particles to promote the cathodic and barrier performance of coating systems. FTIR, XRD, and EDX analysis indicated the chemical composition and created bonds in ZRES coatings. SEM, AFM and TEM images showed the surface roughness and particle size in ZRES structure. Also, TEM confirmed the uniform dispersion of NiO nanoparticles in the coating matrix loaded with 3 wt% NiO particles. The effect of NiO content and the anticorrosion behavior of nanocomposite coatings were investigated by different techniques, including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) and salt spray tests. Results revealed that ZRES coatings containing 3 wt% NiO nanoparticles had boosted sacrificial anode and barrier protection during 120 days of immersion in a 3.5 wt% NaCl solution. The addition of 3 wt% NiO into the coating system significantly reduced corrosion products and blisters while increasing corrosion resistances from 3069 Ω cm2 to 16482 Ω cm2 compared with the control ZRES sample. This high-performance anticorrosion behavior of the nanocomposite coatings is mostly due to the NiO nanoparticles, which have the capability to moderate the zinc dissolution rate in addition to improving the barrier by filling porosity and creating tortuous paths.

Cathodic Polarization Behavior of Steel in Aqueous MgCl2 Solutions Containing Zn2+

So far, we have revealed that the dissolution rate of zinc is accelerated in relative high concentrations of MgCl2 in the corrosion process of galvanic couples consisting of zinc and steel. In this study, we investigated the cathodic polarization behavior of steel in MgCl2 solution containing Zn2+ and the effect of Zn2+ dissolved in the solution on the oxygen reduction reaction and hydrogen evolution reaction.The specimens used in the experiments were carbon steel SS400 (Fe-0.12C-0.60Mn-0.011P-0.019S) machined into a 1.5×1.5×0.3 cm3. One side of the specimen was polished with SiC abrasive paper up to #2000 grit and degreased in acetone before being used for the experiment. The test solution was mixtures of 0.25 M MgCl2 + x mM ZnCl2 (x = 2.5, 5 mM, Mg/Zn molar ratio: 100, 50) at room temperature under a naturally aerated condition. As a comparison solution, 0.5 M NaCl + y mM ZnCl2 (x = 5, 10 mM, molar ratio of Na/Zn: 100, 50) with the same chloride ion concentrations were used. Cathodic polarization curves of steel were measured using a three-electrode method with a platinum wire as the counter electrode and an Ag/AgCl electrode (saturated KCl, SSE) as the reference electrode. The potential sweep rate was 0.5 mV/s. After the polarization test, the specimen surfaces were observed with a scanning electron microscope and analyzed for corrosion products formed during cathodic polarization with XRD and laser Raman spectroscopy.The cathodic polarization behavior of steel in MgCl2 solution without Zn2+ was investigated and compared with that of NaCl solution without Zn2+. Diffusion-limited currents of dissolved oxygen reduction (ORR) were observed at -0.6 V to -0.8 V in MgCl2 and NaCl solutions. Furthermore, cathodic polarization in MgCl2 and NaCl solutions showed an increase in current due to hydrogen evolution reaction (HER), and the cathodic current due to HER on steel was larger in the MgCl2 solution than in the NaCl solution. To investigate the difference in HER in both solutions, the steel surface was observed after constant polarization at -1.0 V for 20 min. Mg(OH)2 deposition was observed on the steel surface in the MgCl2 solution, but not in the NaCl solution. This indicates that the increase in pH due to ORR and HER is mitigated by the formation of Mg(OH)2 during cathodic polarization. Therefore, due to the pH buffering action of Mg2+ associated with the formation of Mg(OH)2, it can be considered that a larger HER current flowed in the MgCl2 solution than in the NaCl solution when compared at the same potential.On the other hand, cathodic polarization curves for steel in MgCl2 and NaCl solution containing Zn2+ were investigated. As a result, ORR and HER were observed at potentials down to -1 V in the MgCl2 and NaCl solutions containing Zn2+; the cathodic current due to ORR and HER in the MgCl2 and NaCl solutions containing Zn2+ was reduced compared to the solutions without Zn2+. The inhibition of ORR and HER can be attributed to the precipitation of Zn corrosion products.These results suggest that in solution environments containing Mg2+ and Zn2+, the promotion of HER by the effect of Mg2+ and the inhibition of HER and ORR by Zn corrosion products occur simultaneously.

The pH dependence of dissolution kinetics of zinc oxide

Zinc oxide (ZnO) powders are used as feed additives for supplementation in diet of animals. Because zinc dissolution rate strongly influences the digestibility of zinc by animals and their stomach has variable pH, the dissolution kinetics of ZnO are studied at the several pH of relevance between 2 and 4. The dissolution of ZnO has been investigated with the help of modeling the dissolution kinetics measured in vitro at various pH. Dissolution is faster in acidic medium. But the acceleration of dissolution at low pH is moderate compared to what would be expected on the basis of the strong pH dependence of ZnO solubility. The concentration of Zn2+ in the quiescent medium at the surface of ZnO particles is much lower than its solubility. It is proposed as a rationale, that hydroxide anions released during dissolution accumulate at the surface of the positively charged ZnO surface, and that the dissolution kinetics is mainly controlled by the diffusion of H+ ions from the bulk solution to the surface.

Dissolution kinetics of marmatite in sulfuric acid-ferric sulfate‑sodium chloride‑oxygen media at atmospheric pressure

An experimental investigation was carried out to improve the zinc dissolution rate in the direct atmospheric leaching of marmatite by adding sodium chloride to the sulfuric acid-ferric sulfate‑oxygen media. The experiments were carried out by using mono-sized marmatite particles varying the concentrations of sulfuric acid from 0.1 to 1.3 M, ferric sulfate from 0 to 0.8 M, sodium chloride from 0 to 1.3 M, and temperature in the range of 60 to 95 °C. The results showed that the addition of 0.7 M of sodium chloride improved drastically the direct leaching kinetics of the zinc sulfide; therefore, this leaching media is an excellent alternative to produce zinc from marmatite concentrates at ambient pressure. The sulfuric acid concentration was also found to have a significant effect on the rate of dissolution, indicating that the non-oxidative dissolution of marmatite plays an important role in the reaction mechanism in this system. A shrinking core model with diffusion through a product layer control was found to fit the reaction rate. An apparent activation energy value of 81.8 kJ/mol was found for the temperature range of 60–95 °C. The direct atmospheric leaching of marmatite in H2SO4-Fe(SO4)1.5-NaCl-O2 is an excellent alternative method to extract zinc due to high dissolution rates obtained in the presence of chloride ions, reducing substantially the treatment times.

Determination of Optimum Process Conditions by Central Composite Design Method and Examination of Leaching Kinetics of Smithsonite Ore Using Nitric Acid Solution

The leaching behavior of Tunceli smithsonite ore in nitric acid was evaluated in two study steps including optimization of leaching process and kinetics modeling. The individual and synergistic effects of effective parameters such as nitric acid concentration, solid-to-liquid ratio, stirring speed, and temperature on the dissolution rate of zinc were investigated using central composite design. Four factors including temperature (30–50 °C), nitric acid concentration (0.2–0.5 mol/L), stirring speed (350–600 rpm), and solid-to-liquid ratio (0.004–0.01 g/L) were investigated. The dissolution percent of zinc (97%) was obtained in 120 min of leaching time: acid concentration 0.5 mol/L, temperature 50 °C, stirring speed 500 rpm, and solid–liquid ratio 2/500 g/mL at the optimum conditions obtained using the central composite design. The dissolution kinetics of smithsonite was examined according to heterogenous models and it was found that the dissolution rate was controlled by ash layer diffusion process. It was found that the leaching rate increased with increasing temperature, stirring speed, and acid concentration as well as decrescent particle size and solid/liquid ratio. The trial data were analyzed by statistical and graphical methods and the activation energy of this leaching process was determined to be 28.63 kJ·mol−1.

Leisure craft sacrificial anodes as a source of zinc and cadmium to saline waters

Sacrificial anodes are attached to the hulls of boats and marine structures to prevent corrosion. Their use inevitably leads to release of zinc as well as impurities in the zinc alloy such as cadmium to the saline environment. Risk assessments and source apportionment exercises require accurate assessments of the potential loads of chemicals into the environment. This research has surveyed a wide variety of zinc anodes for their composition to compare against a reported industry standard as well as using differing methodologies to determine the dissolution rate of zinc and cadmium from anodes. A zinc dissolution rate of 477 g/yr/kg of anode is proposed. Although most anodes tested had concentrations of cadmium within the prescribed limits set by the reported standard, calculated leaching rates from laboratory dissolution experiments suggested as much as 400 g per year of cadmium could leach from zinc anodes used on leisure vessels within UK waters.

Lignosulfonate, anionic surfactants and their mixtures influence on water solutions surface tension and zinc concentrate pressure leaching

The formation of elemental sulfur during sulfide concentrate pressure leaching leads to the appearance of sulfur-sulfide granules, which significantly reduces zinc dissolution rate. The solution for this problem was the use of surfactants, which prevents the negative effect of molten sulfur, avoiding the granule formation during leaching. Lignosulfonates (waste from the woodworking industry) are most often used as reagents for sulfide concentrate pressure leaching. Influence of individual and mixtures of surfactants on surface tension of aqueous solutions, zinc extraction and size-grade distribution of cakes after sulfide zinc concentrate pressure leaching. Surface tension of aqueous solutions was analyzed by stalagmometric method. Leaching was performed in titanium autoclave in presence of lignosulfonate, sodium dodecylbenzenesulfonate and sodium dodecylsulfate. Solutions after leaching were analyzed on zinc by atomic absorption spectroscopy. Size-grade analysis of cakes after leaching was carried out by laser diffraction particle size analyzer. In this work, synergetic influence was observed of anionic surfactants and lignosulfonate on decreasing of aqueous solutions surface tension. The best results were obtained when LS-SDBS mixture was used, namely in the range of sodium dodecylbenzenesulfonate concentrations 400-600 mg / l. Usage of combined surfactants allowed to achieve high rates of zinc extraction and optimal particle size of cakes after leaching. At Ls and SDBS using zinc extraction was increased from 77,2 % up to 82,8 %, with the bulk of the cake (96,7%) having a particle size of -150 μm. Combined surfactants usage (lignosulfonate and sodium dodecylbenzenesulfonate) can be recommended for applying at pressure leaching of sulfide zinc concentrates.

Dissolution kinetics of hemimorphite in trichloroacetic acid solutions

In this study, the dissolution kinetics of hemimorphite in the presence of the organic reagent, trichloroacetic acid (TCAA), was investigated. Experimental variables such as reaction temperature (293–323K), TCAA concentration (0.084–0.184mol/dm3), particle size (0.081–0.214mm), and stirring speed (200–650rpm) were studied to determine the influence on the zinc dissolution rate, and a kinetic model was developed to represent the relationship. The results demonstrated that during the leaching process, zinc was rapidly dissolved in TCAA and the zinc leaching rate increased as a function of increased reaction temperature, TCAA concentration, and stirring speed, and decreased particle size. Among the kinetic models of the porous solids tested, a new variant of the shrinking-core model well described the zinc leaching kinetics. The activation energy was determined to be 54.94kJ/mol, and the rate of reaction equation [1−(2/3)x−(1−x)2/3]2=[11.24(C)3.80946(PS)−2.00833(SS)1.62147exp(−54.94/RT)]t was also obtained to describe the process.

Enhancing the Cycle Life of a Zinc–Air Battery by Means of Electrolyte Additives and Zinc Surface Protection

The commercialization of rechargeable alkaline zinc–air batteries (ZAB) requires advanced approaches to improve secondary zinc anode performance, which is hindered by the high corrosion and dissolution rate of zinc in this medium. Modified (with additives) alkaline electrolyte has been one of the most investigated options to reduce the high solubility of zinc. However, this strategy alone has not been fully successful in enhancing the cycle life of the battery. The combination of mitigation strategies into one joint approach, by using additives (ZnO, KF, K2CO3) in the base alkaline electrolyte and simultaneously preparing zinc electrodes that are based on ionomer (Nafion®)-coated zinc particles, was implemented and evaluated. The joint use of electrolyte additives and ionomer coating was intended to regulate the exposition of Zn, deal with zincate solubility, minimize the shape change and dendrite formation, as well as reduce the hydrogen evolution rate. This strategy provided a beneficial joint protective efficiency of 87% thanks to decreasing the corrosion rate from 10.4 (blank) to 1.3 mgZn cm−1·s−1 for coated Zn in the modified electrolyte. Although the rate capability and capacity are limited, the ionomer-coated Zn particles extended the ZAB cycle life by about 50%, providing battery roundtrip efficiency above 55% after 270 h operation.

Direct sulfuric acid leaching of zinc sulfide concentrate using ozone as oxidant under atmospheric pressure

The use of ozone as an oxidant for the direct leaching of zinc sulfide (sphalerite) concentrate in sulfuric acid medium under atmospheric pressure was explored. The influence of acid concentration, feed gas injection rate, particle size distribution, stirring speed, temperature and slurry density on zinc extraction efficiency was examined. The experimental results showed that the leaching efficiency depends on all of these operating parameters except for stirring speed. It was found that essentially complete dissolution of zinc from the concentrate with the present method can be achieved in only about seven hours under the conditions of sulfuric acid concentration of 2 mol/L, particle size smaller than 74 µm, slurry density of 50 g/L, stirring speed of 420 rpm and feed gas injection rate of 1 L/min at ambient temperature. The experimental results suggest that the dissolution reactions produce independent elemental sulfur that is readily floated and can be easily separated rather than forming a layer on the surface of the reacted particle, as usually observed in a system with ferric-sulfate as oxidizing agent. It was therefore determined that the dissolved ozone play a key role in improving the rate of zinc dissolution from the concentrate. Analysis of the leaching kinetics indicate that the leaching rate follows the shrinking particle model, and the overall dissolution rate of zinc is controlled by a surface reaction.

Photocatalytic and antibacterial properties of ZnO films with different surface topographies on stainless steel substrate

Zinc oxide films with three types of topographies: needle-like and hexagonal rods and flakes, were prepared by hydrothermal synthesis on stainless steel substrates to investigate their photocatalytic and antibacterial properties. The photocatalytic activity was measured with a methylene blue (MB) discoloration test, whereas a method using bioluminescent whole cell bacterial biosensors enabling the constant monitoring of the amount of living cells on the surfaces was used here to study the antibacterial properties. The results showed that photocatalytic activity was clearly influenced by the surface area, which is in turn dependent on the topography. Moreover, it was found that all the examined films decreased notably the amount of Staphylococcus aureus and Escherichia coli on the surfaces. Despite significant differences in the surface areas of the studied samples that led to different zinc dissolution rate in aqueous environment, no notable differences in antibacterial activity between the films with different morphologies could be detected. These results are presented and discussed in this paper.

Role of steel and zinc coating thickness in cut edge corrosion of coil coated materials in atmospheric weathering conditions; Part 1: Laboratory study

Abstract Cathode surface area and its ability to reduce oxygen controlled the rate of zinc dissolution and paint delamination from cut edges of hot dip galvanised steel sheets. Zinc corrosion products deposited on steel in atmospheric exposure conditions inhibited oxygen reduction decreasing galvanic current and zinc dissolution and paint delamination. The opposite effect was observed for iron corrosion products. The initial steel substrate and zinc coating thicknesses affected the availability of zinc ions for formation of the protective film.

A Zn(ClO4)2 Supporting Material for Highly Reversible Zinc–Bromine Electrolytes

In the case of a conventional zinc bromide electrolyte solution using zinc chloride as additive, an undesirable reaction occurs. In this reaction, complex anions form between zinc and the chloride ions during charging and discharging. To overcome this problem, this paper describes an excellent electrolyte solution using zinc perchlorate as the additive, resulting in a highly stable and reversible reaction in zinc–bromine flow cells. To show the effectiveness of the proposed solution, electrochemical analyses are carried out using cyclic voltammetry, a miniature zinc–bromine flow cell, and scanning electron microscopy. The solution is then compared with the conventional electrolyte solution using zinc chloride as the supporting material. Experimental results show that use of the zinc perchlorate additive increases the rate of zinc dissolution by improving the reaction rate of bromine in the catholyte half‐cell. Consequently, this arrangement allows a highly stable operation for improving the current efficiency of zinc–bromine flow batteries.

Leaching performance of imidazolium based ionic liquids in the presence of hydrogen peroxide for recovery of metals from brass waste

The application of ionic liquids (ILs), 1-methylimidazolium hydrogen sulfate (HmimHSO4), 1-ethyl-3-methylimidazolium hydrogen sulfate (HmimHSO4) and 1-butyl-3-methylimidazolium chloride (BmimCl) as leaching agents was investigated in the leaching of copper and zinc from brass waste in the presence of an oxidant, hydrogen peroxide (H2O2). Factors that affect copper and zinc dissolution rates such as ionic liquid concentration, time and temperature were investigated. The results indicated that zinc was dissolved in leach solutions with EmimHSO4 and HmimHSO4, completely. Temperature had no considerable influence on copper dissolution rate whilst the rate increased with decreasing IL concentration. In the EmimHSO4 system, higher copper recoveries were achieved with 40% and 60% IL concentrations compared with IL concentrations of 20% and 80% at 40 °C leaching temperature. Copper dissolution rates decreased with EmimHSO4 concentration at 60 °C and 80 °C in the following order; 40% > 20% > 60% > 80%. On the other hand the leaching system with BmimCl generally resulted in poor extractions of copper and zinc.

The effects of Pb-Zn flotation reagents on the bioleaching process by mesophilic bacteria

The flotation reagents absorbed on the mineral surfaces may have some positive or negative effects on the bacteria involving in the bioleaching process; however a few researches have paid attention to these effects. In this research, the effects of the galena and sphalerite flotation reagents on the activity of mesophilic bacteria were investigated. The bioleaching experiments were carried out using three microbial species including Acidithiobacillus Ferrooxidans (AF), Acidithiobacillus Thiooxidans (AT), Leptosprillum Ferrooxidans (LF), and also the mixed culture of these mesophilic microorganisms. The flotation reagents were used exactly in similar concentrations and in the same way as applied in the industrial lead-zinc flotation plants. Moreover, the effects of two xanthate collectors of potassium ethyl xanthate (KEX) and potassium amyl xanthate (KAX) were separately studied on the bioleaching of zinc sulphide by AF bacteria. The zinc dissolution rate under bioleaching process was increased due to the cumulative effects of the flotation reagents at the concentration ranges needed to float both galena and sphalerite minerals. However, such a positive effects of the reagents was more pronounced on the mixed-culture of bacteria compared to that of single species. The maximum zinc extraction was 97% after 30days using the mixed-culture bacteria in the presence of chemical flotation reagents while it was only 74% in the absence of the flotation reagents. It should be noted that the corresponding percentages of zinc extraction for AF bacteria were 86% and 64% and for the LF bacteria were 70% and 61%, respectively. An increase in the bioleaching rate was also observed when the KAX collector was added into the solid sample instead of adding to the solution of cell culture media. The zinc extraction was increased from 64% to 74% when the solid sample was conditioned by adding 350g/t of KAX to the solid sample before bioleaching.

A Novel Coupling Between Atomic Emission Spectroelectrochemistry and Electrochemical Impedance Spectroscopy: Application to Zn, Zn-Cu and Zn-Al-Mg Alloys

A novel coupling between atomic emission spectroelectrochemistry (AESEC) and electrochemical impedance spectrometry (EIS) is demonstrated. With the AESEC - EIS combination it is possible to distinguish situations in which the oxidation of the metal leads directly to the formation of dissolved ions or passes through a slightly soluble film intermediate. In the former case, it is possible to measure fundamental electrokinetic parameters in a single experiment. In recently published work, this technique was used to investigate the kinetics of dissolution for nearly pure Zn and Mg [1,2]. This poster will present the basic technique and show additional applications to alloys of two and three elements (Zn-Cu and Zn-Al-Mg). The methodology is illustrated with three examples: 1) Zn dissolution versus film formation: This simple system is used to demonstrate the fundamentals of the technique as it involves only a single element. Zn dissolution 0.1 M NH4Cl occurs without any significant solid intermediate as evidenced by the excellent correlation between the AC components of the electrical current and the zinc dissolution rate (See Figure). Analysis of the dissolution rate and total current transients as a function of potential directly yields the anodic and cathodic Tafel slopes for this system. In contrast, for Zn / 0.5 M NaCl, electrochemical oxidation leads directly to the formation of an intermediate corrosion product film with subsequent dissolution. [1] 2) Brass dissolution in a citrate buffer and in synthetic tap water: The AESEC - EIS experiment was used to demonstrate that brass dissolution occurs in a nearly congruent fashion in a citrate buffer of pH = 5. However in a synthetic tapwater solution containing sulfates and carbonates, insoluble Cu(I) species are formed leading to differences between the Zn and Cu partial impedances. 3) Zn-Al-Mg dissolution in an ammonium buffer at pH=10.2: In this situation, Zn and Mg dissolve normally, in phase with the electrical current. However Al dissolution is shifted 180° out of phase with Zn and Mg dissolution, showing an increase with increasing cathodic current, probably due to the cathodic dissolution of Al [3]. 1) V Shkirskiy, K Ogle, "A novel coupling of electrochemical impedance spectroscopy with atomic emission spectroelectrochemistry: Application to the open circuit dissolution of zinc", Electrochimica Acta 168(2015)167-172. 2)V Shkirskiy, AD King, O Gharbi, P Volovitch, JR Scully, K Ogle, N Birbilis, "Revisiting the Electrochemical Impedance Spectroscopy of Magnesium with Online Inductively Coupled Plasma Atomic Emission Spectroscopy", ChemPhysChem 16( 2015)536 – 539.3) M Serdechnova, P Volovitch, F Brisset, K Ogle, "On the cathodic dissolution of Al and Al alloys", Electrochimica Acta 124(2014)9-16 Fig. 1 Open circuit dissolution of zinc (galvanized steel) in 0.1 M NH4Cl showing jZn (Zn dissolution rate expressed as a current) followed by an EIS experiment from 10 kH to 0.00398 Hz . Figure 1

A novel coupling of electrochemical impedance spectroscopy with atomic emission spectroelectrochemistry: Application to the open circuit dissolution of zinc

A novel coupling between atomic emission spectroelectrochemistry (AESEC) and electrochemical impedance spectrometry (EIS) is demonstrated. In this way, it is possible to distinguish situations in which the oxidation of the metal leads directly to the formation of dissolved ions or passes through a slightly soluble film intermediate. It was found that Zn dissolution 0.1M NH4Cl occurs without any significant solid intermediate as evidenced by the excellent correlation between the AC components of the electrical current and the zinc dissolution rate. Analysis of the dissolution rate and total current transients as a function of potential directly yields the anodic and cathodic Tafel slopes for this system. In contrast, for Zn/0.5M NaCl, electrochemical oxidation leads directly to the formation of an intermediate corrosion product film with subsequent dissolution.

Kinetic Study and Mathematical Model of Hemimorphite Dissolution in Low Sulfuric Acid Solution at High Temperature

The dissolution kinetics of hemimorphite with low sulfuric acid solution was investigated at high temperature. The dissolution rate of zinc was obtained as a function of dissolution time under the experimental conditions where the effects of sulfuric acid concentration, temperature, and particle size were studied. The results showed that zinc extraction increased with an increase in temperature and sulfuric acid concentration and with a decrease in particle size. A mathematical model able to describe the process kinetics was developed from the shrinking core model, considering the change of the sulfuric acid concentration during dissolution. It was found that the dissolution process followed a shrinking core model with “ash” layer diffusion as the main rate-controlling step. This finding was supported with a linear relationship between the apparent rate constant and the reciprocal of squared particle radius. The reaction order with respect to sulfuric acid concentration was determined to be 0.7993. The apparent activation energy for the dissolution process was determined to be 44.9 kJ/mol in the temperature range of 373 K to 413 K (100 °C to 140 °C). Based on the shrinking core model, the following equation was established: $$ 1.21\ln \left( {1 - 0.83x} \right) - \left[ {1.02\ln \frac{{0.35 + \left( {1 - x} \right)^{{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-0pt} 3}}} - 0.59\left( {1 - x} \right)^{{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0pt} 3}}} }}{{0.35 + \left( {1 - x} \right)^{{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-0pt} 3}}} + 1.18\left( {1 - x} \right)^{{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0pt} 3}}} }} + 3.52\arctan \left( {1.96\left( {1 - x} \right)^{{{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-0pt} 3}}} - 0.58} \right)} \right] + 2.06 = 42,192.59{\text{e}}^{{ - \frac{44,900}{{{\text{R}}T}}}} t. $$