Effect of Zn and Pb as alloying elements on the electrochemical behavior of brass in NaCl solutions

The electrochemical behavior of brasses with various Zn content (5.5–38 mass%) and brass (Cu–38Zn) with different Pb contents (1–3.4 mass%) in 0.6 M NaCl was investigated. The effects of temperature, immersion time, and concentration of chloride ions on the behavior of the different alloys were studied. The pitting corrosion behavior of Cu–Zn alloys and leaded–brass alloys in 0.6 M NaCl solution was also investigated. Open-circuit potential measurements (OCP), polarization techniques and electrochemical impedance spectroscopy (EIS) were used. The results show that the increase in the Zn content increases the corrosion rate of the brass alloys in chloride solutions, while the increase of Pb content in Cu–38Zn–Pb decreases the corrosion rate of the alloy. Long immersion time of the alloys in the aqueous electrolyte improves their stability due to the formation of passive film on the alloy surface. The breakdown potential is shifted to more negative direction with increasing the Zn content, whereas it shifts towards positive values with increasing Pb content. Equivalent circuit model for the electrode/electrolyte interface under different conditions was proposed to illustrate the electrochemical processes taking place at the interface. The electrochemical behavior of the different alloys was discussed in view of the fitting results.     

Effect of Zn and Pb contents on the electrochemical behavior of brass alloys in chloride-free neutral sulfate solutions

Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of brass alloys with various Zn contents (5.5–38.0 mass%) and Cu–38.0Zn–Pb alloy with different Pb contents (1.0–3.4 mass%) in neutral sodium sulfate solutions. The influence of working conditions, e.g., immersion time, sulfate ions concentration and temperature on the electrochemical behavior of the different alloys was also studied. It was found that the initial corrosion rate is relatively high for alloys with the higher zinc content due to dezincification. The dezincification process initiates by selective dissolution of zinc and continues by a simultaneous dissolution of copper and zinc followed by re-deposition of copper. An increase in the lead content and immersion time in the sodium sulfate solution increases the corrosion resistance of the alloy and improves its stability. The stability of the leaded brass was considered to be due to the formation of an insoluble film of lead sulfate on its surface. The impedance data were fitted to theoretical data obtained according to an equivalent circuit model describing the electrode/electrolyte interface. The mechanism of the alloy dissolution was discussed in view of the obtained results.     

Effects of Na and Cl co-doping on electrochemical performance in LiFePO4/C

Na⁺ and Cl⁻ co-doped LiFePO₄/C composites were prepared via a simple solid state reaction. The structure, valence state and electrochemical performance were carefully investigated. Rietveld refinement on X-ray diffractions reveals that Na⁺ and Cl⁻ have successfully been introduced into the lattice of LiFePO₄. X-ray photoelectron spectroscopy proves that the co-doping of Na⁺ and Cl⁻ does not change the chemical state of Fe(II). Experimental results further show that the co-doping contributes to induce the lattice distortion, modify the particle morphology, and increase the electronic conductivity. Considerably enhanced capacity, coulombic efficiency and rate capability were obtained in the co-doped LiFePO₄. The specific capacities are 157 mAh g⁻¹ at 0.2 C, 115 mAh g⁻¹ at 10 C and 98 mAh g⁻¹ at 20 C for the (Na⁺, Cl⁻) co-doped LiFePO₄/C cathode material. The improvement can be ascribed to the enhanced electronic conductivity and electrode kinetics due to the micro-structural modification promoted by co-doping.     

The Influence of Ni Content on the Stability of Copper—Nickel Alloys in Alkaline Sulphate Solutions

The electrochemical behaviour of copper–nickel alloys with different Ni content (5–65%) in sulphate solutions of pH 12 was investigated. The effects of temperature, immersion time, and concentration of sulphate ions were also studied. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. Potentiodynamic measurements reveal that the increase in nickel content increases the corrosion rate of the alloy in sulphate solution linearly. Nevertheless, an increase in the nickel content along with increase in immersion time improves the stability of the Cu–Ni alloys due to the formation of a stable passive film. An equivalent circuit model for the electrode/electrolyte interface under different conditions was proposed. The experimental impedance data were fitted to theoretical data according to the proposed model. The relevance of the model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.     

A study on the initiation of pitting corrosion in carbon steel in chloride-containing media using scanning electrochemical probes

Scanning electrochemical probes of corrosion potential and chloride ions were developed for the in situ monitoring of localized corrosion processes of reinforcing steel in NaCl-containing solution. The results indicated that the chloride ions (Cl⁻) preferentially adsorbed and accumulated at the imperfect/defective sites, resulting in initiation and propagation of pitting corrosion on the reinforcing steel surface. An electron microprobe analyzer (EMPA) was used to examine the corrosion morphology and elemental distribution at the corroded location to investigate the origins of the preferential Cl⁻ adsorption and pitting corrosion. By combining the in situ and ex situ images, we concluded that manganese sulfide inclusions in reinforcing steel are the most susceptible defects to pitting corrosion in chloride-containing solution.     

Experimental results on the direct electrochemical oxidation of methanol in PEM fuel cells

The cell performance of direct methanol fuel cells (DMFC) is 0.5 V at 0.5 A cm^–2 under high pressure oxygen operation (3 bar abs.) at 110 °C. However, high oxygen pressure operation at high temperatures is only useful in special market niches. Therefore, our work has now focused on air operation of a DMFC under low pressure (up to 1.5 bar abs.). At present, a power density of more than 100 mW cm^–2 can be achieved at 0.5 V on air operation at 110 °C. These measurements were carried out in single cells with an electrode area of 3 cm² and the air stoichiometry only amounted to 10. The effects of methanol concentration and temperature on the anode performance were studied by pseudo half cell measurements and the results are presented together with their impact on the cell voltage. A cell design with an electrode area of 550 cm², which is appropriate for assembling a DMFC stack, was tested. A three-celled stack based on this design revealed nearly the same power densities as in the small experimental cells at low air excess pressure and the voltage–current curves for the three cells were almost identical. At 110 °C a power output of 165 W at a stack voltage of 1.5 V can be obtained in the air mode.     

Effects of Zn or Ti substitution for Ni on the electrochemical properties of LiNiO2

LiNiO₂ and LiNi_1−yM_yO₂ (M = Zn and Ti, y = 0.005, 0.01, 0.025, 0.05, and 0.1) were synthesized with a solid-state reaction method by calcination at 750 °C for 30 h under oxygen stream after preheating at 450 °C for 5 h in air. LiNi_0.995Zn_0.005O₂ among the Zn-substituted samples and LiNi_0.995Ti_0.005O₂ among the Ti-substituted samples showed the best electrochemical properties. For similar values of y, LiNi_1−yTi_yO₂ had in general better electrochemical properties than LiNi_1−yZn_yO₂. Electrochemical properties seem to be closely related to R-factor but less related to I_0 0 3/I_1 0 4 value. In the FT-IR absorption spectra of LiNiO₂ and LiNi_1−yM_yO₂ (M = Zn and Ti, y = 0.005, 0.01, 0.025, 0.05 and 0.1), Li₂CO₃ was detected even if it is not observed from XRD pattern, with the samples LiNi_1−yZn_yO₂ (y = 0.05 and 0.1) showing Li₂ZnO₂ additionally. The smaller cation mixing of the Ti-substituted samples is considered to lead to their better electrochemical properties than the Zn-substituted samples.     

The anodic behaviour of Ebonex® in oxalic acid solutions

A study of the oxidation of aqueous solutions of oxalic acid in various supporting electrolytes, at an Ebonex^® anode is reported. From data obtained by cyclic voltammetry, linear sweep voltammetry, chronopotentiometry, controlled potential coulometry and gas chramatography it has been shown that oxalic acid oxidation at an Ebonex^® anode, does not proceed, to any significant extent. Data collected using different electrolytes showed that sulphuric acid supported higher current densities at similar electrode potentials. Ebonex^® is essentially a selective oxygen evolver and is thus a suitable anode for the electroreduction of oxalic acid to glyoxylic acid in an undivided cell. The behaviour of a platinized titanium anode is also reported and this material has similar electrochemical characteristics to Ebonex^® in aqueous oxalic acid solutions.     

Effects of a small addition of Mn on the corrosion behaviour of Zn in a mixed solution

The effects of a small addition of Mn (0.4 wt%) on the corrosion behaviour of pure Zn (99.995 wt%) in a mixed solution (0.1 M NaCl + 0.1 M Na₂SO₄ + 0.01 M NaHCO₃, pH 8.4) were investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and X-ray photoelectron spectroscopy (XPS). The electrochemical impedances of both Zn and Zn–0.4Mn have been successfully fitted with a suitable EIS equivalent circuit model. Fitted impedance results revealed that 0.4 wt% Mn improved both the pore resistance and charge transfer resistance of Zn in the mixed solution. As a result, both anodic and cathodic reaction rates were reduced. X-ray photoelectron spectroscopy (XPS) analysis showed that the corrosion films formed in the mixed solution consisted of zinc oxide (ZnO), zinc hydroxide (Zn(OH)₂) and zinc hydrozincite (Zn₅(CO₃)₂(OH)₆). The role of small addition of Mn is that it promotes the precipitation of hydrozincite in the pores of corrosion film. An “alleviation of local acidification” mechanism is proposed to explain the investigated results.     

4,4'-Diisothiocyanostilbene-2,2'-disulfonic Acid (DIDS) Ameliorates Ischemia-Hypoxia-Induced White Matter Damage in Neonatal Rats through Inhibition of the Voltage-Gated Chloride Channel ClC-2

Chronic cerebral hypoperfusion is believed to cause white matter lesions (WMLs), leading to cognitive impairment. Previous studies have shown that inflammation and apoptosis of oligodendrocytes (OLs) are involved in the pathogenesis of WMLs, but effective treatments have not been studied. In this study, 4,4''-diisothiocyanostilbene-2,2''-disulfonic acid (DIDS), a chloride (Cl⁻) channel blocker, was injected into chronic cerebral ischemia-hypoxia rat models at different time points. Our results showed that DIDS significantly reduced the elevated mRNA levels and protein expression of chloride channel 2 (ClC-2) in neonatal rats induced by ischemia-hypoxia. Meanwhile, DIDS application significantly decreased the concentrations of reactive oxygen species (ROS); and the mRNA levels of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha TNF-α in neonatal rats with hypoxic-ischemic damage. Myelin staining was weaker in neonatal rats with hypoxic-ischemic damage compared to normal controls in corpus callosum and other white matter, which was ameliorated by DIDS. Furthermore, the elevated number of caspase-3 and neural/glial antigen 2 (NG-2) double-labeled positive cells was attenuated by DIDS after ischemia anoxic injury. Administration of DIDS soon after injury alleviated damage to OLs much more effectively in white matter. In conclusion, our study suggests that early application of DIDS after ischemia-hypoxia injury may partially protect developing OLs.     

The effect of cytosine on the two-step electroreduction of Zn ions in acetic buffers

Cytosine plays an important role in many biological processes since it constitutes the buildings blocks of DNA and RNA. A two-step reduction of Zn²⁺ ions at the dropping mercury electrode in acetic buffers at pH 4 and 5 in the presence of cytosine was examined. The measurements were performed using an impedance method in a wide potential and frequency ranges.The values of the standard rate constants k_s in the both studied system decrease from 3.8 × 10⁻³ to 2 × 10⁻³ cm s⁻¹ at pH 4 and from 5.1 × 10⁻³ to 2.5 × 10⁻³ cm s⁻¹ at pH 5. The values of the standard rate constants k_s1 characterizing the stage of the first electron transfer decrease similarly. However, the values of the standard rate constants k_s2 characterizing the stage of the second electron exchange decrease more markedly in the buffer at pH 4 than in the buffer at pH 5.     

Effect of silicon alloying addition on the corrosion behaviour of aluminium in some aqueous media

The corrosion behaviour of three Al–Si alloys was studied after galvanostatic passivation in 0.1 M sodium tartrate, sulfate and borate solutions using EIS techniques. The degree of passivation depends on the anion type, the degree of polarization and the alloy composition. It was also found that increase in pH led to a decrease in polarization resistance R _p. The effect of formation voltage, V _f, on the growth and dissolution kinetics of the oxide grown on the alloys was studied. The polarization resistance value increases as V _f increases up to a certain value; above this the R _p value decreases. This critical V _f depends on the alloy composition and the test solution. The kinetics of oxide layer dissolution in the absence and presence of Cl^– ions was also studied. Increase in immersion time leads to a more severe attack by Cl^– ions as shown by the decrease in the value of R _p. At low Cl^– ion concentration the value of R _p is higher than that in chloride ion free sulfate solutions, because the rate of passive film repair is much higher than that of barrier layer dissolution. However, at high Cl^– ion concentration penetration of Cl^– through defects in the barrier layer leads to formation of an oxyhalide layer.     

铅、镉和锌污染对芦苇幼苗氧化胁迫和抗氧化能力的影响

对Pb, Cd和Zn胁迫下芦苇幼苗叶片和根内超氧阴离子自由基(O2-)和过氧化产物丙二醛(MDA)的含量、电解质渗漏以及超氧化物岐化酶(SOD)和过氧化物酶(POD)活性进行了研究. 结果表明，受3种重金属的影响，叶片和根内O2- 积累，MDA含量增加，伴随着电解质渗漏增大，显示发生了膜脂过氧化，细胞膜系统遭到破坏；作为植物抗氧化系统中的关键酶，SOD和POD活性高于对照，说明在重金属胁迫下芦苇幼苗体内的抗氧化能力增强. 可见，在重金属污染下细胞内O2- 浓度升高带来的膜脂过氧化增强是重金属伤害植物的主要原因；而保护酶系统SOD和POD活性的升高则可能是芦苇抗过氧化的机理之一.     

Influence of additives on Cu electrodeposition mechanisms in acid solution: direct current study supported by non-electrochemical measurements

The effect of polyethylene glycol (PEG) and chloride ions on copper electrodeposits is investigated by electrochemical measurements (cyclic voltammetry, current and potential pulses) coupled with an ellipsometric study at open circuit. When PEG is added to the Cu²⁺ solution, the modifications of the copper electrodeposition mechanism can be explained by a polymer-electrode interaction instead of a complex formation in solution. Since ellipsometry has shown no PEG adsorption at least at open circuit, that adsorption is assumed to be potential dependent. Moreover, the efficiency of PEG alone in solution, seems to be decreased when the deposit grows. With Cl⁻ alone, an activation of copper deposition is performed. The simultaneous addition of the two additives induces a blocking effect of the copper reduction that continues on with time. X-ray diffraction, optical microscopy and atomic force microscopy (AFM) carried out complementary results, on bulk deposits obtained from solution with and without these additives. It has been found that a bright, compact and homogeneous coating is only obtained in presence of both additives. In that case, the texture of the deposit is modified and the roughness is significantly decreased to 0.5 μm.     

Studies on electrochemical oxidation of azithromycin and Hemomycin at gold electrode in neutral electrolyte

The aim of the present study was to examine the oxidative properties and an assay of azithromycin and Hemomycin^® at a gold electrode in neutral electrolyte using cyclic linear sweep voltammetry. The maximum value of the current of the oxidation peak of pure azithromycin and azithromycin from Hemomycin^® at 0.6 V versus SCE in 0.05 M NaHCO₃ and in a mixture methanol −0.05 M NaHCO₃ (1:1) at a scan rate of 50 mV s⁻¹ is a linear function of the concentration in the range of 0.235-0.588 mg/cm³. HPLC analysis of the bulk of electrolyte confirmed the data obtained by analysis of the values of the current peak concerning the concentration of antibiotic in the investigated concentration range. The role of methanol, when present, is discussed. In the case of azithromycin, the presence of methanol leads to higher current peak values. However, in the case of Hemomycin^®, methanol should be avoided because of its inhibiting influence on the qualitative and quantitative determination of azithromycin and on the azithromycin/lactose separation.     

The influence of chloride ions and benzotriazole on the corrosion behavior of Cu37Zn brass in alkaline medium

This paper describes an investigation of the corrosion behavior of Cu37Zn brass in a solution of sodium tetraborate, at pH 10.0, with the addition of chloride ions and benzotriazole (BTA) inhibitor. The application of cyclic voltammetry has led to the conclusion that the anodic current densities increase with increase in immersion time in sodium tetraborate solution as well as in solutions of sodium tetraborate containing chloride ions of various concentrations. The values of anodic current density are considerably smaller in sodium tetraborate solutions with the addition of BTA compared with those in the inhibitor-free solution.The study also analyses the electrochemical behavior of Cu37Zn brass after various times of alloy exposure to BTA solution, as well as its behavior in BTA solutions of various concentrations. Also, the study describes the electrochemical behavior of Cu37Zn brass after the effect of Cl⁻ ions, but subsequent to the formation of a polymeric protective film on the electrode surface.     

Laboratory study of soil acidification and leaching of nutrients from a soil amended with various surface-incorporated acidifying agents

Granular S, finely-ground S, iron sulphate and aluminium sulphate were added at two rates to the surface (0–6 cm) of a soil and acidification and leaching of nutrients were measured over 12 months in a laboratory study. Iron and aluminium sulphate both rapidly lowered soil pH in the top 0–6 cm of the soil. There was little difference in soil pH after 3 and 12 months reaction of these two amendments. In contrast, for granular S and finely-ground S there were clear decreases in soil pH between 3 and 12 months reaction with the soil. Finely-ground S was oxidized in the soil faster than granular S and therefore had a more acidifying effect. The top 0–6 cm of the soil was acidified by all the agents used but the deeper soil was less affected. The only treatments which lowered the pH of the 12–18 cm layer below pH 6 were the high rates of iron and aluminium sulphate. Soil acidification resulted in a decrease in exchangeable Ca, Mg and K, an increase in exchangeable Al and a decrease in effective CEC in the acidified soil layers.At both levels of addition, total ionic strength of percolates from the soil followed the order: aluminium sulphate = iron sulphate > finely gound S > granular S > control and was higher at the higher rate of addition. The pH values of percolates followed the order: control > granular S > finely ground S > iron sulphate = aluminium sulphate and were lower at the higher rate of addition. For the amended soils there was a very close relationship between the pattern and total amounts of SO ₄ ^2- and Ca²⁺ leached.It was concluded that granular S is not an effective acidifying agent since it is oxidized very slowly in the soil and that acidfying agents should be incorporated to the depth that acidification is required.     

Electrochemical and XPS studies of sputter-deposited ternary Mn-Ta-Cr alloys in chloride-free and chloride-containing sulphuric acid solutions

Amorphous manganese-rich (67-80 at.%) Mn-Ta-Cr alloy films were prepared by DC magnetron sputtering method. The corrosion behavior and stability of the Mn-Ta-Cr alloy films were examined in chloride-free and -containing 1 M H₂SO₄. AC and DC electrochemical techniques in combination with XPS analysis were used. Mn-Ta-Cr alloys exhibited very high corrosion resistance and stability up to transpassive dissolution region of chromium. The high corrosion resistance of Mn-Ta-Cr sputtered films is based on the formation of double oxyhydroxide passive film composed mainly of chromium and tantalum. The partial substitution of tantalum with chromium improves the corrosion resistance of the sputter-deposited alloys via accelerating the preferential dissolution of manganese and stabilizing alloy/passive film interface. A change in the passive film structure was observed when the alloys were anodically polarized at potentials higher than 0.6 V (SCE).     

Studies on promising cell performance with H2SO4 as the catholyte for electrogeneration of Ag2+ from Ag+ in HNO3 anolyte in mediated electrochemical oxidation process

Electrochemical performance of a divided cell with electrogeneration of Ag²⁺ from Ag⁺ in 6 M HNO₃ anolyte has been studied with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte. This work arose because in mediated electrochemical oxidation (MEO) processes with Ag(II)/Ag(I) redox mediator, HNO₃ is generally used as catholyte, which, however, produces NO _x gases in the cathode compartment. The performance of the cell with 6 M HNO₃ or 3 M H₂SO₄ as the catholyte has been compared in terms of (i) the acid concentration in the cathode compartment, (ii) the Ag⁺ to Ag²⁺ conversion efficiency in the anolyte, (iii) the migration of Ag⁺ from anolyte to catholyte across the membrane separator, and (iv) the cell voltage. Studies with various concentrations of H₂SO₄ catholyte have been carried-out, and the cathode surfaces have been analyzed by SEM and EDXA; similarly, the precipitated material collected in the cathode compartment at higher H₂SO₄ concentrations has been analyzed by XRD to understand the underlying processes. The various beneficial effects in using H₂SO₄ as catholyte have been presented. A simple cathode surface renewal method relatively free from Ag deposit has been suggested.