Inhibition Of Zinc Research Articles

The effect of strontium and chromate ions on the inhibition of zinc

The corrosion and inhibition of zinc in artificial acid rain solution (pH 4.5) at a low strontium chromate concentration has been evaluated using electrochemistry, solution analysis and XPS. These techniques have been used to estimate inhibitor efficiency and to determine a possible inhibition mechanism. The results show that strontium chromate at low concentration inhibited significantly more of the cathodic corrosion process, by reduction of Cr 6+ to a solid species containing Cr 3+. The surface film contained a mixture of oxidised zinc and chromium, probably in the form of basic zinc carbonate (hydrozincite) and hydrated chromia. Importantly strontium ions were found to play no significant role in the inhibition process.

Corrosion Inhibition of Zinc by Benzotriazole with an Electrochemical Quartz Crystal Microbalance

The inhibiting effect of benzotriazole (BTA) on the corrosion of electroplated zinc coatings in acidic sodium sulfate solutions was studied by use of an electrochemical quartz crystal microbalance. Experiments showed that BTA is mainly inhibiting the anodic reaction of the zinc dissolution reaction. In quiescent solution, the rate-determining step of the corrosion process is mass transport of dissolved oxygen to the electrode surface so that BTA does not significantly decrease the corrosion rate. When the solution is deaerated by nitrogen bubbling, the corrosion rate is controlled by the charge-transfer process and the corrosion rate of zinc is greatly reduced by BTA. When the solution is bubbled with air, the corrosion rate increases significantly. The rate of the hydrogen evolution reaction is charge-transfer controlled and the oxygen reduction is controlled by mass transport. © 2003 The Electrochemical Society. All rights reserved.

Corrosion inhibition of zinc in phosphoric acid solution by 2-mercaptobenzimidazole

The inhibiting action of 2-mercaptobenzimidazole on the corrosion of zinc in phosphoric acid (H 3PO 4) solution has been investigated by weight loss and polarization. The studies reveal that the inhibitor is effective for the inhibition of zinc in H 3PO 4 solution and retards the anodic and cathodic corrosion reactions with emphasis on the former.

Model Electrochemical Cell Study of Cut-Edge Corrosion Inhibition on Coil-Coated Steel Sheet by Chromate-, Phosphate-, and Calcium-Containing Pigments

Corrosion at cut edges is the most important failure mechanism of organic-coated, profiled galvanized steel architectural claddings. Currently, edge corrosion is generally controlled by the addition of strontium chromate in the paint primers; however, there is substantial interest in chromate replacements due to environmental reasons. This work describes an experimental study of inhibition with specific relevance to the cut-edge situation; essentially equivalent to a small galvanic cell between zinc and steel. Although chromate initially acts as an anodic inhibitor for zinc corrosion at the cut edge, over a few hours of immersion, it was found to also strongly inhibit the steel cathode, hence reducing the cathodic protection current requirement on the zinc and thus acted as a mixed inhibitor in the cut-edge galvanic cell. Although individually, zinc phosphate and calcium ion-exchanged silica pigments had relatively poor inhibition, they showed a strong synergistic effect. Thus, a mixture of the two compounds had comparable inhibitive efficiency to chromate. This was found to be due to a similar mixed inhibition mechanism as chromate. Thus, anodic inhibition of zinc was evident as well as strong cathodic inhibition on the steel due to the formation of a compact, thin film containing zinc, calcium, and phosphate species. © 2001 The Electrochemical Society. All rights reserved.

Mechanisms of inhibitory effects of zinc and cadmium ions on agonist binding to adenosine A1 receptors in rat brain

The dose-dependent inhibition of zinc and cadmium ions of agonist binding to A1 adenosine receptors in rat brain is prevented by histidine and cysteine, respectively. In the present study, the possible different mechanisms of Zn 2+ and Cd 2+ inhibitions were examined. The effects of Zn 2+ and Cd 2+ on equilibrium binding parameters of the agonists N 6-cyclohexyl-[2,8- 3H]-adenosine ([ 3H]CHA) or chloro- N 6-cyclopentyl-adenosine ([ 3H]CCPA) and the antagonist cyclopentyl-1,3-dipropylxanthine ([ 3H]DPCPX) were compared with those effects of reagents or binding conditions which altered histidyl or cysteinyl residues of the A1 receptor. Zn 2+ pretreatment did not change A1 agonist or antagonist affinity, but did reduce the B max. The inhibitory effects of Zn 2+ pretreatments were also maintained after several membrane washings. Diethylpyrocarbonate, a histidine-specific alkylating reagent, behaved like zinc ions: pretreatment with A1 agonist protected the histidyl residues of the [ 3H]CHA binding site against modification by Zn 2+, while the modification of the protonation state of the nitrogen of the imidazole group of histidines by changing pH indicated that the interactions of Zn 2+ with the histidyl residues were feasible with their unprotonated form. These findings suggest the formation of coordination bonds between Zn 2+ and histidines critical for [ 3H]CHA or [ 3H]DPCPX binding, which may prevent the ligand interaction with the specific sites without modifying the binding kinetics of radioligand to the non-chelated recognition sites. Cd 2+ pretreatment reduced the [ 3H]CCPA affinity, but did not modify the affinity of the antagonist [ 3H]DPCPX, the B max remaining unaffected. As with cadmium effects, the oxidation of the thiol group of cysteine by dithionitrobenzoic acid (DTNB) reduced [ 3H]CCPA affinity without changing the number of binding sites. The reducing reagent dithiothreitol, which alone was unable to modify [ 3H]CCPA binding, overcame the inhibiting effects of both Cd 2+ and DTNB. These findings suggest that cadmium ions may oxidize SH groups of cysteines localized on the A1 receptor molecule or a cysteine localized in the region of G iα subunit involved in the coupling with receptors. This mechanism can justify potential conformational modifications of the receptor molecule producing the decrease in affinity.

Zinc downmodulates thf GABAc receptor current in cone horizontal cells acutely isolated from the catfish retina.

1. We studied the effect of zinc on the gamma-aminobutyric acid-C (GABAC) receptor in acutely isolated catfish cone horizontal cells using the whole cell patch-clamp technique. 2. GABA activates the GABAC receptor with a half-activation concentration (EC50) of 2.99 microM. The Hill coefficient is 1.32. Desensitization of the receptor is evident when GABA concentration is > 3 microM. 3. Zinc downmodulates the GABAc receptor current, elicited by 30 microM GABA, with a half-inhibition concentration (IC50) of 8.20 microM. 4. The inhibition of zinc is both competitive and noncompetitive. In the presence of 10 microM zinc, the maximum GABA response was reduced to approximately 60 percent of control and the EC50 increased to 17.32 microM, whereas the Hill coefficient (1.39) was not significantly altered. 5. The steady-state block by zinc is virtually voltage independent. 6. These results suggest that the GABAC receptor of horizontal cells can be modulated by endogenous zinc found in photoreceptors.

Carbonic anhidrase inhibition and level of zinc in aqueous humor and blood

Purpose: To evaluate the influence of heparin-surface-modified (HSM) versus unmodified poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) on the blood-aqueous barrier (BAB) in at-risk eyes.Setting: Department of Ophthalmology, Bundesknappschaft's Hospital, Sulzbach, Germany.Methods: This study comprised 100 patients with predisposing risk factors for BAB destabilization (e.g., diabetes mellitus with or without retinopathy, glaucoma, pseudoexfoliation, uveitis). One eye in each patient received an HSM IOL and the fellow eye, a conventional unmodified PMMA IOL after phacoemulsification by the same surgeon. Anterior chamber flare was measured with the Kowa 500 laser flare meter 1 day before and 1 day, 1 and 6 weeks, and 3 months after surgery.Results: For most risk factors, mean flare was lower in the HSM group than in the PMMA group at most follow-ups. Significantly lower flare values (difference between postoperative and preoperative mean values) were seen in eyes with the HSM IOL at 6 weeks (P < .004) and 3 months (P < .003; Student's t-test). In the group with preoperative elevated flare values, the eyes with the HSM IOL had significantly better results 6 weeks (P < .0006) and 3 months (P < .01) postoperatively. The values in the HSM IOL eyes were also significantly higher in the diabetic with retinopathy group at 3 months (P < .003).Conclusion: The results confirm the efficacy of IOL surface modification in reducing postoperative intraocular reaction in at-risk eyes.

Zinc and polyphosphates as corrosion inhibitors for zinc in near neutral waters

The corrosion and corrosion inhibition of commercial purity zinc, in the presence and absence of polyphosphate, was examined by electrochemical impedance spectroscopy (EIS) and by cyclic voltammetry using artificial waters as electrolytes. The anodic dissolution reaction exhibited mixed kinetics which changed to diffusion control when calcium ions were removed. The effect of calcium to polyphosphate ratio on the corrosion rate of zinc was studied to determine the composition which gives the optimum protection. A recirculating system that utilises galvanised tubing was used to test optimum concentrations found by EIS with good results.

Inhibition of Acid Production by Streptococcus mutans NCTC 10449 by Zinc and the Effect of Metal Speciation

Ionic zinc as zinc sulphate was strongly inhibitory to acid production from glucose by washed cell suspensions of Streptococcus mutans NCTC 10449 in a pH-stat assay (50% inhibition at 0.1 mM zinc). Zinc was adsorbed to the cells (up to 8 micrograms/mg cells). Several other zinc salts that dissociated to free zinc ions were also strongly inhibitory. Zinc in a partially complexed form as zinc citrate was less strongly inhibitory (50% inhibition at 0.2 mM zinc), and adsorption of zinc was lower (up to 3 micrograms/mg cells). Stoichiometric addition of ethylenediaminetetra-acetic acid (EDTA) to assays containing zinc sulphate completely removed inhibition and adsorption of zinc. A good correlation between inhibition of acid production and adsorption of zinc was found, and zinc adsorption was correlated with the levels of free zinc ion in the assay mixtures. The strongly anionic complexes of zinc, Zn(CIT)-, Zn(CIT)4-(2), and Zn(EDTA)2-, were not inhibitory and did not adsorb to the bacterial cells.

ChemInform Abstract: Corrosion Inhibition of Zinc with Cerous Chloride.

AbstractAddition of CeCl3·7 H2O in amounts as low as 100‐1000 ppm inhibit the corrosion of Zn and Zn‐coated steel in 0.1 M NaCl or tap water.

Corrosion Inhibition of Zinc in HCl Solution by Several Pyrazole Derivatives

Abstract The corrosion inhibition of zinc in HCl solutions by several pyrazole derivatives—namely, 3(5) amino, 5(3) phenylpyrazole; 3(5) amino, 5(3) [4′—methylphenyl] pyrazole; 3(5) amino, 5(3) [4′...

The corrosion inhibition of zinc with cerous chloride

The corrosion of zinc and zinc-coated steel in tap water or 0.1 M NaCl solution is inhibited by small additions of cerous chloride. Polarization studies and surface analysis show that corrosion protection is due to the formation of a complex film of cerium-rich oxide which causes cathodic reaction rates to be substantially reduced.

Mössbauer Spectroscopic Study of the Corrosion Inhibition of Zinc by Cobalt Ions

Zinc dipped into solutions doped with 57Co yields a Mössbauer emission spectrum characteristic of oxidized cobalt. Zinc dipped into solution for 30 sec yields an emission spectrum characteristic of metallic cobalt plus oxidized cobalt. Corrosion inhibition in neutral solution is attributed to the presence of oxidized cobalt and the consequent effect on the cathodic half of the corrosion reaction.

Substituted tertiary arsine and phosphines as interfacial adsorption inhibitors for corrosion of zinc in perchloric acid

The effect of triphenylarsine, triphenylphosphine and tri-p-tolylphosphine on the corrosion of zinc in HClO4 at 30° C was studied. A significant decrease in the corrosion rate of zinc is obtained by the addition of these compounds. The corrosion rate is a function of the temperature, pH of the medium and the concentration of the inhibitors. The percentage protection calculated from weight loss and polarization methods are in good agreement. The apparent free energies of adsorption of inhibitors for different possible modes of adsorption are evaluated. The experimental data obtained are in agreement with the corrosion inhibition of zinc by interfacial adsorption of inhibitors.

Role of the thiocyanate ion in the corrosion inhibition of zinc in perchloric acid by n-decylamine

The effect of KSCN on the corrosion of electropolished zinc in 0.1 M HClO 4 and 0.1 M HClO 4 solution containing different concentrations of n-decylamine (nDA) has been investigated using weight loss and polarization methods. The inhibitor efficiency of nDA increased markedly in the presence of KSCN. pH and temperature affected the corrosion inhibition of zinc by nDA in acidic KSCN solution. The weight loss and polarization measurements gave consistent results. nDA in acidic KSCN solution acted mainly as a cathodic inhibitor, but with a smaller degree of anodic control. The increase in the inhibitor efficiency of nDA in the presence of KSCN is discussed from the viewpoint of the co-adsorption of nDA in cationic form and thiocyanate ions.

The synergistic effect of Halide ions on the corrosion inhibition of zinc by n-decylamine

The effect of halide ions on the spontaneous dissolution and the anodic and cathodic polarization of zinc in perchloric acid solution with and without n-decylamine has been studied. Halide ions enhanced the corrosion of zinc, whereas n-decylamine inhibited the corrosion of zinc. The inhibitor efficiency of n-decylamine is increased significantly by the presence of halide ions. A consistent surface coverage value is obtained both from weight loss and polarization studies. n-decylamine acts mainly as a cathodic inhibitor. The change in the free energy of adsorption of n-decylamine in the presence of halide ions is explained in terms of a change in the mechanism of corrosion inhibition. Synergism of n-decylamine and halide ions is discussed from a view point of a model of co-adsorption of halide ions and n-decylamine.

Studies of the esterase activity and the anion inhibition of bovine zinc and cobalt carbonic anhydrases.

The rates of hydrolysis of nitrophenyl esters, catalyzed by bovine carbonic anhydrase, depend on the position of the nitro group and on the size of the acyl residue. The most rapidly hydrolyzed substrate of those investigated is p‐nitrophenyl acetate. The catalyzed rates are proportional to both enzyme and ester concentrations. Only in the case of m‐nitrophenyl acetate could a value of the Michaelis constant, Km, be estimated, approximately 10 mM. Product inhibition by o‐nitrophenol occurs during the enzyme‐catalyzed hydrolysis of o‐nitrophenyl acetate. The metal specificity of the enzyme seems to be independent of the substrate. Zn(II) and Co(II) are about equally effective in restoring esterase activity to the apoenzyme while all other metal ions studied do not activate or have a very small effect. The pH‐dependence of the esterase activity of both Zn(II)‐ and Co(II)‐carbonic anhydrase is very similar to that of the CO2 hydration activity, and the basic form of a group with a pK near 7 is required for both reactions. Anionic inhibitors are strongly bound to the enzyme when this group is in its acidic form, but the inhibition is almost abolished at alkaline pH. The inhibitory powers of cyanide and sulfide decrease at acid as well as at alkaline pH. The results agree with the assumption that, formally, CN− and HS− do not bind to the basic form of the enzyme, while HCN and H2S do not bind to the acidic form.