Zinc Surface Research Articles

Atmospheric Corrosion of Zinc by Organic Constituents: II. Reaction Routes for Zinc-Acetate Formation

The acetic acid and acetaldehyde-induced atmospheric corrosion of a zinc surface was investigated by in situ infrared reflection-absorption spectroscopy. Independent of the relative humidity, both corrosive gases yielded zinc oxide and zinc acetate as reaction products. However, faster kinetics for the acetate formation was observed for acetic acid, which was attributed to an acetate-induced zinc dissolution mechanism as the rate determining step, and a more complicated reaction path for acetaldehyde to form the zinc-acetate surface species. Additionally, the rate varied significantly with the relative humidity, and an enhanced corrosion rate was observed under more humid conditions, when the water adlayer that always covers a metal surface is thicker. Scanning electron microscopy revealed the formation of radial growth of corrosion products in the case of acetic acid and filiform corrosion for acetaldehyde. By X-ray diffraction of the powderlike corrosion products, solely zinc oxide was detected. This implies a minute production of zinc acetate in comparison to zinc oxide, or a noncrystalline phase of the acetate. Reaction paths for acetic acid and acetaldehyde were proposed.

Initial atmospheric corrosion of zinc in presence of Na 2SO 4 and (NH 4) 2SO 4

Initial atmospheric corrosion of zinc in the presence of Na 2SO 4 and (NH 4) 2SO 4 was investigated via quartz crystal microbalance(QCM) in laboratory at relative humidity(RH) of 80% and 25 °C. The results show that both Na 2SO 4 and (NH 4) 2SO 4 can accelerate the initial atmospheric corrosion of zinc. The combined effect of Na 2SO 4 and (NH 4) 2SO 4 on the corrosion of zinc is greater than that caused by (NH 4) 2SO 4 and less than that caused by Na 2SO 4. Fourier transform infrared spectroscopy(FTIR), X-ray diffractometry(XRD) and scanning electron microscopy(SEM) were used to characterize the corrosion products of zinc. (NH 4) 2Zn(SO 4) 2, Zn 4SO 4(OH) 6·5H 2O and ZnO present on zinc surface in the presence of (NH 4) 2SO 4 while Zn 4SO 4(OH) 6·5H 2O and ZnO are the dominant corrosion products on Na 2SO 4-treated zinc surface. Probable mechanisms are presented to explain the experimental results.

Study on factors affecting microstructure of tin coatings cemented on zinc. Part 1

The process of tin cementation on zinc resulting in the formation of fine grained tin coatings was studied. The influence of the experimental conditions such as Sn(II) concentration, duration of the reaction, solution temperature and pH on the microstructure of the cemented tin films was investigated. The dependence between the experimental conditions and the grain sizes of the deposited tin films was established using the method of the design of experiment. The diminution of Sn(II) concentration, the decrease in temperature and the increase in solution pH were found to promote the deposition of fine grained tin coatings with the grain sizes 0·3–1 μm. The fine granulation of tin films was shown to be insufficient for obtaining coatings suitable for the use as protective and/or intermediate layers on zinc surface. The evolution of hydrogen was found to be the most negative factor deteriorating the quality of coatings owing to the formation of pores.

Prevention of zinc corrosion in oxygenated 0.5 M NaCl by treatment in a cerium(III) nitrate solution and modification with sodium hexadecanoate

A self-assembled monolayer (SAM) of hexadecanoate ion C 15 H 31 CO 2 - (C 16A −) was prepared on a zinc electrode covered with a layer of hydrated cerium(III) oxide Ce 2O 3. The protection of zinc against corrosion was examined for the electrode coated with the Ce 2O 3 layer and the C 16A − SAM in an oxygenated 0.5 M NaCl solution. A more positive open-circuit potential of the coated electrode was maintained during immersion in the solution for 4 h than that of the uncoated one and polarization curves showed marked suppression of the anodic process, implying that the layer modified with the SAM acted as a passive film. The protective efficiency of the modified layer was extremely high, more than 99%. The zinc surface coated with the Ce 2O 3 layer and the C 16A − SAM was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement with a drop of water.

Analysis of air adsorptive on solid surfaces by AFM and XPS

Solid surfaces of HOPG, pure copper, chromium, zinc, copper and SUS304 steel were observed in ambient air with an a.c. non-contact mode of atomic force microscope(AFM). A type of film-like-domains (adsorptive) was detected on the above surfaces. The thickness of the adsorptive was about 1.2–2.4 nm in this case. The film-like-adsorptive was confirmed to be a liquid layer by the static contact-mode scanning, the measurement of the elasticity and viscosity images, and the detection of the condensation/evaporation phenomena when the relative humidity changed. The liquid layer is considered to be condensed water covered with organic contaminant.

Smithsonite flotation using potassium amyl xanthate and hexylmercaptan

The influence of potassium amyl xanthate (KAX) and hexylmercaptan (HM) adsorption on smithsonite surface at various concentrations were investigated through using zeta potential, contact angle, microflotation and diffuse reflectance FTIR studies at different pH. The zeta potential measurements of KAX showed that the adsorption of ionic charge (more negative charge after KAX treatment) takes place on the surface of pure crystalline smithsonite. The charges vary between −38 and −45 mV at pH 10·5. Flotation results using potassium amyl xanthate reveal that the maximum recovery of 81·3% and the maximum contact angle of 98·7° occurs at pH 10·5 at KAX concentration of 2·96 × 10−3M in sodium sulphide (2·6 × 10−2M) and copper sulphate (9·4 × 10−3M) solutions. The highest recovery and contact angle for flotation by means of HM occurs at pH 9 at values of 78·6% and 92·3° respectively with HM concentration 1·1 × 10−2M. The FTIR spectra studies of smithsonite conditioned by KAX confirmed the adsorption of KAX and the presence of CS2 on smithsonite surface. The FTIR spectra in HM studies showed the adsorption of RS− on the oxidised zinc surface and the S–H bond in the mercaptan is destroyed on adsorption. The comparison between the results using anionic collectors showed that the presence of different amounts of reagents on smithsonite surface in two cases confer different degree of hydrophobicity on the smithsonite surface.

Application of self-assembly for replacing chromate in corrosion protection of zinc

Due to the toxic and carcinogenic properties of hexavalent chromium ion, the corrosion protection with chromating technique needs replacement. Several environmentally friendly alternative metal pretreatments have already been proposed. One of these methods is the application of self-assembling molecules to form mono- or multilayers on the metal surfaces. These layers can prevent metal dissolution due to their dense and stable structure. The objective of our studies was to protect zinc surface against corrosion, with a thin phosphonate layer. Aqueous solutions of diphosphonic acid with different alkyl chain lengths were applied with different treatment times. The layer formation, stability, and corrosion protection of these films were monitored by electrochemical impedance spectroscopy and the effect of 1,5-diphosphono-pentane (DPP) on zinc was studied by polarization curves. The wetting properties were determined by static contact angle measurement. 1,5-Diphosphono-pentane forms a thin layer, with a pronounced protective ability in neutral aqueous solutions. The application of self-assembling molecules can be a promising method to replace the chromating technique on zinc surface.

Corrosion inhibitor doped protein films for protection of metallic surfaces: appraisal and extension of previous investigations by Brenner, Riddell and Seegmiller

An evaluation of the efficacy of chromated protein coatings, originally proposed by Brenner, Riddell and Seegmiller has been undertaken. Some of their original application methods and coating solution formulations have been utilised to produce films on zinc electroplated steel surfaces. Subsequent morphological and corrosion studies have highlighted the enhanced corrosion resistance afforded by these treatments, attributed to the high level of hexavalent chromium dispersed in the coatings. Additional experiments were undertaken with molybdate, tungstate and cerium trichloride corrosion inhibitors as more environmentally friendly substitutes for the chromate. Although their performance was inferior, cerium trichloride did engender a promising level of corrosion protection to the electroplated zinc surfaces.

Studies on the initial stages of zinc atmospheric corrosion in the presence of chloride

A four-year exposure program was carried out in Taiwan in which 23 test sites with different climatic and pollution conditions were chosen and evaluated according to ISO standards 9223–9226. Examination of the results indicated that most of the tests sites were very corrosive to zinc specimens and there was a severe white rust problem for freshly galvanized items stored in high humidity outdoors environments. In addition, the initial stages of zinc atmospheric corrosion in the presence of chloride were studied quantitatively in a non-aqueous electrolyte (methanol) using ex situ electrochemical impedance spectroscopy (EIS) to determine polarization resistance ( R p). The samples were exposed to the synthetic atmospheres with careful controlled relative humidity, temperature, and contaminating salts. It was observed that a change of R p was accompanied by a change in the corrosion product on the zinc surface, and that the R p increased with relative humidity (RH) during pre-exposure. Furthermore, the corrosion products of zinc were analyzed qualitatively by grazing-angle X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Zinc hydroxycarbonate (Zn 5(CO 3) 2(OH) 6) and zinc oxide (ZnO) in this surface layer were found to provide protection against chloride contaminants.

Adsorption of quaternary ammonium gemini surfactants on zinc and the inhibitive effect on zinc corrosion in vitriolic solution

Adsorption of the quaternary ammonium gemini surfactants alkanediyl-α,ω-bis-(dimethyl dodecyl ammonium bromide), referred as C 12- s-C 12·2Br ( s = 2,3,4,6), on the zinc surface in 0.5 mol/L H 2SO 4 solution was investigated using gravimetric measurements. The adsorption of C 12- s-C 12·2Br on the zinc surface accorded to the Frumkin isotherm model. The maximal inhibition efficiency for zinc was reached at the saturated adsorption concentration C c that was larger than its critical micelle concentration in 0.5 mol/L H 2SO 4 solution. The inhibition efficiency for zinc slightly reduced with increasing s since C 12- s-C 12·2Br formed different morphologies of the surface aggregates. The adsorption ability and the inhibition efficiency for corrosion reduced with increment of temperature.

Cadmium, copper and zinc leaching and surface run-off losses at the Öjebyn farm in Northern Sweden—Temporal and spatial variation

Abstract Quantitative estimates of cadmium (Cd), copper (Cu) and zinc (Zn) flows in percolating soil water and in surface run-off on arable land are rather scarce. Such information is essential for establishing reliable mass balances of trace metals, e.g. on field level, due to the fact that the trace metal outputs in water are quantitatively significant in field balance calculations. The aim of this study was to quantify trace metal leaching and surface run-off for a 5-year period at sites representing different soil types (Eutric Regosol, Thionic Gleysol, Dystric Cambisol) at the Ojebyn experimental farm in Northern Sweden. The metal outputs in water were estimated by combining chemical analysis of elements in soil water with simulations of water flow using the hydrological SOIL model. Average Cd, Cu and Zn concentrations (for three soils and 5 years) in soil water at 50 cm depth were 0.10, 21 and 11 μg L −1 , respectively. However, there was a large variation between years and soil types. The relative variation (coefficient of variation) between soil types for average Cd, Cu and Zn concentrations was in the range 20–60% depending on year. The average Cd, Cu and Zn output by leaching were 0.22 ± 0.20, 50 ± 33 and 24 ± 20 g ha −1 year −1 , respectively, while the average outputs by surface run-off were 0.13 ± 0.09, 43 ± 18 and 16 ± 9 g ha −1 year −1 , respectively. Both the simulated amount of water run-off and metal concentrations in the soil water had a significant impact on the variability of the metal flows. In this study the differences in metal concentrations in soil water due to differences in farming practice were much less important than the inter- and intra-field differences and temporal variability. The definition of the lowermost soil layer boundary of the system was found to have a great influence on the resulting metal mass balance.

Observation of Self-Healing Functions on the Cut Edge of Galvanized Steel Using SVET and pH Microscopy

The scanning vibrating electrode technique (SVET) and pH microscopy were used to study the effect of electrolyte composition and steel thickness on the precipitation of zinc-based corrosion products on the cut edge of galvanized steel. Current distributions were measured with the SVET, and the distribution of pH was measured using liquid membrane glass capillary electrodes. In NaCl solution, a clear correlation was observed between the spatial pattern of precipitated corrosion products, and the anodic/cathodic current and pH distribution:zinc dissolution occurred at localized points on the cut edge, suggesting that the zinc surface was passivated in this solution and that a pitting mechanism was predominate. Precipitated corrosion products formed rings around the anodic sites. In the presence of , the zinc surface was entirely active with only minimal corrosion product precipitation visible on the steel during the early stages of the reaction, and no significant increase in pH was observed in the vicinity of the cathodic reactions. At later stages, a film was formed and identified as a zinc hydroxysulfate compound by Raman spectroscopy. The experimental results are interpreted in terms of the equilibrium chemistry of the electrolytes.

Mechanism of Cluster Formation on Zinc Selenium/Gallium Arsenic Prepared by Metallorganic Vapor Phase Epitaxy

Atomic force microscopy is used to investigate the surface morphology of zinc selenium clusters on gallium arsenic substrate prepared by low-pressure metallorganic vapor phase epitaxy. The density of cluster can reach . The average sizes are 50 nm in height and 112 nm in diameter. From the relationship between the density of cluster and hydrogen selenide flow rate, and the surface and depth compositional variation of zinc and selenium, the ZnSe clusters on GaAs are formed by selenium segregation. The dislocations enhance the selenium segregation. The nonspherical shaped cluster is formed from the mergence of two clusters. The spherical shaped cluster is formed by long-range potential from the nonstoichiometry epi layer.

Preparation of coloured composite films of Ni/organic pigments by immersion plating over zinc surface

Colour coatings of Ni–pigment composite film over a zinc surface using the immersion plating technique were investigated. Two types of approaches were applied in synthesizing the composite films. In one method, composite films were synthesized simply by immersing a zinc substrate in an aqueous solution containing nickel ions and pigment particles dispersed with the aid of a surfactant mixture containing nonionic azobenzene surfactant (AZPEG) and n-sodium dodecyl sulfate (SDS). In the other method, composite films were synthesized in two steps. In the first step, a thin pigment film was deposited on a zinc substrate by micelle disruption technique using AZPEG followed by deposition of nickel in the second step: the immersion of the substrate in an aqueous solution containing nickel ions. Both of these methods produced a uniform coloured composite film with good adhesion. The adherence of these composite films was enhanced by the co-deposition of PMMA latexes with the pigment followed by thermal treatment of the coatings. The contact angle measurement revealed that all the composite films investigated in the present study had a greater degree of water repellency property than that of the electroplated nickel.

Influence of alloying elements on the corrosion resistance of rolled zinc sheet

The influence of alloying elements on the corrosion behaviour of rolled zinc sheet in aqueous media has been investigated by means of electrochemical techniques. All the changes in corrosion behaviour seen in this study could be attributed to modification of the formation or the stability of the passivating oxide film on the zinc surface. A low concentration of copper (0.6 wt.%) inhibited the formation of the passivating film and reduced the stability of the film. Conversely, a low concentration of chromium (0.5 wt.%) accelerated the passivation process and raised the stability of the film. The passivation and corrosion behaviour shown by a commercially produced ternary alloy containing copper and titanium additions was almost the same as the behaviour shown by a model binary alloy containing only copper. All the results obtained in this study were consistent with the hypothesis that alloying elements alter the electron-conducting and/or ion-conducting properties of the passivating oxide film.

Zinc stable isotope fractionation during its adsorption on oxides and hydroxides

Adsorption of Zn on goethite, hematite, birnessite, pyrolusite, corundum, and gibbsite was studied using a batch adsorption technique as a function of pH, zinc concentration in solution, and time of exposure. Adsorption from 0.01 M NaNO 3 solutions undersaturated with respect to zinc (hydr)oxide at 3 < pH < 8 was found to be reversible and equilibrium was achieved in less than 24 h. A 2p K surface complexation model that assumes the constant capacitance of the electric double layer (CCM) and postulates the formation of positively charged >MeO Zn + complexes, where Me = Fe, Mn, and Al, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Zn concentration. The logarithms of surface stability constant for Zn interaction with metal oxy(hydr)oxides (>MeOH 0 +Zn 2+ ⇒ MeO Zn +) vary from −2.5 to 0.5. They are higher for oxy(hydr)oxides than for anhydrous oxides. Stable isotopes of zinc in several filtrates were measured using an ICP-MS Neptune multicollector which made it possible, for the first time, to assess the degree of isotopic fractionation between 66Zn and 64Zn during zinc adsorption on mineral surfaces. The isotopic offset between aqueous solution and mineral surfaces (Δ 66/64Zn soln/solid= δ( 66/64Zn) solution− δ( 66/64Zn) surface) was found to be weakly dependent on percentage of adsorbed metal and equals 0.20 ± 0.03 , 0.17 ± 0.06 , − 0.10 ± 0.03 , − 0.10 ± 0.09 , and − 0.13 ± 0.12 ‰ for goethite, birnessite, pyrolusite, corundum, and Al(OH) 3. For hematite, Δ 66/64Zn varies from − 0.61 ± 0.10 ‰ at pH 5.5 to − 0.02 ± 0.09 ‰ at 5.8 < pH < 6.7. Overall, zinc stable isotopic fractionation induced by adsorption on most mineral surfaces does not exceed 0.2‰. We do not observe any correlation between the sign and magnitude of isotopic offset and the chemical nature of solid phase (hydrous versus anhydrous minerals), zinc surface adsorption constants (surface complexation model of the present work), and coordination and first-neighbor distances of surface >MeO Zn(H 2O) n complexes (available literature data on X-ray absorption spectroscopy). Apparently, the fine structure of surface complexes and the position and bond strength for second neighbors of zinc are likely to control its isotopic fractionation during adsorption on mineral surfaces. Our results strongly suggest that inorganic processes controlling zinc isotope adsorption on soil and sediment minerals should be of second-order importance compared to biological factors.

Protective Action of Vanadate at Defected Areas of Organic Coatings on Zinc

The kinetics of vanadate release from an organic coating and the stability and protective ability of the newly formed vanadate-based films on zinc surfaces have been studied with respect to self-healing ability of vanadate-pigmented organic coatings. The results were compared with those obtained with chromate. The kinetics of vanadate release from a polyester coating was comparable to that of chromate. The methods of X-ray absorption near edge spectroscopy (XANES) and scanning Kelvin probe were used for studying the mechanism of inhibition and the kinetics of vanadate reduction on bare zinc. XANES proved to be a powerful tool for determination of the oxidation state of vanadium in surface films. The experiments showed that vanadate was reduced more rapidly than chromate under the same atmospheric conditions. However, addition of magnesium phosphate resulted in a significantly lower reduction rate of vanadate. The results are discussed in light of the increased adsorption ability of the more negatively charged vanadium(V) species at higher pH, while the oxygen reduction process on zinc is inhibited due to the presence of phosphate. Thus, vanadate in combination with another inhibitor could provide corrosion protection at defects of organic coatings on zinc comparable to that of chromate.

Mechanism of formation of silica–silicate thin films on zinc

The formation of silica–silicate thin films on zinc from a colloidal solution (or sol) of silica was studied using a microbalance. Thin films were made by immersion of zinc foil in a sol composed of colloidal silica particles and sodium silicate. The rest potential and weight gain were recorded simultaneously and correlated with pH changes at the zinc surface measured with a flat-bottomed pH electrode. The effect of the composition, pH, and agitation of the silica sol on the deposition process was thoroughly studied. The various factors governing the deposition were discussed leading to a phenomenological model of the thin-film deposition.

Monitoring of Initial Stages of Atmospheric Zinc Corrosion in Simulated Acid Rain Solution under Wet/Dry Cyclic Conditions

Abstract The exposure of zinc samples in simulated acid rain solution (SARS) was investigated under periodic wet/dry conditions using an alternating current (AC) impedance technique. The influence of relative humidity (RH), temperature, and surface inclination on the atmospheric corrosion of zinc is described. The polarization resistance reciprocal (1/Rp) decreases rapidly during the initial stages and slowly attains a steady state as the overall exposure time progresses. The experiment result shows a pronounced dependence reciprocal polarization resistance on RH. Two main components were identified in the corrosion products on zinc surfaces, namely hydrozincite (Zn5[OH]6[CO3]2) and hydrated zinc hydroxysulfate (Zn4SO4[OH]6·nH2O [n = 1, 2 and 3]). Exposure in the presence of carbonate anions gives rise to more protective corrosion products than it does in a nitrate anion solution.

Investigation of polysiloxane coatings as corrosion inhibitors of zinc surfaces

The corrosion behavior of zinc platelets coated with different polysiloxane layers was investigated using impedance spectroscopy (IS) and measurements of the linear polarization resistance (LPR). Values of the polarization resistance derived were used for the calculation of the corresponding corrosion current densities and the degree of surface passivation. The two electrochemical methods used are both suitable for the characterization of the corrosion protective properties of siloxane layers by considering that a higher polarization resistance results from a better sealed surface and, therefore, indicates a more effective corrosion inhibiting coating. After testing several siloxane layer systems, a three siloxane layer system was developed, forming a stable network, bonded to the zinc surface by covalent bonds and acting as hydrophobic barrier to corrosive media. The corrosion protective properties of these layer systems lead to a significant increase in the corrosion resistance of zinc surfaces, clearly exceeding that of chromate conversion coatings.