Zinc Corrosion Products Research Articles

Protective mechanisms occurring on zinc coated steel cut-edges in immersion conditions

Electrochemical processes occurring on the cut-edge of a galvanized steel immersed in NaCl solutions were studied using numerical simulations, and in situ current and pH profiles measured over the cut-edge. These results clearly demonstrate that only the steel surface remote from the zinc coating is cathodically active, oxygen reduction being strongly inhibited in the vicinity of zinc. This trend was confirmed by local polarization curves recorded on these distinct areas. Ex-situ AES and SEM analysis and cathodic polarization curves in solutions containing Zn 2+ ions led to conclude that this cathodic inhibition was related to the fast nucleation of a dense Zn(OH) 2 film on the steel surface. After a long term exposure, a new galvanic coupling takes place between the Zn(OH) 2 covered area, showing an anodic activity, and the remaining steel surface covered by bulky white zinc corrosion products.

The corrosion behavior of zinc-rich paints on steel: Influence of simulated salts deposition in an offshore atmosphere at the steel/paint interface

The corrosion behavior of an epoxy zinc-rich paint on interface-contaminated carbon manganese-silicon steel was studied. SEM observation on the cross-section of the paint indicates that the zinc corrosion products grew from the surface to the inner of the paint and salts contamination promoted the growth at locations close to the steel/paint interface. The results of electrochemical impedance spectroscopy show that the corrosion resistance of the contaminated paint was significantly influenced by diffusion of zinc corrosion products during the initial stage of immersion, and diffusion of iron corrosion products at the end of immersion. Three transmission line models were applied to account for the corrosion process of the uncontaminated and contaminated zinc-rich paints.

Galvanic Corrosion of a Zn/steel Couple in Aqueous NaCl

Galvanic corrosion of a model Zn/steel couple was investigated in aqueous NaCl solutions by measuring open circuit potentials (OCPs), potential and current distributions, and galvanic currents. The OCP transient of the Zn/steel couple was divided into two stages. The first stage consisted of sacrificial dissolution of zinc. At low concentrations of NaCl (0.01 mol/dm3), the cathodic reaction on the couple surface was an oxygen reduction reaction (ORR). With increasing concentrations of NaCl, the cathodic reaction at the steel surface changed from an ORR to the combination of an ORR and hydrogen evolution reaction (HER). In addition, the precipitation morphology of zinc corrosion products differed as a function of NaCl concentration, suggesting that the pH distribution on the couple surface depended on the relationship between the cathodic reactions and the hydrolysis of Zn2+. Furthermore, the findings demonstrated that both the ORR and HER were inhibited at the steel underlying precipitated zinc corrosion products. The second stage consisted of steel corrosion. The location of the onset of steel corrosion was related to the pH distribution just prior to the extinction of the galvanic action of zinc.

Comparison of corrosion behaviour of zinc in NaCl and in NaOH solutions. Part I: Corrosion layer characterization

The corrosion layer formed on zinc sample in 0.6 M NaCl and 0.5 M NaOH solution under ambient conditions has been investigated. The corrosion layer morphology was analyzed using scanning electron microscopy (SEM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the corrosion products of zinc. The thickness evolution of the corrosion layer was investigated by glow discharge optical emission spectroscopy (GDEOS). The corrosion layer formed in 0.5 M NaOH solution appeared more compact than that formed in 0.6 M NaCl solution. Zinc hydroxide chloride (Zn 5(OH) 8Cl 2·2H 2O) and zinc hydroxide carbonate (Zn 5(CO 3) 2(OH) 6) were formed on zinc surface in 0.6 M NaCl solution while in 0.5 M NaOH solution, zinc oxide (ZnO), zinc hydroxide (Zn(OH) 2) and zinc hydroxide carbonate (Zn 5(OH) 6(CO 3) 2·H 2O) were detected. Probable mechanisms of zinc corrosion products formation are presented.

Optical visualization of concentration field of Zn 2+ during galvanic corrosion of a Zn/steel couple

We applied shadowgraphy and Mach–Zehnder interferometry to investigate concentration field of Zn 2+ above a Zn/steel couple in 0.01 M NaCl. During galvanic corrosion, the marked changes in the concentration of Zn 2+ were visualized in a thin solution layer less than 0.5 mm thick above zinc. The concentration profile of Zn 2+ was also obtained by analyzing the deflection of interference fringes. The obtained concentration profile was in good agreement with that obtained by our group with a scanning probe technique. The formation of zinc corrosion products was also visualized, which occurring on the steel surface a certain distance away from zinc.

Studying phosphate corrosion inhibition at the cut edge of coil coated galvanized steel using the SVET and EIS

The work deals with the effect of sodium phosphate on the corrosion at the cut edge of electrogalvanized steel, studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET). Mapping of the ionic currents revealed that in non-inhibiting solution, the cathode shifts away from the anode as zinc corrosion products precipitate along concentric whitish lines that result from the location of the peak cathodic current. Sodium phosphate inhibits corrosion at the cut edge by precipitation of gel-like zinc phosphate clusters with barrier properties. Breakdown and repassivation of this layer can occur under certain conditions.

Simulation of Solution Chemistry in Edge Corrosion

The objective of this work is to design the calculation model to simulate solution chemistry in edge corrosion of painted metallic coated steel sheets in atmospheric corrosion test with NaCl solution. And the effects of coating, Zn or 55%Al-Zn, and chromate treatment were discussed based on calculation results. For Zn coated steel sheet, zinc works as an anode and carbon steel with corrosion product of zinc works as a cathode. For 55%-Zn coated steel sheet, Zn-rich phase works as an anode, and the cathode is the carbon steel with corrosion product of zinc at early stage and Al-rich phase when blister width is large enough. It was confirmed that growing rate of blister width, dXc/dt, and [Cl-] of 55% Al-Zn coating becomes very low with chromate treatment, because of small potential difference between Zn-rich phase and Al-rich phase in retreated area or cut edge.

Wet/Dry Cycle Corrosion Behavior of Model Cut-Edge Formed on Pre-Painted Zinc Alloy Coated Steels by Laser Fabrication

Laser machining technique, which used focusing pulse YAG laser beam irradiation, was applied to form area ratio of controlled model cut-edge on pre-painted zinc related coated steels. A corrosion behavior of formed model cut-edge was investigated by wet/dry cyclic corrosion test using 10 mol m-3 NaCl solutions in 80 % R.H. atmosphere. In high area ratio zinc specimens, red rust is observed on steel substrate at model cut-edge. The chromate inhibits corrosion of formed model cut-edge on pre-painted zinc coated steels. The behavior of corrosion penetration under the paint depends on composition of coating. In the case of painted zinc-55 mass% aluminum coated steel, zinc rich phase preferentially dissolved. The preferential zinc rich layer dissolution and corrosion products formation cause paint peel off.

Silane Film Obtained from a Sol Constituted with TMSPMA and TEOS and the Hexavalent Chromate Conversion Film: The Comparative Performance as a Post-Treatment of Zinc Coating

Silane films obtained by sol-gel process have been proposed as an alternative to replacement for chromate post-treatment of zinc coatings. The aim of this work was to study the electrochemical behavior of electrodeposited zinc coatings post-treated with silane-cerium film or Cr(VI) conversion coating. Silane-cerium coatings were obtained by dip-coating from a sol constituted by TMSPMA and TEOS silanes precursors with the addition of cerium salt. Electrochemical impedance spectroscopy (EIS) measurements, allied to potentiostatic polarization curves, demonstrated that the post-treatment of zinc with hexavalent chromate conversion or silane film promoted the increase of polarization resistance (Rp) and the reduction of corrosion current density. However it was verified the superior performance of silane-cerium coatings associated to the effect of silane film resistance (Rsi), and the resistance related to the formation of a corrosion product of zinc and cerium (Rzco).

Zinc precipitation runoff from galvanised steel in humid tropical climate

Worldwide hot dip galvanising is the most important application of a zinc coating as an efficient method for steel corrosion protection. In southeastern Mexico, in humid tropical climate, the domestic statistics reports that 63% of roofs and walls are made from galvanised sheets, which suffer corrosion damage. When zinc corrosion products are dissolved by dew and rain, zinc ions are released from the corroded surface and dispersed to the environment. This phenomenon, known today as the metal runoff process, is being paid enormous attention. In order to make an accurate estimation of zinc runoff induced by atmospheric corrosion in humid tropical climate, samples of hot dip galvanised steel have been exposed for two years in the Gulf of Mexico environments. The annual zinc runoff rates in both test sites decreased by ∼50% in the second year (2·70–3·28 g m−2/year), as compared to those measured in the first year of exposure (6·52–7·98 g m−2/year). The zinc mass loss has been related to several independent parameters, which control the runoff process. Runoff solutions collected from the samples in exposure after the first flushes of rain, always showed pH values in the range 5·5–7·0, when the rainwater was more acidic (pH 4·7–6·10). The carbonate ion CO2−3 concentration detected in zinc runoff solutions reached values 1·6–1·7 times higher than those measured in rainwater, due to dissolved zinc carbonate corrosion product. Several chloride containing corrosion products, not released by rain events, were detected as major and minor phases by XRD during the exposure of galvanised steel.

Case study: Analysis of coating failure on hinged steel boxes

A systematic failure analysis was performed on three large steel boxes in which the coating system had blistered, extensively delaminated, and subsequently corroded. These boxes were a sample from a larger batch of boxes that had been recalled due to severe corrosion. Despite the fact that limited information on the process history was provided, we were able to determine that two out of three boxes were neither galvanized nor protected by a zinc-rich primer to provide cathodic protection. The coating system comprised an epoxy primer, zinc-rich intermediate coat followed by an acrylate urethane top coat. A zinc-rich coating should never be applied over a nonmetallic coating because cathodic protection of the underlying steel can only take place if the zinc-rich coating is in direct electrical contact with clean steel. The third box was galvanized and primed with a urethane-alkyd primer followed by an acrylate urethane top coat. Alkyd-type coatings should not be applied over zinc (galvanizing) because the corrosion products of zinc are alkaline. Alkyd-modified coatings are very sensitive to alkalinity and a saponification reaction occurs at the zinc-alkyd interface. This degrades the alkyd and causes it to peel or delaminate from the zinc alloy used for the galvanization. The epoxy primer showed unusually severe air bubbles (or pockets) that could have been due to saponification and/or solvent entrapment. In either case, these large pockets weakened the bond between the primer and galvanized layer and allowed delamination to occur. Our finding that chlorides were present on the surface of the epoxy primer indicated that the boxes might have been exposed to a marine or coastal atmospheric environment. Marine or coastal atmospheric corrosion is generally considered to be one of the most severe atmospheric corrosion environments and the presence of chlorides explains the severity of the corrosion. The boxes were presumed to have been powder coated, yet microscopic and chemical analysis showed the coatings were probably applied as liquids. This was further supported by the thinning of the coatings at the sharp edges and corners of the boxes.

Electrochemical behaviour of zinc in chloride and acetate solutions

The corrosion behaviour of zinc in chloride medium was investigated in the absence as well as the presence, of acetate ions. The temperature effect was also investigated by varying the temperature in a range of 298 to 328 K, while the pH was kept constant at 8.5. Polarization resistance ( R p ) and activation energy ( E a ) val- ues were determined, by means of potentiodynamic and EIS measurements. Thermodynamic properties were evaluated with the current-potential measurements. The temperature, ionic species and the parts of oxide film on anodic and cathodic processes are discussed. It was shown that zinc acetate (Zn ( CH 3 COO ) 2 ) formation could provide important protection with other zinc corrosion products, against the attack of corrosive environment.

Corrosion inhibition at galvanized steel cut edges by phosphate pigments

The corrosion mechanisms and the inhibiting effect of sodium phosphate at cut edges on galvanized steel was studied by potentiodynamic polarization, EIS and monitoring of local ionic currents made by means of the scanning vibrating electrode technique (SVET). Assessment of zinc and of iron single electrodes was also made for comparison. In the absence of phosphate, corrosion of electrogalvanized steel at the cut edge is cathodically inhibited by the precipitation of zinc corrosion products over the steel surface. Mapping of the ionic currents revealed that the cathodic area becomes laterally shifted away from the anode as zinc corrosion products precipitate along parallel lines that are dictated by the location of the maximum cathodic currents. Sodium phosphate revealed inhibiting properties on the cut edge by precipitation of zinc phosphate, in the form of gel-like zinc phosphate clusters. Estimated inhibiting efficiencies for the cut edge were slightly above 80%.

Analytical characterization of silane films modified with cerium activated nanoparticles and its relation with the corrosion protection of galvanised steel substrates

Galvanised steel substrates were pre-treated in bis-1,2-[triethoxysilyilpropyl]tetrasulphide silane solutions containing SiO 2 or CeO 2 nanoparticles activated with cerium ions. The surface composition was investigated by infrared spectroscopy. The film thickness was determined by scanning electron microscopy. The results showed that the barrier properties of silane films modified with nanoparticles depend upon the concentration of nanoparticles. The results also showed that the silane film thickness increases when the nanoparticles are activated with cerium ions. The anti-corrosion behaviour of the cerium activated nanoparticles was also investigated at the microscale level, in artificial induced defects, using the scanning vibrating electrode technique (SVET). The substrates treated with the silane coating modified with CeO 2 nanoparticles revealed improved corrosion behaviour comparatively to the coatings modified with SiO 2 nanoparticles. X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments carried out on the defects after immersion in NaCl solutions revealed the presence of a surface film containing zinc corrosion products and cerium/ceria compounds.

Characterization of atmospheric corrosion products of zinc exposed to SO2 and NO2 using XPS and GIXD

A complete characterization of corrosion products formed on zinc plates after exposure in a climatic chamber was conducted in this study. The dry deposition of NO2, SO2, and SO2 + NO2, at 25 °C and 35 °C, and relative humidity (RH) of 90% was simulated. Pollutant concentrations evaluated were selected to represent highly polluted industrial atmospheric levels. Analysis techniques included X-ray Photoelectron Spectroscopy (XPS) and Grazing Incidence X-ray Diffraction (GIXD). For tests conducted at 25 °C, the relative amount of sulfate was determined to be higher in the SO2 + NO2 atmosphere than in the SO2 atmosphere, and was associated with greater corrosivity in the former atmosphere. NO2 had an indirect role as a catalyst for SO2 reduction to sulfate, as evidenced by the greater proportion of sulfate ions detected and the lack of nitrogen compounds in corrosion products. At 35 °C, effect of NO2 was reduced, and was complicated by a greater tendency for drying so that it was more difficult to maintain the humidity layer. Therefore, no accelerating effect of exposure temperature was observed.

Microbially influenced corrosion of zinc and aluminium – Two-year subjection to influence of Aspergillus niger

Aspergillus niger. Tiegh., a filamentous ascomycete fungus, was isolated from the metal samples exposed to marine, rural and urban sites in Lithuania. Al and Zn samples were subjected to two-year influence of A. niger under laboratory conditions in humid atmosphere. Electrochemical impedance spectroscopy (EIS) ascertained microbially influenced corrosion acceleration (MICA) of Zn and inhibition (MICI) of Al. EIS data indicated a two-layer structure of corrosion products on Zn. The microorganisms reduced the thickness of the inner layer, whose passivating capacity was much higher when compared to that of the outer layer. An increase in aluminium oxide layer resistance but decrease in the layer thickness implied that MICI affected primarily the sites of localized corrosion of Al (pores, micro-cracks, etc.). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies indicated that bioproducts (i.e. organic acids) did not form crystalline phases with corrosion products of zinc. The study suggested a hypothesis that microorganisms could be used as corrosion protectors instead of toxic chemicals, application of which tends to be increasingly restricted.

Effect of Fe–Zn alloy layer on the corrosion resistance of galvanized steel in chloride containing environments

In this study, the effect of Fe–Zn alloy layer that is formed during galvanizing process on the corrosion behavior of galvanized steel has been investigated. The galvanostatic dissolution of galvanized steel was carried out in 0.5 M NaCl solution to obtain the Fe–Zn alloy layer on the base steel. The alloy layer was characterized to be composed of FeZn 13, FeZn 7 and Fe 3Zn 10 intermetallic phases, which constitute the zeta, delta1 and gamma layers of galvanized steel, respectively. It was observed that the alloy layer has similar cathodic polarization behavior but different anodic polarization behavior compared to galvanized steel. The anodic current plateau of alloy layer was up to 100 times lower than that of galvanized coating. Corrosion test performed in wet–dry cyclic condition has shown that the alloy layer has lower corrosion rate as compared to galvanized steel. From the results of corrosion test of alloy layer and base steel, it was concluded that Zn 2+ has positive effect on the protectiveness of the zinc corrosion products. The measurement of surface potential over the alloy/steel galvanic couple has confirmed the galvanic ability of alloy layer to protect both the alloy layer itself and the base iron during initial stage of atmospheric corrosion.

Etapas iniciales del zinc runoff en clima tropical Etapas iniciales del zinc <i>runoff</i> en clima tropical

Frecuently used metals in building application are Zinc and hot dip galvanized steel. The zinc has a relativelly good atmospheric resitance, due to its oxidation in air and formation of protective layer. However, some of the zinc corrosion products can be dissolved by pluvial precipitations and water condensed on the metal surface. This process is called metal runof. In order to estimate el zinc runoff in humid tropical climate, since its firs stages, samples of pure zinc and hot dip galvanized steel have been exposed during 2 years in outdorr atmosphere (rural and urban). The data reveal high annual values of zinc runoff (8,20–12,40 ±0.30 g/m 2 ano), being this process 80% of total mass loss of corroded zinc. The runoff and corrosion processes are more accelerated for zinc, than that of galvanized steel. The principal factors that control the runoff process are discussed.

Composition control of tin–zinc electrodeposits through means of experimental strategies

Tin–zinc coatings offer excellent corrosion protection and do not suffer the drawback of the voluminous white corrosion product of pure zinc or high zinc alloy coatings. The aim of this study was to determine the suitable electroplating conditions (i.e. electrolyte composition and cathode current density) to produce 70Sn–30Zn electrodeposits. Thus, a fractional factorial design (FFD) was carried out to evaluate the effects of experimental parameters (Zn II concentration, Sn IV concentration, pH and current density) on the Zn content of the electrodeposit. On the other hand, the electrodeposits were characterised by glow discharge optical emission spectroscopy (GDOES) and scanning electron microscopy (SEM). Correlation between operating conditions, composition and morphology was attempted.

Research on the Anticorrosion Coating Under the Paved Layer for Highway Steel Box Bridge Deck

The corrosion of the anticorrosion coating and the defects of the asphalt concrete paved layer have been investigated on long-span steel box bridge decks. The anticorrosion coating lies in the middle of two entirely different materials: a highway steel box bridge deck and a paved layer, which is used as anticorrosion and waterproof coating for the steel bridge deck. For our study, electrochemical corrosion and pull strength experiments have been selected for the investigation of the corrosion properties of inorganic zinc rich coating, epoxy zinc rich coating and arc sprayed zinc coating. The adhesive strength between the coatings and the panel, and the effect of the coating corrosion on the shear properties of the paved layers including cast asphalt, thermal asphalt mortar, epoxy asphalt and modified asphalt concrete have been investigated. The results show that the adhesive strength between the coatings and the bridge panel is controlled by the method of pre-processing rust removal. Coating by sandblasting has stronger adhesive strength than coating by shot peening. The results also reveal that shear strength of the paved layer is affected by the corrosion product of zinc coating. The arc sprayed zinc coating has stronger shear strength than zinc rich coatings.