Zinc Corrosion Products Research Articles

Effects of NaCl and SO 2 on the initial atmospheric corrosion of zinc

The influence of NaCl deposition on the corrosion of zinc in atmospheres with and without SO 2 was studied via quartz crystal microbalance. Regularity of the initial corrosion of zinc under these conditions was analyzed. The results show that NaCl can accelerate the corrosion of zinc. Mass gain of zinc increases with the exposure time, which can be correlated by using exponential decay function. The relationship between mass gain and amount of NaCl deposition is well linear at any time in air containing 1 ppm SO 2, but follows quadratic function in air without SO 2. More amount of NaCl deposition will slow down the corrosion to some extent after exposure for certain time in the presence of SO 2. The combined effect of NaCl and SO 2 on the corrosion of zinc is greater than that caused by each single component. Fourier transform infrared spectroscopy and X-ray diffraction were used to characterize the corrosion products of zinc. In the absence of SO 2, simonkolleite, Zn 5(OH) 8Cl 2·H 2O and zincite, ZnO are the dominant corrosion products, while zinc hydroxysulfate (Zn 4SO 4(OH) 6·3H 2O), zinc chloride sulfate hydroxide hydrate (Zn 12(SO 4) 3Cl 3·(OH) 15·5H 2O) and simonkolleite dominate in the presence of SO 2. Brief discussion on the mechanisms of atmospheric corrosion under these conditions was introduced.

Characterization of zinc-rich powder coatings by EIS and Raman spectroscopy

In this work, the protective mechanisms of a single coat zinc-rich powder coating are examined. Powder coating panels were applied on phosphatized steel and were studied when immersed in artificial sea water with flowing conditions. Open circuit potential and electrochemical impedance spectroscopy measurements were recorded to study changes in the coating properties with the exposure time. Moreover, Raman spectroscopy was used to analyze zinc corrosion products. This study reveals that the behavior of powder coating systems is different from solvent-based zinc-rich paints (ZRP). This is mainly attributed to the low porosity of powder coatings, due to their high wetting ability, which insulates some of the zinc particles. However, cathodic protection is active and provides the sealing of the coating pores. Finally, it is found that the barrier effect is higher than the one usually observed with solvent-based ZRP.

Quantitative Analyses of Crystalline Compositions of Iron Rust on Automobiles under Service Conditions.

Quantitative analyses of the crystalline composition of rust that formed on automobiles under service conditions was carried out to investigate the corrosion mechanism of zinc-coated steel panels. The composition of the rust was quantitatively analyzed by X-ray diffraction using the internal-standard technique. The rust compositions in the crevice and on the surface of the outer panels were located within each characteristic region in the α-FeOOH/(γ-FeOOH + Fe 3 O 4 )/remainder ternary diagram that we proposed in the present study. The rust in crevices contained more (γ-FeOOH + Fe 3 O 4 ) than that on the surface. The largest amount of amorphous iron rust formed in the crevices of galvanized steel panels under zinc corrosion products during the initial stage of steel corrosion. Crystalline β-FeOOH then appeared until the amount reached a maximum content of 13 %. The composition of iron rust on zinc-coated steel sheets progresses towards that of the ungalvanized regions. It was found that the production of crystalline iron rust was retarded when zinc corrosion product formed in the crevice of lapped areas.

The effects of 20 kHz and 500 kHz ultrasound on the corrosion of zinc precoated steels in [Cl−] [SO2−4] [HCO−3] [H2O2] electrolytes

The effects of 20 and 500 kHz ultrasound on the corrosion of precoated steels were studied by analysing the behaviour of a zinc coated steel electrode in the corrosion electrolyte [Cl−] [SO2−4] [HCO−3] [H2O2]. The electrolyte was subjected to 20 kHz ultrasound, 500 kHz ultrasound and silent conditions. Zinc plated specimens were exposed to those solutions and growth of the corrosion products was studied by scanning electron microscopy, X-ray microanalysis and grazing incidence X-ray diffraction. Mass transfer measurements were taken on platinum macro- and microelectrodes; they highlighted a specific effect of ultrasound on the growth of zinc corrosion products depending on frequency. Ultrasound greatly influenced corrosion rates; however, the reaction sequence appeared unchanged by the use of an ultrasonic field compared to silent conditions.

Corrosion Products of Galvanized Rebars Embedded in Chloride-Contaminated Concrete

Abstract Iron corrosion products of steel reinforcement result in staining, cracking, and spalling of concrete structures. These effects of corrosion require costly repairs and maintenance during the useful life of the structures. To prevent corrosion of important infrastructure projects, galvanized reinforcing steel occasionally is used. The performance of galvanized steel in chloride-contaminated concrete is attributed to the corrosion product form: zinc oxide (ZnO), which is less voluminous than iron corrosion products. However, zinc corrosion products detected on galvanized reinforcement are rather controversial. Some authors identified another compound: zinc hydroxychloride (Zn5[OH]8Cl2·H2O). This product occupies more space than ZnO and can induce cracking of the cover concrete. Other authors found zinc hydroxychloride and zinc hydroxide (Zn[OH]2). In this work, ZnO and Zn5(OH)8Cl2·H2O were identified. Under some conditions (exposure time in aggressive environment and coating thickness) and after cracking of concrete cover, Zn(OH)2 also was found.

EXAFS study of atmospheric corrosion products on zinc at the initial stage

The corrosion resistance and structural information of zinc atmospheric corrosion products at the initial stage were investigated by using ex-situ electrochemical impedance spectroscopy (EIS) in methanol and extended X-ray absorption fine structure spectroscopy (EXAFS). EIS in methanol performs excellent resolution to the corrosion resistance of the surface layer from various atmospheric exposures. The corrosion resistance of zinc exposed to air of 100% RH for 48 h was found three times larger than that of zinc exposed to an air of 95% RH. The EXAFS data reveal that hydrozincite and amorphous zinc hydroxide are the corrosion products of zinc exposed to atmospheres of 100% RH and 95% RH, respectively.

Atmospheric corrosion of zinc Part 2: Marine atmospheres

AbstractThis paper summarises the results obtained in the MICAT (Mapa Ibero-Americano de Corrosao Atmosferica (Latin American Map of Atmospheric Corrosion)) atmospheric corrosion project (an Iberoamerican project on atmospheric corrosion, involving 14 countries and 75 atmospheric test sites) for zinc specimens exposed in the Latin American region for 1–4 years at 23 pure marine and 19 mixed marine (i.e. SO2 polluted) sites. The atmospheres at these sites were characterised climatologically and in terms of their pollution levels so that their corrosivity could be expressed in accordance with ISO standards. Morphological and chemical characterisation of the zinc corrosion product layers (ZCPLs) was performed using scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and soluble salt evaluation techniques. The results obtained show that the corrosion rate of zinc is a function of both the chloride pollutio...

Atmospheric corrosion of zinc Part 1: Rural and urban atmospheres

AbstractThis paper summarises the results obtianed in the MICAT (Mapa Ibero-Americano de Corrosao Atmosferica (Latin American Map of Atmospheric Corrosion)) atmospheric corrosion project (an Iberoamerican project on atmospheric corrosion, involving 14 countries and 75 atmospheric test sites) for zinc specimens exposed for 1–4 years in 21 rural and urban atmospheres of the Latin American region. During the study, all of these atmospheres were characterised according to international standards. Complementary morphological and chemical studies were carried out using scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to correlate atmospheric characteristics and the properties of zinc corrosion product layers (ZCPLs). Soluble salts retained in these ZCPLs were also determined. The study has provided clear evidence about the wide range of zinc corrosion rates occurring in rural atmos...

Electrochemical corrosion monitoring of galvanized steel under cyclic wet–dry conditions

The corrosion behavior of a galvanized steel was investigated under cyclic wet–dry environments using electrochemical techniques. The wet–dry cyclic was conducted by exposure to alternate conditions of 1 h-immersion in a 0.05 M NaCl solution (or Na 2SO 4 solution) and 7 h-drying at 60% RH. The polarization resistance R p of the galvanized steel was monitored during the wet–dry cycles by AC impedance method. Simultaneously, the corrosion potential E corr was measured only when the specimen was immersed in the solution. The corrosion current density i corr of the zinc coating was estimated from the monitored R p using Stern–Geary equation. The corrosion mass loss Δ M, which was obtained from the i corr vs time curve, was plotted vs the wet–dry cycle number. The average corrosion rate per cycle starts to decrease and the E corr shifts in the noble direction, immediately before the red rust (FeOOH) appears on the coating surface. It seems that the underlying steel corrosion commences when the zinc coating does not act as sacrificial anode due to accumulation of zinc corrosion products on the coating surface. The electrochemical methods, such as impedance and corrosion potential measurements, are an effective tool for monitoring the degradation of metallic coating under atmospheric environments.

Corrosion of Zinc in acetic acid derivatives: Glycollic, mercaptoacetic and cyanoacetic acids and glycine

AbstractThe corrosion behaviour of zinc in glycollic, mercaptoacetic and cyanoacetic acids and glycine was studied by weight loss, pH‐monitoring and polarization measurements. The rate of corrosion was found to be a first order with respect to hydrogen ion activity and strongly dependent of the acid type. The abnormal behaviour in cyanoacetic acid at < 0.5 M was attributed to the hydrolysis of the acid during the corrosion and formation of malonic acid as confirmed by FT‐IR spectroscopy. Morphological investigation of the corroded surfaces showed localized corrosion in cyanoacetic and glycollic acids which increased as the acid concentration or corrosion time increased. The FT‐IR analysis indicated also the formation of zinc glycollate and zinc thioglycollate as the corrosion products of zinc in glycollic and mercaptoacetic acids, respectively (Scheme 1a+b).

Study of corrosion product of zinc in natural sea water

Study of corrosion product of zinc in natural sea water

Study of corrosion product of zinc in natural sea water

AbstractThe electrochemical behaviour of zinc has been studied with special emphasis on the corrosion product formed in natural sea water under laboratory conditions and during in situ tests at sea. The behaviour of corrosion products was studied by a cathodic polarisation method, and the type and amount of zinc compound contained therein were assessed from cyclic polarisation curves. The corrosion product consisted mainly of basic hydroxychloride, which enhanced the compactness of the adherent corrosion product layer. From the cyclic polarisation curves, the area inside the hysteresis loop Q provided a measure of the specific surface area coated by corrosion products and was found to increase as the duration of exposure of zinc in sea water was increased in both laboratory and field tests. It was shown that the corrosion product compactness factor C = Q/Icorr was of value for characterising the barrier to oxygen diffusion provided by this layer.

Identification of thin films on zinc substrates by FTIR and Raman spectroscopies

Raman and FTIR reflectance spectroscopies have been used for the characterization of the following zinc corrosion products formed by atmospheric corrosion : (e-Zn(OH)2 , hydrozincite Zn5 (CO3 )2 (OH)6 , simonkolleite Zn5 Cl2 (OH)8 ,H2 O and zinc sulfates ZnSO4 ,H2 O, Zn4 SO4 (OH)6 , 5H2 O and Zn4 SO4 (OH)6 ,H2 O. The samples to analyze are either developed on metal or obtained by incrustation of submicronic particles of the compound on the surface on zinc substrates. Both the IR reflectance and Raman spectroscopies allow an easy identification of basic zinc salts : chloride by the Zn-O-H bending modes, carbonate and sulfates by the internal mode of the corresponding anion (ν3 region). A multianalytical approach combining FTIR reflectance spectroscopy, grazing incidence X-ray diffraction and SEM/EDS leads to different applications.

Environmental effects on metallic materials – Results of an Outdoor exposure programme running in Switzerland

AbstractAs part of the project “Environmental Effects on Materials” a field exposure programme was begun in 1993 in Switzerland. The exposure sites were chosen near the stations of the National Air Pollution Monitoring Network (NABEL), where climatic data are also recorded. This work presents the results for unalloyed and weathering steel, zinc, hot dip galvanized steel, copper and aluminium specimens after 1 year outdoor exposure, i.e. in an early stage of material degradation.Gravimetric evaluation of the test specimens revealed large differences in material loss due to corrosion for the different test sites that could be correlated with the environmental parameters. A mass balance calculation revealed that for steel, zinc and galvanized steel a considerable portion of corrosion products was lost during the exposure period depending on the environmental conditions at the test site. The losses could be attributed to flake‐off processes for the steels. This was concluded from SEM micrographs. For the zinc samples the most likely mechanism is removal by dissolution and washing away of the corrosion products during rainfall. This is supported by a good correlation of zinc corrosion product loss with the amount of rainfall and the fact that sheltered specimens did not exhibit significant losses of corrosion products. These specimens, on the other hand, showed a considerable accumulation of sulphates, chlorides and nitrates indicating the important role of dry deposition for the adsorption of gaseous pollutants on the metal surface. Generally the corrosive attack was relatively severe and more localized for the sheltered samples although the average corrosion loss was smaller than for those with open exposure.Specimens that had been covered with snow for a longer period of time (exposure site in the mountains) exhibited higher material losses than could be expected from the air pollution situation and climatic data. They also showed a remarkable accumulation of corrosive species on their surface. This unexpected behaviour can be explained by a longer effective time of wetness (compared to the calculated value) and the accumulation of pollutants in the snow layer and on the metal surface.The statistical analysis of the corrosion loss data and the environmental parameters yielded good correlations with the average SO2‐concentration for the different test sites especially when the time of wetness and wind velocity were also taken into account. Sulfur dioxide plays a dominant role among the gaseous pollutants although its concentration could be reduced substantially during the last decade due to various measures taken to reduce sulfur emission. The effect of atmospheric nitrogen compounds (mainly nitrogen dioxide) and ozone for the corrosion of the different metals and the interaction of the different air pollutants is not yet completely understood and is still under investigation under defined conditions in a test chamber.The corrosion products found on different metals surfaces have been analysed using various techniques. Their composition could in some cases be related to the corresponding environmental conditions at the test sites.

Environmental fate of sacrificial zinc anodes and influence of a biofilm

Laboratory experiments were performed to determine the environmental fate of zinc compounds formed during sacrificial dissolution of zinc anodes in seawater and to further determine the role of biofilms in mobilizing/immobilizing zinc corrosion products. Experimental conditions simulated cathodic protection and overprotection (40x normal) of ship ballast tanks with an anode to cathode ratio of 0.091. Anodic dissolution and percentage of soluble zinc increased with the level of protection. For normal cathodic protection in abiotic seawater, approximately 3% of the sacrificed zinc was dissolved in solution. Additionally, weight loss and percent soluble products increased dramatically in the presence of an agar film, but were unchanged due to the presence of natural marine biofilms. Under overprotection conditions, weight loss did not vary in the presence of surface films. Solid zinc corrosion products were precipitated, suspended in solution, and attached to electrode surfaces. Experimental data were compared with zinc concentrations measured in ballast tanks for two United States Navy surface ships.

In Situ Raman Study of the Corrosion of Zinc‐Coated Steel in the Presence of Chloride: I . Characterization and Stability of Zinc Corrosion Products

The different corrosion products formed on zinc specimens (pure or industrially electrodeposited) during exposure to solutions containing two concentrations of chloride were identified by Raman spectroscopy; the crystallographic nature of these products was checked by x‐ray diffraction and their morphology was described by scanning electron microscopy. The conditions of formation of hydroxycarbonates and hydroxychlorides were described, as well as the influence of pH on the growth of the different modifications of . The cathodic or anodic nature of the mechanisms leading to the stabilization of the different products was particularly emphasized.

Corrosion behaviour of electrogalvanized steel in sodium chloride and ammonium sulphate solutions; a study by E.I.S.

Zinc and zinc-nickel (13% Ni) electrodeposits were passivated by dipping in chromate baths and characterized by scanning electron microscopy. The corrosion behaviour was studied using a.c. electrochemical techniques; electrochemical impedance spectroscopy (EIS) measurements were performed at open circuit and under galvanostatic control during the 24 h immersion time. In sodium chloride solution the zinc-nickel electrodeposits show a better corrosion resistance compared to the pure zinc coatings. During the immersion time, a surface nickel enrichment was observed which, together with the zinc corrosion products, acts as a barrier layer reducing the total corrosion rate. In the same solution the passivation treatment improves the corrosion resistance of the electrodeposits; nevertheless, on zinc substrates, the protection exerted by the chromate film is not, always effective during the immersion time. On the contrary the chromate coating on zinc-nickel substrates induces a remarkable and durable improvement of the corrosion resistance reducing the zinc dissolution almost completely. In the ammonium sulphate solution, the corrosion mechanism is significantly influenced by hydrogen reduction on the zinc-nickel surfaces, and by the production of a local surface acidity which is aggressive for the chromate coatings.

Behavior in Seawater of Zinc-Base Coatings on Aluminum Alloy 5086

Abstract The blistering behavior and mechanisms of various kinds of zinc base coatings having a galvanic protection capability (pure zinc or Zn/Al alloys metallic coatings, zinc-rich coatings and zinc-base coatings with a top coating on the aluminum alloy 5086) were studied in seawater immersion. Pure zinc and Zn/Al alloy metallic coatings exhibited significant blistering on the whole coating surface after 10 months immersion, the zinc-rich coatings were more or less insensitive to the blistering. Although the metallic coatings gave sufficient galvanic protection to the alloy 5086, the zinc-rich coatings did not. Blistering of metallic coatings is due principally to the formation of zinc corrosion products in the coating. Some precipitation of calcareous deposits was found also at the coating-substrate interface. Electrochemical impedance measurements showed the inorganic zinc silicate coating to have an excellent pore blocking effect in the coating.

Zinc Layer Characterization on Galvanized Steel by Chemical Methods

Abstract A method has been developed for corrosion product analysis on zinc galvanized steel. Zinc corrosion products are first removed while leaving the underlying metallic zinc unaltered. This method then permits the amount of metallic zinc to be determined by dissolving it, while oxidation compounds at the zinc/iron interface remain unaltered. Zinc corrosion products are dissolved by glycine solution attack (10 minutes at 25°C) by which zinc corrosion layers of 10 A thickness can be analyzed. The zinc metallic layer is dissolved by electrochemical attack (anodic polarization at −900 mV), which does not alter the corrosion products, if any, at the Zn/steel interface. After metallic zinc dissolution, steel corrosion products can also be chemically analyzed by treating the specimens with a series of suitable solvents (glycine, bromine-methanol) for recovery and characterization of iron oxidation compounds.

Interfacial chemistry of corrosion-induced bond degradation for epoxy/dicyandiamide adhesive bonded to cold-rolled and galvanized steels

The interfacial chemistry of a conventional epoxy/dicyandiamide adhesive formulation applied to cold-rolled and galvanized steels has been studied by X-ray photoelectron spectroscopy (XPS). In both cases, the interfacial corrosion process appears to be dominated by attack on the metal substrate, and is reminiscent of crevice corrosion phenomena. On cold-rolled steel, analysis of the interfacial bond failure surfaces suggests that the contamination layer initially present on the substrate is not disturbed during bond formation. Bond failure appears to occur between the substrate and the contamination layer; the contamination layer remains largely intact on the interfacial surface of the adhesive after bond failure. On galvanized steel, the locus of failure appears to be at the adhesive-adherend interface, within a layer of zinc corrosion products. The contamination layer appears to have been partially displaced by the adhesive during bonding.