Influence of SO2, periodical wetting and corrosion products on the atmosperic corrosion of steel

Results from laboratory atmospheric corrosion tests on samples of a carbon and a low-alloy steel, with and without pre-exposure (1, 3 and 12 months) in an out-door atmosphere are reported. The laboratory exposure was performed in SO₂-containing (SO₂-supply: 0.4 μg SO₂ · cm⁻² · h⁻¹) and SO₂-free atmospheres at 90% relative humidity and 22.0° C. The results clearly demonstrate that the influence of atmospheric SO₂ on the instantaneous corrosion rate markedly de-decreases with increasing pre-exposure. Comparisons of corrosion rates calculated from out-door exposures and laboratory exposure tests with and without periodical wettings show that the atmospheric corrosion in the main proceeds during or following periods of atmospheric precipitation or condensation, i. e. under conditions of an apparantly wet rust layer. A synergistic effect of SO₂ and periodical wettings was established. Due to the leaching of sulphate ions from the rust layer, immersion sequences (to simulate rainfall) throughout resulted in lower corrosion rates than the simulation of dew by short spraying sequences. The corrosion of pre-exposed samples could be related to the amount of sulphate leached from the rust during immersions.     

Über den beschleunigenden Einfluß von Schwefeldioxid und Wasser auf die atmosphärische Korrosion von verrosteten Eisen

The accelerating effect of sulphur dioxide and water on the atmospheric corrosion of rusty iron The atmospheric corrosion process of rusty steel was observed in the laboratory in an atmosphere with 1, 10 and 100 p.p.m. SO₂, respectively, at a temperature of 30°C. It was found that the correlation of the corrosion rate with humidity can, in the range between critical humidity and nearly 100 per cent. Relative humidity, be represented by a rising quadratic parabolic equation. The differences in the three SO₂ concentrations had no influence on the corrosion kinetics, which is explained by the fact that, under the testing conditions, the rust was fully saturated with SO₄^2?. On the strength of these and earlier results, the authors submit a new working theory concerning the atmospheric corrosion of already rusty steel, introducing the theories of Heusler and Florianovitsch-Kolotyrkin into the sphere of atmospheric corrosion.     

Corrosion products of tin in humid air containing sulfur dioxide and nitrogen dioxide at room temperature

To obtain a fundamental understanding of the corrosion behavior of tin in corrosive gas environments, in situ infrared reflection absorption spectroscopy measurements were carried out on tin in humid air containing SO₂ and NO₂ at room temperature. A series of time-resolved in situ IR spectra in air of 90% relative humidity (RH) containing 10-22 ppm SO₂ suggested that the oxide films on tin specimens had a protective effect and that no significant corrosion occurred. The corrosion products in air of 80-90% RH containing 10-22 ppm NO₂ were SnO₂, SnO, nitrate and hyponitrite. The synergistic effect of SO₂ and NO₂ on corrosion of tin was not observed in humid air (RH of 90%) containing 0.84 ppm SO₂ and 1.8 ppm NO₂.     

Multianalytical in situ investigation of the initial atmospheric corrosion of bronze

Atomic force microscopy (AFM) and infrared reflection absorption spectroscopy (IRAS) were used for in situ investigations of the initial atmospheric corrosion of bronze. In addition ex situ XPS investigations were carried out on the samples before and after the exposure, as well as on the sputtered bronze sample. Investigations were carried out in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH with 250 ppb SO₂. At 80% RH, small features covering the surface were observed with AFM, whereas IRAS detected that more water is adsorbed on the bronze sample surface compared to pure copper. Large features on top of smaller features were observed with AFM on the bronze surface exposed to SO₂-containing humidified air. These large features were identified as copper sulfite. Furthermore, cuprous oxide was detected approximately 500 min after the introduction of SO₂. This fact and the XPS results indicate the formation of a protective lead oxide layer already during the preparation of the sample, which is destroyed by the SO₂-containing environment and leads to the formation of cuprous oxide and copper sulfite.     

The effects of air pollution and climatic factors on atmospheric corrosion of marble under field exposure

The atmospheric corrosion of marble was evaluated in terms of SO₂ concentration as air pollution and climatic factors such as rainfall, relative humidity, temperature and so on under the field exposure. Marble of calcite type (CaCO₃) was exposed to outdoor atmospheric environment with and without a rain shelter at four test sites in the southern part of Vietnam for 3-month, 1- and 2-year periods from July 2001 to September 2003. The thickness loss of marble was investigated gravimetrically. X-ray diffraction and X-ray fluorescent methods were applied to study corrosion products on marble. The corrosion product of marble was only gypsum (CaSO₄ · 2H₂O) and was washed out by rain under the unsheltered exposure condition. It was found that the most substantial factors influencing the corrosion of marble were rainfall, SO₂ concentration in the air and relative humidity. Based on the results obtained, we estimated the dose-response functions for the atmospheric corrosion of marble in the southern part of Vietnam.     

A Mössbauer spectroscopic study of rust formed during simulated atmospheric corrosion

Steel coupons were subjected to 100% relative humidity and were inoculated every day with 100 μl of 0.01 N solutions of NaCl, Na₂SO₄, LiCl or CsCl. The first solid rust constituent that formed contained significant amounts of both γ-FeOOH and ferrihydrite. In contrast, only γ-FeOOH was observed in the rust formed during atmospheric corrosion and during wet-dry cycling with distilled water in the laboratory. The ferrihydrite in time was converted to γ-FeOOH, α-FeOOH, and γ-Fe₂O₃. The fractions of ferrihydrite + γ-FeOOH in the rust formed as a function of time during atmospheric exposure and during rusting in the laboratory environment were the same in the two cases.     

Atmospheric corrosion of galvanized steel and aluminium in marine and marine‐industrial environments of Saudi Arabia

Three‐year exposure programme was carried out in Saudi Arabia at nine test stations with different climatic and pollution conditions. The aim of this study was to evaluate the joint effect of atmospheric pollutants (Cl^? and SO₂), relative humidity (RH) and temperature (T) on the atmospheric corrosion of galvanized steel (GS) and aluminium (Al). Corrosion rates of the two metals have been obtained by loss of weight after 1, 2 and 3 years exposure. The composition of the corrosion products formed on the specimens was identified by X‐ray diffraction analysis. A classification of the atmospheric corrosion aggressivity of the test sites based both on environmental data and corrosion rate measurements was made according to ISO 9223. In some regions, it can be found that corrosion rate values exceed those established by the ISO standard.     

The influence of sodium chloride on the atmospheric corrosion of steel

The influence of sodium chloride on the atmospheric corrosion of mild steel has been studied. Samples covered with sodium chloride crystals (8 m?g NaCl · cm^?2) have been exposed to an SO₂-free atmosphere at different relative humidities. The combined effect of sodium chloride crystals on a steel surface and sulphur dioxide in the atmosphere has been investigated at an SO₂-supply of 1 m?g SO₂ · cm^–2 · h^–1 (1 ppm SO₂). The corrosion attack was followed by periodic weighings. The corrosion products formed have been studied using the SEM-technique. On exposure of samples with sodium chloride in an SO₂-free atmosphere the extent of corrosion increased with increasing relative humidity from 58% to 90%, interrupted by a sharp minimum at about 87% relative humidity. The SEM-studies showed that tower shaped corrosion products were formed at a high relative humidity while filiform corrosion appeared when the relative humidity was lowered. At 90% relative humidity more corrosion was observed with clean steel samples and an SO₂-supply of 1 m?g ·cm^–2 ·h^–1 than with sodium chloride crystals on the surfaces (8 m?g NaCl ·cm^–2) in the absence of SO₂. In the combined influence of sodium chloride on the steel surfaces and sulphur dioxide in the atmosphere a synergic effect was noticed at 90% relative humidity. At 70% relative humidity no influence of an SO₂-supply of 1 m?g SO₂ ·cm^–2 ·h^–1 on the corrosion of steel samples with sodium chloride crystals on their surfaces could be observed.     

Effects of NaCl,SO2, NH3, O3, and ultraviolet light on atmospheric corrosion of Zn

The atmospheric corrosion behavior of Zn was studied in laboratory environments containing constituents that have not previously received much attention, in particular, humidity, SO₂, NH ₃, and O ₃, along with ultraviolet (UV) light irradiation and a preloading of NaCl. After exposure, corrosion rates were measured using mass loss, and corrosion products were identified by X-ray diffraction, Fourier transform-infrared spectroscopy, and energy dispersive spectroscopy. In this study, UV light and O ₃ did not significantly affect the Zn corrosion rate in the absence of Cl ⁻. However, when NaCl was present, UV light inhibited the Zn corrosion rate below 90% relative humidity (RH) and accelerated the Zn corrosion rate at 99% RH. The presence of UV light also increased the formation of zinc hydroxyl sulfate and gordaite when exposed to 120 parts per billion (ppb) SO ₂ and NaCl. The combination of SO ₂ and O ₃ with the preloading of NaCl increased the corrosion rate of Zn compared with NaCl alone. NH ₃ at a concentration of 550 ppb did not have a significant effect on the Zn corrosion rate.     

Über einige Aspekte der atmosphärischen Korrosion von Stahl

To some aspects of the atmospheric corrosion of steel The corrosion of unalloyed steel (St 38 u 2) in pure moist air and by existence of low molecular saturated monocarbonic acids have been studied with microphotometric method. Moreover the electrochemical behaviour of this steel in adequate aqueous solutions has been characterized. It was found that steel - in distinction to pure iron - corroded already in moist air without pollutants in case the relative humidity is (RH) ≥70%. The action of the volatile monocarbonic acids on the corrosion were dependent on the pH value of water film which had been absorbed on the oxide layer of iron material. Oxygen acted as passivator above of pH_crit and the anions of these carbonic acids stabilized the surface hydroxyl groups on the strength of formation of bridging complexes. Final general conclusions about the mechanism of the atmospheric corrosion of iron materials are deduced.     

加速腐蚀实验研究碳钢的大气腐蚀行为

目的快速研究大气环境对钢制输电铁塔腐蚀的影响。方法采用室内加速腐蚀实验,研究碳钢试样在湿度和SO2浓度不同的气氛中的腐蚀行为。结果用极化曲线法测得的金属腐蚀速率与失重法测得的结果具有很高的一致性。相对湿度较低时,改变腐蚀性气体的浓度,对碳钢的腐蚀影响不显著;碳钢在高湿度的含SO2气氛中会发生严重腐蚀。结论降低湿度是防止或减缓碳钢在含SO2气氛中腐蚀的有效途径。     

Atmospheric corrosion of carbon steel at marine sites in Saudi Arabia

Atmospheric corrosion tests, according to ASTM G50‐76, have been carried out in Saudi Arabia, at eight marine sites representing different environmental conditions. Environmental factors such as average temperature, average relative humidity, and deposition rates of atmospheric pollutants (Cl^? and SO₂) was investigated. X‐ray diffraction has been used to determine the composition of the corrosion products. Corrosion rates have been determined for each sample at each of the exposure sites via loss of weight. The obtained data were used for the classification of atmospheric aggressivity, according to ISO 9223. The results obeyed well with the empirical kinetics equation of the form C = Ktⁿ, where K and C are the corrosion losses in mg/cm² after 1 and t years of the exposure respectively, and n is constant. Based on n values, the corrosion mechanism of carbon steel is predicted. The major constituent of the rust formed in marine environment is goethite (α‐FeOOH). Samples also show the presence of a large proportion of lepidocrocite (γ‐FeOOH) and small amounts of ferrihydrite and maghemite (α‐Fe₂0₃).     

The influence of relative humidity and temperature on the acetic acid vapour-induced atmospheric corrosion of lead

The acetic-acid induced atmospheric corrosion of lead was studied at 22.0 °C and 30-95% RH and at 4 °C and 95% RH. The samples were exposed to synthetic air with careful control of relative humidity, temperature, acetic acid concentration (170 ppb) and flow conditions. Reference exposures were carried out in clean humid air. Samples were analysed by gravimetry, ion chromatography, quantitative carbonate analysis, ESEM and XRD. Traces of acetic acid vapour strongly accelerate the atmospheric corrosion of lead. The corrosion rate is only weakly dependent on relative humidity in the range 95-50% RH. The accumulated amount of acetate is independent of RH in the range 95-40%. Lead corrosion in humid air in the presence of acetic acid vapour exhibits a negative correlation with temperature. The crystalline corrosion products formed on lead in the presence of acetic acid vapour were lead acetate oxide hydrate (Pb(CH₃COO)₂ · 2PbO · H₂O) and massicot (β-PbO) together with plumbonacrite (Pb₁₀O(CO₃)₆(OH)₆) or hydrocerussite (Pb₃(CO₃)₂(OH)₂). The transformation of lead acetate oxide hydrate into hydrocerussite and vice versa was also studied. The mechanism of corrosion is addressed, and the implications of this study for combating the corrosion of lead organ pipes in historical organs are discussed.     

Der Oxidationsmechanismus von Szomolnokit im intermittierend befeuerten Warmwasserkessel

The oxidation mechanism of szomolnokite in intermittently fired domestic boilers Using thermogravimetry and exposure experiments on initially formed iron(II)-sulfate hydrates the consecutive reactions of the primary corrosion product szomolnokite under the typical operating conditions of domestic boilers were investigated. The reaction mechanism thus deduced is in accordance with thermodynamic equilibrium considerations in the system Fe₂O₃? H₂SO₄? H₂O/crystalline phase. The reaction mechanism consists of the following steps: With this reaction mechanism the most frequently occurring crystalline phases in corrosion samples from oil fired domestic boilers can be explained.     

Multianalytical in-situ investigations of the early stages of corrosion of copper, zinc and binary copper/zinc alloys

A new experimental infrared reflection absorption spectroscopy (IRRAS) set-up for in-situ investigation of corrosion phenomena occurring in the metal–atmosphere interface was developed. It was applied in combination with in-situ tapping-mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) to study the early stages of corrosion of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ secondary ion mass spectrometry (SIMS) investigations were carried out on the samples after exposure.The investigations were accomplished in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH and 250 ppb SO₂. The experiments showed that an increase of the zinc content in the brass alloy yields to an increase of the dimension of the corrosion features formed on the metal surface during weathering. Large features on top of smaller features were observed with TM-AFM on the surfaces exposed to SO₂-containing humidified air, which could be identified by IRRAS as metal sulphur compounds. Furthermore, an increased amount of physisorbed water on the metal surfaces was determined with IRRAS in dependence of the increasing zinc content in the brass samples.     

Auswertung dreijähriger atmosphärischer Korrosionsversuche mit Eisen,Kupfer und Zink auf tschechoslowakischen Prüfstationen

Evaluation of atmospheric corrosion tests with iron, copper and zinc, extending over three years, at Czechoslovak testing stations At three testing stations in Czechoslovakia, carbon steel, metallurgical zinc and metallurgical copper were exposed to atmospheric corrosion for three years. Samples were taken for examination after 6 weeks, 14 weeks, 6 months, 12 months and 2 years. The humidity and temperature conditions experienced during the test period were recorded in ?climatographs”?, and the SO₂ contents were measured cumulatively. After a time, the corrosion rate is found to assume a stationary condition which has often not been recognized in previous research work because the initial periods, showing a different behaviour, were included in the evaluation. The results confirm the known close correlation between corrosion and humidity, though different mechanisms must be assumed for the different metals investigated. In the case of Zn and Cu, the SO₂ content in the atmosphere is the decisive factor whilst, for Fe, the content of SO₄^2? ions in the rust is more important. In either case, critical values are encountered which are governed, respectively, by the possibility of adsorbing SO₂ at the phase boundary and by the possibility of compounding the SO₄^2? ions in the rust.     

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 (Zn₅(CO₃)₂(OH)₆) and zinc oxide (ZnO) in this surface layer were found to provide protection against chloride contaminants.     

The temperature-dependence of the SO2-induced atmospheric corrosion of zinc; a laboratory study

The SO₂-induced atmospheric corrosion of zinc was studied at 4, 14, 22 and 30 °C and 95% RH. Each sample was exposed individually to synthetic atmospheres with careful control of SO₂ concentration (107 and 500 ppb), relative humidity and flow conditions. The initial reaction between SO₂ and zinc was studied in a time-resolved manner. Two-week exposures were performed to measure the corrosion rate and study the formation of corrosion products. Corrosion products were analysed by X-ray powder diffraction and ion chromatography. The corrosion rate was inversely dependent on temperature, the maximum rate being found at the lowest temperature. SO₂ deposition showed a similar trend with the highest deposition rate at 4 °C. At low temperature a thick film of ZnSO₄(aq) formed on the metal surface, whereas zinc hydroxysulphate (ZnSO₄ · 3Zn(OH)₂ · 4H₂O(s)) was the main corrosion product at 22 and 30 °C. The inverse temperature-dependence of the corrosion rate of zinc is proposed to be connected to the formation of sparingly soluble zinc hydroxy sulphate which slows down the deposition of SO₂ on the surface.     

Zinc corrosion runoff process induced by humid tropical climate

Zinc and hot dip galvanized steel are frecuently used metals in building application. They have relatively good atmospheric resistance to corrosion, due to its oxidation in air and formation of protective rust on its surface, which acts as barrier between the metal and environment. However, some part of the rust can be dissolved by pluvial precipitations and water condensed on the metal surface. This process, called metal runoff, contributes for zinc dispersion in soils and waters. In order to make accurate estimation of zinc runoff induced by atmosphere in humid tropical climate, samples of pure Zn and hot dip galvanized steel have been exposed in the Gulf of Mexico. The data reveal that this process is strongly influenced by factors which determine the aggressivity of the environment (pluvial precipitations, cycles of dry and rainy periods, atmospheric pollutants, air humidity). High annual rates of zinc runoff (6.5 – 8.5 ± 0.30 g Zn m^?2yr^?1) were released, being the runoff 63 – 87% of the zinc corrosion rust. The zinc mass loss has been related to several independent parameters, presenting linear equation, which indicates the air contaminant SO₂ as the major factor controlling the runoff of zinc. The reported results show higher runoff of zinc samples, compared to that of hot dip galvanized steel     

Laboratory Testing of the Atmospheric Corrosion of Steel

The atmospheric corrosion of a mild steel (0.09 C) has been studied in flowing atmospheres containing 1, 10 and 100ppm SO₂ at 80, 85, 90 and 96% relative humidity. The flow rate was varied to give SO₂-supplies ranging between 0.4 and 250 μg SO₂ cm^?2 h^?1. After an exposure period of 300 h testing was continued up to 5000 h in atmospheres free from SO₂ at 85–100% relative humidity. Some of the samples were sprayed with distilled water to simulate wetting by rain or condensation. The corrosion attacks were followed by successive weighings. The composition of the corrosion products was studied using X-ray diffraction, IR-spectrometry and ESCA-technique. The flow rates of the SO₂-containing atmospheres were found to have a marked influence on the corrosion attack. The corrosion rates could not therefore be related to the SO₂ concentration of the atmosphere alone but rather to the supply of SO₂ per unit surface area and time. Exposures performed at high SO₂-supply resulted in formation of corrosion products more protective than those formed at lower SO₂-supply. ESCA-analysis proved formation of suphide containing corrosion products at SO₂-supply. ESCA-analysis proved formation of sulphide containing corrosion products at SO₂-supplies ≥ 8 μg SO₂ cm^?2 h^?1. Periodic spraying of the samples with distilled water were found to cause a drastic increase in corrosion attack.