Rust formed on cannons of XVIII century under two environment conditions

The corrosion products of two ancient cannons exposed to atmospheric corrosion were analysed by X-ray powder diffraction, transmission Mössbauer spectroscopy and scanning electron microscopy (SEM). After almost three centuries exposed in marine environment one of them was moved to a rural region and was maintained in this environment for approximately 30 years. The inland region has an altitude of 1000 m above sea level and consequently low aggressiveness. The studied rusts were obtained from external and internal surfaces of the cannon barrels. This investigation, using three different techniques, was done to check if the relatively short time (ca. 30 years) in rural area was sufficient to change the characteristics of the thick rust formed during long time exposure (ca. 300 years) in marine atmosphere. The time-environment effects change the physical nature of rust, mainly observed by Mössbauer spectroscopy results.     

Influence of outer rust layers on corrosion of carbon steel and weathering steel during wet–dry cycles

The influence of the rust layers of carbon steel and weathering steel on the corrosion were investigated. It was found that corrosion of carbon steel slows down when its outer rust layer is removed. This phenomenon might be attributed to the shortening of the wetting time in wet–dry cycles when the outer rust layers are removed. What is more, growth time of the corrosion products is shortened as well, which results in the formation of the fine corrosion products. However, the behavior of corrosion of weathering steel is not obviously influenced by the outer rust layer and the wetting time.     

Atmospheric corrosion monitoring of a weathering steel under an electrolyte film in cyclic wet–dry condition

Electrochemical Impedance Spectroscopy (EIS) and film thickness measurements have been employed to study the corrosion monitoring of steel under an electrolyte film in wet–dry cycles simulating a coastal atmosphere. The results indicate that within each cycle, the corrosion rate increases during drying process due to an increase in Cl⁻ concentration and an enhancement of oxygen diffusion by thinning out of the electrolyte. As corrosion process proceeds, the corrosion rate increases greatly and reaches a maximum. During subsequent corrosion stage, the corrosion rate decreases greatly and keeps at a low value due to the formation of a stable rust layer.     

Prohesion and outdoors tests on corrosion products developed over painted galvanized steel sheets with and without Cr(VI) species

Galvanized steel sheets pre-treated with a new product and then painted with a polyester topcoat without primer were submitted to Prohesion G-85 test (PT) and to outdoor marine exposure test (OT). The new product that replaces standard inorganic chromium pre-treatment + primer consists in a water based resin which applied directly to the properly cleaned metal substrate is then dried in place. This scheme sets aside Cr(VI) compounds which cause severe damages on human health.Goethite, lepidocrocite, magnetite, akaganeite and silicates were found in OT samples coinciding with the usual corrosion products obtained for conventional painting schemes (with Cr(VI)).Surprisingly in PT samples greigite was detected, showing that the new painting scheme is susceptible to microbiological corrosion. Goethite, lepidocrocite, pyrite, magnetite and akaganeite were also found.This study allows the conclusion that in the PT the corrosion mechanism is different from that in the OT for the analyzed samples and should not be used to predict the performance of this kind of outdoor exposed materials.     

Corrosion of low carbon steel in atmospheric environments of different chloride content

This investigation aims to analyze the effect of Cl⁻ ion on the atmospheric corrosion rate of carbon steel. The metal samples were exposed to a marine atmospheric environment (95 and 375 m from the sea line) as well as an industrial atmospheric environment. The effects of Cl⁻ ions on the protective characteristics of the rust layers were assessed by IR spectroscopy, SEM-EDAX analyses, linear polarization resistance and electrochemical impedance spectroscopy (EIS). The results show that Cl⁻ ion influences the corrosion rate, as well as the morphology and composition of the rust layer.     

Magnetic property based characterization of rust on weathering steels

The characterization of rusts on weathering steels is important in understanding the origin of their corrosion resistance. Rust consists of several phases, e.g. α-, β- and γ-FeOOH, which are anti-ferromagnetic with different Neél temperatures. Rust on so-called advanced weathering steel containing 3 wt.% Ni [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127-136] contains in addition a ferrimagnetic spinel phase [M. Kimura, H. Kihira, Y. Ishii, T. Mizoguchi, in: Proc. 13th Asian-Pacific Corrosion Control Conference, Osaka, 2003; M. Kimura, H. Kihira, N. Ohta, M. Hashimoto, T. Senuma, Corros. Sci., this volume; M. Kimura, N. Ohta, H. Kihira, Mater. Trans. JIM, in press]. The nanostructure of real rust cannot be elucidated satisfactorily only with conventional analytical methods such as X-ray diffraction, because of the complex mixture of phases with fine and imperfect crystallites. Because of the short range of the super-exchange coupling between Fe ions in a solid, the magnetic properties can give information on local configurations even in the absence of perfect crystalline coherence. Therefore, the magnetic properties of rust samples were investigated in detail using a Superconducting Quantum Interference Device (SQUID) magnetometer and Mössbauer spectroscopy. SQUID magnetometry is effective to determine the quantity of the ferrimagnetic phase. The temperature dependence of the Mössbauer spectrum gives information about not only the fractions of the phases but also the distribution of grain volume, V, in each phase according to the super-paramagnetic relaxation effect. This approach has been applied to rust of conventional [T. Okada, Y. Ishii, T. Mizoguchi, I. Tamura, Y. Kobayashi, Y. Takagi, S. Suzuki, H. Kihira, M. Ito, A. Usami, K. Tanabe, K. Masuda, Jpn. J. Appl. Phys. 39 (2003) 3382] and advanced weathering [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127-136] steels.The grains of the rust formed on advanced weathering steel have clearly bimodal Gaussian distributions of volume with peaks at V ≈ 5 × 10⁻²⁴ m³ and V ≈ 16 × 10⁻²⁴ m³ in α-FeOOH and β-FeOOH phases. The outer layer has grains of γ-FeOOH which are an order of magnitude smaller. The inner layer, in contrast, has a continuous distribution of grain volume, consistent with the formation of a continuous densely packed thin protective rust layer which prevents further corrosion.     

Corrosion resistance of the Dhar iron pillar

The corrosion resistance of the 950-year old Dhar iron pillar has been addressed. The microstructure of a Dhar pillar iron sample exhibited characteristics typical of ancient Indian iron. Intergranular cracking indicated P segregation to the grain boundaries. The potentiodynamic polarization behaviour of the Dhar pillar iron and mild steel, evaluated in solutions of pH 1 and 7.6, indicate that the pillar iron is inferior to mild steel under complete immersion conditions. However, the excellent atmospheric corrosion resistance of the phosphoric Dhar pillar iron is due to the formation of a protective passive film on the surface. Rust analysis revealed the presence of crystalline magnetite (Fe_3−xO₄), α-Fe₂O₃ (hematite), goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH) and phosphates, and amorphous δ-FeOOH phases. The rust cross-section revealed a layered structure at some locations.     

Corrosion mechanism of model zinc-magnesium alloys in atmospheric conditions

Recently, superior corrosion properties of zinc coatings alloyed with magnesium have been reported. Corrosion behaviour of model zinc-magnesium alloys was studied to understand better the protective mechanism of magnesium in zinc. Alloys containing from 1 to 32 wt.% magnesium, pure zinc, and pure magnesium were contaminated with sodium chloride and exposed to humid air for 28 days. Composition of corrosion products was analyzed using infrared spectroscopy (FTIR), ion chromatography (IC), and Auger electron spectroscopy (AES). The exposure tests were completed with scanning Kelvin probe (SKP) and electrochemical measurements. Weight loss of ZnMg alloys with 1-16 wt.% magnesium was lower than that of pure zinc. Up to 10-fold drop in weight loss was found for materials with 4-8 wt.% Mg in the structure. The improved corrosion stability of ZnMg alloys was connected to the presence of an Mg-based film adjacent to the metal surface. It ensured stable passivity in chloride environment and limited the efficiency of oxygen reduction.     

Effect of tensile strain on the rate of marine corrosion of steel plates

It has been observed in the shipping industry that the rate of corrosion of steel plate may increase with longer duration of exposure, typically over many years. This effect has been attributed to the flexure of ships plates causing the loss of protective rust layers. The present paper describes the results of laboratory experiments in which plates with pre-existing rusts were subject to high levels of tensile strain, with and without subsequent exposure and corrosion. All rusts were obtained by exposing the steel to a natural marine environment, including the atmospheric and tidal zones. Careful observation of the rusts under tensile strain conditions showed that only strains near and beyond the elastic limit of the steel have the capacity to cause significant damage to the rust layers. Subsequent short-term exposure tests on pre-corroded and pre-strained steel coupons showed that there can be a moderate (10–15%) increase in the short-term corrosion rate.     

Corrosion behavior of low-alloy steel containing 1% chromium in CO2 environments

Corrosion behavior of low-alloy steel containing 1% Cr (1Cr) with normalized (ferritic–pearlitic) and quenched-and-tempered (tempered martensitic) microstructures was investigated in CO₂ environments at 60 °C. The severe localized corrosion which was observed in N80 carbon steel, did not exist for 1Cr steel due to the formation of a compact and self-repairable Cr-rich scale. For 1Cr steel, the corrosion resistance with ferritic–pearlitic microstructure was better than that with tempered martensitic microstructure. An apparent corrosion scale spallation was observed on the surface of quenched-and-tempered 1Cr steel, while only slight scale spallation was seen for normalized 1Cr steel.     

Corrosion loss of mild steel in high temperature hard freshwater

This paper presents an interpretation of corrosion loss data for mild steel coupons exposed for up to 2.6 years to freshwater under a range of dissolved oxygen levels and temperatures 50-60 °C. The water total alkalinity was 0.5-0.6 mmol/l and pH 8.7-9.2. It is shown herein that the data is consistent with the early stages of the corrosion loss model proposed earlier for steel exposed to seawater, brackish water or freshwaters in the usual environmental range of 0-30 °C. The new data was found to be consistent with the effect of dissolved oxygen and the effect of water hardness on the model.     

Corrosion behavior of TiC particle-reinforced 304 stainless steel

TiC particle-reinforced 304 stainless steels were prepared using a new developed in situ technology and their corrosion behavior was compared with that of 304SS in 5 wt.% HCl solution. As compared to 304SS, E_corr, E_pit and E_rp values had shifted to a more negative region in 304SS containing TiC, indicating faster corrosion rate by TiC addition. The addition of TiC particles to 304SS resulted in no rapid pit propagation but maintained a high corrosion rate in the whole immersion time investigated.     

Atmospheric corrosion resistance of MnCuP weathering steel in simulated environments

In this work, atmospheric corrosion resistance of low cost MnCuP weathering steel in simulated coastal, industrial, and coastal–industrial atmospheric environments was investigated by wet/dry cyclic acceleration corrosion tests. The results indicate that MnCuP weathering steel exhibits high corrosion resistance in the three atmospheres. Besides, the alloying effect of Mn, Cu, and P elements on the anti-corrosion mechanism of MnCuP weathering steel was discussed by techniques of X-ray photoelectron spectroscopy, potential–pH diagram, and electron probe microanalysis.     

A proposal to evaluate the amount of corroded iron converted into adherent rust in steels exposed to corrosion

To calculate the amount of iron corroded from the steels that form part of the adherent rust, α, we propose a procedure that considers mass measurements and the use of spectroscopic techniques to estimate the relative iron phase abundances. We derived an equation to calculate α and evaluate it for carbon steels (CS) and weathering steels (WS) exposed to accelerated outdoor corrosion tests. The values of α are estimated at 0.93 and 0.76 for CS and WS after 2 years of exposure, respectively. The relative iron phase abundances pointed out to a non-protective and active type of rust.     

Corrosion behaviour in alkaline medium of zinc phosphate coated steel obtained by cathodic electrochemical treatment

The present work evaluated the ability of zinc phosphate coating, obtained by cathodic electrochemical treatment, to protect mild steel rebar against the localized attack generated by chloride ions in alkaline medium. The corrosion behaviour of coated steel was assessed by open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The chemical composition and the morphology of the coated surfaces were evaluated by X-ray diffraction and scanning electron microscopy. Cathodically phosphated mild steel rebar have been studied in alkaline solution with and without chloride simulating the concrete pore solution. For these conditions, the results showed that the slow dissolution of the coating generates the formation of calcium hydroxyzincate (Ca(Zn(OH)₃)₂·2H₂O). After a long immersion time in alkaline solution with and without Cl⁻, the coating is dense and provides an effective corrosion resistance compared to mild steel rebar.     

Corrosion performance of conducting polymer coatings applied on mild steel

Conducting polypyrrole electrodes were obtained by galvanostatic electropolymerisation on mild steel electrodes from an aqueous solution. The electrochemical response of the coated electrodes in doped and in undoped state was compared with bare mild steel electrodes. The undoped polypyrrole coated electrode offered a noticeable enhancement of protection against corrosion processes.     

Corrosion performance of epoxy coatings containing silane treated ZrO2 nanoparticles on mild steel in 3.5% NaCl solution

Clear epoxy coatings were modified by adding various levels of ZrO₂ nanoparticles. In order to achieve proper dispersion of nanoparticles in the epoxy-based coating and making possible chemical interactions between nanoparticles and polymeric coating, the surface of the nanoparticles was treated with amino propyl trimethoxy silane (APS). Corrosion performance of mild steel coated specimens was investigated employing EIS, electrochemical noise (ECN) techniques and salt spray test. Coatings with 2–3 wt% ZrO₂ nanoparticles possessed the best corrosion performance among the coating specimens. Possible chemical interactions between polymeric matrix and treated nanoparticles in nanocomposites cause high barrier properties and ionic resistances.     

The influence of chromium content on the electrochemical behavior of weathering steels

To investigate the influence of chromium content on corrosion characteristics of weathering steels, the electrochemical measurements were performed on the steels containing 0–9% Cr (wt.%) in NaHSO₃ aqueous solution. The results indicated that the open circuit potential of these steels shifted to the positive direction remarkably, because the additions of Cr improved the passivation capability of the steels. The corrosion current density of the steels containing more than 7% Cr (wt.%) decreased significantly after pre-rusted treatment, implying the corrosion resistance could be enhanced by the formation of protective goethite rust layer.     

Rust formation and corrosion performance of Si- and Al-bearing ultrafine grained weathering steel

A high Si, Al type ultrafine-grained (UFG) weathering steel was produced by the multi-pass warm rolling method, and its corrosion resistance was estimated by a cyclic wet/dry corrosion test using chloride ions. The Si- and Al-bearing UFG steel exhibited excellent corrosion resistance in comparison with Si–Mn carbon steel (SM).

EPMA and TEM analyses showed that Si and Al mainly exist in nano-scale iron complex oxides in the inner rust layer formed on the developed steel. The Al K X-ray spectrum of Al₂O₃ and metallic Al had different peak positions due to chemical shifts, and that of the test sample was the same as that of Al₂O₃ in the EPMA analysis. This result suggested that Al was present in the complex oxides as Al³⁺. In the same way, Si was identified as an intermediate state such as Si²⁺ in the complex oxides of the inner rust.

EIS (electrochemical impedance spectroscopy) measurement of the corrosion test samples revealed that the rust resistance (R_rust) and corrosion reaction resistance (R_t) of the developed steel were much larger than those of SM. It was found that nano-scale complex iron oxides formed in the lower layer of iron rust in the developed steel, resulting in increased R_rust and R_t, and finally suppressing corrosion.     

Long-term trends in the corrosion state and surface properties of the stainless steel tubes of steam generators decontaminated chemically in VVER-type nuclear reactors

At some VVER-type pressurized water nuclear reactors (Russian-type PWR) different versions of the so-called AP-CITROX method have been widely used for the chemical decontamination of the heat exchanger tubes of steam generators. In the period of 2000–2007, within the frame of a joint-project dealing with the comprehensive investigation of the corrosion state of the steam generators of the Paks Nuclear Power Plant, Hungary, effects of the AP-CITROX chemical decontamination procedure on the corrosion and surface characteristics of the heat exchanger tubes have been studied. These studies provide evidences that some adverse features (formation of a “hybrid” layer with accelerated corrosion rate and great mobility) can be detected after 1–3 years of applying the AP-CITROX procedure. The present work is a continuation of the above program and focused on the long-term trends in the corrosion state and structure of protective oxide-layer grown on the decontaminated surfaces. The results of electrochemical (voltammetric), surface analytical (SEM–EDX, CEMS) and mobility (ICP–OES) studies have revealed that (1) some beneficial changes in the corrosion characteristics, mobility and chemical composition of the inner surfaces of decontaminated heat exchanger tubes can be observed in the long run, and (2) the passivity of the oxide-layers formed on decontaminated surfaces of steel tubes exhibits favorable tendency after 4–7 years under normal operation conditions.