Hydrogen ion reduction in the process of iron rusting

Since the acceptance of the electrochemical rusting mechanism, oxygen reduction has been considered the main cathodic process, while H⁺ reduction has been overlooked for the past four decades because oxygen can be readily renewed due to the thin layer of solution film formed during atmospheric corrosion. This study shows that measurable hydrogen can be detected at the surface opposite to the corroding side of the specimen during wet-dry cycles, and a clear correlation exists between the quantities of hydrogen permeated through iron sheet and weight loss. Results suggest the intrinsic importance of H⁺ reduction that merits further investigation.     

Effect of direct current electric field on atmospheric corrosion behavior of copper under thin electrolyte layer

A thin layer electrochemical cell was successfully developed to study the atmospheric corrosion behavior of copper film in printed circuit board (PCB-Cu) under thin electrolyte layer (TEL) and direct current electric field (DCEF) by electrochemical impedance and electrochemical noise analysis. The electrochemical measurements and SEM morphologies after corrosion test indicate that DCEF decreases the corrosion of PCB-Cu under TEL. The corrosion rate and probability of pitting corrosion of PCB-Cu under DCEF decrease due to the electric migration of aggressive Cl⁻ ion out of working electrode surface.     

Corrosion of aluminium in copper-aluminium couples under a marine environment: Influence of polyaniline deposited onto copper

In this study, we examined how aluminium corrosion in Al-Cu/PANI galvanic couples in a marine environment is influenced by deposition of polyaniline (PANI) on copper. Polarization curves and immersion assays in 0.1 M NaCl were performed. The morphologies of etched Al and corrosion products were observed by SEM, and the Al ions in solution were quantified by atomic absorption spectroscopy. A reduction in aluminium damage due to galvanic corrosion was observed as a result of decreased effective area for the oxygen reduction reaction on Cu/PANI electrode. Furthermore, an electrochemical reduction of PANI from leucoemeraldine to emeraldine base is proposed.     

A field study on the first flush effect of copper roof runoff

The runoff of four copper roof surfaces with different aspects were monitored in a field study in order to identify the existence of the first flush effect and to determine the influences. It was found that almost 40% of all sampled precipitation events exhibited a moderate first flush effect regarding the distribution of copper mass in the roof runoff. There was a significant impact of the roof aspect on the presence and on the magnitude of the first flush. No correlation was found between the first flush effect and weather parameters, such as rain height, rain intensity, and antecedent dry weather period.     

Influence of silicate ions on the formation of goethite from green rust in aqueous solution

We investigated the influence of silicate ions on the formation of goethite converted from hydroxysulphate green rust, which was synthesized by neutralizing mixted solution of Fe₂(SO₄)₃ and FeSO₄ with NaOH solution, by O₂ in an aqueous solution. The pH and oxidation-reduction potential of the suspension and the Fe and Si concentrations in supernatant solutions were analyzed. X-ray diffraction results for the solid particles formed during the conversion were consistent with the results of the solution analyses. The results indicated that silicate ions suppressed the conversion from green rust to α-FeOOH and distorted the linkages of FeO₆ octahedral units in the α-FeOOH structure.     

Ex-situ and in-situ X-ray diffractions of corrosion products freshly formed on the surface of an iron-silicon alloy

Ex-situ X-ray diffraction measurements of a small amount of samples extracted from wet corrosion products freshly formed on a pure iron and iron-2 mass% silicon surfaces have been conducted using synchrotron radiation for clarifying the formation process of corrosion products. The results showed that γ-FeOOH was formed on the outer side of wet corrosion products formed on the surface of the pure iron by sodium chloride solution, while γ-FeOOH, α-FeOOH, Fe₃O₄, and green rusts were formed on the inner side. On the other hand, in comparison to the case of the pure iron, a significant formation of β-FeOOH was observed in the iron-silicon alloy. Influences of silicon alloying on corrosion products formed by aqueous solution containing sulfate ions were also observed. Furthermore, in-situ diffraction measurements by a conventional X-ray source were conducted for analyzing corrosion products formed on the pure iron and iron-silicon alloy surfaces by cyclic exposure to wet and dry atmospheres. The results obtained by the in-situ diffraction and ex-situ diffraction measurements on the corrosion products were consistent.     

Outdoor-indoor corrosion of metals in tropical coastal atmospheres

Results of indoor and outdoor atmospheric corrosion tests conducted during a long period of time at Cuba and Campeche (Mexico) indicated very high corrosion rates at both sites which have humid-tropical marine climate. We found that the outdoor corrosivity ranges from C3 to >C5 according to ISO 9223 nevertheless metals exposed to sheltered conditions presented higher corrosion rates compared to outdoors, whereas in closed (indoor) environments the corrosion rate significantly decreased. It is recommended to define an additional level of corrosivity for tropical coastal atmospheres in outdoor and sheltered conditions as corrosion depends on the geographical position and exposure conditions.     

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 FeZn₁₃, FeZn₇ and Fe₃Zn₁₀ 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 Zn²⁺ 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.     

Differences between corrosion products formed on copper exposed in Tokyo in summer and winter

We analyzed the copper corrosion products that formed during a month in summer and a month in winter at three sites in Tokyo using several analytical techniques. The X-ray diffraction patterns revealed that cuprite Cu₂O and posnjakite Cu₄SO₄(OH)₆·H₂O formed on copper exposed in summer. By contrast, only cuprite was found in winter exposed copper. The X-ray fluorescence results indicated that the amounts of sulfur and chlorine on the copper plates exposed in summer were much greater than those in winter. This could be explained by the change in particulate sulfate and sea salt concentrations. Depth profiling analysis by Auger electron spectroscopy revealed that the oxide layer formed in summer was thicker than that in winter. This difference in oxide layer thickness could have been due to the differences in temperature, relative humidity, and the amount of sulfur and chlorine on the copper plate.     

Corrosion behaviour of copper under chloride-containing thin electrolyte layer

The corrosion behaviour of copper under chloride-containing thin electrolyte layers (TEL) was investigated using electrochemical impedance spectroscopy (EIS), cathodic polarization, linear polarization, SEM/EDS and XRD. The results indicate that the copper corrosion rate increases as TEL thickness decreases during the initial stages. After 192 h of immersion, the corrosion rate of copper under TEL in this order: 300 > 402 > 199 > bulk solution > 101 μm. The corrosion behaviour is uniform under TEL, and pitting is the primary corrosion type in the bulk solution. A corrosion model of the behaviour of copper under chloride-containing TEL is proposed.     

Influence of foreign ions on the atomic scale structure of ferric oxyhydroxides

Quantitative X-ray structural analysis coupled with reverse Monte-Carlo (RMC) simulation and infrared spectroscopy have been used for characterizing the atomic scale structure in α-FeOOH particles with and without anions consisting mainly of carbonate. The results showed that these α-FeOOH particles fundamentally have the α-FeOOH structure, but the linkages of FeO₆ octahedral structural units in the α-FeOOH particles with the anions are significantly distorted, and the distortion appears to be related with the anions in the α-FeOOH particles. As α-FeOOH are formed through olation and oxolation of iron complexes described by FeO₆ structural units with hydrogen in aqueous solution, the atomic scale structure in the α-FeOOH particles may be influenced by anions.     

The atmospheric corrosion of quaternary bronzes: The action of stagnant rain water

The corrosion behaviour of a quaternary bronze UNS C83600 exposed to stagnant acid rain was examined through wet-dry tests. During the tests, parallel monitoring was performed to determine the evolution of both the bronze surface and the weathering solution composition. The results show that the kinetics of bronze oxidation is governed by diffusion through a two-layer patina: an inner Sn-rich layer and an external Cu and Pb-rich layer. The corrosion rate of the alloy decreases with time, but the dissolution of individual metals (Cu, Zn and Pb) in the environment increases with different trends, showing progressive patina destabilisation.     

Difference in precipitation rates of air-borne salts collected by the dry gauze method and the Doken tank method

This study compares the precipitation rates of air-borne salts analyzed by the dry gauze method (JIS Z2382) and the Doken (Public Works Research Institute) tank method. Because of the difference of calculation method, direction of prevailing wind causes the difference of salt precipitation rates by these methods. In addition, the Doken tank method has lower capture ability for air-born salt than the dry gauze method under the condition of low supply of air-born salt. While, air-born salt with wet deposition potentially increases salt precipitation of the Doken tank method. As a result, these methods yield different salt precipitation rates.