The Behaviour of Cobalt in Concentrated Nitric Acid Solutions

In our previous investigation it has been established that cobalt, unlike iron or nickel, does not passivate in concentrated or even fumic nitric acid. The dissolution of cobalt in this aggressive medium is, however, significantly reduced by the formation of a hydrated nitrate salt layer adhering tightly to the metal surface. On the basis of the open-circuit corrosion potential measurements of cobalt electrode, in a wide range of nitric acid concentrations, and polarization curves, obtained in 11 mol dm-3 nitric acid using a regulating device with negative output resistance, along with electrode impedance results, it was proved that the hydration number of nitrate salt plays the crucial role in the electrochemical behaviour of cobalt in concentrated nitric acid solutions. The importance of the free water released through a decrease in the hydration number was clearly observed

Self-healing processes in coil coated cladding studied by the scanning vibrating electrode

The ability of the zinc layer in coil-coated cladding to protect the underlying metal substrate exposed to the environment through a sub-centimetre circular defect was established by using the scanning vibrating electrode technique (SVET). The onset of electrochemical corrosion is observed through the development of local anodes and cathodes in the defective system, with the formation of soluble zinc species. The dissolution process is maintained until a sufficiently high concentration is attained by the metal ions, and their subsequent precipitation inside the holiday blocks the defect as to hinder further corrosion. A self healing effect was thus observed. The role of zinc salts was confirmed by SEM and EDX observation

Two Imidazole Based Corrosion Inhibitors for Protection of Bronze from Urban Atmospheres

Two different imidazole based molecules were investigated as corrosion inhibitors for Cu-6Sn bronze in a sulphate/carbonate solution at pH 3 and 5 which simulate a mild and strong polluted urban environment. The tested corrosion inhibitors were 4-methyl-1-phenylimidazole (PMI) and 4- methy1-1-p- tolylimidazole (TMI). The difference between structures is in the additional para positioned methyl, -CH3, group in the phenyl ring of the TMI molecule. Their protective effect was investigated by different electrochemical methods: polarization in wide and narrow potential range and electrochemical impedance spectroscopy. The investigations have shown that both molecules give good protection to the bronze at pH 3, but only TMI showed a good effect at pH 5. Indicating that the para positioned methyl group serves as a link between the inhibitor molecule and substrate bronze

Corrosion Protection of Synthetic Bronze Patina

Bronze artifacts are generally covered with green or blue coloured corrosion products called patina, which not only enhances the good appearance of the bronze, but also helps to protect it. Because of the increased air pollution and acid rain the large collection of statues and works of art made from bronze exposed in the urban environment could be damaged. The increase of air pollution damages also archaeological bronze objects exposed or stored in a museum. This is why it is necessary to find ways to improve the protection that the patina gives to bronze. In order to preserve metal works from the aggressive atmosphere, organic inhibitors are often employed. The inhibiting effects of two imidazole derivatives (4-methyl-1-phenylimidazole and 4-methyl-1-(p-tolyl)imidazole) on artificial patina were examined. The results of these investigations have shown that both inhibitors studied improve the protective properties of bronze patina in simulated urban acid rains

Effectiveness of pre-treatment method to hinder rebar corrosion in concrete

This paper aims to evaluate the ability of phosphate pretreatments applied on steel rebars to hinder the corrosion reinforcements using synthetic pore electrolyte and mortar contaminated by chloride ions. The electrochemical behaviour of the pretreated substrate was assessed by corrosion potential, polarisation resistance and electrochemical impedance spectroscopy measurements. The results have demonstrated that the treatment of the rebar by immersion in the Na3PO4 (0·5M) solution favours the formation of a passive layer on the steel rebar surface, which increases the resistance to corrosion initiation up to 0·3M Cl– instead of 0·1M Cl– without treatment. The pretreatment also provides enhancement of corrosion protection of the steel rebar in mortar. The evolution of the impedance spectra in function of chloride concentration is in a fairly good agreement with the results obtained from RP measurements

Pasivación de aceros inoxidables dúplex en disoluciones que simulan el hormigón contaminado con cloruros

Most studies published to date on the corrosion behaviour of stainless reinforcing steel are based on austenitic steel. The market presence of corrugated duplex steel is growing, however. The present study compared passivity in 2205 type duplex and 304 type austenitic stainless steel. Polarization tests in chloride-containing Ca(OH)2 solutions confirmed the exceptional performance of duplex steels. X-ray photoelectronic spectroscopy (XPS) showed that the passive layer generated on duplex stainless steel in media simulating concrete pore solutions had a higher Cr content than the layer formed on steel in contact with the air. The XPS results also revealed that in duplex steel the form adopted by the passive layer Fe oxides was Fe3O4 in the solutions simulating concrete, rather than Fe2O3, as in duplex steel exposed to air. Electrochemical impedance spectroscopy (EIS) can be used to monitor the transformations taking place in the passive layer and analyze the factors involved.La mayoría de los estudios publicados hasta el momento sobre el comportamiento frente a la corrosión de armaduras de acero inoxidable se basan en aceros austeníticos. Sin embargo, la presencia en el mercado de aceros corrugados dúplex es cada vez más importante. En este trabajo se analiza la pasividad de un acero inoxidable dúplex tipo 2205 en comparación con la de un inoxidable austenítico tipo 304. Los ensayos de polarización en disoluciones de Ca(OH)2 con cloruros confirman el excepcional comportamiento de los aceros dúplex. La espectroscopía fotoelectrónica de rayos X (XPS) informa de que la capa pasiva generada en aceros inoxidables dúplex en medios que simulan la disolución de los poros del hormigón posee mayor contenido en óxidos de Cr que la formada en aire. También se puede deducir de los resultados de XPS que los óxidos de Fe de la capa pasiva de los aceros dúplex se encuentran en forma de Fe3O4 en las disoluciones que simulan el hormigón en vez de en forma de Fe2O3, como ocurre en aceros dúplex expuestos al aire. La espectroscopía de impedancia electroquímica (EIE) permite realizar un seguimiento de las transformaciones que tienen lugar en la capa pasiva y analizar los factores que influyen en ellas

Modeling effects of tidal and wave mixing on circulation and thermohaline structures in the Bering Sea: Process studies

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95183/1/jgrc11280.pd

Microsonde de corrosion humide (conception, réalisation et application à la corrosion de carrosseries automobiles)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF