Investigation of Mg/Al alloy sacrificial anode corrosion with Scanning Electrochemical Microscopy

Corrosion of Mg/Al alloy was investigated with the scanning electrochemical microscope (SECM) using a Mg2+ ion selective microelectrode (ISME) as measuring tip. Mg/Al alloys have practical application as sacrificial anodes to prevent the corrosion of various metals susceptible to corrosion. A typical application of such sacrificial anodes is in water boilers. A model (Mg/Al)/Fe target was fabricated using boiler sacrificial anode and high purity iron wires. Corrosion current was measured between the electrically connected galvanic pair, and Mg2+ ion flow rate was calculated with Faraday’s law of electrolysis. However, Mg2+ flow rate could not be calculated with this method while the twometals were left electrically-disconnected. For this reason, fixed height lateral scans and retreating scans were performed above the Mg2+ sample with Mg2+ ion-selective electrodes employed as SECM tips. Mg2+ flow rate was estimated using the concentration profiles obtained with SECM. Relatively high-speed scans were possible with robust, solid contact Mg2+ micropipette electrodes, owing to their low resistance compared to conventional micropipettes of the same size

Fundamentos ético-político-econômicos e preservação do meio ambiente: um estudo de caso em três ladeiras, Igarassu – PE

A principal característica de uma sociedade baseada no lucro e crescimento ilimitado é o poder-dominação. Este ganhou corpo histórico-social através da tecnologia, sendo esta a forma primordial de relacionamento com a natureza. Esta atitude rompe com a solidariedade básica da interdependência e coloca a espécie humana numa posição de soberania com quem dispõe dos recursos que estão a sua volta. Este trabalho busca, portanto, provocar a reflexão quanto aos fundamentos ético-político-econômicos em detrimento à preservação efetiva da natureza e, através do estudo de caso em Três Ladeiras, Igarassu - PE, analisar os fundamentos discutidos. Na revisão bibliográfica, autores como Luiz Marques, Leonardo Boff e Gilberto Freyre foram priorizados devido suas influências em reflexões éticas quanto ao assunto proposto. Também foram utilizados trabalhos publicados em revistas. Tornou-se evidente a contradição ética estabelecida entre a origem e manutenção do pensamento humano, baseado no crescimento econômico, e sua relação com os povos e o meio ambiente. Conclui-se, portanto, que uma sociedade, fundada no crescimento dependente de recursos finitos, logo, está fadada ao fracasso, pois, além de explorar seu povo, esgota os recursos naturais, ferindo os direitos básicos e a soberania dos seres humanos e da vida em geral

Kinetics of copper passivation and pitting corrosion in Na2SO4 containing dilute NaOH aqueous solution

The electrochemical behaviour of Cu in alkaline solutions containing Na2SO4 was studied using potentiodynamic and potentiostatic techniques complemented by scanning electron microscopy. The presence of Na2SO4 enhances Cu electrodissolution through the passive layer and decreases the breakdown potential. There is a critical OH-/sulphate concentration ratio for the onset of localized corrosion. The competitive interaction between OH- and sulphate ions at the passive layer can explain the experimental data. Pit initiation fits the point defect model for passivity breakdown. Pit growth involves a number of current contributions which can be distinguished through the analysis of current transients at constant potential by using nucleation and growth models.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Kinetics of copper passivation and pitting corrosion in Na₂SO₄ containing dilute NaOH aqueous solution

The electrochemical behaviour of Cu in alkaline solutions containing Na2SO4 was studied using potentiodynamic and potentiostatic techniques complemented by scanning electron microscopy. The presence of Na2SO4 enhances Cu electrodissolution through the passive layer and decreases the breakdown potential. There is a critical OH-/sulphate concentration ratio for the onset of localized corrosion. The competitive interaction between OH- and sulphate ions at the passive layer can explain the experimental data. Pit initiation fits the point defect model for passivity breakdown. Pit growth involves a number of current contributions which can be distinguished through the analysis of current transients at constant potential by using nucleation and growth models.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Electrochemical behaviour of copper in aqueous moderate alkaline media, containing sodium carbonate and bicarbonate, and sodium perchlorate

The voltammetric polarization of Cu specimens in Na2CO3, NaHCO3 and NaClO4 solutions (8-12pH range) has been investigated. Voltammetry data were complemented with SEM and electron microprobe analysis. Results are found to be in agreement with the passivation model developed for Cu in plain NaOH solutions. For the latter the process can be described in terms of two steps, namely, at low potentials the initial formation of a Cu2O thin layer followed by the growth of a massive Cu2O layer, and at higher potentials the appearance of a CuO-Cu(OH)2 layer. These processes are accompanied by the formation of soluble Cu species. Beyond a certain potential which increases with the solution pH, copper pitting takes place. This model can be extended to Cu in carbonate/bicarbonate containing solutions by considering that Cu carbonates precipitate as long as soluble ionic Cu species are produced, without interfering appreciably with the formation of Cu oxides. The appearance of copper carbonate species is enhanced when pitting corrosion sets in. The precipitation of Cu carbonates occurs principally around pits. Cu pitting, although it is observed for all solutions, becomes more noticeable at the lowest pH values. At a constant pH, the density of pits increases in the order NaClO4 > NaHCO3 > Na2CO3. The influence of the electrolyte composition on Cu pitting is closely related to the blockage capability for pit nucleation and growth of the corresponding copper salts. Passivation in the Cu2O-Cu(OH)2 region hinders pitting corrosion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Electrochemical behaviour of copper in aqueous moderate alkaline media, containing sodium carbonate and bicarbonate, and sodium perchlorate

The voltammetric polarization of Cu specimens in Na2CO3, NaHCO3 and NaClO4 solutions (8-12pH range) has been investigated. Voltammetry data were complemented with SEM and electron microprobe analysis. Results are found to be in agreement with the passivation model developed for Cu in plain NaOH solutions. For the latter the process can be described in terms of two steps, namely, at low potentials the initial formation of a Cu2O thin layer followed by the growth of a massive Cu2O layer, and at higher potentials the appearance of a CuO-Cu(OH)2 layer. These processes are accompanied by the formation of soluble Cu species. Beyond a certain potential which increases with the solution pH, copper pitting takes place. This model can be extended to Cu in carbonate/bicarbonate containing solutions by considering that Cu carbonates precipitate as long as soluble ionic Cu species are produced, without interfering appreciably with the formation of Cu oxides. The appearance of copper carbonate species is enhanced when pitting corrosion sets in. The precipitation of Cu carbonates occurs principally around pits. Cu pitting, although it is observed for all solutions, becomes more noticeable at the lowest pH values. At a constant pH, the density of pits increases in the order NaClO4 > NaHCO3 > Na2CO3. The influence of the electrolyte composition on Cu pitting is closely related to the blockage capability for pit nucleation and growth of the corresponding copper salts. Passivation in the Cu2O-Cu(OH)2 region hinders pitting corrosion.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

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

Shortcomings of international standard iso 9223 for the classification, determination, and estimation of atmosphere corrosivities in subtropical archipelagic conditions—The case of the Canary Islands (Spain)

grant ProID2017010042The classification, assessment, and estimation of the atmospheric corrosivity are fixed by the ISO 9223 standard. Its recent second edition introduced a new corrosivity category for extreme environments CX, and defined mathematical models that contain dose–response functions for normative corrosivity estimations. It is shown here that application of the ISO 9223 standard to archipelagic subtropical areas exhibits major shortcomings. Firstly, the corrosion rates of zinc and copper exceed the range employed to define the CX category. Secondly, normative corrosivity estimation would require the mathematical models to be redefined introducing the time of wetness and a new set of operation constants.publishersversionpublishe

Electrochemical characterization of ZrTi alloys for biomedical applications. Part 2. The effect of thermal oxidation

Oxidation in air of ZrTi alloys at 500 ºC for 2 h produces oxide-covered materials with a very high corrosion resistance in Ringer’s solution at 37 ºC. The oxide layers present a double-layer structure, comprised by a thin and very compact inner layer of ca. 5 nm thickness, and a less compact, more porous and thicker outer layer. The thickness of the outer layer greatly varies with the composition of the base ZrTi alloy, but has very little influence in the overall electrochemical behaviour of the material. The nature of the oxide layer is a mixture of ZrO2 and TiO2, and no evidence of higher oxidation states of the metal could be found using XRD data. Anodic dissolution through the passive layers formed on the oxidized alloys is greatly diminished compared to those measured from the untreated materials, allowing all the alloying ratios between Zr and Ti to be potentially considered for implant application. The combination of alloying with titanium and oxidation in air at 500 ºC resulted in the materials that do not exhibit the characteristic susceptibility of zirconium towards the initiation of localized corrosion processes in aqueous chloride-containing electrolytes even for anodic polarizations up to +1.00 VSCE, a value well above the highest polarization experienced in the human body. Though all the oxidized alloys exhibited remarkable corrosion resistances, the best behaviour was found for oxidized Zr45Ti

The influence of test-panel orientation and exposure angle on the corrosion rate of carbon steel. Mathematical modelling

The effects of both test‐panel orientation and exposure angle on the atmospheric corrosion rates of carbon steel probes exposed to a marine atmosphere were investigated. Test samples were exposed in a tree‐shape metallic frame with either three exposure angles of 30°, 45° and 60° and orientation north‐northeast (N‐NE), or eight different orientation angles around a circumference. It was found that the experimental corrosion rates of carbon steel decreased for the specimens exposed with greater exposure angles, whereas the highest corrosion rates were found for those oriented to N‐NE due to the influence of the prevailing winds. The obtained data obtained were fitted using the bi‐logarithmic law and its variations as to take in account the amounts of pollutants and the time of wetness (TOW) for each particular case with somewhat good agreement, although these models failed when all the effects were considered simultaneously. In this work, we propose a new mathematical model including qualitative variables to account for the effects of both exposure and orientation angles while producing the highest quality fits. The goodness of the fit was used to determine the performance of the mathematical models