Titanium and its alloys have been widely used for clinical applications because of their biocompa... more Titanium and its alloys have been widely used for clinical applications because of their biocompatibility and exceptional chemical inertness, in addition to their outstanding osseointegration characteristics. They are well known to form a robust protective film on the surface that provides a high corrosion resistance with the surrounding environment. Although this passive state of titanium-based materials is often considered to be achieved very rapidly, even when damaged, and to be chemically stable in physiological environments, evidences of passivity breakdown and electron transfer reactions have been collected using high resolution microelectrochemical techniques. Thus, further optimizations are required for their forthcoming applications.
This contribution provides a brief review of the applications of the Scanning Electrochemical Mic... more This contribution provides a brief review of the applications of the Scanning Electrochemical Microscope (SECM) and the Scanning Vibrating Electrode Technique (SVET) in measuring, characterising and evaluating surface inhomogeneity and surface chemical activity in the case of heterogeneous materials exposed to aqueous environments. The SECM is a unique microelectrochemical technique that provides in situ topographic and electrochemical reactivity information about the surface evolution at the micrometer scale in aqueous solution, thus becoming a very powerful tool in elucidating the complex processes occurring in the early stages of surface films degradation and metal corrosion. On the other hand, the SVET uses a small vibrating probe allowing measurement of the local potential in solution taking advantage of a synchronous detection with a lock-in amplifier. In this way, ionic current related to degradation reactions on an investigated surface can be monitored in the electrolytic ph...
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
In this work, the applicability of localized electrochemical impedance spectroscopy (LEIS) to cha... more In this work, the applicability of localized electrochemical impedance spectroscopy (LEIS) to characterize metal-corrosion inhibitor systems has been investigated. Copper corrosion inhibition by benzotriazole (BTA) and 2-mercaptobenzimidazole (MBI) has been studied, and compared to the electrochemical behaviour of the non inhibited metal. A rather wide frequency range of the AC potential signal was employed, namely 50 mHz ≤ f ≤ 65 kHz. The measurements were conducted for different probe-substrate distances in order to explore the effect of the different component of the localized impedance. Nyquist diagrams exhibit inductive loops in the high frequency range, and capacitive semicircles at intermediate and low frequencies for all the systems investigated, though they were affected in a different extent by the variation of the probe-substrate distance depending on the surface condition of the metal samples, this effect being more notorious for distances smaller than the dimensions of the bi-electrode probe.
This paper reports the effect of treatment with 2-mercaptobenzothiazole (2MBT) (a corrosion inhib... more This paper reports the effect of treatment with 2-mercaptobenzothiazole (2MBT) (a corrosion inhibitor) on pH distribution over Cu samples monitored in situ using scanning electrochemical microscopy (SECM) in potentiometric mode. Line scans were conducted over two copper wires embedded in insulating resin, one of which had been pre-treated with 2MBT. It was found that the treated Cu sample had a less acidic character than the non-treated sample. Furthermore, the pH above the resin areas is considerably more acidic than that above either Cu wire. This feature is attributed to the consumption of OHions on the non-treated Cu wire during the formation of atacamite as a corrosion product, and the tautomeric equilibrium established by the detached 2-mercaptobenzothiazole molecules in the bulk electrolyte. These pH distributions are spatially resolved in the SECM mapping above both Cu wires.
Journal of Solid State Electrochemistry, Jan 31, 2014
The local distribution of anodic and cathodic sites in a corroding cut edge using the scanning el... more The local distribution of anodic and cathodic sites in a corroding cut edge using the scanning electrochemical microscope is presented. Platinum and antimony microdisks were used as tips for combined amperometric/potentiometric operation. Local changes in electrochemical activity, oxygen concentration and pH distribution associated to the onset of localized anodes and cathodes were imaged in situ, as well as their evolution with time. Local alkalization and oxygen consumption related to cathodic activity were detected above the zinc layer covered with the thinner polymeric coating, providing a direct evidence of a differential aeration process effectively operating in an asymmetrical cut edge, in addition to the galvanic coupling of aluzinc and steel. Anodic activity leading to local acidification occurred at the other aluzinc layer at all exposures.
The increasing demand for raising the reliability of electronic contacts has led to the developme... more The increasing demand for raising the reliability of electronic contacts has led to the development of methods that protect metal surfaces against atmospheric corrosion agents. This severe problem implies an important economic cost annually but small amounts of corrosion inhibitors can control, decrease or avoid reactions between a metal and its environment. In this regard, surfactant inhibitors have displayed many advantages such as low price, easy fabrication, low toxicity and high inhibition efficiency. For this reason, in this article, the spectroelectrochemical behavior of polycrystalline gold electrode modified by reverse micelles (water/polyethyleneglycol-dodecylether (BRIJ 30)/n-heptane) is investigated by atomic force microscopy (AFM), potentiodynamic methods and electrochemical impedance spectroscopy (EIS). Main results indicate a strong adsorption of a monolayer of micelles on the gold substrate in which electron tunneling conduction is still possible. Therefore, this met...
The effects of both test-panel orientation and exposure angle on the atmospheric corrosion rates ... more 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...
The classification, assessment, and estimation of the atmospheric corrosivity are fixed by the IS... more The 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.
PurposeImpedance data obtained by electrochemical impedance spectroscopy (EIS) are fitted to a re... more PurposeImpedance data obtained by electrochemical impedance spectroscopy (EIS) are fitted to a relevant electrical equivalent circuit to evaluate parameters directly related to the resistance and the durability of metal–coating systems. The purpose of this study is to present a novel and more efficient computational strategy for the modelling ofEISmeasurements using the Differential Evolution paradigm.Design/methodology/approachAn alternative method to non-linear regression algorithms for the analysis of measured data in terms of equivalent circuit parameters is provided by evolutionary algorithms, particularly the Differential Evolution (DE) algorithms (standardDEand a representative of the self-adaptiveDEparadigm were used).FindingsThe results obtained withDEalgorithms were compared with those yielding from commercial fitting software, achieving a more accurate solution, and a better parameter identification, in all the cases treated. Further, an enhanced fitting power for the mod...
The water supply on the island of Tenerife (Canary Islands, Spain) comes mainly from aquifers of ... more The water supply on the island of Tenerife (Canary Islands, Spain) comes mainly from aquifers of volcanic origin that are notable for the high content of fluorides that make it unviable for human consumption without prior conditioning treatment. The treatments that generate a high rejection of water are not viable, since water is a scarce natural resource of high value. An electrocoagulation process was investigated as a method to treat natural groundwater from volcanic soils containing a dangerously high fluoride content. The operating parameters of an electrocoagulation reactor model with parallel plate aluminum electrodes were optimized for batch and continuous flow operations. In the case of batch operation, it was found that acidification of the water improved fluoride elimination efficiency, with a maximum at pH 3. Yet, operation at the natural pH of the water achieved elimination efficiencies between 82 and 92% depending on the applied current density. An optimum current density of 5 mA/cm 2 was found in terms of the highest removal efficiency, and the kinetics of fluoride removal was adjusted to a pseudo-second-order kinetics. In the continuous-flow operation, with an optimal residence time of 10 min and a separation of 0.5 cm between the electrodes, it was observed that the current density that would be applied would depend on the initial concentration of fluoride in the raw water. Then, an initial fluoride concentration of 6.02 mg/L required a current density > 7.5 mA/cm 2 to comply with the legal guidelines in the product water, while for an initial concentration of 8.98 mg/L, the optimum current density was 10 mA/cm 2. Under these operating conditions, the operating costs will vary between 0.20 and 0.26 €/m 3 of treated water.
Fluoride remediation in underground waters of volcanic origin was performed at laboratory scale u... more Fluoride remediation in underground waters of volcanic origin was performed at laboratory scale using an electrocoagulation (EC) technique. The natural waters from certain volcanic springs on the island of Tenerife (Canary Islands, Spain) contain average fluoride concentrations in excess of 7 mg/L. Thus, it is necessary to treat the water for fluoride mitigation below the maximum acceptable concentration of 1.5 mg/L according to Spanish regulations for drinking water. The design and optimization of a sustainable process was accomplished using a progressive scale-up procedure involving three pilot reactors with different configurations and effective working volumes. A bipolar electrode cell design using aluminum electrodes was used in all cases. The good performance of the process was confirmed by reducing the fluoride concentration from 7.35 to 1.4 mg/L. The following optimized operating conditions were determined for a continuous flow cell system: current density, 10 mA/cm 2 ; residence time, 10 min; and, half-period of polarity reversal, 1 min. Furthermore, the kinetics of the remediation process can be fitted using the Variable Order Kinetic (VOK) model, with a power relationship between fluoride concentration and residence time in the EC reactor.
Titanium and its alloys have been widely used for clinical applications because of their biocompa... more Titanium and its alloys have been widely used for clinical applications because of their biocompatibility and exceptional chemical inertness, in addition to their outstanding osseointegration characteristics. They are well known to form a robust protective film on the surface that provides a high corrosion resistance with the surrounding environment. Although this passive state of titanium-based materials is often considered to be achieved very rapidly, even when damaged, and to be chemically stable in physiological environments, evidences of passivity breakdown and electron transfer reactions have been collected using high resolution microelectrochemical techniques. Thus, further optimizations are required for their forthcoming applications.
This contribution provides a brief review of the applications of the Scanning Electrochemical Mic... more This contribution provides a brief review of the applications of the Scanning Electrochemical Microscope (SECM) and the Scanning Vibrating Electrode Technique (SVET) in measuring, characterising and evaluating surface inhomogeneity and surface chemical activity in the case of heterogeneous materials exposed to aqueous environments. The SECM is a unique microelectrochemical technique that provides in situ topographic and electrochemical reactivity information about the surface evolution at the micrometer scale in aqueous solution, thus becoming a very powerful tool in elucidating the complex processes occurring in the early stages of surface films degradation and metal corrosion. On the other hand, the SVET uses a small vibrating probe allowing measurement of the local potential in solution taking advantage of a synchronous detection with a lock-in amplifier. In this way, ionic current related to degradation reactions on an investigated surface can be monitored in the electrolytic ph...
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
In this work, the applicability of localized electrochemical impedance spectroscopy (LEIS) to cha... more In this work, the applicability of localized electrochemical impedance spectroscopy (LEIS) to characterize metal-corrosion inhibitor systems has been investigated. Copper corrosion inhibition by benzotriazole (BTA) and 2-mercaptobenzimidazole (MBI) has been studied, and compared to the electrochemical behaviour of the non inhibited metal. A rather wide frequency range of the AC potential signal was employed, namely 50 mHz ≤ f ≤ 65 kHz. The measurements were conducted for different probe-substrate distances in order to explore the effect of the different component of the localized impedance. Nyquist diagrams exhibit inductive loops in the high frequency range, and capacitive semicircles at intermediate and low frequencies for all the systems investigated, though they were affected in a different extent by the variation of the probe-substrate distance depending on the surface condition of the metal samples, this effect being more notorious for distances smaller than the dimensions of the bi-electrode probe.
This paper reports the effect of treatment with 2-mercaptobenzothiazole (2MBT) (a corrosion inhib... more This paper reports the effect of treatment with 2-mercaptobenzothiazole (2MBT) (a corrosion inhibitor) on pH distribution over Cu samples monitored in situ using scanning electrochemical microscopy (SECM) in potentiometric mode. Line scans were conducted over two copper wires embedded in insulating resin, one of which had been pre-treated with 2MBT. It was found that the treated Cu sample had a less acidic character than the non-treated sample. Furthermore, the pH above the resin areas is considerably more acidic than that above either Cu wire. This feature is attributed to the consumption of OHions on the non-treated Cu wire during the formation of atacamite as a corrosion product, and the tautomeric equilibrium established by the detached 2-mercaptobenzothiazole molecules in the bulk electrolyte. These pH distributions are spatially resolved in the SECM mapping above both Cu wires.
Journal of Solid State Electrochemistry, Jan 31, 2014
The local distribution of anodic and cathodic sites in a corroding cut edge using the scanning el... more The local distribution of anodic and cathodic sites in a corroding cut edge using the scanning electrochemical microscope is presented. Platinum and antimony microdisks were used as tips for combined amperometric/potentiometric operation. Local changes in electrochemical activity, oxygen concentration and pH distribution associated to the onset of localized anodes and cathodes were imaged in situ, as well as their evolution with time. Local alkalization and oxygen consumption related to cathodic activity were detected above the zinc layer covered with the thinner polymeric coating, providing a direct evidence of a differential aeration process effectively operating in an asymmetrical cut edge, in addition to the galvanic coupling of aluzinc and steel. Anodic activity leading to local acidification occurred at the other aluzinc layer at all exposures.
The increasing demand for raising the reliability of electronic contacts has led to the developme... more The increasing demand for raising the reliability of electronic contacts has led to the development of methods that protect metal surfaces against atmospheric corrosion agents. This severe problem implies an important economic cost annually but small amounts of corrosion inhibitors can control, decrease or avoid reactions between a metal and its environment. In this regard, surfactant inhibitors have displayed many advantages such as low price, easy fabrication, low toxicity and high inhibition efficiency. For this reason, in this article, the spectroelectrochemical behavior of polycrystalline gold electrode modified by reverse micelles (water/polyethyleneglycol-dodecylether (BRIJ 30)/n-heptane) is investigated by atomic force microscopy (AFM), potentiodynamic methods and electrochemical impedance spectroscopy (EIS). Main results indicate a strong adsorption of a monolayer of micelles on the gold substrate in which electron tunneling conduction is still possible. Therefore, this met...
The effects of both test-panel orientation and exposure angle on the atmospheric corrosion rates ... more 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...
The classification, assessment, and estimation of the atmospheric corrosivity are fixed by the IS... more The 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.
PurposeImpedance data obtained by electrochemical impedance spectroscopy (EIS) are fitted to a re... more PurposeImpedance data obtained by electrochemical impedance spectroscopy (EIS) are fitted to a relevant electrical equivalent circuit to evaluate parameters directly related to the resistance and the durability of metal–coating systems. The purpose of this study is to present a novel and more efficient computational strategy for the modelling ofEISmeasurements using the Differential Evolution paradigm.Design/methodology/approachAn alternative method to non-linear regression algorithms for the analysis of measured data in terms of equivalent circuit parameters is provided by evolutionary algorithms, particularly the Differential Evolution (DE) algorithms (standardDEand a representative of the self-adaptiveDEparadigm were used).FindingsThe results obtained withDEalgorithms were compared with those yielding from commercial fitting software, achieving a more accurate solution, and a better parameter identification, in all the cases treated. Further, an enhanced fitting power for the mod...
The water supply on the island of Tenerife (Canary Islands, Spain) comes mainly from aquifers of ... more The water supply on the island of Tenerife (Canary Islands, Spain) comes mainly from aquifers of volcanic origin that are notable for the high content of fluorides that make it unviable for human consumption without prior conditioning treatment. The treatments that generate a high rejection of water are not viable, since water is a scarce natural resource of high value. An electrocoagulation process was investigated as a method to treat natural groundwater from volcanic soils containing a dangerously high fluoride content. The operating parameters of an electrocoagulation reactor model with parallel plate aluminum electrodes were optimized for batch and continuous flow operations. In the case of batch operation, it was found that acidification of the water improved fluoride elimination efficiency, with a maximum at pH 3. Yet, operation at the natural pH of the water achieved elimination efficiencies between 82 and 92% depending on the applied current density. An optimum current density of 5 mA/cm 2 was found in terms of the highest removal efficiency, and the kinetics of fluoride removal was adjusted to a pseudo-second-order kinetics. In the continuous-flow operation, with an optimal residence time of 10 min and a separation of 0.5 cm between the electrodes, it was observed that the current density that would be applied would depend on the initial concentration of fluoride in the raw water. Then, an initial fluoride concentration of 6.02 mg/L required a current density > 7.5 mA/cm 2 to comply with the legal guidelines in the product water, while for an initial concentration of 8.98 mg/L, the optimum current density was 10 mA/cm 2. Under these operating conditions, the operating costs will vary between 0.20 and 0.26 €/m 3 of treated water.
Fluoride remediation in underground waters of volcanic origin was performed at laboratory scale u... more Fluoride remediation in underground waters of volcanic origin was performed at laboratory scale using an electrocoagulation (EC) technique. The natural waters from certain volcanic springs on the island of Tenerife (Canary Islands, Spain) contain average fluoride concentrations in excess of 7 mg/L. Thus, it is necessary to treat the water for fluoride mitigation below the maximum acceptable concentration of 1.5 mg/L according to Spanish regulations for drinking water. The design and optimization of a sustainable process was accomplished using a progressive scale-up procedure involving three pilot reactors with different configurations and effective working volumes. A bipolar electrode cell design using aluminum electrodes was used in all cases. The good performance of the process was confirmed by reducing the fluoride concentration from 7.35 to 1.4 mg/L. The following optimized operating conditions were determined for a continuous flow cell system: current density, 10 mA/cm 2 ; residence time, 10 min; and, half-period of polarity reversal, 1 min. Furthermore, the kinetics of the remediation process can be fitted using the Variable Order Kinetic (VOK) model, with a power relationship between fluoride concentration and residence time in the EC reactor.
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