Electrochemical Impedance Spectroscopy Behavior Research Articles

Investigating electrochemical corrosion at Mg alloy-steel joint interface using scanning electrochemical cell impedance microscopy (SECCIM)

Developing strategies to prevent corrosion at the interface of dissimilar metal alloys is challenging because of the presence of heterogenous distribution of galvanic couples and microstructural features that significantly change the corrosion rate. Devising strategies to mitigate this interfacial corrosion requires quantitative and correlative understanding of its surface electrochemical reaction. In this work, scanning electrochemical cell impedance microscopy (SECCIM) was employed to study location-specific corrosion in the interfacial region of dissimilar alloys, such as AZ31 (magnesium alloy) and DP590 (steel) welded using the Friction-stir Assisted Scribe Technique (FAST) processes. Herein, SECCM and SECCIM were used to perform correlative mapping of the local electrochemical impedance spectroscopic and potentiodynamic polarization to measure the effect of electronic and microstructural changes in the welded interfacial region on corrosion kinetics. Microstructural characterization including scanning electron microscopy and electron backscatter diffraction was performed to correlate changes in microstructural features and chemistry with the corresponding electronic properties that affect corrosion behavior. The variations in corrosion potential, corrosion current density, and electrochemical impedance spectroscopy behavior across the interface provide deeper insights on the interfacial region—which is chemically and microstructurally distinct from both bare AZ31 and DP590 that can help prevent corrosion in dissimilar metal structures.

Effects of potassium silicate on corrosion behavior of dacromet coating

Purpose Potassium silicate sealer was applied on solvent-cleaned, acid-pickled, dacromet-coated steel to improve its corrosion resistance. The purpose of this paper is to study the corrosion behavior of dacromet-coated steel. Design/methodology/approach Potassium silicate sealer was applied on solvent-cleaned, acid-pickled, dacromet-coated steel to improve its corrosion resistance. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and salt spray were carried out. SEM was used to study the morphological appearance of the surface. Findings The EIS behavior indicated that solvent-cleaned dacromet-coated steel sealed with potassium silicate showed that the corrosion current density was 2.664E − 5 A.cm2 which was reduced to 8.752E − 6 A.cm2 and the corrosion rate, which was 2.264E − 2 mm.year−1, was reduced to 7.438E − 3 mm.year−1 in NaCl 3.5 wt.per cent. EIS was used in NaCl 3.5 wt.%, and the Bode plot characteristics showed that the corrosion protection of solvent-cleaned, dacromet-coated steel was enhanced when sealed with potassium silicate. The EDS results of salt-sprayed, solvent-cleaned samples after 10 days indicated that the main corrosion products are composed of SiO2, ZnO and Al2O3. Research limitations/implications The detection of Li element in EDS was not possible because of the device limitation. Originality/value The current paper provides new information about the sealing properties of potassium silicate and its effects on the corrosion resistance of dacromet coating, which is widely used in many industries such as the automobile industry.

EIS Behavior of Experimental High-Strength Steel in Near-Neutral pH and Load Conditions

Two thermomechanical heat treatments were applied to a high-strength low carbon steel with an experimental chemical composition, and as a result two different microstructures were obtained. Steel A had a ferritic microstructure, and steel B had a bainitic-martensitic one. The corrosion behavior was reviewed at long times in samples without load by means of Electrochemical Impedance Spectroscopy (EIS) in a near-neutral pH (NNpH) environment. The results showed that the quantity and adherence of corrosion products on the sample surface at long times are different. Hence, the impedance was higher for steel B. Slow strain rate testing (SSRT) was applied to tempered samples of the two steels at 473 K, 673 K, and 873 K (200 °C, 400 °C, and 600 °C), and the corrosion behavior was acquired using EIS at the same time as the SSRT in NNpH conditions. This is a novel result because the tension samples were not electrically isolated from the rest of the load frame. The impedance for the ferritic steel was higher than the bainitic–martensitic one, while it slightly decreased for both steel over time. Tempering improved the corrosion resistance for steel A, while it was not modified for steel B. The corrosion behavior could be associated with the susceptibility of these steels to stress corrosion cracking. A transmission line model was proposed to show qualitatively the corrosion behavior of a crack in the steel, if there is a potential profile inside the crack. A hypothetical potential profile was acquired as well as different impedance behaviors based on electrochemical variables.

Electrochemical Impedance Spectroscopy Behaviour of NdFeB Coated Magnets in Saliva Solution for Orthodontic Applications

In this work the assessment of the corrosion performances in saliva solution of NdFeB magnets coated with silane layers was studied for its application in orthodontic brackets. The silane film, deposited by dip coating technique, has been prepared with varying dipping steps, with the purpose to identify the number of layers able to achieve an optimal protective action. Corrosion protection performance, during immersion in Fusayama synthetic saliva solution, was evaluated by means electrochemical impedance spectroscopy (EIS). The silane coatings evidenced good barrier properties resulting in an improvement of the anti-corrosion performances of the magnets. Better results were observed for samples with at least 15 layers of silane, that evidenced still acceptable protective action after three days of immersion in a Fusayama synthetic saliva solution.

Revisiting the electrochemical impedance spectroscopy of magnesium with online inductively coupled plasma atomic emission spectroscopy.

The electrochemical impedance of reactive metals such as magnesium is often complicated by an obvious inductive loop with decreasing frequency of the AC polarising signal. The characterisation and ensuing explanation of this phenomenon has been lacking in the literature to date, being either ignored or speculated. Herein, we couple electrochemical impedance spectroscopy (EIS) with online atomic emission spectroelectrochemistry (AESEC) to simultaneously measure Mg-ion concentration and electrochemical impedance spectra during Mg corrosion, in real time. It is revealed that Mg dissolution occurs via Mg(2+) , and that corrosion is activated, as measured by AC frequencies less than approximately 1 Hz approaching DC conditions. The result of this is a higher rate of Mg(2+) dissolution, as the voltage excitation becomes slow enough to enable all Mg(2+) -enabling processes to adjust in real time. The manifestation of this in EIS data is an inductive loop. The rationalisation of such EIS behaviour, as it relates to Mg, is revealed for the first time by using concurrent AESEC.

A high-throughput electrochemical impedance spectroscopy evaluation of bioresponsibility of the titanium microelectrode array integrated with hydroxyapatite and silver

This paper reports a transparent Ti microelectrode array (MEA) system for a high-throughput evaluation of bioresponsibility using electrochemical impedance spectroscopy (EIS). The MEA chip integrated with hydroxyapatite (HA) and Ag coatings was selectively prepared by electrochemical deposition based on a novel procedure of multichannel current control. The EIS measurement of living MG63 osteosarcoma cells in the integrated MEA chip was conducted, and the result was analyzed using an equivalent circuit corresponding to a titanium oxide film, protein adsorption layer, cell adhesion layer, and medium. It is shown that the bioresponsibility of Ti–Ag–HA on the MEA chip can be improved, compared with the Ti, Ti–HA, and Ti–Ag coatings. The system was further used for real-time EIS monitoring during continuous cell culture for a long period (12 days). The effect of the long-term cell proliferation on the EIS behavior was discussed. This integrated system is valuable to significantly simplify the operation procedures and quickly evaluate the bioresponsibility of biomaterials.

Structure and electrochemical behavior of ionic liquid analogue based on choline chloride and urea

In this paper the structure and electrochemical stability of ionic liquid analogue based on choline chloride and urea is reported. The microscopic structure of the ionic liquid analogue is preliminary investigated by Fourier transform infrared spectroscopy (FTIR). The cyclic voltammetry behavior of ionic liquid analogue is studied. The decomposition products of chlorine gas and triethylamine are observed. Possible mechanisms for the formation of these products are given. The effects of temperature and cycle index on electrochemical behavior are discussed. The electrochemical impedance spectroscopy behavior on pt electrode is investigated at temperature of 60°C, 80°C and 100°C ranging from 0.001 to 105Hz. The equivalent circuit diagram and the electrochemical element values are given.

Anodic oxide growth on Zr in neutral aqueous solution

Anodization and subsequent cathodic reactions on a thin-film sample of Zr were studied with in-situ neutron reflectometry (NR) and electrochemical impedance spectroscopy (EIS). The NR results during anodization showed the originally 485 A thick Zr film generally behaved similar to a bulk electrode in neutral solution. The anodization ratio measured at applied potentials increased in steps of 0.5 V was somewhat higher than the value determined by coulometry, while the Pilling Bedworth ratio is in good agreement with published data. Thickening of the oxide layer, accelerated immediately after each potential increase, gradually decreased over several hours, but remained nonzero even after ∼12 h. The thickened oxide eventually cracked when its thickness reached ∼120 A, causing loss of passivation. Surprisingly, neither the anodization ratio nor the Pilling Bedworth ratio showed any discontinuity at the time of oxide cracking, and the EIS behaviour remained qualitatively as before. This observation is taken as the evidence that the cracked and intact regions of the electrode behave more or less independently as parallel electrodes. When the potential was eventually switched to cathodic polarity, NR shows, as expected, that the effects of oxide cracking were irreversible. However, the electrode resistance recovered partially suggesting the cracks were rapidly plugged with newly formed oxide.

Surface Pretreatments of Aluminum Alloy AA2024-T3 and Formation of Chromate Conversion Coatings : II. Composition and Electrochemical Behavior of the Chromate Conversion Coating

Aluminum alloy AA2024-T3 samples, subjected to various pretreatments, were conversion coated using Alodine 1200S. The ratio of hexavalent chromium to total chromium in the chromate conversion coating (CCC) was determined by X-ray absorption near-edge spectroscopy. The hexavalent chromium content of the CCC formed on AA2024-T3 varied with the method of pretreatment. The coated surfaces were analyzed by X-ray photoelectron spectroscopy to determine the surface composition of the coatings. Cr(VI) forms the major constituent (46-74% of total chromium) on the surface. Protective passive films of aluminum oxide and aluminum phosphate inhibit the formation of CCCs. Corrosion behavior of the CCCs were studied using open-circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Conversion coated alloys exhibited up to 40-fold higher corrosion resistance when compared to bare pretreated alloys. EIS behavior was modeled using a seven-element equivalent circuit. EIS results indicated industrially used bromate pretreatment to be best suited for CCC formation. Coupling the AA2024-T3 alloy with platinum during bromate pretreatment resulted in lowering the amount of copper intermetallics on the surface. This led to an increase in the corrosion resistance of the subsequently formed CCC by over an order of magnitude as compared to CCCs formed following alternative pretreatments. Therefore, this simple modification of coupling this alloy with platinum is recommended. © 2004 The Electrochemical Society. All rights reserved.

Ion implantation reinforcement of the protective efficiency of nickel in artificial sea-water

Ni bulk specimens have been implanted with Cr, Cu and Ar ions (4×10 16 ions/cm 2, 60 keV) in order to distinguish between chemical and radiation damage effects on protection corrosion. The corrosion behaviour in artificial sea-water of ion-implanted and pure Ni has been studied at room temperature by electrochemical impedance spectroscopy (EIS) technique. EIS spectra of ion-implanted Ni exhibit one capacitance loop while in pure Ni two distinct loops are observed. Moreover an important increase in the polarisation resistance is noticed for all implanted ions. Theses changes in EIS behaviour with implantation is related to the increase of the superficial layer density resulting in a decrease of heterogeneity of the passive layer. Equivalent circuits are proposed to fit the impedance spectra and corresponding electrochemical parameters are deduced.

Influence of a chromium ion implantation on the passive behaviour of nickel in artificial sea-water: An EIS and XPS study

The passive behaviour in artificial sea-water of Cr-implanted ( 4×10 16 ions/cm 2 , 60 keV) and non-implanted Ni was studied at room temperature by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The transfer resistance obtained for the implanted specimen ( R t ∼5586 kΩ cm 2 ) is extremely enhanced compared to the corresponding value of the non-implanted Ni ( R t ∼94 kΩ cm 2 ) indicating a considerable increase in the protective efficiency of the implanted layer. The EIS spectra of ion-implanted Ni exhibit one capacitance loop while in the non-implanted Ni two distinct loops can be observed. These changes in EIS behaviour by the ion-implantation are related to the increase of the superficial layer density resulting in a more stable passive layer. Equivalent circuits were proposed to fit the impedance spectra and corresponding electrochemical parameters deduced. These findings were compared with the results obtained by analysis of the passive film formed on Ni, performed by XPS, and with previous investigations of similar alloys. It appears that the passive film formed on Ni consists of NiO and Ni(OH) 2 whereas the chromium implantation leads to the formation in the passive state of Cr oxides and hydroxides which are responsible of the large increase of the transfer resistance.