Use of EIS for the evaluation of the protective properties of coatings for metallic cultural heritage: a review

The best way to reduce the degradation of metallic cultural heritage is through preventive conservation measures but, in many cases, it is not possible to obtain adequate environmental conditions, and it is necessary to apply coatings to the artefacts in order to protect them against corrosion. There is a continuous search in the metal conservation community for new and improved coatings that provide a better protection to the objects whilst respecting the special requirements of the conservation–restoration ethics. Whilst electrochemical techniques have a long tradition in conservation–restoration treatments for metallic cultural heritage, the evaluation of protective coatings using electrochemical impedance spectroscopy (EIS) has only been used very recently. EIS is a very well-established method to investigate metal coatings for general purposes and has many advantages that make it especially suitable for testing coatings for metallic works of art. This paper makes a review of the use of EIS for testing coatings for metallic cultural heritage from the first publications in the mid-1990s to the last papers. The experimental setup used, the types of coatings and metals investigated and the interpretation of the results are reviewed and compared with the use of EIS for testing general purpose anti-corrosive coatings.     

Time-temperature effects in polymer coatings for corrosion protection as analyzed by EIS

More information is contained in Electrochemical Impedance Spectroscopy (EIS) results at steady-state vs. Temperature data sets than just the low frequency limit/polymer coating film resistance data most often cited. We have analyzed various EIS-Temperature data sets for several coating films in immersion and present the results considering the coating film dielectric constant vs. frequency and temperature. Water up-take can be analyzed by these methods and can be used to estimate the role of this process in the failure of corrosion protective coatings. For coating films that have been subjected to cyclic exposure, analysis of the dielectric constant vs. frequency data resulting from EIS data on these films indicate that cyclic exposure contributes significantly to ‘physical aging’ of the coating polymer.     

Combinatorial materials research applied to the development of new surface coatings X: a high-throughput electrochemical impedance spectroscopy method for screening organic coatings for corrosion inhibition

The objective of the study was to develop a high-throughput electrochemical impedance spectroscopy (HT-EIS) method for rapid and quantitative evaluation of corrosion protective coatings. A 12-element, spatially addressable electrochemical platform was designed, fabricated, and validated. This platform was interfaced to a commercial EIS instrument through an automated electronic switching unit. The HT-EIS system enables four parallel EIS measurements to be run simultaneously, which significantly reduces characterization time compared to that of serial EIS measurements using a multiplexer. The performance of the HT-EIS system was validated using a series of model systems, including a Randles equivalent circuit, an electrochemical reaction (Ti/K4FeCN6, K3FeCN6), a highly uniform polymer film, and several polymer coatings. The results of the validation studies showed that the HT-EIS system enables a major reduction in characterization time and provides high quality data comparable to data obtained with conventional, single-cell EIS measurement systems.     

Analysis of large experimental datasets in electrochemical impedance spectroscopy

An approach for the analysis of large experimental datasets in electrochemical impedance spectroscopy (EIS) has been developed. The approach uses the idea of successive Bayesian estimation and splits the multidimensional EIS datasets into parts with reduced dimensionality. Afterwards, estimation of the parameters of the EIS-models is performed successively, from one part to another, using complex nonlinear least squares (CNLS) method. The results obtained on the previous step are used as a priori values (in the Bayesian form) for the analysis of the next part. To provide high stability of the sequential CNLS minimisation procedure, a new hybrid algorithm has been developed. This algorithm fits the datasets of reduced dimensionality to the selected EIS models, provides high stability of the fitting and allows semi-automatic data analysis on a reasonable timescale. The hybrid algorithm consists of two stages in which different zero-order optimisation strategies are used, reducing both the computational time and the probability to overlook the global optimum. The performance of the developed approach has been evaluated using (i) simulated large EIS dataset which represents a possible output of a scanning electrochemical impedance microscopy experiments, and (ii) experimental dataset, where EIS spectra were acquired as a function of the electrode potential and time. The developed data analysis strategy showed promise and can be further extended to other electroanalytical EIS applications which require multidimensional data analysis.     

On the application of electrochemical impedance spectroscopy to study the self-healing properties of protective coatings

Active corrosion protection based on self-healing of defects in coatings is a vital issue for development of new advanced corrosion protection systems. However, there is a significant lack of experimental protocols, which can be routinely used to reveal the self-healing ability and to study the active corrosion protection properties of organic and hybrid coatings.The present work demonstrates the possibility to use EIS (electrochemical impedance spectroscopy) for investigation of the self-healing properties of protective coatings applied on a metal surface. The model EIS experiments supported by SVET (scanning vibrating electrode technique) measurements show that an increase of low frequency impedance during immersion in the corrosive medium is related to the suppression of active corrosion processes and healing of the corroded areas. Thus, EIS can effectively be employed as a routine method to study the self-repair properties of different protective systems. The 2024 aluminium alloy coated with hybrid sol–gel film was used as a model system to study the healing of artificial defects by an organic inhibitor (8-hydroxyquinoline).     

Understanding Complex Electrochemical Impedance Spectroscopy in Corrosion Systems Using in‐situ Synchrotron Radiation Grazing Incidence X‐ray Diffraction

The difficulty in interpreting electrochemical impedance spectroscopy (EIS) data has limited the potential of the method despite its utility as an electrochemical method for studies of electrode reactions and interfacial structures. Taking the test case of the carbon dioxide corrosion of carbon steel, in‐situ synchrotron radiation grazing incidence X‐ray diffraction (SR‐GIXRD) has been demonstrated to be a powerful technique for validating and understanding the interfacial structures associated with complex EIS data. Carbon dioxide corrosion was found to occur in several steps, which may only be surmised by EIS, but the use of SR‐GIXRD in conjunction with EIS has enabled the establishment of a link between EIS time constants and structural changes associated with the evolution of corrosion products with time. By comparison to previous studies by the authors and others in this field, this communication provides the first direct experimental evidence linking SR‐GIXRD surface compositional data to otherwise indistinctive EIS time constants.     

Electrophoretic deposition of hydroxyapatite–CaSiO3–chitosan composite coatings

Electrophoretic deposition (EPD) method has been developed for the fabrication of hydroxyapatite (HA)–CaSiO₃ (CS)–chitosan composite coatings for biomedical applications. The use of chitosan enabled the co-deposition of HA and CS particles and offered the advantage of room temperature processing of composite materials. The coating composition was varied by the variation of HA and CS concentrations in the chitosan solutions. Cathodic deposits were obtained as HA–CS–chitosan monolayers, HA–chitosan/chitosan multilayers or functionally graded materials (FGM) containing HA–chitosan and CS–chitosan layers of different composition. The thickness of the individual layers was varied in the range of 0.1–20 μm. The deposition yield was studied at different experimental conditions and compared with the results of modeling. It was shown that the moving boundary model for the two component system can explain the non-linear increase in the deposition yield with increasing HA concentration in chitosan solutions. The obtained coatings were studied by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and scanning electron microscopy (SEM). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that these coatings provided corrosion protection of stainless steel substrates in Ringer's physiological solution. The deposition mechanism and kinetics of deposition have been discussed.     

Dielectric and optical studies near the chiral smectic C-smectic A transition of (S)-2-hydroxy-4-decyloxybenzylidene-4'-amino-2p'-methylbutylcinnamate

The complex dielectric permittivity of HDOBAMBC has been measured in the vicinity of the chiral smectic C-smectic A transition as a function of temperature and frequency. The Goldstone mode contribution has been clearly identified and its relaxation frequency has been determined over the whole S*_C range. High accuracy tilt angle measurements have also been performed by using a new method which allows its determination in a direct and virtually continuous way. These experimental results together with additional measurements of the polarization and helical pitch have been compared with those of DOBAMBC and analized in the framework of the generalized Landau theory. As for DOBAMBC a reentrant behaviour S*_C-S_C-S*_C has been observed under an electric field near the S*_C-S_A transition.     

Assessment of corrosion protection and performance of bio-based polyurethane acrylate incorporated with nano zinc oxide coating

In this study, a series of UV-curable anticorrosive PUA coatings embedded with varying concentrations of inorganic ZnO fillers have been successfully prepared from jatropha-based polyol. The electrochemical impedance spectroscopy (EIS) and Tafel polarisation analysis revealed that increasing fillers composition lead to the improvement of the anticorrosive property of the hybrid coatings. Meanwhile, the salt spray test results were found to correlate with the EIS of C_c (F cm⁻²) was 2.71 × 10⁻⁹, Bode plot - 10⁶ Ω cm² and Tafel polarisation results 7.56 × 10⁻⁶ MPY at 3 wt% of ZnO. Physical properties of 3 wt% loading of ZnO fillers in hardness test obtained 6H which was strongly attributed to the low interfacial interaction and poor dispersion of the fillers within the polymer matrix.     

Diffusion coefficients and complex equilibria in solution-IV Experimental determination and manipulation of diffusion data

An experimental method for effectively measuring the change of diffusion current of a metal ion in the presence of increasing concentration of a complexing ligand is described and applied to five metal-ligand systems. The method has been applied to cases of reversible and irreversible electrochemical behaviour and is shown to provide reliable formation-curve data. The systems selected have formation constants which range over some ten orders of magnitude and in most cases the values obtained agree satisfactorily with those reported in the literature. In one case equilibrium data have been calculated for the first time.     

A statistical degradation model for the service life prediction of aircraft coatings: With a comparison to an existing methodology

An advance on the model used by Guseva et al. [1] for estimating the service life of organic coatings under service conditions from accelerated test results has been developed. Instead of modelling just the times to failure, this new approach uses the complete degradation curve and allows for a more general specification of the failure time distribution. This modified model was then applied to the estimation of the service life (defined as gloss loss) for aircraft coatings and the results were compared to those obtained by Guseva et al. It was found that when this model was applied to the naturally weathered data, gloss loss (and thus failure times at a given level of gloss loss) followed a generalised gamma distribution, rather than the Weibull distribution identified by Guseva et al. Further, the new approach suggested a reduction in the warranty time of about one month. When the model was applied to the accelerated test data, it produced more accurate extrapolations of the median failure time associated with the naturally weathered data - (49.3 months compared to a measured 52 months obtained at the naturally weathered site). In fact, the extrapolated distribution obtained by this new approach was much closer to the distribution for the naturally weathered data than the extrapolated distribution obtained by Guseva et al.     

人工破损涂层的电化学阻抗谱研究

利用交流阻抗技术快速评价人工破损涂层的性能 ,并探讨颜料的防锈作用机理     

Curing of an epoxy resin modified with poly(methylmethacrylate) monitored by simultaneous dielectric/near infrared spectroscopies

Simultaneous dielectric and near infrared measurements have been performed in “real-time” to follow polymerisation reactions on blends of a diglycidyl ether of bisphenol-A epoxy resin with 4,4^′-diaminodiphenylmethane hardener and different amounts of poly(methylmethacrylate) as modifier. The effect of the modifier amount on the polymerisation reactions has been studied, as well as that of the curing temperature. Epoxy and amine conversions have been followed by near infrared spectroscopy (NIR), while changes in molecular mobility in the reaction mixture have been analysed by dielectric relaxation spectroscopy (DRS). Evolutions of ionic conductivity and α-relaxation have been analysed and vitrification times have been obtained. The relaxational behaviour has been analysed through curing in the frequency domain, being the change of the main relaxation indicative of the cure reaction advancement. DRS data are also presented as complex impedance Z(ω). Vitrification times, obtained by dielectrometry have been compared with those obtained by rheological measurements and gelation times obtained by NIR have been compared with those obtained by solvent extraction.     

Impedance Response of a Thin Film on an Electrode: Deciphering the Influence of the Double Layer Capacitance

The different contributions of the interfacial capacitance are identified in the case of passive materials or thin protective coatings deposited on the electrode surface. The method is based on a graphical analysis of the EIS results to determine both the passive-film capacitance in the high-frequency domain and the double-layer capacitance in the low-frequency domain. The proposed analysis is shown to be independent of the physicochemical origins of the frequency dispersion of the interfacial capacitances which results, from an analysis point of view of the experimental results, in the use of a constant-phase element However, for a correct evaluation of the thin-film properties such as its thickness, the high-frequency data must be corrected for the double-layer contribution. In particular, it is shown that if the double-layer capacitance gives a frequency-dispersed response, it is necessary to correct the high-frequency part for the double-layer constant-phase elements. This is first demonstrated on synthetic data and then used for the determination of the thickness of thin oxide film formed on Al in neutral pH solution.     

Corrosion protection of aluminium alloy AA2024 with cerium doped methacrylate-silica coatings

The aim of this work is the synthesis and characterization of hybrid coatings doped with cerium salts for corrosion protection of AA2024. The control of the inorganic and organic polymerization process allows the preparation of coatings with an open structure and a hydrophilic character. These facts facilitate the incorporation and mobility of cerium ions through the structure, enhancing its ability to promote a self-healing mechanism. The thermal treatment of the coatings has been limited to 120 °C to preserve the mechanical properties of the alloy. The electrochemical behaviour of the coatings has been evaluated in 0.3 wt% NaCl solution by means of EIS technique. Electrochemical measurements evidence good barrier properties at initial immersion time, and signals of corrosion inhibition from cerium ions at long immersion times could be assigned to the increasing of the impedance modulus at low frequencies and the presence of cerium oxide/hydroxide precipitates.     

WBE联合EIS技术研究缺陷涂层下金属腐蚀

用电化学阻抗谱(EIS)结合丝束电极(WBE)技术研究了缺陷涂层浸泡在3.5%(质量分数)NaCl溶液中的劣化过程.从浸泡开始到完好涂层鼓泡失效,缺陷涂层丝束电极阻抗响应一直是缺陷区电极腐蚀反应过程特征,而完好涂层的劣化过程和涂层下的腐蚀反应过程特征被"平均掉".根据电极表面的电流分布,结合阻抗谱技术实现了对表面任意局部阴极和阳极区阻抗测试.研究发现,浸泡开始时,缺陷涂层阴极电流和阳极电流均出现在缺陷区,随着腐蚀过程的发展,阳极电流仍然保持在缺陷区,但阴极电流逐渐向完好涂层下扩展.根据实验结果,对缺陷处和涂层下金属腐蚀反应发生发展的机理进行了深入讨论.     

Electrochemical corrosion resistance performance of sustainable resource-based nanoconducting polymer composites in alkaline medium

The corrosion resistance performance of poly (otoluidine) (POT)-dispersed castor oil-polyurethane, (COPU) nanocomposite coatings, POT/COPU, with three different compositions (i.e. 0.25, 0.5 and 1.0 wt%) in alkaline medium is studied. The coatings are applied on mild steel specimens by brushing. Corrosion resistance behaviour of these coatings is investigated using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS) and by weight loss. The morphological behaviour of corroded and uncorroded coated specimens is investigated by scanning electron microscopy (SEM). It is interesting to report that the presence of conducting polymer nanoparticles in POT/COPU coatings suppresses the saponification of COPU in an alkaline environment. These investigations show that the dispersion of POT in COPU remarkably improves the corrosion resistance performance of COPU in alkaline media. POT/COPU (1.0 wt%) coatings have potential as anticorrosive-coating materials in alkaline media at higher pH. These coatings have a higher resistance to alkaline medium in comparison to other compositions.     

Use of Concentration Pulse Chromatography for Determining Binary Isotherms: Comparison with Statically Determined Binary Isotherms

The characterization of adsorption properties of binary gas mixtures is an important factor in the design of cyclic periodic adsorption processes. Presently, there are a few methods for determining the binary adsorption behaviour. However, most of these methods are very time demanding (static approaches). One dynamic approach for determining the binary adsorption behaviour is by employing the concentration pulse method. Although this experimental method has been shown to reliably reproduce the data obtained with static approaches, the application has been limited to systems where the adsorption capacities are similar. In our previous work, a novel method (HT-CPM) was shown to be capable of handling systems where the adsorption capacity of the heavy component is much greater than the light component.In order to further validate the novel method, HT-CPM, previously published statically determined binary adsorption data have been used to supply the data required for the concentration pulse method (CPM) data reduction techniques. From this data, the HT-CPM was then applied and the resulting data compared. The two other CPM approaches were also applied and these results are shown.Four binary systems were chosen so that a range of heavy/light adsorption capacities was examined. The results show that the HT-CPM was able to produce results that were consistent with the static data taken from the literature. The other data reduction techniques used with the CPM could only produce meaningful data when the adsorption capacities of the heavy and light components were similar.     

Impedance simulation of a solid oxide fuel cell anode in time domain

The purpose of the current study is to simulate the behavior of a solid oxide fuel cell (SOFC) anode under sinusoidal excitation. The obtained harmonic response is used as a base for electrochemical impedance spectra simulation. The electrochemical impedance spectroscopy (EIS) is a powerful non-destructive tool for SOFC researches. In order to evaluate the EIS experimental results, efforts are devoted to develop EIS numerical simulation tools. In this study, a planar SOFC is modeled, and the steady state behavior and frequency response, as well as the electrochemical spectra of the anode, are obtained. The developed model couples the electrochemical kinetics with mass transport. The Butler–Volmer equation is used for the anode electrochemistry, and the species equations are used for gas transport in the anode channel. In order to solve the system of the nonlinear equations, an in-house code based on finite difference method is developed and utilized. A parametric study is also carried out, and the results are discussed. The simulation results are in good agreement with published data. Results show a capacitive semicircle in the Nyquist plot, which is identical to the gas diffusion impedance as reported in literatures.     

Inter-level differences in iron group atomic systems in the extended method of calculation

The extended method of calculation has been applied to calculate the inter-level differences of the shell of 3d-electrons in the iron group atomic system. The hydrogen-like radial orbitals have been used. The results are compared with those obtained by ordinary methods of calculation as well as with experimental data.