Insights into the Importance of Native Passivation Layer and Interface Reactivity of Metallic Lithium by Electrochemical Impedance Spectroscopy

Lithium-metal batteries offer substantial advantages over lithium-ion batteries in terms of gravimetric and volumetric energy densities. However, their widespread practical use is hindered by safety concerns, often attributed to the poor stability of the metallic lithium interface, where electrochemical impedance spectroscopy (EIS) can provide crucial information. The EIS spectra of metallic lithium electrodes proved to be more complex than expected, especially when studying thin lithium metal foils. Here, it is identified that charge-transfer impedance becomes one of the main components of the EIS spectra, the magnitude of which is found to be strongly dependent on the native passivation layer of metallic lithium and on the nature of electrolyte. “Asymmetricity” of the EIS spectra in symmetric cells when separated the working and counter electrode contributions to the total impedance using three-electrode cells is also identified.     

Improved electrochemical performance of nitrocarburised stainless steel by hydrogenated amorphous carbon thin films for bone tissue engineering

In this study, hydrogenated amorphous carbon thin films, structurally similar to diamond‐like carbon (DLC), were deposited on the surface of untreated and plasma nitrocarburised (Nitrocarburizing‐treated) stainless steel medical implants using a plasma‐enhanced chemical vapour deposition method. The deposited DLC thin films on the nitrocarburising‐treated implants (CN+DLC) exhibited an appropriate adhesion to the substrates. The results clearly indicated that the applied DLC thin films showed excellent pitting and corrosion resistance with no considerable damage on the surface in comparison with the other samples. The CN+DLC thin films could be considered as an efficient approach for improving the biocompatibility and chemical inertness of metallic implants.Inspec keywords: tissue engineering, bone, biomedical materials, electrochemistry, amorphous state, carbon, hydrogen, thin films, plasma CVD, adhesion, corrosion resistance, surface hardeningOther keywords: electrochemical performance, plasma nitrocarburised stainless steel medical implants, hydrogenated amorphous carbon thin films, bone tissue engineering, plasma‐enhanced chemical vapour deposition method, adhesion, corrosion resistance, biocompatibility, chemical inertness, metallic implants, C:H     

Microstructure and corrosion behavior of electrodeposited nickel prepared from a sulphamate bath

Electrodeposited nickel was prepared from a sulphamate bath at different current densities ranging from 0.01 A cm^− 2 to 0.1 A cm^− 2. Based on the analysis of the microstructure, the corrosion behavior of the electrodeposited nickel in 3.5%NaCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). All the electrodeposits display active-passive-transpassive behavior in potentiodynamic polarization process. The electrodeposits with the best corrosion resistance are obtained at 0.05 A cm^− 2. As for other electrodeposits, the corrosion potential and breakdown potential decrease with increasing current density used to prepare electrodeposits. However, the variation of both corrosion current density and passive current density is opposite to that of the corrosion potential. The changes in the charge-transfer resistance determined from the impedance spectra are consistent with the results determined from potentiodynamic measurements.     

Effect of Y on the bio-corrosion behavior of extruded Mg–Zn–Mn alloy in Hank's solution

The bio-corrosion properties of Mg–Zn–Mn alloys with and without Y in Hank's solution at 37 °C were investigated by using electrochemical test and electrochemical impedance spectra (EIS). The results of open circuit potential (OCP) and polarization tests indicated that Y could reduce the cathodic current density. A passivative stage appeared in the Tafel curve of the Y containing magnesium alloy, indicating that a passivative film was formed on the surface of the Y containing magnesium alloy. EIS results showed that the Y containing alloy had higher charge transfer resistance and film resistance, but lower double layer capacity than the alloy without the Y element. The surface reaction product identification by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed that the surface corrosion products were hydroxide and phosphate (Mg₃Ca₃(PO₄)₄) for Mg–Zn–Mn alloy and phosphate (MgNaPO₄) for the Y containing Mg–Zn–Mn alloys. The XPS results also showed that a Y₂O₃ protective film was formed on the surface of the Y containing magnesium alloy which contributed mainly to the low cathodic current density and the high resistance.     

Polylactic acid coating on a biodegradable magnesium alloy: An in vitro degradation study by electrochemical impedance spectroscopy

Polylactic acid (PLA) was coated on a biodegradable magnesium alloy, AZ91, using spin coating technique for temporary implant applications. The degradation behaviour of the coated alloy samples was evaluated using electrochemical impedance spectroscopy (EIS) method in simulated body fluid (SBF). EIS results suggested that the PLA coating enhanced the degradation resistance of the alloy significantly. Increase in the PLA coating thickness was found to increase the degradation resistance, but resulted in poor adhesion. Long-term EIS experiments of the PLA coated samples suggested that their degradation resistance gradually decreased with increase in SBF exposure time. However, the degradation resistance of the PLA coated samples was significantly higher than that of the bare metal even after a 48 h exposure to SBF.     

Zn-Ni-V热浸镀层组织及腐蚀电化学行为研究

在锌浴中添加少量的Ni和V,获得了Zn-0.05%Ni-0.05%V镀层.研究了Zn-0.05%Ni-0.05%V镀层组织和在5%NaCl溶液浸泡过程中的腐蚀行为.结果表明:在Zn-0.05%Ni镀浴中添加0.05%V可以有效地抑制Fe-Zn反应,控制ζ相层的超厚生长.与Zn-0.05%Ni镀层相比,浸泡20min后,...     

Study of the in vitro corrosion behavior and biocompatibility of Zr-2.5Nb and Zr-1.5Nb-1Ta (at%) crystalline alloys

The in vitro corrosion behavior and biocompatibility of two Zr alloys, Zr-2.5Nb, employed for the manufacture of CANDU reactor pressure tubes, and Zr-1.5Nb-1Ta (at%), for use as implant materials have been assessed and compared with those of Grade 2 Ti, which is known to be a highly compatible metallic biomaterial. The in vitro corrosion resistance was investigated by open circuit potential and electrochemical impedance spectroscopy (EIS) measurements, as a function of exposure time to an artificial physiological environment (Ringer’s solution). Open circuit potential values indicated that both the Zr alloys and Grade 2 Ti undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Zr-1.5Nb-1Ta alloy and that this oxide has better corrosion protection characteristics than the ones formed on Grade 2 Ti or on the Zr-2.5Nb alloy. EIS study showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The fit obtained suggests a single passive film presents on the metals surface, improving their resistance with exposure time, presenting the highest values to the Zr-1.5Nb-1Ta alloy. For the biocompatibility analysis human osteosarcoma cell line (Saos-2) and human primary bone marrow stromal cells (BMSC) were used. Biocompatibility tests showed that Saos-2 cells grow rapidly, independently of the surface, due to reduced dependency from matrix deposition and microenvironment recognition. BMSC instead display a reduced proliferation, possibly caused by a reduced crosstalk with the metal surface microenvironment. However, once the substrate has been colonized, BMSC seem to respond properly to osteoinduction stimuli, thus supporting a substantial equivalence in the biocompatibility among the Zr alloys and Grade 2 titanium. In summary, high in vitro corrosion resistance together with satisfactory biocompatibility make the Zr-2.5Nb and Zr-1.5Nb-1Ta crystalline alloys promising biomaterials for surgical implants.     

Electrolytic deposition and corrosion resistance of Zn-Ni coatings obtained from sulphate-chloride bath

Zn-Ni coatings were deposited under galvanostatic conditions on steel substrate (OH18N9). The influence of current density of deposition on the surface morphology, chemical and phase composition was investigated. The corrosion resistance of Zn-Ni coatings obtained at current density 10–25 mA cm⁻² are measured, and are compared with that of metallic cadmium coating. Structural investigations were performed by the X-ray diffraction (XRD) method. The surface morphology and chemical composition of deposited coatings were studied using a scanning electron microscope (JEOL JSM-6480) with EDS attachment. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the ground of these research, the possibility of deposition of Zn-Ni coatings contained 24–26% at. Ni was exhibited. It was stated, that surface morphology, chemical and phase composition of these coatings are practically independent on current density of deposition. On the basis of electrochemical investigations it was found that corrosion resistance of these Zn-Ni coatings is also independent of current density. These coatings are more corrosion resistant in 5% NaCl solution than metallic cadmium. It was suggested that the Zn-Ni coating may be used as a substitute for toxic cadmium.     

In vitro corrosion behaviour of Ti–Nb–Sn shape memory alloys in Ringer’s physiological solution

The nearly equiatomic Ni–Ti alloy (Nitinol) has been widely employed in the medical and dental fields owing to its shape memory or superelastic properties. The main concern about the use of this alloy derives form the fact that it contains a large amount of nickel (55% by mass), which is suspected responsible for allergic, toxic and carcinogenic reactions. In this work, the in vitro corrosion behavior of two Ti–Nb–Sn shape memory alloys, Ti–16Nb–5Sn and Ti–18Nb–4Sn (mass%) has been investigated and compared with that of Nitinol. The in vitro corrosion resistance was assessed in naturally aerated Ringer’s physiological solution at 37°C by corrosion potential and electrochemical impedance spectroscopy (EIS) measurements as a function of exposure time, and potentiodynamic polarization curves. Corrosion potential values indicated that both Ni–Ti and Ti–Nb–Sn alloys undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the aggressive environment. It also indicated that the tendency for the formation of a spontaneous oxide is greater for the Ti–18Nb–5Sn alloy. Significantly low anodic current density values were obtained from the polarization curves, indicating a typical passive behaviour for all investigated alloys, but Nitinol exhibited breakdown of passivity at potentials above approximately 450 mV(SCE), suggesting lower corrosion protection characteristics of its oxide film compared to the Ti–Nb–Sn alloys. EIS studies showed high impedance values for all samples, increasing with exposure time, indicating an improvement in corrosion resistance of the spontaneous oxide film. The obtained EIS spectra were analyzed using an equivalent electrical circuit representing a duplex structure oxide film, composed by an outer and porous layer (low resistance), and an inner barrier layer (high resistance) mainly responsible for the alloys corrosion resistance. The resistance of passive film present on the metals’ surface increases with exposure time displaying the highest values to Ti–18Nb–4Sn alloy. All these electrochemical results suggest that Ti–Nb–Sn alloys are promising materials for biomedical applications.     

Superior photocatalytic NOx removal of cementitious materials prepared with white cement over ordinary Portland cement and the underlying mechanisms

This study presents experimental results in an attempt to explain why photocatalytic cementitious materials prepared with white cement (WC) had superior photocatalytic NO_x removal performance than those prepared with ordinary Portland cement (OPC). The UV–Vis diffuse reflectance spectra (DRS) of dry WC and OPC demonstrated that OPC had a stronger light absorption ability. And electrochemical impedance spectroscopy (EIS) analysis revealed that OPC incurred higher charge transfer resistance on the inter-surface of OPC and TiO₂. Moreover, the OPC/P25 dry mixtures displayed a relatively lower photoluminescence (PL) intensity at 420 nm. The addition of iron oxide (Fe₂O₃) in WC caused a decrease in NO_x removal, a boost in light absorption, an increase in the resistance of charge transfer, and a reduction in PL intensity. Collectively, the relatively poor performance of OPC/P25 mixtures in photocatalytic NO_x removal is due to a combination of stronger light absorption and lower charge separation caused by OPC.     

Study of in vitro degradation of brushite cements scaffolds

An interest path to fabricate supports for tissue engineering is to foam calcium phosphate cement’s pastes leading to an increase on material’s total porosity and interconnectivity which facilitates cells’ adhesion, proliferation and differentiation. The aim of this work is to develop scaffolds of brushite cement and to evaluate its in vitro degradation rate. Macroporosity was obtained by foaming the liquid phase with different non-ionic surfactants (Tween 80 and Lutensol ON-110). The foam stability was achieved by adding chitosan. The scaffolds were immersed in Ringers^® solution during 7, 14, 21 and 28 days and samples’ microstructure, weight loss, mechanical resistance and apparent porosity were evaluated. Both scaffolds presented interconnected macropores with sizes ranging from 100 to 360 µm and total porosities higher than 60 %. These properties could facilitate cell infiltration, bone growth and vascularization. The scaffolds obtained in this work should be considered as promising materials for application in bone tissue engineering.     

Analysis of degradation process during the incorporation of ZrO2:SiO2 ceramic nanostructures into polyurethane coatings for the corrosion protection of carbon steel

Three different molar ratios of ZrO₂:SiO₂ mixed oxides (25:75, 50:50, 75:25) were produced by the sol–gel technique and sintered at different temperatures (400, 600, 800, and 1000 °C) in order to analyze differences in mechanical and electrochemical properties of a wide variety of organic–inorganic hybrid coatings on AISI 1018 commercial carbon steel. For this purpose, 2, 4, and 6 wt% of the obtained ZrO₂:SiO₂ nanoparticles were incorporated to the polymeric matrix under vigorous stirring and spread on metallic substrates to reach between 40 and 55 μm of dry film. Light microscopy, scanning electron microscopy, confocal laser scanning microscopy studies, atomic force microscopy, and nanoindentation tests were used to evaluate morphological, topographical, and mechanical properties; whereas atmospheric corrosion and electrochemical impedance spectroscopy (EIS) were performed using a 3 wt% NaCl medium in continuous immersion for 226 days. The crystallite size of the as-prepared ZrO₂:SiO₂ nanoparticles changed according to the sintering temperature from 4 to 9 nm. It was found that an adequate dispersion and homogeneity was achieved when 2 wt% of sintered ZrO₂:SiO₂ nanoparticles were mechanically mixed with polymer (MDI) to produce hybrid coatings on the metallic substrate. Free-bubble surface and hardness enhancement can be achieved by adding nanostructures assuming fact that the particles are capable of occupying the gas bubble sites. Atmospheric corrosion in the coatings without reinforced particles was more severe than that observed in hybrid coatings, and for these, corrosion was higher according to the increasing zirconia molar ratio. The EIS studies indicated that the synergetic effect between the organic–inorganic phases to seal the surface enhances the barrier properties on this metallic substrate.     

Microstructure,corrosion behavior and cytotoxicity of Zr–Nb alloys for biomedical application

In this work, the effects of Nb content on microstructure and corrosion behaviors of biomedical Zr–Nb alloys were systematically studied. The results of XRD analysis and optical microscopy indicated that the experimental Zr–Nb alloys had a duplex structure of α and β phases, and the content of β phase increased with the increase of Nb content. The electrochemical impedance spectroscopy (EIS) studies showed an improvement on the resistance of the spontaneous oxide film with increasing Nb content. The EIS data, fitted by R_s(Q_pR_p) model, suggested a single passive film formed on the experimental material surfaces. Polarization tests in Hank's solution revealed a nobler electrochemical behavior of the Zr–Nb alloys after alloying Nb to pure Zr. The corrosion resistance increased with increasing Nb content, as indicated by lower corrosion current densities and passive current densities and higher pitting potentials. The major components on the surfaces of the corroded Zr–Nb alloy samples detected by XPS were ZrO₂ and Nb₂O₅. The biocompatibility of Zr–Nb alloys was primarily evaluated by culturing L-929 cells in the extraction media of Zr–Nb alloy samples and excellent results were obtained. All of these above results suggested that the Zr–22Nb alloy, among the experimental alloys, showed a promising potential for biomedical applications.     

The pigment influence on the anticorrosive performance of some alkyd films

This paper presents the results regarding the pigments effect on the protective properties of alkyd films in 3% natrium chloride solution. The films were realized on carbon steel substrate from an alkyd resin using the pigments of metallic, mineral and organic type. Dry films thickness in 30–35 μm range was obtained. Electrochemical techniques (electrochemical impedance spectroscopy (EIS) and stepwise polarization) were used. The interpretation of the impedance spectra (Nyquist and Bode diagrams) with the immitance analysis Equivcrt. Programme established two electrical equivalent circuits (with two and four time constants) for the carbon steel/alkyd film systems in electrolyte solution, fitted to the experimental data. The electric capacitance and resistance of the alkyd films were monitored with the immersion time to establish the water and ions permeability of these paint films. The electrochemical parameters of alkyd coated carbon steel from the anodic potentiostatic polarisation curves were determined. The correlation of all experimental results established that the tested pigments except the green organic pigment increase the protective performances of alkyd coatings. Best protection of the carbon steel was found for the alkyd film with aluminum powder pigment.     

Quantification of fibroblast adhesion to biomaterials using a fluid mechanics approach

Adhesion of cells to the surface of a biomaterial is one of the major factors mediating its biocompatibility. Despite the importance of this parameter, reliable means for its quantification still need to be developed. In the research described here, the jet impingement method has been investigated as to its ability to resolve differences in fibroblast adhesion. A wide spectrum of materials has been studied. To visualize the cell layer on opaque surfaces, a fluorescent staining method has been developed. The measurements show statistically significant differences between material classes, with the highest degree of adhesion about twice that of the lowest degree of adhesion. The greatest adhesion was observed with metallic materials which exhibit a shear stress to erode cells from the material surface of about 5.65×10^-3 N cm^-2. The tensile stress of adhesion (about 2.15×10^-2 N cm^-2) was similar for most materials. The interpretation of the results of jet impingement testing and their relation to in vivo cell and soft tissue adherence to biomaterials merits further investigation.     

Influence of aging temperature on corrosion behavior of Al–Zn–Mg–Sc–Zr alloy

Al–Zn–Mg–Sc–Zr alloy sheets were prepared using water chilling copper mould ingot metallurgy processing which was protected by active flux. The effect of aging temperature on the corrosion characteristics of Al–Zn–Mg–Sc–Zr alloy was investigated by means of exfoliation corrosion testing, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) combined with transmission electron microscopy, scanning electron microscopy and optical microscopy observation. It is found that with increasing the aging temperature the susceptibility to exfoliation corrosion decreases. Electrochemical measurements reveal that at early stage of immersion in testing solution, EIS plots of the samples are composed of a capacitive arc and an inductive loop. Inductive loop disappears with the increasing of immersion time and two time constants in impedance diagrams appear. Moreover, the trends of corrosion resistance are further confirmed by polarization curve and EIS test. In addition, transmission electron microscopy observations show that the improved corrosion resistance from increasing aging temperature is duo to the coarsening of matrix and separated precipitates at the grain boundary, and the increased spacing of grain boundary precipitates.     

Engineered Functional Surfaces by Laser Microprocessing for Biomedical Applications

Metallic biomaterials are increasingly being used in various medical applications due to their high strength, fracture resistance, good electrical conductivity, and biocompatibility. However, their practical applications have been largely limited due to poor surface performance. Laser microprocessing is an advanced method of enhancing the surface-related properties of biomaterials. This work demonstrates the capability of laser microprocessing for biomedical metallic materials including magnesium and titanium alloys, with potential applications in cell adhesion and liquid biopsy. We investigate laser-material interaction, microstructural evolution, and surface performance, and analyze cell behavior and the surface-enhanced Raman scattering (SERS) effect. Furthermore, we explore a theoretical study on the laser microprocessing of metallic alloys that shows interesting results with potential applications. The results show that cells exhibit good adhesion behavior at the surface of the laser-treated surface, with a preferential direction based on the textured structure. A significant SERS enhancement of 6 × 10³ can be obtained at the laser-textured surface during Raman measurement.     

Electrochemical characterization of LaBaCuCoO5+δ–Sm0.2Ce0.8O1.9 composite cathode for intermediate-temperature solid oxide fuel cells

In order to improve the electrochemical performance of the LaBaCuCoO_5+δ (LBCC) electrode, LaBaCuCoO_5+δ–Ce_0.8Sm_0.2O_1.9 (LBCC–SDC) are prepared and characterized for potential application as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on an SDC electrolyte. Electrical conductivity, thermal expansion and electrochemical properties are investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. It is found that the thermal expansion coefficient (TEC) and electrical conductivity decrease with the increase of SDC content in LBCC–SDC composites. AC impedance spectra based on SDC electrolyte measured at intermediate temperatures show that the addition of SDC to LBCC improves the electrochemical performance of a LBCC cathode, and that a LBCC–SDC20 cathode exhibits superior electrochemical performance in the LBCC–SDCx composite cathodes. Moreover, even when the content of SDC is up to 40 wt%, the area specific resistance of the LBCC–SDC40 composite cathode on SDC electrolyte is lower than the corresponding interfacial resistance for pure LBCC at 650–800 °C. The power density of the Ni–SDC/SDC/LBCC–SDC20 cell is 615 mW cm^?2 at 800 °C. These results indicate that LBCC–SDCx is a potential cathode material for application in IT-SOFCs.     

Electrochemical properties of TiN coatings on 316L stainless steel separator for polymer electrolyte membrane fuel cell

TiN films for metallic bipolar plates were synthesized by closed-field unbalanced magnetron sputtering (CFUBM) and the properties were controlled by adjusting the N₂ partial pressure. The corrosion behaviors of TiN films were investigated by potentiodynamic tests and electrochemical impedance spectroscopy (EIS) measurements under the condition of an aerated 1 M H₂SO₄ + 2 ppm HF solution at 70 °C with a constant potential of 600 mV_SCE. The results revealed that the variation of N₂ pressure had an influence on the corrosion resistance of TiN coating. N₂ partial pressure of 0.4 mTorr showed good corrosion resistance with the lowest corrosion current density and the highest charge transfer resistance due to the low porosity.     

Determination of the chemical diffusion coefficient of lithium in Li3V2(PO4)3

The chemical diffusion of lithium ion in Li₃V₂(PO₄)₃ were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods. The CV results show that there exists a linear relationship between the peak current (i_p) and the square root of the scan rate (ν^1/2). The impedance spectrum exhibits a single semicircle and a straight line in a very low frequency region. A linear behavior was observed for every curve of the real resistance as a function of the inverse square root of the angular frequency in a very low frequency region. The obtained chemical diffusion coefficient from EIS measurements varies within 10^− 9 to 10^− 8 cm²·s^− 1, in good agreement with those from CV results.