Early Debonding Detection of Rebar-Concrete Interface due to External Loading Utilizing AC Impedance Spectroscopy

A novel method for detecting early damage at the steel-concrete interface due to external loading based on AC impedance spectroscopy technology was proposed.Firstly,alkali pretreatment was introduced to ensure the accuracy and repeatability of the AC impedance test.Secondly,the AC impedance spectroscopy between the steel bar and concrete surface of different bonding positions was tested,and then the physical quantities reflecting the bonding damage condition were obtained by equivalent circuit fitting.Theoretical debonding position calculation and AC conductive structure analysis indicate that the change of interface resistance and interface capacitance can seize the development of bonding damage during the loading process.As the interface damage develops,obvious changes in interface resistance and interface capacitance are observed,and they cannot be recovered after unloading.

Degradation diagnosis of lithium-ion batteries using AC impedance technique in fixing the state of charge of an electrode

A sustainable society requires an increase in electrified vehicles(xEVs) with a low environmental impact. Among various types of xEVs, battery electric vehicles (BEVs) with lithium-ion batteries(LIBs) have received considerable research attention.

Hydration Process of Cement-Based Materials by AC Impedance Method

AC impedance is a new method to study the changes of pore structure and the hydration degree during the hydration and hardening process of cement paste by the change of the electrochemical parameters. Employing AC impedance method, we studied the hydration and hardening process of cement paste with fly ash and slag, and analyzed the influence of different hydration age, water-binder ratio and mineral admixture on the impedance parameters. Moreover, we compared the results with those by the conventional porosity testing method and X-ray diffraction method. The results showed that AC impedance could be taken as a new technology in cement and concrete research.

AC IMPEDANCE OF PHENYL ISO-THIOCYANATE ADSORBED ON PT ELECTRODE

The paper presents ac impedance behaviours of phenyl iso-thiocyanate adsorbed on Pt electrode.Nyquist plots are analysed and simulated,and parameters of relative equivalent circuits are obtained.

AC IMPEDANCE STUDY OF HYDROGEN STORAGE ELECTRODES

The impedance diagram of hdrogen storage electrodes(AH electrodes )displayed twosemicircles.Thelow frequency one is affected by cycle number and composition of MH electrodes.

Structures,dielectric properties and AC impedance characteristics of BiFeO_(3)–BaTiO_(3)high-temperature lead-free piezoceramics synthesized by the hydrothermal method

Among the lead-free piezoceramics,(1-x)BiFeO_(3)-xBaTiO_(3)(BF-BT)is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature(TC>400℃)and good electromechanical properties.In this work,the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO_(3)and BaTiO_(3),and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions.The influence of the hydrothermal reaction times(12–24 h)of BiFeO_(3)on the structures and electric properties of the sintered ceramics was instigated.First,all the samples synthesized with the tetragonal BaTiO_(3)and BiFeO_(3)powders were identified with relatively stable dielectric properties.As the hydrothermal reaction time to synthesize BiFeO_(3)increased,the dielectric properties as well as the temperature stability of the 0.7BiFeO_(3)–0.3BaTiO_(3)ceramics also improved.At the condition of a hydrothermal reaction time of 24 h,the sample obtained possesses both the lowest temperature coefficient of dielectric constant(Tkε=1.53×10^(-2)=℃between RT and 300℃)and the highest Curie temperature(TC?471℃at 100 kHz).Moreover,at high temperatures,it exhibits a higher AC impedance than others.The calculating result based on the resistive constant-phase-element model(R-CPE)circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures.In summary,the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

Investigations on the Sensing Mechanism of Humidity Sensors Based on Poly(4-vinylpyridine)/carbon Black Composite by AC Impedance Spectra

1 Results Investigations on the sensing mechanism is important for understanding the electrical responses of humidity sensors to humidity change,and could provide guidelines for the design and synthesis of humidity sensitive materials with desirable properties.In this work,the sensing mechanism of humidity sensors based on quaternized poly(4-vinylpyridine) (PVP)/carbon black (CB) composite[1] was studied by measuring their AC impedance spectra at various humidities at room temperature.Under low humidity...

Impedance Characteristics of MgO-ZrO_2 Ceramics Doped with CeO_2

The ultrafine CexMg0.06Zr1-xO1.94 （ x = 0 16% ） powders were synthesized by a chemical co-precipitated method. The pressed compacts were sintered in air at 1300, 1400, 1500, 1600℃ for 3 h, respectively. The phase of the ceramics was characterized by the X-ray diffraction （XRD） method. The conductivity of the ceramics was measured by the AC complex impedance technique at 700- 1200 ℃. The ratio of the cubic phase in the ceramics improves with increasing CeO2 content, leading to a enlargement of the oxygen ionic migration channel. The contact resistance between conductive phase particles decreases with increasing CeO2 content, leading to a lower migration hindrance of the oxygen ionic. Consequently, the ionic conductivity of the ceramics improves with increas- ing CeO2 content. Additionally, an analysis for this phenomenon was also presented.

Study of the electrochemical properties of a transition metallic ions modified electrode in acidic VOSO_4 solution

Graphite material was used as the electrode for an all-vanadium redox flow battery, and the electrode was modified by transition metallic ions to enhance its electrochemical behavior. An porous graphite composite electrode has high specific surface area and high current density. The electrode modified by transition metallic ions has improved catalysis behavior that can catalyze the V（Ⅱ）-V（Ⅴ） redox reaction showed by cyclic voltammograms. This article studied the impedance of the modified electrode by electrochemical impedance spectroscopy （EIS）, and approved that the electrode modified by Co^2＋ and Mn^2＋ has a lower charge transfer resistance than the non-modified electrode. The effect of average particle size distribution is at lower frequencies that the slope of Warburg impedance is reduced by large particle size distribution. The voltage efficiency of the Co^2＋ modified electrode test cell is 81.5%, which is higher than that of the non-modified electrode.

Passivation Mechanism of 316L Stainless Steel in Oxidizing Acid Solution

The compositions and the chemical valence states of elements of 316L stainless steel passive film formed in the oxidizing acid solution were studied by X-ray Photoelectron Spectroscopic (XPS) analysis. The electrochemical polarization curve was measured. The passivation process in the oxidizing acid solution was studied by AC impedance technology. The results indicated that the stable compounds layer was formed on the surface of the sample and the adsorption was the main step in the nitrite solution during passivation process. The catalysis passivation mechanism was put forward according to the experimental results. During passivation process, the water molecule was adsorbed on the surface of the sample at first in the oxidizing acid solution. The oxidizer in the solution played a role as catalyst. The oxide and hydroxide, which could be changed each other and finally formed stable passive film, were generated from adsorbing intermediate under the catalytic action. The mathematical models for predicting the steady polarization curve and the AC impedance spectra at certain conditions have been obtained. The passivation mechanism of 316L stainless steel in the oxidizing acid solution can be interpreted by the catalysis passivation mechanism.

Anodic Layer of Pb-Ca-Sn-Ce Alloy for Maintenance-Free Lead/Acid Batteries

The anodic films of novel Pb-Ca-Sn-Ce alloy, traditional Pb-Ca-Sn and Pb-Sb alloys formed in sulfuric solution at anodic +0.9 V potential corrosion for 6 h were investigated by means of XPS, XRD methods and AC impedance measurement. The results show that the growth of Pb(Ⅱ) oxide on the new Pb-Ca-Sn-Ce alloy surface is inhibited. The AC impedance measurement shows that resistance of the corrosion layer of novel Pb-Ca-Sn-Ce alloy decreases. It is found that the novel Pb-Ca-Sn-Ce alloy can encourage the development of PbO2 in the scale, and enhance the conductivity of the anodic scale. Hence the deep recycling properties of the battery can be expected better.

The Phenomenon of Mutual Media in Polypyrole with Electroactive Ions

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An Experimental Study on Constant Current Load Test of Reinforced Concrete based on 3D Paraffin Isolation

Aiming at the complex corrosion degradation factors of reinforced concrete and clearing the deterioration mechanism in the constant stress state,a new type of constant current accelerated corrosion method in the saline soil environment was developed.The three-dimensional paraffin isolation specimens and the three-dimensional penetration specimens were taken as the research objects,and the Cl−content and AC impedance Bode diagram were measured.The macro morphology and micro analysis were also used to evaluate the corrosion degradation laws of the two groups of specimens.A constant current three-factor system accelerated model was established for the current acceleration factor,chloride ion,and sulfate ion acceleration factor.The experimental results show that,in the constant stress test of the saline soil environmental conditions,the paraffin isolation layer can effectively isolate corrosive chloride ions,which is a brand-new research method of single factor variable control in the constant stress test.According to the basic corrosion data,the law of constant current acceleration test is summarized and divided into five corrosion degradation stages,and each stage has significant changes in the accelerated corrosion efficiency.The corrosion degradation of a constant stress test is the combined effect of constant current,positive and negative penetration of chloride ions and sulfate ions.

Effect of Cerium on Gas Evolution Behavior of Pb-Ca-Sn Alloy

The effect of Ce on the behavior of gas evolution on Pb-Ca-Sn alloy in 4.5 mol·L^-1 H2SO4 was investigated using cyclic voltammetry （CV）, cathodic polarization curves and AC impedance （EIS）. Cyclic voltammetry experiments show that the current of oxygen evolution on Pb-Ca-Sn-Ce electrode is lower than that of Pb-Ca-Sn electrode in the same anodic voltage. Moreover, the oxygen evolution potential on the former electrode is greater than that on the latter, and this means that Ce can increase the potential of oxygen evolution on Pb-Ca-Sn alloy. The AC impedance experiments show that Ce can also enhance the resistance of hydrogen evolution on Pb-Ca-Sn electrode, i.e., Ce can inhibit the hydrogen evolution on Pb-Ca-Sn electrode. The reason why Ce decreases the volume of hydrogen evolution on Pb-Ca-Sn alloy is that Ce increases the resistance of absorbing step of hydrogen evolution reaction. All the experimental results indicate that Pb-Ca-Sn-Ce alloy can rapidly decrease the oxygen and hydrogen evolution on Pb-Ca-Sn-Ce alloy. It is concluded that Pb-Ca-Sn-Ce alloy can promote the maintenance-free property of lead acid battery, and can serve as the candidate of the grid material for maintenance-free lead acid battery.

Synthesis and Electrical Conductivities of Sm_2O_3-CeO_2 Systems

Doped Ceria nano-powders were synthesized via a Pechini-type gel rout. The specific surface area of Ce_(0.8)Sm_(0.2)O_(1.9) powder measured by the multilayer BET method is 41 m2.g^(-1). The electrical conductivities of Sm_2O_(3)-CeO_2 systems were measured by the ac impedance technique in air at temperatures ranging from 513 to 900 ℃. Typical impedance spectra consist of two depressed semicircles at reduced measuring temperature and one depressed semicircle at elevated measuring temperature respectively, from which the grain interior and grain boundary conductivities were calculated. The relationship between the conductivities of Sm_2O_3 doped CeO_2 (SDC) electrolyte and measuring temperature obeys Arrhenius equation. The grain interior conductivity of SDC varies slightly with improving sintering temperature, while the total conductivity increases with enhancing sintering temperature. The effective index has a significant effect on the ionic conductivity of ceria doped based electrolyte. When the effective index improves, the ionic conductivity increases and the apparent conductance activation energy decreases.

Electrochemical Studies of Glutathione Monolayer Assembled on A Polycrystalline Gold Electrode

The glutathione (GSH) monolayer and complex monolayer of GSH-metallic ion on polycrystalline gold electrode were studied by using K3Fe(CN)6 as the redox probe. As for the GSH monolayer, it was found that the metallic ions could open the ion-gate in the monolayer dramatically in the order La3+> Pb2+>>Ba2+>Ca2+ whereas Zn2+ ion closed the ion-gate. The complexes of GSH-metallic ions were capable of self-assembling the different kind of monolayer. All the differences were related to the structural configuration of the anchored GSH molecule, which changed with different metallic ions or pH.

Synthesis and performance of carbon-modified LiFePO_4 using an in situ PVA pyrolysis procedure

LiFePOa/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 atmosphere with polyvinyl alcohol （PVA） as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special micro-morphology of the optimum sample was observed. The discharge capacity of the cell with the optimum cathode was 135 mAh.g^-1, close to the charge capacity of 153 mAh.g^-1 at 17 mA.g^-1. The influence of ambient temperature on the cell capacity was investigated. The temperature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC impedance spectra. The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the capacity of the optimum cathode.

Rare Earth Co Permeation of K_6HCoGeW_(11)O_(40) and Its Conductivity

Rare earth co permeation of K 6HCoGeW 11 O 40 was reported. The co permeation temperature was decided by TG DTA and the ICP results of permeated sample indicate that La and Ce have permeated into the body of this compound. The results of XPS imply that chemical bonds exist between La, Ce and other components of this sample. The XRD patterns show great difference between K 6HCoGeW 11 O 40 and permeated sample. Such result gives evidence that the structure of K 6HCoGeW 11 O 40 is destroyed and new compounds perhaps formed. Four probe method and AC impedance spectra were used to measure the conductivities of K 6HCoGeW 11 O 40 and permeated complex. The conductivity of complex, at room temperature, improves 2.95×10 3 times after being permeated. Analyses of AC impedance spectra of permeated compound at different temperatures show that current carrier has changed.

Ionic conduction in Ba_xCe_(0.8)Pr_(0.2)O_(3–α)

BaxCe0.8Pr0.2O3-α (x=0.98-1.03) ceramics were prepared by high temperature solid-state reaction. X-ray diffraction (XRD) patterns showed that the materials were perovskite-type orthorhombic single phase. By using gas concentration cell and AC impedance spectroscopy methods, the electrical conduction behavior of the materials was investigated in different gases at 500-900 °C. The influence of non-stoichiometry in the materials with x≠1 on conduction properties was studied and compared with that in the material with x=1. The results indicated that Ba1.03Ce0.8Pr0.2O3-α was a pure protonic conductor, and Ba0.98Ce0.8Pr0.2O3-α was a mixed conductor of protons and electrons in wet hydrogen at 500-900 °C. BaCe0.8Pr0.2O3-α was a pure protonic conductor in 500-600 °C, and a mixed conductor of protons and electrons above 600 °C in wet hydrogen. In 500-900 °C, they were all mixed conductors of oxide ions and electronic holes in dry air, and mixed conductors of protons, oxide ions and electronic holes in wet air. Both the protonic and oxide ionic conductivities increased with increasing barium content in the materials in wet hydrogen, dry air and wet air, respectively.