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.

Micro-Structure, Ac Conductivity and Spectroscopic Studies of Cupric Sulphate Doped PVA/PVP Polymer Composites

A series of polyvinyl alcohol/polyvinyl pyrrolidone polymer composite films doped with different amount of cupric sulphate (CuSO4) were prepared by means of solution casting technique. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Ultraviolet-Visible absorbance spectroscopy (UV-Vis) and Ac conductivity measurement studies. XRD patterns of these films recorded at room temperature show the increase in amorphousity of the matrix with the increase in the concentration of CuSO4 in polymer composites. Microstructural parameters were computed using an in-house program employing XRD data. Recorded FT-IR spectra give information about the stretching and bending of the characteristic absorption bands in these films. The variation in the transmittance has been studied with the help of recorded UV-Vis spectra and hence the optical band gap present in the samples is also calculated. The measured Ac conductivity shows how the conductivity varies in these films with the presence of different amount of CuSO4 in these films.

Characteristics of alternating current hopping conductivity in DNA sequences

This paper presents a model to describe alternating current （AC） conductivity of DNA sequences, in which DNA is considered as a one-dimensional （1D） disordered system, and electrons transport via hopping between localized states. It finds that AC conductivity in DNA sequences increases as the frequency of the external electric field rises, and it takes the form of σac（ω） - ω2 ln^2（1/ω）. Also AC conductivity of DNA sequences increases with the increase of temperature, this phenomenon presents characteristics of weak temperature-dependence. Meanwhile, the AC conductivity in an offdiagonally correlated case is much larger than that in the uncorrelated case of the Anderson limit in low temperatures, which indicates that the off-diagonal correlations in DNA sequences have a great effect on the AC conductivity, while at high temperature the off-diagonal correlations no longer play a vital role in electric transport. In addition, the proportion of nucleotide pairs p also plays an important role in AC electron transport of DNA sequences. For p 〈 0.5, the conductivity of DNA sequence decreases with the increase of p, while for p ≥ 0.5, the conductivity increases with the increase of p.

AC Conductivity of (As_2Te_3)_(100-x)Ge_x Bulk Glassy System

The ac conductivity of the bulk amorphous chalcogenide system (As2Te3)100-xGex (where x=0,5,10,15 and 25 at. pct) was investigated at variable frequencies ranging from 50 Hz to 100 kHz and at different temperatures ranging from 3O to 160℃. lt was found that at a fixed temperature, where n <1 and decreases with temperature. The complex impedence Z was measured over the same frequency and temperature ranges. All samples give a semicircle arc originating at the origin point. This indicates that each composition can be described only by one resistance R and one capacity C, both parallelly combined. The centre below the real axis indicates the relaxation behaviour of the system. The activation energies for conduction were calculated.

Using AC Conductivity Measurements to Study the Influence of Mechanical Stress on the Strength of Geomaterials

The Dielectric Spectroscopy technique is a tool that can be used to provide information regarding the physical and chemical properties of materials. In this work Dielectric Spectroscopy (DS) measurements were conducted on marble specimens that were previously subjected to uniaxial compressive stress up to fracture in order to investigate the influence of the mechanical stress on the dielectric properties of the specimens. Specifically, the ac conductivity (σac) was measured when an ac electric field in the frequency range 1 kHz - 1 MHz was applied upon dry and saturated specimens which were subjected successively to higher levels of mechanical stress. The experimental results indicate that there are systematic variations in the values of the ac conductivity after each stress application at a higher stress level. Such variations become more intense at higher stress values and can be used to indicate the upcoming fracture since significant increase of conductivity is recorded when microcracks formations appear and propagate in the sample bulk.

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.

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.

Electrical conductivity of MO(MO=FeO,NiO)-containing CaO-MgO-SiO_2-Al_2O_3 slag with low basicity

As a fundamental study on recovery of valuable metals from nonferrous metallurgical slags,electrical conductivity values of MO（MO=FeO,NiO）-containing CaO-MgO-SiO2-Al2O3 slag with a low basicity were measured at different temperatures using AC impedance spectroscopy.The result shows that the electrical conductivity increased from 1.4 S/m to 14.4 S/m with the increase of the temperature from 1 573 to 1 773 K and the content of MO which is less than 12% under the constant mass ratio of （CaO＋MgO） to （SiO2＋Al2O3） of 0.47.Moreover,the increase magnitude of the electrical conductivity was also promoted with the increase of the content of MO.The electrical conductivity of FeO-containing slags was close to that of NiO-containing slags when the content was less than 8%;however,it was obviously larger than that of NiO-containing slags when the content was 12%.The activation energy of the electrical conductivity decreased with the increase of MO content.

Features of the Conductivity of the Ag8Ge1-xMnxTe6 Solid Solutions

Samples of Ag8Ge1-xMnxTe6 solid solutions with different manganese content (x = 0, 0.05, 0.1, 0.2) were prepared by fusing and further pressing their powders under the pressure of 0.6 GPa. In addition of Mn atoms to the Ag8GeTe6 compound leads to compression of their lattice. All p-type samples acquire a high resistance below the transition at temperatures of 180 - 220 K. The electrical conductivity of all compositions in the range of 220 - 300 K increases due to hopping mechanism, and at temperatures T > 320 K, a semiconductor characteristic is observed. By studying impedance spectra of samples, it was established that at 80 K solid solutions behave like a homogeneous dielectric material. At high temperatures and frequencies of an external electric field, a significant role of grain boundaries in conductivity was revealed. The dielectric anomaly occurring at low frequencies is also associated with an effect that manifests itself in the grain boundary.

Influence of europium doping on conductivity of LiNiPO_4

Europium doped LiNiPO4 and undoped LiNiPO4 were prepared by Pechini method. Compound formation temperature was confirmed from thermogravimetry and differential thermal analysis （TG/DTA）. Powder X-ray diffraction （XRD） pattern confirmed the formation of pure LiNiPO4 compound with an orthorhombic structure. The conductivity and modulus analyses of the samples were carried out at different temperatures and frequencies using the complex impedance spectroscopy technique. The conductivity parameters such as ion hopping frequency and the charge cartier concentration term were calculated using Almond and West formalisms. An increase of one order of magnitude in the ionic conductivity has been observed for 1.0% Eu-doped LiNiPO4. （mole fraction）. The complex modulus studies suggest the presence of non-Debye type of relaxation in the materials.

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.

Asymmetrical Conductivity of TCNQ Modificd Au/Thiol-Lipid Bilayers in Fe(CN)_6^(3-/4-)solution

In this work. elcctron transfer across Au supported octadecanethiolphosphatidyl choline (Au/ODT-PC) bilayers, which were modified with 7.7.8.8-tetracyanoquinodimethane (TCNQ). were investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Results of EIS experiments show that the TCNQ molecules act as electron conductors in the bilayer. Cyclic voltammetry indicates that the TCNQ modified Au/thiol-lipid bilayers display strong asymmetrical conductivity in Fe(CN)3-/4-6 solution.

The Conductivity of Co-dopant Ceria Electrolyte

A kind of novel ceria electrolyte was examined.Various trivalent oxides were added as co-dopants to Ce 0.8Gd 0.2O 1.9,and their effects on the conductivity of ceria electrolyte were discussed.It has been found that the co-dopant of trivalent oxides of Sm,Nd,La and Y improves the ionic conductivity notably.Furthermore,the fine original powders,co-dopant and higher sintering temperature may hasten the sintering.

Ionic Conductivity of Nano-LaF_3 Bulk Material at Room Temperature

Nanocrystalline powder of LaF3 was synthesized by a method of direct precipitation from water solution. Particle size and shape of LaF3 nanocrystalline powder was analysed with TEM. Particles were mainly spherical with narrow particle size distribution （10 20 nm）. The average particle size analysed with XRD is 16.7 nm. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and a vacuum of 10^-4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material （1 × 10^-5 S·cm^-1 ） at room temperature is significantly increased compared to that of single crystal LaF3 （1 × 10^-6 S·cm^-1）. A special phenomenon was observed firstly time that the ionic conductivity increased gradually with multiple testing in result of relaxation.

Reconstruction of conductivity distribution of brain tissue from two components magnetic flux density

In this paper the recent Magnetic resonance electrical impedance imaging (MREIT) technique is used to image non-invasively the three-dimensional continuous conductivity distribution of the head tissues. With the feasibility of the human head being rotated twice in the magnetic resonance imaging (MRI) system, a continuous conductivity reconstruction MREIT algorithm based on two components of the measured magnetic flux density is introduced. The reconstructed conductivity image could be obtained through solving iter- atively a non-linear matrix equation. According to the present algorithm of using two magnetic flux den- sity components, numerical simulations were per- formed on a concentric three-sphere and realistic human head model (consisting of the scalp, skull and brain) with the uniform and non-uniform isotropic target conductivity distributions. Based on the algorithm, the reconstruction of scalp and brain conductivity ratios could be figured out even under the condition that only one current is injected into the brain. The present results show that the three-dimensional continuous conductivity reconstruction method with two magnetic flux density components for the realistic head could get better results than the method with only one magnetic flux density component. Given the skull conductivity ratio, the relative errors of scalp and brain conductivity values were reduced to less than 1% with the uniform conductivity distribution and less than 6.5% with the non-uniform distribution for different noise levels. Furthermore, the algorithm also shows fast convergence and improved robustness against noise.

Anisotropic WM conductivity reconstruction based on diffusion tensor magnetic resonance imaging: a simulation study

The present study aims to estimate the in vivo anisotropic conductivities of the White Matter (WM) tissues by means of Magnetic Resonance Electrical Impedance Tomography (MREIT) technique. The realistic anisotropic volume conductor model with different conductivity properties (scalp, skull, CSF, gray matter and WM) is constructed based on the Diffusion Tensor Magnetic Resonance Imaging (DT- MRI) from a healthy human subject. The Radius Basic Function (RBF)-MREIT algorithm of using only one magnetic flux density component was applied to evaluate the eigenvalues of the anisotropic WM with target values set according to the DT-MRI data based on the Wolter’s model, which is more physiologically reliable. The numerical simulations study performed on the five-layer realistic human head model showed that the conductivity reconstruction method had higher accuracy and better robustness against noise. The pilot research was used to judge the feasibility, meaningfulness and reliability of the MREIT applied on the electrical impedance tomography of the complicated human head tissues including anisotropic characteristics.

Conduction Mechanism and Conductivity Behaviour of Pure Polypropylene (PP) and Polypropylene-Banana Fiber (PP-B) Composites

Fibers reinforced composite materials offer a combination of strength and modulus that are either comparable to or better than many traditional metallic materials.The research on natural fiber based composite materials fit well into this ecological image.This paper reports the conduction mechanism and ac conductivity,activation energy behavior of Polypropylene and banana fiber reinforced thermoplastic composites.Polypropylene[-CH_(2)-CH_(2)-CH_(2)-]n and different fiber content(wt.%)of polypropylene-banana fibers(natural fiber)composites were fabricated using a hot-press molding system.The optimum fabrication parameters were established(initial pressure,temp.etc.).These composite test samples were fabricated so the short fibers were randomly oriented in the matrix.The detail investigation of the a.c.conductivity and conduction mechanism of polymer composites would provide information about the relaxation processes,activation energy etc.which are dependent on frequency,temperature and time.The activation energy involved in the above processes can also be estimated from this study.The measurements were performed over a wide range of frequency of 60 Hz to 3 MHz and temperature range from 30℃(303°K)to 110℃(383°K).Experimental results of the ac properties of pure polypropylene and polypropylene-natural banana fiber composites were compared.It has been established that the fabricated composition changes its insulating property after adding the natural fibers and gives the better conductivity properties.

Synthesis and room temperature ionic conductivity of nano-LaF_3 bulk material

The ionic conductivity (at room temperature) of nano-LaF3 bulk material and a new discovered phenomenon of increasing ionic conductivity caused by grain boundary relaxation activated by AC (alternating current) shocking were reported. Nano-crystalline powder of LaF3 with average grain size of 16.7 nm was synthesized with a method of direct precipitation from aqueous solution. Particle size and shape of LaF3 nano-crystalline powder were analyzed by XRD and TEM. Nano-LaF3 bulk material was prepared by compacting the powder to 1 GPa at room temperature and vacuum of 10?4 Pa. The ionic conductivity of nano-LaF3 bulk material was studied with complex impedance spectra at room temperature. The ionic conductivity of nano-LaF3 bulk material (10?5 S/cm) at room temperature is significantly increased compared with that of single crystal LaF3 (10?6 S/cm). A special phenomenon is observed for the first time that the ionic conductivity increases gradually with AC scanning times.