Papers by Keyword: AC Impedance

Abstract: Gel phantoms are useful materials for medical diagnostics and impact testing. The gel phantoms can be tailored to suit various tissues from the bulk, microscopic and molecular components. These components have responses under an AC electric field. In this work, a gel phantom was prepared using a commercially-available gel powder. Cylindrical samples with varying degrees of defects were cut from the prepared gel phantom and tested using an AC impedance analyzer. The defects were created by piercing a needle along the center plane of the sample and the degree of defects was varied by increasing the number of piercings in the sample. The conductivity of the sample at lower frequencies was influenced by the mechanism involved in water leakage due to piercing while the conductivity at higher frequencies was dominantly affected by space charge relaxation and structural conductivity barriers. The Nyquist plots obtained were seen to exhibit modified Randles-type behavior. Equivalent circuit fittings showed the parameters to be distinct with varying degrees of defects.

Abstract: The 3 at% Al doped ZnO thin films were deposited on p-Si substrate with a native SiO₂ layer by spray pyrolysis method. Low temperature conduction behaviors were studied by analysis of impedance spectroscopy and low temperature ac conductivity. The results of impedance spectroscopy showed that the grain boundaries contributed to the resistivity of Al doped ZnO/SiO₂/p-Si heterojunction. The calculated activation energy was 0.073 eV for grain boundaries. The equivalent circuit to demonstrate the electrical properties of Al doped ZnO/SiO₂/p-Si heterojunction was a series connection of two parallel combination circuits of a resistor and a universal capacitor. Low temperature ac conductivity measurements indicated that the conductivity increased with temperature. Low temperature conductivity mechanism was electron conductivity, and the activation energy was 0.086 eV.

Abstract: The electrochemical properties of Al-Zn-Ga-In-(Pb/Bi) anode alloy are studied by electrochemical test, including constant current test, polarization curve test, AC impedance test. Metallographic microscope is used to observe the microstructure of the alloy . energy spectrum technical is used to analyze the second phase elements. The results showed that the adding of element Pb or Bi both can attain more negative open-circuit potential; the adding of Bi makes the working potential shift positively, and reduces the current efficiency; 2% Pb content can attain more negative working potential, and current efficiency are increased slightly; the series anode the morphology of dissolution relatively uniformly in 3% NaCl solution; anodic polarization are all relatively smaller than cathodic polarization, and they have good anodic polarization properties. The overall electrochemical properties of Al-3Zn-0.015Ga-0.025In-2Pb alloy are the best in these five aluminum alloy anode.

Abstract: This paper analyzed the morphology and reasons of pitting corrosion perforation of 0Cr18Ni9 stainless steel cooling water pipes in a power plant and pointed out the measures to prevent the pitting corrosion under this condition. The results showed that: the reason of pitting corrosion of 0Cr18Ni9 stainless steel cooling water pipes was the existence of multiple Cl^-and easily fouling Ca²⁺ and Mg²⁺ in water, with the corrosion products mainly the oxides of Fe and Cr; the economic measures to prevent pitting corrosion were to increase the pH of water and decrease the content of Ca²⁺ and Mg²⁺.

Abstract: In this paper, using ZrO₂ and Ca (NO₃)•4H₂O as raw materials, we prepared a series of calica stabilized zirconia (CSZ) ceramics by pressureless sintering method. The results show that the relative densities of all sintered samples are above 90%, and the sintered samples are composed of cubic, tetragonal and monoclinic ZrO₂, and the main phase is cubic ZrO₂ and tetragonal ZrO₂. The content of cubic phase increases with the increase of sintering temperature and adding CaO content. The grain size of the sintered samples is relatively uniform and some pores exist. Increasing the additive amount of CaO, the conductivity first rises and then decreases, and the conductivity value of the sample containing 5wt% CaO is the maximum. When the sintering temperature is up to 1600 ^oC, the conductivity of the sample containing 5wt% CaO is up to 0.016S•cm^-1 at 800 ^oC. Furthermore, the conductivity of sintered samples is increasing with the increase of test temperature according to the Arrhenius equation.

Abstract: Reinforced concrete structures have been increasingly widely used through numerous industrial fields. These structures are often exposed to severely corrosive environments such as sea water, contaminated water, acid rain, and the seashore. Thus, corrosion problems of the steel bars embedded in concrete are very important from a safety and economic point of view. In this study, the effects of cover thickness on the corrosion properties of reinforced steel bar embedded in mortar specimen (W/C:0.6) were investigated using electrochemical methods such as corrosion potentials, polarization curves, cyclic voltammograms, galvanostat and potentiostat. Corrosion potentials shifted to the noble direction, and the value of AC impedance also exhibited a higher value with increasing cover thickness, furthermore, polarization resistance also increased with increasing cover thickness. This is probably that the thinner cover thickness, seawater solution is easy to arrive at embedded steel compared to other thicker cover thickness, so, its steel bar may be easily corroded due to chloride ion, which is resulted in shifting corrosion potential to negative direction, decreasing polarization resistance. Consequently, it is considered that the relation between corrosion resistance of reinforced steel and cover thickness is nearly matched with each other. However, its corrosion resistance estimated by measurement of corrosion potential was not well in agreement with value obtained by polarization curves.

Abstract: Reinforced concrete structures have been increasingly widely used in numerous industrial fields. These structures are often exposed to severely corrosive environments such as sea water, contaminated water, acid rain, and the seashore. Thus, corrosion problems of the steel bars embedded in concrete are very important from a safety and economic point of view. In this study, the effects of cover thickness on the corrosion properties of reinforced steel bar embedded in mortar specimen were investigated using electrochemical methods such as corrosion potentials, polarization curves, cyclic voltammograms, galvanostat and potentiostat. Corrosion potentials shifted in the noble direction, and the value of AC impedance also exhibited a higher value with decreasing cover thickness, furthermore, polarization resistance also increased with decreasing cover thickness. This is probably that the thinner cover thickness, it is easy for the dissolved oxygen and chloride ion to intrude and diffuse to the steel bar, thereby making it easier to corrode on the steel surface compared to thicker cover thickness, which is resulted in forming the corrosive products on the steel surface. Therefore, it is considered that the corrosive products plays a role to provide nobler value of corrosion potential and higher value of impedance. Consequently, it seems that the corrosion resistance of inner steel bar may depend on mainly not cover thickness but the resistance polarization due to corrosive products in the case of immerged for 5 years in this experiment.

Abstract: High temperature proton exchange membrane (HT-PEM) fuel cell is considered as one of the most probable fuel cells to be large-scale applied due to characteristics of high efficiency, friendly to environment, low fuel requirement, ease water and heat management, and so on. However, carbon monoxide (CO) content in fuel plays an important role in the performance of HT-PEM fuel cells. Volt-ampere characteristics and AC impedance of HT-PEM fuel cell are tested experimentally in this paper, and effects of CO in fuel on its performance are analyzed. The experimental results show that CO in fuel increases remarkably the Faraday resistance of HT-PEM fuel cell and decreases the electrochemical reaction at anode; the more CO content in fuel is, the less HT-PEM fuel cell performance is; with the increasing cell temperature, the electrochemical reaction on the surface of catalyst at anode is improved and the poisonous effects on the HT-PEM fuel cell are alleviated.

Abstract: A new fabrication methods of thin-film gold electrode is reported. Electrochemical characteristics of self-assembly aptasensor based on MEMS thin-film gold electrode has been studied by lots of experiments, characteristics include immobilizing time, AC impedance, CV curves. Experiments indicate immobilizing time of DNA-SH on gold electrode is more than 15 hours. CV curves and AC impedance of MEMS thin-film gold electrode show the same conclusion that 20μm/L DNA is optimum concentration when DNA is immobilized on gold electrode. Those results present a potential universal method for other aptasensors.

Abstract: Property of polymer-concrete in the interface has been dealt with from the view of thermodynamics. Gibbs function or free enthalpy was applied to characterize the binding ability of the interface. AC impedance spectroscopy was used to measure the electrical capacitance of the interface between the polymer particle and mortar. Lippmann equation was used to estimate the thermodynamic functions for the estimation of the binding ability. A typical example was given.