Authors: Cheng Ju Zhang, Jin Feng Wang, Wen Bin Su, Guo Zhong Zang, Hong Cun Chen
Abstract: The effects of Pr on the microstructure and nonlinear electrical properties of the (Co,Ta)-doped SnO2 varistors were investigated. It was found by characterizing the samples sintered at 1350 oC that the breakdown voltage increases significantly from 500v/mm to 1200v/mm, and the relative permittivity decreased rapidly from 2525 to 1199 with increasing Pr6O11 concentration from 0 to 1.20 mol%. The
analysis of samples’ microscopic structure showed that the grain size of SnO2 rapidly decreases from 5.1 to 3.7 µm with increasing Pr6O11 concentration from 0 to 1.20mol% .The significant decrease of SnO2 grain size is the main reason for raising breakdown voltage and reducing permittivity.
275
Authors: S. Chauffaille, Olivier Devos, Julien Jumel, Martin E.R. Shanahan
Abstract: Preliminary results on a technique of Electrochemical-Impedance Spectroscopy (EIS) applied to the characterization of diffusion and absorption properties of water in an epoxy resin are reported. Thin films of polymer adhering to aluminum constitute simulated adhesive bonds. Immersion in water and assessment via electro-chemical impedance measurements allowed estimation of diffusion rates and water uptake. In parallel, classic gravimetric experiments were undertaken on thin, free films of the same polymer. Results of the two techniques are acceptably comparable, and thus EIS could be developed as a new tool for in situ assessment of adhesives.
239
Authors: Ming Zhang, Zhu Ding, Peng Liu, Ming Ke Wang, Feng Xing
Abstract: Electrodeless resistivity and impedance spectroscopy measurement are reliable equipments of test online for monitoring the hydration process of cement-based materials continuously and accurately. Phosphoaluminate cement (PAC) sets quickly and develops high early strength. In order to understand the mechanism, the hydration products and microstructure formation of PAC in early age need to be studied. In the study, early hydration process and impedance spectroscopy characteristics of PAC with different dosage of retarder were investigated. According to the test, resistivity of freshly mixed PAC paste decreases sharply and then rises slowly, some characteristic peaks appear at different hydration stages of PAC, which indicates the hydration process of PAC includes four stages which are dissolution, induction, acceleration and deceleration. Impedance spectroscopy can reflect the change of micro-structure and ion concentribution of PAC matrix by resistance and capacitance.
926
Authors: Jin Hua Ju, Hua Wang, Ji Wen Xu, Ling Yang, Si Jia Liu, Jie Chang Di
Abstract: The electrical responses of Zn-Bi-Co-Mn-Ti system low-voltage varistor ceramics were prepared by solid-state reaction method and were analyzed by AC impedance spectroscopy over a wide range of temperature (100~270°C) in the frequency range of 40~13MHz. The equivalent circuit adopts R (RQ)(RC) model. Imaginary part of impedance and modulus with frequency plot exhibits the varistor ceramics including resistance and capacitance. Impedance analysis enables us to separate the contributions from grains and grain boundaries of our samples. It indicates that grain boundary impedance is the main contributor for ceramic resistance, and grain boundary relaxation effects are most obvious in Zn-Bi-Co-Mn-Ti system. The AC grain boundary conductivity activation energy is attributed to the motion of oxygen vacancies within the bulk, and calculated by Arrhenius equation.
1354
Authors: Ivo Kusak, Miroslav Lunak, Pavel Schauer
Abstract: Concrete setting and hardening designate the concrete grade. The impedance spectroscopy method, as one of the non-destructive testing method group, was used to characterize concrete specimens and track the changes in the concrete spectrum. Variances in the tan δ (f) and Im Z(f) or Re Z(f) of the specimens under investigation have been observed. The specimen quality has been described by means of the loss type prevailing in the material. The results of this study are expected to provide information about the correlation between the n-factor and the concrete setting time.
370