Papers by Keyword: Polarisation

Abstract: The torsional effect of a rectangular piezoelectric quartz is studied in the article. Using the anisotropic elasticity and Maxwell electromagnetic theory, the stress field and electrostatic field is founded, and then by the Finite Element Method the distribution of the electric field in the piezoelectric body is obtained. Based on theoretical analysis of the bound charge distribution, the measuring electrodes are effectively disposed on the surfaces of the piezoelectric wafers. The theoretical and experimental results show that the measurement charge is linear with the torque. The research will provide the basis for the torque measuring technique.

Abstract: Sulfate reducing bacteria (SRB) were most common bacteria involved in microbiologically influenced corrosion (MIC). In this paper, the influences of surface free energy and electrochemical polarization on sulfate reducing bacteria (SRB) attachment were investigated. Microbial adhesive to hydrocarbons experiment and zeta potential test showed that SRB were relative hydrophobic and were negative charged. SRB showed affinity to substratum with higher water contact angle and its biofilm formation led to alterations in the hydrophocibity of the substratum surface. The mild steel was used to systematically examine the effect of electrochemical polarization on SRB attachment. At -800mV (vs.SCE), the sessile number was similar to those without polarization. At -950mV and -1000mV, the polarization promoted SRB attachment. At -1100mV and -1200mV, the adhered cell number decreased sharply compared to those at -1000mV. SRB attachment was inhibited, at an applied potential of -1300mV. These results indicated that the infuence of negative polarization on SRB attachment was dependent on applied potential.

Abstract: The corrosion performance of Ag-Cu-Ni-RE alloys in Na2S has been studied in order to assess the influence of rare earth (lanthanum and cerium) on the Ag-Cu-Ni alloys. Optical microscopy has been used to characterize the microstructures of the samples prior to the electrochemical tests. SEM, EDS and XRD have been used to observe the corrosion morphologies and chemical compositions of the samples. The electrochemical tests has been carried out at room temperature in 0.5, 1and 2% (wt. %) Na2S. The results reveal that the Ag-Cu-Ni-RE alloys exhibit improved corrosion resistance, as well as fine and uniform microstructures. Moreover, surface layers forming on Ag-Cu-Ni-RE alloys exhibit improved protective properties compared to the film growing on the Ag-Cu-Ni alloy. Here, it is also found that when comparing to the dilute Na2S solution conditions, there would be a little decrease of the corrosion rate in 2wt. %Na₂S solution. In addition, Ag-Cu-Ni-La-Ce alloy generally exhibits the best corrosion resistance.

Abstract: In this essay, the effects of grain refinement on corrosion behavior and hardness of equal-channel-angular-pressed (ECAPed) AISI 304 austenitic SS were studied. Finer grains with average size of 5μm in the specimen were obtained after four ECAPed passes compared with as-received one with grain size in range of 55μm Strain-induced grain refinement process can increase grain boundary and dislocation. Thus, the corrosion resistance of ECAPed AISI 304 austenitic SS would be improved.The refined microstructure achieves more positive open circuit potential (OCP) and lower corrosion current density in polarization corrosion tests.Through this process, austenitic stainless steel with better performance in corrosion resistance can be gained.

Abstract: In order to enhance measurement precision of the piezoelectric micro-actuator, by means of the transformation rule of tensor the research on the Bending Charge Sensitivity Distribution of Piezoelectric Quartz is conducted. First by the theories of elasticity and electromagnetism the torsion stress and bound charge are calculated, and the charge measured by the detection electrodes is obtained, which depend on the piezoelectric coefficient d12. Then using the transformation rule of tensor the piezoelectric coefficient d12 in the new coordinate system is calculated, and according to the unrestrained multipurpose optimization method the optimization Cut is obtained. Finally a special designed experiment is performed, and the experimental results show that the bound charge produced by the optimized Cut is about twice larger than that primitive Cut. This research on the bending charge sensitivity will provide a theoretical foundation for disposing the detection electrodes of a new piezoelectric micro-actuator

Abstract: Metal matrix composites considered especially for marine application are typically aluminum-based. Utilization of the composites in marine environments requires adequate corrosion resistance. In this work, the effect of aging and aluminum as resistive coating on the corrosion behavior of 6061 Al / SiCp composite in 1N and 3.5N NaCl solution in the temperature range of 300C-500C is studied by means of electrochemical techniques, scanning electron microscope (SEM) and weight loss measurements. Aging results in precipitation of intermetallics in the matrix, this in turn leads to galvanic and pitting corrosion. Pitting initiation and propagation as the main corrosion mechanism was driven by the aging kinetics which is ruled by the reduction in the retained vacancy concentration and at the same time by dislocation density due to the presence of SiCp. Sputtered aluminum coating on the composite effectively resists the pitting initiation and propagation and hence corrosion process. Also the intermetallic precipitates are unexposed to the Chloride solution by the presence of aluminum coating. Hence aluminum coating acts as corrosion resistive coating for the 6061 Al / SiCp aged composites.

Abstract: In this paper, there is an attempt to present the two dimensional electron gas (2DEG) transport characteristics of AlxGa1-xN/(AlN)/GaN-based High Electron Mobility Transistor (HEMT) using a self-consistent numerical method for calculating the conduction-band profile and subband structure. The subband calculations take into account the piezoelectric and spontaneous polarization effects and the Hartree and exchange-correlation interaction. Here the dependency of conduction band profile, subband energies, 2DEG sheet concentration and sheet resistance on various Al mole fractions of AlxGa1-xN barrier layer are presented by incorporating simulation as well as available experimental data. Introduction of very thin binary AlN layer at the heterojunction of AlxGa1-xN/GaN resulting high mobility at high sheet charge densities by increasing the effective and decreasing alloy disorder scattering. Devices based on this structure exhibit good DC and RF performance as an increase of . Owing to high 2DEG density , the proposed device leads to operate in microwave and millimeter wave applications.

Abstract: The compression induced by the assembly of proton exchange membrane (PEM) fuel cells causes partial deformation of the gas-diffusion layers (GDLs) and, consequently, influences the performance of PEM fuel cells. In order to investigate how assembly pressure affects electric efficiency of PEMFC, performance of PEMFC experiments with a miniature self-humidifying, breathing PEMFC stack are conducted under different clamping pressures. The polarization and power efficiency curves of PEMFC under different clamping pressures show that the best performance can be obtained at the allowable lower limit of working parameters. The research shows that the effect of assembly clamping pressure is significant, and the low clamping pressure is beneficial to improve the performance of the PEMFC stack while keeping sealing. The experimental results indicate that a clamping pressure of 1MPa improves the fuel cell performance in this paper.

Abstract: The electrochemical behaviors of the cold-rolled steel strip were investigated at the range of ordinary current density (10A/dm2-30A/dm2). The power consumption, which is caused by overpotential of the cold-rolled steel strip per unit area (PCOC), was used to evaluate the energy consumption which is caused by polarization effectively. The effects of electrolysis time, current density, temperature and the concentration of electrolyte on the PCOC were examined. The PCOC increased with time, but the growth rate of the PCOC decreased with time. After about 8 seconds, the increasing rate of the PCOC closed to zero. The value of the PCOC was in direct proportion to current density, and there was a significant increase when the current density is beyond 25A/dm2. Both raising temperature and increasing the concentration of electrolyte are effective ways of decreasing the PCOC.

Abstract: In this paper, a 2x2 and a 4x4 indoor MIMO measurement campaign at a (2 -5) GHz is presented. A statistical analysis to study the effects of a 2x2 and a 4x4 MIMO on the channel capacity with their respective received fixed signal to noise ratios were analyzed both in the LOS and in NLOS scenarios. Furthermore, investigations were carried out on all the possible wide band antenna polarizations in order to ascertain which mode of propagation yields a highly decorrelated spatial channel. The three received signal to noise ratios namely 10dB, 20dB and 30dB were used to model various received signal powers. It was found that copolar configurations HH and VV yielded the maximum capacity values both in the LOS and in NLOS respectively. Finally, a validity test was conducted and it was realized that the empirical distribution is similar and within the theoretical (i.i.d) distribution.