The corrosion behavior of AZ31 alloy in chloride and sulfate media-A comparative study through electrochemical investigations

The magnesium alloys are considered to be the best structural materials,because of their advantageous weight to strength ratio.But,the limitation in their real field applications lies on the fact that magnesium alloys are highly susceptible for corrosion.The corrosion behaviour of AZ31 alloy was investigated by electrochemical methods in sodium chloride and sodium sulphate of different concentrations at different temperatures.The corrosion rate was monitored by potentiodynamic polarization technique and electrochemical impedance spectroscopy method.The surface morphology and surface composition of the freshly polished surface of the alloy was compared with that of the corroded surface by recording their SEM images and EDS,respectively.The results showed that the corrosion rate of AZ31 alloy increased with the increase in the temperature of the medium and also with the increase in the salt concentration of the medium.The activation parameters for the corrosion process were calculated and interpreted.

A Review of Wideband Circularly Polarized Dielectric Resonator Antennas

This article presents a technical review of circularly polarized(CP) dielectric resonator antennas(DRA) for wideband applications.The primary objective of this review is,to highlight the techniques used by different researchers for generating circular polarization in DRA.First,a general idea of circular polarization and it advantages over linear polarization is presented,and then all the major developments made in the CP DRA are highlighted.The emphasis of the paper is on the wideband circularly polarized dielectric resonator antenna.The current state of the art and all the realizable features of the CP DRA are addressed comprehensively.Finally,some recommendations for future CP DRAs are given and the paper ends with concluding remarks.

Solar sail time-optimal interplanetary transfer trajectory design

The fuel consumption associated with some interplanetary transfer trajectories using chemical propulsion is not affordable. A solar sail is a method of propulsion that does not consume fuel. Transfer time is one of the most pressing problems of solar sail transfer trajectory design. This paper investigates the time-optimal interplanetary transfer trajectories to a circular orbit of given inclination and radius. The optimal control law is derived from the principle of maximization. An indirect method is used to solve the optimal control problem by selecting values for the initial adjoint vari- ables, which are normalized within a unit sphere. The conditions for the existence of the time-optimal transfer are dependent on the lightness number of the sail and the inclination and radius of the target orbit. A numerical method is used to obtain the boundary values for the time-optimal transfer trajectories. For the cases where no time-optimal transfer trajectories exist, first-order necessary conditions of the optimal control are proposed to obtain feasible solutions. The results show that the transfer time decreases as the minimum distance from the Sun decreases during the transfer duration. For a solar sail with a small lightness number, the transfer time may be evaluated analytically for a three-phase transfer trajectory. The analytical results are compared with previous results and the associated numerical results. The transfer time of the numerical result here is smaller than the transfer time from previous results and is larger than the analytical result.

Corrosion property of copperized layer on Zr formed by double glow plasma surface alloying technique

Zr and its alloys have excellent mechanical properties as new structural material,but in specific application environment,its corrosion resistance still needs to be further explored.In this work,double glow plasma surface alloying technique was used for copperizing on pure Zr surface.Besides,X-ray diffraction（XRD）,scanning electron microscope（SEM） and energy dispersion spectrum（EDS） were employed to characterize the samples.Furthermore,research was also conducted on the polarization curve of the samples in different solutions.Copperizing on surface can improve corrosion resistance of pure Zr in 3.5 % Na Cl and 0.5 moláL-1Na OH solutions.Especially in 0.5 moláL-1Na OH solution,the corrosion resistance can achieve significant improvement.However,copperizing has no influence on the improvement of corrosion resistance of pure Zr in 0.5 moláL-1H2SO4 solution.The results may provide new insight into way for improving the corrosion property of zirconium alloys.

A cased-hole acoustic logging technique using the dual source of opposite polarity

It is usually difficult to measure acoustic velocities through a casing, especially when the casing is poorly bonded with formation. An acoustic logging technique using the dual source of opposite polarity is proposed to enhance the Signal to Noise Ratio of the formation signal and to reduce the casing wave in the data acquisition process. In what follows, a theoret- ical modeling is used to caculate the wavefroms of cased wells. And then, a scaled experiment was conducted in the 1：10 scaled experimental well using the proposed technique in the poorly- bonded condition. The results show that this technique can effectively suppress the casing wave and enhance the formation wave, even in the poorly-bonded condition. By analyzing the measured wavefroms, the amplitude of casing wave is reduced to 12% compared to the conventional one-source technique, and the compressional wave velocity can be easily obtained by using this technique. Both the theoretical modeling and experiment results demonstrate the feasibility of the proposed technique. This study establishes the theoretical and experimental foundation for the cased-hole, dual source of opposite polarity, acoustic logging tool development.