Papers by Keyword: AC Impedance

Abstract: Ternary lithium-ion battery is currently one of the hot cathode materials. In this paper, with acetate of nickel, manganese and cobalt as raw materials and lithium hydroxide as precipitation agent, LiCo1/3Mn1/3Ni1/3O2 was prepared by chemical coprecipitation method. LAND charge-discharge testing was used to study the electrochemical performance of materials at different rates (0.5C, 1C, 2C), and AC impedance spectroscopy was employed to study the rate performance and reasons of cyclical stability. The results showed that the stable SEM film formed under high rate was the main reason for the increased rate.

Abstract: In this study, AC impedance behaviors of Ti-Zr binary alloys for biomaterials have been investigated using by electrochemical impedance spectroscopy. Ti-10wt%, 20wt%, 30wt%, and 40wt% Zr alloys were prepared by arc melting and homogenized for 24 hr at 1000 °C in argon atmosphere. Phase constitutions and microstructure of the specimens were conducted by using XRD, OM and SEM. The corrosion properties of the specimens were examined through potentiodynamic test (potential range of -1500 ~ 2000 mV), AC impedance spectroscopy(100kHz~10mHz) in artificial saliva solution by potentiostat (EG&G Co, PARSTAT 2273. USA). In as-cast and homogenized Ti-xZr alloys, α-phase was identified by XRD. Microstructures were changed from lamellar structure to needle-like structure as Zr content increased. From the results of polarization behavior in the Ti-xZr alloys, it was found that the corrosion resistance was increased with increasing Zr content. From results of AC impedance spectroscopy, passive film resistance value of homogenized Ti-40Zr specimen(1.60×106 Ωcm2) showed higher than that of as-cast specimen.

Abstract: ALDC8 alloy was often corroded with form of intergranular corrosion in corrosive environments. Thus in order to improve its corrosion, the effect of annealing to corrosion resistance and hardness was investigated with parameters of heating temperatures such as 100°C, 200°C, 300°C, 400°C and 500°C for 1hr. Hardness was slightly decreased with annealing, especially, the decreasing of hardness was remarkably revealed in annealing temperature at 300°C. Corrosion potential was shifted to noble direction, and both AC impedance at 10m㎐ and polarization resistance on the cyclic voltammogram was also increased with annealing. Intergranular corrosion was not nearly observed at annealing temperature of 400°C, 500°C. Therefore the optimum annealing temperature for corrosion resistance as well as mechanical property is thought to be 400°C or 500°C.

Abstract: Ceria electrolytes co-doped with Gd3+ and Y3+ (Ce0.8Gd0.2-xYxO1.9) were synthesized by GNP. The crystal structures, lattice parameters and crystallite sizes were determined by XRD. The morphology of the powders was observed by TEM. Sintered at 1250oC for 4 h, all die-pressed ceria pellets achieved densities higher than 95% of theoretical values. The ionic conductivities were measured using AC impedance technique and Ce0.8Gd0.05Y0.15O1.9 showed a higher ionic conductivity than those of other compositions at 500-750oC, indicating that it is an attractive electrolyte material for IT-SOFC.

Abstract: The selected dihydroxamic acid derivatives, namely oxalyl-dihydroxamic acid (C2) and pimeloyl-1,5-di-hydroxamic acid (C7) have been synthesized and evaluated as corrosion inhibitors for carbon steel in neutral aqueous solution by potentiodynamic polarization and ac impedance methods. C2 molecule acts as good inhibitor with inhibition efficiency value reached 91%; it is well adsorbed most likely throughout the two hydrophilic groups, and forms a protective film on the metal surface. C7 has moderate inhibition efficiency probably due to the presence of long single hydrocarbon chain in the molecule, negatively affect the adsorption process. Addition of Ni2+ to C7 significantly improve the inhibition efficiency, throughout the formation of a dense compact layer of complexes between Ni2+ and C7.