Papers by Keyword: Diffusion Coefficient

Abstract: The electrochemical dynamics of a film of FeCo nanoparticles were studied on a glassy carbon electrode (GCE). The film was found to be electroactive in 1 M LiClO₄ containing 1:1 v/v ethylene carbonate dimethyl carbonate electrolyte system. Cyclic voltammetric experiments revealed a diffusion-controlled electron transfer process on the GCE/FeCo electrode surface. Further interrogation on the electrochemical properties of the FeCo nanoelectrode in an oxygen saturated 1 M LiClO₄ containing 1:1 v/v ethylene-carbonate-dimethyl carbonate revealed that the nanoelectrode showed good response towards the electro-catalytic reduction of molecular oxygen with a Tafel slope of about 120 mV which is close to the theoretical 118 mV for a single electron transfer process in the rate limiting step; and a transfer coefficient (α) of 0.49. The heterogeneous rate constant of electron transfer (k_et), exchange current density (i_o) and time constant (τ) were calculated from data obtained from electrochemical impedance spectroscopy and found to have values of 2.3 x 10^-5 cm s^-1, 1.6 x 10^-4 A cm^-2 and 2.4 x 10^-4 s rad^-1, respectively.

Abstract: We present investigation of carrier recombination and optical trap recharge in sublimation grown n- and p-type 3C layers by using time-resolved nonlinear optical techniques. Carrier lifetime and recharged trap recovery were measured by differential transmittivity technique. By monitoring nonequilibrium carrier dynamics, we analyzed impact of carrier density and temperature on carrier lifetime and recharged trap recovery rate. Large carrier lifetime and small diffusivity at low injections in highly compensated samples and their dependences on injection were explained by optical recharge of compensating aluminum impurities. The complete recharge of the compensating impurities by optical means allowed us to calculate the compensating aluminum density in n-type samples and compensating nitrogen in p-type ones.

Abstract: It is necessary to compare the reinforced concrete’s performance degradation caused by the use of sea sand. This should be done by conducting long-term outdoor-exposure tests on the test pieces and deterioration acceleration tests on other test pieces with the same mix proportions. This will enable you to identify the relationship between the speed of deterioration by promotion tests and the deterioration speed in the natural environment.

Abstract: Molecular dynamics simulation has been performed to explore the thermodynamics and dynamics properties of liquid Cu-Ni alloy based upon developed embedded atom methods (EAM), namely due to G. Bonny. The calculated liquid density shows that the potential underestimates the measured atomic density for Ni-rich composition. The calculated mixing enthalpy predicts the potential underestimates the mixing enthalpy when the concentration of Ni is increased beyond roughly 30 at. %. We make a conclusion from the fact that the G. Bonny’s model is not full perfect in describing the density and mixing enthalpy of Cu-Ni melts at the Ni-rich composition.

Abstract: Considering the concrete as a three-phase composite material composed of aggregate, interface and cement matrix, an octagon unit cell is constructed based on ellipse, and the numerical solution of concrete chloride diffusion coefficient considering the aggregate shape is obtained using the finite element method. The validity of the proposed algorithm is preliminary verified after compared with the available test results, and the effect of interfacial crack opening angle and aggregate shape on the concrete chloride diffusion coefficient is quantitatively evaluated. Through numerical calculation, it is found that the chloride diffusion coefficient of concrete increases with the increase of interfacial crack opening angle and decreases with the increase of aggregate shape coefficient.

Abstract: Under dry argon atmosphere, the colourless and transparent ionic liquid [C₂mim][GaCl₄] was synthesized. Using [C2mim][GaCl₄] as solvent, a solution of GaCl₃ with molarity 5.227×10-3 mol/cm3 was prepared at 303.15 K and there is a equilibrum between the solute and the solvent: GaCl₃ + [C₂mim][GaCl₄] → [C₂mim][Ga₂Cl₇]. The cyclic voltammogram of the solution had been carried out relative to Al/Al³⁺ reference electrode, with GC working electrode and Ga counter electrode, with various scan rates from 30 to 700mV/s, in a temperature range of 303.15 to 343.15 K, respectively. The results indicated that (1) there were two processes: Ga(Ⅲ)→Ga(I)→Ga(0), which corresponded to the double reduction peaks in the cyclic voltammogram; (2) the first reduction process was a diffusion controlled and quasi-reversible process. Plotting current density of the peak vs the square root of scan rate, a series of straight lines were obtained, then the diffusion coefficients were obtained according to Randles-Sevcik equation in various temperature. The values of diffusion coefficient were fitted to Arrhenius equation with least-square method and value of diffusion activation energy, ED = 41.5 kJ/mol, was obtained from Arrhenius slope.

Abstract: Chloride induced corrosion of reinforcing steel is one of major causes of deterioration of tunnel concrete lining under chloride attack. In this paper, a finite element model for chloride ions transport in tunnel concrete lining was proposed based on the Fick’s second law of diffusion. The governing partial differential equation was solved numerically in space as a boundary-value problem and in time as an initial-value problem by means of the finite element formulations. The maximum allowable value of chloride diffusion coefficient of tunnel concrete lining with service life of 100a was achieved and some constructive suggestions for durability design of tunnel concrete lining under chloride attack were also proposed.

Abstract: In this paper, the diffusion coefficient of vacancy-solute complex and diffusion coefficient of solute atoms, P, in non-equilibrium grain-boundary segregation under low tensile stress in steel 12Cr1MoV are calculated based on the model developed by Xu. Both the simulation and experimental kinetics curves are achieved. Results show that the calculated result with the kinetic equations perfectly fits with the experimental observations for phosphorus in steel 12Cr1MoV under low tensile stress. In the segregation process, the rate of phosphorus segregation is high due to a large diffusivity of the complex. In the de-segregation process, the level of phosphorus segregation decreases with increasing stress aging time. But the rate of phosphorus desegregation from grain boundaries to centre is slower compared with that in segregation for the diffusion coefficient of phosphorus atoms is far lower than the complexes.

Abstract: In the case of the modeling of sintering and heat treatments, the diffusion coefficients are an essential input. However, experimental data in the literature about diffusion coefficients for rare-earth transition metal intermetallics is scarce. In this study, the available data concerning diffusion coefficients relevant for rare-earth transition metal magnets are reviewed and commented. Some empirical rules are discussed, for example the activation energy is affected by the size of the diffusing impurity atom. Diffusion coefficients for Dy, Nd and Fe into Nd₂Fe₁₄B are given according an Arrhenius equation D=D₀ exp (-Q/RT). For Dy diffusion into Nd₂Fe₁₄B, Q 315 kJ/mol and D₀ 8 . 10^-4 m²/s.

Abstract: The lithium ions transferring into cathode material are similar as nonequilibrium carrier in semiconductor while the cell discharges at constant current small enough. The inpouring Li-ions can be called nonequilibrium Li-ions. The electrochemical diffusion coefficient, named as D, can be worked out approximately in terms of the relationship between the concentration of nonequilibrium Li-ions and the relevant potential difference. The D was found 3.21×10-10cm²/s for LiFePO₄ doped with 10% acetylene black.