Activation Energy Of Diffusion Coefficient Research Articles

Chemical kinetic analysis of the activation energy of diffusion coefficient of sulfate ion in concrete

Based on the Arrhenius equation, a key solution formula for activation energy of diffusion coefficient of sulfate ion was derived in concretes. The effects of the temperature and sulfate solution concentration on the distribution of sulfate content in concrete were investigated. The results showed that the concentration of sulfate ion in concrete increased with increase of temperature and solution concentration. The concentration of sulfate ion in concrete decreased with depth. Based on the concentration of sulfate ion in concrete attacked by sulfate at 20 °C and 40 °C, the activation energy of diffusion coefficient of sulfate ion in concrete was calculated.

Molecular dynamics study of small helium cluster diffusion in titanium

The diffusions of He atom and small He clusters in Ti at different temperatures are simulated by molecular dynamics. The prefactors and the activation energies of diffusion coefficients are calculated. It can be concluded that the diffusion is anisotropic. Simulations show that prefactors of diffusion coefficients are different from those of He species diffusing in different directions, but the activation energies are the same. The result demonstrates that it is insufficient to predict the diffusion behavior of He in metal when only the energy barrier in static lattice is considered. Dynamics calculations are necessary to obtain the correct prefactors. Another counterintuitive observation is that He-dimer migrates more quickly than single He atom does at room temperature. The results emphasize the importance of dynamics simulations in predicting diffusion behavior of He in metals.

Theoretical study of the initial stage of the aluminium-induced layer-exchange process

In this work, the initial stage of the aluminium-induced layer-exchange (ALILE) process is studied theoretically. The diffusion of silicon atoms from an amorphous Si layer into an Al layer through a permeable membrane prior to Si grain nucleation within the Al layer is considered. A kinetic model is derived to describe this process. In the framework of this model, the evolution of the Si concentration within the Al layer prior to Si grain nucleation and the nucleation time are investigated for different annealing temperatures and preparation conditions of the membrane. From the comparison of results of calculations with experimental data, the pre-exponent factors and activation energies of diffusion coefficients of Si in membranes are determined.

Characteristics of Zn diffusion in planar and patterned InP substrate using Zn 3P 2 film and rapid thermal annealing process

Characteristics of Zn diffusion in patterned InP substrates was investigated and compared with that of Zn diffusion in InP planar substrates. The activation energy of diffusion coefficient was 1.3∼1.4 eV in both patterned and planar diffusion, which indicates that there is no difference in the diffusion mechanism and that the diffusion was controlled by an interstitial-substitutional mechanism. The diffusion coefficient in patterned substrates was smaller than that in planar substrates when a Si 3N 4 encapsulation layer was employed. As the Si 3N 4 encapsulation layer thickness increased, the diffusion coefficient decreased in both planar and patterned substrates. But, the diffusion coefficient showed little dependence on the thickness of the SiO 2 encapsulation layer in both patterned and planar substrates.

The mass transport of methanolic ferric chloride hexahydrate solution in poly(methyl methacrylate) and related optical properties

The mass transport of methanol mixed with ferric chloride hexahydrate (FeCl 3·6H 2O) in poly(methyl methacrylate) (PMMA) and the related optical properties have been investigated. The ratio of FeCl 3·6H 2O to methanol in the solvent mixture is X=0.013, 0.038 and 0.063 g/g. The mass transport is anomalous, which is a mixture of Case I with Case II transport. Both diffusion coefficient for Case I and velocity for Case II transport satisfy the Arrhenius equation. The activation energy of diffusion coefficient in Case I transport decreases with increasing X, but the trend for that of velocity in Case II transport is opposite. The mass transport is an endothermic process and satisfies the van't Hoff's plot. The heat of mixing increases with X. The transmittances of PMMA saturated with the solvent and solvent of methanol mixed with FeCl 3·6H 2O decrease with increasing X. The scattering intensity of the specimens after desorption is inversely proportional to the visible wavelength with an exponent, n, in the range from 1.02 to 3.25. The exponent is equal to 4 corresponding to the Rayleigh scattering. The wavelength dependence of scattering intensity is attributed to holes, the size of which is smaller than the visible wavelength, and to clouds. The holes and clouds in the solvent-treated specimen are observed by the scanning electron microscope and optical microscope. The deviation of the exponent n from 4 is due to the fractal dimension of hole and cloud. The FTIR spectra of specimens treated with solvent of different concentrations of FeCl 3·6H 2O are also studied.

A model for thermal growth of ultrathin silicon dioxide in O/sub 2/ ambient: a rate equation approach

A new thermal oxidation model based on a rate equation approach with concentration dependent diffusion coefficient is proposed for ultrathin SiO/sub 2/ for thicknesses of the order of 100 /spl Aring/. The oxidation reaction of silicon is assumed to be dependent on the concentrations of unreacted silicon and oxygen. The results of oxide thickness versus oxidation time for various growth conditions and activation energies for diffusion coefficients are in agreement with various experimental data for O/sub 2/ ambient.

The measurement of the diffusion coefficient of U(VI) in aqueous uranyl sulfate solutions

The diffusion coefficients of U(VI) in aqueous uranyl solutions were determined between 293.5 and 311.0 K by comparing the limiting current densities between the copper electrodeposition and the electrolytic reduction of uranyl sulfate under the same hydrodynamic condition. The diffusion coefficients thus determined were almost constant despite the change in agitation speed of electrolyte solutions, which suggests the appropriateness of the method employed in this study. On the other hand, the diffusion coefficients of U(VI) showed a slightly decreasing trend with increase in uranyl sulfate concentration, but when total uranium concentration was kept constant the diffusion coefficient appeared to be almost constant. The activation energies of diffusion coefficients of U(VI) were found to be 21 to 22 kJ mol−1 for the solution studied.

Formation of the Conductive Layer near the Surface of Semi-Insulating GaAs Covered with Oxide Film

Thin conductive layer is formed near the surface of i-GaAs doped with Cr, when the surface of i-GaAs is covered with SiO2 or phospho-silicate glass (PSG) grown by means of thermal decomposition of alchoxyl silicate and phosphate. The thickness of the layer increases with increasing duration and temperature of heat treatment. This layer shows n-type conduction, and the concentration and mobility of electron in this layer are 1∼2×1017 cm-3 and about 2500 cm2/V·sec, respectively. It is concluded that the cause of the conductive layer formation is a decrease of the concentration of Cr which compensates undesirable donors in i-GaAs, as a result of the diffusion of Cr into the oxide film. The formation of such conductive layers can be prevented by covering i-GaAs with sputtered SiO2 from fused quartz or Si3N4. The activation energy of diffusion coefficient of Cr in i-GaAs is estimated to be 3.6 eV.