Formation Of Concentration Profiles Research Articles

Local nonequilibrium mass transfer in a two-component system under external pulsed irradiation with energy fluxes

The nonisothermal mass transfer in metal materials under irradiation with concentrated energy fluxes is studied in the one-dimensional approximation. Local nonequilibrium equations of extended irreversible thermodynamics are used to describe the transfer phenomena. It is established that, for short times (on the order of the time required for relaxation of the diffusion flow to its local-equilibrium value), the wave mechanism for mass transfer is dominant over the diffusion one, ensuring that the impurity-concentration profiles have a nonmonotonous form. The degree of influence of the space-time nonlocality of the transfer processes on the formation of concentration profiles is estimated, and the model results are compared with the experimental data.

Formation of concentration profiles of implanted ions in metallic materials under polyenergetic implantation

A physical and mathematical model of mass transfer in polycrystalline metallic materials under exposure to ion beams is proposed. Alongside bulk indiffusion from the irradiated surface, diffusion along the migrating extensive defects interacting with an impurity is considered. For a polyenergetic ion beam, the con- tribution of bulk indiffusion is presented as an integral over energy of the product of two functions; one of them describes the energy distribution of ions in a beam and the second represents the implantation profile of monoenergetic ion beam.

A novel method improving low separation performance for W/O/W ELM permeation of erythromycin

The permeation of erythromycin, macrolide antibiotics, into a W/O emulsion globule was simulated with the multi-layer liquid membrane model and the formation of the unfavorable concentration profile in an emulsion globule, this would cause the low separation performance. It was, therefore, proposed that to control the formation of the concentration profile, the feed phase and emulsion should be contacted as the dispersed and continuous phases, respectively, in a spray column contactor. A series of permeation experiments were conducted by both batch and continuous operations with a spray column (height: 0.5 m, i.d.: 0.027 m). In the cases of batch permeation runs, erythromycin permeated through the membrane phase and was concentrated in the stripping phase. By the new contacting method, the improvement in the separation performance was achieved, also the stability of the emulsion membrane improved, specifically mechanical entrainment. Finally, a theoretical evaluation of the permeations with respect to the dispersion in the column is discussed.

On the formation of concentration profiles by low-energy ion bombardment and sputter depth profiling

An analytical model is developed to describe the generation of concentration profiles in binary solids under low-energy ion bombardment. The model accounts, in particular, for preferential sputtering and radiation-enhanced particle transport in the solid, and is found to apply for a quantitative representation of steady-state concentration microprofiles in the near surface region of initially homogeneous binary targets as Fe-silicides. A model-based evaluation of such profiles delivers absolute values of the corresponding coefficients for radiation-enhanced diffusion. The numerical solution enables to trace the profile evolution in dependence of the bombarding time or ion fluence. When being applied to sputter depth profiling of a pre-existing concentration profile, a severe influence of the actual sputter yield ratio of the target components is found which may completely deteriorate the characteristics of the profile to be analyzed.