Migration, electrical

Synge, RLM, Experiments on Electrical Migration of Peptides and Proteins Inside Porous Membranes Influences of Adsorption, Diffusion, and Pore Dimensions, Biochemical Journal 65, 266,1957. 

A portion of the solution was subjected to a qualitative electrical migration experiment using a three-component cell similar to that described by Hardwick and Robertson (79). The solution under investigation was placed in the center compartment, and in the outer compartments were placed sulfuric acid solutions of concentrations similar to that of the test solution. No diffusion occurred over a period of 24 hours. Application of about 50 volts d.c. across the electrodes caused migration of violet color to the cathode and no violet color to the anode. The results indicate a positively charged chromium species. 

What Is the Effect of Electrical Migration on the Limiting Diffusion Current Density ... 

In volume 1 (Chapters 4 and 5) a fairly detailed treatment of the movement and transport of ions was presented qualitative pictures and quantitative accounts were given of the diffusion and electrical migration of ions in the bulk of the electrolyte. In the treatment of electrodic processes, no mention was made at first of a connection between the transport in solution and processes at electrodes. It was then realized that this neglect of ion transport in solution (ionics) was tantamount to assuming that at no stage in the course of a charge-transfer reaction did the interfacial concentrations of electron acceptors and donors depart from their bulk values. 

The charge mobility of an ion represents the speed that acquires the ion per unit of electric field. The electric migration current corresponding to the ionic movement of a single kind of charge is equal to the flux of charge, i.e., to the rate at which the charge cross any plane normal to the flow (see Eq. 1.141) [56]... 

When neither an external fluid flow nor an electrical field is imposed, the diffuse double layer is at equilibrium and the net ion fluxes due to the electrical migration and Brownian diffusion should vanish. Thus, the ions have Boltzmann distributions,... 

Electrical migration method. An interesting electrical migration method for rapid separation of carrier-free radioisotopes has been reported (9 ) The apparatus consists of a stack of filter papers (30 filter papers were used) moistened with electrolyte and placed between two platinum electrodes. ... 

Carrier-Free Radioisotope Separation Accomplished by Electrical Migration in Filter Paper... 

Mass transport by diffusion can be regarded as the last resort. When movement of the electroactive species is not promoted by the input of external energy, either electrical (migration) or mechanical (convection), diffusion takes over. The driving force in this case is the... 

In coulometry the stoichiometry of the electrode process should be known and should proceed with 100% current efficiency, and the product of reaction at any other electrode must not interfere with the reaction at the electrode of interest. If there are intermediate reactions, they too must proceed with the desired accuracy. In practice the electrolytic cell is designed to include isolation chambers. Losses of solute through diffusion, through ionic or electrical migration, and simply through bulk transfer must be minimal. Finally, the end point has to be determined by one of the many techniques used in titrations generally, whether coulometric or not. Both indeterminate and determinate end-point errors limit the overall accuracy achieved. Cooper and Quayle critically examined errors in coulometry, and Lewis reviewed coulometric techniques. 

Therefore, in reverse time t the electric migrated field satisfies the ordinary vector diffusion equation. However, in direct time, t = —r, the migrated anomalous electric field satisfies the equation adjoint to (11.71) ... 

Movement of reactant molecules into the interfacial region by convection, diffusion, or electrical migration. 

Sample introduction To introduce the sample, the left end of the capillary is dipped into a sample vial with several centimeters hydrostatic pressure for a fixed number of seconds. This will force a small volume of liquid sample into the end of the capillary. Another method of sample introduction is to dip the end of the capillary into the sample vial and turn on the power for a few seconds. Sample ions thus flow into the system by electrical migration. 

When the governing model is given by the convection-diffusion equation (no electrical migration effects are considered), well-established numerical methods can be used directly in electrochemical cell design. When using commercial software, it should be remembered that the code has probably been benchmarked for applications different from those found in metallization, where spatial distributions of flux at high Schmidt numbers may be of more interest than the spatial average flux. Freitas has recently provided a comparison of several commercial CFD codes. Many of these codes are based on a finite-volume method (FVM) or a finite-element method. West jj yg discussed the application of... 

Deposition of copper at various fractions of the limiting current in the presence of either excess or a limited amount of sulfuric acid was studied. For the analysis of the latter conditions where electrical migration is... 

Figure 5, where V7= 0.99, shows results for an excess supporting electrolyte the results could be simulated with a standard convection-diffusion solver as well as the coupled-field solver outlined below. Discrepancies between experiment and simulation at the limiting current density are believed to be due to surface roughness. In contrast, Fig. 6, with V7= 0.3, shows results for a case where electrical migration is important and was treated in the manner described below. 

Overall flux = (advection) + (Fickian diffusion) t (electrical migration)... 

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