Current, electrical diffusion

Charge number of an ion Conductivity Diffusion rate constant Electric current Electric current density Electric mobility Electrode potential Electrolytic conductivity Electromotive force (emf) Elementary charge Faraday constant Half-wave potential Ionic strength... 

Hammett acidity function enthalpy change, J solvation enthalpy change, J electric current, A ionic strength, mol kg mol dm anodic current, A cathodic current, A diffusion current, A... 

The bipolar junction transistor (BIT) consists of tliree layers doped n-p-n or p-n-p tliat constitute tire emitter, base and collector, respectively. This stmcture can be considered as two back-to-back p-n junctions. Under nonnal operation, tire emitter-base junction is forward biased to inject minority carriers into tire base region. For example, tire n type emitter injects electrons into a p type base. The electrons in tire base, now minority carriers, diffuse tlirough tire base layer. The base-collector junction is reverse biased and its electric field sweeps tire carriers diffusing tlirough tlie base into tlie collector. The BIT operates by transport of minority carriers, but botli electrons and holes contribute to tlie overall current. 

The procedure of Mason and Evans has the electrical analog shown in Figure 2.2, where voltages correspond to pressure gradients and currents to fluxes. As the argument stands there is no real justification for this procedure indeed, it seems improbable that the two mechanisms for diffusive momentum transfer will combine additively, without any interactive modification of their separate values. It is equally difficult to see why the effect of viscous velocity gradients can be accounted for simply by adding... 

The resulting overall energy balance for the plant at nominal load conditions is shown in Table 3. The primary combustor operates at 760 kPa (7.5 atm) pressure the equivalence ratio is 0.9 the heat loss is about 3.5%. The channel operates in the subsonic mode, in a peak magnetic field of 6 T. AH critical electrical and gas dynamic operating parameters of the channel are within prescribed constraints the magnetic field and electrical loading are tailored to limit the maximum axial electrical field to 2 kV/m, the transverse current density to 0.9 A/cm , and the Hall parameter to 4. The diffuser pressure recovery factor is 0.6. 

Metalliding. MetaUiding, a General Electric Company process (9), is a high temperature electrolytic technique in which an anode and a cathode are suspended in a molten fluoride salt bath. As a direct current is passed from the anode to the cathode, the anode material diffuses into the surface of the cathode, which produces a uniform, pore-free alloy rather than the typical plate usually associated with electrolytic processes. The process is called metalliding because it encompasses the interaction, mostly in the soHd state, of many metals and metalloids ranging from beryUium to uranium. It is operated at 500—1200°C in an inert atmosphere and a metal vessel the coulombic yields are usually quantitative, and processing times are short controUed... 

The individual membrane filtration processes are defined chiefly by pore size although there is some overlap. The smallest membrane pore size is used in reverse osmosis (0.0005—0.002 microns), followed by nanofiltration (0.001—0.01 microns), ultrafHtration (0.002—0.1 microns), and microfiltration (0.1—1.0 microns). Electro dialysis uses electric current to transport ionic species across a membrane. Micro- and ultrafHtration rely on pore size for material separation, reverse osmosis on pore size and diffusion, and electro dialysis on diffusion. Separation efficiency does not reach 100% for any of these membrane processes. For example, when used to desalinate—soften water for industrial processes, the concentrated salt stream (reject) from reverse osmosis can be 20% of the total flow. These concentrated, yet stiH dilute streams, may require additional treatment or special disposal methods. 

Commercially available membranes are usually reinforced with woven, synthetic fabrics to improve the mechanical properties. Several hundred thousand square meters of IX membranes are now produced aimuaHy, and the mechanical and electrochemical properties are varied by the manufacturers to suit the proposed appHcations. The electrochemical properties of most importance for ED are (/) the electrical resistance per unit area of membrane (2) the ion transport number, related to current efficiency (2) the electrical water transport, related to process efficiency and (4) the back-diffusion, also related to process efficiency. 

In concentrated electrolytes the electric current appHed to a stack is limited by economic considerations, the higher the current I the greater the power consumption W in accordance with the equation W = P where is the electrical resistance of the stack. In relatively dilute electrolytes the electric current that can be appHed is limited by the abflity of ions to diffuse to the membranes. This is illustrated in Eigure 4 for the case of an AX membrane. When a direct current is passed, a fraction (t 0.85-0.95) is carried by anions passing out of the membrane—solution interface region and... 

Hence ia any given situation the maximum current density that can be carried by a combination of electrical conduction and diffusion occurs when c, the concentration ia the solutioa at the membrane surface, approaches 2ero, ie,... 

Dijfusion Dialy The propensity of and OH" to penetrate membranes is useful in diffusion dialysis. An anion-exchange membrane will block the passage of metal cations while passing hydrogen ions. This process uses special ion-exchange membranes, but does not employ an applied electric current. 

The amorphous orientation is considered a very important parameter of the microstructure of the fiber. It has a quantitative and qualitative effect on the fiber de-formability when mechanical forces are involved. It significantly influences the fatigue strength and sorptive properties (water, dyes), as well as transport phenomena inside the fiber (migration of electric charge carriers, diffusion of liquid). The importance of the amorphous phase makes its quantification essential. Indirect and direct methods currently are used for the quantitative assessment of the amorphous phase. 

---