Electrical potential effects

Figure 3.24. Electrical potential effects of various electrolytes (from Taylor and Ashroft, 1972, with permission).

On dissociation of a salt, ions start to diffuse in a solution. Without an electric potential effect, however, the diffusion of a single salt is treated as molecular diffusion. For dilute solutions of a salt, the Nemst-Haskell equation is used to estimate the dilfusivity coefficient... 

Abstract The combination of surface plasmon resonance (SPR) and electrochemical methods has become a powerful technique for simultaneous observation of optical and electrochemical properties at substrate/electrolyte interfaces. The fundamental aspects of the electric potential effects on surface plasmons are introduced and the use and applications of this combined electrochemical and optical technique are discussed. Electrochemical-Surface Plasmon Resonance (ESPR) has several advantages, such as spatial resolution, which is particularly attractive for studying heterogeneous reactions optical properties of reactive species that may assist identification action mechanisms, and high surface sensitivity for studying surface binding of the reaction species. The electrochemistry-SPR spectroscopy technique has also been used for many applications, including bio-analytical systems that will be further described in more detail. 

Here, is the local fluid velocity in the pore and Gc is a factor by which the solute velocity is reduced from the fluid velocity (Anderson and Quinn, 1974). One can also average this flux expression over the whole pore cross section in the manner of expression (3.1.112g). The quantity Gc is called the convective hindrance factor a pore-average value of this may be developed as in expression (3.1.112i). The treatment provided assumes that there are no solute-pore wall interactions via adsorption or electrical potential effects. 

The measurement of mass using a quartz crystal microbalance is based on the piezoelectric effect.When a piezoelectric material, such as a quartz crystal, experiences a mechanical stress, it generates an electrical potential whose magnitude is proportional to the applied stress. Gonversely, when an alternating electrical field is... 

Bombardment of a liquid surface by a beam of fast atoms (or fast ions) causes continuous desorption of ions that are characteristic of the liquid. Where the liquid is a solution of a sample substance dissolved in a solvent of low volatility (often referred to as a matrix), both positive and negative ions characteristic of the solvent and the sample itself leave the surface. The choice of whether to examine the positive or the negative ions is effected simply by the sign of an electrical potential applied to an extraction plate held above the surface being bombarded. Usually, few fragment ions are observed, and a sample of mass M in a solvent of mass S will give mostly [M + H] (or [M - H] ) and [S -I- H]+ (or [S - H] ) ions. Therefore, the technique is particularly good for measurement of relative molecular mass. 

Note that Equation 25.1 shows that the field (F) has no effect along the direction of the central (z) axis of the quadmpole assembly, so, to make ions move in this direction, they must first be accelerated through a small electric potential (typically 5 V) between the ion source and the assembly. Because of the oscillatory nature of the field (F Figure 25.3), an ion trajectory as it moves through the quadmpole assembly is also oscillatory. 

Sodium and potassium ions are actively absorbed from the intestine. As a consequence of the electrical potential caused by transport of these ions, an equivalent quantity of Cf is absorbed. The resulting osmotic effect causes absorption of water (56). 

Fig. 1. General dialysis is a process by which dissolved solutes move through a membrane in response to a difference in concentration and in the absence of differences in pressure, temperature, and electrical potential. The rate of mass transport or solute flux, ( ), is directly proportional to the difference in concentration at the membrane surfaces (eq. 1). Boundary layer effects, the difference between local and wall concentrations, are important in most...

These three terms represent contributions to the flux from migration, diffusion, and convection, respectively. The bulk fluid velocity is determined from the equations of motion. Equation 25, with the convection term neglected, is frequently referred to as the Nemst-Planck equation. In systems containing charged species, ions experience a force from the electric field. This effect is called migration. The charge number of the ion is Eis Faraday s constant, is the ionic mobiUty, and O is the electric potential. The ionic mobiUty and the diffusion coefficient are related ... 

Binary Electrolyte Mixtures When electrolytes are added to a solvent, they dissociate to a certain degree. It would appear that the solution contains at least three components solvent, anions, and cations, if the solution is to remain neutral in charge at each point (assuming the absence of any applied electric potential field), the anions and cations diffuse effectively as a single component, as for molecular diffusion. The diffusion or the anionic and cationic species in the solvent can thus be treated as a binary mixture. 

The principle of the measurement is described with the help of Fig. 2-7 [50]. Potential measurement is not appropriate in pipelines due to defective connections or too distant connections and low accuracy. Measurements of potential difference are more effective. Figure 3-24 contains information on the details in the neighborhood of a local anode the positions of the cathodes and reference electrodes (Fig. 3-24a), a schematic representation of the potential variation (Fig. 3-24b), and the derived values (Fig. 3-24c). Figure 2-8 should be referred to in case of possible difficulties in interpreting the potential distribution and sign. The electrical potentials of the pipeline and the reference electrodes are designated by... 

Kelvin effect The electrical potential gradient caused by a temperature gradient along a conducting wire. Also known as the Thomson Effect. 

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