Saturation charges

According to Eq. (13.52), saturation charge is directly proportional to the square of the particle diameter and the external electric field. Particle charging depends also on the composition of the particle, which is taken into account by the relative dielectric constant e,. It is worth noticing that the field charging model should not be applied for small particles (dp < 0.5 pm). 

Huyghe, J.M. and Janssen, J.D. (1999) Thermo-chemo-electro-mechanical formulation of saturated charged porous solids, Transport in Porous Media 34, 129-141... 

For an electron number density of 1015 m 3 and a mobility of 0.022 (m2/V-s), calculate the time required to reach 99 percent of the saturation charge of an initially neutral particle by field charging. If the length of the charging chamber is 5 cm, what is the maximum particle velocity allowed to ensure 99 percent saturation charge ... 

Equation 12.18 can be rewritten in terms of the saturation charge na. Thus... 

The factor t0 can be considered to be a time constant which determines the rate or rapidity of charging the smaller the value of t0, the shorter the time it takes to approach saturation charge. Figure 12.7 shows a plot of Eq. 12.27 indicating that with sufficient time n/na reaches the asymptotic value of 1. 

One-half the final charge is reached at t = t0 and 91 percent at t = 10fo. Even though larger particles carry much higher saturation charges, the time constant is not size-dependent, and relative charg-... 

Ftgure 12.7 Plot of fractional saturation charge as a function of dimensionless time. Note that as t approaches infinity, nln. approaches 1. 

For cT spherical particles of diameter d per cubic centimeter carrying the saturation charge,... 

Consider the case where r > 1. The electrical drift velocity is given by Eq. 13.306. Denoting the particle velocity in an electric field as w and assuming a saturation charge, for field charging Eq. 13.306 becomes... 

Celsius temperature (°C) internal energy (J) transformed internal energy (J) volume (m ) molar volume (m mol ) work done on a system (J) fractional saturation charge number of ion j... 

The particle saturation charge 2 according to Cochet, is given by the following formula ... 

In practice, both field and diffusion charging occur simultaneously and are basically inseparable. It can be shown that all particles reach around 90% of their full saturation charge in less than 0.1 sec. Hence, for all practical conditions, it can be assumed that on entering the precipitation field, having a typical expo-sure/treatment time of 3-5 sec, the particles rapidly achieve their saturation charge. 

Assuming the fluid has no component acting toward the passive electrode and all particles achieve their saturation charge, the equation of motion of a charged spherical particle in an electric field is... 

Chierche et al. [110] were first to study copper underpotential deposition on poly crystalline palladium. They assigned different copper voltammetric peaks to the contributions of the different low Miller index crystallographic planes of palladium. They also proposed that copper underpotential deposition obeys a Temkin-type isotherm with a saturation charge density of 420 pC cm 2. The electrochemical response on polyfaceted palladium is observed in Figure 9.6. 

Motion in Electrostatic Fields. When particles larger than 1 jum pass through a corona discharge, they acquire charges from electrons and adsorbed gas ions proportional to the surface area of the particle. The saturation charge acquired is given by (7, 14, 15)... 

The parameter. 4 sat characterizes the saturation of the pore space with sediment, i.e., the fraction of the pore volume occupied by sediment in fully saturated charge beds. 

Polymer Comonomer Comonomer HOMO energy level Saturated charge carrier mobility (cm s ) ... 

The maximum charge buildup on the surface can be represented by the total saturation charge. 

The saturation charge decreases as the surface finish becomes rougher. High saturation chargine seems to be attributable to electrostatic forces. 

Slow charge fully saturated charge takes 14 to 16 hours Must be stored in charged condition to prevent sulfation Limited cycle life repeated deep cycling reduces battery life Flooded version requires watering Transportation restrictions on the flooded type Not environmentally friendly... 

Ultimately, the charge builds up to the point where no incoming field lines converge on the particle (Fig. 15.2c) and no ions can reach the particle. At this maxi-mum-charge condition, the particle is said to be at saturation charge. 

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