Compensated resistance

The fact that either the peak-to-peak separation, AEp, somewhat departs from the value of 59 mV or the current function ipJvl/2 is not rigorously constant seems to contrast with the diagnostic criteria (illustrated in Chapter 2, Section 1.1.1) for an electrochemically reversible one-electron process. This can be largely attributed to the non-compensated resistance given by the dichloromethane solution, which is a low conducting solvent. 

The above treatment is easily extended to include the effect of a non-compensated resistance of value Rn. Replacing AE by AV — RnAjF, eqn. (47), with eqn. (48), becomes... 

For any given set of resistors, the potentiometer may be calibrated in ohms of compensated resistance through the relation... 

Figure 9.1 Equivalent circuit of an electrochemical cell. A, Auxiliary electrode R, reference electrode W, working electrode Rc, compensated resistance R , uncompensated resistance Rr, reference electrode impedance Zf, faradaic impedance Cdl, doublelayer capacitance.

The theory of the deflection potentiometer has been developed in detail by Brooks, and instruments of this type have been designed by Brooks and by White. A compensating resistance is mounted as an integral part of the dial so that turning the dial... 

Reactants must diffuse through the network of pores of a catalyst particle to reach the internal area, and the products must diffuse back. The optimum porosity of a catalyst particle is deterrnined by tradeoffs making the pores smaller increases the surface area and thereby increases the activity of the catalyst, but this gain is offset by the increased resistance to transport in the smaller pores increasing the pore volume to create larger pores for faster transport is compensated by a loss of physical strength. A simple quantitative development (46—48) follows for a first-order, isothermal, irreversible catalytic reaction in a spherical, porous catalyst particle. 

External-Cake Tubular Filters Several filter designs are available with vertical tubes supported by a filtrate-chamber tube sheet in a vertical cylindrical vessel (Fig. 18-115). The tubes may be made of wire cloth porous ceramic, carbon, plastic, or metal or closely wound wire. The tubes may have a filter cloth on the outside. Frequently a filter-aid precoat will be applied to the tubes. The prefilt slurry is fed near the bottom of the vertical vessel. The filtrate passes from the outside to the inside of the tubes and into a filtrate chamber at the top or the bottom of the vessel. The sohds form a cake on the outside ofthe tubes with the filter area actually increasing as the cake builds up, partially compensating for the increased flow resistance of the thicker cake. The filtration cycle continues until the differential pressure reaches a specified level, or until about 25 mm (1 in) of cake thickness is obtainea... 

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