Cylinder electrode

Robinson and Walsh have reviewed earlier cell designs. The performance of a 500 A pilot plant reactor for copper ion removal is described. Simplified expressions were derived for mass transport both in single pass [243] and batch recirculation [244]. For a detailed discussion of the principle and the role of the rotating cylinder electrode reactor in metal ion removal the reader is referred to Refs. [13] and [241] (46 references). 

A typical 5 kA Eco cell has a cathode drum with a radius of 0.37 m, a height of 0.74 m and a cathode-membrane gap of about 1 cm. The cathode is rotated at 100-200 rev.min-1. In rotating-cylinder electrode cells, high fractional conversion can be obtained by employing an Eco cascade cell. 

Walsh FC, The role of the rotating cylinder electrode reactor in metal ion removal in ref (23), p 101, and references therein... 

Robinson D, Walsh FC (1991) The performance of a 500 Amp rotating cylinder electrode reactor, Part 1. Current-potential data and single pass studies, Hydrometallurgy 26 93 Chem Abstr 114 (1991) 194767w... 

The following relationship (White, W4) gives the electric field for concentric-cylinder electrodes, as modified by the space-charge effect of the corona ions,... 

Both disk-shaped and cylinder electrodes can be fashioned with metal microwires and carbon fibers. Two practical considerations that must be kept in mind when working with small wires and fibers are their resistivity and their delicacy. The former consideration demands that only short sections of the microwire or fiber be used for electrode construction, while the latter mainly represents a significant source of frustration for the novice electrode maker. A 5-/ m-radius platinum wire at times seems to break just because you ve looked at it With a little practice, however, handling these small materials becomes straightforward. 

The equivalency found between the behavior of hemisphere and that of disk electrodes also exists between cylinder and band electrodes [29]. Diffusion to a cylinder electrode is linear and described by Equation 12.7, while diffusion to a band is nonlinear. A plane of symmetry passes through the center of the band and normal to its surface, so the nonlinear diffusion process can be broken down into two planar components, one in the direction parallel to the electrode surface, x, and the other in the direction perpendicular to the electrode surface, y. So Fick s second law for a band electrode is... 

Spatially resolved absorbance spectroelectrochemistry has been used to observe the concentration profile of an absorbing species generated at the surface of a cylinder electrode with a radius of 6 /xm. The observed concentration profiles agreed very closely with those predicted by solution of Equation 12.7 by digital simulation [32]. As with the disk electrode, simple analytical expressions for the current-time and current-voltage relationships of cylinders and bands do not exist. 

In the case of disc electrodes, a similar behavior to that observed for spherical ones is obtained (although in this case the diffusion layer thickness is an average magnitude), whereas for band or cylinder electrodes, the diffusion layer thickness is always potential dependent, and no constant limit is achieved, even for very small values of the electrode characteristic dimension, confirming the impossibility of these electrodes achieving a true stationary response [5, 8, 16, 29, 30]. 

Rotating cylinder electrode cell High High Small... 

Many electrode patterns have been used for cure studies. Kienle and Raceused parallel cylindrical conductors immersed in the medium. Coaxial cylinder electrodes, with the sample placed between the two cylinders, were first used by Fineman and Puddington 5,6), and later by Aukward, Warfield, and Petree 16). The coaxial electrodes, like the parallel plates, have a relatively simple calibration, but are tedious to construct reproducibly for each thermoset cure experiment. Generally, any electrode configuration can be used for observing trends, but electrode size and location must be reproducibly controlled if calibrated measurements are desired. 

The rotating cylinder electrode (Fig. 8) is operated in the turbulent flow regime at Re > 200, although flow can be complicated with vortexing until much higher Re, where tme turbulence develops (4). A Re number >200 is readily achieved at modest rotation rates and cylinder diameters. Therefore the cylinder can be... 

Figure 8 The rotating cylinder electrode, (a) Electrode specimen and mandrel shown as partially disassembled, (b) Typical laboratory setup for the RDE. (From Ref. 3.)...

A. Current and Potential Distributions for the Rotating Cylinder Electrode... 

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