Rotating spherical electrode

Fig. 9. Types of rotating spherical electrodes reported in the literature, (a) Rotating micro-sphere electrode, (b, c) rotating hemisphere electodes (d) rotating ring-hemisphere electrodes (e) rotating dropping mercury electrode.

D.-T. Chin, "Convective Diffusion on a Rotating Spherical Electrode," Journal of The Electrochemical Society, 118 (1971) 1434-1438. 

CC, Capillary cell (stagnant diffusion) DS, diffusion to spherical electrode ICT. from mobility measurements (International Critical Tables) LFA. laminar-flow annular cell (Leveque relation) LM, from limiting mobility at infinite dilution POL. polarographic cell RDE, rotating-disk electrode. 

The DigiSim program probably represents the current state of the art which is achievable for simulating and analysing cyclic voltammograms. This package can perform cyclic voltanunetry for a wide range of mechanisms at planar, spherical, cylindrical or rotated disc electrodes. It also computes concentration profiles. 

Unfortunately, the to-electrode precipitation required for conventional (photo)electrochemical measurements on colloidal semiconductors necessarily perturbs the (assumed) spherical diffusion fields and surface adsorption equilibria that obtain at particles in the free solution state, phenomena which are instrumental in determining the dynamic and static charge transfer characteristics of the semiconductor. Consequently, there is a requirement for photoelectrochemical techniques capable of in situ, non-per-turbative investigations of the mechanistic details and catalytic properties of colloidal semiconductors in solution conditions typical of their intended ultimate application. Two such techniques are photoelectrophoresis and the Optical Rotating Disc Electrode (ORDE, developed by Albery et al.). As mentioned above, the former technique has already been reviewed by this author elsewhere [47]. Thus, the remainder of this review will concentrate on measurements that can be made with the latter... 

In cases where the mass transport conditions reach a steady state, e.g. with a microelectrode where spherical diffusion dominates (Section 11.2.4) or with a rotating disc electrode where hydrodynamic convection controls the diffusion layer thickness (Section 11.2.5), the current-voltage curve takes the form of a sigmoidal wave (Figure 11.7). The voltammogram is described by equation (11.2.49) when the kinetics are reversible. If however the... 

In electrochemistry, spherical and hemispherical electrodes have been commonly used in the laboratory investigations. The spherical geometry has the advantage that in the absence of mass transfer effect, its primary and secondary current distributions are uniform. However, the limiting current distribution on a rotating sphere is not uniform. The limiting current density is highest at the pole, and decreases with... 

Rotating Electrode Atomization (REP, PREP) -20 Standard deviation 1.3-1.5 Armco Fe, Cu, Al, Zn, Co-Cr, Ti, Zr, Ni alloys. Low carbon steels SlO2 1-10 -0.04 Spherical, very smooth, ultraclcan particles, Relatively high EE High cost, Low capacity and volume, D Relatively Coarse particles I... 

REP, a rod of metal or alloy, referred to as a consumable electrode, is rotated at high speed about its longitudinal axis. Simultaneously, it is melted gradually at one of its ends by a heat source, such as an arc, a plasma, or an electron beam, etc. A thin film of the molten metal is detached from the rod end and ejected from the periphery of the rod by centrifugal force, forming spherical droplets. The atomization is conducted in an inert atmosphere, usually argon. Helium may be used to increase arc stability and convective cooling efficiency of droplets. 

For many mechanisms, the steady-state Eia or N tt value is a function of just one or two dimensionless parameters. If simulations are used to generate the working curve (or surface) to a sufficiently high resolution, the experimental response may be interpolated for intermediate values without the need for further simulation. A free data analysis service has been set up (Alden and Compton, 1998) via the World-Wide-Web (htttp //physchem.ox.ac.uk 8000/wwwda/) based on this method. As new simulations are developed (e.g. for wall jet electrodes), the appropriate working surfaces are simulated and added to the system. It currently supports spherical, microdisc, rotating disc, channel and channel microband electrodes at which E, EC, EC2, ECE, EC2E, DISP 1, DISP 2 and EC processes may be analysed. 

For t values very close to to (zone Ila), where the nucleation process becomes very important, a linear relationship (/ — iof = at + b was found. At the same time, the formation of small hemispherical crystallites whose radius increases with t until the electrode is covered completely was observed by scanning electron microscopy (SEM) [148]. The fact that the current is proportional to t indicates that nucleation is progressive and that crystallite formation is kinetically controlled by planar or spherical diffusion [166]. When a rotating electrode was used, a sharp decrease in the current was observed in zone lib while no significant change of i occurred in zone Ila, a result which proves that nucleation is controlled by the spherical diffusion of the monomer. 

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