Rotating disc

The limiting current, iL, of the rotating disc electrode is given by the Levich equation [1] 

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The rotating-disc is also well suited to tlie study of coupled chemical reactions [2, 4]. 

It is essential for the rotating-disc that the flow remain laminar and, hence, the upper rotational speed of the disc will depend on the Reynolds number and experimental design, which typically is 1000 s or 10,000 rpm. On the lower lunit, 10 s or 100 rpm must be applied in order for the thickness of tlie boundary layer to be comparable to that of the radius of the disc. 

T. Misek, Rotating Disc Extractors and Their Calculation, State Publishing House, technical Hterature, Prague, C2echoSlovakia, 1964. 

K. Liquid-liquid extraction in Rotating-disc contactor (RDC)... 

In the fixed-film reactor, the organisms grow on an inert surface that is maintained in the reactor. The inert surface can be gramJar material, proprietary plastic packing, rotating discs, wood slats, mass-transfer packing, or even a sponge-type material. The reacior can be flooded or have a mixed gas-hquid space (Fig. 25-52). The biomass level on the... 

Solvent Extraction - Solvent extraction uses solvents to dissolve and remove aromatics from lube oil feed stocks, improving viscosity, oxidation resistance, color, and gum formation. A number of different solvents are used, with the two most common being furfural and phenol. Typically, feed lube stocks are contacted with the solvent in a packed tower or rotating disc contactor. Each solvent has a different solvent-to-oil ratio and recycle ratio within the tower. 

Where momentum is transfeiTed by shearing stresses, in which the transfer is perpendicular to the direction of flow. This category includes the rotating disc and cone agitators. 

Spinning disc A rotating disc onto which a fine jet of water impinges, resulting in fine droplets that add moisture to the air supply. 

These valves are relatively inexpensive, quarter-turn valves. The seal is made by a rotating disc that remains in the flowstream subject to erosion while in the open position (Figure 15-4). Except in low-pressure service, they should not be used to provide a leak-tight seaL but they can be u.sed to throttle where a tight shut-off is not required. 

Craig, H. L., Rotating Disc Study of the Pitting of Aluminium in Alkaline Chloride Solutions , J. Electrochem. Soc., 113, 203c (1966)... 

Zembura has made specific use of the rotating disc for investigation of the effect of flow on corrosion reactions. This work has shown that it is possible to determine the type of control (activation or concentration polarisation) of zinc dissolving in 0.1 N Na2S04 (de-aerated), which followed closely the predicted increase in hydrogen ion reduction as the flow rate increased, and proved that in this example... 

Correlations Between Flow Rate In Rotating Discs,... 

The rotating disc and rotating cylinder have been successfully applied in the laboratory to study the effect of flow on corrosion rates and are much easier to use than actual pipelines and other real geometries. The results of these tests can now be correlated to geometries likely to be found in pipes, pumps, bends, etc. in plant by use of dimensionless group analysis. There-... 

Table 2.2 Correlation between rotating disc, rotating cylinder and smooth tubes...

Fig. 2.5 Corrosion rate of a copper rotating disc in air-saturated 0-1 n H2SO4 at various temperatures (after Zembura )...

Platinum has also had its share of attention in recent years. The effect of phosphoric acid concentration on the oxygen evolution reaction kinetics at a platinum electrode using 0-7 m-17-5 m phosphoric acid at 25°C has been studied with a rotating disc electrode . The characteristics of the ORR are very dependent on phosphoric acid concentration and H2O2 is formed as an intermediate reaction. Also, platinum dissolution in concentrated phosphoric acid at 176 and 196°C at potentials up to 0-9 (SHE) has been reported . 

Fig. 19.3 (a) Distribution of corrosion on surfaces of rotating disc specimens and b) assembly of specimens attached to rotating discs... 

The use ot rotating discs to carrv itsi spaiiiicns has been extended to studies rtf protective coatings in what are considered to be accelerated tests o( such coatings tor service underwater... 

Kassner used a rotating disc, for which the hydrodynamic conditions are well defined, to study the dissolution kinetics of Type 304 stainless steel in liquid Bi-Sn eutectic. He established a temperature and velocity dependence of the dissolution rate that was consistent with liquid diffusion control with a transition to reaction control at 860 C when the speed of the disc was increased. The rotating disc technique has also been used to investigate the corrosion stability of both alloy and stainless steels in molten iron sulphide and a copper/65% calcium melt at 1220 C . The dissolution rate of the steels tested was two orders of magnitude higher in the molten sulphide than in the metal melt. 

Fig. 8-3. Distribution of atomic (or molecular) velocities from ihe rotating disc.

Polythiophene electrogeneration on a rotating disc electrode. The water content influence on polymerization and on the polymeric properties. J. Electroanal Chem., 310, 219, 1991, Fig. 9. Copyright 1991. Reprinted with permission of Elsevier Science.)... 

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