Disk cathode

One important application of amperometry is in the construction of chemical sensors. One of the first amperometric sensors to be developed was for dissolved O2 in blood, which was developed in 1956 by L. C. Clark. The design of the amperometric sensor is shown in Figure 11.38 and is similar to potentiometric membrane electrodes. A gas-permeable membrane is stretched across the end of the sensor and is separated from the working and counter electrodes by a thin solution of KCl. The working electrode is a Pt disk cathode, and an Ag ring anode is the... 

Differential pulse voltammetry at rotated glassy carbon disk cathodes proved successful for the accurate determination of inor-... 

When the oxygen sensor is immersed in a flowing or stirred solution of the analyte, oxygen diffuses through the membrane into the thin layer of electrolyte immediately adjacent to the disk cathode, where it diffuses to the electrode and is immediately reduced to water. Two diffusion processes are involved—one through the membrane and the other through the solution between the membrane and the... 

When the oxygen sensor is immersed in a flowing or stirred solution of the analyte, oxygen diffuses through the membrane into the thin layer of electrolyte immediately adjacent to the disk cathode, where it diffuses to the electrode and is immediately reduced lo water. In contrast with a normal hydrodynamic electrode, two diffusion processes are involved — one through the membrane and the other through the solution between the membrane and the electrode surface. For a steady-state condition to be reached in a reasonable period (10 to 20 s), the thickness of the membrane and the electrolyte film must be 20 pm or less. Under these conditions, it is the rale of equilibration of the transfer of oxygen across the membrane that determines the steadv-stalc current that is reached. 

Figure 7.6 shows schematic and oversimplified electrowinning cells containing non-planar electrodes. Cylindrical and disk cathodes have been used for over... 

Other hydrodynamic cases for corrosion studies can be found elsewhere [10]. On the other hand, for a continuous metal removal from solution in electrowinning, rotating cylinders and disks are used as cathodes (Figme 7.6). The classical rotating-disk cathode is known as Weber s disk [25-26] having a diameter of 2a. The corresponding differential equation in cylindrical coordinates is free of the diffusivity and it is given by... 

Electrolytic cells consisting of rotating disk cathodes and various constructional types of anodes, as well as descriptions and illustrations of cells, which are especially suited for such procedures, are described in [508, 524, 581, 594] see also [562]. 

Fig. 4. Electrolyzer with rotating disk cathode. 1) Replaceable lead anodes 2) rotating cathode 3) axis of rotating cathode 4) pinion of cathode drive mechanism 5) mercury container 6) body of electrolyzer, 7) airtight cover.

A large-scale construction was undertaken in the development of a suitable electrolyzer for the production of tetraethyllead. Figure 4 shows diagrammatically one model for such an electrolyzer, provided with replaceable lead anodes and rotating amalgamated copper disk cathodes [57]. It was constructed and tested for a loading of 200 A. It is, however, very complicated. 

Phototypesetting represented an easier way to compose type. Eady phototypesetters used an optical process, whereby a disk of characters, ia different sizes and typefaces, was spun under computer control. Each character was projected ia turn onto photosensitive film or paper. This was followed by systems where characters drawn on a cathode ray tube (CRT) exposed the photosensitive material. In each case, the operator iateracted with the system at a video screen that only showed the characters of the text (the iaformation content) and codes that iadicated how the characters were to look on paper. An experienced operator was required to obtain high quaUty results. 

Fig. 2. Configuration for spirally wound rechargeable lithium ceU. A, Cap B, cathode tab C, insulating disk (2) D, mandrel E, can F, bak G, safety vent ...

The cathode of coin-type batteries consists of Mn02 with the addition of a conductive material and binder. The anode is a disk made of lithium metal, which is pressed onto the stainless steel anode can. The separator is nonwoven cloth made of polypropylene, which is places between the cathode and the anode. 

Hyodo, H., Yamamoto, T., and Toyoguchi, T., "Properties of Tetrahedral Amorphous Carbon Film by Filtered Cathodic Arc Deposition for Disk Overcoat, IEEE Trans. Magn., Vol. 37, 2001,pp. 1789-1791. 

In such systems the researcher can electrochemically clean and precondition the metal electrode before each run to provide an identical surface for the anodic and the cathodic half-reactions as well as for the catalytic reaction between them. Use of a rotating disk electrode/ckatalyst also allows surface- and diffusion-controlled processes to be easily distin-guished. ... 

Experiments by Freund and Spiro/ with the ferricyanide-iodide system showed that the additivity principle held within experimental error for both the catalytic rate and potential when the platinum disk had been anodically preconditioned, but not when it had been preconditioned cathodically. In the latter case the catalytic rate was ca 25% less than the value predicted from adding the current-potential curves of reactions (15) and (16). This difference in behavior was traced to the fact that iodide ions chemisorb only on reduced platinum surfaces. Small amounts of adsorbed iodide were found to decrease the currents of cathodic Fe(CN)6 voltam-mograms over a wide potential range. The presence of the iodine couple (16) therefore affected the electrochemical behavior of the hexacyanofer-rate (II, III) couple (15). 

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