Tube electrode

One of the simplest flow systems is the tube electrode with the electrode set into the wall of a tube. The solution flows by under laminar conditions. 

As shown in Fig. 4, the normal parabolic velocity profile is established. The limiting current for this type of electrode is [8] 

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Fig. 1. Scheme of apparatus. 1—Discharge tube 2—flask with water 3—nozzle 4—reaction vessel 5—electrical furnace 6—stopcock valve 7—thermocouple 8—trap 9—manometer 10—slides 11—spectrograph slit 12—hydroxyl source 13—discharge tube electrodes 14—transformer 15—vessel of prefixed volume. 

A. Rotating ring—disc electrode. Wall-tube electrode. 

C. Double tube electrode. Double channel electrode. 

In the case of the wall-tube electrode, the electrode is smaller than the jet diameter. The original treatment was due to Frossling [47] who demonstrated that, close to the wall... 

Using these formulae, Albery and Bruckenstein have derived the limiting current at a wall-tube electrode [49]. 

Fig. 6. Wall tube electrode geometry—schematic streamlines. (From ref. 49.)...

Radicals are generated at a tubular electrode and are then transported by laminar flow into the ESR cavity which, as a downstream detector, is analogous to a second electrode. The theoretical response for the cases where the radicals are stable or decompose by first- or second-order kinetics has been derived and experimentally confirmed [126, 301, 302]. The flow-rate dependence is different for each of the three situations which provides a diagnostic for the type of kinetics. Further information may be obtained from galvanostatic transients which allow the elucidation of electrode and radical surface processes [303]. Very recently, an in situ channel tube electrode has been described for electrochemical ESR which also allows shorter-lived species to be observed and smaller surface coverages to be analysed [304—306]. 

A common type of oxygen sensor takes the form of an yttria stabilized zirconia (YSZ, see earlier) tube electroded on the inner and outer surfaces with a porous catalytic platinum electrode. The electrode allows rapid equilibrium to be established between the ambient, the electrode and the tube. Such a system is shown schematically in Fig. 4.36. 

Fig. 10.5(a). Transfer function, H, relating modulated current response to modulated flow rate for tube electrode (Reference [20]), rectangular electrode embedded in a wall (Reference [12]) and modulated RDE (amplitude only). The dimensionless modulation frequency see text) is the ratio of the time scale for diffusion across the concentration boundary layer to the timescale for modulation of the hydrodynamics. 

The fundamentals of the electrochemical response at electrodes operating in a regime of forced convection, hydrodynamic electrodes, and the information that can be obtained have been reviewed [23, 24]. Some of these electrodes are good candidates for direct introduction into flow systems, in particular tube/channel electrodes and impinging jet (wall-jet and wall-tube) electrodes. Particular practical advantages of these flow-past hydrodynamic electrodes are that there is no reagent depletion while the sample plug passes the electrodes, and there is no build-up of unwanted intermediates or products. Recent advances in instrumentation also mean... 

Hydrodynamic electrodes — are electrodes where a forced convection ensures a -> steady state -> mass transport to the electrode surface, and a -> finite diffusion (subentry of -> diffusion) regime applies. The most frequently used hydrodynamic electrodes are the -> rotating disk electrode, -> rotating ring disk electrode, -> wall-jet electrode, wall-tube electrode, channel electrode, etc. See also - flow-cells, -> hydrodynamic voltammetry, -> detectors. 

Suppose two electrodes are arranged so that the field strength between them is not constant. (This could be done, e.g., with a wire and tube electrode system or a point and plane system.) Then if the potential across the two electrodes is increased, a voltage will be reached where electrical breakdown of the gas occurs nearest either the wire... 

Stainlc ij Steel Stainless Steel 1 ube. (t leetrode Tube. (Electrode Grounded to Amplirier)... 

PLATE 7.1. An experimental gas discharge tube electrode. Tungsten wires sealed through Pyrex glass. 

Bulb inside a Bulb and Vacuum Vessels- Dewar Flasks and Tubes —Electrodes, . . , . ... 

Fig. 12. The ex-situ flow cell of Albery et al., based upon the tube electrode, and located upstream of the ESR cavity.

For a semi-annular tube electrode, the limiting current is given by the appropriate form of the Levich equation... 

Fig. 20. The in-situ semi-annular tube electrode of Albery and co-workers.

FIGURE 6-30 Unrolled view cf electrode configuration ofANL solid/gas capacitive flowmeter all dimensions in cm electrodes are on outside surface of a ceramic tube electrode gap is 0.23 cm guard strip width, 0.34 cm and all electrodes are 0.036-mm copper foil. 

H. Ma, L. Jin, and H. Yan, Studies on the Application of an Amperometric Gold Tube Electrode Flow Through Detector. II. The Determination of Micro Quantities of Cyanide in Surface Waters [in Chinese]. Huanjing Huaxue, 2 (1983) 58. 

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