Slurry electrodes

A number of recent cell designs have used particulate electrodes. The early versions had slurry electrodes (Butler and Fawcett, 1964 Gerischer, 1963) but more recently the electrodes have been packed or... 

The air-oxidation of 1-phenylethanol to acetophenone in an aqueous alkaline solution has been chosen as a model reaction. The catalytic experiments were completed with the application of an in-situ electrochemical method for studying catalyst deactivation and the role of promoters. The potential of the catalyst, which was considered as a slurry electrode, was measured during the oxidation reaction. More details of the method can be found elsewhere 13,14). 

Boudenne, J. L. and Cerclier, O. (1999) Performance of carbon black-slurry electrodes for 4-chlorophenol oxidation. Water Res. 33,494-504. 

Boudenne, J. L., Cerclier, O., Galea, J. and Vlist, E. V. D. (1996) Electrochemical oxidation of aqueous phenol at a carbon black slurry electrode. Appl. Catal. A General 143, 185-202. 

Self-discharge 394 Sherwood number 134 Short crack 175, 183 Shuttle mechanism 391 Slurry electrode 350 Solvent molecular dynamics 14 Spin-orbit coupling 20 Stainless steel 127,128,140,142,154,160, 175, 185 188... 

In addition to the techniques that have already been mentioned, with which to investigate photocatalytic reactions, including laser flash photolysis and EPR, there are several others that can yield very useful information. These include the slurry electrode technique, the use of biased electrodes or photoelectrodes, the scanning electrochemical microscopic (SECM) technique, and the Langmuir-Blodgett (LB) film technique. These will be discussed briefly. 

Slurry Electrodes The slurry electrode technique enables one to carry... 

Duim, W. Aikawa, Y Bard, A. J. 1981. Semiconductor electrodes. XXXV. Slurry electrodes based on semiconductor powder suspensions. J. Electrochem. Soc., 128 222-224. 

Fig. 7. Fabrication process for MLC capacitors. Steps are (a) powder (b) slurry preparation (c) tape preparation (d) electroding (e) stacking (f) lamination (g) dicing (h) burnout and firing and (i) termination and lead attachment.

Two main operational variables that differentiate the flotation of finely dispersed coUoids and precipitates in water treatment from the flotation of minerals is the need for quiescent pulp conditions (low turbulence) and the need for very fine bubble sizes in the former. This is accompHshed by the use of electroflotation and dissolved air flotation instead of mechanically generated bubbles which is common in mineral flotation practice. Electroflotation is a technique where fine gas bubbles (hydrogen and oxygen) are generated in the pulp by the appHcation of electricity to electrodes. These very fine bubbles are more suited to the flotation of very fine particles encountered in water treatment. Its industrial usage is not widespread. Dissolved air flotation is similar to vacuum flotation. Air-saturated slurries are subjected to vacuum for the generation of bubbles. The process finds limited appHcation in water treatment and in paper pulp effluent purification. The need to mn it batchwise renders it less versatile. 

Electromagnetic flow meters ate avadable with various liner and electrode materials. Liner and electrode selection is governed by the corrosion characteristics of the Hquid. Eor corrosive chemicals, fluoropolymer or ceramic liners and noble metal electrodes are commonly used polyurethane or mbber and stainless steel electrodes are often used for abrasive slurries. Some fluids tend to form an insulating coating on the electrodes introducing errors or loss of signal. To overcome this problem, specially shaped electrodes are avadable that extend into the flow stream and tend to self-clean. In another approach, the electrodes are periodically vibrated at ultrasonic frequencies. 

Samples that contain suspended matter are among the most difficult types from which to obtain accurate pH readings because of the so-called suspension effect, ie, the suspended particles produce abnormal Hquid-junction potentials at the reference electrode (16). This effect is especially noticeable with soil slurries, pastes, and other types of colloidal suspensions. In the case of a slurry that separates into two layers, pH differences of several units may result, depending on the placement of the electrodes in the layers. Internal consistency is achieved by pH measurement using carefully prescribed measurement protocols, as has been used in the determination of soil pH (17). 

Alkalinity (Soluble Soda) Determination. The surface alkalinity or soluble or leachable soda is determined by making a fixed weight percent slurry in water and determining the alkalinity of the solution by pH measurement or acid titration. Sodium ion-sensitive electrodes have been investigated. 

Magnetic flow meters are sometimes utilized in corrosive Hquid streams or slurries where a low unrecoverable pressure drop and high rangeabiHty is required. The fluid is required to be electrically conductive. Magnetic flow meters, which use Faraday s law to measure the velocity of the electrically conductive Hquid, are relatively expensive. Their use is therefore reserved for special situations where less expensive meters are not appropriate. Installation recommendations usually specify an upstream straight mn of five pipe diameters, keeping the electrodes in continuous contact with the Hquid. 

Nickel—2iiic batteries containing a vibrating zinc anode lias been reported (83). In this system zinc oxide active material is added to the electrol 1 e as a slurry. During charge the anode substrates are vibrated and the zinc is electroplated onto the surface in a unifomi mamier. Tlie stationary positive electrodes (nickel) are encased in a thin, open plastic netting which constitutes the entire separator system. 

The slurries of electro-catalysts were prepared by mixing together the catalysts and appropriate amount of 5wt % Nafion solution(Du Pont) including some kinds of dispersant[8]. The electrodes were made by spraying method with these well mixed inks. Two electrodes and Nafion 112 membrane were hot pressed with the condition of 50kgf/cm, 120°C for 3min to fabricate MEAs(Membrane Electrode Assembly). 

Electrode Preparation. Glassy carbon (GC-20, Tokal Carbon, Ltd., Japan) was polished successively with 600 grit, 1.0, 0.3, and 0.05 pm alumina powder (Buehler Ltd., Chicago, IL) slurried with triple... 

Certain three-dimensional electrodes, also known as slurry or fluidized-bed electrodes, are sometimes used as well in order to have a strongly enhanced working surface area. Electrodes of this type consist of fine particles of the electrode material (metal, oxide, carbon, or other) kept in suspension in the electrolyte solution by intense mixing or gas bubbling. A certain potential difference is applied to the system between an inert feeder elecnode and an auxiliary electrode that are immersed into the suspension. By charge transfer, the particles of electrode material constantly hitting the feeder electrode acquire its potential (fully or at least in part), so that a desired electrochemical reaction may occur at their surface. In this reaction, the particles lose their charge but reacquire it in subsequent encounters with the feeder electrode. 

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