Parallel-plate electrode system

Two-stage precipitators consist of separate sections for particle charing and collection. Particle charging is realized with corona wires between grounded metal plates. The collection of particles rakes place in a system of parallel plate electrodes of opposite polarities. Two-stage precipitators are typically used in indoor air cleaning and light industrial applications. 

One of the key components in the system is the mass spectrometer. Fragments are ionized by a VUV laser pulse between a pair of plane parallel-plate electrodes (6 x 14 cm). One of the plane electrodes has a slit of 1 x 10 cm, which is covered by a metal mesh. The slit is parallel to the VUV laser beam and is the entrance of the mass spectrometer. Ions are accelerated by a pulsed electric field present between the plane parallel-plate electrodes, and then pass through the slit before they enter the mass spectrometer. 

X-ray diffraction conducted on the codeposited powder revealed that the deposit obtained from a suspension of gamma alumina, which had been partially converted to the alpha phase, contained both phases of alumina. Whereas, the powder codeposited from a suspension having a 50 50 mixture of alpha to gamma alumina powder, consisted only of the alpha phase. Using a parallel plate electrode configuration, Chen et al. [31] concluded that only alpha alumina can be codeposited. Chen also observed a difference in codeposition with copper when using two different phases of the titanium oxide particle system rutile readily codeposited but anatase titania did not... 

If both electrodes have to be made of materials, that are available only as foils or sheets or are not machinable, or for example, for materials, such as graphite felt, a cell design like the one in Fig. 9 is not realizable. Inlet and outlet systems have to be integrated in the electrolyte compartments. The parallel-plate and frame design of a laboratory flow-trough cell in Fig. 10 consists of easy-to-produce parts, using the fixing method for PTFE tubes in Fig. 4. 

To a first approximation, the BLM can be considered to behave like a parallel plate capacitor immersed in a conducting electrolyte solution. In reality, even such a thin insulator as the modified BLM (designated by and R, in Fig. 108) could block the specific adsorption of some species from solution and/or modify the electrochemical behavior of the system. Similarly, System C may turn out to be a semiconductor(l)-insulator-semiconductor(2) (SIS ) rather than a semiconductor(l)-semiconductor(2) (SS ) junction. The obtained data, however, did not allow for an unambiguous distinction between these two alternative junctions we have chosen the simpler of the two [652], The equivalent circuit describing the working (Ew), the reference (Eg), and the counter (Ec) electrodes the resistance (Rm) and the capacitance (C of the BLM the resistance (R ) and capacitance (Ch) of the Helmholtz electrical double layer surrounding the BLM as well as the resistance of the electrolyte solution (RSO ) is shown in Fig. 108a [652],... 

If we restrict our attention to one set of chemical precursors (SiH4, NH3, N2), we have available more detailed data describing the quality of PECVD silicon nitride thin films as a function of the several operating parameters.3 Experiments were carried out in a parallel-plate reactor placed in a horizontal hot tube system where the wafer was placed on the grounded electrode. 

The process of "characterizing" a reactor can be illustrated for a parallel-plate cold-wall reactor operated at 50 kHz.8 System power was kept at 500 W, pressure at 200 mTorr, and wafer temperature of 240°C. Wafers are placed on a circular electrode which is rotated to promote uniformity of deposition. Therefore, we are only interested in the radial variation of deposition rate. Reactive gases enter at the center and flow out at the periphery. 

Based on these fundamentals, many systems and apparatus have been built, being operative on an industrial scale. Different types of reactors have also been designed. The electrodes may be parallel plates [162, 163] or sacrificial Al pellets as anode [164,165]. The feeding of pressurized air has been implemented in many electrocoagulation-electroflotation systems [159,166-168]. Some plants have a press to remove water from the sludge [169,170] and a processing tank with a closed S-shaped one-way flow path [171]. 

Fig. 5.4 Electric field patterns in parallel-plate electrode systems (a) un-guarded, (b) guarded.

In the traditional parallel-plate cells, the Walker system is the most commonly used electrical arrangement (Fig. 13). In this system, the current flows from a copper busbar on one side of the cell to the anodes, and the cathodes are connected to another busbar on the opposing side of the cell. The second busbar feeds current to the anodes of the second cell, and so on. In the Walker system, only one side of each electrode is connected to the electric circuit. The intercell busbars do not require so much thickness as the end busbars as the current flows through the path of least resistance. 

Fig. 14.9 The sequential-parallel electroanalytical set-up showing the Faraday cage with the microtiter-plate compatible electrode system, relais board, personal computer, and potentiostat. The relais board and the electrode holder are magnified on the right.59 (Reproduced by permission of The Royal Society of Chemistry)...

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