Internal electrode reactors

Internal electrode reactor with dc power supply... 

Internal electrode reactors have several names, e.g., flat bed, parallel plate, planar, diode, etc. However, this system is rarely used to develop the plasma polymerisation because it breaks the insulation between the electrodes due to polymerisation on the cathode by the dc glow discharge. 

The basketlike tumbler rotates in a vacuum reactor, into which the monomer is fed. Therefore, there are three basic volumes involved (1) the volume of the vacuum reactor, Vg, (2) the volume of basketlike tumbler, V2, and the volume of the internal electrode, F3, as depicted in Figure 22.3. Since F3 is a dead volume, the effective... 

Figure 14-2. Schematic representation of a glow-discharge reactor with internal electrodes...

In addition, the use of electrodless glow discharge will produce different results than those with internal electrodes. In the former case, rare gases such as He, Ar was introduced from one end of the tubular reactor and the plasma was sustained by a rf coil outside the reactor. Gaseous monomer was fed into the afterglow of a rare gas and polymer film deposited on the substrate placed downstream. Yasuda, et. al. (18) observed that the deposition rate in electrodeless discharge was independent of the power input and increased in proportional to the square of the monomer pressure. 

The effect of reactor type on the quality of polymer film deposited is important to know. Use of the plasma probe could detect differences, although these were not investigated systematically. Tg decreased about 2x10 K in an internal electrode type reactor (compared to the electrodeless one). The geometry and size was close to that used by Kobayashi et al. ( ). In the former case, it was found that Tg remained essentially unchanged when the probes were placed at the center of the two disk electrodes and scanned across the diameter. 

A typical system consists of a gas inlet, reactor vessel, vacuum pump, matching network and power source. Various reactors have been used in plasma processing. For EXT and low-frequency glow discharges, internal electrodes are necessary. As the frequency increases, electrodes may be placed outside the reactor vessel. 

Modelling plasma chemical systems is a complex task, because these system are far from thennodynamical equilibrium. A complete model includes the external electric circuit, the various physical volume and surface reactions, the space charges and the internal electric fields, the electron kinetics, the homogeneous chemical reactions in the plasma volume as well as the heterogeneous reactions at the walls or electrodes. These reactions are initiated primarily by the electrons. In most cases, plasma chemical reactors work with a flowing gas so that the flow conditions, laminar or turbulent, must be taken into account. As discussed before, the electron gas is not in thennodynamic equilibrium... 

R 22] Here, a very interesting solution for the heating of the catalytic converter is presented. The thin metal foil is connected to electrodes and used as a resistance heater. The actual supply circuit is not described but the basic principle of such an internal reactor heating can easily be derived by an approximate calculation to clarify the heating mechanism. If one assumes a well-insulated stainless-steel foil with a length of 50 m, a width of 100 mm, a thickness of 30 pm and a resistance of 0.12 Q mm2 nT1 connected to a car battery which delivers 12 V, one can directly calculate a heating performance of 72 W. This heat performance is balanced by the amount of heat necessary to heat the catalytic converter defined by the heat capacity ... 

Kodym, R., Bergmann, H. and Bouzek, K. (2006) Results of modelling electrodes and reactors for the direct electrochemical drinking water electrolysis. Proceedings 57th Annual Meeting of the International Society of Electrochemistry, 27 Aug. to 1 Sept., Edinburgh/UK, p. S5-P16. 

The CVD reactor consists of a vitreous silica tube of about 20 cm in diameter (8") and a height of 30.5 cm (1 ft). The filament was made from tantalum wire with 0.5 mm diameter and attached to water-cooled copper electrodes. Heat treatment in a methane atmosphere produces a thin layer of tantalum carbide that protects the sample from contamination with metallic tantalum. A gas-leaking unit allows the introduction of various gases and their mixtures into the reaction chamber under controlled pressure. Before introducing or changing the gas the unit s internal pressure was reduced by a mechanical pump to about 0.1 Pa. 

One way to impart specificity is to ensure that only the component of interest is allowed into the electrochemical cell. This may be achieved by the use of a membrane which will separate the Internal components of the cell (the electrolyte and electrodes) from its working environment. Another method, which has been used in the development of solid state sensors, is to incorporate a chemical reactor into the sensor [1]. In the... 

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