Reactor design, plasma reactors

Wang, D., Namihira, T., Fujiya, K. et al. (2004) The reactor design for diesel exhaust control using a magnetic pulse compressor, IEEE Trans. Plasma Sci. 32, 2038 14. 

A significant disadvantage of the bell jar configuration is that the monomer flow is not constrained to pass totally through the plasma formed between the electrodes. To overcome this problem, the electrodes can be mounted in a rectangular flow channel. By adding channel sections before and after the plasma zone, it is further possible to establish a well-developed flow profile for the gas as it enters the plasma zone. This reactor design is particularly well suited for studies of film deposition kinetics. 

For the surface modification of silica and carbon black, a radiofrequency (13.56 MHz) electrode-less tumbler plasma reactor at the University of Cincinnati was used. The schematic reactor design is shown in Fig. 5. It consists of a Pyrex cylinder chamber of 40 cm in length and 20 cm in diameter, with a motor-driven shaft at its center, and two vanes running in opposite directions. The reactor is based on a horizontal mixing principle and is capable of treating 350 g per batch. The powdery materials to be coated are placed at the bottom of the chamber. The plasma... 

Like CVD units, plasma etching and deposition systems are simply chemical reactors. Therefore, flow rates and flow patterns of reactant vapors, along with substrate or film temperature, must be precisely controlled to achieve uniform etching and deposition. The prediction of etch and deposition rates and uniformity require a detailed understanding of thermodynamics, kinetics, fluid flow, and mass-transport phenomena for the appropriate reactions and reactor designs. 

Like the literature of plasma-assisted etching, the literature on the PECVD of specific materials is considerable. Because film properties are ultimately determined by chemical reaction mechanisms, reactor design, and film structure (Figure 5), the determination of the exact relationships between properties and processing is difficult. At present, the fundamental understanding of such relationships is limited, and thus, empirical efforts have been the norm. In this chapter, the more widely studied film materials deposited by PECVD will be briefly discussed. More extensive information on these and other films can be found in a number of review articles (9-14, 32, 50, 200-203) and references therein. 

This lack of fundamental understanding of the science and engineering of plasma processing is reminiscent of the situation in the catalytic field a few decades ago. With the proper research efforts in surface- and gas-phase chemistry, engineering, and reactor design, most of the current problems can be overcome, and the ultimate capabilities of plasma processing can be realized. 

Most reliable are the data on neutron fluxes which are determined by the plasma power density, reactor geometry and structural parameters. Most of the conceptual power reactor design studies contain a detailed neutronics analysis giving the energy as well as the spatial distribution of neutron fluxes. 

The substance was found to consist exclusively of silver nanopartides (for partide size distribution see Figure 10.12). Silica nanopartides were frequently found in the product. We attribute this to sputter effects of the glass reactor walls. These sputter effects can easily be reduced by a more sophisticated design of the plasma reactor. 

Classification by Phase Despite the generic classification by operating mode, reactors are designed to accommodate the reactant phases and provide optimal conditions for reaction. Reactants may be fluid(s) or solid(s), and as such, several reactor types have been developed. Singlephase reactors are typically gas- (or plasma- ) or liquid-phase reactors. Two-phase reactors may be gas-liquid, liquid-liquid, gas-solid, or liquid-solid reactors. Multiphase reactors typically have more than two phases present. The most common type of multiphase reactor is a gas-liquid-solid reactor however, liquid-liquid-solid reactors are also used. The classification by phases will be used to develop the contents of this section. 

There are numerous modifications which can be made to the basic reactor design. The initial dissociation of the silane gas can be by ultraviolet (UV) light illumination (photo-CVD), which either excites the silane directly, or by energy transfer from mercury vapour introduced into the chamber. Photo-CVD reactors eliminate the electric discharge and prevent the bombardment of the growing film by ions from the plasma, which may be a source of defects. A different way of reducing bombardment is to separate the plasma from the growing... 

This chapter discusses four methods of gas phase ceramic powder synthesis by flames, fiunaces, lasers, and plasmas. In each case, the reaction thermodynamics and kinetics are similar, but the reactor design is different. To account for the particle size distribution produced in a gas phase synthesis reactor, the population balance must account for nudeation, atomistic growth (also called vapor condensation) and particle—particle segregation. These gas phase reactors are real life examples of idealized plug flow reactors that are modeled by the dispersion model for plve flow. To obtain narrow size distribution ceramic powders by gas phase synthesis, dispersion must be minimized because it leads to a broadening of the particle size distribution. Finally the gas must be quickly quenched or cooled to freeze the ceramic particles, which are often liquid at the reaction temperature, and thus prevent further aggregation. 

Plasma-enhanced (PECVD) or plasma-assisted (PACVD) CVD, (see chapters in Refs. 5,14, and 15), constitute a smaller category of CVD processes that also involves a variety of reactor designs. In these systems, a plasma is... 

The inclusion of particles in a film of plasma polymer was once considered by some investigators to be a characteristic problem due to the plasma polymerization mechanism, which hampers the practical use of plasma polymers in some applications. In contrast to this view, the formation of powder or the inclusion of particles in a film is related to the polymer deposition part of polymerization-deposition mechanisms. The inclusion or elimination of particles, therefore, could be accomplished by selection of the proper operational parameters and reactor design. The data of Tiepins and Sakaoku [7] are a typical demonstration that powders can be formed nearly exclusively if all conditions are selected to favor powder formation. An important point is that the monomers used in their study were those commonly used by other investigators for the study of film formation by plasma polymerization in other words, no special monomer is needed to form powders exclusively. 

The plasma deposition step when the anode assembly was removed in flow system is designated by the process code Tfs. In the plasma deposition in a closed reactor system, the reactor chamber was first pumped down to less than 1 mtorr. The reactor chamber was then isolated from the pumping system by closing the main valve located in between. TMS gas, controlled by an MKS mass flow meter (model 247C), was then fed into the reactor. After the system pressure reached a preset point, TMS gas feeding was stopped and DC power was applied to initiate the glow... 

There are several types of microwave plasma CVD (MPCVD) reactors designed by several organizations. The widely known reactors are presented in Section 3 ... 

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