Vacuum reactor

Ultra-High Vacuum Reactors. CVD reactions at extremely low pressures (i.e., 10 Torr) are being developed for the deposition of semiconductor materials, such as silicon-germanium and some optoelectronic materials. Advantages appear to be better control of the deposit structure and reduction of impurities. 

The new generation of vacuum reactors are linked with the docking systems via telescopic pipes to the silos. This allows automatic charging and discharging... 

Fig. 3 a Immobilization of DPE initiator precursor and activation by addition of -BuLi. Monomer is eventually added and results in polymerization, b Specially made high-vacuum reactor with filter for handling LASIP of nanoparticles. The scheme shows the A ampule containing styrene, B ampule containing -BuLi, C ampule containing MeOH [28,29]... 

Fig. 5.11. Vacuum reactor for chlorination of metals. A Reaction vessel (100 ml) B beryllia crucible containing titanium metal C silica cradle D crucible support also serving as evacuation duct, and finally sealed off at the top at E F capillary tube G duct for breaker H appendix containing liquid chlorine J fragile capillary tip K weighted glass breaker L glass-coated magnetic retainer.

Steps 2-4 were carried out in a vacuum reactor consecutively. Thus, the plasma reactor follows the cycle (1) pump down from ambient environment (2) O2 plasma (3) TMS plasma (4) HFE plasma (5) exposure to ambient air. The sequences of plasma processes are O2/TMS, TMS/HFE, and HFE/O2, or can be expressed -(02/TMS/HFE/)-. 

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 22.3 Relative position of basket and electrode in a vacuum reactor.

Rgure 9.1. Microwave lead-through insulator of porous glass for a vacuum reactor. The dielectric constant n can be made low by making a glass-air composite with closed porosity. Adapted with permission from the Journal of Materials Education. 

Problem 5.5. A vacuum reactor is used to synthesize WO3 nanoparticles for use in an electrochromic window device. To create the WO3 nanoparticles, a tungsten (W) metal filament 1.0 mm in diameter and 10 cm long is heated to 2200 °C in a vacuum with a trace pressure of oxygen gas. Assuming all of the W evaporating from the surface of the filament is rapidly and completely oxidized to WO3, determine the maximum rate of production of WO3 from this reactor (g/s). The equilibrium vapor pressure of W at 2200 °C is approximately 10 atm. 

In most pyrolysis systems, an inert gas such as helium or nitrogen is used to purge the air out of the system and promote a nonoxidant environment where pyrolysis takes place. The vacuum pyrolysis reactor is the only exception to this rule. As the name implies, the air is removed from the system by the use of vacuum rather than an inert gas. This requires the use of a vacuum pump after the system, which may complicate operation and make equipment more expensive. In principle, a variety of reactor configurations could be used for vacuum pyrolysis. The only characteristic that is common to any vacuum reactor is the absence of the requirement for inert gases, which can be considered an advantage. 

In a vacuum reactor, heat transfer becomes more difficult because of the absence of a medium for convection, however. As a consequence, this type of reactor is characterized by slower heating rates. Still, it is possible for the vacuum pump to remove organic volatiles rapidly. Typically, bio-oU yields in vacuum reactors stay in the range 60-65 wt.%. Despite its use on the lab scale, the vacuum pump requirements make the vacuum reactors very difficult to scale up. 

Chen X, Anthamatten M. Multicomponent vapor deposition polymerization of poly(methyl methacrylate) in an axisymmetric vacuum reactor. Polymer 2008 49 1823. 

Van der Voort et al. [261-263] prepared vanadium oxide species in the meso-porous material MCM-48 by reacting the support with gaseous vanadyl acetyla-cetonate [VO(acac)2]. The vapor deposition was carried out in a vacuum reactor (see Fig. 9). VO(acac)2 is sublimed and reacts with the heated substrate at 150°C until a saturation loading is achieved. This takes approximately 16 h, visible by the formation of crystals of the complex on colder parts of the reactor [261]. Subsequently, the sample is purged with dry nitrogen at reaction temperature and calcined in ambient air at 500 °C. The uncalcined zeolite-supported vanadium complex and the calcined catalyst were characterized by X-ray diffraction, nitrogen absorption, IR and UV-Vis spectroscopy. 

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