Silica soot

Fresh air filters are an important part of the ventilation system and contribute to the health ot, crop. Their function is to screen out atmospheric dust particles like smoke, silica, soot and decay biological matter. Atmospheric dust also contains spores, bacteria and plant pollen, some of which, are detrimental to mushroom culture. Furthermore, spores and microorganisms originating within" f the cropping room can also be spread by air movement. To counteract this clanger, some mush- ... 

Figure 8.16 Comparison of the sintering data for silica soot preform sintered in air with the predictions of Scherer s model. (Prom Ref. 23.)...

Sakaguchi S., Behavior of closed pores formed in consolidation process for silica soot precursor. J. Non-Cryst. Solids 1995 189 43-49... 

The gas phase within the flame becomes supersaturated with respect to solid SiOj, which precipitates as molten droplets of transparent soot, approximately 10 nm in diameter. These droplets are subsequently expelled from the flame. (If the expelled soot is given sufficient room to cool to the solid state, it can be collected as a fine white powder, called fumed silica, such as is sold under the trade name Cab-O-SU .) In the Type III silica processes, the silica soot is deposited on a hot (greater than 1600°C) surface where it continuously consolidates to produce a homogeneous boule. 

Heraeus, Shin-Etsu, and Nippon Silica Glass employ variations of this process called vapor axial deposition (VAD), whereby the silica soot is deposited on the end of a continuously withdrawing rotating mandrel and is consohdated to full density in a separately heated zone of the processing apparatus. This process is illustrated in Fig. 6.7. 

Dispersion processing (aqueous or nonaqueous). Precursor fumed silica/silica soot dispersed in polymerizing gels or potassium sihcate aqueous solutions colloidal silica for dispersion can be prepared from aerosols as soot or fumed silica by flame hydrolysis, or other suitable methods. Examples of fumed silica are Cab-O-Sil (Cabot (7orp.) and Aerosil OX-50 (Degussa Corp.). Process pore sizes 100 to 3(X) nm. 

Similar gels were prepared by Rabinovich et al. [40,41] using Cab-O-Sil , another flame-generated silica soot, in aqueous suspension. The small... 

Immiscible wetting in mixers Sol-gel processes Pellet flocculation <0.3 Low Up to 10 ton/hr Wet processing based on flocculation properties of particulate feed Coal fines, soot and oil removal from water Metal dicarhide, silica hydrogels Waste sludges and slurries... 

Carbon soot from resistive heating of a carbon rod in a partial helium atmosphere (0.3bar) under specified conditions is extracted with boiling C H or toluene, filtered and the red-brown soln evapd to give crystalline material in 14% yield which is mainly a mixture of fullerenes C q and C70. Chromatographic filtration of the crude mixture with allows no separation of components, but some separation was observed on silica gel... 

There are four principal processes that may be used to manufacture the glass body that is drawn into today s optical fiber. "Outside" processes—outside vapor-phase oxidation and vertical axial deposition— produce layered deposits, of doped silica by varying the concentration of SiCl4 and dopants passing through a torch. The resulting "soot" of doped silica is deposited and partially sintered to form a porous silica boule. Next, the boule is sintered to a pore-free glass rod of exquisite purity and transparency. 

Photolysis half-lives on different atmospheric particulate substrates (approx. 25 (xg/g on substrate) t,2 = 7.0 h on silica gel, t,/2 = 22 h on alumina and t,/2 = 29 h on fly ash (Behymer Hites 1985) first order daytime photodegradation rate constants for adsorption on wood soot particles in an outdoor Teflon chamber k = 0.0077 min-1 with 1000-2000 ng/mg loading and k = 0.0116 min-1 with 30-350 ng/mg loading (Kamens et al. 1988) ... 

Silica and Unimin Corporation. Alternatives to the natural quartz powder, including fumed silica, flame-hydrolyzed soot, and sol—gel-derived powder, have also been tried as feedstock for these processes (11). 

Application of a plasma coating onto carbon black is very difficult compared to silica. It was only practically feasible for fullerene soot (left over from the fullerene production), which contains a large amount of reactive groups on its surface. Polyacetylene-plasma-treated fullerene soot provides an improved dispersion in SBR and in a SBR/EPDM blend compared to untreated fullerene black. However, the effect on the stress-strain properties is rather limited and the coating has only a slight effect on the final properties. 

Blanks can also be made using Vapor Axial Deposition (VAD) (Fig. 21). The process involves simultaneous flame deposition of both core- and cladding-glass soots onto the end (ie, axially) of a rotating fused-silica target rod. The finished perform is then consolidated in a process similar to the OVD process. 

EXHAUST FLOW. The exhaust flow system has perhaps the least stringent requirements of all the parts of the FID. Yet even here a variety of possible problems have been uncovered. It is necessary not only to get the gases out of the detector, but also the heat generated, and in the case of large samples or heavy column loadings, soot and silica. The soot is a problem if particles of it occasionally fall back into the flame,giving spikes. The bleed from a silicon-coated column burns to silica which can... 

---