Electron-beam system, compound

Figure 42. Diagram of a compound shape electron beam system...

The Massachusetts Institute of Technology (MIT) has developed the tunable hybrid plasma (THP) system for the treatment of volatile organic compounds (VOCs) in gaseous waste streams. The reactor uses an electron beam to generate a plasma. The electron density of the plasma can be adjusted. This allows for the chemical reaction rates to be controlled as well as the intensity... 

This reaction is based on a stoichiometric reaction of multifunctional olefins (enes) with thiols. The addition reaction can be initiated thermally, pho-tochemically, and by electron beam and radical or ionic mechanism. Thiyl radicals can be generated by the reaction of an excited carbonyl compound (usually in its triplet state) with a thiol or via radicals, such as benzoyl radicals from a type I photoinitiator, reacting with the thiol. The thiyl radicals add to olefins, and this is the basis of the polymerization process. The addition of a dithiol to a diolefin yields linear polymer, higher-functionality thiols and alkenes form cross-linked systems. 

The process produces no air emissions. Because this is an aqueous-based technology, neither NO, nor SO is produced. The delivery system is closed so no volatilization of toxic organic compounds occurs. The electron beam can be used efficiently and effectively as pretreatment for biological remediation. The electron beam can break complex organic compounds, making them suitable for microbiological degradation. 

Reactions of organic compounds with the electron-beam-induced reactive species are very rapid, and occur in less than a second. This allows the design of a flow-through system with good process flexibility at full scale... 

Surfaces with oil or grease contamination should be cleaned by an organic solvent such as methanol or acetone in an ultrasonic cleaner. It is also important to avoid touching the cleaned specimen with bare hands because fingerprints contain volatile hydrocarbon compounds. Sometimes a dark mark occurs on a well-cleaned specimen. This might result from hydrocarbon contamination from a dirty vacuum system. Hydrocarbons escaping from the diffusion pump oil into the SEM chamber can also contaminate a specimen under electron beam. 

Zinc, calcium and magnesium oxides, silica gel, and other compounds are used as solid additives in radiation-induced polymerization carried out by a cationic mechanism. Recently, Crivello shown that very useful for electron-beam induced cationic polymerization are onium salts, which presence in the systems allow to achieve high conversion of monomers at very low doses [5, 6],... 

The polymerization of all these systems can be divided into initiation, propagation, and termination steps. The initiation step involves generation of a reactive species (free radical or acid). During irradiation with UV light, the reactive species are formed by chemical decomposition of a photoinitiator. In electron-beam (EB) curing, reactive species (radicals) are generated by interaction of accelerated electrons with organic compounds. 

The analysis of C levels in electron beam instruments is notoriously difficult due to the formation of adventitious C on sample surfaces under the influence of the electron beam. This will occur even on samples that have been fractured in ultra-high voltage (UHV), where C from hydrocarbon compounds in the vacuum system or from the sample itself will form on surfaces that, under UHV conditions, have become extremely reactive. Fisher et a/. developed a methodology that enables the measurement of C segregation using AES. It involves ... 

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