Other Volatile Materials Produced Chemically

The chemical structure of a typical divalent metal acetylacetonate, for which the abbreviation would be M(acac)j. These compounds are internally bonded ionically and complexed to oxy en at the same time Thus, their intramolecular forces are very strong (they are stable), but their intermolecular forces are weak (they are volatile). 

Sample Inlets for Plasma Torches, Part A Gases 

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Many valuable chemicals can be recovered from the volatile fractions produced in coke ovens. Eor many years coal tar was the primary source for chemicals such as naphthalene [91-20-3] anthracene [120-12-7] and other aromatic and heterocycHc hydrocarbons. The routes to production of important coal-tar derivatives are shown in Eigure 1. Much of the production of these chemicals, especially tar bases such as the pyridines and picolines, is based on synthesis from petroleum feedstocks. Nevertheless, a number of important materials continue to be derived from coal tar. 

Exposure of Si02, Si3N4, or SiC to XeFiCgas) produces an adsorbed layer of fluorine . The xenon does not remain on the surface, but it is immediately desorbed into the gas phase. This is all that happens in the absence of electron bombardment. However, in the presence of electron bombardment, SiF4(gas) and other volatile products are produced . Since the reaction products are removed from the surface, the reaction proceeds until all the material is volatilized. This is illustrated for the case of SiOj in Fig. 32. Similar data has been obtained for SijN4 which reacts faster and for SiC which reacts slower. These are examples of a class of chemical reactions which require both active species (in this case fluorine) and energetic radiation (in this case electrons). 

Chemically reacting a volatile compound of a material to be deposited, with other gases, to produce a nonvolatile solid or... 

Activated carbons comprise elementary microcrystallites stacked in random orientation and are made by the thermal decomposition of various carbonaceous materials followed by an activation process. Raw materials include hard and soft woods, rice hulls, refinery residuals, peat, lignin, coals, coal tars, pitches, carbon black and nutshells, such as coconut. There are two types of manufacturing process, involving gas activation or chemical activation. The gas activation process first involves heating in the absence of air at 400-5(X)°C to drive off volatile materials and to form small pores. Activation is then carried out with, for example, steam at between 800 and 1000 C. Other gases such as carbon dioxide or flue gases can be used instead. Chemical activation (Keller et al. 1987) can be carried out using, for example, zinc chloride or phosphoric acid to produce an activated carbon... 

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