Gases and Materials

Air is made up of a mixture of different gases and material from natural processes such as wind erosion, evaporation from the sea, earthquakes, and from human activity in the form of combustion products from processes and vehicles. 

In some cases periodic analysis of the seal fluid should he done to check for the accumulation of fouling materials, such as gels, which may he due to reaction of the seal fluid with process gases and materials. 

At, = log mean temperature difference between hot gases and material, °F... 

Table 5.6 Compatibility of Various Gases and Materials (continued f...

Depending on the type of gas and membrane material, the importance of these two variables, D and S, will vary. Both the diffusion and the solubility coefficients for the gas are temperature dependent, while pressure dependency is only observed for certain gases and materials. 

Carbon dioxide, COj. Sublimes — 78 5 C. A colourless gas at room temperature, occurs naturally and plays an important part in animal and plant respiration. Produced by the complete combustion of carbon-containing materials (industrially from flue gases and from synthesis gas used in ammonia production) and by heating metal carbonates or by... 

Gases and vapors of volatile liquids can be introduced directly into a plasma flame for elemental analysis or for isotope ratio measurements. Some elements can be examined by first converting them chemically into volatile forms, as with the formation of hydrides of arsenic and tellurium. It is important that not too much analyte pass into the flame, as the extra material introduced into the plasma can cause it to become unstable or even to go out altogether, thereby compromising accuracy or continuity of measurement. 

These effects of differential vapor pressures on isotope ratios are important for gases and liquids at near-ambient temperatures. As temperature rises, the differences for volatile materials become less and less. However, diffusion processes are also important, and these increase in importance as temperature rises, particularly in rocks and similar natural materials. Minerals can exchange oxygen with the atmosphere, or rocks can affect each other by diffusion of ions from one type into another and vice versa. Such changes can be used to interpret the temperatures to which rocks have been subjected during or after their formation. 

Gases and volatile materials can be swept into the center of an argon plasma flame, where they are fragmented into ions of their constituent elements. The m/z values of ions give important information for identification of the elemental composition of a sample, and precise measurement of ion abundances is used to provide accurate isotope ratios. 

Forum on Process Gases, FechWeekjEast, Semiconductor Equipment and Materials International, Cambridge, Mass., Sept. 29,1992. 

Uses. The chemical inertness, thermal stability, low toxicity, and nonflammability of PFCs coupled with their unusual physical properties suggest many useflil applications. However, the high cost of raw materials and manufacture has limited commercial production to a few, small-volume products. Carbon tetrafluoride and hexafluoroethane are used for plasma, ion-beam, or sputter etching of semiconductor devices (17) (see loN implantation). Hexafluoroethane and octafluoropropane have some applications as dielectric gases, and perfluorocyclobutane is used in minor amounts as a dielectric fluid. Perfluoro-1,3-dimethyl cyclohexane is used as an inert, immersion coolant for electronic equipment, and perfluoro-2-methyldecatin is used for... 

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