CFC material

Table 2. Effect of neutron irradiation on some graphite or CFC materials studied for fusion applications [12]...

Next generation machines will impose inereasingly greater thermal loads on their PFCs. High thermal conductivity CFC materials may offer a solution to the high-heat loads, but further research is needed to overeome the problems noted above and to assure the place of earbon materials in future fusion power reaetors. 

The development of low erosion doped graphites has reached a point where chemical erosion at elevated temperatures can be suppressed. The important parameter appears to be the atomic distribution of metal carbide dopants. The future development must go in the direction of the production of doped bulk CFC materials. 

Even though the CFC materials will be around for a number of years in recycled form, there are a number of non-CFC-containing solvent systems that are being used or are under consideration as alternatives to CFC cleaners. One desirable aspect of using CFC solvents is their non-corrosive nature. Many of the proposed replacements for the CFCs are much more aggressive. An interim replacement for the CFCs could be the HCFCs, which have a lower ozone depletion factor, but these will also be phased out in the near future. Information on CFC replacements can be obtained from the EPA s Ozone Information Hotline (see www.epa.gov). 

One of the chief uses of chloromethane is as a starting material from which sili cone polymers are made Dichloromethane is widely used as a paint stripper Trichloromethane was once used as an inhalation anesthetic but its toxicity caused it to be replaced by safer materials many years ago Tetrachloromethane is the starting mate rial for the preparation of several chlorofluorocarbons (CFCs) at one time widely used as refrigerant gases Most of the world s industrialized nations have agreed to phase out all uses of CFCs because these compounds have been implicated m atmospheric processes that degrade the Earth s ozone layer... 

Certain CFCs are used as raw materials to manufacture key fluorinated olefins to support polymer apphcations. Thermolysis of HCFC-22 affords tetrafluoroethylene and hexafluoropropylene [116-15 ] under separate processing conditions. Dechlorination of CFC-113 forms chlorotrifluoroethylene [79-38-9]. Vinyhdene fluoride [75-38-7] is produced by the thermal cracking of HCFC-142b. 

Another area of potential interest is in refrigerator liners. The move away from the ozone-layer-damaging chlorofluorocarbons (CFCs) to HCFCs in the USA and pentane/cyclopentane blends in Europe has not been without problems. These newer materials have an adverse effect on ABS whereas the nitrile resin appears satisfactory, if more expensive. 

The use of CFCs such as fluorotrichloromethane became quite widespread, particularly as for many years the material was believed to cause few toxic and environmental problems. However, evidence that such materials were damaging the ozone layer became substantial and the use of such materials is to be discouraged and is illegal in many countries. To some extent CFCs have been substituted by methylene chloride (also illegal in some countries) and other fluoro compounds, but these too may prove to be environmentally unacceptable. For this reason there has been increased dependence on the use of the isocyanate-water reaction to generate sufficient carbon dioxide to give products of the required density. 

An algorithm has been developed to predict the thermal conductivity degradation for a high thermal conductivity composite ( 555 W/m-K at room temperature) as a function of radiation dose and temperature [33]. The absence of irradiation data on CFCs of this type required the use of data from intermediate thermal conductivity materials as well as pyrolitic graphite to derive an empirical radiation damage term [14, 17, 19, 25, 26]. 

Parts containing chlorofluorocarbons (CFCs) (refrigeration cycle in refrigerators/insula-tion materials)... 

The objectives sought to be achieved through disposal of refrigeration and air conditioning waste appliances are (a) separate disposal of the CFCs from the circulation system and the insulating material (b) further stripping of hazardous substances (e.g., mercury switches) and (c) recovery of ferrous metals, the priority in metal recycling. 

The halogenated hydrocarbons known as chlorofluorocarbons are a second class of materials that comprise water-repellent coatings. In particular, the substance known as l,l,2-trichloro-l,2,2-trifluoroethane or CFC-113 (Fig. 7.5.2) is... 

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