SUBJECTS enamels

Among nonmetallic materials, glass, chemical stoneware, enameled steel, acid-proof brick, carbon, graphite, and wood are resistant to iodine and its solutions under suitable conditions, but carbon and graphite may be subject to attack. Polytetrafluoroethylene withstands Hquid iodine and its vapor up to 200°C although it discolors. Cloth fabrics made of Saran, a vinyHdene chloride polymer, have lasted for several years when used in the filtration of iodine recovered from oil-weU brines (64). 

Coal-tar pitch for other uses is similarly subject to a few national specifications but mainly sold to users specifications. Pitch intended for roofing, dampproofing, and waterproofing is the subject of ASTM specification D450 and Federal specification R-P-381 hot-appHed tar-based coatings (pipeline enamels) are the subject of BSS 4164/1987, amended in 1988, and, in the United States, of American Water Works Association (AWWA) specification C203. 

The tables given under this subject are reprinted by permission from the Smithsonian Tables. For more detadea data on thermal expansion, see International Critical Tables tabular index, vol. 3, p. 1 abrasives, vol. 2, p. 87 alloys, vol. 2, p. 463 building stones, vol. 2, p. 54 carbons, vol. 2, p. 303 elements, vol. 1, p. 102 enamels, vol. 2, p. 115 glass, vol. 

To fulfil the above requirements the material inputs for the motor, such as stampings, steel, enamelled copper wire, insulations and varnishes, bearings, enclosure materials and hardware must be subjected to a series of acceptance tests according to norms and standard specifications. For example, enamelled copper wire used... 

Protective measures range from chemical conversion coatings and anodising to the application of more substantial protective layers, e.g. enamels. For a more detailed treatment of the subject, the reader is advised to consult References 19, 20, 21 and 22. 

Internal At one time open-weave hessian cloth was very largely used as an internal reinforcement material, but experience showed that this is subject to rotting in the soil. Even when the material appears to be covered with enamel, some of the fibres must protrude, and thus moisture is absorbed so that after a period of years the hessian is generally found to be in a waterlogged condition and forming food for bacteria. 

In general, moderate and severe fluorosis is rare. However, mild fluorosis has been detected at significant levels, for example, in 26% of subjects in one recent study [93]. However, the mildness of the fluorosis detected is associated with only very slight changes in the appearance of the teeth, which suggests that, even at these levels, it is not a major public health problem. Nonetheless, it is appropriate to ensure that parents or guardians of children continue to receive sound advice on safe levels of fluoride for those in their care to be exposed to and, since the cariostatic effect of fluoride is known to occur well after enamel formation during tooth development, treatment to reduce caries should concentrate on those measures that carry the lowest possible risks of fluorosis [91]. 

Among the apatite substituents, carbonate has been the subject of many studies. The apatite present in dental enamel is not a pure HA, but rather a corbonate apatite with a carbonate content of 2—3 %. There is still a controversy about the location of the carbonate in enamel, dentine and bone. While most recent studies agree that carbonate appears to be substituting within the lattice rather than existing in an amorphous phase, there is still some disagreement as to the actual position of the carbonate. The presence and location of the carbonate in dental enamel may relate directly to the risk of carious attack. Carbonate has been shown to be leaked preferentially from early carious lesions81. ... 

Suet and lard form the body of pomades and that the quality of these latter maybe unexceptionable, the fat material must be perfectly flush, inodorous, and pure. The rendered suet being almost always more or loss deficient in those respects, it must, therefore, be subjected to a purifying process, in order to fit it for use in perfumery. This is done by melting the fat by the heat of a saline ot steam bath, in an enamelled iron vessel, and adding to it, gradually, powdered alum and chloride of sodium, in the proportion of one ounce of the former, and two ounces of the latter, to every fifty pounds of fat undsr treatment. 

The nature of mineral phases present in bone, dentin, enamel and other phosphatic tissues, and their mode of formation have been subjects of lively discussions among health scientists and crystallographers. Bioscientists most commonly accept the viewpoint that the inorganic phase of bones or teeth is principally hydroxyapatite, Caio(P04)6(OH)2, and deviation in Ca/P ratio from common hydroxyapatite (Ca/P = 1.667) observed in mineralized tissues is explained by the presence of amorphous phosphates. In contrast, many crystallographers favor the idea of carbonate apatite, i.e. dahllite, as the major crystalline phase in biophosphates and they doubt the existence of amorphous phases. The topic has been reviewed14,15,22,28, 37,44,47,348-358) no common consent has yet been reached. In the following an attempt is made to at least coordinate the controversial findings. 

Molybdenum salts used as catalysts include cobalt molybdate for hydrogen treatment of petroleum stocks for desulfurization, and phospho-molybdates to promote oxidation. Compounds used for dyes are sodium, potassium, and ammonium molybdates. With basic dyes, phosphomolyb-dic acid is employed. The pigment known as molybdenum orange is a mixed crystal of lead chromate and lead molybdate. Sodium molybdate, or molybdic oxide, is added to fertilizers as a beneficial trace element. Zinc and calcium molybdate serve as inhibitory pigments in protective coatings arid paint for metals subjected to a corrosive atmosphere. Compounds used to produce better adherence of enamels are molybdenum trioxide and ammonium, sodium, calcium, barium, and lead molybdates. 

Asphalt mastic is a heavy duty system that is shop-applied in thicknesses up to 1 in. (25.4 mm). Although asphalt mastics perform well, they are very costly. Their use is usually limited to river crossing and swamp areas. Coal-tar enamel has more than 50 y of successful performance underground, but it is subject to cracking when the temperature is below 20° F (-7°C), and there are environmental constraints. The EPA has shut down applicators in the middle of production because of air pollution. These problems rule out asphalt mastic and coal-tar enamel as feasible materials for most pipelines. In addition, coal-tar enamels are often ruled out because of long-term deterioration. Asphalt enamel is generally considered inferior to coal-tar enamel therefore, its use is limited. Polyvinyl chloride tape is becoming obsolete because of the superior performance of polyethylene tape. 

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