INDEX enamel

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. 

Uses. About 60% of the MA produced is used to make unsaturated polyester and aikyd resins, which are formed by reaction of MA with glycols. Polyester resins are used in the fabrication of glass fiber reinforced parts. Applications include boat hulls, automobile body parts, patio furniture, shower stalls, and pipe. Aikyd resins are mostly used in coatings (paint, varnish, lacquers, and enamels). MA also is widely used as a chemical intermediate in the manufacture of plasticizers and dibasic acids (fumaric, maleic, and succinic). About 15% of MA production goes into the manufacture of viscosity index improvers and dispersants used as additives in lube oils. Several agricultural chemicals are based on maleic anhydride, the best known being Malathion. 

This fluorspar contains 85-95% CaF2 and is used as a flux in the steel industry, production of enamel glass to control refractive index and obtain desired opacity. It is also used in coatings of welding rods. 

For ceramic use, the most important mineral containing fluorine is fluorite (CaF2) which occurs in fluorspar. Natural deposits have a purity of 90-98% with silica as the principal impurity. Fluorite mineral powders have angular surfaces which result from cleavage and conchoidal fracture of the mineral [14]. Fluorspar is used in many forms of optical glass of low index of refraction and in enamels. 

Cerium oxide has a high refractive index, and is an opacifying agent in enamel compositions [28] used as protective coatings on metals. 

Dr. H. Trendley Dean, US PHS Reported on his on observation of thousands of children in community with varying fluoride levels. His research established mottled enamel index, which measured the severity of the discoloring of the teeth enamel from fluoride. 

Fluoride is both incorporated into enamel crystals and also affects the enzymes involved in enamel formation (Sect. 16.2.2), causing mottled enamel, a severe example of enamel fluorosis. Enamel fluorosis is evident as specks or white flecks on the enamel surface (Fig. 16.2b). In 1941, the public water supply of Aurora (IL) contained 1.2 ppm of fluoride (F), but only 5% of teeth exhibited fluorosis, mostly premolars and second molars. A sensitive index of... 

Fig. 16.5 Relationship of DMFT and index of fluorosis to water fluoride content. The left y-axis indicates the number of decayed missing and filled teeth from caries (DMFT) and the right y-axis indicates the index of fluorosis, a measure of the deleterious effect of fluoride on the enamel surface (see text). The x-axis indicates the ppm fluoride found naturally in the drinking water supply. Triangles indicate DMFT and circles indicate the fluorosis index in the same populations. The curves showing the decrease in caries and decrease in fluorosis intersect at 1 ppm fluoride in the water supply on the x-axis (Copy of Fig. 3 from Hodge HC, Smith FA. (1954). Some public health aspects of water fluoridation. American Association of the Advancement of Science Publication No 19 Washington DC 1954 AAAS 1954, pp. 79-109)...

The fluoride ion can replace the hydroxide ion in a crystal without significantly altering its structure, an isomorphous ion replacement. Fluoride also affects the enzymes involved in enamel formation, causing mottled enamel, a severe example of enamel fluorosis. White opaque patches on the normally translucent enamel indicate mild fluorosis. Fluorosis is measured on a grade of 0-5 where 1 through 3 indicate an increased cover of opaque white patches on the tooth surface, and 4 and 5 indicate an increased mottling. The two worst affected teeth make up an individual s score. The community s index of fluoridation is the mean score for all individuals. As the natural or artificial fluoride concentration of the water supply increases to 1 ppm, the mean number of cavities in 10-12 year-old children decreases from 7 to 3. Above 1 ppm fluoride, caries does not decrease much more, but the index of fluorosis increases markedly. This is the reason why public water supplies are fluoridated to only 1 ppm and not more or less. 

The suitability of an enameled wire for a particular application depends to a very large extent on the thermal class to which it belongs. Classification of a wire according to the usual IEC standards is carried out primarily on the basis of its temperature index, breakdown voltage at nominal temperature, and the heat shock characteristics of the insulation. The IEC specifications are internationally binding. In many countries the national standards are completely IEC-harmo-nized. 

Solderable wires are used in telecommunications and the construction of analytical instruments, but they are becoming more and more common in small motors and dry-type transformers. The special characteristic of solderable wire enamels is the direct soldering. When the enameled wire is dipped in a solder bath at temperatures above 350 °C the coating melts and leaves the bare copper wire, avoiding the need for elaborate mechanical or chemical removal of the enamel. This characteristic achieved in solderable poly(ester-imide) by a special polymer composition and in polyurethane based wire enamels is due to the thermally reversible splitting of the polyurethane group. Nevertheless, good thermal stability is necessary and product temperature indexes >155 are required. For temperature indexes of 130, simply polyurethane wire enamels were used. 

Long-term behavior of insulation systems can be estimated after the temperature index has been determined by the impregnated twisted pair test (IEC 172, criterion breakdown voltage) or helical coil test (IEC 1033, Method B, criterion bond strength). The two tests lead to differing results that do not correlate and the end user of the system enameled wire/impregnating resin has to decide which test is applicable for his electrical appliance. It is important to choose a suitable combination of materials and to ensure close cooperation between manufacturers of electrical insulating materials and those who later process them. 

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