Zinc coaling

Apparenlly Gl seems la be the best metal as a grounding electrode. But if part ol the zinc coaling of the metal is chipped due to poor coaling or to any other reason, the metal is rendered prone to rapid corrosion and erosion and may fail sviih passage of time. Some users therefore prefer to use bare MS conductor rather llian Gl. 

Porter, F. C. and Walden, G. K., Inspection of sprayed zinc coalings, 2nd Conf. Institute of Welding Spraying and Plastic Coating Div. London, Reprint/ZDA, London (1967)... 

Sprayed zinc coalings Details of the method and the nature of the coatings are given in Section 12.4. In this method there is no alloy formation and the bond is primarily mechanical. Although porous, the coating is protective partly due to its sacrificial action and partly due to the zinc corrosion products which soon block up the pores, stifling further attack. 

Technical Notes on Zinc. Separate leaflets entitled Zinc Coalings, Galvanising, Zinc Spraying, Sherardising, Zinc Plating and Zinc Dust are available from Zinc E>evelopment Association, London... 

P. antarctica in Antarctic waters. These factors include growth limitation/co-limitation by other resources, such as zinc (Coale et al. 2003) or vitamin B12 (Bertrand et al. in press) luxury uptake of iron integrated effects of prior changes in availability of iron and/or light physiological... 

Goodwin, T. J., Isaac, J. S., and Parsons, T. (1991). Exterior corrosion tests for the automotive industry. 3rd Int. Zinc Coaled Steel Sheet Conf., EGGA, London, S3C/1-15. 

Lamberigts, M., Leroy, V., and Goodwin, F. E. (1991). Corrosion resistance and ductility Extent and origins of the advantage of Galfan over classical galvanizing. 3rd Ira. Zinc Coaled Sheet Conf., E(jGA/ATEG, Paper SlD/7-13. 

Chromates and dichromates are used in industry as oxidising agents, for example in the coal tar industry, in the leather industry (chrome taiming), and in the dye industry as mordants. Some chromates are used as pigments, for example those of zinc and lead. Chromates and dichromates are poisonous. 

Pure pyridine may be prepared from technical coal-tar pyridine in the following manner. The technical pyridine is first dried over solid sodium hydroxide, distilled through an efficient fractionating column, and the fraction, b.p. 114 116° collected. Four hundred ml. of the redistilled p)rridine are added to a reagent prepared by dissolving 340 g. of anhydrous zinc chloride in a mixture of 210 ml. of concentrated hydrochloric acid and 1 litre of absolute ethyl alcohol. A crystalline precipitate of an addition compound (probable composition 2C5H5N,ZnCl2,HCl ) separates and some heat is evolved. When cold, this is collected by suction filtration and washed with a little absolute ethyl alcohol. The yield is about 680 g. It is recrystaUised from absolute ethyl alcohol to a constant m.p. (151-8°). The base is liberated by the addition of excess of concentrated... 

The principal ores of zinc are sphalerite (sulfide), smithsonite (carbonate), calamine (silicate), and franklinite (zine, manganese, iron oxide). One method of zinc extraction involves roasting its ores to form the oxide and reducing the oxide with coal or carbon, with subsequent distillation of the metal. 

The element is commercially obtained from the dusts of smelters processing zinc ores, as well as recovered from combustion by-products of certain coals. A large reserve of the elements for future uses in insured in coal sources. 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

Flotation or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

In the United States there was Httie interest in solvent processing of coals. A method to reduce the sulfur content of coal extracts by beating with sodium hydroxide and zinc oxide was, however, patented in 1940 (116). In the 1960s the technical feasibiHty of a coal deashing process was studied (117),... 

Medicated Dandruff Shampoos. Dandmff is a scalp condition characterized by the production of excessive cellular material (18). A number of shampoos have been marketed which are designed to control and alleviate this condition, and many additives have been included in shampoo compositions to classify them as treatment products for dandmff. These additives include antimicrobial additives, eg, quaternary ammonium salts keratolytic agents, eg, saUcychc acid and sulfur heavy metals, eg, cadmium sulfide coal tar resorcinol and many others. More recent (ca 1993) systems use selenium sulfide [7488-56-4] or zinc pyrithione [13463-41 -7] as active antidandmff shampoo additives. Both of these additives are classified as dmgs, but can be found in over-the-counter products. A stronger version, incorporating the use of higher levels of selenium sulfide in a shampoo, is available but requires a prescription for purchase. 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

Alkyl Isoquinolines. Coal tar contains small amounts of l-methylisoquinoline [1721-93-3] 3-methylisoquinoline [1125-80-0] and 1,3-dimetliylisoquinoline [1721-94-4J. The 1- and 3-methyl groups are more reactive than others in the isoquinoline nucleus and readily oxidize with selenium dioxide to form the corresponding isoquinoline aldehydes (174). These compounds can also be obtained by the hydrolysis of the dihalomethyl group. The 1- and 3-methyhsoquinolines condense with benzaldehyde in the presence of zinc chloride or acetic anhydride to produce 1- and 3-styryhsoquinolines. Radicals formed by decarboxylation of carboxyUc acids react to produce 1-aIkyhsoquinolines. 

Zinc, like most metals, is found in all natural waters and soils as well as the atmosphere and is an important trace element in plant and animal life (see Mineral nutrients). Rocks of various kinds contain 20—200 ppm zinc and normal soils 10—30 ppm (average ca 50 ppm) in uncontaminated areas. The average zinc content of coal is 33 ppm. Seawater contains 1—27 )-lg/L (median ca 8 p.g/L), and uncontaminated freshwater usually <10 / g/L. 

The level of natural versus man-made emissions to the environment are of a similar magnitude. SoH erosion is the major contributor of natural emissions with zinc mining, zinc production facHities, iron and steel production, corrosion of galvanized stmctures, coal and fuel combustion, waste disposal and incineration, and the use of zinc fertilizers and pesticides being the principal anthropogenic contributors. 

The zinc is normally melted in a gas, oU, or coal-fired reverberatory furnace with a capacity up to 100 tons or in a low frequency induction furnace with a capacity of a few tons. The more highly aUoyed compositions are more effectively melted and mixed in low frequency induction furnaces. The furnace must be refractory-lined to eliminate iron pickup by the molten metal. The metal temperature is maintained below 500°C to minimize loss by oxidation. A ladle is used to transfer the metal for casting into molds the pouring temperature is usuaUy ca 440°C. Zinc scrap is not generaUy suitable for remelting because it may contain undesirable impurities. 

The traveling-grate furnace requires less labor, increases the output per unit of grate area, and produces more uniform product than the WetheriU. furnaces. The traveling grate is an endless chain of cast-iron bars, driven by sprockets, which traverses a firebrick chamber. Anthracite briquettes are fed to a depth of ca 15 cm. After ignition by the previous charge, the coal briquettes are covered by 15—16.5 cm of ore/coal briquettes. The latter are dried with waste heat from the furnace. Zinc vapor evolves and bums in a combustion chamber and the spent clinker faUs into containers for removal (24,25). 

Zinc—bromine storage batteries (qv) are under development as load-leveling devices in electric utilities (64). Photovoltaic batteries have been made of selenium or boron doped with bromine. Graphite fibers and certain polymers can be made electrically conductive by being doped with bromine. Bromine is used in quartz—haUde light bulbs. Bromine is used to etch aluminum, copper, and semi-conductors. Bromine and its salts are known to recover gold and other precious metals from their ores. Bromine can be used to desulfurize fine coal (see Coal conversion processes). Table 5 shows estimates of the primary uses of bromine. 

The U.S. Department of Energy has funded a research program to develop the Hquid-phase methanol process (LPMEOH) (33). This process utilizes a catalyst such as copper—zinc oxide suspended in a hydrocarbon oil. The Hquid phase is used as a heat-transfer medium and allows the reaction to be conducted at higher conversions than conventional reactor designs. In addition, the use of the LPMEOH process allows the use of a coal-derived, CO-rich synthesis gas. Typical reactor conditions for this process are 3.5—6.3 MPa (35—60 atm) and 473—563 K (see Methanol). 

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