Spraying with zinc

Gartner, F. W., Corrosion Protection of Iron and Steel by Thermal Spraying with Zinc and Aluminium . Proc. 8th Int. Thermal Spray. Conf, American Welding Society, pp. 214-222 (1976)... 

A deficiency of zinc causes serious disease in apple and citrus trees and grape vines. Lack of zinc in the soil causes poor yields of cereals. In the 1930s, the uneconomic sparse scrub in the Ninety Mile Plain in South Australia was converted to lush grasslands by regular aerial spraying with zinc salts it now supports a large population of sheep. 

Within the family of zinc coatings (except zinc-rich paints), corrosion rates are similar at all exposed surfaces, and the choice of coating is usually made for other reasons (Fig. 1.7). For long-term exposure, the metal coating choice for fabricated work is normally between hot dip galvanizing and thermal spraying (with zinc, zinc-15% aluminum, or aluminum). Figures 2.30 and 2.31 show the choices in the British Standards Institution Code of Practice BS 5493 1977 as depicted by AM S Europe (1981). 

The Anglian Water Authority lock gates at Little Paxton were similarly grit-blasted and sprayed with zinc to 100 p.m plus a multicoat paint system. 

Metal fume fever is an old syndrome that is quite well known, not so much by doctors, but by those who are especially at risk of suffering from it, such as welders or other workers in metal trades (Blanc 1993). The most frequent and best documented cause of metal fume fever is that caused by heating zinc. Zinc fumes, which oxidize to fine particles of zinc oxide (ZnO), are produced, for instance, when zinc is smelted to make alloys, when zinc-containing scrap metal is molten, when metal surfaces are sprayed with zinc or when galvanized steel is welded or cut. Metal fume fever occurs when the fumes are not properly exhausted, which is often the case when these jobs are done in enclosed spaces. Both freshly formed zinc fumes and fine zinc oxide dust have the ability to cause metal fume fever. 

Because of its resistance to corrosion, zinc may be used to coat iron. This may be done by dipping the iron into molten zinc or by spraying zinc on the iron articles, for example iron sheets. This is known as galvanising. Smaller iron articles may be coated by heating with zinc dust, a process known as sherardising, or suspensions of zinc may be used in paints. 

The problem can be overcome by spraying the zinc vapour with lead as it leaves the top of the furnace. This chills and dissolves the zinc... 

Where the end use of the product is known, there is usually preference to use either zinc or aluminium, both technically and because of the works problems associated with use of an alloy (identification, separation of overspray). However, in some countries (such as the United States) where there has been a recent-surge in anti-corrosion uses of metal spraying, a zinc-15%-aluminium alloy wire has been widely used. The original commercial experience was with 65-35% alloys used in powder form. Both have many of the advantages of the parent metals. At one time, the zinc-5%-aluminium alloy was also of interest. These alloy coatings may prove particularly satisfactory for sprayed coatings on articles where service conditions are not known in advance. 

Protecting a surface from corrosion by coating can be accomplished by a number of well-established processes which include paints, metal plating (with zinc or cadmium), diffusion, thermal spraying, and, more recently, vapor deposition processes. Of these physical vapor deposition (PVD) is used extensively in corrosion protection. Typical applications are ... 

Averell and Norris (3) have developed an analytical method adapted to the determination of parathion in spray or dust residues, which is sensitive to about 20 micrograms. It is based upon the reduction of parathion with zinc to the amino compound, diazotiza-tion, and coupling with Bratton and Marshall s amine, which gives an intense magenta color with an absorption peak at 555 millimicrons. Bowen and Edwards (6) have used the polarograph to assay technical grades of parathion and its formulations. 

The deliberate poisoning of harmful birds leads to unexpected consequences. In three districts of the former GDR in 1964-65, com was sprayed with methyl parathion and grain with zinc phosphide to fight rooks. As was expected, a large number of birds died, but rooks made up only 3% of the total [32]. 

The pure compound is a pale yellow, nearly odourless oil, soluble in organic solvents, but almost insoluble in water. Averell and Norris2 describe the detection of minute quantities of parathion (20 /ig.) in spray and dust, by reduction with zinc, diazotization and coupling with an amine to give an intense magenta colour. It is effective (at concentrations of 25-600 p.p.m.) against many insect species, but of course, like the majority of organo-phosphorus insecticides, it is toxic to man and to animals. 

Salt spray tests, humidity tests, and other accelerated tests, some using sulfur dioxide and carbon dioxide, have shown favorable results for tin—zinc in comparison with zinc, cadmium, and tin deposits. Chromating improves the performance. 

Zinc—Cobalt. Alloys of Zn—Co usually contain 0.3—0.8% cobalt. Higher cobalt alloys, from 4—8%, have shown better salt spray resistance (156), but the commonly plated alloy is 0.3—0.8%. One automotive company specifies 0.3—1.0%. Cobalt is expensive, and economics favor the lower alloys. Costs have been quoted for zinc—cobalt at 1.2 times the cost of chloride zinc, with zinc—nickel alloys at 1.5—1.6 times the chloride zinc. Deposits can be very bright, but the improved corrosion resistance advantage requires yellow or bronze chromates. Alkaline baths give fewer problems in plating components with lapped, spot-welded seams. 

Zinc is frequently applied to the surface of iron or steel by other methods. In the Schoop process, molten zinc is sprayed onto the surface by a blast of air in a manner similar to that used in spraying paint. In addition to metals, objects made of wood, leather, paper, and the like may be coated with zinc by this process. In the process of sherardizing, iron is covered with a thin layer of zinc dust at temperatures of 700 to 800°C. Under these conditions, zinc penetrates the surface of the iron to a considerable extent. 

Uses Zineb is a light-colored powder or crystal. It is a polymer of ethylene (bis) thiocarbamate units linked with zinc. Zineb is used to prevent crop damage in the field and to protect harvested crops from deterioration during storage or transport. It was used to protect fruit and vegetable crops from a wide range of foliar and other diseases. It was available in the United States as wettable powder and dust formulations. Zineb can be formed by combining nabam and zinc sulfate in a spray tank.7121319... 

Atoms absorb light at wavelengths specific to each element and this property is used in the analytical technique of atomic absorption spectroscopy. For example, in the determination of zinc, when a solution containing zinc compounds is sprayed into a flame at about 1000 °C, zinc atoms are produced. These will absorb light at the specific wavelengths associated with zinc. 

Parzate [Du Pont]. TM for a series of fungicides. Parzate hquid is a solution containing 22% nabam to be combined with zinc sulfate in the spray tank. Parzate carbon is a wettable powder containing 75% zineb. Parzate D is a finely divided powder containing 85% zineb. 

The TLC solvent systems hexane and diethyl ether (8 2) or hexane and benzene (1 1) best separated chemicals on F254 silica gel TLC plates. The Series 2 compounds had the highest RfS, followed by the Series 1 compounds, and then the nitroethanes. The TLC plates were then sprayed with a solution made from zinc chloride and diphenylamine (1 1), dissolved in acetone. After the plates were sprayed, they were placed in a 125°C oven overnight. Generally, carbinols turned green, nitroethanes turned pink, Series 1 and Series 2 compounds turned purple. Color and Rf on the plate confirmed the identity of a product. 

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