Protection from Oxidation

Ruhho, H., Radi, R., Ansehni, D., Kirk, M., Bames, S., Butler, J., Fiserich, J. P., and Freeman, B. A., 2000, Nitric oxide reaction with hpid peroxyl radicals spares alpha-tocopherol during hpid peroxidation. Greater oxidant protection from the pair nitric oxide/alpha-tocopherol than alpha-tocopherol/ascorbate, J. Biol. Chem. 275 10812-10818. 

Rubbo H, Radi R, Anselmi D, Kirk M, Barnes S, Butler J, Eiserich JP, Freeman BA (2000) Nitric oxide reaction with lipid peroxyl radicals spares a-tocopherol during lipid peroxidation. Greater oxidant protection from the pair nitric oxide/a-tocopherol than a-to-copherol/ascorbate. J Biol Chem 275 10812-10818... 

Weak base (neutral to phenolphthalein). forms water-soluble salts with strong acids pK 9.5. Difficultly so] in cold wa. ter, more easily in hot water. Miscible with alcohol, ether, carbon disulfide. Dissolves sulfur, phosphorus, arsenic tri-oxide. Protect from light and moisture. LDW orally in rats 460 mg /kg (Smyth). 

Storage Store 40-100 F away from strong oxidizers protect from freezing Alcosperse 747 [Aico]... 

Storage Do not store near extreme heat, strong oxidizers protect from freezing QEMI DF 8322 [QemI Int l.]... 

For gear trains Protection from seizing and rapid wear Extreme-pressure and anti-wear properties Resistance to oxidation Thermal stability High viscosity Low pour point Anti-foaming properties Anti-corrosion properties... 

Dry chlorine has a great affinity for absorbing moisture, and wet chlorine is extremely corrosive, attacking most common materials except HasteUoy C, titanium, and tantalum. These metals are protected from attack by the acids formed by chlorine hydrolysis because of surface oxide films on the metal. Tantalum is the preferred constmction material for service with wet and dry chlorine. Wet chlorine gas is handled under pressure using fiberglass-reinforced plastics. Rubber-lined steel is suitable for wet chlorine gas handling up to 100°C. At low pressures and low temperatures PVC, chlorinated PVC, and reinforced polyester resins are also used. Polytetrafluoroethylene (PTFE), poly(vinyhdene fluoride) (PVDE), and... 

Dowtherm LE is a mixture of diphenyl oxide and methylated biphenyl for use in Hquid-phase systems. The low crystal point and low viscosity obviate protection from freezing at temperatures down to —30°C. 

Polyunsaturated fatty acids in vegetable oils, particularly finolenic esters in soybean oil, are especially sensitive to oxidation. Even a slight degree of oxidation, commonly referred to as flavor reversion, results in undesirable flavors, eg, beany, grassy, painty, or fishy. Oxidation is controlled by the exclusion of metal contaminants, eg, iron and copper addition of metal inactivators such as citric acid minimum exposure to air, protection from light, and selective hydrogenation to decrease the finolenate content to ca 3% (74). Careful quality control is essential for the production of acceptable edible soybean oil products (75). 

Shipment and Storage. Anhydrous sodium sulfite is suppHed in 22.7- and 45.4-kg moistureproof paper bags or 45.4- and 159-kg fiber dmms. Most sodium sulfite is shipped by rail in hopper cars. Sodium sulfite should be protected from moisture during storage. When dry it is quite stable, but when wet it is oxidized by air. 

Physical Properties. Sodium metabisulfite (sodium pyrosulfite, sodium bisulfite (a misnomer)), Na2S20, is a white granular or powdered salt (specific gravity 1.48) and is storable when kept dry and protected from air. In the presence of traces of water it develops an odor of sulfur dioxide and in moist air it decomposes with loss of part of its SO2 content and by oxidation to sodium sulfate. Dry sodium metabisulfite is more stable to oxidation than dry sodium sulfite. At low temperatures, sodium metabisulfite forms hydrates with 6 and 7 moles of water. The solubiHty of sodium metabisulfite in water is 39.5 wt % at 20°C, 41.6 wt % at 40°C, and 44.6 wt % at 60°C (340). Sodium metabisulfite is fairly soluble in glycerol and slightly soluble in alcohol. 

Reactions with zinc or aluminum are typically carried out in hydrocarbon solvents. Many of the methyknetal derivatives undergo protonolysis or oxidation very readily, and must be protected from exposure to air or water. 

An especially insidious type of corrosion is localized corrosion (1—3,5) which occurs at distinct sites on the surface of a metal while the remainder of the metal is either not attacked or attacked much more slowly. Localized corrosion is usually seen on metals that are passivated, ie, protected from corrosion by oxide films, and occurs as a result of the breakdown of the oxide film. Generally the oxide film breakdown requires the presence of an aggressive anion, the most common of which is chloride. Localized corrosion can cause considerable damage to a metal stmcture without the metal exhibiting any appreciable loss in weight. Localized corrosion occurs on a number of technologically important materials such as stainless steels, nickel-base alloys, aluminum, titanium, and copper (see Aluminumand ALUMINUM ALLOYS Nickel AND nickel alloys Steel and Titaniumand titanium alloys). 

Platinum and Platinum Alloys. Platinum has excellent resistance to strong acids and, at elevated temperatures, to oxidation. Under reducing conditions at high temperatures it must be protected from low-fusing elements or their oxides. Easily reduced metals at high temperatures may form low-fusing alloys with platinum. 

Clearly the best protection from oxidation by a silicide as a coating on a reactive substrate would be the disilicide, which has the highest silicon content, and could be expected to provide a relatively protective silica coating. 

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