Marine oxidisable

Slides Pitting corrosion on a marine turbine blade [4] corroded tie bars, etc., in furnaces, heat exchangers, etc. oxidised cermets. 

Sulphur attack on nickel-chromium alloys and nickel-chromium-iron alloys can arise from contamination by deposits resulting from the combustion of solid fuels, notably high-sulphur coals and peat. This type of corrosion, which has been observed on components of aircraft, marine and industrial gas turbines and air heaters, has been associated with the presence of metal-sulphate and particularly sodium sulphate arising directly from the fuel or perhaps by reaction between sodium chloride from the environment with sulphur in the fuel. Since such fuels are burned with an excess of air, corrosion occurs under conditions that are nominally oxidising although the deposits themselves may produce locally reducing conditions. 

Considerable interest has been expressed in the industrial use of stabilised hypothatous acids (water reacted with chlorine, bromine or iodine). This innovation imitates the stabilisation of oxidised bromide that occurs in natural systems.51 These occur as mechanisms of control on the surface of some aquatic plants in the mammalian immune defences.52 Certain marine algae produce hypobromous acid using bromoperoidases53 which is not only an effective mechanism but exhibits good specific toxicity. 

Hinrichs K.-U., Summons R. E., Orphan V., Sylva S. P., and Hayes J. M. (2000) Molecular and isotopic analysis of anaerobic methane-oxidising communities in marine sediments. Org. Geochem. 31, 1685-1701. 

It has been inferred from carbon and sulfur dating that the concentration of oxygen in the Earth s atmosphere was less than I part per million volume (ppmv) prior to around 2.4 billion (Ga) years ago, whereas methane would have been present at levels of around 10 to 10 ppmv (compared with its present value of around 1.7 ppmv). Methane is generated in signihcant amounts by the anaerobic decomposition of organic matter in modem marine sediments, but is oxidised by sulfate under the ocean sea floor and never reaches the atmosphere. Prior to the watershed constituted by the appearance of oxygenic photosynthesis, the ocean had little sulfate to support anaerobic oxidation of methane, but as atmospheric oxygen and seawater sulfate levels rose, the consequent anaerobic oxidation of methane would have steadily reduced the net release of methane. 

VHPOs also accept the pseudohalides CN and SCN as alternative substrates, and even oxidise cyanide and thiocyanate preferentially to bromide.I l Thiocyanate is generated in vivo by thiosulfate sulfur transferase in the process of cyanide detoxification, and is present in concentrations comparable to that of bromide. Organic thiocyanate compounds have been discovered in marine environments (12 in Figure 4.14, suggesting that their formation is also catalysed by, inter alia, VHPOs. Laboratory experiments have shown... 

Widely-used alternatives to the alum-based tawing pastes were the various oxidisable marine oils, which were applied in the production of the chamois and buff leathers. The oils were trampled into the skins in a similar manner to that used in tawing. The skins were then hung in warm, airy stoves for the oxidation process to take place. After the oiling and stoving sequence had been repeated three or four times, the leather was washed off in alkaline liquors to remove excess oil, dried and worked mechanically to soften them. 

Remarkably, Zhun and Ignatenko used triprenylborane as prenyl source and were able to attack indole in the 2-position without prior oxidation to the chloroin-dolenine. The 2-marine natural product debromoflustrabromine [95]. 

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