Phosphorous fixation

The acid treatment was conducted by soaking PBI films in 2% aqueous phosphoric acid. Analyses indicated that 27 weight percent (%) acid was absorbed which was not appreciably eluted by water but was quantitatively extracted by strongly alkaline solutions. Heat treatments fixed the phosphorous to various extents depending on treatment temperatures and durations. Physical property changes, accompanying phosphorous fixation were consistent with polymer crosslinking, i.e., modulus increases, and eventually brittleness. 

The earlier works by Mague et al. (1974 1977), Venrick (1974), and Kimor (1978) attempted to define some of the environmental factors and conditions that control the N2 fixation activity and distribution of DDA populations. Some have argued that distribution and activity is largely controUed by latitude, temperature, nutrients (i.e., iron, phosphorous), and wind stress for the other co-occurring cyanobacteria. 

Researchers at the Eastern Forest Products Laboratory in Canada have evaluated the urea and melamine amino-resin systems (9, 57, 99-110). Their work demonstrates that both systems show good leach resistance and reduced flame spread. The stability of these resins is controlled by the rate of methylolation of the urea, melamine, and dicyandiamide. The optimum mole ratio for stability of these solutions is 1 3 12 4 for urea or melamine, dicyandiamide, formaldehyde, and orthophosphoric acid. However, even at the optimum mole ratios, the pot life of the melamine system is less than that of the urea system. In both systems the nitrogen is fixed to a greater degree than the phosphorus. However, the degree of fixation of the phosphorus is greater with the melamine than with the urea. The melamine structure may promote formation of compounds with phosphoric acid that are less soluble than those from urea and dicyandiamide. 

Capone DG, Raven JA and Carpenter EJ (2001) Phosphorous limitation of nitrogen fixation by Tri-chodesmium in the central Atlantic ocean. Nature 411 66-69. 

The evolution of stainless steel composition can be used to illustrate the importance of materials purity in reducing corrosion susceptibility. Chromium and molybdenum are the key elements in promoting resistance to pitting and crevice attack of stainless steels, but high chromium and molybdenum concentrations are not sufficient to ensure an adequate corrosion resistance. Low concentrations of impurities, like carbon, silicon, phosphorous and sulphur, are required. Type 316L and 316LVM stainless steels are commonly employed to fabricate a variety of fracture fixation devices. They both have low carbon concentration, below 0.03 wt%, which is indicated by the letter L. VM stands for vacuum-melted, a technique... 

Appelt C, Westenberg H, Bertini P, Ehlers AW, Slootweg JC, Lammertsma K, Uhl W (2011) Geminal phosphorous/aluminum-based frustrated Lewis pairs C-H versus C=C activation and CO2 fixation. Angew Chem Int Ed 50 3925-3928 and references therein... 

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