Critical oxygen pressure

Armstrong, W. and D. J. Gaynard. 1976. The critical oxygen pressures for respiration in intact plants. Physiol. Plant. 37 200-206. 

A more rigorous treatment of the problem yields a slightly different expression for the critical oxygen pressure, Equation (4.39) ... 

As might be expected, lower critical oxygen pressures were required for the propagation of the combustion than for the ignition. If the molten spot was formed by an external means, propagation and consumption of the entire sample occurred with about 20% oxygen. 

Oxidation stability (gasoline) (induction period) NFM 07-012 ISO/DlS 7536 ASTM D 525 Time necessary for a sample bomb under oxygen pressure to reach the critical induction point... 

Phosphine-oxygen mixtures are relatively stable above the upper and below the lower critical explosion pressures. However, on irradiation with UV-light reaction occurs. It is assumed that the reaction is initiated by the photolytic dissociation of the PH3 molecule according to the equation ... 

The central role of mitochondria in mediating the biosynthesis of FeS clusters in unicellular eukaryotes is noteworthy. It is this physiological function which may provide a critical selective pressure to retain highly reduced mitochondria over the course of the protist s adaptation, either to a parasitic lifestyle or to inhabiting oxygen-poor or anaerobic niches. 

Arsenic is oxidised, mainly to arsenious oxide, when heated in nitrous oxide 8 the reaction becomes appreciable at 250° to 270° C. and ignition occurs at 400° to 450° C. This reaction takes place specifically between arsenic and the nitrous oxide and is not due to reaction with oxygen after thermal decomposition of the nitrous oxide, as such decomposition does not occur below 400° C. and is very slight at 460° C. Nor does the reaction resemble that which occurs in oxygen, except that, like the reaction in the dark with the latter gas (see p. 47), it is a surface reaction. No chemi-luminescence is observed, however, and there is no upper critical oxidation pressure. At 360° C. the product contains at least 99 per cent, of pure arsenious oxide, and at 420° C. it contains about 5-8 per cent, of arsenic pentoxide. 

The oxidation of CO on a Mn02 surface is approximately a first order reaction independent of the oxygen pressure, in the range of 760 to 10 mm., with a heat of activation of 7 kcal. At pressures below 0.52 mm., the reaction is almost of zero order and is practically independent of the temperature. At this critical low pressure limit, the Mn02 is reduced by CO as the molecular oxygen in the gas phase is not utilized (16). 

In many cases (except for PE), the critical O2 pressure Pc, beyond which the assumption of oxygen excess can be considered valid, is far from atmospheric pressure. As an example, in the case of PP, Pc 12 MPa (2). Thus, reactions involving P° radicals cannot be neglected ... 

In the earlier studies [1] the phase 3-NiAl was found to be very oxidation resistant, forming a protective alumina scale in a wide range of temperature and oxygen pressure. However, in more recent studies [2-5] many critical features were detected in this alumina formation and even accelerated attack by intergranular and internal oxidation was observed under special conditions. 

Alternating aerobic-anaerobic cycles in wetland soils promote N2O emissions to the atmosphere, whereas under continuously flooded conditions most of the N2O formed will be reduced to N2. Like methane, appreciable amounts of N2 and N2O produced from denitrification remain entrapped in wetland soils and sediments (Lindau and DeLaune, 1991). A low partial oxygen pressure during the denitrification process enhances the formation of N2O. The critical redox potential for N2O production in soil is between +100 and +300 mV (Figure 16.7). 

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