Activated oxygen pressure

Strontium Peroxide. Commercial strontium peroxide contains about 85% Sr02 and 10% active oxygen. It can be made by heating strontium oxide ia the preseace of oxygea gas uader 20 MPa (200 atm) pressure, or by reactiag a soluble stroatium salt with hydrogea peroxide. The only substantial appHcation for this compound is ia pyrotechnics (qv). Strontium peroxide [1314-18-7] produces a red color ia flames. 

A fresh surface of siUcon carbide is thus constantiy being exposed to the oxidizing atmosphere. Active oxidation takes place at and below approximately 30 Pa (0.23 mm Hg) oxygen pressure at 1400°C (66). Passive oxidation is determined primarily by the nature and concentration of impurities (67). 

An increase from 2 to 5 bar total pressure increases the space-time yield by about 20% (15 vol.-% ethylene, 85 vol.-% oxygen, 2-20 bar 0.235-3.350 s 11 h ) [4], At higher pressures, 10 and 20 bar, a decrease activity is observed. Since industrial processes occur at up to 30 bar, at first sight this result is surprising. The decreasing activity with pressure was partially explained by catalyst deactivation, probably as a consequence of the longer residence times applied. 

Relatively detailed study has been done for the reaction pathways over Au/Ti02 catalysts mainly because of simplicity in catalytic material components. The rate of PO formation at temperatures around 323 K does not depend on the partial pressure of C3H6 up to 20vol% and then decreases with an increase, while it increases monotonously with the partial pressure of O2 and H2 [57]. A kinetic isotope effect of H2 and D2 was also observed [63]. These rate dependencies indicate that active oxygen species are formed by the reaction of O2 and H2 and that this reaction is rate-determining [57,63,64]. 

A different situation arises with a preliminary reduced surface. In this case the measured value of y is within lO - 10 2, and as the temperature increases, the y grows by the Arrhenius Law (Equation) with the activation energy of 5.2 kcal/mole. In addition, there is dependence of y upon the triplet oxygen pressure in the set-up, though the experiment conditions allow us to neglect a priori the impact of homogeneous processes on the spatial distribution of 02( A ) molecules. Prolonged... 

Palozza, P, Calviello, G, and Bartoli, GM, 1995. Prooxidant activity of beta-carotene under 100-percent oxygen pressure in rat liver microsomes. Free Radic Biol Med 19, 887-892. 

The partial oxygen pressure, p02, is particularly significant in metabolic processes of cells, and its variation from normal values often indicates pathologies (ischemic diseases, strokes, tumors). Accurate and localized measurements of the oxygen concentration are also desirable for differentiation between venous and arterial blood, or for cerebral mapping of task activation. In the past, invasive methods were used involving oxygen-sensitive electrodes which had to be placed directly in the blood or tissue and could only offer p02 from a few body points. 

Examples 24-27 are for oxidation reactions, three of hydrocarbons and one of CH3OH. Examples 24 and 25 are for the same reaction, with Example 24 for high oxygen pressure and coverage and Example 25 at low oxygen pressure and coverage. For the low-pressure case, Korchak and Tretyakov (98) postulated for their system that the surface-active oxygen is atomic ... 

For Example 27 the order with respect to oxygen was not reported, but the oxygen pressure was evidently large enough for the reaction to be zero order in oxygen. Step 5 is therefore relevant. Either the site density is very low or the entropy of activation is not zero. In a reaction of this type the latter reason is probably the correct one. 

Fig. 35. Oscilloscope tracings of oxygen effects. Top decay of EPR signal of coals, charred sugars and activated carbons heated above 100° with increase in oxygen pressure. Bottom decay of EPR signal in activated carbons with increase in oxygen pressure (181).

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