Glow pressure limits

Jorissen reviewed the literature to 1918 on the pressure limits for the autooxidation of phosphorus. Later he discussed the effect of the formation of an oxide coating on burning phosphorus and concluded that it was unimportant. 

The upper glow limit as a function of pressure of various foreign gas was examined by several investigators who found that foreign gases lower the upper limit. Tausz and G6rlacher °° also found that some gases acted as poisons and affected the upper limit in accordance with the expression 

The lower glow limit was apparently first examined in detail by Chariton and Walta , who found the oxidation of phosphorus was accompanied by chemiluminescence if a certain critical pressure of O2 (dependent on temperature and surface effects) was exceeded. The addition of Ar diminished the critical pressure and light yield. Bodenstein criticized the claim of Chariton and Walta that oxidation 

Some unpublished experimental work by Shalnikov indicated that a d relationship better fitted the data than a d one. Semenov reported these results and felt that his own measurements were sufficiently inaccurate so that either relationship could be accommodated, 

Kowalsky reported that the oxidation of phosphorus vapor occurred only between certain upper and lower limits of O2 pressure. At the lower limit [02]i varied inversely with the phosphorus pressure. The upper pressure limit was independent of T between —40 and +15° C, with [Ozh about 4 x 10 [P4]. Between the lower and upper critical pressures oxidation occurred and was accompanied by chemiluminescence. The results were interpreted in terms of Semenov s theory of branched-chain reactions. ° ° . Kowalsky s experimental work was consistent with eqn. (c) and Semenov himself discarded eqn (b). 

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Figure 3.5 reveals that the low-pressure ignition of CO—02 is characterized by an explosion peninsula very much like that in the case of H2—02. Outside this peninsula one often observes a pale-blue glow, whose limits can be determined as well. A third limit has not been defined and, if it exists, it lies well above 1 atm. 

Heating method. Once again the reactants, say CO and 02 , are pre-mixed in the RV but at a low temperature. The temperature is gradually raised when the pressure increases according to Charles Law. At a critical pressure a blue glow appears. At this point contraction occurs due to reaction. As the temperature is raised, the intensity of the glow increases and finally a flash occurs. This is accompanied by a pressure kick. The pressure limit is taken as that at which the blue glow first appears. A variation of this is also used with a flow system (see p. 24). 

Arsenic, when gently heated in the presence of air or oxygen, exhibits phosphorescence 7 which, as with phosphorus and sulphur, is accompanied by oxidation, arsenious oxide containing about 3 per cent, of arsenic oxide being produced. No ozone is formed, nor is there ionisation, as in the phosphorescence of the two elements mentioned. The arsenic oxide appears to be a primary product formed directly from the arsenic, as the lower oxide does not yield it under such conditions. Arsenious oxide is formed slowly below 200° C. without luminescence, but between 250° and 310° C. the glow appears suddenly 8 so long as the pressure is between certain limits,9 outside of which no luminescence is observed. The lower limit, 4 to 10 mm. Hg, falls with increasing temperature, while the upper limit, 200 to 700 mm. Hg, rises... 

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