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Vol. 60
COMMUNICATION TO THE EDITOR SECOND EXPLOSION LIMITS OF CARBON It is by now common knowledge that the unravelling of the thermal reaction between hydrogen MONOXIDE-OXYGEN MIXTURES and oxygen rested on the ability to observe second Sir: explosion limits unmarred by surface chain breakWe wish to comment on the recent paper "Second ing. In the case of the carbon monoxide-oxygen Explosion Limits of Carbon Monoxide-Oxygen reaction, there is a surprisingly large number of Mixtures" by Gordon and Knipe.l imaginable reaction sequences for chain breaking In any system of reacting gases, the existence of and chain branching and the demand for second an explosion peninsula in a pressure-temperature limit data free of surface chain breaking is even diagram bounded by a first explosion limit a t lower more urgent. No such data have been produced pressures and by a second explosion limit a t higher by Gordon and Knipe. On the contrary, their pressures, js evidence that a branched chain reac- second limit data show a marked effect of the vessel tion occurs which competes with two chain break- surface. It is impossible to utilize such data for ing mechanisms, one predominating a t lower and discerning the actual reactions occurring in the the other a t higher pressures. The chain breaking large catalogue of imaginable reactions. Hence, mechanism predominating- a t l"+pessures is the specific mechanism proposed by thes&mrd$pthe diffusion-controlled destruction of chain car- tors is ad hoc. riers a t the surface of the vessel, whereas the chain The present authors have developed a probreaking mechanism predominating a t higher pres- cedure2 which, over a wide range of mixture comsures is a gas phase reaction or a sequence of reac- position and temperature, effectively suppresses tions controlled by a gas phase reaction, which is of the surface chain breaking reaction. A very interhigher order than the branched chain reaction. esting dependence of the second limit on the mole Both chain breaking mechanisms are, of course, fractions of oxygen and of diluent nitrogen was operative a t either limit. If the vessel surface is found. While we do not consider that the problem suitably treated so that it becomes strongly re- of the nature of the chain breaking and branching flective to the chain carriers in question, or if the reactions is entirely solved, it is nevertheless no!ed vessel diameter is made sufficiently large, surface that Gordon and Knipe's reaction scheme is inchain breaking can be effectively suppressed. The consistent with the observed dependence of the second explosion limit is then solely determined by second explosion limit on mixture composithe competing gas phase chain branching and chain tion. breaking reactions. Under these conditions, a WALTER ROTH~ study of the trend of the second explosion limit CUENTHER VON ELBE' pressure with mixture composition a t constant BERNARD LEWIS' MARCH 13, 1956 temperature provides a clue to the nature of the RECEIVED specific reactions occurring. On the other hand, if (2) G. von Elbe. B. Lewis and W. Roth. Fifth Symposium on Comthere is significant disturbance of the second limit bustion, Reinhold Publishing Co., New York, Pg. 610, 1955. Thia data by surface chain breaking, the utility of such work was done while all three authors were at the U. 8. Bureau of Pittsburgh, Pa. data for elucidating the specific reactions involved Minea, (3) General Electric Co., Resoarch Laboratory, Schenectady, N. Y. vanishes. (4) Combustion and Explosives Research, Ino.. Pittsburgh, Penn(1) A. 8. Gordon and R. € Knipe, I . TEISJOURNAL, 69, 1160 (1955).
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