The upper pressure limit in the chain reaction between hydrogen and oxygen

Mixtures of hydrogen and oxygen above 450°C. possess two critical pressure limits between which the normally slow combination of the gases becomes explosive. The most satisfactory theory attributes the explosion to the “branching” of reaction chains, and explains the existence of the lower limit by the deactivation of chain carriers at the wall of the vessel, and the upper limit by deactivation in the gas phase. At the limits one or other of these deactivation processes is just rapid enough to balance the multiplication of the chains. The conditions governing the position of the lower limit have been investigated in some detail and found to be accounted for fairly well by the simple theory. With regard to the upper limit, while several investigations have left little room for doubt that it is governed by gas phase deactivation, the exact nature of this process has not hitherto been satisfactorily worked out. A more complete investigation of the problem therefore seemed to be called for. In order to make this as thorough as possible, certain alternative theories have first been reconsidered, namely those which make the limit a function of surface adsorption relationships, and those which make it depend on various thermal conductivities. But the results show that neither the surface of the vessel, nor the thermal conductivity of the gas are fundamentally important in determining the limit, which proves to depend upon ternary collisions in the gas phase. On the basis of the latter hypothesis an approximate quantitative theory can be constructed.