Abstract
Experiments on the slow oxidation of methane in lead monoxide-coated vessels are described. Relative to the behaviour in a new or ‘hydrofluoric acid-treated’ silica vessel, the lead monoxide coating causes (1) comparatively little effect on the induction period to the onset of a marked rate of pressure rise, but a very marked diminution of the maximum rate of pressure rise; (2) at temperatures near 500° C a rise in over-all activation energy of the maximum rate of pressure rise from
ca
. 25 to
ca
. 58 kcal/mole; (3) a small increase in the dependence of the maximum rate of pressure rise upon the total initial pressure. It is shown that effects (1) and (2) are due to the suppression by a lead monoxide coating of the ‘degenerate branching’ normally introduced into the oxidation of methane by the secondary oxidation of the formaldehyde formed as an intermediate product. The conclusion is reached that this suppression is probably due to efficient destruction by the lead monoxide surface of HO
2
(and perhaps HCO
3
) radicals, though under other experimental conditions a lead monoxide surface may destroy other species of chain carriers. Incidental deductions are that hydrogen and oxygen atoms and hydroxyl radicals do not play an important role in the secondary, formaldehyde oxidation, chains; and therefore that certain reactions proposed for the initiation of the formaldehyde oxidation chains are incorrect.
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