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Electron Spin Resonance in Carbons: The Effect of Surface Oxide Formation

H. Harker, C. Jackson, W. F. K. Wynne-Jones
1961 Proceedings of the Royal Society A  
When surface oxide is formed on a carbon by reaction with oxygen, the intensity of the electron spin resonance signal decreases. This effect can easily be distinguished from the 'reversible effect'. When the oxidized carbon is reheated in vacuo, the signal is partially recovered. This process is facilitated by addition, to the oxidized sample, of sodium hydroxide, which evidently lowers the thermal stability of surface oxide. It is not yet known whether free-radical centres are actually lost
more » ... re actually lost during oxidation or merely converted to centres of a new type, in which the unpaired electrons are localized on oxygen atoms. The existence of new centres is suggested by the appearance of a second resonance peak at a new gr-value in certain highly oxidized carbons. The loss or recovery of a free-radical centre is apparently associated with a large number of surface oxygen atoms. This may be a consequence of the chemical heterogeneity of surface oxide; or it may be due to partial localization of unpaired electrons in the surface. The results are relevant to the theory of carbon reactivity.
doi:10.1098/rspa.1961.0122 fatcat:yslzvsol5rdl3m6ios2anxpb3m