Samples of P33 carbon black, heat treated in the range 1600"-26OO"C, were studied by E.P.R. The lineintensity, localized and free spins contributions, and g-factor, are examined as a function of residence time at H.T.T. (a few minutes to several hours). The correlation between the g-factor and diamagnetic anisotropies is also discussed. 169. Study of carbon blacks by electron spin resonance J. B. Donnet, M. Rigaut and R. Furstenberger (Laboratoire & Chimie Physique, ESCM, 68 Mulhouse, France).
According to physical and chemical results of the last years carbon blacks could be considered as having a free radical character. Our laboratory had notably proposed to put in reaction carbon blacks and free radicals obtained by thermolysis of the 2-2' azobisisobutyronitrile (AIBN) or organic peroxides. The E.S.R. study of the carbon blacks in such a way gave some results whose interpretation was not easy and led several authors to propose contradictory hypotheses. We began a systematic study of this problem and some recent results pointed out that the chemical method (AIBN) was correct only in complete absence of oxygen. The carbon blacks studied were treated by AIBN in benzene. All the reagents were carefully outgassed. The amount of nitrogenous products fixed was determined by radiochemistry. The carbon blacks studied by E.S.R. before the AIBN treatment exhibit a paramagnetism independent of the temperature. The carbon blacks chemically treated exhibit no decrease of the paramagnetic susceptibility. From all the results obtained, it can be concluded that the fixation of the thermolysis products of the AIBN does not involve superficial free radical of carbon blacks and that the paramagnetism of carbon blacks has not a radical origin.
- Phonon-drag thermoelectric power of graphite in strong magnetic fields.