Unpaired Electrons in Carbon Blacks

Abstract

An appreciable concentration of unpaired electrons has been found in colloidal carbon blacks through the application of electron spin resonance spectroscopy. The unpaired electrons in a typical channel process carbon black, Spheron 6, have been studied by noting the changes in the electron spin resonance spectrum produced by heat treatment (HT) to 3000°C and by various degrees of evacuation of the sample. The results indicate that the unpaired electrons in the original material are mobile π electrons, which are stabilized by condensed aromatic ring structures. Their concentration decreases slowly to 750°C HT and then declines more rapidly and vanishes above 1400°C HT. A different species of unpaired electrons arises at 1400°C HT. These are believed to be immobile σ electrons resulting from broken carbon-carbon bonds at lattice defects. The unpaired electrons present in several commercial carbon blacks have been examined and are believed to be π electrons also. A tentative theory of the origin of the unpaired electrons is given.