Unpaired Electrons in Carbon Blacks

Abstract Two types of unpaired electrons have been observed in a heat treated channel process carbon black. In the original black, and for this material heat treated up to 1400° C, the unpaired electrons are believed to consist of unpaired mobile π electrons stabilized by resonance energy in large condensed ring structures, many of which probably contain oxygen. These disappear with heat treatment above 1400° C and a new species of unpaired spins appear which have been assigned to localized σ electrons at defects in the graphitizing lattice. The unpaired electrons in most commercial carbon blacks are believed to be π electrons, similar in concentration and g value, but varying considerably in line width and oxygen sensitivity. The highly graphitic acetylene black may contain σ electrons also, for its line width is little affected by oxygen. A tentative explanation has been formulated for the origin of unpaired electrons in charred materials and carbon blacks.