ESR OF CARBONS IN THE TRANSITION RANGE .1.

The main purpose of this work was the clarification of the ESR behavior of carbons in the heattreatment range 900-1500°C by trying to pin down the reasons for the large broadening of the ESR line observed in this range. The quartz broadening occurring in heating samples in vavuo, and the Hennig-Smaller graphite furnace broadening were investigated and techniques developed for their avoidance. Although the broadening observed upon reheat of carbons heattreated to above 1600°C (Hennig-Smaller effect) has been practically eliminated and in spite of the purity of heating runs achieved, large broadening is still observed for raw carbon materials on first heattreatment (with a maximum of about HTT 1300°C) and for highly heattreated (HTT ≥ 1600°C) carbons upon anneal, if, previous to anneal, their structure has been damaged by neutron irradiation. The variation in position of the maximum broadening with HTT indicates that the broadening is connected with some changes occurring in the structure of carbons in this range. Decrease in width was obtained by chlorination at 1000°C but the post-chlorination anneals have shown that such chlorination must be a complex process, not amenable to a simple explanation. © 1979.