Abstract
X-ray diffraction curves, densities, number of unpaired electrons, electric resistivities and the amounts of ammonia and hydrogen cyanide formed by heating were measured on flame-proofed polyacrylonitrile fibers (prepared by heating at 300°C in air) heat-treated at various temperature up to 1000°C. Results are as follows:
1) X-ray diffraction intensity of the halo at 2θ=24_??_25° seems to increase with rising of heating temperature. Maximum peak of the halo appears at 25° below 600°C while it appears at 24° above 600°C.
2) Density increases with elevation of heating temperature. It is observed on the density vs. temperature curve that there is a singular point at 600°C.
3) Number of unpaired electrons increases with rising of heating temperature, following a sharp drop above 600°C. Electric resistance tends to decrease markedly above 600°C.
4) Amount of hydrogen cyanide increases with heating temperature up to 800°C. Amount of ammonia also increases with heating temperature, but does not increase above 600°C.
It is thought that these results correspond mainly to changes in structure of cyclic systems. Namely, with elevation of heating temperature, the system B which co-exists with the system A in the flame-proofed fiber changes to the system A between 300°C and 500_??_600°C, and further above 500_??_600°C the system C (graphite-type carbon condensed ring) is formed by decomposition and recombination of the system A (or B).
