Changes of X-ray diffraction profiles of neutron-irradiated graphite with annealing

Annealing effects on the X-ray diffraction profiles of a neutron-irradiated graphite dosed to 7.2×1020nvt (Ni) were studied. The stepwise annealing was performed at various temperatures between 800 and 2300 °C for 60 min. under the reduced pressure of about 10-2 Torr.The (00l) diffraction lines were observed to shift gradually to higher angle side with the increase in annealing temperature, accompanied by sharpening of the profiles themselves. The dependence of apparent co-spacing measured from (002) line on the annealing time was very similar to those found for soft carbons on their graphitization process. Three-dimensional diffraction line (112) was observed after the annealing above 1200°C. These results are consistent with the behaviors of electronic and mechanical properties obtained for the same kind specimen of neutron-irradiated graphite.Both (002) and (004) diffraction profiles were unsymmetrical up to the annealing temperature of 1400°C. However, (004) profile was apparently less unsymmetrical than (002), and co-spacing obtained from (004) profile was always less than that from peak position of (002). This fact seems to suggest that the irradiated graphite on annealing process consists of multiple structural components, which have different concentration of some imperfections (for example, displacement of carbon atoms from graphite-like layer plane), and produce different contributions to (002) and (004) reflections. Based upon this assumption, a graphical separation of the observed (002) profile into two structural components was examined.