STABILITY OF GRAPHITE-INTERCALATION COMPOUNDS WITH TACL5 OR NBCL5 AGAINST WATER OR DILUTE ACIDS - A STUDY WITH XRD, SEM/EDS AND ELECTRON-MICROPROBE ANALYSIS (EMPA)

Graphite intercalation compounds were prepared from flakes of natural graphite and Thornel P-120 carbon fibers. Stage 2 compounds were obtained with TaCl5 at 400 degrees C, and stage 4 compounds with NbCl5 at 200 degrees C. The compounds with TaCl5 were stable in ambient air or under water at 25 degrees C. At 90 degrees C with water or dilute hydrochloric acid small quantities of the stage 3 compound appeared. The NbCl5 compound did not change at all under these conditions. In contrast, the intercalated Thornel P-120 fibers were deintercalated after 30 minutes' exposure to air. Point analysis by EDS of the exposed flakes showed only Ta (or Nb) and Cl to be present in the central regions of the flakes whilst oxygen could be detected in addition in a small border zone at the edge of the flakes of a few micrometers width. Quantitative electron microprobe analysis (EMPA) indicated that TaOCl3 had formed. This polymeric and therefore immobile compound protects the interior from attack by water. The diameter of the fiber is too small to allow protection by this mechanism.