The electrochemical insertion of sodium into graphite was studied in molten sodium fluoride at 1025 degrees C. The results obtained evidenced two mechanisms for sodium insertion into graphite: sodium intercalation between the graphite layers and sodium sorption into the porosity of the material. Subsequent internal rearrangement of inserted sodium occurred, via transference from the pores towards the intercalation sites. In addition, the intercalation compound was found to undergo a fast decomposition process (k = 2.55 x 10(-9) mol s(-1)). X-ray diffraction analysis was used to confirm the formation of a high stage compound (Na0.1C8), the composition of which was consistent with compositions observed in the case of chemical vapor and electrochemical insertion of sodium, during experiments in the sodium perchlorate-ethylene cabonate electrolyte. (c) 2006 Elsevier Ltd. All rights reserved.