Evolution with heat treatment of crystallinity in carbons

The variation with heat treatment of the dimensions La and Lc of the graphite-like crystallites of graphitizable and non-graphitizable carbons is studied. The increases of La and Lc with heat treatment temperature (HTT) owing to three processes (crystallite growth in-plane, coalescence of crystallites along the c-axis and coalescence of crystallites along the a-axis) are functionally separated. The evolution with HTT of the number of crystallites (Ncr), the mean volume of the crystallites (vcr) and the total volume occupied by the crystallites (Vcr) are determined in terms of the changes of La, Lc and d002. Since among other characteristics the crystallites form the electrical and thermal conducting phase of the carbon, Ncr, vcr and Vcr are important parameters in many physical properties of these materials. The developed expressions were applied to a non-graphitizable and to a graphitizable carbon.