The real density of molded graphite, that is the density exclusive of open porosity but including closed–internal porosity, is 2.20-2.23 g/cm3. This value is near the theoretical density of the graphite crystal (2.25g/cm3), indicating that the amount of internal porosity is small and the structure of the material is well ordered.
The apparent density of molded graphite, that is the density inclusive of porosity, varies considerably, depending on the process, the impregnation cycle and other factors. Values generally quoted in the industry are 1.4-2.0 g/cm3, corresponding to an open porosity of 10-35%. A common method of measuring apparent density is the Avogadro (or water–weight) method. To avoid overstating the result, air bubbles must be eliminated and the part must be perfectly dry before testing.
Typical pore–size distribution of several molded graphite materials is shown in Fig.5.5.
fig.5.5-pore-size distribution of various grades of molded graphite