MASS-SPECTROMETRIC INVESTIGATIONS OF FULLERENES .1. VAPOR-PRESSURE OVER THE C-60 C-70 BINARY-SYSTEM/

The absolute vapour pressures over pure C-60, C-70, fullerite and over the binary C-60/C-70 system are calculated from ion intensities vs. t emperature up io 800 K using the Knudsen effusion mass spectrometric m ethod. The vapour pressures (Pa) of C-60 and C-70 are given as a funct ion of temperature (K) by the equations: log p=-(8276.4+/-120)/T+10.49 +/-0.14, for C-60 log p=-(9106.4+/-130)/T+10.70+/-0.15, for C-70 Corre sponding Second Law enthalpy and entropy changes for sublimation are: Delta H degrees(subl) = 158+/-3 kJ/mol Delta S degrees(subl) = 105+/-1 .5 kJ/mol, for C-60, Delta H degrees(subl) = 174 + 3 kJ/mol Delta S de grees(subl) = 109+/-1.5 kJ/mol, for C-70. Results are discussed in ter ms of sample purity and pretreatment and correlated with data obtained by other authors. Fullerenes containing residual organic solvents (fu llerite) partly decompose upon thermal treatment to amorphous carbon.