VAPOR-PRESSURE AND HEATS OF SUBLIMATION OF CAF2 AND SRF2

Vaporization and sublimation of CaF2 and SrF2 were determined in the temperature range of 1425-1731 and 1381-1720 K, respectivley by the mass-spectrometric, double Knudsen cell method. The thermodynamic data from IVTANTERMO bank were chosen to establish the vapor pressure of the reference substance. Five series of measurements were carried out: two for the beta-modification of solid CaF2, one for liquid CaF2, and two for solid SrF2. The results of the vapor pressure measurements as a function of temperature were approximated by the following equations: [GRAPHICS] The heats of sublimation of CaF2 and SrF2 were calculated according to the second and third laws of thermodynamics. The established vapor pressures were compared with the available data. The recommended values for the heats of sublimation are: DELTA(s)H(o)o(CaF2) = 438 +/- 8 kJ/mol and DELTA(s)H(o)o(SrF2) = 443.5 +/- 8 kJ/mol.