Mass Spectrometric Study of Vaporization of Lithium Fluoride

Abstract

The vaporization of lithium fluoride was studied by using a mass spectrometer attached with a tungsten Knudsen cell over a temperature range of 1,006–1,200 K. As the ion species, Li+, LiF+, Li2F+ and Li3F2 + were identified, where Li+ and LiF+ were mainly attributed to the monomer (LiF) as their precursor. While, Li2F+ and Li3F2 + were identified to be formed from the dimer (Li2F2) and the trimer (Li3F3), respectively. Partial vapor pressures of these vapor species were obtained by estimating their relative ionization cross sections and comparing their peak heights with those of the internal standard. The heats of vaporization of the monomer, dimer and trimer were obtained by the second law as well as the third law treatments. The heats of vaporization of liquid lithium fluoride were obtained by approximation through differentiation of the quadric regression curves of partial vapor pressures. The fairly good agreement was attained between the second law and the third law heats of vaporization.