VAPORIZATION BEHAVIOR AND MEASUREMENT OF DIFFUSION COEFFICIENTS OF FLUORIDES VAPORIZED FROM VARIOUS MOLTEN SLAGS

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Spontaneous fluoride emission from high temperature processes can result in increased atmospheric fluorine contents and environmental contamination. Slags containing SiO_2, Na_2O and CaF_2 tend to be unstable at high temperatures and gaseous species such as NaF and SiF_4 evolve simultaneously. Furthermore, a reaction between NaF and SiF_4 can occur to produce Na_2SiF_6 (sodium hexafluorosilicate), whose behavior and properties are not well established.The diffusivity of NaF in argon, nitrogen and helium was measured. Moreover, the rate of NaF vaporization in a SiF_4-Ar atmosphere was investigated and the rates of formation and dissociation of Na_2SiF_6 were measured.Kinetic analyses were carried out and the rate constants of formation and dissociation of Na_2SiF_6 were obtained.