Abstract
The self-diffusion coefficients and their temperature dependences of fluorine in molten Li2BeF4 and LiBeF3 have been investigated by the capillary reservior technique using a tracer Fluorine-18. The observed diffusion coefficients of fluorine DF (cm2 sec−1) are written in the form of DF=D0exp[−ED(F)⁄RT], where ED(F) and D0 are calculated by the least squares method from all experimental data. Those of molten Li2BeF4 and LiBeF3 are as follows:(This article is not displayable. Please see full text pdf.) \ oindentThese results for fluorine diffusion are considerably difficult to explain by a simple model because of the unusual combination of the relatively large diffusion coefficients and a high activation energy and cannot be explained solely by mass transfer due to migration of large fluoroberyllate anions. One of the possible explanations for these results could be the exchange of fluorine atom between neighboring beryllate units including the rotation of beryllate anions. Another possible explanation could be the diffusion mechanism of a neutral pair of, for example, LiF. Both diffusion mechanisms give high activation energy and are consistent with the observed results. The close analogy between the diffusion behavior of fluorine in molten LiF-BeF2 mixture and that of oxygen in molten CaO-SiO2-Al2O3 slag was also discussed.
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