Chronopotentiometric methods showed that, in melts for which the equivalent fraction of AlF3 was 0.136, the diffusivity at temperatures of between 1128 and 1273K could be described by the expression:

D (m2/s) = exp[-3980/T - 15.904]

In melts for which the equivalent fraction of AlF3 was 0.25, the diffusivity could be described by the expression:

D (m2/s) = exp[-5532/T - 14.609]

The Fick's law values of the diffusion coefficient were very high, and were of the order of 10-7m2/s at a temperature of 1270K and an equivalent fraction of 0.685. This was attributed to the existence of a strong thermodynamic driving force in the system. Suitable modification of Fick's law, to take account of the density changes caused by electrolysis, gave thermodynamic diffusivities having more usual values (table 198).

E.W.Dewing: Journal of the Electrochemical Society, 1984, 131[5], 1073-8

 

 

Table 198

Interdiffusion Data for LiF-AlF3 Melts

 

AlF3 (equivalent fraction)

Temperature (C)

D (m2/s)

0.500

860

8.4 x 10-10

0.500

900

1.2 x 10-9

0.500

950

1.7 x 10-9

0.500

1000

2.2 x 10-9

0.500

1020

1.6 x 10-9

0.562

860

7.2 x 10-10

0.562

900

1.3 x 10-9

0.562

950

1.7 x 10-9

0.562

1000

4.2 x 10-9

0.562

1020

2.7 x 10-9

0.618

860

5.1 x 10-10

0.618

900

1.2 x 10-9

0.618

950

5.1 x 10-10

0.685

860

1.0 x 10-9

0.685

950

1.3 x 10-9

0.685

1000

2.6 x 10-9

0.685

1020

2.3 x 10-9