1987 Volume 51 Issue 4 Pages 328-337
The viscosity of all kinds of the alkali fluoride melts has been measured over the temperature range from the respective melting temperature to about 1370 K by the use of a high temperature oscillating vessel viscometer. The viscometer has been modified so as to be able to measure the period and the logarithmic decrement from the observed intervals between the times when the oscillation passes two deflection angles, and to calculate the viscosity automatically. Discussion has been made on the sources of error accompanying the measurement. The results are summarized as follows:
(1) The largest error in the measurement is considered to be the one in the determination of radius of crucible. The limit of error is estimated to be 1-2%.
(2) Values of the viscosity of alkali fluorides at the melting temperatures lie in the range of 1.35-1.9 mPa·s. LiF and KF show the highest and lowest values, respectively, at their melting temperatures. Values of apparent activation energy for viscous flow of molten alkali fluorides are nearly identical with those of molten alkali chlorides.
(3) Values of the viscosity obtained were analyzed on the basis of the corresponding state principle. By the use of Dymond’s equation, the relation among the reduced temprature, volume and viscosity has been calculated. The reduced volume is the ratio of volume at the experimental temperature to that at the melting temperature. Values of the viscosity of molten alkali fluorides calculated from the equation agreed well with the experimental ones within 10%.
