Viscosity of molten alkali molybdates, tungstates, and sulfates

The viscosities of molten M2MoO4 and M2WO4 (M = Li, Na, K) have been detd. as a function of temp. up to 1000 Deg by the method of the oscillating hollow cylinder. Viscosity values, ranging from 2 to 10 cP, are higher for the tungstates than for the corresponding molybdates and decrease in the order Li -> Na -> K. In addn., viscosity values of Li2SO4 and Na2SO4 are reported, in order to allow a comparison with the behavior of other high-melting salts with complex anions. The relations between viscosity and temp. can be represented satisfactorily by an Arrhenius equation. Values of the activation energy for viscous flow Eh are as follows (in kcal mole-1): Li2MoO4, 7.0; Na2MoO4, 6.8; K2MoO4, 5.1; Li2WO4, 12.0; Na2WO4, 9.2; K2WO4, 8.6; Li2SO4, 12.8; Na2SO4, 10.0. The Eh values are predicted reasonable well by the semiempirical relation Eh = 3.7 RTm. The relatively low values of the ratio Eh/EL, i.e., activation energy of viscosity vs. activation energy of equiv. conductivity, in the case of molten alkali molybdates, tungstates, and sulfates would suggest that the melts have a more or less assocd. character. [on SciFinder (R)