MEASUREMENT OF ELECTRONIC CONDUCTION IN CRYOLITE ALUMINA MELTS AND ESTIMATION OF ITS EFFECT ON CURRENT EFFICIENCY

The electronic conductivity of molten Na3AlF6 saturated with Al2O3 was determined as a function of the activity of Na at 1000-degrees-C by u sing the Wagner polarization technique. Typical results showed electro nic conductivities of 0.298 ohm-1 cm-1 at a(Na) = 0.04 and 0.084 ohm-1 cm-1 at a(Na) = 0.01. A transient technique employing the same experi mental cell was used to determine the diffusion coefficient and the mo bility of electrons in this melt. The mobility is 0.33 cm2 V-1 s-1. A model calculation for electrolysis of a melt of cryolite saturated wit h alumina to produce aluminum metal is presented to show how electroni c conductivity effects current efficiency (CE). Under various assumed conditions, which are tabulated, CEs ranged from around 85 to 98 pct a t 1000-degrees-C.