The Solid Oxide Membrane (SOM) process for magnesium production involves the
direct electrolysis of magnesium oxide for energy efficient and low-carbon
magnesium production. In the SOM process, magnesium oxide is dissolved in a
molten oxy-fluoride flux. An oxygen-ion-conducting SOM tube, made from yttria
stabilized zirconia (YSZ), is submerged in the flux. The operating life of
the electrolytic cell can be improved by understanding degradation processes
in the YSZ, and one way the YSZ degrades is by yttria diffusion out of the
YSZ. By adding small amounts of YF3 to the flux, yttria diffusion can be
controlled. The diffusion of yttria into the flux was quantified by
determining the yttria concentration profile as a function of immersion time
in the flux and distance from the flux-YSZ interface. Yttria concentrations
were determined using x-ray spectroscopy. The diffusion process was modeled
using a numerical approach with an analytic solution to Fick?s second law.
These modeling and experimental methods allowed for the determination of the
optimum YF3 concentration in the flux to minimize yttria diffusion and
improve membrane stability. Furthermore, the effects of common impurities in
magnesium ores, such as calcium oxide, silica, and sodium oxide/sodium
peroxide, on YSZ stability are being investigated.
Yttria stabilized zirconia membrane stability in molten fluoride fluxes for low-carbon magnesium production by the SOM process