stable than aluminum fluoride (Figure 3), the calcium oxide and magnesium oxide content of the lunar feed material would undergo the following reactions: Calcium fluoride and magnesium fluoride dissolve in the electrolyte, lowering electrical conductivity, ore solubility and liquidus temperature. Their concentration will be allowed to build up until they pose an operation problem in the electrolytic cell. Once this limit approaches, the electrolyte will be purified. An attractive technique for this purification would be to discontinue feeding ore. When the oxides have been exhausted, the cell will start to electrolyze calcium and magnesium fluorides, at a somewhat higher voltage, producing fluorine instead of oxygen and a Ca-Mg alloy instead of the Al-Si-Ti-Fe alloy (Reaction 3). It might be more convenient to take a side stream of electrolyte off from the main cell and do this electrolysis in a separate small electrolytic cell: The fluorine gas produced will be reacted with aluminum to make aluminum fluoride. This will be added back to the aluminum producing cells where it will combine with sodium fluoride to produce cryolite. Calcium magnesium alloy produced by Reaction 3 can further be separated into its constituent elements calcium and magnesium by vacuum fractional distillation. 8. PURIFICATION OF ALUMINUM ALLOY The existence of near vacuum (about 10 14 Torr) on the lunar surface, absence of any oxidizing gas, and wide differences in the vapor pressure of different elements (Figure 4) make the vacuum fractional distillation technically feasible for separating the Al-Si-Fe-Ti alloy into its constituent elements. REFERENCES I. R.D. Waldron et al., Chemical Engineering, Feb. 12,80, 1979. 2. D.B. Raoe/u/., NASA SP-428, U.S. Government Printing Office, 1979. 3. D. Kesterke, U.S. Dept, of Interior, Bureau of Mines, Report of Investigation RI 7587, 1971. 4. D.J. Lindstrom and L.A. Haskin, Fourth Princeton/AIAA Conference on Space Manufacturing Facilities, Princeton, NJ. May 14-17, 1979. 5. U.S. Patents 3,578,580 and 3,930,967. 6. U.S. Patent 3,400,061.
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