Fluorine reaction

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Fluorine reaction refers to a series of chemical reactions intended to produce oxygen (and possibly other materials) by the reduction of lunar regolith. It is a form of In Situ Resource Utilization.

In the basis process, fluorine is reacted with the lunar material at elevated temperature. The fluorine attacks the oxides, liberating oxygen and producing fluoride salts. The fluoride salts are then separated into fluorine and reduced metals by electrolysis.[1]

In a variant version of the process, hydrofluoric acid, rather than gaseous fluorine, is used to attack the lunar material.

The fluorine reaction has the advantage that, since fluorine is more electronegative than oxygen, fluorine will displace oxygen from any composition of lunar rock. Hence, in principle, the process chemistry does not require finding any particular mineral source, or beneficiation of the soil to enhance the content of a particular mineral.

Fluorination

Recently Geoffrey A. Landis of NASA's John Glenn Research Center has proposed that the use of the fluoride reaction sequence could be a method by which processing lunar materials could be done to produce silicon as well as iron, aluminum, and the basic oxide components of glass, which could be used in manufacturing, as well as producing oxygen. In his proposal the fluorine is brought to the moon in the form of potassium fluoride, and is liberated from the salt by electrolysis in a eutectic salt melt. Tetrafluorosilane produced by this process is reduced to silicon by a plasma reduction stage; and the fluorine salts are reduced to metals by reaction with metallic potassium to form potassium fluoride, KF, the original starting material). Fluorine is recovered from residual MgF and CaF2 by reaction with K2O.

Hydrofluoric Acid Leach

While a far more complex reaction sequence, the primary benefit of the HF acid leach system is much lower reaction temperatures. Lower temperature requirements result in a lower energy input and power savings which can be used for other life support functions.

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Reaction Materials

The system used to carry out any reaction must be well suited and as inert as possible towards the reactants.

  • When the fluoride salt is put through electrolysis, the neutral charge of the ions is restored and fluorine gas is produced. Fluorine, like other elements, is more reactive in its unionized state. The gas is highly reactive and tends to cause stress crack corrosion in many kinds of metal piping. This issue can be mitigated at lower temperatures by coating the inside of metal pipes with Teflon. Teflon is also a excellent material for low temperature gaskets.
  • The eutectic melt and electrolysis will need to be carried out in a suitable container. Nickel and Monel crucibles, using copper gaskets, are compatible with the fluorine gas. At higher temperatures platinum crucibles would be needed, but the eutectic electrolysis should have a temperature low enough that platinum isn't required.


Common/Main Materials Used to Handle Fluorine[2]
Material Highest Working
Temperature (C)
Gaseous Fluorine
Use
Liquid Fluorine
Use
Nickel 650 Lines, fittings, flanges,
storage tanks
Lines, fittings, flanges,
storage tanks
Monel 550 Lines, fittings, flanges,
valves, storage tanks,
valve bellows
Lines, fittings, flanges,
valves, storage tanks,
valve bellows
Copper 400 Lines, fittings, flanges,
valve seats, gaskets
Lines, fittings, flanges,
valve seats, gaskets
Brass 200, low pressure Lines, fittings, flanges,
valve bodies
---
Stainless
Steel
200 Lines, fittings, flanges,
storage tanks, valve bodies
Lines, fittings, flanges,
storage tanks, valve bodies
Aluminum 400 Lines, fittings (Al 2017),
2024), gaskets (Al 1100)
Lines, fittings (Al 2017),
2024), gaskets (Al 1100)
Teflon 80 Valve packing (low static pressure), gaskets Valve packing (low static pressure), gaskets


External Links

References

  1. J. Grannec and L. Lozano, "2: Preparative Methods", in the book Inorganic Solid Fluorides, P. Hagenmuller (ed.), Academic Press, NY, 1985, pp. 17-76.
  2. (P. S. Gakle, et al., "Design Handbook for Liquid Fluorine Ground Handling Equipment, Aerojet-General Corp., WADD TR-60-159,December 1960