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Material science the moon[and back] ‘I
f you want to go to the Moon and bring the astronauts back you must carry enough oxygen to power the rocket on the way back,’ explains materials scientist Derek
Fray of the University of Cambridge, UK. ‘It costs a million dollars per tonne to ship material to the Moon, so it would be much cheaper to generate the oxygen on the Moon for breathing and for propulsion,’ he adds. Rocks on the Moon are mainly oxides, so it should be possible to build a reactor on site that provides a structural metal and oxygen gas.
Planetary geochemist Larry Taylor, of the University of Tennessee, Knoxville, US, gave advice to astronauts as they collected samples on the Moon during what turned out to be the last Apollo mission in 1972. He spent years studying lunar rocks and in 1993 reviewed the various options for their potential to produce oxygen. At that time, two oxygen-generation schemes were in the limelight: the chemical reduction of
ilmenite (FeTiO3) with hydrogen, though carbon
In the conventional set-up, a porous metal oxide body is the cathode and a carbon-based
monoxide and methane were also being considered as reductants; and molten magma electrolysis. The reduction of ilmenite with hydrogen depends on the purity of the feedstock and, if sulphides are present, a purification step is required to remove the toxic hydrogen sulphide. Reduction with methane requires high operating temperatures and a multi-step process. But it is the electrolysis route that Taylor now favours. ‘It has come a long way and has great potential for the production of oxygen on the Moon today,’ he says. The process could produce oxygen from any metal oxide. It is derived from the FFC- Cambridge process, named for the inventors, Fray, Farthing and Chen, for the electro-deoxidation of metals and metal oxides, which involves placing a metal-oxide cathode into a molten calcium chloride salt bath (CaCl2
).
Chemistry&Industry • November 2013 33
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