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Ilmenite has a hexagonal structure comparable to that of corundum. Fe is in the +2 oxidation state, whilst Ti is in the +4 state. Terrestrial ilmenite usually contains some Fe3+, but Fe3+ is never found in lunar ilmenite. This is due to the lack of oxidising conditions on the Moon.
Mg and Mn readily substitute for Fe atoms, although Mg is much more common than Mn in the case of lunar ilmenites.
Colour is opaque black, but in reflected light is a lightish grey with a pink-brown tinge.
Density: 4.44-4.9 g/cm3 (room temp. and pressure) Molar volume: 31.7 cm3 Molecular weight: 151.75 g Melting Point: 1640 K Eutectic with Fe2TiO2 1593 K Dimorphous Transition: 488 K
See NASA's Handbook of Lunar Materials for thermodynamic (enthalpy changes,etc) information.
Ilmenite is commonly found in mare basalts as bladed crystals up to a few millimetres long and often associated with pyroxene. It is formed at lower temperatures, where it is associated with native Fe and troilite. In Apollo 17 samples, an association with Armalcolite is also seen - the ilmenite forming a mantle on the armalcolite crystals.
It is very slowly soluble in HCl, and has variable solubility in HF.
Commercial terrestrial extraction of Ti from ilmenite, involves reduction by CO in the range of 900-1200C. The reduction proceeds by different sequences above and below 1150C to produce metallic iron.
Oxygen might also be extracted from ilmenite by reducing it to rutile and iron. Rao et al (1979) first suggested this, but temperatures of 1150C are required. Ideally, 10.5 wt% O2 could be produced by this reductions. Reduction could be from hydrogen (eg. solar wind hydrogen trapped in the regolith). Prelimary studies have shown this method to be feasible (Williams, 1985; Gibson and Knudson, 1985). Ulvöspinel could be subjected to similar reactions, although this is not as common as ilmenite, and compositions vary much more.
Rao D.B., Chondary U.V., Erstfeld T.E., Williams R.J., and Chang Y.A. (1979) Extraction processes for the production of aluminium, titanium, iron, magnesium, and oxygen from nonterrestrial sources. In Space Resources and Space Settlements (J. Billingham et al eds), pp 257-274. NASA SP-428
Williams R.J. (1985) Oxygen extraction from lunar materials. An experimental test of an ilmenite reduction process. In Lunar Bases and Space Activities of the 21st Century (W.W. Mendell, ed) pp 551-558. Lunar and Planetary Institute, Houston.
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