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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ca2Al2SiO7 by Materials Project

Ca2Al2SiO7 is Esseneite-like structured and crystallizes in the tetragonal P-42_1m space group. The structure is three-dimensional. Ca2+ is bonded in a 6-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.42–2.99 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share a cornercorner with one AlO4 tetrahedra and corners with two equivalent SiO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.73–1.80 Å. Si4+ is bonded to four equivalent O2- atoms to form SiO4 tetrahedra that share corners with four equivalent AlO4 tetrahedra. All Si–O bond lengths are 1.65 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to three equivalent Ca2+ and one Al3+ atom to form a mixture of distorted corner and edge-sharing OCa3Al tetrahedra. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Ca2+, one Al3+, and one Si4+ atom. In the third O2- site, O2- is bonded to two equivalent Ca2+ and two equivalent Al3+ atoms to form a mixture of distorted corner and edge-sharing OCa2Al2 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca2Al2SiO7 by Materials Project

Ca2Al2SiO7 crystallizes in the orthorhombic P2_12_12_1 space group. The structure is three-dimensional. there are two inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.28–2.61 Å. In the second Ca2+ site, Ca2+ is bonded in a 2-coordinate geometry to four O2- atoms. There are a spread of Ca–O bond distances ranging from 2.15–2.79 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share a cornercorner with one AlO5 square pyramid, corners with two equivalent SiO4 tetrahedra, and an edgeedge with one AlO5 square pyramid. There are a spread of Al–O bond distances ranging from 1.75–1.97 Å. In the second Al3+ site, Al3+ is bonded to five O2- atoms to form AlO5 square pyramids that share a cornercorner with one AlO4 tetrahedra, corners with two equivalent SiO4 tetrahedra, and an edgeedge with one AlO4 tetrahedra. There are a spread of Al–O bond distances ranging from 1.76–1.92 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two equivalent AlO5 square pyramids and corners with two equivalent AlO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 5-coordinate geometry to three Ca2+, one Al3+, and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Al3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and two Al3+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Al3+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two Al3+ and one Si4+ atom. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and two Al3+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1975

The effect of C/O ratio on the condensation of planetary material

The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the C/O ratio. As the ratio increases from 0.4 to 0.9, condensation temperatures of compounds such as Al2O3, Ca2Al2SiO7, MgAl2O4, Mg2SiO4, and MgSiO3 decrease by 50-100 degrees. As C/O increases from 0.9 to 1.0, these temperatures drop an additional 300-400 degrees. Other chemical differences result when C/O approximately equals or exceeds 0.9. A new suite of high-temperature minerals appears (graphite, CaS, Fe3C, SiC and TiN); the reaction CO + 3H2 yields CH4 + H2O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.

Larimer, J. W.↗