Structure and speciation in hydrous silica melts. 2. Pressure effects

Kelly E. Anderson; Lorna C. Grauvilardell; Marc M. Hirschmann; J. Ilja Siepmann

doi:10.1021/jp802255y

Structure and speciation in hydrous silica melts. 2. Pressure effects

Kelly E. Anderson, Lorna C. Grauvilardell, Marc M. Hirschmann, J. Ilja Siepmann

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Abstract

The effect of pressure on structure and water speciation in hydrated liquid silica is examined over a range of temperatures and compositions. The Feuston-Garofalini (FG) potential is used in isobaric-isothermal Monte Carlo simulations carried out at four pressures (0.25, 1.0, 2.5, and 10 GPa) for seven temperatures (2000 ≤ T ≤ 9000 K) and five compositions (0.0 ≤ x _w ≤ 0.4). The FG potential yields a stable melt phase for p ≥ 1.0 GPa and/or x_w ≤ 0.1 for all temperatures. The volume minimum seen in previous simulations of pure and hydrated liquid silica using the FG potential persists up to 2.5 GPa but is no longer evident at 10 GPa. This is correlated with gradual structural changes of the liquid up to 2.5 GPa and with more significant changes at 10 GPa. Even at high overall concentrations of water (x_w =0.4), only about 2% of oxygen atoms are present as molecular water species at the lowest temperature. This percentage decreases with increasing pressure and temperature.

Original language	English (US)
Pages (from-to)	13015-13021
Number of pages	7
Journal	Journal of Physical Chemistry B
Volume	112
Issue number	41
DOIs	https://doi.org/10.1021/jp802255y
State	Published - Oct 16 2008

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abstract = "The effect of pressure on structure and water speciation in hydrated liquid silica is examined over a range of temperatures and compositions. The Feuston-Garofalini (FG) potential is used in isobaric-isothermal Monte Carlo simulations carried out at four pressures (0.25, 1.0, 2.5, and 10 GPa) for seven temperatures (2000 ≤ T ≤ 9000 K) and five compositions (0.0 ≤ x w ≤ 0.4). The FG potential yields a stable melt phase for p ≥ 1.0 GPa and/or xw ≤ 0.1 for all temperatures. The volume minimum seen in previous simulations of pure and hydrated liquid silica using the FG potential persists up to 2.5 GPa but is no longer evident at 10 GPa. This is correlated with gradual structural changes of the liquid up to 2.5 GPa and with more significant changes at 10 GPa. Even at high overall concentrations of water (xw =0.4), only about 2% of oxygen atoms are present as molecular water species at the lowest temperature. This percentage decreases with increasing pressure and temperature.",

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AU - Anderson, Kelly E.

AU - Grauvilardell, Lorna C.

AU - Hirschmann, Marc M.

AU - Siepmann, J. Ilja

PY - 2008/10/16

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N2 - The effect of pressure on structure and water speciation in hydrated liquid silica is examined over a range of temperatures and compositions. The Feuston-Garofalini (FG) potential is used in isobaric-isothermal Monte Carlo simulations carried out at four pressures (0.25, 1.0, 2.5, and 10 GPa) for seven temperatures (2000 ≤ T ≤ 9000 K) and five compositions (0.0 ≤ x w ≤ 0.4). The FG potential yields a stable melt phase for p ≥ 1.0 GPa and/or xw ≤ 0.1 for all temperatures. The volume minimum seen in previous simulations of pure and hydrated liquid silica using the FG potential persists up to 2.5 GPa but is no longer evident at 10 GPa. This is correlated with gradual structural changes of the liquid up to 2.5 GPa and with more significant changes at 10 GPa. Even at high overall concentrations of water (xw =0.4), only about 2% of oxygen atoms are present as molecular water species at the lowest temperature. This percentage decreases with increasing pressure and temperature.

AB - The effect of pressure on structure and water speciation in hydrated liquid silica is examined over a range of temperatures and compositions. The Feuston-Garofalini (FG) potential is used in isobaric-isothermal Monte Carlo simulations carried out at four pressures (0.25, 1.0, 2.5, and 10 GPa) for seven temperatures (2000 ≤ T ≤ 9000 K) and five compositions (0.0 ≤ x w ≤ 0.4). The FG potential yields a stable melt phase for p ≥ 1.0 GPa and/or xw ≤ 0.1 for all temperatures. The volume minimum seen in previous simulations of pure and hydrated liquid silica using the FG potential persists up to 2.5 GPa but is no longer evident at 10 GPa. This is correlated with gradual structural changes of the liquid up to 2.5 GPa and with more significant changes at 10 GPa. Even at high overall concentrations of water (xw =0.4), only about 2% of oxygen atoms are present as molecular water species at the lowest temperature. This percentage decreases with increasing pressure and temperature.

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Structure and speciation in hydrous silica melts. 2. Pressure effects

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