Structure and Speciation in Hydrous Silica Melts. 2. Pressure Effects

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

doi:10.1021/jp802255y

Cited by 10 publications

(5 citation statements)

References 31 publications

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“…17 This paper will proceed as follows: in section 2, we will provide the methodological details of the study; in section 3, an analysis of the simulations; and in section 4, a summary of these findings. In the companion to this paper, 18 pressure effects on hydrated silica are discussed.…”

Section: Introductionmentioning

confidence: 99%

Structure and Speciation in Hydrous Silica Melts. 1. Temperature and Composition Effects

2008

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Monte Carlo simulations were used to investigate the phase behavior of hydrated liquid silica as a function of temperature and overall water mole fraction, x w. Simulations using the Feuston-Garofalini potential were performed in the isobaric-isothermal ensemble at p = 1 GPa for 15 temperatures (2000 < or = T < or = 9000 K) and 25 compositions (0.0 < or = x w < or = 0.4). The unusual volume minimum exhibited by tetrahedrally coordinated liquid silica is found to persist up to x w approximately 0.267, although the temperature of the volume minimum decreases with increasing water content. Structural properties of the pure and hydrated systems are compared and the addition of water to liquid silica disrupts the silica network more dramatically than temperature alone. The simulations yield very low concentrations of molecular water, e.g. only about 1.2% of the oxygen atoms are bound to exactly two hydrogen atoms at x w = 0.4 and T = 3000 K.

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Section: Introductionmentioning

confidence: 99%

Structure and Speciation in Hydrous Silica Melts. 1. Temperature and Composition Effects

2008

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“…Can hydrous silica liquid be a potential proton conductor? A first-principles approach [13-15] correctly describing hydrogen bond, which is an issue in widely used (dominantly) ionic models [16], can answer these questions.Here, we use the first-principles molecular dynamics method [17] to investigate the structure and dynamics of hydrous (with 8.25 wt% water) and anhydrous silica liquids as a function of pressure (P) and temperature (T) and evaluate or isolate the effects of water unlike in the case of other silicates (e.g., MgSiO 3 ) that are already depolymerized due to other cations. The local density approximation [18] and projector augmented wave method [19] (with a cutoff of 450 eV and gamma point) were used.…”

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confidence: 99%

“…Can hydrous silica liquid be a potential proton conductor? A first-principles approach [13][14][15] correctly describing hydrogen bond, which is an issue in widely used (dominantly) ionic models [16], can answer these questions.…”

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confidence: 99%

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First-Principles Study of Enhancement of Transport Properties of Silica Melt by Water

Karki

Stixrude²

2010

Phys. Rev. Lett.

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First-principles molecular dynamics simulations show that water (8.25 wt%) dramatically affects the transport properties of SiO2 liquid increasing the diffusivity and decreasing the viscosity by an order of magnitude. At 3000 K, the diffusivity of Si, O, and H, and the viscosity vary anomalously with pressure. Highly mobile protons make the hydrous liquid a potential superionic conductor. The predicted dynamical changes are associated with structural depolymerization and water speciation, which changes from being dominated by hydroxyls at low pressure to extended structures at high pressure.

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“…In terms of isochemical compaction with increasing pressure, FPMD simulations [ Anderson et al ., ; Mookherjee et al ., ; Karki and Stixrude , ; Karki et al ., ] and in situ structural observations [ Yamada et al ., ] have shown that bond lengths of O–H and Si–O increase monotonously with increasing pressure. The coordination of Si–O, O–H, and H–O also increases with increasing pressure.…”

Section: Resultsmentioning

confidence: 98%

Density and seismic velocity of hydrous melts under crustal and upper mantle conditions

Ueki

Iwamori

2016

Geochem. Geophys. Geosyst.

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We present a new model for calculating the density of hydrous silicate melts as a function of P, T, H2O concentration, and melt composition. We optimize VPr,Tr, ∂V/∂T, ∂V/∂P, ∂V2/∂T∂P, and K′ of H2O end‐member components in hydrous silicate melts, as well as K′ of anhydrous silicate melts, using previously reported experimental results. The parameter set for H2O end‐member component in silicate melt optimized in this study is internally consistent with the parameter values for the properties of anhydrous silicate melt reported by Lange and Carmichael (1987, 1990). The model calculation developed in this study reproduces the experimentally determined densities of various hydrous melts, and can be used to calculate the relationships between pressures, temperatures, and H2O concentrations of various hydrous melts from ultramafic to felsic compositions at pressures of 0–4.29 GPa. Using the new parameter set, we investigate the effects of H2O content on the seismic velocity of hydrous melts, as well as seismic velocities in partially molten regions of subduction zones. The results show that water content in silicate melt plays a key role in determining seismic velocity structure, and therefore must be taken into account when interpreting seismic tomography.

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Structure and Speciation in Hydrous Silica Melts. 2. Pressure Effects

Cited by 10 publications

References 31 publications

Structure and Speciation in Hydrous Silica Melts. 1. Temperature and Composition Effects

Structure and Speciation in Hydrous Silica Melts. 1. Temperature and Composition Effects

First-Principles Study of Enhancement of Transport Properties of Silica Melt by Water

Density and seismic velocity of hydrous melts under crustal and upper mantle conditions

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