Nature of polymerization and properties of silicate melts and glasses at high pressure

Lee, Sung Keun; Cody, George D.; Fei, Yingwei; Mysen, Bjørn O.

doi:10.1016/j.gca.2004.04.002

Cited by 139 publications

(181 citation statements)

References 44 publications

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“…The results are therefore pertinent for understanding the properties of high-density liquids to aid, e.g., in the design of glasses with new network topologies (8,(38)(39)(40). They are also relevant to magma-related melts because the onset of higher coordinated modifying species changes the network polymerization (i.e., the ratio of bridging versus nonbridging oxygen atoms), thereby affecting the transport properties (e.g., viscosity) and compressibility (3)(4)(5)(6)(7).…”

Section: Discussionmentioning

confidence: 99%

“…For materials in which the network-forming motifs are three-, four-or sixfold-coordinated, regular polyhedra were assumed such that r O = ð ffiffiffi 3 p =2Þr AO for planar AO 3 triangles, r O = ð ffiffiffiffiffiffiffiffi 2=3 p Þr AO for AO 4 tetrahedra, and r O = r AO = ffiffiffi 2 p for AO 6 octahedra, where r AO is the mean nearest-neighbor A-O distance. The r O values for AlO 5 and GeO 5 units are given in SI Text, sections 3.2 and 4.3, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…Examples range from the dependence on network connectivity of the transport properties (e.g., viscosity) of glass-forming and/or magma-related oxide melts (3)(4)(5)(6)(7) to the role played by atomic packing in determining the elastic behavior of glass (8)(9)(10). In the case of open glass-forming structures, the network connectivity often follows from Zachariasen's rules (11), but there is no reliable guide for predicting the conditions under which transformations occur in the character of network-forming motifs, e.g., from AO 3 to AO 4 or from AO 4 to AO 6 polyhedra.…”

mentioning

confidence: 99%

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Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Zeidler

Salmon

Skinner

2014

Proc. Natl. Acad. Sci. U.S.A.

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Liquid and glassy oxide materials play a vital role in multiple scientific and technological disciplines, but little is known about the part played by oxygen-oxygen interactions in the structural transformations that change their physical properties. Here we show that the coordination number of network-forming structural motifs, which play a key role in defining the topological ordering, can be rationalized in terms of the oxygen-packing fraction over an extensive pressure and temperature range. The result is a structural map for predicting the likely regimes of topological change for a range of oxide materials. This information can be used to forecast when changes may occur to the transport properties and compressibility of, e.g., fluids in planetary interiors, and is a prerequisite for the preparation of new materials following the principles of rational design. Examples range from the dependence on network connectivity of the transport properties (e.g., viscosity) of glass-forming and/or magma-related oxide melts (3-7) to the role played by atomic packing in determining the elastic behavior of glass (8-10). In the case of open glass-forming structures, the network connectivity often follows from Zachariasen's rules (11), but there is no reliable guide for predicting the conditions under which transformations occur in the character of network-forming motifs, e.g., from AO 3 to AO 4 or from AO 4 to AO 6 polyhedra.With increasing density, oxygen-oxygen interactions are expected to manifest themselves in the structural transformations that occur (12), but the nature of this role is unknown. For example, the oxygen atom number density ρ O will depend on the type of network-forming motifs, can be altered by adding network modifiers, and will increase with density. Nevertheless, a plot of ρ O versus the measured mean A-O coordination number n O A for network-forming structural motifs does not offer a basis for generalization (Fig. 1). It will be shown, however, that if the data are scaled by the volume occupied by an oxide ion V O , and an adjustment is made for the volume occupied by any network-modifying atoms (i.e., atoms other than oxygen that are not at the centers of network-forming motifs), then the resultant oxygenpacking fraction η O does offer a means for rationalizing the structural transformations that occur. An important proviso is that a constant oxide ion size cannot be assumed. Instead, the oxide ion environment has a profound influence as evidenced by the instability of these ions in the gas phase but their omnipresence in condensed matter (13,14). This variability was recognized in the construction of well-known tables of ionic radii (15, 16), although a constant size was assumed for a given oxide ion coordination number. The variability of the oxide ion size is also a key theme in the development of transferable aspherical ion models which have been successful in accounting for many of the structure-related properties of oxide materials (13,14). In the following we use an empirical approach to tac...

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Zeidler

Salmon

Skinner

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…Alternatively, silicate glasses have been studied as analogues for quenched silicate melts to simulate high-pressure melt behaviour [16][17][18][19][20][21] . Recent experimental research on the possible spin-pairing electronic transition of iron in silicate glasses at midlower mantle pressures 22 has renewed interest in understanding the thermal transport mechanisms in dense silicate melts at the bottom of the mantle, as changes in the optical properties of ironbearing phases associated with spin transitions may significantly influence the radiative component of thermal conductivity.…”

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confidence: 99%

High-pressure radiative conductivity of dense silicate glasses with potential implications for dark magmas

et al. 2014

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The possible presence of dense magmas at Earth's core-mantle boundary is expected to substantially affect the dynamics and thermal evolution of Earth's interior. However, the thermal transport properties of silicate melts under relevant high-pressure conditions are poorly understood. Here we report in situ high-pressure optical absorption and synchrotron Mössbauer spectroscopic measurements of iron-enriched dense silicate glasses, as laboratory analogues for dense magmas, up to pressures of 85 GPa. Our results reveal a significant increase in absorption coefficients, by almost one order of magnitude with increasing pressure to B50 GPa, most likely owing to gradual changes in electronic structure. This suggests that the radiative thermal conductivity of dense silicate melts may decrease with pressure and so may be significantly smaller than previously expected under coremantle boundary conditions. Such dark magmas heterogeneously distributed in the lower mantle would result in significant lateral heterogeneity of heat flux through the core-mantle boundary.

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“…Although the trend in the silica activity in the melts at high pressure is not known, phase relations of mantle melts and minerals imply varying activity coefficients of the oxide in silicate melts with changes in pressure (12)(13)(14). Changes of up to two orders of magnitude in the element partitioning coefficient between melts and crystal/coexisting phases have been reported stemming mostly from the effect of the melt composition, constraining the fate of radioactive nuclides in the Earth's interior (15-18).The key to understanding these nonlinear changes in melt properties with pressure is the melt structure at high-pressure in a short-(e.g., coordination number) to medium-range scale (19)(20)(21). While recent progress in mineral physics provides the link between the macroscopic properties and the structures of the crystals, the nature of changes in the melt structure at high pressures, such as those deep within the magma-ocean, remain poorly constrained as detailed knowledge about the structure of melts cannot be determined based on their compositions alone.…”

mentioning

confidence: 99%

Simplicity in melt densification in multicomponent magmatic reservoirs in Earth’s interior revealed by multinuclear magnetic resonance

Lee

2011

Proc. Natl. Acad. Sci. U.S.A.

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Pressure-induced changes in properties of multicomponent silicate melts in magma oceans controlled chemical differentiation of the silicate earth and the composition of partial melts that might have formed hidden reservoirs. Although melt properties show complex pressure dependences, the melt structures at high pressure and the atomistic origins of these changes are largely unknown because of their complex pressure-composition dependence, intrinsic to multicomponent magmatic melts. Chemical constraints such as the nonbridging oxygen (NBO) content at 1 atm, rather than the structural parameters for melt polymerization, are commonly used to account for pressure-induced changes in the melt properties. Here, we show that the pressure-induced NBO fraction in diverse silicate melts show a simple and general trend where all the reported experimental NBO fractions at high pressure converge into a single decaying function. The pressure-induced changes in the NBO fraction account for and predict the silica content, nonlinear variations in entropy, and the transport properties of silicate melts in Earth's mantle. The melt properties at high pressure are largely different from what can be predicted for silicate melts with a fixed NBO fraction at 1 atm. The current results with simplicity in melt polymerization at high pressure provide a molecular link to the chemical differentiation, possibly missing Si content in primary mantle through formation of hidden Si-rich mantle reservoirs. E arly in Earth history, during the magma-ocean phase, the chemical differentiation of the silicate earth, formation of core, and evolution of atmosphere were controlled by the properties of silicate melts at high pressure (1-6). Pioneering experimental studies show that these thermodynamic and transport properties relevant to the chemical evolution of the Earth vary nonlinearly with changes in pressure (7-9). For instance, the solubility of Ar into melts increases with increasing pressure and then decreases drastically with a further increase in pressure, with data suggesting a strong composition dependence (7,10,11). Similarly, complex behaviors were reported for the diffusivity and viscosity of silicate melts at high pressure (8). Although the trend in the silica activity in the melts at high pressure is not known, phase relations of mantle melts and minerals imply varying activity coefficients of the oxide in silicate melts with changes in pressure (12)(13)(14). Changes of up to two orders of magnitude in the element partitioning coefficient between melts and crystal/coexisting phases have been reported stemming mostly from the effect of the melt composition, constraining the fate of radioactive nuclides in the Earth's interior (15-18).The key to understanding these nonlinear changes in melt properties with pressure is the melt structure at high-pressure in a short-(e.g., coordination number) to medium-range scale (19)(20)(21). While recent progress in mineral physics provides the link between the macroscopic properties and the structures of...

show abstract

Nature of polymerization and properties of silicate melts and glasses at high pressure

Cited by 139 publications

References 44 publications

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

Packing and the structural transformations in liquid and amorphous oxides from ambient to extreme conditions

High-pressure radiative conductivity of dense silicate glasses with potential implications for dark magmas

Simplicity in melt densification in multicomponent magmatic reservoirs in Earth’s interior revealed by multinuclear magnetic resonance

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