Multicomponent Silicate Melts Research Articles

The Effects of Alkalis Content on Zircon Solubility in Silicate Melts

The experimental study of the effects of alkalis content on zircon solubility in multicomponent model silicate melts was conducted in temperature range 1300–1400°С and at 1 atm total pressure. It was demonstrated that the addition to the melt of Na2O and K2O results in comparable increase of zircon solubility. The advantages and disadvantages of the parameters describing zircon solubility are shortly discussed.

Unravelling the effect of nano-heterogeneity on the viscosity of silicate melts: Implications for glass manufacturing and volcanic eruptions

Traditionally depicted as homogeneous materials, manmade and volcanic glasses are often subjected to nanostructuration during demixing and crystallization of their parental melt. While the controlled formation of nanocrystals has been exploited for decades in the industrial production of glass-ceramics to obtain materials with superior properties, nano-heterogeneities have been recently recognized in volcanic products erupted explosively. Here, a multi-pronged approach is adopted to highlight how the emergence of nano-heterogeneities exerts a previously unexplored influence on the viscosity of multicomponent silicate melts. Calorimetry and viscometry provide evidence of how the formation of TiO2- and FeO-bearing nanocrystals increases the effective viscosity of suspensions. Raman spectroscopy and transmission electron microscopy allow the correlation between the increase in viscosity and the degree of sample modification. This study has implications for glass and glass-ceramics manufacturing and for the development of better numerical models of volcanic eruptions, which are key for the operational assessment of volcanic risk.

Ferric/ferrous ratio in silicate melts: a new model for 1 atm data with special emphasis on the effects of melt composition

The effect of MgO and total FeO on ferric/ferrous ratio in model multicomponent silicate melts was investigated experimentally in the temperature range 1300–1500 °C at 1 atm total pressure in air. We demonstrate that the addition of these weak network modifier cations results in an increase of Fe3+/Fe2+ ratio in both mafic and silicic melts. Based on present and published experimental data, a new empirical equation is proposed to predict the ferric/ferrous ratio as a function of oxygen fugacity, temperature and melt composition. In contrast to previous equations, the compositional effect of melts on the Fe3+/Fe2+ ratio is not only modeled by the sum of the molar fraction of the individual oxide components. Additional interactions terms have also been incorporated. The main advantage of the proposed model is its applicability for a wide compositional range. However, its application to felsic melts (> 68 wt% SiO2) is not recommended. Other advantages of this equation and differences when compared with previous models are discussed.

Role of partial molar enthalpy of oxides on Soret effect in high-temperature CaO\u2013SiO2 melts

The Soret effect or thermodiffusion is the temperature-gradient driven diffusion in a multicomponent system. Two important conclusions have been obtained for the Soret effect in multicomponent silicate melts: first, the SiO2 component concentrates in the hot region; and second, heavier isotopes concentrate in the cold region more than lighter isotopes. For the second point, the isotope fractionation can be explained by the classical mechanical collisions between pairs of particles. However, as for the first point, no physical model has been reported to answer why the SiO2 component concentrates in the hot region. We try to address this issue by simulating the composition dependence of the Soret effect in CaO–SiO2 melts with nonequilibrium molecular dynamics and determining through a comparison of the results with those calculated from the Kempers model that partial molar enthalpy is one of the dominant factors in this phenomenon.

Towards a structural model for the viscosity of geological melts

The viscosity of silicate melts is the most important physical property governing magma transport and eruption dynamics. This macroscopic property is controlled by composition and temperature but ultimately reflects the structural organization of the melt operating at the microscale. At present, there is no explicit relationship connecting viscosity to silicate melt structure and vice versa. Here, we use a single Raman spectroscopic parameter, indicative of melt structure, to accurately forecast the viscosity of natural, multicomponent silicate melts from spectroscopic measurements on glasses preserved on Earth and other planets. The Raman parameter is taken as the ratio of low and high frequency vibrational bands from the silicate glass by employing a green source laser wavelength of 514.5 nm (R514.5). Our model is based on an empirical linkage between R514.5 and coefficients in the Vogel–Fulcher–Tammann function for the temperature dependence of melt viscosity. The calibration of the Raman-based model for melt viscosity is based on 413 high-temperature measurements of viscosity on 23 melt compositions for which published Raman spectra are available. The empirical model obviates the need for chemical measurement of glass compositions, thereby, providing new opportunities for tracking physical and thermochemical properties of melts during igneous processes (e.g., differentiation, mixing, assimilation). Furthermore, our model serves as a milepost for the future use of Raman spectral data for predicting transport (and calorimetric) properties of natural melts at geological conditions (e.g., volatiles and pressure) and production.

Effects of strong network modifiers on Fe3+/Fe2+ in silicate melts: an experimental study

The effect of CaO, Na2O, and K2O on ferric/ferrous ratio in model multicomponent silicate melts was investigated in the temperature range 1450–1550 °C at 1-atm total pressure in air. It is demonstrated that the addition of these network modifier cations results in an increase of Fe3+/Fe2+ ratio. The influence of network modifier cations on the ferric/ferrous ratio increases in the order Ca < Na < K. Some old controversial conceptions concerning the effect of potassium on Fe3+/Fe2+ ratio in simple model liquids are critically evaluated. An empirical equation is proposed to predict the ferric/ferrous ratio in SiO2–TiO2–Al2O3–FeO–Fe2O3–MgO–CaO–Na2O–K2O–P2O5 melts at air conditions.

Modelling configurational entropy of silicate melts

The Adam-Gibbs theory provides a robust connection between the transport or relaxation properties of melts and their thermochemical properties. In its expanded form:logη=A+BTScTg+CpclnTTgthe equation has adjustable unknown parameters A, B and Sc (Tg) which can be estimated from experimental estimates of configurational heat capacity (Cpc), glass transition temperature (Tg) and viscosity (η). Here, we use recently published datasets for anhydrous and hydrous silicate melts and glasses (N~50) for which there are measurements of log η and calorimetric measurements of Cpc and Tg. Our fitting strategy follows the approach developed by previous workers with the sole exception that we assume all silicate melts converge to a common, but unknown, high temperature limit to melt viscosity (e.g., A=log η∞). Our optimal value for A is −3.51±0.25. A consequence of a common, high-temperature limit to silicate melt viscosity is that the corresponding model values of glass transition temperature (Tg12), melt fragility (m), and the ratio Cpc/Sc are constrained to lie on a single plane approximated as:CpcSc=−Tg12243399−m15.518+0.996thereby establishing a quantitative connection between calorimetric and rheological measurements. Lastly, we show a good correspondence between values of Tg12 and fragility (m) from this Adam-Gibbs based model of melt viscosity and values predicted by the GRD viscosity model for multicomponent silicate melts (cf. Giordano et al., 2008).

Current limitations of molecular dynamic simulations as probes of thermo-physical behavior of silicate melts

Molecular dynamic simulations offer promise as an essential tool, complementary to experiments, for expanding the reach of computational thermodynamics in igneous petrology by evaluating excess thermodynamic properties of multicomponent silicate melts. However, we present evidence suggesting that current practices in simulation may not achieve the precision needed to predict complex phase equilibria relevant to modeling the Earth’s interior evolution. We highlight the importance of quantification of the chemical short-range order in terms of cation-cation pairs in the melt and its impact on different kinetic aspects of molecular dynamic simulations. We analyze published molecular dynamic simulation studies of silicate melts to identify specific criteria and best practices for achieving and demonstrating equilibrium and producing accurate results. Finally, we propose a list of experimental and numerical investigations that need to be performed in the future to ensure full consistency between these two approaches to reduce the gap in our fundamental understanding of silicate melts between the atomic level and the macroscopic scale.

High-resolution solid-state NMR study of the effect of composition on network connectivity and structural disorder in multi-component glasses in the diopside and jadeite join: Implications for structure of andesitic melts

The structural evolution of andesitic melts with varying compositions remains one of the unsolved questions in high-temperature geochemistry and petrology. In this article, we report the structural details of model andesitic glasses [CaO–MgO–Na2O–Al2O3–SiO2 (CMNAS)] in the diopside (CaMgSi2O6) and jadeite (NaAlSi2O6) join using high-resolution, multi-nuclear, solid-state nuclear magnetic resonance (NMR). The 27Al NMR spectra of CMNAS glasses confirm that [4]Al is dominant. While a minor fraction of [5]Al is observed, its presence is only prevalent in the glasses with higher Ca–Mg content. Topological disorder in the glass network also tends to increase with Ca–Mg content as evidenced by the increase in the quadrupolar coupling constant (Cq) of [4]Al for glasses with increasing diopside contents (XDiopside). Despite the complex nature of the glasses studied here (with five oxide components), the 17O 3QMAS NMR spectra resolve diverse bridging oxygens (BOs) and non-bridging oxygens (NBOs), from which the degree of Al avoidance among framework cations (Si and Al) and preferential proximity among non-network cations (Ca2+, Mg2+, and Na+) and each oxygen site can be estimated: presence of Al–O–Al in jadeite glass implies a violation of the Al-avoidance rule in the glasses and the decrease in the fraction of NBOs with increasing XDiopside is consistent with a decrease in their viscosity. Analysis of the peak position of {Ca, Mg}-mixed NBOs, along with the absence of Na-NBO peak, and the peak shape of Si–O–Al reveals preferential partitioning of Ca2+ and Mg2 into NBOs and the proximity of Na+ to BOs. The fraction of highly coordinated Al has been linked to thermodynamic and transport properties of the melts. Considering all the experimental Al coordination environments available in the literature, together with the current experimental studies, we attempt to establish the relationship between the fractions of highly coordinated Al and composition, particularly average cationic potential of non-network forming cations (<c/r>ave, defined as cationic potential normalized by the mole fraction of each non-network cation). The fraction of highly coordinated Al increases nonlinearly with increasing <c/r>ave. The fraction of [5,6]Al is negligible up to <c/r>ave=∼1.7, then it increases above <c/r>ave>∼1.7 regardless of changes in other compositional variables (e.g., Si/Al, NBO content). This indicates the presence of a threshold <c/r>ave value for the formation of [5,6]Al. The current experimental results with the changes in network polymerization, coordination environments, and the degree of disorder in the CMNAS glasses can improve understanding of the structure–property (particularly, configurational thermodynamic properties) relationships of multi-component natural silicate melts, including andesitic melts and glasses.

Competitive Dissolution Mechanism of Sulfur in CaMnSilicate Melts: Structural View

AbstractThe sulfide capacities of the CaOSiO2MnO(Al2O3MgO) slags were measured at 1873 K over a wide composition range using a gas‐slag equilibration method. The effects of MnO content and the MnO ↔ CaO substitution on the sulfide capacity of molten slag were also investigated based on the structural view of silicate melts. In the multicomponent silicate melts containing high MnO (up to about 50 wt%), the sulfide capacity mainly increased with increasing MnO content. Also, the sulfide capacity and the activity of MnO showed a linear relationship with a slope of unity, indicating that MnO is dominant component controlling the sulfur dissolution behavior into CaMnsilicate melts. The sulfide capacity increased as MnO substituted for CaO in the high silica melts (&gt;30 (±5) wt% SiO2), whereas it decreased by increasing the MnO/CaO ratio in the low silica melts (&lt;30(±5) wt% SiO2). This tendency of sulfide capacity resulted in the clock‐wisely rotating iso‐capacity contours from MnO‐free side to MnO‐rich corner in CaMnsilicate melts. The dissolution mechanism of sulfur in CaMnsilicate melts can be explained by the “Competitive dissolution mechanism.”

Modeling the viscosity of silicate melts containing manganese oxide

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing manganese oxide. The model requires three pairs of adjustable parameters that describe the viscosities in three systems: pure MnO, MnO-SiO2 and MnO-Al2O3-SiO2. The viscosity of other ternary and multicomponent silicate melts containing MnO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by MnO with SiO2, Al2O3, CaO, MgO, PbO, Na2O and K2O. The deviation of the available experimental data from the viscosities predicted by the model is shown to be within experimental error limits.

고상 NMR을 이용한 비정질 알루미나의 상전이 연구: 마그마 바다 구성 용융체의 결정화 과정의 의의

In order to have better insights into the chemical differentiation of Earth from its magma ocean phase to the current stratified structure, detailed information of crystallization kinetics of silicate melts consisting of the magma ocean is essential. The structural transitions in oxide glasses and melts upon crystallization provide improved prospects for a systematic and quantitative understanding of the crystallization processes. Here, we report the 3QMAS NMR spectra for sol-gel synthesized glass with varying temperature and annealing time. The NMR spectra for the amorphous show well-resolved Al coordination environments, characterized with mostly and a minor fraction of . The fraction of in the alumina phase decreases with increasing annealing time at constant temperature. The NMR results of phases also imply that multiple processes (e.g., crystallization and/or changes in structural disorder within glasses) could involve upon its phase transition. The current results and method can be useful to understand crystallization kinetics of diverse natural and multi-component silicate glasses and melts. The potential result may yield atomic-level understanding of Earth`s chemical evolution and differentiation from the magma ocean.

Sulfide Capacity of CaO&amp;ndash;SiO&lt;sub&gt;2&lt;/sub&gt;&amp;ndash;MnO&amp;ndash;Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;&amp;ndash;MgO Slags at 1873 K

The sulfide capacities of the CaO–SiO2–MnO–Al2O3–5 mass% MgO slags were measured at 1873 K over a wide composition range using a gas–slag equilibration method. The effects of basicity and the activity coefficient of sulfide on the sulfide capacity of molten slag were also investigated based on the structural view of silicate melts. In the multicomponent silicate melts containing high MnO (up to about 50 mass%), the sulfide capacity mainly increased with increasing MnO content. The capacity and modified Vee ratio, i.e. (CaO+MnO+MgO)/ (SiO2+Al2O3), showed a good linear relationship. Assuming that the basicity and the stability of sulfide ions in the slag are proportional to the activity of basic oxides and the activity coefficient of sulfides, the composition dependency of the sulfide capacity is well described by changes in the aMO to γMS (M=Ca, Mn) ratio. The substitution of silica by alumina did not affect the sulfide capacity of the slags not only because of an increase in the activity of basic oxides but also because of a decrease in the stability of sulfides as Al2O3/SiO2 ratio increased. In the high silica melts of which silica content greater than about 30 mass%, the sulfide capacity increased with increasing MnO/CaO ratio, whereas it decreased by increasing the MnO/CaO ratio in the low silica melts (< about 30 mass%). This tendency of sulfide capacity resulted in the clock-wisely rotating iso-capacity contours in the CaO–SiO2–MnO–Al2O3–MgO system at 1873 K. The dissolution mechanism of sulfur in the MnO–containing calcium silicate melts can be explained not only by the difference in the structural role of Ca2+ and Mn2+ ions but also by the changes in the content of O2– ions according to the silica content.

Modeling the Viscosity of Silicate Melts Containing Lead Oxide

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing lead oxide. The model requires three pairs of adjustable parameters that are fitted to the experimental viscosities in the following systems: pure PbO, PbO-SiO2, and PbO-Al2O3-SiO2. The viscosity of other ternary and multicomponent silicate melts containing PbO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by PbO with SiO2, Al2O3, CaO, MgO, Na2O, and K2O. The deviation of the available experimental data from the viscosities predicted by the model is within experimental error limits.

Modeling the viscosity of silicate melts containing zinc oxide

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing zinc oxide. The model requires three pairs of adjustable parameters which describe the viscosities in three systems: pure ZnO, ZnO–SiO2 and ZnO–Al2O3–SiO2. The viscosity of multicomponent silicate melts containing ZnO is then predicted by the model without any additional adjustable model parameters. Experimental viscosity data are reviewed for melts formed by ZnO with SiO2, Al2O3, PbO, CaO, MgO, Na2O and K2O. The deviation of the available experimental data from the viscosities predicted by the model is shown to be within experimental error limits.

A new approach to the equation of state of silicate melts: An application of the theory of hard sphere mixtures

A comparison of compressional properties of silicate solids, glasses, and liquids reveals the following fundamental differences: (1) Liquids have much smaller bulk moduli than solids and glasses and the bulk moduli of various silicate melts have a narrow range of values; (2) Liquids do not follow the Birch’s law of corresponding state as opposed to solids and glasses; (3) The Grüneisen parameter increases with increasing pressure for liquids but decreases for solids; (4) The radial distribution functions of liquids show that the interatomic distances in liquids do not change upon compression as much as solids do. The last observation indicates that the compression of silicate melts occurs mostly through the geometrical arrangement of various units whose sizes do not change much with compression, i.e., the entropic mechanism of compression plays a dominant role over the internal energy contribution. All of the other three observations listed above can be explained by this point of view. In order to account for the role of the entropic contribution, we propose a new equation of state for multi-component silicate melts based on the hard sphere mixture model of a liquid. We assign a hard sphere for each cation species that moves in the liquid freely except for the volume occupied by other spheres. The geometrical arrangement of these spheres gives the entropic contribution to compression, while the Columbic attraction between all ions provides the internal energy contribution to compression. We calibrate the equation of state using the experimental data on room-pressure density and room-pressure bulk modulus of liquids. The effective size of a hard sphere for each component in silicate melts is determined. The temperature and volume dependencies of sphere diameters are also included in the model in order to explain the experimental data especially the melt density data at high pressures. All compressional properties of a silicate melt can be calculated using the calibrated sphere diameters. This equation of state provides a unified explanation for most of compressional behaviors of silicate melts and the experimental observations cited above including the uniformly small bulk moduli of silicate melts as well as the pressure dependence of Grüneisen parameters. With additional data to better constrain the key parameters, this equation of state will serve as a first step toward the unified equation of state for silicate melts.

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

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.

Thermodynamic simulation of the behavior of network-modifying cations in multicomponent silicate melts

1128 The structure and physicochemical properties of silicate and magmatic melts are currently described mostly within the scope of a model representing the structure of melts as an ensemble of silicon–oxygen structural units Q n (where n is the number of bridging oxygen atoms). The concentrations of these structural units depend on the composition and temperature and can be experimentally determined from Raman spec� tra or calculated by means of thermodynamic simula� tions [1–3].

Diffusion Data in Silicate Melts

Atomic scale diffusion in silicate melts plays a critical role in a variety of magmatic processes, as long recognized by geologists (Bowen 1921). Geochemists have investigated diffusion in silicate melts (including stable liquids and supercooled liquids and glasses) using a variety of methods as micro-analytical tools becoming available (e.g., Medford 1973; Jambon and Carron 1976; Magaritz and Hofmann 1978a,b; Hofmann 1980; Shimizu and Kushiro 1984; Zhang et al. 1991a; Koepke and Behrens 2001; Saal et al. 2008). The investigations were aimed at understanding the mechanisms of diffusion, the effect of temperature, pressure, H2O content, f O2, and more generally melt composition on the diffusivities, and to measure the diffusivity values for geological applications. A large database is now available. This chapter reviews diffusion data relevant to magmatic systems. The large body of literature on diffusion in simple-system melts, of interests to glass and ceramic scientists, is not included in this review, nor are the calculated diffusivities from ab initio and molecular dynamics methods. This review covers literature diffusion data (except multicomponent diffusion matrix data, and those of H, C, O and noble gases) in multicomponent silicate melts (the term melts as used in this chapter also includes glasses), including melts with mineral compositions and including glasses. This chapter complements the other chapters on diffusion in silicate melts, which cover H, C and O diffusion (Zhang and Ni 2010, this volume), noble gas diffusion (Behrens 2010, this volume), theories and models of self and tracer diffusion (Lesher 2010, this volume), and multicomponent diffusion (Liang 2010, this volume). We have compiled experimental data on self, tracer and effective binary diffusion in Online Supplementary Table 1 (found at http://www.minsocam.org/MSA/RIM ), with about 3600 entries of individual diffusivity …

A model to calculate the viscosity of silicate melts

Abstract Our recently developed model to describe the viscosity of binary silicate melts is extended to describe and predict the viscosities of multicomponent silicate melts. The viscosity of multicomponent melts containing no AlO1.5 is modeled to vary linearly as a function of the mole fractions of the basic oxides at constant SiO2 mole fraction. Systems containing AlO1.5 show a more or less pronounced viscosity maximum close to the charge compensating composition. This maximum is caused by some of the Al3+ taking on the same structural role as Si4+, thereby participating in the formation of the silica network. The network-forming Al3+ must remain associated with either one Na+, or two Al3+ ions must remain associated with one Mg2+ or Ca2+, in order to assure charge neutrality. To take this into account we introduce the associates NaAlO2, CaAl2O4 and MgAl2O4 that correspond to charge compensated network-forming Al3+. The Gibbs energy of formation of these associates determines the amount of Al3+ that takes on the network-forming role. We assume the effect on viscosity of network-forming Al3+ to be the same as Si4+ and optimize the Gibbs energies of the associates to reproduce the experimental viscosity data. Viscosities in ternary silicate systems without AlO1.5 are quantitatively predicted with no additional ternary model parameters. Ternary systems MeO x – SiO2 – AlO1.5 are modeled with only two temperature-independent ternary parameters per system. The model not only reproduces the magnitude of the observed viscosity maximum, but also its complex shape, asymmetry and temperature dependence.