Viscosity Of Silicate Melts Research Articles

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.

A model to calculate the viscosity of silicate melts

Abstract Our recently developed model for the viscosity of borosilicate melts is extended to describe and predict the viscosities of melts containing alkali oxides. In addition to the two model parameters that are required for each B2O3–MO x melt, where MO x is a basic oxide, three more parameters are needed when MO x is an alkali oxide to account for the formation of clusters near the tetraborate composition. The additional parameters represent the size and Gibbs energy of formation of these clusters and their contribution to the activation energy of the viscous flow. A general algorithm for the calculation of the viscosity is presented which summarizes the application of the viscosity model to melts that can contain two network formers, SiO2 and B2O3, any basic oxide and amphoteric oxides exhibiting the Charge Compensation Effect such as Al2O3. The predictive ability of the model is tested on all ternary subsystems of the B2O3–Na2O–K2O–CaO–MgO–PbO–ZnO–Al2O3–SiO2 system containing both an alkali oxide and B2O3 for which experimental data are available and on several multicomponent glass-forming melts around commercial glass compositions.

A model to calculate the viscosity of silicate melts

Abstract Our recently developed model for the viscosity of silicate melts is extended to describe and predict the viscosities of oxide melts containing boron. The model requires three adjustable parameters to reproduce the viscosity of B2O3–SiO2 melts and two parameters for each B2O3–MO x melt, where MO x is a basic oxide other than an alkali oxide. All available experimental data have been collected for binary melts formed by B2O3 with SiO2, Al2O3, CaO, MgO, ZnO, PbO to calibrate the model. The viscosities of the B2O3-containing ternary and higher-order subsystems of the B2O3–CaO–MgO–PbO–ZnO–SiO2 system and of the B2O3–CaO–MgO–PbO–ZnO–Al2O3 system are then predicted by the model without any additional adjustable parameters. Experimental data were found for only five such subsystems: B2O3–PbO–SiO2, B2O3–CaO–SiO2, B2O3–PbO–ZnO, B2O3–PbO–Al2O3 and B2O3–CaO–Al2O3. Predictions of the model are compared to these experimental data.

A model to calculate the viscosity of silicate melts

Abstract Our recently developed model to describe the viscosity of silicate melts is extended to describe and predict the viscosities of alkali-rich silicate melts. The model requires one additional binary parameter for each M 2O–SiO2 system, where M is an alkali metal, to a total of three binary parameters per binary system alkali oxide – silica. In addition to unary and binary parameters, the model requires two ternary parameters for each alumina-containing ternary system MOx–Al2O3 –SiO2, where MOx is a basic oxide, to describe the viscosity maxima in these ternary systems due to the Charge Compensation Effect. The viscosity of multicomponent melts and of ternary melts MOx–NOy–SiO2, where MOx and NOy are basic oxides, is predicted by the model solely from the unary, binary and ternary parameters. The available viscosity data for the alkali-containing subsystems of the Al2O3–CaO–MgO–Na2O–K2O–SiO2 system are reviewed. The model reproduces the experimental data for binary and ternary melts and predicts the viscosities of multicomponent melts within experimental error limits. In particular, the viscosities of glass melts and melts of importance for petrology are well predicted by the model.

Viscosity model for fully liquid silicate melt

A model for estimating the viscosity of silicate melt as derived in our previous paper is extended to the system containing MgO, CaO, SrO, BaO, Li2O, Na2O, K2O, which can express the nonlinear variation of activation energy of viscosity with the composition. It is found that the optimized parameters of model which characterize the deforming ability of bonds around non-bridging oxygen decrease with increasing the bond strength of M-O bond expressed by I=2Q/RMz+ + rO2-)2 (where Q is the valence of cation M; r is the radius). It is pointed out that viscosity is not only determined by the bond strength, but also by the radius of cation which is defined as the size effect. The radius of cation plays paradox roles in the two factors: smaller radius leads to a stronger bond, thus a higher viscosity; while cations with smaller radius are easier to diffuse when neglecting the interaction force, thus a lower viscosity will be.

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 Viscosities of CaO-MgO-FeO-MnO-SiO2 Molten Slags

A model for estimating the viscosity of silicate melts is proposed in this article. The structural characteristics of a silicate slag can be described by the numbers of the bridging oxygen, nonbridging oxygen, and free oxygen present in the slag. A method of calculating the numbers of the different types of oxygen ions is presented in this article, which involves a simple approximation of “complete bridge breaking.” With just a few parameters, the model provides both the temperature and composition dependencies of viscosity for the pure component: SiO2; the binary systems: MgO-SiO2, CaO-SiO2, FeO-SiO2, and MnO-SiO2; the ternary systems: CaO-MgO-SiO2, CaO-FeO-SiO2, MgO-FeO-SiO2, and CaO-MnO-SiO2; and the quaternary systems: CaO-MgO-MnO-SiO2 and CaO-FeO-MnO-SiO2. It was found that the ability of different basic metal oxides to decrease viscosity varies and is in the following hierarchy: FeO > MnO > CaO > MgO. Two factors influence the viscosity: The first is related to the mutual interaction among different ions, and the stronger the interaction, the higher the viscosity. The second factor is the size (radius) of basic oxide cation, with viscous flow becoming increasingly more difficult (i.e., viscosity increases) as the cation size increases. However, there is a paradox in the effect of cation radius (of the basic oxide) on the two factors. Thus, varying cation size causes competitive effects; smaller cationic radii give stronger interactions among ions but less hindrance to viscous flow (and vice versa for large cation radii).

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.

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x i of all oxides dissolved in SiO 2 , the molar fraction of the latter being 1 − x . It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T r , at which viscosity is η r = 10 13 [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l i is a product of molar part x i and a specific dimensionless coefficient 0 ≤ k i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0 , the reference temperature is related to the “lubricant fraction” l through the reference temperature T r,SiO2 of pure SiO 2 .

Seismogenic Shear Zones in the Lithospheric Mantle: Ultramafic Pseudotachylytes in the Lanzo Peridotite (Western Alps, NW Italy)

At Mt. Moncuni (Lanzo Massif, Western Alps) plagioclase peridotites and early mid-ocean ridge basalt (MORB) gabbroic dykes are deformed by shear zones containing cataclastic bands and both fault-vein and injection-vein pseudotachylytes, which are crosscut by late MORB porphyritic dykes. Fault-vein pseudotachylytes have thicknesses of the order of 1 mm; injection-vein pseudotachylytes have a typical thickness of 1–10 cm and contain spinifex textures. Structural, petrological and geochemical data show that the pseudotachylytes formed by near-complete melting of the host peridotite, at ambient temperature–pressure conditions (T = 600 ± 100°C, P < 0·5 GPa) close to the brittle–ductile transition of ultramafic rocks, during exhumation of the lithospheric mantle in the early stages of formation of the Ligurian Tethys oceanic basin. Estimates of the average volume fraction of unmelted clasts and of the ambient and liquidus temperature, together with thermophysical parameters, allow the determination of the melting energy per unit volume. Coseismic displacement is not observable at Mt. Moncuni, and consequently the dynamic shear resistance cannot be inferred. We show that commonly proposed relations between fault-vein thickness and displacement are of limited value, given the difficulty in identifying ‘single-event’ pseudotachylytes and the mobility of the melt. However, we also show that dynamic shear resistance can be predicted to decrease sharply if the melt coats the whole fault plane, partly as a consequence of the nonlinear viscosity of silicate melts at high strain rates. The Mt. Moncuni pseudotachylytes are the result of upper mantle seismicity at shallow depth (z < 20 km) over a time period of at most 5 Myr. Estimation of the total seismic energy release and moment (caused by an unspecified number of small to moderate earthquakes) requires an assessment of the total pseudotachylyte volume. This is highly uncertain, with a probable qualitative error margin of ±1 order of magnitude. The inferred values of cumulative seismic energy release and moment are of the order of 1015 ± 1 J and 1019 ± 1 N m, respectively, resulting in a seismic energy release rate of approximately 108 ± 1 J/a. This value is compatible with present-day seismic rates at extensional plate margins.

The influence of atomic size and charge of dissolved species on the diffusivity and viscosity of silicate melts

Molecular dynamics simulations are used to determine how a dissolved species alters the transport properties of a silicate melt. To identify the specific factors that affect the transport properties, we examine the effects of generic dissolved species for which the atomic interaction parameters can be systematically varied. We focus on the role of the size and charge of the dissolved species. Our results show that neutral dissolved species have negligible effects on the structure and bonding of the silica network, regardless of the size of the species. These neutral species are decoupled from the network, and can diffuse orders of magnitude faster than the network ions. In contrast, charged species strongly disrupt the silica network, which leads to significant enhancement of the transport properties (e.g., lower viscosity and higher diffusivity of the network ions). The effects of the charged dissolved species are strongly dependent on their size.

Use of a pressless multianvil high-pressure split-sphere apparatus to measure the silicate melt viscosity

The possibility of using a pressless multianvil high-pressure split-sphere apparatus to measure the viscosity of silicate melts was studied experimentally using as an example diopside melt (CaMgSi2O6) at a pressure of 4.0 GPa and a temperature of 1800°C. The viscosity was calculated by the Stokes formula. The measurement error of the melt viscosity was estimated by the falling ball method. Prospects for using devices of this type to estimate the viscosity of silicate melts at high pressures and temperatures are shown.

An experimental study on the pressure dependence of viscosity in silicate melts

The effect of pressure on melt viscosity was investigated for five compositions along the join An(CaAl(2)Si(2)O(8))-Di(CaMgSi(2)O(6)) and four alkali silicates containing lithium, sodium, and potassium in constant ratio of approximately 1:1:1, but alkali-silica ratios are varying. The experiments were performed in an internally heated gas pressure vessel at pressures from 50 to 400 MPa in the viscosity range from 10(8) to 10(11.5) Pas using parallel plate viscometry. The polymerized An composition shows a negative pressure dependence of viscosity while the other, more depolymerized compositions of the join An-Di have neutral to positive pressure coefficients. The alkali silicates display neutral to slightly positive pressure coefficients for melt viscosity. These findings in the high viscosity range of 10(8)-10(11) Pas, where pressure appears to be more efficient than in low viscous melts at high temperature, are consistent with previous results on the viscosity of polymerized to depolymerized melts in the system NaAlSi(3)O(8)-CaMgSi(2)O(6) by Behrens and Schulze [H. Behrens and F. Schulze, Am. Mineral. 88, 1351 (2003)]. Thus we confirm that the sign of the pressure coefficient for viscosity is mainly related to the degree of melt polymerization in silicate and aluminosilicate melts.

Residual and configurational entropy: Quantitative checks through applications of Adam–Gibbs theory to the viscosity of silicate melts

Abstract In this paper the traditional view that glasses possess residual entropy, which can be determined by calorimetric means, is quantitatively supported by applications of Adam and Gibbs configurational entropy theory to the temperature, composition and pressure dependences of the viscosity of silicate melts. This theory is also in harmony with the mechanisms of viscous flow, as understood from NMR experiments, according to which viscosity is controlled by the rate of bond rearrangements between network-forming cations and oxygens. As a matter of fact, Adam and Gibbs basic expression relating structural relaxation times to the reciprocal of the product of temperature and configurational entropy can be derived from a phenomenological analysis of the temperature dependence of the activation energy for viscous flow. Adam–Gibbs theory thus works well for silicate melts because network-modifying cations also play a role in bond rearrangements such that, as a bulk property, configurational entropy is actually relevant to structural relaxation and flow.

Pressure dependence of viscosity of rhyolitic melts

Viscosity of silicate melts is a critical property for understanding volcanic and igneous processes in the Earth. We investigate the pressure effect on the viscosity of rhyolitic melts using two methods: indirect viscosity inference from hydrous species reaction in melts using a piston cylinder at pressures up to 2.8 GPa and direct viscosity measurement by parallel-plate creep viscometer in an internally-heated pressure vessel at pressures up to 0.4 GPa. Comparison of viscosities of a rhyolitic melt with 0.8 wt% water at 0.4 GPa shows that both methods give consistent results. In the indirect method, viscosities of hydrous rhyolitic melts were inferred based on the kinetics of hydrous species reaction in the melt upon cooling (i.e., the equivalence of rheologically defined glass transition temperature and chemically defined apparent equilibrium temperature). The cooling experiments were carried out in a piston-cylinder apparatus using hydrous rhyolitic samples with 0.8–4 wt% water. Cooling rates of the kinetic experiments varied from 0.1 K/s to 100 K/s; hence the range of viscosity inferred from this method covers 3 orders of magnitude. The data from this method show that viscosity increases with increasing pressure from 1 GPa to 3 GPa for hydrous rhyolitic melts with water content ⩾0.8 wt% in the high viscosity range. We also measured viscosity of rhyolitic melt with 0.13 wt% water using the parallel-plate viscometer at pressures 0.2 and 0.4 GPa in an internally-heated pressure vessel. The data show that viscosity of rhyolitic melt with 0.13 wt% water decreases with increasing pressure. Combining our new data with literature data, we develop a viscosity model of rhyolitic melts as a function of temperature, pressure and water content.

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.

A model to calculate the viscosity of silicate melts

AbstractA model has been developed that links the viscosities of silicate melts to their thermodynamic properties. Over the past several years, through critical evaluation of all available thermodynamic and phase equilibrium data, we have developed a quantitative thermodynamic description of multicomponent silicate melts using the Modified Quasichemical Model for short-range ordering. The local structure of the liquid, in terms of the bridging behavior of oxygen, calculated using our thermodynamic model allows us to characterize the structure of the liquid semi-quantitatively using the concepts of Q-species and connectivity of Q-species. The viscosity is modeled by optimizing viscosity parameters that are related to the structure of the liquid. The viscosity of pure liquid silica is modeled using four model parameters and every other unary liquid is modeled using two. The viscosity of all binary liquids is reproduced within experimental accuracy by optimizing one or at most two binary viscosity parameters for each system. In the present article the equations for the viscosity model are derived and analyses for the experimentally well-established systems CaO – SiO2MgO – SiO2, NaO0.5– SiO2, KO0.5– SiO2and AlO1.5– SiO2are presented. This is the first step in the development of a predictive model for the viscosity of multicomponent silicate melts that will be presented in part II.

The viscosity of latitic melts from Lipari (Aeolian Islands, Italy): Inference on mixing–mingling processes in magmas

The viscosity of latitic melts occurring as enclaves in the rhyolitic lava flow of Rocche Rosse (RR, Lipari, Aeolian Islands, Italy) has been measured in the high T range (1323–1473 K) for a dissolved water content varying from 1.23 to 4.39 wt.%. Measurements were performed by the falling sphere method in an internally heated gas pressure vessel. As expected, the viscosity of latite decreases with increasing water content and temperature. No pressure effect was detected between 200 and 500 MPa. Combining the new viscosity data for hydrous melts with data for dry latite of similar base composition [Giordano, D., Mangiacapra, A., Potuzak, M., Russell, J.K., Romano, C., Dingwell, D.B., Di Muro, A., 2006. An expanded non-Arrhenian model for silicate melt viscosity: a treatment for metaluminous, peraluminous and peralkaline liquids. Chemical Geology 229, 42–56.] we propose an empirical equation to estimate the viscosity of latitic melts as a function of temperature and water content over the range 10 1 to 10 12 Pa s. The obtained relationship reproduces the experimental data with a 1σ standard deviation of 0.22 log units. However, the empirical model is not constrained by data for hydrous melts at high viscosity and, therefore, it can only be used at low temperatures for water-poor melts. The viscosity data were used to model mixing–mingling processes between latitic and rhyolitic magmas at conditions relevant for the Rocche Rosse (RR, Lipari, Aeolian Islands) and La Fossa Cone 1888–1890 (LFC, Vulcano, Aeolian Islands) eruptions. The results demonstrate that the ratio between mafic and silicic end-members is the main parameter governing mixing–mingling interactions between magmas. This study suggests a faster ascent of magma underneath Vulcano compared to Lipari, which may be taken into account in hazard forecasting.

Viscosity of magmatic liquids: A model

The viscosity of silicate melts controls magma transport dynamics, eruption style and rates of physicochemical processes (e.g., degassing, crystallization) in natural magmas. Thus a comprehensive viscosity model for magmatic liquids has long been a goal of earth scientists. Here we present a model that predicts the non-Arrhenian Newtonian viscosity of silicate melts as a function of T and melt composition, including the rheologically important volatile constituents H 2O and F. Our model is based on > 1770 measurements of viscosity on multicomponent anhydrous and volatile-rich silicate melts. The non-Arrhenian T-dependence of viscosity is accounted for by the VFT equation [log η = A + B / (T(K) − C)]. The optimization assumes a common, high-T limit (A) for silicate melt viscosity and returns a value for this limit of − 4.55 ( + 0.2) (e.g., log η ~ 10 − 4.6 Pa s). All compositional dependence is ascribed to the parameters B and C and is accounted for by an additional 17 model coefficients. Our model is continuous in composition- and temperature-space and predicts the viscosity of natural volatile-bearing silicate melts (SiO 2, Al 2O 3, TiO 2, FeO tot, CaO, MgO, MnO, Na 2O, K 2O, P 2O 5, H 2O, F 2O − 1 ) over fifteen log units of viscosity (10 − 1 – 10 14 Pa s). The model for viscosity can also predict other transport properties including glass transition temperatures ( T g) and melt fragility ( m). We show strong systematic decreases in T g and m with increasing volatile content. This pattern has implications for predicting styles of volcanic eruption and understanding silicate melt structure. Our model transforms a quarter-century of experimental study of melt viscosities, into a parameterisation having a predictive capacity that makes it relevant to diverse fields of research including: volcanology, geophysics, petrology and material sciences.

Silicate melt properties and volcanic eruptions

Knowledge about the properties of silicate melts is needed by volcanologists and petrologists to evaluate the dynamics of volcanic eruptions and magmatic processes. These properties include the solubility and diffusivity of volatile components in silicate melts, silicate melt viscosity, and the fragmentation condition. Data and models of each property are reviewed and assessed. For rhyolitic melts many properties are sufficiently well known to allow realistic modeling of volcanic and magmatic processes. One interesting example is the role of speciation in the solubility and diffusivity of H2O and CO2. Even though both H2O and CO2 are present in silicate melts as at least two species, the complexity in the solubility and diffusion behavior of H2O and the simplicity of CO2 are due to differences in the speciation reaction: For the H2O component the stoichiometric coefficient is one for one hydrous species (molecular H2O) but is two for the other hydrous species (OH) in the species interconversion reaction, whereas for CO2 the stoichiometric coefficients for all carbon species are one. The investigation of the species reaction not only helps in understanding the solubility and diffusion behavior, but the reaction among the hydrous species also serves as a geospeedometer (cooling rate indicator) for hydrous rhyolitic pyroclasts and glass and provides a method to infer viscosity. For melts other than rhyolite, a preliminary description of their properties is also available, but much more experimental and modeling work is necessary to quantify these properties more accurately.