Multicomponent Silicate Melts Research Articles

Diamond formation in carbonate-silicate-sulfide-carbon melts: Raman- and IR-microspectroscopy

An experimental study on diamond nucleation and growth in a carbon solution in multicomponent carbonate, carbonate-silicate, silicate and sulfide melts was performed using a high-pressure toroidal anvil-with-hole cell with graphite resistive furnace. The boundary conditions of diamond spontaneous crystallization and seeded growth are determined for all the diamond growth media with the use of the PT diagram of diamond crystal growth. A density of diamond nucleation in the studied carbonate, carbonate-silicate, silicate, and sulfide melts with dissolved carbon exceeds (3.0–5.0) × 10 2 nuclei/mm 3 with a maximum around 1.0 × 10 5 nuclei/mm 3 at formation of polycrystalline “diamondite”. Raman spectra of quenched carbonate-carbon, carbonate-silicate-carbon, silicate-carbon and sulfide-carbon melts contain bands relating to the region of C-C stretching modes in diamond and graphite microphases. FTIR spectra show that nitrogen defects in the carbonate-synthetic diamond are characterized with the mixed Ib-IaA type and reveal a high nitrogen concentration (up to 850 ppm).

Effect of Small Glass Composition Changes on Flue Gas Emissions of Glass Furnaces

Relatively small changes in glass composition might have drastic consequences on the evaporation rates of volatile glass components in glass melting furnaces. Transpiration evaporation tests have been applied to measure the impact of minor glass composition changes on the evaporation rates of volatile glass components in simulated furnace atmospheres. The results of these laboratory evaporation tests were used to develop and optimize an universally applicable evaporation model to estimate evaporation rates and dust emissions for industrial glass melt furnaces. Mass transfer relations for the transport of volatile glass melt species into the turbulent gas phase were used to upscale the evaporation models valid for the lab tests to applications for industrial glass furnaces. In this paper, the impact of sulfur and chlorides on the evaporation rates of sodium and potassium from multi-component silicate melts for industrial glass production will be demonstrated.

The effect of H2O on the olivine liquidus of basaltic melts: experiments and thermodynamic models

We designed and carried out experiments to investigate the effect of H2O on the liquidus temperature of olivine-saturated primitive melts. The effect of H2O was isolated from other influences by experimentally determining the liquidus temperatures of the same melt composition with various amounts of H2O added. Experimental data indicate that the effect of H2O does not depend on pressure or melt composition in the basaltic compositional range. The influence of H2O on melting point lowering can be described as a polynomial function \( {\left( {\rm C^{{\rm melt}}_{{\rm{H_{2} O}}} \;{\text{in}}\;{\text{wt}}\% } \right)}:\Updelta {T}\;{\left( {^{ \circ }\rm C} \right)} = 40.4 {\left( {\rm C^{{\rm melt}}_{{\rm {H_{2} O}}} } \right)} - 2.97 {\left( {\rm C^{{\rm melt}}_{{\rm {H_{2} O}}} } \right)}^{2} + 0.0761 {\left( {\rm C^{{\rm melt}}_{{\rm{H_{2} O}}} } \right)}^{3} . \) This expression can be used to account for the effect of H2O on olivine-melt thermometers, and can be incorporated into fractionation models for primitive basalts. The non-linear effect of H2O indicates that incorporation of H2O in silicate melts is non-ideal, and involves interaction between H2O and other melt components. The simple speciation approach that seems to account for the influence of H2O in simple systems (albite-H2O, diopside-H2O) fails to describe the mixing behavior of H2O in multi-component silicate melts. However, a non-ideal solution model that treats the effect of H2O addition as a positive excess free energy can be fitted to describe the effect of melting point lowering.

Temperature independent thermal expansivities of calcium aluminosilicate melts between 1150 and 1973 K in the system anorthite–wollastonite–gehlenite (An–Wo–Geh): A density model

The thermal expansivities of 10 compositions from within the anorthite–wollastonite–gehlenite (An–Wo–Geh) compatibility triangle have been investigated using a combination of calorimetry and dilatometry on the glassy and liquid samples. The volumes at room temperature were derived from densities measured using the Archimedean buoyancy method. For each sample, density was measured at 298 K using glass that had a cooling-heating history of 10–10 K min −1. The thermal expansion coefficient of the glass from 298 K to the glass transition interval was measured by a dilatometer and the heat capacity was measured using a differential scanning calorimeter from 298 to 1135 K. The thermal expansion coefficient and the heat flow were determined at a heating rate of 10 K min −1 on glasses which were previously cooled at 10 K min −1. Supercooled liquid density, molar volume and molar thermal expansivities were indirectly determined by combining differential scanning calorimetric and dilatometric measurements assuming that the kinetics of enthalpy and shear relaxation are equivalent. The data obtained on supercooled liquids were compared to high-temperature predictions from the models of (Lange, R.A., Carmichael, I.S.E., 1987. Densities of Na 2O–K 2O–CaO–MgO–FeO–Fe 2O 3–Al 2O 3–TiO 2–SiO 2 liquids: New measurements and derived partial molar properties. Geochim. Cosmochim. Acta 51, 2931–2946; Courtial, P., Dingwell, D.B., 1995. Nonlinear composition dependence of molar volume of melts in the CaO–Al 2O 3–SiO 2 system. Geochim. Cosmochim. Acta 59 (18), 3685–3695; Lange, R.A., 1997. A revised model for the density and thermal expansivity of K 2O–Na 2O–CaO–MgO–Al 2O 3–SiO 2 liquids from 700 to 1900 K: extension to crustal magmatic temperatures. Contrib. Mineral. Petrol. 130, 1–11). The best linear fit combines the supercooled liquid data presented in this study and the high temperature data calculated using the Courtial and Dingwell (1995) model. This dilatometric/calorimetric method of determining supercooled liquid molar thermal expansivity greatly increases the temperature range accessible for thermal expansion. It represents a substantial increase in precision and understanding of the thermodynamics of calcium aluminosilicate melts. This enhanced precision demonstrates clearly the temperature independence of the melt expansions in the An–Wo–Geh system. This contrasts strongly with observations for neighboring system such as anorthite–diopside and raises the question of the compositional/structural origins of temperature dependence of thermal expansivity in multicomponent silicate melts.

Structure and the extent of disorder in quaternary (Ca-Mg and Ca-Na) aluminosilicate glasses and melts

The structure of multi-component silicate melts and glasses (e.g., Ca-Mg and Ca-Na aluminosilicates) can provide insight into the properties of natural silicate melts and has implications for relevant magmatic processes. In spite of its importance, the atomic and molecular structure of most multi-components (e.g., quaternary) melts and glasses has not been fully described, primarily because of insufficient resolution obtained with conventional spectroscopic and scattering methods; the information obtained by these methods is compromised by severe inhomogeneous peak broadening due to structural complexity. Here we report the first 1 7 O and 2 7 Al 3QMAS NMR spectra for quaternary, Ca-Mg and Ca-Na peralkaline aluminosilicate glasses (i.e., M/Al > 1, M is one monovalent or one-half a divalent cation). These data reveal new details into the molecular structure of multi-component aluminosilicate melts, which include the presence of a substantial fraction of V Al in the Ca-Mg aluminosilicate glasses and I V Al-O- I V Al in both glasses at 1 atm. Traditional models of glass structure do not support the presence of such species given these high-silica, peralkaline compositions. These results suggest that Al avoidance is violated in the multi-component peralkaline aluminosilicate glasses, and that the presence of Mg 2 + in the melts increases the extent of disorder in the melts (compared with Ca 2 + and Na + ). These factors lead to an increase in configurational entropy and the activity coefficients of the oxides, and may provide an explanation for the decrease in viscosity of these complex melts.

The kinetic fragility of natural silicate melts

Newtonian viscosities of 19 multicomponent natural andsynthetic silicate liquids, with variable contents of SiO2 (41–79 wt%), Al2O3 (10–19 wt%),TiO2 (0–3wt%), FeOtot(0–11 wt%); alkali oxides (5–17 wt%), alkaline-earth oxides (0–35 wt%), andminor oxides, obtained at ambient pressure using the high-temperatureconcentric cylinder, the low-temperature micropenetration, and theparallel plates techniques, have been analysed. For each silicate liquid,regression of the experimentally determined viscosities using the well knownVogel–Fulcher–Tammann (VFT) equation allowed the viscosity of allthese silicates to be accurately described. The results of these fits, whichprovide the basis for the subsequent analysis here, permit qualitative andquantitative correlations to be made between the VFT adjustable parameters(AVFT,BVFT, andT0). The valuesof BVFT andT0, calibratedvia the VFT equation, are highly correlated. Kinetic fragility appears to be correlatedwith the number of non-bridging oxygens per tetrahedrally coordinated cation (NBO/T).This is taken to infer that melt polymerization controls melt fragility in liquid silicates. ThusNBO/Tmight form an useful ingredient of a structure-based model of non-Arrhenianviscosity in multicomponent silicate melts.

Empirical method of calculating the viscosity of peraluminous silicate melts at high temperatures

Shaw's method for the calculation of the viscosities of magmatic silicate liquids has been extended to multicomponent silicate melts in which Al 2O 3 exceeds the sum of alkali metal oxides and alkaline earth oxides. Al 2O 3 was converted to AlO 2 and divided into the network-forming part, AlO 2 0, and the excess part, AlO 2 *. AlO 2 0 and AlO 2 * differed in their effect on viscosity. S AlO 2 * ∘ value, which evaluates the effect of AlO 2 * on viscosity, was chosen to compensate for the difference in Arrhenius slope between the data obtained by viscosity measurement and the data calculated from the chemical compositions other than AlO 2 *. From the viscosity measurement data of synthesized multicomponent melts, S AlO 2 * ∘ value was 5.6. This is smaller than the S AlO 2 0 ∘ value of 6.7. Using the S AlO 2 * ∘ value with other S i ∘ values from Shaw (1972), the viscosities of peraluminous glassy rocks produced by the 1988–1989 eruptions of Tokachi-dake volcano (Hokkaido, Japan) were calculated. The calculated viscosities agreed well with the measured ones.

Convection in multicomponent silicate melts driven by coupled diffusion

THE simplest convecting systems are driven by buoyancy forces arising from the density variations produced by the diffusion of a single quantity, usually heat. In such systems, the necessary condition for the onset of convection is that density decreases downwards. But the convection process can be very different if there are two or more diffusing quantities that affect the density1–5, a situation often encountered in geological settings. For example, multicomponent convection plays an important role in the convec-tive evolution and differentiation of terrestrial magmas6–8. A typical terrestrial silicate magma is made up of a number of diffusing components, which not only have different diffusion rates but may also exhibit diffusive coupling — that is, the diffusive flux of one component can be strongly dependent on the spatial gradients of other components9–12. We have investigated convection in a geologically relevant fluid — a multicomponent silicate melt in the system CaO–Al2O3–SiO2 — and we find that diffusive coupling plays a key role in promoting convection. Perhaps the most striking feature of these experiments is that convection can occur regardless of whether the density decreases or increases with depth.

Comparison of element and isotope diffusion of K and Ca in multicomponent silicate melts

Recent experimental work has shown that the homogenization of elemental concentrations can be much slower than that of isotopic ratios when there are strong concentration gradients in SiO 2 and Al 2O 3. The ramifications of this result for magma homogenization and other petrological problems related to diffusion are significant. We report here a comparison of experimental profiles of elemental concentrations and isotopic fractions of K and Ca in rhyolite-andesite (large concentration gradients) and rhyolite-rhyolite (small concentration gradients) melt couples. When the concentration profile and the isotopic profile of the same element in a single couple are compared, the former is much shorter than the latter in the rhyolite-andesite couple, consistent with other recent studies. However, the lengths of both concentration and isotopic profiles are similar in the rhyolite-rhyolite couple. Therefore, diffusion of an element or oxide may be decoupled from or coupled with isotopic ‘diffusion’, depending on whether large concentration gradients of major components are present. When the two couples are compared, the intrinsic effective binary diffusivities obtained from isotopic profiles are similar for each element in the two couples, whereas the effective binary diffusivity of K obtained from the concentration profile in the rhyolite-rhyolite couple is 37 times that in the rhyolite-andesite couple. Therefore, isotopic homogenization is roughly independent of elemental homogenization and the presence of SiO 2, Al 2O 3, and other concentration gradients, whereas elemental homogenization is strongly affected by concentration gradients. Our experimental data (isotopic and concentration profiles including uphill diffusion profiles) can be modeled quantitatively to a good approximation using a modified effective binary diffusion model in which the flux of a component is assumed to be proportional to its activity gradient instead of its concentration gradient. Therefore, the multicomponent diffusion effect in the silicate systems of our experiments seems to be largely due to contributions of non-ideal mixing to the cross-terms of the diffusivity matrix.

多元系珪酸塩融体の表面張力の推算

In order to estimate surface tension for multicomponent silicate melts, expanded approximation rules was proposed in view of practical use, on the basis of the regular solution approximation rules of excess molar quantities for binary system melts. Necessary parameters for the above rules have been derived using the previous data in binaries and ternaries, etc.. Using these parameters, it was found that near the melting point, surface tensions of pure oxides and halides 0σi were related to (Ti)mp/0Vi2/3, where (Ti)mp and 0Vi are the melting point and molar volume of pure oxides and halides, respectively.From the collation with the data of multicomponent silicate melts, it was confirmed that the above expanded approximation rules were applicable to predict the surface tension of melts over the wide range of composition and temperature discussed.

多元系珪酸塩融体の粘度の概略推算

A method of approximate prediction of the viscosity of multicomponent silicate melts was proposed in view of practical use, on the basis of the relationship between the network parameter deduced from the viscosity of melts and the anion-cation attraction parameter. It was postulated in the method that the anion-cation attraction parameter is considered to be melt-structure (or polymerization)-dependent. The generalized relationship exists between the network parameter and the modified anion-cation attraction parameter.In order to check the validity of the above estimation method, viscosity data for multicomponent silicate melts have been collated. Theoretical values based on the method show excellent agreement with the experimental data.

A modified effective binary diffusion model

Uphill diffusion, the diffusion of a component up its own concentration gradient, has often been observed in experimental studies of diffusion in synthetic multicomponent systems and natural silicate melts. To apply experimental data to natural processes, it is necessary to quantify this effect. A modified effective binary diffusion model is developed in this paper. The diffusive flux of a component is assumed to be proportional to its activity gradient (instead of concentration gradient). The activity coefficient is related to its concentration at quasi‐equilibrium distribution in a compositional continuum with the help of the two‐liquid partition concept. The concentration at quasi‐equilibrium distribution is approximately expressed as a simple function of SiO2 or SiO2+Al2O3 concentration. The diffusion of SiO2 or SiO2+Al2O3 is assumed to be effectively binary. With these assumptions, diffusion of a major or trace component can be described by two adjustable parameters, D (the intrinsic effective binary diffusivity) and Cƒ. (a parameter related to two‐liquid partition coefficients). The simple model fits well the experimental uphill diffusion profiles produced by diffusive crystal dissolution into an andesitic melt using constant diffusivities when compositional variation across the whole profile is small. The parameters fit to the profiles are generally physically meaningful. The model is able to predict the direction of diffusion (occurrence or absence of uphill diffusion) in previous experiments and can be used to simulate the development of chemical concentration and isotopic ratio profiles during diffusion. When compositional dependence of diffusivities is allowed, the model may be applied to systems with greater compositional variation. This model can be tested in several ways and should be useful in studying diffusion in a variety of natural systems.

The Viscoscity of Synthetic and Natural Silicate Melts and Glasses at High Temperatures and 1 Bar (105 Pascals) Pressure and at Higher Pressures, U.S. Geol. Surv. Bull. 1764

Over the past decade, I have routinely collected papers dealing with the physical properties of rocks and other materials. Their dog‐eared and coffee‐stained appearance is just one indication of their continuing value to me. Focusing on viscosity of silicate melts, Michael Ryan and James Blevins have considerably extended and formalized this collection process, resulting in the publication of a massive report containing viscosity data on an extensive variety of melt compositions. According to the authors, this report represents an initial step in establishing a comprehensive U.S. Geological Survey (USGS) data base for the properties of multicomponent silicate melts.

Diffusion of major and trace elements in compositionally complex Cl- and F-bearing silicate melts

Chemical diffusion experiments on halogenated, multicomponent silicate melts at 10 MPa, 200 MPa and 1.0 GPa have yielded diffusivities for both major (Al, Fe, Si) and trace elements (Mn, Zn, Y, Zr, Nb) over the temperature range 900 to 1400 ° C. At any given temperature and pressure, diffusivities of all elements are the same within an order of magnitude; they display no apparent dependence upon cation size, but do correlate crudely with cation field strength ( Z/ r). Comparison with diffusion data on unhalogenated melts revealed that addition of Cl and F tends to increase cation diffusivities and lower activation energies for diffusion. The effect of increasing pressure is also to enhance diffusion for all elements studied except the high field-strength network-modifiers Zr and Nb. As pressure increases, low Z/ r elements experience a decrease in activation energy for diffusion, whereas high Z/ r elements display increasing activation energies. It is proposed that the change in activation energy is related to the existence of two distinct network structures characterized by different TOT angles. The network structures with lower TOT angles apparently can provide charge-balanced sites for low Z/ r cations but not for high Z/ r cations. The effect of elevated pressure on the melt structure may be to increase the proportion of network structures having low TOT angles. The resulting increase in available sites for low Z/ r cations is believed responsible for the observed reduction in activation energy for diffusion of the cations.

A network model for the thermodynamics of multicomponent silicate Melts. I. Binary mixtures MOSiO 2

We have developed a network model for the thermodynamics of liquid silicate mixtures. Variation of the interaction parameter with composition is incorporated quite naturally by assuming a functional dependence, not on the silica content, but on the actual degree of polymerization of the silicate network. In this paper, which describes the model for binary mixtures, the interaction parameter is fitted to activity data for binaries of SiO 2 with CaO, FeO, K 2O, MgO, MnO, Na 2O and PbO. For the system MgOSiO 2 we have also fitted the temperature-composition phase diagram.

Derivation of a Revised Model for Activity Calculation in Multisilicate Melts

Hollitt's model for prediction of thermodynamic properties in multicomponent silicate melts has been revised to better reflect network modifier depolymerization effectiveness as a function of basicity and melt composition. This model is based on the free energy changes in a melt caused by the breaking of silicate polyions by the addition of basic oxides; these free energy changes are in turn related to the change in the concentration of various oxyanion molarities caused by such additions. Application of the revised model to actual systems shows good agreement with experimental data; possible model improvements are discussed.