Yan Bottinga

Viscosity of liquid silica, silicates and alumino-silicates

Viscosity measurements are reported for amorphous silica and liquids belonging to the systems SiO2-M, SiO2-Al2O3-M, where M is an alkali-earth metal oxide, MnO, or alumina, and the systems SiO2-“FeO”, SiO2-FeO-Fe2O3-CaO, and SiO2-Al2O3-N, where N = Na2O or K2O. The implications of these measurements concerning the coordination of Al and the structure of these liquids are briefly discussed. Stable liquids in the systems SiO2-Al2O2-M show a non-Arrhenian temperature dependence of their viscosity, in general. Results obtained with empirical methods to calculate the viscosity of silicate liquids are compared with our observations.

Thermodynamic properties of quartz, cristobalite and amorphous SiO2: drop calorimetry measurements between 1000 and 1800 K and a review from 0 to 2000 K

We report relative enthalpy measurements on quartz, cristobalite and amorphous SiO2 between 1000 and 1800 K. We have observed a glass transition around 1480 K for amorphous SiO2. From our results and available Cp, relative enthalpy, and enthalpy of solution data we have derived a consistent set of thermodynamic data for these phases. Our calculated enthalpies of fusion are 8.9 ± 1.0 kJ mole−1 for cristobalite at 1999 K and 9.4 ± 1.0 kJ mole−1 at 1700 K for quartz.

Density calculations for silicate liquids. I revised method for aluminosilicate compositions

Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature Tr, is given by , where the summation is taken over all oxide components except A12O3, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and is the composition-dependent apparent partial molar volume of Al2O3. The thermal expansion coefficient of aluminosilicate liquids is given by , where terms are constants independent of temperature and composition, and is a composition-dependent term representing the effect of Al2O3 on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = Vrexp[α(T-Tr)], where Tr = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of is discussed in terms of several possible interpretations of the structural role of Al3+ in aluminosilicate melts.

Glass transitions and thermodynamic properties of amorphous SiO2, NaAlSinO2n+2 and KAlSi3O8☆

Abstract A drop calorimetric study, between 900 and 1800 K, of amorphous SiO 2 , NaAlSi 3 O 8 , NaAlSi 2 O 6 , NaAlSiO 4 and KAlSi 3 O 8 shows the increase in heat capacity which results from glass transitions. For these glasses, the fictive temperature has a negligible effect on the heat capacity above room temperature, but it has an important influence on the enthalpy of formation as obtained from solution calorimetry. From these results and published Cp and enthalpy of solution data, several properties have been calculated: the enthalpies of fusion of high albite, nepheline, Jadeite and high sanidine, the thermodynamic functions of amorphous NaAlSi 3 O 8 and KAlSi 3 O 8 between 0 and 2000 K, and some mixing properties of liquids along the join SiO 2 -NaAlSi 3 O 8 . The latter data suggest that these liquids behave more closely as athermal solutions than as regular solutions.

Anorthite, andesine, wollastonite, diopside, cordierite and pyrope: thermodynamics of melting, glass transitions, and properties of the amorphous phases

Abstract Drop calorimetry measurements between 900 and 1850 K are reported for amorphous anorthite, andesine, wollastonite, diopside, cordierite and pyrope. The isobaric heat capacities of the glassy and liquid phases of these materials, and the enthalpies of fusion of the minerals have been derived. The calorimetric entropies of fusion of these substances and of other oxide minerals are generally consistent with the calculated volume changes on melting and with the observed pressure dependences of the melting points. The thermodynamics of mixing of liquid plagioclases have been examined, and it is concluded that their enthalpies of mixing are markedly different from the values derived directly from solution calorimetry measurements at 985 K.

Heat capacity of aluminum-free liquid silicates

Abstract Drop calorimetry measurements made between 900 and 1800 K are reported for six MO-SiO 2 liquids ( M = Li 2 , K 2 , Sr and Ba ) and two titanium alkalisilicate melts. These results, together with data from the literature, are used to derive a model for calculating the heat capacity of Al-free silicate melts as a function of temperature and chemical composition. Twenty-one major or minor oxides have been considered and, except for K 2 O-bearing melts, the available data do not indicate deviations of the heat capacities from an additive function of composition. Simple energy calculations show that large variations of the temperature of the liquids result in structural changes of a magnitude similar to those of crystal-liquid transitions. It is suggested that network-modifier cations play an important role in changing the configuration of the liquid in response to temperature variations. The specificity of the behavior of the cations is shown by the lack of a simple relationship between the heat capacities of the liquids and characteristics of the alkali and alkaline-earth cations such as ionic potential or field strength.

Thermodynamics of liquid silicates, a preliminary report

Abstract We propose a model for the calculation of the thermodynamic properties of silicate liquids. In our model we make use of the Flory-Huggins regular solution formalism for liquid solutions. In this preliminary paper we have limited ourselves to demonstrating that the Flory-Huggins formalism describes satisfactorily the thermodynamic properties of simple liquid silicate solutions, i.e. systems in which only end-member components or solid solutions thereof occur as solid phases and where there is only one well-behaved liquid phase. To compare theoretical results with laboratory observations we need thermodynamic data for liquid silicates. For this reason we have included in this report a review of the available information on the latent heat of fusion of silicate minerals.

On the isothermal compressibility of silicate liquids at high pressure

From the fusion curves of six silicate/aluminosilicate minerals (Mg 2 SiO 4 , MgSiO 3 , CaMgSi 2 O 6 , Mg 3 Al 2 Si 3 O 12 , NaAlSi 2 O 6 , NaAlSi 3 O 8 ) and availble thermodynamic data, isothermal compressibilities were calculated for pressures ranging from 0.001 to 150 kbar. In all cases the compressibility decreases with increasing pressure, but for liquid pyrope and jadeite this decrease is quite important at 40 P P

Viscosity regimes of homogeneous silicate melts

The effect of the addition of 5, 10, and 20 wt% of the alkali oxides on the viscosity of a haplogranitic melt composition has been investigated at I atm and in the temperature range of 400-1650 0c. The high-temperature viscosity data were obtained with concentric cylinder viscometry and the low-temperature viscosity data using micropenetration viscometry. The combined data sets for lowand high-temperature viscosities have been fitted for each composition using the Tamann-Vogel-Fulcher (TVF) equation. The effect of alkali oxide on the viscosity of a haplogranite melt is extreme. The viscosity decreases with added alkali oxide content in a nonlinear fashion. The first few mole percent of alkali oxide added decreases viscosity several orders of magnitude, whereas subsequent addition of alkali oxide has a much smaller effect. The effects of each of the alkalis are broadly similar, implying that the structural role of the alkalis is common to all. In detail however, the viscosity of the strongly peralkaline melts investigated here increases with the size of the added alkali cation in the order Li < Na < K,Rb,Cs. This trend probably reflects a minor influence ofthe alkali-O bond strengths on the melt viscosity. This distinction of a dominant depolymerizing influence and a minor alkali specific bond-strength influence has important implications for the comparison of these data with those for the addition of other depolymerizing agents on the viscosity ofhaplogranitic melt (e.g., H20, F20-1).

Heat capacity of liquid silicates: new measurements on NaAlSi3O8 and K2Si4O9☆

Drop calorimetric measurements of HT-H273 are reported for glassy and liquid albite and potassium tetrasilicate for the temperature interval 600–1500 K. Analysis of these observations as well as data for 13 other stable and supercooled silicate liquids suggests strongly that the isobaric heat capacities of stable and supercooled liquids are equal and thus temperature independent. Available evidence indicates that the isochoric heat capacities of liquid alkali silicates are also temperature independent within present experimental uncertainties.