No extended species e. Silicate melts, however, become non-Newtonian as the strain rate approaches the equilibration rate of the Si-O bonds. Such a correlation between Si-O bond exchange and the viscous flow mechanism, in turn, explains the success of the Eyring relationship in relating high temperature oxygen and silicon self-diffusion to viscosity.
Knowledge of the structural relaxation timescale is important in extracting equilibrium information from studies of the structure and properties of quenched glasses. Quench rate-dependent speciation data for glasses imply a temperature-dependence of the species equilibrium in the liquid state. Estimation of the relaxation times associated with the quench rates allows reconstruction of the temperature-dependence of homogeneous equilibria in liquids.
Experimental work on silicate melts should consider the location of the experimental method in time-temperature space, with respect to the glass transition. Diffusivity measurements, for example, are influenced by the glass transition. When the duration of a diffusivity experiment crosses the volume relaxation time, an inflection in the temperature-dependence of diffusivity of cations is observed. A second "transition" in diffusivity behavior is expected to occur at higher temperatures when the diffusivity of network oxygen and silicon approaches that of other cations.
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Iron-bearing silicate melts: Relations between pressure and redox equilibria
RSS feeds All publications more feeds American Mineralogist 75, Physic and Chemistry of Minerals 19, Zotov, N. American Mineralogist 83, Malfait, W. American Mineralogist 94, Spiekermann, G.
The Journal of Chemical Physics , View in Supplementary Information. See Cody et al. View in Supplementary Information In alkali tetrasilicate melts at their glass transition temperature, water is dissolved as H 2 O mol molecules and as OH groups bonded to Si or the alkalis Cody et al.
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View in Supplementary Information With increasing water content in the glasses, the signals between cm -1 become more intense, reflecting the depolymerisation of the tetrahedral network that occurs with solution of water Zotov and Keppler, ; Cody et al. For water content determination, the treatment of the Raman spectra is slightly different as the baseline is also fitted to the basis of the bands located near and cm -1 , respectively assigned to O-D and O-H stretching see Foustoukos and Mysen, , and references cited therein.
Such a process allows quantitative comparison of spectra e.
Structure and properties of silicate melts
View in Supplementary Information Water concentrations of the 1 H 2 O- and 2 H 2 O-bearing glasses were checked with Raman spectroscopy, using the calibration that links the glass water content measured by Infrared or another technique to the ratio between the areas of the Raman bands assigned to silicate vibrations and to the O- 1 H or O- 2 H stretching vibration as described by Le Losq et al. View in Supplementary Information Hydrous glasses, containing pure 1 H 2 O, pure 2 H 2 O or a mixture of 1 H 2 O- 2 H 2 O, were formed by temperature-quenching melts hydrated at high pressure and temperature in platinum capsules by using a piston-cylinder apparatus, following the protocol described in Le Losq et al.
View in Supplementary Information Table S-1 [ View in Supplementary Information Increasing the alkali ionic radius promotes the latter effect Le Losq et al. View in Supplementary Information See Cody et al. View in Supplementary Information These features correspond to protons and deuterons existing in, at least, 5 different environments in the silicate glasses Le Losq et al.
View in Supplementary Information Therefore, at constant water content, changes in the 1 H and 2 H isotropic NMR spectra reflect how both 1 H and 2 H populate environments with smaller O-O distances, and hence, smaller structural volumes with increasing ionic radius of the alkali metal Figs. This peak is typically assigned to vibrations of OH groups bonded to the silicate network McMillan et al. The method has been shown to determine accurately the water content of natural glasses Shea et al.
In alkali tetrasilicate melts at their glass transition temperature, water is dissolved as H 2 O mol molecules and as OH groups bonded to Si or the alkalis Cody et al. View in Supplementary Information Such a process allows quantitative comparison of spectra e. View in article At any given water content and alkali metal radius, differences between the isotropic 1 H and 2 H MAS NMR spectra are not due to instrumental or quench effects Wang et al.
Figure S-1 [ View in Supplementary Information Figure S-2 [ Submit here. Track your paper. Abiogenesis not required to explain the origin of volcanic-hydrothermal hydrocarbons J. Fiebig, A.
Ricci, F. Tassi, F. Viveiros, C. Silva, T. Lopez, C. Schreiber, S.
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Hofmann, B. Liu, S. Dorfman, M. Lv, J. Li, F. Zhu, Y. Geochemical Perspectives Letters. Geochemical Perspectives. Intramolecular fractionation of hydrogen isotopes in silicate quenched melts C. Such a process might affect other isotopic systems e. Figure 1 Figure 2 Figure 3 View all figures and tables.
Show in context This hypothesis is supported by the fact that the quench rate affects the Tg and the water speciation e. View in article Chacko, T. View in article Dalou, C. View in article Dauphas, N. Show in context Further, the behaviour of Fe isotopes in silicate melts is affected by the effects of melt composition on the Fe environment Dauphas et al.
View in article De Hoog, J.
View in article Driesner, T. Show in context Wang et al. View in article Gibbs, G. Show in context Figure 2 [ View in article Greaves, G. View in article Horita, J. View in article Labidi, J. View in article Labrosse, S. View in article Le Losq, C. Show in context Indeed, with increasing alkali ionic radius, both the distribution of Q n species and the proton environment change Le Losq et al. View in article Maekawa, H. Show in context This is analogous to the alkali ionic radius effect on the Q n units distribution in silicate melts e.
View in article Mysen, B. View in article Novak, A. Show in context The present data indicate that, in such conditions, 2 H populates the environments characterised by short O-O distances, and, hence long O-H bonds, slightly more than does 1 H Fig. View in article Robert, E. Show in context The decrease of the Q 2 abundance and the increase of the Q 3 abundance by substitution of 1 H for 2 H seen in the Raman spectra of the glasses explain the variations of the 1 H and 2 H NMR signals. View in article Schauble, E. Show in context Therefore, it may enhance the differences of O- 1 H and O- 2 H bond strengths between silicate melts and aqueous fluids, and, as a result, promote a strong fractionation of both isotopes between those substances Schauble, and references therein.
View in article Wang, Y.
Transport properties of carbonated silicate melt at high pressure
View in article Wood, B. View in article Xue, X. View in Supplementary Information Brawer, S. View in Supplementary Information Cody, G. Show in context See Cody et al. View in Supplementary Information Dalou, C. View in article Foustoukos, D. Show in context For water content determination, the treatment of the Raman spectra is slightly different as the baseline is also fitted to the basis of the bands located near and cm -1 , respectively assigned to O-D and O-H stretching see Foustoukos and Mysen, , and references cited therein.
View in article Furukawa, T. Show in context Such a process allows quantitative comparison of spectra e.
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View in Supplementary Information Maekawa, H.