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3QMAS NMR

The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform

Jonathan F Stebbins – 1st expert on this subject based on the ideXlab platform

  • Cation order/disorder behavior and crystal chemistry of pyrope-grossular garnets: An 17O 3QMAS and 27Al MAS NMR spectroscopic study
    American Mineralogist, 2015
    Co-Authors: Kimberly E Kelsey, Jonathan F Stebbins, Linshu Du, Jed L Mosenfelder, Paul D Asimow, Charles A Geiger

    Abstract:

    The thermodynamic mixing properties of the pyrope-grossular solid solution show large deviations from ideality, which could be partly related to Ca-Mg order/disorder. In this study, synthetic pyrope-grossular garnets with X_(Mg) = 1.00, 0.91, 0.75, 0.50, 0.24, 0.10, and 0.00 are observed using ^(17)O 3QMAS, ^(27)Al MAS, and ^(29)Si MAS NMR to examine Ca-Mg order/disorder behavior and crystal chemical variations. The ^(17)O 3QMAS NMR spectra show four distinct resonances, assigned to four different local oxygen coordination environments; two resemble end-member garnets (oxygen bonded to two Mg or two Ca) and two are intermediate (oxygen bonded to one Ca and one Mg), indicating that there are two distinct bond distances for the Mg-O and/or Ca-O bonds through the entire solid solution. Noticeable changes in the NMR peak position for two of the oxygen sites suggest that as X_(Mg) increases, the longer Ca-O bond shortens. The relative areas for the different oxygen sites are close to those predicted using a model of random Ca/Mg mixing. The maximum allowed reduction in configurational entropy from first neighbor Ca-Mg ordering is insignificant relative to other configurational entropy reductions and excess vibrational entropy. These conclusions are not inconsistent with published theoretical calculations suggesting some Ca-Mg ordering that involves correlations beyond the first neighbor, as suggested by published theoretical calculations. Even at 18.8 Tesla, the ^(27)Al MAS NMR spectra do not resolve different local Al sites with varying combinations of X cation neighbors. The ^(29)Si MAS NMR spectra have resonance broadening, probably caused by the addition of 0.15 wt% Fe_2O_3 in the synthetic samples, and are consistent with published results suggesting a small degree of Ca-Mg ordering that is not reflected in the ^(17)O NMR spectra.

  • Non-bridging oxygen and high-coordinated aluminum in metaluminous and peraluminous calcium and potassium aluminosilicate glasses: High-resolution 17O and 27Al MAS NMR results
    American Mineralogist, 2011
    Co-Authors: Linda M. Thompson, Jonathan F Stebbins

    Abstract:

    Change in configuration and structure with composition are important components of thermodynamic and transport properties of most aluminosilicate melts, but the complex interactions, particularly in metaluminous and peraluminous compositions, are not yet well understood. In this paper, we present high-resolution 27 Al and 17 O MAS and 3QMAS NMR data on several calcium and potassium aluminosilicate glasses prepared at several SiO 2 isopleths, ranging from peralkaline to peraluminous compositions. In all calcium aluminosilicate glasses, the V Al content increases with increasing Al content, while the NBO content decreases (in one series, below the limit of detection), consistent with other recent NMR studies of calcium aluminosilicate glasses. An increase in V Al content per total Al is also observed as the glass approaches the calcia-silica binary. In the potassium aluminosilicate glasses, NBO is directly quantified for the first time in metaluminous and peraluminous compositions; V Al is below the detection limit. We discuss possible mechanisms for the incorporation of alumina into the melt structure and show how changes in the V Al content as a function of composition may be used to eliminate mechanisms that do not fit the observed data. We also explore reactions, which show the difficulty of explaining the NBO present on the metaluminous join with only the observed V Al, implying the necessity of multiple reactions producing NBO in such compositions.

  • Quench rate and temperature effects on boron coordination in aluminoborosilicate melts
    Journal of Non-crystalline Solids, 2010
    Co-Authors: Jingshi Wu, Jonathan F Stebbins

    Abstract:

    Abstract The effect of temperature on the structure of aluminoborosilicate liquids has been studied by 11 B MAS NMR, 11 B 3QMAS NMR, 23 Na and 27 Al MAS NMR spectroscopies using glass samples prepared with different cooling rates and thus different fictive temperatures. The abundance of BO 3 group and non-bridging oxygen (NBO) increases with increasing fictive temperature, indicating that the reaction BO 4  ↔ BO 3  + NBO shifts to the right with increasing temperature. The observed temperature dependence of BO 4 species abundance allows us to estimate the ∆ H of this reaction to be 24 to 50 kJ mol −1 in different glass compositions, and closely related with the amount of NBOs in the glass. Configurational heat capacities have been measured by differential scanning calorimetry (DSC). We found that the redistribution of boron species (BO 4 /BO 3 ) contributes a varying range of configurational heat capacity, from 7% to 30%, with different glass compositions. 11 B 3QMAS NMR indicates two different BO 3 sites, the populations of which are also affected by fictive temperature. The exchange between two different BO 3 sites should also contribute to configurational heat capacity.

Maria Cristina Menziani – 2nd expert on this subject based on the ideXlab platform

  • unambiguous description of the oxygen environment in multicomponent aluminosilicate glasses from 17o solid state NMR computational spectroscopy
    Journal of Physical Chemistry C, 2012
    Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Maria Cristina Menziani

    Abstract:

    Classical molecular dynamics simulations, density functional theory calculations, and spin-effective Hamiltonians have been used to simulate the 17O MAS and 3QMAS NMR spectra of Ca–Na silicate and aluminosilicate glasses and melts employed as simplified models for basaltic, andesitic, and rhyolitic magmas. The direct comparison of the theoretical NMR spectra of molecular dynamics derived structural models with the experimental counterparts available in the literature has allowed the investigation of the nature of nonframework cation mixing and the extent of intermixing among framework units in Na–Ca aluminosilicate glasses. In particular, in agreement with previous experimental evidence, the results show a nonrandom distribution of the network-modifying Ca and Na in soda-lime glasses with the prevalence of dissimilar Na–Ca pairs around nonbridging oxygens. The oxygen sites are not completely resolved in the MAS spectra of the aluminosilicate glasses. On the contrary, in the 17O 3QMAS spectra the multiple …

  • First-principles simulations of the ^27Al and ^17O solid-state NMR spectra of the CaAl_2Si_3O_10 glass
    Theoretical Chemistry Accounts, 2012
    Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Gianluca Malavasi, Maria Cristina Menziani

    Abstract:

    The local and medium-range structure of the 20CaO·20Al_2O_3·60SiO_2 glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the ^27Al and ^17O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.

  • First-principles simulations of the 27Al and 17O solid-state NMR spectra of the CaAl2Si3O10 glass
    Theoretical Chemistry Accounts, 2012
    Co-Authors: Alfonso Pedone, Elisa Gambuzzi, Gianluca Malavasi, Maria Cristina Menziani

    Abstract:

    The local and medium-range structure of the 20CaO·20Al2O3·60SiO2 glass generated by classical molecular dynamics simulations has been compared to NMR experiments by computing the 27Al and 17O NMR parameters and NMR spectra from first-principles simulations. The calculation of the NMR parameters (chemical shielding and quadrupolar parameters), which are then used to simulate solid-state MAS and 3QMAS NMR spectra, is achieved by the gauge including projector augmented-wave and the projector augmented-wave methods on the DFT-PBE relaxed structure. The NMR spectra calculated with the present approach are found to be in excellent agreement with the experimental data, providing an unambiguous view of the local and medium-range structure of aluminosilicate glasses.

Bjorn O Mysen – 3rd expert on this subject based on the ideXlab platform

  • Effect of Network Polymerization on the Pressure-Induced Structural Changes in Sodium Aluminosilicate Glasses and Melts: 27Al and 17O Solid-State NMR Study
    Journal of Physical Chemistry C, 2011
    Co-Authors: Yoo Soo Yi, George D Cody, Kenji Mibe, Bjorn O Mysen

    Abstract:

    Probing the pressure-induced structural changes and the extent of disorder in aluminosilicate glasses and melts at high pressure remains a challenge in modern physical and chemical sciences. With an aim of establishing a systematic relationship between pressure, composition, and glass structures, we report 27Al and 17O 3QMAS NMR spectra for sodium aluminosilicate glasses [Na2O:Al2O3:SiO2 = 1.5:0.5:2n with n = 1 (NAS150520, XSiO2 = 0.5), 2 (NAS150540, XSiO2 = 0.67), and 3 (NAS150560, XSiO2 = 0.75)], quenched from melts at pressures up to 8 GPa. We also explore the stability of the [4]Al–O–[4]Al cluster in the highly depolymerized, NAS150520, glass at high pressure. For given glass composition, the [5,6]Al peak intensity increases with increasing pressure. The population of [5,6]Al increases linearly with XSiO2 from NAS150520 (XSiO2 = 0.5) to NAS150560 glass (XSiO2 = 0.75) at both 6 and 8 GPa. The [5,6]Al/XSiO2 ratio also tends to increase with pressure, indicating a possible relationship between [5,6]Al fr…

  • oxygen 17 nuclear magnetic resonance study of the structure of mixed cation calcium sodium silicate glasses at high pressure implications for molecular link to element partitioning between silicate liquids and crystals
    Journal of Physical Chemistry B, 2008
    Co-Authors: George D Cody, Bjorn O Mysen

    Abstract:

    The structure of silicate glasses and the corresponding liquids at high pressure and their structure−property relations remain difficult questions in modern physical chemistry, geochemistry, and condensed matter physics. Here we report high- resolution solid-state O-17 3QMAS NMR spectra for mixed cation Ca−Na silicate glasses quenched from melts at high pressure up to 8 GPa. The spectra provide the experimental evidence for the varying pressure-dependence in two different types of nonbridging oxygen (NBO) environments (i.e., Na−O−Si and mixed {Ca,Na}−O−Si) in the single glass composition. The percentage of NBO drops significantly with increasing pressure and is a complex function of melt composition, including cation field strength of network modifying cations. A decrease in NBO fraction with pressure is negatively correlated with the element partitioning coefficient between crystals and liquids at high pressure.

  • The effect of Na/Si on the structure of sodium silicate and aluminosilicate glasses quenched from melts at high pressure : A multi-nuclear (Al-27, Na-23, O-17) 1D and 2D solid-state NMR study
    Chemical Geology, 2006
    Co-Authors: George D Cody, Bjorn O Mysen

    Abstract:

    Abstract We report multi-nuclear (Na-23 and O-17) solid-state NMR [MAS and triple quantum (3Q) MAS] spectra for sodium tetrasilicate glasses (NS4) quenched from melts at high pressure up to 8 GPa. The results show clear evidence for the pressure-induced structural changes in the glasses, forming oxygen linking [4] Si and [5,6] Si ( [4] Si–O– [5,6] Si) with increasing pressure. Whereas the general trend in the effect of pressure is consistent with that of sodium trisilicate glasses (NS3), detailed pressure-induced structural changes for NS4 are largely different from NS3. These differences include the larger fraction of [4] Si–O– [5,6] Si and smaller fraction of Na–O– [5,6] Si for NS4 than NS3 at isobaric conditions. Topological disorder due to Si–O bond length distribution in [4] Si–O– [4] Si is also larger for more polymerized NS4 than that for NS3, demonstrating the complexity in structural rearrangement with pressure in silicate glasses and melts with composition at elevated pressure. Na-23 MAS NMR spectra at 14.1 T for the NS4 and aluminosilicate glasses (albite composition) reveal distinct differences in Na environments within sodium silicate and aluminosilicate glasses at high pressure. Variation of isotropic chemical shift with pressure for NS4, though minor, may suggest increasing Na–O distance with pressure, possibly due to a slight increase in Na coordination at high pressure. On the other hand, Na-23 isotropic chemical shift for albite composition glass increases with increasing pressure, implying the decrease in average Na–O distance and thus free volume for non-framework cations with pressure. Higher magnetic field, coupled with 2D Al-27 3QMAS NMR, improves the resolution of Al sites for aluminosilicate glasses at high pressure and may suggest two [5] Al sites in partially polymerized aluminosilicate glasses (Na 2 O/Al 2 O 3 /SiO 2  = 15:5:60) quenched from melts at 8 GPa. The current results, together with our previous results, imply that the pressure-induced structural changes and the corresponding changes in properties in silicate melts and glasses are complex function of composition.