Schmidt, Burkhard C.

[["dc.bibliographiccitation.firstpage","231"],["dc.bibliographiccitation.issue","3-4"],["dc.bibliographiccitation.journal","Chemical Geology"],["dc.bibliographiccitation.lastpage","241"],["dc.bibliographiccitation.volume","256"],["dc.contributor.author","Yamashita, Shigeru"],["dc.contributor.author","Behrens, Harald"],["dc.contributor.author","Schmidt, Burkhard C."],["dc.contributor.author","Dupree, Ray"],["dc.date.accessioned","2018-11-07T11:09:08Z"],["dc.date.available","2018-11-07T11:09:08Z"],["dc.date.issued","2008"],["dc.identifier.doi","10.1016/j.chemgeo.2008.06.029"],["dc.identifier.isi","000261563200015"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/52940"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Elsevier Science Bv"],["dc.relation.issn","0009-2541"],["dc.title","Water speciation in sodium silicate glasses based on NIR and NMR spectroscopy"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","151"],["dc.bibliographiccitation.journal","Geochimica et Cosmochimica Acta"],["dc.bibliographiccitation.lastpage","169"],["dc.bibliographiccitation.volume","132"],["dc.contributor.author","Baasner, A."],["dc.contributor.author","Schmidt, Burkhard C."],["dc.contributor.author","Dupree, Ray"],["dc.contributor.author","Webb, Sharon L."],["dc.date.accessioned","2018-11-07T09:40:57Z"],["dc.date.available","2018-11-07T09:40:57Z"],["dc.date.issued","2014"],["dc.description.abstract","The incorporation mechanisms of fluorine (F) into peralkaline and peraluminous Na2O-CaO aluminosilicate glasses with similar to 65 mol% SiO2 (model system for phonolites) were investigated by magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. In F-19 MAS NMR spectra of the fluorine-bearing peralkaline glasses at least five F sites could be distinguished, while only three of these sites could be found in the corresponding peraluminous glasses, which shows that there are more F incorporation mechanisms in peralkaline than in peraluminous glasses. In the peralkaline glasses containing up to 6.2 mol% F the following F environments were identified: F-Ca(n) at similar to-113 ppm, Si-F-Na(n) or Al-F-Ca(n) at similar to-146 ppm, Al-F-Al at similar to-168 ppm, Al-F-Na(n) at similar to-188 ppm and F-Na(n) at similar to-225 ppm (\"n\" indicates that the number of atoms is variable or uncertain). F-Ca(n) is the most abundant site which is surprising as Ca is the least common cation in the glasses. The fraction of F-Ca(n) sites increases from 42% to 53% as the F content increases from 1.2 to 6.2 mol%. The addition of up to 16.5 mol% (5.3 wt%) water strongly affects F speciation in peralkaline glasses and results in a decrease in the fraction of F-Al sites compared to F-Ca(n) sites. It seems that hydroxyl groups (OH) and F occupy similar Al environments and that F cannot compete with OH. In the peraluminous glasses containing up to 18.3 mol% F only three F environments Si-F-Na(n) or Al-F-Ca(n) at similar to-149 ppm, Al-F-Al at similar to-170 ppm and Al-F-Na(n) at similar to-190 ppm are observed. Al-F-Na(n) is the most abundant site with a fraction of 54-61%. The F speciation also changes with the F concentration, with a minimum in Al-F-Na(n) sites between 3.5 and 9.7 mol% F. Fluorine has only a small effect on the Na-23 and Si-29 MAS NMR spectra. Al-27 MAS NMR spectra of the peralkaline glasses show only four-coordinated Al while in the peraluminous glasses similar to 5% of the Al was found to be five-coordinated. The amount of five-coordinate Al does not change with increasing F content, but the environment of the five-coordinate Al becomes more symmetric with increasing F. (C) 2014 Elsevier Ltd. All rights reserved."],["dc.identifier.doi","10.1016/j.gca.2014.01.041"],["dc.identifier.isi","000334832100010"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/33614"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Pergamon-elsevier Science Ltd"],["dc.relation.issn","1872-9533"],["dc.relation.issn","0016-7037"],["dc.title","Fluorine speciation as a function of composition in peralkaline and peraluminous Na2O-CaO-Al2O3-SiO2 glasses: A multinuclear NMR study"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1713"],["dc.bibliographiccitation.issue","8-9"],["dc.bibliographiccitation.journal","American Mineralogist"],["dc.bibliographiccitation.lastpage","1723"],["dc.bibliographiccitation.volume","99"],["dc.contributor.author","Baasner, Amrei"],["dc.contributor.author","Hung, Ivan"],["dc.contributor.author","Kemp, Thomas F."],["dc.contributor.author","Dupree, Ray"],["dc.contributor.author","Schmidt, Burkhard C."],["dc.contributor.author","Webb, Sharon L."],["dc.date.accessioned","2018-11-07T09:37:00Z"],["dc.date.available","2018-11-07T09:37:00Z"],["dc.date.issued","2014"],["dc.description.abstract","Incorporation mechanisms of Cl in peralkaline and peraluminous Na2O-CaO-Al2O3-SiO2 glasses as a model system for phonolitic melts were investigated using Cl-35, Na-23, Al-27, and Si-29 magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The size and large distribution of electric field gradients for Cl-35 causes loss of signal in the MAS NMR experiment arid this, in combination with the low concentration of Cl and the large chemical shift dispersion, means that even at the highest available fields we are at the limits of MAS NMR. Nevertheless clear differences in the Cl environment in peralkaline and peraluminous glasses can readily be seen. In both glass types Cl exists in relatively symmetric Na-Ca-Cl environments. The Cl-35 chemical shift indicates that the Cl environment is dominated by the presence of Na cations, consistent with the Na/Ca ratio of 5/1 in the glasses. Cl-35 MAS NMR spectra of the peraluminous glasses show a larger chemical shift distribution and a more positive isotropic chemical shift, similar to-75 ppm, than the peralkaline glasses, similar to-100 ppm. They also have a larger quadrupole coupling constant with a larger distribution, indicating greater disorder in the peraluminous glasses. It is likely that there are more Ca cations present in the Cl environments in the peraluminous glasses than in the peralkaline glasses despite their having the same Na/Ca ratio. In the peralkaline glasses the formation of Na-Ca-Cl environments leads to a decrease in the number of network-modifying cations, which causes a polymerization of the glass network. No effect on the glass polymerization was observed in the peraluminous glasses. Some Cl-35 signal is also lost in the static spectra indicating that similar to 20% of Cl for a peralkaline glass and more than similar to 70% for a peraluminous glass must be in environments where there is a large enough electric field gradient that the resulting very broad line is unobservable. These environments could be simply Na-Ca-Cl with higher electric field gradients than those producing the observed Cl-35 signal or non-bridging Cl environments like for example Al-Cl. The Cl environment in the present mixed Na2O-CaO aluminosilicate glasses appears to be more disordered than was to be expected from previous NMR spectroscopic studies on simpler glass compositions."],["dc.identifier.doi","10.2138/am.2014.4717"],["dc.identifier.isi","000340580500019"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/32736"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Mineralogical Soc Amer"],["dc.relation.issn","1945-3027"],["dc.relation.issn","0003-004X"],["dc.title","Constraints on the incorporation mechanism of chlorine in peralkaline and peraluminous Na2O-CaO-Al2O3-SiO2 glasses"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]