Fluorine speciation as a function of composition in peralkaline and peraluminous Na sub(2)O-CaO-Al sub(2)O sub(3)-SiO sub(2) glasses: A multinuclear NMR study

The incorporation mechanisms of fluorine (F) into peralkaline and peraluminous Na sub(2)O-CaO aluminosilicate glasses with similar to 65 mol% SiO sub(2) (model system for phonolites) were investigated by magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. In super(19)F MAS NMR...

Full description

Saved in:
Bibliographic Details
Published in:Geochimica et cosmochimica acta 2014-05, Vol.132, p.151-169
Main Authors: Baasner, A, Schmidt, B C, Dupree, R, Webb, S L
Format: Article
Language:English
Subjects:
Aluminosilicates
Aluminum
Aluminum silicates
Fluorine
Glass
Nuclear magnetic resonance
Speciation
Spectra
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The incorporation mechanisms of fluorine (F) into peralkaline and peraluminous Na sub(2)O-CaO aluminosilicate glasses with similar to 65 mol% SiO sub(2) (model system for phonolites) were investigated by magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. In super(19)F 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 super(23)Na and super(29)Si MAS NMR spectra. super(27)Al 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.
ISSN:0016-7037
DOI:10.1016/j.gca.2014.01.041