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GEOREF RECORD

Constraints on the incorporation mechanism of chlorine in peralkaline and peraluminous Na (sub 2) O-CaO-Al (sub 2) O (sub 3) -SiO (sub 2) glasses

Amrei Baasner, Ivan Hung, Thomas F. Kemp, Ray Dupree, Burkhard C. Schmidt and Sharon L. Webb
Constraints on the incorporation mechanism of chlorine in peralkaline and peraluminous Na (sub 2) O-CaO-Al (sub 2) O (sub 3) -SiO (sub 2) glasses
American Mineralogist (August 2014) 99 (8-9): 1713-1723

Abstract

Incorporation mechanisms of Cl in peralkaline and peraluminous Na (sub 2) O-CaO-Al (sub 2) O (sub 3) -SiO (sub 2) glasses as a model system for phonolitic melts were investigated using (super 35) Cl, (super 23) Na, (super 27) Al, and (super 29) Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The size and large distribution of electric field gradients for (super 35) Cl causes loss of signal in the MAS NMR experiment and 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 (super 35) Cl chemical shift indicates that the Cl environment is dominated bythe presence of Na cations, consistent with the Na/Ca ratio of 5/1 in the glasses. (super 35) Cl MAS NMR spectra of the peraluminous glasses show a larger chemical shift distribution and a more positive isotropic chemical shift, approximately -75 ppm, than the peralkaline glasses, approximately -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 (super 35) Cl signal is also lost in the static spectra indicating that approximately 20% of Cl for a peralkaline glass and more than approximately 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 (super 35) Cl signal or non-bridging Cl environments like for example Al-Cl. The Cl environment in the present mixed Na (sub 2) O-CaO aluminosilicate glasses appears to be more disordered than was to be expected from previous NMR spectroscopic studies on simpler glass compositions.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 99
Serial Issue: 8-9
Title: Constraints on the incorporation mechanism of chlorine in peralkaline and peraluminous Na (sub 2) O-CaO-Al (sub 2) O (sub 3) -SiO (sub 2) glasses
Affiliation: Georg-August-University Goettingen, Mineralogy Department, Gottingen, Germany
Pages: 1713-1723
Published: 201408
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 49
Accession Number: 2014-104715
Categories: General geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
Secondary Affiliation: Florida State University, USA, United StatesUniversity of Warwick, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201452
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