Structural control on bulk melt properties: Single and double quantum 29Si NMR spectroscopy on alkali-silicate glasses

• Published in: Geochimica et cosmochimica acta Vol. 71; no. 24; pp. 6002 - 6018
• Main Authors: Malfait, Wim J., Halter, Werner E., Morizet, Yann, Meier, Beat H., Verel, Rene
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2007; Elsevier
• Subjects: Earth Sciences; Sciences of the Universe
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2007.09.011

The structure of 21 binary potassium, rubidium and cesium silicate glasses (in the range 15–50 mol% alkali oxide) was analyzed by 29Si single quantum and double quantum MAS NMR spectroscopy. Their glass transition temperatures ( T g) were measured by calorimetry. The chemical shifts and the relative abundance of Q n species correlate with the cationic field strength ( Z/ r) of the network modifier. A correlation is observed between T g and the inverse of the entropy of mixing of the different Q n species, which is explained in the framework of the Adam–Gibbs relaxation theory. At high alkali content, up to 44% of the SiO 4 tetrahedra are part of three-membered rings. At a given alkali content, the abundance of these rings increases with increasing cation size. The abundance of three-membered rings in K-silicate melts correlates with a temperature and a non-linear composition dependence of the heat capacity. It is also a possible cause for the anomalous volumetric behavior of potassium silicate glasses.