Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59..325m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 2, pp.325-342
Computer Science
9
Scientific paper
The interaction of Ti 4+ with the anionic structure of glasses and melts along the join Na 2 Si 2 O 5 ---Na 2 Ti 2 O 5 has been examined in situ at temperatures between 25 and 1316°C with microRaman spectroscopy. In the Ti-free endmember system the expression, (1) 2Q 3 Q 2 + Q 4 describes the anionic equilibria adequately. Solution of Ti 4+ stabilizes an additional unit, Q 1 . This structural change requires an additional expression, (2) 2Q 2 Q 3 + Q 1 , to represent the equilibria. The H x 1 for reaction 1 is ~24 kJ/mol, whereas that for reaction 2 is ~ -40 kJ/mol. These values differ from those in the analogous Na 2 Si 2 O 5 ---Na 2 (NaAl) 2 O 5 system (Mysen and Frantz, 1994a), where H x 1 for Al-bearing melts is -11--14 kJ/mol, and that of reaction 2 is 17-33 kJ/mol, depending on the Al/(Al + Si). Increasing TiO 2 concentration is positively correlated with the abundance of Q 2 and Q 1 structural units, whereas those of Q 3 and Q 4 are negatively correlated. In the equivalent Al-system (Mysen and Frantz, 1994a), the Q 2 , Q 1 , and Q 4 are positively correlated and the Q 3 abundance is negatively correlated with increasing Al 2 O 3 . The Raman spectra of Ti-bearing glasses and melts are consistent with Ti 4+ in at least three different structural positions (Si 4+ Ti 4+ substitution, clusters perhaps of TiO 2 type, and Ti 4+ as a network-modifying cation). This behavior depends on both temperature and TiO 2 concentration. The fraction of tetrahedrally coordinated Ti 4+ increases from near 0% for 3.5 mol% TiO 2 to nearly 80% in glasses and melts with 20 mol% TiO 2 . Increasing temperature above that of the glass transformation interval (400-500°C) results in a 10-30% decrease in the fraction Ti 4+ in tetrahedral coordination. As the temperature is raised beyond 800-900°C, this trend reverses. It is suggested that the temperature- and composition-dependent structural behavior of Ti 4+ in the melts might be reflected in unusual behavior of melt properties such as viscosity, thermal expansion, and thermodynamic properties.
Mysen Bjorn
Neuville Daniel
No associations
LandOfFree
Effect of temperature and TiO 2 content on the structure of Na 2 Si 2 O 5 ---Na 2 Ti 2 O 5 melts and glasses does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Effect of temperature and TiO 2 content on the structure of Na 2 Si 2 O 5 ---Na 2 Ti 2 O 5 melts and glasses, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Effect of temperature and TiO 2 content on the structure of Na 2 Si 2 O 5 ---Na 2 Ti 2 O 5 melts and glasses will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1820955