title: Q-Speciation and Network Structure Evolution in Invert Calcium Silicate Glasses.
abstract: Binary silicate glasses in the system CaO-SiO2 are synthesized over an extended composition range (42 mol % ≤ CaO ≤ 61 mol %), using container-less aerodynamic levitation techniques and CO2-laser heating. The compositional evolution of Q speciation in these glasses is quantified using (29)Si and (17)O magic angle spinning nuclear magnetic resonance spectroscopy. The results indicate progressive depolymerization of the silicate network upon addition of CaO and significant deviation of the Q speciation from the binary model. The equilibrium constants for the various Q species disproportionation reactions for these glasses are found to be similar to (much smaller than) those characteristic of Li (Mg)-silicate glasses, consistent with the corresponding trends in the field strengths of these modifier cations. Increasing CaO concentration results in an increase in the packing density and structural rigidity of these glasses and consequently in their glass transition temperature Tg. This apparent role reversal of conventional network-modifying cations in invert alkaline-earth silicate glasses are compared and contrasted with that in their alkali silicate counterparts.
authors.affiliation: †Department of Materials Science, University of California at Davis, Davis, California 95616, United States.
authors.forename: Derrick C
authors.initials: DC
authors.lastname: Kaseman
authors.affiliation: ‡Institute of Chemical Engineering and High Temperature Chemical Processes FORTH, P.O. Box 1414, GR-26504, Patras, Greece.
authors.forename: A
authors.initials: A
authors.lastname: Retsinas
authors.affiliation: ‡Institute of Chemical Engineering and High Temperature Chemical Processes FORTH, P.O. Box 1414, GR-26504, Patras, Greece.|§Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
authors.forename: A G
authors.initials: AG
authors.lastname: Kalampounias
authors.affiliation: ‡Institute of Chemical Engineering and High Temperature Chemical Processes FORTH, P.O. Box 1414, GR-26504, Patras, Greece.
authors.forename: G N
authors.initials: GN
authors.lastname: Papatheodorou
authors.affiliation: †Department of Materials Science, University of California at Davis, Davis, California 95616, United States.
authors.forename: S
authors.initials: S
authors.lastname: Sen