Q-Speciation and Network Structure Evolution in Invert Calcium Silicate Glasses

Area of Science:

• Materials Science
• Solid State Chemistry
• Geochemistry

Background:

• Silicate glasses are crucial in various industries.
• Understanding their structure-property relationships is key for material design.
• Calcium oxide (CaO) acts as a network modifier in silicate systems.

Purpose of the Study:

• To investigate the structural evolution of CaO-SiO2 glasses.
• To quantify the speciation of silicon (Q species) as a function of CaO content.
• To correlate structural changes with glass properties like glass transition temperature (Tg).

Main Methods:

• Synthesis of binary CaO-SiO2 glasses using container-less aerodynamic levitation and CO2-laser heating.
• Quantification of Q speciation via (29)Si and (17)O magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy.
• Measurement of glass transition temperature (Tg).

Main Results:

• Progressive depolymerization of the silicate network with increasing CaO content.
• Significant deviation of Q speciation from the ideal binary model.
• Increased packing density, structural rigidity, and Tg with higher CaO concentrations.
• Equilibrium constants for Q species disproportionation are comparable to Mg-silicate glasses, not Li-silicate glasses.

Conclusions:

• CaO acts as a network modifier, leading to depolymerization and increased Tg in CaO-SiO2 glasses.
• The behavior of CaO differs from alkali modifiers, showing a role reversal in alkaline-earth silicate glasses.
• These findings provide insights into the structure-property correlations in silicate glasses.