Effects of temperature on silicate melt sructure: A high temperature 29Si NMR study of Na2Si2O5

摘要: Abstract The effects of temperature on the structure Na2Si2O5 glass and supercooled liquid has been investigated by high-temperature 29Si NMR measurements from room to 719°C. asymmetric line shape spectra was reproduced well a simulation concerning chemical shift anisotropy. A three-site (Q2, Q3, Q4) abundances for yields quantitative estimation population each species, where Qn represents SiO4 tetrahedra with n bridging O atoms. dependence disproportionation reaction, 2 Q 3 ↔ + 4 obtained results in region up 603°C. equilibrium constant above K, its were determined. free energy change, ΔG°, reaction determined van't Hoff equation. ΔG° evaluated be 33 ± 5 kJ at 538°C. variation quite small, suggesting small entropy contribution reaction. plot ΔG°/T vs. 1/T an estimate standard enthalpy, ΔH°, as 27 kJ. interpreted terms exchange between species. multi-site model applied this system, simple Eyring viscosity calculation estimated rate compared measured viscosity.