The effects of different heat treatment and atmospheres on the NMR signal and structure of TiO2-ZrO2-SiO2 sol-gel materials

The effects of different heat treatment schemes (i.e. successively or directly heated to particular temperatures) and atmospheres (air or nitrogen) on the solid-state NMR spectra obtained from (TiO2)(0.15)(ZrO2)(0.05)(SiO2)(0.80) sol-gel materials are investigated. A combination of H-1, C-13, O-17 and Si-29 NMR is used. Si-29 MAS NMR indicates that the extent of condensation of the silica-based network strongly depends on the maximum temperature the sample has experienced, but the condensation is largely independent of the details of the heat treatment scheme and atmosphere used. For sol-gel produced silicate-based materials the results show that the equilibrium structure at each temperature is reached rapidly compared to the time (2 h) spent at that temperature. The O-17 NMR results confirm that a nitrogen atmosphere does significantly reduce loss of O-17 from the structure but care must be taken since there could be differential loss of O-17 from the regions having different local structural characteristics. (C) 2003 Elsevier Science (USA). All rights reserved.