Analysis of precursor residues in lithium aluminosilicate gels using XPS and RGA

Lithium aluminosilicate gels of composition 15 mol% lithia-2 mol% alumina-83 mol% silica were prepared by adding nitrates to tetraethyl-orthosilicate (TEOS) and going through the sol-gel process. Samples were prepared in thin film and bulk form. Dried and outgassed samples were studied with X-ray photoelectron spectroscopy (XPS) d residual gas analysis (RGA). XPS spectra show similar species in both thin film and bulk samples, but different relative quantities of each species. Some oxidation of organic groups by nitrate is evident in bulk samples which were heated to 70°C during the drying process. In both thin film and bulk samples, the O 1s spectra indicate oxygens associated with a silicate network and higher binding energy species such as - -O-. The C 1s spectra of bulk gels heated to 140° and 350°C in vacuum show some organics are vaporized at low temperature, while the oxidized-organic residues are decomposed to CO₂ at high temperature. These species are also observed with residual gas analysis at the corresponding temperatures.