Influence of titanium diboride additions on the sintering behavior of nanoporous fumed silica composites

The sinterability of fumed silica composites used for thermal insulation is strongly activated by TiB2 additions. Shrinkage kinetics measured by dilatometry are in good agreement with viscous flow model predictions. In these materials, mass transport is accelerated after TiB2 oxidation, which starts around 450 °C. This is due to the formation of small liquid pockets by reaction between boron containing oxides and the surrounding fumed silica particles. At temperatures below 1000 °C, activation energies calculated from shrinkage data are close to those reported for silica gels. At higher temperatures, activation energies are much higher due to the rapid loss of surface area. TiB2 additions also induce a hardening effect that can be used to improve the material consistency after sintering.