From porous silica xerogels to bulk optical glasses: The control of densification

The sol–gel technique constitutes an interesting way of producing pure or doped silicate materials for use in the optics domain. Furthermore, mastering the porous structure of xerogels turns out to be relevant in preparation of a post-doping or a fluidic treatment. Pure silica xerogel rods, with length and diameter of several centimeters, have been obtained without any cracks from two alkoxide precursors and using different methods. Various ways of changing the pore size distribution and the specific surface area of these gels are presented. Hence, mean pore diameters may be adjusted from 5 to 32 nm. Moreover, bulk transparent glasses could be then derived from these gels through a densification heat-treatment in ambient air, but in this case, all of the samples contain non-negligible amounts of hydroxyl groups. In order to remove most of these OH groups, a suitable chlorination process has been implemented.