HIGH-PURITY SILICA MONOLITHS AND PROCESS FOR THE SYNTHESIS THEREOF

摘要

The present invention relates to a process for the synthesis of a silica monolith according to a process known as a "sol-gel process" that comprises the following steps: ° hydrolysis of a silicon alkoxide in order to form a hydrolysis precursor followed by a condensation of said hydrolysis precursor in the presence of an organic solvent, in the presence of water and of a basic catalyst in order to form oligomeric clusters containing several silicon atoms; ° dispersion of said oligomeric clusters in a solution in order to form a sol; ° polymerization of the sol in order to obtain a gel via a first heat treatment, at a temperature below the boiling point of the constituents of the sol; ° drying of the gel via a second heat treatment including an exposure of the gel to around 90°C for at least 24 hours followed by an increase in temperature, under vacuum, between around 90°C and around 180°C, said temperature increase being between 0.1°C/min and 5°C/min; ° conversion of the gel to a xerogel via a third heat treatment, said heat treatment including a hold at a drying temperature between 850 and 1000°C for at least an hour; ° dehydration and densification of the xerogel until the silica monolith is obtained via a fourth heat treatment, said fourth heat treatment comprising a hold at a temperature above 1100°C for at least one hour. The present invention also relates to a silica monolith obtained by the process of the invention, having a concentration of -OH groups of less than 1 ppm. The present invention also discloses the use of the monolith of the invention for producing optical fibres.