| abstract |
The invention reflects discovery of a liquid phase dopingntechnique that, unlike previous techniques, exhibits very littlenfluorine depletion upon subsequent heating. The invention involvesnthe steps of providing a silica sol comprising a tetraalkylammoniumnhydroxide and a di-, tri-, or tetra-alkylammonium fluoride, the solnhaving pH of about 10 to about 14, adding a gelling agent to the solnto induce gelation, casting or extruding the sol to form a gel body,nand then drying, heat treating, and sintering the body.nAdvantageously, the fluorine-containing compound isntetramethylammonium fluoride. |