Fabrication including sol-gel processing

Details Fabrication including sol-gel processing Fabrication including sol-gel processing

1998-06-03

1999-08-31

Griffin, Steven P.

Glass manufacturing

Processes of manufacturing fibers, filaments, or preforms

Process of manufacturing optical fibers, waveguides, or...

65 172, 65901, 501 12, 501 54, 264 121, 264621, C03B 802, C03B 37016

Patent

active

059448660

ABSTRACT:
The invention provides an alternative to conventional sol-gel methods that utilize undesirably high amounts of a stabilizing agent such as TMAH and a gelling agent such as methyl formate. The method involves the steps of (a) providing a colloidal silica dispersion containing a stabilizing/gelling agent, where only a portion of the molecules of the agent ionize, and (b) subsequently adding to the silica dispersion a pH-reducing additive. The stabilizing/gelling agent has a dual function. The agent, e.g., an amine, initially acts as a stabilizer in the silica dispersion in that a portion of its molecules ionize, while an appreciable amount of the agent remains non-ionized. The agent later transforms in situ to a gelling agent upon addition of a pH-reducing additive. Specifically, as the pH-reducing additive lowers the pH to values at or around the pK.sub.a of the stabilizing/gelling agent, more of the agent's molecules are ionized, these cations contributing to charge neutralization, and thus gellation, of the colloidal silica particles.

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