Electrochemical Method for Removal of Particulate Gel Body from a Mold

It has been shown that vitreous silica monoliths can be made out of a dispersion containing small silica particles. However, complex shapes are difficult to release from molds without fracture due to friction between the gel and mold and low mechanical strength of the gel body. Lubrication with oils frequently fails to avoid fracture. We have found that electrolytic change in the pH at the gel/mold interface can provide a lubricating sol layer between the gel body and mold, allowing low friction release. This process is based on the fact that gelation is a function of pH. The sol before gelation has a pH near 10.5. An agent added to promote gelation gradually reduces the pH to ~8. However, if a DC voltage (2-9 v) is applied between the metal mold and an electrode in the sol, hydroxyl ions are generated at the negative electrode (cathode) maintaining a pH at the cathode/sol interface that is sufficiently high to prevent gelation at that interface. If a mold is designed in such a way that its walls serve as the cathode, a thin layer of the ungelled sol provides good lubrication, and the gelled body easily slips out of the mold. Different mold designs for different gel bodies are described and discussed.