Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Utilizing sol or gel
Reexamination Certificate
1999-09-03
2001-02-27
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Utilizing sol or gel
C264S642000
Reexamination Certificate
active
06193926
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for making molded glass and ceramic articles. More particularly, the present invention relates to an improved sol-gel method for making molded glass and ceramic articles using aqueous fluorine to initiate a gel reaction.
2. Description of the Related Art
One of the established methods of making glass and ceramic articles is known as the “sol-gel” method. When making articles using this process, a base material in the form of fine particles is mixed with water and various stabilizing ingredients to form a stable dispersion or “sol.” To this sol, an “initiator” is added to destabilize the dispersion, causing the fine particles to bond together and form a “gel.” One common initiator is aqueous fluorine, which is typically added as hydrofluoric acid or ammonium hydrofluoride. Upon adding the initiator, the dispersion may be transferred to a mold. After the dispersion gels, the gel is removed from the mold, dried, and fired.
One problem inherent in the sol-gel method arises from adding the initiator. If the initiator is added directly to the sol, problems may arise in controlling the gelling process. For example, the sol may gel before it can be transferred to the mold. One technique to solving this problem when using fluorine as the initiator is disclosed in U.S. Pat. No. 4,840,653, issued to Rabinovich. This patent discloses reacting a silicon-containing organic chemical with water and hydrofluoric acid to create a fluorinated form of finely divided silica. A small amount of this material is then added to a dispersion of nonfluorinated fine silica to initiate the gelling reaction in a timely and controlled fashion.
SUMMARY OF INVENTION
It is an object of the invention to provide an improved method of making molded glass and ceramic articles using the sol-gel process in which an aqueous fluorine initiator can be added directly to the dispersion of fine base particles without premature gelling.
To achieve this and other objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention includes a method for making molded glass and ceramic articles comprising (i) dispersing base particles having an average particle of size below 1 micron in water to form a dispersion of fine base particles, (ii) adding base particles having an average particle size above 1 micron to the dispersion of fine base particles to form a dispersion of bimodal base particles, (iii) adding aqueous fluorine to the dispersion of bimodal base particles to form a dispersion of bimodal base particles and fluorine, (iv) agitating the dispersion of bimodal base particles and fluorine with sufficient force to delay gel formation, (v) transferring the dispersion of bimodal base particles and fluorine to a mold; (vii) allowing the dispersion of bimodal base particles and fluorine to form a gel, and (vii) removing the gel from the mold for drying and firing.
The advantages of the present invention are that premature gelling is avoided using a simplified process, adding aqueous fluorine directly as an initiator without requiring the additional steps of making a fluorinated ingredient, and that the process is adaptable to a continuous production method rather than a batch process.
It is to be understood that both the foregoing general description and the following detailed description are exemplar and explanatory and are intended to provide further explanation of the invention as claimed.
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Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fiorilla Christopher A.
Heraeus Amersil, Inc.
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