# US 4,397,670 A · Method of making alkali metal, calcium fluorosilicate glass-ceramic articles

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- Number: US 4,397,670 A
- Document ID: US4397670A
- Status: Granted
- Kind: A
- Application number: 06/416,961
- Filed: 1982-09-13
- Granted: 1983-08-09
- Earliest claimed: 1981-10-05
- Assignees: Corning Glass Works
- Inventors: George H. Beall
- Web page: https://patentgrep.com/patent/US4397670A

## CPC

- C03C 10/16: Halogen containing crystalline phase
- C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS

## Abstract

The instant invention is directed to the production of highly crystalline glass-ceramic articles demonstrating high intrinsic mechanical strength and toughness containing crystals of canasite and/or agrellite and/or fedorite as the predominant crystal phase. The articles have overall compositions consisting essentially, expressed in terms of weight percent on the oxide basis, of about ______________________________________ SiO.sub.2 45-75 CaO 8-30 F 3.5-12 Na.sub.2 O 3-15 K.sub.2 O 0-20 Na.sub.2 O + K.sub.2 O 5-25 B.sub.2 O.sub.3 0-6 Al.sub.2 O.sub.3 0-7 ZrO.sub.2 0-12. ______________________________________

## Claims

### Claim 1

A method for preparing a highly crystalline glass-ceramic article exhibiting high toughness and a modulus of rupture in excess of 20,000 psi, wherein the predominant crystal phase is canasite and/or agrellite and/or fedorite, which comprises the following steps:
(a) melting a batch for a glass consisting essentially, expressed in terms of weight percent on the oxide basis, of about
______________________________________ SiO.sub.2 45-75 CaO 8-30 F 3.5-12 Na.sub.2 O 3-15 K.sub.2 O 0-20 Na.sub.2 O + K.sub.2 O 5-25 B.sub.2 O.sub.3 0-6 Al.sub.2 O.sub.3 0-7 ZrO.sub.2 0-12 ______________________________________
(b) simultaneously cooling the melt to a temperature at least below the transformation range thereof and shaping a glass article of a desired configuration therefrom; and
(c) exposing said glass article to a temperature between about 500.degree.-1000.degree. C. for a time sufficient to cause the growth therein of the desired crystals.

### Claim 2 (depends on 1)

A method according to claim 1 wherein said glass consists essentially of about
______________________________________ SiO.sub.2 50-65 CaO 15-24 F 5-9 Na.sub.2 O 3-13 K.sub.2 O 3-15 Na.sub.2 O + K.sub.2 O 11-22 B.sub.2 O.sub.3 0-3 Al.sub.2 O.sub.3 0-3 ZrO.sub.2 0-8. ______________________________________

### Claim 3 (depends on 1)

A method according to claim 1 wherein said glass article is exposed to a temperature between about 500.degree.-750.degree. C. for about 0.5-6 hours to develop nucleation and then to a temperature between about 800.degree.-1000.degree. C. for about 0.5-8 hours to cause the growth of the desired crystals.