# US 4,396,720 A · Transparent glass-ceramics containing mullite

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- Number: US 4,396,720 A
- Document ID: US4396720A
- Status: Granted
- Kind: A
- Application number: 06/395,617
- Filed: 1982-07-06
- Granted: 1983-08-02
- Earliest claimed: 1982-07-06
- Assignees: Corning Glass Works
- Inventors: George H. Beall; John F. MacDowell; Mark P. Taylor
- Web page: https://patentgrep.com/patent/US4396720A

## CPC

- C03C 10/0054: {containing PbO, SnO2, B2O3}
- 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

This invention is concerned with the production of substantially transparent glass-ceramic articles containing mullite as the predominant crystal phase which can be prepared by crystallizing in situ precursor glasses capable of being melted at temperatures no higher than 1650.degree. C. The inventive articles consist essentially, in weight percent, of 1070% SiO.sub.2, 7-40% B.sub.2 O.sub.3, 14-50% Al.sub.2 O.sub.3, 0-35% RO, wherein RO consists of at least one member of the group in the indicated proportions of 015% MgO, 0-20% CaO, 0-30% SrO, 0-30% BaO, and 0-30% PbO, and 0-30% R.sub.2 O, wherein R.sub.2 O consists of at least one member of the group in the indicated proportions of 0-10% Li.sub.2 O, 0-15% Na.sub.2 O, 0-25% K.sub.2 O, 0-25% Rb.sub.2 O, and 0-25% Cs.sub.2 O, the mole ratio Al.sub.2 O.sub.3 :RO+R.sub.2 O>1.3. Where 0.01-1% Cr.sub.2 O.sub.3 is included in the composition, the glass-ceramic will exhibit broad absorption over the visible region of the radiation spectrum, strong fluorescence in the red and near infrared portions of the spectrum where exposed to ultraviolet and/or visible radiation, and relatively little overlap of the absorption and fluorescent spectra.

## Claims

### Claim 1

A substantially transparent glass-ceramic article containing mullite as the predominant crystal phase which can be prepared from a precursor glass capable of being melted at temperatures no higher than 1650.degree. C. and which can be crystallized at high viscosities, i.e., about 10.sup.9 -10.sup.12 poises, said glass-ceramic article consisting essentially, expressed in terms of weight percent on the oxide basis, of 40-60% SiO.sub.2, 12-30% B.sub.2 O.sub.3, 17.5-27.5% Al.sub.2 O.sub.3, and 3-13% Na.sub.2 O and/or K.sub.2 O, and wherein the mole ratio Al.sub.2 O.sub.3 :Na.sub.2 O+K.sub.2 O 1.75.

### Claim 2

A substantially transparent glass-ceramic article containing mullite as the predominant crystal phase which can be prepared from a precursor glass capable of being melted at temperatures no higher than 1650.degree. C. and which can be crystallized in situ at high viscosities, i.e., about 10.sup.9 -10.sup.12 poises, said glass-ceramic article consisting essentially, expressed in terms of weight percent on the oxide basis, of 15-45% SiO.sub.2, 20-30% B.sub.2 O.sub.3, 20-40% Al.sub.2 O.sub.3, and 5-30% RO, wherein RO consists of at least one member of the group in the indicated proportions of 0-15% MgO, 0-20% CaO, 0-30% SrO, and 0-30% BaO, and wherein the mole ratio Al.sub.2 O.sub.3 :RO<1.75.

### Claim 3 (depends on 1)

A glass-ceramic according to claim 1 also containing up to 1% total of transition metal oxides and/or up to 5% total of rare earth metal oxides as colorants.

### Claim 4 (depends on 2)

A glass-ceramic according to claim 2 also containing up to 1% total of transition metal oxides and/or up to 5% total of rare earth metal oxides as colorants.

### Claim 5 (depends on 1)

A glass-ceramic according to claim 1, which, also containing 0.01-1% Cr.sub.2 O.sub.3, demonstrates broad absorption over the visible region of the radiation spectrum, strong fluorescence in the red and near infrared portions of the spectrum when exposed to ultraviolet and/or visible radiation, and relatively little overlap of the absorption and fluorescent spectra.

### Claim 6 (depends on 2)

A glass-ceramic according to claim 2 which, also containing 0.01-1% Cr.sub.2 O.sub.3, demonstrates broad absorption over the visible region of the radiation spectrum, strong fluorescence in the red and near infrared portions of the spectrum when exposed to ultraviolet and/or visible radiation, and relatively little overlap of the absorption and fluorescent spectra.