Tough cordierite glass-ceramics

• US 20070281850A1
• Filed: 05/31/2006
• Published: 12/06/2007
• Est. Priority Date: 05/31/2006
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Beall, George Halsey
• Granted Patent: US 7,465,687 B2
• Time in Patent Office: Days
• US Class Current: 501/9
• CPC Class Codes: C03C 10/0045 containing SiO2, Al2O3 and MgO as main constituents
• CPC Class Codes: C03C 10/16 Halogen containing crystalline phase
• CPC Class Codes: C04B 2235/3206 Magnesium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3208 Calcium oxide or oxide-forming salts thereof, e.g. lime
• CPC Class Codes: C04B 2235/3213 Strontium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3222 Aluminates other than alumino-silicates, e.g. spinel (MgAl2O4)
• CPC Class Codes: C04B 2235/3232 Titanium oxides or titanates, e.g. rutile or anatase
• CPC Class Codes: C04B 2235/3234 Titanates, not containing zirconia
• CPC Class Codes: C04B 2235/3236 Alkaline earth titanates
• CPC Class Codes: C04B 2235/3445 Magnesium silicates, e.g. forsterite
• CPC Class Codes: C04B 2235/3454 Calcium silicates, e.g. wollastonite
• CPC Class Codes: C04B 2235/3463 Alumino-silicates other than clay, e.g. mullite
• CPC Class Codes: C04B 2235/3481 Alkaline earth metal alumino-silicates other than clay, e.g. cordierite, beryl, micas such as margarite, plagioclase feldspars such as anorthite, zeolites such as chabazite
• CPC Class Codes: C04B 2235/445 Fluoride containing anions, e.g. fluosilicate
• CPC Class Codes: C04B 2235/6567 Treatment time
• CPC Class Codes: C04B 2235/662 Annealing after sintering
• CPC Class Codes: C04B 2235/72 Products characterised by the absence or the low content of specific components, e.g. alkali metal free alumina ceramics
• CPC Class Codes: C04B 2235/724 Halogenide content
• CPC Class Codes: C04B 2235/767 Hexagonal symmetry, e.g. beta-Si3N4, beta-Sialon, alpha-SiC or hexa-ferrites
• CPC Class Codes: C04B 2235/78 Grain sizes and shapes, product microstructures, e.g. acicular grains, equiaxed grains, platelet-structures
• CPC Class Codes: C04B 2235/788 : Aspect ratio of the grains
• CPC Class Codes: C04B 2235/80 : Phases present in the sintered or melt-cast ceramic products other than the main phase
• CPC Class Codes: C04B 2235/96 : Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 2235/9607 : Thermal properties, e.g. thermal expansion coefficient
• CPC Class Codes: C04B 35/195 : Alkaline earth aluminosilicates, e.g. cordierite or anorthite
• CPC Class Codes: C04B 35/653 : Processes involving a melting step

Abstract

An internally nucleated, toughened cordierite glass-ceramic is disclosed. The cordierite glass-ceramic has good oxidation resistance and fracture toughness and coefficient of thermal expansion rivaling that of silicon nitride. The glass-ceramic may be cast as a liquid. Annealing produces a material of high crystallinity combining high hardness, high Young'"'"'s modulus, good thermal stability, high strength, low density and good dielectric properties. The glass-ceramic comprises interlocking crystalline phases dominated by cordierite and a second phase having an elongated or acicular structure. A third phase may comprise a crystalline ceramic that promotes acicularity of the second phase. The third phase is preferably capable of twinning.

Claims

1. A glass-ceramic having high fracture toughness and low coefficient of thermal expansion, the glass-ceramic formed from a composition comprising, in weight percent:

2. The glass-ceramic of claim 1, wherein the first phase comprises hexagonal cordierite.

3. The glass-ceramic of claim 1, wherein the second phase is acicular and comprises a titanate.

4. The glass-ceramic of claim 3, wherein the titanate is selected from a group consisting of magnesium titanate, aluminum titanate and combinations thereof.

5. The glass-ceramic of claim 2, wherein the first phase comprises from 50-80 vol. % of the glass-ceramic.

6. The glass-ceramic of claim 1, wherein the acicular phase comprises from 8-20 vol. % of the glass-ceramic.

7. The glass-ceramic of claim 1, wherein the glass-ceramic comprises up 20% of a third crystal phase comprising a twinning ceramic compound.

8. The glass-ceramic of claim 7, wherein the twinning ceramic compound is selected from a group consisting of anorthite, Sr-feldspar, Ba-feldspar, enstatite and aluminous enstatite.

9. The glass-ceramic of claim 1 wherein the glass-ceramic includes up to 20% of a third crystal selected from the group consisting of fluormica, fluoramphibole, norbergite, spinel, sapphirine, mullite, forsterite and xonotlite.

10. The glass-ceramic of claim 7, wherein the glass-ceramic comprises up to 20 vol. % of the third phase.

11. The glass-ceramic of claim 1, wherein the glass-ceramic has a CTE from 20-50×

10<sup>−

7</sup>/°

C. in the temperature range 25-1000°

C. and a Knoop hardness greater than 800.

12. The glass-ceramic of claim 1, wherein the glass-ceramic has a Young'"'"'s modulus greater than 10 GPa.

13. The glass-ceramic of claim 1, wherein the glass-ceramic has a fracture toughness from 2.5 to 6.0 MPa·

m^0.5.

14. A method of forming a toughened, cordierite glass-ceramic article, the method comprising:

a) blending a composition comprising, in weight percent, 35-50% SiO₂, 10-35% Al₂O₃, 10-25% MgO, 7-20% TiO₂, up to 5% CaO, up to 10% SrO, where the amount of CaO and SrO comprises at least 0.5%, and F is up to 5%;

b) heating the composition to a fluid glass;

c) forming the composition to a desired shape;

d) cooling the shape to solid glass;

e) annealing the solid glass at 1100-1300°

C. for a sufficient amount of time to achieve a crystallinity of at least 85 vol. %.

15. The method of claim 14, wherein forming includes casting the fluid glass.

16. The method of claim 14, wherein the method further includes heat-treating after cooling the shape and before annealing, where heat-treating includes heating the shape to at least 800°

C. for more than one hour.

17. A cordierite glass-ceramic comprising at least three phases including:

a) 50-80 vol. % of a first phase consisting essentially of cordierite having an aspect ratio of at least 2;

1;

b) 8-20 vol. % of a second phase consisting essentially of titanate having an aspect ration of at least 5;

1; and

c) up to 20 vol. % of a third phase selected from a group consisting of anorthite, enstatite, aluminous enstatite, forsterite, fluormica, fluoramphibole, norbergite, Sr-feldspar, Ba-feldspar, spinel, sapphirine, mullite and xonotlite.

18. The cordierite glass-ceramic of claim 17, wherein the first phase has an aspect ratio of at least 5:

1.

19. The cordierite glass-ceramic of claim 17, wherein the glass-ceramic comprises from 10-20 vol. % of the third phase.

20. A glass-ceramic having a CTE from 20-50×

10<sup>−

7</sup>/°

C. in the temperature range 25-300°

C. and a fracture toughness from 2.5 to 6.0 MPa·

m^0.5, the glass-ceramic formed from a composition comprising, in weight percent;

21. The glass-ceramic of claim 20, wherein the second phase comprises a titanate selected from a group consisting of magnesium titanate, aluminum titanate and combinations thereof.

22. The glass-ceramic of claim 20, wherein the glass-ceramic includes a third crystal phase comprising a twinning ceramic compound selected from a group consisting of anorthite, Sr-feldspar, Ba-feldspar, enstatite, and aluminous enstatite.

23. The glass-ceramic of claim 20, wherein the glass-ceramic includes a third crystal phase selected from the group consisting of forsterite, fluormica, fluoramphibole, norbergite, spinel, sapphirine, mullite and xonotlite.