Low-expansion cordierite glass ceramics

Details Low-expansion cordierite glass ceramics Low-expansion cordierite glass ceramics

1999-12-16

2001-10-09

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

Devitrified glass-ceramics

C065S033700, C264S631000

Reexamination Certificate

active

06300263

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a family of low-expansion cordierite ceramic bodies made from glass frits, and methods of their fabrication.
BACKGROUND OF THE INVENTION
The realm of low-expansion cordierite bodies (CTE<10×10
−7
°/C.) has previously been limited to ceramics prepared by firing mixtures of crystalline raw materials (e.g., clay+talc+alumina) at temperatures above 1375° C. These low expansions rely largely upon microcracking, which is induced by the anisotropic thermal expansion/contraction of cordierite crystals or crystal aggregates that form as a consequence of the manner by which cordierite nucleates and grows from the reactive raw materials.
In extruded honeycomb bodies in which platelet-shaped particles of the raw materials tend to orient with their longest dimensions in the direction of extrusion, it is commonly observed that the cordierite crystals grow with their negative-expansion c-axes lying in the plane of the walls of the honeycomb. This feature further contributes to the lowering of the thermal expansion of the honeycomb body. However, the attainment of the proper microstructure required for these low expansions in conventional cordierite ceramic bodies is highly dependent on the chemistry, crystalline structural state, and particle sizes of the individual raw material components.
It would be highly desirable and an advancement in the art to have a method of making low-expansion cordierite bodies in which the low thermal expansion does not rely on preferred orientation of the cordierite crystallites and in which the thermal expansion coefficient is less sensitive to the chemistry, mineralogy, and particle size of the raw materials.
This invention provides such a method by utilizing certain glass frit powders.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a crystalline glass-ceramic article composed of a cordierite phase of cordierite crystals or aggregates of near-parallel crystallites, having a formula of either Mg
2
Al
4
Si
5
O
18
or A
x
B
y
Mg
2
Al
4+x+2y
Si
5−x−2y
O
18
. With the first formula, the average size of the cordierite crystals or aggregates is less than 70 micrometers, and the mean coefficient of thermal expansion from 22° C. to 800° C. (CTE) is less than 9×10
−7
/° C. With the second formula, A is either sodium or potassium, B is either strontium or barium, the sum of x and y is not less than 0.01, and when either x or y equal zero, the CTE is not more than 14×10
−7
/° C.
The article is especially suitable as a filter or catalyst substrate.
In accordance with another aspect of the invention, there is provided a method of making the article that involves providing a glass having a glass compositional formula expressed in moles of oxides of either 2MgO+2Al
2
O
3
+5SiO
2
or (x/2)A
2
O+yBO+2MgO+[(4+x+2y)/2]Al
2
O
3
+(5−x−2y)SiO
2
, with A, B, and the sum of x and y as described above. The glass is melted, quenched, and crushed to a frit of median particle diameter no greater than 150 micrometers. The frit is consolidated into a body, which is then sintered for a sufficient time and temperature to devitrify the glass into a predominately cordierite-type phase and to coarsen the size of the cordierite crystals or aggregates of near-parallel crystallites to yield microcracks in the subsequently cooled body.


REFERENCES:
patent: 3926648 (1975-12-01), Miller
patent: 3940255 (1976-02-01), Harrington
patent: 4015048 (1977-03-01), Martin
patent: 4063955 (1977-12-01), Fritsch, Jr. et al.
patent: 4142879 (1979-03-01), Fritsch, Jr. et al.
patent: 4191583 (1980-03-01), Armistead et al.
patent: 4219344 (1980-08-01), Armistead et al.
patent: 4225354 (1980-09-01), Rao
patent: 4292080 (1981-09-01), Martin
patent: 5250474 (1993-10-01), Siebers
patent: 5552349 (1996-09-01), Ichii et al.
patent: 5607885 (1997-03-01), Ichii et al.
patent: 6080345 (2000-06-01), Chalasani et al.
patent: 6210626 (2001-04-01), Cornelius et al.
Ikawa, H et al. (1987) “Thermal expansion of cordierite ceramics—effects of doping with alkali and he treatments.” Sintering '87. vol. 2. Proc. 4th Int. Symp. on Science and Technology of Sintering Tokyo, Nov. 1987, p. 854-859 Japan, Int. Inst. for the Science of Sintering; Elsevier Applied Science Publishers Ltd.

Affiliated with

Also associated with

Rating

Low-expansion cordierite glass ceramics does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Low-expansion cordierite glass ceramics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low-expansion cordierite glass ceramics will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2603677