Claims
- 1. A process for the preparation of a fiber-reinforced ceramic tube with fluid permeable walls comprising the steps of
- A. plying separate yarns of
- 1. a refractory oxide fiber having a softening point above about 750.degree. C. or a fiber of a precursor of the refractory oxide and
- 2. a ceramic binder fiber having a softening point above about 750.degree. C. but at least 50.degree. C. lower than the yarn sag temperature of refractory oxide fiber
- B. winding the plied yarn on a tubular core in multiple layers of spaced helical coils in a criss-cross fashion to form a tube of yarn having a multitude of channels of quadrilateral-shaped cross-sections extending through the walls of the tube of yarn,
- C. firing the tube of yarn for a time and temperature sufficient to
- 1. convert any precursor fibers present to refractory oxide fibers and
- 2. soften the ceramic binder fiber to such an extent that it at least partially flows around the refractory oxide fibers to bind adjacent fibers upon cooling, and
- D. placing a coating composition on the bonded structure and firing to form a refractory oxide matrix at least partially surrounding said fibers but not closing said channels and to provide said tube with a compressive strength of at least 30 psi.
- 2. The process of claim 1 wherein the coating composition contains 60-90% by weight of particles of a refractory oxide and 10-40% by weight of particles of a refractory oxide precursor.
- 3. The process of claim 1 wherein the ceramic binder fiber has a maximum softening point of about 1300.degree. C.
- 4. The process of claim 1 wherein the plied yarns are wound at winding angles of 3.degree. to 52.degree..
- 5. The process of claim 1 wherein said refractory oxide fibers contain at least 70% by weight Al.sub.2 O.sub.3.
- 6. The process of claim 1 wherein said firing converts said ceramic binder fiber to fused glass which constitutes 15 to 40% by weight of said tube, and said refractory oxide matrix constitute 15 to 60% by weight of said tube.
CROSS REFERENCE TO RELATED APPLICATION
This is a division of application Ser. No. 566,319, filed Apr. 9, 1975, which is in turn, now U.S. Pat. No. 3,986,528 a continuation-in-part of application, Ser. No. 290,643, filed Sept. 20, 1972 and now abandoned.
This invention relates to a catalyst carrier for fluid reactors, and more particularly, to a reticulated tube of reinforced ceramic fibers suitable as a catalyst support for the catalytic conversion of internal combustion engine exhaust fumes at elevated temperatures.
There have been two general approaches to making catalytic exhaust convertors for automobiles. One has involved the use of a loose bed of ceramic pellets as a carrier for the catalyst, and the other has involved the use of rigid ceramic elements as the catalyst carrier. The bed of ceramic pellets has the great disadvantage of attrition of the pellets due to self-abrasion so that the bed has to be replaced at frequent intervals, while the use of rigid ceramic carriers has had the disadvantage of inadequate resistance to theremal shock and to mechanical shock.
A ceramic carrier that overcomes the foregoing disadvantages has now been found. The ceramic carrier of this invention is a reticulated tube of reinforced ceramic fibers which comprises:
1. Multiple layers of continuous yarn wound in helical coils to form the walls of the tube. The yarn is wound in a spaced criss-crossed fashion to form a multitude of channels having quadrilateral-shaped cross-sections extending through the walls of the tube and is comprised of ceramic fiber having a "softening point" above about 750.degree. C. The yarn is at least about 20% Al.sub.2 O.sub.3 by weight and comprises from about 20% to about 85% of the weight of the tube.
2. A fused, substantially nonporous ceramic binder having a "softening point" above about 750.degree. C. The binder secures adjacent fibers of the yarn to one another and comprises between about 0% and about 40% of the weight of the tube.
3. A refractory oxide matrix having a "softening point" above about 1000.degree. C. and a porosity of between about 20 and 70%. The matrix is affixed and positioned to at least partially surround the ceramic fibers and the ceramic binder, when present, but not to substantially close the channels, and comprises between about 15% and about 80% of the weight of the tube.
The tubes have a compressive strength of at least about 30 psi, and preferably at least about 60 psi which can be as high as 800 psi, particularly for automotive purposes. In the applications such as, for example, in treatment of stack gas, where the tube is under no load, such compressive strengths are not required.
By the term "ceramic" is meant a body of crystalline or partly crystalline structure, or of glass, which body is produced from essentially inorganic, nonmetallic substances, generally oxides, and either is formed from a molten mass which solidifies on cooling, or is formed and simultaneously or subsequently subjected to heat to drive off any chemically or mechanically bound water by the action of heat. The term "ceramic" is intended to include refractory oxides; that is, a composition of one or more oxides that has a melting point of at least 1000.degree. C.
The phrase "softening point" is used herein to mean both the softening point of a glass (i.e., a non-crystalline ceramic material) and the melting point of a crystalline ceramic material (e.g., .alpha. -alumina, mullite, etc.).
Another embodiment of this invention is a process for the preparation of a fiber-reinforced ceramic tube with fluid permeable walls comprising the steps of:
Another process comprises the steps of:
US Referenced Citations (6)
Divisions (1)
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Number |
Date |
Country |
| Parent |
566319 |
Apr 1975 |
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Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
290643 |
Sep 1972 |
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Patent Grant
4092194
