Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
2001-04-19
2003-09-23
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C428S293400, C428S293700
Reexamination Certificate
active
06624105
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oxide ceramic fiber/oxide ceramic composite material which is an oxide ceramic reinforced with an oxide ceramic fiber and which has high toughness and is machinable; as well as to a process for producing such a composite material.
2. Description of the Prior Art
Oxide ceramics have been employed, for their oxidation resistance, as a heat-shielding sheet for high temperatures or as a spacer used in a heat treatment of metal or the like in high-temperature oxidizing atmosphere.
Monolithic oxide ceramics easily give cracking or warpage when subjected to thermal shock and are therefore unusable in the above applications for a long period of time. Moreover, these ceramics are inferior in mechanical impact resistance and, when subjected to mechanical impact, give much chipping and cracking; therefore, they need elaborate handling. For example, alumina ceramics are generally known to be inferior in thermal shock resistance and mechanical impact resistance.
In order to obtain an improved resistance to thermal shock, there are ceramic materials comprising a non-oxide ceramic of high thermal shock resistance and an oxidation-resistant film formed thereon.
Also, there are being investigated materials comprising a carbon material of low oxidation resistance and an oxidation-resistant ceramic layer formed thereon.
The above non-oxide ceramic or carbon material having an oxidation-resistant film or layer formed thereon, however, has defects (e.g. cracks) in the surface film or layer, in some cases. Further, in the surface film or layer, cracks tend to generate owing to the thermal expansion difference between the base material and the surface film or layer. The presence of such defects and cracks accelerates the oxidation of the inner base material, posing a limit to an increase in the life of the base material. Thus, the technique of covering the surface of a base material with a film or a ceramic layer is low in reliability with respect to oxidation resistance.
Meanwhile, there are composite materials of various kinds, obtained by reinforcing an oxide ceramic with ceramic particles or whiskers.
These composite materials obtained by reinforcing an oxide ceramic with ceramic particles or whiskers have shown some improvements in toughness to impact fracture. However, they are not improved in fragility which is the biggest weakness of ceramic materials, and still have a drawback that once they start fracture, it leads to total fracture owing to the fragility.
There have also been developed composite materials obtained by reinforcing an oxide ceramic with an oxide fiber.
These composite materials, unlike the monolithic oxide ceramics, are confirmed to have a large fracture resistance. When in producing such a composite material, the oxide ceramic and the oxide fiber react with each other during sintering, the resulting composite material is very low in strength. In order to avoid such a reaction, a reaction-preventive coating material has been applied to each oxide fiber. Incidentally, the coating material is applied to each fiber uniformly in a thickness of several microns or less {e.g. Advanced Ceramic Materials, Vol. 3, [3], 235-237 (1990); Ceram. Eng. Sci. Proc., 11 [9-10], 1761-1777 (1990)}.
FIG. 2
is a schematic view showing the section of a conventional oxide ceramic fiber/oxide ceramic composite material.
As shown in
FIG. 2
, in a conventional oxide ceramic fiber/oxide ceramic composite material
200
, ceramic fibers
20
are dispersed in an oxide ceramic matrix
22
. The surface of each ceramic fiber
20
is covered uniformly with a coating material
24
of several microns or less in thickness. The coating material
24
separates each ceramic fiber
20
from the matrix
22
and prevents their reaction.
In some of the composite materials obtained by reinforcing an oxide ceramic with an oxide fiber, the oxide fiber is coated with a porous oxide (e.g. Al
2
O
3
or ZrO
2
), BN or carbon {Ceram. Eng. Sci. Proc., 9 [7-8] 705-720 (1988)}, or with monazite under controlled conditions (U.S. DOE Reports DOE-MC-32085-99-Vol. 2).
When an oxide ceramic is reinforced with an oxide fiber bundle consisting of large number of fibers, however, it is difficult to coat the surface of each fiber of the fiber bundle uniformly with the coating material
24
. Moreover, since the coating material
24
peels off easily, the fibers after coating must be handled elaborately.
If in producing the above composite material, part of the coating material
24
is detached from each fiber
20
, and each fiber
20
and the matrix ceramic
22
come into direct contact, the composite material is deteriorated in strength at the site of direct contact. As a result, the merit of using the fibers for obtaining a composite material is reduced.
Further, elaborate handling of the fibers, prevention of the coating material from peeling, and realization of optimum interfacial state require a very complicated operation, leading to an increase in production cost.
Furthermore, in selecting the raw materials for use in production of composite material, it is necessary to consider the fiber, the coating material and the oxide from the overall standpoints of their chemical and physical properties and judge the mutual compatibility of the raw materials. Therefore, the selection range of the raw materials is restricted and the selection of the raw materials most suitable for an intended composite material is restricted.
SUMMARY OF THE INVENTION
The present inventors made a study in order to solve the above-mentioned problems. As a result, the present inventors found out that the above problems could be solved by, in producing an oxide ceramic fiber/oxide ceramic composite material, first producing a primary composite material and then producing a secondary composite material using the primary composite material. This finding has led to the completion of the present invention.
Objects of the present invention are to provide an oxide ceramic fiber/oxide ceramic composite material which is superior in high-temperature oxidation resistance and thermal shock resistance, which is free from fragility (this is a weak point of oxide ceramics) and which is easy to produce; and a process for producing such a composite material.
The above objects are achieved by the present invention which follows.
1. An oxide ceramic fiber/oxide ceramic composite material comprising:
primary composite materials each consisting of (a) an assembly of ceramic fibers composed mainly of a metal oxide and (b) a metal oxide ceramic which includes the ceramic fiber assembly (a) therein, the metal oxide of the ceramic (b) being different from the main component metal oxide of the ceramic fiber assembly (a) and the amount of the metal oxide ceramic (b) being 1 to 85% by weight relative to the weight of the ceramic fiber assembly (a), and a metal oxide ceramic which is a matrix for the primary composite materials and which includes the primary composite materials therein, the metal oxide of the ceramic being the same as or different from the main component metal oxide of the ceramic fiber assembly (a), which composite material is integrally sintered and has a relative density of 20 to 95% as compared with the density of the total metal oxides in the composite material.
2. A composite material according to the above 1, wherein the main component metal oxide of the ceramic fiber assembly (a) is at least one kind of metal oxide selected from alumina, silica, alumina-silica, mullite, titania, YAG and zirconia.
3. A composite material according to the above 1, wherein the metal element of the metal oxide ceramic (b) including the ceramic fiber assembly (a) therein is an element selected from group IV (titanium group), group V (vanadium group) and group VI (chromium group) of the periodic table.
4. A composite material according to the above 1, wherein in any section of the composite material, the fiber axes of different ceramic fiber assembli
Iwanaga Katsusuke
Kagawa Yutaka
Komatsubara Yoshinobu
Nakamura Hiroshi
Group Karl
Mitsui Mining Material Co., Ltd.
Norris & McLaughlin & Marcus
LandOfFree
Oxide ceramic fiber/oxide ceramic composite material and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Oxide ceramic fiber/oxide ceramic composite material and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Oxide ceramic fiber/oxide ceramic composite material and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052873