Compositions: ceramic – Ceramic compositions – Refractory
Reexamination Certificate
1999-02-25
2001-12-18
Group, Karl (Department: 1755)
Compositions: ceramic
Ceramic compositions
Refractory
C501S087000, C501S088000, C501S085000
Reexamination Certificate
active
06331496
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a matrix for ceramic matrix composite which contains inorganic fiber for reinforcement.
2. Related Art
A ceramic matrix composite is typical of various materials having excellent heat resistance and mechanical characteristics that have been proposed for use in the aerospace industry.
Conventional ceramic matrix composites include one composed of silicon carbide ceramic as a matrix and silicon carbide fiber as reinforcing inorganic fiber for its high heat resistance and high-temperature oxidation resistance. Composites for large-sized parts are generally produced by forming a silicon carbide matrix on fabric of silicon carbide fiber by chemical vapor infiltration (CVI), polymer impregnation and pylorysis (PIP), or a like technique.
However, where the conventional techniques are followed, pores or microcracks often remain in the silicon carbide matrix. Stress is concentrated around the pores and microcracks, and the stress cannot be transmitted sufficiently to the reinforcing fiber, resulting in reduction of the strength of the composite. Further, oxygen tends to enter through the pores or microcracks to oxidize the fiber in an elevated temperature oxidizing atmosphere, also resulting in reduction of the strength.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a matrix for high-strength composites excellent in heat resistance, oxidation resistance and mechanical characteristics.
As a result of extensive studies, the inventors of the present invention have found that the above object can be accomplished by using a matrix comprising silicon carbide ceramic having dispersed therein an oxide phase.
Having been completed based on the above finding, the present invention provides a matrix for high-performance ceramic matrix composite containing inorganic fiber for reinforcement, which comprises silicon carbide ceramic and an oxide phase having dispersed in the silicon carbide ceramic.
According to the present invention, there is provided a matrix for a high-performance composite having excellent heat resistance, oxidation resistance and mechanical characteristics in high temperature. Ceramic matrix composites produced by using the matrix of the present invention are particularly useful for various formed parts in the aerospace industry.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The matrix for high-performance ceramic matrix composite according to the present invention will hereinafter be described in detail. The matrix comprises silicon carbide ceramic and an oxide phase that is dispersed in the silicon carbide ceramic. In other words, the matrix is a complex matrix comprising the silicon carbide ceramic and the oxide phase.
The oxide phase includes a crystalline oxide, glass such as amorphous silicate glass, phosphate glass and borate glass, and glass-ceramics (crystallized glass).
Specific examples of the crystalline oxide are oxides and complex oxides of aluminum, magnesium, silicon, yttrium, calcium, titanium, zirconium, niobium, iron, barium, strontium, beryllium, indium, uranium, tantalum, neodymium, scandium, ruthenium, rhodium, nickel, cobalt, molybdenum, manganese, germanium, hafnium, vanadium, gallium, iridium, rare earth elements, etc. Among of them, those having a coefficient of thermal expansion of 8×10
6
or smaller at 1000° C., e.g., SiO
2
, Al
2
O
3
, Y
2
O
3
, HfO
2
, MgO·Al
2
O
3
, BaO·ZrO
2
, MgO·Cr
2
O
3
, ZrSiO
4
, 3Al
2
O
3
·2SiO
2
, 2MgO·2Al
2
O
3
·5SiO
2
, and &agr;—Al
2
O
3
·TiO
2
, are preferred, and ZrSiO
4
is particularly preferred.
Specific examples of the glass-ceramics include LiO
2
—Al
2
O
3
—MgO—SiO
2
glass-ceramics and LiO
2
—Al
2
O
3
—MgO—SiO
2
—Nb
2
O
5
glass-ceramics whose main crystalline phase is &bgr;-spodumene; MgO—Al
2
O
3
—SiO
2
glass-ceramics whose main crystalline phase is cordierite; BaO—Al
2
O
3
—SiO
2
glass ceramics and SrO—Al
2
O
3
—SiO
2
glass-ceramics whose main crystalline phase is mullite or celsian; CaO—Al
2
O
3
—SiO
2
glass-ceramics whose main crystalline phase is anorthite; and BaO—MgO—Al
2
O
3
—SiO
2
glass-ceramics whose main crystalline phase is barium osumilite. Preference is given to SrO—Al
2
O
3
—SiO
2
glass-ceramics and BaO—MgO—Al
2
O
3
—SiO
2
glass-ceramics.
The oxide phase may be dispersed in the form of particles or may form a continuous phase (a network structure) in the matrix. The oxide phase can be made up of a single substance or a combination of two or more substances.
While the method for forming the oxide phase is not particularly limited, the following methods A to C are preferred for ease of formation.
Method A
A method using powdered substance or substances forming the oxide phase.
Method B
A method comprising impregnating silicon carbide ceramic with a solution of an oxide precursor capable of forming the oxide phase after being rendered inorganic, for example, a solution of an alkoxide (precursor) in a solvent, e.g., an alcohol (called a sol-gel solution), or a solution of a salt (precursor) in a solvent, e.g., water, and heat treating the impregnated ceramic in an atmosphere containing NO
2
gas and/or O
2
gas and/or H
2
O gas.
Method C
Vapor phase techniques, such as chemical vapor deposition (CVD), CVI or physical vapor deposition (PVD). CVD or CVI can be carried out in a known manner by using a mixture of gas or steam of at least one of a halide, a hydride and an organometallic compound of the metal(s) constituting the oxide phase and NO
2
gas and/or O
2
gas and/or H
2
O gas as a raw material gas. In carrying out PVD, a compound or a mixture having the same or nearly the same composition as the desired oxide phase is used as a target, or a plurality of such compounds or mixtures are used alternately to give the same composition as the desired oxide phase. If desired, PVD treatment is followed by heat treatment to form the oxide phase.
It is preferable in view of the characteristics of the ceramic matrix composite that the oxide phase be present in the matrix in an amount of 1 to 80% by weight, particularly 5 to 60% by weight, based on the whole weight of the matrix.
The silicon carbide ceramics preferably include those having the following structure (1) or (2) from the standpoint of elastic modulus, heat resistance, oxidation resistance, creep resistance and the like.
Structure (1)
(a) an amorphous substance substantially comprising Si, Ti and/or Zr, C, and O;
(b) (b-1) the amorphous substance (a) and (b-2) an aggregate of a crystalline substance having a grain size of 1000 nm or smaller, particularly 10 to 500 nm, comprising &bgr;-SiC and TiC and/or ZrC; or
(c) a mixed system of (c-1) the crystalline substance (b-2) and (c-2) an amorphous structure which is present in the vicinity of the crystalline substance and comprises SiO
x
and TiO
x
and/or ZrO
x
(0<x≦2); and the average elemental composition of (a), (b) and (c) comprising 30 to 80 wt % of Si, 15 to 69 wt % of C, and 0.005 to 20 wt % of O.
Structure (2)
(d) an amorphous substance substantially comprising Si, C, and O;
(e) an aggregate of (e-1) an aggregate of a crystalline substance comprising &bgr;-SiC having a grain size of 1000 nm or smaller, particularly 10 to 500 nm, and (e-2) amorphous SiO
2
and/or the amorphous substance (d); or
(f) a mixture of (f-1) the crystalline substance (e-1) and/or the aggregate (e) and (f-2) a carbon flocculate; and
the average elemental composition of structure (d), (e) and (f) comprising 30 to 80 wt % of Si, 10 to 65 wt % of C, and 0.005 to 25 wt % of O.
The term “an aggregate of a crystalline substance” as used for the structure (b) denotes an aggregate comprising a plurality of crystals having a grain size of 0.1 to 1000 nm. The term “in the vicinity of” as used for the structure (c) preferably means the region within a distance of 100 nm from the crystalline particle. The above-specified average elemental composition of Si, C and O of the structure (a), (b) and (c) is preferred for strength, elastic modulus, heat resistance, oxidation resistance, cr
Group Karl
Research Institute of Advanced Material Gas-Generator, Ltd.
Young & Thompson
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