JPH0797268A - Composite ceramic and its production - Google Patents

Abstract

PURPOSE:To produce a light-weight composite ceramic having a low thermal conductivity. CONSTITUTION:This composite ceramic can be produced by using a powdery mixture composed of Si and a composite oxide as the raw material, molding the powdery mixture, nitriding and sintering the resultant molding and then oxidizing the sintered material. This composite ceramic has a phase composed of all elements of Si, O and N and one or more kinds of elements selected from a group of elements containing Al, Zr, Li, P and Mg and <=2.6 specific gravity. In the above-mentioned phase, a phase composed of Si, Al, O and N and another phase composed of Si, O and N are respectively formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight composite ceramic having low thermal conductivity and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a method of adding an oxide to silicon Si for the purpose of accelerating nitriding and increasing strength and reacting and sintering is known.
For example, JP-A-58-88173 and JP-A-59-88
No. 1522271, JP-A-59-207876, JP-A-59-207877, and JP-A-59-2.
17673, JP-A-60-186470,
JP-B-59-34677, JP-B-59-3467
No. 8 publication. Further, as the low thermal conductive ceramics, aluminum titanate Al ₂ TiO ₅ , partially stabilized zirconia ZrO _{2 and the} like have already been studied as an engine material and partially used.

Further, Japanese Patent Laid-Open No. 3-261662 discloses a ceramic composition and a method for producing a ceramic member using the same. The ceramic composition contains metal Si powder or a mixed powder obtained by adding ceramic powder to the powder, an organic binder in an addition amount range of 6 to 25 wt% of the total weight, a deflocculant, and water. Further, the ceramic powder includes Si ₃ N ₄ , Al ₂ TiO ₅ , mullite,
It contains at least one kind of potassium titanate and is fired in a nitrogen gas atmosphere.

Further, Japanese Patent Application Laid-Open No. 2-296771 discloses a composite ceramic and a method for manufacturing the same.
The composite ceramics is a dense sintered body composed of composite particles formed of a material in which second ceramics particles having a sintering temperature lower than that of the first ceramics are dispersed and contained. The second ceramic has a small thermal conductivity.

[0005]

However, the ceramics obtained by adding an oxide to the above silicon Si for the purpose of accelerating nitriding and increasing the strength and reacting and sintering the ceramics do not have a sufficiently low thermal conductivity. Is. In addition, Al ₂ Ti
O ₅ has a strength of 50 MPa or less, which is low as a structural ceramic for an engine or the like and cannot be used as it is. Furthermore, ZrO ₂ has high strength,
It has a drawback that the coefficient of thermal expansion is large and a high thermal stress is generated.

The amount Q of heat transferred to the member in the unsteady state can be expressed by the following equation. That is, Q = (2
・ Κ ・ c ・ ρ ・ T / π) ^1/2 × Δθ ₀ × A. However, A: surface area, Δθ ₀ ; temperature amplitude on the surface, T: temperature on the surface, κ: thermal conductivity, c: heat capacity or specific heat, ρ: density or specific gravity.

As can be seen from the above equation, in order to reduce Q, it is necessary to reduce the product of thermal conductivity κ × specific heat c × specific gravity ρ as a physical property value of the material used. However, with ZrO ₂ , the square root of that value (κ × c × ρ) ^1/2
Is 5, and for Si ₃ N ₄ the square root of that value (κ × c ×
ρ) ^1/2 is 8.7. Therefore, if the thermal conductivity κ, the specific heat c and the specific gravity ρ become small, for example, the thermal conductivity κ
Is 2.1 w / m · K and specific heat c is 0.7 J / g · K
If the specific gravity ρ is a lightweight and low heat conductive material of about 2.2, the above value is about 1.8, and the heat transfer amount Q is ZrO 2.
_{2 and} Si ₃ N ₄ can be reduced to about 36% and about 20%.

[0008] Therefore, an object of the present invention is to solve the above-mentioned problems. A mixed powder of Si and a complex oxide is used as a raw material, and after nitriding firing, that is, reaction sintering in a nitrogen atmosphere, oxidation treatment, that is, atmospheric air. It is heat-treated in an atmosphere to obtain a material which is lightweight and has a low thermal conductivity as compared with a conventional composite with a single oxide. As a composite oxide, Al ₆ S
i ₂ O _{1 3} (mullite), (ZrO) ₂ P ₂ O ₇ , Li
₂ O ・ Al ₂ O ₃・ SiO ₂ ie LAS, MgO ・ Al
It is an object of the present invention to provide a composite ceramic which can use ₂ O ₃ .SiO ₂ or MAS, Al ₂ TiO ₅ (aluminum titanate) and a method for producing the same.

[0009]

In order to achieve the above object, the present invention is configured as follows. That is,
This invention is applicable to all elements of Si, O, N, as well as Al,
The present invention relates to a composite ceramic having a phase composed of at least one element selected from the group consisting of Zr, Li, P, and Mg and having a specific gravity of 2.6 or less.

This composite ceramic is made of Si,
All elements of O and N, as well as Al, Ti, Zr, Li,
Consists of at least one element from the P element group, 1
One dispersed phase is composed of a plurality of adjacent phases or a plurality of surrounding phases.

Further, in the composite ceramics, Si, Al, O, N and Si, O,
A phase composed of N is formed respectively.

Further, in this composite ceramic, the phase or the dispersed phase has an Al-rich phase in the center thereof.

Further, this composite ceramic has a port,
It can be applied to manifolds and piston heads.

Alternatively, according to the present invention, a mixed powder of Si and a complex oxide is used as a raw material, the mixed powder is molded into a molded body, and the molded body is nitrided and fired to manufacture a sintered body.
Then, the present invention relates to a method for producing a composite ceramic, characterized in that the sintered body is subjected to an oxidation treatment.

Further, in this method for producing a composite ceramic, the composite oxide is Al ₆ Si ₂ O _{1 3} , Li ₂
O ・ Al ₂ O ₃・ SiO ₂ , (ZrO) ₂ P ₂ O ₇ , M
It contains at least one member selected from the group consisting of gO.Al ₂ O ₃ .SiO ₂ and Al ₂ TiO ₅ .

Further, in this method for producing a composite ceramic, the composite oxide is 15 to 65 w in terms of weight.
t% is included.

[0017]

The composite ceramic and the method for producing the same according to the present invention are configured as described above, and operate as follows. That is, this composite ceramics contains all elements of Si, O and N, as well as Al, Zr, Li, P, Mg and Ti.
It is composed of at least one or more elements from the group of elements and has a specific gravity of 2.6 or less, so that a plurality of phases are adjacent to one phase, or one phase is surrounded by a plurality of phases, and it is lightweight and A composite ceramic with low thermal conductivity can be provided.

This composite ceramic is made of Si,
All elements of O and N, as well as Al, Zr, Li, P and M
Since at least one element is selected from the group of elements g and Ti and one dispersed phase is composed of a plurality of adjacent phases or a plurality of surrounding phases, a lightweight and low thermal conductivity composite ceramic is obtained. Can be provided.

Alternatively, since this composite ceramic is produced by nitriding and heat-treating Si and a composite oxide as raw materials, compared to simple compounding with an oxide, a mixed phase at a nano level or a peculiarity is obtained. A solid solution is formed,
They have low thermal conductivity because they promote phonon scattering.

[0020]

Embodiments of the composite ceramics and the manufacturing method thereof according to the present invention will be described below with reference to the drawings and tables. Fig. 1 is a graph showing the thermal conductivity of the reaction-sintered ceramics produced by using mixed powders of various oxide powders and Si as raw materials, and Fig. 2 is the result of reaction sintering of Si and Al ₆ Si ₂ O _{1 3} as raw materials. FIG. 3 is an explanatory view showing a fine structure of the composite ceramic further subjected to the oxidation treatment, and FIG. 3 is a diagram showing an identification result by X-ray diffraction of a produced phase of the composite ceramic of FIG.

In this method for producing composite ceramics, a predetermined amount of raw materials consisting of Si and oxide powder is weighed, distilled water 1.5 times the total weight of the powder is added, and a Si ₃ N ₄ ball is used as a medium in a ball mill. Mix for about 24 hours to make a mixture. After sufficiently drying this mixture, the dry mixture was pulverized for about 15 hours using a ball mill to prepare a mixed powder. This mixed powder is put in a mold, pre-formed by uniaxial pressure, and then CIP about 15 × 15 × 80.
A mm shaped body was prepared. The compact was placed in a firing furnace and heated to a maximum of 1400 ° C. in a N ₂ atmosphere of 0.93 MPa to produce a sintered body. This sintered body was oxidized. In the oxidation treatment, the temperature was raised at 320 ° C./hr in the air, the temperature was raised to a predetermined temperature, and then the temperature was maintained for 1 hour.

In order to measure the thermal conductivity of the obtained sintered body, 1.5 ± 0.03 was used as the thermal conductivity for the sintered body.
mm pellets were used as a thermal conductivity measurement test piece, and a bending test piece was prepared by performing a grinding process for a bending test so as to have a size of 3 × 4 × 40 mm. The thermal conductivity was measured at room temperature by the laser flash method. The strength was measured by bending at four points. The number of test pieces was 20 or more per each oxidation treatment condition, the span was 30 mm, and the crosshead speed was 5 mm / min.

The test piece was immersed in water in a vacuum vessel for 60 m.
The pressure was reduced to mHg or less, and the state was maintained for about 48 hours. After lightly wiping the water droplets on the surface with a paper towel, weigh the weight, obtain the value obtained by dividing the increase in weight before and after water absorption by the density of water at that temperature and the test piece deposition, and calculate the value as porosity. did. When calculating the thermal conductivity of the solid part in the porous body, if the thermal conductivity λ _S of the solid part is known, the thermal conductivity λ of the porous material is taken as an unknown number, and its relationship with the porosity is expressed by the following equation. It In the present invention, λ _S and P are calculated from the experiment by similarly using the equations. λ = 1 / A + B where A; (1-P ^1/3 ) / λ _S B; P ^1/3 / [(1-P ^2/3 ) × λ _S + P ^2/3 ×
λ _g ]. P: Porosity, λ: Thermal conductivity of porous body, λ _S : Thermal conductivity of solid part, λ _g : Thermal conductivity of gas, thermal conductivity of air (= 0.0478 w / mK) Was used.

FIG. 1 shows a solid part of a reaction-sintered composite material, that is, a composite ceramic, prepared by using several kinds of oxides and nitrides as additives and using a mixed powder of these additive powders and Si powder as a raw material. The thermal conductivity λ _S is shown. In FIG. 1, the vertical axis is the thermal conductivity λ _S of the solid part, and the thermal conductivity λ
_S is a value (w / m · K) calculated from the measured value λ of the thermal conductivity and the porosity using the above formula. In FIG. 1, the horizontal axis represents the blending ratio of the oxide and nitride additives, and the blending ratio of the additive with respect to the total weight is shown in mol%. The additives used are Al ₂ TiO ₅ , Al ₂ O ₃ + Ti.
O ₂ , ZrO ₂ , Al ₂ O ₃ , (ZrO) ₂ P ₂ O ₇ ,
Li ₂ O · Al ₂ O ₃ · SiO ₂ (ie LAS), Y ₂
O ₃ , TiO ₂ , Al ₆ Si ₂ O _{1 3} , TiN, MgO
・ Al ₂ O ₃ .SiO ₂ (that is, MAS) and Si alone.

Considering the thermal conductivity (w / m · K) shown in FIG. 1, it can be seen that the reduction rate of the thermal conductivity varies depending on the kind of the additive. For example, Al ₂ O ₃ and Al ₂ O ₃
And a composite material in which TiO ₂ is added at the same time, or a composite oxide of Al ₂ TiO ₅ , Al ₆ Si ₂ O _{1 3} ,
It can be seen that oxides such as (ZrO) ₂ P ₂ O ₇ , LAS, and MAS have a large effect of reducing the thermal conductivity. Also,
In the material to which ZrO ₂ , La ₂ O ₃ , CeO ₂ , and Y ₂ O ₃ were added, after heating at 800 ° C. in the air, microcracks were generated and the strength was remarkably lowered.

Next, Table 1 shows the characteristics of the sintered body obtained by using the mixed powder of Si and the complex oxide as a raw material. In Table 1, the blending amount (wt%) under the manufacturing conditions is a value obtained by dividing the oxide weight by the total powder weight (Si + oxide weight) and multiplying by 100.

[Table 1]

In this method for producing a composite ceramic, 35 wt% of Al ₆ Si ₂ O ₁₃ is added to 65 wt% of Si.
% Of the mixed powder to prepare a mixed powder, which is molded using the mixed powder as a raw material, and the molded body is reacted and sintered at 1400 ° C. to prepare a sintered body. Heat treatment, that is, oxidation treatment, was performed to produce a sintered body of composite ceramics. After cutting the composite ceramics produced in this way and polishing the cut surface, the element distribution was investigated by an X-ray microanalyzer, and the results shown in FIGS. 2 and 3 were obtained.

FIG. 2 shows the microstructure of the obtained sintered body and the identification result of the produced phase by an X-ray microanalyzer, which is reproduced to show the existing state of Si, Al, O and N. It was done. Alternatively, FIG. 3 is an analysis diagram drawn by an X-ray microanalyzer of the structure of the composite ceramic produced by this method for producing the composite ceramic. In FIG. 3, the darkest and darkest part is Al ₂ O.
₃ (Al-O), and then the dark black part is Si-O-
N, and white portions is Si-Al-O-N ( Si 3 Al
₃ O ₃ N ₅ ), and the finely scattered white portions are Si—Al—O (Al ₆ Si ₂ O ₁₃ ). As can be seen from FIG. 2 or 3, the Si—O—N phase, that is, Si, O
Is rich in Si, Al, and O so that a phase rich in Si, Al, and O is formed around it.
It can be seen that a phase rich in l and O is formed.

Further, in FIG. 6, Al ₆ Si ₂ O is added to Si.
Si ₃ Al ₃ O ₃ N ₅ was detected although the identification result by X-ray diffraction, that is, the X-ray diffraction pattern, of the produced phase of the sintered body obtained by blending 35 wt% of ₁₃ was shown. In the X-ray diffraction pattern, Si detected by X-ray microanalyzer
Considering that ON was not detected, SiON
May be amorphous. Further, it is considered that the SiAlON phase is also a solid solution and has a low thermal conductivity.

Therefore, this composite ceramic is
It is considered that N amorphous or a solid solution of SiAlON phase is formed at an extremely fine level and constitutes a multiple phase, which promotes phonon scattering and has low thermal conductivity.

Further, in the method for producing a composite ceramic according to the present invention, a composite ceramic produced by using a mixed powder of Si and Al ₂ TiO ₅ as a raw material is shown in FIGS.
Shown in. FIG. 4 is an analysis diagram of the structure of the composite ceramic produced by this method for producing the composite ceramic, which is drawn by an X-ray microanalyzer, and FIG. 5 is an explanatory view for explaining a part of the analysis diagram of FIG. This composite ceramic is made of Si
Of 65 wt% of Al ₂ TiO ₅ and 35 wt% of Al ₂ TiO ₅ as a raw material, and after molding the mixed powder, 1400
It can be manufactured by reacting and sintering in a nitrogen atmosphere at 0 ° C. and then performing heat treatment, that is, oxidation treatment at 1000 ° C. in the atmosphere. After cutting the composite ceramics produced in this way and polishing the cut surface, the element distribution was investigated by an X-ray microanalyzer, and the results shown in FIGS. 4 and 5 were obtained. In FIG. 4, the blackest and darkest core part is Al ₂ O ₃ (Al-O), the next darkest and darkest part is Si-Al-O-N, and the white part is Si-.
An Al-Ti-O-N, phase surrounding the dark core of Al ₂ O ₃ is rich phase of Ti-O. As can be seen from FIGS. 4 and 5, the Al-rich phase is centered on the outer side of which the Ti- and Al-rich phase is adjacent.
i, Al so as to surround the rich phase Si-Al-T
It can be seen that the i-O-N phase is present.

From the above, in this composite ceramic, a mixture prepared by using a composite oxide such as aluminum titanate (Al ₂ TiO ₅ ) and mullite (Al ₆ Si ₂ O _{1 3} ) and Si as a raw material, The composite ceramics that can be produced by nitriding firing are different from conventional single oxides, for example, ceramics produced by adding aluminum oxide (Al ₂ O ₃ ), in that the dispersed phase is composed of multiple layers. It is a feature. It is considered that the multiple phases were formed by decomposition of the complex oxide during nitriding and firing, and complicated reaction with the atmosphere of Si or nitrogen gas (N ₂ ). It is considered that phonon scattering, which is a carrier of heat, is generated at the boundary due to the multiple phases in the composite ceramic, and the composite ceramic has a property of low heat conduction.

[0033]

The composite ceramics and the method for producing the same according to the present invention are configured as described above and have the following effects. That is, this composite ceramic is
All elements of i, O, N, as well as Al, Zr, Li,
Since it has a phase composed of at least one or more elements of P and Mg and has a specific gravity of 2.6 or less, it is possible to manufacture a ceramic that is lightweight and has a low thermal conductivity, and therefore a component such as an engine. When applied to the heat-shielding component, the heat transfer amount in an unsteady state can be reduced.

Further, in this method for producing a composite ceramic, a mixed powder composed of Si and a composite oxide is used as a raw material,
The mixed powder is formed into a molded body, the molded body is nitrided and fired to form a sintered body, and then the sintered body is subjected to an oxidation treatment. ₆ S
_{i 2 O 1 3, Li 2} O · Al 2 O 3 · SiO 2, (Zr
O) ₂ P ₂ O ₇ , MgO.Al ₂ O ₃ .SiO ₂ can be used.

This composite ceramic is made of Al ₂ TiO ₅
Since it is possible to manufacture a mixture prepared by using a composite oxide such as Al, Si ₂ O _{1 3} and Al ₆ Si ₃ as a raw material and nitriding and firing, and then subjecting it to an oxidization treatment, it is possible to produce a mixture such as a conventional Al ₂ O ₃ Unlike ceramics produced by the addition of monoxide, the dispersed phase is composed in multiple layers. The multiple phases are formed by decomposition of the complex oxide during nitriding firing and reaction with the Si or N ₂ atmosphere. Then, this composite ceramic has a property of low heat conduction because phonon scattering, which is a carrier of heat, is generated at the boundary due to the multiple phases.

[Brief description of drawings]

FIG. 1 is a graph showing the thermal conductivity of reaction-sintered ceramics prepared by using a mixed powder of various oxide powders and Si as a raw material.

FIG. 2 is an explanatory view showing a fine structure of a composite ceramic which is obtained by reacting and sintering Si and Al ₆ Si ₂ O ₁₃ as raw materials and further oxidizing the composite ceramic.

[FIG. 3] In the method for producing the composite ceramic, S
FIG. 3 is an analysis diagram drawn by an X-ray microanalyzer of the structure of a composite ceramic obtained by reacting and sintering a mixture of i and Al ₆ Si ₂ O ₁₃ ;

FIG. 4 is a diagram showing a method of manufacturing a composite ceramic according to S
FIG. 3 is an analysis diagram drawn by an X-ray microanalyzer of the structure of composite ceramics obtained by reacting and sintering a mixture of i and Al ₂ TiO ₅ .

5 is an explanatory diagram for explaining a part of the analysis diagram of FIG.

FIG. 6 is a diagram showing an identification result by X-ray diffraction of a produced phase of the composite ceramic of FIG.

Claims (11)

[Claims] 1. All elements of Si, O, N and A
A composite ceramic having a phase composed of at least one element selected from the group consisting of 1, Zr, Li, P, and Mg and having a specific gravity of 2.6 or less. 2. The composite ceramic according to claim 1, wherein one of the phases is composed of a plurality of adjacent phases or a plurality of surrounding phases. 3. The phases include Si, Al, O, N and S.
The composite ceramics according to claim 1, wherein a phase composed of i, O, and N is formed. 4. The composite ceramic according to claim 1, wherein the phase has a phase rich in Al at the center thereof. 5. All elements of Si, O, N and A
A composite characterized in that it comprises at least one element from the element group of l, Ti, Zr, Li, P, and one dispersed phase is composed of a plurality of adjacent phases or a plurality of surrounding phases. Ceramics. 6. The composite ceramic according to claim 5, wherein the dispersed phase is formed with phases of Si, Al, O, N and Si, O, N, respectively. 7. The composite ceramic according to claim 5, wherein the dispersed phase has a phase rich in Al at the center thereof. 8. The composite ceramic according to claim 1, which is applicable to a port, a manifold and a piston head. 9. A mixed powder of Si and a complex oxide is used as a raw material, the mixed powder is molded into a molded body, and the molded body is subjected to nitriding firing to form a sintered body. A method for producing a composite ceramic, characterized in that a composite is subjected to an oxidation treatment. 10. The composite oxide is Al ₆ Si.
₂ O ₁₃ , Li ₂ O.Al ₂ O ₃ .SiO ₂ , (Zr
O) ₂ P ₂ O ₇ , MgO · Al ₂ O ₃ · SiO ₂ , Al
_The method for producing a composite ceramics according to claim 9, characterized in that it contains at least one kind of ₂ TiO ₅ group. 11. The composite oxide is 15 in terms of weight.
The composite ceramics manufacturing method according to claim 9, wherein the composite ceramics is contained in an amount of ˜65 wt%.