JP2002167268A - Cordierite sintered compact and method of manufacturing it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cordierite sintered compact having both high fracture toughness and high strength, and its manufacturing method. SOLUTION: The cordierite sintered compact is characterized in that the sintered compact contains cordierite as a main component, and zirconium of 2-35 wt.% in terms of oxides, at least one element selected from group 2a and 3a elements of the periodic table in 1-10 wt.% in terms of oxides, and has means pore size of <=4.0 μm, pore occupancy rate of <3%, relative density of >=97%, the strength of >=179 MPa, and the fracture toughness of >=2.4 MPa.m1/2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dense cordierite sintered body having high strength, high fracture toughness, and a method for producing the same.

[0002]

2. Description of the Related Art Cordierite-based sintered bodies have been known as low thermal expansion and low thermal expansion ceramics.
It is applied to filters, honeycombs, refractories, thermal insulation, etc. This cordierite-based sintered body is generally mixed with cordierite powder or MgO, Al ₂ O ₃ , and SiO ₂ powder that forms cordierite, and a rare earth element oxide or a sintering aid is added thereto. SiO ₂ , CaO,
After adding MgO or the like and forming into a predetermined shape, 1000-1
It is produced by firing at a temperature of 400 ° C. (JP-A-2-229760).

Recently, ceramics having low thermal expansion or low thermal conductivity such as cordierite have been used as structural materials. For example, Japanese Patent Application Laid-Open No.
It has been proposed in Japanese Patent Application Laid-Open No. 1-278921.

[0004]

However, when a cordierite-based sintered body is used as a structural member, the conventional cordierite-based sintered body has at least one of fracture toughness and low strength, and is liable to be damaged or broken. There was a problem. For example, in the method described in JP-A-11-278921, the strength can be improved up to 220 MPa. However, there is a problem that the fracture toughness is low, so that it is susceptible to mechanical impact, cracks are liable to occur, and breakage easily occurs.

[0005] Further, since it is difficult to obtain a dense body, high-pressure firing such as hot pressing or hot isostatic pressing (HIP) is performed to reduce pores in the sintered body, so that the product shape is limited to a simple shape. And the cost increases.

Accordingly, an object of the present invention is to provide a cordierite-based sintered body having both high fracture toughness and high strength, and a method for producing the same.

[0007]

SUMMARY OF THE INVENTION According to the present invention, zirconia is not reacted with cordierite by low-temperature sintering and sintering atmosphere control to suppress the formation of zircon. It is based on the knowledge that the strength can be improved while improving the strength.

That is, the cordierite-based sintered body is mainly composed of cordierite, and zirconium is converted to oxide in an amount of 2 to 2 in terms of oxide.
35% by weight, at least one of Group 2a element and Group 3a element of the periodic table in a proportion of 1 to 10% by weight in terms of oxide, average pore diameter of 4.0 μm or less, pore occupancy Is 3% or less, relative density is 97% or more, and strength is 1
A cordierite sintered body having both high fracture toughness and high strength can be realized by being 70 MPa or more and fracture toughness of 2.4 MPa · m ^1/2 or more.

In particular, in the X-ray diffraction spectrum,
The peak intensity of the con (112) plane is I _{Z (112)}, Zirconia
The peak intensity of the (110) plane is I_{ZrO2 (110)}, Cordillera
The peak intensity of the_{CJ (132)}And
The peak intensity ratio I_{Z (112)}/ I_{C J (132)}Is 0.05 or less
Bottom, I_{ZrO2 (110)}/ I_{CJ (132)}Is 0.05 or more
Is preferred. This reduces fracture toughness and strength
And reduce the effect of zircon
The mechanical properties can be improved due to the presence of (a).

The method for producing a cordierite-based sintered body according to the present invention comprises a cordierite powder as a main component, 2 to 35% by weight of zirconia, and at least one of a Group 2a element and a Group 3a element in the periodic table. Characterized in that a molded body composed of a mixed powder containing 1 to 10% by weight of a kind oxide is fired in an atmosphere having an oxygen partial pressure of 0.1 atm or less,
According to this method, the synthesis of zircon due to the reaction between zirconia and cordierite can be suppressed and a dense body can be obtained, so that cordierite in which zirconia is dispersed and strengthened can be easily realized.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method for producing zirconium in an amount of 2 to 35% by weight as an oxide, mainly comprising cordierite.
It is important that at least one of the Group 2a element and the Group 3a element of the periodic table be contained at a ratio of 1 to 10% by weight in terms of oxide.

When the content of zirconium is less than 2% by weight in terms of oxide, improvement of fracture toughness and strength is insufficient, and when it exceeds 35% by weight, sinterability is reduced and sintering temperature is lowered. This is because the formation of zircon due to the reaction between the zirconia and cordierite components accompanying the rise becomes remarkable, and the fracture toughness and strength are reduced. The content is particularly preferably 3 to 25% by weight, more preferably 5 to 15% by weight.

Further, by selecting a Group 2a element or a Group 3a element of the periodic table as a sintering aid, low-temperature sintering becomes possible, and its content is made 1 to 10% by weight in terms of oxide. This makes it possible to obtain a dense body at a low temperature, particularly preferably 2 to 8% by weight, more preferably 3 to 7% by weight.

According to the present invention, the sintered body has an average pore diameter of 4.0 μm or less, a pore occupancy of 3% or less, a relative density of 97% or more, a strength of 170 MPa or more, and a fracture toughness of 2.4 MPa. ^-It is important that it is not less than ^m1 / ² .

It is important to control the average pore diameter, pore occupancy, and relative density within the above ranges, whereby chipping on the surface of the porcelain can be significantly suppressed.
Since the pore diameter serving as a fracture source is small, high strength is promoted, the smoothness of the porcelain surface is remarkably improved, and a mirror surface state is easily obtained. In particular, the relative density is 98% or more, and more preferably 99%. The average pore diameter is preferably 3.5 μm or less, more preferably 3 μm or less, more preferably 2.5 μm or less, and the pore occupancy is particularly 2.5% or less.
Further, it is preferably at most 2%, more preferably at most 1.5%.

It is important that the strength is 170 MPa or more and the fracture toughness is 2.4 MPa · m ^1/2 or more, and particularly the strength is 190 MPa or more, and furthermore, 225 MPa.
a is preferable, and the fracture toughness is particularly 2.6 MPa · m.
^It is preferably at least ^1/2, more preferably at least 2.8 MPa · m ^1/2 .

By simultaneously improving both the strength and the fracture toughness, the range of application as a structural material having a complicated shape such as a lattice-like structure from a conventional simple shape is expanded. As a result, the degree of freedom in product design is increased, and it is possible to contribute to labor saving and space saving such as weight reduction and hollowing.

Further, according to the present invention, the presence of zirconium in the sintered body can be evaluated by X-ray diffraction, and the mechanical properties can be improved from the value of the peak intensity ratio. That is, in the X-ray diffraction spectrum at least 2θ of 20 to 40 °, the zircon (112) plane and the zirconia (11
0) and the peak intensity of the cordierite (132) plane
Assuming that I _{Z (112)} , I _{ZrO2 (110)} and I _{CJ (132)} respectively, the peak intensity ratio I _{Z (112)} / I _{CJ (132)} is 0.05 or less, especially 0.03 or less, and furthermore 0.01 or less, I _{ZrO
2 (110) / I CJ (} 132) is 0.05 or more, particularly 0.07 or more, further preferably 0.1 or more.

This is because zircon lowers fracture toughness and strength, so it is necessary to reduce the zircon content. When the peak intensity ratio I _{Z (112)} / I _{CJ (132)} is 0.05 or less, the influence of zircon is small,
The transformation strengthening mechanism of zirconia functions well, and as a result, fracture toughness and strength are improved.

The above peak intensity ratio I _{ZrO2 (110)} / I
_{If CJ (132)} is 0.05 or more, the content of zirconia becomes sufficient, and the effect of improving the fracture toughness and strength by the transformation strengthening mechanism can be obtained.

Therefore, by setting the peak intensity ratio between zircon and cordierite and the peak intensity ratio between zirconia and cordierite to the above values, cordierite having excellent mechanical properties can be realized.

For example, FIG. 1 shows an example of an X-ray diffraction spectrum of the cordierite-based sintered body of the present invention, which is evaluated by using three peaks existing independently from many peaks. That is, based on the peak intensity I _{CJ (132)} of the peak 11 on the cordierite (132) plane, the zirconia (11
The ratio of the peak intensity I _{ZrO2 (110)} of the peak 12 on the 0) plane and the peak intensity I _{Z (112)} of the peak 13 on the zircon (112) plane to the reference peak intensity is calculated. In this case, the background is calculated by subtracting the background.

From FIG. 1, I _{Z (112)} / I _{CJ (132)} is 0, and I _{ZrO2 (110)} / I _{CJ (132)} is 0.14. Also,
FIG. 2 shows an example of an X-ray diffraction spectrum of a conventional cordierite-based sintered body, and when similarly evaluated, I _{Z (112)} / I
_{CJ (132)} is 0.17, _{IZrO2 (110 )} / _{ICJ (132)} is 0.0
It is 11.

Next, a method for producing the cordierite-based sintered body of the present invention will be described.

First, as a starting material, the purity is 99% or more and the average particle size is 0.3 to 2.5 μm, particularly 0.4 to 0.9 μm.
Then, the compositions of MgO, Al ₂ O ₃ and SiO ₂ are respectively 13.3 to 14.1, 34.9 to 37.1, 49.6 to
A cordierite powder having a ratio of 52.0 and a zirconia powder having a purity of 99% or more and an average particle diameter of 0.3 to 1.2 μm, particularly 0.5 to 0.9 μm are prepared. The coarse raw material powder may be used after being pulverized so as to have an average particle size in the above range, or the mixed raw material may be used after being pulverized.

As a sintering aid, the purity is 99% or more.
Average particle size is 0.4 to 1.2 μm, especially 0.5 to 0.9 μm
Periodic Table 2a such as ytterbium oxide powder or yttrium oxide powder or calcium oxide powder or barium oxide powder or strontium oxide powder having a purity of 99% or more and an average particle size of 0.8 to 5 μm, particularly 0.9 to 2.5 μm. A Group 3 element oxide or a Group 3a element oxide is prepared.

The use of these sintering aids facilitates densification and promotes densification over a wide range of firing temperatures. If the amount of the sintering aid is less than 1% by weight, the firing temperature required for densification exceeds 1400 ° C., and zircon formation becomes remarkable. If it exceeds 10% by weight, the liquid phase component increases. As a result, the production of zircon increases, and the effect of improving the strength decreases.

Next, zirconia powder is used in an amount of 2 to 35% by weight, preferably 3 to 35% by weight, based on 100 parts by weight of the cordierite powder.
25% by weight, more preferably 5 to 15% by weight, and at least one of Group 2a element oxides and Group 3a element oxides in the periodic table, 1 to 10% by weight, particularly 2 to 8% by weight, Is weighed at a ratio of 3 to 7% by weight and mixed using a hole mill or the like.

Since the average particle diameter of the mixed powder is preferably 1 μm or less from the viewpoint of a low firing temperature, a pulverizer can be used for mixing the raw materials, thereby obtaining a fine mixed powder. Can be.

The mixed powder is formed into a desired molding means, for example,
It can be formed into a desired shape by a method such as mold pressing, casting, cold isostatic pressing, or extrusion. After degreasing this molded body as desired, 1250
~ 1400 ° C temperature range, preferably 1270-1375
Baking is performed at ℃.

It is important that the firing atmosphere be a low oxygen atmosphere having an oxygen partial pressure of 0.1 atm or less. For example, a porcelain having desired characteristics can be obtained by a nitrogen atmosphere, a nitrogen / oxygen mixed atmosphere, an inert gas atmosphere such as argon, a vacuum atmosphere, burying in carbon or non-oxide powder, or the like. By firing at low temperature in this low oxygen concentration atmosphere,
A compact sintered body with less defects and less melting can be obtained, and the production of zircon due to the reaction between cordierite and zirconia is suppressed, and dispersion in the zirconia state becomes possible. The effect of improving strength is remarkably exhibited.

The cordierite-based sintered body thus obtained has a dense and smooth porcelain surface, high fracture toughness and high bending strength.

According to the present invention, when the oxygen partial pressure exceeds 0.1 atm, the amount and size of pores increase significantly. Therefore,
From the viewpoint of densification, the oxygen partial pressure is particularly preferably at most 0.05 atm, more preferably at most 0.01 atm.

If the firing temperature is lower than 1250 ° C., the porosity exceeds 3%, making it difficult to obtain a smooth porcelain surface or mirror surface. If the temperature exceeds 1400 ° C., cordierite and zirconia react with each other, and zircon is remarkably formed, so that the strength is significantly reduced. Therefore, the firing temperature is 1250 to
A good sintered body can be obtained at a temperature of 1400 ° C, particularly 1270 to 1375 ° C.

According to the cordierite-based sintered body of the present invention thus obtained, it is dense, has high toughness and high strength, and has low thermal expansion and low thermal conductivity. And it can be used for a structure such as a column or a column of a three-dimensional measuring machine which is desired to be lightweight.

[0036]

EXAMPLE 1 Zirconia having a purity of at least 99% and an average particle size of 0.9 μm, a purity of 99% and an average particle size of 1.0 μm were compared with cordierite powder having a purity of 99.0% and an average particle size of 2.0 μm. Yb
₂ O _3, purity 99.5%, average particle size 5.0 .mu.m Y ₂ O _3,
CeO ₂ , Sm ₂ O ₃ , Lu ₂ O ₃ , SrO, BaO and C
aO was weighed at the ratio shown in Table 1.

These mixed powders were mixed with IPA as a solvent.
(Isopropyl alcohol), and the average particle size was 0.9 to 1.0 μm by a microtrack method using a rotary mill.
m and crushed and mixed.

Next, paraffin wax was added as a binder so as to be 10% by weight based on the mixed powder, and IPA was added.
After evaporating and removing the raw material powder, the raw material powder is granulated into granules, and 80MP
6mm long, 7mm wide, length 4
A 5 mm molded body was produced. Then, this molded body is shown in Table 1.
It baked on condition of. The firing atmosphere is an air atmosphere and a nitrogen atmosphere, a nitrogen-oxygen mixed atmosphere, a nitrogen-air mixed atmosphere,
Either a vacuum atmosphere or a burying and burning of carbon powder (C burying) was used.

The bulk density of the obtained sintered body is determined by the Archimedes method, and then the sintered body is pulverized to obtain a JISR162.
The relative density was calculated in comparison with the true density obtained by the helium displacement method based on 0.

The peak intensity ratio was obtained by measuring a spectrum by X-ray diffraction and calculating each peak intensity ratio. At the time of measurement, a background removal process was performed by a computer at the time of X-ray diffraction measurement.

The average pore diameter of the sample was mirror-finished, and a 200-fold metal microscope image of the surface was obtained from Luzex F manufactured by Nireco.
The data was taken in the S type and processed. The pore occupancy was defined as the area ratio of the pores to the observation area, and the pore area was calculated assuming that the pores were circular.

The bending strength is in accordance with JIS R1601,
It was measured by a four-point bending test method. Fracture toughness is JIS R1
607 was evaluated by the IF method.

[0043]

[Table 1]

Sample No. of the present invention 2-4, 7, 8, 10
Nos. To 16 and 18 to 27 have an average pore diameter of 3.2 μm or less, a pore occupancy of 3% or less, a relative density of 97% or more, a strength of 176 MPa or more, and a fracture toughness of 2.4 MPa.
・ M ^1/2 or more.

On the other hand, Sample No. which does not contain zirconia and is out of the range of the present invention. Sample No. 1 was as low as 135 MPa and the fracture toughness was 1.9 MPa · m ^1/2 .

The zirconia content was as large as 40% by weight, and the sample No. which was out of the range of the present invention was used. 5 has a void occupancy of 3.2
It was as large as%.

Further, since no relative density was obtained because of no inclusion of Yb ₂ O ₃ , Sample No. which was out of the range of the present invention. In No. 6, no dense body was obtained, and the mechanical properties could not be evaluated. In addition, Yb ₂
O ₃ is the most 12 wt%, the sample outside the scope of the present invention No.
No. 9 has a large porosity of 9.8% and a fracture toughness of 1.9M.
Pa · m ^1/2 was low.

Further, when the oxygen partial pressure was as high as 0.21 atm and the sample No. was out of the range of the present invention. In No. 17, the porosity was as high as 3.6% and the fracture toughness was as low as 1.9 MPa · m ^1/2 .

[0049]

According to the present invention, the production of zircon is suppressed by low-temperature sintering and the control of the sintering atmosphere, and zirconia is dispersed in cordierite. A cordierite-based sintered body can be provided.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction spectrum of a cordierite sintered body of the present invention.

FIG. 2 is an X-ray diffraction spectrum of a conventional cordierite-based sintered body.

[Explanation of symbols]

 11 ... peak of cordierite (132) plane 12 ... peak of zirconia (110) plane 13 ... peak of zircon (112) plane

Claims (3)

[Claims] 1. Zirconium is mainly composed of cordierite, 2 to 35% by weight in terms of oxide, and at least one of Group 2a element and Group 3a element in the periodic table is 1 to 10% by weight in terms of oxide. And an average pore diameter of 4.0 μm or less, a pore occupancy of 3% or less, a relative density of 97% or more, a strength of 170 MPa or more, and a fracture toughness of 2.4 MPa · m ^1/2 or more. A cordierite-based sintered body, characterized in that: 2. A X-ray diffraction spectrum, I _{Z (112)} peak intensity of zircon (112) plane, zirconia (1
10) _Assuming that the peak intensity on the plane is I _{ZrO2 (110)} and the peak intensity on the cordierite (132) plane is I _{CJ (132)} , the peak intensity ratio I _{Z (112 )} / I _{CJ (132)} is 0.05. Hereinafter, I
_2. The cordierite-based sintered body according to claim 1, wherein _{ZrO2 (110)} / _{ICJ (132)} is 0.05 or more. 3. A mixture mainly comprising cordierite powder, containing 2 to 35% by weight of zirconia and 1 to 10% by weight of an oxide of at least one of Group 2a and 3a elements of the periodic table. A method for producing a cordierite-based sintered body, characterized in that a compact made of powder is fired in an atmosphere having an oxygen partial pressure of 0.1 atm or less.