JPH0520385B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to low expansion ceramics and a method for producing the same, and more particularly to low expansion zirconyl phosphate ceramics having excellent thermal shock resistance and heat resistance, and a method for producing the same. be. (Prior Art) With the progress of industrial technology in recent years, there has been an increasing demand for materials with excellent heat resistance and thermal shock resistance. The thermal shock resistance of ceramics is influenced by the material's properties such as coefficient of thermal expansion, thermal conductivity, strength, modulus of elasticity, and Poisson's ratio, as well as the size and shape of the product, as well as heating,
It is also influenced by the cooling state, ie the rate of heat transfer. Among these factors that affect thermal shock resistance, the contribution rate of the coefficient of thermal expansion is particularly large.In particular, it is known that when the heat transfer rate is high, it is greatly influenced only by the coefficient of thermal expansion. The development of low-expansion materials with excellent impact resistance is strongly desired. (Problem to be solved by the invention) Conventionally, the coefficient of thermal expansion between 40℃ and 800℃ was 5.
Cordierite (MAS) and lithium aluminum silicate (LAS) are ceramic materials with relatively low expansion of ~20×10 ^-7 (1/℃), but the melting point of the former is 1450℃ and the latter is 1423℃. ℃
For example, in the case of a ceramic honeycomb used as a catalyst carrier in an automobile catalyst purification system, the installation position of the catalytic converter must be changed from the conventional underbed to the vicinity of the engine in order to increase the catalyst purification efficiency, or to improve fuel efficiency and output. Due to design changes such as installing a turbocharger for the purpose of this, the exhaust gas temperature rises compared to before, and the catalyst bed temperature also rises by 100 to 200 degrees Celsius, so even cordierite honeycomb carriers with a high melting point can melt. There was a strong desire to develop a low-expansion material with excellent heat resistance and thermal shock resistance equal to or higher than that of cordierite. In addition, ceramics with relatively low thermal expansion and high heat resistance include mullite (3Al ₂ O ₃ 2SiO ₂ , coefficient of thermal expansion: 53×10 ^-7 /℃, melting point: 1750℃), zircon (ZrO ₂・SiO ₂ , Thermal expansion coefficient: 42 × 10 ^-7 /℃, melting point: 1720℃), both of which have high thermal expansion coefficients,
It has the disadvantage of low thermal shock resistance. Furthermore, as a known example of a low expansion ceramic containing zirconyl phosphate as a main component,
A high-strength zirconyl phosphate sintered body containing 2 to 10 mol% of a SiO ₂ /Nb ₂ O ₅ :1 to 8 molar ratio mixture and 1 to 6 mol% of Al ₂ O ₃ as shown in Japanese Patent Publication No. 12867, and 60
-Zirconium phosphate low expansion porcelain containing 0.5 to 6% by weight of magnesium phosphate as a sintering aid as shown in Publication No. 21853, and also in Nagoya Institute of Technology Ceramic Technology Research Institute Annual Report 9 P.23-30 (1982) There is a zirconium phosphate ceramic containing 2% by weight of additives such as MgO, MnO ₂ , Fe ₂ O ₃ , ZnO, etc., as shown in Fig. Since liquid phase sintering is performed by producing a liquid phase with a low melting point, heat resistance is poor, and the above requirements cannot be met. An object of the present invention is to eliminate the above-mentioned problems and provide a zirconyl phosphate/zircon composite sintered body having high heat resistance and a low coefficient of thermal expansion, and a method for manufacturing the same. (Means for Solving the Problems) The heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body of the present invention has a chemical composition of _ZrO2 : 61.3 _to 64.0% by weight, _P2O5 : 32.0 to 37.1% by weight, _SiO2 : 1.6~4.0
By weight, 90% or more zirconyl phosphate as the main crystalline phase and 5-10% by weight as the second crystalline phase.
It is characterized by a thermal expansion coefficient of 30×10 ^-7 /°C or less from room temperature to 1400°C and a melting point of 1600°C or higher. Further, the method for producing a zirconyl phosphate/zircon composite sintered body of the present invention includes adding 5 to 10 zircon (ZrSiO ₄ ) to zirconyl phosphate ((ZrO) ₂ P ₂ O ₇ ).
By adding % by weight and sintering, the main crystalline phase is zirconyl phosphate, the second crystalline phase is zircon, the coefficient of thermal expansion from room temperature to 1400℃ is less than 30 × 10 ^-7 /℃, and the melting point is 1600℃. The present invention is characterized by obtaining a zirconyl phosphate/zircon composite sintered body having a temperature of at least .degree. (Function) In the above structure, zircon (ZrSiO ₄ ), which has high heat resistance and relatively low expansion, is combined with zirconyl phosphate ((ZrO) ₂ P ₂ O ₇ ), which is a low expansion ceramic.
It is made into a ^composite by coexisting with
℃ or higher, and ceramics with excellent heat resistance and thermal shock resistance can be obtained. Zircon coexisting with zirconyl phosphate compensates for the difficulty of sintering of zirconyl phosphate and promotes sintering. In addition, zirconyl phosphate tends to form a low melting point liquid phase with alkali/alkaline earth metal oxides, so if these impurities coexist, abnormal grain growth may occur resulting in a sintered body with low strength or softening at high temperatures. Although deformation may occur, such abnormal grain growth and softening deformation at high temperatures can be suppressed by coexisting zircon. In the production method of the present invention, the reason why zircon is added to zirconyl phosphate in an amount of 5 to 10% by weight is that if the amount of zircon is less than 5% by weight, the specified strength cannot be obtained, and if it exceeds 10% by weight, the specified strength cannot be obtained. This is because the coefficient of thermal expansion becomes large. The total amount of alkali/alkaline earth metal oxides contained in the heat-resistant, low-expansion ceramics of the present invention is 0.5
It is preferable that the amount is at most % by weight because heat resistance can be improved. Therefore, in order to limit the amount of alkali and alkaline earth metal oxides in the sintered body, the raw materials used are zirconyl phosphate raw materials and Zircon raw materials are preferred. The ZrO ₂ /P ₂ O ₅ molar ratio of the zirconyl phosphate raw material is
It is preferably 1.80 to 2.00. By using a zirconyl phosphate raw material limited to such a molar ratio, it is possible to suppress the precipitation of m-ZrO ₂ in the sintered body, reduce the coefficient of thermal expansion of the sintered body, and further reduce the precipitated m-ZrO2. Abnormal expansion and contraction caused by phase transformation of ZrO ₂ can be suppressed. Abnormal expansion and contraction of precipitated m-ZrO ₂ occurs reversibly at a temperature of about 1000°C, which can damage the sintered body when used under thermal cycles, lowering its strength and causing micro-cracks to grow. This causes dimensional changes and is extremely harmful in practice. (Example) Examples of the present invention will be described below. Zirconyl phosphate, zircon, magnesia, mullite, aluminum phosphate, alumina, spinel, kaolin, and silica whose particle sizes had been adjusted in advance according to the proportions listed in Table 1 were mixed. To adjust the particle size of zirconyl phosphate, a particle with a diameter of approximately 5 mm is used.
A vibratory mill, pot mill or attritor filled with ZrO ₂ sintered cobbles was used. ZrO ₂ sintered cobblestone stabilized with MgO and Y ₂ O ₃ were used. The chemical composition of the boulders used is shown in Table 2. Table 3 also shows the chemical analysis values of the raw materials used. 10% in 100 parts by weight of the mixture of the formulations shown in Table 1
Add 5 parts by weight of PVA aqueous solution and mix thoroughly.
After press molding in a 25 x 80 x 6 mm mold at a pressure of 100 kg/cm ² , a rubber press was performed at a pressure of 2 ton/cm ² and dried. After drying this molded body, it was fired in an electric furnace in the atmosphere under the conditions shown in Table 1. The temperature increase rate was 5°C/h to 1700°C/h. After firing, this sintered body is 3×4 as shown in JIS R1601 (1981).
It was processed into a 40 mm x 40 mm anti-analytical test piece, and its thermal expansion coefficient from 40 to 1400°C, 4-point bending strength, softening amount under its own weight, open porosity, and melting point were measured. A push rod differential thermal expansion meter using a high-purity alumina sintered body was used to measure the thermal expansion coefficient. The measurement temperature range is 40-1400℃.
The four-point bending strength was measured according to the method shown in JIS R1601. The self-weight softening amount is 30mm as shown in Figure 7.
A 3 x 4 x 40 mm anti-resistance specimen was placed between supports with a width of . Self-weight softening rate = Δx/×100 (%) The open porosity was measured by the Archimedes method. The melting point is calculated using a sintered body cut into a shape of 3 x 4 x 5 mm.
Heat treatment was performed for 10 minutes in an electric furnace at 1650°C, and whether or not it melted was visually determined. The amount of crystalline phase in the sintered body is determined using the (101) plane reflection peak of zircon (ZrSiO ₄ ) and the (002) plane reflection peak value of zirconyl phosphate ^* (β(ZrO) ₂ P ₂ O ₇ ). did. Regarding other different crystal phases, only their presence or absence was identified by X-ray diffraction patterns. * Communication of the American
Ceramic Society, c-80 (1984)

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[Table] From the results of Examples 1 to 2 and Comparative Examples 6 to 23 shown in Table 1, ZrO ₂ : 61.3 to 64.0% by weight, P ₂ O ₅ : 32.0 to
37.1% by weight, _SiO2 : 1.6 to 4.0% by weight, containing 90% by weight or more of zirconyl phosphate as the main crystalline phase and 5 to 10% by weight of zircon as the second crystalline phase,
Thermal expansion coefficient from room temperature to 1400℃ is 30×10 ^-7 /℃
A sintered body with a melting point of 1600°C or higher was obtained. Further, such a sintered body was obtained by sintering a mixture of zirconyl phosphate and zircon in a mixing ratio of 5 to 10% by weight under the firing conditions shown in Table 1. FIG. 1 shows the relationship between the amount of zircon added and the coefficient of thermal expansion, and FIG. 2 shows the relationship between the amount of zircon added and the four-point bending strength. Furthermore, if the total amount of alkali/alkaline earth oxides in the sintered body exceeds 0.5%, the self-weight softening rate at 1300℃ increases and the heat resistance decreases. This is clear from Figure 3, which shows the relationship between the softening rate under the body's own weight at 1300°C and the total amount of alkali/alkaline earth oxides. In order to obtain such a sintered body, it is necessary that the total amount of alkali/alkaline earth metal oxides contained in the zirconyl phosphate and the zircon raw material be 0.5% by weight or less. It is also important to control the molar ratio of ZrO ₂ and P ₂ O ₅ in the zirconyl phosphate raw material within the range of 1.80 to 2.00; if this value exceeds 2.00, monoclinic ZrO ₂ will precipitate and the sintered body will increase the coefficient of thermal expansion of monoclinic
Rapid contraction due to phase transformation of ZrO ₂ to tetragonal crystal,
The rapid expansion during the phase transformation from tetragonal to monoclinic gives a serious damage to the sintered body, making it unusable for practical use. If this value is smaller than 1.80, the (ZrO) ₂ P ₂ O ₇ phase is not sufficiently precipitated, so the coefficient of thermal expansion of the sintered body increases and it cannot be used as a low expansion material. Figure 4 shows ZrO ₂ /P ₂
The relationship between O ₅ molar ratio and thermal expansion coefficient is shown. FIG. 5 shows the X-ray diffraction pattern of the zirconyl phosphate/zircon composite sintered body of Comparative Example 6. It can be seen that the main component of the crystal phase is zirconyl phosphate and the second crystal phase is zircon. FIG. 6 is a thermal expansion curve of the zirconyl phosphate/zircon composite sintered body of Comparative Example 6, and it can be seen that there is no softening from room temperature to 1400°C. (Effects of the Invention) As is clear from the detailed explanation above, the heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body of the present invention and its manufacturing method have the following effects:
_ZrO2 : 61.3-64.0% by weight, _P2O5 : 32.0-37.1% by weight, _SiO2 : 1.6-4.0% by weight, with 90% or more of zirconyl phosphate as the main crystal phase, and 5-5% _of zirconyl phosphate as the second crystal phase. 30×10 ^-7 in the temperature range from room temperature to 1400℃ by including 10% by weight of zircon
It is possible to obtain heat-resistant, low-expansion ceramics having the following low expansion properties and a melting point of 1600°C or higher. Therefore, its application range is wide as a low expansion material that requires thermal shock resistance.For example, when it is formed into a honeycomb structure by extrusion molding etc., it can be used as a rotating regenerator type ceramic heat exchanger, a heat transfer type heat exchanger, etc. It has sufficient practicality for applications such as ceramic turbo charger rotor housings or heat insulating materials in engine manifolds molded by slurry casting, press molding, injection molding, etc.

[Brief explanation of drawings]

Figure 1 shows the dependence of the coefficient of thermal expansion on the amount of zircon added in the zirconyl phosphate/zircon composite sintered body, and Figure 2 shows the amount of zircon added on the four-point bending strength of the zirconyl phosphate/zircon composite sintered body. Figure 3 is a diagram showing the relationship between the self-weight softening rate of a zirconyl phosphate/zircon composite sintered body at 1300°C and the total amount of alkali/alkaline earth oxides.
Figure 4 shows the zirconyl phosphate raw materials used in the production of zirconyl phosphate/zircon composite sintered bodies.
Figure 5 showing the relationship between the ZrO ₂ /P ₂ O ₅ molar ratio and the coefficient of thermal expansion of the zirconyl phosphate/zircon composite sintered body.
The figure shows an X-ray diffraction pattern of the zirconyl phosphate/zircon composite sintered body of Comparative Example 6, and FIG. 6 shows the thermal expansion curve of the zirconyl phosphate/zircon composite sintered body of Comparative Example 6. , FIG. 7 is a diagram showing a method of measuring the self-weight softening rate.

Claims (1)

[Claims] 1. Chemical composition: ZrO ₂ : 61.3 to 64.0% by weight, P ₂ O ₅ :
32.0 to 37.1% by weight, _SiO2 : 1.6 to 4.0% by weight, contains 90% by weight or more of zirconyl phosphate as the main crystal phase, 5 to 10% by weight of zircon as the second crystalline phase, and is suitable for temperatures from room temperature to 1400℃. Thermal expansion coefficient is 30×
A heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body characterized by a melting point of 10 ^-7 /℃ or less and a melting point of 1600℃ or more. 2 The total amount of alkali and alkaline earth metal oxides is
The heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body according to claim 1, wherein the content is 0.5% by weight or less. 3 By adding 5 to 10% by weight of zircon (ZrSiO ₄ ) to zirconyl phosphate ((ZrO) ₂ P ₂ O ₇ ) and sintering it, the main crystal phase is zirconyl phosphate and the second crystal phase is zircon. including room temperature
A method for producing a zirconyl phosphate/zircon composite sintered body, characterized by obtaining a zirconyl phosphate/zircon composite sintered body having a thermal expansion coefficient of 30×10 ^-7 /°C or less up to 1400°C and a melting point of 1600°C or higher. . 4 Claim 3 using zirconyl phosphate and zircon raw materials in which the content of alkali and alkaline earth metal oxides is 0.5% by weight or less, respectively.
A method for producing a zirconyl phosphate/zircon composite sintered body as described in . 5. The method for producing a zirconyl phosphate/zircon composite sintered body according to claim 3, wherein the ZrO ₂ /P ₂ O ₅ molar ratio of the zirconyl phosphate raw material is a value of 1.80 to 2.00.