JPS63297268A - Heat-resistant, low-heat expansion zirconyl phosphate-zircon composite sintered product and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title composite sintered product which contains prescribed amounts of ZrO2, P2O5, and SiO2 respectively, specifies the total amount of resting MgO and Al2O3 below a certain level, and contains zirconyl phosphate as the main crystal phase, and zircon as the second crystal phase, thus showing excellent thermal shock resistance and heat resistance. CONSTITUTION:The present invention provides a low thermal expansion zirconyl phosphate-zircon composite sintered product with is composed of 58.2-65.3wt.% of ZrO2; 17.4-37.1wt.% of P2O5; 1.6-19.0wt.% of SiO2; and less than 2wt.%, based on the rest amount, of MgO and Al2O3 and has following properties: containing zirconyl phosphate as the main crystal phase and zircon as the second crystal phase, having less than 30X10<-7>/ deg.C heat expansion coefficient from room temperature to 1,400 deg.C and melting over 1,600 deg.C. The composite sintered product according to the present invention has a promising potential to be used widely as a low thermal expansion material with high thermal shock resistance, such as a rotary regeneration type ceramic heat exchanger or transfer type heat exchanger, when it is, for example, extruded in a honeycomb structure.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to low expansion ceramics and a method for producing the same, and more particularly, to low expansion ceramics based on zirconyl phosphate and zircon that have excellent thermal shock resistance and heat resistance. and its manufacturing method.

(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 and cooling conditions, that is, heat transfer rate. affected.

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. There is a strong desire to develop low-expansion materials with excellent properties.

(Problem to be solved by the invention) Conventionally, the coefficient of thermal expansion between 40°C and 800°C is 5 to 2.
There are cordierite (MAS) and lithium aluminum silicate (LAS) as ceramic materials with relatively low expansion of about 0x10-' (1°C).
The melting point of the former is 1450°C and the latter is 1423°C. For example, in the case of ceramic honeycomb used as a catalyst carrier in an automobile catalyst purification system, the mounting position of the catalytic converter is changed from the conventional underbed to the engine engine in order to improve the catalyst purification efficiency. Due to design changes such as changing the location nearby or installing a turbocharger to improve fuel efficiency and output, the exhaust gas temperature will rise compared to before, and the catalyst bed temperature will also rise by 100 to 200 degrees Celsius. It has been found that even cordierite honeycomb carriers with a high melting point can cause clogging due to melting, and there is 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. Ta.

In addition, as a ceramic with relatively low thermal expansion and high heat resistance, mullite (3A1□03・2SiO□, coefficient of thermal expansion: 53 x 10-'/''c, melting point: 17
50°C) and zircon (ZrO2.SiO2, thermal expansion coefficient: 42X10-7/°C1 melting point; 1720''C)L, both of which have the drawbacks of high thermal expansion coefficients and low thermal shock resistance.

Furthermore, as a known example of a low expansion ceramic mainly composed of zirconyl phosphate, there is a mixture of 5iOz/NbzOs: 1 to 8 molar ratio of 2 to 10 mol% and Alz03 of 1 to 10 mol%, as shown in Japanese Patent Publication No. 12867/1986. High-strength zirconyl phosphate sintered body containing 6 mol% and JP-A-60=2185
Zirconium phosphate low expansion porcelain containing 0.5 to 6% by weight of magnesium phosphate as a sintering aid shown in Publication No. 3, ZnO+MgO as a sintering accelerator shown in JP-A-61-219753 , Bi, O,.

MnO2l CozO= l' Nto 1 T10t
, + Ce0t + a set of NbzOs or TazOs and a set of Sing or silicate as a grain growth inhibitor, one or more from each set and a total of two or more of 0.3 to 10
Production method of low thermal expansion zirconyl phosphate ceramics with addition of 0.1% by weight or more by weight, and Nagoya Institute of Technology Ceramic Technology Research Institute Annual Report 9 p. 23-30 (
(1982) MgO.

There are zirconium phosphate ceramics containing 2% by weight of additives such as MnO, Fe2O, and ZnO, but none of them contain zircon as the main second phase, and their sintering mechanism creates a low-melting liquid phase. Due to the liquid phase sintering involved in the formation, heat resistance was poor, and the above requirements could not 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 8.2 to 65.3% by weight of ZrO□s.
, p, os17.4-37.1% by weight, Si8□1.6
~19.0% by weight, the balance consisting of MgO and Ah (h,
The total amount of MgO and At20° is 2.5% or less, contains zirconyl phosphate as the main crystal phase and zircon as the second crystal phase, has a thermal expansion coefficient of 30X10-'/°C or less from room temperature to 1400"C, and has a melting point is characterized by a temperature of 1600° C. or higher. Further, the method for producing the zirconyl phosphate/zircon composite sintered body of the present invention is characterized in that zirconyl phosphate ((ZrO)zhOt
) to 100 parts of a batch mixture with 5 to 50% by weight of zircon (ZrSi04) added to cordierite (2MgO.
2AI! By adding and mixing 0.1 to 5 parts of 03 ・5SiOt) and sintering, the main crystal phase is zirconyl phosphate and the second crystal phase contains zircon.
The coefficient of thermal expansion up to 400℃ is 30X10-? /℃ or less,
The present invention is characterized in that a zirconyl phosphate/zircon composite sintered body having a melting point of 1600° C. or higher is obtained.

(Function) In the above structure, zircon (ZrSiOn), which has high heat resistance (relatively low expansion), coexists with zirconyl phosphate ((ZrO)zP20t), which is a low expansion ceramic, to form a composite. Thermal expansion coefficient up to 1400℃ is 30X10-'/”C or less, melting point is 1600℃
As described above, ceramics having 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 sintered body containing zircon, M
By further adding gO, Al2O, and 5i(h), the open porosity can be reduced and the strength can be improved without reducing heat resistance.

In the manufacturing method of the present invention, the reason why zircon is added to zirconyl phosphate in an amount of 5 to 50% 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 50% by weight, the specified strength cannot be obtained. This is because the coefficient of thermal expansion becomes large, so a range of 5 to 35% by weight is more preferable. Mg
The reason why O, AhOs, and SiO□ are added as a cordierite compound is that the cordierite phase has a relatively high melting point and is stable. This is because growth can be suppressed.

The total amount of alkali/alkaline earth metal oxides excluding MgO contained in the heat-resistant, low-expansion ceramic 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 material to be used is a zirconyl phosphate raw material in which the content of alkali and alkaline earth metal oxides is 0.5% by weight or less, respectively. , a zircon raw material and a cordierite raw material in which the content of alkali/alkaline earth metal oxides excluding MgO is 1% by weight or less are preferred.

The Zr0z/PJs molar ratio of the zirconyl phosphate raw material is 1.
It is preferable that it is 80-2.00. By using a zirconyl phosphate raw material limited to such a molar ratio, m-Zr0. The precipitation of m can be suppressed, the coefficient of thermal expansion of the sintered body can be reduced, and
- Abnormal expansion and contraction due to phase transformation of Zr0z can be suppressed.

The precipitated m-Zr0. The abnormal expansion and contraction of
Since this phenomenon occurs reversibly at a temperature of 100 mL, it damages the sintered body when used under thermal cycles, lowering its strength and causing dimensional changes due to the growth of microcracks, which 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 cordierite, 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, Zr with a diameter of approximately 5 mm is used.
(A vibrating mill, pot mill, or attritor filled with sintered cobblestones was used. ZrO □ Sintered cobblestones were MgO
We used one stabilized with and one stabilized with Y2O. 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% PV in 100 parts by weight of the mixture of formulations shown in Table 1.
Add 5 parts by weight of aqueous solution A, mix thoroughly, and prepare a 25×80
After press molding in a x6 mm mold at a pressure of 100 kg/cm'', rubber pressing was performed at a pressure of 2 ton/cm'' 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 is 5℃/
h~1, 700°C/h. After firing, the sintered body was sized 3×4× as shown in JIS R1601 (1981).
It was processed into a 40 mm bending 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 dilatometer using a high-purity alumina sintered body was used to measure the coefficient of thermal expansion. The measurement temperature range is 40 to 1400°C. 4-point bending strength is JIS
It was measured according to the method shown in R1602. The amount of softening due to its own weight is calculated as follows:
The 3 x 4 x 40 mm bending test piece was placed and heat treated at 1300° C. for 5 hours in the atmosphere, and the deformation amount ΔX due to its own weight was measured using the following formula.

Self-weight softening rate = IJ x / i x 100 (%) The open porosity was measured by the Archimedes method. The melting point is 3X4
A sintered body cut into a shape of
It was quantified using the (101) surface reflection peak value of Si04) and the (002) surface reflection peak value of zirconyl phosphate 1 (β(ZrO) 2P207). Regarding other different crystal phases, only their presence or absence was identified by X-ray diffraction patterns.

*Communication of the
American Ceramic 5oci
ety +C-80 (1984) -] Self 2. From the results of Examples 1 to 9 and Comparative Examples 10 to 23 shown in Table 1, Zr0z 58.2 to 65.3% by weight, PzOs
17.4-37.1% by weight, 5i021.5-19.0
% by weight, the balance consists of MgO and AIZO3, MgO and A
When the content of IZO:l is 2.5% by weight or less and contains zirconyl phosphate as the main crystal phase and zircon as the second crystal phase, the temperature range from room temperature to 1400
A sintered body with a thermal expansion coefficient of 30xlO-'/"c or less and a melting point of 1600°C or higher was obtained. Such a sintered body was prepared by adding 5 to 50% by weight of zircon to zirconyl phosphate.
Cordierite was added to 100 parts of the batch mixture.
This was obtained when a mixture of 1 to 5 parts was sintered under the firing conditions shown in Table 1. Figure 1 shows the relationship between the amount of zircon added and the coefficient of thermal expansion, and Figure 2 shows the relationship between the amount of zircon added and the coefficient of thermal expansion.
The relationship between point bending strength is shown.

Furthermore, the content of alkali/alkaline earth oxides other than MgO in the sintered body exceeds 0.5% by weight or l'1
If the total amount of gO and Alt (h exceeds 2.5% by weight, 130
When the zirconyl phosphate/zircon composite sintered body is heated to 1300°C, the softening rate under its own weight at 0°C increases and the heat resistance decreases.
Figure 3 shows the relationship between the self-weight softening rate and the amount of alkali/alkaline earth oxidation anastomosis excluding MgO.
This is clear from FIG. 4, which shows the relationship between the total amount of MgO and Al2O3. In order to obtain such a sintered body, the total amount of alkali/alkaline earth metal oxides contained in zirconyl phosphate and zircon raw material 1 must be 0.5% by weight or less. It is necessary that the content of alkaline earth metal oxides be 1% by weight or less.

It is also important to control the molar ratio of ZrO□ and P2O5 in the zirconyl phosphate raw material within the range of 1.80 to 2.00; if this value exceeds 2.00, monoclinic ZrO will precipitate. Increasing the coefficient of thermal expansion of the sintered body, monoclinic Zr0
It cannot be used practically because it causes serious damage to the sintered body due to rapid contraction due to phase transformation of z to tetragonal and rapid expansion during phase transformation from tetragonal to monoclinic. Also, if this value is smaller than 1.80, (ZrO)
Since the zhot phase is not sufficiently precipitated, the coefficient of thermal expansion of the sintered body increases and it cannot be used as a low expansion material. FIG. 5 shows the relationship between the ZrO□/has molar ratio and the coefficient of thermal expansion.

FIG. 6 shows the X-ray diffraction pattern of the zirconyl phosphate/zircon composite sintered body of Example 3. It can be seen that the main component of the crystal phase is zirconyl phosphate and the second crystal phase is zircon.

FIG. 7 is a thermal expansion curve of the zirconyl phosphate/zircon composite sintered body of Example 3, and it can be seen that no softening occurs from room temperature to 1400°C.

(Effects of the Invention) As is clear from the detailed explanation above, according to the heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body of the present invention and its manufacturing method, Zr8□58.2 to 65.3
Weight %, has 17.4-37.1 weight %, 5i02
It has a chemical composition of 1.6 to 19.0% by weight, the balance being MgO and Ah03, and the total amount of MgO and Ah03 is 2.5% by weight or less, and contains zirconyl phosphate as the main crystal phase and zircon as the second crystal phase. 1 from room temperature by
It is possible to obtain a heat-resistant, low-expansion ceramic having a low expansion property of 30×10 −7 /°C or less in a temperature range up to 400°C and a melting point of 1600°C or more.

Therefore, its application range is wide as a low expansion material that requires thermal shock resistance.For example, when 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 in applications such as ceramic turbocharger rotor housings or heat insulating materials in engine manifolds, which are 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.
Figure 3 shows the dependence of point bending strength on the amount of zircon added.
Figure 4 shows the relationship between the self-weight softening rate at 300°C and the amount of alkali/alkaline earth oxidation anastomosis excluding MgO.
Figure 5 shows the relationship between the self-weight softening rate at 300°C and the amount of cordierite added.
Figure 6 is a diagram showing the relationship between the molar ratio and the coefficient of thermal expansion of the zirconyl phosphate/zircon composite sintered body. The figure shows the thermal expansion curve of the zirconyl phosphate/zircon composite sintered body of Example 3, and FIG. 8 shows the method for measuring the softening rate under its own weight. Fig. 1 ZFSi044 force 171 (%) Fig. 3 0.5 0.7 10 MfOn! (Full HS/Alkaline Earth Me Friendly Ze 1 Membership (
History fz) 2.0 Emperor Soft Ihi t,. Rate figure 4

Claims (1)

[Claims] 1. Chemical composition is ZrO_2 58.2-65.3% by weight
, P_2O_5 17.4-37.1% by weight, SiO_
2 1.6-19.0% by weight, balance MgO and Al_2
It consists of O_3 and the total amount of MgO and Al_2O_3 is 2.5
% by weight or less, contains zirconyl phosphate as the main crystal phase and zircon as the second crystal phase, and has a temperature range from room temperature to 140%.
Thermal expansion coefficient up to 0℃ is 30 x 10^-^7/℃ or less,
A heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body characterized by a melting point of 1600°C or higher. 2. Chemical composition is ZrO_2 58.2-64.7% by weight
, P_2O_5 22.5-37.1% by weight, SiO_
2 1.6-14.1% by weight, balance MgO and Al_2
It consists of O_3 and the total amount of MgO and Al_2O_3 is 2.5
% by weight or less, contains zirconyl phosphate as the main crystal phase and zircon as the second crystal phase, and has a temperature range from room temperature to 140%.
The heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body according to claim 1, which has a coefficient of thermal expansion up to 0°C of 20×10^-^7/°C or less. 3. The heat-resistant, low-expansion zirconyl phosphate/zircon composite sintered body according to claim 1, wherein the total amount of alkali/alkaline earth metal oxides excluding MgO is 0.5% by weight or less. 4. Zirconyl phosphate ((ZrO)_2P_2O_7)
Cordierite (2MgO.
By adding and mixing 0.1 to 5 parts of 2Al_2O_3.5SiO_2) and sintering, the main crystal phase is zirconyl phosphate, the second crystal phase contains zircon, and the coefficient of thermal expansion from room temperature to 1400°C is 30 × 10. ＾−＾7／℃
Hereinafter, a method for producing a zirconyl phosphate/zircon composite sintered body, which is characterized by obtaining a zirconyl phosphate/zircon composite sintered body having a melting point of 1600° C. or higher. 5. The amount of zircon added is 5 to 35% by weight, and the coefficient of thermal expansion from room temperature to 1400°C is 20 x 10^-^7/
5. The method for producing a zirconyl phosphate/zircon composite sintered body according to claim 4, wherein the temperature is below .degree. 6. Zirconyl phosphate and zircon raw materials each having an alkali/alkaline earth metal oxide content of 0.5% by weight or less, and cojet having an alkali/alkaline earth metal oxide content of 1% by weight or less excluding MgO. The zirconyl phosphate according to claim 4 using a light raw material.
A method for producing a zircon composite sintered body. 7. ZrO_2/P_2O_5 as raw material for zirconyl phosphate
The method for producing a zirconyl phosphate/zircon composite sintered body according to claim 4, wherein the molar ratio is a value of 1.80 to 2.00.