JPH0242788B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to low expansion ceramics,
More specifically, it is dense, thermal shock resistant, airtight,
This invention relates to cordierite-based dense, low-expansion ceramics that have excellent heat resistance and dimensional stability during actual use. (Prior art and problems to be solved) With the progress of industrial technology in recent years, the demand for materials with excellent heat resistance and thermal shock resistance has increased. 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. There is a strong desire to develop low-expansion materials with excellent properties. Cordierite is conventionally known as a relatively low-expansion ceramic material, but cordierite is generally difficult to sinter into a dense sintering process, especially from room temperature.
For cordierite substrates that exhibit low expansion, with a thermal expansion coefficient of 2.0×10 ^-6 or less up to 800°C, it is necessary to limit the amount of impurities that serve as fluxing agents, such as calcia, alkali, potash, and soda, to an extremely small amount. Because of this, there is very little glass phase, making it porous.
In particular, cordierite honeycomb structures, which have been used as catalyst carriers for automobile exhaust gas purification in recent years, have a coefficient of thermal expansion of 1.5× from room temperature to 800°C.
10 ^-6 /℃ or less, raw materials with few impurities such as talc, kaolin, and alumina are used, and the porosity of cordierite sintered bodies can only be in the range of 25 to 45% at most. do not have. Therefore, if such cordierite ceramics is used in a rotating regenerative heat exchanger with a honeycomb structure, the pores on the surface of the partition wall that form the through holes of the honeycomb structure will be reduced due to its large open porosity.
In particular, fluid leakage occurs between the heating fluid and the heat recovery fluid through the communication holes, which has a serious disadvantage that the heat exchange efficiency and the efficiency of the entire system in which the heat exchanger is used decreases. There is. Furthermore, when applied to the housing exhaust manifold of a turbocharger rotor, etc., the large open porosity causes high pressure air to leak, resulting in a serious drawback. For these reasons, there has been a strong desire for low-expansion, dense cordierite ceramics that have excellent thermal shock resistance. Furthermore, high-temperature structural materials exposed to such high temperatures are required to have dimensional stability, and it is desired that the rate of dimensional change during actual use is ±0.05% or less. Conventionally, as a method for obtaining dense cordierite ceramics, a method is known in which a batch mixture of cordierite composition is melted, molded, and then subjected to crystallization treatment to form glass ceramics. For example, a paper by Topping and Marsui published in Volume 46 of the Journal of the Canadian Ceramics Society, published in 1977, proposed replacing up to 20% of the SiO ₂ in cordierite with AlPO ₄ . are doing. According to the same paper, cordierite glass is produced by melting the main ingredient of the raw material to which AlPO ₄ is added at 1,600°C and cooling it, and then reheating and cooling it to produce cordierite crystals. Although the resulting cordierite is dense, it still has a large drawback, as the orientation of the precipitated cordierite crystal phase cannot be controlled, so even one with a small coefficient of thermal expansion is 2.15×10 ^-6 /°C. The inventions of JP-A-59-13741 and JP-A-59-92943 are based on the method of adding B ₂ O ₃ and/or P ₂ O ₅ to the main raw material component to which Y ₂ O ₃ or ZnO is added, and firing the mixture. We have proposed a crystallized glass body obtained by finely pulverizing the obtained crystallized glass component to 2 to 7 microns to form glass frit, molding it into a desired shape, and then firing and crystallizing it again.
This material has the disadvantage of a large thermal expansion coefficient of 2.4 to 2.6×10 ^-6 . The reason why cordierite ceramics exhibit low expansion properties is, for example, the US patent entitled "Anisotropic Cordierite Monolith" granted to Irwin M. Rutschman et al. on May 27, 1975. As disclosed in the specification of No. 3885977 (corresponding Japanese application: Japanese Patent Application Laid-open No. 75611/1983), due to the planar orientation caused by plate clay and laminated clay, cordierite ceramics after firing are oriented. This is because dense cordierite formed into glass ceramics has a high coefficient of thermal expansion of 2.0×10 ^-6 /°C or more. Furthermore, these conventional examples do not contain any description regarding dimensional stability. The object of the present invention is to solve the above-mentioned problems, to provide a low thermal expansion coefficient of 2.0×10 ^-6 /℃ or less, an open porosity of 15% or less, and preferably at a temperature of 500 to 1200℃.
The aim is to provide dense cordierite ceramics with a dimensional change rate of ±0.05% or less after being held for 1000 hours. (Means for solving the problem) The low expansion ceramics of the present invention has a chemical composition of
MgO7.5-20.0% by weight, _{Al2O3 22.0-44.3} % by weight,
SiO ₂ 37.0-60.0% by weight, P ₂ O ₅ 2.0-10.0% by weight, the main component of the crystal phase is cordierite phase, the open porosity is 15% or less, and the thermal expansion coefficient is between 25-800℃. It is characterized by a temperature of 2.0×10 ^-6 /°C or less. P ₂ O ₅ contained in cordierite is released during firing.
AlPO ₄ forms a solid solution by replacing SiO ₂ in cordierite crystals, producing a cordierite solid solution with a slightly lower melting point than cordierite ceramics, increasing the amount of liquid phase generated during sintering, and making cordierite easier. It is made more precise. Moreover, after sintering, most of this liquid phase crystallizes into a cordierite solid solution during cooling.
Unlike cordierite ceramics densified using fluxing agents such as alkali, potash, and soda, the coefficient of thermal expansion does not increase. Furthermore, by heat-treating at a temperature of 1150 to 1350℃ after sintering, the remaining glass phase is completely crystallized, so even after being held at 500 to 1200℃ for 1000 hours, the dimensional change rate is ± It will be 0.05% or less. In addition, raw materials such as talc, clay, alumina, brucite, which are used in conventional cordierite,
By selecting from magnesite and aluminum hydroxide, it is possible to orient the cordierite crystals, so it is possible to obtain dense cordierite ceramics with a low thermal expansion coefficient of 2.0×10 ^-6 /°C or less. The total pore volume with pore diameters of 5 μm or more is usually 0.04
cc/g or less. Mg in the cordierite phase is Zn and/or Fe
It may be iron cordierite or iron-zinc cordierite substituted with 10 mol% or less. The low expansion ceramics of the present invention have a chemical composition of
MgO7.5-20.0% by weight, _{Al2O3 22.0-44.3} % by weight,
A batch containing 37.0 to 60.0% by weight of SiO ₂ and 2.0 to 10.0% by weight of P ₂ O ₅ is prepared, and the prepared batch is subjected to slip cast molding, plastic molding such as extrusion molding, and pressure molding such as press molding. A molded product of any shape is formed, and after drying, the molded product is heated at 1250 to 1450°C for 2 to 30 minutes.
It is produced by further crystallizing the remaining glass phase by firing for 20 hours and heat treating preferably at a temperature of 1150 to 1350°C. The raw material serving as the P ₂ O ₅ source is preferably a combination of one or more selected from aluminum phosphate, magnesium phosphate, zinc phosphate, and iron phosphate, and MgO,
The Al ₂ O ₃ and SiO ₂ source material is preferably selected mainly from brucite, magnesite, talc, clay, and alumina. In addition, by reducing the average particle size of MgO source materials such as brucite, magnesite, and talc to 5 μm or less, the diameter of remaining open pores can be suppressed to 5 μm or less, and even with an open porosity of 15% or less, the Dense cordierite ceramics with excellent airtightness can be obtained. (Function) The present invention contains 2 to 10 P ₂ O ₅ in the cordierite phase.
Dense, low-expansion cordierite ceramics with an open porosity of 15% or less and a coefficient of thermal expansion of 2.0×10 ^-6 /℃ or less between 25 and 800℃ by solid-dissolving AlPO ₄ in weight%. This is due to the new discovery that . 2% by weight of P ₂ O ₅
The reason for limiting P ₂ O ₅ to 10% by weight or less is that if it is less than that, a liquid phase sufficient for densification will not be generated and densification will _not occur. This is because ₅ exceeds the solid solubility limit as AlPO ₄ and becomes highly expanded. Preferably
The reason why we set the dimensional change rate after holding at 500 to 1200℃ for 1000 hours to be less than ±0.05% is because the dimensional change would have been more than this if used as a mechanical part.
This is because it poses a problem in actual use. Chemical composition: MgO7.5~20.0% by weight, _{Al2O3 ~} 22.0%
44.3 wt%, _SiO2 37.0~60.0 wt%, _{P2O5 2.0} ~
The reason why it is limited to 10.0% by weight is that beyond this range, the cordierite phase will not be sufficiently formed.
This is because it becomes highly inflated. If the firing temperature is below 1250°C, the cordierite phase will not be sufficiently formed, and if the firing temperature is higher than 1450°C, it will be softened and deformed. Similarly, if the firing time is shorter than 2 hours, the cordierite phase will not be sufficiently formed, and if the firing time is longer than 20 hours, changes due to softening will occur, depending on the temperature. In addition, the reason why the total pore volume of remaining open pores with a diameter of 5 μm or more was limited to 0.04 cc/g or less is as follows.
This is because the amount of leakage of pressurized gas depends on the total pore volume of pores with a diameter of 5 μm or more, and by reducing the amount to 0.04cc/g or less, the amount of leakage can be suppressed to less than half that of conventional cordierite. be. Also cordierite phase 2MgO・2Al ₂ O ₃・5SiO ₂
Even if up to 10 mol % of Mg is substituted with Zn and/or Fe, cordierite ceramics having the same properties as the cordierite ceramics defined in the present invention can be obtained. The reason why the heat treatment temperature was limited to 1150 to 1350℃ is
This is because at temperatures below 1150°C, the crystallization rate of the remaining glass phase is slow, requiring a very long heat treatment, and at temperatures above 1350°C, no crystallization of the remaining glass phase occurs. . The reason why the P ₂ O ₅ source is one or a combination of two or more phosphate compounds selected from aluminum phosphate, magnesium phosphate, zinc phosphate, and iron phosphate is because phosphoric acid is a liquid and cannot be mixed. difficult,
This is because it becomes uneven. Furthermore, since phosphoric acid locally melts at low temperatures below the formation temperature of cordierite and forms huge pores, it is difficult to add it in the form of a phosphate compound that has a relatively high melting point and is insoluble in water. desirable. The reason why MgO, Al ₂ O ₃ , and SiO ₂ sources were selected from brucite, magnesite, talc clay, alumina, and aluminum hydroxide is that cordierite ceramics made from these raw materials exhibit particularly low expansion. However, the MgO source may be selected from magnesium oxide, the SiO ₂ source may be selected from silica, etc. The reason why the average particle size of the MgO source material was set to 5 μm or less was because
In cordierite ceramics, MgO after sintering
Since pores in the source material particles remain and cause open pores, by limiting the average particle size of the MgO source material to 5 μm or less, open pores larger than 5 μm can be suppressed, which is the object of the present invention. This is because cordierite ceramics with high airtightness can be obtained. (Example) Examples of the present invention will be described below. Brucite, magnesite, talc whose particle size has been adjusted in advance according to the proportions listed in Table 1,
Alumina, aluminum hydroxide, clay, aluminum phosphate, magnesium phosphate, and iron phosphate were mixed. Table 2 shows the chemical analysis values of the raw materials used. Add 5 to 10 parts by weight of water and 20 parts by weight of starch paste (80% water) to 100 parts by weight of this mixture, knead thoroughly with a kneader, and use a vacuum extruder to form a pitch of 1.0 mm.
It had a triangular cell shape with thin walls and a thickness of 0.10 mm, and was extruded into a honeycomb columnar body measuring 65 mm square and 120 mm in length. After drying, this honeycomb molded body was fired under the firing conditions listed in Table 1, and after it was heat-treated at a high temperature of 1150°C to 1350°C under the conditions shown in Table 1,
Cordierite ceramic honeycombs of Examples 1 to 26 and Reference Examples 31 to 45 of the present invention were obtained. For the various cordierite-based ceramic honeycombs shown in Table 1, the cordierite crystals were quantified by powder X-ray diffraction, and the coefficient of thermal expansion, open porosity, and mercury intrusion porosimeter were measured in the temperature range of 25°C to 800°C. The total pore volume with a diameter of 5 μm or more and the amount of pressurized air leaking from the thin walls were measured and compared. The amount of pressurized air leaking from the thin wall is 20 mm x 20 at the center of one end face of the cordierite ceramic honeycomb.
Attach a 65mm x 65mm rubber gasket with a mm square hole, and attach a 65mm x 65mm rubber gasket with a 65mm x 65mm square hole on the other end.
After attaching and sealing ^a rubber gasket with a diameter of Kg/m ² sec). 5 more
1200 mm x 5 mm x 50 L ceramic honeycomb samples
The rate of dimensional change when held at ℃ for 1000 hours was measured using a micrometer. The results are shown in Table 1. Furthermore, in Table 1, the * symbol for talc indicates that the average particle diameter is 2.0 μm, the ** symbol indicates that the average particle diameter is 10.0 μm, and the average particle diameter of all others is 5.0 μm.

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[Table] It is clear from the results of Examples 1 to 26 and Reference Examples 31 to 43 shown in Table 1, and Figure 1 showing the relationship between P ₂ O ₅ content, open porosity, and coefficient of thermal expansion based on the results. P ₂ O ₅ to cordierite composition as 2.0
When the content is ~10.0% by weight, low expansion ceramics with an open porosity of 15% or less and a thermal expansion coefficient of 2.0×10 ^-6 /°C or less between 25 and 800°C, which is the objective of the present invention, can be obtained. Ta. Also, P ₂ O ₅ is 2.0 ~
within the range of 10.0 wt% and MgO7.5~20.0 wt%,
It can be seen from Table 1 that a range of 22.0 to 44.3% by weight of Al ₂ O ₃ and 37.0 to 60.0% by weight of SiO ₂ is preferable. In addition, MgO in the cordierite phase can be replaced with Zn or Fe.
The low expansion ceramics of the present invention can also be obtained by partial substitution with . Furthermore, as is clear from Figure 2, which shows the correlation between the amount of 1.4Kg/ ^cm2 pressurized air leaking from the ceramic honeycomb thin wall and the volume of pores with a diameter of 5 μm or more, the amount of leakage and the amount of pores A high correlation is observed with the volume of pores with a diameter of 5 μm or more. FIG. 4 shows the pore size distribution curves of Example 11 and Reference Examples 32 and 34. Example with a small total pore volume of 5 μm or less in diameter
In case of No. 11, the amount of leakage is significantly lower than that of Reference Examples 32 and 34, as is clear from FIG. Furthermore, from Figure 2, the total pore volume of pores larger than 5 μm is 0.04
By reducing the amount to cc/g or less, the amount of leakage could be reduced to less than half that of normal cordierite. Furthermore, as is clear from Figure 3, which shows the time dependence of the dimensional change rate when held at 1200°C,
1200 in examples heat-treated at high temperatures of 1150-1350℃
Even after being held at ℃ for 1000 hours, we were able to achieve a dimensional change rate of ±0.05% or less, which is almost the same as that of cordierite, which was conventionally considered to have a small dimensional change rate and was good. From the above, the ceramics within the scope of the present invention not only have good airtightness, but also have good impact resistance because the thermal expansion coefficient and dimensional change rate at high temperatures are on the same level as normal cordierite.
We were able to obtain extremely excellent properties as a high-temperature structural material. Figures 4 and 5 are Reference Example 32 and Reference Example 34.
It can be seen that the microstructure of each material is porous and that large pores are present. Furthermore, FIG. 6 shows the microstructure of Example 7, and it can be seen that it has fewer large pores and is denser than the reference example mentioned above. In addition, FIG. 7 shows the results for Example 7.
An X-ray diffraction chart using CuK α-rays is shown, and it can be seen from this chart that the main crystalline phase is cordierite phase, and the secondary crystalline phases are mullite, corundum, and spinel. (Effects of the Invention) As is clear from the detailed explanation above, according to the low expansion ceramics of the present invention, the cordierite phase containing 2 to 10% by weight of P ₂ O ₅ has an additional 1150% by weight after firing. By heat-treating at ~1350℃, it is possible to achieve densification of the base material while maintaining low expansion properties equivalent to cordierite.
It is possible to obtain a low-expansion ceramic in which the dimensional change rate at high temperatures, which is impaired by the addition of P ₂ O ₅ , can be reduced to the same degree as cordierite. Therefore, its application range is not limited to ceramic regenerators as heat exchangers, but also has sufficient practicality as a low-expansion material that requires airtightness, such as ceramic recuperators and housings for ceramic turbo charger rotors. .

[Brief explanation of the drawing]

Figure 1 shows the relationship between the P ₂ O ₅ content, open porosity, and coefficient of thermal expansion of cordierite ceramic honeycomb, and Figure 2 shows the relationship between the leakage amount of 1.4 Kg/cm ² pressurized air from the thin wall of the ceramic honeycomb and The diameter of the hole is
A diagram showing the correlation with the total pore volume of 5 μm or more, Figure 3 is a diagram showing the time dependence of the dimensional change rate when held at 1200 ° C, Figure 4 is a diagram showing the pore distribution curve, Figures 5 and 6 are photographs showing enlarged crystal structures of conventional low expansion ceramics, Figure 7 are photographs showing enlarged crystal structures of low expansion ceramics of the present invention, and Figure 8 is chemical composition. It is a figure showing the X-ray diffraction chart used for identification.

Claims (1)

[Claims] 1. The chemical composition is MgO7.5 to 20.0% by weight,
_{Al2O3 22.0} ~44.3wt%, _SiO2 37.0~60.0wt%,
P ₂ O ₅ 2.0~10.0% by weight, the main component of the crystalline phase is cordierite phase, the open porosity is 15% or less, and the thermal expansion coefficient between 25~800℃ is 2.0 × 10 ^-6 /℃
Low expansion ceramics that are: 2. The low expansion ceramic according to claim 1, which has a dimensional change rate of ±0.05% or less after being held at 500 to 1200°C for 1000 hours. 3 Total pore volume of pores with a diameter of 5 μm or more is 0.04
cc/g or less, the low expansion ceramic according to claim 1 or 2. 4 Mg in cordierite phase is 10 mol% with Zn and Fe
A low expansion ceramic according to any one of claims 1 to 3 as substituted below.