JPH0436113B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing low-expansion ceramics, and more specifically, the present invention relates to a method for producing low-expansion ceramics, and more specifically, the present invention relates to the production of cordierite-based dense low-expansion ceramics that are dense and have excellent thermal shock resistance, airtightness, and heat resistance. It is about the 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,
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 thermal expansion coefficient is particularly large.In particular, when the heat transfer rate is high, it is known that it is greatly influenced only by the thermal expansion coefficient. 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 thermal expansion up to 800°C, with a coefficient of thermal expansion of 2.0×10 ^-6 /°C or less, the amount of impurities such as calcia, alkali, potash, and soda that should be added to the flux should be limited to an extremely small amount. This requires very little glass phase and makes 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, when such cordierite ceramics is applied to a rotating regenerative heat exchanger with a honeycomb structure, for example, the open porosity is large, so that the pores on the surface of the partition wall that form the through holes of the honeycomb structure, especially the communicating pores. This has a serious disadvantage in that fluid leakage occurs between the heating fluid and the heat recovery fluid through the heat exchanger, reducing the heat exchange efficiency and the efficiency of the entire system in which the heat exchanger is used. 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. Because of this, it has excellent thermal shock resistance.
There was a strong desire for low-expansion, dense cordierite ceramics. The purpose of the present invention is to have a coefficient of thermal expansion of 2.0×10 ^-6 /°C.
The present invention aims to provide a method for producing dense cordierite ceramics with low expansion and an open porosity of 25% 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, describes cordierite in which up to 20% by weight of SiO ₂ is replaced with AlPO ₄ . is suggesting. According to the same paper,
Cordierite glass is produced by melting the main raw material to which AlPO ₄ is added at 1,600°C and then cooling it, which is then reheated and cooled to produce cordierite crystals. The resulting cordierite is dense, but because the orientation of the precipitated cordierite crystal phase cannot be controlled, even those with a small coefficient of thermal expansion have a coefficient of thermal expansion of 2.15×10 ^-6 /
℃ and still has a big drawback. 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 a drawback of having a large thermal expansion coefficient of 2.4 to 2.6×10 ^-6 /°C. 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), the planar orientation caused by plate clay and laminated clay causes cordierite ceramics after firing to be oriented. This is because dense cordierite has a high coefficient of thermal expansion of 2.0×10 ^-6 /°C or more when made into glass ceramics. (Means for solving the problems) The method for manufacturing expanded ceramics of the present invention includes:
Contains less than 2% P ₂ O ₅ , the main component of the crystalline phase is cordierite phase, the open porosity is 25% or less, and the coefficient of thermal expansion between 25 and 800°C is 1.0 × 10 ^-6 /°C
It offers the following: The preferred chemical composition is 8.0-20.5% by weight MgO;
24.0~ _45.0 wt% _Al2O3 and 40.5~61.0 wt%
It contains SiO ₂ and less than 2.0% by weight of P ₂ O ₅ . The total pore volume of pores with a diameter of 5 μm or more is approximately 0.06
cc/g or less. Mg in the cordierite phase may be iron cordierite, zinc cordierite, or iron-zinc cordierite substituted with 10 mol % or less of either or both of Zn and Fe. The low expansion ceramics of the present invention contains 7.5-20% by weight of MgO, 22.0-44.3% by weight of _Al2O3 , and 37.0% by weight of _Al2O3 .
A batch with a chemical composition containing ~60.0% by weight of SiO ₂ and 2.0-10.0% by weight of P ₂ O ₅ is prepared, and the prepared batch is subjected to casting molding such as slip casting, plastic molding such as extrusion molding, press molding, etc. A molded body of any shape is formed by pressure molding, and after drying this molded body,
It is produced by firing at 1250 to 1450°C for 2 to 20 hours, and then treating the fired body with acid to selectively remove mainly P ₂ O ₅ . It is preferred to use a P ₂ O ₅ source selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate and iron phosphate as P ₂ O ₅ . Brucite, as MgO, Al ₂ O ₃ and SiO ₂
a MgO source selected from the group consisting of magnesite, talc, clay, alumina and aluminum hydroxide;
It is preferable to use one or more of the Al ₂ O ₃ source and the SiO ₂ source. It is necessary for the average particle size of the MgO source to be 5 μm or less in order to keep the open porosity at 25% or less. (Function) The present invention contains 2 to 10 P ₂ O ₅ in the cordierite phase.
P ₂ O ₅ is selectively removed by further acid treatment based on dense, low-expansion cordierite ceramics with an open porosity of 15% or less by solid solution as AlPO ₄ (wt%). This is because it has been newly discovered that dense, low-expansion ceramics can be obtained with a thermal expansion coefficient of 1.0×10 ^-6 /°C or less at 25 to 800°C and an open porosity of 25% or less.
The reason why P ₂ O ₅ is limited to 2% by weight or more in the batch composition is that if it is less than that, a liquid phase sufficient for densification will not be generated and densification will not occur, so P ₂ O ₅ is limited to 10% by weight or less The reason is that more than P ₂ O ₅
This is because the solid solubility limit of AlPO ₄ is exceeded, resulting in high expansion. The reason why the P ₂ O ₅ content after acid treatment is set to be less than 2% is because if it exceeds the amount, the effect of reducing swelling by acid treatment cannot be sufficiently obtained. The chemical composition of the batch is MgO7.5~20.0% by weight,
_{Al2O3 22.0} ~44.3wt%, _SiO2 37.0~60.0wt%,
The reason why P ₂ O ₅ is limited to 2.0 to 10.0% by weight is that if it exceeds this range, the cordierite phase will not be sufficiently formed, resulting in high expansion. MgO8.0-20.5% by weight,
_{Al2O3 24.0} ~45.0wt%, _SiO2 40.5~61.0wt%,
P ₂ O ₅ less than 2% by weight means that the open porosity is 25% or less,
This is because dense low-expansion ceramics with a thermal expansion coefficient of 1.0×10 ^-6 /°C or less at 25 to 800°C cannot be obtained. If the firing temperature is lower than 1250°C, the cordierite phase will not be sufficiently formed, and if it 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, deformation 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 0.06 cc/g or less is as follows.
This is because the leakage amount of pressurized gas depends on the total pore volume with an open porosity of 5 μm or more, and by setting it to 0.06cc/g or less, the leakage amount can be controlled to less than half that of conventional cordierite. . 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 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. In addition, phosphoric acid locally melts at a constant temperature below the cordierite formation temperature and forms huge pores, so 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, etc. 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 the pores of the source material particles remain and cause an increase in 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. The purpose is
This is because cordierite ceramics with high airtightness can be obtained. (Example) The present invention will now be described in more detail with reference to Examples. Examples 1 to 13 and Reference Examples 14 to 22 Brucite, magnesite, talc, alumina, aluminum hydroxide, clay, aluminum phosphate, magnesium phosphate whose particle size was adjusted in advance according to the formulation proportions listed in Table 1 below. , mixed with iron phosphate. Table 2 shows the chemical analysis values of the raw materials used.
To 100 parts by weight of this mixture, 5 to 10 parts by weight of water and 20 parts by weight of starch paste (80% water) were added, thoroughly kneaded in a kneader, prepared into a material using a vacuum kneader, and made into pitches using an extrusion molding machine. It had a triangular cell shape of 1.0 mm and a thin wall thickness of 0.10 mm, and was extruded into a honeycomb columnar molded 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 was further acid-treated with sulfuric acid, nitric acid, hydrochloric acid, etc. to selectively remove P ₂ O ₅ . Cordierite ceramic honeycombs of Examples 14 to 22 were obtained. For the various cordierite-based ceramic honeycombs shown in Table 1, the cordierite crystals were determined by powder X-ray diffraction, and the coefficient of thermal expansion, open porosity, and thin wall of the ceramic honeycomb were measured using a mercury intrusion porosimeter in the temperature range from 25°C to 800°C. The total pore volume of pores with a diameter of 5 μm or more and the amount of pressurized air leaking from the thin wall were measured and compared. To measure the amount of pressurized air leaking from thin walls, a 65 x 65 mm rubber gasket with a 20 mm x 20 mm square hole in the center is attached to one end of the cordierite ceramic honeycomb, and the other end has no hole. A 65 x 65 mm rubber gasket is attached and sealed, and pressurized air of 1.4 kg/cm ² is introduced into the hole in the rubber gasket, and the flow rate of the pressurized air is measured to determine the leakage per unit time per unit area. (Kg/m ² seconds). The results were as shown in Table 1. Some of the results are also shown in Figures 1-6. As is clear from the results of Examples 1 to 13 and Reference Examples 14 to 22 in Table 1 and from Figure 1, the chemical composition is
MgO7.5-20.0% by weight, _{Al2O3 22.0-44.3} % by weight,
By acid-treating a sintered body containing 37.0-60.0% by weight of _SiO2 and 2.0-10.0% by weight _{of P2O5} , the chemical composition can be changed.
MgO8.0~20.5wt%, _Al2O324.0 ~ _45.0wt %,
SiO ₂ 40.5-61.0% by weight, P ₂ O ₅ less than 2.0% by weight, the main component of the crystalline phase is cordierite phase, the open porosity is 25% or less, and the thermal expansion coefficient between 25-800℃ is 1.0 Low expansion ceramics with a temperature of ×10 ^-6 /°C or less were obtained. Figure 2 shows Example 4 and reference example.
Table 1 shows the relationship between acid treatment time and weight loss rate when a sintered body obtained by firing the formulation No. 14 under the conditions shown in Table 1 was acid-treated with 1.5N sulfuric acid at 95°C. Figure 3 shows the acid treatment time and the reduction rate of each chemical component when the sintered body of Example 4 was fired under the conditions shown in Table 1 and was acid-treated with 1.5N sulfuric acid at 95°C. Show relationships. Figure 4 shows the formulations of Example 4 and Reference Example 14.
The sintered body fired under the conditions shown in the table was heated to 95℃.
The relationship between acid treatment time and thermal expansion coefficient when acid treated with 1.5N sulfuric acid is shown. As is clear from the figure
It can be seen that the effect of reducing the coefficient of thermal expansion by acid treatment is more remarkable in the case of the present invention containing P ₂ O ₅ . Furthermore, as is clear from Figure 5, there is a high correlation between the amount of leakage and the total pore volume of pores with a diameter of 5 μm or more. volume 0.06
By reducing the amount to cc/g or less, the amount of leakage can be reduced to less than half that of normal cordierite. FIG. 6 shows the pore size distribution curves of Example 6, Reference Examples 14 and 16. In Example 6, in which the total pore volume of pores with a diameter of 5 μm or more is small, the amount of leakage is significantly lower than that in Reference Example 14, as is clear from FIG. Furthermore, as shown in Figure 5, by reducing the total pore volume of pores of 5 μm or more to 0.06 cc/g or less, the amount of leakage can be reduced to less than that of normal cordierite. It had extremely excellent properties as a structural material. Figures 7 and 8 are Reference Example 14 and Reference Example 23.
It can be seen that the microstructure of each material is porous and that large pores are present. Further, FIG. 9 shows the microstructure of Example 13, and it can be seen that it has fewer large pores and is denser than the reference example mentioned above. In addition, FIG. 10 shows the results for Example 4.
An X-ray diffraction chart using CuKα radiation is shown, and it can be seen from this chart that the main crystal phase is cordierite phase. In Table 1, * indicates talc with an average particle size of 2.0 μm, ** indicates talc with an average particle size of 10.0 μm,
All others have an average particle size of 5.0 μm.

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[Table] (Effects of the invention) The present invention is made of cordierite that is densified while maintaining its low expansion property, and its application range is not limited to ceramic resin generators (CRG) but also widely to ceramic resin generators (CRP). , ceramic turbo charger rotor (CTR) housings, gas turbines, nuclear reactor materials, various automobile parts such as engine mufflers, exhaust ports, exhaust manifolds, exhaust gas purification catalyst carriers, heat exchangers, and others that require airtightness. It is extremely useful industrially as it has sufficient practicality as a low thermal expansion material.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between P ₂ O ₅ content, open porosity, and coefficient of thermal expansion of cordierite ceramic honeycomb, and Figure 2 is a characteristic diagram showing the relationship between the P 2 O 5 content, open porosity, and coefficient of thermal expansion of cordierite ceramic honeycomb. Figure 3 is a characteristic diagram showing the time dependence of weight loss rate at 95℃.
Figure 4 is a characteristic diagram showing the time dependence of the reduction rate of each component when acid treated with 1.5N sulfuric acid at 95℃.
A characteristic diagram showing the time dependence of the thermal expansion coefficient when acid treated with 1.5N sulfuric acid. Figure 5 shows the leakage amount of 1.4Kg/ ^cm2 pressurized air from the ceramic honeycomb thin wall and the pore diameter of 5μ. Characteristic diagrams showing the correlation with the pore volume, Figure 6 is the pore diameter distribution curve, Figure 7 -
FIG. 8 is an enlarged photograph showing the microstructure of conventional low expansion ceramics, FIG. 9 is an enlarged photograph showing the microstructure of the low expansion ceramic of the present invention, and FIG. 10 is an X-ray diffraction chart.

Claims (1)

[Claims] 1. A chemical containing 7.5-20% by weight of MgO, 22.0-44.3% by weight of Al ₂ O ₃ , 37.0-60.0% by weight of SiO ₂ , and 2.0-10.0% by weight of P ₂ O ₅ By preparing a batch of the composition, molding the batch, firing the molded body, and treating the fired body with acid to selectively remove mainly P ₂ O ₅ , the composition contains less than 2% by weight of P ₂ O ₅ . The main component of the crystal phase is an oriented cordierite phase, the open porosity is 25% or less, and the thermal expansion coefficient between 25 and 800°C is 1.0 × 10 ^-6 /°C or less. A method for producing low expansion ceramics. 2. As _P2O5 , a _P2O5 source selected from the group consisting of aluminum phosphate, magnesium phosphate, _zinc phosphate _and iron _phosphate was used, and as MgO, _Al2O3 and _SiO2 , brucite, magnesite, talc, clay. ,
The manufacturing method according to claim 1, using one or more of a MgO source, an Al ₂ O ₃ source, and a SiO ₂ source selected from the group consisting of alumina and aluminum hydroxide. 3. The manufacturing method according to claim 1, wherein the MgO source has an average particle size of 5 μm or less. 4. The manufacturing method according to claim 1, wherein the molded body is fired at 1250° to 1450°C for 2 to 20 hours.