JP5142650B2 - Heat resistant ceramic member and filter - Google Patents

Description

  The present invention relates to a heat-resistant ceramic member and a filter, for example, a heat insulating material, a support member for a high-temperature member, a honeycomb structure for an exhaust gas purification catalyst carrier for automobiles, and a honeycomb structure for particulate trap (particulate matter removal) for diesel engine automobiles. The present invention relates to a heat-resistant ceramic member and a filter that can be used for a honeycomb structure for consumer use such as a body, a deodorizing body, and a hot air body.

  Conventionally, low thermal expansion ceramic materials such as cordierite, β-eucryptite, β-spodumene lithium aluminosilicate (common name: LAS), and aluminum titanate have been used as a honeycomb structure of a thermal shock-resistant member.

In general, the low thermal expansion ceramic material is a ceramic having a thermal expansion coefficient of 20 ° C. to 800 ° C. of 3.0 × 10 ⁻⁶ / ° C. or less. These low thermal expansion ceramic materials have long been used as materials resistant to thermal shock. Recently, it has been used as a material for parts requiring particularly thermal shock resistance, such as honeycomb carriers for exhaust gas purification catalysts of automobiles, ceramic gas turbine housings and heat exchangers.

Cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) has excellent thermal shock resistance and has been put to practical use as a honeycomb carrier for exhaust gas purification catalysts for automobiles.

  However, since cordierite has a high heat resistance temperature of about 1350 ° C., it is difficult to use it above this temperature.

On the other hand, aluminum titanate (Al ₂ TiO ₅ ) is a low thermal expansion ceramic material having a high melting point of 1860 ° C. and higher heat resistance than cordierite, but when kept at a temperature of 900 ° C. to 1200 ° C., alumina There was a problem of thermal decomposition to titania, and there was a limit to its use.

Therefore, in order to improve the thermal decomposition resistance of such aluminum titanate, additives such as SiO ₂ , Fe ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , MgO, and CaO are added to aluminum titanate. (For example, refer to Patent Document 1).

Further, in order to further improve the thermal decomposition resistance and mechanical strength, Mg compound, Al compound, Ti compound and alkali feldspar (Na _y K _1-y AlSi ₃ O ₈ ) containing Na or K are mixed and sintered. A sintered ceramic sintered body has been reported (see Patent Document 2).

The ceramic sintered body obtained by the technique disclosed in this Patent Document 2 has a heat decomposition resistance when Si is dissolved in an aluminum magnesium titanate (Al ₂ TiO ₅ —MgTi ₂ O ₅ ) sintered body. In addition to being able to obtain an excellent ceramic sintered body, alkali feldspar containing Na or K forms a liquid phase in the firing process, and a dense crystal is formed. Therefore, a ceramic sintered body with high mechanical strength can be obtained. Can be formed.
JP-A-8-290963 JP 2005-46667 A

However, the low thermal expansion ceramic of Patent Document 2 has a problem that heat resistance is low because alkali feldspar containing Si exists as a grain boundary phase. That is, in the low thermal expansion ceramic of Patent Document 2, although Si can be dissolved in an aluminum magnesium titanate (Al ₂ TiO ₅ —MgTi ₂ O ₅ ) crystal, thermal decomposition of the crystal can be suppressed. In the grain boundary, there is a glass with a low melting point containing Si due to alkali feldspar, and when the use temperature is high, the glass with a low melting point containing Si is melted. There was a problem that it was difficult to use.

  An object of the present invention is to provide a heat resistant ceramic member and a filter excellent in heat decomposition resistance and heat resistance.

  Since the present inventors do not substantially contain Si, the grain boundary phase containing low melting point Si does not exist at the grain boundary of the pseudo-brookite crystal, so that the heat resistance can be improved and the alkali metal can be added. It has been found that heat resistance can be improved by containing a predetermined amount, and the present invention has been achieved.

That is, the heat-resistant ceramic member of the present invention contains Al, Ti, and Mg, and the composition formula based on the molar ratio is Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0. a refractory ceramic member having a pseudobrookite type crystal represented by 5) contains substantially no Si, and in a total volume in terms of oxide of the alkali metal from 0.21 to 0.7 9 wt% It is characterized by containing.

In other words, the heat-resistant ceramic member of the present invention contains Al, Ti, and Mg, and the composition formula based on the molar ratio is Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0). .5) is a heat-resistant ceramic member having a pseudo-brookite type crystal, wherein a powder containing an alkali metal is added to a mixed powder containing Al, Ti and Mg, and is fired. It is characterized by not containing Si.

The heat-resistant ceramic member may contain about 0.2% by mass of an alkali metal as an impurity in terms of oxide, but in the present invention, it contains substantially no Si and the alkali metal is converted to an oxide. in order to contain from 0.21 to 0.7 9 wt% in the total amount, in other words, in the case of adding powder containing an alkali metal, even if not containing Si substantially be improved thermal decomposition resistance.

When it contains from 0.21 to 0.7 9 wt% in the total amount in terms of oxide of an alkali metal, but the reason is not clear which can improve the thermal decomposition resistance, the present inventors have alkali metal pseudobrookite type crystal It is considered that aluminum titanate (Al ₂ TiO ₅ ) can be prevented from being thermally decomposed into alumina and titania because it dissolves sufficiently in the inside.

  Also, since there is virtually no Si at the grain boundaries of the pseudo-brookite type crystal grains, there is no grain boundary phase containing low melting point Si, which improves heat resistance and is used even in high temperature environments. can do.

Furthermore, in the present invention, the composition formula based on the molar ratio is composed of pseudo-brookite crystals represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0.5), The heat resistance can be improved and the heat resistance can be further improved.

  In the heat-resistant ceramic member of the present invention, the alkali metal is Na or K. With such a heat-resistant ceramic member, the heat-decomposability can be greatly improved.

  The filter of the present invention is characterized by comprising a porous body using the above heat-resistant ceramic member. Such a filter can improve the heat resistance and heat decomposability of the heat resistant ceramic member, and can be used to purify gas in a higher temperature atmosphere.

  In the heat-resistant ceramic member of the present invention, by not containing Si substantially, there is no grain boundary phase containing low melting point Si at the grain boundary of the pseudo-brookite crystal, so that the heat resistance can be improved, By containing a predetermined amount of alkali metal, the thermal decomposition resistance can be improved. Thereby, the filter of the present invention can be used to purify gas in a higher temperature atmosphere.

  FIG. 1 shows an example of a filter 1 according to the present invention, in which a rectangular column-shaped gas flow path 3 is formed in the height direction of a cylindrical heat-resistant ceramic member surrounded by an outer peripheral wall 2, and a partition wall 4 therebetween is formed. It is assumed to be porous. FIG. 1 shows a honeycomb structure in which a square columnar cell is used as a basic structure and a plurality of the cells are arranged. However, the filter 1 of the present invention is not necessarily limited to the one having a quadrangular columnar cell as a basic structure. . For example, the shape can be other than the honeycomb, and even in the honeycomb structure, the cell shape can be a triangle, a hexagon, a rhombus, or a mixture of these.

  Further, all or part of the opening direction of the honeycomb may be blocked to give a sandwich structure to give impact resistance, and it can be used as a filter. In some cases, a filter is formed by adding a catalyst to a heat-resistant ceramic member.

The heat-resistant ceramic member of the present invention contains Al, Ti, and Mg, and the composition formula based on the molar ratio is Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0.5). in a heat-resistant ceramic member having a pseudobrookite type crystal represented, it contains substantially no Si, and containing from 0.21 to 0.7 9 wt% in the total amount in terms of oxide of an alkali metal It is characterized by that.

  In the present invention, “substantially not containing Si” means that Si is not positively added, and may contain 0.05% by mass or less as impurities.

  Since the heat-resistant ceramic member of the present invention does not substantially contain Si, there is no grain boundary phase containing low melting point Si at the grain boundary of the pseudo-brookite crystal, so that it can be exposed to a high temperature atmosphere. Thus, heat resistance can be improved. As described above, Si may be contained as an impurity level, but it is desirable that Si does not exist.

Further, the heat-resistant ceramic member of the present invention, because it contains 0.21 to 0.7 9 wt% in the total amount in terms of oxide of the alkali metal in the refractory ceramic member the total amount, the reason is not clear, titanate The thermal decomposition of aluminum at 850 to 1200 ° C. can be suppressed (heat decomposition resistance can be improved).

  In the heat-resistant ceramic member of the present invention, an alkali metal may be contained as an impurity in an amount of about 0.2% by mass in terms of oxide, but the present inventors have stated that the alkali metal as an impurity is a pseudo-brookite crystal. Although it easily dissolves in the solution, the added alkali metal is less likely to dissolve in the pseudo-brookite crystal and easily exists at the grain boundary. We believe that the strength tends to decrease. In other words, the alkali metal may be present at the grain boundary of the pseudo-brookite type crystal, but in the present invention, the added alkali metal is sufficiently dissolved in the pseudo-brookite type crystal, thereby causing the suspicious brookite crystal. Is believed to stabilize and improve thermal decomposition resistance. On the other hand, most of the added alkali metal is sufficiently dissolved in the pseudo-brookite crystal, so that elution of the alkali metal is suppressed and the mechanical strength can be maintained high.

  The alkali metal is preferably Na or K. Thereby, the thermal decomposition resistance can be further improved.

  The contents of Si, Na, and K in the heat-resistant ceramic member can be measured using a fluorescent X-ray analysis method or an ICP (Inductively Coupled Plasma) emission analysis method.

Furthermore, in the heat-resistant ceramic member of the present invention, a pseudo brookite type in which the composition formula by molar ratio is represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0.5). It consists of crystals. As a result, not only the heat decomposability but also the heat resistance can be improved, the thermal expansion coefficient can be 2 × 10 ⁻⁶ / ° C. or less, and the thermal shock resistance of the ceramic can be improved. x is preferably 0.25 ≦ x ≦ 0.5 from the viewpoint of improving the thermal decomposition resistance.

  The structure of the heat-resistant ceramic member of the present invention is substantially composed of pseudo-brookite crystals, and nothing exists or an alkali metal oxide exists at the grain boundary. The average particle size of such pseudo-brookite crystals is 0.5 to 50 μm.

  Next, the manufacturing method of the heat resistant ceramic member of this invention is demonstrated.

  Of the heat-resistant ceramic members, here, an example of a method for manufacturing a honeycomb structure used for exhaust gas purification of an automobile or the like will be specifically described.

_{Al 2 (1-x) Mg} x Ti (1 + x) O 5 to prepare a raw material required to form a solid solution composed of (0.21 ≦ x ≦ 0.5). For example, alumina raw material, titania raw material, and magnesium carbonate are prepared so as to have the same ratio as the metal components of Al, Mg, Ti represented by the above composition formula, and a predetermined amount of alkali metal carbonate raw material powder is added to this mixed powder Add and mix. As long as a solid solution having the above composition formula can be formed, raw materials such as hydroxides and nitrates may be used in addition to the raw materials of metal oxides and carbonates, and these compounds may be used. Examples of the alkali metal carbonate raw material powder include K ₂ CO ₃ powder and Na ₂ CO ₃ powder.

  As the alumina raw material, titania raw material, and magnesium carbonate, it is desirable to use a high-purity material, and it is desirable to use a material having a purity of 99.0% or more, particularly 99.5% or more.

  In addition, the mixed raw materials are mixed by a dry method or put into a mill such as a rotary mill, a vibration mill, a bead mill, etc., and a slurry obtained by wet mixing with at least one of water, acetone, and isopropyl alcohol (IPA) is dried. You may do it. In order to sufficiently mix the alkali metal carbonate raw material powder, for example, when using a rotary mill, it is desirable to use ceramic balls having a diameter of 10 mm or more.

At that time, it is necessary to suppress mixing of SiO ₂ by mixing as much as possible. As a method for drying the slurry, the slurry may be heated in a container and dried, or may be dried by a spray dryer, or may be dried by another method.

  Next, a molding aid and a pore former are added to the obtained mixed raw material. As a molding aid, a known binder may be used. For example, methyl cellulose, polyvinyl alcohol, paraffin wax, glycerin and the like are preferable. It is preferable to add and mix 1 to 10 parts by mass of the molding assistant with respect to 100 parts by mass of the mixed raw material, since the generation of cracks and cracks in the molded body can be suppressed during molding described later.

  The pore-forming agent is suitably used when the heat-resistant ceramic member is porous, and has a function of disappearing during pore formation and forming a hole. As the pore-forming agent, for example, activated carbon, polyethylene resin and graphite are preferable. Moreover, you may add a mold release agent, an antifoamer, etc. suitably according to the objective. It should be noted that the pore diameter and porosity of the low thermal expansion ceramic can be freely adjusted by changing the size and amount of the pore former.

  Furthermore, after adding a solvent such as water and pre-kneading with a universal mixer or a triple mill, the mixture is degassed and kneaded using a vacuum kneader or the like to prepare a clay suitable for extrusion molding.

  Furthermore, it is formed into, for example, a honeycomb shape using a die by extrusion molding. The obtained molded body is sufficiently dried and then held in an oxidizing atmosphere at 800 to 1000 ° C. for 1 to 10 hours, and then fired at 1200 to 1700 ° C. for about 3 to 5 hours, whereby the honeycomb shaped present invention is obtained. The heat-resistant ceramic member can be formed.

  Examples of the present invention will be specifically described below, but the present invention is not limited to these examples.

  A commercially available alumina raw material, titania raw material, magnesia raw material, and alkali metal carbonate raw material are prepared so as to have the composition of the sintered body shown in Table 1, isopropyl alcohol (IPA) as a solvent, and an alumina ball having a diameter of 10 mm as a medium. Was mixed for 72 hours with a rotary mill to prepare a slurry.

  The alumina raw material used was LS110 manufactured by Nippon Light Metal Co., Ltd., having an average particle size of 1.5 μm, an alkali metal impurity amount of 0.1 mass%, and a silicon impurity amount of 0.1. The titania raw material used was JA-3 manufactured by Teika Co., which had an average particle size of 0.2 μm and an alkali metal impurity amount of 0.3 mass%. The magnesium carbonate raw material used is TT manufactured by Tokuyama Corporation, which has an apparent specific gravity of 0.23 g / ml and does not contain impurities of alkali metal and silica.

  As alkali metal carbonate raw materials, potassium carbonate manufactured by Asahi Glass Co., Ltd. which does not contain silicon impurities, and sodium hydrogen carbonate manufactured by Asahi Glass Co., Ltd. which does not contain silicon impurities were used.

  As a molding aid, 5 parts by mass of paraffin wax was added to the slurry as a molding aid with respect to 100 parts by mass of the raw material powder, mixed, and then dried to form a molding powder. Next, a disk-shaped molded body having a diameter of 20 mm × thickness of 10 mm and a cylindrical molded body having a diameter of 10 mm × height of 15 mm were produced by using this molding powder by a powder pressure molding method. Each molded body was heated in the atmosphere at 1000 ° C. for 1 hour and then fired at 1400 ° C. for 4 hours to obtain a sample for evaluation of the sintered body. The temperature increase rate from room temperature to the sintering temperature was 20 ° C./h.

Regarding the thermal decomposition resistance of each sintered body, each sample of the disk-shaped sintered body was further subjected to a thermal decomposition test at 1100 ° C. for 300 hours in an air atmosphere to evaluate the thermal decomposition resistance. The samples prepared before and after the thermal decomposition test were measured for peak intensity by X-ray diffraction, and Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0.5 ) and the diffraction angle 2θ is the main peak intensity of 25-27 ° of a solid solution of _{(I AMT),} the peak intensity of the diffraction angles 2θ of TiO ₂ phase 36.1 ° (the _{I T)} from the peak intensity ratio _{a = I AMT} / (I _AMT + I _T ) was calculated. Furthermore, the value of (1-A ₁ / A ₀ ) was calculated with the peak intensity ratios before and after the thermal decomposition test as A ₀ and A ₁ , respectively. Next, Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0.5) and TiO ₂ are mixed at different amounts, and (1-I _AMT / I _T Table 1 shows the thermal decomposition rate obtained by comparing the calibration curve created by determining the value of) and the value of (1-A ₁ / A ₀ ).

  Moreover, about the thermal expansion coefficient, the thermal expansion coefficient of 20 degreeC-800 degreeC of the sample of the cylindrical sintered compact was measured on the conditions of the temperature increase rate of 20 degree-C / min based on JISR1618.

  Moreover, about the produced sample, the peak intensity | strength was analyzed by the X ray diffraction method, and the crystal | crystallization was identified. Further, other metal components excluding Al, Mg, Ti and O were analyzed by ICP (Inductively Coupled Plasma) emission analysis and described as other metal components in Table 1. In addition, the quantity of the other metal component described in Table 1 is an oxide conversion.

In addition, about the total amount of Si, Na, and K with comparatively much quantity among other metal components, each quantity in a sintered compact was described in conversion into the oxide. Moreover, although Ca, P, etc. were detected as a component with comparatively little quantity, this numerical value was not described separately, but described the total amount of other metal components.

  From Table 1, Sample No. which is a sample out of the scope of the present invention. Nos. 8 and 9 had a thermal decomposition rate of 30% or more and insufficient thermal decomposition. On the other hand, sample no. 1-3, 5-7, and 10 had high thermal decomposition resistance and a small thermal expansion coefficient.

  And sample no. It can be seen from 4 to 9 that the thermal decomposition resistance is improved as the amount of alkali metal is increased to 0.202 to 0.77 mass%.

  In addition, sample No. 5 parts by mass and 2 parts by mass of methylcellulose and polyvinyl alcohol are added to 100 parts by mass of the raw material as a molding aid to the mixed raw material having the composition of 1 to 11, respectively, and 20 parts by mass of water as a solvent and a pore agent 8 parts by mass of activated carbon was added and kneaded with a universal mixer and a vacuum kneader to obtain an extrusion molding clay. Further, the clay is formed into a cylindrical honeycomb shape having a diameter of 100 mm and a height of 150 mm using a die by an extrusion molding method, sufficiently dried, and then kept in air at 1000 ° C. for 1 hour, and then at 1400 ° C. for 4 hours. Was used as a sample for evaluation of a honeycomb structure having a porosity of 35%.

Next, after carrying out a heat resistance test in which each honeycomb structure was held at a temperature of 1500 ° C. in the atmosphere for 5 hours, it was examined whether there was any dimensional change of the entire honeycomb structure, deformation of the outer peripheral wall or partition wall, or melting. As a result, sample No. ₁ with 1.973% by mass of SiO ₂ added in the honeycomb structure was obtained. In the honeycomb structure using 12 materials, a part of the partition walls was melted. On the other hand, sample No. In Nos. 1 to 11, no dimensional change of the entire honeycomb structure, deformation or melting of the outer peripheral wall and partition walls were observed, and the heat resistance was good.

Next, after performing a moisture resistance test in which the heat treatment at 1100 ° C. × 10 hours was repeated 10 times in an atmosphere of air (moisture of 51 g / m ³ ) in which the honeycomb structure was humidified, the length of the cylinder from the honeycomb structure was measured. A sample having a length of 15 mm in the direction and a width and width of 5 mm × 5 mm was cut out, and the compressive strength in the length direction was measured according to JIS R1608. As a result, in the sample of the present invention, the compressive strength was 11 MPa or more.

It is a perspective view which shows the filter of the honeycomb structure using the heat resistant ceramic member of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Honeycomb structure 2 ... Outer peripheral wall 3 ... Cell 4 ... Partition

Claims (3)

From a pseudo-brookite type crystal containing Al, Ti and Mg and having a compositional formula by molar ratio represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.21 ≦ x ≦ 0.5) comprising a refractory ceramic member, substantially without containing Si, and refractory ceramic member, characterized in that it contains from 0.21 to 0.7 9 wt% in the total amount in terms of oxide of an alkali metal.   The heat-resistant ceramic member according to claim 1, wherein the alkali metal is Na or K.   A filter comprising a porous body using the heat-resistant ceramic member according to claim 1.

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