JP2008239401A - Heat-resistant ceramic member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-resistant ceramic member in which the elution of an alkaline metal does not occur even when used at a high temperature in the presence of moisture and heat-resistant resolvability and heat resistance are excellent. <P>SOLUTION: The heat-resistant ceramic member 1 is constituted of a sintered compact which is composed of a solid solution of a composition represented by Al<SB>(21-x)</SB>MgxTi<SB>(i+x)</SB>O<SB>5</SB>(0.3≤x≤0.9) and is ≤1.0 mass% in the oxide equivalent amount of other metallic components excluding Al, Mg, Ti, and O, and thereby, the heat-resistant ceramic member 1 which is free from melt loss and is excellent in the heat resistance and the heat-resistant resolvability can be provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes, for example, a heat insulating material, a support material for a high-temperature member, a honeycomb structure for an exhaust gas purification catalyst carrier of an automobile, a honeycomb structure for particulate trap (particulate matter removal) of a diesel engine automobile, for deodorization, and for hot air The present invention relates to a heat-resistant ceramic member excellent in heat resistance, heat decomposition, and moisture resistance, which can be used for a consumer honeycomb structure.

  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 the honeycomb structure of the 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, when the low thermal expansion ceramic obtained by the technique disclosed in Patent Document 2 is used in the presence of moisture, Na or K in the ceramic sintered body is eluted or segregated, and this phenomenon is caused by the ceramic sintered body. When heated in the presence of moisture, the progress is remarkably accelerated and the mechanical strength decreases.

  The present invention has been devised to solve such problems, and alkali metals do not elute even when used at high temperatures in the presence of moisture, and are heat resistant ceramics excellent in heat decomposition resistance and heat resistance. An object is to provide a member.

The heat-resistant ceramic member of the present invention is made of a solid solution whose composition formula is represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.3 ≦ x ≦ 0.9), and includes Al, Mg, The oxide conversion amount of other metal components excluding Ti and O is 1.0% by mass or less.

  In the heat-resistant ceramic member of the present invention, the x is preferably 0.3 ≦ x ≦ 0.8.

The heat-resistant ceramic member of the present invention is made of a solid solution whose composition formula is represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.3 ≦ x ≦ 0.9), and includes Al, Mg, The oxide conversion amount of other metal components excluding Ti and O is 1.0% by mass or less. Thereby, the heat resistant ceramic member excellent in heat decomposition resistance and heat resistance can be provided.

  In addition, the heat-resistant ceramic member of the present invention is a heat-resistant ceramic member having small thermal expansion in addition to heat-resistant decomposability and heat resistance when x is 0.3 ≦ x ≦ 0.8.

  FIG. 1 shows an example of the heat-resistant ceramic member of the present invention. FIG. 1 shows a honeycomb structure in which a quadrangular prismatic cell is used as a basic structure, and a plurality of the honeycomb structures are arranged. However, the heat-resistant ceramic member of the present invention is not necessarily limited to one having a quadrangular prismatic cell as a basic structure. It is not a thing. 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.

  It is also possible to block all or part of the honeycomb in the opening direction to have a sandwich structure to give impact resistance, or to use as a filter.

The heat-resistant ceramic member of the present invention is a heat-resistant ceramic member having such a form, and the composition formula is Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.3 ≦ x ≦ 0.9). ), And the oxide equivalent amount of other metal components excluding Al, Mg, Ti and O is 1.0% by mass or less.

Although aluminum titanate has a problem that it is thermally decomposed into alumina and titania when held at a temperature of 900 ° C. to 1200 ° C., the heat-resistant ceramic member of the present invention is titanium in a solid solution of magnesium titanate and aluminum titanate. Magnesium oxide is dissolved in 30-80 mol% aluminum titanate to substantially contain an alkali element which is another metal component excluding Al, Mg, Ti and O, and SiO ₂ which is an oxide of another metal component. Even when the composition is not included, it is based on the new knowledge that the heat-resistant ceramic member is excellent in heat resistance and heat-decomposability.

That is, when x is in the range of 0.3 ≦ x ≦ 0.9, the solid solution represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.3 ≦ x ≦ 0.9) is Since the sintering temperature is lower than that of aluminum titanate, the sinterability is higher than that of aluminum titanate.

  In such a region, the effectiveness of other metal components such as alkali elements and Si is not found. Rather, when other metal components such as alkali elements and Si are segregated locally in the heat-resistant ceramic member, the region The melting point of the solid solution is extremely low, and there is a possibility of partial melting even at 1400 ° C. or lower.

On the other hand, for example, when x is less than 0.3 in the absence of other metal components such as an alkali element and SiO ₂ used as an auxiliary component, the thermal decomposition resistance is insufficient, and x is If it is larger than 0.9, the coefficient of thermal expansion becomes high, which is not suitable.

  Further, when x is in the range of 0.3 ≦ x ≦ 0.8, a heat resistant ceramic member made of low thermal expansion ceramics having particularly high heat decomposition resistance and a low thermal expansion coefficient can be obtained.

Here, it is important that the heat-resistant ceramic member of the present invention is substantially free of Na and K alkali metals. The fact that the alkali metal of Na and K is substantially not included is calculated assuming that Na and K contained in the ceramic member are oxides when the heat-resistant ceramic member is 100 parts by weight, This means that the total amount of Na ₂ O and K ₂ O is 0.2 parts by mass or less, and particularly preferably 0.16 or less. When the content of Na and K exceeds 0.2 parts by mass, when the heat-resistant ceramic member is repeatedly heated and lowered in an atmosphere containing moisture or moisture, Na and K in the heat-resistant ceramic member Alkali metal reacts with moisture in the atmosphere or condensed moisture and elutes from the inside of the heat-resistant ceramic member, so that the heat-resistant ceramic member is deteriorated or, in some cases, a component that is in contact with the heat-resistant ceramic member is deteriorated. Therefore, even when the heat-resistant ceramic member of the present invention is repeatedly heated and lowered in an atmosphere containing moisture, it does not deteriorate and break down.

  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.

  Moreover, it is important that the heat-resistant ceramic member of the present invention satisfies 0.3 ≦ x ≦ 0.9. When x <0.3, it is impossible to sufficiently sinter the heat-resistant ceramic member at a temperature of 1400 ° C. or less, and sufficient mechanical strength cannot be obtained. On the other hand, the heat-resistant ceramic member of the present invention has x ≧ 0.3, and magnesium titanate having a melting point of 1550 ° C. is added to aluminum titanate having a melting point of 1860 ° C. A dense honeycomb structure with high mechanical strength can be manufactured.

  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 (0.3 ≦ x ≦ 0.9). For example, an alumina raw material, a titania raw material, and magnesium carbonate are prepared and mixed so as to have the same ratio as the metal components of Al, Mg, and Ti represented by the above composition formula. 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.

  As these raw materials, those having high purity are desirably used, and those having a purity of 99.0% or more, particularly 99.5% or more are desirably used.

  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.

At that time, it is necessary to suppress mixing of SiO ₂ by mixing as much as possible. In particular, it is desirable to use a low alkali product with few alkali components such as Na and K as the alumina raw material. 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 resulting molded body is sufficiently dried and then fired at 1200 to 1700 ° C. for about 3 to 5 hours in an oxidizing atmosphere, whereby a honeycomb-shaped heat-resistant ceramic member of the present invention 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, and magnesia raw material are prepared so as to have the composition of the sintered body shown in Table 1, and mixed in a rotary mill for 72 hours using isopropyl alcohol (IPA) as a solvent and alumina balls as a medium. A slurry was prepared.

  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.

  Sample No. 10 instead of LS110, which is the alumina raw material, A-172 manufactured by Showa Denko KK having an average particle diameter of 2 μm, an alkali metal impurity amount of 0.3 mass%, and a silicon impurity amount of 0.1 mass%. Using.

  Sample No. 7 and 8 include SP-3, which is a silica raw material having an average particle diameter of 1.2 μm and containing no alkali metal impurities, manufactured by Marumama Kamado Ceramics Co., Ltd. in addition to the above-mentioned alumina raw material, titania raw material, and magnesium carbonate raw material. And sample no. 11 is potassium carbonate manufactured by Asahi Glass Co., Ltd., which does not contain silicon impurities. No. 12 was added with sodium hydrogen carbonate that does not contain silicon impurities.

  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, using this molding powder, 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 × length of 15 mm are produced by a powder pressure molding method, and each molded body is further produced. Was fired in the atmosphere at 1400 ° C. for 4 hours to obtain a sample for evaluation of a sintered body.

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 (0.3 <x ≦ 0.9 ) 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 peak intensity ratios before and after the thermal decomposition test were set as A ₀ and A ₁ , respectively, and the thermal decomposition rates of the respective samples were obtained by the following formulas and shown in Table 1.

  Regarding the coefficient of thermal expansion, the coefficient of thermal expansion of 20 ° C. to 800 ° C. of the sample of the cylindrical sintered body was measured according to JIS R1618 under the condition of a temperature rising rate of 20 ° C./min.

  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.

As shown in Table 1, Sample No. which is a sample outside the scope of the present invention. Nos. 15 and 16 had a thermal decomposition rate of 50% or more and insufficient heat resistance. Sample No. which is a sample outside the scope of the present invention. 1 had a large thermal expansion coefficient of 4.0 × 10 ⁻⁶ / ° C.

  On the other hand, sample no. 2-6, 9, 10, 13, and 14 had high thermal decomposition resistance and a small thermal expansion coefficient.

  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 in a mixed raw material having a composition of 1 to 16, respectively, and 20 parts by mass of solvent water and a pore agent are added. 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 was 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 and dried sufficiently, followed by firing at 1400 ° C. for 4 hours in the atmosphere, and a porosity of 35%. A sample for evaluation of the honeycomb structure was used.

  Next, each honeycomb structure was subjected to a heat resistance test at 1300 ° C. for 5 hours in the atmosphere, and then examined for dimensional change of the entire honeycomb structure, deformation of the outer peripheral wall and partition walls, and melting. .

  As a result, among the honeycomb structures, sample No. 1 to which silica raw material was added was added. In the honeycomb structure using the materials 7 and 8, a part of the partition walls was melted. On the other hand, sample No. In Nos. 2 to 6 and 9 to 14, 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, sample no. 11 and 12, the compressive strength was as low as 6 and 4 MPa. On the other hand, sample no. In 2-6, 9, 10, 13, and 14, the compressive strength was 12 MPa or more.

It is the perspective view which showed an example 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 (2)

Other metal components excluding Al, Mg, Ti and O, which are composed of a solid solution whose composition formula is represented by Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ (0.3 ≦ x ≦ 0.9) The heat-resistant ceramic member characterized by having an oxide conversion amount of 1.0% by mass or less. The heat resistant ceramic member according to claim 1, wherein x is 0.3 ≦ x ≦ 0.8.

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