JP2010116289A - Method for producing aluminum titanate ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a method whereby an aluminum titanate ceramic can be produced, provided that the ceramic shows a low thermal expansion, high mechanical strengths and little dimensional change upon firing. <P>SOLUTION: The method for producing the aluminum titanate ceramic comprises steps of: exposing a precursor mixture containing a titanium source powder, an aluminum source powder, a magnesium source powder and a silicon source powder to a temperature ranging from 900 to 1,350°C for at least 3 hr, provided that a temperature change per hr falls within the range of from -50 to +50°C/hr; and subsequently raising the temperature to 1,400°C or higher for firing. Here, in the oxide components contained in the precursor mixture, a silicon source is an amorphous aluminosilicate having a melting point of 800-1,350°C and accounting for 2-8 wt.% of oxide components contained in the precursor mixture. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing an aluminum titanate ceramic, and more specifically, a precursor mixture containing a titanium source powder, an aluminum source powder, a magnesium source powder, and a silicon source powder is fired under predetermined conditions to produce an aluminum titanate ceramic. It relates to a method of manufacturing.

  An exhaust gas filter for a diesel engine is a filter that filters and collects soot contained in the exhaust gas, and is generally made of a ceramic sintered body having a high porosity. When a certain amount of soot is collected in the filter made of this porous ceramic, the gas flow resistance increases, and therefore, a regeneration process is performed in which the clogged soot is burned on the filter. At this time, a rapid temperature rise occurs in the filter, and the filter is exposed to a high temperature and is subjected to a large thermal shock. For this reason, exhaust gas filter materials for diesel engines are required to have high thermal shock resistance and small characteristic deterioration due to thermal fatigue.

Aluminum titanate (Al ₂ TiO ₅ ) is known as a ceramic having a high melting point and low thermal expansion, and has attracted attention as an exhaust gas filter material. However, aluminum titanate is generally low in mechanical strength and has a problem of poor thermal stability near 900 to 1100 ° C close to the operating temperature range of the filter (decomposes into TiO ₂ and Al ₂ O ₃ ). It has become. In conventional aluminum titanate, various additive elements have been added, and attempts have been made to improve mechanical strength and thermal stability while maintaining low thermal expansion.
Patent 3612943 JP 11-060240 A JP 2005-534474 A Japanese Patent Laid-Open No. 06-040766

  In order to realize the low thermal expansion property of aluminum titanate, heat treatment at high temperature is indispensable. However, it is known that heat treatment at high temperature impairs the mechanical strength of aluminum titanate. As a method for producing porous aluminum titanate, Japanese Patent No. 3612943 (Patent Document 1) discloses a method in which a raw material powder such as titanium oxide, aluminum oxide, silicon dioxide or the like is directly molded together with an organic binder to obtain a porous body by a single heat treatment. A method for obtaining a porous sintered body from an aluminum titanate powder has been proposed in JP-A-11-060240 (Patent Document 2) and the like. However, when the compacts obtained by these methods are sintered at a high temperature, low thermal expansion can be realized, but there is a problem that the volume change accompanying the sintering shrinkage is large and the mechanical strength is remarkably lowered.

  There is also a method of suppressing the sintering shrinkage rate by using coarse particles of aluminum titanate in order to suppress the sintering shrinkage of aluminum titanate. However, the coarse particles of aluminum titanate are poor in shape retention and sinterability, and in the sintering of porous bodies, there is a problem that the molded body collapses during the sintering or large cracks are likely to occur in the sintered body. is there.

In order to achieve low thermal expansion and high mechanical strength at once with aluminum titanate, mullite (3Al ₂ O ₃ · 2SiO ₂ , melting point = 1850 ° C) and cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ , melting point = 1460 ° C) is proposed in Japanese Patent Application Laid-Open No. 2005-534474 (Patent Document 3) and Japanese Patent Application Laid-Open No. 06-040766 (Patent Document 4). However, these materials are ceramics with the same or low melting point as aluminum titanate (melting point = 1860 ° C). Even if these composite materials are sintered at high temperatures, the dimensional change due to sintering shrinkage remains large. .

  Therefore, the present inventors have intensively studied to develop a method capable of producing an aluminum titanate-based ceramic with small dimensional change by sintering while realizing low thermal expansion and high mechanical strength, and as a result, the present invention has been achieved. .

  That is, the present invention provides a precursor mixture containing a titanium source powder, an aluminum source powder, a magnesium source powder and a silicon source powder at a temperature range of 900 to 1350 ° C. and a temperature change per hour of −50 to + 50 ° C./h. After holding for 3 hours or more, the temperature is raised to a temperature of 1400 ° C. or higher, and when firing at the same temperature, among the oxide components contained in the precursor mixture, the weight ratio of the silicon source is 2 to 8%, Aluminum titanate ceramics with high dimensional accuracy during sintering while achieving both low thermal expansion and high mechanical strength by using an aluminosilicate with an amorphous silicon source and a melting point of 800-1350 ° C It is to provide a method that can be used.

  The method for producing an aluminum titanate-based ceramic of the present invention comprises a precursor mixture containing a titanium source powder, an aluminum source powder, and a silicon source powder at a temperature range of 900 to 1350 ° C., and the temperature change per hour is −50 to + 50 ° C. After maintaining for 3 hours or more at / h, the temperature is raised to a temperature of 1400 ° C. or higher, and the aluminum titanate-based ceramics is fired at the same temperature. Of the oxide components contained in the precursor mixture, It is characterized by being an amorphous aluminosilicate having a weight ratio of 2 to 8%, an amorphous silicon source, and a melting point of 800 to 1350 ° C.

  The precursor mixture in the method of the present invention may further contain a magnesium source powder or an iron source powder, and particularly preferably further contains a magnesium source powder for the purpose of improving the heat stability of the aluminum titanate.

  In the aluminum titanate-based ceramics according to the present invention, ceramics having a melting point higher than that of aluminum titanate may be uniformly dispersed in the aluminum titanate matrix as fine particles having a particle diameter of 0.1 to 20 μm. When the high melting point ceramic fine particles are uniformly dispersed in the aluminum titanate, the sintering shrinkage of the aluminum titanate can be suppressed, and the mechanical strength of the aluminum titanate ceramic can be greatly improved.

Examples of ceramics having a higher melting point than aluminum titanate dispersed in the aluminum titanate matrix include aluminum oxide (α-Al ₂ O ₃ ), zirconium oxide (ZrO ₂ ), and silicon carbide (SiC). In particular, it is preferable to contain aluminum oxide.

An aluminosilicate having a melting point of 800 to 1350 ° C. is used as the silicon source of the aluminum titanate-based ceramics in the present invention. In particular, SiO ₂ = 70 to 80%, Al ₂ O ₃ = 5 to 15 by weight ratio of the oxide. %, (Na ₂ O + K ₂ O) = 5 to 25%, MgO = 0 to 3.0%, and (CaO + SrO + BaO) <4.0%, it is desirable that the amorphous aluminosilicate.

  As described in claim 3 of the present invention, it is known that when aluminum oxide or titanium oxide is present in aluminum titanate, the thermal stability of aluminum titanate is remarkably lowered. However, when an aluminum titanate ceramic is produced by the manufacturing method according to claims 1 and 4 of the present invention, aluminum oxide is coated with amorphous aluminosilicate which is a silicon source, and it is not in direct contact with aluminum titanate. Therefore, it has the effect that good thermal stability can be obtained.

A desirable composition for carrying out the present invention is the composition formula: Al _{2 (1-x)} Mg _x Ti _{1 + x} O ₅ -aAl ₂ O ₃ -bSiO ₂ , x = 0.05 to 0.30, a = 0.1 to 0.3, b = 0.05 to 0.25.

  The present invention also provides a ceramic plastic kneaded material containing the aluminum titanate ceramic powder according to claim 4 and an organic binder, molded into a predetermined shape, and the molded ceramic plastic kneaded material. An aluminum titanate sintered body sintered at an arbitrary temperature is also provided.

  According to the present invention, an aluminum titanate-based ceramic that produces a sintered body having a small coefficient of thermal expansion, excellent mechanical strength and heat stability, small sintering shrinkage, and small dimensional change before and after sintering is manufactured. can do.

  In the method for producing an aluminum titanate ceramic according to the present invention, first, a precursor mixture containing a titanium source powder, an aluminum source powder, and a silicon source powder is prepared.

  The titanium source powder constituting the precursor mixture refers to a powder of a compound that can be a titanium component constituting the aluminum titanate. Examples of such a titanium source powder include titanium (IV) oxide, titanium (III) oxide, and titanium (II) oxide, and titanium (IV) oxide is preferably used. Examples of the crystal type of titanium oxide (IV) include anatase type, rutile type, brookite type, and the like, and may be amorphous.

  In addition, examples of the titanium source powder include a powder of a compound that is led to titania (titanium oxide) by firing alone in the air. Examples of such compounds include titanium salts, titanium alkoxides, titanium hydroxide, titanium nitride, titanium sulfide, and titanium metal. Specific examples of the titanium salt include titanium trichloride, titanium tetrachloride, titanium sulfide (IV), titanium sulfide (VI), titanium sulfate (IV), and the like. Specific examples of the titanium alkoxide include titanium (IV) ethoxide, titanium (IV) methoxide, titanium (IV) t-butoxide, titanium (IV) isobutoxide, titanium (IV) n-propoxide, titanium (IV) tetraiso Examples thereof include propoxides and chelating products thereof.

  As the titanium source powder in the present invention, anatase type or rutile type titanium oxide (IV) which is inexpensive and easily available industrially is preferable. In addition, the average particle size of the titanium oxide powder is preferably 0.1 to 50 μm from the viewpoint of industrial availability, uniform mixing with other raw material powders, improved reactivity, etc., and 0.1 to 1 μm. It is particularly preferred that The particle size referred to in the present invention is a value measured by a laser diffraction method, and the average particle size is a particle whose cumulative mass of particles is 50% of the total weight measured in the measured particle size. Size (d50).

  Examples of the aluminum source powder constituting the precursor mixture include alumina (aluminum oxide) powder. Examples of the crystal type of alumina include γ type, δ type, θ type, and α type, and may be amorphous. The aluminum source powder is preferably α-type alumina.

  Examples of the aluminum source powder include a powder of a compound that is led to alumina by firing alone in air. Examples of such a compound include an aluminum salt, aluminum alkoxide, aluminum hydroxide, and metal aluminum. The aluminum salt may be an inorganic salt with an inorganic acid or an organic salt with an organic acid. Specific examples of the aluminum inorganic salt include aluminum nitrates such as aluminum nitrate and ammonium nitrate, and aluminum carbonates such as ammonium aluminum carbonate. Examples of the aluminum organic salt include aluminum oxalate, aluminum acetate, aluminum stearate, aluminum lactate, and aluminum laurate. Specific examples of the aluminum alkoxide include aluminum isopropoxide, aluminum ethoxide, aluminum sec-butoxide, aluminum tert-butoxide and the like. Examples of the crystal type of aluminum hydroxide include a gibbsite type, a bayerite type, a norosotrandite type, a boehmite type, and a pseudoboehmite type, and may be indefinite (amorphous). Examples of the amorphous aluminum hydroxide include an aluminum hydrolyzate obtained by hydrolyzing an aqueous solution of a water-soluble aluminum compound such as an aluminum salt or an aluminum alkoxide.

  The aluminum source powder is preferably alumina powder, particularly preferably α-type alumina.

In the present invention, when alumina particles are precipitated on aluminum titanate, the amount of aluminum source in the raw powder is set to the stoichiometric composition of aluminum titanate (Al ₂ TiO ₅ or Al _{2 (1-x)} Mg _x Ti _{1+ x} O ₅ ) may be added in excess. In this case, when the size of the alumina powder used as the raw material is increased, the size of the alumina particles contained in the aluminum titanate ceramic of the present invention also tends to be increased.

  For the reasons described above, the average particle size of the alumina powder used in the present invention is preferably 0.1 to 50 μm, and particularly preferably 1 to 30 μm from the viewpoint of uniform mixing with other raw material powders. When the particle size of the alumina powder exceeds 50 μm, the reactivity with other raw material powders decreases, and depending on the amount of alumina added, the size of the alumina particles contained in the sintered aluminum titanate-based ceramics is 20 μm. May be exceeded. If the size of alumina particles contained in the aluminum titanate ceramic exceeds 20 μm, the effect of suppressing the sintering shrinkage of aluminum titanate and the effect of improving the strength cannot be obtained.

  The silicon source powder constituting the precursor mixture is an aluminosilicate powder that is amorphous and has a melting point of 800 to 1350 ° C., and includes, for example, crystalline silica such as silicon dioxide and silicon monoxide. Make it not exist.

  In the present invention, for the purpose of improving the mechanical strength and heat stability of the aluminum titanate ceramics, it is characterized by using an aluminosilicate powder that is amorphous and has a melting point of 800 to 1350 ° C. as the silicon source powder. It is. The melting point of this aluminosilicate is preferably 900 to 1100 ° C, and particularly preferably an aluminosilicate having a yield point of 700 to 1000 ° C. In the present invention, the melting point of aluminosilicate is the temperature (softening point) at which an endothermic peak is observed in a differential thermal analyzer (DTA), and the yield point is the glass due to softening of the glass in the measurement of the thermal expansion curve of aluminosilicate. This indicates the temperature at which the thermal expansion cannot be detected and appears as the inflection point of the thermal expansion curve.

  When an aluminosilicate having a melting point of less than 800 ° C. is used, the heat resistance stability of the aluminum titanate is significantly lowered. Further, when an aluminosilicate having a melting point exceeding 1350 ° C. or an aluminosilicate in which crystalline silica remains is used, the effect of improving the heat stability and the thermal shock resistance tends to be reduced.

  The amount of silicon source powder used is preferably in the range of 2 to 8% by weight, particularly preferably in the range of 2 to 4%, among the oxide components contained in the precursor mixture. When the silicon source is less than 2% of the oxide component contained in the precursor mixture, the heat resistance stability and mechanical strength of the aluminum titanate-based ceramics are lowered, and when it exceeds 8% Sintering shrinkage increases, and aluminum titanate ceramics with high dimensional accuracy cannot be obtained, and the coefficient of thermal expansion tends to increase.

Further, the silicon source used in the present invention is amorphous, and the weight ratio of oxide is SiO ₂ = 70 to 80%, Al ₂ O ₃ = 5 to 15%, (Na ₂ O + K ₂ O) = 5 to 25 %, MgO = 0 to 3.0%, and (CaO + SrO + BaO) <4.0% are preferred. By using such a silicon source powder, an aluminum titanate-based ceramic excellent in heat resistance stability and mechanical strength can be obtained.

  Examples of the silicon-containing oxide having the same composition include natural minerals such as alkali feldspar, but these are a mixture of a plurality of oxides including crystalline silica. The melting point and yield point of these natural minerals are generally higher than the temperature range of the present invention, and when used as a raw material, crystalline silica may remain at the grain boundaries of the aluminum titanate ceramics. Crystalline silica may cause a phase transformation accompanied by a large volume change at low temperature like cristobalite, which lowers the strength characteristics of aluminum titanate ceramics. For this reason, it is not preferable to use natural minerals such as alkali feldspar as the silicon source. The amount of crystalline silica contained in the silicon source powder is preferably 0.1% or less by weight with respect to aluminum titanate.

In the aluminosilicate described above, when SiO ₂ is less than 70% by weight, the heat resistance stability tends to decrease, and when it exceeds 80%, crystalline silica tends to precipitate. The weight ratio of SiO ₂ in the aluminosilicate described above is more preferably in the range of 70 to 75%.

Further, in the aluminosilicate described above, when Al ₂ O ₃ is less than 5% and / or Na ₂ O + K ₂ O exceeds 20%, the chemical stability of the silicon-containing phase tends to decrease, and Al ₂ When O ₃ exceeds 15% and / or when Na ₂ O + K ₂ O is less than 10%, crystalline silica and silicon-containing crystalline compounds having a melting point of 1350 ° C. or more (for example, mullite) tend to precipitate. is there. The weight ratio of Al ₂ O ₃ in the aluminosilicate described above is preferably 7 to 12%, and the weight ratio of Na ₂ O + K ₂ O is preferably 10 to 20%, and the weight ratio of Na ₂ O and K ₂ O is and more preferably Na ₂ O / in _{(Na 2 O + K 2 O} ) is 0.10 to 0.60.

  In the aluminosilicate described above, inevitable impurities may be included within a range in which the melting point and viscosity of the glass are not changed. Inevitable impurities include Li, B, F, Mg, P, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Nb, Sn, Ba, La, Ta, Ce, Pb, Bi and the like can be mentioned. The total amount of these impurities is preferably 5% or less in terms of oxide (F and P are in terms of pure substances). In particular, Mg, Ca, Sr, Ba greatly changes the properties of the glass, so Mg in terms of oxide is preferably 3.0% or less, (Ca + SrO + BaO) is preferably 4% or less, (Ca + SrO + BaO) is more preferably 3% or less.

  In addition, the average particle size of the silicon source powder used in the present invention is preferably 0.1 to 50 μm from the viewpoints of industrial availability, uniform mixing with other raw material powders, and improved reactivity. And 0.5 to 20 μm is particularly preferable.

The precursor mixture in the present invention is made of magnesium (Mg) or iron (Fe) separately from the titanium source, aluminum source and silicon source for the purpose of improving the heat resistance stability of aluminum titanate and lowering the sintering temperature. Raw material powder may be included, and it is particularly preferable that magnesium source powder is further included. Here, the magnesium source powder is a powder of a compound serving as a magnesium component constituting aluminum magnesium titanate (Al _{2 (1-x)} Mg _x Ti _{1 + x} O ₅ ), for example, magnesia (magnesium oxide) powder. Is mentioned.

  Examples of the magnesium source powder include compounds that are led to magnesia by firing alone in air. Examples of such a compound include magnesium salt, magnesium alkoxide, magnesium hydroxide, magnesium nitride, and magnesium metal. Specific examples of magnesium salts include magnesium chloride, magnesium perchlorate, magnesium phosphate, magnesium pyrophosphate, magnesium oxalate, magnesium nitrate, magnesium carbonate, magnesium acetate, magnesium sulfate, magnesium citrate, magnesium lactate, magnesium stearate, Examples include magnesium salicylate, magnesium myristate, magnesium gluconate, magnesium dimethacrylate, and magnesium benzoate. Specific examples of the magnesium alkoxide include magnesium methoxide and magnesium ethoxide.

As the magnesium source powder, a compound having both a magnesium source and an aluminum source, and a magnesium source and a titanium source can be used. Examples of such compounds include magnesia spinel (MgAl ₂ O ₄ ), magnesium titanate (MgTiO ₃ , Mg ₂ TiO ₅ ) and the like, and particularly magnesia spinel is inexpensive and easily available industrially. It is preferable as the magnesium source powder of the present invention.

  In addition, the average particle size of the magnesium source powder used in the present invention is preferably 0.1 to 50 μm from the viewpoint of industrial availability, uniform mixing with other raw material powders, and reactivity improvement. And 0.5 to 20 μm is particularly preferable.

Still further, the composition of the aluminum titanate ceramic according to the present invention is an aluminum titanate ceramic represented by the composition formula: Al _{2 (1-x)} Mg _x Ti _{1 + x} O ₅ -aAl ₂ O ₃ -bSiO ₂ . X = 0.05 to 0.30, a = 0.1 to 0.3, b = 0.05 to 0.20 are preferably satisfied, and x = 0.10 to 0.20, a = 0.1 to 0.3, and b = 0.05 to 0.12 are particularly satisfied. preferable. For example, when the weight ratio of the silicon source used in Example 1 is 2 to 4%, the above b is in the range of 0.05 to 0.10.

  The precursor mixture in the present invention may contain additive powders other than titanium, aluminum, magnesium and silicon as long as the effects of the present invention are not impaired. Examples of additives include Li, B, F, P, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, Y, Zr, Nb, Sn, Ba, La, Ta, Ce, Pb , Bi, etc., and the total amount of these impurities is preferably 3% or less in terms of oxide (F and P are in terms of pure substances).

  Such a precursor mixture can be obtained, for example, by mixing a titanium source powder, an aluminum source powder and a silicon source powder, or a titanium source powder, an aluminum source powder, a silicon source powder and a magnesium source powder. Mixing may be performed by either a dry mixing method or a wet mixing method, but it is preferable to use a method in which a compound containing a metal element can be mixed more uniformly. Is more preferable. In this case, examples of the mixing apparatus include apparatuses such as a ball mill, a V-type mixer, a vibration mill, an attritor, a dyno mill, and a dynamic mill.

  Among the above-described mixing methods, since it is easy to implement on an industrial scale, a method of simultaneously mixing and pulverizing the precursor powder with a vibration mill is preferably used. Mixing may be carried out in a continuous manner or in a batch manner, but it is preferably carried out in a continuous manner from the viewpoint that implementation on an industrial scale is prepared.

  As the pulverization container, one made of a metal material such as stainless steel is usually used, and the inner surface may be coated with a fluorine resin, a silicon resin, a urethane resin, or the like.

  Examples of the grinding media include alumina beads and zirconia beads having a particle diameter of 1 to 100 mm, preferably 5 to 50 mm. Alumina beads are preferably used from the viewpoint of contamination with impurities.

In pulverization, additives such as a dispersant, a pulverization aid, and a peptizer may be added.
Examples of the grinding aid include alcohols such as methanol and ethanolpropanol, glycols such as propylene glycol, polypropylene glycol and ethylene glycol, amines such as triethanolamine, and higher fatty acids such as palmitic acid, stearic acid and oleic acid. Carbon materials such as carbon black and graphite can be used, and these can be used alone or in combination of two or more.

  When using the additive, the total amount used is usually 0.1 to 10 parts by weight, preferably 0.5 per 100 parts by weight of the total amount of raw material powder (that is, titanium source powder, aluminum source powder, silicon source powder and magnesium source powder). -5 parts by mass, more preferably 0.75-2 parts by mass.

  Moreover, when using an additive, you may remove an additive from the precursor mixture after mixing. For example, when an additive that can be eliminated by heating in the atmosphere is used, the additive may be removed by heating in the atmosphere. The heating temperature at this time is usually 500 ° C. or lower.

  In the present invention, the precursor mixture may be molded before firing. As a method of forming the precursor mixture, a normal method, for example, a method of pressurizing in a mold using a single screw press, a tableting machine, etc., after adding a liquid component such as water to the precursor mixture, granulation And a method of forming and drying using a machine, an extruder, and the like.

  In the present invention, after the precursor mixture described above is held at a temperature range of 900 to 1350 ° C. at a temperature change per hour of −50 to + 50 ° C./h for 3 hours or more, preferably 4 hours or more, 1400 The temperature is raised to a temperature of ℃ or higher to obtain an aluminum titanate ceramic. The temperature change per time referred to in the present invention means, for example, when the temperature change when held at 3 hours for 50 ° C / h is 150 ° C in the temperature range of 900-1350 ° C, and 900-1350 ° C While the temperature range is maintained, the precursor mixture may be maintained at a constant temperature unless the temperature range is deviated, the temperature increase rate is changed at any time, and the temperature increase and decrease are repeated alternately. May be. When holding the precursor mixture in the temperature range of 900 to 1350 ° C, the temperature change per hour is normally held at -50 to + 50 ° C / h for 3 hours or more, and the temperature change is 0 ° C / h for 3 hours or more. It is preferable to hold.

  In the above temperature range, after maintaining the temperature change per hour at -50 to + 50 ° C / h for 3 hours or more, raise the temperature to 1400 ° C or more, usually less than 1600 ° C, and heat-treat at the same temperature The target aluminum titanate ceramic can be obtained. The time required for the heat treatment may be a time sufficient for the precursor powder to transition to the aluminum titanate-type ceramic, and varies depending on the type of raw material powder and heat treatment conditions, but is usually 10 minutes to 24 hours, preferably 3 hours or more and less than 12 hours.

  In the method for producing an aluminum titanate-based ceramic of the present invention, when the temperature change per hour is kept at −50 to + 50 ° C./h for 3 hours or more in the temperature range of 900 to 1350 ° C. The aluminosilicate which is a silicon source contained in the molten metal melts, and the aluminosilicate melt uniformly spreads in the precursor powder by capillary action. Due to this phenomenon, the raw material powder aggregates, and a more uniform and efficient generation reaction of aluminum titanate proceeds, and alumina that is uniformly dispersed in the aluminum titanate ceramic obtained by the above method. Each particle becomes coated with an aluminosilicate layer. Alumina particles are known to act as accelerators for the thermal decomposition reaction of aluminum titanate and significantly deteriorate their heat resistance stability. However, by the above manufacturing method, the alumina particles are uniformly distributed in the aluminosilicate layer. It became possible to coat, and it was found that the effect of promoting thermal decomposition of alumina particles can be suppressed by this aluminosilicate coating layer, and the present invention has been completed.

  Even if the precursor powder is held at a temperature lower than 900 ° C., which is lower than the above temperature range of 900 to 1350 ° C., the aluminosilicate contained in the precursor mixture does not melt or even if melted, the melt remains between the particles. In other words, the distribution of aluminosilicate in the aluminum titanate ceramics becomes non-uniform. Even when the precursor powder is held at a temperature of 1350 ° C. or higher, the formation reaction of aluminum titanate proceeds in parallel with the dissolution of the aluminosilicate. For this reason, even if the precursor powder is held outside the temperature range of 900 to 1350 ° C., the aluminosilicate is not uniformly distributed in the obtained aluminum titanate ceramic, and is present in the aluminum titanate matrix. The alumina particles are no longer covered with the aluminosilicate layer, the heat resistance stability is lowered, and the strength of the resulting aluminum titanate ceramic is also lowered.

  In the above-described method for producing an aluminum titanate-based ceramic, after holding the precursor powder in a temperature range of 900 to 1350 ° C., heat treatment is performed at 1400 ° C. or higher to generate aluminum titanate from the precursor powder. At this time, when the heat treatment temperature is 1500 ° C. or more, it is confirmed that when the precursor powder contains magnesium, the magnesium is dissolved into the glass layer, and the composition of the aluminum titanate phase changes. May not be obtained. For this reason, the heat treatment temperature of 1400 ° C. or higher is preferably 1400 ° C. or higher and lower than 1500 ° C., more preferably 1430 ° C. or higher and 1470 ° C. or lower.

  When raising the temperature to the above temperature range and maintaining the atmosphere is usually in the air, the raw material powder to be used, that is, the type and usage ratio of the titanium source powder, aluminum source powder, magnesium source powder and silicon source powder Depending on the case, it may be fired in an inert gas such as nitrogen gas or argon gas, or may be fired in a reducing gas such as carbon monoxide gas or hydrogen gas. Moreover, you may heat up in the atmosphere which made water vapor partial pressure low.

  The temperature rise is usually performed using a normal heating furnace such as a tubular electric furnace, a box-type electric furnace, a tunnel furnace, a far-infrared furnace, a microwave heating furnace, a shaft furnace, a reflection furnace, a rotary furnace, or a roller hearth furnace.

Thus, a fired product of the aluminum titanate ceramic is obtained.
The fired product is usually obtained in the form of a lump or sintered body, and the ceramic fired product powder can be obtained by pulverizing and classifying the lump or sintered ceramic fired product. Crushing can be performed using a normal crusher such as hand crushing, mortar, ball mill, vibration mill, planetary mill, medium stirring mill, pin mill, jet mill, hammer mill, roll mill, and the like. The ceramic powder obtained by crushing may be classified by a usual method. Since the ceramic powder thus obtained has a generally spherical shape, the handling container or the like is not worn when the ceramic powder is handled.

  If the ceramic powder is molded and sintered, it can be suitably used for a honeycomb for exhaust gas filters, a catalyst carrier and the like. When used as a raw material powder for a honeycomb or a catalyst carrier, the average particle diameter is preferably adjusted to d50 = 10 to 40 μm, more preferably d50 = 10 to 30 μm. This is because when the average particle size is less than 10 μm, the shrinkage accompanying the sintering of the honeycomb becomes extremely large, and the honeycomb is deformed. This is because the molded body collapses during the process.

When the fired product obtained by the above-described method for producing an aluminum titanate ceramic is pulverized into a powder having the above particle size distribution, the BET specific surface area of the powder is 0.2 to 0.5 m ² / g, and the pore volume is 1.5 to 3.0 mm ³ / g. The pore volume mentioned here is a value when pores existing on the surface of the powder are measured by a mercury intrusion method, and the smaller the pore volume value, the more dense and baked the powder. When compared with the same particle size distribution, the pore volume of the powder of the fired product obtained by the above production method is compared with the pore volume of the powder that did not hold the precursor mixture in the temperature range of 800-1350 ° C. When the honeycomb is made from these powders, the dimensional change due to sintering is smaller in the powder having a small pore volume.

Further, the ceramic powder may be granulated by a known powder molding technique.
Furthermore, the present invention provides a process for producing a ceramic plastic kneaded material containing the above-mentioned aluminum titanate ceramic powder and an organic binder, and molding the ceramic kneaded clay into a predetermined shape, and the formed ceramic plastic kneaded material at an arbitrary temperature. In addition, an aluminum titanate sintered body sintered in step 1 is also included.

  In order to use the aluminum titanate-based ceramics of the present invention as an exhaust gas filter material, a porous sintered body having low ventilation resistance is required, and usually a porous body having communication holes with a porosity of 30% or more and 60% or less. A quality sintered body is preferably used.

  A well-known technique can be used as a manufacturing method of said porous aluminum titanate ceramic sintered body. As the pore-forming agent used in the present invention, a conventionally known pore-forming agent can be used without particular limitation. As the pore-forming agent, for example, graphite, foamed resin, water-absorbing resin, wheat flour, starch, phenol resin, polymethyl methacrylate, polyethylene, polyethylene terephthalate, or the like is used.

  Examples of the binder include hydroxypropyl, methylcellulose, hydroxyethylcellulose, and polyvinyl alcohol. Examples of the dispersant include ethylene glycol, dextrin, fatty acid tartaric acid, polyalcohol and the like.

  Examples of the dispersion medium for dispersing the ceramic powder and the organic binder described above include water and wax. Among these, water is preferably used for reasons such as a small volume change during drying, less gas generation, and ease of handling.

  The above-mentioned forming raw materials are mixed and kneaded to produce a ceramic plastic kneaded clay and then molded into a predetermined shape. As an apparatus for molding the plastic kneaded clay, for example, a combination of a kneader and an extrusion molding machine And a continuous kneading extruder.

  Such an aluminum titanate-based ceramic of the present invention has both low thermal expansion, high heat stability, and excellent mechanical strength, and the powder of the present invention has little sintering shrinkage during sintering. The molded body produced in this way exhibits high dimensional accuracy. The aluminum titanate ceramic powder of the present invention can be suitably used as a raw material for a filter or a honeycomb for a catalyst carrier used for exhaust gas purification of an internal combustion engine such as a diesel engine.

  EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples.

The aluminum titanate conversion rate [AT conversion rate] of the aluminum titanate-based ceramics obtained in each example is a peak [titania-rutile phase (110) plane appearing at 2θ = 27.4 ° in the powder X-ray diffraction spectrum. integrated intensity of] and (I [TiO _2]), because the peak appearing at the position of 2 [Theta] = 33.7 ° [integrated intensity of aluminum magnesium titanate phase (230) plane] [I [AT]], from the formula (1) Calculated.

AT conversion rate (%) = I [AT] / (I [AT] + I [TiO ₂ ]) × 100 (1)
The heat resistance stability refers to the residual rate of the aluminum titanate crystal phase after holding the aluminum titanate-based ceramic in a temperature range of 900 to 1100 ° C. for an arbitrary time. In the present invention, heat stability evaluation was obtained by obtaining a sample for thermal decomposition evaluation by holding aluminum titanate ceramic powder in a box-type electric furnace at 950 ° C. for 48 hours in the air. The constituent phase of the sample for pyrolysis evaluation is measured by powder X-ray diffraction spectrum measurement (XRD) to see the change in AT conversion rate before and after heat treatment. It means that the thermal decomposition rate calculated from 1.0 is 1.0% or less.

Decomposition rate (%) = 100-I [AT] / (I [AT] + I [TiO ₂ ]) x 100 (2)
In the present invention, the produced aluminum titanate-based ceramic is pulverized into a powder having a particle size distribution of d50 = 15 to 30 μm. Polyethylene particles (d50 = 23 μm) are used as pore-forming agents with respect to 100 parts by mass of the ceramic powder. ) 10 parts by weight, 7.5 parts by weight of methyl cellulose as a binder, 9.3 parts by weight of polyoxyalkylene alkyl ether as a surfactant, 0.8 parts by weight of glycerin as a lubricant to form a molding raw material, and 38 parts by weight of water as a dispersion medium After adding the part, the kneaded material was kneaded to prepare a kneaded material, and the kneaded material was extruded to form a honeycomb formed body. The obtained honeycomb formed body was degreased at 400 ° C. in an air atmosphere and sintered at a maximum temperature of 1450 ° C. for 5 hours to obtain a porous honeycomb sintered body.

The thermal expansion coefficient (K ^-1 ) of the aluminum titanate ceramic porous sintered body is about 4 mm x 4 mm x 10 mm from the aluminum titanate ceramic porous sintered body obtained in each example. Using this thermomechanical analyzer (SII Technology Co., Ltd., TMA6300), the thermal expansion curve of the above prismatic sample was measured by raising and lowering the temperature from room temperature to 1000 ° C at a rate of 600 ° C / h. The expansion coefficient between room temperature and 1000 ° C. was calculated.

Example 1
47.3% by mass of aluminum oxide (Sumitomo Chemical, AT-50) particles as the aluminum source, 41.0% by mass of titanium oxide (DuPont, R-900) as the titanium source, and magnesia spinel as the magnesium source (Made by Saint-Gobain) 6.2% by mass, glass frit (SiO ₂ = 77.9%, Al ₂ O ₃ = 9.7%, Na ₂ O = 3.1%, K ₂ O = 7.5%, CaO = 2.7) %, MgO = 2.8%) particles were used at 5.6% by mass. The glass frit used had a melting point of 948 ° C. and a yield point of 768 ° C. In this case, when expressed by the composition formula: Al _{2 (1-x)} Mg _x Ti _{1 + x} O ₅ -aAl ₂ O ₃ -bSiO ₂ , x = 0.08, a = 0.16, and b = 0.14. 10 kg of these raw material powders were put together with 5 kg of alumina beads (diameter 15 mm) into an alumina pulverization container (internal volume 50 L), and the pulverization container was mixed and pulverized in a vibration mill for 30 minutes to obtain a precursor mixture. The obtained precursor powder was heated to 1300 ° C at 300 ° C / h in an electric furnace, held at 1300 ° C for 3.5 hours, then heated again to 1450 ° C at 300 ° C / h, and then at 1450 ° C for 3.5 hours The target aluminum titanate ceramic fired product was obtained by holding and firing. The obtained ceramic fired product was pulverized by an alumina disk mill and classified by a vibrating sieve to obtain a powder having d50 = 27 μm.

As a result of analyzing the powder prepared in Example 1 by powder X-ray diffraction, the AT conversion rate of this ceramic powder was 100%. As the crystalline phase composing this powder, only aluminum magnesium titanate (Al _1.84 Mg _0.08 Ti _1.08 O ₅ ) and alumina (Al ₂ O ₃ ) were confirmed, and a diffraction peak showing the crystalline phase of SiO ₂ or Si-containing oxide. Was not confirmed. The AT conversion rate after heat-treating this powder at 1100 ° C. for 48 hours remained 100% (decomposition rate was 0%), confirming excellent heat stability. As a result of fine structure observation, the average particle size in the aluminum titanate matrix (observing the cross-sectional structure of the powder with a scanning electron microscope and measuring the size of 200 to 400 alumina particles) was 4 μm. It was confirmed that the amorphous aluminosilicate layer was thinly present at the grain boundaries so as to cover the alumina particles and the aluminum titanate particles.

  Based on 100 parts by mass of the powder prepared in Example 1, 10 parts by mass of polyethylene particles (d50 = 23 μm) as a pore-forming agent, 7.5 parts by mass of methylcellulose as a binder, and 9.3 parts by mass of polyoxyalkylene alkyl ether as a surfactant Part, 0.8 parts by weight of glycerin as a lubricant is added to form a raw material, and 38 parts by weight of water is further added as a dispersion medium, and then kneaded with a kneader to prepare a clay, and the clay is extruded and formed into a honeycomb. The body was made. The honeycomb formed body was dried at 100 ° C. for 12 hours in a dryer, then passed through a degreasing process to remove the binder at 400 ° C. in an air atmosphere in a box-type electric furnace, and then heated to 1450 ° C. at 300 ° C./h. The honeycomb sintered body was obtained by sintering at 1450 ° C. for 5 hours.

The porosity of the obtained honeycomb body measured by the Archimedes method was 42%, and the dimensional change after drying and sintering was 10%. The thermal expansion coefficient of the honeycomb sintered body was 1.6 × 10 ⁻⁶ K ⁻¹ . The analysis results are summarized in Table 1.

(Examples 2-3)
Precursor mixtures were prepared with the compositions described in Table 1, and then fired and ground under the same conditions as in Example 1 to obtain powder. All powders had an AT conversion rate of 100%, and a diffraction peak indicating a crystal phase of SiO ₂ or Si-containing oxide was not confirmed. The decomposition rate after heat-treating this powder at 1100 ° C. for 48 hours was 0% in all cases.

Using the powders of Examples 2 to 3, a porous honeycomb sintered body was produced under the same conditions as in Example 1. In each sample, it was confirmed that the sintering shrinkage rate was 10% or less, the porosity was 40% or more, and the CTE was 2.0 × 10 ⁻⁶ K ⁻¹ or less.

(Comparative Example 1)
In Example 1, a powder and a honeycomb sintered body were produced under the same conditions as Example 1 except that the amount of the silicon source powder was 8.1 wt%. The decomposition rate of the powder was 0%, and the CTE of the honeycomb sintered body was 1.5 × 10 ⁻⁶ K ^−1, which was almost the same result as in Example 1. However, the shrinkage rate was 15% and the porosity was 38%. A large sintering shrinkage was exhibited.

Claims (5)

  Precursor mixture containing titanium source powder, aluminum source powder, magnesium source powder and silicon source powder was held at a temperature range of 900 to 1350 ° C at a temperature change per hour of -50 to + 50 ° C / h for 3 hours or more. Thereafter, the temperature is raised to a temperature of 1400 ° C. or higher, and the aluminum titanate-based ceramics is manufactured by firing at the same temperature. The oxide component contained in the precursor mixture has a silicon source weight ratio of 2 to 8%. A method for producing an aluminum titanate-based ceramics, wherein the silicon source is amorphous and the melting point is 800 to 1350 ° C. aluminosilicate. The silicon source powder is amorphous, and the oxide weight ratio is SiO ₂ = 70 to 80%, Al ₂ O ₃ = 5 to 15%, (Na ₂ O + K ₂ O) = 5 to 25%, MgO = 0 to 2. The method for producing an aluminum titanate-based ceramic according to claim 1, wherein the aluminosilicate is 3.0% and (CaO + SrO + BaO) <4.0%. The method for producing an aluminum titanate-based ceramic according to claim _{2, wherein} the amount of crystalline SiO ₂ contained in the silicon-containing phase is 0.1% or less by weight with respect to aluminum titanate. Aluminum titanate-based ceramics has a composition formula: Al _{2 (1-x)} Mg _x Ti _{1 + x} O ₅ -aAl ₂ O ₃ -bSiO ₂
The method for producing an aluminum titanate-based ceramics according to claim 3, wherein x is from 0.05 to 0.30, a is from 0.1 to 0.3, and b is from 0.05 to 0.20.   A step of producing a ceramic plastic kneaded material containing the aluminum titanate-based ceramic powder according to claim 4 and an organic binder and molding the ceramic plastic kneaded material into a predetermined shape, and the formed ceramic plastic kneaded material at an arbitrary temperature. The manufacturing method of the aluminum titanate sintered compact sinterd by.