JPH0930872A - Porous inorganic material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable ready use of properties of whiskers at their maximum by making mutual bonds of whiskers of an aluminum borate whisker group share aluminum borate constituted by the mutual bonds of whiskers of an aluminum borate whisker group. SOLUTION: (A) Aluminum oxide or an aluminum compound which is heated at <=1,000 deg.C in air to form aluminum oxide is uniformly mixed with (B) a boron oxide (boron trioxide, B2 o3 ) or a compound which is heated at 1,000 deg.C in air to form a boron oxide and (C) a nickel auxiliary such as nickel hydroxide in a powdery state in the molar ratio of Al2 O3 :B2 O3 of 9:2 to 9:6 so that the amount of the component C is 0.1-10wt.% calculated as nickel oxide based on the total of the components A and B. The mixture is compression molded to give a compact having 0.4-1.5g/cm<3> density. The compact is heated in an air atmosphere at 1,100-1,400 deg.C so as to grow crystal of aluminum borate having 9Al2 O3 .2B2 O3 composition in a whisker state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous inorganic material and a method for producing the same, and more particularly, to a reinforcing material for producing a whisker reinforced metal material (WRM), a structural material for high temperature, a heat insulating material, The present invention relates to a porous inorganic material composed of aluminum borate whiskers, which is useful as a friction material, a filter material, and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Ceramic type whiskers made of silicon nitride, silicon carbide, alumina, aluminum borate, potassium titanate, titanium oxide, etc. have mechanical properties, heat resistance, corrosion resistance, heat insulation, abrasion resistance and electrical insulation. Because of its excellent properties, it has come to be used in many fields as it is or as a molded product.

One of the uses of whiskers which has become widespread in recent years is that the whiskers are reinforced by being preformed into a porous molded body called a preform and then the molten metal is press-fitted into the voids. This is a method of obtaining a metal material / WRM.

Preforms made of whiskers have hitherto been produced by a method in which whiskers dispersed in water together with a binder are dehydrated, dried, and fired. However, this method has some problems. First,
Since the whiskers are light and fine, they easily scatter in the process of dispersing in water, and if workers inhale them, it may be harmful to their health, so strict measures against scattering are necessary. Also,
It is unavoidable that needle-shaped whiskers are oriented or unevenly distributed in a specific direction during the process of dehydration molding of the whisker dispersion liquid, and the orientation and uneven distribution are directly inherited by the preform. Needless to say, a uniform reinforcing effect cannot be expected by using a preform in which whiskers are oriented or non-uniformly distributed. Further, the physical properties such as strength and heat resistance of the preform are greatly influenced by the binder used in the production, so that the excellent properties of the whiskers themselves cannot be fully utilized. In addition, it is difficult to obtain a preform having a predetermined density and dimensional accuracy because the volume change from dehydration molding to the end of firing is large.

Similar problems have been pointed out not only in preforms but also in other fields of application in which molded products of whiskers are used, making it difficult to utilize the excellent properties of whiskers.

[0006] Japanese Patent Publication No. 6-33193 discloses a method for producing a hard mullite whisker felt which has succeeded in solving the above-mentioned problems associated with the production of a molded body composed of whiskers for a mullite whisker. Have been. In this production method, a green body is formed from a mixture of AlF ₃ and SiO ₂ , and is formed in an anhydrous SiF ₄ atmosphere for about 7 hours.
By heating to 100 to 950 ° C., rod-like topaz crystals are formed from AlF ₃ and SiO _2.
By heating to 1700 ° C., the above topaz crystals are converted into needle-like single crystal mullite whiskers. According to this method, mullite whiskers are formed by a reaction in the formed base material, and the whiskers are bonded to each other during the formation process, so that the formation of the whisker is completed at the same time when the formation of the whiskers is completed. Therefore, the whisker dewatering with many difficulties is not required, and the product does not have the above-mentioned disadvantages derived from the whisker dewatering.

However, this production method, which is considered to be advantageous, has a problem in that it requires calcination in a toxic anhydrous SiF ₄ atmosphere, so that the cost of equipment and process management increases, and implementation is not easy. Needless to say, the products are limited to those of mullite quality, and their uses are naturally limited. Such a method of causing the generation of whiskers and the formation of the porous molded body to proceed in parallel has not been known for whiskers having other chemical compositions.

[0008]

Therefore, the present invention intends to provide a novel high-physical porous inorganic material consisting only of whiskers, which makes it possible to utilize the excellent properties of whiskers to the maximum extent and easily. To do.

[0009]

The novel porous inorganic material successfully provided by the present invention comprises a group of uniformly and randomly distributed aluminum borate whiskers, each aluminum borate whisker being at least one other place. And the whiskers are bonded to each other by sharing the aluminum borate constituting the whiskers.

That is, in this porous inorganic material, the whiskers are bonded by sharing the aluminum borate forming the individual whiskers without using a binder, and the aluminum borate whiskers grow. It is a bonded state formed by further growth while sharing a part of aluminum borate, which is a constituent of the whiskers, in the contact portion when the whiskers come into contact with other whiskers in the process.

Therefore, in the porous inorganic material according to the present invention, in addition to the bond similar to the fusion between the side surfaces of the whiskers, a whisker prepared in advance in which one whisker crosses through the other whisker is used as a binder. There is a form of bonding that is never seen when glued or sintered in.

Bonds formed entirely by non-oriented, entirely randomly (but uniformly) distributed whiskers, and the bonds between the whiskers are formed by sharing the whisker constituents without the use of a binder. Therefore, the porous inorganic material of the present invention exhibits high strength and high heat resistance and corrosion resistance that are incomparable to those of conventional whisker moldings using a binder and sintered whiskers.

The porous inorganic material according to the present invention comprises an aluminum compound which produces aluminum oxide when heated in aluminum oxide or air, and a boron compound which produces boron oxide when heated in boron oxide or air. , Nickel oxide, nickel or a nickel compound that produces nickel oxide when heated in air is uniformly mixed in a powder state, and the resulting mixture is compressed in a mold to form a molded product. Can be produced by a method of heating aluminum borate whiskers from an aluminum compound and a boron compound.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a porous inorganic material comprising aluminum borate whiskers will be described in detail below.

The aluminum compound used as a raw material is aluminum oxide or an aluminum compound that produces aluminum oxide when heated in air (hereinafter referred to as aluminum oxide precursor). The aluminum compound that can be used as the aluminum oxide precursor is one that produces aluminum oxide by heating in air, preferably at about 1000 ° C. or lower, and preferred specific examples thereof include aluminum hydroxide, aluminum sulfate, aluminum nitrate, and chloride. Aluminum etc.

The boron compound to be reacted with the aluminum compound is boron oxide (boron trioxide.B ₂ O ₃ ) or, preferably, a boron compound which produces boron oxide by heating in air at about 1000 ° C. or lower (hereinafter, boron oxide precursor). For example, boric acid (H ₃ BO ₃ ), tetraboric acid (H ₂ B ₄ O ₇ ), metaboric acid (HBO ₂ ), etc. are used.

Nickel oxide, nickel metal powder, or nickel oxide when heated in air to form whiskers from the reaction of the aluminum compound and boron compound described above at high temperature to form aluminum borate. A nickel compound (hereinafter, collectively referred to as a nickel auxiliary agent) is used. The aluminum compound and the boron compound alone do not form the whiskers of aluminum borate, although it is not clear why the aluminum borate whiskers are formed in the presence of the nickel auxiliary. Specific preferred examples of the nickel compound that can be used as the nickel oxide source include nickel hydroxide, nickel chloride, nickel carbonate and nickel sulfate. These may be used in combination of two or more.

The above-mentioned aluminum compound, boron compound and nickel auxiliary are made into a fine powder and uniformly mixed.
The mixing ratio is such that the molar ratio of Al ₂ O ₃ : B ₂ O ₃ is 9: 2 to 9: 6, and the nickel auxiliary is converted into nickel oxide based on the total amount of the aluminum compound and the boron compound. about 0.1 to 10% by weight (particularly preferably about 1-2 wt%) it is desirable to be in, whereby the composition of _{9Al 2 O 3 · 2B 2 O} 3 heat resistance is particularly excellent It is possible to efficiently form the aluminum borate whiskers having.

Once a homogeneous mixture is obtained, it is placed in a mold and compressed to form. If the molding pressure is increased to increase the density of the molded product, the density of the product also increases. By adjusting the molding pressure, the density is about 0.4-1.5g / cm ³
A product having a porosity of about 86 to 50% can be obtained. In order to obtain a product having a lower density than that, it is effective to mix a powdery organic substance such as starch with a forming raw material. The mixed powdery organic matter is burned off in the subsequent whisker forming step, leaving voids to reduce the product density. By this method, the density is about 0.15 g / cm ³ (porosity is about 95
%) Low density products can be obtained.

The molding aid for facilitating the molding may be used within a range that does not hinder the formation of whiskers, but it is not essential in the production method of the present invention.

The molded product taken out of the mold is transferred to a heating furnace and heated. The atmosphere may be air. When an aluminum oxide precursor or a boron oxide precursor is used as a raw material compound, an oxide is generated from the precursor during the heating process. The temperature required to produce aluminum borate whiskers from aluminum oxide and boron oxide is about 1100-14.
00 ° C. At this temperature, the boron oxide vaporizes considerably, so that the partial pressure of boron oxide in the atmosphere rises.

[0022] Boron oxide and aluminum oxide in the presence of nickel oxide reacts, crystals of aluminum borate having a composition of normal _{9Al 2 O 3 · 2B 2 O} 3 is grown to a whisker. The starting points of whisker growth are uniformly distributed in the raw material compound molded product, and the growth direction is three-dimensionally random. Since this whisker formation proceeds in the densely molded product, the growing whiskers come into contact with other growing whiskers as well. At the contact point, aluminum borate shared by both whiskers is formed, and the whiskers are bonded to each other.

Excess boron oxide remaining after the reaction to form aluminum borate whiskers can be completely removed by further heating and vaporizing it (excess boron oxide is formed by whisker formation). After completion of the reaction, it can be removed by a method of washing with hot water to dissolve it.).

After completion of the reaction, the reaction mixture is left to cool to obtain a porous inorganic material composed of aluminum borate whiskers. The product has substantially the same shape as the raw material molded product before heating, and the shrinkage due to the structural change is about 10% at the maximum. Fine communicating voids, which are determined by the density of the pre-heated molded product and the amount of excess boron oxide, remain in the product, and the volume of the voids is usually 5 to 50% of the product volume. As a result, the product density is about 0.15 to 1.5 g / cm ³ .

The nickel aids involved in the formation of whiskers are believed to form a solid solution in the form of oxides in the whiskers aluminum borate.

The porous inorganic material according to the present invention can be used for any purpose as it is in the shape given in the manufacturing process or by appropriately cutting. For example, by utilizing the excellent heat resistance and corrosion resistance of aluminum borate whiskers and high strength based on covalent bonding of constituent substances, it is used for WRM and other composite material manufacturing preforms, high temperature structural materials, heat insulating materials, filter media, etc. can do.

[0027]

【Example】

Example 1 Aluminum hydroxide was used as an aluminum oxide precursor.
0 g, orthoboric acid (H ₃ B) as a boron oxide precursor
O ₃ ), 3.5 g, nickel oxide, 0.13 g, were thoroughly mixed in a mortar, filled in a die and compressed to obtain a molded product having a density of 0.32 g / cm ³ , which was placed in an electric furnace. 12
It heated at 50 degreeC for 6 hours, and produced the aluminum borate whisker. After that, in order to vaporize and remove the residual boron oxide, it was heated at the same temperature for 4 hours and then left to cool.

A porous inorganic material having a weight of 7.66 g, a density of 0.47 g / cm ³ and a compressive strength of 70 kgf / cm ² was obtained. The aluminum borate whiskers constituting this material had an average diameter of 0.6 μm and a length. Was 20 to 30 μm. FIG. 1 is a scanning electron micrograph (magnification: 2000) of this material.

Example 2 1 part of aluminum hydroxide was used as a precursor of aluminum oxide.
0 g, orthoboric acid (H ₃ B) as a boron oxide precursor
O ₃ ) 3.5 g, nickel oxide 0.13 g, were mixed well in a mortar, filled in a die and compressed to obtain a molded product having a density of 0.45 g / cm ³ , which was placed in an electric furnace. 12
It heated at 50 degreeC for 10 hours, and produced the aluminum borate whisker. After cooling down, the weight is 7.66g and the density is 0.71.
A porous inorganic material having g / cm ³ and a compressive strength of 105 kgf / cm ² was obtained. The aluminum borate whiskers constituting this material had an average diameter of 0.6 μm and a length of 20 to 30 μm.

Example 3 One aluminum hydroxide was used as an aluminum oxide precursor.
0 g, orthoboric acid (H ₃ B) as a boron oxide precursor
2.19 g of O ₃ ) and 0.1 g of nickel oxide were thoroughly mixed in a mortar, filled in a die and compressed to obtain a molded product having a density of 0.65 g / cm ³ , which was placed in an electric furnace. Thirteen
It heated at 00 degreeC for 6 hours, and produced the aluminum borate whisker. After the heating was completed, heating was further performed at 1250 ° C. for 4 hours in order to vaporize and remove the residual boron oxide.

After cooling, the weight was 7.63 g and the density was 0.94 g / cm.
^3. A porous inorganic material having a compressive strength of 150 kgf / cm ² was obtained. The aluminum borate whiskers constituting this material had an average diameter of 0.8 μm and a length of 10 to 20 μm.

Example 4 22 aluminum sulfate was used as an aluminum oxide precursor.
g, 1.97 g of boron oxide as a boron oxide precursor,
Mix 0.13 g of nickel oxide in a mortar, fill in a die and compress to obtain a molded product with a density of 0.35 g / cm ³ , put it in an electric furnace and heat it to 1200 ° C for 6 hours. To produce aluminum borate whiskers. Then, it was washed with hot water to remove the residual boron oxide and dried by heating.

A porous inorganic material having a weight of 7.68 g, a density of 0.43 g / cm ³ and a compressive strength of 65 kgf / cm ² was obtained. The aluminum borate whiskers constituting this material had an average diameter of 0.4 μm and a length. Was 10 to 25 μm.

[0034]

As described above, according to the present invention, a porous inorganic material composed of aluminum borate whiskers can be obtained by simply molding, heating and reacting a mixture of inexpensive raw material compounds, and the whiskers are dehydrated and molded. There is no need to use expensive whiskers as in the conventional manufacturing method, and various inconveniences due to scattering, non-uniform distribution, orientation, etc. of whiskers in the molding process are completely eliminated.

Since the product density can be changed only by changing the pressure for dry-forming the raw material mixture, it is easy to change the product density according to the application, and the changeable density range is wide.

The porous structure in which a group of completely non-oriented aluminum borate whiskers is integrated by a bond that does not depend on the binder and shares aluminum borate, because the performance of the material whiskers is highly utilized, the strength, It has excellent heat resistance, corrosion resistance, etc., as well as excellent uniformity of its properties.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph (× 2000) of a porous inorganic material according to Example 1.

Claims (8)

[Claims] 1. A group of aluminum borate whiskers uniformly and randomly distributed, wherein each aluminum borate whisker is bonded to another whisker at least at one position, and the mutual binding of whiskers constitutes boric acid. A porous inorganic material characterized by sharing aluminum. 2. The porous inorganic material according to claim 1, which has a density of 0.15 to 1.5 g / cm ³ . 3. A porous inorganic material according to claim 1 or claim 2 wherein the composition of aluminum borate is 9Al ₂ O ₃ · 2B ₂ O ₃ constituting the whiskers. 4. An aluminum compound which forms aluminum oxide when heated in aluminum oxide or air, a boron compound which forms boron oxide when heated in boron oxide or air, nickel oxide, nickel or in air A nickel compound that produces nickel oxide when heated in a uniform mixture in a powder state, the resulting mixture is compressed in a mold and molded, and the resulting molded product is heated to produce an aluminum compound and boron. A method for producing a porous inorganic material, which comprises producing aluminum borate whiskers from a compound. 5. An Al ₂ O ₃ : B comprising an aluminum compound which forms aluminum oxide when heated in aluminum oxide or air and a boron compound which forms boron oxide when heated in boron oxide or air. _The method for producing a porous inorganic material according to claim 4, wherein the molar ratio of ₂ O ₃ is 9: 2 to 9: 6. 6. A total amount of 0.1 with respect to the total amount of the aluminum compound which forms aluminum oxide when heated in aluminum oxide or air and the boron compound which forms boron oxide when heated in boron oxide or air. ~
The porous material according to claim 4 or 5, wherein 10% by weight of nickel oxide or 0.1 to 10% by weight of nickel oxide or a nickel compound which produces nickel oxide when heated in air is mixed. Manufacturing method of inorganic materials. 7. The method for producing a porous inorganic material according to claim 4, wherein the heat treatment for forming aluminum borate whiskers is performed at 1100 to 1400 ° C. 8. The method for producing a porous inorganic material according to claim 4, wherein excess boron compound is removed by heating at high temperature or washing with hot water after forming aluminum borate whiskers.