JPH05201799A - Production of aluminum borate-based whisker - Google Patents

Abstract

PURPOSE:To more easily produce aluminum borate-based whiskers with higher productivity because bauxite as a natural starting material can be used in place of an artificial starting material. CONSTITUTION:A mixture of bauxite with a starting material contg. boron, a flux and sulfuric acid is heat-treated. Components other than alumina contained in the bauxite act as additives and aluminum borate-based whiskers can easily be produced with high productivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing aluminum borate whiskers. The whiskers of the present invention are excellent in mechanical strength, chemical resistance, heat insulation, heat resistance, neutron absorption and electric insulation, and in addition to heat insulation materials, heat resistant materials and food materials, especially thermoplastic resins, thermosetting It is useful as a reinforcing material for organic materials such as resins, inorganic materials such as cement, glass and various ceramics, and metal materials such as aluminum alloys, magnesium alloys and titanium alloys.

[0002]

2. Description of the Prior Art Ceramics whiskers having excellent thermal and mechanical properties are roughly classified into non-oxide type and oxide type whiskers. Non-oxides generally have high melting points (19
Although it has excellent heat resistance, it requires a controlled atmosphere at the time of manufacture, which increases the cost of equipment and raw materials and limits its use. Examples of non-oxide type whiskers include silicon carbide and silicon nitride. On the other hand, for oxides, calcium sulfate, calcium titanate, magnesium borate and aluminum borate (JP-A-63-319298).
And JP-A-63-319299). These oxide-based whiskers have a lower melting point than that of non-oxide-based whiskers (1000 to 1600 ° C) and thus have poor heat resistance, but they can be manufactured by the flux method using a melting agent in the air, so they are facility-friendly. Raw material cost is low. Among oxide type whiskers, it has been clarified and noted that aluminum borate exhibits mechanical strength comparable to non-oxide type whiskers when used as a reinforcing material for aluminum (Katsuaki Suganuma: New Ceramics, No. 5, p63 ~ 6
9 (1990)).

Methods for producing aluminum borate whiskers which are excellent in mechanical strength and chemical resistance can be roughly classified into a vapor phase method and a flux method using a melting agent. As a vapor phase method, by passing water vapor through gaseous aluminum fluoride and boron oxide at 1000 to 1400 ° C, 4Al ₂ O ₃ · B
It is known that whiskers having a composition of ₂ O ₃ are obtained (US Pat. No. 3,350,166).

[0004] As the other hand flux method, by 1400 ° C. heat treatment of the mixture of aluminum hydroxide with an excess of boron oxide, whiskers composition of _{3Al 2 O 3 · B 2 O} 3 and _{9Al 2 O 3 · B 2 O} 3 Is known (US Pat. No. 3,080,242). Also, according to a report from the US Department of the Interior Mining Bureau
By heating a mixture of aluminum oxide, sodium tetraborate and lithium chloride at 1200 ° C, 2.5Al ₂ O ₃ · B ₂ O
Whiskers having a composition of ₃ are obtained, and a mixture of aluminum oxide, sodium tetraborate and boron oxide is obtained.
It is known that whiskers having a composition of 4.8Al ₂ O ₃ · B ₂ O ₃ can be obtained by heating to 00 ° C (Bureau of Mines Report of Investigation 6
575 "(1965)).

[0005] In Japan, 9Al ₂ O ₃ · 2B whiskers and a manufacturing method thereof having a composition of ₂ O ₃ (JP 63-319298) and 2Al
A whisker having a composition of ₂ O ₃ · B ₂ O ₃ and a method for producing the whisker (Japanese Patent Laid-Open No. 63-319299) are known. Further, a method in which a trialkali aluminum trisulfate and a raw material containing a boric anhydride component are mixed and heat-treated at 700 to 1200 ° C.
-107600), a method of heat treating aluminum sulfate as a raw material containing aluminum and a raw material containing boric anhydride at 1000 to 1200 ° C. in the presence of an alkali metal sulfate and an alkali metal carbonate (JP-A-2-164797), aluminum. A method of heat treating a mixture of at least one of aluminum oxide, hydroxide and oxyhydroxide and aluminum sulfate as a component-containing raw material, and a mixture of boric anhydride component-containing raw material and an alkali metal sulfate at 900 to 1200 ° C ( Japanese Patent Laid-Open No. 2-
164798), at least one of aluminum oxide and hydroxide as an aluminum component-containing raw material, a boric anhydride component-containing raw material, and at least one of alkali metal sulfates and chlorides and a mixture of sulfuric acid and 900-1200. ℃
There is a method of heat treatment in (Japanese Patent Laid-Open No. 3-131600).

[0006]

In the above flux method, artificial materials such as aluminum inorganic salts such as aluminum oxide, aluminum hydroxide and aluminum sulfate are used as the aluminum component-containing raw material, but natural materials such as bauxite are used. A manufacturing method using raw materials is not known. If natural raw materials can be used, the manufacturing process can be simplified and a highly productive manufacturing method can be provided at low cost. The present invention was made to utilize bauxite, which is a natural raw material.

[0007]

That is, the present invention is a method for producing aluminum borate whiskers, which comprises heat-treating a mixture of bauxite, a raw material containing a boron component, a melting agent and sulfuric acid.

The present invention will be described in more detail below. The main element contained in bauxite used in the present invention is A
l, Fe, Si, and Ti, which exist as compounds or mixtures of oxides, hydrous oxides, hydroxides, carbonates, etc. of these elements. The content of these elements varies depending on the place of production, but it is 45 to 90% as Al ₂ O _{3 and} 2 to 25 as Fe ₂ O _3.
%, SiO ₂ is 5 to 20%, and TiO ₂ is 2 to 5%.

Next, as a raw material containing a boron component, boron oxides such as boron oxide and boron oxyacids such as orthoboric acid (H ₃ BO ₃ ) and tetraboric acid (H ₂ B ₄ O ₇ ), Known compounds such as metaboric acid (HBO ₂ ) or alkali metal salts thereof such as sodium tetraborate, potassium tetraborate, sodium metaborate and alkoxide compounds of boron such as boron ethoxide (B (OC ₂ H ₅ ) ₃ ) Examples thereof include salts, and these may be used alone or in combination of two or more.

Preferred examples of the melting agent used in the present invention include alkali metal sulfates and chlorides. Specific examples thereof include lithium sulfate, sodium sulfate, potassium sulfate, lithium chloride, sodium chloride, potassium chloride and hydrates thereof, which may be used alone or in combination of two or more. ..

The mixing ratio of the bauxite, the raw material containing the boron component and the melting agent varies depending on the composition of the intended aluminum borate whiskers. For example, in the case of whiskers in which the molar ratio of Al ₂ O ₃ and B ₂ O _{3 in} the whiskers is 2: 1, the mixing ratio of the bauxite and the boron component-containing raw material is
The molar ratio of aluminum and boron contained in bauxite is preferably in the range of 1: 9 to 6: 4,
The melting agent is preferably in the range of 10 to 95% by weight based on the total weight. Further, in the case of whiskers having a molar ratio of Al ₂ O ₃ and B ₂ O ₃ of 9: 2, the mixing ratio of the bauxite and the boron component-containing raw material is:
The molar ratio of aluminum and boron contained in bauxite is preferably in the range of 1: 4 to 9: 1,
The melting agent is preferably in the range of 10 to 95% by weight based on the total weight.

The amount of sulfuric acid added is preferably in the range such that the molar ratio of aluminum contained in bauxite to sulfuric acid is 1: 1 to 1:20. This is because if the addition amount of sulfuric acid is smaller than 1: 1, a product having a particle shape other than whiskers is likely to be produced, and if the addition amount exceeds 1:20 mol%, the addition effect is not improved.

The heat treatment temperature varies depending on the intended composition of the aluminum borate whiskers. For example, 2Al ₂ O ₃
-A temperature of 600 ° C to 1000 ° C is preferable for whiskers of B ₂ O ₃ composition. This is because the reaction is insufficient at temperatures below 600 ° C, and B ₂ in the whiskers formed above 1000 ° C.
This is not preferable because a decomposition reaction in which the O ₃ component is gradually released occurs. For whiskers with 9Al ₂ O ₃ and 2B ₂ O ₃ composition, the temperature is 900 ° C.
~ 1200 ° C is preferred. This is 2A at temperatures below 900 ° C.
This is because whiskers with the composition of l ₂ O ₃ and B ₂ O ₃ are preferentially generated, or the raw materials remain unreacted.
If it exceeds the range, a decomposition reaction occurs in which the B ₂ O ₃ component in the generated whiskers is gradually released, which is not preferable. 4.8Al ₂ O ₃
The whiskers of the amount of B ₂ O ₃ less composition, such as B ₂ O ₃ and _{9Al 2 O 3 · B 2 O} 3, is preferably a high temperature of about 1400 ° C..

To isolate aluminum borate whiskers from a reaction product containing a melting agent, hot hydrochloric acid, hot sulfuric acid, hot nitric acid or a mixture thereof of about 1N, hot caustic soda, hot water or the like is used. After removing the melting agent and other water-soluble substances, thoroughly wash with water. If there are water-insoluble by-products, the whiskers may be separated from the residue by a treatment such as decantation and then washed sufficiently with water.

[0015]

EXAMPLES Examples of the present invention will be specifically described below. [Example 1-6] Chinese bauxite (analysis terms of oxides shown in Table 1), boron component-containing raw material (orthoboric acid: H ₃ BO _3), melting agents (potassium sulfate: K ₂ SO ₄₎ and Raw materials were weighed and mixed at a ratio of sulfuric acid shown in Table 2.

[0016]

[Table 1]

Here, the molar ratio of Al in Table 2 refers to the molar amount of aluminum contained in the raw material bauxite.
It is shown in terms of conversion. The ratio of the molar amount of aluminum to the molar amount of added sulfuric acid is shown as aluminum: sulfuric acid molar ratio.

[0018]

[Table 2]

Next, this mixture was placed in an alumina crucible in air.
Heat treatment was performed at 1120 ° C for 3 hours. Cooling the reaction product,
Hydrochloric acid was added and the mixture was boiled to remove the melting agent and other water-soluble substances, then thoroughly washed with water and dried. The generated whiskers were all light brown. Table 2 shows the shape of the obtained whiskers and the result of the crystal structure analysis by X-ray diffraction.
In the crystal structure column, 9A2B represents an Al ₁₈ B ₄ O ₃₃ (9Al ₂ O ₃ .2B ₂ O ₃ ) crystal structure. In addition, as a result of analyzing the abundances of SiO ₂ , Fe ₂ O ₃ , and TiO ₂ contained in the raw material bauxite by ICP emission spectroscopy (ICAP-575 manufactured by Jarrel Ash Co., Ltd.). Is shown in Table 2.

Comparative Example A whisker was obtained under the same conditions as in Example 1 except that aluminum sulfate [Al ₂ (SO ₄ ) ₃ ] was used in place of Chinese bauxite in Example 1. Table 2
The value shown in the Al column of the molar ratio of is the Al component in aluminum sulfate in terms of metal. The shape of the obtained whiskers was smaller than that of Example 1 as shown in Table 2,
Turns out it's not growing. This indicates that the growth of whiskers was promoted by using Chinese bauxite as a raw material.

[0021]

According to the method of the present invention, bauxite, which is a natural raw material, can be used, the process is simpler than when an artificial raw material is used, and aluminum borate whiskers can be produced with high productivity. Furthermore, components other than aluminum in bauxite have the effect of promoting the growth of whiskers, and are therefore suitable as an industrial production method.

Claims (1)

[Claims] 1. A method for producing an aluminum borate whisker, which comprises heat-treating a mixture of bauxite, a raw material containing a boron component, a melting agent and sulfuric acid.