JPH05238900A - Production of alumina whisker - Google Patents

Abstract

PURPOSE:To simply and readily form an alumina whisker by treating an aluminum borate whisker at a temperature within a specific range. CONSTITUTION:An aluminum borate whisker is filled in a vessel for heat treatment such as a crucible at about 0.2-0.5g/cm<2> density. The vessel filled with the whisker is then arranged in a heating furnace and the aluminum borate whisker is heat-treated at a temperature within the range of 1200 to 1400 deg.C in an oxidizing or nonoxidizing atmosphere under ordinary or reduced pressure for >=50hr to volatilize the boric acid component in the raw material. Thereby, the objective alumina whisker is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alumina whisker which is useful as a reinforcing material for thermoplastic resins, thermosetting resins, glass, ceramics, cement and metals.

[0002]

2. Description of the Related Art Conventionally, alumina has a high mechanical strength,
Utilizing properties such as heat resistance, it is used as a reinforcing material for synthetic resins and ceramics in the form of long fibers or short fibers of polycrystalline alumina. However, these fibers do not exhibit the original strength of the alumina crystals because they break from the grain boundaries when they break due to tensile stress, and when exposed to high temperatures, the strength decreases due to the growth of alumina particles. There was such a problem. On the other hand, alumina whiskers
Has no such problems as described above, and has excellent properties such as mechanical strength and heat resistance, and is suitable as a reinforcing material for synthetic resin, glass, ceramics, cement, metal and the like. Alumina whiskers have hitherto been mainly produced by a vapor phase method and contain Al—S containing 30 to 50 mol% of Al.
Method of heating and evaporating n-based alloy at 1300 to 1500 ° C. (US Pat. No. 3,505,014), wet hydrogen gas and Al
Cl 1400 to 1600 the Zr-Al alloy in ₃ gas
Method of heat treatment at ℃ (US Pat. No. 3,582,271),
Al with water whose concentration is controlled in an inert gas
Method of reacting at 00 to 1600 ° C. (US Pat. No. 365
8469) or a mixture of Al-containing alloy and carbon in an aluminum halide gas stream,
Method of reacting at 1800 ° C. (US Pat. No. 3,945,756)
No. 2) etc. are known. However, these methods for producing alumina whiskers by the vapor phase method are often difficult as industrial production methods because they require strict concentration control of the raw material gas and complicated production processes.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in the production of alumina whiskers and to provide a method for producing alumina whiskers by a simple process that does not rely on a vapor phase method.

[0004]

Means for Solving the Problems The inventors of the present invention have made extensive studies as to a method for producing alumina whiskers which does not use a vapor phase method. As a result, aluminum borate is used as a raw material and the boric anhydride component is removed by heating. By the simple process of
The present invention has been completed by finding that an alumina whisker can be produced at a relatively low temperature. That is, the present invention is a method for producing an alumina whisker, which comprises heat-treating an aluminum borate whisker in a temperature range of 1200 to 1400 ° C. to volatilize a boric acid component to obtain an alumina whisker. . In the present invention, the aluminum borate whisker used as a raw material is 1000 to 1
4Al ₂ O ₃ · B produced by a vapor phase method in which steam is passed through aluminum fluoride and boron oxide in a gaseous state at 400 ° C
₂ O ₃ whisker having a composition of - or 3Al ₂ O ₃ · B ₂ O _3, which aluminum hydroxide is produced by liquid phase method of heat treating a mixture of boron oxide at _{1400 ℃, 9Al 2 O 3 ·} B 2 O 3 A whisker or aluminum compound having the composition of 900, a mixture of a boron compound and a melting agent component at 900 to 1200 ° C.
9Al ₂ O ₃ · 2B ₂ O ₃ manufactured by solid phase method
Whiskers and the like having the above composition can be preferably used. here,
The whiskers may be used alone or as a mixture. Further, in order to obtain a high-purity alumina whisker, the higher the purity of the aluminum borate whisker used as a raw material, the more preferable. It should be noted that impurities such as alumina may be mixed depending on the purpose of use of the alumina whisker. In that case, the aluminum borate whisker used as a raw material contains a small amount of alumina or the like as impurities. It doesn't matter.

Aluminum borate whiskers as the raw material are filled in a vessel for heat treatment, such as an alumina crucible, at a bulk density of about 0.2 to 0.5 g / cm ³ , and this is filled in a heating furnace at 1200 to By heat treatment in the temperature range of 1400 ° C., the boric acid component in the raw material is volatilized to obtain an alumina whisker. An electric furnace, a gas furnace, or the like can be used as the heating furnace, but a furnace having a structure having an exhaust port for discharging the volatilized boric acid component to the outside of the heating furnace or a forced exhaust device is preferable. Further, it is not preferable to fill the heat-treating container with the above raw materials if the bulk density is increased too much because the conversion rate to alumina whiskers is lowered. If the heat treatment time is too short, the reaction proceeds slowly and the conversion rate decreases, so the holding time at the heat treatment temperature is preferably 50 hours or more, preferably 8 hours.
0 hours or more. Further, when the heat treatment temperature exceeds 1400 ° C., no alumina whiskers are generated due to the melting of the raw material, and below 1200 ° C., the conversion rate to alumina whiskers becomes slow. The holding temperature for the heat treatment time may be set as appropriate depending on the composition of the raw material used, the amount to be treated, the filling bulk density and the like. In addition, the heat treatment is an oxidizing atmosphere (atmosphere atmosphere) or a non-oxidizing atmosphere (nitrogen, argon atmosphere, etc.)
It is carried out under normal pressure or reduced pressure. The treatment under reduced pressure has the effect of shortening the treatment time as compared with the treatment under normal pressure. When the unconverted raw material is present, the whole amount can be converted into alumina whiskers by heat treatment again.

[0006]

EXAMPLES The present invention will be described in more detail below with reference to examples. First, in order to synthesize aluminum borate whiskers as a raw material used in the present invention, 223 g of aluminum hydroxide, 47 g of aluminum sulfate, and 4 boric acid were prepared.
A mixture of 8 g and 682 g of potassium sulfate was prepared, and a mixture having a molding pressure of 100 kg / cm ² and a diameter of 50 m was prepared.
Several disk-shaped molded bodies each having a thickness of m and a thickness of 20 mm were molded. Then, the disc-shaped compact was reacted at 1100 ° C. for 4 hours using an electric furnace having an exhaust port to obtain a sintered compact. A crushed product of this sinter was treated with hydrochloric acid, and components that were soluble in hydrochloric acid were removed by filtration. The undissolved product was washed with water to give a diameter of 0.5 to 1.0 μm and a length of 5 to 5. in 50 [mu] m, the composition of aluminum borate whisker is _{9Al 2 O 3 · 2B 2 O} 3 - was obtained. Using this aluminum borate whisker as a raw material, an alumina crucible having a diameter of 150 mm and a height of 150 mm was filled to a bulk density of 0.4 g / cm ³ ,
Under the conditions shown in Table 1, heat treatment was performed using an electric furnace having an exhaust port to obtain whiskers. The obtained whiskers were identified by X-ray diffraction and confirmed to be alumina whiskers. Also, the alumina whisker was observed by an electron microscope.
The shape of is a hexagonal column. The X-ray diffraction results of the whiskers obtained in Example 1 are shown in FIG. 1, and the electron microscope observation results are shown in FIG. The reduced pressure atmosphere in Table 1 is a reduced pressure of about 0.1 Torr. The conversion rate to alumina whiskers was calculated from the intensity ratio of alumina and aluminum borate in X-ray diffraction, and the conversion rate was 90% or more. Comparative Example 1
4 to 4 are examples when the heat treatment time or the heat treatment temperature is insufficient.

[0007]

[Table 1]

[0008]

The method of the present invention is different from the gas phase method which requires strict concentration control of the source gas and complicated operation, and requires a relatively simple manufacturing facility, and more
Alumina whisker by heat treatment at low temperature over 00 ℃
Can be produced and is extremely useful as an industrial method for producing alumina whiskers. Since the obtained alumina whiskers are single crystals, they have a useful effect as a reinforcing material for thermoplastic resins, thermosetting resins, glass, ceramics, cement, metals and the like.

[0009]

[Brief description of drawings]

FIG. 1 shows an alumina whisker obtained by the method of the present invention.
2 is an example of the X-ray diffraction diagram of FIG. 2, and FIG. 2 is an electron micrograph showing its crystal shape.

[Figure 1]

[Fig. 2]

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[Procedure amendment]

[Submission date] March 8, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is an example of an X-ray diffraction diagram of an alumina whisker obtained by the method of the present invention.

FIG. 2 is an electron micrograph showing the crystal shape of the alumina whiskers of FIG.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Koyanagi 1st Kokufucho, Tochigi City, Tochigi Prefecture Mitsui Mining Co., Ltd. Central Research Institute

Claims (1)

[Claims] 1. An aluminum borate whisker comprising 12
A method for producing an alumina whisker, which comprises performing heat treatment in a temperature range of 00 to 1400 ° C.