JPH0365600A - Production of aluminum oxide needle crystal - Google Patents

Abstract

PURPOSE:To industrially stably obtain highly purified aluminum oxide needle crystal with simple treatment by mixing organic polymer to specific aluminum borate acicular crystal and subjecting to heat treatment at a fixed temperature. CONSTITUTION:An organic polymer is added to aluminum borate acicular crystal having >=1 average aspect ratio and mixed, then subjected to heat treatment at 800-1500 deg.C to afford the aimed aluminum oxide needle crystal. Besides, removing of boron becomes incomplete and aluminum oxide is not generated at a temperature below 800 deg.C of the heat treatment. On the other hand, although aluminum oxide needle crystal is generated at a temperature above 1500 deg.C of the heat treatment, aggregation of crystal is apt to be generated and handling of the crystal becomes difficult in using as a raw material. Furthermore, removing of boron is further accelerated by existence of carbon in said heat treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to a novel method for producing acicular aluminum oxide, which can be used, for example, in fiber-reinforced metals, plastics, or ceramics.

(Prior Art) Aluminum oxide (Al□03) is used in various fields as the most common ceramic material. In addition, inorganic materials consisting of needle-like crystals include, for example, S
As typified by iC whiskers, they tend to be used in many fields such as fiber-reinforced ceramics.

Therefore, if a needle crystal material of aluminum oxide, which is more common than SiC, can be obtained, its application fields will be even more diverse.

(Problems to be Solved by the Invention) However, a method for producing acicular aluminum oxide has not yet been established, and it is not commercially available domestically or internationally. In addition, some products are made on a trial basis using CVD methods, etc., but it is difficult to control the manufacturing conditions.
At present, it was difficult to obtain high-quality products.

(Objective of the Invention) The object of the present invention is to provide a novel method capable of producing acicular aluminum oxide.

(Means for Solving the Problems) As a result of repeated research into the above problems, the present inventors have developed a method that directly attempts to obtain the acicular crystal 'JjyJ' quality as has been done in the past. However, since it is extremely difficult, we created a needle-like substance of aluminum borate as an intermediate, and by removing the boron while retaining this needle-like form through a specific heat treatment, we created needle-like aluminum oxide. It was previously proposed that .

However, 800% of aluminum borate consisting of acicular particles
When heat treated at 1500"C, the particles bonded to each other and formed strong agglomerated particles. Therefore, the present inventors dispersed aluminum borate having acicular crystal particles in a liquid, and then It has been discovered that agglomeration of aluminum oxide needle particles can be prevented by adding an organic polymer, entangling individual aluminum borate needle particles with polymer molecular chains, and then heat-treating them at a predetermined temperature.

That is, in the present invention, aluminum borate consisting of acicular particles having an average aspect ratio of more than 1 and an organic polymer, particularly a polymer having a molecular weight of more than 1000, are sufficiently dispersed in a liquid, then dried, and then heated at 800 to 1500°C. It is characterized by heat treatment at high temperatures.

The present invention will be explained in detail below.

The main feature of the present invention is that acicular aluminum borate is used as an intermediate, and an organic polymer is further mixed therein to prevent agglomeration.

The acicular aluminum borate used in the present invention itself has an average aspect ratio of more than 1, especially from 10 to 100. When the average aspect ratio is 1,
This is because aluminum oxide hardly becomes acicular crystals even after the subsequent heat treatment.

Next, the aluminum borate is dispersed in a suitable liquid. At this time, in the conventional method, since the aluminum borate particles come into contact with each other in the liquid, this bond is strengthened by the heat treatment described below, and the particles tend to aggregate with each other.

Therefore, according to the present invention, a solvent such as alcohol or water is used as the liquid to be dispersed, and an organic polymer is added to the solvent. By adding this organic polymer, the acicular particles of aluminum borate can be entangled with the molecular chains and mesh molecules of the polymer, thereby preventing the acicular particles from coming into contact with each other. Note that this organic polymer is preferably one consisting of C, H, O, and N in order to maintain its purity. The molecular weight of the polymer is suitably about 1,000 or more; if the molecular weight is less than 1,000, the effect of preventing contact between the acicular particles tends to be reduced.

There is no particular disadvantage when the molecular weight is large, but 100,00
If it exceeds 0, the viscosity of the solution containing it will increase, making it difficult to mix it with aluminum borate. A commercially available dispersant may also be used during this mixing. However, since the dispersant usually contains a metal element, the amount used should be kept to a minimum in order to maintain the purity of the acicular aluminum oxide.

Next, the organic solvent in which aluminum borate is dispersed is heated to 800 to 1500° C. after volatilizing the organic medium, if desired.
heat treated at a temperature of The atmosphere at this time can be vacuum, inert gas, reducing gas, or oxidizing gas atmosphere. This heat treatment releases the boron in the aluminum borate, and finally produces aluminum oxide in the form of needle-like crystals without agglomerates.

Note that the temperature during the heat treatment was set within the above range because if the temperature is lower than soo'c, boron removal will be incomplete and aluminum oxide will not be generated. - direction, 1500'
This is because, although acicular aluminum oxide is produced at a temperature exceeding C, the crystals tend to aggregate, making it difficult to handle when used as a raw material.

Further, according to the present invention, the removal of boron can be further promoted by making carbon present during the heat treatment. The carbon source at this time may be carbon powder or a substance that can be converted into carbon under heat treatment conditions, such as phenol resin, mixed into argonium borate, or heat treatment may be performed in a carbon forest.

As is clear from the X-ray diffraction chart in Figure 1, the acicular aluminum oxide obtained by the above heat treatment has the following properties:
It is understood that it is made of high purity aluminum oxide and its crystals are of the α type.

The invention will now be explained with the following examples.

(Example) A predetermined amount of boron oxide and aluminum hydroxide were thoroughly mixed, placed in a crucible, and heated to 1300'C in an air atmosphere. After holding at 1300°C for 30 minutes, it was slowly cooled to room temperature.

After washing the obtained solid with water, acid treatment was performed to obtain 9A1zOs 2820 having acicular crystals with an average aspect ratio of 50.
3 aluminum borate was obtained.

An X-ray diffraction chart of this aluminum borate is shown in FIG.

Next, using alcohol as a solvent, 80 g of polyethylene polymers having various molecular weights were added to 50 g of this aluminum borate and mixed well, and then heat treated under various conditions shown in Table 1.

The crystal morphology after treatment was observed using an electron microscope, and the presence of α-type aluminum ξ oxide was identified from the X-ray diffraction curve.

In addition, the X-ray diffraction curve of the sample of Nα8 in Table 1 is shown in FIG.

(Left below) According to Table 1, when the treatment temperature is lower than 800°C, a large amount of acicular aluminum borate is present and no aluminum oxide is produced. When the temperature exceeded 1500°C, solids were formed.

In addition, when the molecular weight of the organic polymer is smaller than 1,000, the bond between particles is strong and the formation of needle-like particles is small (,1
, 000 to 100,000, good acicular particles were obtained. When the molecular weight exceeds 100,000, needle-like particles can be produced well, but the work is difficult due to the high viscosity. Therefore, the viscosity range of the organic polymer is preferably from 1,000 to 100,000.

According to the method of the present invention excluding these, high purity acicular aluminum oxide was produced in all cases.

(Effects of the Invention) As detailed above, according to the present invention, acicular aluminum oxide can be produced by simple processing, and therefore acicular aluminum oxide can be produced industrially stably. be able to.

This acicular aluminum oxide is effective in strengthening materials, especially when combined with metals, plastics, or ceramics, and can be applied in various fields.

[Brief explanation of drawings]

FIG. 1 is an X-ray diffraction chart of acicular aluminum oxide of the present invention, and FIG. 2 is an X-ray diffraction chart of aluminum borate, which is an intermediate of the present invention.

Claims (1)

[Claims] An organic polymer is added to and mixed with acicular aluminum borate having an average aspect ratio of 800 to 1500.
A method for producing acicular aluminum oxide, characterized by heat treatment at a temperature of °C.