JP2522981B2 - Method for producing fibrous magnesium pyroborate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing fibrous magnesium pyroborate. Fibrous magnesium pyroborate is useful as a composite reinforcing material such as plastic, metal, ceramics, concrete, friction material, excess material, battery diaphragm, pigment, insulating material, and heat resistant material.

Conventional technology and its problems Conventionally, fibrous magnesium pyroborate is produced by dry-mixing a magnesium source compound, a boron source compound and a flux by a mechanical method using a mixer or the like, and heat-treating this mixture. (For example, JP-A-60-204697
(See the official gazette).

However, according to this method, most of the fibrous magnesium pyroborate is inevitably formed as an aggregated mass (shot) in which most of the fibers are solidified into a mass. Thus, in the operation of defibrating the fibers constituting such a shot, the fibers are broken or crushed, so that the fiber length is shortened, the quality of the fibers and the fiber yield are decreased, etc. The problem of occurs.

Means for Solving the Problems An object of the present invention is to provide a method for producing fibrous magnesium pyroborate, which has no shots, is easy to be defibrated, and has a uniform length and thickness, and is of good quality.

The object of the present invention is to produce a fibrous magnesium pyroborate, a raw material mixed solution containing a magnesium source compound, a boron source compound and a flux and atomizing the magnesium source compound to uniformly disperse the raw material mixed solution in the raw material mixture. It is achieved by spray-drying, then raising the temperature of the resulting spray-dried product to about 850 ° C. at a rate of about 10 ° C./minute or less, and treating at this temperature.

As the magnesium source compound used in the present invention,
Conventionally known compounds can be widely used, and in addition to magnesium oxide and hydroxide, magnesium compounds such as inorganic acid, carbonic acid, sulfuric acid, nitric acid, and magnesium salt of hydrohalic acid can be mentioned. As such a compound, specifically, magnesium oxide, magnesium hydroxide, basic magnesium carbonate, magnesium sulfate, magnesium chloride,
Examples include magnesium bromide and the like. These may be used alone or in combination of two or more.

As the boron source compound used in the present invention, conventionally known compounds can be widely used, and examples thereof include boron oxides such as boron oxide, orthoboric acid (H ₃ BO ₃ ), tetraboric acid (H ₂ B _2
4 O ₇ ), oxyboric acid such as metaboric acid (HBO ₂ ), or alkali metal salts thereof (for example, sodium borate, sodium pyroborate, potassium pyroborate, sodium metaborate, etc.) and the like. These may be used alone or in combination of two or more.

Examples of the flux used in the present invention include potassium chloride and sodium chloride,
These may be used alone or in combination.

The mixing ratio of the magnesium source compound, the boron source compound and the flux is not particularly limited, but usually the molar ratio of the magnesium source compound and the boron source compound is 1: 4 to 1: 1 and the total flux. It is advisable to mix the three components so that the amount is 10 to 95% by weight based on the weight.
In the present invention, it is particularly preferable to mix the magnesium source compound, the boron source compound and the flux at a ratio of 2: 3: 7 (molar ratio).

In the present invention, it is necessary to atomize the magnesium source compound and uniformly disperse it in the raw material mixture. Examples of the method for atomizing and uniformly dispersing the magnesium source compound include the following methods A and B.

Method A: An insoluble magnesium source compound is solubilized by the action of an acid or an alkali and dissolved in water to give an aqueous solution, or a soluble magnesium source compound (for example, a soluble magnesium salt) is dissolved in water. To what was made into an aqueous solution,
Upon addition of an alkali or acid to neutralize, the colloidal insoluble magnesium source compound can be obtained in the form of a suspension. When the boron source compound and the flux are added to and mixed with the suspension of the colloidal insoluble magnesium source compound, a raw material mixture in which the magnesium source compound is atomized and uniformly dispersed can be obtained.

Method B: Dispersion, ball mill dispersion, grain mill dispersion, etc., which are often used for high dispersion during paint preparation, are used to disperse an insoluble magnesium source compound in water and obtain a highly dispersed slurry of the magnesium source compound. When the boron source compound and the flux are added to the liquid and mixed, a raw material mixture in which the magnesium source compound is atomized and uniformly dispersed can be obtained.

In the present invention, the raw material mixed solution obtained above is then spray-dried. The spray drying means is not particularly limited, and conventional methods can be widely applied.

In the present invention, the spray-dried product obtained is then heated to about 850 ° C. at a rate of about 10 ° C./minute or less and treated at this temperature. When the heating rate is much faster than 10 ° C / min, the generation and crystallization of magnesium pyroborate will proceed rapidly, causing the crystal growth to occur in an indefinite direction and hindering the growth of fibers of uniform length and thickness. However, as a result, the intended purpose of the present invention cannot be achieved, which is not preferable (Comparative Example 2 described later).
reference). The temperature of the heat treatment needs to be around 850 ° C., and the treatment time at that temperature is preferably about 1 to 5 hours. By heat treatment at 650 ° C. or 750 ° C., only fine particles of magnesium pyroborate are produced, and it is impossible to obtain fibrous magnesium pyroborate having uniform length and thickness as in the present invention.

EFFECTS OF THE INVENTION According to the method of the present invention, fibrous magnesium pyroborate having no shots, easy to be defibrated, and good quality with uniform length and thickness can be easily obtained. Fibers of uniform length and thickness have advantages such as exhibiting excellent reinforcing performance, and therefore the fibrous magnesium pyroborate obtained by the method of the present invention has great industrial utility value.

Examples The present invention will be further clarified below with reference to Examples and Comparative Examples.

Example 1 4M-hydrochloric acid aqueous solution 0.1 was added to 8.06 g of magnesium oxide and dissolved, and then 2M-potassium hydroxide aqueous solution 0.2l was gradually added to the solution while stirring to neutralize the solution to obtain colloidal magnesium hydroxide. Is generated. Next, 18.55 g of orthoboric acid and 22.37 g of potassium chloride are added thereto, and they are dissolved by stirring. This mixed solution is Yamato Scientific Mini Spray
A raw material mixture of Mg, B and KCl was prepared by spray drying with DL-21. As a result of observation with an electron microscope, this raw material mixture is fine particles with a diameter of about 3 to 10 μm, in which Mg
Were distributed almost uniformly. In addition, as a result of X-ray diffraction, Mg
A and B were amorphous.

50 g of the above raw material mixture was filled in an alumina crucible, and 850
Temperature rises to ℃ (temperature rise rate of 10 ℃ in the temperature range of 650 to 850 ℃
/ Min), and kept at 850 ° C. for 3 hours for heat treatment. The baked product was boiled in hot water to dissolve and remove KCl, washed with water and dried. As a result, the diameter is around 0.3 μm and the average fiber length is 15 μm.
8.7 g of the desired fibrous magnesium pyroborate without m shots were obtained. An electron micrograph of this fibrous magnesium pyroborate is shown in FIG. The average fiber length of the fibers was measured using Luzex II (manufactured by Toyo Ink Mfg. Co., Ltd.), and this is the same in the following examples.

Example 2 In 0.1 of a mixed aqueous solution of 40.64 g of magnesium chloride (MgCl ₂ .6H ₂ O) and 22.37 g of potassium chloride, borax (Na ₂ B ₄ O ₇
10H ₂ O) 0.21 of an aqueous solution of 28.59 g, and then 0.1 parts of 2.5 M sodium hydroxide aqueous solution were gradually added with stirring,
Spray drying and heat treatment were performed under the same conditions as in Example 1 above. The product does not contain shots, has a diameter of around 0.3 μm,
It was the desired fibrous magnesium pyroborate with an average fiber length of 15 μm.

Example 3 16.12 g of magnesium oxide was dispersed in 0.5 l of water and highly dispersed by a ball mill to prepare a slurry liquid. The particle size of magnesium oxide in the prepared slurry is 3μ
It was m or less. Orthoboric acid 3 in the resulting slurry
7.1 g and 44.74 g of potassium chloride were added, stirred and dissolved, and then sprayed under the same conditions as in Example 1 except that the temperature rising rate in the temperature range of 650 to 850 ° C. was 5 ° C./min. It was dried and heat-treated. Product does not include shot, diameter
It was a desired fibrous magnesium pyroborate having a mean fiber length of about 0.3 μm and 12 μm.

Example 4 50 g of the raw material mixture obtained by the same operation as in Example 1
In an alumina crucible and heated to 800 ° C (650-80 ° C).
The temperature was raised in the temperature range of 0 ° C. at a rate of 10 ° C./min) and the temperature was kept at 800 ° C. for 4 hours for heat treatment. The post-treatment is performed in the same manner as in Example 1,
8.7 g of fibrous magnesium pyroborate was obtained. The diameter of the obtained fiber was around 0.2 μm, the average fiber length was 10 μm, and it was a desired fibrous magnesium pyroborate containing no shot.

Example 5 50 g of the raw material mixture obtained by the same operation as in Example 1
In an alumina crucible and heated to 900 ° C (650-90
The temperature was raised in the temperature range of 0 ° C. at a rate of 10 ° C./min) and kept at 900 ° C. for 2 hours for heat treatment. The post-treatment is performed in the same manner as in Example 1,
8.7 g of fibrous magnesium pyroborate was obtained. The diameter of the obtained fiber was about 0.6 μm, the average fiber length was 25 μm, and it was a desired fibrous magnesium pyroborate containing no shot.

Comparative Example 1 In the raw material mixing ratio of Example 1 above, 18.55 g of orthoboric acid and 52.19 g of potassium chloride were sufficiently mixed in a mortar without solubilizing 8.06 g of magnesium oxide. As a result of treating 50 g of this raw material mixture under the same conditions as in Example 1, 9.3 g of a product was obtained. This product has a diameter of 0.
In addition to fibrous magnesium pyroborate having a diameter of about 3 μm, a considerable proportion of shots having a diameter of about 10 to 30 μm were included. An electron micrograph of this product is shown in FIG.

Comparative Example 2 About the raw material mixture prepared under exactly the same conditions as in Example 1 above
An alumina crucible filled with 50 g was inserted into an electric furnace previously kept at 850 ° C., heated rapidly, and then reacted at 850 ° C. for 3 hours. The calcined product was treated under the same conditions as in Example 1, resulting in 8.1 g of product. The product contained no shots, but had columnar or plate-like crystals with a width of 10 μm or more. An electron micrograph of this product is shown in FIG.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the shape of the fibers of the fibrous magnesium pyroborate obtained in Example 1. Second
The figure is an electron micrograph showing the shape of the fibers of the fibrous magnesium pyroborate containing the shot obtained in Comparative Example 1. FIG. 3 is an electron micrograph showing the fiber shape of the fibrous magnesium pyroborate obtained in Comparative Example 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Ogawa 463 Kagasuno, Kawauchi Town, Tokushima City, Tokushima Prefecture Otsuka Chemical Co., Ltd. Tokushima Factory Examiner Koji Amemiya

Claims (1)

(57) [Claims] 1. A raw material mixed solution containing a magnesium source compound, a boron source compound and a flux, which is atomized and uniformly dispersed in a raw material mixture, in producing fibrous magnesium pyroborate. A method for producing fibrous magnesium pyroborate, which comprises drying, then heating the resulting spray-dried product to a temperature of about 850 ° C. at a rate of about 10 ° C./minute or less, and treating at this temperature.