JP2911207B2 - Method for producing fine boron carbide powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a fine powder of boron carbide, which is a suitable raw material for producing an abrasive, a thermal neutron absorber, and a sintered body.

[Conventional technology]

Conventional methods for producing boron carbide include (a) a method of reacting a boron compound with carbon, (b) a method of reacting a boron compound with carbon and metal Mg, (c) a method of reacting metal boron with carbon, (D) A method of causing a gas phase reaction using BCl _4, CH _4, or the like is known.

In the method (a), a carbon material is blended with a boron compound such as boron oxide, and reduced and carbonized at a high temperature of 2000 ° C. or more in an arc furnace or the like. 49-44880, JP-A-48-39400).

[Problems to be solved by the invention]

When the boron compound is reacted with carbon using an arc furnace to produce boron carbide, a molten and solidified massive boron carbide is formed below the electrode. When the powder is obtained, it is pulverized to a desired particle size, but since boron carbide itself has high hardness, it takes a lot of energy to pulverize the ingot to fine powder, and furthermore, it takes a long time to pulverize. Therefore, it is necessary to reduce the purity and to perform a treatment such as pickling to remove impurities, and to obtain high-purity fine powder has a very low yield.

In the above-mentioned JP-B-49-44880, an induction furnace is used in place of an arc furnace, and heated to 1700 to 2000 ° C. in an inert gas to obtain a fine boron carbide powder, whose particle size is as coarse as 1 to 150 μm. In some cases, fine powder of 5 to 10 μm is obtained, but it is difficult to say that it is a fine powder.

Also, a method of reducing and carbonizing a boron compound with carbon and metal Mg (Japanese Patent Publication Nos. 41-15166, 41-15167, and
-175717, JP-A-60-46909 and JP-A-60-46910), boron carbide can be synthesized at a lower temperature than the method of simply reacting a boron compound with carbon, but the particle size is not described. In this method, 75 to 80 vol% of the reaction zone in the furnace is occupied by MgO as a reaction by-product, the actual yield of boron carbide per one batch of the calcination reaction is extremely small, There is a disadvantage that the sample is easily expanded and the sample is easily scattered. To overcome this latter drawback, MgO
Such a diluent is added to make the reaction proceed slowly, or a metal sulfate is added as a catalyst, and the reaction is carried out at a lower temperature to improve the reaction, thereby further reducing the yield.

An object of the present invention is to solve the above-mentioned various problems of the conventional production method and to produce boron carbide fine powder at low cost.

[Means for solving the problem]

The present inventor has conducted various studies to achieve the above object, and as a result, a production method in which boron carbide powder is previously added to a raw material as a fine particle accelerator, that is, a production method of boron carbide using a boron source and a carbon source as raw materials. In 5 to 6 parts by weight of boron carbide newly generated by the reaction,
The present inventors have found a method for producing fine boron carbide powder, which comprises mixing 0 parts by weight of boron carbide powder with the raw material and heating the mixture at 1500 to 2000 ° C. in an inert gas atmosphere.

As a boron source as a raw material, metal boron, boron oxide, or a compound that generates boron oxide after thermal decomposition is used.

The compound that generates boron oxide after thermal decomposition refers to boric acid, boric acid esters, and the like. The borate ester has the general formula B
(OR) n (OH) _3-n (n is an integer of 1 to 3, R is an alkyl group, a cycloalkyl group, a phenyl group).

As the carbon source, solid carbon such as carbon black or a compound that generates carbon after pyrolysis is used. The compound capable of forming carbon after thermal decomposition may be any compound as long as carbon remains after being thermally decomposed in an inert gas such as phenol resin or sugar.

The carbon black that can be used in the present invention may be any of those produced by a furnace method, an acetylene method, or the like, and is not particularly limited.

The amount of the boron carbide powder to be added as the micronization accelerator is preferably 5 to 60 parts by weight based on 100 parts by weight of the newly generated boron carbide by the reaction. If the amount is less than 5 parts by weight, there is no effect on the formation of fine particles of boron carbide. If the amount exceeds 60 parts by weight, the effect of the formation of fine particles is not more excellent, and the economic efficiency is inferior. A more preferred addition amount is 10 to 30 parts by weight.

In addition, the particle size of the boron carbide powder to be added and mixed is effective even if it is coarse, because the boron carbide generated by the reaction is finely divided, but remains as it is in the reaction product powder. A fine boron carbide powder is preferable, and a powder having a center diameter of 10 μm or less is desirable. Needless to say, a smaller particle diameter is more desirable.

The boron carbide produced by adding boron carbide in advance, which is the point of the present invention, is finely divided, because the added boron carbide acts as a nucleus, compared with the case without boron carbide powder addition. It is considered that the total number of nuclei increased, and as a result, the growth of the nuclei was suppressed and the atomization proceeded. In addition, the reaction in which boron carbide is generated between boron oxide and carbon is an exothermic reaction, and by adding boron carbide powder in advance in the raw material, the actual raw material of the reaction system is diluted, and the heat is generated. It is considered that the heat generated by the reaction is dispersed and the reaction proceeds slowly, so that the produced boron carbide is finely divided.

This suggests that the smaller the particle size of boron carbide added to the raw material, the smaller the particle size of boron carbide produced, but this is due to the fact that the same weight parts of boron carbide were added to the raw material. In this case, the smaller the particle size of boron carbide, the larger the number of particles and the larger the total number of nuclei.

In the present invention, it is preferable that the raw materials of the boron source and the carbon source and the added boron carbide are sufficiently mixed and then pelletized in view of handling problems and the like. It Ar, it is fired in an inert gas atmosphere such as N _2.

The firing temperature for forming boron carbide is preferably from 1500 to 2000 ° C. If the temperature is lower than 1500 ° C, a large amount of unreacted boron oxide or carbon remains, and if it exceeds 2000 ° C, the generated boron carbide is unfavorably grown.

Boron carbide produced by the present invention is the X-ray diffractive, B ₄ C or B ₁₃ C _2, or mixtures thereof.

〔Example〕

 The present invention will be described in detail with reference to examples.

Examples 1 to 9 7.2 g of metallic boron (Amorphous B manufactured by Stark, particle size 5 μm, purity 95 to 97%) as a boron source, and 2.0 g of carbon black (Showa Cabot Co., Ltd., Show Black N220) as a carbon source. On the other hand, as shown in Table 1, boron carbide
B ₄ C powder (Stark F-1500, particle size 1-2 μm, purity 95
9%) in the range of 0.46 to 5.52 g (equivalent to 5 to 60 parts by weight per 100 parts by weight of boron carbide produced)
And wet ball mill mixing for 5 hours using 40 ml of acetone as a dispersion medium. After drying and crushing the obtained slurry,
It was formed into pellets and fired in an Ar gas flow at 1700 ° C. for 1 hour.

When the product was identified by X-ray diffraction, only a B ₄ C (or B ₁₃ C ₂ ) diffraction peak was observed in each case.

Further, when the primary particle diameter of the synthesized powder was observed by SEM, it was found to be about 1.5 to 2.5 μm, and it was found that the larger the amount of B ₄ C added, the smaller the primary particle diameter.

Except that added in five amount ranging from Comparative Example 1 to 5 B ₄ C powder in a raw material mixing step 0~0.37g (1~4 parts corresponding relative boron carbide production amount), Example 1 to 9 and the same procedure was synthesized B ₄ C (or B ₁₃ C ₂₎ in the condition. Table 1 shows the raw material composition and the characteristics of the formed powder. When B ₄ C is not added as a raw material,
The particle size of the generated B ₄ C (or B ₁₃ C ₂ ) reached 50 μm. Even in the case of adding 4 parts by weight, the average particle size of the primary particles produced exceeded 10 μm.

Examples 10 to 17 20 g of a commercially available product H ₃ BO ₃ (manufactured by Kanto Kagaku Co., Ltd., special grade product) as a boron source and sugar (granulated sugar manufactured by Mitsui Seika Co., Ltd., a commercial product, residual carbon ratio 20%) as a carbon source ) Using 12g, and
As shown in Table 2, 0.32 g (equivalent to 20 parts by weight based on the amount of boron carbide produced) of eight kinds of B ₄ C having different particle sizes was added, and 120 ml of pure water was added.
Was used as a dispersion medium and mixed in a wet ball mill for 5 hours.

In this case, the average particle B ₄ C powder of diameter 2μm or more coarse granularity, various granularity Stark Co. brand F-1500 F-400 from (particle size 1 to 3 [mu] m) (particle size 8～32Myuemu) formulated as a raw material of it was used as a commercial product, for those particle size of less than 2 [mu] m, the commercially available products B ₄ C powder was dispersed in water, it was classified to collect fine powders B ₄ C by sedimentation.

The mixed slurry obtained by blending the raw materials is dried and crushed, then formed into pellets, and heated at 1700 ° C., 1 ° C. in an Ar gas flow.
Fired in time.

The properties of the resulting B ₄ C (or B ₁₃ C ₂ ) are shown in Table 2.

Even when coarse B ₄ C is used, relatively fine B ₄ C (or B ₄ C
_{Although 13} C ₂ ) is produced, B ₄ C added to the raw material remains as it is, so that the average particle size becomes slightly coarse. B ₄ C added to raw material
More fine-grained, resulting B ₄ C (or B ₁₃ C ₂₎ is finer, the B ₄ C in the raw kaolin is submicron, generated B
The average particle size of ₄ C (or B ₁₃ C ₂ ) also became submicron.

Comparative Example 6-13 raw material to, 0～0.06G an average particle diameter 0.2μm and 2.0 .mu.m B ₄ C powder of (0 to 3.75 parts by weight corresponding to a boron carbide production amount) but with addition as shown in Table-2 Are from Examples 10 to
B ₄ C (or B ₁₃ C ₂ ) was synthesized in the same manner as 17.

 Table 2 shows the properties of the obtained synthetic powder.

When the amount of B ₄ C added was the same, the particle size of the synthesized B ₄ C (or B ₁₃ C ₂ ) was smaller when B ₄ C with a smaller average particle size was used, The particle size was above 10 μm.

Examples 18 to 25, Comparative Examples 14 to 19 10 g of B ₂ O ₃ (manufactured by Kanto Chemical Co., Ltd., special grade product) as a boron source and carbon black (Example 1) as a carbon source
Average particle size as shown in Table 3 for 5.0 g of
0.49 g (equivalent to 15 parts by weight with respect to the amount of boron carbide formed) of B ₄ C classified powder of 0.5 and 1.0 μm was added, and mixed with a wet ball mill for 5 hours using 57 ml of pure water as a dispersion medium. The obtained slurry was dried and crushed, formed into pellets, and calcined in an Ar gas stream while maintaining the temperature range of 1300 to 2200 ° C. for 2 hours as shown in Table 3.

If the firing temperature is below 1500 ° C, the oxygen content of the product will be high, and if it is below 1500 ° C, the oxygen content will increase sharply,
This indicates that B ₂ O ₃ remains. This is evident from the carbon content, which translates from a theoretical carbon content of B ₄ C of 21.74% to 15
At a firing temperature of 00 ° C. or less, the temperature exceeds the limit, and at a firing temperature of less than 1500 ° C., extremely unreacted carbon is contained.

When the firing temperature is 1600 ° C. or higher, a carbon-boron powder having a low concentration of oxygen and free carbon is obtained. However, when the firing temperature is higher than 2000 ° C., it can be seen that the boron carbide grains are growing.

Comparative Examples 20 to 27 Example 20 except that the amount of B ₄ C having an average particle size of 0.5 and 1.0 μm added to the raw material was 0 to 0.13 g (corresponding to 0 to 4.0 parts by weight with respect to the generated boron carbide). And boron carbide were synthesized in the same procedure and under the same conditions as in Example 21. Therefore, the firing condition is 1700 ° C. for 2 hours.

When the amount of B ₄ C added is the same, the smaller the average particle size,
Although the particle size of the synthesized boron carbide powder was small, the average particle size of the synthesized boron carbide was all over 10 μm.

Examples 26 to 28 A phenol resin (solid phenol resin,
Using Showa High Polymer Co., Ltd. BRM-595, residual carbon ratio 40%)
Except for mixing the various boron source and B ₄ C powder in 10 parts by weight corresponding to a boron carbide production amount as shown in Table-5, the same conditions as in Example 1-9 was synthesized boron carbide in the procedure.

As a result, the powder particle size of the synthesized boron carbide is also shown in Table 5.
Shown in

Example 29 The synthetic boron carbide powder of Example 10 was ground with a vibration mill for 1 hour using SiC balls as media.

The average particle size corresponding to the secondary particles obtained by measuring the particle size of the obtained powder with a particle size distribution analyzer was 0.4 μm. In addition, analysis of the impurities after the pulverization revealed that the largest amount of Si impurities probably due to the SiC balls was 350 ppm.

Example 30 The synthetic powder of Example 14 was subjected to vibration mill pulverization in the same manner as in Example 29. However, the grinding time was 5 hours.

When the average particle size of the obtained powder was measured in the same manner as in Example 29, it was 0.7 μm, and the Si impurity content was 700 ppm.

Comparative Example 28 The synthetic boron carbide powder of Comparative Example 1 was subjected to vibration mill grinding in the same manner as in Example 29. However, the crushing time was 10 times, that is, 10 hours. However, the average particle size of the obtained pulverized powder
It was 8.0 μm when measured in the same manner as in Example 29, and the Si impurity content was 5.2 wt%.

〔The invention's effect〕

According to the present invention, a boron carbide powder having a primary particle diameter of 2 μm or less can be easily synthesized, and a submicron fine powder having a secondary particle diameter can be easily obtained by pulverization.

Claims (1)

(57) [Claims] In a method for producing boron carbide using a boron source and a carbon source as raw materials, 5 to 60 parts by weight of boron carbide powder is used as the raw material for 100 parts by weight of newly generated boron carbide by the reaction. After mixing, 15 minutes in an inert gas atmosphere
A method for producing fine boron carbide powder, characterized by heating at 00 to 2000 ° C.