JPH10203806A - Production of boron nitride powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain BN powder with a high crystallinity that has excellent shape retention and handling properties with high N2 gas permeability via bulk B2 O3 , as an intermediate, that can suitably cope with blocking of the production process by dehydrating a mixture containing an orthoboric acid powder and a carbonaceous powder having an average particle size, respectively and heating the mixture. SOLUTION: A mixture of an orthoboric acid powder with an average particle size of >=100μm, preferably >=500μm, particularly 700-1,000μm and a carbonaceous powder (for example, acetylene black), in a preferred embodiment, the average diameter of the powders other than orthoboric acid is less than 1/5 that of the orthoboric acid particle, is dehydrated, preferably at 300-450 deg.C to prepare bulk boron oxide, preferably with a density of 0.4-0.7g/cm<3> , particularly of 0.5-0.6g/cm<3> , then fired in a nitrogen atmosphere, preferably over 1,600 deg.C.

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 a boron nitride powder which can easily obtain a high crystalline boron nitride powder in a high yield and is advantageous for blocking during the production process.

[0002]

2. Description of the Related Art Hexagonal boron nitride (hereinafter referred to as BN) has thermal conductivity, electrical insulation, lubricity, mold release, high temperature stability, chemical stability, and the like. Since it has many excellent properties such as molten metal and poor wettability with molten glass, it can be used as a filler for electronic components, a lubricant for sliding members, a molten metal, a mold release agent such as a molten glass mold, and other It is used for a wide variety of applications such as degreasing and burning prevention agents for ceramics.

[0003] Many studies have been made on the above-mentioned BN synthesis method, and typical examples thereof are shown below.

[0004]

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However, the methods (1) and (2) are difficult to industrialize because of the high raw material costs.

In the above methods (3) and (4), a high airtightness is required for the nitriding furnace because NH ₃ gas is used.
In addition, amorphous B which can be synthesized at a low temperature of usually 1200 ° C. or less
Unlike the production of N, it is necessary to perform a heat treatment at a high temperature of 1900 ° C. or more in order to obtain a BN powder in which crystals have developed. However, when NH ₃ gas is used, H ₂ gas is thermally decomposed by NH ₃ gas. Since gas is generated and water vapor is produced as a result of the reaction, it is difficult to continuously perform the steps from the synthesis of the BN powder to the crystallization in a single-stage reaction under that atmosphere. For this reason, it is necessary to perform the treatment in the heating furnace in two or more stages in a batch system, and the productivity is low.

On the other hand, the method (5) can continuously synthesize BN with developed crystals by one-step reaction, and can be said to be the most suitable method for producing a highly crystalline BN powder.

However, the B used in the method (5)
₂ O ₃ easily combines with atmospheric moisture to form boric acid (hereinafter referred to as H).
₃ BO ₃ ), and is commercially available only in reagent grade.

Therefore, when the method (5) is carried out industrially, a process of mixing H ₃ BO ₃ and carbonaceous powder, heating and dehydrating to obtain B ₂ O ₃ is effective. .

Here, during the dehydration treatment, the mixed powder tends to solidify due to the surface tension of water to form a bulk body. In general, it is known that a bulk body has better handleability than a powder, and conventionally, a ceramic raw material mixed powder is mixed with an excipient, extruded,
Although it is performed by injection molding or the like into a bulk body of a ceramic material, if a bulk body having good handling properties can be obtained by effectively utilizing the tendency of bulking at the time of dehydration,
No molding machine is required, which simplifies the process.

[0011] However, in the method of producing BN powder, although various studies have been made on the types and blending ratios of the raw materials, various characteristics required for intermediates at each stage throughout the production process, particularly, the final properties, BN powder as a product can be produced with high yield and high productivity, and sufficient study has not been made on the particle size properties of each raw material powder that satisfies the condition that it can be obtained with good workability.

The present invention has been made in view of the above circumstances, and in the process of producing a boron nitride powder by the above method (5), a process of obtaining a bulk material having desired properties as an intermediate and having excellent handling properties. Which can obtain a highly crystalline BN powder with high yield and good workability
An object of the present invention is to provide a method for producing N powder.

[0013]

Means for Solving the Problems and Embodiments of the Invention The present inventors have conducted intensive studies in order to achieve the above object, and as a result, have found that a mixture of H ₃ BO ₃ and carbonaceous powder is dehydrated. If the nature of bulking in is effectively used, equipment and processes for molding are not required, and the equipment can be simplified and the process can be simplified, leading to cost reduction, and appropriate shape retention. Further, a bulk body having good handling properties, appropriate pores, good N ₂ gas permeability, and capable of uniformly reacting inside was further studied.

[0014] As a result, as H ₃ BO ₃ powder raw material mixed powder of H ₃ BO ₃ and the carbonaceous powder, the average particle size of 100
μm or more, more preferably H ₃
By setting the average particle size of the raw material powder such as the carbonaceous powder in the mixture other than BO _{3 to} 1/5 or less of the average particle size of the H ₃ BO ₃ powder, the H ₃ BO ₃ has an appropriate strength at the time of dehydration. The present inventors have found that a bulk body suitable for obtaining a highly crystalline BN powder having pores can be obtained, and have accomplished the present invention.

Therefore, the present invention provides an average particle size of 100 μm
After dehydrating the mixture containing the H ₃ BO ₃ powder and the carbonaceous powder, a method for producing a BN powder characterized by producing a BN powder by heating in a nitriding atmosphere; the average particle diameter of the powder other than H ₃ BO ₃ powder provides a method of manufacturing the BN powder is 1/5 or less of the average particle size of H ₃ BO ₃ powder.

Hereinafter, the present invention will be described in more detail. The method for producing a BN powder according to the present invention is characterized in that a mixture containing H ₃ BO ₃ powder and carbonaceous powder is heated and dehydrated to provide a handling property. And a step of obtaining a bulk body capable of stably producing a highly crystalline BN powder in a later step with good yield. In the present invention, the H ₃ BO ₃ powder in the above mixture is provided. It is essential to use those having an average particle diameter of 100 μm or more, especially 500 μm or more.

This point will be described in more detail with reference to FIG. 1. First, the carbonaceous powder C is adsorbed on the surface of the H ₃ BO ₃ particles before the dehydration treatment as shown in FIG. It is in a state where it has been done. When dehydration is performed in this state,
(B), the order pores of diameter in proportion to the particle size of the H ₃ BO ₃ vapor from the inside occurs before dehydration H ₃ BO ₃ occurs, B ₂ O ₃ after dewatering, steam Move along with the occurrence of, forming a neck with B ₂ O ₃ generated from the adjacent H ₃ BO _3, thereby forming a porous bulk body. That is, H ₃ BO ₃
Is dehydrated by the following three-stage reaction.

H ₃ BO ₃ → HBO ₂ + H ₂ O ↑ 4HBO ₂ → H ₂ B ₄ O ₇ + H ₂ O ↑ H ₂ B ₄ O ₇ → 2B ₂ O ₃ + H ₂ O ↑

Here, the HBO produced by the above reaction is
₂ (Metaboric acid) is a substance having a low melting point (about 170 to 200 ° C), temporarily forming a liquid phase at this stage,
_A neck is formed and connected with HBO ₂ generated from ₃ BO ₃ . Next, when dehydration progresses to B ₂ O ₃ , the powder is connected to form a bulk body in a connected state.

In this case, when the entire amount of H ₃ BO ₃ in the mixture powder is melted during dehydration and has fluidity, the carbonaceous powder is uniformly dispersed in the melt, so that the bulk material is not formed. Whether it is acceptable or not and its shape retention do not depend on the granularity of H ₃ BO ₃ .

However, in practice, the surface layer of H ₃ BO ₃ coated with the carbonaceous powder is stable and does not flow during dehydration, and HBO ₂ contained therein is mixed with water vapor generated during dehydration. Spatters, breaking the epidermis layer. Therefore, HBO ₂ generated from adjacent particles adheres and solidifies to form a bulk body.
It depends on the amount of scattered components contained inside the epidermis layer.

Therefore, in order to ensure a sufficient amount of the scattered component, the average particle diameter of H ₃ BO ₃ should be 100 μm or more, particularly 500 μm or more, more preferably 700 to 1000 μm.
If this shape is satisfied, the powder may be a primary particle or a secondary particle of an aggregate of fine particles, but when a secondary particle is used, it is considered to be a porous aggregate. ,
When the raw materials are mixed, the carbonaceous powder may enter the agglomerate of H ₃ BO ₃ and hinder the scattering of the contained components. Is preferred. If the average particle diameter of the H ₃ BO ₃ is less than 100 μm, when the raw material mixed powder described later is dehydrated, it is not bulked at all, or even if bulked, the strength is low and the handling property is poor. Inconvenience.

In the present invention, the carbonaceous powder used together with the above H ₃ BO ₃ powder acts as a reducing agent for B ₂ O ₃ during the nitriding reaction, and known carbonaceous powders can be used. Furnace black, acetylene black,
Examples thereof include carbon powder such as graphite, and carbonizable resins such as vinyl chloride resin and phenol resin.

The properties of the carbonaceous powder are not particularly limited either. As shown in FIG.
It is preferable that the particles are uniformly adsorbed on the surface of the H ₃ BO ₃ particles before the dehydration treatment, and that the particles are uniformly adsorbed inside the pores of the bulk body after the dehydration treatment. It is preferable to use one having a particle diameter of 1/5 or less, particularly 1/10 or less, of the average particle diameter of the H ₃ BO ₃ powder used. If it exceeds 1/5, when the components inside the H ₃ BO ₃ particles scatter, the formation of a neck with the scattered components from adjacent particles may be hindered.

The mixing ratio of H ₃ BO ₃ and carbonaceous powder is as follows:
Stoichiometrically, it can be calculated by the following formula. However, in reality, the reaction rate cannot be 100%. Therefore, considering the difficulty of removing unreacted substances, H ₃ BO ₃ is set to a theoretical value of 10 to 10. 20
It is preferable to increase the amount by about mol%.

2H ₃ BO ₃ → B ₂ O ₃ + 3H ₂ O ↑ B ₂ O ₃ + 3C + N ₂ → 2BN + 3CO

The raw material mixture may optionally contain Fe, Co, Ni, Ca, Mg as a nitriding catalyst.
And the like, or a compound thereof, and the average particle diameter thereof is preferably 1/5 or less of the H ₃ BO ₃ powder for the same reason as the carbonaceous powder.

The above-mentioned raw material mixture can be subjected to dehydration treatment by mixing and heating according to a known method. In this case, the dehydration treatment is preferably performed at a temperature of 300 to 450 ° C. If the temperature is lower than 300 ° C., the dehydration of H ₃ BO ₃ may be insufficient. May be volatilized.

The density of the obtained bulk body is not particularly limited, but is preferably 0.4 to 0.7 g / cm ³ , particularly preferably 0.5 to 0.6 g / cm ³ . If the density exceeds 0.7 g / cm ^3, may nitrogen gas into the pores can not enter the well and thus there is a possibility that unreacted substances often remain, also it is less than 0.4 g / cm ^3, produced In some cases may lead to a decrease in performance. In addition, density 0.4
The bulk body of about 0.7 g / cm ³ can be reliably obtained by setting the secondary particle diameter of the H ₃ BO ₃ powder to be used to 100 μm or more.

The bulk body molded here has an appropriate strength, so that it can be easily moved as a bulk body, and can suitably cope with the blocking of the manufacturing process. It is also possible to store it as it is in a bulk state.

In the production method of the present invention, the BN powder is obtained by heating the bulk body obtained by the above-mentioned operation in an atmosphere containing nitrogen gas by a known method. In this case, the nitriding temperature is preferably set to 1600 ° C. or higher,
If the temperature is lower than 1600 ° C., the nitrogen gas may not sufficiently contribute to the reaction.
In some cases, powder cannot be obtained. In addition, the atmosphere at the time of synthesis, but it is essential to include a nitrogen gas, NH ₃ in order to further promote the reduction of the B ₂ O ₃ of the bulk body,
To include H ₂ gas and to protect the furnace body,
Localization of an inert gas such as Ar or He can be arbitrarily performed. In addition, in consideration of productivity, the equipment used for the synthesis is most preferably a continuous furnace such as a tunnel furnace, but the use of a batch furnace or the like does not cause any particular problem.

The bulk body of the silicon nitride powder synthesized as described above is crushed and, if necessary, subjected to a purification step such as an acid treatment, whereby a high-purity, crystalline BN powder can be obtained in good yield. .

According to the method for producing BN powder of the present invention, since the bulk body produced as an intermediate is in a porous state having excellent nitrogen gas permeability, it is possible to obtain high-purity, crystalline BN powder in good yield. BN powder can be manufactured with high productivity using simplified equipment and simple processes.

[0034]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Example 1 H ₃ having an average particle diameter of 102 μm
500 g of BO ₃ powder, 130 g of acetylene black having an average particle diameter of 16 μm, and Ca having an average particle diameter of 10 μm
After mixing 30 g of O with a mixer, 200 mm × 200
The resultant was placed in a stainless steel container having a size of 100 mm (height) mm, placed in an air furnace, and subjected to a dehydration treatment at 330 ° C. for 20 hours to form a bulk body. The bulk density, bulk strength, and handleability of this bulk body were examined. Table 1 shows the results.

Next, the above-mentioned bulk body is put into a base plate of a tunnel-type pusher furnace, and subjected to nitriding treatment at 1900 ° C. for 6 hours in a nitrogen stream. After stirring for 2 hours, filtration, washing with water and drying were performed to obtain BN powder.

The yield and LC value of the obtained BN powder were measured. Table 1 shows the results.

Example 2 H having an average particle diameter of 510 μm
₃ except for using BO ₃ powder was prepared in the same manner as in Example 1, were evaluated bulk body and the BN powder. Table 1 shows the results.

Example 3 A bulk material and BN powder were evaluated in the same manner as in Example 1 except that acetylene black having an average particle size of 25 μm was used. Table 1 shows the results.

Comparative Example 1 H ₃ having an average particle diameter of 92 μm
Except for using BO ₃ powder, it was manufactured in the same manner as in Example 1, and the bulk body and BN powder were evaluated. Table 1 shows the results.

Comparative Example 2 H ₃ having an average particle diameter of 42 μm
The production was attempted in the same manner as in Example 1 except that BO ₃ powder was used. However, the production did not proceed to a bulk during dehydration, and the production was stopped.

[0042]

[Table 1] * 1 Judgment was made based on the perception of the person who performed the work of collecting from the dehydration heater and charging into the nitriding furnace. * 2 The theoretical yield of 179.1 g was defined as 100%. * 3 Based on the Gakushin Carbon Materials 117 Committee Law.

From the above results, in the embodiment of the present invention, the bulk product, which is an intermediate product in the manufacturing process, has both good density and strength, excellent handling properties, and the BN powder obtained from this bulk product The yield was also found to be high. On the other hand, in Comparative Example 1 using the H ₃ BO ₃ powder slightly shorter than the average particle diameter of the H ₃ BO ₃ powder of the present invention, there was a problem in the shape retention of the bulk body, and the yield of the BN powder was reduced. In addition, in the case of using the H ₃ BO ₃ powder having a too short average particle diameter in Comparative Example 2, a bulk body could not be produced.

With the exception of Comparative Example 2 in which a bulk body could not be formed, a highly crystalline BN powder could be obtained by a one-step reaction.

[0045]

According to the present invention, a bulk material which is excellent in shape retention, porous, has good gas permeability of nitrogen gas, has excellent handling properties, and is suitable for promoting the blocking of the manufacturing process.
Since N powder is obtained, highly crystalline BN powder can be manufactured with little loss during the process and with good productivity and workability.

[Brief description of the drawings]

FIG. 1 is a state diagram showing a state in which a mixture according to a production method of the present invention is made into a bulk, and FIG.
(B) shows the state after the dehydration treatment.

Claims (2)

[Claims] 1. A method for producing boron nitride powder, comprising dehydrating a mixture containing boric acid powder and carbonaceous powder having an average particle diameter of 100 μm or more, and then heating the mixture in a nitriding atmosphere to produce boron nitride powder. Method. 2. The method for producing boron nitride powder according to claim 1, wherein the average particle diameter of the powder other than boric acid powder contained in the mixture is 1/5 or less of the average particle diameter of boric acid powder.