JPS6158806A - Manufacture of high-purity hexagonal boron nitride powder - Google Patents

Abstract

PURPOSE:To make crude hexagonal boron nitride (h-BN) powder high-purity for a short time at the comparatively low temp. by heat-treating the crude h-BN powder contg. anhydrous borax and/or borax of prescribed proportion in the prescribed conditions. CONSTITUTION:The crude h-BN powder is manufactured by adding 5-50wt% anhydrous borax and/or borax powder to boric acid or boron oxide as main raw material. 0.5-2wt% carbonaceous powder is added to the crude h-BN powder, mixed with each other and heat-treated at >=1300 deg.C temp. in the inert gas current.

Description

[Detailed Description of the Invention] This invention has heat resistance,! Regarding the production method of hexagonal nitride VA powder, which is known as a high-temperature material with excellent properties such as Thl slipperiness, electrical insulation, and thermal conductivity, we have recently developed a hexagonal crystal nitride powder using boron oxide and/or boron oxide as a starting material. The present invention relates to a method for highly purifying boron nitride powder.

As is well known, hexagonal boron nitride (hereinafter referred to as h-BN) has excellent heat resistance, lubricity, electrical insulation, thermal conductivity, etc. Therefore, in order to take advantage of these excellent specific properties, it is manufactured as a powder. is used for solid In materials, mold release materials, etc., and h-
Sintered bodies made from sintered BN powder are used in a wide variety of applications, including melting crucibles, electrical insulating materials, and various electronic materials.

By the way, h-BN is produced using In plates or boron oxide as a raw material.
As a conventional method for industrially manufacturing powder, the first method is to nitride the boron in the raw material by heating these boron compounds to 700 to 1100°C in an ammonia gas stream. It has been known. However, in the case of this method, when the boron oxide derived from the raw material melts during the heating process, it becomes an extremely viscous liquid, which reduces the contact interface with ammonia gas, and as a result, the reaction with ammonia gas is inhibited. It has the disadvantage of low reaction efficiency. In order to improve this, it is generally done to add and mix a filler with a high melting point, such as calcium phosphorus, into the raw materials.In this case, although the reaction efficiency increases to some extent, it is still not fully satisfactory. The reality is that it cannot be said that it is possible. Further, when a filler is added in this manner, it is necessary to wash with hydrochloric acid or the like to remove the filler after the synthesis reaction is completed, but such a wet washing step using hydrochloric acid or the like has a problem of poor processing efficiency.

As a second conventional method for industrially producing h-BN powder using VA or boron oxide as a raw material, a mixture of these boron compounds and a nitrogen-containing R or Iso compound is used.
A method of reducing and nitriding by heating to 800° C. or higher in a stream of ammonia or nitrogen gas is known. In the case of this method, the obtained h-BN powder is in a so-called crude state with a purity of about 80 to 90%. Therefore, after the synthesis reaction, the crude h-BN powder must be treated to achieve a high purity of about 99% or more. It is necessary to apply As this high purification method, as disclosed in Japanese Patent Publication No. 47-43440,
There is a method of repeatedly removing impurities such as oxygen, hydrogen, and carbon by heating crude 1h-BNyI powder in a stream of inert gas such as nitrogen or argon at 160oC to 21oO0C, or as described in Japanese Patent Publication No. 47-26600. Addition of trace amounts of alkali metal compounds such as sodium, potassium, and lithium, i.e., any of the oxides, hydroxides, carbonates, and borates of these alkali metals, to the crude h-B N powder as described. However, a method of heat treatment at 1000°C or higher has been adopted. However, crude Bh-B
The method of heating N powder in an inert gas for purification requires treatment at a high temperature of 1,600 to 2,100°C, which has the problem of significantly increasing operating and equipment costs. -BN A method in which an alkali metal compound is added to N and then heat treated has the problem that the treatment takes a long time and the treatment efficiency is low.

This invention solves the above circumstances! It was done as a scenery,
The purpose of the present invention is to provide a method for efficiently producing h-BN powder of high purity.

Specifically, the present invention, as described above, uses tIff! In this method, crude 'FJh-BN powder is synthesized using acid or boron oxide as the main raw material, and the crude h-BN powder is further purified at a relatively low temperature. Furthermore, the purpose is to provide a method that can be accomplished in a short period of time.

In order to achieve the above-mentioned objectives, the inventors of the present invention have diligently studied the actual situation and investigated the actual situation, and as a result, a conventional method (specially Publication No. 47-26600), [!
Before synthesizing h-BN, an alkali metal compound is added to the starting material and mixed, and especially anhydrous borax (Na:LB+ 07 ) is used as the alkali metal compound.
Alternatively, by using borax (N82B407 ・10H20), adding and mixing carbonaceous powder to crude h-BN powder, and performing heat treatment for high purity, high purity can be achieved at a relatively low temperature and in a short time. They discovered that this can be achieved by heat treatment, leading to the creation of this invention.

That is, the method for producing high-purity h-B N of this invention has vA
When producing h-BN using acid or allotropic oxide as the main raw material, anhydrous borax or /
and borax powder to boric acid or boron oxide.
0.5 to 2.0% by weight of carbonaceous powder is added to and mixed with the crude h-BN powder produced by adding % by weight, and the mixture is heat-treated at a temperature of 1000°C or higher in an inert gas stream. This is a characteristic feature.

The method of the present invention will be explained in more detail below.

In the method of this invention, as described above, crude h-B
Anhydrous borax (N82B40? )
Or borax (Naa8+ 07 ・10H20) (D
Add powder and mix. Then, the mixed powder was placed in a stream of inert gas such as ammonia gas or nitrogen at 80%
Crude h-BN is first synthesized by heating to 0-1000°C.

Here, the Na content of anhydrous borax or borax is crude h-BN.
It acts effectively when the crude h-B N is highly purified at a stage after the synthesis of the crude h-B N .
By mixing in the step before the synthesis, as described above, the conventional technique 1 in which an alkali metal compound is added and mixed to the crude h-BN after synthesis and subjected to heat treatment for high purity. In comparison, crude h-BNH5>The distribution of Na content in rice is uniform and finely distributed, so ffi crack 1+
- The processing time in the high purification process for BNN powder is shortened, and the i5 purification to a purity of 99% or more is achieved at a relatively low temperature range (approximately 1300 to 1500°C).

In addition, when anhydrous sand or river sand is added, the melting point (745°C) of these compounds is increased by a margin fj (ii) the melting point of M (
<450"C), even after the boron interoxide melts during the temperature raising process for the synthesis of crude h-BN, it remains as a solid and acts as a filler. Furthermore, anhydrous borax Alternatively, if the sand is melted, the sodium oxide added thereto reacts with the boron oxide solution, reducing the viscosity of the melt, increasing the gas-liquid interface with ammonia gas or inert gas, and thus making it anhydrous. The reaction efficiency is improved compared to the case where borax or borax is not added.Anhydrous borax or borax not only functions to provide Na content in the raw material as described above, but also acts as a source of grain itself. will play the role of

After synthesizing the crude 1t-BN powder as described above, the crude tfih-BN powder was pulverized, a small amount of carbonaceous powder was added and mixed therein, and the mixture was heated at 1300 °C in a stream of inert gas such as nitrogen or argon. If heat treated at temperatures above ℃,
High purity h-BN powder with a purity of 99% or more can be obtained.

In this way, a small amount of carbonaceous powder is added to the coarse 1jh-BN powder, and anhydrous borax or borax is added to the 1811-BN powder in advance at the fi stage before synthesis, and then heated for high purity. By processing, 9
aFi of over 9%! The processing time for obtaining ff is shortened, and at the same time, the processing temperature is low, about 1300 to 1500°C, and the process becomes light. That is, FIG. 1 shows that boric acid and melamine are used as starting materials, <a> anhydrous borax is added in an ioam% to 11lr11 at a stage before the synthesis of the crude h-BN powder, and the synthesized h-BN powder is In the case of the method of the present invention in which 1.5% by weight of carbonaceous powder was added and heat treatment was performed for high purity, (b) anhydrous borax was added to 1 [[ 10% by weight to the crude h-B after synthesis.
(C) Case in which heat treatment is performed for high purification without adding carbonaceous powder to N powder (C) Case in which anhydrous borax or borax is not added in the stage before synthesis of coarse 11+-BN powder and crude after synthesis ! When no carbonaceous powder is added to jh-BN powder, for the above three cases, the i degree of h-BN powder after heat treatment for high purity is determined by the heat treatment temperature during heat treatment for high purity. The results were investigated with various changes. From FIG. 1, in the case of method (a) of the present invention in which both anhydrous borax was added before synthesis of crude h-BN powder and carbonaceous powder was added to crude h-BN powder, both anhydrous borax and carbon powder were added. J! is much lower than the case without additives (C).
l! l! It can be seen that a high purity of 99% or more was achieved at the processing temperature, and even when compared with the case (b) in which anhydrous borax was added alone, high purity was achieved at a low heat treatment temperature.

Therefore, the addition of anhydrous borax before the synthesis of the crude h-BN powder and the addition of carbonaceous powder to the crude h-BN powder are the heat treatment steps for achieving high purity. It is clear that it is very effective in lowering the temperature. In this experiment, 102 parts of melamine were added to 100 parts of Fl Shun, and the heat treatment for synthesizing the crude h-BN powder was carried out by holding it at 900°C for 2 hours in an ammonia gas stream. The heat treatment time for purifying BN was kept constant at 30 minutes, and the heat treatment was carried out in a nitrogen gas stream.

Furthermore, Figure 2 shows that 10 wt. %, and the same sphere as in (C) without the addition of both anhydrous borax and carbonaceous powder. ! I! temperature 1500
℃, and the treatment time was changed from h to h after treatment.
-The purity of BN powder was investigated. From Figure 2, t
In the case of this invention, the heat treatment time for high purity is also (a)
It is clear that this will be significantly shortened. The other conditions in the experiment shown in FIG. 2 were the same as those in the experiment shown in FIG.

Each process condition and material compounding condition in the method of the present invention as described above will be further explained.

First, the amount of anhydrous borax or borax added to 1 m or boron oxide as a starting material must be within the range of 5 to 50% by weight based on the weight of WI acid or boron oxide. The reason is as follows. That is, 5ffif
With a small amount of less than fi%, these addition effects, namely Na
It cannot be said that the dispersion in the entire reaction system is good, and 130
High purity is not achieved in a relatively low temperature range of 0 to 1500°C, and the reaction rate is not significantly improved compared to the case without additives.

In addition, if it is added in an amount exceeding 50%, the dispersion state of Na becomes good.
The time required for volatilization of a component becomes longer, and in some cases, Na component may remain in the powder after heat treatment. Here, it goes without saying that either anhydrous borax or borax may be used alone or in combination.

The amount of nitrogen-containing insensitive or dominant compounds specified as starting materials or added to nitric oxide is as follows:
In the conventionally known method, boric acid or oxidized 'vA element 10
It is sufficient to use about 70 to 200 parts by weight based on the oi foot, and the nitrogen-containing nitrogen-containing or organic compounds are the same as conventional ones (for example, countless compounds such as urea, thiourea, biuret, guanidine, or melamine, dicyandiamide). , semicarbazide cyanuric compound, and the like can be used.

As mentioned above, the heat treatment of the mixed powder obtained by adding and mixing anhydrous borax or boron to 61 or an inorganic or major compound containing boron oxide and nitrogen as a starting material, that is, the P treatment for synthesizing crude h-BN, is conventional. As in the method, it may be carried out at a temperature of 800 to 1000°C in a stream of ammonia or inert gas. processing)] degree is 800
If the temperature is below ℃, the reaction will not proceed completely and the yield will drop significantly. On the other hand, if the temperature exceeds 1000°C, the reaction rate can be increased, but it is not economically advantageous. Note that the processing time may be about 30 minutes to 5 hours.

The amount of carbonaceous powder added to the lrJ crude h-BN powder is 0.5 to the weight of the crude h-8N powder.
It needs to be within the range of ~2.0ffiffi%. When the amount of carbonaceous powder added is less than 0.5% by weight, it is difficult to obtain the desired high-purity h-BN powder in a short time and at a relatively low temperature [! ! ] It becomes difficult. On the other hand, the addition amount of determinant powder is 2.
If it exceeds 0% by weight and 1% by weight, it may remain in the rice after treatment depending on the heat treatment conditions as a carbon source or impurity, which is not appropriate. Here, coarse! As the carbonaceous powder added to the 411-BN powder, any carbonaceous powder can be used, from amorphous to highly graphitized powder.
Preferably, an amorphous material is more effective.

Crude h-BN mixed with carbonaceous powder in this way
The heat treatment for high purity of the powder may be performed in a flow of an inert gas such as nitrogen or argon, as in conventionally known methods. Regarding the processing temperature, as mentioned above, in the method of this invention, the temperature is lower than that of the conventional method.
% or more, but if the temperature is below 1300°C, the time required for high purification becomes significantly longer, which is contrary to the purpose of this invention, which is to shorten the thermal 7A processing time. The temperature must be at least 1300°C or higher. On the other hand, the upper limit of the processing temperature is not particularly limited, but in order to produce 99% or more '1B' 12 degree powder at low cost, it is necessary to
It is desirable that the temperature be less than 600°C, preferably 1500°C or less. Furthermore, the heat treatment time for B purification is !
! ! Although it is difficult to determine clearly due to the relationship with the processing temperature, 30 minutes to 2.5 hours is usually sufficient, and if the processing temperature is the same, the processing time is much shorter than that of the conventional method. r
It goes without saying that the degree of A degree will be "r5".

Comparative examples of the present invention and the conventional method will be described below.

1Ml5!11 Starting materials: 100 parts by weight of boric acid and methi 42102
Anhydrous borax powder corresponding to 10% by weight of the wall strength was added thereto and dry mixed.

This mixed powder was filled into an iron reaction container and heat-treated at 900°C for 2 hours in an ammonia gas stream to give a +1
-BN was synthesized. (The purity of the obtained crude 11+-BN powder was 90.8%. 2.3 g of non-quality graphite powder was added to this crude 1fl11-8N powder 1509,
After dry mixing, it was filled into a graphite crucible and heat treated in a nitrogen stream at 1500°C for 2 hours using Tammans.
9g was obtained.

Example 2 In the same manner as in Example 1, borax powder in an amount corresponding to 20% by weight of the boric acid was added to 100 parts by weight of boric acid and 102 parts by weight of melamine and dry mixed. This mixed powder was filled into an iron reaction vessel and heat-treated in an ammonia gas stream at 900° C. for 3 hours to synthesize h-BN. The obtained crude h
-The purity of the BN powder was 88.6%. This crude h-
2.6g amorphous graphite powder 8 for 8N powder 1509
After adding and dry mixing, it was filled into a graphite crucible and heat-treated in a nitrogen stream at 1500°C for 2 hours using Tammans. As a result, high purity h-BN with a purity of 99.8% was obtained.
120 g of powder was obtained.

Comparative Example: After dry-combining Boron 1!100 mouth portion and Melazine 102 heavy portion as starting materials, the mixed powder was charged into an iron reaction vessel and heated at 900°C in an ammonia gas stream.
Nai WJh-81'J powder was produced under the condition of holding for 2R. The longitude of the 2fl 1+-BN powder was 84.4%. This ff1l (1 for 150g of h-8N powder
After adding and mixing 3g of sodium powder, it was filled into a graphite crucible and heated to 1500 ml in a N gas stream using Tammans.
As a result of heat treatment under the conditions of holding at °C for 3 hours, the purity was 99.6.
% h-8N yj powder was removed.

The above comparative example is a crude 1l-B without adding carbonaceous powder and after synthesizing sodium anthracite as an alkali metal compound.
Compared to such a comparative example, according to the method of this invention, high-purity h-B N powder was added in a shorter amount of time than in the comparative example. It is clear that the product can be obtained in good yield in a short period of time.

As is clear from the above explanation, the high purity h-8N of this invention
According to the I powder [& method, anhydrous borax or borax is used as an alkali forming compound, the anhydrous borax or borax is added and mixed to the starting material at the stage of the synthesis value of coarse 1h-BN, and the I after synthesis is By adding and mixing a small amount of carbonaceous powder to manufactured h-BN powder and performing heat treatment for high purity, crude I+-BN can be obtained by heating in a short time and at a relatively low temperature.
The V of the powder can be purified, and the yield of high-purity 1l-BN powder is also low. The manufacturing cost] can be significantly reduced compared to the conventional method.

[Brief explanation of the drawing]

Figure 1 is a phase IF1 diagram showing the relationship between the heat treatment temperature and the purity of the h-BN powder after treatment in heat treatment for high purity of the crude h-BN powder, and Figure 2 is the same as the crude h-BN powder. Addition for high purity! ! ! FIG. 2 is a correlation diagram showing the relationship between heat treatment time in 1rlS process and h-BNN powder purity after treatment.

Claims (1)

[Claims] When producing hexagonal boron nitride using boric acid or boron oxide as the main raw material, a crude product produced by adding 5 to 50% by weight of anhydrous borax and/or borax powder to the boric acid or boron oxide when mixing the raw material powder. A high-purity hexagonal crystal characterized by adding and mixing 0.5 to 2.0% by weight of carbonaceous powder to hexagonal crystal boron nitride powder and heat-treating the mixture at a temperature of 1300°C or higher in an inert gas flow. Method for producing boron nitride powder.