JPH05853A - Production of ordinary pressure sintered body of boron nitride - Google Patents

Abstract

PURPOSE:To enhance purity by heating a powdery mixture of B4C with B2O3 or a B-contg. compd. in a specified weight ratio in an N-contg. nonoxidizing atmosphere, molding the resulting BN-contg. unreacted B4C and sintering the molded body in an N-contg. nonoxidizing atmosphere. CONSTITUTION:B,0, powder or powder of a B-contg. compd. forming B2O3 by a reaction is added to B4C powder by 30-46wt.% (expressed in terms of B2O3) and they are mixed in a solvent such as acetone, dried, pelletized and fired by heating at 1,300-1,800 deg.C in an Ncontg. nonoxidizing atmosphere of N2, NH3, etc. The resulting BN contg. <=10wt.% unreacted B4C is pulverized to form fine particles having 10-50m<2>/g specific surface area, the particles are molded and this molded body is sintered at 1,500-2,100 deg.C in an N-contg. nonoxidizing atmosphere of N2, NH3, etc., to obtain a high density and high purity ordinary pressure sintered body of BN.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Hexagonal boron nitride has excellent thermal shock resistance, corrosion resistance, lubricity, electrical insulation, and high thermal conductivity, and its molded product has various heat resistance, lubricity, and thermal conductivity. Widely used in fields that require sex. The present invention is a high-density and beautiful atmospheric pressure sintered boron nitride (B
N) relates to a method for producing a body.

[0002]

2. Description of the Related Art Hexagonal boron nitride is a material having many excellent properties such as excellent thermal, chemical and electrical properties, lubricity, and ease of machining. However, since it is difficult to sinter, the pressure sintering method has hitherto been required to obtain a high-density sintered body, resulting in a high cost. Although such a problem of cost was one of the constraints in application, there is a wide demand for utilizing the excellent characteristics of hexagonal boron nitride sintered body, and inexpensive atmospheric pressure sintering method has been studied. Is coming.

Up to now, there are many atmospheric pressure sintering methods for hexagonal boron nitride, which have been proposed by patents and literatures. The main ones are pulverized high-purity BN powder or low-purity amorphous BN at 2 ton / cm ² by metal molding or rubber press molding, and then the compact is placed in a crucible together with BN packing powder. , Atmospheric pressure sintering in argon at 1400 to 2000 ° C. (Japanese Patent Laid-Open No. 2-9763, J. Am. Ce.
ram. Soc. , 72 (1989) 1482) amorphous boron was added to the turbostratic structure BN of low purity, and nitrogen (N
₂ ) Method of reacting and sintering at 1500 to 1800 ° C. in medium (Journal of Japan Society for Natural Resources, 105 (1989) 201) Amorphous B and XO.B ₂ O ₃ (X
Is an alkaline earth metal), N ₂
Method of reacting and sintering in a chamber (JP-A-62-123070)
Method of adding 30 wt% of SiO ₂ · B ₂ O ₃ to BN and sintering at atmospheric pressure (Japanese Patent Publication No. 47-38047) S
Metal such as i, Al, Ti and Cr is 10 to BN.
A method of adding 50 wt% and performing reaction sintering (Japanese Patent Laid-Open No. 59-16
9982) A method in which B ₂ O ₃ is added to BN and pressure-sintered (Japanese Patent Publication No. 38-12547). Further, as a method developed by the present inventors, highly pure and highly crystalline BN
To 5 m ² / g or more, preferably 20 m ² / g or more, and 0.1 to 20 wt% of boron carbide (B ₄ C) and 0.
A method of adding 1 to 20 wt% of one or more alkaline earth metal compounds and sintering under normal pressure in N ₂ at 1600 to 1800 ° C. (Japanese Patent Laid-Open No. 64-3074) for BN powder crushed to 30 m ² / g or more 0.1-40 wt% B ₄ C and baking in N ₂ (JP-A-1-103960)
1-30 m 0.1 to 40% relative to the ² / g of powder and 100 m ² / g or more powder BN powder obtained by blending
Of B ₄ C and firing in N ₂ (Japanese Patent Application Laid-Open No. 1-1.
03959). and so on.

However, these proposed methods for producing a BN atmospheric pressure sintered body have the following problems.

For example, the methods (1) to (3) are methods by which a sintered body having a relatively high BN purity can be obtained. However, in both cases, it is difficult to obtain a high-density sintered body because the volume expansion and the weight reduction occur during sintering. When the density of the sintered body is low, the corrosion resistance is reduced, which may limit the use under severe conditions.

[0006] Volume expansion is one of the characteristics of the BN normal pressure sintered body, and it is unavoidable at the present when no sintering aid that causes shrinkage during sintering has been found. The weight reduction is mainly due to the fact that the oxygen originally contained as an impurity in the raw material, or the oxygen introduced by oxidation / hydrolysis when BN is pulverized, volatilizes as B ₂ O ₃ during sintering. Caused by. However, even if highly pure BN having high crystallinity is used without crushing in order to reduce weight loss, sintering does not occur at all because of poor activity.

In the method of adding a large amount of additives and sintering as in the methods (1) to (4), the BN purity of the obtained sintered body is lowered, and the original characteristics of BN such as corrosion resistance, insulation, and easy workability are reduced. Be damaged. Further, when used at a high temperature, contamination of the vicinity due to volatilization of the additive, cracking of the BN sintered body itself, and the like may occur, limiting the operating temperature.

According to the above method, the strength of the sintered body is only 5K.
Since it is g / cm ² , it is unlikely to be practical.

On the other hand, the methods (1) to (3) disclosed by the present inventors have been made in consideration of these problems, and have hitherto been high density-low purity or low density-high purity sintering. It was intended to provide a method for producing a high-density and high-purity sintered body, which is different from the conventional method in which only a body was obtained.

The feature of the above method is that boron carbide is used as a sintering aid. Even if boron carbide is used as a sintering aid, no contraction occurs during sintering, and the expansion coefficient does not decrease, as in many other atmospheric pressure sintering methods. However, when boron carbide reacts with oxygen (B ₂ O ₃ ) contained in the BN powder to generate BN, a weight increase occurs, so that a decrease in density after sintering is small as compared with other methods, Moreover, the purity is high. According to the above method, a BM normal pressure sintered body having a BN purity of 99% or more and a sintered body density of 1.80 g / cm ³ or more can be obtained.

However, there is still room for improvement in the above method. That is, it is difficult to completely nitrid (boronize) boron carbide added as an auxiliary agent, and when the thickness of the sintered body becomes several mm or more, unreacted boron carbide becomes black in the center of the sintered body. It was a core and it was easy to remain.

[0012]

The boron nitride sintered body is
Since it is usually used as a thin plate or a thin-walled article such as a crucible, a technique with a nitridable thickness of about several mm can be used in these fields, but there is a large restriction on the shape. Therefore, in order to expand the range of application, it is desirable to be able to make thicker BN pressureless sintered bodies having high density and high purity, and it is an object of the present invention to provide a method for manufacturing the same.

[0013]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors to make up for the above-mentioned drawbacks of the prior art, a boric anhydride compound or a boron-containing compound which produces boric anhydride under reaction conditions was converted to boric anhydride. A small amount of unreacted boron carbide is obtained by heating and reacting a mixture with a boron carbide powder having a content of 30 to 46 wt% as converted boric anhydride in a non-oxidizing atmosphere containing nitrogen such as nitrogen and ammonia. After leaving boron as a boron nitride reaction product, then crushing and molding,
If a boron nitride atmospheric pressure sintered body characterized by being heated and sintered at 1500 to 2100 ° C. in a non-oxidizing atmosphere containing nitrogen such as nitrogen or ammonia, it is completely nitrided even if the thickness is more than double that of the conventional one. Possible high-density and high-purity BN
The inventors have found that an atmospheric pressure sintered body can be obtained, and completed the present invention. The present invention will be described in detail below.

In the present invention, first, a mixture of B ₄ C powder and B ₂ O ₃ or a boron compound which produces B ₂ O ₃ under reaction conditions is fired in a non-oxidizing atmosphere containing nitrogen such as nitrogen or ammonia. Then, BN conversion reaction of B ₄ C is caused.
The boron compound used in this reaction is not particularly limited as long as it can generate boric anhydride by thermal decomposition of B ₂ O ₃ or boric acid, etc., but with respect to B ₄ C, a nitriding (BN conversion) reaction is easy. It is preferable to use a finer particle from the viewpoint of proceeding to the above step.

It is considered that the reaction between B ₄ C and a boron compound such as B ₂ O ₃ proceeds as shown in the following formula (1). 3B ₄ C + B ₂ O ₃ + 7N ₂ → 14BN + 3CO (1) According to the formula (1), the theoretical formulation for producing BN from B ₄ C and B ₂ O ₃ is 70.42 wt% B ₄ C-2.
It is 9.58% B ₂ O ₃ . However, even if both are mixed at the theoretical value calculated from the formula (1) and reacted in N ₂ , the low boiling point component B ₂ O ₃ volatilizes in a considerable ratio before the reaction, so If the mixture is simply calcined, B ₄ C
Is difficult to completely nitride. Therefore, B ₂ O
Boron compounds such as ₃ should be added in excess of the value represented by the formula (1).

[0016] B for the mixing ratio of ₂ O more containing compounds such as _3, B ₂ O ₃ is to exceed the formula twice (B ₂ O ₃ about 46 wt% in the mixture) of the theoretical value indicated by (1) Even if compounded with, the unnecessary B ₂ O ₃ is volatilized, and only the precipitation of B ₂ O ₃ on the pipe or the like is increased, and the reaction of the formula (1) is not promoted any more. On the other hand, when the compounding ratio of the boron compound to B ₄ C decreases, the unreacted B ₄ C
Increase the residual amount of. However, in the method according to the present invention, since a complete nitriding may be performed in the second heating and sintering described later, a small amount of B ₄ C may remain at this stage.
However, when B ₂ O ₃ is less than 1.0 times the theoretical value, the residual amount of B ₄ C becomes excessive, and it becomes difficult to perform complete nitriding even in the second heating and sintering.

Therefore, the boron compound such as boric acid is
It is preferable that the amount is 1.0 to 2.0 times the theoretical value represented by the formula (1) in terms of B ₂ O ₃ .

The B ₄ C and boron-containing compound adjusted to the above composition is thoroughly mixed with water or a general organic solvent such as acetone or ethanol, and then dried. The dried mixture may be stored in a crucible or the like as it is and baked,
Since it is difficult to handle, it is better to mold it into a suitable size with a suitable pressure to form a pellet.

These are put into a crucible and heated and reacted in a non-oxidizing atmosphere containing nitrogen such as N ₂ or ammonia. Regarding the reaction temperature, the reaction rate is slow at 1300 ° C or lower, and a considerable amount of B ₄ C is generated even after heating for a long time.
Remains. On the other hand, if heated to 1800 ° C or higher, B ₂ O
The volatilization loss of ₃ is only large, but rather B ₄ C
The residual amount of will increase. Therefore, the heating reaction temperature is preferably 1300 to 1800 ° C.

Next, the obtained pellets are finely pulverized and used as a raw material for producing a sintered body. When the unreacted B ₄ C content does not exceed 10 wt% by the first heating reaction, the BN reaction product can be molded as it is and heat-sintered in an N ₂ stream.

The unreacted B ₄ C content is 10 wt%
In the case of the above, BN powder not containing B ₄ C, for example, commercially available BN powder is mixed in an appropriate ratio so that the B ₄ C content is 10%.
It is preferable that the content of the mixed powder is not more than wt%, and the mixed powder is molded by a conventional method and heated and sintered. When B ₄ C is present in an amount of 10 wt% or more in the green body before heat-sintering, complete nitriding of B ₄ C not only requires a long sintering time but also causes a black core to remain.

The specific surface area of the crushed powder is 10 m ² /
If it is less than g, the activity of the pulverized powder is poor and it is difficult to sinter. On the other hand, when the specific surface area exceeds 50 m ² / g, the filling property is lowered and the density is lowered. Further, since the pore diameter between the particles becomes small, the nitriding reaction of the remaining B ₄ C becomes difficult to proceed, and the black core is likely to remain in the sintered body. Therefore, the specific surface area of the pulverized powder is preferably 10 m ² / g or more and 50 m ² / g or less.

In the case of molding the sintered body, a binder for molding or the like is added to these finely pulverized raw materials, if necessary, and water or a general organic solvent such as ethanol / acetone is added, in a conventional manner. And mix well. The obtained slurry is dried and granulated using an appropriate drying means such as a spray dryer, and molded into a predetermined shape by die molding, rubber press molding or a combination thereof. In order to increase the molding density, pressure molding is performed at 1 ton / cm ² or more, preferably about 2 ton / cm ² . However, the method is not limited to the pressure molding method as long as the density of the molded body can be sufficiently increased, and any method such as a slip casting method or an extrusion molding method may be used.

The obtained molded body is white to black gray in color depending on the amount of B ₄ C remaining in the raw material used, and this is usually kept in a non-oxidizing atmosphere containing nitrogen or nitrogen such as ammonia. A white sintered body is obtained by pressure sintering. Regarding the sintering temperature, when the temperature is 1500 ° C. or lower, the reaction rate of the formula (1) becomes slow, so that it is difficult to whiten a black sintered body in particular, and a black core remains in the center even after firing for a long time. Further, when the residual amount of B ₄ C is small, whitening is possible even if sintering is performed at a low temperature, but the bond between particles is weak and a sintered body having high strength cannot be obtained. On the other hand, when the sintering is performed at 2100 ° C. or higher, the reaction easily proceeds, but the crystal grains become coarse and the strength is lowered. Therefore, the sintering temperature is 1500 ℃
Above 2100 ° C. is desirable.

When a BN atmospheric pressure sintered body is produced by the method of the present invention, B ₄ C is directly used as an auxiliary agent.
3074, JP-A-1-103959, and JP-A 1-1
A thicker sintered body with a high density and no black core can be obtained more easily than the method disclosed by 03960. Although the details are unknown so far, it is presumed that one of them is related to the existence state of boron carbide contained in the powder.

As described above, the amount of boron carbide contained in the powder obtained by firing B ₄ C and the boron-containing compound in nitrogen can be arbitrarily adjusted by changing the compounding ratio and firing conditions. When these obtained powders were examined by X-ray analysis, the peak intensity of B ₄ C increased as the carbon content increased. However, B ₄ C calculated back from carbon analysis values
Content is B ₄ measured by X-ray quantitative analysis
The value was clearly smaller than the C content.

For boron-carbon compounds, B ₄ C (B
_It is thought that there are B ₁₃ C ₂ , B ₁₂ C, etc. in addition to ₁₂ C ₃ ), but these have the same crystal structure and only the elements at lattice points are replaced, so only X-ray analysis is possible. It is not possible to determine with, and the state diagram has not been finalized. However, it is certain that boron carbide has a wide composition range. In (1), if B ₄ C the more increases the weight increase with try the B ₁₂ C by replacing B ₁₂ C, in order to obtain the same weight gain in the case of using B ₄ C is It can be seen that the addition amount is smaller than that of B ₄ C. Further, it is easily estimated that the amount of carbon to be removed to the outside of the system is smaller than that in the case of using B ₄ C, and nitriding becomes easier.

From the above points, the carbon contained in the powder obtained from boron carbide and the boron-containing compound does not exist as B ₄ C but as a boron carbide having a low carbon content such as B ₁₂ C. Therefore, it is considered that nitriding proceeds more easily and a high-density sintered body can be obtained more easily than when B ₄ C is used.

Another cause is considered to be the particle size of unreacted B ₄ C present in the BN reaction product. That is, during the reaction of the B ₄ C powder used in the heating reaction, the BN formation reaction proceeds from the surface, leaving a B ₄ C core finer than the particle size mixed in the central portion. Therefore,
Commercially available B ₄ containing coarse particles even if the B ₄ C content is the same.
The method of the present invention using a reaction product of B ₄ C and B ₂ O ₃ in which fine particles of B ₄ C are uniformly dispersed is easier to nitride and leaves a black core, as compared with the case where C is directly used as an auxiliary agent. It is considered difficult.

This means that when 10 wt% of commercially available B ₄ C containing coarse particles is added to BN powder and molded and sintered in a nitrogen stream, the fine particles of B ₄ C become BN relatively easily. ,
Coarse-grained B ₄ C leaves an unreacted core.

On the other hand, when BN powder was added to the reaction product obtained by reacting a mixture of B ₄ C and B ₂ O _{3 in} a nitrogen stream to adjust the B ₄ C content to 10 wt%, and this was molded and sintered. , Even if the content of B ₄ C contained in the molded product is the same, B ₄ C
Since the particle size of B is smaller than that of the commercially available product, the nitriding reaction easily proceeds and B ₄ C disappears, which also suggests that the above estimation is correct.

[0032]

In the present invention, B ₂ O ₃ powder and B ₄ C powder are heated and reacted so that a small amount of B ₄ C powder remains.
An attempt is made to produce a high-density and high-purity BN sintered body by using an N reaction product as a raw material.

Boron carbide (not necessarily B ₄ C as described above)
However, in the present invention, it is represented by B ₄ C. ) Has a peculiar property of increasing the weight during sintering, and it becomes a high density sintered body even at normal pressure.

In this case, the particle size of the B ₄ C powder is sufficiently pulverized before the reaction, and the B ₄ C powder is further subjected to the BN conversion reaction so that the B particles are sequentially B
It is considered that the particle size of B ₄ C in the BN reaction product is further reduced by the above reaction because it is converted to N, and only the core remains.

The core-like B ₄ C reaction product was pulverized,
Since it is molded and sintered in a nitrogen-containing non-oxidizing atmosphere, there is almost no chance that B ₄ C remains unreacted, and it easily becomes BN, so a high-density, high-purity white BN fired molded product is produced. I think it can be done.

[0036]

【Example】

(Examples 1 to 9) 40 wt% of B ₂ O ₃ was added to 60 wt% of B ₄ C, sufficiently mixed in acetone, and then dried. This was molded into pellets with a diameter of 20 × 15 mm at 1 ton / cm ² , and the temperature was 1300 ° C and 1500 ° C in a nitrogen stream.
After holding at 1700 ° C. for 4 hours and firing, the powder was pulverized with a ball mill so that the specific surface area was about 30 m ² / g. A binder of 2 wt% was added to the obtained fired powder, thoroughly mixed in acetone, and then dried. This was molded into a size of φ50 × 10 mm at 2 ton / cm ² , and 1500 ° C. × 8 hr, 1700 ° C. × 6 in a nitrogen stream.
It was sintered under each condition of hr and 2000 ° C. × 4 hr. The density of each of the obtained sintered bodies was 1.80 g / cm.
^It was over ³ . Further, when the sample was cut and the cross section was observed, no black core was observed in any of them. The strength of the sintered body tends to increase as the sintering temperature increases,
400Kg / c when sintered above 1700 ℃
The value was m ² or more.

(Comparative Example 1) Sintering conditions were 2200 ° C. × 4 h
Sintered bodies were prepared in the same procedure as in Examples 7 to 9 except that the r was used. No black core was found in the obtained sintered body, but both the density and strength were lower than those of the sample sintered at 2000 ° C., and the density was 1.75 g / cm ³ and 200 Kg / cm ² , respectively. there were.

Comparative Examples 2 to ₃ 40 wt% of B ₂ O ₃ was added to 60 wt% of B ₄ C, thoroughly mixed in acetone, and then dried. Φ20 × 1 at 1 ton / cm ²
Molded into 5 mm pellets, 1200 ° C in a nitrogen stream
After being held at 1,900 ° C. for 4 hours for firing, they were pulverized with a ball mill so that the specific surface area was about 30 m ² / g. A binder of 2 wt% was added to the obtained fired powder, thoroughly mixed in acetone, and then dried. This was die-molded at 2 ton / cm ² into a size of φ50 × 10 mm and sintered in a nitrogen stream at 2000 ° C. × 4 hr. The density and strength of the obtained sintered body were both 1.9.
Although it exceeded 0 g / cm ³ and 500 Kg / cm ² , a thick black core remained in the center of the sintered body.

(Comparative Example 4) B ₄ C 30 wt% B
70% by weight of ₂ O ₃ was added, thoroughly mixed in acetone, and then dried. Φ20 × 15 at 1 ton / cm ²
mm pellets, and kept at 1700 ° C. for 4 hours in a nitrogen stream and baked, and then has a specific surface area of about 30 m ² / g.
It was crushed with a ball mill so that A binder of 2 wt% was added to the obtained fired powder, thoroughly mixed in acetone, and then dried. Φ5 at 2 tons / cm ²
Molded into a size of 0 x 30 mm and put in a nitrogen stream for 20
Sintering was carried out under the conditions of 00 ° C. × 4 hr. The obtained sintered body had no black core, and had a density and strength of 1.59 g / each.
cm ³ and 440 Kg / cm ² . But B
₄ C and not be obtained only a low sintered body density by using the powder completely nitrided, also reduces the yield per one batch of composite obtained from B ₄ C and B ₂ O _3, B ₂ In-furnace contamination due to volatilization of O ₃ also increased.

(Comparative Example 5) B ₄ C 75 wt% B
25% by weight of ₂ O ₃ was added, thoroughly mixed in acetone, and then dried. Φ20 × 15 at 1 ton / cm ²
mm pellets, and kept at 1700 ° C. for 4 hours in a nitrogen stream and baked, and then has a specific surface area of about 30 m ² / g.
It was crushed with a ball mill so that A binder of 2 wt% was added to the obtained fired powder, thoroughly mixed in acetone, and then dried. Φ5 at 2 tons / cm ²
Molded into a size of 0 x 10 mm and put in a nitrogen stream for 20
Sintering was carried out under the conditions of 00 ° C. × 4 hr. The density and strength of the obtained sintered body were 1.89 g / cm ³ and 570 Kg.
/ Cm ² , but a thick black core remained in the center of the sintered body.

[0041]

(Examples 10 to 12) 35 wt% of B ₂ O ₃ was added to 65 wt% of B ₄ C, thoroughly mixed in acetone, and then dried. Φ20 at 1 ton / cm ²
Molded into pellets of × 15mm, 170 in nitrogen stream
After baking at 0 ° C for 4 hours, the specific surface area is about 30m.
^It was crushed with a ball mill so that the amount became ² / g. The B ₄ C content of the obtained fired powder was quantitatively analyzed by an X-ray analysis method and found to be about 15%. 35.1 for this powder
Commercially available highly crystalline BN powder pulverized to m ² / g of 30, 5
0 and 70 wt%, and 2 wt% of each binder were further added, thoroughly mixed in acetone, and then dried. This was die-molded at 2 ton / cm ² into a size of φ50 × 30 mm and sintered in a nitrogen stream at 2000 ° C. × 4 hr. When the obtained sintered body was cut and the cross section was observed,
No black core was observed in any of them. The density and strength of the sintered body tended to decrease with an increase in the compounding ratio of BN powder, but in both cases, the density showed a value of 1.80 g / cm ³ or more and the strength showed a value of 400 Kg / cm ² or more. .

(Comparative Example 6) The compounding ratio of BN powder was 0 wt%.
A sintered body was prepared by the same procedure as in Examples 11 to 13 except for the above. The density and strength of the obtained sintered body were 1.90 g / cm ³ and 600 Kg / cm ² , respectively, but a thick black core remained at the center.

[0044]

[0045]

INDUSTRIAL APPLICABILITY The present invention provides a method for producing a thick atmospheric pressure sintered compact having excellent properties such as heat shock resistance, corrosion resistance, electrical insulation, high thermal conductivity, heat resistance and lubricity that hexagonal BN has. It was developed.

The atmospheric pressure sintered body obtained by the method of the present invention has a stable physical property because no black core remains even if it is thick, and it has high purity and high density because there is no extra additive. Since it has the corrosion resistance peculiar to BN and does not contain any additives, it does not pollute the neighborhood even at high temperatures and has a wide operating temperature range.

Further, since the BN reaction product is easily sinterable and can be sintered under normal pressure, a sintered body can be manufactured with high productivity, and the molded body does not crack during molding and sintering. An excellent BN molded body can be obtained.

Claims (4)

[Claims] 1. A boric anhydride powder or a mixture of a boron-containing compound which produces boric acid anhydride under reaction conditions and a boron carbide powder having a boric anhydride content of 30 to 46 wt% is converted into nitrogen. , Ammonia and other nitrogen-containing non-oxidizing atmospheres are heated and reacted to form a boron nitride reaction product that leaves a small amount of unreacted boron carbide, which is then crushed and shaped to contain nitrogen and ammonia and other nitrogen. A method for producing a boron nitride atmospheric pressure sintered body, which comprises heating and sintering at 1500 to 2100 ° C. in a non-oxidizing atmosphere. 2. The boron nitride atmospheric pressure sintered body according to claim 1, wherein the heating reaction temperature of the mixture of boron-containing compound or boron-containing compound that produces boric acid anhydride under reaction conditions is 1300 to 1800 ° C. Production method. 3. A boron nitride reaction product having a boron carbide content not exceeding 10 wt% in a boron nitride reaction product obtained by heating reaction is molded as it is, and heated and sintered in a nitrogen stream. A method for producing a boron nitride atmospheric pressure sintered body according to claim 1. 4. A boron nitride reaction product having a boron carbide content of 10% or more by weight, and boron nitride powder containing no boron carbide so as to have a boron carbide content of 10% or less. The method for producing a boron nitride atmospheric pressure sintered body according to claim 1, wherein the boron nitride atmospheric pressure sintered body is formed by molding and heat sintering in a nitrogen stream.