JPH07110763B2 - Boron Nitride Manufacturing Method - Google Patents

Description

The present invention relates to a method for producing boron nitride. More specifically, boric acid, boric anhydride, borate, and urea, an organic compound having an NH ₂ group such as melamine are reacted by heating to produce boron nitride, an inert gas or reducing gas The present invention relates to a novel method for producing boron nitride, which is heated without flowing.

Boron nitride has excellent heat resistance, chemical stability, and lubricating properties,
Furthermore, since it also has a neutron absorbing effect, it has many uses such as various high temperature structural materials such as heat and corrosion resistant materials, electrical insulating materials, electric circuit parts, high temperature lubricants, release agents, neutron shielding material fillers, etc. It is a material that is expected to develop into other uses.

[Conventional technology]

Boron nitride is industrially (1) nitriding boron by heating boric acid, boric anhydride, borate such as borax, ammonium borate, etc. in an ammonia gas or nitrogen gas atmosphere, (2) Alternatively, these boron compounds are mixed with a nitrogen-containing compound such as melamine, urea or guanidine, and the mixture is mixed with a reducing gas such as ammonia, nitrogen, argon or helium or an inert or non-oxidizing gas atmosphere. It is produced by a method of nitriding boric acid by heating in an atmosphere (Japanese Patent Application Laid-Open No. S60-18753).
47-27200, JP-A-60-151202, JP-A-60-155507
JP-A-61-63505, JP-A-61-191505, JP-A-6
1-286207, JP-A-61-295211, JP-A-62-59506, etc.).

[Problems to be solved by the invention]

As described above, in the conventional industrial production method of boron nitride, a reducing gas or an inert or non-oxidizing gas is circulated as described above, and a boron compound or a boron compound and a nitrogen-containing compound are introduced in the atmosphere. It is manufactured by heating. A furnace is generally used as the heating means, and in order to maintain the inside of the furnace in the above atmosphere, a method of heating the furnace from the outside with an electric heater or the like is adopted.

Therefore, the heating furnace is required to be airtight in order to prevent air from being mixed in from the outside, which causes a problem that the structure of the heating furnace becomes complicated. This becomes an even bigger problem as the heating furnace becomes larger. Further, since a heating furnace is often used for heating from the outside with a heater or the like, there is a big problem that the thermal efficiency is low.

Further, among the conventional manufacturing methods described above, the method (1) of nitriding in an atmosphere of ammonia gas or nitrogen gas requires a large amount of ammonia gas or nitrogen gas. (2)
In the above method, the ratio of the boron compound such as boric acid and the nitrogen-containing compound such as melamine is usually such that the nitrogen-containing compound is excessive. However, since this excess nitrogen-containing compound is thermally decomposed to generate a harmful nitrogen-containing gas, it is necessary to treat this gas (exhaust gas). Further, this method is also similar to the method (1), that is, a reducing gas or an inert gas,
There is a problem that a non-oxidizing gas is required, and particularly when argon, helium, or the like is used as the inert gas, these gases are expensive, which makes the economy less economical.
Also in the method (1), when ammonia gas is used as the reducing gas, the excess ammonia content is contained in the exhaust gas, so that there is a problem that the exhaust gas must be treated.

These problems are greatly highlighted with the adoption of mass production, which economically constrains the widespread application development of boron nitride.

[Means for Solving Problems] The inventors of the present invention have diligently studied for the purpose of producing the high-purity boron nitride inexpensively and in large quantities to solve the above-mentioned various problems, resulting in a boron compound. It was found that the above object can be achieved by placing a mixture of a nitrogen-containing compound and a nitrogen-containing compound in a heat-resistant container with a lid and heating the container, and further, it is possible to continuously and efficiently produce boron nitride. Has been completed.

That is, the present invention puts a mixture of one or more boron compounds selected from boric acids, boric anhydride and borate salts and an organic compound having an NH ₂ group in a heat-resistant lidded container,
Provided is a method for producing boron nitride, which comprises heating the lidded container without circulating an inert gas or a reducing gas, and particularly, the periphery of the heat-resistant lidded container is oxidizable. The manufacturing method is a gas atmosphere.

The present invention will be described in more detail.

The boron compound used as the raw material in the present invention is selected from boric acid, boric anhydride (B ₂ O ₃ ) and borate salts (these compounds are collectively referred to as the raw material boron compound). Among these, orthoboric acid, metaboric acid, tetraboric acid, etc. can be mentioned as boric acid. In addition, examples of the borate include ammonium salts, sodium salts, potassium salts, magnesium salts, calcium salts of these boric acids. These borates include an anhydrous salt and a hydrated salt depending on the presence or absence of crystal water. Although any of them can be used in the present invention, when a hydrated salt is used, the content easily foams during a heating reaction with an organic compound having an NH ₂ group in a container with a lid, so that an anhydrous salt is used. Is preferred.

Incidentally, the quality of these raw material boron compounds does not need to be particularly high purity, and usually commercially available industrial chemicals are preferably used, but uniform mixing properties when mixed with a nitrogen-containing compound having an NH ₂ group In order to obtain good quality, powdery materials are preferable, but there is no particular need to make them finer.

Examples of the nitrogen-containing compound having an NH ₂ group (hereinafter abbreviated as raw material nitrogen-containing compound) include urea, melamine, melon, melem, melam, dicyandiamide, ammelide, acetoguanamine, guanidine hydrochloride, melamine chloride and the like. As for the quality of these raw material nitrogen-containing compounds, powdery industrial chemicals are preferably used as in the case of the raw material boron compounds.

In the present invention, after the raw material boron compound and the raw material nitrogen-containing compound are mixed, the mixture is placed in a heat-resistant container with a lid,
This is heated to nitrid the boron atom in the raw material boron compound by a reduction reaction to generate boron nitride.

Then, boron nitride (BN) is N / N as shown by its molecular formula.
The B atomic ratio is 1.0. Therefore, the mixing ratio of the raw material boron compound and the raw material nitrogen-containing compound should theoretically be 1.0 as the N / B atomic ratio, but in the present invention, the N / B atomic ratio is 1.0 or less to obtain boron nitride. You can However, in this case, the yield of boron nitride decreases, which is not preferable.

The method for producing boron nitride in the present invention is a method of nitriding the boron atoms in the raw material boron compound by a reduction reaction using the raw material nitrogen-containing compound as described above, so that the mixing ratio of the raw material boron compound and the raw material nitrogen-containing compound is Is usually performed in excess of nitrogen, that is, at an N / B atomic ratio of 1.0 or more. However, excessive nitrogen excess only causes the loss of the raw material nitrogen-containing compound, and therefore, in the present invention, the N / B atomic ratio is usually 1.0 to 4.0, more preferably 1.5 to 3.0.

The present invention requires a heat-resistant lidded container as described above, but since the reduction reaction in the present invention is carried out at 600 to 1600 ° C, the lidded container is required to have a material that can withstand this temperature, The material is not particularly limited as long as it has corrosion resistance. As a container with a lid having such performance,
Various ceramics sintered bodies such as alumina, titania, zirconia, silica, magnesia, calcia and silica, cordierite and mullite containing alumina as a main component are suitable, and heat resistant stainless steel can also be used.

In the present invention, when a mixture of the raw material boron compound and the raw material nitrogen-containing compound is heated, boron nitride is generated and various gases are generated. For example, when a mixture of ammonium borate and urea is heated, ammonia, carbon dioxide gas, and water vapor are generated as shown in the following formula (1).

(NH ₄₎ The _{2 B 4 O 7 +2 (NH} 2) 2 CO → 4BN + 2NH 3 + 2CO 2 + 5H 2 O ...... (1), if the raw material nitrogen-containing compound is excessive, also pyrolysis excess nitrogen-containing compound To generate various gases.

In the present invention, however, since the mixture of the raw material boron compound and the raw material nitrogen-containing compound is heated in the lidded container, the gas generated by this heating is automatically generated without much pressurization in the lidded container. In addition, the container must be structured so that combustion gas such as propane, which will be described later, does not easily flow out into the container with a lid (some ventilation is possible).

Therefore, in the case of the container with the lid, it is preferable that the lid is placed on the container body, the lid seals the container by its own weight, and the gas generated in the container is pressurized to a great extent in the container. Instead, the pressure needs to be so high that the lid is lifted slightly upward and the gas is discharged to the outside of the container. Further, it is desirable that the surface of the upper part of the container which comes into contact with the lid and the surface of the lid which comes into contact with the container come into close contact with each other when the lid is placed on the container. Further, the shape of the container is selected from any shape such as a cylindrical shape with a bottom or a square shape such as a heavy box. However, since the container is used in a state where heating and cooling are repeated, it is preferable that the container has a cylindrical shape in order to prevent the damage of the container caused by the distortion due to the heating and cooling as much as possible. Examples of the container having such a shape include those having the shapes shown in FIGS. 1 to 4, but are not necessarily limited thereto.

The shape shown in FIG. 4 is preferable because it can further prevent damage due to strain of the container.

The present invention is a method for producing boron nitride by heating a lidded container without circulating an inert gas or a reducing gas, and preferably, the periphery of the lidded container is an oxidizing gas atmosphere. Such a heating method uses, for example, a furnace, and in a state where a heat-resistant container with a lid containing the uniformly mixed raw material boron compound and raw material nitrogen-containing compound is inserted into the furnace, hot air is fed into the furnace. It can be easily implemented. Such hot air can be easily obtained by burning a fuel such as propane, butane, kerosene, or heavy oil with air. Furthermore, if this combustion is performed with excess air,
The surrounding of the lidded container can be naturally made into an oxidizing gas atmosphere. According to the present invention, since the lidded container can be heated by such a method, the heating device is extremely simple and easy to be upsized, and the fuel cost is low, so that the energy cost is low and the thermal efficiency is good.

Further, if the heating furnace is of a type such as a horizontal tunnel furnace, the container with a lid moves horizontally in the furnace, so that it is possible to continuously produce boron nitride.

And as described above, since the surrounding of the lidded container can be easily made into an oxidizing gas atmosphere, therefore, it is generated by the reaction of the raw material boron compound and the raw material nitrogen-containing compound and the decomposition of the excess raw material nitrogen-containing compound. Hazardous gas is discharged to the outside of the container with the lid and burned to be harmless, so that it is not necessary to treat the exhaust gas.

In the present invention, the mixture of the raw material boron compound and the raw material nitrogen-containing compound is heated at a temperature of 600 to 1600 ° C, preferably 800 to 1300 ° C. If the heating temperature is lower than 600 ° C, the boron nitride formation reaction is slow, which is inconvenient. If the heating temperature exceeds 1600 ° C, not only the loss of heat energy but also the heat resistance of the device must be considered.

In the above heating, the heating time varies depending on the shape, volume, etc. of the container, but is usually 1 to 10 hours.

The boron nitride thus obtained is, for example, after cooling, as disclosed in JP-A-61-61.
High purity can be easily obtained by washing with a dilute mineral acid such as dilute hydrochloric acid or dilute sulfuric acid and then washing with water as in the method described in JP-A-63505.

[Action]

According to the method of the present invention, the heating of the mixture of the raw material boron compound and the raw material nitrogen-containing compound does not need to be performed under an atmosphere of a reducing gas or an inert gas or a non-oxidizing gas as in a conventionally known method, Further, it can be suitably carried out even in an oxidizing gas atmosphere, which was not possible by the conventionally known method.

The reason is that, in the present invention, the mixture of the raw material boron compound and the raw material nitrogen-containing compound is heated in the container with the lid, but the inside of the container is filled with the decomposition gas generated by this heating.
Since this decomposed gas is a non-oxidizing gas or a reducing gas, therefore, in the present invention, it is not necessary to circulate an inert gas or a reducing gas or a non-oxidizing gas during the heating, and the surroundings of the lidded container are also It is possible to make an oxidizing gas atmosphere.

〔Example〕

The present invention will be described in more detail with reference to the following examples. still,
In the examples, parts and% are based on weight, unless otherwise specified.

Example 1 201 g of powdered anhydrous borax as a raw material boron compound and 360 g of powdered urea as a raw material nitrogen-containing compound were mixed well (N / B atomic ratio = 3.0), and the mixture was mixed with an internal volume of 1 shown in FIG. The crucible was placed in an alumina crucible, and the crucible was allowed to stand in a combustion furnace equipped with a propane burner. Thereafter, propane was burned to gradually raise the temperature in the furnace, and then the crucible was heated at about 1000 ° C. for 4 hours. After completion of heating, the crucible was allowed to cool and the powdery contents were taken out. Next, this powder is treated with tap water and a concentration of 5%.
It was washed with an aqueous nitric acid solution and dried at 120 ° C. for 4 hours to obtain 91 g of powder (yield of boron: 95%).

When this powder was analyzed by an X-ray diffractometer, a diffraction diagram as shown in FIG. 5 was obtained, and it was confirmed that the powder was boron nitride. The obtained boron nitride was analyzed by an atomic absorption spectrometer, and impurities such as sodium, iron, silica, and calcium were 0.1% or less, respectively, and the powder was highly pure boron nitride.

The decomposition gas of urea generated during heating of the crucible is
It was incinerated in the furnace and no organic matter was detected in the exhaust gas from the furnace.

Example 2 402 g of powdered anhydrous borax as a raw material boron compound and 504 g of powdered melamine as a raw material nitrogen-containing compound were well mixed (N / B atomic ratio = 3.0), and the mixture was shaped as shown in FIG. Put it in the cordierite crucible of product 2 and send it to a butane combustion type tunnel kiln whose internal temperature is kept at about 800 ℃ with the crucible placed on the carriage, and the residence time in the kiln is about 4 hours. The trolley speed was controlled so that the above, and the crucible was heated. The crucible on the trolley taken out from the tunnel kiln was allowed to cool and the powdery contents were taken out in the same manner as in Example 1, then the powder was washed with tap water and a 3% strength aqueous sulfuric acid solution, and then at 4 ° C at 120 ° C. Dried for 1 hour
84 g of powder was obtained (boron yield 93%).

When this powder was analyzed by an X-ray diffractometer and an atomic absorption spectrometer, sodium, iron, silica,
Impurities such as calcium were less than 0.1%, respectively, and high-purity boron nitride was obtained.

No organic matter was detected in the exhaust gas from the tunnel kiln.

Examples 3 to 15 Raw material boron compounds in powder form and raw material nitrogen-containing compounds were mixed at the ratios shown in Table 1, and the mixture was mixed with the internal volume 2 shown in FIG.
It was placed in a cordierite crucible having the shape shown in FIG. 4, and boron nitride was obtained in the same manner as in Example 2 below. The heating conditions of the crucible and the amount of boron nitride obtained were as shown in Table 1.

The results of analyzing the obtained boron nitride with an X-ray diffractometer and an atomic absorption spectrometer were all of high purity. No organic matter was detected in the exhaust gas from the tunnel kiln.

[Effects of the Invention] As described in detail above, the conventional method for producing boron nitride is boric acid, boric anhydride, borate compounds or a boron-containing compound and melamine, a nitrogen-containing compound such as urea,
In contrast to the method of heating in a reducing gas or an inert gas or non-oxidizing gas atmosphere, the method of the present invention puts a mixture of a raw material boron compound and a raw material nitrogen-containing compound in a heat-resistant lidded container, This is a method of heating the lidded container without circulating the reducing gas or the like as described above, and in particular, the surrounding of the lidded container is carried out in an oxidizing gas atmosphere.

Therefore, the method of the present invention does not require reducing gas,
This is not limited to this, and brings various great effects as described below. That is, the conventional method has a problem that the heating furnace requires airtightness and thus requires a complicated structure, and the heating furnace is a method of heating with an electric heater or the like from the outside, resulting in poor thermal efficiency. Further, since the exhaust gas contains harmful nitrogen-containing gas, there is also a problem that the exhaust gas must be treated.

On the other hand, since the method of the present invention is the method as described above,
Combustion gas of inexpensive fuel such as propane, butane, kerosene, heavy oil, etc. can be used for heating the heat-resistant lidded container, and the structure of the heating furnace is simple and the size can be easily increased. Combined with this, mass production becomes possible. Also, the thermal efficiency is significantly improved compared to the conventional heating furnace. Moreover, if the fuel is burned in an air-excessive state, the combustion gas can be easily converted into an oxidizing gas. Therefore, the nitrogen-containing harmful gas generated by the reaction due to the heating and the thermal decomposition of the excess nitrogen-containing compound is Since it is decomposed and rendered harmless, no exhaust gas treatment is required.

Moreover, if a heating furnace such as a horizontal tunnel furnace is adopted, the heating furnace can be easily made continuous and the working efficiency can be greatly improved.

Incidentally, the boron nitride thus obtained is subjected to a simple purification method of washing with dilute mineral acid followed by washing with water as described above,
It can be of high purity quality.

INDUSTRIAL APPLICABILITY As described above, the present invention has various advantages as compared with the conventionally known methods, and as a result, it is possible to inexpensively produce a large amount of high-purity boron nitride, and the economical effect thereof is extremely large. Is.

[Brief description of drawings]

1 to 4 are vertical cross-sectional views showing the shape of a heat-resistant container with a lid used for carrying out the present invention, and FIG. 5 is an X-ray diffraction of the boron nitride obtained in Example 1. A diagram is shown. In the figure, 1 ... container, 2 ... lid are shown.

Claims (4)

[Claims] 1. A mixture of at least one boron compound selected from boric acid, boric anhydride, and borate and an organic compound having an NH ₂ group is placed in a heat-resistant lidded container, and an inert gas or A method for producing boron nitride, which comprises heating the container with a lid without circulating a reducing gas. 2. The method according to claim 1, wherein the heat-resistant container with a lid is surrounded by an oxidizing gas atmosphere. 3. The method according to claim 1 or 2, wherein the borate is one or more of ammonium salt, sodium salt, potassium salt, magnesium salt and calcium salt. 4. The organic compound having an NH ₂ group is any one or more of urea, melamine, melon, melem, dicyandiamide, guanidine and salts thereof, ammelide, acetoguanamine, and melamine hydrochloride. The method according to item 3.