JPH0280308A - Production of boron nitride powder having low crystallinity - Google Patents

Abstract

PURPOSE:To obtain BN powder having low crystallinity and low metal content by heating and washing BN powder having low crystallinity prepd. by heating and washing an alkali or alkaline earth borate together with an N-contg. compd., in inert gas or reducing atmosphere. CONSTITUTION:BN powder having low crystallinity, 50-450m<2>/g specific surface area and >=1000ppm content of alkali or alkaline earth metal (expressed in terms of atom) is prepd. by reducing a powder mixture consisting of a borate of an alkali or alkaline earth metal (e.g., sodium borate) with an N-contg. compd. (e.g., urea) mixed in 1.0-4.0 atomic ratio N/B, by heating at 650-1100 deg.C for 1-7hr in a reducing gas or inert gas atmosphere, and washing the product with dil. mineral acid having 0.1-10wt.% concn. and with water. Obtd. BN powder is then heated at 500-1100 deg.C for 30min-2hr in inert gas or reducing gas atmosphere or in a covered vessel, then washed with dil. mineral acid and water, to obtained thus BN powder having low crystallinity, 50-450m<2>/g specific surface area and <=150ppm content of alkali or alkaline earth metal (expressed in terms of atom).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing boron nitride powder, which is suitable as a raw material for boron nitride sintered bodies, which is a type of new ceramics.

(Problems to be solved by the prior art and the invention) Boron nitride is chemically and thermally stable and has excellent fainting properties. In addition, the sintered body is one of the so-called new ceramics, and is a material that is expected to be widely used in the future as a heat-resistant and corrosion-resistant material and electrical components.

Boron nitride sintered bodies are obtained by sintering boron nitride powder, but the boron nitride powder is required to have good sinterability and low crystallinity.

Methods for industrially producing boron nitride powder include t) a method of reducing and nitriding boric acid, borates, boron oxides, etc. with ammonia gas; 2) boron compounds such as boric acid, borates, boron oxides, etc. There is a method of reducing and nitriding a mixture of nitrogen and nitrogen-containing compounds in an inert gas or reducing gas atmosphere such as nitrogen gas or ammonia gas.

Among these methods, a method for obtaining a low-crystalline boron nitride powder is to heat a powder of an alkali metal or alkaline earth metal borate and a nitrogen-containing compound at 650 to +100'C.
A method of heating at a relatively low temperature is suitable. However, the low-crystalline boron nitride powder obtained by this method still contains a large amount of alkali metal or alkaline earth metal derived from the raw material borate, so if such powder is used as a raw material for a sintered body, This is a problem because the strength etc. of the obtained sintered body decreases.

As a method for removing alkali metals or alkaline earth metals from boron nitride powder, a method is known in which boron nitride powder is washed with a dilute mineral acid aqueous solution such as hydrochloric acid, sulfuric acid, or nitric acid (Japanese Patent Laid-Open No. 61-63505). Public bulletin).

However, in experiments conducted by the present inventors, when boron nitride i5) powder is washed with dilute mineral acid using this method, the remaining amount of metal derived from the raw material borate is reduced by 6'α, but it is not sufficient. It was confirmed that more than 1,100,011 pp of metal remained based on atomic IA calculation.

On the other hand, there is a method in which boric acid is used as a raw material instead of metal borate in the above method, but this is inconvenient because a large amount of amorphous boron nitride powder, which is easily soluble in water, will be produced if the heating temperature is within the above range. However, when the heating temperature is raised, the degree of crystallinity increases and there is a problem that a product with low crystallinity cannot be obtained.

[Means to solve the problem]

In view of this situation, the present inventors have conducted extensive studies with the aim of obtaining low-crystalline boron nitride powder with a low metal content, which is suitable as a raw material for boron nitride sintered bodies.
The above can be obtained by heating low crystalline boron nitride powder obtained by heating a powder of an alkali metal or alkaline earth metal borate and a nitrogen-containing compound at a relatively low temperature, heating it again to the same temperature, and then washing it. [We have discovered that one objective can be achieved and have completed the present invention.

That is, in the present invention, a powder containing an alkali metal or alkaline earth metal borate and a nitrogen-containing compound is heated at 650 to 1100°C.
The low-crystalline boron nitride powder obtained by heating to a temperature of
Alternatively, the present invention provides a method for producing a low-crystalline boron nitride powder, which is characterized in that the powder is heated again to 500-1100''C in a container with a stopper and then washed.

[Detailed disclosure of the invention]

The present invention will be explained in detail below.

The borates of alkali metals or alkaline earth metals used in the present invention include borates of sodium, potassium, magnesium, calcium, etc. (hereinafter, these are collectively referred to as raw material borates).

The raw material borates do not need to be of particularly high purity, and usually reprinted industrial quality ones are preferably used. In addition, depending on the presence or absence of crystallization water, the raw material borates can be either crystalline water salts or anhydrous salts.In the present invention, either of these can be used, but anhydrous salts are preferable.
In order to mix well with the nitrogen-containing compound, it is preferable to use powder, but it is not necessary to make it particularly fine.

As nitrogen-containing compounds, N1 such as urea, melamine, etc.
(An organic compound having two groups is used. Similar to the raw material borates, industrial quality, usually reprinted, nitrogen-containing compounds are preferably used. Similarly, powdered materials are preferred.

The mixing ratio of raw material borates and nitrogen-containing compounds is N/B.
The atomic ratio is ζ1.0-4.0, preferably 1.5-3.
Implemented at 0.

Next, in the present invention, the powder of the mixture of the raw material borates and the nitrogen-containing compound is heated to 650 to 110°C (1°C, preferably 750°C).
By heating to a temperature of ~1000°C, the boron atoms in the raw material borate are nitrided by a reduction reaction to produce crystalline boron nitride powder. The mixed powder with the compound is heated by a conventionally known method under an atmosphere of an inert gas such as nitrogen gas or a reducing gas such as ammonia gas, or by a method previously proposed by the present inventors. The method of Japanese Patent Application No. 174751/1982 is to carry out the process in a container with a lid, or by any of the following methods.
fli.

In addition, when the above-mentioned heating is performed in a fermenting container, the atmosphere does not necessarily have to be an inert gas or a reducing gas. The reason for this is that ammonia (Nl+) gas, carbon dioxide gas, water vapor, etc. are generated due to the nitriding reaction of the raw material borates and the thermal decomposition of excess nitrogen-containing compounds, which naturally causes the inside of the container to become inert gas. This is because a reducing gas atmosphere is created.

In the above heating, if the heating temperature is lower than 650° C., the nitriding reaction is delayed and unreacted raw material borates remain, which is disadvantageous. On the other hand, if the heating temperature exceeds 1100° C., crystallization of the resulting boron nitride will proceed, making it impossible to obtain a product with low crystallinity, which is also disadvantageous.

The heating time varies depending on the heating temperature. Heating temperature is 6
At 50-800℃, 4-7 hours are required;
At 1100°C, 1 to 4 hours is sufficient. However, if the above heating is performed in a container with a lid, the heating time may need to be extended depending on the size of the container and the amount of raw material borates and nitrogen-containing compounds. .

As a heating device, when heating is performed under an inert gas or reducing gas atmosphere, an electric furnace or the like that can create the above gas atmosphere inside is used, but when heating is performed in a container with a lid, an electric furnace or the like is used. Since the atmosphere does not necessarily have to be an inert gas or reducing gas,
Batch-type heating furnaces such as shuttle kilns and continuous heating furnaces such as 1-thin flannel kilns can also be used.

Particularly for mass production, a continuous heating furnace such as a tunnel kiln is preferred.

However, when the above heating is performed in a shuttle kiln or tunnel/run, the heating source may be an electric heater, but a fuel such as butane gas, kerosene, etc. may be used as the heating source! ! It is more preferable to heat with the hot air obtained by A baking because it is a pre-heating method.

When a container with a lid is used in the above, the container with a lid is required to be made of a material that can withstand temperatures of 650 to 1 ion°C, which is the heating temperature of the present invention, and preferably has a corrosion resistance of 111. Various ceramic sintered bodies such as alumina, titania, zirconia, silica, magnesia, calcia and silica, cordierite and mullite whose main component is alumina are suitable for the 6rl volume 2=, and heat-resistant stainless steel. Steel can also be used.

The shape of the container with a lid is such that the gases such as NH3, Co□, water vapor, etc. generated in the container with a lid (=j)
Automatically flows out of the container with a lid without significantly pressurizing the inside of the container, and the external atmospheric gas is 2G.
The container must be shaped so that it will not flow into the container with an M.

Therefore, in a container with a lid, it is preferable that the lid is placed on the container body, and the lid seals the container by its own weight, and the gas generated inside the container does not pressurize the container too much. The weight must be such that the pressure causes the gas to be lifted slightly upward and the gas to be discharged out of the container.

Further, the surface of the upper part of the container that comes into contact with the lid and the surface of the lid that comes into contact with the container need to be surfaces that come into close contact when the lid is placed on the container. Furthermore, the shape of the container may be selected from any shape, such as a cylindrical shape with a bottom or a rectangular shape like a box. Containers with such shapes include, for example, those shown in FIGS. 1 to 4, but are not necessarily limited thereto.

The boron nitride thus produced is a white powder with low crystallinity, which is removed from the heating device and washed.

For this cleaning, it is preferable to adopt the method described in JP-A No. 61-63505, in which cleaning is performed with dilute mineral acid and then with water.

The dilute mineral acids used here are hydrochloric acid, sulfuric acid, lil'l acid ζ
Rino water? 8 liquid, its concentration is 0.1-10% (
below! (1 inch % is not simply written as %), preferably 1 to 5%. The low-crystalline boron nitride powder obtained in i) above is washed with dilute mineral acid until the ρ11 of the washing solution becomes 2 or less, and then washed with water.
There are no particular limitations on the method of washing with the dilute mineral acid and washing with water, which are carried out until the pH reaches the above value.

Note that the washing with dilute mineral acid and washing with water described in "2" may be carried out at room temperature, but is preferably carried out at a temperature of 20 to 80°C.

However, for example, low-crystalline boron nitride powder is suspended in dilute mineral acid at the above concentration, stirred well, filtered, and washed with dilute mineral acid if necessary to bring the pH to 2 or less. After that, it is convenient to wash with water so that the pH of the washing water becomes 5 or more.

The thus washed low-crystalline boron nitride powder is then dried, and the drying is usually carried out at normal pressure or reduced pressure using a known drying device.
Although 51 powder is a powder with a specific surface area of 50 to 450 rrr/g, more than 1000 weight ppm of alkali metals or alkaline earth metals remain in terms of atoms.

Therefore, in the present invention, the alkali metal or alkaline earth metal is removed by treating the dried low crystalline boron nitride powder obtained above in an inert gas or reducing gas atmosphere. Alternatively, it can be carried out by heating again to a temperature of 500 to 1100'C in a container with a lid and then washing.

This method is carried out in the same manner as in heating a mixture of raw material borates and nitrogen-containing compounds to obtain boron nitride, but the heating temperature is 500-1100'.
C, preferably 600 to 800°C. Heating temperature is 5
If the temperature is below 00°C, the removal of alkali metals or alkaline earth metals from the low-crystalline boron nitride powder, which is the object of the present invention, is not sufficient. Conversely, if the heating temperature exceeds 1100°C, crystallization of boron nitride will occur, which is disadvantageous. The heating time is S■ depending on the heating temperature. That is, when the heating temperature is 500 to 800°C, 1 to 2 hours is required, but 8
At a temperature of 0.00 to 1100"C, 30 minutes to 1 hour is sufficient.

The low-crystalline boron nitride powder heated in the above manner is cooled, then washed, filtered, and dried. At this time, washing may be carried out with water only, but it is more preferable to use dilute mineral acid as in the case of washing the boron nitride powder obtained by heating the mixed powder of the raw material borates and the nitrogen-containing compound. It is preferable to use a method of washing and then rinsing with water. In addition, Nozomi 3 Nol at this time
The acid concentration, PLL during washing, PLL during water washing, temperature during washing, etc. are preferably carried out under the same conditions as in the above-mentioned washing.

The same applies to filtration and drying.

The boron nitride thus obtained has a specific surface area of 50
It is a powder with low crystallinity of ~450rrr/g.

In addition, in the present invention, the above-mentioned low crystalline boron nitride powder is repeatedly washed, heated, and washed, so that the content of alkali metals or alkaline earth metals is 150% in terms of atoms.
It is small in weight, less than ρρ1, and is suitable as a raw material for a sintered body.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, below, % and ppm represent weight 75 standard.

In the examples, the content of alkali metals or alkaline earth metals was analyzed using an atomic absorption spectrometer. The specific surface area of boron nitride powder can be measured using the nitrogen adsorption method (BET).
(According to the law).

Examples 1 to 4 Anhydrous alkali metal or alkaline earth metal borate powder and nitrogen-containing compound powder shown in Table 1 were mixed, and the mixture was mixed with an internal volume of 3 p. The crucible was placed in an alumina crucible without a lid, and the crucible was placed in an electric furnace. After heating the inside of the electric furnace under the gas atmosphere and heating conditions shown in Table 1, the crucible was taken out of the electric furnace and allowed to cool naturally. Boron nitride was obtained by cooling to room temperature.

After taking out this boron nitride from the crucible, it is
After stirring and filtration in a mineral acid aqueous solution 11 of the type and concentration shown in the table, the mixture was washed with the mineral acid again until the pll of the washing solution became 2 or less.

Next, this boron nitride was washed with water until the pll of washing water became 5 to 1, and then dried to obtain boron nitride with the physical properties shown in Table 1. The specific surface area of the boron nitride obtained by drying was as shown in Table 1, and it was a powder.

This boron nitride powder was again put into an open crucible with a capacity of 11, and this was placed in an electric furnace, and the inside of the electric furnace was heated under the gas atmosphere and heat conditions shown in Table 1. After heating! The crucible was taken out from the electric furnace and cooled to room temperature at a natural number of 61, and the boron nitride powder was taken out from the crucible.

This boron nitride powder was stirred and filtered in an aqueous mineral acid solution l2 of the type and concentration shown in Table 1, and then the f. It was washed with acid until the ρ11 of the washing solution became 2 or less.

Next, this boron nitride powder was washed with water until the pll of washing water became 5 or more, and then dried to obtain boron nitride powder shown in Table 1. As shown in Table 1, the total content of alkali or alkaline earth metal in the obtained boron nitride powder was 150 ppm or less.

Examples 2 to 4 Anhydrous alkali metal or alkaline earth metal borate powder shown in Table 2 and cave-containing compound powder were mixed, and this was mixed into a powder having an internal volume of 3e(1) in the shape shown in Fig. 1. :+ - The mixture was placed in a Thierai 17 crucible with a kettle, and this crucible with a kiln was heated in a tunnel kiln.

Heating was carried out under the conditions shown in Table 2 using hot air obtained by burning Bukun gas.

After heating, the crucible with a cough lid was taken out from the tunnel kiln and allowed to cool naturally to room temperature to obtain boron nitride.

After taking out this boron nitride from the crucible, it was stirred and sterilized in an acid aqueous solution Il with a concentration of 1 type 4 formula shown in Table 2, and then the boron nitride was sterilized again in the same manner as in Examples 1 to 4. The boron nitride is washed with mineral acid until the pl+ of the washing solution becomes 2 or less, and then the boron nitride is washed with water until the pH of the washing water becomes 5 or more, and then dried to form boron nitride with the physical properties and m shown in Table 2. I got it. The specific surface area of the boron nitride obtained by drying was as shown in Table 2, and it was a powder.

This boron nitride powder was placed in a cordierite lidded crucible having an internal volume of 1 p and the shape shown in Figure 1, and the crucible with a lid was placed in the tunnel kiln used above using hot air as a heat source. It was heated again under the conditions shown. After heating, the crucible was taken out from the tunnel kiln and allowed to cool naturally to room temperature, and the boron nitride powder was taken out from the crucible.

This boron nitride powder was stirred and filtered in a 1N FL acid aqueous solution of the type and concentration shown in Table 2 in the same manner as in Examples 1 to 4, and then washed again with cough mineral acid until the pl+ of the washing solution became 2 or less. Then, the powder was washed with water until 1+11 of the washing water became 5 or more, and then dried to obtain boron nitride powder in the amount shown in Table 2. The content of alkali metal or alkaline earth metal in the obtained boron nitride t5) bundle was 150 ppm or less as shown in Table 2.

〔Effect of the invention〕

As explained in detail above, the present invention is a method for producing boron nitride powder from a borate of an alkali metal or 7-alkali Tsuchikawa metal and a nitrogen-containing compound, the method comprising: The boron nitride powder obtained by heating and washing is heated to a specific temperature again in an atmosphere of non-proprietary gas or reducing gas, or in a container with Xi, and then washed. It's a method.

The method of the present invention is a method in which the previously obtained boron nitride powder is reheated and washed, so the obtained boron nitride powder has low crystallinity, and also contains alkali metals or alkaline earth metals. The amount of h1 contained in the boron nitride sintered body is small, and is therefore suitable as the raw material of the boron nitride sintered body.

[Brief explanation of the drawing]

Figures 1 to 4 show 2I;
FIG. 3 is a cross-sectional view showing the shape of the container. shows.

Claims (2)

[Claims] (1) Low-crystalline boron nitride powder obtained by heating a powder of alkali metal or alkaline earth metal borate and nitrogen-containing compound to a temperature of 650 to 1100°C and then washing it with an inert gas or a reducing agent. 500 ~ again under gas atmosphere
A method for producing low-crystalline boron nitride powder, which comprises heating to a temperature of 1100°C and then washing. (2) The low-crystalline boron nitride powder obtained by heating the alkali metal or alkaline earth metal borate and nitrogen-containing compound powder to a temperature of 650 to 1100°C and then washing it is re-injected into a container with a lid. A method for producing low-crystalline boron nitride powder, which comprises heating to a temperature of 500 to 1100°C and then washing.