JPS6291409A - Production of easy-to-sinter boron nitride powder - Google Patents

Abstract

PURPOSE:To obtain the titled ultrafine boron nitride powder having an excellent sintering property by mixing a oxygen-contg. boron compd. and a nitrogen-contg. org. compd., carrying out nitriding at a specified temp. in a nonoxidizing atmosphere, crushing the product in an alcoholic solvent, and heating and removing the solvent. CONSTITUTION:The oxygen-contg. boron compd. and the nitrogen-contg. org. compd. are mixed and nitriding is carried out at 1,250-1,550 deg.C in a nonoxidizing atmosphere. The reaction product is crushed in an alcoholic solvent or the crushed product is washed with the alcoholic solvent. Then the solvent is heated and removed. Boric acid or boron oxide is exemplified as the oxygen-contg. compd. and urea, melamine, dicyandiamide, cyanuric acid, etc., are exemplified as the nitrogen-contg. org. compd. Both compds. are preferably mixed so that the molar ratio of the N in the nitrogen source to the B in the boron source is adjusted to about 2. Methyl or ethyl alcohol is preferably used as the solvent to be used in crushing.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing boron nitride (hereinafter simply referred to as BN) powder, and particularly for easily producing ultrafine N powder with excellent sinterability. Relating to a method of manufacturing.

[Conventional technology]

BN has many excellent properties such as corrosion resistance against molten metals, high electrical insulation, high thermal conductivity, and lubricity, so it can be used as a sintered body in many fields such as crucibles for metal melting, heat dissipation substrates, and high-frequency electrical insulation materials. It is applied to.

A BN sintered body is generally produced by a hot press method, but since BN itself is a substance that is extremely difficult to sinter, the following characteristics are desired for a BN powder for sintering. That is, as a component other than BN, it contains several percent of free refractory boron or oxygen, which is thought to remain as a B-N-0 system precursor in the BN crystal, and that the crystallinity The crystallite size Lc in the C-axis direction, which is the index of
00 Å or less.

Various methods have been proposed for the production of BN powder.
Method of heating above 160°C (Special Publication No. 38-1)
There is a method of heating to 0°C or higher (Japanese Patent Publication No. 48-14559).

However, (D) method inevitably contains Na components in the product BN powder, making it unsuitable for use in sintered bodies such as electronic materials. After heating the reaction product to 800°C or less in
5-30457) is also known. However, this method also (1
) There is a problem in using it for sintered bodies for the same reason.

Next, the method (2) above differs from the present application in that it relates to a method for producing BN powder with excellent crystallinity. Furthermore, according to experiments conducted by the present inventors, although the crystallite size Lc can be kept low by lowering the heating temperature using the method (2), it is inevitable that the purity will also decrease significantly at the same time. It is difficult to control c when [Nf.

[Problem that the invention seeks to solve]

As a result of intensive research into a method for easily producing BN powder that is extremely fine and has appropriate purity and is easy to sinter, the inventor found that B2O3 or H3BO3, which is an impurity component in BN, is mixed with alcohol. Ester compounds are easily formed and the ester compounds evaporate at low temperatures.
Finally, the present invention was completed.

An object of the present invention is to provide a method that can easily produce ultrafine N powder with excellent sinterability.

[Means for solving problems]

That is, the BN powder manufacturing method of the present invention mixes an oxygen-containing boron compound and a nitrogen-containing organic compound, performs a nitriding reaction at a temperature of 1250°C to 1550°C in a non-oxidizing atmosphere, and then converts the product into alcohol. The characteristic technical means is to pulverize in a solvent or wash with an alcohol solvent after pulverization, and then remove the solvent by heating.

[Effect]

Below, the method for producing easily sinterable BN powder of the present invention and its operation will be explained in detail.

As the oxygen-containing boron compound serving as the boron source, boric acid or boron oxide is used, and as the nitrogen-containing organic compound serving as the nitrogen source, urea, melamine, dicyandiamide, cyanuric acid, etc. are selected. Regarding the mixing ratio of both, it is necessary that the molar ratio (N/B) of N and B in the boron source and the nitrogen source is 1 or more. If the nitrogen source is insufficient, the nitriding rate will decrease, and unreacted boric acid will remain, resulting in a decrease in yield. Excess nitrogen source is thermally decomposed and exits from the reaction system as a gas, so there is no problem, but from the viewpoint of nitriding rate and economical efficiency, it is preferable to use a nitrogen source of about (N/B)-2.

Next, this mixture is heated to a temperature of 1550° C. or lower in a non-oxidizing atmosphere to perform a nitriding reaction.

The reaction vessel must not react with the mixture, and can be used up to 1550°C, such as B
A sintered body of N or a container made of graphite is preferable. It is also possible to carry out the reaction in two or three stages, in which case stainless steel or the like can be used in the low temperature range.

The heating atmosphere must be a non-oxidizing atmosphere,
It is preferable to use inexpensive nitrogen, but ammonia,
Argon, etc. may also be used.

Heating temperature is 1250°C to 1550°C, preferably 130°C
0°C to 1500°C, more preferably 1350°C to 14
50℃ is good. The reason why the heating temperature is defined in this way is as follows. That is, easily sinterable BN which is the object of the present invention
One of the conditions for the powder is that the crystallite size Lc corresponding to the crystal grain size is 300 Å or less,
When the heating temperature exceeds 1550° C., the size of the crystallites Lc reaches 300 to 42, and sinterability becomes poor.

However, simply performing heat treatment at 1550° C. or higher causes the following problems.

When reducing and nitriding a boron source, a considerable amount of oxygen exists as an impurity component in the resulting N powder. This oxygen includes oxygen in free boron oxide derived from unreacted raw materials and oxygen as a B-N-0 precursor at an intermediate stage before complete conversion to BN. The oxygen in the latter BN precursor becomes mainly B2 o3 with increasing nitriding temperature.
It is thought that it leaves the crystal as . However, the vapor pressure of B2O3 is several mm Hg at 1550°C, and the evaporation rate is very slow below 1550°C.
The majority remains in the product. Figure 1 shows the nitriding temperature and the purity of BN determined from the nitrogen analysis value (N analysis value
72) and the relationship between the crystallite size Lc, when processing at 1550°C or lower to suppress the crystallite size, the purity of the resulting N powder is 82 to 87% by weight, and if it is left as it is, it will not be sintered. It cannot be said that the BN powder is suitable for use as a liquid.

Therefore, we next considered a method to achieve high purity without growing crystallites, and found that it was extremely difficult to wet-pulverize the BN powder using alcohol as a solvent, or to wash the BN powder with an alcohol solvent after crushing, and then heat-dry the slurry. found that it is effective.

FIG. 2 shows the relationship between the purity of BN after pulverization and drying and the nitriding temperature. B after grinding using alcohol as a solvent
Although the purity after nitriding is almost constant, the purity of N increases with the nitriding temperature, reaching 9 at 1300°C.
Double fit%, reaching 97% by weight at 1500°C. This is because free boron oxide in the emptied product reacts with alcohol to become an ester compound, which is evaporated and diffused by heating. The reason why the BN purity after pulverization differs depending on the nitriding temperature is that the ratio of free boron oxide damage in impurities increases as the nitriding temperature increases. As can be seen from FIG. 2, if the processing temperature is lower than 1250° C., the purity of the B and N powders finally obtained will be less than 90% by weight, making them unsuitable as powders for sintered bodies.

Various alcohols can be used as the solvent for pulverization, but monohydric alcohols such as ethyl alcohol and methyl alcohol are particularly effective because the ester compound produced by the reaction with boron oxide easily evaporates. Although it is possible to use propatool or butanol, since the boiling point of the alcohol itself or the ester compound is -1-A, it is disadvantageous to remove it by heating to achieve high purity. For example, in the case of methyl alcohol, trimethyl borate (C, H, a O
)-3B has a Buddha point of about 68°C, and evaporates and transpires at this temperature. The evaporated mixture of ester, alcohol and water can be recovered, separated and used again.

〔Effect of the invention〕

According to the present invention, it has become possible to easily produce ultrafine BN powder with excellent sinterability.

BN obtained by the method of the present invention is a pure white powder, the crystallite size Lc is about 100 to 300, and the purity is 9.
It is 2 to 98% by weight. FIG. 3 is a photograph showing a TEM image of fine BN powder produced by the method of the present invention.

Additionally, as a result of X-ray diffraction, no free boric acid or boron oxide was found.1. It has superior fluidity compared to commercially available B, 1 yen powder. - According to the method of the present invention, ultrafine BN powder with excellent sinterability can be obtained very easily and economically without using any special additives, especially since the raw material does not contain sodium. Ultrafine BN powder containing almost no sodium is obtained.

When this BN powder is used as a raw material for sintering, it has the excellent effect that sintering is completed at a lower temperature due to its high activity, and a fine, homogeneous, and high-strength sintered body can be obtained.

〔Example〕

Example 1 Boric acid H3BOB and melamine C3N5 (Nl2
) 3 and mixed so that the N78 molar ratio was 2, the mixture was placed in a graphite crucible, and the temperature was raised at 300 ° C / hr in a N2 gas atmosphere in a graphite resistance heating furnace, After being maintained at 1300° C. for 2 hours, it was cooled and the product was taken out. The reaction product is a white lump with a BN content of 81
．． It was 7% by weight. .

Next, this sample was milled for 30 hours in an alumina ball mill using methanol as a solvent, and then the slurry was heated to about 70° C. on a hot plate to remove the solvent. The BN content of the dried product was 92.1% by weight, and the crystallite size Lc was 100%.

Example 2 The same operation as in Example 1 was performed except that the holding temperature was 1400°C. The BN content of the product is 82.
1% by weight, 95.7 after alcohol treatment (after pulverization and dry smoke)
Heavy liquid % and crystallite size Lc were 197 people.

Example 3 The same operation as in Example 1 was performed except that ethanol was used as the solvent. The BN content after alcohol treatment was 92.0% by weight.

Comparative Example The same operation as in Example 1 was performed except that the treatment temperature for the nitriding reaction was 1600°C. Although the BN content of the product was 96.1% by weight after the nitriding reaction and 99.0% by weight after the alcohol treatment, the crystallite size Lc was 53%.
0 people, and the sinterability was not favorable.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between nitriding temperature, BNN content of the product, and crystal T-Lc size when boric acid and melamine are used as raw materials, and Figure 2 is a graph showing the relationship between the product in Figure 1 and the size of crystal T-Lc. A graph showing the relationship between BN content and nitriding temperature after wet pulverization as a solvent and heat drying. Figure 3 is a particle structure (TEM image) of BN powder according to the method of the present invention.
This is a photo showing.

Claims (1)

[Claims] 1. Mix an oxygen-containing boron compound and a nitrogen-containing organic compound, perform a nitriding reaction in a non-oxidizing atmosphere at a temperature of 1250 to 1550°C, and then grind the product in an alcohol solvent or wash it with an alcohol solvent after grinding. , and then removing the solvent by heating.