JPS6033204A - Manufacture of powdered bn - Google Patents

Abstract

PURPOSE:To develop crystals and to improve a packing property by mixing a specified amt. of 1 kind of compd. among oxides or fluorides of alkaline-earth metal or compds. forming oxides and fluorides on heating into a specified amt. of powdered BN of undeveloped crystals contg. oxygen, molding, sintering under specified conditions, and crushing. CONSTITUTION:1-10wt% (especially 2-7wt%) expressed in terms of oxide and fluoride of >=1 kind of compd. among oxides and fluorides of alkaline-earth metal of compds. forming oxide and fluoride on heating is added to powdered BN of undeveloped crystals contg. 1-12wt% (especially 2-10wt%) oxygen. The admixture is mixed, molded, and sintered at >=1,700 deg.C in an inert gas or a gaseous NH3 stream. The sintered body is crushed and classified, and the powdered BN of developed crystals having a good packing property is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing hexagonal BN (hereinafter referred to as BN) powder, and particularly aims to obtain a BN powder with high filling properties and high crystallinity.

In addition to being used as a ftfl lubricant, 8N has excellent thermal conductivity and electrical insulation, and also has neutron absorption properties, so it is also used as a filler for heat dissipation materials and neutron shielding materials that use resin, rubber, ceramic materials, etc. as binding materials. ing.

What is important for these fillers is that they have high filling properties and, furthermore, they have great crystallinity.

BN is generally produced by heating ioric acid, anhydrous boronic oxide, or borax in ammonia gas, or by mixing these boric acids with nitrogen-containing organic compounds that generate ammonia gas by thermal decomposition of urea, diamine, etc. , heat and coarsely
BN is obtained and then heated to a higher temperature to recrystallize it to produce a product.

Crude BN is usually obtained by reaction at a temperature of 100 to 1400°C, and the crystals are underdeveloped, the size of the primary crystal is smaller than 0.1μ, and the C axis measured by X-ray diffraction method. The index 10 value, which indicates the degree of crystallinity in the direction, is also small, ranging from 50 to 300 (according to JSPS Carbon Materials Research 117 Committee Method).

In addition, crude BN contains 1 to 12% of oxygen in the BN crystal in the form of a B-0-N intermediate compound as a precursor for converting anhydrous boron oxide to BN. Unlike oxygen in the boron state, it is thought that the oxidation of

When this crude BN is reheated in an inert atmosphere at a temperature higher than the reaction temperature of crude BN, the oxygen in the BN crystal is separated from the BN crystal as free anhydrous boron oxide, and Ji dissipation is removed ξ It will be done. As the degree of re-addition W4 increases, the amount of MM liberated as boron oxide increases, and when the temperature exceeds 2000'C, almost all m is separated from M.

In parallel with this, BN crystals also develop, the size of the primary crystals becomes 1 to 10μ, and the LC value exceeds 1oooo8.

Commercially available BN is heated to about 1900"C or higher, has a primary crystal density of 1μ or more, and has an LC value of 1.
000 Å or more.

In this way, in order to obtain BN powder with developed crystals, it is sufficient to reheat crude BN in an inert atmosphere, etc.
By itself, it has poor biviscosity, and the bulk density of the powder after reheating is low, and the bulk density of commercially available powder is 0.1 to 0.3 a/c.
When attempting to obtain a composite of resin and BN powder without C, the filling properties are poor and it is difficult to obtain a composite exhibiting the characteristics of 8N.

Conventionally, the methods for obtaining BN powder with good filling properties are as follows:
Commercially available BN powder is oxidized (J), or boronic oxide-calcium oxide is added as a binder and a hot-pressed sintered body is crushed and covered, or the same BN powder is mixed with 8203-Ca.
There is a method of pulverizing a sintered body that has been sintered by adding calcium borate salt such as O or silicate glass, but in the case of hot press sintering, the productivity of the hot press sintered body itself is low, and the resulting powder is Becomes expensive. In addition, in the latter method, it is difficult to obtain calcium phosphate or silicate with a predetermined composition as a commercially available product, and it is difficult to produce the calcium phosphate or silicate in-house by melting because the molten material creeps up due to wetting with the container.

The present inventors have found that BN with well-developed crystals and good fillability
As a result of studying the method for manufacturing the powder, we found that by utilizing the fact that the oxygen present in crude B N l becomes 8203 when reheated, and by adding an oxide or fluoride of an alkaline earth metal thereto, these The inventors have discovered that, as a sintering binder, they are effective in increasing m-density and are also effective in crystal growth, leading to the present invention.

That is, the present invention provides 1 to 12%, preferably 2%, of BN in the BN crystal.
1-10 for crude 13N powder containing ~10% oxygen
%, preferably 2-7% of alkaline earth metal oxides,
Alternatively, one or more powders of fluorides are added and formed into a green compact, and this is sintered at a temperature of at least 61,700'C or higher in a stream of inert gas or the like, This method involves crushing and classifying 4 g of BN powder with developed crystals and good filling properties.

If the oxygen-containing chains in the crude BN are less than 1%, the BN crystals will develop too much, making it difficult to form a green compact, and if it exceeds 12%, the amount of volatilization during heating will increase, resulting in a low sintered compact density. As a result, the bulk density of the powder obtained by pulverizing it also decreases.

Alkaline earth metal oxides and fluorides form double salts with 8203, and CaO is effective for BN crystal development.
, Mg0,3a o, Ca F2, MgF2 , Ba
F2 is preferred.

Also, instead of these oxides and fluorides, oxides,
Use carbonates, hydroxides, basic carbons, basic fluorides, etc. to form fluorides. The D may be set to the peak of Ca in terms of oxide and fluoride.

Addition m of alkaline earth metal oxide or fluoride is 1
If it is less than 10% or more than 10% (internal percentage), sinterability and crystallinity will be poor, and in the case of fluoride, if it exceeds 10%, it will be difficult to sinter or use alumina protection tubes or gas blowing tubes. Severe damage. Therefore, the appropriate amount of these additions is 1 to 10%.
Preferably it is 2 to 7%.

A green compact made by mixing these additives with BN powder is formed using a molding device such as a mold press or a rubber press.
It is preferable that the raw high density is 1.3 g/cc or more. If this bulk density is low, the vibration packing density of the powder obtained by pulverization after sintering will not increase. The density of the green compact is 1.
If it is 3 g/cc or more, a product powder of 0.6 g/cc or more, which is desirable as a high-density vibration-filled product, can be obtained. □ Heating the green compact using inert gas such as Ar1N2 gas, NH3
The test is carried out in an atmosphere of gas or a mixture of these gases.

The heating temperature is 1,700°C or higher, preferably 2,000 to 22
It is 00℃. Below 1700°C, the crystals are not sufficiently developed, and above 2200°C, the reaction between graphite used as a heating container and BN begins, producing 84G.
Undesirable.

After heating, the green compact is cooled, pulverized in a pulverizer such as a roll mill or a ball mill, and classified. Normally, when used as a filler for synthetic resins, etc., it is preferable to classify with a 40 mesh sieve and select crushing conditions so that the average particle size under the sieve is 45 to 80 μnl.

If there are particles coarser than 40 mesh, the surface will be rough when combined with resin, etc. If the average particle size exceeds 80μIII, the bulk density will be low, and if it is smaller than 45μ111, the hygroscopicity of the fine powder will affect the fluidity. It's going to decline.

Since the BN powder of the present invention has good filling properties and crystallinity, a large amount of BN can be contained in a composite with a resin or silicone rubber. For example, if it is a heat dissipation sheet, the heat dissipation property will be good.

Examples 1 to 4 Mixing and pulverizing oxalic acid with calcium phosphate (filler),
After granulation and drying, it was heated to 850°C in ammonia gas, nitrided, and the filler and unreacted substances were removed by a conventional method to obtain crude B.
I got N. The amount of oxygen in this crude BN was 10%.

Calcium carbonate, magnesium carbonate, barium carbonate, and calcium fluoride were added and mixed to this crude BN, respectively. The amount added is 11 and 13 in the form of oxides and fluorides.
It was set to 5% with respect to N. This is 1500kg/cm2
Formed into a cylindrical shape with a resistance of 60 with a pressure of 1.37~
A green compact of -1.47 g/cc was obtained. This green compact was placed in a graphite crucible, inserted into a high-frequency heating furnace, and heated for 200 hours for 2 hours while flowing nitrogen gas at IQ/+11 inches into the crucible.
The temperature was raised to 0 to 2100°C and maintained at this temperature for 21-1 r. Cool while flowing nitrogen gas, and transfer to BN from a graphite crucible.
Even when the green compact was used as a filler, it was a high-density powder.

Comparative Example 1 Crude 13N obtained in the same manner as in the above example was made into a compact of 60 m nlφ under the same conditions as in the example, and heated, cooled, pulverized, and classified while flowing nitrogen gas. (9 BN
Powder vibration high density 1U As shown in Table 1, 0.55g/c
It was c.

Examples 5 to 8 Dry Hosui sand and urea were mixed and mixed in ammonia gas for 1
The mixture was nitrided by heating to 000° C., and unreacted substances were removed by a conventional method to obtain C crude BN powder. The amount of oxygen in this crude BN powder was 3%.

CaO and MgO were added to this crude BN powder, respectively.

MgF2.3a F2 was added and mixed, heated in the form of a green compact in the same manner as in Examples 1 to 4, and then crushed and classified to obtain BN powder having a bulk density as shown in Table 1.

Comparative Example 2 Crude BN obtained in the same manner as in Examples 5 to 8 above was treated under the same conditions as above without adding any additives to obtain BN powder.

The BN powders obtained in Examples 5 to 8 have a sintering effect and a higher vibration density than those obtained in Comparative Example 2.

Comparative Example 3 Crude BN powder obtained in the same manner as Examples 5 to 8 was
By reheating to ℃, washing with water, and drying, the oxygen-containing ff! 0
．． 5% crude [3N powder was obtained. This hypoxic crude PNI
Calcination, pulverization, and classification were performed in the same manner as in the above examples with the addition of 12% (+n) Aika's Kishimi calcium, but in this case, molding was difficult and the high density of the green compact Because of the low density, the m-density of the powder after sintering was also lower than that of the example.

(Margin below)

Claims (1)

[Claims] At least one powder selected from alkaline earth metal oxides, fluorides, or compounds that become oxides or fluorides upon heating is added to undeveloped BN powder containing 1 to 12% by weight of oxygen. A method for producing BN powder, which comprises mixing 1 to 10% by weight in terms of compounds, molding, sintering at 1700°C or higher in an inert gas or NH3 stream, and pulverizing and classifying the sintered body.