JP3521178B2 - Hexagonal boron nitride powder and applications - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hexagonal boron nitride powder having high crystallinity, high orientation or high crystallinity and high oxygen content, and normal pressure sintering of hexagonal boron nitride produced using the same. Regarding union.

[0002]

2. Description of the Related Art Hexagonal boron nitride powder has a white, graphite-like layered structure, and has excellent properties such as thermal conductivity, electrical insulation, chemical stability, solid lubrication, and thermal shock resistance. Utilizing these characteristics, it is applied to solid lubricating / release agents, resin or rubber fillers, heat-resistant / insulating sintered bodies, and the like.

[0003] Highly crystalline hexagonal boron nitride powder has a flaky morphology due to its layer structure similar to graphite. However, since the flaky shape is not sufficiently developed, it is naturally deposited without pressure molding. In the powdered state, the orientation is generally low.

If such a hexagonal boron nitride powder having a low orientation is used as a solid lubricating / release agent without pressure molding, the friction coefficient on the sliding surface becomes large and sufficient lubricity / release is obtained. There was a problem that the property could not be obtained.

Therefore, the appearance of hexagonal boron nitride powder having high crystallinity and high orientation has been expected.

[0006] Highly crystalline hexagonal boron nitride powder is
It is suitable for a raw material powder for a normal pressure sintered body because of its good filling property, but because of its high purity, the content of insoluble oxygen as a sintering aid is less than 0.50% by weight.

For this reason, even when used alone as a raw material powder for a normal pressure sintered body, sufficient strength of the sintered body cannot be obtained and usually mixed with a low-crystal hexagonal boron nitride powder containing a large amount of insoluble oxygen. Used.

However, low-crystal hexagonal boron nitride powder has poor filling properties, so that when used in large amounts, the deformation during sintering increases. In addition, if the mixing is insufficient, cracks and cracks occur during normal-pressure sintering.
For this reason, the emergence of hexagonal boron nitride powder having high crystallinity and high oxygen content, which can be used alone as a raw material powder for a normal pressure sintered body, has been awaited.

[0009]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a hexagonal boron nitride powder having high crystallinity, high orientation or high crystallinity and high oxygen content, And a normal pressure sintered body of hexagonal boron nitride produced using the powder.

[0010]

That is, the present invention provides a B
A mixture of boric acid and melamine having an N / N atomic ratio of 1/1 to 1/6 was mixed with a Ca compound by 15 to 50% by weight of calcium borate based on hexagonal boron nitride formed during crystallization. (Ca O) x · _{B 2} After adding so that a liquid phase of O ₃ (where X is more than 1 and 3 or less) is formed,
Temperature T (° C.), relative humidity Ψ (%) and holding time t (h
r) is the following relational expression, T ≧ −20 · log ₁₀ (t /
^{4) + {(Ψ-100} ) 2/20} +60, to form a boric acid melamine and held under conditions that satisfy the further non-oxidizing gas atmosphere it was fired, crystallized at a temperature 1800-2,200 ° C. to give Powder , characterized in that
Graphite index (GI) by powder X-ray diffraction method is 1.20 or less
Below, (002) diffraction line intensity I ₀₀₂ and (100) diffraction
The ratio (I ₀₀₂ / I ₁₀₀ ) of the line intensity to I ₁₀₀ is 2
Hexagonal boron nitride powder of 5.0 or more . Also,
In the present invention, the half width of the (002) diffraction line obtained by the powder X-ray diffraction method is 0.30 ° or less, and the insoluble oxygen is reduced to 0.50 to 0.50 °.
It is a hexagonal boron nitride powder characterized by containing 1.50% by weight. Further, the present invention is a normal pressure sintered body of hexagonal boron nitride, which is obtained by sintering the hexagonal boron nitride powder under normal pressure.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The evaluation of the crystallinity of the hexagonal boron nitride powder is usually carried out by using a graphitization index (GI
= Graphitization Index). GI represents the integrated intensity ratio, that is, the area ratio of the (100), (101), and (102) lines in the X-ray diffraction diagram, as GI = [area ｛(100)
+ (101)｝] / [area (102)] (J. Thomas, et.al, J. Am. Chem. Soc. 84, 4619).
(1962)), the smaller this value, the higher the crystallinity.

As described above, GI is an index of the crystallinity of hexagonal boron nitride powder. The higher the crystallinity, the smaller this value becomes, and if the crystal is completely crystallized (graphitized), GI = 1.
It is said to be 60. However, in the case of hexagonal boron nitride powder having high crystallinity and sufficiently grown particles, the GI is further reduced because the powder is easily oriented.

The hexagonal boron nitride powder of the present invention is characterized by having a GI value of 1.20 or less, is a powder having sufficiently grown particles, and having high crystallinity. Conventionally,
Hexagonal boron nitride powder having a GI value of 1.20 or less is not known.

On the other hand, regarding the evaluation of the orientation of the hexagonal boron nitride powder, the ratio of the intensity I ₀₀₂ of the ( ₀₀₂ ) diffraction line to the intensity I ₁₀₀ of the (100) diffraction line by the powder X-ray diffraction method was calculated as follows.
₀₀₂ / I ₁₀₀ (hereinafter referred to as “OI”. OI is Orientati
on Index = short for orientation index. ). OI = 6.25 in hexagonal boron nitride powder that is not oriented at all. OI increases as the hexagonal boron nitride flake shape develops and the orientation increases.

The OI value of the hexagonal boron nitride of the present invention is 2
5.0 or more. This is unique compared to the conventional high crystalline hexagonal boron nitride having an OI value of about 7.5 to 22.5.

On the other hand, regarding the evaluation of the crystallinity of the hexagonal boron nitride powder, in addition to the GI, the powder X-ray diffraction method (00) was used.
2) The half width of the diffraction line is often used. (002)
The half width of the diffraction line is the size of the crystallite in the c-axis direction (Lc).
Lc is larger as this value is smaller. In the case of hexagonal boron nitride, as Lc increases, the crystallinity also increases.

That is, the half width of the (002) diffraction line is an index of the crystallinity of the hexagonal boron nitride powder. The higher the crystallinity, the smaller the value. The half width of the (002) diffraction line by the line is 0.3
0 ° or less. In particular, when evaluating the crystallinity of hexagonal boron nitride powder as a raw material for a sintered body, the size (Lc) of the crystallite in the c-axis direction may also contribute to the sintering characteristics. Often the half width of the line is used.

The hexagonal boron nitride powder of the present invention comprises (00
2) It is characterized in that the half width of the diffraction line is 0.30 ° or less, the crystallite in the c-axis direction is sufficiently large, and the powder has high crystallinity.

On the other hand, oxygen contained in the hexagonal boron nitride powder is classified into soluble oxygen and insoluble oxygen.

The soluble oxygen is oxygen that is loosely bound to the surface of the hexagonal boron nitride powder particles. If the hexagonal boron nitride powder is fired by normal pressure sintering or the like, no sintering occurs.
At a relatively low temperature of less than 00 ° C., it is separated from the hexagonal boron nitride substrate and volatilized. Therefore, it has no function as a sintering aid.

The soluble oxygen is dissolved in methanol to form volatile trimethyl borate by dipping hexagonal boron nitride powder in heated methanol, and is completely removed. The amount of soluble oxygen can be calculated from the weight loss of the powder at this time.

On the other hand, insoluble oxygen is oxygen that is strongly bound to hexagonal boron nitride powder particles and, unlike soluble oxygen, is not removed by washing with methanol. When the hexagonal boron nitride powder is calcined by normal pressure sintering or the like, the insoluble oxygen is separated from the hexagonal boron nitride substrate at a relatively high temperature of 1500 ° C. or more to form boron oxide (B ₂ O ₃ ). Form a liquid phase. Since this liquid phase acts as a sintering aid, normal pressure sintering of hexagonal boron nitride becomes possible.

The amount of insoluble oxygen can be determined by subtracting the amount of soluble oxygen from the measured value of oxygen by a generally used oxygen / nitrogen analyzer.

The hexagonal boron nitride powder of the present invention has a content of 0.5
It contains 0 to 1.50% by weight of insoluble oxygen. Conventionally,
(002) A hexagonal boron nitride powder having a half width of diffraction line of 0.30 ° or less and containing 0.50 to 1.50% by weight of insoluble oxygen is not known.

When the amount of insoluble oxygen is less than 0.50% by weight, the strength of the normal pressure sintered body of hexagonal boron nitride becomes insufficient. On the other hand, if the content exceeds 1.50% by weight, the amount of the liquid phase, which is a normal-pressure sintering aid, becomes excessive and volatilization becomes remarkable, so that cracks and cracks are easily generated in the sintered body. Therefore, none of them is suitable for the present invention.

The hexagonal boron nitride powder of the present invention has a B / N
In a mixture containing boric acid and melamine having an atomic ratio of 1/1 to 1/6, a Ca compound is added with 5 to 20% by weight of calcium borate (CaO 2) based on hexagonal boron nitride generated during crystallization. ) X · B ₂ O ₃ liquid phase (where X ≦ 1), and then added at a temperature T (° C.) and relative humidity Δ
(%) And the holding time t (hr) are expressed by the following relational expression T ≧ −20 · log ₁₀ (t / 4) + ｛(Ψ−100) ²
/ 20 ° + 60 to form melamine borate, which is further heated under a non-oxidizing gas atmosphere at a temperature of 1800 to 220
It can be manufactured by firing and crystallization at 0 ° C.

The boric acid used in the present invention includes orthoboric acid (H ₃ BO ₃ ), metaboric acid (HBO ₂ ), tetraboric acid (H ₂ B ₄ O ₇ ), boric anhydride (B ₂ O ₃ ) and the like.
General formula (B ₂ O ₃ ) · (H ₂ O) _X [where X = 0 to
Among these compounds, one or more of the compounds represented by 3) are preferred, and among them, orthoboric acid is suitable for the present invention because it is easily available and has a good mixability with melamine.

The mixing of boric acid and melamine is performed using a ball mill,
This can be performed using a general mixer such as a ribbon blender or a Henschel mixer. The mixing ratio is B / B of boron atom (B) of boric acid and nitrogen atom (N) of melamine.
The ratio at which the N atomic ratio is 1/1 to 1/6, preferably 1 /
The ratio is 2 to 1/4. The B / N atomic ratio is 1/1
If it exceeds, the residual unreacted boric acid becomes noticeable after firing,
If it is less than 1/6, sublimation of unreacted melamine during firing becomes remarkable, and in any case, the hexagonal boron nitride of the present invention cannot be produced.

According to the present invention, boric acid and
Ramin (C_ThreeN₆H₆The specific compounding ratio of boric acid is
Is orthoboric acid (H_ThreeBO_Three), Then H_ThreeBO_Three
/ C _ThreeN₆H₆Is a molar ratio of 6/1 to 1/1 and a weight ratio of
Is from 2.94 / 1 to 0.49 / 1.

[0031] In the present invention, hexagonal boron nitride crystallization catalyst is a boric acid calcium-containing (CaO) _X · B ₂ O
After adding a Ca compound to a mixture of boric acid and melamine in advance, a liquid phase of [ ₃ ] (where X ≦ 1) is generated in an amount of 5 to 20% by weight with respect to hexagonal boron nitride during crystallization. T (° C), relative humidity Ψ (%) and holding time t
The mixture is maintained in an atmosphere where (hr) satisfies the following relational expression to form melamine borate.

T ≧ −20 · log ₁₀ (t / 4) + ｛(Ψ
-100) ^2/20} + 60

Such an atmosphere can be easily formed using a thermo-hygrostat, a steam heating furnace, or the like.
Specific examples of temperature, relative humidity, and time are, for example, 80
° C, 80%, 10 hours and the like. There are no particular restrictions on gases other than water vapor that form the atmosphere.
Examples include nitrogen gas and inert gas.

The Ca compound added in the present invention is a solid compound.
Calcium borate may be used.
Calcium-forming compounds, especially cheap and readily available
Calcium carbonate (CaCO_ThreeIs preferred. CaCO
_ThreeWhen using boric acid, only the raw material for hexagonal boron nitride
Not only as a raw material for calcium borate liquid phase
It is necessary to use boric acid as a raw material for the calcium borate liquid phase.
Is significantly smaller than boric acid, the raw material for hexagonal boron nitride.
CaCO_ThreeBoric acid and melamine
Min (C_ThreeN₆H₆))
Uric acid (H_ThreeBO _Three), Then H_ThreeBO_Three/ C_ThreeN₆
H₆In a molar ratio of 6/1 to 1/1 and a weight ratio of 2.94
/ 1 to 0.49 / 1.

Calcium borate (CaO)_X・ B
_TwoO_ThreeLiquid phase [where X ≦ 1] is hexagonal nitrided during crystallization
Ca to be 5-20% by weight based on boron
CO _ThreeThe specific compounding ratio depends on the firing method.
The volatilization amount of melamine and boric acid reacting to 1 mole of melamine
Varies depending on the firing method.
Melamine does not evaporate at all, and
2 moles of boric acid always reacts with 1 mole of melamine to form 6
Boron acid, melamine
And CaCO_ThreeIs a specific compounding ratio of 2
2.3-99.7 / 10.1-48.2 / 0.1-1.
0, 13.8-61.6 / 12.7-60.7 in weight ratio
/0.1 to 1.0.

In the present invention, a mixture of boric acid, melamine and a Ca compound is held under the conditions that the temperature (T), the relative humidity (Ψ) and the holding time (t) satisfy the above formula to form melamine borate. Melamine borate is not formed if any of the temperature, the relative humidity and the holding time are out of the range of the above formula.

By adding the Ca compound before the above holding, the Ca compound is uniformly mixed in the melamine borate. When boric acid, melamine and Ca compound are simply mechanically mixed, or when melamine borate is formed and then Ca compound is mixed, water is further added to boric acid, melamine and Ca compound to form melamine borate and Ca compound. When the mixing is performed simultaneously, the mixing state of the Ca compound becomes non-uniform, and the hexagonal boron nitride powder after crystallization becomes non-uniform, containing a large amount of coarse particles or fine particles with undeveloped crystals. In such a case, the hexagonal boron nitride powder of the present invention cannot be produced.

Usually, when a hexagonal boron nitride material is fired, amorphous boron nitride is formed at a relatively low temperature (1000 ° C. or lower), and then the amorphous boron nitride is crystallized at a higher temperature to form a hexagonal boron nitride. Crystalline boron nitride forms. At this time, crystallization is promoted by the coexistence of a crystallization catalyst, but the size and amount of the generated hexagonal boron nitride particles vary depending on the type and amount of the catalyst used.

The crystallization catalyst used in the present invention, calcium borate _{(CaO) X · B 2 O} 3 [ where, X ≦ 1] is a liquid phase at the crystallization temperature. The amorphous boron nitride is dissolved therein, and hexagonal boron nitride precipitates when the amount of the solution reaches supersaturation. At this time, if the amount of the catalyst, that is, the amount of the liquid phase is large, the distance between adjacent hexagonal boron nitride particles increases, so that coarse particles are easily generated. Conversely, if the amount of the liquid phase is small, the amount of the amorphous boron nitride dissolved is also small, so that fine grains with undeveloped crystals tend to be generated. On the other hand, the composition of the catalyst, that is, the molar ratio between CaO and B ₂ O ₃ affects the shape of the particles. In the composition where X is 1 or less, that is, in the composition rich in B ₂ O ₃ , the generated hexagonal boron nitride particles develop a scale shape, but in the composition rich in CaO where X is larger than 1, the amount of the catalyst is relatively small. In this case, agglomerated particles are easily generated, and when the amount of the catalyst is relatively large, thick particles are easily generated.

When the amount of the catalyst, that is, the amount of the liquid phase is large,
The amount of oxygen taken into the hexagonal boron nitride particles, that is, the amount of insoluble oxygen increases. Conversely, if the amount of the liquid phase is small, the amount of insoluble oxygen will also be small. On the other hand, the composition of the catalyst, that is, Ca
The molar ratio between O and B ₂ O ₃ also contributes to the amount of insoluble oxygen. In the case where X is 1 or less, that is, in a composition rich in B ₂ O ₃ , insoluble oxygen is easily taken into the generated hexagonal boron nitride particles, but when a crystallization catalyst having a composition rich in CaO in which X is larger than 1 is used, Since oxygen is trapped in CaO in the catalyst liquid phase, insoluble oxygen is less likely to be taken into hexagonal boron nitride particles.

In the present invention, B is used as a crystallization catalyst._TwoO_ThreeRe
Calcium borate (CaO) _X・ B_TwoO_ThreeLiquid phase
[However, the presence of X≤1]
5-20% by weight of crystallization catalyst
And adjusted to an appropriate amount not too much and not too little
By doing so, coarse grains or fine grains with undeveloped crystals
High orientation without containing, 0.50 to 1.50 weight
Produces hexagonal boron nitride powder containing 5% insoluble oxygen
can do. (CaO)_X・ B_TwoO_ThreeX of 1
If this is exceeded, aggregated or thick particles will be formed,
Also, since the composition of the crystallization catalyst is CaO-rich,
The amount of insoluble oxygen contained in the boron nitride powder is 0.50% by weight
%, Which is not suitable for the present invention. Also, the amount of crystallization catalyst
Exceeds 20% by weight, coarse particles are formed.
In the present invention, fine grains that have not developed crystals are generated.
Not suitable.

The firing and crystallization are performed under a non-oxidizing gas atmosphere.
It is performed at a temperature of 1800 to 2200 ° C. If the temperature is lower than 1800 ° C., crystallization of hexagonal boron nitride does not proceed sufficiently, and a powder having high crystallinity and high orientation cannot be obtained. Also, 2
If the temperature exceeds 200 ° C., hexagonal boron nitride is decomposed.

As the gas forming the non-oxidizing gas atmosphere, there may be used a nitrogen gas, an ammonia gas, a hydrogen gas, a hydrocarbon gas such as methane or propane, or a rare gas such as helium or argon. Among them, nitrogen gas which is easily available, inexpensive, and has a large effect of suppressing the decomposition of hexagonal boron nitride in a high temperature range of 2000 to 2200 ° C. is optimal.

As the firing furnace, a batch furnace such as a muffle furnace, a tubular furnace, and an atmosphere furnace, and a continuous furnace such as a rotary kiln, a screw conveyor furnace, a tunnel furnace, a belt furnace, a pusher furnace, and a vertical continuous furnace are used. . These can be used depending on the purpose. For example, a batch type furnace is used when a large number of varieties of hexagonal boron nitride are manufactured little by little, and a continuous type furnace is used when a certain type of varieties is manufactured in large quantities.

The hexagonal boron nitride powder produced as described above undergoes post-treatment steps such as pulverization, classification, removal (purification) of residual catalyst by acid treatment, washing, and drying, if necessary. Provided for practical use.

The hexagonal boron nitride powder of the present invention contains coarse particles,
It does not contain agglomerated particles or fine particles with undeveloped crystals and is uniform, consisting of highly crystalline and flake-shaped particles. Sex. For this reason, it is particularly suitable for applications such as solid lubrication and release agents that are used without molding powder. Solid lubrication and mold release agents exhibit lubricity and mold release properties as they are, or by dispersing them in oil or grease and interposing them in the contact / sliding parts of multiple materials. If the friction coefficient of the release agent is large, seizure tends to occur. The conventional hexagonal boron nitride powder has a low orientation in the state of a powder naturally deposited without forming, and therefore has a large friction coefficient and is liable to cause seizure. On the other hand, if the hexagonal boron nitride powder of the present invention is used,
Such troubles can be reduced.

Further, the hexagonal boron nitride powder of the present invention comprises:
Since it is composed of highly crystalline and flake-shaped particles and has good filling properties, when used as a raw material powder for normal pressure sintering, a high molding density (CIP density) is obtained during pre-molding by cold isostatic pressing (CIP). And the amount of deformation during sintering can be kept small.

Further, the hexagonal boron nitride powder of the present invention contains 0.50 to 1.50% by weight of insoluble oxygen suitable for normal pressure sintering, and has sufficient strength when used alone. In addition, it is possible to produce a good normal pressure sintered body without cracks and cracks.

[0049]

The present invention will be described below more specifically with reference to examples and comparative examples.

Example 1 70 kg of orthoboric acid, 50 kg of melamine, and 1 kg of calcium carbonate as a Ca compound were mixed by a Henschel mixer, and then mixed in a thermo-hygrostat at a temperature of 80 ° C. and a relative humidity of 8%.
Hold at 0% for 10 hours to form melamine borate.
Then, in a batch atmosphere furnace, under a nitrogen atmosphere,
It was fired and crystallized at 950 ° C.

The obtained fired product was ground and was examined the composition by X-ray diffraction, B ₂ O ₃ and CaO · B ₂ O ₃ in addition to the solidification of the crystallization catalyst hexagonal boron nitride Was observed. When this was washed with nitric acid to remove the crystallization catalyst, the weight was reduced by 9% by weight.

The GI value and the OI value of the hexagonal boron nitride powder after the removal of the crystallization catalyst were measured with an X-ray diffractometer “GF-2013” manufactured by Rigaku Corporation. As a result, GI
The value was 0.89 and the OI value was 30.7.

Further, the coefficient of friction of the hexagonal boron nitride powder obtained above was measured using a powder shear tester “D
S-086 ", it was 0.56.

Examples 2 to 4 Boric acid, melamine and a Ca compound were mixed, humidified and heated under various conditions shown in Table 1 to form melamine borate, and then calcined and crystallized to form a crystallization catalyst. The powder was removed to produce a hexagonal boron nitride powder, and the performance was evaluated in the same manner as in Example 1. Table 2 shows the results.

COMPARATIVE EXAMPLE 1 Boric acid, melamine and a Ca compound were mixed, humidified and heated under the conditions shown in Table 1 to form melamine borate.
When calcination and crystallization were performed at 00 ° C., peaks of B ₂ O ₃ and CaO.B ₂ O ₃ were recognized in the solidified product of the crystallization catalyst in the calcination product. The weight reduction rate of this calcined product by washing with nitric acid was 12% by weight. GI value of this powder,
Table 2 shows the measurement results of the OI value and the coefficient of friction.

Comparative Example 2 A raw material having a higher proportion of Ca compound than that of Example 1 was used.
It was fired and crystallized at 1950 ° C. As a result, the calcined product contained CaO.B ₂ O ₃ and 2Ca
An O.B ₂ O ₃ peak was observed. The proportion was 20% by weight based on the weight reduction rate of the fired product due to washing with nitric acid. Table 2 shows the measurement results of the GI value, OI value, and coefficient of friction of this powder.

Example 5 The hexagonal boron nitride powder obtained in Example 1 was
(002) The half-value width of the diffraction line is shown in Table 3 using an X-ray diffractometer “JDX-3500” manufactured by JEOL Ltd. and according to Rigaku Denki's “Guide to X-ray Diffraction”, pp. 76-78 (1981). It was measured under the conditions. As a result, the half width was 0.27 °.

The hexagonal boron nitride powder 5.00
After adding 15 ml of methanol to 0 g and heating at a temperature of 80 ° C. for 1 hour, the mixture was dried in a dryer at a temperature of 120 ° C. for 1.5 hours to completely remove the liquid phase by volatilization.
Assuming that 05 g is a volatile component from hexagonal boron nitride powder, the amount of soluble oxygen was calculated assuming that this was volatilized in the form of B ₂ O ₃ reacting with methanol to form volatile trimethyl borate. 0.07% by weight.

Further, the oxygen content of the hexagonal boron nitride powder was measured using an oxygen / nitrogen analyzer "EMGA" manufactured by Horiba, Ltd.
-2800 ", which was 0.92% by weight, and the amount of insoluble oxygen was calculated by subtracting the amount of soluble oxygen therefrom to be 0.85% by weight.

Examples 6 to 8 and Comparative Examples 3 to 4 The hexagonal boron nitride powders obtained in Examples 2 to 4 and Comparative Examples 1 and 2 were evaluated for performance in the same manner as in Example 5. Table 4 shows the results.

Example 9 The hexagonal boron nitride powder of Example 1 was replaced with 2.7 ton / cm
300m long by cold isostatic pressing (CIP) with pressure of ²
m, a width of 200 mm and a thickness of 10 mm were obtained. The density (CIP density) measured from the size and weight of the molded body is 2.
It was 0 g / cm ³ .

This was heated at a temperature of 2100 ° C. in a nitrogen atmosphere for 1 hour.
By firing for 0 hour, a normal pressure sintered body of hexagonal boron nitride was manufactured. The sintered body exhibited a good appearance without any warpage, cracks, cracks, etc., and the density (sintered density) measured from the dimensions and weight was 1.6 g / cm ³ . In addition, a square bar having a length of 36 mm, a width of 4 mm, and a thickness of 3 mm was prepared by processing the sintered body, and the “Autograph AG-2000D” manufactured by Shimadzu Corporation was manufactured.
30m between fulcrums according to JIS R1601
The three-point bending strength measured at m was 27 MPa.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

[0066]

[Table 4]

[0067]

According to the present invention, since hexagonal boron nitride powder having high crystallinity and high orientation can be obtained, troubles such as seizure can be reduced when used as a solid lubricant / release agent. Excellent lubricity and releasability are obtained.

Further, according to the present invention, a hexagonal boron nitride powder having high crystallinity and high oxygen content can be obtained. A hexagonal boron nitride normal-pressure sintered body having comparable characteristics can be manufactured with high productivity.

The hexagonal boron nitride powder of the present invention can be used as a solid lubricant / release agent, an additive such as oil or grease, a filler for resin or rubber, and a raw material for producing a boron nitride sintered body. .

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-10-59702 (JP, A) JP-A-63-46278 (JP, A) JP-A-7-315937 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C01B 21/064 C04B 35/626

Claims (3)

(57) [Claims] 1. A mixture containing boric acid and melamine having a B / N atomic ratio of 1/1 to 1/6 is mixed with a Ca compound in an amount of 5 to 5% in hexagonal boron nitride formed during crystallization. 20
% Of calcium borate (CaO) x.B ₂ O ₃ was added so that a liquid phase (where X ≦ 1) was formed, and then the temperature T (° C.), the relative humidity Ψ (%), and the holding time t ( hr) is the following relational expression T ≧ −20 · log ₁₀ (t / 4) +
^{{(Ψ-100) 2/} 20} +60 to form a boric acid melamine held in conditions satisfying, those obtained further under a non-oxidizing gas atmosphere it was fired, crystallized at a temperature 1,800-2,200 ° C. X-ray powder characterized by the fact that
Graphitization index (GI) by diffraction method is 1.20 or less, (0
02) Diffraction line intensity I ₀₀₂ and (100) diffraction line intensity
The ratio of the _{I 100 (I 002 / I 100} ) is 25.0 or more
Hexagonal boron nitride powder. 2. The (002) diffraction line according to the powder X-ray diffraction method has a half width of 0.30 ° or less and insoluble oxygen of 0.5% or less.
A hexagonal boron nitride powder comprising 0 to 1.50% by weight. 3. A normal pressure sintered body of hexagonal boron nitride obtained by normal pressure sintering of the hexagonal boron nitride powder according to claim 1 .