JPH07196372A - Boron nitride ceramic and its production - Google Patents

Abstract

PURPOSE:To produce a boron nitride ceramic excellent in heat resistance, corrosion resistance, lubricity, insulating properties, etc., at low cost by pyrolyzing a specified polyborazine-based compound. CONSTITUTION:This ceramic is produced by pyrolyzing a polyborazine-based compound composed mainly of a repeating unit represented by the formula and having 300 to 100000 number-average molecular weight. This ceramic is a boron nitride ceramic composed essentially of boron, nitrogen and silicon and only pyrolytic BN is discovered by XRD measurement. After heat treatment at 200 deg.C in an atmosphere of an inert gas, this ceramic has <=500Angstrom average crystallite size of (002) plane and (100) plane based on calculation by Seherre equation. In the formula, A show H, R<8> or SIR<2>R<3>R<4> (R<2>, R<3>, R<4> and R<8> are each H, a 1 to 20C alkyl or an aryl) and may be same or mutually different in the intra-repeating unit or the inter-repeating units. All A are not H.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boron nitride ceramics and a method for producing the same, and the boron nitride ceramics is a material excellent in heat resistance, corrosion resistance, lubricity, insulation and the like. It can be expected to be widely used in industries such as aviation, space, machinery, precision, and automobiles.

[0002]

2. Description of the Related Art The main known atmospheric pressure synthesis methods of pyrolytic boron nitride (t-BN) and hexagonal boron nitride (h-BN) have been (1) metallic boron and boron oxide. A method of reacting borate with NH ₃ , metal cyanide or the like,
(2) A method of reacting a gas such as BCl ₃ or B ₂ H ₆ with NH ₃ , or a method of passing through a precursor polymer similarly to the present application, (3) a polymer synthesized from a borazine ring compound as a raw material is heated. For example, the method of disassembling. The main synthetic methods of (3) are as follows.

A borazine compound having an alkyl group, a phenyl group and a methylamino group is thermally condensed to synthesize a boron nitride ceramic precursor polymer (polyaminoborazine), which is decomposed by heating. (RH Toeniskoetter,
FR Hall, Inorg. Chem., 2, 29 (1963) and Japanese Patent Publication No. 51
-53000 (1976)] B-triamino-N-tris (trimethylsilyl)
Borazine is thermally condensed to synthesize a boron nitride ceramic precursor polymer, which is thermally decomposed in N ₂ or NH ₃ . (KJLPaclorek, W.Krone-Schmidt, DHHar
ris, RHKratzer, K.Wynne, J.Am.Chem.Soc.Symp.Se
r., 360, 392 (1988) and US Patent 4707556 (1987)] B-triaminoborazine is thermally condensed to synthesize a boron nitride ceramic precursor polymer, which is compression molded and pyrolyzed in a nitrogen stream. . [Nobuyuki Hayashi, Yoshiharu Kimura et al., 8th Symposium on Inorganic Polymers, 12 (1989)]

[0004]

The above problems have the problems that the reaction requires high temperature / high pressure and the moldability is poor. In the method (1), it is difficult to manufacture a molded product having an arbitrary shape because gas is used as a raw material, and since these gases are highly dangerous, they are difficult to handle. The method of passing through the ceramic precursor polymer is excellent in high moldability as in the present application, but has the following problems.

The methods known in the past via a boron nitride precursor polymer have the following characteristics. (A) Those containing a carbon component such as an alkyl group and a phenyl group are soluble in a solvent and are relatively stable, so that molding is easy, but a large amount of carbon component remains in the ceramics after thermal decomposition. Since free carbon causes phase separation and reaction in ceramics at high temperatures, there are problems that the strength characteristics of the ceramics are deteriorated and the high insulation property and thermal shock resistance inherent to boron nitride and boron oxide are significantly decreased. (B) If the carbon content of an alkyl group or a phenyl group is not contained or is small, the amount of carbon in the ceramics after thermal decomposition is small, but it is difficult to dissolve in a solvent and the stability is low, resulting in poor moldability. Therefore, it is impossible for the existing method to achieve both the moldability of the precursor polymer and the low carbonization of the ceramics after pyrolysis.

The conventionally known boron nitride ceramics produced by the atmospheric pressure synthesis method form hexagonal crystals at a temperature of around 1200 ° C. Boundary of different crystal planes (grain boundaries) generated during the process of crystal growth
Generally causes a decrease in strength of ceramics.・ Manufacturing cost is high because an expensive borazine ring compound is used as a raw material.

[0007]

In order to solve the above-mentioned problems of the prior art, the present invention uses boron, nitrogen and silicon as essential elements, and uses XRD (X Ray Diffrac).
Pyrolysis type BN (turbost)
nitriding characterized in that the average crystallite diameter of the (002) plane and the (100) plane after the heat treatment at 2000 ° C. in an inert gas is 500 Å or less. Boron ceramics and a method for producing the boron nitride ceramics are mainly represented by the following general formula.

[0008]

[Chemical 2]

(In the formula, A may be the same or different in the repeating unit and between repeating units, and is a hydrogen atom, R ⁸ or —SiR ² R ³ R ⁴ , and R ² , R ³ , R ⁴ , R
Each ⁸ independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an aryl group,
Is not a hydrogen atom. And a polyborazine compound having a number average molecular weight in the range of 300 to 100,000 is thermally decomposed.

The first feature of the boron nitride ceramics of the present invention is that silicon is an essential element together with boron and nitrogen. This is due to the fact that the starting polymer contains an organic silyl group, but since the starting polymer contains an organic silyl group, the starting polymer is solvent-soluble, which facilitates molding, improves the yield of ceramics, It is advantageous for reducing carbon.

Specifically, the boron nitride ceramics of the present invention contains elements having the following atomic ratios. N / B 0.05-3.0, preferably 0.3-2.
0, more preferably 0.5 to 1.5 Si / B 0.05 to 3.0, preferably 0.05 to
1.0, more preferably 0.05 to 0.5 O / B 10 or less, preferably 3 or less, more preferably 1 or less C / B 1 or less, preferably 0.5 or less, more preferably 0.1 or less. Secondly, the boron nitride ceramics of the present invention is characterized by comprising pyrolytic boron nitride (t-BN). This means that crystal growth is suppressed up to a high temperature (up to 1800 ° C. or higher), which has the advantage of high strength, particularly high temperature strength. With conventional boron nitride, hexagonal BN and thermal decomposition BN appear at temperatures above 1200 ° C.

Thirdly, in relation to the above, the boron nitride ceramics of the present invention is characterized in that the average value of the crystallite diameter of t-BN is small, and the (002) plane (d = The average value of the crystallite diameters of the 3.33Å) and (100) planes (d = 2.17Å) is 500Å or less, and more preferably 100Å or less. Generally, when diffraction lines are measured by an X-ray diffractometer (XRD), the spread of the profile is (a) the X-ray source and the slit are not infinitesimally small, (b) the optical system such as absorption of X-rays into the sample. And (A) crystallite size, (B) non-uniform strain, and (C) stacking irregularity. The Scherrer equation shown below is a crystal assuming that the crystal does not have imperfections such as (B) and (C), the profile spread is due only to the crystallite size, and that the size is uniform. This is a theoretical formula for obtaining the child diameter.

D _hkl = Kλ / (β cos θ) D _hkl : Size of crystallite on hkl plane (A) λ: Wavelength of measured X-ray (A) β: Spread of diffraction line depending on crystallite size (radian) θ: Black angle of diffraction line K: Constant (0.9 in case of full width half maximum method) Calculation of the crystallite diameter of the boron nitride ceramics of the present invention is carried out by 002 plane (d = 3.33 A) of pyrolytic BN (turbostatic). ) And 100 planes (d = 2.17A)
From the average value of the half width of the X-ray profile of
The value calculated by the error formula is used.

This small crystallite size is maintained even when at least the nitrogen-boron ceramics are heat-treated at 1800 ° C. for 48 hours or more, more preferably 2000 ° C. for 48 hours or more. Further, the boron nitride ceramics of the present invention has an advantage of low manufacturing cost because the starting polymer is inexpensive. Such a boron nitride ceramic of the present invention has the following general formula (I).

[0015]

[Chemical 3]

(In the formula, A may be the same or different in the repeating unit and between the repeating units, and is a hydrogen atom, R ⁸ or --SiR ² R ³ R ⁴ , and R ² , R ³ , R ⁴ , R
Each ⁸ independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an aryl group,
Is not a hydrogen atom. ), And the polyborazine compound (I) having a number average molecular weight in the range of 300 to 100,000 can be thermally decomposed to be produced.

This polyborazine compound (I) is mainly represented by the general formula B (OR ¹ ) ₃ (wherein R ¹ may be the same or different, and is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an aryl group). Represents a group and represents at least one R
¹ is the above-mentioned alkyl group or aryl group. ) A boron alkoxide represented by NH ₃ or R ⁸ NH
₃ and the general formula R ² R ³ R ⁴ SiNHSiR ⁵ R ⁶ R ⁷ (wherein R ² ,
R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , and R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an aryl group, and at least one R ¹ is the above alkyl group. Alternatively, it represents an aryl group. The reaction can be carried out in the presence of the disilazane compound represented by the formula (1), and further the thermal polymerization can be carried out, if necessary.

Among the above production methods, boron alkoxide and NH
The method of reacting ₃ in the presence of alkyldisilazane is
The present applicant has previously disclosed it in Japanese Patent Application No. 5-272351.
This synthetic reaction can be typically represented by the following reaction formula.

[0019]

[Chemical 4]

For details of the production method, refer to Japanese Patent Application No. 5-272351, but generally speaking, it suffices to allow each reactant to be present in a solvent and react at a temperature of about 30 to 300 ° C. This production method is characterized in that the production cost is low because the starting material is inexpensive, the reaction control is easy, and the polyborazine-based compound produced is a solvent-soluble and stable compound.

The polyborazine compound produced by the above-mentioned production method is mainly represented by the general formula

[0022]

[Chemical 5]

(In the formula, A may be the same or different in the repeating units and between the repeating units, and is a hydrogen atom, R ⁸ or —SiR ² R ³ R ⁴ , and R ² , R ³ , R ⁴ , R
Each ⁸ independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an aryl group,
Is not a hydrogen atom. ), The polymer is a linear structure in which a borazine ring is bonded via —NH— in the general formula, but —OR ¹ bonded to a boron atom. Is bound to a nitrogen atom A
Alternatively, H or a raw material disilazane compound (R ² R ³ R ⁴
It is also possible to react with SiNSiR ⁵ R ⁶ R ⁷ ) to form a more complicated structure or a crosslinked structure.

In the polyborazine compound (I) of the present invention, NH ₃ is replaced with R ⁸ NH in the above synthetic method.
₂ (R ⁸ represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms or an aryl group). This synthetic reaction can be typically represented by the following reaction formula.

[0025]

[Chemical 6]

Then, in this synthetic method, NH ₃ is replaced with R ⁸ N
The method is basically the same as the method disclosed in Japanese Patent Application No. 5-272351, except that H ₂ is used. In addition, R ¹
It is preferable that R ⁸ to R ⁸ are substituents having a small number of carbon atoms. This is because it is advantageous for improving the ceramic yield and reducing the carbon number in the ceramic. These polymers have H and --OR ¹
With group and alkylsilyl group ^{(-SiR 2 R 3 R 4)} .
H, —OR ¹ groups and —SiR ² R ³ R ⁴ in the polymer
The amount of the group present can be adjusted by changing the mixing ratio of the reaction raw materials. Since the polymer has an —OR ¹ group and an alkylsilyl group (—SiR ² R ³ R ⁴ ), it is soluble in benzene, toluene, xylene, tetrahydrofuran (THF) and the like.

Further, these polymers have sufficient stability. If it is stored in a dry atmosphere at room temperature for a long time, the physical properties of the polymer do not change. This is because the stable functional group -OR ¹ group and alkylsilyl group (-SiR ² R ³
It is believed that this is because it has R ⁴ ). The above-mentioned polymer (polyborazine compound) is usually converted into boron nitride ceramics through a solidification and firing process.

The above-mentioned polymer may be solidified alone or by mixing a curing agent or a ceramic powder. The conditions of the solidification step, that is, the temperature, the pressure, the atmosphere gas, the holding time, etc. are appropriately selected depending on the presence or absence of the curing agent or the ceramic powder or the amount used. Although not particularly limited, it is generally as follows. For example, in the case of the polymer alone, this is dissolved in an organic solvent such as hydrocarbons, halogenated hydrocarbons, ethers, etc., and this is filled in a mold of any shape as required. Next, it can be solidified by heating at a temperature not lower than the boiling point of the organic solvent used under normal pressure, or by heating under reduced pressure to remove the organic solvent.

When a liquid polymer is used, it is filled in a mold having an arbitrary shape, if necessary, and then under vacuum or under various gas atmospheres described below at atmospheric pressure to 10 atm. It is solidified by raising the temperature from room temperature to an arbitrary temperature of 400 ° C. and maintaining the temperature. The setting time is in the range of 0.5 to 72 hours. further,
A method in which a solid polymer is filled in a molding die of an arbitrary shape and the temperature is maintained from room temperature to 400 ° C. under the atmospheric gas in the range of atmospheric pressure to 10 atmospheres may be used.

As the atmosphere gas, an inert gas such as nitrogen and argon, a reducing gas such as ammonia, hydrogen, methylamine and hydrazine, an oxidizing gas such as air, oxygen and ozone, or a mixed gas thereof can be used. Further, as the curing agent, alkylamine, organic amines such as alkylenediamine, oxalic anhydride, carboxylic acid anhydride such as malonic anhydride, alkyl isocyanate, isocyanates such as dimethylsilyl diisocyanate, butanedithiol, benzenedithiol, etc. , Carboxylic acid imides such as malonic acid imide and succinimide, metal alkoxides containing metals selected from the groups IIa and III to V of the Periodic Table of the Elements, iron, cobalt,
Halides such as nickel, copper, silver, gold, mercury, zinc, ruthenium, palladium, indium, titanium, hafnium, zirconium, aluminum, boron and phosphorus are used.

Further, for the purpose of preventing crack generation and increasing strength, examples of the ceramic powder added as necessary include nitrides, carbides and oxides of various metals. Any conventionally known mold can be used as the mold, but a mold release agent such as a silicone-based compound may be applied to the mold to protect the removability of the molded product and the back surface of the molded product. Alternatively, it is preferable to apply grease thinly or apply grease dispersed in an organic solvent by an application means such as spraying or brush coating.

After the above solidification step, heating and baking are preferably performed in the presence of the above-mentioned inert gas, reducing gas, oxidizing gas or a mixed gas thereof. The conditions for this calcination are not limited, but generally 20 ° C./min or less, preferably 5 ° C./min or less and 400 ° C. to 1800 ° C.
The temperature is raised to 2300 ° C, and at this temperature it is usually 48
Perform by holding for less than an hour. In some cases, good results can be obtained by pressure firing such as hot pressing.

In this firing step, OR ¹ in the polymer is
Group and an alkylsilyl group (-SiR ² R ³ R ⁴⁾ to produce a B-N bond by reacting. At this time, R ¹ obtained by bonding an OR ¹ group and an alkylsilyl group (—SiR ² R ³ R ⁴ )
OSiR ² R ³ R ⁴ is produced. As a result, carbonization in the polymer scatters as ceramicization progresses, and ceramics having a low carbon content can be obtained. Since the produced R ¹ OSiR ² R ³ R ⁴ is a stable compound, it does not re-react with the polymer or the ceramics after firing.

Further, in the boron nitride ceramics of the present invention, crystal growth is suppressed up to a high temperature of 1800 ° C. or higher, preferably 2000 ° C. or higher. It is considered that this is because the same ceramic was synthesized via the precursor polymer. If the firing temperature is less than 400 ° C., ceramization is insufficient and sufficient hardness cannot be imparted. On the other hand, if the temperature exceeds 2300 ° C., undesired crystal growth becomes remarkable and the strength is greatly reduced.

The ceramics (particularly the molded body) of the present invention is manufactured by the method as described above. It is preferable to impregnate the ceramics (molded body) after firing with the above-mentioned polymer, and solidify and fire repeatedly. Sometimes ceramics are obtained. The precursor polymer of the present invention can also be baked after coating to provide a boron nitride ceramic coating. Alternatively, the obtained ceramics can be pulverized into a boron nitride ceramic powder.

[0036]

【Example】

Example 1 After the inside of a SUS-316 reactor having an internal volume of 2 L was replaced with dry nitrogen, the pressure was increased to 1 kg / cm ² G with dry nitrogen. 601.4 g of dry pyridine (C ₅ H ₅ N) is introduced into this reactor. While stirring, trimethyl borate (B
62.5 g (0.601 mol) of (OMe) ₃ ) and then hexamethyldisilazane [((CH ₃ ) ₃ Si) ₂ NH]
290.3 g (1.803 mol) was added. Then NH ₃ 3
After introducing 0.8 g (1.812 mol) into the reactor, the reactor was closed. When this was reacted at 160 ° C., a pale red solution was obtained. After completion of the reaction, the solvent was removed under reduced pressure to obtain 36.5 g of a pale red viscous liquid. This viscous liquid easily dissolved in benzene, toluene, xylene, and THF.

The number average molecular weight of the produced polymer was 750 as measured by the freezing point depression method (solvent: dry benzene). NH (3350 cm ⁻¹ ), CH ₃ and OCH ₃ (2960 and 2850 cm ⁻¹ ), B—O and BN (1300 to 1540 cm ⁻¹ ), Si—Me (1
Absorption of 250 cm ^-1 ) and BN [borazine ring] (860 cm ^-1 ) was observed. The elemental ancestral analysis results (% by weight) of the product are B: 17.6; N: 24.8; Si: 14.0;
It was O: 7.9; C: 28.1; H: 7.6. A benzene solution (50 wt%) of this polymer was placed under a nitrogen atmosphere,
After being left to stand at room temperature for 6 months, no change was observed in the molecular weight and elemental composition. The structure of this polymer was certified as follows.

[0038]

[Chemical 7]

The obtained polymer was dissolved in toluene, the concentration was adjusted, and the mixture was poured into a Teflon molding die, and the solvent was removed at 200 ° C. under a nitrogen stream to obtain a transparent molding (20 mmφ × 10 mm). Next, in an NH ₃ gas atmosphere, 1
The temperature is raised to 1000 ° C. at a heating rate of ℃ / min, and then 1700 at a heating rate of 10 ° C./min in a nitrogen gas atmosphere.
The temperature was raised to 0 ° C. and firing was performed at 1700 ° C. for 1 hour to obtain a white disc-shaped ceramic. The elemental ancestry analysis result (% by weight) of this ceramic was B: 35.4; N: 5.
4.2; Si: 6.8; O: 3.5; C: 0.1.

Subsequently, this sample was placed in N ₂ gas at 2000 ° C.
002 calculated by the Scherrer equation after firing in
The average value of the crystallite diameters of the 100 and 100 planes was 85A. Example 2 The inside of a reactor made of SUS-316 having an internal volume of 2 L was replaced with dry nitrogen, and then pressurized to 1 kg / cm ² G with dry nitrogen. 601.4 g of dry pyridine (C ₅ H ₅ N) is introduced into this reactor. While stirring, trimethyl borate (B
62.5 g (0.601 mol) of (OMe) ₃ ) and then hexamethyldisilazane [((CH ₃ ) ₃ Si) ₂ NH]
290.3 g (1.803 mol) was added. Then NH ₃ 3
After introducing 0.8 g (1.812 mol) into the reactor, the reactor was closed. When this was reacted at 160 ° C., a pale red solution was obtained. After completion of the reaction, the solvent was removed under reduced pressure to obtain 36.5 g of a pale red viscous liquid. This viscous liquid easily dissolved in benzene, toluene, xylene, and THF.

The number average molecular weight of the produced polymer was 750 as measured by the freezing point depression method (solvent: dry benzene). NH (3350 cm ⁻¹ ), CH ₃ and OCH ₃ (2960 and 2850 cm ⁻¹ ), B—O and BN (1300 to 1540 cm ⁻¹ ), Si—Me (1
Absorption of 250 cm ^-1 ) and BN [borazine ring] (860 cm ^-1 ) was observed. The elemental ancestry analysis result (% by weight) of the product is B: 17.6; N: 24.8; Si: 14.0;
It was O: 7.9; C: 28.1; H: 7.6. A benzene solution (50 wt%) of this polymer was placed under a nitrogen atmosphere,
After being left to stand at room temperature for 6 months, no change was observed in the molecular weight and elemental composition.

The obtained polymer was dissolved in toluene, the concentration was adjusted, and the mixture was poured into a Teflon mold and the solvent was removed at 200 ° C. under a nitrogen stream to obtain a transparent molded body (20 mmφ × 10 mm). Next, in a nitrogen gas atmosphere at 3 ° C
1700 ° C at a heating rate of 1 / min
A white disc-shaped ceramic was obtained by firing at 1 ° C. for 1 hour. The elemental ancestry analysis results (% by weight) of this ceramic are B: 38.5; N: 54.0; Si: 3.4;
It was O: 1.5; C: 2.6.

Subsequently, this sample was placed in N ₂ gas at 2000 ° C.
002 calculated by the Scherrer equation after firing in
The average value of the crystallite diameters of the 100 and 100 planes was 150A. Example 3 The interior of a SUS-316 reactor having an internal volume of 2 L was replaced with dry nitrogen, and then pressurized with dry nitrogen to 1 kg / cm ² G. 801.4 g of dry pyridine (C ₅ H ₅ N) are introduced into this reactor. While stirring, trimethyl borate (B
62.5 g (0.601 mol) of (OMe) ₃ ) and then hexamethyldisilazane [((CH ₃ ) ₃ Si) ₂ NH]
290.3 g (1.803 mol) was added. Then NH ₃ 3
After introducing 0.8 g (1.812 mol) into the reactor, the reactor was closed. When this was reacted at 160 ° C., a pale red solution was obtained. After completion of the reaction, the solvent was removed under reduced pressure to obtain 36.5 g of a pale red viscous liquid. This viscous liquid easily dissolved in benzene, toluene, xylene, and THF.

The number average molecular weight of the produced polymer was 750 as measured by the freezing point depression method (solvent: dry benzene). NH (3350 cm ⁻¹ ), CH ₃ and OCH ₃ (2960 and 2850 cm ⁻¹ ), B—O and BN (1300 to 1540 cm ⁻¹ ), Si—Me (1
Absorption of 250 cm ^-1 ) and BN [borazine ring] (860 cm ^-1 ) was observed. The elemental ancestral analysis results (% by weight) of the product are B: 17.6; N: 24.8; Si: 14.0;
It was O: 7.9; C: 28.1; H: 7.6. A benzene solution (50 wt%) of this polymer was placed under a nitrogen atmosphere,
After being left to stand at room temperature for 6 months, no change was observed in the molecular weight and elemental composition.

The obtained polymer was dissolved in toluene, the concentration was adjusted, and the mixture was poured into a Teflon mold and the solvent was removed at 200 ° C. under a nitrogen stream to obtain a transparent molded body (20 mmφ × 10 mm). Next, in an air atmosphere, 1 ℃ / mi
The temperature was raised to 1200 ° C. at a temperature rising rate of n, and the white disc-shaped ceramics were obtained by firing at 1200 ° C. for 1 hour. Elemental ancestry analysis result of this ceramics (wt%)
Is B: 30.2; N: 39.7; Si: 7.5; O: 2
2.5; C: 0.1.

Subsequently, this sample was subjected to 2000 ° C. in N ₂ gas.
002 calculated by the Scherrer equation after firing in
The average value of the crystallite diameters of the 100 and 100 planes was 210A.

[0047]

The present invention has the following advantageous effects. Since the boron nitride ceramics of the present invention are synthesized via the above-mentioned precursor polymer, it is possible to obtain a ceramic of any shape under a relatively mild temperature and pressure.

Since the polymer shown in the present invention contains an —OR ¹ group and an alkylsilyl group (—SiR ² R ³ R ⁴ ), it has high solubility in an organic solvent. This facilitates molding. The —OR ¹ group and the alkylsilyl group (—SiR ² R ³ R ⁴ ) contained in the polymer of the present invention have an effect of stabilizing the polymer to some extent. Therefore, handling such as molding is easy.

The polymer shown in the present invention has both —OR ¹ group and alkylsilyl group (—SiR ² R ³ R ⁴ ).
These groups react with each other in the firing step and are stable compounds R
^{Since 1} OSiR ² R ³ R ⁴ is generated and scattered, the carbon content in the ceramics after firing can be reduced. Since the boron nitride ceramics of the present invention is synthesized via the above-mentioned precursor polymer, the growth of crystal grains can be suppressed up to a high temperature of 2000 ° C.

Since the precursor polymer of the boron nitride ceramics of the present invention is synthesized by using boron alkoxide, NH ₃ , and alkylsilazanes as raw materials, the production cost is lower than that when the borazine ring compound is used as the raw material.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Funayama Toru Funayama 1-3-3 Nishitsurugaoka, Oi-cho, Iruma-gun, Saitama Prefecture Tonen Corporation Research Laboratory (72) Inventor Takeshi Isoda Nishitsuruga, Oi-cho, Iruma-gun, Saitama Prefecture Oka 1-33-1 Tonen Co., Ltd. Research Institute

Claims (5)

[Claims] 1. Boron, nitrogen and silicon are essential elements, and X
Only the thermal decomposition type BN (turbostatic BN) was observed by RD (X Ray Diffractometer) measurement, and the average of the crystallite diameters of the (002) plane and the (100) plane calculated by the Scherrre equation after heat treatment at 2000 ° C. in an inert gas. A boron nitride ceramics having a value of 500 Å or less. 2. The ratio of constituent elements is atomic ratio and N / B is 0.
The boron nitride ceramics according to claim 1, wherein the boron nitride ceramics have an S / B value of 0.05 to 3.0, a Si / B value of 0.05 to 3.0, an O / B value of 10 or less, and a C / B value of 1.0 or less. 3. The boron nitride ceramics according to claim 1, which is a molded body. 4. The following general formula: (In the formula, A may be the same or different in the repeating unit and between the repeating units, and a hydrogen atom, R ⁸ or —SiR ²
It is a ^{R 3 R 4, R 2,} R 3, R 4, R 8 represents independently a hydrogen atom, an alkyl group or an aryl group having 1-20 carbon atoms, all of A hydrogen atom Absent. And a polyborazine compound having a number average molecular weight in the range of 300 to 100,000 is pyrolyzed, which is a method for producing a boron nitride ceramics. 5. The method for producing a boron nitride ceramics according to claim 4, wherein the polyborazine compound is molded and thermally decomposed to obtain a boron nitride ceramics molded body.