JPH0718521A - Boron nitride fiber and its production - Google Patents

Abstract

PURPOSE:To obtain a boron nitride fiber having low carbon content and high strength, resistant to the thermal deterioration of the strength and having a crystallite diameter of 10-30Angstrom . CONSTITUTION:This boron nitride fiber is composed of hexagonal and/or turbostratic boron nitride and has crystallite diameter of 10-30Angstrom . This boron nitride fiber is produced by heating an adduct of a boron trihalide such as boron trichloride to a nitrile compound such as acetonitrile and benzonitrile together with an ammonium halide or a primary amine hydrohalogenic acid salt in the presence of a boron trihalide at about 125 deg.C, dissolving the obtained boron nitride precursor in a solvent of the precursor (e.g. N,N'- dimethylformamide), spinning the produced dope, heating the fiber in an inert gas atmosphere and then heating in an ammonia gas atmosphere.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a boron nitride fiber and a method for producing the same.

[0002]

2. Description of the Related Art Boron nitride fibers are excellent in chemical stability and heat resistance and are useful as reinforcing fibers for composite materials having ceramics or metals as a matrix phase.

Regarding the crystallite size of the hexagonal or turbostratic type boron nitride fiber obtained thus far, the following two examples are known.

R. Y. Lin et al. Obtained boron nitride fibers by melt-spinning boron oxide, heating in ammonia gas to 800 ° C., and then heating in nitrogen to 2000 ° C. The crystallite diameter was 48 Å at a firing temperature of 1700 ° C and 105 Å at 2000 ° C [Applied Polymer Symposium (AppliedP
polymer Symposium), 29, 175-
188 (1976). ].

D. A. Lindquist et al. Spun precursor fibers from an ammonia solution of a borazine polymer crosslinked by amino groups, heated to 1200 ° C. in ammonia gas, and then heated to 1650 ° C. in nitrogen to obtain boron nitride fibers. Its crystallite size was 120 Å [Chemistry of Materials (Chemis
try of Materials), 4, 1, 17-
19 (1992). ].

[0006]

When using boron nitride fiber as a reinforcing fiber, it is required that the strength of the fiber is high, and at the same time, a process of producing a composite material using the boron nitride fiber, or It is required that the strength does not deteriorate in the high temperature condition of the usage environment. In general,
The strength of the ceramic fiber remarkably depends on the crystallite diameter, and the strength decreases as the crystallite diameter increases. However, until now, it has not been possible to obtain a boron nitride fiber having a small crystallite diameter, specifically, 30 angstroms or less.

Therefore, it is strongly desired to establish a boron nitride fiber for reinforcement, which has a finer crystallite diameter and does not cause coarsening of the crystallite diameter even at high temperatures, and a method for producing the same. It was

[0008]

DISCLOSURE OF THE INVENTION The present inventors have proposed a boron nitride precursor which is a reaction product of an addition product of a boron trihalide and a nitrile compound and an ammonium halide or a primary amine hydrohalide. The boron nitride precursor fiber spun from the body was heat-treated under specific conditions to find a boron nitride fiber having a fine crystallite size and showing no significant coarsening even at high temperatures, and completed the present invention. I came to propose here.

That is, the present invention is a boron nitride fiber characterized by comprising hexagonal and / or turbostratic type boron nitride and having a crystallite diameter of 10 to 30 angstroms. Is a boron nitride precursor obtained by reacting an adduct of a boron trihalide with a nitrile compound and an ammonium halide or a primary amine hydrohalide in the presence of boron trihalide as a solvent. In the method for producing the boron nitride fiber, it is dissolved in, and the solution is spun, then heat-treated in an inert gas atmosphere and then heat-treated in an ammonia gas atmosphere.

The crystal structure of the boron nitride fiber of the present invention is a hexagonal crystal structure and / or a turbostratic structure.

The hexagonal crystal structure is a structure in which planes composed of a six-membered ring formed by bonding boron and nitrogen are regularly stacked. In addition, the turbostratic structure is a structure in which the plane composed of a six-membered ring formed by bonding boron and nitrogen is laminated without having regularity in the vertical direction. is there. Generally, hexagonal boron nitride and turbostratic boron nitride are caused by in-plane symmetry perpendicular to the c-axis of a boron nitride crystal, such as a diffraction peak from the (110) plane by powder X-ray diffraction. It can be distinguished by the presence or absence of the diffraction peak. However, when the crystallite size is very fine as in the case of boron nitride of the boron nitride fiber of the present invention, the width of the diffraction peak by powder X-ray diffraction becomes very wide, so that the (110) peak or the like is generated. It is difficult to detect the diffraction peak that distinguishes the hexagonal structure from the turbostratic structure.

Therefore, it can be said that the boron nitride fiber in the present invention is composed of hexagonal boron nitride, turbostratic boron nitride, or a mixture of hexagonal boron nitride and turbostratic boron nitride. The boron nitride fiber of the present invention may contain carbon in an amount of about 5% or less. When the carbon content exceeds 5%, when the boron nitride fiber is exposed to a high temperature oxidizing atmosphere, the carbon component tends to burn and a void or the like tends to occur, which is not preferable.

The crystallite size of the boron nitride constituting the boron nitride fiber of the present invention depends on the thermal history during the production or use of the boron nitride fiber under normal conditions unless it is exposed to decomposition or combustion conditions. It is kept in the range of 10 to 30 angstroms.

The crystallite diameter in the present invention indicates the size in the c-axis direction of a boron nitride crystal having a hexagonal crystal and / or a turbostratic structure which constitutes a boron nitride fiber.

The crystallite diameter was determined by measuring the spread of the diffraction peak in powder X-ray diffraction of the obtained boron nitride fiber, and using the Scherrer formula [B. D. C
by Ullity, translated by Gentaro Matsumura, "New Edition X-ray Diffraction Essentials"
Agne (1980). ] Is used for the calculation. This will be specifically described below.

The boron nitride fiber is crushed in an agate mortar and used as a sample for powder X-ray diffraction. From the obtained powder X-ray diffraction pattern, the hexagonal boron nitride (0
The half width of the diffraction peak due to the plane formed by the 6-membered ring formed by bonding boron and nitrogen of the turbostratic boron nitride is determined. The full width at half maximum of the diffraction peak appearing in the powder X-ray diffraction pattern includes the device-specific spread due to the width of the X-ray source, etc.
It is corrected by the method of En (formula 1).

B ² = (Bm) ² − (Bs) ² (1) [where B is the full width at half maximum depending on the crystallite diameter of the sample, Bm
Represents the full width at half maximum of the sample obtained by actual measurement, and Bs represents the full width at half maximum of the standard sample (each unit is radian). The standard sample only needs to have a sufficiently large crystallite size, that is, a crystallite size of 1000 angstroms or more, and for example, high-purity silicon powder can be used. When silicon is used as a standard sample, Bs is defined as the full width at half maximum of the diffraction peak from the (111) plane.

Diffraction peak by (002) plane of hexagonal boron nitride obtained by correction by Warren's method or plane formed by six-membered ring formed by bonding boron and nitrogen of turbostratic type boron nitride According to Scherrer's equation (Equation 2), the crystallite diameter of the hexagonal and / or turbostratic boron nitride constituting the boron nitride fiber is determined from the half-width of the diffraction peak by

T = 0.9 · λ / (B · cos θ) (2) [where t is the crystallite diameter in the plane direction of the diffraction peak, λ is the wavelength of the X-ray used for powder X-ray diffraction, and the unit is Both are Angstroms. B is the full width at half maximum of the sample corrected by the Warren method, and the unit is radian. Next, a method for obtaining the boron nitride fiber of the present invention will be described.

The boron trihalide used in the present invention includes boron trifluoride, boron trichloride, boron tribromide, boron triiodide and the like, and they can be used without particular limitation.

As the nitrile compound, a known compound having a nitrile group can be used without particular limitation. Specifically, acetonitrile, propionitrile, capronitrile, acrylonitrile, crotonnitrile,
Examples include tolunitrile and benzonitrile. When the number of carbons contained in the nitrile compound increases, the carbon contained in the obtained boron nitride precursor increases, and as a result, the elimination component increases when the boron nitride precursor is nitrided by heat treatment. Therefore, defects such as voids are likely to occur in the finally obtained boron nitride fiber. Therefore,
It is more preferable to use a nitrile compound having a small number of carbon atoms such as acetonitrile or acrylonitrile.

Examples of ammonium halides or primary amine hydrohalides include ammonium chloride, ammonium bromide, ammonium iodide, ammonium fluoride, methylamine hydrochloride, ethylamine hydrochloride, propylamine hydrochloride, aniline hydrochloride, Specific examples include methylamine hydrobromide, aniline hydrobromide, methylamine hydroiodide and aniline hydroiodide. For the same reason as the above-mentioned nitrile compound, it is preferable that the number of carbon atoms is as small as possible, and from the viewpoint of easy availability, ammonium chloride or lower alkyl primary amine hydrochloride is preferably used.

To obtain the boron nitride fiber of the present invention,
First, an adduct of the above boron trihalide and a nitrile compound is synthesized, and then the adduct is reacted with an ammonium halide or a primary amine hydrohalide to synthesize a boron nitride precursor.

The adduct of boron trihalide with a nitrile compound is a product in which boron halide is additionally bonded to the non-bonded electron pair of the nitrogen atom of the nitrile group, and the boron trihalide and nitrile compound are Reacts readily with to form an adduct.

The method for producing the adduct is not particularly limited. For example, at room temperature, a method in which a boron trihalide is dissolved in a solution obtained by dissolving a nitrile compound in the organic solvent, a method in which the nitrile compound is dissolved in an organic solvent and then boron trihalide is blown thereinto, or a trihalogen compound in the organic solvent The adduct can be formed by, for example, dissolving boron oxide and then dropping a nitrile compound.
Since the boron trihalide and the nitrile compound easily react to form an adduct, they may be contacted with each other immediately before the reaction.

When the above-mentioned adduct is reacted with ammonium halide or a primary amine hydrohalide to produce a boron nitride precursor, it is essential that boron trihalide is present. When boron trihalide is not present during the reaction, the yield of the boron nitride precursor of the present invention is low, and a spinning solvent for spinning, such as N, N-, which will be described later, is used.
Reaction by-products insoluble in dimethylformamide (hereinafter also referred to as DMF) are produced.

The boron trihalide may be present at least during the reaction between the boron trihalide / addition product of the nitrile compound and the ammonium halide or the primary amine hydrohalide, and the addition timing is not limited. For example, even if unreacted boron trihalide is previously contained in the adduct by using an excess amount of boron trihalide when forming an adduct of a nitrile compound and boron trihalide. good.

The amount of boron trihalide added to the nitrile compound can be arbitrarily selected from the range of 1.05 to 2.00 in terms of molar ratio (boron trihalide / nitrile compound). However, when the amount of boron trihalide added is small, a DMF-insoluble component is produced, and when the amount of boron trihalide added is large, the amount of boron trihalide that does not contribute to the reaction increases, so that a more preferable nitrile compound is obtained. The addition molar ratio of boron trihalide is 1.1 to 1.5. At this time, the boron trihalide and the nitrile compound are 1
Since the adduct of 1 is produced, when the adduct is subsequently reacted with ammonium halide or the like, the boron trihalide is added in a molar ratio (boron trihalide / adduct) to the adduct. It will exist in the range of 0.1 to 0.5.

The concentration of the nitrile compound in the reaction solvent is not particularly limited, but it is preferably in the range of 0.1 to 10 mol / l. If the concentration of the nitrile compound is less than 0.1 mol / l, the amount of the boron nitride precursor obtained is small and it is not efficient, which is not preferable.
Further, if the concentration of the nitrile compound exceeds 10 mol / l, the amount of the adduct formed as a solid with respect to the solvent becomes too large, and the formation of the adduct becomes non-uniform, which is not preferable.

The ammonium halide or primary amine hydrohalide salt is added in a molar ratio (ammonium halide or primary amine hydrohalide salt / nitrile compound) of 0.67 to the nitrile compound.
It is preferable to select from the range of 1.5. If the amount of ammonium halide or primary amine hydrohalide is large, a component insoluble in DMF is formed, and if the amount of nitrile compound is large, the amount of unreacted adduct tends to increase. It may be selected from the range of 1.2.

The solvent used for synthesizing the boron nitride precursor of the present invention is not particularly limited, but when separating the reaction product boron nitride precursor, the reaction by-product borazine compound is dissolved. It is preferable that it is easy to remove. From this point of view, a non-polar organic solvent such as benzene, toluene, xylene, chlorobenzene is preferably selected.

The heating temperature for reacting the adduct with the ammonium halide or the primary amine hydrohalide is generally low at low temperatures, and D at high temperatures.
The components insoluble in MF increase and the reaction yield decreases. Therefore, the heating temperature may be selected from the range of 100 ° C to 160 ° C. The heating time may vary depending on the temperature, but may be selected from the range of 3 to 30 hours.

By performing the above heat treatment, a boron nitride precursor is formed as an orange or brown precipitate.

The reactor for obtaining the boron nitride precursor is not particularly limited. However, since both the boron trihalide and nitrile compound adducts and the boron nitride precursor are hydrolyzed, the inside of the reaction system should be sufficiently dried with nitrogen gas, etc. It is necessary to place a hygroscopic agent such as calcium chloride in the open part of the device so that moisture inside does not enter.

As a method for producing a boron nitride precursor fiber from this boron nitride precursor, a known spinning method can be used without limitation.

For example, when performing wet spinning, the boron nitride precursor is dissolved in a soluble solvent to prepare a spinning solution. Examples of the precursor-soluble solvent include DMF and the like. By dissolving the boron nitride precursor in DMF, an orange or brown transparent spinning solution can be obtained. The preferred concentration range of the spinning solution depends on the spinning method, but is 0.01 to 3.0 g / ml, and the viscosity at that time is 10 to 100,000 poises.

A widely known method can be used for spinning the boron nitride precursor fiber from the obtained spinning solution. For example, by rotating a container having a small hole containing the spinning solution, the spinning solution is discharged by utilizing centrifugal force, a method of discharging the spinning solution by gas pressure through the small hole,
Boron nitride precursor fibers can be spun by a method such as discharging a spinning solution from a small hole using a gear pump.

By heating the boron nitride precursor fiber thus obtained, a boron nitride fiber is obtained. In order to produce a boron nitride fiber made of boron nitride having a crystallite size of 10 to 30 angstroms according to the present invention, first, heat treatment (hereinafter referred to as heat treatment under inert gas) is performed in an inert gas atmosphere. , Then heat treatment in ammonia atmosphere (hereinafter referred to as heat treatment under ammonia)
Is essential. It is not possible to remove the carbon derived from the boron nitride precursor by performing only heat treatment under an inert gas,
The resulting fiber has a black color. Further, when only heat treatment under ammonia is performed, the crystallite diameter of boron nitride in the obtained boron nitride fiber becomes coarse, and defects and scratches are generated on the fiber surface, and high-strength boron nitride fiber is obtained. Absent.

Nitrogen, argon, helium or the like can be used as an atmospheric gas in the heat treatment under an inert gas. The heat treatment temperature in the heat treatment under an inert gas is 1
It can be arbitrarily selected from the range of 00 to 600 ° C. 1
When the heat treatment is performed at a temperature lower than 00 ° C., the crystallite diameter of boron nitride is increased in the heat treatment under ammonia performed after the heat treatment under the inert gas, and the boron nitride fiber having a small crystallite diameter according to the present invention. Can't get Also, 600 ℃
When the heat treatment is performed at a higher temperature, the carbon derived from the precursor is easily graphitized, and it is difficult to remove it.
As a result, 5 to 15% by weight of carbon remains in the boron nitride fiber.

The heating device for heat-treating the boron nitride precursor fiber in an inert gas atmosphere may be any one having a chamber or a furnace core tube for controlling the atmosphere, such as an electric furnace and a gas furnace. The heating device of is used without particular limitation. As the heat treatment method, a batch-type heat treatment in which a certain amount of boron nitride precursor fibers are heat-treated at one time, and continuous boron nitride precursor fibers are sequentially fed to a heating device which has been heated to a heat treatment temperature in advance and heated. Process and
There is a continuous heat treatment for winding and collecting heat-treated fibers, and any heat treatment method may be used in the present invention.

When the batch type heat treatment is carried out in an inert gas atmosphere, the boron nitride precursor fiber is put in a heat treatment apparatus which has been preheated to the heat treatment temperature, or the heat treatment apparatus is used. After the boron nitride precursor fiber is added to the above, the temperature is raised to reach the heat treatment temperature and heat treatment can be performed. However, when the boron nitride precursor fiber is rapidly heated, evaporation of the solvent DMF and desorption of the thermal decomposition product occur rapidly, resulting in voids in the obtained boron nitride fiber.
Defects such as cracks may occur and the strength may be reduced. Therefore, it is preferable to perform the heat treatment by a method in which the boron nitride precursor fiber is placed in the heat treatment apparatus and then the temperature is gradually raised to reach the heat treatment temperature. In this case, the heating rate is 20 ° C./min or less. Is more preferable.

The holding time at the heat treatment temperature is 0 to 10
It can be arbitrarily selected from the range of time. Hold time is 0
The time means that immediately after the boron nitride precursor fiber reaches the heat treatment temperature, the heat treatment is finished by lowering the temperature of the heating device or taking out the boron nitride precursor fiber from the heating device. .

Even in the case of continuous heat treatment in an inert gas atmosphere, when the boron nitride precursor fiber is rapidly heated, the strength of the obtained boron nitride fiber may decrease due to the generation of defects, It is preferable to heat up to a predetermined heat treatment temperature at a heating rate of 20 ° C./min or less. Also,
The holding time at the heat treatment temperature may be selected from the range of 0 to 10 hours. In the case of continuous heat treatment, depending on the feed rate of the boron nitride precursor fiber, the take-up speed of the fiber after the heat treatment, the length of the soaking part of the heating device, the temperature gradient of the heating device, etc. It is possible to control the heating rate of the elementary precursor fibers and the holding time at the heat treatment temperature.

The heat treatment atmosphere in the heat treatment under an inert gas is not only during the heat treatment but also during the temperature rising process until reaching the heat treatment temperature, the holding process at the heat treatment temperature, and the temperature lowering process after the heat treatment is completed. Also in the process of (1), that is, while the boron nitride precursor fiber is in the chamber of the heating device, the furnace core tube, and the like in the inert gas atmosphere, the inert gas atmosphere is preferable. In order to create an inert gas atmosphere, the chamber of the heating device, the furnace core tube, or the like, which has been replaced with the inert gas, may be sealed, or the inert gas may be passed through the chamber of the heating device, the furnace core tube, or the like.

The temperature of the heat treatment under ammonia followed by the heat treatment under inert gas can be arbitrarily selected from the range of 600 to 1300 ° C. When the heat treatment under ammonia is performed at a temperature lower than 600 ° C., carbon derived from the precursor is not sufficiently removed, and 5 to 15% by weight of carbon remains in the boron nitride fiber. Further, since the carbon derived from the precursor is almost decomposed and removed by the heat treatment at a temperature of 600 to 1300 ° C, it is not necessary to perform the heat treatment under ammonia at a temperature higher than 1300 ° C.

The heating device for heat-treating the boron nitride precursor fiber in an ammonia gas atmosphere may be any one having a chamber or a furnace core tube for controlling the atmosphere, such as known in electric furnaces and gas furnaces. A heating device can be used without particular limitation. As the heat treatment method, either a batch heat treatment or a continuous heat treatment method may be used similarly to the heat treatment in an inert gas atmosphere.

When the batch type heat treatment is carried out in an ammonia gas atmosphere, the boron nitride precursor fiber is put into a heat treatment apparatus which has been preheated to the heat treatment temperature, or the heat treatment is carried out. After the boron nitride precursor fiber is added, the temperature is raised to reach the heat treatment temperature and heat treatment is performed.
However, when the boron nitride precursor fiber is rapidly heated,
Desorption of thermal decomposition products may occur rapidly, resulting in defects such as voids and cracks in the obtained boron nitride fiber, leading to a decrease in strength. Therefore, it is preferable to perform the heat treatment by a method in which the boron nitride precursor fiber is placed in the heat treatment apparatus and then the temperature is gradually raised to reach the heat treatment temperature. In that case, the heating rate is 20 ° C./min or less. Is more preferable.

The holding time at the heat treatment temperature depends on the amount of the boron nitride precursor fibers to be heat treated, but it is 0-10.
It can be arbitrarily selected from the range of time. Hold time is 0
The time means that the temperature of the heating device is lowered immediately after the boron nitride precursor fiber reaches the heat treatment temperature, or the boron nitride precursor fiber is taken out of the heating device and the heat treatment is completed.

Even in the case of continuous heat treatment in an atmosphere of ammonia gas, when the boron nitride fiber is rapidly heated, the strength of the boron nitride fiber obtained may be lowered due to the generation of defects, so that the temperature is 20 ° C./min. It is preferable to heat up to a predetermined heat treatment temperature at the following temperature rising rate. The holding time at the heat treatment temperature may be selected from the range of 0 to 10 hours, though it depends on the amount of the boron nitride precursor fiber to be heat treated. In the case of continuous heat treatment, depending on the feed rate of the boron nitride precursor fiber, the take-up speed of the fiber after the heat treatment, the length of the soaking part of the heating device, the temperature gradient of the heating device, etc. It is possible to control the heating rate of the elementary precursor fibers and the holding time at the heat treatment temperature.

The heat treatment atmosphere in the heat treatment under ammonia is not only during the heat treatment at the heat treatment temperature but also during the temperature rising process until the heat treatment temperature is reached, the holding process at the heat treatment temperature, and the temperature lowering process after the heat treatment is completed. In any process, that is, while the boron nitride precursor fiber is in the chamber of the heating device in the ammonia atmosphere, the furnace core tube, or the like, it is preferable to use the ammonia gas atmosphere. In order to obtain an ammonia gas atmosphere, the chamber of the heating device, the furnace core tube, or the like, which has been replaced with ammonia gas, may be sealed, or the ammonia gas may be circulated in the chamber of the heating device, the furnace core tube, or the like.

In the present invention, first, heat treatment is performed in an inert gas atmosphere, and then heat treatment is performed in an ammonia atmosphere. As a method for switching the heat treatment atmosphere, first, heat treatment in an inert gas atmosphere is performed, and when the heat treatment in an inert gas atmosphere is completed, the atmosphere gas is switched to ammonia and the ammonia gas atmosphere is continuously changed. The heat treatment in an inert gas atmosphere may be completed by lowering the temperature of the heating apparatus or by taking out boron nitride fiber from the heating apparatus. Heat treatment may be performed.

[0052]

INDUSTRIAL APPLICABILITY The boron nitride fiber of the present invention having a crystallite size in the range of 10 to 30 angstroms has a low carbon content, high strength, and is hardly affected by heat history, and therefore, is affected by heat. It is a boron nitride fiber that does not cause strength deterioration. It also provides industrially useful technology for producing the boron nitride fiber.

[0053]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. In particular, the strength of the fiber largely depends not only on the crystallite size but also on the spinning method and spinning conditions. Therefore, the change in the crystallite diameter when produced under the same spinning method and conditions and the change in the strength at that time are significant.

Example 1 A 1 L capacity three-necked flask was equipped with a stirrer in one tube, a Dewar type cold finger in which a cylinder containing boron trichloride was connected to one of the side tubes, and a ball containing cooling tube in the remaining side tube. I installed each. A Dewar cold finger was attached to the ball cooling tube, and a calcium chloride tube was attached to the outlet of the cold finger. Dry nitrogen was passed through this device at 200 ml / min for 4 hours to dry the inside of the device.
Chlorobenzene 30 dried overnight over anhydrous sodium sulfate
0 ml and 16.4 g of acetonitrile were added. Two cold fingers were filled with dry ice-acetone and stirred with a stirrer, and 60 g of boron trichloride was obtained from the cold fingers directly attached to the three-necked flask.
Was condensed and added dropwise over 2 hours. This produced a white boron trichloride-acetonitrile adduct. After the addition of boron trichloride was completed, the cold finger directly attached to the three-necked flask was removed, and 21.5 g of ammonium chloride dried at 110 ° C. overnight was added. When this suspension was heated to 125 ° C. for 8 hours, hydrogen chloride was hardly generated and a brown precipitate was formed. The formed precipitate was separated by filtration, washed with 100 ml of chlorobenzene and dried under reduced pressure to obtain 24 g (yield 83%) of a boron nitride precursor.

10 g of this boron nitride precursor was added to DMF20.
After dissolving in 0 ml, 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution has a diameter of 6
A continuous boron nitride precursor fiber having a diameter of about 20 μm was spun by discharging from a spinning nozzle having a hole of 0 μm and winding.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a temperature rising rate of 1 ° C./min from room temperature to 400 ° C. and heat-treated. After reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere, the temperature was raised from room temperature to 1000 ° C. at a heating rate of 2 ° C./min to perform heat treatment, and after reaching 1000 ° C., the temperature was cooled to room temperature. As a result, white boron nitride fiber having a diameter of about 15 μm was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 17.2 Å. The tensile strength of this boron nitride fiber was 191 MPa. The carbon content of this boron nitride fiber determined by the combustion method was 1.4% by weight.

The obtained boron nitride fiber was separately heated in a nitrogen stream from room temperature to 1600 ° C. at a temperature rising rate of 2 ° C./min, and then kept at 1600 ° C. for 1 hour for heat treatment, and then at room temperature. Cooled down. As a result of powder X-ray diffraction, only hexagonal or turbostratic type boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal is 19.8 angstroms, and it can be seen that the change in crystallite diameter is slight even when heated at high temperature. The tensile strength of this boron nitride fiber was 194 MPa. The carbon content of this boron nitride fiber determined by the combustion method was 0.7% by weight.

The obtained boron nitride fiber was similarly heated in a separate nitrogen stream at a temperature rising rate of 2 ° C./min from room temperature to 2000 ° C.
The temperature was raised to 2000 ° C., then the temperature was maintained at 2000 ° C. for 1 hour to perform heat treatment, and then the temperature was cooled to room temperature. As a result of powder X-ray diffraction, only hexagonal or turbostratic type boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal is 21.6 angstroms, and it can be seen that the crystallite diameter does not change significantly even when heated at a higher temperature. The tensile strength of this boron nitride fiber was 202 MPa. The carbon content of this boron nitride fiber determined by the combustion method was 0.7% by weight.

Example 2 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 40 at a heating rate of 1 ° C./min in a nitrogen stream.
The temperature was raised to 0 ° C., heat treatment was performed, and after reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere,
The temperature was raised from room temperature to 800 ° C. at a heating rate of 2 ° C./min for heat treatment, and after reaching 800 ° C., it was cooled to room temperature. As a result, white boron nitride fiber was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 16.4 angstroms. The carbon content of this boron nitride fiber determined by the combustion method was 1.8% by weight.

Example 3 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 40 at a temperature rising rate of 1 ° C./min in a nitrogen stream.
The temperature was raised to 0 ° C., heat treatment was performed, and after reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere,
The temperature was raised from room temperature to 1200 ° C. at a heating rate of 2 ° C./min, heat treatment was performed, and after reaching 1200 ° C., the temperature was cooled to room temperature. As a result, white boron nitride fiber was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 18.3 angstrom. The carbon content of this boron nitride fiber determined by the combustion method was 1.1% by weight.

Example 4 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 20 at a temperature rising rate of 1 ° C./min in a nitrogen stream.
The temperature was raised to 0 ° C., heat treatment was performed, and after reaching 200 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere,
The temperature was raised from room temperature to 1000 ° C. at a heating rate of 2 ° C./min, heat treatment was performed, and after reaching 1000 ° C., the temperature was cooled to room temperature. As a result, white boron nitride fiber was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 17.5 Å. The carbon content of this boron nitride fiber determined by the combustion method was 1.5% by weight.

Example 5 A stirrer was placed in the middle tube of a three-necked flask having a capacity of 1 liter, and a dropping funnel containing 128 g of boron tribromide in one of the side tubes.
A ball containing cooling tube was attached to the remaining side tube. A calcium chloride tube was attached to the outlet of the ball containing cooling tube. Dry nitrogen was passed through this device at 200 ml / min for 4 hours to dry the inside of the device, and then 300 ml of chlorobenzene and 16.4 g of acetonitrile dried overnight with anhydrous sodium sulfate were added. While stirring with a stirrer, boron tribromide was added dropwise from the dropping funnel over 2 hours. This produced a white boron tribromide-acetonitrile adduct. After the addition of boron tribromide was completed, the dropping funnel attached to the three-necked flask was removed, and 21.5 g of ammonium chloride dried at 110 ° C. overnight was added. The suspension was heated to 125 ° C. for 8 hours, filtered, washed with 100 ml of chlorobenzene and dried under reduced pressure to give a brown precipitate (48 g, yield 80%).
Got

15 g of this boron nitride precursor was added to DMF20.
After dissolving in 0 ml, 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution has a diameter of 6
A continuous boron nitride precursor fiber having a diameter of about 20 μm was spun by discharging from a spinning nozzle having a hole of 0 μm and winding.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a heating rate of 1 ° C./min from room temperature to 400 ° C. and heat-treated. After reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate 2
The temperature was raised from room temperature to 1000 ° C. at a heating rate of 1,000 ° C./min, and heat treatment was performed. After reaching 1000 ° C., the temperature was cooled to room temperature. As a result, white boron nitride fiber having a diameter of about 15 μm was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 16.8 Å. The carbon content of this boron nitride fiber determined by the combustion method was 1.5% by weight.

Example 6 A stirrer was attached to the middle tube of a three-necked flask having a capacity of 1 liter, a dropping funnel containing 16.4 g of acetonitrile was placed in one of the side tubes, and a beaded cooling tube was attached to the remaining side tubes. A calcium chloride tube was attached to the outlet of the ball containing cooling tube. Dry nitrogen was passed through this device at 200 ml / min for 4 hours to dry the inside of the device, and then 300 ml of chlorobenzene and 200 g of boron triiodide dried overnight with anhydrous sodium sulfate were added.
While stirring with a stirrer, acetonitrile was added dropwise from the dropping funnel over 2 hours. This produced a white boron triiodide-acetonitrile adduct. After the addition of boron triiodide was completed, the cold finger directly attached to the three-necked flask was removed, and 21.5 g of ammonium chloride dried at 110 ° C. overnight was added. The suspension was heated to 125 ° C. for 8 hours, filtered, washed with 100 ml of chlorobenzene and dried under reduced pressure to obtain 65 g of brown precipitate (yield 79%).

20 g of this boron nitride precursor was added to DMF20.
After dissolving in 0 ml, 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution has a diameter of 6
A continuous boron nitride precursor fiber having a diameter of about 20 μm was spun by discharging from a spinning nozzle having a hole of 0 μm and winding.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a temperature rising rate of 1 ° C./min from room temperature to 400 ° C. for heat treatment, and after reaching 400 ° C., cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate 2
The temperature was raised from room temperature to 1000 ° C. at a heating rate of 1,000 ° C./min, and heat treatment was performed. After reaching 1000 ° C., the temperature was cooled to room temperature. As a result, white boron nitride fiber having a diameter of about 15 μm was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 17.5 Å. The carbon content of this boron nitride fiber determined by the combustion method was 1.6% by weight.

Example 7 A stirrer was placed in the middle tube of a three-necked flask having a capacity of 1 liter, a Dewar cold finger in which a cylinder containing boron trichloride was attached to one of the side tubes, and a ball containing cooling tube was attached to the remaining side tubes. I installed each. A Dewar cold finger was attached to the ball cooling tube, and a calcium chloride tube was attached to the outlet of the cold finger. Dry nitrogen was passed through this device at 200 ml / min for 4 hours to dry the inside of the device, and then 300 ml of chlorobenzene and 16.4 g of acetonitrile dried overnight with anhydrous sodium sulfate were added. Two
Fill one cold finger with dry ice-acetone and stir with a stirrer. Boron trichloride 60 from a cold finger directly attached to a three-necked flask.
g was condensed and added dropwise over 2 hours. This produced a white boron trichloride-acetonitrile adduct. After the addition of boron trichloride was completed, the cold finger directly attached to the three-necked flask was removed, and 27.2 g of monomethylamine hydrochloride dried overnight at 110 ° C. was added. When this suspension was heated to 125 ° C. for 8 hours, hydrogen chloride was hardly generated and a brown precipitate was formed. The formed precipitate was separated by filtration, washed with 100 ml of chlorobenzene, and then dried under reduced pressure to obtain 25 g of a boron nitride precursor (yield: 80%).
%) Was obtained.

10 g of this boron nitride precursor was added to DMF20.
After dissolving in 0 ml, 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution has a diameter of 6
A continuous boron nitride precursor fiber having a diameter of about 20 μm was spun by discharging from a spinning nozzle having a hole of 0 μm and winding.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a heating rate of 1 ° C./min from room temperature to 400 ° C. and heat-treated. After reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate 2
The temperature was raised from room temperature to 1000 ° C. at a heating rate of 1,000 ° C./min, and heat treatment was performed. As a result, white boron nitride fiber having a diameter of about 15 μm was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 18.1 Å. The carbon content of this boron nitride fiber determined by the combustion method was 1.6% by weight.

Example 8 A stirrer was placed in the middle tube of a three-necked flask having a capacity of 1 liter, a Dewar cold finger in which a cylinder containing boron trichloride was attached to one of the side tubes, and a ball containing cooling tube was placed in the remaining side tubes. I installed each. A Dewar cold finger was attached to the ball cooling tube, and a calcium chloride tube was attached to the outlet of the cold finger. After passing dry nitrogen at 200 ml / min for 4 hours to the device to dry the inside of the device, 300 ml of chlorobenzene and 41.2 g of benzonitrile dried overnight with anhydrous sodium sulfate were added. Two
Fill one cold finger with dry ice-acetone and stir with a stirrer. Boron trichloride 60 from a cold finger directly attached to a three-necked flask.
g was condensed and added dropwise over 2 hours. This produced a white boron trichloride-benzonitrile adduct. After the addition of boron trichloride was completed, the cold finger directly attached to the three-necked flask was removed, and 21.5 g of ammonium chloride dried at 110 ° C. overnight was added. When this suspension was heated to 125 ° C. for 8 hours, hydrogen chloride was hardly generated and a brown precipitate was formed. The formed precipitate was separated by filtration, washed with 100 ml of chlorobenzene and then dried under reduced pressure to obtain 27 g of boron nitride precursor (yield 79%).

10 g of this boron nitride precursor was added to DMF20.
After dissolving in 0 ml, 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution has a diameter of 6
A continuous boron nitride precursor fiber having a diameter of about 20 μm was spun by discharging from a spinning nozzle having a hole of 0 μm and winding.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a temperature rising rate of 1 ° C./min from room temperature to 400 ° C. and heat-treated. After reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate 2
The temperature was raised from room temperature to 1000 ° C. at a heating rate of 1,000 ° C./min, and heat treatment was performed. After reaching 1000 ° C., the temperature was cooled to room temperature. As a result, white boron nitride fiber having a diameter of about 15 μm was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic type boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 17.6 Å. The carbon content of this boron nitride fiber determined by the combustion method was 2.1% by weight.

Example 9 A stirrer was attached to a medium tube of a three-necked flask having a capacity of 1 liter, a Dewar type cold finger having a cylinder containing boron trichloride was attached to one of the side tubes, and a ball containing cooling tube was attached to the remaining side tubes. I installed each. A Dewar cold finger was attached to the ball cooling tube, and a calcium chloride tube was attached to the outlet of the cold finger. After passing dry nitrogen at 200 ml / min for 4 hours to the device to dry the inside of the device, 300 ml of chlorobenzene and 41.2 g of acrylonitrile dried overnight with anhydrous sodium sulfate were added.
Fill two cold fingers with dry ice-acetone and stir with a stirrer. Boron trichloride 6 from a cold finger directly attached to the three-necked flask.
0 g was condensed and added dropwise over 2 hours. This produced a white boron trichloride-acrylonitrile adduct.
After the addition of boron trichloride was completed, the cold finger directly attached to the three-necked flask was removed, and 21.5 g of ammonium chloride dried at 110 ° C. overnight was added. When this suspension was heated to 125 ° C. for 8 hours, hydrogen chloride was hardly generated and a brown precipitate was formed. The precipitate formed was filtered off, washed with 100 ml of chlorobenzene and then dried under reduced pressure to give 24 g of boron nitride precursor (yield 77%).
Got

10 g of this boron nitride precursor was added to DMF20.
After dissolving in 0 ml, 100 ml of DMF was removed by evaporation to obtain a uniform viscous solution. This solution has a diameter of 6
A continuous boron nitride precursor fiber having a diameter of about 20 μm was spun by discharging from a spinning nozzle having a hole of 0 μm and winding.

The spun boron nitride precursor fiber was heated in a nitrogen stream at a temperature rising rate of 1 ° C./min from room temperature to 400 ° C. for heat treatment, and after reaching 400 ° C., cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate 2
The temperature was raised from room temperature to 1000 ° C. at a heating rate of 1,000 ° C./min, and heat treatment was performed. As a result, white boron nitride fiber having a diameter of about 15 μm was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic type boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 16.7 Å. The carbon content of this boron nitride fiber determined by the combustion method was 1.8% by weight.

Comparative Example 1 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 80 at a temperature rising rate of 1 ° C./min in a nitrogen stream.
The temperature was raised to ℃, and after reaching 80 ℃, it was cooled to room temperature. Then, in an ammonia gas atmosphere, the temperature rising rate is 2 ° C /
The temperature was raised from room temperature to 1000 ° C. in min, and after reaching 1000 ° C., it was cooled to room temperature. As a result, white boron nitride fiber was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic type boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 44.2 angstroms. The tensile strength of this boron nitride fiber was 64 MPa.

Comparative Example 2 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 1000 ° C. at a temperature rising rate of 2 ° C./min in an ammonia gas atmosphere without heat treatment in a nitrogen stream.
The temperature was raised to 1000 ° C. and, after reaching 1000 ° C., it was cooled to room temperature. As a result, white boron nitride fiber was obtained.

As a result of powder X-ray diffraction, only hexagonal or turbostratic type boron nitride was detected as the crystal phase constituting the boron nitride fiber. The crystallite diameter of this boron nitride crystal was 54.6 angstroms. The tensile strength of this boron nitride fiber was 43 MPa.

Comparative Example 3 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 80 at a temperature rising rate of 1 ° C./min in a nitrogen stream.
The temperature was raised to 0 ° C., and after reaching 800 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate is 2 ° C.
/ Min to increase from room temperature to 1000 ℃, 1000 ℃
After reaching, the mixture was cooled to room temperature. The obtained fiber was black and the crystallite size of boron nitride was 16.8 angstroms. The carbon content determined by the combustion method was 7.8% by weight.

Comparative Example 4 A boron nitride precursor fiber produced in the same manner as in Example 1 was heated from room temperature to 40 at a temperature rising rate of 1 ° C./min in a nitrogen stream.
The temperature was raised to 0 ° C., and after reaching 400 ° C., it was cooled to room temperature. Then, in an ammonia gas atmosphere, the heating rate is 2 ° C.
The temperature was raised from room temperature to 400 ° C./min, and after reaching 400 ° C., the temperature was cooled to room temperature. The resulting fiber is black,
The crystallite size of boron nitride was 15.5 Å. Carbon content determined by combustion method is 12.3% by weight
Met.

Claims (2)

[Claims] 1. A hexagonal and / or turbostratic boron nitride having a crystallite size of 10 to 30.
Boron nitride fiber characterized by being angstrom. 2. A boron nitride precursor obtained by reacting an adduct of boron trihalide with a nitrile compound and an ammonium halide or a primary amine hydrohalide in the presence of boron trihalide. The body is dissolved in a solvent, the solution is spun, and then 1
The method for producing a boron nitride fiber according to claim 1, wherein the heat treatment is performed at 00 to 600 ° C., and then the heat treatment is performed at 600 to 1300 ° C. in an ammonia gas atmosphere.