JP5407999B2 - Method for producing crystalline silicon nitride powder - Google Patents

Description

  The present invention relates to a method for producing a high-purity crystalline silicon nitride powder comprising only granular crystals suitable as a raw material for producing a silicon nitride sintered body useful as a high-temperature structural material.

  A method for producing a crystalline silicon nitride powder by calcining an amorphous silicon nitride powder and / or a nitrogen-containing silane compound in an inert gas atmosphere or a reducing gas atmosphere is already known. For example, Non-Patent Document 1 describes a method of synthesizing crystalline silicon nitride powder by heat-treating amorphous silicon nitride powder produced by a monosilane-ammonia-based gas phase reaction. According to this document, crystallization of silicon nitride is a reaction accompanied by a very large exotherm, and when a green compact of amorphous silicon nitride is heated, it becomes a red-hot state due to crystallization heat from around 1450 ° C. It has been reported that crystallization completes within seconds with increasing temperature. At that time, the green compact breaks apart into powder.

Patent Document 1 discloses an article made of fibrous crystalline silicon nitride, in which an amorphous silicon nitride powder synthesized by a silicon tetrachloride-ammonia gas phase reaction is compression-molded and then fired at 1550 to 1750 ° C. A manufacturing method is disclosed. According to this document, the bulk density of the compacted product of amorphous silicon nitride is 0.1 to 0.8 g / cm ³ . Further, Non-Patent Document 2 describes densification and crystallization behavior when amorphous silicon nitride powder synthesized by thermal decomposition of silicon diimide is hot-press sintered.

  By the way, in general, the crystalline silicon nitride powder obtained by firing the amorphous silicon nitride powder has a drawback that the packing density is low because a large number of needle-like crystals or columnar crystals are formed during crystallization. Therefore, when this was used as a sintering raw material, there was a problem that only a compact with a low bulk density was obtained. Therefore, various methods for producing crystalline silicon nitride powder composed of fine granular crystals have been proposed in order to eliminate such drawbacks.

For example, Patent Document 2 discloses that a nitrogen-containing silane compound having a light loading density of 0.1 g / cm ³ or more as silicon is controlled to have a temperature rise rate of 15 ° C./min or more in the entire temperature range of 1350 to 1550 ° C. A method for producing a silicon nitride powder, characterized by heating to a temperature not lower than 1 ° C. and lower than 1700 ° C. is disclosed. According to this invention, the silicon nitride powder which consists only of the granular crystal which does not contain an acicular crystal | crystallization can be manufactured.

  However, as can be seen from the examples, the present invention is based on a small-scale firing experiment, and there are still problems to be solved when considering powder firing on a mass production scale. That is, when the amorphous silicon nitride powder is heated to around 1350 ° C. where crystallization of silicon nitride is considered to proceed, the temperature of the powder layer is remarkably increased due to the generation of crystallization heat, and the rate of temperature rise is several tens to Several thousand degrees centigrade / minute is required, and various measures must be taken to control this. However, Patent Document 2 does not describe any means for solving this problem.

A method for controlling heat transfer during crystallization of amorphous silicon nitride powder has also been proposed. For example, in Patent Document 3, an amorphous silicon nitride powder and / or a nitrogen-containing silane compound is compression molded to have a bulk density of 0.3 to 0.8 g / cm ³ , a minor axis diameter of 1 mm or more, and a major axis diameter of 20 mm. Making the following granules, and setting the heating rate in the entire temperature range of 1200 to 1400 ° C. to 10 ° C./min or less in the temperature rising process, and the light weight density of the granular material during firing is 0.15 to A method for producing crystalline silicon nitride powder characterized by 0.52 g / cm ³ is disclosed. Patent Document 4 discloses that amorphous silicon nitride powder and / or nitrogen-containing silane compound is compression-molded to have a bulk density of 0.3 to 0.8 g / cm ³ , a minor axis diameter of 1 mm or more, and a major axis diameter. The granular material is 20 mm or less, and the granular material is fired at a temperature of 1400 to 1700 ° C. using a continuous firing furnace, and the light weight density of the granular material at the time of firing is 0.15 to 0.52 g / cm. ^{No. 3} , a method for producing crystalline silicon nitride powder is disclosed.

  In order to produce a large amount of crystalline silicon nitride powder at low cost, an amorphous silicon nitride powder and / or a nitrogen-containing silane compound is fired in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere. In order to obtain crystalline silicon nitride powder, it is important to make amorphous silicon nitride powder and / or nitrogen-containing silane compound into a granular material having a high bulk density. In firing in a furnace, it is desirable that the light weight density of the granular material is high.

However, in Patent Documents 3 and 4, when an amorphous silicon nitride powder and / or a nitrogen-containing silane compound is molded into a granular material having a bulk density of 0.8 g / cm ³ or more, the molding pressure is 5 ton / cm ^2. Since the above high pressure is required and it becomes impractical, there is no solution for increasing the bulk density. Moreover, if the light weight density of the granular material at the time of firing is 0.52 g / cm ³ or more, not only the heat capacity of the granular material aggregate becomes too large, but also the gap between the granular materials becomes too small due to close packing. Since the heat transfer due to radiation is reduced and granular crystalline silicon nitride suitable for sintering cannot be obtained, it has not been possible to solve the problem of increasing the density of granular materials.

U.S. Pat. No. 4,161,616 (1978) Japanese Patent Publication No. 61-11886 JP-A-4-209706 Japanese Patent Laid-Open No. 5-148032

Ceramic Bulletin Vol.57 No.6 (1978), P579-586 US National Technical Information Service Final Annual Report A-C3316 Report (1974)

  An object of the present invention is to obtain a crystalline silicon nitride powder by firing an amorphous silicon nitride powder and / or a nitrogen-containing silane compound in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere. A high-quality crystalline material with a constant particle shape and size by molding a granular material of amorphous silicon nitride powder and / or nitrogen-containing silane compound with high bulk density and firing under controlled temperature rise conditions It is to provide a novel production method capable of producing a large amount of silicon nitride powder at low cost.

As a result of intensive studies to solve the above problems, the present inventors have compression-molded an amorphous silicon nitride powder and / or a nitrogen-containing silane compound, and have a bulk density of 0.8 g / cm ³ to 1. A granular material having a minor axis diameter of 1 mm or more and a major axis diameter of 20 mm or less is set to 0 g / cm ³ or less. Thus, it has been found that a crystalline silicon nitride powder composed of granular particles suitable for sintering can be produced in large quantities at low cost.

Thus, the present invention provides the following.
(1) Amorphous silicon nitride powder and / or nitrogen-containing silane compound is baked in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere to produce a crystalline silicon nitride powder. A silicon nitride powder and / or a nitrogen-containing silane compound is compression molded to form a granular material having a bulk density of 0.8 g / cm ^{3 to} 1.0 g / cm ³ or less, a minor axis diameter of 1 mm or more, and a major axis diameter of 20 mm or less. And a temperature rising rate in the entire temperature range of 1000 to 1200 ° C. is 10 ° C./min or less in the temperature raising process.

(2) The method for producing a crystalline silicon nitride powder according to the above (1), wherein the light weight density of the granular material at the time of firing is more than 0.52 g / cm ^{3 to} 0.80 g / cm ³ or less.

(3) The light weight density of the amorphous silicon nitride powder and / or the nitrogen-containing silane compound to be compression-molded is 0.10 to 0.30 g / cm ³ , wherein the above (1) or (2) Method for producing crystalline silicon nitride powder.

  (4) Production of compression-molded amorphous silicon nitride powder and / or nitrogen-containing silane compound is allowed to react by mixing a halogenated silane compound with liquid ammonia, and the halogenated silane compound is solvent-free or halogenated silane. The crystalline nitriding according to any one of (1) to (3) above, which is carried out by a method of supplying a solution of an inert organic solvent having a compound concentration of 50 vol% or more by discharging from a supply port installed in liquid ammonia A method for producing silicon powder.

  (5) In the production of the amorphous silicon nitride powder and / or the nitrogen-containing silane compound, the halogenated silane compound is supplied without solvent or as a solution of an inert organic solvent having a halogenated silane compound concentration of 50 vol% or more. The method for producing crystalline silicon nitride powder according to (4) above, wherein the discharge linear velocity is 5 cm / sec or more.

  (6) In the production of the amorphous silicon nitride powder and / or the nitrogen-containing silane compound, the reaction temperature is in the range of −10 to 40 ° C., and the reaction pressure is in the range of 0.3 to 1.6 MPa (absolute pressure). The method for producing a crystalline silicon nitride powder according to (4) or (5) above, wherein

  According to the present invention, it is possible to produce a large amount of crystalline silicon nitride powder composed of equiaxed granular particles having uniform particle diameters and excellent in filling characteristics, sintering characteristics, etc. at low cost and with high productivity.

It is a scanning electron micrograph of the powder obtained in Example 2 of this invention. It is a scanning electron micrograph of the powder obtained in Example 7 of this invention. It is a scanning electron micrograph of the powder obtained in Comparative Example 4 of the present invention.

  The present invention is described in detail below.

In the present invention, a nitrogen-containing silane compound having a light packing density of 0.10 to 0.30 g / cm ³ is used. Examples of the nitrogen-containing silane compound include silicon diimide, silicon tetraamide, silicon nitrogen imide, silicon chlorimide, etc., and these include known methods such as silicon tetrachloride, silicon tetrabromide, silicon tetraiodide and the like. It is produced by a method of reacting silicon halide with ammonia in a gas phase, a method of reacting the liquid silicon halide with liquid ammonia, or the like.

  The amorphous silicon nitride powder is obtained by a known method, for example, a method in which the nitrogen-containing silane compound is thermally decomposed at a temperature in the range of 600 to 1200 ° C. in a nitrogen or ammonia gas atmosphere having an oxygen content of 5% or less, silicon tetrachloride. And silicon halides such as silicon tetrabromide and silicon tetraiodide, and a method of reacting ammonia at a high temperature. Preferably, it can be produced by the production method described later.

  The light packing density of the powder in the present invention was determined by a method based on JIS R9301-2-3. Specifically, the mass of the powder collected by allowing the powder to freely fall into a container of known capacity that was allowed to stand still was collected and this mass was divided by the volume of an equal amount of water.

The nitrogen-containing silane compound and amorphous silicon nitride that are usually produced by the above-mentioned known methods are composed of very fine particles, and the average particle size is usually 0.005 to 0.05 μm. Is very bulky and generally has a light weight density of about 0.045 to 0.090 g / cm ³ . Furthermore, the bulk density of the granular material compression-molded from such a nitrogen-containing silane compound and amorphous silicon nitride is only about 0.3 to 0.8 g / cm ³ . However, if a nitrogen-containing silane compound and / or amorphous silicon nitride having a light packing density of 0.10 to 0.30 g / cm ^{3 is used as} the raw material powder, a granular material having a high bulk density can be produced.

A nitrogen-containing silane compound having a light packing density of 0.10 to 0.30 g / cm ³ can be produced, for example, by the following method. Further, amorphous silicon nitride powder of diatomaceous density 0.10~0.30g / cm ³ is loosed density 0.10~0.30g / cm ³ of the nitrogen-containing silane oxygen content less than 5% of the nitrogen compound Or it can manufacture by thermally decomposing at the temperature of the range of 600-1200 degreeC in ammonia gas atmosphere.

The nitrogen-containing silane compound having a light loading density of 0.10 to 0.30 g / cm ³ used in the present invention is diluted with a small amount of organic solvent or no solvent in the reaction of halogenated silane with liquid ammonia. It can synthesize | combine by supplying as a prepared solution. Examples of halogenated silanes include fluorinated silanes such as SiF ₄ , H ₂ SiF ₆ , HSiF ₃ , H ₃ SiF ₅ , H ₃ SiF, and H ₅ SiF ₃ , SiCl ₄ , HSiCl ₃ , H ₂ SiCl ₂ , and H ₃ SiCl. silane chloride _etc., can be used _{SiBr 4, HSiBr 3, H 2} SiBr 2, H 3 bromide silane such as _SiBr, the _{SiI 4, HSiI 3, H 2} SiI 2, H 3 iodide silane such as SiI . _{Further, RSiX 3, R 2 SiX 2} , R 3 SiX (R is an alkyl or alkoxy group, X is a halogen) can also be used halogenated silane such.

  The organic solvent used for diluting the halogenated silane can be appropriately selected from those which dissolve the halogenated silane and do not react with the halogenated silane or liquid ammonia. For example, C5-C12 chain aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, cyclic aliphatic hydrocarbons such as cyclohexane and cyclooctane, toluene And aromatic hydrocarbons such as xylene. The preferable halogenated silane concentration in the mixed solution of the organic solvent and the halogenated silane is 50 vol% or more, more preferably 66 vol% or more. If the concentration is less than 50 vol%, a sufficient increase in light weight density cannot be obtained for the nitrogen-containing silane compound powder produced.

  In carrying out the above method, a discharge port for supplying the halogenated silane as a solution without solvent or diluted with a small amount of an organic solvent is installed in liquid ammonia in the reactor. At this time, the discharge linear velocity from the supply port is preferably maintained at 5 cm / sec or more, more preferably 8 cm / sec or more. The upper limit is not particularly limited, but is generally 200 cm / sec or less.

  A suitable reaction temperature range when carrying out the present invention without introducing an inert gas into the reactor is -10 to 40 ° C, more preferably 0 to 30 ° C. A suitable range of pressure is 0.3 to 1.6 MPa, more preferably 0.4 to 1.6 MPa (absolute pressure).

  The discharge pressure of the supply pump when supplying the halogenated silane without solvent or as a solution diluted with a small amount of an organic solvent is not limited, but is preferably 5.9 MPa or more with respect to the pressure of the reactor, It is desirable to have the capability of an apparatus capable of producing a pressure difference of 7.8 MPa or more, more preferably 9.8 MPa or more.

  The mixing ratio of the halogenated silane and liquid ammonia in the reactor is halogenated silane volume / liquid ammonia volume = 0.01 to 0.1.

The nitrogen-containing silane compound produced by the above method can have a light weight density after production of 0.10 to 0.30 g / cm ³ , but is not limited thereto. Is 1.4 to 1.9 g / cm ³ , more preferably 1.5 to 1.7 g / cm ³ , and the specific surface area can be 700 to 1100 m ² / g, more preferably 800 to 1000 m ² / g. .
The nitrogen-containing silane compound produced by the above method easily absorbs or releases NH ₃ even near room temperature, and has various compositions such as Si ₆ N ₁₃ H ₁₅ , Si ₆ N ₁₂ H ₁₂ , and Si ₆ N ₁₁ H _9. Si—N—H compounds that may exist in the formula. This nitrogen-containing silane compound is often represented by the formula Si (NH) ₂ , but is considered to be a compound having an imino group or amino group bonded to silicon, and has the chemical formula Si (NH _x ) _y (wherein , X is 1 or 2, and y is 2-4. Alternatively, Si (NH _x ) _y (x is 0.7 to 1.3, y is 1.8 to 2.2) is generally expressed as a composition formula, but is limited to the range of this composition formula. It is not a thing.

When a granular product is formed using the nitrogen-containing silane compound and amorphous silicon nitride as raw material powder, the bulk density is more than 0.8 g / cm ^{3 to} 1.0 g / cm ³ or less, the minor axis diameter is 1 mm or more, and the major axis Granules having a diameter of 20 mm or less can be formed.

In the present invention, the amorphous silicon nitride powder and / or the nitrogen-containing silane compound is baked in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere to produce a crystalline silicon nitride powder. Granules obtained by compression-molding crystalline silicon nitride powder and / or nitrogen-containing silane compound to have a bulk density of 0.8 g / cm ^{3 to} 1.0 g / cm ³ or less, a minor axis diameter of 1 mm or more, and a major axis diameter of 20 mm or less. In the temperature rising process, the granular material is fired by controlling the temperature rising rate in the entire temperature range of 1000 to 1200 ° C. to 10 ° C./min or less.

  Examples of the nitrogen-containing inert gas include nitrogen or a mixed gas such as nitrogen and argon, helium. Moreover, as nitrogen-containing reducing gas, what discharge | releases nitrogen gas by thermal decomposition at high temperature, such as ammonia and hydrazine, or mixed gas, such as nitrogen, hydrogen, and carbon monoxide, is mentioned.

  In order to compress the amorphous silicon nitride powder and / or the nitrogen-containing silane compound into granules, the powder is filled into a rubber mold and isotropic pressure is applied to a rubber press mold or a metal mold. Various molding methods such as press molding in which powder is filled and pressed with a piston, tableting molding, or briquette molding in which powder is compressed by a roll with a hole and pressed can be employed.

The bulk density of the granular material in the present invention is more than 0.8 g / cm ^{3 to} 1.0 g / cm ³ or less. When the bulk density of the granular material is lower than 0.8 g / cm ³ , the light weight density is lowered, for example, the filling amount when firing with a carbon crucible is reduced, the productivity is lowered, and the production cost is increased. . On the other hand, in order to form a granule having a bulk density exceeding 1.0 g / cm ³ , a high pressure of 5 ton / cm ² or more is required, which is not preferable in practice. 0.85g ^/ cm ³ ~0.95g ^/ cm 3 or less.

  In the present invention, the size of the granular material is defined as a minor axis diameter of 1 mm or more and a major axis diameter of 20 mm or less. If the size of the granular material (for example, the short axis diameter) is smaller than 1 mm, the gap between the granules becomes too small, and the effect of heat transfer by radiation becomes small. For this reason, the heat transfer of the granular material aggregate is deteriorated, the temperature distribution between the granules during firing is expanded, and acicular crystals are likely to be generated due to rapid heat generation, which is not preferable. Use granules with moderate dimensions of short axis diameter of 1 mm or more and major axis diameter of 20 mm or less, preferably minor axis diameter of 2.5 mm or more and major axis diameter of 18 mm or less, more preferably minor axis diameter of 5 mm or more and major axis diameter of 15 mm or less. Then, the heat transfer state is good, the release of crystallization heat to the outside of the system is smooth, and the rapid temperature rise of the granular material due to heat generation can be minimized. As a result, a crystalline silicon nitride powder consisting only of fine granular crystals as shown in the examples described later is obtained.

  Further, when the size of the granular material (for example, the major axis diameter) is larger than 20 mm, the temperature distribution inside the individual granular material becomes a problem. That is, since the heat storage inside the granular material due to the heat of crystallization becomes too large, the temperature rises too much, and a crystalline silicon nitride powder containing a large amount of columnar crystals or rod-like crystals is generated, which is not preferable. In addition, the production rate of β-type silicon nitride, which is a high-temperature stable phase and is undesirable for sintering, also increases.

In the present invention, the light weight density of the granular material is also referred to as a loose apparent density, and is a value calculated from the weight and volume of the granular material slowly dropped into a measuring container through a chute. As the measurement container, a graduated cylinder of 50φ × 50h is usually used. However, when the granular material is large, a measurement container having a large size may be used. Diatomaceous density of the granulate according to the present invention is less than 0.52 g / cm ³ super ~0.80g / cm ^3. If the light packing density is 0.52 g / cm ³ or less, the productivity is not preferable. On the other hand, when the light packing density is larger than 0.80 g / cm ³ , the filling amount increases, so that not only the heat capacity of the granular material aggregate becomes too large, but also the gap between the granular materials becomes smaller due to close packing. The thermal conductivity due to radiation decreases. Therefore, the balance between the heat capacity and the thermal conductivity is lost, the heat generated during crystallization is increased, and crystalline silicon nitride containing a large amount of columnar crystals or rod-like crystals is generated, which is not preferable. 0.55 g / cm ³ super ~0.70g / cm ³ or less.

  In the present invention, when the granular material is fired, the temperature is slowly raised by controlling the temperature raising rate in the entire temperature range of 1000 to 1200 ° C. to 10 ° C./min or less in the temperature raising process. Such a slow temperature increase is an effective means for reducing the surface energy due to the amorphous silicon nitride grain growth, ensuring the generation density of crystal nuclei, and suppressing the grain growth in the initial stage of crystallization. Such an effect is not observed when the holding temperature is lower than 1000 ° C., and conversely, when the holding temperature is higher than 1200 ° C., rapid crystallization proceeds and the powder characteristics of the generated crystalline silicon nitride powder ( It becomes difficult to control the particle shape, particle diameter, crystal phase, and the like.

  In this invention, the temperature increase rate in the whole temperature range of 1000-1200 degreeC is 10 degrees C / min or less. When the rate of temperature rise exceeds 10 ° C./min, rapid crystallization occurs when the temperature is raised to 1200 ° C. or higher, and the temperature rise due to the heat of crystallization reaches up to several hundreds of degrees C., thereby forming a desired fine crystal. α-type silicon nitride powder cannot be obtained. The heating rate in the entire temperature range of 1000 to 1200 ° C is preferably 8 ° C / min or less, more preferably 5 ° C / min or less, and particularly preferably 3 to 0.5 ° C / min. In particular, if the holding time at 1000 to 1100 ° C. is excessively long, crystal growth proceeds in a state in which nucleation is slightly suppressed, so that the shape of the generated granular crystal becomes a beautiful polyhedral shape, On the contrary, the particle diameter becomes larger, and the powder has a small specific surface area which is not preferable for sintering.

  After raising the temperature of the object to be fired under the above heating conditions and setting the crystallinity to 40% or more, the temperature may be raised to a higher temperature, for example, 1700 ° C., and the rate of temperature rise is not limited. . When the final calcination temperature is 1500 ° C., it is preferable to maintain the same temperature for 15 to 60 minutes to complete crystallization. Further, if the final firing temperature exceeds 1700 ° C., not only the coarse crystals grow, but also the generated crystalline silicon nitride powder starts to decompose, which is not preferable. Although it does not necessarily limit, the calcination temperature for obtaining crystalline silicon nitride powder is generally 1400-1700 degreeC, and 1450-1650 degreeC is preferable.

  There is no particular limitation on the heating furnace used for heating the amorphous silicon nitride powder and / or the nitrogen-containing silane compound. A pusher furnace or the like can be used.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

In the examples and comparative examples, the crystallinity of the crystalline silicon nitride powder was determined by the hydrolysis test described in pages 394 to 397 of Journal of Ceramics Association, Vol. 93, No. 4 (1985). -It calculated according to the X-ray-diffraction method of 777-780 of bulletin 56 vol.9 (1977), and the specific surface area was measured by BET method by a nitrogen gas adsorption method. Moreover, the press density was calculated | required by the volume after filling 0.65g of powders in the metal mold | die with a diameter of 13 mm, and press-molding by ² ton / cm < ² >.

  The bulk density of the granular material was measured by Archimedes method using kerosene as a solvent. The light weight density of the granular material is also called a loose apparent density, and is a density when the granular material is naturally dropped into a container. Therefore, it is the same as the filling density when the granular material is filled in a container such as a fired crucible. The light weight density of the granular material was calculated from the weight of the granular material and the volume of the measuring container by slowly dropping the granular material into the measuring container through the chute. As the measurement container, a graduated cylinder having an inner diameter of 50 mm and a height of 50 mm is usually used. When the sample is large, the measurement container may be changed to a larger one accordingly.

6 parts by weight of Y ₂ O ₃ and ₂ parts by weight of Al ₂ O ₃ were added to 90 parts by weight of silicon nitride powder as a sintering aid, ethanol was added, and the mixture was wet mixed in a ball mill for 48 hours and then dried. Granules whose particle size was adjusted with a 280 μm sieve were charged with a rubber mold and subjected to rubber press molding at a pressure of ² ton / cm ² to produce a green molded body having a diameter of 5 mm. This molded body is filled in a silicon nitride crucible, heated in an electric furnace at a rate of temperature increase of 300 ° C./hour in a nitrogen gas atmosphere of 1 atm, and maintained at 1750 ° C. for 3 hours. A ligature was prepared. The bulk density of the obtained sintered body was measured by the Archimedes method.

Examples 1 to 5 and Comparative Example 1
For the reaction, a SUS pressure-resistant reactor with an internal volume of about 2 L equipped with a stirrer and a condenser was used. After replacing the inside of the reactor with nitrogen gas, 1 L of liquid ammonia was charged. Next, while rotating the stirring blade at 400 rpm, 50 mL of SiCl ₄ was supplied by a pump without being diluted with an organic solvent, and a batch-type reaction was performed. For the supply of SiCl ₄ , a SUS nozzle having an inner diameter of 0.8 mm installed in liquid ammonia was used. The upper limit of the pump discharge pressure was 6.9 MPa (gauge pressure), the flow rate was 2.5 mL / min, and 50 mL of the total amount of SiCl ₄ was supplied. The temperature of the reaction mixture during the supply of SiCl ₄ is 18 to 20 ° C., the pressure in the reactor is 0.7 to 0.8 MPa (gauge pressure), and the pressure of the supply pipe is 5.7 MPa (gauge pressure) at the maximum. Reached.

  After completion of the reaction, the produced slurry was transferred to a SUS pressure-resistant vessel (Nutsche type) with a jacket having an internal volume of about 2 L equipped with a stirrer and a sintered metal filter, and filtered. The resulting wet cake was further batch washed with about 1 L of liquid ammonia and then filtered. This washing / filtration operation was repeated a total of 7 times.

  The wet cake thus obtained was dried to obtain a nitrogen-containing silane compound powder. In the drying operation, hot water of 90 ° C. is circulated through the jacket of the filtration tank and heated, the pressure in the tank is kept at 0.6 MPa (gauge pressure) while appropriately releasing the internal pressure, and the temperature in the tank is 60 ° C. The end point was reached.

Next, the filtration tank was carried into a large glove box, and nitrogen gas was circulated overnight, thereby sufficiently expelling internal oxygen and moisture. Thereafter, the filtration tank was opened in the glove box, and the produced nitrogen-containing silane compound powder was taken out. 26.0 g of silicon diimide was obtained, and its light weight density was 0.21 g / cm ³ .

An amorphous silicon nitride powder having a specific surface area of 650 m ² / g and oxygen content of 0.8 wt% obtained by thermally decomposing silicon diimide having a light packing density of 0.21 g / cm ³ at 1000 ° C. has a diameter of 160 mm and a height of A cylindrical rubber mold of 240 mm was filled and rubber-pressed at a pressure of 1500 kg / cm ² to produce a cylindrical block. The obtained amorphous silicon nitride block was crushed and sieved to obtain granules having various particle sizes shown in Table 1. The bulk density of the granulate is 0.86 g / cm ^3, diatomaceous density was 0.60~0.62g / cm ^3. 1.5 kg of this granular material was filled in a carbon crucible having an inner diameter of 280 mm and a height of 150 mm, and set in a batch type electric furnace.

  Next, after the inside of the electric furnace was vacuum degassed to 13 Pa or less, nitrogen gas was introduced, and heating was started under a nitrogen gas flow. The temperature was raised from room temperature to 1000 ° C. in 2 hours, held at the same temperature for 1 hour, and then heated to 1200 ° C. at a temperature rising rate of 1.3 ° C./min. Further, the temperature was raised to 1500 ° C. at a rate of 4.2 ° C./min, kept at the same temperature for 1 hour, and then allowed to cool in the furnace. Table 1 shows the chemical composition, crystallinity, α phase content, specific surface area, press density, particle shape and other characteristics of the obtained crystalline silicon nitride powder, and the sintered density of the sintered body using the powder as a raw material. Shown in A scanning electron micrograph of the powder obtained in Example 2 is shown in FIG.

Comparative Example 2
800 g of the amorphous silicon nitride powder used in Example 1 was filled in a carbon crucible having the same dimensions as in Example 1 and baked under the same conditions as in Example 1. Table 1 shows various characteristics and sintered body characteristics of the obtained crystalline silicon nitride powder.

Examples 6-8 and Comparative Examples 3-4
Specific surface area of 660 m ² / g obtained by thermally decomposing silicon diimide having a light loading density of 0.21 g / cm ³ obtained by the methods shown in Examples 1 to 5 and Comparative Example 1 at 1000 ° C., oxygen content of 0 .9 wt% amorphous silicon nitride powder was filled into rubber molds for ball molding of various sizes and rubber-pressed at a pressure of 1500 kg / cm ³ to obtain spherical granules having the diameters shown in Table 2. The bulk density of the spherical granules was 0.85 g / cm ³ . 1.5 kg of spherical granules were filled in a carbon crucible having the same dimensions as in Example 1, and set in a batch type electric furnace. Next, baking was performed under the same conditions as in Example 1 except that the rate of temperature increase from 1000 to 1200 ° C. was 2 ° C./min. Table 2 shows various characteristics and sintered body characteristics of the obtained crystalline silicon nitride powder. A scanning electron micrograph of the powder obtained in Example 7 is shown in FIG.

Comparative Example 5
800 g of amorphous silicon nitride powder used in Example 6 was filled in a carbon crucible having the same dimensions as in Example 6 and fired under the same conditions as in Example 6. Table 2 shows various characteristics and sintered body characteristics of the obtained crystalline silicon nitride powder.

Examples 9 to 11 and Comparative Example 6
Amorphous silicon nitride powder used in Example 1 was filled in a mold having a diameter of 15 mm and uniaxially pressed at the molding pressure shown in Table 3 to obtain a large number of cylindrical shaped bodies having various bulk densities. Produced. The obtained molded body has a cylindrical shape with a diameter of 15 mm and a height of 12 to 15 mm, and is a granular product with a short axis diameter of 12 to 14 mm and a long axis diameter of 15 mm when expressed in terms of a short axis diameter and a long axis diameter. The obtained cylindrical granules (1.5 kg) were filled in a carbon crucible having the same dimensions as in Example 1 and set in a batch type electric furnace. Next, in the same manner as in Example 1, the temperature was raised from room temperature to 1000 ° C. over 2 hours and held at the same temperature for 1 hour, and then from 1000 ° C. to 1100 ° C. at 1.3 ° C./min from 1100 ° C. The temperature was increased to 1200 ° C. at a rate of 2 ° C./min. Furthermore, it heated to 1530 degreeC with the temperature increase rate of 4.2 degree-C / min, and hold | maintained for 40 minutes, Then, it stood to cool in a furnace. Table 3 shows various characteristics and sintered body characteristics of the obtained crystalline silicon nitride powder.

Comparative Example 7
800 g of amorphous silicon nitride powder used in Example 9 was filled in a carbon crucible having the same dimensions as in Example 9 and fired under the same conditions as in Example 9. Table 3 shows various characteristics and sintered body characteristics of the obtained crystalline silicon nitride powder.

Examples 12 to 14 and Comparative Example 8
Specific surface area of 670 m ² / g obtained by thermally decomposing silicon diimide having a light loading density of 0.21 g / cm ³ obtained by the methods shown in Examples 1 to 5 and Comparative Example 1 at 1000 ° C., oxygen content of 0 A cylindrical rubber mold having the same dimensions as in Example 1 was filled with .9 wt% amorphous silicon nitride powder, and rubber-pressed at a pressure of 1500 kg / cm ² to prepare a cylindrical block. In the same manner as in Example 1, this block was crushed and sieved to obtain granules having a minor axis diameter of 4.0 to 10.0 mm and a major axis diameter of 5.0 to 12.0 mm. The bulk density of the granular material was 0.87 g / cm ² . 1.5 kg of this granular material was filled in a carbon crucible having the same dimensions as in Example 1, and set in a batch type electric furnace. Next, in the same manner as in Example 1, the temperature was raised from room temperature to 1000 ° C. over 2 hours, held at the same temperature for 1 hour, and then heated to 1200 ° C. at the rate of temperature rise shown in Table 4. Furthermore, it heated up to the final calcination temperature described in the same table | surface at the rate of 4.2 degree-C / min, and hold | maintained at the same temperature for 1 hour, Then, it stood to cool in a furnace. Table 4 shows various characteristics and sintered body characteristics of the obtained crystalline silicon nitride powder.

  The present invention relates to a method for producing a high-purity crystalline silicon nitride powder comprising only granular crystals suitable as a raw material for producing a silicon nitride sintered body useful as a high-temperature structural material.

Claims (5)

The halogenated silane compound is mixed with liquid ammonia and allowed to react, and the halogenated silane compound is discharged from a supply port installed in liquid ammonia as a solvent-free or inert organic solvent solution having a halogenated silane compound concentration of 50 vol% or more. Supplying amorphous silicon nitride powder and / or a nitrogen-containing silane compound,
The obtained amorphous silicon nitride powder and / or nitrogen-containing silane compound is compression-molded to have a bulk density of 0.8 g / cm ^{3 to} 1.0 g / cm ³ or less, a minor axis diameter of 1 mm or more, and a major axis diameter of 20 mm. Make the following granules:
When the crystalline silicon nitride powder is produced by firing the amorphous silicon nitride powder and / or the nitrogen-containing silane compound in a nitrogen-containing inert gas atmosphere or a nitrogen-containing reducing gas atmosphere , A method for producing crystalline silicon nitride powder, characterized in that the temperature rising rate in the entire temperature range of ˜1200 ° C. is 10 ° C./min or less. Method for producing a crystalline silicon nitride powder of claim 1, wherein the diatomaceous density of the granulate during the firing is not more than 0.52 g / cm ³ super ~0.80g / cm ^3. The crystalline silicon nitride according to claim 1 or 2, wherein the light weight density of the amorphous silicon nitride powder and / or the nitrogen-containing silane compound to be compression-molded is 0.10 to 0.30 g / cm ^3. Powder manufacturing method. In the production of the amorphous silicon nitride powder and / or the nitrogen-containing silane compound, the discharge is performed when the halogenated silane compound is supplied as a solventless or a solution of an inert organic solvent having a halogenated silane compound concentration of 50 vol% or more. The method for producing crystalline silicon nitride powder according to any one of claims 1 to 3, wherein the linear velocity is 5 cm / sec or more. In the production of the amorphous silicon nitride powder and / or the nitrogen-containing silane compound, the reaction temperature is in the range of −10 to 40 ° C., and the reaction pressure is in the range of 0.3 to 1.6 MPa (absolute pressure). The method for producing crystalline silicon nitride powder according to any one of claims 1 to 4 , wherein the method is characterized in that: