JPH07206409A - Silicon nitride powder and its production - Google Patents

Abstract

PURPOSE:To obtain silicon nitride powder capable of producing a silicon nitride sintered compact excellent in high-temp. strength and high-temp. creep characteristics and suitable for use as a high-temp. member of a gas turbine, etc. CONSTITUTION:Metallic silicon powder is nitrided to obtain the objective silicon nitride powder having >=10m<2>/g specific surface area or <=0.8mum average particle diameter, <=1.5wt.% in total of oxygen content, <=500ppm (F+Cl) content and <=300ppm F content.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride powder capable of producing a sintered body having excellent high temperature characteristics such as high temperature strength and high temperature creep characteristics, and a method for producing the same.

[0002]

2. Description of the Related Art Sintered silicon nitride has strength, hardness, toughness,
It is a material with excellent heat resistance, corrosion resistance, and thermal shock resistance, and is being used for various industrial mechanism parts, automobile parts, and the like. Further, since the silicon nitride sintered body is less deteriorated in its characteristics even at high temperatures, its use in a gas turbine component or the like which is required to be used at 1200 ° C. or higher is being studied.

Since silicon nitride is a substance having a strong covalent bond, in order to obtain a densified sintered body, it is sintered by adding an oxide or the like as a sintering aid. However, the sintering aid reacts with silica or the like present on the surface of the silicon nitride powder and remains as a grain boundary glass phase in the sintered body, which causes the high temperature characteristics of the silicon nitride sintered body to deteriorate. .

Hitherto, as a means for improving the high temperature characteristics of a silicon nitride sintered body, a rare earth oxide has been added in order to raise the softening point of the grain boundary glass phase (Japanese Patent Publication Nos. 48-7486 and 49-49). No. 21091, Japanese Patent Publication No. 52-3
649) and crystallizing the grain boundary glass phase to increase the softening point (Japanese Patent Publication No. 56-388). There is also a method of crystallizing the grain boundary phase by HIP treatment or annealing treatment of the sintered body. However, even by these methods, it was not possible to manufacture a silicon nitride sintered body having sufficiently improved high temperature characteristics.

On the other hand, as a method for producing a silicon nitride powder as a raw material, there are a metal silicon direct nitriding method, a silica reduction method, a silicon halide method and the like. The powder obtained by these production methods is
They have different powder characteristics, which greatly affect the sinterability and the characteristics of the sintered body. In general, the high temperature characteristics are greatly influenced by the characteristics of the grain boundary phase, and therefore high-purity silicon nitride powder is required to improve the high temperature characteristics.

In the case of the metal silicon direct nitriding method, high-purity Si is used.
Although the powder is used as a raw material and is refined with an acid in order to reduce metal impurities in the obtained silicon nitride powder, even the high-purity silicon nitride powder produced in this manner does not necessarily have high-temperature characteristics. It was not possible to manufacture a sintered body excellent in heat resistance.

[0007]

The object of the present invention is to
Provided is a silicon nitride powder having excellent sinterability, which can produce a sintered body excellent in high-temperature characteristics such as high-temperature strength and high-temperature creep characteristics, which can be used as a gas turbine component used at a high temperature of 200 ° C. or higher. It is to be.

That is, the present invention is a silicon nitride powder and a method for producing a silicon nitride powder, which are summarized below.

Silicon nitride powder obtained by nitriding metallic silicon powder, having a specific surface area of 10 m ² / g or more or an average particle diameter of 0.8 μm or less, a total oxygen content of 1.5% by weight or less, F and Cl The total content of Fe is 500 ppm or less and the F content is 300 ppm or less. A silicon nitride powder (claim 1).

The silicon nitride powder according to claim 1, wherein the surface oxygen content is 0.3% by weight or more (claim 2).

High-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is heated at a temperature of 1000 to 1 under a reducing atmosphere in which the partial pressure of hydrogen and / or ammonia is 0.2 atm or more.
The method for producing a silicon nitride powder according to claim 1, wherein the treatment is performed at 500 ° C for 30 minutes or more (claim 3).

The high-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is treated at a temperature of 1200 to 1400 ° C. for 30 minutes or more under a reduced pressure atmosphere of 1 torr or less. A method for producing silicon powder (claim 4).

High-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is treated at a temperature of 1000 to 1500 ° C. for 30 minutes or more in an atmosphere having a chlorine gas partial pressure of 0.2 atm or more, and then hydrogen and / or Or the partial pressure of ammonia is 0.2 at
The method for producing a silicon nitride powder according to claim 1, wherein the treatment is performed at a temperature of 1000 to 1500 ° C for 30 minutes or more in a reducing atmosphere of m or more (claim 5).

High-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is treated at a temperature of 1000 to 1500 ° C. for 30 minutes or more in an atmosphere having a chlorine gas partial pressure of 0.2 atm or more, and then at 1 torr or less. Under reduced pressure, temperature 1200
The method for producing a silicon nitride powder according to claim 1, wherein the treatment is performed at -1400 ° C for 30 minutes or more (claim 6).

The silicon nitride powder according to claim 1 is heat-treated in an atmosphere containing oxygen.
A method for producing the silicon nitride powder as described above (claim 7).

The present invention will be described in more detail below.

The inventors of the present invention prototyped various silicon nitride powders having different amounts of metal impurities, oxygen content, grain size, etc. by the direct silicon nitriding method, evaluated them under various sintering conditions, and evaluated the powder characteristics and the sintering characteristics. The relationship between the properties and the properties of the sintered body was examined in detail. As a result, in the high-purity silicon nitride powder subjected to the refining treatment, even if the amount of metallic impurities such as Fe is similar, F and Cl of the silicon nitride powder obtained by the kind and concentration of the acid used at the time of refining are obtained. It was found that the amount of halogen impurities such as, for example, differed significantly affecting the high temperature strength.

That is, the halogen impurities in the silicon nitride powder remain in the sintered body even after sintering, and the high temperature characteristics of the silicon nitride sintered body are governed by the softening temperature of the grain boundary phase and the like. It was found that the temperature decreases as the amount of halogen impurities present therein increases, and that the high temperature properties such as high temperature strength and high temperature creep properties of the silicon nitride sintered body deteriorate as the amount of halogen impurities in the silicon nitride powder increases. It was

Therefore, in the present invention, F in the silicon nitride powder is
And the total content of Cl was limited to less than 500 ppm.
Further, even if the total content of F and Cl is less than 500 ppm, the high temperature characteristics change greatly depending on the amount of F content, which greatly affects the high temperature characteristics of the grain boundary phase. Therefore, in the present invention, the F content is 300 ppm. Limited to less than. That is, the total content of F and Cl in the silicon nitride powder is 500
When the content is ppm or more or the F content is 300 or more, the softening temperature of the grain boundary phase of the silicon nitride sintered body produced using the same is lowered, and the high temperature characteristics of the silicon nitride sintered body are lowered. .

Next, regarding the particle size of the silicon nitride powder of the present invention, the specific surface area is 10 m ² / g or more or the average particle size is 0.8.
μm or less. The particle size of the silicon nitride powder is closely related to the sinterability and the microstructure of the sintered body. The finer the powder, the better the sinterability and the finer and more uniform sintered body can be obtained. In particular, in order to improve the high temperature characteristics of the silicon nitride sintered body, it is necessary to reduce the amount of grain boundary phases and increase the melting point thereof, so that the raw material silicon nitride powder should have excellent sinterability. Will be needed. Therefore, in the present invention, the particle size is limited to the above, and the specific surface area is less than 10 m ² / g or the average particle size is 0.8 μm.
When it exceeds m, the sinterability is lowered and it becomes difficult to obtain a sufficiently densified sintered body. The upper limit of the specific surface area and the lower limit of the average particle size are not particularly limited as long as it becomes extremely dry and cannot be molded.

The total oxygen content of the silicon nitride powder of the present invention is 1.5.
It is less than or equal to weight%. If the total oxygen content exceeds 1.5% by weight, the amount of the grain boundary phase generated by reacting with the sintering aid added during sintering increases, and the melting point also decreases, resulting in a silicon nitride sintered body High temperature characteristics deteriorate.

On the other hand, regarding the amount of metallic impurities of the silicon nitride powder of the present invention, the total content of Fe, Ca and Al is 3
It is preferably 000 ppm or less, and particularly preferably 500 ppm or less. Such metal impurities form a solid solution in the grain boundary phase during sintering to lower the melting point, or segregate in the grain boundary phase to deteriorate high temperature characteristics.

Next, the invention of claim 2 of the present invention is such that the amount of surface oxygen of the silicon nitride powder of claim 1 is 0.3% by weight or more. This can be manufactured by heat-treating the silicon nitride powder of claim 1 in an atmosphere containing oxygen.

As a method for improving the high temperature characteristics of the silicon nitride sintered body, in addition to the above-mentioned method, Japanese Patent Laid-Open No. 4-21937.
There is a method of adding a sintering aid and silica as shown in Japanese Patent Publication No. 4 or the like. The amount of silica in this case is determined from the target grain boundary phase composition, the amount of sintering aid and the amount of oxygen of the silicon nitride powder, but when added together with the sintering aid,
There is a problem in the uniformity of the obtained sintered body. In consideration of this point, the present invention solves the problem by subjecting the silicon nitride powder to a heat treatment in an atmosphere containing oxygen to form a uniform silica phase on the surface thereof.

The surface oxygen content of the silicon nitride powder of the present invention is 0.
The total oxygen content is 3% by weight or more and 1.5% by weight or less. If the amount of surface oxygen is less than 0.3% by weight, sufficient effects cannot be obtained for improving sinterability and homogenizing the sintered body. The surface oxygen content was measured by measuring the total oxygen content, then stirring in a hydrofluoric acid solution at a temperature of 50 ° C or higher for 2 hours to remove the silica phase on the surface of the silicon nitride powder, followed by washing and drying, and then again measuring the oxygen content (internal Oxygen amount)
Can be measured and calculated from the difference between the total oxygen content and the internal oxygen content.

The invention of claim 7 relates to the method for producing silicon nitride powder of claim 2, wherein the silicon nitride powder of claim 1 is heat-treated in an oxidizing atmosphere containing oxygen. The oxygen concentration is oxygen partial pressure 0.02-0.5a.
It is preferably tm. When the oxygen partial pressure is less than 0.02 atm, the oxidation rate of the silicon nitride powder is slow, and the treatment time is long in order to give the desired surface oxygen.
If it exceeds 5 atm, the oxidation rate of the silicon nitride powder becomes too fast, and it becomes difficult to adjust the surface oxygen content.

The treatment temperature of the present invention is preferably 500 to 1100 ° C. If the treatment temperature is less than 500 ° C., the treatment time will be long in order to give a desired amount of surface oxygen. It becomes too fast and it becomes difficult to control the surface oxygen content.

The surface oxygen morphology of the silicon nitride powder obtained by the heat treatment of the present invention was analyzed by a high resolution transmission electron microscope. As a result, it was confirmed that some samples were amorphous silica.

Next, four preferable manufacturing methods for obtaining the silicon nitride powder of claim 1 will be described. In the first manufacturing method (the invention of claim 3), the silicon nitride powder obtained by nitriding the metal silicon powder is heated at a temperature of 1000 to 1000 in a reducing atmosphere in which the partial pressure of hydrogen and / or ammonia is 0.2 atm or more.
The treatment is performed at 1500 ° C. for 30 minutes or more.

Usually, when producing a high-purity fine powder by the metal silicon direct nitriding method, the produced powder is purified by a mixed acid such as hydrochloric acid or hydrofluoric acid in order to reduce oxygen and metal impurities. However, the high-purity silicon nitride powder produced by such a method contains a considerable amount of halogen impurities such as F and Cl, and these halogen impurities are very strongly adsorbed on the surface of the silicon nitride powder. However, it is difficult to sufficiently remove even by simply washing with water or ammonia or performing heat treatment in an inert atmosphere.

The present inventors have made various investigations by changing the treatment temperature of silicon nitride powder containing halogen impurities under various atmospheres. Surprisingly, the partial pressure of hydrogen and / or ammonia in the silicon nitride powder is surprisingly changed. It was found that halogen impurities can be remarkably reduced by treating at a temperature of 1000 to 1500 ° C. for 30 minutes or more in a reducing atmosphere of 0.2 atm or more.

In the present invention, the processing atmosphere of the silicon nitride powder is set to the reducing atmosphere containing hydrogen and / or ammonia, because most of the halogen impurities in the silicon nitride powder remain in the normal inert atmosphere, In a reducing atmosphere containing ammonia and / or ammonia, it reacts with hydrogen atoms etc.
It is based on the fact that it becomes F, HCl, etc. and can be removed outside the system. The partial pressure of hydrogen and / or ammonia in the atmosphere must be 0.2 atm or more,
If it is less than 0.2 atm, halogen impurities cannot be sufficiently removed.

The processing temperature in the present invention is 1000 to 15
If the temperature is less than 1000 ° C., the reactivity between the atmosphere and the halogen impurities in the silicon nitride powder becomes small, and the halogen impurities cannot be sufficiently removed.
If it exceeds the range, other powder characteristics are deteriorated, such as a decrease in the specific surface area of the silicon nitride powder.

Further, the treatment time in the present invention is required to be 30 minutes or more, and if it is less than 30 minutes, halogen impurities cannot be sufficiently removed. The upper limit of the treatment time is not particularly limited, but if it is extremely long, the production cost may increase and partial sintering due to metal impurities or the like may occur, so a shorter time is preferable although it depends on the filling state.

Next, the second manufacturing method (the invention of claim 4)
In the present invention, the silicon nitride powder obtained by nitriding metallic silicon powder is treated at a temperature of 1200 to 1400 ° C. for 30 minutes or more under a reduced pressure atmosphere of 1 torr or less.

The present inventors have conducted various studies on the behavior of halogen impurities contained in the silicon nitride powder by changing the pressure and temperature of the atmosphere, and as a result, under the reduced pressure atmosphere of 1 torr or less, the temperature is 1200 to 1400 ° C. for 30 minutes. It has been found that the above treatment can considerably reduce the amount of halogen impurities as in the treatment in the reducing atmosphere described above.

The treatment atmosphere of the present invention is set to a reduced pressure atmosphere of 1 torr or less, because most of the halogen impurities strongly adsorbed on the surface of the silicon nitride powder remain in the atmospheric pressure atmosphere, but under the reduced pressure atmosphere, the halogen impurities are removed from the system. It is based on being able to be removed.

The processing temperature in the present invention is 1200-14.
If it is less than 1200 ° C., the amount of halogen impurities volatilized in the silicon nitride powder is small and the halogen impurities cannot be sufficiently removed. On the other hand, if it exceeds 1400 ° C., the decomposition of silicon nitride becomes severe. Weight reduction, metal Si
There is a problem such as the generation of

The treatment time of the present invention is required to be 30 minutes or more, and if it is less than 30 minutes, the amount of halogen impurities volatilized is too small to be removed sufficiently. There is no particular limitation on the upper limit of the treatment time, but if it is extremely long, there are problems such as an increase in manufacturing cost and decomposition of silicon nitride.
Shorter times are preferred.

In the third manufacturing method (the invention of claim 5), the silicon nitride powder obtained by nitriding the metal silicon powder is heated at a temperature of 1000 to 1 in an atmosphere having a chlorine gas partial pressure of 0.2 atm or more.
Treatment at 500 ° C for 30 minutes or longer (hereinafter referred to as primary treatment)
After that, it is further treated in a reducing atmosphere of hydrogen and / or ammonia at a temperature of 1000 to 1500 ° C. for 30 minutes or more (hereinafter referred to as secondary treatment 1).

The present inventors have found that F, Cl in silicon nitride powder
As a result of detailed examination of the behavior of halogen impurities such as, it was found that F and Cl have different behaviors, and it is more difficult to remove F than Cl. Therefore,
After further studying the method of removing F from the silicon nitride powder, surprisingly, when the treatment was carried out in an atmosphere containing chlorine gas, the amount of Cl was significantly increased, but the amount of F was extremely decreased.
Moreover, it has been found that the amount of metal impurities also decreases.

That is, in the present invention, after the F content in the silicon nitride powder is reduced by the primary treatment, the residual Cl is removed by the secondary treatment 1. This secondary process 1 is the same process as the above-mentioned first manufacturing method.

The chlorine gas partial pressure of the primary treatment in the present invention is 0.2 atm or more, and if it is less than 0.2 atm, F cannot be sufficiently removed. The processing temperature is 100
It is 0 to 1500 ° C., and if it is less than 1000 ° C., the reactivity between Cl in the atmosphere and F in the silicon nitride powder is small and it is difficult to sufficiently remove F. On the other hand, when the temperature exceeds 1500 ° C., other powder characteristics are deteriorated such that the specific surface area of the silicon nitride powder is reduced. A treatment time of 30 minutes or more is necessary, and if it is less than 30 minutes, F cannot be sufficiently removed.

Further, the fourth manufacturing method (the invention of claim 6)
In the above, the primary-treated silicon nitride powder is further treated at a temperature of 1200 to 1400 ° C. for 30 minutes or more (hereinafter referred to as secondary treatment 2) under a reduced pressure atmosphere of 1 torr or less.
The secondary process 2 is the same process as the second manufacturing method described above.

As the silicon nitride powder used in the above-described four manufacturing methods, the total of metallic impurities of Fe, Al, and Ca is 3000 ppm or less, and the specific surface area is 7.
High-purity silicon nitride fine powder having a m ² / g or more is preferable. Such high-purity silicon nitride fine powder is obtained by crushing, for example, metallic silicon powder to a specific surface area of about 1 to ² m ² / g and a bulk specific gravity of 0.8.
Molded into a molded body of about 1.5 to about 1.5 ° C. in an atmosphere containing nitrogen and / or ammonia at a temperature of 1200 to 1500 ° C.
It can be manufactured by heating and nitriding to produce a silicon nitride ingot, crushing it to a desired particle size, and then purifying it with a mixed acid such as hydrochloric acid and hydrofluoric acid.

[0046]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Examples 1 to 10 Comparative Examples 1 to 8 Metallic silicon powder (specific surface area 1.5 m ² / g) was purified by a mixed acid of hydrochloric acid and hydrofluoric acid at a temperature of 50 ° C. for 2 hours, washed and dried. Then, a molded body having a bulk density of 1.0 g / cm ³ was molded. This compact was nitrided at a temperature of 1100 to 1450 ° C. in an atmosphere containing nitrogen and ammonia to produce a silicon nitride ingot having an α phase content of 92%. Then, it was coarsely crushed / medium crushed and wet-milled to a desired particle size by a ball mill, and then purified by changing the concentration of the mixed acid for 2 hours to produce a silicon nitride powder (silicon nitride powder A). The total of metallic impurities of Fe, Al, and Ca of the silicon nitride powder A is 360 ppm or less, and the specific surface area is 11 m ² / g.
Met.

In Comparative Example 7, after the pulverization, the purification treatment was carried out with hydrochloric acid alone, and in Comparative Example 8, the pulverization time was halved and the same purification treatment as in Example 1 was performed.

100 g of the obtained silicon nitride powder was added with a diameter of 5
A 0 mm alumina tube was filled and treated in a tubular furnace under various conditions shown in Table 1 to produce silicon nitride powder. Example 9
Nos. 10 and 10 are commercially available powders produced by the direct nitriding method of metallic silicon, and subjected to the same purification treatment as in Example 2. The powder properties are shown in Table 2.

[0050]

[Table 1]

[0051]

[Table 2]

Next, 90 parts by weight of these silicon nitride powders,
5 parts by weight of Y ₂ O ₃ powder having an average particle size of 1.5 μm and 5 parts by weight of Yb ₂ O ₃ powder having an average particle size of 1.2 μm were blended, wet-mixed in methanol for 4 hours and dried, and then 100 k
2700 kg / cm after molding with a pressure of g / cm ²
CIP molding was performed at a pressure of ² . Next, these CIP compacts were set in a carbon crucible together with a filler made of silicon nitride powder and BN powder, and sintered at a temperature of 1900 ° C. for 2 hours in a nitrogen pressure atmosphere of 10 kg / cm ² to obtain a sintered compact. Manufactured.

After grinding the obtained sintered body, the relative density,
Four-point bending strength at 1300 ° C and high temperature creep properties at a temperature of 1250 ° C were measured. The results are shown in Table 3.

[0054]

[Table 3]

Examples 11 to 16 Comparative Examples 9 to 12 100 g of the silicon nitride powder A produced in Example 1 was charged into an electric furnace of a carbon heating element, and the atmospheric pressure shown in Table 4 was applied.
Processed at temperature and time. Table 5 shows the powder characteristics of the obtained silicon nitride powder.

[0056]

[Table 4]

[0057]

[Table 5] (Note) In Comparative Example 11, there was a weight loss of about 10%, and metallic Si was detected in an amount that could be confirmed by X-ray diffraction.

Examples 17 to 23 Comparative Examples 13 to 16 100 g of the silicon nitride powder A produced in Example 1 was filled in an alumina tube having a diameter of 50 mm and subjected to a primary treatment in a tubular furnace under various conditions shown in Table 6. went. Then, Examples 17-2
For No. 2, secondary treatment 1 was carried out for 1 hour at a temperature of 1400 ° C. in an atmosphere consisting of nitrogen and hydrogen with a hydrogen partial pressure of 0.4 atm, and for Example 23, the primary treated powder was treated with a carbon heating element. Charged into an electric furnace of 0.5
Secondary treatment 2 was performed at a temperature of 1300 ° C. for 1 hour under a reduced pressure atmosphere of torr. In Comparative Examples 13 to 16, silicon nitride powder was manufactured by subjecting the primary treatment powder to a heat treatment at a temperature of 1400 ° C. for 1 hour in a nitrogen atmosphere. The powder characteristics are shown in Table 7.

[0059]

[Table 6]

[0060]

[Table 7]

Next, 94 parts by weight of these silicon nitride powders and 6 parts by weight of Y ₂ O ₃ powder having an average particle size of 1.5 μm were mixed,
50 g of powder obtained by wet-mixing in methanol for 4 hours and then drying was filled in a carbon die having a diameter of 60 mm,
Under nitrogen gas atmosphere, temperature 1800 ℃, pressure 400kg /
Hot press sintering was performed at 1 cm ² for 1 hour to produce a sintered body, and the same evaluation as in Example 1 was performed. The results are shown in Table 8.

[0062]

[Table 8]

Examples 24 to 25 Comparative Examples 17 to 18 The total amount of metallic impurities of Fe, Ca and Al is 1000 pp.
High-purity metallic silicon powder having a specific surface area of 1.5 m or less (specific surface area 1.5 m ² /
g) is molded into a molded body having a bulk density of 1.0 g / cm ³ , and the temperature is 1100 to 1450 in an atmosphere containing nitrogen and ammonia.
Nitriding was performed at a temperature of ° C to produce a silicon nitride ingot having an α phase content of 92%. Then, it is roughly crushed / medium crushed by a ceramic crusher and wet crushed by a ball mill made of silicon nitride to a desired grain size to obtain silicon nitride powder B (Example 24) and silicon nitride powder C (Example 25). Was manufactured. The powder characteristics are shown in Table 9. Comparative Example 17 (silicon nitride powder D) and Comparative Example 18 (silicon nitride powder E) are both commercially available silicon nitride powders.

[0064]

[Table 9]

Next, 90 parts by weight of these silicon nitride powders,
5 parts by weight of Y ₂ O ₃ powder having an average particle diameter of 1.5 μm and 5 parts by weight of Yb ₂ O ₃ powder having an average particle diameter of 1.2 μm were mixed, wet-mixed in methanol for 4 hours and dried, and then 100 kg / cm ²
After die molding at a pressure of 2700 kg, CIP molding was performed at a pressure of 2700 kg / cm ² . Next, these CIP compacts are set in a carbon crucible together with a stuffing consisting of silicon nitride powder and BN powder, and sintered at a temperature of 1900 ° C. for 2 hours in a nitrogen pressure atmosphere of 10 kg / cm ² to obtain a sintered compact. Manufactured,
The same evaluation as in Example 1 was performed. The results are shown in Table 10.
Shown in.

[0066]

[Table 10]

Examples 26 to 28 Comparative Example 19 An alumina tube having a diameter of 50 mm was filled with 100 g of the silicon nitride powder A produced in Example 1, and the tube was heated in a tube furnace in the air.
Heat treatment was performed at the temperature shown in 1 for 30 minutes to provide surface oxygen. Table 11 shows the measurement results of the total oxygen amount and the surface oxygen amount of the obtained silicon nitride powder. The other powder characteristics were the same as those of the silicon nitride powder A.

Next, these silicon nitride powders were mixed with Yb ₂ O ₃ powder having an average particle diameter of 1.2 μm and SiO ₂ powder having an average particle diameter of 1.0 μm in the proportions shown in Table 11, and the mixture was added in methanol to obtain 4 parts. After wet mixing and drying for 100 hours / 100kg / cm
Was CIP molded under a pressure of 2700 kg / cm ² after molding with ² pressure. Next, these CIP compacts were set in a carbon crucible together with a filler made of silicon nitride powder and BN powder, and sintered at a temperature of 1850 ° C. for 2 hours in a nitrogen pressure atmosphere of 10 kg / cm ² to obtain a sintered compact. Manufactured,
The relative density and bending strength were measured in the same manner as in Example 1.
The results are shown in Table 12.

[0069]

[Table 11]

[0070]

[Table 12]

The physical properties shown in the table were measured as follows. (1) Total oxygen content (% by weight): Measured with LECO O / N simultaneous analyzer "TC-136". (2) Surface oxygen content (% by weight): The internal oxygen content was measured by the above method, and the difference from the total oxygen content was calculated. (3) Specific surface area (m ² / g): Cantersorb Jr. manufactured by Yuasa Ionics Inc. It was based on the BET one-point method. (4) Average particle size (μm): Measured with a particle size distribution meter “Microtrac-SPA” manufactured by L & N. (5) F amount, F + Cl amount (ppm): Virohydrolysis distillation, ion chromatography method.

(6) Metal impurities (ppm) of Fe, Al and Ca: Measured according to JIS G1322. (7) Relative density (%): By the Archimedes method. (8) Bending strength (MPa): Four-point bending strength at 1300 ° C was measured according to JIS R1601. (9) Creep characteristics: Sintered body in air, temperature 1250
A high temperature creep evaluation was performed for 200 hours by a tensile test method at a temperature of 250 ° C. and a tensile stress of 250 MPa.

[0073]

According to the present invention, there is provided a silicon nitride powder which is excellent in high temperature strength, high temperature creep characteristics and the like and which can produce a silicon nitride sintered body suitable for a high temperature member such as a gas turbine.

Claims (7)

[Claims] 1. A silicon nitride powder obtained by nitriding metallic silicon powder, which has a specific surface area of 10 m ² / g or more or an average particle diameter of 0.8 μm or less, a total oxygen content of 1.5% by weight or less, and F And a total content of Cl of 500 ppm or less and an F content of 300 ppm or less. 2. The silicon nitride powder according to claim 1, wherein the amount of surface oxygen is 0.3% by weight or more. 3. A high-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is heated in a reducing atmosphere having a partial pressure of hydrogen and / or ammonia of 0.2 atm or more at a temperature of 1000 to 1.
The method for producing a silicon nitride powder according to claim 1, wherein the treatment is performed at 500 ° C. for 30 minutes or more. 4. The high-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is treated at a temperature of 1200 to 1400 ° C. for 30 minutes or more under a reduced pressure atmosphere of 1 torr or less. 1. A method for producing a silicon nitride powder according to claim 1. 5. A high-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is treated with hydrogen at a temperature of 1000 to 1500 ° C. for 30 minutes or more in an atmosphere having a chlorine gas partial pressure of 0.2 atm or more. And / or the partial pressure of ammonia is 0.2a
1000 to 1500 ° C. in a reducing atmosphere of tm or more
The method for producing a silicon nitride powder according to claim 1, wherein the treatment is performed for 30 minutes or more. 6. A high-purity silicon nitride fine powder obtained by nitriding metallic silicon powder is treated at a temperature of 1000 to 1500 ° C. for 30 minutes or more in an atmosphere having a chlorine gas partial pressure of 0.2 atm or more, and then 1 torr. Under the following reduced pressure atmosphere, temperature 120
The method for producing a silicon nitride powder according to claim 1, wherein the treatment is performed at 0 to 1400 ° C. for 30 minutes or more. 7. The method for producing a silicon nitride powder according to claim 2, wherein the silicon nitride powder according to claim 1 is heat-treated in an atmosphere containing oxygen.