JPH11292522A - Silicon nitride powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a powder with which a ceramic material having high toughness and high reliability can be stably produced with good reproducibility by controlling the amorphous ratio, α-phase ratio and β-phase ratio to specified ranges. SOLUTION: The amorphous ratio, α-phase ratio and β-phase ratio of the obtd. powder measured by the cross polarimetry magic angle spinning nuclear magnetic resonance spectroscopy of Si are 1.0 to 5.0 wt.%, 80 to 99 wt.% and <=19 wt.%, respectively. Further, preferably the α-phase particles have <=0.1 μm crystal diameter, 5 to 25 m<2> /g specific surface area, <=0.12 wt.% carbon content, 0.8 to 2.0 wt.% oxygen content, 0.3 to 0.8 wt.% surface oxygen content. Preferably, the obtd. powder has 1.5 to 5.0 aggregation index D2 /D1 , wherein D2 is the median average diameter of the secondary particles obtd. from the grain size distribution based on weight measured by a laser diffraction method and D1 is the average particle size of the primary particles. As for the producing method, an imide decomposing method is most preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an easily sinterable silicon nitride powder suitable as a raw material for producing silicon nitride ceramics having high toughness and high reliability, among silicon nitride ceramics used as structural ceramics. It is about.

[0002]

2. Description of the Related Art Silicon nitride ceramics have excellent properties of high strength, high toughness, and high corrosion resistance, and are used in various fields as structural members and mechanical parts used at temperatures of 1000 ° C. or less. Applications are expanding. However, in the sintering of silicon nitride ceramics, oxides such as Y ₂ O ₃ and Al ₂ O ₃ are usually 5 to 10% by weight.
S grown under sintering conditions in order to perform sintering by adding
There is a problem that the fracture toughness of the obtained sintered body changes depending on the particle size, the aspect ratio, and the like of the i ₃ N ₄ particles. In order to prevent the fluctuation of fracture toughness due to such sintering conditions and to produce silicon nitride ceramics that can stably maintain high toughness regardless of sintering conditions, Y ₂ O ₃ , MgO, Al ₂ O ₃ Search for sintering aids such as Cr ₂ N, NbB, TaSi ₂ , Zr
In parallel with the study of dispersion strengthening by hard particles of Si _2, etc.,
Development of a raw material powder having characteristics suitable as a raw material for producing a sintered body has been performed.

[0003] Conventionally, as a method for producing silicon nitride powder,
(1) Direct nitriding method of metal silicon powder, (2) reduction nitriding method of silica powder, (3) imide decomposition method of reacting silicon halide with ammonia, and the like are known. Silicon nitride powders manufactured by these methods have different manufacturing histories, even if the metal impurity amount, oxygen content, particle size, etc. have the same value, the sinterability of the powder and the obtained sintered body There are significant differences in characteristics. Generally, it is said that the silicon nitride powder produced by the method (3) is easily sinterable and exhibits excellent sintered body performance.

[0004] As the research on powder properties, sinterability and sintered body properties has progressed, the controlling factors of sinterability and sintered body properties have been elucidated. As a result, the influence of the above manufacturing history is not absolute. Rather, due to the interaction of various powder properties. This will be described below. Silicon nitride has two crystal forms, α phase and β phase.
There are types, and the β phase is known to be pure silicon nitride that does not dissolve oxygen, whereas the α phase is known to dissolve oxygen in the crystal lattice. In sintering silicon nitride,
During the heating process, the sintering aid reacts with the silica on the surface of the silicon nitride particles to form a melt phase, and the densification proceeds due to the dissolution of silicon nitride in the melt phase and the reprecipitation as a β phase. I do. For this reason, it is said that a silicon nitride powder having a high α-phase fraction is desirable as a raw material for producing a sintered body.

However, in the conventional method, since the crystal phase has been identified and quantified by the powder X-ray diffraction method, the phase composition including the amorphous phase (β phase fraction, α phase fraction, and amorphous fraction) and the sintering property And analysis of the correlation with the properties of the sintered body was not sufficient. JP-A-63-147867 discloses an α-Si ₃ N ₄ powder having a β phase content of less than 2% and a β phase content of 10%.
The above-mentioned Si ₃ N ₄ powder is mixed and the β phase content is adjusted to 2-3.
By using Si ₃ N ₄ powder adjusted to the range of 0%, 92 wt% of Si ₃ N ₄ , 4 wt% of Al ₂ O ₃ , and Y ₂ O ₃ 6
A method for producing a high-density and high-strength silicon nitride sintered body with a composition of wt% is disclosed. However,
Since the raw material powder used had a slightly coarse center particle size of 0.5 μm, the powder having a low β phase content had a low α → β phase transition speed, and even when an oxide having a total amount of 10 wt% was added. High-density sintered bodies have not been obtained. Also, Japanese Patent Application Laid-Open No. 2-1
Japanese Patent No. 75662 discloses that a compact comprising an Si ₃ N ₄ powder having an α phase content of 98% or more and an average particle size of 0.3 to 0.5 μm and a sintering aid is sintered at 1600 to 1800 ° C. Discloses a method for producing a silicon nitride sintered body having a high strength from room temperature to a high temperature. However, there is no description other than the average particle diameter and the α phase content as the powder properties of the raw material powder used, and the effects of other powder properties on the sinterability and the properties of the sintered body are not mentioned at all. Not. If the SiO ₂ content is less than 6 mol%, a high-density sintered body cannot be obtained. JP-A-8-12306 discloses that
Β-phase fraction 0 to 1.8% by weight, α-phase fraction 9 suitable as a raw material for producing highly tough and highly reliable silicon nitride ceramics
3.2 to 100% by weight, crystallite diameter 0.10 μm or less, amorphous fraction 5.0% by weight or less, carbon content 0.10% by weight
The following silicon nitride powders are disclosed: However, in the same publication, since the amorphous fraction was measured by a hydrolysis method, even in the range of 0 to 5.0% by weight of the amorphous fraction, the silicon nitride ceramic obtained by the amorphous fraction could be used. I overlook that the strength characteristics change. A more detailed analysis is required for the effect of the amorphous in the silicon nitride powder, and the silicon nitride powder disclosed in the publication is not the same as the present invention.

[0006] Incidentally, Analytical Che
Mystery Vol. 59, No. 23, 2794-2797
The page describes the β-phase fraction, α-phase fraction, and amorphous fraction of Si ₃ N ₄ powder measured by magic angle rotation nuclear magnetic resonance spectroscopy (MAS NMR) of ²⁹ Si nuclei. However, this reference does not mention at all the specific surface area and the chemical composition (oxygen content, carbon content, etc.) which are essential requirements of the raw material for producing a sintered body. Si ₃ N ₄ powder as a raw material for producing a sintered body has optimum values for specific surface area, particle size distribution, and chemical composition (oxygen content, carbon content, etc.). Even if the phase composition (β phase fraction, α phase fraction, and amorphous fraction) is controlled, sufficient sinterability and sintered body characteristics are not exhibited. In this document, since the amorphous fraction is obtained from the peak analysis of the MAS NMR spectrum measured by the Bloch Decay method, the measurement accuracy of the amorphous fraction is extremely poor, and a measurement error of less than ± 5% by weight is included. Was out.

In the above-mentioned known documents, the amorphous fraction of the raw material powder is not accurately determined, and no quantitative analysis has been performed on the correlation between the amorphous fraction and the sinterability and the characteristics of the sintered body. . In order to elucidate the correlation between the phase composition of the raw material powder and the sinterability and characteristics of the sintered body, it is needless to say that establishing a highly accurate method for measuring the amorphous fraction is very important. is there. Under such circumstances, it has been difficult with the conventional technology to stably produce silicon nitride ceramics having excellent characteristics such as high toughness and high reliability with good reproducibility. An object of the present invention is to solve the above-mentioned problems and to provide a silicon nitride powder capable of stably producing silicon nitride ceramics having high toughness and high reliability with good reproducibility.

[0008]

The present inventors have conducted various studies on the relationship between the powder characteristics of silicon nitride, the sinterability and the characteristics of the sintered body, and as a result, the sinterability and the characteristics of the sintered body are controlled. Factors include phase composition (β phase fraction, α phase fraction and amorphous fraction), specific surface area, oxygen content, surface oxygen content,
There are carbon content, particle size distribution, degree of agglomeration, and crystallite size. In particular, the amorphous fraction, α-phase fraction, β-phase fraction, crystallite diameter, measured by cross-polarization MAS NMR spectroscopy of ²⁹ Si nuclei, It has been found that a silicon nitride powder having a specific surface area and a carbon content within a specific range respectively achieves the above object.

[0009] The present invention has been made based on the above findings, ²⁹ Si nuclear cross polarization method magic angle spinning nuclear magnetic resonance spectroscopy by measures amorphous fraction 1.0 to 5.
The present invention provides a silicon nitride powder characterized by being 0% by weight, having an α phase fraction of 80 to 99% by weight and a β phase fraction of 19% by weight or less. Further, the present invention, in addition to these powder properties, further, the crystallite diameter is 0.1μm or less,
The present invention provides a silicon nitride powder having a specific surface area of 5 to 25 m ² / g and a carbon content of 0.12% by weight or less.

Hereinafter, the silicon nitride powder of the present invention will be described in detail. The silicon nitride powder of the present invention was measured by cross-polarization magic angle rotation nuclear magnetic resonance spectroscopy of ²⁹ Si nuclei.
An amorphous fraction of 1.0 to 5.0% by weight, preferably 1.5 to 4.5% by weight, an α-phase fraction of 80 to 99% by weight,
The silicon nitride powder is preferably 85 to 98% by weight, and has a β phase fraction of 19% by weight or less, preferably 1.9 to 13.5% by weight.

Amorphous silicon nitride has an α phase, a β phase, etc.
Higher activity than crystalline silicon nitride
Accelerates mass transfer of constituent atoms to achieve rapid densification
I do. Therefore, the amorphous fraction is less than 1.0% by weight.
When the concentration of perfect crystal grains is low, the densification rate decreases.
As a result, the sinterability deteriorates. 5.0 weight of amorphous component
%, The sintering rate becomes non-uniform,
In addition to the formation of residual pores inside the sintered body,
The aspect ratio (major axis diameter / short axis diameter ratio) of the formed columnar particles is
This causes the strength characteristics of the sintered body to deteriorate.
The amorphous fraction of silicon nitride powder can be determined by various methods.
It is possible to measure²⁹ Intersection of Si nuclei
Measured with good reproducibility by polarization method MAS NMR spectroscopy
be able to.

Regarding crystalline silicon nitride, α phase particles and β phase particles have different contributions to the sintering behavior. That is, the α-phase particles dissolve rapidly in the sintering aid-silicate-based liquid phase generated in the heating process, whereas the β-phase particles dissolve at a slower rate. Is advantageous. For this reason, when the α fraction is less than 80% by weight, the densification rate decreases, and a high-density sintered body cannot be obtained under ordinary sintering conditions. When the α fraction exceeds 99% by weight,
Since the concentration of the amorphous component decreases, the densification rate also decreases, and the sinterability deteriorates.

When the β phase particles in the silicon nitride powder become fine particles having a crystallite diameter of 0.1 μm or less, they act as nuclei for promoting the α → β phase transition during sintering, and the phase transition rapidly proceeds at a low temperature. It is thought that there is an action to make it. As a result, the densification rate increases, and a high-density sintered body can be obtained. Therefore, it is preferable that a small amount of β-phase particles be present. further,
When the ratio of the β phase is 19% by weight or less, anisotropic grain growth occurs at the time of precipitation of the β phase particles, a large number of columnar crystals having a high aspect ratio are generated, and the fracture toughness is improved. When the ratio of the β phase exceeds 19% by weight, the growth of columnar crystals accompanying the α → β phase transition during sintering is suppressed, the equiaxed crystal increases, and the ratio of the columnar crystals having a high aspect ratio decreases. Therefore, the fracture toughness of the sintered body decreases.

[0014] Silicon nitride powder of the present invention, the crystallite diameter of the α-phase grains, the main component is 0.1μm or less, preferably 0.01～0.08Myuemu, specific surface area of 5~25m ² /
g, preferably 7 to ²⁰ m ² / g, and a carbon content of 0.1
It is desirably 2% by weight or less, preferably 0.10% by weight or less. The progress of sintering itself is accelerated by reducing the particle size of the raw material powder and increasing the specific surface area. Because of this,
Powders having a specific surface area of less than 5 m ² / g have a low densification rate,
Unless a large amount of a sintering aid is added, a high-density sintered body cannot be obtained. When the specific surface area exceeds 25 m ² / g, not only does the bulk density of the molded body decrease, shrinkage during sintering increases, but also
Since the sintering shrinkage becomes non-uniform, the sintered body is deformed and micro cracks are generated, which is not preferable. The carbon in the raw material powder reacts with the oxide auxiliary added at the time of sintering to generate carbon monoxide gas, which causes the generation of residual pores. is there.

In the sintering of silicon nitride, the oxygen content and the surface oxygen content of the raw material powder have a great influence on the densification rate. The oxygen content is 0.8-2.0% by weight, preferably 0.9-1.8% by weight, and the surface oxygen content is 0.3-0.8% by weight, preferably 0.4-0.7%. % By weight. 0.8% oxygen content
If it is less than 3, the amount of the sintering aid-silicate liquid phase generated during the temperature raising process becomes insufficient, and the viscosity also becomes high, so that the densification is hindered. When the oxygen content exceeds 2.0% by weight, the mechanical properties of the obtained sintered body deteriorate. In particular, the decrease in fracture toughness and the decrease in high-temperature strength are remarkable. Surface oxygen plays an important role in densifying silicon nitride. If the surface oxygen content is less than 0.3 weight, the amount of sintering aid-silicate liquid phase generated in the early stage of the sintering process is insufficient, so that grain boundary pores grow and a high-density sintered body is formed. I can't get it. If the surface oxygen content exceeds 0.8% by weight, the mechanical properties of the obtained sintered body will deteriorate. In particular, the fracture toughness is significantly reduced.

The amorphous fraction of the silicon nitride powder of the present invention was measured by cross-polarization MAS NMR spectroscopy of ²⁹ Si nuclei. That is, for ²⁹ Si nuclear MAS NMR measurement, Journal of American C
Eramic Society Vol. 79, No. 2 (19
1996), pages 513 to 517. In the measurement, 10% by weight of sodium trimethylsilylpropionate (TSP) was added to the sample as an internal standard. Contact time 2ms to improve measurement accuracy,
Under the condition that the cycle time is 4 seconds, the integration was performed 8000 times or more. Cross-polarization MAS of amorphous Si ₃ N ₄
The NMR spectrum is a single peak with a broad line width,
It was observed around 43 ppm.

The amorphous fraction obtained by the hydrolysis method described in JP-A-8-12306 and the cross-polarized MA of the present invention
Comparing with the amorphous fraction by S NMR method,
The value of 0.1 to 0.5% by weight measured by the hydrolysis method corresponds to 1.0 to 5.0% by weight in the measurement method of the present invention, and more accurate measurement is possible. In the conventional measurement method, it was difficult to calculate the amorphous fraction with high accuracy, so that the amorphous fraction was 1.0 to 5.0.
Attempts have not been made to produce silicon nitride powder in a weight percentage with good reproducibility. In the present invention, the cross-polarization method MA
It was possible to improve the quantification accuracy of a small amount of amorphous fraction by S NMR spectroscopy, and it became possible to produce a silicon nitride powder in which the amorphous fraction was controlled.

The β-phase fraction and α-phase fraction in the silicon nitride powder of the present invention are determined by the Rietveld of the powder X-ray diffraction pattern obtained by step-scanning the diffraction angle (2θ) range of 15 to 80 ° in steps of 0.02 °. Analysis [Journal of
Materials Science, Volume 19, 311
5-3120 pages (F. Izumi, M. Mitom
o and Y. Bando, 1984)). According to Rietveld analysis, the proportion of the constituent crystal phases can be quantified with higher accuracy than the conventional powder X-ray diffraction method.

Similarly, the crystallite diameter of the silicon nitride powder of the present invention can be calculated by calculating the half-width of the powder X-ray diffraction peak at a diffraction angle (2θ) of 15 to 80 ° with high accuracy. Is the average of the crystallite diameters obtained from the Scherrer's formula.
In calculating the half width of the diffraction peak, it is necessary to correct the line width by the optical system of the diffraction device. This amendment includes the NIST (National Institute of Standads
and Technology) was used.

[0020]

(Equation 1) D _hkl : crystallite diameter (nm) λ: measured X-ray wavelength (nm) β: spread of diffraction angle (radian) θ: Bragg angle of diffraction angle K: constant [0 when β is half width (FWHM). 94]

The oxygen content of the silicon nitride powder of the present invention is measured by the LECO method, and the surface oxygen content is determined by the chemical method described in the Ceramic Society of Japan, Vol. 101, No. 12 (published in 1993), pp. 1419-1422. It was measured by an analytical method. The difference between the oxygen content and the surface oxygen content is the internal oxygen content. Further, the particle size distribution is also an important factor affecting the sinterability and the characteristics of the sintered body of the powder. The average particle diameter ratio cohesion index D ₂ / D ₁ is 1.5 which is the D ₁ of the median average size D ₂ and the primary particles of the secondary particles determined from the particle size distribution of the weight measured by a laser diffraction method It is desirable to be in the range of 5.0. If the cohesion index is smaller than 1.5, the sinterability is hindered. If the cohesion index is larger than 5.0, the structure of the sintered body becomes non-uniform, and residual pores, micro cracks, etc. are generated, and High strength and high reliability cannot be realized. Incidentally, the average particle size of the primary particles is described in Industrial Material Magazine No. 3
As described in Vol. 8, No. 12, page 114, TE
The primary particles constituting the secondary particles are two-dimensionally traced on a transparent sheet from an M photograph and processed by an image analyzer to obtain the primary particles.

Next, a method for producing the silicon nitride powder of the present invention will be described. The silicon nitride powder of the present invention is a direct nitridation method of metal silicon powder, a reduction nitridation method of silica powder,
Although it can be produced by various methods such as an imide decomposition method, the imide decomposition method that can arbitrarily adjust powder properties such as a crystal phase ratio, an internal oxygen amount, a secondary particle diameter, a primary particle diameter, and a specific surface area is most preferable. Are suitable. In the imide decomposition method, for example, the specific surface area of imide is adjusted to 500 to 950 m ² / g, the light packaging density is adjusted to 0.035 to 0.075 g / cm ³ , and 1400
It can be manufactured by crystallization under a temperature condition of １1700 ° C. In the present invention, the crystalline silicon nitride powder obtained by the above-mentioned calcination is mixed with 4 to 30 oxygen.
%, With the balance being inert gas. The atmosphere gas may be an atmosphere containing 4 to 30% of oxygen and the balance being an inert gas such as nitrogen, helium, or argon. For example, an air atmosphere is preferably used. The milling method is not particularly limited, and a commonly used milling device, for example, a vibration mill,
An attritor or the like is used. By this milling, not only can fusion and aggregation between particles occurring during firing be broken, but also the thickness of the amorphous layer on the particle surface can be increased.

In the direct nitriding method of metal silicon powder, for example, a silicon nitride powder having an α phase fraction of 70% or more and a specific surface area of 10 m ² / g or more is converted to a specific surface area of 10 m ² / g or more and an oxygen content of 2.0% by weight. The following metal silicon powder is added and mixed in an amount of 5 to 20% by weight, and the mixture is mixed under a mixed atmosphere of hydrogen gas and nitrogen gas or an mixed atmosphere of ammonia gas and nitrogen gas at a heating rate of 10 to 50 ° C./h. 1400-16
By raising the temperature to 00 ° C., the silicon nitride powder of the present invention can be produced. In order to control the crystal phase of the produced powder, it is necessary to pay particular attention to the hydrogen partial pressure in the atmosphere and the charged amount and packing density of the raw material silicon metal powder. After the resulting powder is pulverized, if necessary, it is subjected to an acid treatment to adjust the particle size and remove impurities to obtain a desired powder.

The silicon nitride powder of the present invention is mixed with a sintering aid such as aluminum oxide, yttrium oxide and magnesium oxide in the same manner as in the case of the conventional silicon nitride powder, and the mixture is formed into a predetermined shape. Then, by sintering, a silicon nitride ceramic (sintered body) can be manufactured. The molding pressure is 0.5 to 10 tons
/ Cm ^2, and the sintering conditions are a sintering temperature of 1500 to 2000 ° C., an atmospheric pressure of 0.5 to 100 atm, and a sintering time of about 1 to 10 hours.

The silicon nitride ceramics (sintered body) produced using the silicon nitride powder of the present invention has particularly high fracture toughness and high strength and high Weibull coefficient. It is particularly suitable as a raw material for the production of silicon nitride ceramics used as heat engine parts and mechanical parts such as turbo rotors, engine valves, diesel engine sub-combustion chambers and the like used at a temperature of 1300 ° C. or lower.

[0026]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
The present invention will be described in more detail. Examples 1 to 14 and Comparative Examples 1 to 4 Silicon nitride powders were produced according to the following production method (imide decomposition method) and the production conditions shown in the following [Table 1]. The powder properties of the obtained silicon nitride powder are shown in Table 2 below. [Method for producing silicon nitride powder] Diameter 3 cooled to 0 ° C
After the air in the vertical reaction vessel having a height of 0 cm and a height of 45 cm was replaced with nitrogen gas, predetermined amounts of liquid ammonia and toluene were charged. In the reaction tank, it was separated into liquid ammonia in the upper layer and toluene in the lower layer. Pre-prepared silicon tetrachloride 20
A solution consisting of .about.35% by weight, with the balance being toluene, was fed via a conduit to the slowly stirred lower layer. With the supply of the toluene solution, a white reaction product was deposited near the interface between the upper and lower layers. After the completion of the reaction, the reaction solution was transferred to a filtration layer, and the product was separated by filtration and washed four times with liquid ammonia to obtain purified silicon diimide.

By changing the ratio (by volume) of silicon tetrachloride and liquid ammonia in the reaction in the range of 1/50 to 2/50, the specific surface area is 500 to 950 m ² / g.
Was synthesized. In the initial stage of the above-mentioned reaction, liquid ammonia is present in a large excess, but since ammonia is consumed as the reaction proceeds, liquid ammonia is also continuously supplied to the reaction tank. By changing the volume ratio of silicon tetrachloride and liquid ammonia supplied into the reaction tank in the steady state in the range of 1/50 to 2/50, the specific surface area is 500 to 950.
m ² / g of silicon diimide was synthesized. Also, by changing the drying time and the stirring rotation speed when drying the produced silicon diimide, the light packing density of the silicon diimide is reduced to 0.5.
It was varied in the range of 035 to 0.075 g / cm ³ .

The produced silicon diimide was thermally decomposed at 1000 ° C. while flowing a nitrogen gas having an oxygen concentration shown in the following Table 1 to obtain an amorphous silicon nitride powder. Next, the obtained amorphous silicon nitride powder was ground by a vibration mill, and then, in an electric furnace, under a nitrogen atmosphere, under the conditions described in [Table 1] (heating rate, maximum temperature and the same temperature). Heating time and CO concentration in the furnace)
An off-white silicon nitride powder was obtained. The CO concentration in the furnace was adjusted by the purity (oxygen concentration, dew point) and flow rate of the nitrogen gas to be circulated. This crystalline silicon nitride powder was put into a vibration mill, and the water content was 0.02% and the oxygen content was 10%.
%, And milling was performed for a predetermined time at an amplitude of 8 mm in an atmosphere consisting of an inert gas with the balance being an inert gas. Observation of the obtained silicon nitride powder with a scanning electron microscope revealed that the silicon nitride powder had a particle diameter of 0.05 to 0.5.
Only equiaxed granular particles of μm were observed. In addition, the chlorine content of the silicon nitride powder is 50 pp in any case.
m or less. The specific surface area of the silicon nitride powder was measured by the BET one-point method, and the carbon content was measured by the LECO method (combustion-infrared absorption method).

[Preparation of Standard Silicon Nitride Sample] The calcined amorphous Si ₃ N ₄ powder obtained in Example 1 at 1000 ° C. was calcined again at 1100 ° C. for 2 hours in a nitrogen atmosphere to obtain ²⁹ Si MAS NMR measurement. standard amorphous Si ₃ N ₄ samples of use, similarly, the 1500 ℃ α-Si ₃ N ₄ powder calcined obtained in the example, by baking for 2 hours at 1750 ° C. in a nitrogen atmosphere again, ²⁹ Si
A standard α-Si ₃ N ₄ sample for MAS NMR measurement was prepared.

[Cross-polarization method MAS NMR measurement]
Morphas Si_ThreeN_FourTo trimethylsilyl as internal standard
Addition of 10% by weight of sodium propionate (TSP)
And the contact time is 2 milliseconds and the cycle time is 4 seconds.
By condition,²⁹Si nucleus cross polarization MAS NMR spectrum
Is measured and the amorphous Si_ThreeN_FourAnd TSP absorption peaks
Was determined. Similarly, Examples 1 to 14 and the ratio
10 weights of TSP was added to the powder samples obtained in Comparative Examples 1 to 4.
% And the cross-polarization method MAS NMR spectrum was measured.
And amorphous Si_Three N_FourProduct of absorption peak of TSP
The partial intensity ratio was determined. Amorphous Si of each measurement sample_ThreeN_Four
Of the integrated intensity ratio between TSP and TSP to standard amorphous TSP
Compared to the integrated intensity ratio for
The fraction was determined.

[X-ray Diffraction Measurement] The powder X-ray diffraction pattern of the obtained silicon nitride powder was measured by a regular step scanning method using a copper tube as a target and a graphite monochromator. Step scanning was performed at a diffraction angle (2θ) of 15 to 80 ° in increments of 0.02 °, and α- and β-fractions were obtained by Rietveld analysis.

[0032]

[Table 1]

[0033]

[Table 2]

Using Test Examples Using the silicon nitride powders obtained in Examples 1 to 14 and Comparative Examples 1 to 4 as raw materials, respective sintered bodies were produced by the following production methods. [Production Method of Sintered Body] 5 wt% of Y ₂ O ₃ , ₂ wt% of Al ₂ O ₃ and 0.5 wt% of HfO ₂ were added to silicon nitride powder, and wet-mixed with a ball mill, followed by 2 ton / cm. ^Two
A green compact was produced by rubber press molding under the following pressure. This compact was filled in a silicon nitride crucible and heated in an electric furnace in a nitrogen gas atmosphere at 1 atm.
h, and the temperature was maintained at 1760 ° C. for 4 hours to obtain a silicon nitride sintered body.

The bulk density of the obtained sintered body was measured by the Archimedes method. A 3 × 4 × 40 mm equivalent bending test piece in accordance with JIS R1601 was cut out from the sintered body, and JIS
According to R 1601, a four-point bending test was performed under the conditions of an outer span of 30 mm, an inner span of 10 mm, and a crosshead speed of 0.5 mm / min. The bending strength at room temperature is an average value of 40 pieces. In the bending test at a high temperature, after holding the test pieces in a nitrogen atmosphere at 1300 ° C. for 10 minutes, the strength of eight or more test pieces was measured, and the average value was calculated. Further, the fracture toughness value is S in accordance with JIS R 1607.
It was measured by the EPB method. Ultimate density, bending strength (room temperature strength,
The following Table 3 shows the measurement results of the Weibull coefficient at room temperature strength and high-temperature strength) and the fracture toughness value.

[0036]

[Table 3]

[0037]

EFFECT OF THE INVENTION The silicon nitride powder of the present invention can stably produce silicon nitride ceramics having high toughness and high reliability with good reproducibility.

Claims (5)

[Claims] 1. The amorphous silicon fraction measured by cross-polarization magic angle rotation nuclear magnetic resonance spectroscopy of ²⁹ Si nuclei is 1.0.
~ 5.0 wt%, α phase fraction is 80 ~ 99 wt%,
A silicon nitride powder having a β phase fraction of 19% by weight or less. 2. The amorphous fraction measured by the cross-polarization magic angle rotation nuclear magnetic resonance spectroscopy of ²⁹ Si nuclei is 1.5.
４4.5% by weight, and the α-phase fraction was 85-98% by weight,
A silicon nitride powder having a β phase fraction of 1.9 to 13.5% by weight. 3. The silicon nitride according to claim 1, wherein the crystallite diameter is 0.1 μm or less, the specific surface area is 5 to 25 m ² / g, and the carbon content is 0.12% by weight or less. Powder. 4. The method according to claim 1, wherein the oxygen content is 0.8 to 2.0% by weight and the surface oxygen content is 0.3 to 0.8% by weight.
4. The silicon nitride powder according to 3. Claims wherein the ratio cohesion index D ₂ / D ₁ is the average particle diameter D ₁ of the median average size D ₂ and the primary particles of the secondary particles is in the range of 1.5 to 5.0 The silicon nitride powder according to any one of claims 1 to 4.