JP3382666B2 - Method for producing silicon nitride powder - Google Patents

Description

Description: 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 a high strength and a small variation.
And a method for producing the same by a direct silicon nitride method . 2. Description of the Related Art Silicon nitride sintered bodies are used as engineering ceramics as materials having excellent properties such as strength, hardness, heat resistance and abrasion resistance, particularly for heat-resistant wear-resistant parts for automobiles and industrial machine parts. Applied. [0003] Silicon nitride powder for producing such a silicon nitride sintered body has two crystal forms, α-type and β-type, but has advantages and disadvantages. Silicon nitride, which has a lot of α-type crystal morphology, can easily obtain a sintered body with high strength and excellent wear resistance at low temperature sintering, but it is accompanied by α → β transition generated in the sintering process When the columnar crystals are deposited, there is a disadvantage that the growth of the columnar crystals is not uniform, abnormal grain growth occurs, and fine densification is hindered. In particular, in the case of a large-sized sintered body, there is a problem that the strength characteristics vary. Japanese Patent Application Laid-Open No. 1-145380 describes that silicon nitride having a high β-phase content can provide a sintered body having high strength and high toughness by controlling the particle size. In order to manufacture this, a nitriding reaction at a high temperature is necessary, and there is a problem that it is difficult to obtain a fine powder. [0005] For both α-type and β-type silicon nitride, it takes a long time to pulverize to obtain a fine powder. It cannot be avoided that impurities are mixed in,
It has been difficult to produce a sintered body having high strength and small variations in strength and wear resistance. In particular, in the pulverizing step, from the viewpoint of energy efficiency, stainless steel, Fe-Cr,
Since Fe-Mn-based Fe-based metal media is often used,
Only those containing a large amount of impurities are practically used, or even if the amount of Fe impurities is small, coarse particles of Fe-based impurity particles are present as jump-in particles. Further, since the sintering mechanism of silicon nitride powder is liquid phase sintering, usually silicon nitride powder and a sintering aid are wet-mixed to form a slurry and then used after drying. As a medium for slurrying, industrial water containing coarse particles of Fe-based impurity particles was generally used, so it is necessary to produce a silicon nitride sintered body having sufficiently excellent mechanical properties. Could not. SUMMARY OF THE INVENTION It is an object of the present invention to provide a silicon nitride powder capable of producing a sintered body having a high strength and a small variation by a direct metal silicon nitride method.
It is to be. [0008] That is, the present invention provides a method of
A silicon powder with a iron removal machine or a mesh of 200μm or less
To remove 200μm or more Fe-based impurities
From a bulk density of about 0.8 to 1.5,
Temperature 1200 in an atmosphere containing nitrogen and / or ammonia
Heat nitriding at ~ 1500C to synthesize nitrided ingot,
It is characterized in that it is pulverized or crushed and then de-ironed.
Has an Fe impurity content of 1.0% by weight or less,
Also Fe-based impurity particles with a maximum size of 200 μm or more
Is a method for producing silicon nitride powder containing no . Hereinafter, the present invention will be described in more detail. [0010] The crystalline form of the silicon nitride powder of the present invention is α
Type or β type, but if emphasis is placed on the strength characteristics of the sintered body and the dimensional stability during firing, the proportion of the α phase is preferably less than 80% silicon nitride powder, To increase the strength characteristics and toughness of the sintered body, the ratio of α phase
% Is desirable, but in this case, the firing temperature needs to be adjusted. In the present invention, the ratio of the α phase of the silicon nitride powder is determined by the ratio of the α phase Iα ₁₀₂ and I α ₁₀₂ in the X-ray diffraction method.
It can be calculated from the diffraction peak intensities of Iβ ₁₀₁ and Iβ ₂₁₀ of α ₂₁₀ and β phases by the following equation. α phase (%) = ｛(Iα ₁₀₂ + Iα ₂₁₀ ) / (Iα ₁₀₂ +
_{Iα 210 + Iβ 101 + Iβ 210} )} × 100 [0012] Iα _102: αSi ₃ N ₄ in (102) diffraction peak intensity of the face Iα _210: αSi ₃ N ₄ in (210) diffraction peak of the plane intensity Iβ _101: βSi ₃ N ₄ (101) plane diffraction peak intensity Iβ ₂₁₀ : β Si ₃ N ₄ (210) plane diffraction peak intensity In the present invention, the silicon nitride powder has an Fe impurity content of 1.0% by weight or less. It is important that the content is preferably 0.5% by weight or less. Since Fe precipitates in the grain boundary phase in the process of sintering silicon nitride, if it exceeds 1.0% by weight, the transverse rupture strength at high temperatures is significantly reduced. When high-temperature strength at 1200 ° C. or higher is required, the Fe impurity content is preferably 200 ppm or less. Next, it is important that the silicon nitride powder of the present invention does not contain Fe-based impurity particles having a maximum size of 200 μm or more. Fe impurities, if they are fine particles, are present in the grain boundary layer together with the sintering aid components, so there is no problem as long as the amount is 1.0% by weight or less. Since it disappears, it remains on the sintered body as it is, causing a variation in the strength of the sintered body as a sintering defect. According to the study of the present inventors, the maximum dimension 200
Since Fe-based impurity particles with a size of μm or more always remain as sintering defects in the sintered body and always greatly reduce the strength of that portion, it was found that such particles should not be included. . In particular, as a silicon nitride powder raw material for producing a sintered body having high strength and wear resistance, the maximum size of Fe-based impurity particles is desirably 50 μm or less. With respect to the fineness of the silicon nitride powder of the present invention, the specific surface area measured by the BET method is desirably 2 m ² / g or more. If the specific surface area is less than 2 m ² / g, the sinterability may decrease and the strength may decrease. The upper limit of the specific surface area is not particularly limited, and the upper limit of the specific surface area is not required to be excessively large and the moldability is not impaired. The silicon nitride powder of the present invention is a metal silicon
Manufacture silicon nitride by oxynitridation and pulverize or dissolve
Can be manufactured by crushing and then de-ironing
You. In the metal silicon direct nitriding method of the present invention, a metal silicon powder is passed through a strong iron removing machine or a sieve having an opening of 200 μm or less to remove Fe-based impurities of 200 μm or more, and then has a bulk density of 0.8 to less. It was molded to about 1.5, and it was heated in an atmosphere containing nitrogen and / or ammonia at a temperature of 120.
It is heated and nitrided at 0 to 1500 ° C. to synthesize a nitrided ingot, and is crushed and refined as necessary . When a metal material containing Fe is used for the pulverization medium or the lining material for the pulverization, an acid treatment is performed to dissolve the Fe-based impurity particles,
200 μm
The above-mentioned Fe-based impurity particles are removed and purified. In processes such as drying, mixing, and bagging after purification, Fe-based impurity particles are generated.
Use a device that does not cause contamination. In order to produce a sintered body using the silicon nitride powder of the present invention, a sintering aid such as Y ₂ O ₃ , MgO, Al ₂ O ₃ or the like is mixed and molded as it is. In this case, the silicon nitride powder or a mixed powder of the silicon nitride powder and the sintering aid is slurried, and powdered at the time of molding and used to obtain mechanical properties such as strength. Excellent complex shape products can be manufactured. As a medium for converting the silicon nitride powder into a slurry, conventional industrial water may be used. However, in order to sufficiently exhibit the characteristics of the silicon nitride powder of the present invention, the maximum size is required.
It is preferable to use water and / or an organic medium that does not contain Fe-based impurity particles having a size of 200 μm or more. As the organic medium, methanol, ethanol, 1,1,1
-Trichloroethane and the like. The amount of the medium used cannot be unconditionally determined depending on its type and use, but it is generally 100 to 400 parts by weight per 100 parts by weight of silicon nitride powder or a mixed powder of silicon nitride powder and a sintering aid. It is a target. At the time of slurrying, an apparatus that does not cause generation and mixing of Fe-based impurity particles is used. The present invention will be described more specifically below with reference to examples and comparative examples. Examples 1 to 15 Various silicon metal powders having a specific surface area of 2 m ² / g and different contents of Fe impurities were passed through a 10,000 gauss deironer, and then the bulk density was increased.
Formed into a 1.0 g / cm ³ nitriding specimen (100 × 100 × 25 mm), filled in an electric furnace, and heated in a nitrogen atmosphere at a temperature of 1200 to
Various types of silicon nitride ingots with different Fe impurity contents and α phase ratios were synthesized by controlling the nitridation pattern at 1500 ° C. The obtained silicon nitride ingot is coarsely and medium crushed by a jaw crusher, a top grinder, or the like.
After removing Fe-based impurity particles with a 10,000 gauss powerful iron removal machine, the powder was subjected to dry pulverization or wet pulverization with a ball mill, and then purified, followed by filtration and vacuum freeze-drying to produce silicon nitride powder. The dry pulverization was carried out by charging 200 g of coarse powder and 3 L of silicon nitride balls into a ball mill having an internal volume of 5 L. The wet grinding was performed by charging a ball mill having an internal volume of 5 liters with 200 g of coarse powder, 3 liters of silicon nitride balls and 500 g of water. Purification was performed with hydrochloric acid and hydrofluoric acid. Comparative Examples 1 to 5 Silicon nitride powder was produced in the same manner as in Example 1 without performing the iron removal treatment on the metal silicon powder and the silicon nitride powder after the coarse and medium crushing. 92% by weight of the silicon nitride powder obtained above,
As a sintering aid, 5% by weight of Y ₂ O _{3 with} an average particle size of 1.5 μm and 3% by weight of Al ₂ O _{3 with} an average particle size of 0.8 μm are added, and the maximum size is 200 μm.
1, which does not contain Fe-based impurity particles
After adding 1,1-trichloroethane and wet-mixing with a ball mill for 4 hours, followed by drying and press molding at a molding pressure of 100 kg / cm ² , they were subjected to CIP molding at a molding pressure of 2700 kg / cm ² . Example 16 In Example 4, a slurry concentration of 30% by weight was used in place of 1,1,1-trichloroethane using distilled water containing no Fe-based impurity particles having a maximum size of 200 μm or more.
Was prepared. This was dried to form a mixed powder of silicon nitride powder and a sintering aid, and a CIP molded body was manufactured using the same under the same conditions as in Example 4. Example 17 A CIP molded body was manufactured in the same manner as in Example 16 except that industrial water mixed with piping scale and the like not subjected to purification and filtration was used instead of distilled water. did. Comparative Example 6 A CIP compact was prepared in the same manner as in Example 17 except that the silicon nitride powder of Comparative Example 5 was used instead of the silicon nitride powder obtained in Example 4. Manufactured. 10 kg of the CIP compact obtained as described above
/ Nitrogen gas atmosphere cm ^2, in the case of using a silicon nitride powder of α fraction less than 80% calcined 4 hours at a temperature of 1850 ° C.,
When silicon nitride powder having an α fraction of more than 80% was used, a sintered body was produced by firing at a temperature of 1800 ° C. for 6 hours. Ten specimens were cut out from these sintered bodies, ground to 3 × 4 × 40 mm, and measured for relative density, four-point bending strength at room temperature and at 1000 ° C. In addition, about room temperature bending strength, n = 10
The average value and the minimum value were measured. The results of Examples 1 to 15 and Comparative Examples 1 to 5 are shown in Table 1, and the results of Examples 16 to 17 and Comparative Example 6 are shown in Table 2. (1) Average particle diameter (μm): particle size distribution meter (laser diffraction method, “Microtrack SP” manufactured by N & L)
A)). (2) α fraction (%): by Geiger flux RAD-IIB type X-ray diffraction manufactured by Rigaku Corporation. (3) Fe impurity content (ppm): Based on JIS G1322. (4) Number of Fe-based impurity particles: 100 g of silicon nitride powder was completely dispersed by applying ultrasonic waves to 500 cc of pure water to form a slurry, and a 10,000 Gauss magnet was put therein and magnetized.
The number of particles of m or more and 50 μm or more was counted using a stereo microscope of 40 times. (5) Relative density (%): by Archimedes' method. (6) Four-point bending strength: Autograph AG manufactured by Shimadzu Corporation
According to -2000A type. [Table 1] [Table 2] According to the present invention, high strength and high strength
Silicon nitride capable of producing sintered bodies with small roughness
Elemental powder provided by inexpensive silicon metal direct nitridation
It is.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Isozaki 1 Shinkaicho, Omuta City, Fukuoka Prefecture Inside the Omuta Plant of Electrochemical Industry Co., Ltd. (56) References JP-A-63-30370 (JP, A) JP-A-59- 54680 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 21/068 C04B 35/626

Claims (1)

(57) [Claims] [Claim 1] A metal silicon powder is removed from a iron removal machine or 200 μm.
Sieve with a sieve having the following openings
After removing system impurities, make the bulk density 0.8 ~ 1.5
Molding and atmosphere containing nitrogen and / or ammonia
Medium nitriding by heating at 1200 to 1500 ° C
Synthesize the got, pulverize or disintegrate it, and then remove iron.
Fe content is 1.0% by weight
Or less, and a maximum size of 200 μm or more
Production of silicon nitride powder that does not contain Fe-based impurity particles
Construction method.