JP2970400B2 - Method for producing high α-type silicon nitride powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high α-type silicon nitride powder.

[0002]

2. Description of the Related Art Silicon nitride sintered bodies are expected to increase in demand as heat-resistant structural materials due to their excellent material strength, thermal shock resistance and corrosion resistance at high temperatures. In particular, the α-type crystal phase ratio (hereinafter, referred to as
Silicon nitride powder having 90% (weight%, hereinafter the same) or more of which is referred to as “high α-type silicon nitride powder”
It is known that a sintered body obtained by sintering this powder has extremely high material strength at high temperatures. Conventionally, (1) direct nitriding method, (2) reduction nitriding method, and (3) halogenated imide method are well known as industrial methods for producing silicon nitride.
Among these, the direct nitriding method is excellent in cost, and its product is widely used as the most common method.

[0003] In this method, as shown in the following chemical formula,
Anti-gas with a large amount of heat generation of 176 kcal / mol
It is known to be responsive. 3Si + 2N_Two→ Si_ThreeN _Four+ 176kcal

[0004] Therefore, when a tunnel furnace is used as a reactor in order to suppress a rapid reaction and obtain a uniform reaction temperature distribution as much as possible, the amount charged to a tray is adjusted or the rate of temperature rise is controlled. And Japanese Patent Application Laid-Open No. 61-97110, 61-26630 to obtain a more uniform reaction temperature.
No. 5, JP-A-3-60410, etc., it has been proposed to use a rotary furnace or a fluidized bed as a reactor.

On the other hand, this reaction is a so-called gas-solid reaction between nitrogen gas and solid metallic silicon, and apparently diffusion of nitrogen gas into metallic silicon and diffusion into generated silicon nitride limit the reaction. Is said to be. Therefore, in order to increase the diffusion rate, a method of increasing the reaction temperature or a method of increasing the reaction pressure is usually considered. However, in the production reaction of silicon nitride, there is a problem that β-type silicon nitride is generated as the temperature increases, and the desired α-type silicon nitride cannot be obtained. It has been reported that almost no effect can be expected (surface; 24 (No. 7), 36).
3, '86). Also, considering the implementation on an industrial scale, it is not economical to use a device for maintaining an ultra-high pressure as a reactor, and implementation on an industrial scale becomes difficult.

Therefore, it is well known that one method of solving this problem is to use a mixture of hydrogen gas and a reaction gas.

Further, there has been proposed a method for relatively easily producing a high α-type silicon nitride powder by adding a catalyst. For example, K, Na, and Li compounds are disclosed in JP-A-50-128698, magnesium oxide in JP-A-51-48800, metallic iron and iron compounds in JP-A-54-15499, and JP-A-54-15499. No. 22000 discloses halides of alkaline earth metals.
No. 57499 discloses aluminum nitride.
No. 58700 discloses palladium oxide,
Japanese Patent No. 120298 discloses a calcium compound,
Japanese Patent Application Laid-Open No. 61-256 discloses a copper compound.
No. 906 discloses that each vanadium compound is effective in producing high α-type silicon nitride.

The present inventors have conducted intensive studies with reference to these known methods. As a result, the use of copper or a copper compound as a catalyst makes it possible to produce a high α-type silicon nitride powder much more efficiently than other catalysts. It has been found that it can be produced, but in the method proposed in JP-A-59-92906, the amount of copper or copper compound added is as large as 0.5% to 10% with respect to metal silicon. In addition, there is a problem in removing copper or a copper compound in a product refining process. In other words, the purification usually performed in the art is generally performed by acid treatment,
It is difficult to completely remove copper or a copper compound economically by a method of adding a large amount of copper or a copper compound, and in a product obtained by molding and sintering the resulting silicon nitride powder as a raw material, However, there is a problem that a predetermined strength cannot be obtained. In addition, it is not preferable to add a maximum of 10% of copper to metal silicon as a catalyst from the viewpoint of an economical production method of silicon nitride.

The present invention has been made in view of the above circumstances, and is an efficient and industrial scale capable of removing copper or a copper compound by a usual method to such an extent that the strength of a silicon nitride sintered body is not reduced. It is an object of the present invention to provide an economical and economical method for producing high α-type silicon nitride powder.

[0010]

Means and Action for Solving the Problems The present inventors have
As a result of intensive studies to solve the above problems, as disclosed in JP-A-59-92906, a catalyst in which copper or a copper compound is indispensable for efficient production of high α-type silicon nitride powder. At the same time as confirming that it has the effect, copper or copper compound is added to the silicon metal powder with an addition amount smaller than the amount indicated in the gazette, and a mixture sufficiently mixed with a mixer is used as a raw material. 1,000 to 1,500 ° C under a non-oxidizing atmosphere containing nitrogen or ammonia
It has been found that a high α-type silicon nitride powder can be efficiently produced by performing a nitridation reaction at, and the effect of the copper catalyst can be sufficiently exerted.

That is, the present inventors have conducted various studies on a catalyst for producing a high α-type silicon nitride powder. As a result, silicon nitride having a high α-formation ratio can be easily obtained by using copper as a catalyst. Was obtained. In this case, among the catalysts used in the study, copper has a significantly higher diffusion coefficient in metallic silicon compared to other catalytically active substances such as iron and calcium. It is considered that it is more likely to contribute to the reaction promotion than a substance having an effect [E. M. Pell: P
hys. Rev .. , 119, 1014 and 122.
2 (1960)]. Furthermore, the fact that copper has a higher thermal conductivity than other catalysts also has a favorable effect on the control of the heat of reaction, and may possibly suppress the production of high-temperature stable β-type silicon nitride.

However, on the other hand, the density of copper is 8.93 g /
cm ³ (20 ° C.) and the density of metallic silicon is 2.35 g
/ Cm ³ (amorphous at 15 ° C.), it is difficult to uniformly mix the two. Therefore, in order to easily obtain a sufficient catalytic effect, a method of excessive addition as in the prior art is generally adopted.
However, the excessively added copper does not necessarily disperse uniformly, but segregates in the nitrided product. In the production process of silicon nitride by the direct nitridation method, there is generally an impurity removal process using an acid to secure the purity of the product, and most of the impurities are removed to an allowable level in the process, but excessively added. Copper or copper compounds cannot be removed to an acceptable level by ordinary methods, and as a result, have adversely affected the strength of the sintered body using the silicon nitride powder.

However, according to the study of the present inventors, a small amount of copper or copper compound is added to the metal silicon powder in a small amount of less than 0.5%, more preferably 0.4% or less in terms of copper. Is uniformly dispersed so as to be not less than 0.9, a high α-conversion rate equivalent to the case where a copper catalyst is added in a large amount of 0.5% or more is achieved, and the obtained silicon nitride is simply produced by a conventional method. It has been found that a high α-type silicon nitride powder which is highly purified only by treating with acid and gives a sintered body with high strength can be produced efficiently, at low cost, easily and reliably.

In this case, in order to more reliably exert the effect of adding a small amount of a copper catalyst, and particularly when using a reactor such as a fluidized bed or a rotary furnace which is likely to cause classification, copper or metal is added to the metal silicon powder. The copper powder was added and mixed, and the mixed powder was molded or granulated using a binder such as polyvinyl alcohol, methylcellulose, cellulose derivative or starch, or further under an inert gas atmosphere such as argon or helium (normal pressure, It is possible to use a compact or powder sintered under an inert atmosphere such as under reduced pressure or vacuum, or to use a pulverized product obtained by melting the above mixed powder to obtain a silicon-copper alloy and pulverizing it to a predetermined particle size. The inventors have found that the present invention is effective, and have accomplished the present invention.

Therefore, the present invention provides: (1) at least one of copper or a copper compound is added to metallic silicon powder in an amount of 0.05% by weight or more and less than 0.5% by weight in terms of copper with respect to metallic silicon; High α-type nitriding, wherein the mixture is mixed at a temperature of 1,000 to 1,500 ° C. in a non-oxidizing gas atmosphere containing nitrogen or ammonia. (2) At least one of copper or a copper compound is added to metal silicon powder in an amount of 0.05% by weight or more and less than 0.5% by weight in terms of copper with respect to metal silicon, and the degree of mixing is 0.9. The mixture is mixed as described above, and the mixture is molded using a binder, or a molded product obtained by sintering the molded product in an inert atmosphere at normal pressure or reduced pressure or in a vacuum is a non-containing product containing nitrogen or ammonia. 1,0 in an oxidizing gas atmosphere A method for producing a high α-type silicon nitride powder characterized by nitriding in a temperature range of 00 to 1,500 ° C., and (3) at least one of copper or a copper compound to metal silicon A silicon-copper alloy is prepared by blending and melting 0.05% by weight or more and less than 0.5% by weight in terms of copper, and then pulverized to a predetermined particle size again in a non-oxidizing gas atmosphere containing nitrogen or ammonia. 1,000 ~
Provided is a method for producing a high α-type silicon nitride powder characterized by nitriding in a temperature range of 1,500 ° C.

Hereinafter, the present invention will be described in more detail.
The method for producing a high α-type silicon nitride powder of the present invention is based on a direct nitridation method, in which a metal silicon powder is prepared in a non-oxidizing gas atmosphere containing nitrogen or ammonia for 1,000 to 1,500.
When nitriding at ° C., copper or a copper compound is added in a small amount of less than 0.5%.

In this case, it is preferable to use a metal silicon powder having a particle size of several μm to 149 μm, particularly, several μm to 44 μm. Particle size of metallic silicon powder is 149
If it exceeds μ, the nitridation reaction becomes too slow, and unreacted metallic silicon may remain in the nitrided product. In addition, as the purity, metal silicon obtained on an industrial scale is sufficient, but if necessary, it can be selectively used from semiconductor-grade metal silicon to metal silicon used for Al alloys.

In the present invention, the above metal silicon powder is
Direct nitridation reaction using copper or a mixture of copper compounds
But copper added as a catalyst to the metal silicon powder
Or, from the viewpoint of uniformity, the particle size of the copper compound
Particles of the same weight as the silicon particles
Preferably. However, in the case of a thin film,
Regardless of the particle size, 0.1 to 5m in specific surface area^Two / G,
Preferably 0.3 to 3 m^Two / G physical properties
Is good.

The copper compound added to the metal silicon as a catalyst may be any of copper fluoride, copper oxide, copper chloride and other copper compounds, and is not particularly limited. However, most copper compounds have a low melting point and decompose at low temperatures, and the by-products produced at that time erode metallic silicon and remain in silicon nitride produced as impurities, reducing the strength of the silicon nitride sintered body. Purity 9
It is desirable to add 9% or more of metallic copper. Also, the shape of the copper is not particularly limited, and may be spherical,
Commercially available materials such as a thin film and an amorphous shape may be used.

The amount of the copper or copper compound added is 0.05% or more and less than 0.5% in terms of copper relative to the raw metal silicon;
In particular, 0.1% to 0.4% is preferable. 0.05 added
%, The effect of addition is no longer recognized. If the addition amount is 0.5% or more, copper or a copper compound at an allowable level or more remains in the silicon nitride powder obtained by the ordinary purification treatment because the amount of copper or copper compound remains. This has an adverse effect on the strength of the sintered body using the metal silicon powder, and the object of the present invention cannot be achieved.

Here, in the first invention of the present invention, the mixing ratio of copper or a copper compound to the metallic silicon powder is adjusted to 0.9 or more, more preferably 0.93 or more, and still more preferably 0.95 or more. It is necessary to mix, and by setting the mixing degree to 0.9 or more as described above, the effect can be achieved even when the addition amount of copper or copper compound is as small as less than 0.5%. Things. On the other hand, when the mixing degree is smaller than 0.9, the addition amount of copper or copper compound is 0.5
If not, the effect cannot be effectively achieved.

The degree of mixing is a value obtained from the following equation of Rose. The degree of mixing approaches 1 by performing mixing, and the degree of mixing is completely mixed (when x _i = x _{0 in} the following equation). It is one.

[0023]

(Equation 1)

In this case, the value of N (the number of samples)
Means that as many as possible can measure the degree of mixing accurately,
According to the study of the present inventors, if N ≧ 20, there is no significant difference. Therefore, in the present invention, the mixing degree is
It indicates the value when 20 or more samples of 1 to 50 g are collected from the mixture by a spot sampling method using a rod type or a midget spoon type sampler (N ≧ 20).

In the present invention, copper or a copper compound is mixed with metal silicon powder and uniformly dispersed. As a mixer for uniform mixing, a container rotating type such as a V blender or a screw type is used. A fixed-type mixer such as a high-speed shearing type mixer is suitable, but not limited thereto.

The metal silicon powder in which copper or copper compound is uniformly mixed and dispersed as described above can be suitably used particularly for a fixed-bed type reactor such as a tunnel furnace type. The raw material can maintain its state during the reaction process in such a reactor, and can perform a favorable direct nitriding reaction.

In this case, the mixing conditions such as the mixing speed and the mixing time are determined by the shape, size and operating conditions of the mixer (rotational speed, mixing speed, etc.).
For example, when a 20-liter Henschel mixer, which is a high-speed shearing mixer, is used and the mixing is performed for 30 minutes or more at a powder charging rate of 30% and a rotation speed of 1000 rpm, The mixing degree is usually 0.9 or more.

On the other hand, even when the raw materials are uniformly mixed, as in the case of a fluidized bed or a rotary furnace type reactor, the difference in density and particle size between silicon metal and copper or a copper compound causes a difference in the reactor. If there is a risk of classification in the, it is adjusted to a predetermined mixing ratio in advance, the metal silicon powder and copper or copper compound with a mixing degree of 0.9 or more polyvinyl alcohol, methyl cellulose, cellulose derivative, starch and the like Optimum size using suitable binder, preferably 100 μm
A molded product molded to 30 mm or the molded product is
A sintered body obtained by heat treatment in an inert gas atmosphere in a temperature range of 0 to 1,400 ° C., under a reduced pressure of an inert gas atmosphere, or in an inert atmosphere such as a vacuum may be used as a reaction raw material. (2 invention), or it is recommended to once melt a compound adjusted to a predetermined mixing ratio to form a silicon-copper alloy and then pulverize it again to a predetermined particle size to use as a raw material (3rd invention). Is done. In the case of the third invention, the degree of mixing does not necessarily have to be 0.9 or more.

When the former method using a binder is employed, the binder is added and mixed in an amount of 0.5 to 10%, preferably 1 to 3% in terms of solids, and the mixture is granulated by an extrusion granulator or the like. After granulating to an average particle diameter of 100 μm to 30 mm, preferably 300 μm to 5 mm using a molding machine, the mixture is subjected to atmospheric or reduced pressure (preferably 100 Torr or less) in an inert gas atmosphere such as argon or helium, or 000 ~
It is preferable to use a material which is sintered at 1,400 ° C., preferably 1,200 to 1,400 ° C., for a short time so that silicon is slightly fused. In this case, in this step, a binder such as polyvinyl alcohol added during granulation is removed.

Further, the method is not limited to the granulated product, but is formed into a rod-shaped, block-shaped or spherical shaped product using a screw type or hydraulic type extruder with the same prescription. It is also an effective method when pretreating by the method described and nitriding using a fixed-bed furnace such as a tunnel furnace. In the case where nitriding is performed using the molded product as described above, the powder is ground to an appropriate particle size after nitriding to obtain a silicon nitride powder.

The method for producing a high α-type silicon nitride powder according to the present invention comprises the steps of directly nitriding the homogeneous mixture of metallic silicon and copper or a copper compound according to an ordinary method of nitriding, in a non-oxidizing gas atmosphere containing nitrogen or ammonia. Bottom, 1,000-1,500
The nitriding reaction is carried out in a temperature range of ° C. to produce a high α-type silicon nitride powder. As the non-oxidizing gas, either nitrogen alone or a mixed gas of nitrogen and at least one of ammonia, argon, helium, and hydrogen gas can be used.

The silicon nitride powder obtained as described above usually has an α conversion of 90% or more, particularly 92% or more.

The obtained silicon nitride powder was prepared by adding hydrochloric acid,
After treating with an acid such as nitric acid or hydrofluoric acid at room temperature to 80 ° C. for 10 minutes to 3 hours, it is preferable to wash and dry with a conventional method. The impurities such as reactive metal silicon and the copper or copper compound used as the catalyst are removed, so that a high-purity silicon nitride powder can be obtained. In this case, the copper content in the silicon nitride powder is reduced to 5 ppm or less by the acid treatment, and a silicon nitride sintered body having a normal temperature sintering strength of 900 MPa or more is obtained by using such a high-purity silicon nitride powder. be able to.

[0034]

According to the present invention, α is obtained by adding a trace amount of copper or a copper compound as a catalyst to raw metal silicon.
Silicon nitride powder with high conversion rate can be easily and stably manufactured, and copper and copper compounds can be efficiently removed by ordinary acid treatment, and silicon nitride powder that gives a high-purity sintered body can be efficiently manufactured at low cost. And can be sufficiently applied to production on an industrial scale.

[0035]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[Examples 1 and 2, Comparative Examples 1 to 7] Metal silicon powder having an average particle size of 2 to 3 μm was added to an average particle size of 35 μm.
Copper (specific surface area: 0.4 m ² / g) was added at the ratio shown in Table 1 and mixed for 20 hours using a 20-liter Henschel mixer at a powder loading rate of 30% and a rotation speed of 1,000 rpm for the time shown in Table 1. . Thereafter, using a midget spoon, the mixture was sampled by N = 30 samples by the spot sampling method for each 3 g, and the degree of mixing was determined from the above Rose equation.

Next, 200 g of the mixture was charged into a silicon nitride tray, and a central reaction temperature of 1,300 ° C. was introduced while flowing a mixed gas of nitrogen gas / hydrogen gas = 4/1 by volume.
And a nitriding reaction was carried out. The obtained silicon nitride was subjected to X-ray diffraction analysis to determine the α conversion and the reaction rate.

Further, the reaction product thus obtained was subjected to a 5 liter wet pulverizer to obtain an average particle diameter of 0.4 to 4.5.
After pulverization to 0.5 μm, 200 g of each of hydrofluoric acid and nitric acid was added to the slurry, and an acid treatment was performed at 80 ° C. for 1 hour. Thereafter, the product was obtained through washing and drying. For this product, the residual Cu ratio was measured by ICP emission spectrometry, and the three-point bending strength at room temperature was measured.

For comparison, a product without copper was commercialized under the same conditions. Table 1 shows the above results and each condition.

[0040]

[Table 1]

Example 3, Comparative Examples 8 to 11 Copper was added to the same metallic silicon raw material as in the above Examples and Comparative Examples in the amount shown in Table 2, and mixed for 60 minutes to increase the degree of mixing to 0.9 or more. Aqueous solution of polyvinyl alcohol was added to
% By weight, kneaded, and granulated and molded to an average particle diameter of 0.5 mm with a granulator. This was dried at 150 ° C. for 1 hour to remove water, and then 100 mmHg under flowing argon gas.
A material treated at 1,200 ° C. for 1 hour and sintered was used as a raw material. The granulated powder was supplied to a rotary kiln at a rate of 100 g / hour, and a nitriding reaction was performed at 1,300 ° C. while flowing a mixed gas of nitrogen gas / hydrogen gas = 4. Thereafter, the treatment was carried out by the methods shown in the above Examples and Comparative Examples. For comparison, a product without copper was commercialized under the same conditions. Table 2 shows the above results and each condition. In addition, when it supplied to the rotary kiln without performing granulation molding as mentioned above, it aggregated in the middle of the kiln and the reaction could not be continued.

[0042]

[Table 2]

Example 4 1 kg of metallic silicon and 3 g of copper
Was melted and mixed at 1600 ° C. in a crucible, cooled, and pulverized into a powder having an average particle diameter of 2 to 3 μm. 200 g of the mixture was placed in a silicon nitride tray, and nitrogen gas /
The nitriding reaction was performed by heating and maintaining the central temperature at 1,350 ° C. while flowing a mixed gas of hydrogen gas = 4. Thereafter, the same processing as in Example 3 was performed. The α-rate of the obtained silicon nitride powder was 94.3%, the reaction rate was 98.5%, the content of residual copper was 5 ppm or less, and the three-point bending strength of the sintered compact was 950 MPa.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Maki Watanabe 2-3-1-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Gunma Office (56) References JP-A-57-188465 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C01B 21/068 C04B 35/626

Claims (3)

(57) [Claims] At least one kind of copper or a copper compound is added to metallic silicon powder in an amount of 0.05% by weight or more and less than 0.5% by weight in terms of copper with respect to metallic silicon so that the degree of mixing is 0.9 or more. And nitriding the mixture in a non-oxidizing gas atmosphere containing nitrogen or ammonia at a temperature in the range of 1,000 to 1,500 ° C. to produce a high α-type silicon nitride powder. 2. At least one kind of copper or a copper compound is added to metal silicon powder in an amount of 0.05% by weight or more and less than 0.5% by weight in terms of copper with respect to metal silicon so that the mixing degree becomes 0.9 or more. And a molded product obtained by molding the mixture using a binder, or a sintered product obtained by sintering the molded product in an inert atmosphere at normal pressure or reduced pressure or in a vacuum is a non-oxidizing gas atmosphere containing nitrogen or ammonia. 1,000 to 1,500
A method for producing a high α-type silicon nitride powder, comprising nitriding in a temperature range of ° C. 3. A silicon-copper alloy is prepared by blending and melting at least one of copper or a copper compound with metal silicon powder with respect to metal silicon in an amount of 0.05% by weight or more and less than 0.5% by weight in terms of copper. Then, the pulverized product which has been pulverized again to a predetermined particle size is placed in a non-oxidizing gas atmosphere containing nitrogen or ammonia for 1,000 hours.
A method for producing a high α-type silicon nitride powder, comprising nitriding in a temperature range of 0 to 1,500 ° C.