JPH0610082B2 - Method for producing α-type silicon nitride fine powder - Google Patents

Description

The present invention relates to a method for producing α-type silicon nitride (α-Si ₃ N ₄ ) fine powder. More specifically, the present invention provides a method for obtaining fine and fine α-type silicon nitride fine powder with high yield and at low cost.

Silicon nitride sinter has excellent heat resistance and high temperature strength. As a high strength heat resistant material and high precision wear resistant material, it can be used as a material that can achieve high temperature, light weight and high efficiency of heat engines such as diesel and gas turbines. Is expected. The thermal and mechanical properties of these sintered bodies largely depend on the properties of the raw material powder of the sintered body, and are inexpensive, high-quality α-type silicon nitride fine powders with a shape close to a sphere of 1 μm or less and a narrow particle size distribution. Supply is desired.

Among the silicon nitride synthesis methods, the reduction nitriding method of silicon oxide has a relatively easy reaction operation, does not use raw materials that may corrode the equipment or cause an explosion, and It is attracting attention as an industrially advantageous method in that high silicon nitride can be easily obtained.

However, this method can only obtain a silicon nitride powder having a size of several μm, even if a silicon oxide fine powder and a carbon powder, which are sufficiently selected as raw materials, are used. In some cases, needle crystals and rod-shaped particles are mixed, The problem that a uniform α-type silicon nitride fine powder having a spherical shape of 1 μm or less cannot be obtained, and when the carbon / silicon oxide ratio in the raw material is small, the nitriding reaction rate is low and unreacted silicon oxide remains. I have a problem. Further, these problems are more remarkable when a coarse-grained silicon oxide powder having a central particle size of 1 μm or more is used, and it becomes a large barrier for obtaining α-type silicon nitride powder at a lower cost.

In order to increase the nitriding reaction rate, a method of adding oxides of iron, manganese, magnesium or the like as a catalyst (see Ceramic Industry Association vol. 85 [11] 1977 P. 537-542) has been proposed. However, iron oxide, magnesium oxide, calcium oxide, manganese dioxide, cobalt oxide, chromium oxide, which are mentioned as substances that accelerate the nitriding reaction,
The addition of vanadium pentoxide as a catalyst also improves the nitriding rate, but the particle size of the generated silicon nitride is usually several μm.
m and acicular crystals and rod-shaped particles are mixed. This tendency is more remarkable when oxidized silica having a large particle size is used as a raw material. In addition, addition of iron oxide, manganese dioxide, cobalt oxide, and chromium oxide facilitates the formation of silicon carbide together,
Addition of vanadium pentoxide facilitates the formation of β-type silicon nitride. That is, the substances described here are effective as a catalyst for accelerating the nitriding reaction, but have a problem in controlling the particle size and shape of the silicon nitride particles to be produced, and have a spherical shape with a uniform particle shape. It has almost no effect on the purpose of producing the fine powder.

As a method of accelerating the nitriding reaction and controlling the particle shape, a method of adding fine powder of silicon nitride of 2 μm or less (Japanese Patent Publication No. 54-23917, Japanese Patent Laid-Open No. 58-91005, 1st next-generation industrial basic technology) Symposium Proceedings, 1983 11
(See P.27-46 on 11th of March) is proposed. However, as described in the above-mentioned publications and literatures, this method is effective if the raw material silicon oxide powder is a fine powder having a particle size of 20-40 mμ, but it is a coarse particle having a particle size of 1 μm or more. When silicon oxide powder was used, the nitriding reaction rate was slow, the α-type silicon nitride content was low, and the particle shape of the silicon nitride produced could not be controlled, resulting in a mixture of needle-shaped crystals and rod-shaped particles. Only silicon nitride having a uniform particle shape can be obtained. That is, this method is not effective when the particle size of silicon oxide used as a raw material is as large as 1 μm or more.

In the synthesis of silicon nitride by the reduction and nitriding reaction of silicon oxide, the weight of raw material cost to the production cost thereof is very important.

In particular, the price of silicon oxide used as a raw material depends on the particle size, etc., and silicon oxide fine powder having a particle size of 20-40 mμ is expensive, and in order to significantly reduce the production cost, a coarse particle size of 1 μm or more is used. There is a strong demand for development of a method capable of using granular silicon oxide.

In view of such circumstances, the present inventors have added at least one selected from Mg and Mg compounds as a reduction nitriding reaction catalyst in the reduction nitriding reaction using silicon oxide and carbon as raw materials, and have a BET specific surface area of 15 to 15 When 100 m ² / g of silicon nitride fine powder is added, the nitriding ratio is high and the center particle size is 1 μm due to the synergistic effect of these additives even when using silicon oxide coarse particles having a center particle size of 1 μm or more.
The inventors have found that a uniform α-type silicon nitride fine powder having a spherical shape of m or less can be obtained with a high yield, and have reached the present invention.

That is, the present invention is a method for producing silicon nitride by heat-treating a mixture of silicon oxide powder and carbon powder at a high temperature in an atmosphere containing nitrogen, and having a central particle diameter of 1 to 100 μm.
0.4 to 4 carbon powder to 1 part by weight of silicon oxide powder
Parts by weight, at least one selected from Mg and Mg compounds is converted to Mg element weight by 0.0005 to 0.1 parts by weight, B
ET fine powder having a specific surface area of 15 to 100 m ² / g
The present invention provides a method for producing α-type silicon nitride fine powder, which is characterized by using a mixture of 0.005 to 1 part by weight.

According to the present invention, silicon nitride fine powder having good particle properties can be obtained at low cost, and its industrial value is very large.

The present invention will be described in detail below.

The silicon oxide powder used in the present invention preferably has a center particle size of 100 μm or less and is as pure as possible.
According to the present invention, even if a silicon oxide fine powder having a center particle size of 1 μm or less is used, a uniform α having a center particle size of 1 μm or less and a spherical shape is obtained.
Type silicon nitride fine powder can be obtained, but the price is nearly 10 times as high as that of silicon oxide powder having a central particle size of 1 to 100 μm, and α type silicon nitride fine powder cannot be obtained at a lower cost. Therefore, the central particle size is 1 to 100μ when viewed industrially.
Coarse particles of m are preferred. Further, when using a silicon oxide powder having a central particle diameter of 100 μm or more, in order to make the mixing with the carbon powder uniform, the mixing time in a ball mill or the like is lengthened, and a crushing effect is expected, It is necessary to pulverize the silicon oxide powder to 100 μm or less with a vibration mill before use. When impurities such as B, Al, and Zn compounds are contained in the silicon oxide powder,
These functions to suppress the reduction nitriding reaction, while V,
Impurities such as Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni and Cu compounds are included as much as possible in the raw material silicon oxide powder in order to easily generate needle-like crystals as well as to generate SiC. It is desirable that it is not.

Therefore, it is desirable to use silicon oxide which does not contain impurities containing these metals in an amount of 0.3% by weight or more as a total amount of each metal element. Examples of such silicon oxide powder include silicic acid anhydride, quartz, cristobalite, quartz glass, and silica gel, but natural quartz powder is most preferably used because it can be obtained at low cost.

Similarly, it is desirable to use carbon powder that does not contain impurities containing the above metals as a total amount of the metal elements in an amount of 0.3% by weight or more. Typical examples thereof are powders such as acetylene black and furnace black. Also, the particle size can be used from several mμ. From a handling point of view, if it can be pulverized during mixing, it is granulated 0.3 to 1.5
It is advantageous to use a granular material having a size of about mm or a granular material which is press-molded.

If the amount of carbon is less than 0.4 parts by weight relative to 1 part by weight of the silicon oxide powder, the reduction nitriding reaction formula 3SiO ₂ + 6C + 2N ₂ → Si ₃ N ₄ + 6CO becomes less than the reaction equivalent and unreacted SiO ₂ remains. On the other hand, if the amount is more than 4 parts by weight, the content of α-type silicon nitride is lowered, unreacted carbon remains in a large amount, the removal thereof is difficult, and the cost is high, which is not preferable.
Therefore, the amount of carbon powder added is preferably 0.4 to 4 parts by weight, more preferably 0.5 to 1.2 parts by weight. As Mg or a compound thereof used in the present invention, metal magnesium, magnesium nitrate, magnesium chloride, magnesium sulfate, magnesium hydroxide, magnesium oxide, magnesium carbonate, basic magnesium carbonate, magnesium isopropoxide, magnesium nitride or the like is used. However, raw powders such as coarse-grained silicon oxide powder and carbon powder are mixed in a wet ball mill by adding water in order to make the mixing more uniform. preferable. When it is insoluble in water, it can be added after being dissolved in an acidic aqueous solution in advance. The substances listed above may be added alone or in combination of two or more.
In terms of the weight of Mg element, it is 0.
It is preferably in the range of 0005 to 0.1 part by weight. 0.0005
Addition of less than 1 part by weight has almost no effect on the promotion of the reduction nitridation reaction and shape control and atomization of the produced α-Si ₃ N ₄ , while on the other hand, over 0.1 part by weight of the produced α-Si ₃ N ₄ Mg in
Is contained in a large amount, which is not preferable as a raw material for a sintered body. A more preferable addition amount is in the range of 0.001 to 0.03 parts by weight. At this time, together with Mg, Be, Sr, Ca, Zr, Ti, H
Metals such as f, Sn, and Ge or compounds thereof may coexist, but it is not preferable that the total amount of each metal element exceeds 0.1 parts by weight.

The silicon nitride fine powder used in the present invention is an α-type silicon nitride fine powder having a BET specific surface area of 15 to 100 m ² / g, and preferably has an α phase content of 90% or more.

If the BET specific surface area is less than 15 m ² / g even for fine particles having a median particle diameter of 1 μm or less, the effect of the present invention will not be exhibited, and the resulting α-type silicon nitride will have a large median particle diameter of 1 μm or more. Needle-shaped crystals and rod-shaped particles are mixed. This phenomenon is particularly remarkable when coarse particles of silicon oxide having a size of 1 μm or more are used as a raw material.

Further, even if the BET specific surface area exceeds 100 m ² / g, the effect is not further improved. On the other hand, manufacturing is difficult and costly,
Since it is industrially disadvantageous, it is preferably 100 m ² / g or less. More preferably, it is in the range of 15 to 50 m ² / g.

Further, when a silicon nitride fine powder having an α-phase content of less than 90% and a large amount of β-phase or Armophas phase is used, the α-phase content of silicon nitride produced becomes low, needle-shaped crystals,
Since the rod-shaped particles are mixed, it is preferable to use silicon nitride fine powder having an α phase content of 90% or more.

The particle size of the α-Si ₃ N ₄ fine powder added in the present invention is usually not more than 1 μm and preferably 0.3 to 0.8 μm.

The α-type silicon nitride fine powder obtained in the present invention has a central particle size of 0.
Even with fine particles of 3 to 0.5 μm, the BET specific surface area is 15 m ² /
Since it is much smaller than g, BET is usually applied to a crusher such as a vibration mill that has a strong impact destructive force (impact value 3G to 15G).
It is preferably obtained by applying until the specific surface area becomes 15 m ² / g or more. It is considered that the BET specific surface area is increased by roughening the particle surface because the particle diameter of the silicon nitride powder having a particle diameter of 1 μm or less hardly changes even when subjected to these pulverizers.

In addition, since a generally used ball mill has a small breaking force, the BET specific surface area hardly increases in about 200 hours.

When crushing, depending on the material of the crusher such as a vibration mill, Al,
Metal impurities such as Fe, Ni and W are mixed. When such a silicon nitride fine powder is used, its effect does not appear remarkably, and needle crystals and rod-shaped particles are mixed in the generated silicon nitride. Such is the case has been adjusted processed BET specific surface area by a pulverizer such as a vibration mill to 15m ² / g~100m ² / g α-
It is preferable to use the Si ₃ N ₄ fine powder after cleaning with a mineral acid containing hydrofluoric acid.

Further, when the particles are crushed, the surface layer of the particles may be covered with the oxide, so that the above washing is preferable in order to remove them.

An appropriate amount of the α-Si ₃ N ₄ fine powder added is 0.005 to 1 part by weight with respect to 1 part by weight of the silicon oxide powder. If the amount of the α-Si ₃ N ₄ fine powder added is less than 0.005 parts by weight, the effect is hardly seen, and only α-Si ₃ N ₄ powder of 1 μm or more mixed with needle-like crystals and rod-shaped particles is obtained. I can't. Further, if the amount is more than 1 part by weight, the additive α-Si ₃ N _{4 is} more than the newly formed α-Si ₃ N _4.
However, the production efficiency is poor, and therefore the more preferred range is 0.005 to 0.1 part by weight.

In the present invention, the above-mentioned raw materials, as a method for uniformly mixing the additives, a known method can be adopted and is not particularly limited, but preferably silicon oxide powder, carbon powder, Mg
Alternatively, the Mg compound and the silicon nitride powder are wet mixed with water.

As a mixing method, a main mixing stage such as a ball mill or a ceramic kneader can be adopted, but it is necessary to select the material so that impurities such as Fe and Al which may be harmful to the reaction are not mixed. Usually, in the case of a ball mill, it is preferable to use balls coated with quartz glass, silicon nitride or plastic, and mix them in a plastic pocket. Further, since carbon powder is generally several hundred mμ or less and has a small specific gravity and is difficult to handle, as described above, particles which are granulated or press-molded to have a particle size of 0.3 to 1.5 mm are used. The method of mixing is preferable.

When the mixing is carried out by a wet method, the mixture is dried, but it is preferable to take measures such as spray drying and a rotary evaporator so that the silicon oxide and the carbon powder and the like are not separated during the drying due to a difference in specific gravity.

The mixture is heat-treated in an atmosphere containing nitrogen and subjected to a reduction nitriding reaction, and the atmosphere is N ₂ , NH ₃ , N ₂
A reaction gas system containing nitrogen such as —H ₂ or N ₂ —Ar can be used. The heat treatment temperature can be selected in the range of 1,400 to 1,600 ° C, preferably 1,450 to 1,550 ° C. If the temperature is lower than 1,400 ° C, it takes a long time for the nitriding reaction to proceed sufficiently.
Above 600 ° C, the amount of SiC produced increases. Including the economical point, it is most suitable to maintain the temperature at 1,450 to 1,550 ° C for 2 to 6 hours. Further, after the reduction nitriding reaction, heat treatment is performed in an oxidizing atmosphere for the purpose of removing the residual excess carbon, and the treatment is generally 600 to 800 ° C.
4 hours is appropriate.

In the method of the present invention, not only the catalytic effect on the reduction nitriding reaction of Mg or its compound, but also the atomization effect by the synergistic action of these substances and the BET specific surface area of 15 to 100 m ² / g α-Si ₃ N ₄ fine powder is expressed. Therefore, even if an inexpensive coarse-grained silicon oxide having a particle size of 1 to 100 μm is used, a uniform α-Si ₃ N ₄ fine powder having a particle size of 1 μm or less and a nearly spherical shape can be easily obtained. The α-Si ₃ N ₄ fine powder obtained by the present invention has the property of being well dispersed in water and an alcohol solvent such as isopropyl alcohol.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to industrially advantageously produce a raw material powder for a silicon nitride sintered body, which is excellent in heat resistance and high temperature strength.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

Example 1 Commercially available quartz sand powder as silicon oxide powder (central particle size: 6 μm)
m, BET specific surface area 1.2 m ² / g), and a commercial acetylene black pressed product was used as carbon powder.

Mg (NO ₃ ) ₂ .6H ₂ O was used as the Mg compound. As the silicon nitride powder, a commercially available α-Si ₃ N ₄ fine powder (LC-12 manufactured by Starck) having a central particle size of 0.5 μm, a BET specific surface area of 17 m ² / g and an α phase content of 96% was used. These powders were mixed in the composition ratios shown in Table 1, water was added, and wet ball mill mixing was performed for 2 hours using a plastic-coated ball and a plastic pot. The obtained slurry-like mixture was dried under heating and reduced pressure while rotating using a rotary evaporator.

The dried mixture was placed in a graphite container and heat-treated at a temperature and a time shown in Table 1 for 4 to 6 hours while flowing N ₂ gas to reduce and nitride SiO ₂ . The obtained powder is further heat-treated in air at 700 ° C. for 4 hours to burn and remove unreacted C.
Si ₃ N ₄ fine powder was obtained.

The average particle size, N content, and α-Si ₃ N ₄ content (obtained from the X-ray diffraction pattern) of each of the Si ₃ N ₄ fine powders thus synthesized were measured, and the values are shown in Table 1. did.

Example 2 Median particle diameter obtained by synthesizing in Example 1 as silicon nitride powder
Powder having 0.5 μm, BET specific surface area of 7 m ² / g, and α phase content of 98% was subjected to wet vibration mill treatment for 75 hours and 100 hours using silicon nitride balls and pots with isopropyl alcohol as a dispersion medium. Using. The silicon nitride powder treated by the wet vibration mill for 75 hours had a central particle size of 0.5 μm, a BET specific surface area of 17 m ² / g, and an α phase content of 96%.

On the other hand, the silicon nitride powder treated by the wet vibration mill for 100 hours has a central particle diameter of 0.5 μm, a BET specific surface area of 21 m ² / g, and an α phase content of 96.
%, And this was designated as silicon nitride powder B.

Using the silicon nitride powders A and B as the silicon nitride powder, the Si ₃ N ₄ powder was synthesized according to the procedure of Example 1. Average particle size, N content, α-Si ₃ N ₄ for each powder
The content is shown in Table 1.

Comparative Example 1 The powder synthesized in Examples 1 and 2 was used as the silicon nitride powder. The powder synthesized in Example 1 has a central particle size of 0.5 μm.
m, a BET specific surface area of 7 m ² / g, and an α phase content of 98% to obtain a silicon nitride powder C. The powder synthesized in Example 2 was designated as silicon nitride powder D having a central particle size of 0.4 μm, a BET specific surface area of 9 m ² / g and an α phase content of 99%.

Using the silicon nitride powders C and D as the silicon nitride powder, the Si ₃ N ₄ powder was synthesized according to the procedure of Example 1. For each powder, average particle size, particle shape, N content,
The α-Si ₃ N ₄ content is shown in Table 1.
Unlike the above, the obtained silicon nitride powder had a large particle size and contained needle crystals.

Example 8 A central particle size of 0.5 synthesized in Example 1 as a silicon nitride powder.
μm, BET specific surface area 7 m ² / g, α phase content 98% powder using isopropyl alcohol as a solvent, using a silicon nitride ball and high alumina pot for 100 hours wet vibration mill treatment to obtain a powder It was

This silicon nitride powder was added to a mixed solution of 50% hydrofluoric acid aqueous solution and 70% nitric acid aqueous solution at a volume ratio of 1: 5 so as to have a concentration of 50 g /, stirred for 1 hour, and then washed and dried powder was used. This powder has a central particle size of 0.5 μm and a BET specific surface area of 22.
m ² / g, α phase content 96%, Al content 0.02%,
This was designated as silicon nitride powder E.

Using silicon nitride powder E as the silicon nitride powder, Si ₃ N ₄ powder was synthesized according to the procedure of Example 1. Table 1 shows the average particle size, N content, and α-Si ₃ N ₄ content of each powder.

Example 4 Commercially available silicic acid anhydride (central particle size: 17 μm) was used as the silicon oxide powder.
m, BET specific surface area 0.3 m ² / g), and acetylene black granular product was used as carbon powder. The compound of Mg is Mg (NO ₃ ) ₂ ·
6H ₂ O, and silicon nitride powder B was used as the silicon nitride powder.

Using these powders, Si ₃ N ₄ powder was synthesized according to the procedure of Example 1, and the average particle size, N content and α-Si ₃ N ₄ content were measured for each powder, and the results are shown in Table 1. .

Example 5 The same powder used in Example 1 was used, except that Mg (OH) ₂ was used as the Mg compound, and Si ₃ N was used according to the procedure of Example 1.
₄ powders were synthesized. Average particle size for each powder, B
Table 1 shows the ET specific surface area, N content, and α-Si ₃ N ₄ content.

Comparative Example 2 Using the same powder as that used in Example 1, no silicon nitride powder was added, no Mg (NO ₃ ) ₂ .6H ₂ O was added, and none of them was added. A Si ₃ N ₄ powder was synthesized according to the procedure described in 1. Average particle size, particle shape, N content, α-Si ₃ N for each powder
_{The 4} contents are shown in Table 1.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the α-type silicon nitride fine powder obtained in Example 1-1, and FIG. 2 is an electron micrograph of the silicon nitride powder obtained in Comparative Example 1-9.

Claims (1)

[Claims] 1. A method for producing silicon nitride by heat-treating a mixture of silicon oxide powder and carbon powder at a high temperature in an atmosphere containing nitrogen, wherein 1 part by weight of silicon oxide powder having a central particle diameter of 1 to 100 μm is used. , 0.4 to 4 parts by weight of carbon powder, 0.0005 to 0.1 parts by weight of at least one selected from Mg and Mg compounds in terms of Mg element weight, BET
0.005 of silicon nitride fine powder having a specific surface area of 15-100 m ² / g
A method for producing an α-type silicon nitride fine powder, characterized in that a mixture obtained by mixing 1 to 1 part by weight is used.