JPS58151310A - Manufacture of silicon nitride - Google Patents

Abstract

PURPOSE:To form fine powder of alpha-type silicon nitride suitable for use in the manufacture of a high strength sintered body of silicon nitride by using a precipitate obtd. by bringing a carbonaceous starting material into contact with a silicic acid soln. as a starting material and heating the precipitate in a nonoxidizing atmosphere contg. nitrogen. CONSTITUTION:A soln. or a liq. dispersion prepared by dissolving or dispersing a carbonaceous starting material such as saccharides or a vinyl polymer in water, alcohol or the like is mixed with a (modified) silicic acid soln. so that about 0.4-5pts.wt. as C of the carbonaceous starting material and about 1 part as SiO2 of silicic acid are contained, and a formed solid precipitate is used as a starting material. The solid precipitate is heat treated at about 1,300-1,600 deg.C in a nonoxidizing atmosphere contg. nitrogen to manufacture fine powder of silicon nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing α-type silicon nitride, and in particular to a method for producing α-type silicon nitride fine powder suitable as a raw material for producing a high-strength silicon nitride sintered body. .

Silicon nitride has excellent heat resistance and high-temperature strength, and is expected to be applied as a sintered body to various high-temperature structural materials such as high-temperature gas turbine components. The thermal and mechanical properties of these sintered bodies largely depend on the properties of the raw materials for the sintered bodies, and silicon nitride that contains as much α-type silicon nitride as possible and has small particle size is desired. .

Methods for synthesizing silicon nitride include (1) a method of nitriding metallic silicon, (11) a method using silicon tetrachloride and ammonia as raw materials,
(iii) A method of reducing and nitriding silica (5i02) powder by heating it together with carbon powder in nitrogen is known.

Among these methods, method Q++) has many industrial advantages, such as inexpensive raw materials, simple and easy reaction operations, and no use of raw materials that may corrode the equipment. be.

However, in the method of (fil), nitriding of the 7-liquor powder does not proceed easily and <<1. Special! Since it is difficult to nitride crystalline silica, it is common to use amorphous powder. However, even when amorphous silica powder with relatively good reactivity is used, amorphous silica powder to which fluoride or silica fluoride is attached is used to increase the reactivity (see Japanese Patent Publication No. 12320/1983). , using special evaporated silica powder (see JP-A-53-75200)
Efforts have been made. However, the addition of heptadide and the like lowers the purity of the silicon nitride produced, and the use of special silica powder has the drawback of being expensive.

Furthermore, the product of the method (Ill) is generally a mixture of α-type silicon nitride, β-type silicon nitride, silicon carbide, etc., and in some cases, unreacted silica, silicon oxynitride, etc. are also mixed in. -22919), there is a drawback that the product has a low content of the target α-type silicon nitride.

It overcomes these drawbacks and has many industrial advantages (Ill.
) Many methods have been proposed so far in an attempt to obtain a product with a high α-type silicon nitride content. For example, metallic silicon (
Japanese Patent Publication No. 52-38500. JP-A-53-137899), silicon nitride, silicon carbide, etc. (see JP-A-54-23)
917 reference, Silicon Nitrogenimide (Japanese Unexamined Patent Publication No. 1983
-126696) Adding a third component or using specific carbon powder (%Kasho 52-90)
499) is disclosed. However, the disclosed method of adding the third component is not economically preferable because the third component is more expensive than the main raw materials silica and carbon, and furthermore, the third component itself has special requirements, e.g. In the case of metallic silicon, ultrafine powder with an average particle size of 0.5μ or less (Japanese Patent Application Laid-Open No. 137899) is required because
This trend is becoming stronger. Furthermore, in the method using a specific carbon powder, the shape of the silicon nitride produced is non-uniform and the particle size is large.

As a result of various studies on industrially advantageous production methods for α-type silicon nitride, the present inventors have found that by treating carbonaceous powder with silicic acid liquid instead of silica powder and using this as the nitriding raw material, a high We first discovered that α-type silicon nitride of high purity could be easily obtained, and filed a patent application (Japanese Patent Application 1984-'11.84).
No. 63.

According to this method, a fine product with a high α-type silicon nitride content can be obtained by simply using a silicic acid liquid instead of silica powder without adding a third component.

However, it is necessary to remove the solvent derived from the silicic acid liquid, and from a practical standpoint, a removal method that is possible and has low energy costs is desired. It is desirable to be able to remove most of it.

The inventors of the present invention have conducted studies to establish a method that is more advantageous for practical application while taking advantage of the advantages of using silicic acid liquid. As a result, they have developed a method in which a carbonaceous raw material and silicic acid liquid are brought into contact and then precipitated. This is the heading that led to the present invention.

That is, the present invention provides a method for obtaining silicon nitride by heating a raw material containing siliceous material and carbonaceous material in a non-oxidizing atmosphere containing nitrogen. This is a method for producing silicon nitride, which is characterized by using a mixture obtained by contacting a solution of a substance with a silicic acid solution or a modified silicic acid solution and precipitating the mixture.

According to the present invention, most of the solvent can be removed by ordinary solid-liquid separation means that do not require heat, such as f-filtration, centrifugation, or press dehydration. The nitriding reaction yields fine silicon nitride with highly uniform particle size.

The detailed description of the present invention refers to St(OH)4 or a dehydrated mesh thereof. Silicic acid can be easily produced by various known methods. For example, using an alkali silicate as a raw material, it can be prepared by acid decomposition of its aqueous solution, electrolytic dialysis, or dealkalization using an ion exchange method, or a method using a silicate ester such as ethyl silicate or a hydrolyzable silicon compound such as a silicon halide as a raw material. It can be easily obtained by methods such as hydrolysis. Economically preferred is a method using an alkali silicate as a raw material.

Furthermore, in the present invention, the modified silicic acid solution refers to a silicic acid solution or silicic acid solution in which at least one selected from the group consisting of ammonium ions, organic amines, and quaternary ammonium ions is dissolved.

The modified silicic acid solution used in the present invention can be easily prepared by various known methods. Industrially preferred is a method in which an aqueous alkali silicate solution is treated with an ion exchange resin that retains ammonium ions, organic amines, or quaternary ammonium ions.

The silicic acid concentration in the silicic acid liquid or modified silicic acid liquid is 5i
02 minutes equivalent: 50% or less, preferably 20% or less, especially 1
5% or less is desirable. High concentrations tend to cause gelation, and gelation makes contact with carbonaceous material uneven, which is not preferable. The lower limit of concentration is determined by economics, but 0.5% by weight
Above, preferably 1% by weight or more, particularly 4% or more.

The amount of modifier such as ammonium ion in the modified silicic acid solution is preferably 4 times the mole or less, usually 2 times the mole or less, relative to the Si in the silicic acid from an economical point of view, but even if it is present in excess, it is technically There is no inconvenience.

Powdered carbon, a powdered carbon precursor, or a solution of a carbon precursor can be used as the carbon material, and by combining these with a silicic acid liquid or a modified silicic acid liquid, high-grade silicon nitride can be easily produced. Obtainable.

Examples of powdered carbon include carbon black and activated carbon.

In the present invention, carbon precursors are substances that generate carbon at high temperatures;
That is, it means an organic substance that becomes a carbonaceous residue when heated to any temperature within the temperature range of 200 to 1500'C, at least in a non-oxidizing atmosphere. For example, starch, cellulose, hemicellulose, pectin, natural cum,
Polysaccharides and their derivatives such as textrin and dextran, oligosaccharides and monosaccharides and their derivatives such as sucrose, maltose and glucose, proteins and their derivatives such as gluten, polyvinyl alcohol, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate There are many types of polymers, such as vinyl polymers and their derivatives, such as polyptagent, copolymers containing these as main components, thermosetting resins such as phenolic resins, and petroleum pitch.

The form of the carbon precursor is preferably a powder or a solution, and a solution is particularly preferred.

In the present invention, a carbon precursor in a solution state means a carbon precursor in a solution or sol state in which the carbon precursor is present as a solute or a dispersoid. Particularly suitable carbon precursors for the present invention are therefore carbon precursors that are in solution or sol, and monosaccharides, oligosaccharides, polysaccharides, vinyl polymers and their derivatives are particularly suitable.

The concentration of the carbon precursor in solution is effective over a wide range, but at high concentrations it may become highly viscous and difficult to handle, and at low concentrations it is economically unfavorable.
80% by weight, preferably 0.5-60% by weight, particularly preferably 1-50% by weight.

As the solvent or dispersion medium for the carbon precursor in solution, any solvent or dispersion medium suitable for the carbon precursor may be used, but particularly preferred are solvents or dispersion media that have a high affinity for silicic acid, such as water, polar organic solvents, etc. Examples include alcohols, ketones, esters, organic acids, amides, sulfoxides, and the like.

The ratio of carbon or carbon precursor to silicic acid liquid or modified silicic acid liquid is calculated by converting the silicic acid content in the silicic acid liquid or modified silicic acid liquid to 5i02, and the ratio of carbon or carbon precursor to 5i021 parts by weight. Of these, 4 to 5 parts by weight, particularly 0.4 to 2 parts by weight, of C00 is preferred.

If C is too small, unreacted 5i02 remains. Even if there is too much C, there is no particular disadvantage, but it is economically unfavorable.

The carbonaceous material is brought into contact with the silicic acid liquid or the modified silicic acid liquid at such a ratio, and various methods such as dipping, impregnation, spraying, coating, kneading, and mixing can be used. In addition, the contact between the carbonaceous material and the silicic acid liquid or the modified silicic acid liquid in the present invention is not a contact in which silicic acid is produced in a system where the carbonaceous material is present, but a silicic acid liquid produced in a separate system. It is something to do. Specifically,
For example, a powder of carbon or a carbon precursor may be made into a fluid state and then a silicic acid solution is sprayed on it, or a powder of carbon or a carbon precursor may be added to a silicic acid solution and mixed by stirring with a high-speed mixer. good. Alternatively, the solution or sol of the carbon precursor may be mixed with the silicic acid liquid, or the carbon precursor may be added to the silicic acid liquid and dissolved and mixed. In other words, carbon or the carbon precursor and the silicic acid liquid may be mixed. It is important to uniformly mix the acid liquid or modified silicic acid liquid. After uniformly mixing the carbon or carbon precursor and the silicic acid liquid or modified silicic acid liquid, the silicic acid or modified silicic acid is added. After precipitation, the solid content and liquid are separated and subjected to reaction.

Precipitation of silicic acid is achieved by adjusting the pH in the presence of ammonium salts,
Various methods can be used, such as adjusting the pH in the presence of a surfactant and using a non-solvent.

Particularly effective precipitation methods for obtaining fine silicon nitride powder include adjusting the pH in the presence of a surfactant and mixing a carbon precursor in solution with a silicic acid solution and precipitating both together. It is.

In addition, separation of the solid content including the generated precipitate and the liquid can be done by filtration,
A conventional solid-liquid separation method such as centrifugation may be used. After separation, it is subjected to a reductive nitriding reaction with or without drying.

The reductive nitriding reaction is carried out in a non-oxidizing atmosphere containing nitrogen at 130
This is carried out by heating to 0 to 1600°C, preferably 1350 to 1550°C. Ammonia can also be used in place of chlorine, methane, and chlorine. Furthermore, an atmosphere consisting of these gases and hydrogen or an inert gas such as helium, argon, or neon can be used, but nitrogen alone is most practical. At temperatures below 1,600°C, the reaction is difficult to occur, and at temperatures above 1,600°C, silicon carbide is slightly produced.

The alpha content of silicon nitride produced by the method of the present invention is at least 80% or more, usually 90% or more.

In addition, the particle size of the silicon nitride produced is small, usually 1.5
When a solution carbon precursor is used and precipitated together with silicic acid, the fineness is particularly fine, reaching 0.5 μ or less.

The present invention will be explained below with reference to Examples. The proportion of α-type crystals in silicon nitride can be determined by X-ray diffraction (α, 2
θ) From the figure, α-type silicon nitride (1・02), (210)
The intensity (I) of the diffraction line and the ([N), (210) diffraction line of β-type silicon nitride was measured and calculated using the following formula. =×100 Example 1 Water Glass No. 3 diluted aqueous solution (concentration: 5i02min 8%) 6
0y- to cation exchange resin Amberlite 200C (H
Raw mold) 6 Column filled with Q7d (diameter 1 tooth x length 9
0 river, glass column with cold outer tube) at a flow rate of 4.5 mA/
Desodium was removed by passing it through sm, and a silicic acid aqueous solution (
Concentration: 5i02min 5% by weight) was obtained.

Carbon black 2? is added to the obtained silicic acid aqueous solution 901? Add 21 parts of ammonium chloride and 1 part with a homogenizer.
After treating for 5 minutes, the pH was adjusted to 7:2 with 2% aqueous ammonia and filtered to obtain a precipitate.

This was heated to 1510° C. for 4 hours in a nitrogen atmosphere to obtain silicon nitride. No formation of by-products such as silicon carbide and silicon oxynitride was observed. The proportion of α-type crystals in silicon nitride was 94%, and the grain size was about 1.2 μm.

Example 2 Nonionic surfactant (NOF, MS-230) 0.3
% solution 101 was added to Carbo/Black 1.81 and mixed, and further 6% silicic acid aqueous solution 301 was added. While stirring well, add 2% ethylenediamine aqueous solution to this.
Neutralized to H7,1 and immediately filtered to obtain a precipitate.

This was reacted in the same manner as in Example 1 to obtain silicon nitride.

The particle size was approximately 0.8μ, the α-type crystal ratio was 95%, and no unreacted S or io2 remained.

Example A filtered water glass No. 3 diluted solution (Si02: 7.5%) was treated with 7% aqueous ammonia and passed through a column of ion exchange resin Amberly (IRC50) washed with water to obtain a modified silicic acid solution.

Using this modified silicic acid solution and ammonium alginate, ammonium alginate 3.5%-silicic acid (5i0
2 (1.5%) mixed aqueous solution was prepared.

This was mixed with 2% HCQ-10% NH while stirring vigorously.
It was added to an ACQ aqueous solution to obtain a finely powdered coagulum, which was washed with water and then reacted at 1500°C for 5 hours + N2 flow.

The obtained silicon nitride had a grain size of 0.3 μm and an α type crystal ratio of 96%.

Example 4 The ammonium alginate/silicic acid mixed aqueous solution used in Example 3 was dropped into boiling isopropyl alcohol to obtain a precipitate. This was heated at 1510℃ under N2 flow.
, 4 hours of reaction. The obtained silicon nitride has a particle size of 1
．． The proportion of 1 μ and α type crystals was 92%.

Applicant Asahi Dow Co., Ltd. Agent Yutaka 1) Yoshio

Claims (1)

[Claims] 1) A method for obtaining silicon nitride by heating a raw material containing siliceous material and carbonaceous material in a non-oxidizing atmosphere containing nitrogen, in which carbon or a powder of a carbon precursor, or a solution of a carbon precursor is used as a raw material. A method for producing silicon nitride, characterized by using a mixture obtained by contacting with an acid solution or a modified silicic acid solution and then precipitation.