JPH01301596A - Production of silicon nitride whisker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing silicon nitride whiskers, and more particularly to a method for producing silicon nitride whiskers with high quality and high yield.

(Prior art and its problems) Silicon nitride whiskers have excellent performance that other composite material fibers do not have in terms of specific strength, specific elasticity, heat resistance, oxidation resistance, and chemical stability. Because it has good wettability with various metals, it is attracting attention as a reinforcing material for composite materials such as ceramics, metals, and plastics.

However, in order for silicon nitride whiskers to exhibit excellent performance as a composite reinforcing material, in addition to the shape characteristics such as whisker diameter and length, the content of metal impurities contained in the whiskers, unreacted silica content, and powder Less is required.

In general, methods for producing silicon nitride whiskers include a gas-phase synthesis method in which a mixture of a carbon-containing raw material and a silicon-containing raw material is reacted in a gaseous state at high temperature, and a solid-state synthesis method in which a solid is used as both the carbon-containing raw material and the silicon-containing raw material. It is broadly divided into phase synthesis method.

However, conventionally known gas phase synthesis methods have the advantages of high purity raw materials and the ease with which whiskers with high aspect ratios can be obtained, but the design of reactors and product recovery are complicated and yields are low. It has the disadvantage that it is low and is not suitable as an industrial manufacturing method. On the other hand, in the solid-phase synthesis method, silica and carbon are mixed and heated to generate whiskers mainly between the powders, making it easy to recover and serialize the product, but the shape of the whiskers is irregular. It has the drawback that powdery or curved silicon nitride is likely to be produced, and unreacted silica is difficult to remove.

Therefore, various manufacturing techniques have been proposed to obtain high-yield and high-quality silicon nitride whiskers.

For example, JP-A-57-17500. Japanese Patent Publication No. 58-172
298, the raw material (silicon source) is selected, or JP-A-61-205699. As in JP-A-59-147000, there are many methods in which a catalyst (transition metal) and a third component are added and various reaction conditions are combined.

However, these production methods have not been industrially advantageous due to limitations in raw materials, workability and reaction operability, and the need for post-treatment due to the large amount of third components added. .

(Means and effects for solving the problem) The present inventor:
As a result of intensive research to solve the above-mentioned problems in the production of conventional silicon nitride whiskers, a transition metal element-containing hydrolysis product was obtained by adding transition metals and their compounds to silicon alkoxide and hydrolyzing it. The present invention was based on the discovery that powdery or curved silicon nitride whiskers can be obtained at high yields by using as a raw material.

That is, a silicon alkoxide is hydrolyzed in the coexistence of a trace amount of a transition metal or its compound, and the obtained hydrolysis product containing a trace amount of a transition metal or its compound is mixed with a carbon source, and then the hydrogen concentration is O~ It is characterized by heating at a temperature of 1,300 to 1,600°C in a nitrogen atmosphere of 50χ.

In the present invention, the product obtained by hydrolyzing a silicon alkoxide uniformly containing trace amounts of the above-mentioned transition metal elements is
This is achieved by mixing a trace amount of a transition metal or its compound when hydrolyzing a silicon alkoxide.

In the hydrolyzed product obtained by this method, the transition metal element that serves as a catalyst during crystallization is finely and uniformly dispersed in the silicon compound, and the amount of catalyst is small compared to a simple impregnation operation. Effectively promotes crystal growth of silicon nitride whiskers and improves yield. Moreover, by carrying out the crystallization reaction in a hydrogen-containing atmosphere, the effect is further enhanced, and the grain content is reduced and the shape becomes uniform with excellent linearity.

The generation of whiskers is presumed to proceed by the VLS mechanism, and the catalyst component, which is uniformly dispersed in a fine state inside and on the surface of the silicon compound, becomes SiO2 when heated.
It is easy to form a solid solution in
It is thought that gaseous silicon compounds and carbon compounds such as , GO, etc. are dissolved, and when the saturation concentration is exceeded, they are precipitated as 5iJ4 whiskers.

The method of adding catalyst components as in the present invention facilitates the creation of extremely effective growth active points (droplets) in the VLS mechanism, and the coexistence of hydrogen promotes the production of gaseous silicon compounds and carbon compounds. It is thought that this synergistic effect significantly promotes the production of silicon nitride whiskers with excellent properties.

The whiskers obtained by such a method have a small amount of added catalyst, so the amount remaining in the product is small, and the yield is high, so it contains almost no unreacted SiO□.

In terms of shape, it contains almost no particulate matter and is uniform in a straight line, so it does not require separation and classification operations and can be a high-quality product.

The alkoxide used in the present invention is not particularly limited as long as it can be easily produced by hand, but it is generally an aliphatic alkoxide, preferably a 01-C4 alkoxide such as methoxide, ethoxide, propoxide, butoxide, etc. It is.

Specific examples include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. These alkoxides can be used alone or as a mixture of two or more. In addition, oligomers such as dimers, trimers, and tetramers of these alkoxides can also be suitably used.

In the method of the present invention, the alkoxides are treated with Fe, Co, Ni, or C, which is a catalyst component in the crystallization reaction.
The hydrolysis is carried out in the coexistence of the transition metal r or its compound, and the transition metal compounds used include oxides, chlorides, nitrates, carbonates, and sulfates of the above metals.

Among these compounds, Fe1Co +
Water-soluble compounds such as Ni chlorides and nitrates are more preferred.

The hydrolysis may be carried out by dissolving or uniformly dispersing the catalyst component in the amount of water required to hydrolyze the silicon alkoxy compound, and then mixing the catalyst component with the silicon alkoxide compound. In order to proceed with a homogeneous hydrolysis reaction, it is preferable to suppress the amount of water to a minimum, and add alcohols as necessary to prevent separation into two layers, so as to conduct the reaction in a homogeneous solution state.

Furthermore, in order to control the reaction rate, volatile bases or acids can be added or the hydrolysis reaction can be allowed to proceed while heating, but care must be taken to prevent local reactions from occurring.

After the reaction is completed, the resulting hydrolyzed product is dried and pulverized to 150 mesh or less.

When carrying out the present invention, the amount of catalyst is 0.002 to 0 as the amount of metal element relative to the silicon content in the hydrolysis product.
．． It is prepared to have a proportion of 5% by weight, but if this content is less than 0.002% by weight, the effect will be small, and if it exceeds 0.5% by weight, the desired effect will no longer be obtained and the purity of the product will decrease. This is not desirable.

Next, the hydrolysis product containing the transition metal element obtained in this manner and a carbon source are mixed.

As this carbon source, carbon such as carbon black or powdered activated carbon that is commonly used in this type of reaction can be used, but carbon black such as acetylene black or furnace black is preferable.

The carbon source is mixed in a kneader or mixer at a ratio of carbon to silicon content in the hydrolysis product, C/5i = 2 to 4, and the bulk density of the mixture is 0.02 to 0.02. 2g
It is preferable to prepare it so that it becomes /cc.

A lower bulk density forms an effective growth space for developing needle-like crystals and promotes linear whisker growth.

If the amount of carbon is small, unreacted silicon oxide remains,
Moreover, if there is a large amount, the burden of post-processing increases and it is not economical.

The mixture of carbon sources was packed in a carbon container in a low bulk density state, and heated to 1300 to 16 ml under a nitrogen atmosphere containing hydrogen.
The reaction is carried out by heating at a temperature of 00°C. At this time, hydrogen concentration is used at 50% or less. Also, the heating temperature is 1300°
If the temperature is lower than 1600°C, this reaction will not substantially proceed.
This is undesirable and undesirable because the diameter of the whiskers higher than C becomes thicker and fusion of the whiskers occurs.

If excess carbon remains after the reaction, it may be burned off in air at 600 to 800°C.

The silicon nitride whiskers thus obtained are of high purity, containing almost no unreacted SiO2 and a small amount of heavy metals. In addition, the aspect ratio is in the range of 20 to 200,
It is a straight whisker with a diameter of 0.2 to 2.0 um and is of high quality containing almost no particulate silicon nitride.

(Effects of the Invention) As described above, the present invention achieves a high yield by mixing a silicon alkoxide hydrolysis product uniformly containing a trace amount of a catalyst component with a carbon source and heating the mixture in a hydrogen-containing atmosphere. High quality silicon nitride whiskers can be obtained.

Moreover, the products according to the invention can be used as high-performance composite reinforcements without the need for cumbersome post-treatments such as the removal of particulate silicon nitride, unreacted 5iOz, and heavy metals.

Examples of the present invention are shown below.

Example 1 Cobal chloride (COCl2) 0 was added to a solution of 152 g of tetramethoxysilane and 64 g of methanol.
．． 72 g of water in which 0.015 g of 0.015 g was dissolved was added to react, and a transparent hydrolysis product was obtained.

After drying the obtained hydrolysis product and pulverizing it to less than 150 mesh, 40g of carbon black of 0.03g/cc was added.
was added and mixed again to obtain a mixed raw material with a bulk density of 0.07 g/cc. After filling the mixed raw material into a carbon container, it was heated at 1450″C for 4 hours in a nitrogen gas atmosphere with a hydrogen gas concentration of 10χ.
r reacted. Next, the remaining carbon black was heated to 70%
It was burnt off for lhr at 0°C.

The obtained silicon nitride whiskers had a diameter of 1.0 μm.

It is a straight whisker with an aspect ratio of about 100,
Grain powder equinox was less than 3%.

In addition, oxygen concentration 1.0χ, Co 80ppm, Fe
, other heavy metal impurity types such as Ni+ Cr+Ca are 5
It was 0 ppm or less.

Example 2: Iron chloride (FeCls) 0.0 instead of cobalt chloride.
Silicon nitride whiskers were synthesized in the same manner as in Example 1 except that 019g was used.

The obtained silicon nitride whiskers had a diameter of 1.0 μm.

It is a straight whisker with an aspect ratio of about 100,
Grain powder equinox was less than 5%.

In addition, oxygen concentration 1.2χ + Fe 1100pp,
Co, Ni+Cr.

The amount of other heavy metal impurities such as Ca was 50 ppm or less.

Comparative Example 60 g of silica gel with a weight of 1°150 mesh or less was immersed in an aqueous solution containing 0.1 g of cobalt chloride (CoC1z), and after it had penetrated sufficiently, it was heated and dried to obtain a silica gel with a Co element content of 0.24 weight 2 based on the silicon content. Prepared.

40 g of the carbon blank used in Example 1 was mixed with the silica gel, and silicon nitride whiskers were produced under the same crystallization conditions as in Example 1.

The resulting silicon nitride whiskers contain unreacted SiO
2 was as high as 10χ, and the granular silicon nitride was also as large as 30χ.

Procedural amendment (voluntary) July 25, 1986

Claims (3)

[Claims] (1) Adding a transition metal or its compound to silicon alkoxide and hydrolyzing it, mixing the resulting transition metal element-containing hydrolysis product with a carbon source, and then heat-treating in a nitrogen atmosphere containing hydrogen. A method for producing silicon nitride whiskers characterized by: (2) The transition metal or its compound is Fe, Co, Ni
, Cr, or their compounds, and the amount of the transition metal element is adjusted to 0.002 to 0.5% by weight based on the silicon content in the hydrolysis product. Method of manufacturing silicon nitride whiskers. (3) The method for producing silicon nitride whiskers according to claim 1, wherein the nitrogen atmosphere containing hydrogen is a mixed flow of nitrogen gas and hydrogen gas containing 50% or less hydrogen.