JPS60141698A - Manufacture of silicon carbide whisker - Google Patents

Abstract

PURPOSE:To obtain a high-quality whisker in good yield by introducing a powdery silicon material, a carbonaceous material, and a catalyst into a reaction vessel along with hydrochloric acid, and allowing to react at a specified temp. CONSTITUTION:A mixture of a powdery silicon material such as SiO2 and Si3N4, a carbonaceous material such as carbon black and powdered activated carbon, and a finely powdered catalyst such as Fe, Ni, and Co is packed uniformly into a reaction vessel. Then the nonoxidative atmosphere is formed by introducing gaseous nitrogen, etc., and the temp. in the vessel is increased to 1,350-1,600 deg.C. Gaseous hydrogen chloride or chlorine is mixed with the nonoxidative gas, and introduced into the vessel to carry out the reaction. The reaction product is introduced into a muffle furnace, etc., and heated to oxidized and burn the unreacted carbonaceous material. The desired silicon carbide whisker is obtained in this way. The yield and purity of the whisker can be increased by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing charcoal and arsenic whiskers, and particularly provides a method for producing high-quality whiskers with good yield.High quality here refers to fiber diameter. This means that the fibers are thin, have long fibers, have no bends or branches in appearance, and are free of impurities. Also, the whisker yield refers to the raw material silicon [
This refers to the ratio of silicon carbide whiskers produced in arsenic compounds (based on silicon).

Methods for producing silicon carbide whiskers can be broadly classified into vapor phase growth methods and base growth methods. In the former method, a solid or liquid starting material is once brought into a gaseous state in a high-temperature reaction system at a constant temperature, or a gaseous starting material is fed into the reaction system from the beginning, and the charcoal is produced in the system. This is a method of synthesizing arsenic in a whisker-free manner, and the latter is a method in which silicon-based and carbon solid raw materials are placed on a 90-degree substrate and whiskers are grown in that place. The former has a cross-sectional diameter of several microns in terms of shape and a length of several micrometers, so that so-called "wool-like" whiskers can be obtained, but the yield is low and there are problems in terms of productivity from an industrial production standpoint. In some cases, compounds other than silicon carbide may adhere to and form on the whiskers as impurities, which may require reed treatment.

The latter is characterized by a high yield, but its fiber length is short so that it has a 6-fold appearance, and it is often difficult to separate from the starting material due to bending and branching.

It is most preferable to produce high-quality exposed silicon whiskers that are elongated, have large aspect pores, and have a good yield using a base growth method similar to that obtained using a vapor phase growth method. As an example of technology in that direction, JP-A-57
There are methods described in 209813, 58-125/+97 and 58-145700, but these methods use silicon raw materials such as ash and silica gel, and carbon black. The system is characterized in that it uses a mixture of carbon sources as the main raw material, mixed with a catalyst for the purpose of promoting the reaction and an alkali metal halide represented by Na0Il for the purpose of flux effect. However, in terms of results, these methods are no more than base growth methods, and high-quality whiskers that are elongated and have large aspect pores cannot be obtained.

The present inventors have completed the present invention by conducting intensive studies on a method for producing the desired high-quality reproducible silicon whiskers in a high yield based on a completely different growth method. reached.

In the method of the present invention, a mixture of a powdered silicon raw material, a carbon raw material, and a catalyst is uniformly filled into a reaction vessel, and chlorinated hydrogen or chlorine gas is mixed and introduced in the presence of a non-acid [arsenic gas] at a temperature of 1350 to 1600°C. It is characterized by causing a reaction.

That is, the method of the present invention is based on a solid raw material consisting of a silicon raw material containing 5102 as a main component and a powdered carbon raw material, and an acid (from any of iron, nickel, and cobalt, typified by arsenate). Finely powdered metals or their supermetallic acid compounds are used as catalysts as reaction accelerators, and salt 1, arsenic or chlorine gas is used as a carrier gas and non-acid specificity is used as a reaction accelerator. It is possible to flow into the reaction system together with at least one gas such as hydrogen, nitrogen, argon, and helium.

In this case, a silicon raw material containing SiO2 as the main component and a solid raw material such as powdered carbon are mixed with an acid (a catalyst represented by arsenate), and a carrier gas consisting of a non-oxidizing gas is passed through.
However, in this reaction system, a gear 1.1
They discovered that when hydrogen chloride or d-chlorine gas is mixed and introduced with Yagas, the fiber length of the whiskers produced becomes longer and the generation rate becomes faster.

In principle, the base growth method generates whiskers according to the following unreacted results. That is, 51o2+c −+ sio + a.

SiO+20 -* SiO+ C0 By introducing salt (arsenic or chlorine gas) into this system, the arsenic silicon compound can be generated rapidly and in large quantities, resulting in an improvement over conventional substrate growth methods. As the fiber length of the whiskers becomes longer, they are formed within a shorter period of time.

The method of the present invention will be explained in more detail below.

The silicon raw materials used in the method of the present invention are 5i02, 5i5N
The shape of the peaks is preferably fine powder in any case. Examples of 5i02 include silica powder, powdered silica gel, rice husk ash, and precipitated silica.

Carbon black and powdered activated carbon can be used as the powdered carbon raw material, but carbon black is preferable because it is finer and has higher reactivity as the bulkier raw material.

As the catalyst used as a reaction accelerator, metals such as iron, nickel, and cobalt, or acids of these metals (arsenic powder) are used.

The above-mentioned three components, the fine powder silicon raw material, the carbon raw material, and the catalyst, are thoroughly and uniformly mixed and used, and the ratio of the carbon raw material to the silicon raw material is 100 to 400 parts per 100 parts by weight. All percentages are by weight unless otherwise specified.) In this case, if the amount of carbon raw material used is 100 parts or less, the silicon raw material will not be converted to coal-based silicon after the reaction under 9 constant conditions;
Both cases are unfavorable because the amount of unreacted and residual materials increases, and if the amount exceeds 400 parts, the amount of carbon raw materials that do not participate in the reaction increases.

The amount of catalyst used is usually 0.05 to 20 parts per 100 parts of silicon raw material, and if the amount is less than 0.05 parts, whisker formation is insufficient due to lack of catalytic efficacy, and unreacted remains after the reaction under the treatment conditions. A large amount of the silicon raw material remains, and even if 20 parts or more of the catalyst powder is used, the catalyst powder tends to remain in the generated whiskers, making subsequent purification of the generated whiskers complicated.

When the reaction vessel of the present invention is small-scale, a mullite ring, an alumina porcelain tube, or a graphite pipe is usually used, and when the scale is expanded, a box-shaped vessel made of these ceramic materials is used.

The firing temperature in the present invention is at least 1350°C or higher, 1
Below 600°C, preferably above 1400°C, 1550°C
The temperature range is 1450 to 1500°C, most preferably 1450 to 1500°C. At temperatures below 1350°C, whisker formation is insufficient and a large amount of unreacted silicon raw material remains;
If the temperature exceeds 0°C, the reaction conditions become extreme, and the fiber diameter of the whiskers increases.
<Jr. Although any heating means may be used, an electric heating system is easily used.

In the method of the present invention, it is essential to use hydrogen chloride or chlorine gas as a reaction accelerator; For every 100 parts of salt, add 5 to 50 parts of arsenic or chlorine gas. In this case, the amount is preferably 1 to 20 parts, more preferably 3 to 15 parts. However, the mixed gas is 10 to 1000 mf
Preferably from 30 to 500 with a flow rate of f/min
It is introduced into the reaction system at a rate of mA/min.

If the mixing ratio of hydrogen chloride or chlorine gas is less than 0.5 parts, the effect of promoting the reaction in substrate growth tends to be poor. On the other hand, when the mixing ratio exceeds 50 parts, the reaction between the silicon raw material and the gas becomes dominant, and the generation of whiskers tends to decrease.

The reaction time in the method of the present invention is usually from 30 minutes to 4 hours, but if it is less than 50 minutes, unreacted silicon raw materials tend to remain.
Further, a reaction time exceeding 4 hours is meaningless, and a reaction time of 1 to 2 hours is particularly preferred.

The powder mixture of the silicon raw material, carbon raw material, and catalyst according to the present invention can be normally dispersed and filled directly into the reaction tube or filled into the reaction system by being spread on a porcelain or graphite plate. However, it is desirable to uniformly fill the gas to ensure sufficient contact with the reaction accelerator, i.e., arsenic or chlorine gas.

When hydrogen is used as a carrier gas, the reaction system is first sufficiently purged with an inert gas such as nitrogen, argon, or helium, and then a mixed gas of hydrogen and a reaction accelerator, a salt of arsenic or chlorine, is added. The mixed gas is introduced and heated to proceed with the reaction, and after 9 fixed hours have elapsed, the introduction of the mixed gas is stopped, and then the introduction of an inert gas is resumed. After replacing the gas in the system, the reaction product is taken out. The reaction product is usually 700 to 800
The material is placed in a Matsufuru furnace heated by CK, and the remaining unreacted carbon material is incinerated with an acid ratio to obtain the desired silicon carbide whiskers. When removing the reaction product from the reaction vessel,
Normally, a bulky and desired whisker product is formed at the bottom of the silicon raw material, and in the reaction under the treatment conditions related to the method of the present invention, there is almost no unreacted silicon raw material remaining at the bottom. Even if a small amount exists, it can be easily separated from the product due to its poor shape.
Another feature of the method of the present invention is that 121 can be simply separated. The whiskers obtained by the above-mentioned incineration treatment after separation are made of silicon carbide with almost no impurities, but if F# product is required, the whiskers obtained are usually
It is immersed in dihydrofluoric acid and heated at room temperature or 70 to 80'C to dissolve silicon f arsenide other than silicon carbide, and then purified by washing with water.

In the case of the method of the present invention, the yield of silicon whiskers is 85 to 100% due to charcoal based on silicon as a silicon raw material, and compared to the case where salt 1 arsenic or chlorine gas as a reaction accelerator is not used. It has the great advantage of achieving high values for both purity and yield.

Furthermore, when the method of the present invention is used, the bulk density of the resulting whiskers tends to be smaller than when the reaction accelerator salt 1 arsenide or chlorine gas is not used under the same conditions. That is, 0.15 to 0.2 g/c when no reaction accelerator is used.
j, whereas in the powder method it is 0.1-0.15g/
− Bulky whiskers are obtained. Comparing this with the whisker fiber diameter, fiber length, and aspect ratio, in the control method under the former condition, the values are 0.5 to 1μ, 50 to 100μ, and 5μ, respectively.
0 to 100, when the latter condition is involved in the method of the present invention, it is 0.5 to 1μ, 100 to 500μ, 100 to
500, the morphological characteristics of this manufacturing method are obvious.

When producing whiskers and using them as reinforcing agents for metals, ceramics, and plastics, it is important to use strong additives that are as cheap as possible, and as long as they can be composited using conventional molding methods. Although whiskers are more preferable, the method of the present invention has the greatest feature in that it is a manufacturing method that achieves just that.

The present invention will be described in detail below based on Examples.

Example 1 After thoroughly mixing and dispersing 5 g of precipitated silica with an average particle size of 5 to 10 μm, 5 g of powdered acid Arsenic Q, 05 g and 10 g of Carpon Thick (Keg Yun Black EC manufactured by Lion Oil Co., Ltd.), an outer diameter of 65 MX was prepared. It was evenly distributed and filled in the center of an alumina tube with an inner diameter of 60 mm and a length of 1000 mm, and then inserted into a siliconite electric furnace.
5℃/mi after placing 4 people in the tube for 1 hour at a flow rate of /ml1m
The furnace was heated at a heating rate of n until the temperature at the center of the furnace reached 1480°C. Stop the nitrogen gas supply while the internal temperature reaches 1000°C, then add 5 m2/min of salt] arsenic and 50 m2/min of hydrogen.
The mixture was introduced into the reaction tube while being mixed at a flow rate of n+fi/min, and the temperature inside the tube was maintained at 1480° C. for 90 minutes. Next, the introduction of arsenic and hydrogen was stopped while the temperature was gradually lowered, the inside of the reaction tube was switched to nitrogen gas, and the contents were taken out. The contents were a bulky, lightweight mass with black edges, and no unreacted silica was observed in the area in contact with the alumina tube.

This lump was fired in a Matsufuru furnace at 800° C. for 3 hours, resulting in 3.3 g of charcoal (arsenic whiskers).

It was 99cm as a pickup truck based on silicon, which is a silica raw material. After immersing this material in 46-hydrofluoric acid at 40°C for 70 hours, thoroughly washing it with water and drying it, the purified product was 95%
It was Chi. The shape of the obtained whiskers has no branches or bends, and the fiber diameter, fiber length, and aspect ratio are
Q, 5-I It, 100-400. c+, 20
0-400, bulk density is Q, 129/eII! Met.

Comparative Example 1 The reaction was carried out under the same conditions as in Example 1 except that no salt (arsenic) was used and only hydrogen was introduced as a carrier gas at a flow rate of 53 mIt/win. After the reaction was completed, the lumpy reaction product was taken out, and unreacted silica in the form of white powder was observed in the area in contact with the alumina tube. The lumps from which the powder was separated were fired under the same conditions as in Example 1 to obtain 2.8 g of new coal (as arsenic whiskers). This amount was 65 yen based on the silicon of the silica raw material used. This product was further purified with hydrofluoric acid under the same conditions as in Example 1, resulting in a purification yield of 71. The shape of the obtained whiskers was such that the fiber diameter, fiber length, and aspect ratio were 0.5 to 1 μ, 40 to 80 μ, and 80 to 150, and the bulk density was 0.2 g/cd.

Example 2 Fine iron powder llL01 on silicon nitride powder 5p with an average diameter of 10μ
g and 5 g of the carbon black used in Example 1 were added and mixed well.

Next, an alumina flat plate of 5 (INL

In this state, a mixed gas of 80 mN/m1n of SC gas and rtrN/min of Ji hydrogen gas was introduced into the reaction tube.
The temperature was externally heated to 1480° C. at the same temperature increase rate as in Example 1, and the temperature was maintained for 120 minutes. Next, the introduction of chlorine gas was stopped, and while only nitrogen gas was allowed to flow, the temperature was lowered, and then the contents were taken out.

The contents were a dark green, bulky cake with white powder adhered to the surface in contact with the alumina flat plate.

The cake-like material excluding the white powder was baked in a Matsufuru furnace at 700°C for 4 hours, resulting in a silicon carbide whisker of 2.4
g was obtained. This was achieved by a 93-chi model based on the silicon-based arsenic raw material used. This product was soaked in 46-hydrofluoric acid at 70° C. for 24 hours, thoroughly washed with water, and dried, and the so-called yield was 90e6. The resulting whisker shape had no bending, and the bulk density was 0.1 g/Ci.

Comparative Example 2 Under the reaction conditions of Example 2, all chlorine gas (no use,
All experiments were conducted under the same conditions except that only nitrogen was introduced as a gear+1 gas at a flow rate of 84 mA/min.

When the reaction product in the form of a lump was removed after the reaction was completed, a layer of white powder remained in the area in contact with the alumina flat plate.

New coal (0.72y as arsenic whiskers) was obtained by burning the lumps from which the layered residue was removed under the same conditions as in Example 2. This material was further treated with hydrofluoric acid under the same conditions as in Example 2, and the f1M yield was l-1:544.The bulk density of the obtained whiskers was α24 g/-. .

Example 3 Finely powdered metal silicon 10FK acid ratio nickel powder a5g and carbon black 25.9 were thoroughly mixed to form Example 1
It was evenly distributed and filled in the center of the alumina porcelain tube used in , and then inserted into a tubular electric furnace. Then add nitrogen gas for 10
After introducing it into the tube for 1 hour at a flow rate of 0 yJ/min, the center temperature of the furnace reached 1500°C under the same temperature increase rate as in Example 1.
It was heated until it was. After the internal temperature reaches 500℃, reduce the flow rate of nitrogen gas to 10 mQ/rn1nIC and add 2 m+j of salt 1 arsenic! /min and hydrogen at 50 m
The six gases were introduced into the reaction tube while being mixed at a flow rate of fl/min, and the reaction tube temperature was maintained at 1500° C. for 1\60 minutes. Next, while gradually lowering the temperature, the introduction of salt 1 arsenic and hydrogen was stopped, and only nitrogen gas was introduced at 1 [10 rJ! /min
After all the gas in the tube was replaced with nitrogen, the contents were taken out.

Claims (5)

[Claims] (1) Mixing of powdered silicon raw material, carbon raw material and catalyst
Fill the reaction container uniformly, and in the presence of non-acidic arsenic gas,
A method for producing silicon carbide whiskers, which comprises introducing a mixture of salt (arsenic or chlorine gas) and reacting at a temperature of 1350 to 1600°C. (2) The method according to claim 1, wherein the silicon raw material is 5i02, Si3N4, or metallic silicon. (3) The method according to claim 1, wherein the carbon raw material is carbon black or powdered activated carbon. (4) The method according to claim 1, wherein the catalyst is a finely powdered metal of iron, nickel, or cobalt, or an oxide of these metals. (5) The method according to claim 1, wherein the non-oxidizing gas is hydrogen, nitrogen, helium or argon.