JPH01197400A - Production of sic whisker - Google Patents

Abstract

PURPOSE:To obtain the title high-grade SiC whisker having excellent straightness in good yield by supplying nitrogen as the atmospheric gas at a specified flow velocity while avoiding its contact with a reaction heating zone, and heating the continuously supplied raw materials at a specified temp. increasing rate. CONSTITUTION:A mixture of the silicon source contg. SiO2 such as quartz sand and silica gel, the carbon source such as graphite powder, and a catalyst of the water-soluble compd. of Fe, Ni, Co, etc., are continuously supplied onto a belt conveyor 3 in a reaction furnace 1 from a feeder 6, and gaseous N2 is introduced over an N2 current zone separating plate 4 provided in the furnace at the flow velocity of <=10cm/min. The loaded condition of a heater part 2 and the velocity of the belt conveyor are controlled to set the temp. increasing rate at >=10 deg.C/min in the temp. range 1200-1400 deg.C at which Si reacts with N2 in the reaction heating zone A. The reaction zone is then kept at the reaction temp. of 1500-1700 deg.C to form SiC whisker.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing SiC whiskers useful as composite reinforcing materials for metals, plastics, ceramics, etc. The present invention relates to a method for producing the product with good yield.

(Prior art) SiC whisker manufacturing technology can be broadly divided into methods using gas-phase raw materials and methods using solid-phase raw materials, but the former gas-phase method uses expensive raw materials and has poor yields. This method has not been established as a production method at present because there are problems and it is difficult to make the process continuous due to handling issues.

On the other hand, in addition to the batch method using a fixed furnace, continuous manufacturing techniques have also been proposed for the solid phase method. For example, a method of filling a closed reaction container such as a crucible with a raw material and moving it sequentially and continuously in a heating furnace, or a method of continuously supplying a raw material to an open reaction heating zone equipped with a rotating bed mechanism ( Japanese Patent Publication No. 58-502096> is known and is recognized to be superior in practicality compared to the gas phase method.

[Problem to be solved by the invention]

Among the continuous manufacturing technologies using the solid-phase method mentioned above, there is a method using a closed reaction container such as a crucible (hereinafter referred to as "closed system").
A method using an open reaction heating zone (hereinafter referred to as "open system") is more advantageous in terms of continuous production in terms of equipment and process. However, in an open system, the properties and production yield of SiC whiskers obtained may deteriorate due to the influence of atmospheric gas.

Normally, the generation of SiC whiskers requires keeping the reaction environment in a non-oxidizing or reducing atmosphere, and for this purpose, N2, Ar, and Co are added to the reactor.

Measures have been taken to introduce gas such as H2.

At this time, in a closed system, the interior of the reaction vessel such as a crucible is filled with the reaction product gas, so it is not affected by the introduced gas components, but in an open system, the introduced gas comes into contact with the reaction heating zone. This is accompanied by phenomena such as inhibition of SiC whisker generation and loss of straightness.

It has been confirmed that this phenomenon occurs particularly when N2 gas is introduced into the furnace.

N2 is optimal as a gas component for maintaining the furnace atmosphere in terms of handling, price, etc., and if the above problems are solved, the continuous production method of SiC whiskers using an open system will be greatly improved.

[Means to solve the problem]

As a result of extensive research into the adverse effects of atmospheric gases that occur in open systems, the inventor found that the cause of this is that the equilibrium state of the reaction product gas generated from the raw materials is disturbed by the atmospheric gas, which leads to the growth of the whiskers that are precipitated by the reaction. If you know that it is having an adverse effect and are in a N2 gas atmosphere,
In addition to the above-mentioned effects, it has been found that N2 gas causes a preliminary reaction with the Si component of the raw materials in the reaction heating zone, which adversely affects the growth of whiskers, leading to the present invention.

That is, the method for producing SiC whiskers according to the present invention is a method of producing SiC whiskers by continuously supplying a raw material consisting of a silicon source material, a carbonaceous material, and a catalyst to an open reaction heating zone (1500 to 17006 C). In this step, N2 gas used as an atmospheric gas was introduced at a flow rate of 10 cm/min or less without contacting the reaction heating zone, and a heating step of 1200 to 1400°C was performed.
A structural feature is that the temperature increase rate is set to 0° C./min or more.

For example, a reactor (1) as shown in the figure is used as an apparatus for continuous production of SiC whiskers in an open system, but the first requirement of the present invention is a means for introducing N2 gas without contacting the reaction heating zone. is part of the heater (2)
A N2 region separation plate (4) is interposed on the upper surface of the reaction heating zone (A), which is divided by a belt conveyor (3), so that the N2 gas introduced into the furnace does not come into contact with the reaction heating zone (A). Designed to be discharged outside the furnace.

However, in the case of an open system, it is not possible to maintain a state in which the reaction heating zone (A) is always filled with the reaction product gas, so the above-mentioned first requirement alone cannot completely eliminate the adverse effects of the N2 atmosphere. I can't.

As a solution to this, the third requirement is to set the heating stage of 1200 to 1400"C at a rapid temperature increase rate of 10°C/min or more. Also, the equilibrium state of the reaction product gas is In order to maintain stability, the second requirement is to set the flow rate of N2 gas in the reactor to 10 am/min or less.

By applying the above three requirements, the generation of SiC whiskers can proceed smoothly without interference from N2 atmospheric gas. In order to further improve these effects and facilitate the reaction, it is desirable to use a water-soluble compound of Fe + Ni or Co as a catalyst in an amount of 5 to 25% by weight based on the silicon source.

The raw materials used in the present invention include 5t02-containing powder such as silica sand, silica stone, and silica gel as a silicon source material, carbon black, coke powder, graphite powder, etc. as a carbon material, and Fe as a catalyst. .

As a water-soluble compound of Ni or Co, for example, FeCl
2・4H20, Ni (NO3)2 ・6H20°C
oCl2.6H20 and the like are preferably used.

[Effect]

Based on the configuration of the present invention, the first requirement is to introduce N2 gas so as not to contact the reaction heating zone, the second requirement is to set the flow rate of N2 gas to 101/min or less, and 1200 to 1/min.
The third requirement of setting the heating stage at 400° C. to a heating rate of 10° C./min or more makes it possible to completely eliminate the adverse effects that occur when using N2 atmosphere gas.

As for the action according to the second requirement, it is said that SiC whiskers are first generated through a reaction between raw materials and a gas phase. In order to keep the equilibrium state of the reaction product gas generated in this reaction system stable, the flow rate of N2 gas was reduced to 1.
The yield is kept below 0cn/min.

The effect of the second requirement can be considered as follows.

In other words, the reaction between N2 gas and Si source is thermodynamically
C whisker formation temperature (1500-1700'C)
It has been confirmed that this occurs at a lower temperature of 1250 to 1400°C, but the second requirement accelerates the temperature rise at this temperature stage, and this action effectively suppresses the nitriding reaction and increases the Si
This results in smooth generation of C whiskers and imparting straightness.

These effects can be achieved by using Fe, Ni or G as a catalyst.

This can be further promoted by using a water-soluble compound in an amount of 3.0 to 6.0% by weight based on the Si source.

〔Example〕

Silica gel containing 5.0% Go C12.6H20 was ground to 100 mesh or less to use as a St source raw material, and carbon black ["5EAS75H"] was added as a carbon material to this.
(manufactured by Tokai Carbon Co., Ltd.) at a weight ratio of 1:1.2 and mixed until sufficiently homogeneous to achieve a bulk density of 0-1 g/
A raw material for cc was prepared.

Using a reactor having the structure shown, raw materials stored in a reserve tank (5) were continuously supplied from a feeder (6) onto a running belt conveyor (3). N2 gas is introduced at a flow rate of 5 am/min above the N2 region separator plate installed in the furnace, and the reaction heating zone is controlled by controlling the load condition of the heater part (2) and the speed of the belt conveyor (3). (A
) at 1200-1400'C heating rate at 30
The reaction temperature was set at 1500 to 1700° C. and SiC whiskers were generated.

For comparison, a reactor without the N2 region separator (4) was used, and the introduced gas was 2N2 (flow rate 203/min), 1
Temperature increase rate from 200 to 1400°C: 5°C/min, catalyst: C
o C12.6 N205.0% by weight (relative to Si source) manufacturing conditions Example Comparative Example 1> Using the same type of reactor, introduced gas: Ar (flow rate 20 cm/min), temperature increase rate of 1200 to 1400°C :5℃/min, catalyst: CoCl2・6H205,
SiC whiskers were produced by applying the manufacturing conditions of 0% by weight (based on the Si source), such as Comparative Example 2.

The properties and yields of SiC whiskers obtained in these three examples are compared and shown in the table below.

From the results shown, it was recognized that the properties and yield of the SiC whiskers obtained in the examples of the present invention were greatly improved compared to Comparative Example 1.2.

〔Effect of the invention〕

According to the present invention, it is possible to continuously produce high-quality SiC whiskers with high yield by open system means using N2, which is easy to handle and inexpensive, as an atmosphere gas, and therefore it makes a great contribution to industry.

[Brief explanation of the drawing]

The figure is a cross-sectional view illustrating an SiC whisker manufacturing apparatus used in the present invention. (1) Reaction furnace (2) Part of the heater (3) Belt conveyor (4) N2 basin separation plate (A) Reaction heating zone Patent applicant Tokai Carbon Co., Ltd. company

Claims (1)

[Claims] 1. In a method for producing SiC whiskers by continuously supplying a raw material consisting of a silicon source material, a carbonaceous material, and a catalyst to an open reaction heating zone (1500 to 1700°C), the atmosphere N_2 gas used as a gas is introduced at a flow rate of 10 cm/min or less without contacting the reaction heating zone, and a heating step of 120 to 1400°C is performed.
S characterized by setting the temperature increase rate to 0°C/min or more
Method for producing iC whiskers. 2. The method for producing SiC whiskers according to claim 1, wherein a water-soluble compound of Fe, Ni or Co is used as a catalyst in an amount of 5.0 to 25% by weight based on the silicon source.