JPS5822571B2 - Carbon fiber manufacturing method using vapor phase method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for producing carbon fiber by a vapor phase method.

Carbon fibers used in high-temperature furnace insulation and various composite materials are generally made from organic synthetic fibers, but in addition to this, gaseous hydrocarbons are introduced into a high-temperature zone to extract carbon fibers from the gas phase. The method for precipitating
It is known from etc.

However, when using the gas phase method, it often happens that no carbon fibers are produced at all unless the precipitation conditions are carefully adjusted, and this has not led to industrial production.

Therefore, as a method for promoting the formation of carbon fibers, the present applicant previously proposed a devised method as shown in JP-A-50-58321, but as a result of further research, he discovered a method that significantly promotes the formation of carbon fibers, leading to the present invention. Ta.

Its feature is that the heating zone where carbon fibers are precipitated contains elements selected from Groups I and VA of the periodic table, or their compounds, such as Fe, Co, Ni, V, Nb, Ta, or their compounds. The purpose is to bring into existence.

As is already known, in order to produce carbon fiber by the vapor phase method, hydrocarbon gas is diluted with a carrier gas and introduced into a furnace core tube heated to a predetermined temperature, and a heat-resistant Carbon fibers are deposited on Seiki Murakami.

Here, the furnace core tube is usually made of corundum, quartz, etc., and the heating temperature is 1030 to 1300°C1 Hydrocarbons include benzene, toluene, methane, ethane, ethylene, fluoropane, etc.
Almost all hydrocarbons such as saturated or unsaturated aliphatic and aromatic hydrocarbons such as methane, ethylene, propylene, and cyclohexane can be used, and mixtures thereof, volatile oil, kerosene, etc. can also be used.

Hydrogen or argon is used as the carrier gas, and graphite, quartz, and corundum are known as heat-resistant base materials placed in the furnace core tube.

In the present invention, the above elements or their compounds are present in the heating zone, and the reason why the amount of carbon fiber produced is increased by this is that these elements become the core of fiber production, and the fibers grow from there. It seems to be.

In fact, when we examine grown fibers, we find that these elements are present in the fiber heads.

Therefore, since it is the metal element that acts, when a compound is used, its form does not matter, and a wide range of compounds such as carbides and oxides can be used.

Note that when hydrogen is used as a carrier gas, some oxides are reduced, but there is no problem because the metal elements remain.

As a method of making these elements or compounds exist in the heating zone, it is possible to configure the furnace core tube itself with these elements or compounds, but it is convenient to take out the grown fibers, and it is also possible to move the fibers inside the furnace core tube as they grow. When considering the case where the long fibers are made by using these elements, it is desirable to place a substrate made of these elements or their compounds in the furnace core tube, or to make these elements or their compounds exist on another heat-resistant substrate.

If the substrate is moved as the fibers grow, fairly long fibers can be obtained.

In the present invention, even if the substrate itself is made of the above elements or their compounds, for example by sintering, casting, rolling, etc. of fine powder, it is more effective than conventionally known substrates, but most preferably, the effect of the present invention is As can be understood from the mechanism, this is a method in which fine powder of the element or its compound is dispersed on a heat-resistant substrate.

The fine powder preferably has a particle diameter of less than 50 microns, and can be sprayed after being suspended in a dispersion medium, or simply sprinkled as a powder.

Furthermore, if the substrate is porous, the generation of three nuclei that can be impregnated into the substrate mainly occurs on the surface, so in the case of powder dispersion, a thickness of several microns is sufficient.

As the hydrocarbon and carrier gas, the conventionally known ones mentioned above are used as they are, and the mixing ratio thereof is 1 to 60 mol % in terms of the concentration of hydrocarbon in the mixed gas.

To explain this mixing ratio in more detail, the problem in the heating zone is the carbon concentration, so materials with a high C/H ratio like benzene require a large amount of carrier gas.
The appropriate benzene concentration is within the above range of 1 to 30 mol%, and for substances with low C/H such as methane, the concentration can be increased, and 3 to 60 mol% is appropriate. be.

When mixing hydrocarbons and carrier gas, if the hydrocarbons are gaseous at room temperature, they can be mixed as is, or if they are liquid, the amount of vaporization can be controlled by selecting the temperature, and the carrier gas can be bubbled through the mixture. You can mix it using the following method.

The feeding flow rate of the mixed gas is determined by the cross-sectional area of the heating zone of the furnace core tube.
(Cm), approximately (5 to 150) SCJ/min in terms of room temperature is appropriate.

The preferred temperature of the heating zone is 1030 to 1300°C, and lower (or higher) temperatures will reduce the amount of fiber produced.

Further, to explain this in detail, it is most preferable for a substance with a low molecular weight such as methane to be in the range of 1,200 to 1,300°C (although as the molecular weight becomes larger, it becomes lower).

Further, for aromatic systems, the optimum temperature is 1030 to 1100°C.

The growth rate of fibers varies depending on the flow rate of the mixed gas, temperature, and other conditions, but it can grow from 5 to 15 cr after heating for 30 minutes to 1 hour.
It grows to about fL.

If it is desired to obtain even longer fibers, the heating zone may be lengthened or the substrate may be moved to the mixed gas inlet side as the fibers grow.

Then, when the desired fiber is obtained, the substrate is removed, and a new substrate containing the element or its compound is introduced,
Once fiber production is started, carbon fibers can be efficiently produced.

According to the present invention, fibers can be stably produced without the need for operational hassles such as increasing the gas flow rate at the start of fiber production to create a nucleus and slowing down the gas flow rate during growth, as in the past. I can do it.

And since the carbon fiber produced by this vapor phase method has good crystallinity,
Compared to carbon fiber made from organic synthetic fibers, it has considerably superior properties, such as tensile strength.

Example: An alumina furnace core tube (inner diameter 5Q mm, length 100100 mm) was placed horizontally in an electric ring furnace equipped with a SiC heating element, and an artificial graphite substrate (width 40 mm, length 200 mm, thickness 5 mm), and the temperature was about 1080°C.

One end of the furnace core tube was connected to a gas introduction tube, and the other end was connected to a discharge tube.

Here, hydrogen gas containing 10% by volume of benzene was added at a rate of 700 per minute.
cc (room temperature) was flowed.

After 45 minutes, the gas to be supplied was changed to argon, and the substrate was allowed to cool, and then the substrate was taken out, and the produced carbon fibers were peeled off and weighed.

The following table shows the results of using the graphite substrate by uniformly scattering various powders on the graphite substrate, together with the above examples.

As the above results show, conventional graphite, SiO,
Compared to the one using Al2O3, the one of the present invention has a marked difference in the amount of carbon fiber produced, and the effect is particularly remarkable when the above element or its powder is sprinkled on the substrate.

This fiber exhibits greater strength than commercially available carbon fibers made from organic synthetic fibers.

Claims (1)

[Claims] 1. In a method of producing carbon fiber by a vapor phase method from a mixed gas of hydrocarbon and carrier gas, the heating zone in which carbon fiber is produced is set at 1030 to 1300°C, and in this zone, groups 1 and Va of the periodic table are added. A method characterized by producing and growing carbon fibers in the presence of a fine powder of an element or a compound thereof selected from the above, and under the flow of the mixed gas.