KR20140122315A - Method of manufacturing silicon carbide fiber by using ozon gas and manufacturing system for the same - Google Patents

Abstract

The present invention provides a method for manufacturing silicon carbide fiber, including the steps of preparing poly carbosilane fiber by spinning poly carbosilane, stabilizing the poly carbosilane fiber by treating the poly carbosilane fiber with ozone gas, and heat treating the stabilized poly carbosilane. According to the present invention, process time can be reduced and environmentally friendly work environment can be made.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a silicon carbide fiber using ozone gas, and a manufacturing system of the silicon carbide fiber,

This technology is a technology in the field of carbon materials, specifically, a technique for manufacturing silicon carbide (SiC) fibers.

Silicon carbide fiber has high strength and elasticity, and is resistant to high temperature environment of 1000 ° C or more, and is a source material expected as a composite material reinforcing fiber. The most widely used process for the production of silicon carbide fibers is the synthesis of Polycarbosilane (PCS) polymer by S. Yajima in 1975, which is the starting material. This polymer is an organic silicon polymer having a structure of -Si-C- as a main axis. Silicon carbide (SiC) fibers that can be used for a long period of time without loss of mechanical strength at the final high temperature can be obtained by using PCS as a raw material through subsequent radiation, curing, and pyrolysis steps. PCS is composed of an oligomer (oligomer) which is oligomer. Although the fiber obtained by spinning has a circular shape, since the bond between the oligomers is weak, the fiber is hard to be cut, even when a slight load is applied , And also easily breaks into a powder form. Thus, a so-called green fiber, which is obtained immediately after spinning, is melted and does not maintain the shape of the fiber when heat treatment is performed at a high temperature immediately without a curing process. Therefore, it is a very important process to allow the PCS fiber to undergo a hardening process before the high-temperature pyrolysis or high-temperature heat treatment. Since the crosslinking occurs on the surface of the PCS fiber by the above curing process, can do. The incompatibility of the PCS fibers is a very important characteristic in preventing the PCS fibers from being melted until the high temperature heat treatment and further obtaining the high yield ceramics. The curing process of the PCS fiber is generally referred to as a stabilization process, and the physical properties of the SiC fiber tend to be highly dependent on the conditions of the stabilization process.

As such a stabilization step, a step of oxidizing the surface of the PCS fiber by performing a curing step at a temperature of 200 to 300 DEG C for a long time in the air has been used. This process is a process of forming a crosslink by forming free radicals by inducing bond breakage of the surface of PCS fibers and connecting them to each other. In the curing process, the 'Si-H' and 'Si-CH ₃ ' bonds are oxidized in the PCS material to form a bond between 'Si-O-Si' and 'Si-O-C'. Stabilized fibers are infusible and are thermally stable with little degradation until reaching the final heat treatment temperature.

Another stabilizing method is to cause cross-linking on the surface of the PCS fiber through electron beam or γ-ray irradiation. Since this process is performed in an oxygen-free atmosphere, it has the advantage of reducing oxygen binding to the PCS fiber and greatly reducing the oxygen content in the final SiC fiber. However, the SiC fibers obtained by this process have a disadvantage in that they have lower mechanical properties than fibers obtained by curing in air.

Since the first stabilization step involves heating at 200 to 300 ° C at a very slow rate for surface oxidation of the PCS fiber, it is necessary to maintain the fiber at a final temperature for a long period of time, so that the process time is very long and a continuous process is impossible .

 The stabilization process by the electron beam treatment is disadvantageous in terms of process economy because expensive equipment for generating electron beams must be manufactured and installed. In the industrial field where high mechanical properties are required, the application is not required Somewhat difficult.

In order to solve such a problem, a method of stabilizing PCS fiber with iodine, which is one of halogen elements, has recently been introduced. In this method, iodine is sublimated at a temperature of 100 to 140 ° C., and the generated gas is brought into contact with the PCS fiber surface to cause a reaction with PCS. In order to perform this process, iodine gas treatment is required. Therefore, this process can cause environmental pollution due to release of iodine gas from the environmental aspect. In case of exposure to a high concentration gas, And may be very harmful to the human body. As a result, this process requires a long process time, tight control of the work, and high cost.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of a stabilization process which is an essential process for manufacturing silicon carbide in the past and to improve the conventional hardening process and to provide a silicon carbide And a method for manufacturing the same.

Another object of the present invention is to provide a continuous manufacturing system for realizing the above manufacturing method.

A method for producing a silicon carbide fiber according to an embodiment of the present invention includes the steps of preparing a polycarbosilane fiber by spinning a polycarbosilane, treating the polycarbosilane fiber with an ozone gas to stabilize the polycarbosilane fiber And a heat treatment step of heat-treating the stabilized polycarbosilane.

The treatment of the ozone gas may be performed in the presence of a light source, and ultraviolet rays may be used as the light source. On the other hand, the ultraviolet ray may be an ultraviolet ray having a wavelength of 178 nm to 250 nm.

The stabilization step may be performed for 1 minute to 120 minutes, thereby enabling a drastic reduction of the processing time. In addition, the stabilization step can be performed at a temperature of room temperature to 200 ° C, which is very advantageous from the viewpoint of energy efficiency.

The polycarbosilane used for preparing the PCS fibers as the SiC precursor fiber can be adjusted to have a melting temperature of 150 to 300 DEG C and the polycarbosilane has a weight average molecular weight of 1500 to 3500 and a polydispersity index Polycarbosilanes having a polydispersity index (PI) may be used.

In the heat treatment step, the heat treatment temperature is adjusted so that the maximum temperature is 1000 to 1800 ° C, and the temperature is the highest temperature interval of the temperature increasing stepwise. The heat treated PCS fiber is then cooled.

It is preferable that the spinning of the PCS fiber is performed in a state where the viscosity of the polycarbosilane is controlled to 10 to 20 Pa.

Meanwhile, the stabilization step may further include decomposing and discharging the unreacted ozone gas at a temperature of 100 to 200 ° C. By including these steps, it is possible to shut off the discharge of ozone gas into the air and discharge the oxygen instead.

The heat treatment step may include a first heat treatment step of heat treating the stabilized polycarbosilane fiber at a temperature of 300 DEG C or less and a heat treatment step of heating the cured polycarbosilane fiber to a silicon carbide fiber at a temperature of 300 to 1800 DEG C And a second heat treatment step in which the second heat treatment step is performed. This step separation means that after the first heat treatment step, the second heat treatment step can be performed after the cured state of the polycarbosilane fiber is grasped, as the case may be.

A silicon carbide manufacturing system according to an embodiment of the present invention is a reaction chamber for treating irradiated polycarbosilane fibers with ozone gas, comprising: a first chamber having an ultraviolet lamp therein; An ozone generating unit disposed in the first chamber and supplying ozone to the first chamber, an oxygen supplying unit spatially connected to the ozone generating unit to supply oxygen to the ozone generating unit, and a moving direction of the polycarbosilane fiber And a second chamber disposed in an adjacent region of the first chamber for heat treating the polycarbosilane fibers discharged from the first chamber.

Heating means for spatially connecting the first chamber to decompose the unreacted ozone gas in the first chamber and for applying heat to the ozone gas, and oxygen gas generated by decomposition of the ozone gas, And an ozone gas filter unit including an oxygen outlet for discharging the ozone gas.

The first chamber or the ozone gas filter portion has a tube shape, so that the movement path of the continuous process can be made efficient.

According to the method of manufacturing silicon carbide according to an embodiment of the present invention, the stabilization process of the PCS fiber can be performed within a few minutes, and the manufacturing process of the silicon carbide can be remarkably shortened. This is because the reaction time with the PCS fiber surface is shortened by using ultraviolet rays to accelerate the decomposition of the ozone gas.

In addition, since the ozone used in the stabilization process is easily decomposed by oxygen, the process is environmentally friendly, unlike the conventional process using halogen gas, which does not cause environmental pollution or gives harm to the work environment of a worker .

The process for producing silicon carbide according to the present invention is expected to be very effective as a process which is excellent in mechanical properties of silicon carbide as a final product, and is environmentally friendly and economical in consideration of the above advantages.

1 is a cross-sectional view conceptually illustrating a silicon carbide manufacturing system according to an embodiment of the present invention.
2 is a graph showing the FT-IR spectrum of the PCS fiber according to Comparative Example 1. Fig.
3 to 8 are graphs showing FT-IR spectra of the PCS fibers according to Examples 2 to 7, respectively.
9 is a graph showing absorption intensity changes at 1260 cm ^-1 (Si-CH ₃ ) and 2100 cm ^-1 (Si-H) peaks for the PCS fibers according to Examples 2 to 7, respectively.
10 is a photograph showing a state of PCS fiber after stabilization according to an embodiment of the present invention.
11 is an SEM photograph showing the appearance of the SiC fiber obtained after the heat treatment step according to Example 8 is performed on the PCS fiber after the stabilization step of Example 4. Fig.
12 is a graph showing the results of XRD (X-ray duffing) analysis of the SiC fibers obtained after the heat treatment step according to Example 8 for the PCS fibers having undergone the stabilization step of Example 4. FIG.

Hereinafter, a silicon carbide manufacturing technique according to the present invention will be described in detail with reference to the accompanying drawings. However, the following description is only an exemplary description of the present invention, and the technical idea of the present invention is not limited by the following description, and the technical idea of the present invention is defined by the claims that follow.

On the other hand, the component names of the drawings used for the explanation of the silicon carbide manufacturing system are merely illustrative, and the technical features of the present invention are not limited by the concept of such names.

1 is a cross-sectional view conceptually illustrating a silicon carbide manufacturing system according to an embodiment of the present invention.

Referring to FIG. 1, the synthesized polycarbosilane (PCS) is radiated and passes through the first chamber 100 in a fibrous form along the PCS transfer path 50 for an immobilization process or a stabilization process. The spinning is carried out by melt spinning, and at the time of spinning the viscosity of the PCS is maintained at an appropriate viscosity, which is important for maintaining the physical properties of the PCS fiber in the subsequent process.

The viscosity of the synthesized PCS is variable depending on the temperature, and it is preferable to start the spinning in a range where the viscosity of the PCS is 10-20 Pa.S. by measuring the viscosity by temperature. In addition, the polymer properties of synthetic polycarbosilane have a causal relationship with the final product, SiC. Therefore, considering the causal relationship between the properties of the polycarbosilane and the application fields of SiC, . ≪ / RTI > According to one embodiment of the present invention, the polycarbosilane has a weight average molecular weight of 1500 to 3500, a number average molecular weight of 800 to 1300, and a polydispersity index (PI) of 1.5 to 3.0. It is also preferable that polycarbosilane having a melting temperature of 150 to 300 캜 is used as the polycarbosilane.

Hereinafter, the synthesis and spinning steps of the polycarbosilane will be described with specific examples. However, the content of the present invention is not limited by the following examples.

[Synthesis Example 1] Synthesis of PCS

Dichlorodimethylsilane was used as a PCS precursor used in the present invention, and dechlorination was performed to synthesize a polysilane. PCS was synthesized by thermally decomposing the polysilane under high temperature and high pressure for a long time. The weight average molecular weight (Mw) of the synthesized PCS measured by gas chromatography (GPS) was 1600 to 3000 and the number average molecular weight (Mn) was 1000 to 1300.

[Example 1] Radiation

The viscosity of the synthesized PCS was measured by temperature and irradiation was started at a viscosity ranging from 10 to 20 Pa.S. First, the PCS powder was melted in an inert atmosphere and stirred to remove air bubbles, and spinning was carried out using a nozzle having 30 holes. The extruder type was used for the spinning equipment, and the fibers from the nozzle were wound several hundred RPM in the winder to control the fiber diameter. The irradiated PCS fibers had little strength and easy to break, and the average diameter was about 30 μm.

Referring again to FIG. 1, the PCS fiber prepared by melt-spinning in the extrusion method as in Example 1 is a so-called green fiber type fiber which is easy to be crumbled and must undergo a hardening or stabilization step for the final heat treatment step do. The PCS fibers are introduced into the first chamber 100 along the PCS traveling path 50 as described above. The PCS moving path 50 may be a moving means such as a conveyor belt. The first chamber 100 is a chamber in which the PCS fiber stabilization step is performed, and the stabilizing step according to the present invention can be performed by treating the polycarbosilane fiber with ozone gas.

The first chamber 100 is provided with an ultraviolet lamp 110 as a kind of energy supplying means for supplying ozone gas to the inside of the first chamber 100 to decompose the ozone gas to promote oxygen generation. The wavelength of ultraviolet rays emitted from the ultraviolet lamp 110 may be 178 nm to 250 nm. Further, the ultraviolet lamp 110 preferably has a power of 10 w or more. In order to form an ozone gas atmosphere in the first chamber 100, an ozone generating unit 300, which is spatially connected to the first chamber 100 by a tube structure or the like, is provided outside the first chamber 100, Respectively. The type of the ozone generator 300 is not particularly suggested, and various known ozone generators may be introduced into the ozone generator 300. Oxygen gas is used as a source for generating ozone in the ozone generating unit 300 and the ozone generating unit 300 receives oxygen from the oxygen supplying unit 400 disposed outside the ozone generating unit. That is, the ozone generating unit 300 receives oxygen from the oxygen supplying unit 400, generates ozone gas, and supplies the generated ozone gas to the first chamber 100.

The concentration of ozone in the first chamber 100 may be considered according to the characteristics of the process, but according to an embodiment of the present invention, the concentration of the ozone may be 100 g / m ³ or less. Meanwhile, the temperature inside the first chamber 100 may be room temperature, and in some cases, the stabilization process may be performed under heating conditions. Even if heating is performed, the temperature inside the first chamber 100 is preferably maintained at 200 ° C or lower.

The PCS fibers passing through the first chamber 100 may be stabilized under ultraviolet rays and ozone gas irradiated by the ultraviolet lamp 110, and the stabilization treatment time may be within several minutes. Specifically, the ultraviolet ray and ozone treatment time may be 1 to 120 minutes. The process time of the stabilization step may be variable depending on the intensity of the ultraviolet lamp 110, the concentration of the ozone gas, the temperature condition inside the first chamber 100, and the like. However, compared with the conventional curing method or the stabilization process using iodine gas, .

After the PCS fiber stabilization process is completed in the first chamber 100, the remaining unreacted ozone gas is not discharged but passes through the ozone gas filter unit 500 connected to the first chamber 100, Lt; / RTI > The ozone gas filter unit 500 includes heating means 510 for supplying heat to unreacted ozone gas discharged from the first chamber 100 and decomposing the ozone gas into oxygen. The type and manner of the heating means 510 are not limited to a great extent. The heating means 510 can heat the ozone gas discharged into the ozone gas filter unit 500 to a temperature of 100 to 200 ° C to decompose the ozone gas into oxygen within a short time within a few seconds. That is, it is possible to prevent the ozone gas type emission by simply passing through the ozone gas filter unit 500 without staying. The ozone gas decomposed by the ozone gas filter unit 500, that is, oxygen, is finally discharged into the atmosphere. Therefore, it does not cause any additional environmental problems due to the direct discharge of ozone gas. Furthermore, problems such as environmental problems and work risks, which have been a problem in the stabilization process using iodine gas, which is one of the conventional methods, can be easily overcome.

When the stabilization process is completed and the PCS fiber is incompatible, the molecular structure of PCS represented by the following formula (1) or (2) exhibits the following bonding phase change, .

The PCS fiber having the above-described chemical structure undergoes an infusibility process, and crosslinking is formed on the fiber surface. Specifically, the -Si-H- moiety is modified to the covalent bond form to the -Si-O-Si- moiety, and the -Si-CH3- moiety is changed to the Si-CO- moiety to form the covalent bond. This structural change can be confirmed by measuring the FT-IR spectrum. For example, FT-IR spectrum in the spam 2100cm ^-1 in a wave number indicates a strong absorption band 'Si-H' stretching vibration (stretching vibration) of PCS, 1260cm ^-1 frequencies, 'Si-CH _3' deformation vibration (deformation vibration absorption peaks are strongly shown, so that the absorption strengths thereof are compared and the effects of the stabilization step before and after curing can be confirmed and confirmed. In the PCS, the 'Si-H' site appears to be reduced due to the curing process and crosslinking with the 'Si-O-Si' bond is formed. Likewise, the 'Si-CH ₃ ' site has the same tendency. Therefore, the state change after stabilization can be quantified by comparing the degree of decrease of each group at 1260 cm ^-1 and 2100 cm ^-1 peaks by the following equations (1) and (2) .

Hereinafter, a stabilization process according to an embodiment of the present invention will be described with specific examples, and the validity of the stabilization process will be verified as a result of the experiment.

[Examples 2 to 7] Stabilization process

Oxygen was used as the ozone source, and ozone gas was generated in the ozone generator (300 in FIG. 1). The ozone concentration in the ozone generator 100 was 10 g / m ³ , the flow rate was 1 LPM, and the ozone gas discharge pressure was 0.5 kg / cm ² . In the ozone reaction chamber 100, the ultraviolet lamp 110 was used to increase the reaction rate by activating the ozone gas. As the ultraviolet lamp 110, a mercury lamp which emits ultraviolet rays having a wavelength of 178 nm and has a power of 15 W was mainly used. (Example 2), 10 minutes (Example 3), 15 minutes (Example 4), 20 minutes (Examples 2 to 5) (Example 2) 5), 30 minutes (Example 6), and 60 minutes (Example 7). On the other hand, in order to exhaust only oxygen into the atmosphere after the decomposition of the unreacted ozone gas, a heater tube which can be used at 100 to 200 ° C is installed in the ozone gas filter (500 in FIG. 1) Respectively. The unreacted ozone gas decomposed in less than 1 second at 140 ℃.

FT-IR spectrum analysis

The FT-IR spectra of the PCS fibers subjected to the stabilization process as in Comparative Example 1 and Comparative Examples 1 and 2 to 7 were analyzed, and the results thereof were shown in Figs. 2 to 8 Respectively.

FIG. 2 is a graph showing the FT-IR spectrum of the PCS fiber according to Comparative Example 1, and FIGS. 3 to 8 are graphs showing the FT-IR spectrum of the PCS fiber according to Examples 2 to 7, respectively. 9 is a graph showing changes in absorption intensity with time of stabilization at peaks at 1260 cm ^-1 (Si-CH ₃ ) and 2100 cm ^-1 (Si-H), respectively, for the PCS fibers according to Examples 2 to 7 to be.

Referring to FIG. 9, in the case of specimens treated with ultraviolet-ozone for 30 minutes and 60 minutes, stabilization treatment was performed only up to 250 ° C at the time of curing. As shown in FIG. 9, the infrared spectroscopic absorption intensity changes of Si-H and Si-CH ₃ bonds are the same from 5 minutes to 20 minutes. However, PCS fibers are generally 15 to 25% . These changes were slightly larger in Si-CH ₃ bonds.

From the above results, even after five minutes of ultraviolet-ozone treatment, sufficient crosslinking of the PCS fiber was induced, which ultimately prevented melting of the PCS fiber. From this result, it can be said that the UV-ozone hardening process can be applied in a very short time compared with any existing process technology, so that it can be applied also in mass production, and it is possible to reduce the manufacturing cost of expensive SiC I hope.

10 is a photograph showing a state of PCS fiber after stabilization according to an embodiment of the present invention.

As shown in FIG. 10, after the completion of the curing process (stabilization process), no melting phenomenon of fibers was observed in all the specimens (PCS fibers) of Examples 2 to 7, It can be confirmed that the fiber is heterogeneously changed from the PCS fiber before running and is not broken. On the other hand, the PCS specimen of Comparative Example 1, which had not undergone the stabilization process, failed to maintain the shape of the fiber due to melting phenomenon.

Referring again to FIG. 1, the PCS fibers, which have not been melted through the first chamber 100, that is, stabilized and secured at high temperature stability, are continuously moved to the second chamber 200. In the second chamber, a firing reaction for curing and SiC fiber formation is performed, and the second chamber 200 is a kind of heat treatment furnace. In the second chamber 200, a first heat treatment step for primarily curing the stabilized PCS fiber is performed while raising the temperature to about 300 ° C. Thereafter, a second heat treatment step is performed in which the second chamber 200 is sequentially heated to a maximum temperature of 1000 to 1800 ° C, followed by cooling. The cooling may be a natural cooling method in which it is left at room temperature. On the other hand, the rate of temperature rise (temperature gradient) and the like can be designed organically in consideration of the target SiC properties. Between the first heat treatment step and the second heat treatment step, the melting state or the molten state of the PCS fiber can be confirmed.

The stabilization step and the heat treatment step described above can be performed in a continuous process, and although not described in detail, in the method of manufacturing silicon carbide according to an embodiment of the present invention, all the steps from the spinning to the heat treatment step are performed in a series of continuous processes .

Hereinafter, a heat treatment step according to an embodiment of the present invention will be described with specific examples.

[Example 8] Heat treatment step

The PCS fiber having completed the ultraviolet ray-ozone treatment (stabilization step) was subjected to heat treatment only in the second chamber 200 under a nitrogen atmosphere up to 300 ° C (first heat treatment step). The temperature cycle was heated at a rate of 10 ° C / min up to -160 ° C and at 1 ° C / min up to 160 ° C to 300 ° C. After the hardening treatment, the test pieces were placed in a second chamber (or a continuous heat treatment furnace) and heat treatment was performed at 1250 ° C. Min to 300 ° C to 600 ° C. The temperature was raised to 5 ° C / min up to 1250 ° C after the temperature was maintained for 1 hour, and a heat treatment cycle of cooling to room temperature after 1 hour was applied. The second heat treatment step was performed under a nitrogen or argon gas atmosphere.

11 is an SEM photograph showing the appearance of the SiC fiber obtained after the heat treatment step according to Example 8 is performed on the PCS fiber after the stabilization step of Example 4. Fig. Referring to Fig. 11, the SiC fibers were circular and had a diameter of about 13 mu m.

FIG. 12 is a graph showing the results of XRD (X-ray duffing) analysis of the SiC fibers obtained after the heat treatment step according to Example 8 for PCS fibers having undergone the stabilization step of Example 4. FIG. Referring to FIG. 12, it was confirmed that the main peak was observed at 2? = 35.7 and 2? = 60.0 in the obtained SiC fiber to form a? -SiC structure.

Claims (13)

Spinning the polycarbosilane to prepare a polycarbosilane fiber;
Stabilizing the polycarbosilane fiber by treating ozone gas to stabilize the polycarbosilane fiber; And
And a heat treatment step of heat-treating the stabilized polycarbosilane.
The method according to claim 1,
Wherein the treatment of the ozone gas is performed in the presence of a light source.
3. The method of claim 2,
Wherein the light source is ultraviolet light.
The method of claim 3,
Wherein the wavelength of the ultraviolet ray is 178 nm to 250 nm.
The method according to claim 1,
Wherein the stabilizing step is performed for 1 to 120 minutes.
The method according to claim 1,
Wherein the stabilizing step is performed at a temperature of from room temperature to 200 ° C.
The method according to claim 1,
Wherein the polycarbosilane has a melting temperature of from 150 to < RTI ID = 0.0 > 300 C. < / RTI >
The method according to claim 1,
Wherein the polycarbosilane has a weight average molecular weight of 1500 to 3500 and a polydispersity index (PI) of 1.5 to 3.0.
The method according to claim 1,
Wherein the heat treatment temperature is adjusted so that the maximum temperature is 1000 to 1800 占 폚.
The method according to claim 1,
Wherein the stabilizing step comprises decomposing and discharging the unreacted ozone gas at a temperature of 100 to 200 캜.
The method according to claim 1,
The heat treatment step may include: a first heat treatment step of performing heat treatment at 300 ° C or less to cure the stabilized polycarbosilane fiber; And
And a second heat treatment step of heat treating the hardened polycarbosilane fiber to a silicon carbide fiber under a temperature of 300 to 1800 ° C.
1. A reaction chamber for treating radially introduced polycarbosilane fibers with ozone gas, comprising: a first chamber having an ultraviolet lamp inside;
An ozone generator disposed in an adjacent region of the first chamber and supplying ozone to the first chamber;
An oxygen supply unit spatially connected to the ozone generator to supply oxygen to the ozone generator; And
And a second chamber disposed in an adjacent region of the first chamber along the direction of movement of the polycarbosilane fiber and for heat treating the polycarbosilane fibers discharged from the first chamber.
13. The method of claim 12,
The first chamber being spatially connected to decompose the unreacted on-off gas in the first chamber,
Heating means for applying heat to the ozone gas; And
Further comprising an ozone gas filter portion including an oxygen outlet for discharging oxygen gas generated by decomposition of the ozone gas to the outside.

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