Method for producing silicon carbide fiber

Abstract

Provided is a method for producing a polycarbosilane using a liquid phase / gas phase pyrolysis condensation method, wherein a polycarbosilane for silicon carbide fiber production is produced with fewer steps than conventional production methods. A method for producing a polycarbosilane for silicon carbide fiber production according to one aspect of the present invention comprises a polycarbosilane synthesis step for synthesizing a polycarbosilane having a weight-average molecular weight of 9000 or more, the polycarbosilane synthesis step comprising: a treatment for generating a gas phase by heating a starting material containing a cyclic silane compound at a first temperature; a treatment of heating the gas phase at a second temperature higher than the first temperature to produce polycarbosilane; and cooling the polycarbosilane, returning the cooled polycarbosilane to the starting material, and heating the cooled polycarbosilane at the first temperature, thereby performing a treatment in which the polycarbosilane has a high molecular weight.

Description

Technical Field

[0001] The present invention relates to a method for producing polycarbosilane for producing silicon carbide fibers and a method for producing silicon carbide fibers. Background Art

[0002] Patent Document 1 discloses a method for synthesizing polycarbosilane from polysilane by a liquid-gas phase pyrolysis condensation method and producing silicon carbide fibers from the synthesized polycarbosilane.

[0003] Patent Document 2 discloses super heat-resistant silicon carbide fibers and a method for producing the same, and describes a method for producing polycarbosilane by an autoclave method using cyclic polysilane as a raw material.

[0004] Patent Document 3 discloses a method for producing a ceramic molded body, and describes a method for producing polycarbosilane by an autoclave method using polysilane as a raw material.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-137935

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 4-194028

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 1-257177 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] In the method for producing polycarbosilane for producing silicon carbide fibers, the number of steps is large, which leads to complexity and high production cost. Therefore, a technology for producing polycarbosilane for producing silicon carbide fibers more simply and at a low cost is required.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for producing polycarbosilane for producing silicon carbide fibers by using a liquid-gas phase pyrolysis condensation method, wherein the method comprises fewer steps than conventional methods.

[0013] Technical Solution

[0014] The present inventors conducted intensive research and found that by using a cyclic silane compound as a raw material, polycarbosilane for producing silicon carbide fibers can be produced in a method for producing polycarbosilane using a liquid-gas phase pyrolysis condensation method with fewer steps than in conventional production methods, thereby completing the present invention.

[0015] A method for producing polycarbosilane for use in manufacturing silicon carbide fibers according to one embodiment of the present invention includes a polycarbosilane synthesis step for synthesizing polycarbosilane having a weight-average molecular weight of 9,000 or more, wherein the polycarbosilane synthesis step includes the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to thereby generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to thereby increase the molecular weight of the polycarbosilane.

[0016] A method for manufacturing silicon carbide fibers according to one embodiment of the present invention includes the following steps: a polycarbosilane synthesis step for synthesizing polycarbosilane having a weight-average molecular weight of 9,000 or more; a spinning step for forming the polycarbosilane synthesized by the polycarbosilane synthesis step into a fibrous form; and a calcining step for calcining the polycarbosilane fibers generated by the spinning step, wherein the polycarbosilane synthesis step includes repeatedly performing the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material and heating it at the first temperature to increase the molecular weight of the polycarbosilane. The method for manufacturing silicon carbide fibers does not include a step for adjusting the molecular weight by removing low-molecular-weight polycarbosilane from the polycarbosilane synthesized by the polycarbosilane synthesis step.

[0017] Beneficial Effects

[0018] According to one aspect of the present invention, in a method for producing polycarbosilane using a liquid-gas phase pyrolysis condensation method, polycarbosilane for producing silicon carbide fibers can be produced with fewer steps than in conventional production methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 1 is a diagram showing a liquid-gas phase pyrolysis apparatus 10 that can be used for synthesizing polycarbosilane.

[0020] Figure 2 This is a graph showing the melting behavior of polycarbosilane and the tensile strength of SiC fibers obtained by calcining at 1000°C.

[0021] Figure 3 This is a graph showing the relationship between the number of molecular weight adjustments and the total yield after the synthesis step. DETAILED DESCRIPTION

[0022] [1. Method for producing polycarbosilane for producing silicon carbide fiber]

[0023] A method for producing polycarbosilane for producing silicon carbide fibers according to one embodiment of the present invention (hereinafter referred to as "the method for producing polycarbosilane") includes a polycarbosilane synthesis step for synthesizing polycarbosilane having a weight average molecular weight of 9,000 or more, wherein the polycarbosilane synthesis step includes the following treatments: a treatment for heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase (hereinafter referred to as "the first heating treatment"); a treatment for heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane (hereinafter referred to as "the second heating treatment"); and a treatment for cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to increase the molecular weight of the polycarbosilane (hereinafter referred to as "the high molecular weight treatment"). According to such a configuration, in the method for producing polycarbosilane using a liquid-gas phase pyrolysis condensation method, polycarbosilane for producing silicon carbide fibers can be produced with fewer steps than in conventional production methods.

[0024] The reason is as follows. That is, the polycarbosilane produced by the method for producing polycarbosilane for silicon carbide fiber according to one embodiment of the present invention has the characteristic that the fiber is not easily fused during the firing process in the process of producing silicon carbide fiber. Therefore, there is no need to perform a process of adjusting the molecular weight in order to remove low molecular weight polycarbosilane that causes fusion. In the method for producing polycarbosilane using the liquid-gas phase pyrolysis condensation method, polycarbosilane for silicon carbide fiber can be produced with fewer processes than the conventional production method. Here, low molecular weight polycarbosilane refers to, for example, polycarbosilane with a molecular weight of 5500 or less.

[0025] In this specification, "molecular weight adjustment process" refers to the process of removing low molecular weight polycarbosilane from the polycarbosilane synthesized by the polycarbosilane synthesis process. As a method for removing low molecular weight polycarbosilane, for example, a method of adding a solvent to the polycarbosilane synthesized by the polycarbosilane synthesis process and removing the dissolved components to remove the low molecular weight polycarbosilane can be cited. Generally, as a solvent added to the polycarbosilane, any solvent that can extract low molecular weight polycarbosilane can be used without particular limitation, and it is appropriately selected according to the molecular weight range to be removed.

[0026] (Polycarbosilane synthesis process)

[0027] The polycarbosilane synthesis step is a step of synthesizing polycarbosilane having a weight average molecular weight of 9,000 or more, and includes a first heat treatment, a second heat treatment, and a molecular weight increasing treatment.

[0028] The first heat treatment is a treatment in which a raw material containing a cyclic silane compound is heated at a first temperature to generate a gas phase. The raw material containing the cyclic silane compound may be a solid, a liquid, or a mixture of a liquid and a solid. In this specification, the first temperature represents the measurement result of the internal temperature of the reaction container after the raw material is added. That is, the first temperature is the temperature of the contents of the reaction container itself. The first temperature is not particularly limited as long as it is a temperature at which at least a portion of the cyclic silane compound can be vaporized to generate a gas phase. Typically, it can be in the range of 100°C to 500°C, and can be in the range of 400°C to 500°C. By heating at this temperature, the cyclic silane compound is pyrolyzed to generate a gas phase, and a gas phase is also generated by sublimation of the cyclic silane compound or gasification from liquefaction.

[0029] In the method for producing polycarbosilane of one embodiment of the present invention, the cyclic silane compound is a compound having a skeleton consisting only of Si-Si bonds as the main chain and the main chain forming a ring. The number of atoms of the cyclic silane compound used in the method for producing polycarbosilane is preferably 15 or less, more preferably 10 or less, and further preferably 7 or less. In addition, the cyclic silane compound may be a single ring or may have multiple rings. In addition, the side chain of the cyclic silane compound may have an arbitrary structure. Examples of the cyclic silane compound include octamethylcyclotetrasilane, decamethylcyclopentasilane, dodecamethylcyclohexasilane, and tetradecamethylcycloheptasilane. From the viewpoint of raw material supply, the cyclic silane compound is preferably dodecamethylcyclohexasilane.

[0030] The amount of the cyclic silane compound used in the polycarbosilane synthesis step can be appropriately adjusted according to the apparatus for synthesizing polycarbosilane and the desired amount of polycarbosilane to be synthesized.

[0031] The second heat treatment is a treatment for heating the gas phase generated in the first heat treatment at a second temperature higher than the first temperature to generate polycarbosilane. The second heat treatment can cause free radical cleavage and rearrangement of Si-Si bonds of the cyclic silane compound to generate polycarbosilane. In this specification, the second temperature refers to the measurement result of the internal temperature of the reaction tube after the gas phase is added when the gas phase generated by the raw material containing the cyclic silane compound is heated. That is, the second temperature is the temperature of the gas phase itself heated in the second heat treatment. The generated polycarbosilane is cooled and returned to the raw material undergoing the first heat treatment.

[0032] From the perspective of the oxygen content of the synthesized polycarbosilane, in order to prevent the oxygen content of the polycarbosilane from increasing, the second temperature is preferably below 670°C, more preferably below 650°C, and further preferably below 600°C. The results of the study confirmed that in the method of the present embodiment using cyclic polysilane as a raw material, when the second temperature is increased, the viscosity of the generated polycarbosilane increases significantly, which may cause clogging of the piping depending on the device. Therefore, from the perspective of the operability of the device for synthesizing polycarbosilane, in order to prevent the piping of the device from being clogged by the synthesized polycarbosilane, the second temperature is preferably below 650°C. In addition, from the perspective of rearranging the cyclic silane compound, the second temperature is preferably above 500°C, and from the perspective of increasing the branching of the polycarbosilane, the second temperature is preferably above 600°C. It should be noted that the branching of polycarbosilane will be described later.

[0033] The high molecular weight treatment is to cool the polycarbosilane generated in the second heat treatment and return it to the raw material, and then heat it at the first temperature to perform a high molecular weight treatment of the polycarbosilane. The high molecular weight treatment can condense the polycarbosilane generated by the second heat treatment to achieve a high molecular weight. The cooling temperature is not particularly limited as long as the polycarbosilane in a gaseous state can be cooled to a degree that it becomes a liquid. The first temperature is the same as the description of the first temperature in the first heat treatment.

[0034] By repeating this series of reactions, the molecular weight of the polycarbosilane gradually increases, and a polycarbosilane with a higher molecular weight can be obtained.

[0035] The synthesis time of the polycarbosilane synthesis process can be appropriately adjusted according to the first temperature. By adjusting the first temperature and the synthesis time, the weight average molecular weight of the polycarbosilane can be adjusted. From the viewpoint of obtaining a polycarbosilane having a weight average molecular weight of 9000 or more, when the first temperature is 400 to 500° C., the synthesis time can be 6 hours or more. The synthesis time can be made longer as the first temperature becomes lower, and the synthesis time can be made shorter as the first temperature becomes higher.

[0036] As described above, the polycarbosilane synthesized by the polycarbosilane synthesis step has a weight average molecular weight of 9000 or more. Therefore, the method for producing polycarbosilane for producing silicon carbide fibers according to one embodiment of the present invention can produce polycarbosilane for producing silicon carbide fibers without performing a step of adjusting the molecular weight.

[0037] Furthermore, from the viewpoint of increasing the tensile strength of the silicon carbide fiber, the bonding index represented by the following formula (1), which is an index of the degree of branching of the polycarbosilane produced by the polycarbosilane synthesis step, is preferably 2.52 or more.

[0038] [Formula 1]

[0039]

[0040] [In formula (1),

[0041] X CH3 , X CH2 , X CH and X C It is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12.

[0042] Y SiH3 , Y SiH2 , Y SiH and Y Si It is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086.]

[0043] The "bonding index" in this specification is an indicator of the degree of branching of polycarbosilane, and is a value obtained by the above formula (1). In this specification, "branching" refers to the portion where carbon atoms or silicon atoms are bonded to atoms other than hydrogen atoms. For example, the branching of CH3-CH3 refers to the portion where the carbon atoms recorded on the left are bonded to atoms other than hydrogen atoms and the portion where the carbon atoms recorded on the right are bonded to atoms other than hydrogen atoms. Similarly, the branching of silicon atoms refers to the portion where all silicon atoms are bonded to atoms other than hydrogen atoms. Therefore, the larger the bonding index, the more highly branched the polycarbosilane is.

[0044] In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12. In this specification, "primary carbon" refers to carbon with three hydrogen atoms bonded to it. "Secondary carbon" refers to carbon with two hydrogen atoms bonded to it. "Tertiary carbon" refers to carbon with one hydrogen atoms bonded to it. "Quaternary carbon" refers to carbon with no hydrogen atoms bonded to it. In addition, in formula (1), 12 is the atomic weight of carbon. Therefore, X CH3 , X CH2 , X CH and X C The details are as shown in the following formulas (2) to (5).

[0045] [Formula 2]

[0046]

[0047] [Formula 3]

[0048]

[0049] [Formula 4]

[0050]

[0051] [Formula 5]

[0052]

[0053] Wherein, the weight % of primary carbon atoms, secondary carbon atoms and tertiary carbon atoms is the value obtained by dividing the weight % of hydrogen atoms of each carbon by the product of the number of hydrogen atoms bonded to each carbon and the atomic weight of hydrogen, multiplied by the atomic weight of carbon. It should be noted that in this specification, the atomic weight of hydrogen is used as 1 for calculation. In addition, the weight % of quaternary carbon atoms is the value obtained by deducting the weight % of primary carbon atoms, secondary carbon atoms and tertiary carbon atoms from the elemental analysis value of carbon atoms. Therefore, the weight % of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms are shown in detail in the following formulas (6) to (9). The elemental analysis value of carbon atoms can be obtained by a known method.

[0054] [Formula 6]

[0055]

[0056] [Formula 7]

[0057]

[0058] [Formula 8]

[0059]

[0060] [Formula 9]

[0061] Weight % of quaternary carbon atoms =

[0062] Elemental analysis value of carbon atoms (weight %) -

[0063] (weight % of primary carbon atoms + weight % of secondary carbon atoms + weight % of tertiary carbon atoms)

[0064] …(9)

[0065] The weight percent of hydrogen atoms in primary carbon, secondary carbon, and tertiary carbon is calculated by multiplying the elemental analysis value of hydrogen atoms by the weight percent of hydrogen atoms in primary carbon, secondary carbon, and tertiary carbon. 1 The area ratio of primary, secondary and tertiary carbon is obtained by H-NMR. 1 The area ratio of H-NMR is the ratio of each area ratio of hydrogen atoms of primary carbon, secondary carbon and tertiary carbon to the total area ratio obtained as follows: 1The area values ​​of Si-H and hydrogen atoms of primary, secondary and tertiary carbons measured by H-NMR are normalized. Therefore, the weight % of hydrogen atoms of primary, secondary and tertiary carbons are shown in detail in the following formulas (10) to (12).

[0066] [Formula 10]

[0067] Weight % of hydrogen atoms of primary carbon =

[0068] Primary Carbon 1 H-NMR area ratio × elemental analysis value of hydrogen atoms (weight %) (10)

[0069] [Formula 11]

[0070] Weight % of hydrogen atoms of secondary carbon =

[0071] Secondary carbon 1 H-NMR area ratio × elemental analysis value of hydrogen atoms (weight %) (11)

[0072] [Formula 12]

[0073] Weight % of hydrogen atoms of tertiary carbon =

[0074] Tertiary 1 H-NMR area ratio × elemental analysis value of hydrogen atoms (weight %) (12)

[0075] 1 The area values ​​of hydrogen atoms of primary carbon, secondary carbon and tertiary carbon in polycarbosilane in H-NMR can be obtained as follows: the signal of 5.5 to 3.5 ppm is taken as the signal from hydrogen (-SiH<) on tertiary silicon, the signal of 1.0 to 0 ppm is taken as the signal from hydrogen (CH3-) on primary carbon, the signal of 0 to -0.4 ppm is taken as the signal from hydrogen (-CH2-) on secondary carbon, and the signal of -0.4 to -1.0 ppm is taken as the signal from hydrogen (-CH<) on tertiary carbon, and the integral value is calculated. In addition, the elemental analysis value of hydrogen atoms can be obtained by a known method.

[0076] In addition, in formula (1), Y SiH3 , Y SiH2 , Y SiH and Y Si is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086. In this specification, "primary silicon" refers to silicon with three hydrogen atoms bonded to it. "Secondary silicon" refers to silicon with two hydrogen atoms bonded to it. "Tertiary silicon" refers to silicon with one hydrogen atoms bonded to it. "Quaternary silicon" refers to silicon with no hydrogen atoms bonded to it. In addition, in formula (1), 28.086 is the atomic weight of silicon. Therefore, Y SiH3 , Y SiH2, Y SiH and Y Si The details are as shown in the following formulas (13) to (16).

[0077] [Formula 13]

[0078]

[0079] [Formula 14]

[0080]

[0081] [Formula 15]

[0082]

[0083] [Formula 16]

[0084]

[0085] The weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms is obtained by multiplying the elemental analysis value of silicon atoms by the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms. 29 The area ratio of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms is obtained by Si-NMR. 29 The area ratio of Si-NMR is the ratio of each area ratio of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms to the total area ratio obtained by standardizing the area ratios of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms with quaternary silicon atoms. Therefore, the weight % of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms are shown in detail in the following formulas (17) to (20).

[0086] [Formula 17]

[0087] Weight % of primary silicon atoms =

[0088] Primary silicon atom 29 Area ratio of si-NMR × elemental analysis value of silicon atoms (weight %)…(17)

[0089] [Formula 18]

[0090] Weight % of secondary silicon atoms =

[0091] Secondary silicon atoms 29 Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(18)

[0092] [Formula 19]

[0093] Weight % of tertiary silicon atoms =

[0094] Tertiary silicon atom 29 Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(19)

[0095] [Formula 20]

[0096] Weight % of quaternary silicon atoms =

[0097] Quaternary silicon atom 29 Area ratio of Si-NMR × elemental analysis value of silicon atoms (weight %)…(20)

[0098] 29 The area ratio of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms in polycarbosilane in Si-NMR can be obtained as follows: the signal of 10 to -8 ppm is taken as the signal from quaternary silicon (>Si<), the signal of -8 to -24 ppm is taken as the signal from tertiary silicon (-SiH<), the signal of -30 to -50 ppm is taken as the signal from secondary silicon (-SiH2-), and the signal of -40 to -70 ppm is taken as primary silicon (-SiH3), and the integral value is calculated. In addition, the elemental analysis value of silicon atoms can be obtained by a known method.

[0099] By the above calculation method, the bonding index can be calculated.

[0100] In addition, the polycarbosilane produced by the polycarbosilane synthesis process has a higher softening point than the polycarbosilane obtained using acyclic polysilane. In this specification, the "softening point" refers to the temperature at which polycarbosilane begins to melt. Therefore, the polycarbosilane in the present embodiment can prevent the welding of fibers during firing. Specifically, the polycarbosilane in the present embodiment is preferably partially melted but maintained in a powder state, and more preferably completely maintained in a powder state when the polycarbosilane powder is heated at 390°C for 2 minutes. More specifically, the softening point in the present embodiment is preferably above 400°C, more preferably above 500°C at which polycarbosilane is actively molecularized and cross-linked, and further preferably above 600°C at which thermal decomposition from polycarbosilane to silicon carbide actively occurs.

[0101] Reference Figure 1 , an embodiment of the polycarbosilane synthesis process is described. Figure 1 This is a diagram showing a liquid-gas phase pyrolysis device 10 used for synthesizing polycarbosilane.

[0102] The liquid-gas phase pyrolysis device 10 includes a liquid phase reaction container 1 , a liquid phase heater 2 , a liquid phase thermocouple 3 , a gas phase reaction tube 4 , a gas phase heater 5 , a gas phase thermocouple 6 , a first cooling tube 7 , a flow meter 8 , and a valve 9 .

[0103] First, a cyclic silane compound is placed in a liquid phase reaction vessel 1, and heated at a first temperature using a liquid phase heater 2 under an inert gas, thereby generating a gas phase. As the inert gas, for example, nitrogen and argon can be used. The first temperature is measured using a liquid phase thermocouple 3. In addition, the amount of the inert gas is adjusted using a flow meter 8.

[0104] Next, the generated gas phase moves to the gas phase reaction tube 4 and is heated at a second temperature using the gas phase heater 5 to generate polycarbosilane. The second temperature is measured using the gas phase thermocouple 6.

[0105] Next, the generated polycarbosilane is cooled by the first cooling pipe 7, and the liquid phase is returned to the liquid phase reaction vessel 1, and heated at the first temperature by the liquid phase heater 2, thereby increasing the molecular weight of the polycarbosilane.

[0106] This series of reactions is repeated, and after a predetermined synthesis time has passed, the liquid phase and the gas phase are cooled, and then the synthesized polycarbosilane is collected from the liquid phase reaction apparatus 1. In this way, polycarbosilane is obtained.

[0107] (Other processes)

[0108] The production method according to one embodiment of the present invention may include other steps in addition to the polycarbosilane synthesis step. The other steps are not particularly limited as long as the effects of the present invention are not impaired.

[0109] The manufacturing method of one embodiment of the present invention may also include a removal step of adding a solvent to the synthesized polycarbosilane to remove insoluble components after the polycarbosilane synthesis step. The impurities contained in the polycarbosilane can be removed by the removal step. The insoluble components can be removed, for example, by filtration. The solvent is not particularly limited as long as it can extract polycarbosilane. As solvents, for example: aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene and mesitylene; aliphatic hydrocarbons such as hexane, heptane, octane and nonane; and halogenated hydrocarbons such as chloroform and dichloromethane. The amount of solvent added can be an amount in which polycarbosilane can be dissolved, and can be appropriately set by a person skilled in the art. The extraction temperature can be appropriately set by a person skilled in the art, for example, it can be room temperature (22°C).

[0110] In addition, the yield of polycarbosilane after molecular weight adjustment is higher than that of polycarbosilane produced by a process of adjusting the molecular weight. It should be noted that in this specification, "the yield of polycarbosilane after molecular weight adjustment" refers to the yield of PCS after molecular weight adjustment and subsequent removal of insoluble components from synthesized PCS.

[0111] [2. Method for producing silicon carbide fiber]

[0112] A method for producing silicon carbide fiber (hereinafter also referred to as "SiC fiber") according to one embodiment of the present invention includes a polycarbosilane synthesis step of synthesizing polycarbosilane having a weight average molecular weight of 9,000 or more, a spinning step of forming the polycarbosilane synthesized by the polycarbosilane synthesis step into a fiber shape, and a calcining step of calcining the polycarbosilane fiber produced by the spinning step, wherein the polycarbosilane synthesis step includes the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material, and heating it at the first temperature to increase the molecular weight of the polycarbosilane. With such a configuration, SiC fibers with high tensile strength can be produced.

[0113] In addition, according to the method for manufacturing silicon carbide fibers of one embodiment of the present invention, the yield of polycarbosilane after molecular weight adjustment is improved, so the total yield after the synthesis process is improved. Therefore, according to the method for manufacturing silicon carbide of one embodiment of the present invention, the yield of silicon carbide fibers from polycarbosilane can be improved. In this specification, "total yield after the synthesis process" refers to the product of the PCS yield (%) after molecular weight adjustment and the ceramic yield (%). "Ceramic yield (%)" refers to the yield of SiC fibers after sintering from raw silk.

[0114] (Polycarbosilane synthesis process)

[0115] The polycarbosilane synthesis step is the same as the description of the polycarbosilane synthesis step in [1. Method for producing polycarbosilane for producing silicon carbide fiber].

[0116] (Spinning process)

[0117] The spinning step is a step of forming the polycarbosilane synthesized in the polycarbosilane synthesizing step into a fiber shape.

[0118] As the spinning method, melt spinning, dry spinning and wet spinning can be listed. Dry spinning is preferred from the viewpoint that spinning can be performed even without high temperature conditions and there is no sharp temperature drop after spinning, thereby reducing the deviation of the fiber diameter. In the case of dry spinning, spinning can be performed, for example, by the following method. That is, the polycarbosilane of one embodiment of the present invention is dissolved in a solvent to adjust a dry spinning solution. Then, the dry spinning solution is supplied to a spinning device to generate polycarbosilane fibers.

[0119] The solvent for dissolving polycarbosilane may be any solvent that can dissolve polycarbosilane, and examples thereof include aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylene, and mesitylene; aliphatic hydrocarbons such as hexane, heptane, octane, and nonane; and halogenated hydrocarbons such as chloroform and dichloromethane. Toluene or xylene is preferably used to improve the solubility and volatility of polycarbosilane.

[0120] The concentration of the dry spinning solution can be appropriately adjusted by those skilled in the art, and can be, for example, 50 to 70%.

[0121] The viscosity of the dry spinning solution can be appropriately adjusted by a person skilled in the art according to the nozzle diameter of the spinning device, for example, when the nozzle diameter is 65 μm, it can be 10 to 30 Pa·s at 25° C. The viscosity can be obtained by a known method for measuring the viscosity of a solution, for example, it can be measured using an E-type viscometer.

[0122] The spinning device used for spinning can be any device commonly used in the art. For example, raw silk can be obtained by supplying a dry spinning solution to a spinning device and spinning under the conditions of a spinning nozzle diameter of 65 μm, a discharge pressure of 2 to 3.5 MPa, and a spinning speed of 10 to 30 mg / min. The raw silk produced under such conditions can be, for example, polycarbosilane fibers having a raw silk diameter of 17.0 to 19.0.

[0123] (Firing process)

[0124] The calcining step is a step of calcining the polycarbosilane fibers produced in the spinning step. The polycarbosilane fibers are calcined to form ceramics, thereby producing silicon carbide fibers.

[0125] The calcination conditions can be appropriately set by a person skilled in the art. For example, the calcination can be performed under the conditions described in Table 1 described later. In addition, the calcination can be performed under the conditions where the maximum temperature in Table 1 is changed to 1400° C. From the perspective of obtaining SiC fibers with high tensile strength, it is preferred that the maximum temperature be set to 1000° C.

[0126] The tensile strength can be measured by a known method. For example, a tensile test of a single fiber can be performed to measure the breaking stress, and the breaking stress can be divided by the cross-sectional area of ​​the SiC fiber to obtain the tensile strength.

[0127] The elastic modulus is a value calculated by dividing the obtained tensile strength by the elongation relative to the gauge length during the tensile test.

[0128] 〔Summarize〕

[0129] The method for manufacturing silicon carbide fibers of scheme 1 of the present invention includes the following steps: a polycarbosilane synthesis step for synthesizing polycarbosilane having a weight-average molecular weight of 9,000 or more; a spinning step for forming the polycarbosilane synthesized by the polycarbosilane synthesis step into a fibrous form; and a calcining step for calcining the polycarbosilane fibers generated by the spinning step, wherein the polycarbosilane synthesis step includes repeatedly performing the following treatments: heating a raw material containing a cyclic silane compound at a first temperature to generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; and cooling the polycarbosilane and returning it to the raw material and heating it at the first temperature to increase the molecular weight of the polycarbosilane, and the method for manufacturing silicon carbide fibers does not include a step for adjusting the molecular weight by removing low-molecular-weight polycarbosilane from the polycarbosilane synthesized by the polycarbosilane synthesis step.

[0130] In the method for producing silicon carbide fibers according to aspect 2 of the present invention, it is preferred that in the polycarbosilane synthesis step, polycarbosilane having a bonding index of 2.52 or more represented by the following formula (1), which is an index of the degree of branching, is synthesized.

[0131] [Formula 21]

[0132]

[0133] [In formula (1),

[0134] X CH3 , X CH2 , X CH and X C It is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12.

[0135] Y SiH3 , Y SiH2 , Y SiH and Y Si It is the value obtained by dividing the weight percentage of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms and quaternary silicon atoms by 28.086.]

[0136] In addition, the method for producing silicon carbide fibers according to aspect 3 of the present invention is preferably such that, in aspect 1 or 2, in the polycarbosilane synthesis step, polycarbosilane satisfying the following conditions is synthesized:

[0137] When the synthesized polycarbosilane powder was heated at 390°C for 2 minutes, it was able to maintain the powder state.

[0138] Furthermore, in the method for producing silicon carbide fibers according to aspect 4 of the present invention, in aspect 1 or 2, the cyclic silane compound is dodecamethylcyclohexasilane.

[0139] Furthermore, in the method for producing silicon carbide fibers according to aspect 5 of the present invention, in aspect 3, the cyclic silane compound is dodecamethylcyclohexasilane.

[0140] Example

[0141] The following examples are shown to further illustrate embodiments of the present invention. Of course, the present invention is not limited to the following examples, and it is beyond doubt that various schemes can be adopted for details. It should be noted that the reagents and devices of the manufacturers not recorded in the examples use the reagents and devices commonly used in the art.

[0142] 〔1. Synthesis of polycarbosilane (PCS)〕

[0143] [Synthesis example 1]

[0144] Dodecamethylcyclohexasilane (DMCHS) was added to Figure 1 The liquid phase in the liquid phase reaction vessel of the liquid phase-gas phase pyrolysis device shown in FIG. Next, the liquid phase in the liquid phase reaction vessel is heated to 400-500° C., and the gas phase in the gas phase reaction tube is heated to 600° C., and the reaction is carried out for 6 hours and 30 minutes to synthesize PCS. DMCHS uses DMCHS produced according to a known production method.

[0145] [Synthesis example 2]

[0146] PCS was synthesized in the same manner as in Synthesis Example 1 except that the reaction time was 6 hours.

[0147] [Synthesis example 3]

[0148] PCS was synthesized in the same manner as in Synthesis Example 1 except that polydimethylsilane (PDMS) was added to the liquid phase reaction vessel instead of DMCHS and the reaction time was changed to 8 hours.

[0149] [Synthesis Example 4]

[0150] PCS was synthesized in the same manner as in Synthesis Example 1 except that the reaction time was 5 hours.

[0151] 〔2. Molecular weight adjustment and impurity removal〕

[0152] [Examples 1 and 2 and Comparative Examples 1 and 2]

[0153] The PCS synthesized in Synthesis Examples 1 to 4 were dissolved in toluene at room temperature without molecular weight adjustment. After removing the insoluble components by filtration, the PCS obtained by removing the solvent were designated as Examples 1 to 2 and Comparative Examples 1 to 2.

[0154] [Comparative Examples 3-4]

[0155] The PCS synthesized in Synthesis Examples 3 to 4 was washed 4 times at 50° C. using ethyl acetate 5 times by weight, thereby separating into a soluble component and an insoluble component, thereby adjusting the molecular weight. Then, the insoluble component was dissolved in toluene at room temperature. After removing the insoluble component by filtration, the PCS obtained by removing the solvent was used as Comparative Examples 3 to 4.

[0156] [Reference Example 1]

[0157] PCS was obtained in the same manner as in Comparative Examples 3 and 4 except that ethyl acetate was used in an amount 5 times the weight of PCS synthesized in Synthesis Example 1.

[0158] [Reference Examples 2 to 5]

[0159] PCS was obtained in the same manner as in Comparative Examples 3 and 4 except that ethyl acetate was used in an amount 5 times the weight of PCS synthesized in Synthesis Example 2 and the PCS was washed 1 to 4 times at 50° C. to adjust the molecular weight.

[0160] 〔3. Spinning〕

[0161] The PCS from which the insoluble components were removed was dissolved in xylene so that the viscosity of the spinning solution at 25°C was 16 to 25 Pa·s to prepare a dry spinning solution. The prepared solution was then extruded from a spinneret (nozzle) having a nozzle diameter of 65 μm and wound to obtain polycarbosilane fibers (raw silk) having a yarn diameter of 17 to 19 μm.

[0162] 〔4. Firing〕

[0163] The PCS raw yarns of Examples 1 to 2, Comparative Examples 1 to 4, and Reference Examples 1 to 5 were sintered at a maximum temperature of 1000° C. under the conditions shown in Table 1 to obtain silicon carbide fibers.

[0164] [Table 1]

[0165]

[0166] Silicon carbide fibers were obtained by firing the PCS raw yarns of Example 1 and Reference Example 1 under conditions where the maximum temperature was changed to 1400°C.

[0167] 〔5. Evaluation〕

[0168] (Confirmation of the melting behavior of PCS)

[0169] The PCS of Examples 1 to 2 and Comparative Examples 1 to 2 were filled into glass tubes, respectively, and the inside of the tubes was replaced with argon and sealed. It was placed in a melting point measuring machine (Buchi, B-545) with the temperature in the device pre-heated to 390°C, and allowed to stand for 2 minutes. After standing, the state of the PCS filled in the tube was visually confirmed. It can be said that the longer the PCS powder state is maintained, the higher the softening point, and the more the amount melted, the lower the softening point.

[0170] (Elemental Analysis)

[0171] The oxygen content of the PCS synthesized in Synthesis Examples 1 to 4 and the PCS of Examples 1 to 2, Comparative Examples 1 to 4 and Reference Examples 1 to 5 was measured using EMGA-930 manufactured by Horiba, Ltd., the elemental analysis value of carbon atoms was measured using a carbon-sulfur analyzer CS844 manufactured by LECO, and the elemental analysis value of hydrogen atoms was measured using Series II CHNS / OANLYZER 2400 manufactured by Perkin Elmer. The elemental analysis value of silicon atoms is the remaining amount after removing the elemental analysis values ​​of carbon and hydrogen and the oxygen content from the total ratio (100%).

[0172] (Determination of Molecular Weight)

[0173] The molecular weights of the PCS synthesized in Synthesis Examples 1 to 4, and the PCS of Examples 1 to 2, Comparative Examples 1 to 4, and Reference Examples 1 to 5 were determined by GPC measurement under the following conditions.

[0174] Apparatus name: HPLC manufactured by Shimadzu Corporation.

[0175] Chromatographic columns: One each of KF-604, KF-602, and KF-601 (all manufactured by Showa Denko K.K.) were connected and used so as to flow liquid in sequence from the pump side.

[0176] Measurement solvent: toluene.

[0177] Flow rate: analytical part and reference: 0.40 mL / min.

[0178] Oven: 40℃.

[0179] Detector: Differential refractometer (RID-20A manufactured by Shimadzu Corporation).

[0180] Sample solution: 0.5 wt%.

[0181] ( 1 H-NMR analysis)

[0182] The PCS synthesized in Synthesis Examples 1 to 4, as well as the PCS of Examples 1 to 2, Comparative Examples 1 to 4, and Reference Examples 1 to 5 were dissolved in deuterated chloroform and subjected to the following conditions:1 H-NMR analysis. The signal of 5.5 to 3.5 ppm is taken as the signal from hydrogen on tertiary silicon (-SiH<), the signal of 1.0 to 0 ppm is taken as the signal from hydrogen on primary carbon (CH3-), the signal of 0 to -0.4 ppm is taken as the signal from hydrogen on secondary carbon (-CH2-), and the signal of -0.4 to -1.0 ppm is taken as the signal from hydrogen on tertiary carbon (-CH<), and the integral value is calculated. It should be noted that the signal from hydrogen on primary and secondary silicon cannot be confirmed.

[0183] Measuring equipment: JNM-ECZ600R / S1 (manufactured by JEOL Ltd.).

[0184] Cumulative number of times: 8 times.

[0185] ( 29 Si-NMR analysis)

[0186] The PCS synthesized in Synthesis Examples 1 to 4, as well as the PCS of Examples 1 to 2, Comparative Examples 1 to 4, and Reference Examples 1 to 5 were dissolved in deuterated chloroform and subjected to the following conditions: 29 Si-NMR analysis: The signal from 10 to -8 ppm was regarded as the signal from quaternary silicon (>Si<), and the signal from -8 to -24 ppm was regarded as the signal from tertiary silicon (-SiH<), and the integral value was calculated. It should be noted that the signals from primary silicon and secondary silicon could not be confirmed.

[0187] Measuring equipment: JNM-ECZ600R / S1 (manufactured by JEOL Ltd.).

[0188] Details of the measurement method: The measurement was carried out under a pulse sequence with no rotation; 45 degree pulse irradiation; acquisition time 0.659 seconds; and delay interval 16 seconds.

[0189] Cumulative number of times: 512 times.

[0190] (Determination of Spinning Solution Viscosity)

[0191] An E-type viscometer (ARES-G2 manufactured by TA Instruments) was used at a temperature of 25°C and a shear rate of 200 sec. -1 The viscosity of the dry spinning solution was measured under the conditions of .

[0192] (Calculation of bonding index)

[0193] Calculations were performed according to the formulas (1) to (20) described in the above embodiment. However, primary silicon and secondary silicon were not confirmed.

[0194] (yield)

[0195] The yield in the polycarbosilane synthesis step was calculated as a weight yield expressed as a percentage by dividing the weight of PCS obtained from the liquid phase reaction vessel by the weight of the raw materials charged into the reaction vessel.

[0196] The PCS yield after molecular weight adjustment was calculated as a weight yield in percentage by dividing the dry weight of PCS obtained after molecular weight adjustment and subsequent removal of insoluble components by the weight of PCS before molecular weight adjustment.

[0197] The ceramic yield in the firing step was calculated as a weight yield in percentage by dividing the weight of the SiC fiber after firing by the weight of the raw silk charged into the firing device.

[0198] The total yield after the synthesis step was calculated as the product of the molecular weight-adjusted PCS yield and the ceramic yield. However, when the molecular weight adjustment was not performed, the molecular weight-adjusted PCS yield was set to 100% for calculation.

[0199] (Wire diameter)

[0200] The diameter of the SiC fiber was measured at a magnification of 2000 times using an optical microscope VHX-5000 manufactured by KEYENCE CORPORATION.

[0201] (Tensile Strength)

[0202] Using STA-1150 manufactured by ORIENTEC Co., Ltd., a tensile test of a single filament was performed with a gauge length of 25 mm and a crosshead speed of 5 mm / min to determine the breaking stress. The measured breaking stress was divided by the cross-sectional area of ​​the SiC fiber to obtain the tensile strength. The tensile strength of the present application was the average value of 10 tensile tests.

[0203] (Elastic modulus)

[0204] The elastic modulus is calculated by dividing the obtained tensile strength by the elongation relative to the gauge length during the tensile test.

[0205] 〔6. Results〕

[0206] The above evaluation results are shown in Tables 2 to 5. Specifically, the evaluation results of PCS after synthesis are shown in Table 2, the evaluation results of PCS after the molecular weight adjustment and insoluble component removal process are shown in Table 3, the evaluation results of PCS fibers after spinning are shown in Table 4, and the evaluation results of SiC fibers after calcination are shown in Table 5. In addition, the results of confirming the melting behavior of PCS and the tensile strength of SiC fibers obtained by calcination at 1000°C are shown in Table 3. Figure 2 It should be noted that Tables 2 to 5 and Figure 2In the data, straight lines are recorded for items where no data was measured, and data that could not be measured are recorded as unmeasured. In addition, "PCS yield after molecular weight adjustment (%)", "ceramic yield (%)" and "total yield after synthesis step (%)" are the same as those described in [1. Method for producing polycarbosilane for silicon carbide fiber production] and [2. Method for producing silicon carbide fiber].

[0207] [Table 2]

[0208]

[0209] [Table 3]

[0210]

[0211] [Table 4]

[0212]

[0213] [Table 5]

[0214]

[0215] In addition, a graph showing the relationship between the number of molecular weight adjustment of the polycarbosilane synthesized in Synthesis Example 1 and Synthesis Example 2 and the total yield (%) after the synthesis step is shown in FIG. Figure 3 .exist Figure 3 In the graph, the horizontal axis represents the number of molecular weight adjustments, and the vertical axis represents the total yield (%) after the synthesis step.

[0216] From Tables 2 to 5 and Figure 3 It is known that the polycarbosilane produced by the method for producing polycarbosilane according to one embodiment of the present invention can produce silicon carbide fibers without performing a molecular weight adjustment step. Figure 2 It can be seen that the polycarbosilane produced by the method for producing polycarbosilane according to one embodiment of the present invention has a high softening point. Therefore, it is shown that the polycarbosilane produced by the method for producing polycarbosilane according to one embodiment of the present invention is not easy to fuse during the firing process in the process of producing silicon carbide fibers. The above shows that according to the method for producing polycarbosilane according to one embodiment of the present invention, in the method for producing polycarbosilane using the liquid-gas phase pyrolysis condensation method, polycarbosilane for producing silicon carbide fibers can be produced with fewer steps than in the conventional production method.

[0217] In addition, from Table 3, Table 5 and Figure 3It can be seen that the yield of polycarbosilane after molecular weight adjustment is increased in the polycarbosilane produced by the method for producing polycarbosilane according to one embodiment of the present invention compared to the polycarbosilane produced by the process of adjusting the molecular weight. Therefore, it can be seen that the total yield after the synthesis process is increased. The above shows that the method for producing silicon carbide according to one embodiment of the present invention can improve the yield of silicon carbide fibers obtained from polycarbosilane.

[0218] Industrial Applicability

[0219] The invention can be used for manufacturing silicon carbide fibers.

[0220] Description of Reference Numerals

[0221] 1: Liquid phase reaction vessel;

[0222] 2: Liquid phase heater;

[0223] 3: Liquid phase thermocouple;

[0224] 4: Gas phase reaction tube;

[0225] 5: Gas phase heater;

[0226] 6: Gas phase thermocouple;

[0227] 7: first cooling pipe;

[0228] 8: Flow meter;

[0229] 9: Valve;

[0230] 10: Liquid-gas phase pyrolysis device.

Claims

1. A method for producing silicon carbide fiber, comprising the following steps: A polycarbosilane synthesis step of synthesizing polycarbosilane having a weight average molecular weight of 9000 or more; a spinning step of forming the polycarbosilane synthesized in the polycarbosilane synthesizing step into a fiber shape; and a calcining step of calcining the polycarbosilane fibers produced by the spinning step; in, The polycarbosilane synthesis process comprises repeatedly performing the following treatments: A process of heating a raw material including a cyclic silane compound at a first temperature to generate a gas phase; heating the gas phase at a second temperature higher than the first temperature to generate polycarbosilane; as well as The polycarbosilane is cooled and returned to the raw material, and then heated at the first temperature, thereby performing a treatment to increase the molecular weight of the polycarbosilane. The method for producing silicon carbide fibers does not include a step of removing low-molecular-weight polycarbosilane from the polycarbosilane synthesized in the polycarbosilane synthesizing step to adjust the molecular weight.

2. The method for producing silicon carbide fiber according to claim 1, wherein: In the polycarbosilane synthesis step, a polycarbosilane having a bonding index of 2.52 or more represented by the following formula (1) as an index of the degree of branching is synthesized. [Formula 1] In formula (1), X CH3 , X CH2 , X CH and X C is the value obtained by dividing the weight percentage of primary carbon atoms, secondary carbon atoms, tertiary carbon atoms and quaternary carbon atoms by 12. SiH3 , Y SiH2 , Y SiH and Y Si These are values ​​obtained by dividing the weight % of each of primary silicon atoms, secondary silicon atoms, tertiary silicon atoms, and quaternary silicon atoms by 28.

086.

3. The method for producing silicon carbide fiber according to claim 1 or 2, wherein: In the polycarbosilane synthesis step, polycarbosilane satisfying the following conditions is synthesized: When the synthesized polycarbosilane powder was heated at 390°C for 2 minutes, it was able to maintain the powder state.

4. The method for producing silicon carbide fiber according to claim 1 or 2, wherein: The cyclic silane compound is dodecamethylcyclohexasilane.

5. The method for producing silicon carbide fiber according to claim 3, wherein: The cyclic silane compound is dodecamethylcyclohexasilane.

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