Porous silicon carbide body and its manufacturing method

Abstract

To provide a method for easily producing a silicon carbide porous body having the distribution of a large number of pores having an average pore diameter in the range of several tens nm to several hundreds nm, without causing a load on the environment.SOLUTION: A raw material which is an organosilicon polymer is continuously heated to a predetermined temperature within a range from room temperature to 1000 to 1400°C in a vacuum and maintained at the predetermined temperature for a predetermined time, thereby evaporating the raw material and adhering the generated raw material vapor to a substrate. Thereby, a silicon carbide porous body in which a large number of pores having an average pore diameter within a range of 30 to 300 nm are formed in a base material mainly composed of silicon carbide having a β structure can be easily obtained without causing a load on the environment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a porous silicon carbide (SiC) body used for filters, catalyst supports, etc., and a method for producing the same. [Background technology]

[0002] Porous silicon carbide is a material in which numerous pores are formed within a silicon carbide matrix. Such porous silicon carbide is a material that can be used as a filter that removes particles, viruses, and other substances contained in liquids or gases by trapping them in the pores, or as a carrier that supports a catalyst in the pores.

[0003] Non-Patent Document 1 describes a method for producing a porous silicon carbide body by mixing spherical silica (SiO2) particles (pore-forming material) with a silicon-containing organic compound and firing the mixture at 1200°C to produce a composite of silica particles and silicon carbide, and then dissolving and removing the silica particles with hydrofluoric acid. According to Non-Patent Document 1, the average pore size (diameter) of the pores in the porous silicon carbide body produced by this method is 340 nm. Examples of the silicon-containing organic compound that can be used include polymethylsilane (PMS) and polycarbosilane (PCS).

[0004] On the other hand, Patent Document 1 describes that a silicon-containing polymer compound is heated in a vacuum or in an inert gas such as nitrogen gas or argon gas at a temperature of 200 to 400°C for at least one hour to form a crosslinked body in which the polymer compounds are crosslinked to each other, and that a silicon carbide porous body having a large number of pores with an average pore size of 2 nm or less is obtained by subsequently heating at a temperature in the range of 500 to 1300°C (however, in the examples, only 653°C or 700°C) for at least one hour. Patent Document 1 also describes that the silicon-containing polymer compound can be polymethylsilane, polydimethylsilane (PDMS), polysilylenemethylene, polycarbosilane, etc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-022823 [Non-patent literature]

[0006] [Non-Patent Document 1] In-Kyung Sung and 3 others, "Fabrication of macroporous SiC from templated preceramic polymers", Chemical Communications, (UK), Royal Society of Chemistry, June 10, 2002, Vol. 38, No. 14, pp. 1480-1481. [Non-patent document 2] "Development of Silicon Carbide Materials," edited by Kiyoto Okamura, (Japan), CMC Publishing Co., Ltd., September 2003, p. 132 Summary of the Invention [Problem to be solved by the invention]

[0007] In general, it is considered appropriate that the pore size of a filter used to remove microorganisms such as viruses and bacteria from a fluid is in the range of several tens to several hundreds of nanometers. The silicon carbide porous body described in Patent Document 1 has an average pore size of 2 nm or less as described above, and therefore cannot be used as a filter for removing microorganisms.

[0008] On the other hand, the silicon carbide porous body produced by the method described in Non-Patent Document 1 has an average pore diameter of 340 nm, and therefore can be used as a filter for removing microorganisms. However, the method described in Non-Patent Document 1 requires skill to mix the silica particles used as the pore-forming material and the silicon-containing organic compound to a nearly uniform degree. In addition, the hydrofluoric acid used in the process of removing the pore-forming material is designated as a toxic substance, and the process generates a waste liquid (solution) in which silica is dissolved in hydrofluoric acid, which places a burden on the environment.

[0009] The problem to be solved by the present invention is to provide a method for easily producing a silicon carbide porous body having a large number of pores distributed therein, each having an average pore size in the range of several tens to several hundreds of nanometers, without imposing a burden on the environment. [Means for solving the problem]

[0010] The present invention provides a method for producing a silicon carbide porous body, which is achieved in order to solve the above problems, comprising: containing carbon atoms The raw material, which is an organosilicon polymer, is continuously heated in a vacuum from room temperature to a predetermined temperature within the range of 1000 to 1400°C, and maintained at that temperature for a predetermined time, thereby evaporating the raw material and attaching the generated raw material vapor to the substrate. It is characterized by:

[0011] In the method of the present invention, an organosilicon polymer, which is a polymer containing silicon atoms and carbon atoms, is used as a raw material, and the raw material is continuously heated in a vacuum from room temperature to a predetermined temperature within the range of 1000 to 1400°C (preferably 1100 to 1300°C). Here, "continuously raising the temperature from room temperature to the predetermined temperature" means raising the temperature to the predetermined temperature without temporarily stopping the temperature rise between room temperature and the predetermined temperature (for example, a temperature within the range of 200 to 400°C as described in Patent Document 1). The rate of temperature rise does not need to be constant.

[0012] By raising the temperature of the raw material to the predetermined temperature in this manner, the raw material decomposes and evaporates as a low-molecular-weight gas. The vapor of the evaporated raw material (raw material vapor) is then deposited on the substrate. At this time, the low-molecular-weight molecules in the raw material vapor decompose on the surface of the substrate. As a result, carbon atoms and silicon atoms are deposited on the surface of the substrate, and these deposits form a silicon carbide porous body on the surface of the substrate. Note that if a specific temperature of 400°C or less is maintained during the temperature rise to the predetermined temperature, the raw material is less likely to evaporate even when heated to the predetermined temperature.

[0013] Examples of organosilicon polymers, which are raw materials used in the method of the present invention, include polysilane, polycarbosilane, polysiloxane, polysilazanes, polymetallosiloxanes, polycarboranesiloxanes, etc. The raw materials are not limited to these examples, and any organosilicon polymer can be used as long as it decomposes and evaporates at the predetermined temperature.

[0014] The silicon carbide porous body produced by the method of the present invention has a large number of pores with an average pore size in the range of 30 to 300 nm. Porous bodies with such pore sizes are suitable for use as filters for removing microorganisms such as viruses and bacteria, suspended particulate matter, and the like. For example, coronaviruses and influenza viruses have diameters of approximately 100 nm, noroviruses have diameters of approximately 30 nm, and suspended particulate matter contained in cigarette smoke has diameters of 100 nm to several hundred nm, all of which can be captured by the pores of the silicon carbide porous body produced by the method of the present invention. These substances to be removed can be attached to the silicon carbide porous body and then heated to burn and remove them, allowing the filter made of the silicon carbide porous body to be reused.

[0015] The method of the present invention makes it possible to easily produce a silicon carbide porous body without the need to mix multiple materials, and does not generate waste such as waste liquids that are a burden on the environment.

[0016] The substrate can typically be plate-shaped, but may have other shapes. Alternatively, the substrate may be the wall of a vacuum vessel used to place raw materials in a vacuum (i.e., the silicon carbide porous body is formed on the wall surface of this wall). After the silicon carbide porous body is formed on the surface of the substrate, it may be peeled off from the surface of the substrate, but may be left deposited on the surface of the substrate depending on the application of the silicon carbide porous body.

[0017] In addition, the silicon carbide porous body produced by the method of the present invention may contain, in addition to silicon carbide, elemental carbon that does not constitute the crystal structure of silicon carbide (hereinafter simply referred to as "elemental carbon"), and unavoidable impurities.

[0018] In the method according to the present invention, it is preferable to further heat the deposit formed on the substrate by adhering the raw material vapor to the substrate in air at a second predetermined temperature in the range of 500 to 800°C. This removes at least a portion of the elemental carbon from the deposit as carbon dioxide or carbon monoxide, thereby obtaining a silicon carbide porous body with a lower elemental carbon content and higher purity. This improves the performance as a filter or catalyst support.

[0019] If the deposit is heated to a temperature exceeding 800°C, the shape of the porous silicon carbide cannot be maintained, so the second predetermined temperature is set to 800°C or lower. Furthermore, if the deposit is heated in air at a temperature below 500°C, almost no elemental carbon can be removed. Therefore, the second predetermined temperature is set to 500°C or higher.

[0020] It is also known that silicon carbide does not decompose when heated in air at the second predetermined temperature. For example, Figures 1 and 4 of Non-Patent Document 2 show that a sample of silicon carbide fiber heated in air at 800°C (the highest temperature within the second predetermined temperature range) for 10 hours shows almost no decrease in tensile strength compared to before heating, indicating that the silicon carbide is maintained stably without decomposition by this heating. This indicates that heating the deposit in air at the second predetermined temperature selectively removes carbon that does not constitute the silicon carbide crystal structure.

[0021] Heating to the second predetermined temperature in air may be performed while the deposit remains on the substrate, or may be performed after the deposit has been peeled off from the substrate.

[0022] Silicon carbide is a substance that can have more than 100 different crystal structures (so-called polymorphism). The silicon carbide in the silicon carbide porous body obtained by the method of the present invention has a cubic crystal structure called β-type, among the many crystal structures.

[0023] The silicon carbide porous body according to the present invention is characterized in that a large number of pores having an average pore diameter within a range of 30 to 300 nm are formed in a base material mainly composed of silicon carbide having a β structure.

[0024] In addition to silicon carbide, the base material may contain carbon that does not constitute the crystal structure of silicon carbide, and unavoidable impurities.

[0025] When the silicon carbide porous body according to the present invention is produced by the above-described production method, not only a plate-shaped silicon carbide porous body having a shape corresponding to the surface shape of the substrate used in production is obtained, but also a granular silicon carbide porous body having an average particle size in the range of 1 to 10 μm (mostly 5 μm or less). Such fine granular silicon carbide porous bodies can be suitably used, for example, as a filler material for a silicon carbide matrix to fill gaps formed in a ceramic matrix composite (CMC) formed by embedding fine silicon carbide fibers in a silicon carbide matrix. [Effects of the Invention]

[0026] According to the present invention, a porous silicon carbide body having a large number of pores with an average pore size in the range of 30 to 300 nm distributed therein can be easily produced without imposing a burden on the environment. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flowchart showing a first embodiment of a method for producing a silicon carbide porous body according to the present invention. [Figure 2] A conceptual diagram showing the state in which the raw material and the substrate are contained in a vacuum container. [Figure 3A]FIG. 1 is a diagram showing a process of vacuum-sealing raw materials in a quartz tube, which is part of the process of an experiment conducted by the inventor. [Figure 3B] FIG. 1 is a diagram showing a state in which raw materials are vacuum-sealed in a quartz tube in one step of an experiment conducted by the present inventor. [Figure 4A] A micrograph of a porous silicon carbide body made from PCS as the raw material at a target temperature (predetermined temperature) of 1000°C. [Figure 4B] A micrograph of the same sample as in Figure 4, taken at a higher magnification. [Figure 5A] A micrograph of a porous silicon carbide body made from PCS as the raw material at a target temperature of 1100°C. [Figure 5B] Micrograph of the same sample as in Figure 5A, taken at higher magnification. [Figure 6A] A micrograph of a porous silicon carbide body made from PCS as the raw material at a target temperature of 1200°C. [Figure 6B] Micrograph of the same sample as in Figure 6A, taken at higher magnification. [Figure 6C] A micrograph of the same sample as in Figures 6A and 6B, taken at a higher magnification. [Figure 7A] A micrograph of a porous silicon carbide body made from PCS as the raw material at a target temperature of 1300°C. [Figure 7B] Micrograph of the same sample as in Figure 7A, taken at higher magnification. [Figure 8A] A micrograph of a porous silicon carbide body made from PCS as the raw material at a target temperature of 1400°C. [Figure 8B] Micrograph of the same sample as in Figure 8A, taken at higher magnification. [Figure 9A] 1 is a comparative example, a micrograph of a silicon carbide porous body produced using PCS as a raw material at a target temperature of 800°C. [Figure 9B] 1 is a comparative example, a micrograph of a porous silicon carbide body produced using PCS as a raw material at a target temperature of 900°C. [Figure 10] 1 shows the results of X-ray photoelectron spectroscopy of a porous silicon carbide body produced using PCS as the raw material at a target temperature of 1200°C. [Figure 11] FIG. 1 shows the results of X-ray diffraction measurements of porous silicon carbide bodies produced using PCS as the raw material at target temperatures of 1000°C and 1200°C, as well as the raw material. [Figure 12] 1 is a graph showing the results of X-ray diffraction measurement of a porous plate formed on the inner surface of a quartz tube, prepared using PCS as the raw material at a target temperature of 1200°C, together with the quartz tube. [Figure 13] This figure shows the results of elemental analysis of a silicon carbide porous body fabricated using PCS as the raw material at a target temperature of 1200°C, using an energy dispersive X-ray analyzer attached to a scanning electron microscope. [Figure 14] A micrograph of a porous silicon carbide body made using PDMS as the raw material at a target temperature (predetermined temperature) of 1200°C. [Figure 15] 4 is a flowchart showing a second embodiment of a method for producing a silicon carbide porous body according to the present invention. [Figure 16A] 10 is a micrograph of a silicon carbide porous body obtained by heating in air at a second predetermined temperature of 500°C for a second predetermined time of 8 hours. [Figure 16B] 10 is a micrograph of a silicon carbide porous body obtained by heating in air at a second predetermined temperature of 600°C for a second predetermined time of 2 hours. [Figure 16C] 10 is a micrograph of a porous silicon carbide body obtained by heating in air at a second predetermined temperature of 800°C for a second predetermined time of 2 hours. [Figure 17] 10 is a micrograph of a comparative example of silicon carbide that was obtained by heating in air at a second predetermined temperature of 800° C. for a second predetermined time of 2 hours, and that was unable to maintain its porous shape. [Figure 18] 6 is a graph showing the results of measuring the carbon content of the silicon carbide porous body obtained by the method of the second embodiment using an energy dispersive X-ray analyzer (SEM-EDS) mounted on a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0028] 1 to 18, an embodiment of a porous silicon carbide body and a method for producing the same according to the present invention will be described.

[0029] (1) Method for producing a silicon carbide porous body according to the first embodiment Figure 1 shows the process flow for the first embodiment of the method for producing a silicon carbide porous body. First, an organosilicon polymer is prepared as a raw material (step S1). In the experiments conducted by the inventors, polydimethylsilane (PDMS, a type of polysilane) and polycarbosilane (PCS) were used as organosilicon polymers, but the present invention is not limited to these two types.

[0030] Next, as shown in Fig. 2, the raw material 11 and the substrate 12 prepared in step S1 are placed in a vacuum vessel 13. An exhaust pipe 14 is connected to the vacuum vessel 13, and a valve 15 and a vacuum pump 16 are connected to the exhaust pipe 14. Next, the vacuum pump 16 is operated and the valve 15 is opened to evacuate the vacuum vessel 13, thereby creating a vacuum inside the vacuum vessel 13 (step S2). After that, the valve 15 Close the vacuum pump 16 Stop.

[0031] The substrate 12 may be separate from the vacuum vessel 13, but since porous silicon carbide is deposited on the inner wall surface 131 of the vacuum vessel 13 as described below, the inner wall surface 131 of the vacuum vessel 13 may also be used as the substrate 12. The vacuum vessel 13 may be made of quartz, for example. Alternatively, a disposable vacuum vessel 13 may be used.

[0032] In an experiment conducted by the inventor, a quartz tube was used as the vacuum vessel 13. In this experiment, first, one end of a quartz tube 133, which has both open ends, was heated and sealed with a gas burner. After cooling the quartz tube 133, raw material 11 was introduced into the quartz tube 133 from the other end 135 of the quartz tube 133. Then, a portion 136 of the quartz tube 133 between the position where the raw material 11 was introduced and the other end 135 was heated with a gas burner or the like to narrow the tube diameter (FIG. 3A). While evacuating the inside of the quartz tube 133 from the other end 135, the narrowed portion 136 was further heated with a gas burner or the like to seal it (FIG. 3B). As a result, the raw material 11 (and the substrate, which is the inner wall surface 131 of the quartz tube 133) was introduced into the vacuum vessel 13, which was made of the quartz tube 133, and the inside was placed in a vacuum state. In this case, a separate valve was used to seal the quartz tube 133 itself. 15 In this case, since the vacuum vessel 13 (quartz tube 133) needs to be destroyed when the silicon carbide porous body is taken out from the vacuum vessel 13, the vacuum vessel 13 becomes disposable.

[0033] Next, the inside of the vacuum vessel 13 is cooled to room temperature T R to a target temperature (predetermined temperature) T within the range of 1000 to 1400 ° C. t The temperature is continuously increased to the target temperature T t The temperature is maintained at room temperature T for a predetermined time (for example, 1 to 10 hours) (step S4). R and target temperature T t The temperature is increased without stopping the temperature increase temporarily between the temperatures. The temperature increase rate may be constant or may change during the temperature increase. After that, the temperature inside the vacuum vessel 13 is increased to room temperature T R The temperature is lowered to 100° C., and the substrate 12 or the deposits deposited on the surface of the substrate 12 are removed (step S5).

[0034] As described above, while the inside of vacuum vessel 13 is being heated, raw material 11 evaporates, and silicon atoms and carbon atoms contained in the evaporated raw material 11 form a porous silicon carbide body (the deposit) on the surface of substrate 12. Note that, as described above, valve 16 is closed or quartz tube 133 is sealed before heating begins, so the evaporated raw material 11 does not flow out of vacuum vessel 13. This porous silicon carbide body has a large number of pores with an average pore diameter in the range of 30 to 300 nm in a base material mainly composed of silicon carbide having a β structure.

[0035] In addition, the raw materials 11, PCS and PDMS, contain hydrogen atoms in addition to silicon and carbon, but the hydrogen atoms remain in the vacuum vessel 13 as gas or as residues of the raw materials 11 and do not contribute to the formation of a silicon carbide porous body.

[0036] If the temperature rise is stopped for a certain period of time at a specific temperature below 450°C, the target temperature T t , the raw material 11 is difficult to evaporate even when the temperature reaches room temperature T R to target temperature T t The temperature is increased continuously until

[0037] (2) Examples of porous silicon carbide bodies produced by the method of the first embodiment Next, an example of a silicon carbide porous body manufactured by the method of the first embodiment will be described. Here, PCS is used as the raw material, and the silicon carbide porous body is heated to a target temperature T t Five examples are shown, where the temperatures are 1000°C, 1100°C, 1200°C, 1300°C, and 1400°C, respectively, and PDMS is used as the raw material and the target temperature T t In addition, PCS is used as the raw material and the target temperature T t The experimental results are also shown for two comparative examples in which the target temperature T tThe time for which the temperature was maintained at this temperature (the predetermined time) was 2 hours. PDMS used was a commercially available product manufactured by Nippon Soda Co., Ltd. The PCS (the raw material for the silicon carbide porous body) was prepared by baking PDMS (as the raw material for PCS) in a vacuum at a temperature in the range of 335 to 450°C (preferably in the range of 350 to 450°C at which PDMS is completely liquefied) for 10 hours, and then cooling it to room temperature.

[0038] 4 to 8 show micrographs taken with a scanning electron microscope of porous silicon carbide bodies fabricated using PCS as a raw material. t are 1000°C (Fig. 4), 1100°C (Fig. 5), 1200°C (Fig. 6), 1300°C (Fig. 7), and 1400°C (Fig. 8). Each figure shows two (each figure except Fig. 6) or three (Fig. 6) micrographs at different magnifications. Fig. 9 shows a micrograph of the sample of the comparative example (the target temperature during fabrication was 800°C in Fig. 9A and 900°C in Fig. 9B).

[0039] From these micrographs, it is clear that the target temperature during heating, T t It can be seen that in all cases where the temperature was within a range of 1000 to 1400°C, spherical granules were obtained as granular porous bodies 20 in which numerous pores 22 were formed in the base material 21. Furthermore, as shown in Figs. 6A and 8B, for example, a plate-like porous body 20A was formed behind the granular porous body 20. In contrast, in the comparative example, although spherical granules were formed, no pores were observed.

[0040] The diameter of the pores 22 in each sample of this example, estimated from these micrographs, was t The thickness is 30 to 50 nm for the 1000 °C sample, 100 to 300 nm for the 1200 °C sample, and around 100 nm for the 1400 °C sample. t In the sample at 1400° C., the area occupied by the base material 21 is larger than in the other samples of this embodiment.

[0041] The overall diameter of the granular porous body 20 is in the range of 1 to 10 μm in all samples, with most being 5 μm or less.

[0042] Figure 10 shows the target temperature T t The results of X-ray photoelectron spectroscopy (XPS) measurements on a sample prepared at 1200°C are shown. This measurement was performed after the sample surface was exposed and cleaned by sputtering to a depth of 35.9 nm. Measurements of the binding energy of the 2p electrons of silicon atoms (Si) showed a peak in the binding energy range (99.8-100.8 eV) when SiC was formed, but no peak was observed in the binding energy range (103.2-103.8 eV) when SiO2 was formed. Therefore, it can be said that SiC was formed in the obtained sample, and SiO2, which is unnecessary in the present invention, was not formed.

[0043] Measurements of the binding energy of the 1s electrons of carbon atoms (C) show peaks spanning both the binding energy range of elemental carbon (284.2–285.1 eV) and the binding energy range of carbides (280.6–283.0 eV). This suggests that elemental carbon exists in the sample along with SiC. Measurements of the binding energy of the 1s electrons of oxygen atoms (O) show a peak in the binding energy range of carbonates (530.5–531.5 eV), but not in the binding energy range of SiO2 (532.5–533.3 eV). This, like the Si measurement results, indicates that SiO2 is not being formed. Furthermore, it is believed that carbonates are formed by the impurity oxygen and excess carbon.

[0044] Figure 11 shows the target temperature T t The results of X-ray diffraction measurements were performed on samples at 1000°C and 1200°C, which were peeled off from the quartz substrate, and on the raw material PCS. Peaks different from those of PCS were observed in both samples of this example. tIn the sample with a target temperature of 1200°C, peaks due to Bragg reflections were observed on the (111), (220), and (311) planes of β-structure SiC (β-SiC). t In the sample with a temperature of 1000°C, a peak due to Bragg reflection from the (111) plane of β-SiC was observed (T t (Because the signal is weaker than that of the 1200°C sample, the peaks of the (220) and (311) planes cannot be distinguished.) In Fig. 11, a slight peak of the (101) plane of quartz is observed in the data of the two samples of this example, but this is thought to be due to the fact that part of the quartz tube 133, which is the vacuum vessel 13, was mixed into the sample.

[0045] Next, the target temperature T t X-ray diffraction measurements were performed on the sample, which had been heated to 1200°C, while it was still deposited on the quartz substrate (together with the quartz substrate). The results are shown in Figure 12. Figure 12 also shows the results of X-ray diffraction measurements (background measurements) on the quartz substrate alone. Around 2θ (indicated by the arrow in Figure 12) at which peaks due to Bragg reflection from the (111) plane of β-SiC are observed, the data obtained by measuring the sample and quartz substrate together are larger than the data obtained by measuring the quartz substrate alone, suggesting that β-SiC has formed in the sample.

[0046] Figure 13 shows the target temperature T t The results of elemental analysis of a sample heated to 1200°C were performed using an energy dispersive X-ray analyzer attached to a scanning electron microscope. Although a slight peak due to oxygen (O) can be seen, the peaks due to silicon (Si) and carbon (C) are significantly larger than this peak, indicating that the resulting porous body is composed of SiC, i.e., a silicon carbide porous body has been obtained. The oxygen peak is thought to be due to the small amount of carbonate that has been produced.

[0047] Up to this point, we have shown an example using PCS as the raw material, but we will also show an example using PDMS as the raw material and heating it to a target temperature T t A sample with a target temperature of 1200°C was also prepared.t The time for maintaining the temperature at this temperature was 2 hours. A micrograph of the obtained sample is shown in Figure 14. As in the case of using PCS, it can be seen that a granular porous body 20 was obtained in which a large number of pores 22 were formed in the base material 21.

[0048] (3) Method for producing a silicon carbide porous body according to the second embodiment In the method for producing a silicon carbide porous body of the second embodiment, the silicon carbide porous body (the deposit) formed on the surface of the substrate 12 by the method of the first embodiment is further subjected to a heating treatment in air, thereby performing an operation to remove at least a portion of the elemental carbon from the deposit.

[0049] 15 shows the flow of steps in the method for producing a silicon carbide porous body according to the second embodiment. Steps S1 to S5 are the same as those in the first embodiment. The deposit obtained by these steps is heated in air to a second predetermined temperature in the range of 500 to 800°C (step S6), and is maintained at this second predetermined temperature for a predetermined time (second predetermined time) (step S7).

[0050] If the second predetermined time is too long, the shape of the silicon carbide porous body cannot be maintained and the pores will be blocked or disappear, so it can be appropriately determined by conducting preliminary experiments within a range that allows the shape to be maintained. According to experiments by the present inventors, as long as the second predetermined time is within 2 hours, the shape of the silicon carbide porous body can be maintained at any second predetermined temperature within the range of 500 to 800°C. Furthermore, if the second predetermined temperature is 500°C, the shape of the silicon carbide porous body can be maintained even if it is maintained for approximately 8 hours.

[0051] After the second predetermined time has elapsed, the temperature is lowered to room temperature (step S8), thereby obtaining a porous silicon carbide body from which at least a portion of the elemental carbon has been removed.

[0052] (4) Example of a silicon carbide porous body produced by the method of the second embodiment 16A-C show micrographs of porous silicon carbide bodies produced by the method of the second embodiment, taken with a scanning electron microscope. In this example, several samples were used. The raw material, PCS, was heated in a vacuum at a target temperature (the predetermined temperature) of 1200°C for two hours. The resulting vapor was then attached to a substrate and cooled to room temperature. The resulting deposit was then heated in air at a second predetermined temperature for a second predetermined time. The second predetermined temperature and second predetermined time are 500°C and 8 hours in the example of FIG. 16A, 600°C and 2 hours in the example of FIG. 16B, and 800°C and 2 hours in the example of FIG. 16C. It can be seen that the porous shape is maintained in all of the examples shown in FIGS. 16A-C.

[0053] When the second predetermined temperature was 600°C or 800°C and the second predetermined time was 4 hours, the surface became almost flat and the porous shape could not be maintained (FIG. 17). Therefore, it is advisable to determine the second predetermined time according to the second predetermined temperature by conducting such an experiment in advance.

[0054] The carbon content (carbon content) of the samples in which the second predetermined temperature was 500°C and the second predetermined time was 2 hours, 4 hours, and 8 hours, respectively, and the samples in which the second predetermined temperature was 600°C and the second predetermined time was 2 hours, respectively, were measured using an energy dispersive X-ray analyzer (SEM-EDS) mounted on a scanning electron microscope. Similar measurements were also performed on samples that were not heated in air. Furthermore, for reference, similar measurements were also performed on samples in which the porous shape could not be maintained, in which the second predetermined temperature was 600°C and the second predetermined time was 4 hours and 8 hours, and in which the second predetermined temperature was 800°C and the second predetermined time was 4 hours. The measurement results are shown in the graph in Figure 18.

[0055] This graph shows that, at all second predetermined temperatures, heating in air reduces the carbon content compared to before heating. Since silicon carbide is known to remain stable without decomposition even when heated in air at 800°C, this decrease in carbon content is thought to mean that unnecessary carbon other than the silicon carbide porous body is reduced, resulting in a silicon carbide porous body with higher purity.

[0056] Furthermore, the higher the second predetermined temperature and the longer the second predetermined time, the higher the reduction rate (the smaller the carbon content value). Therefore, in order to remove unnecessary carbon, it is desirable that the second predetermined temperature be higher within the above range and the second predetermined time be longer. However, when the second predetermined temperature is 600°C or higher, if the second predetermined time is too long, the shape of the porous body cannot be maintained, as described above, so the second predetermined time is set within a range in which the shape can be maintained.

[0057] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. For example, although PCS or PDMS is used as the raw material in the above-described embodiments, polysilanes other than PDMS may be used, or other organosilicon polymers may be used. [Explanation of symbols]

[0058] 11...Raw materials 12...Base 13...Vacuum container 131...Inner wall surface of vacuum vessel 133...Quartz tube 134...One end of quartz tube 135...other end of quartz tube 136...The part of the quartz tube between the position where the raw material is contained and the other end 20...Granular porous body (porous silicon carbide body) 20A...Plate-shaped porous body (porous silicon carbide body) 21...Base material 22...Vacancy

Claims

1. A method for producing a porous silicon carbide body, comprising continuously raising the temperature of a raw material, which is an organosilicon polymer containing carbon atoms, in a vacuum from room temperature to a predetermined temperature within the range of 1000 to 1400°C, and maintaining the raw material at the predetermined temperature for a predetermined period of time, thereby evaporating the raw material and adhering the generated raw material vapor to a substrate.

2. 2. The method for producing a porous silicon carbide body according to claim 1, wherein the organosilicon polymer is selected from the group consisting of polysilane and polycarbosilane.

3. 3. The method for producing a silicon carbide porous body according to claim 1, wherein the predetermined temperature is within the range of 1100 to 1300°C.

4. 4. The method for producing a silicon carbide porous body according to claim 1, further comprising the step of heating a deposit formed on the substrate by adhering the raw material vapor to the substrate in air at a second predetermined temperature within a range of 500 to 800°C.

5. A porous silicon carbide body characterized in that a large number of pores having an average pore diameter within the range of 30 to 300 nm are formed within a base material whose main component is silicon carbide having a β structure.

6. 6. The silicon carbide porous body according to claim 5, which is in the form of particles having an average particle size in the range of 1 to 10 μm.

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