JP4665132B2 - Wall thickness control method by cooling irradiation of silicon carbide microtube - Google Patents

Description

  The present invention relates to a manufacturing method capable of arbitrarily controlling the wall thickness of a SiC microtube within a range of 2 to 20 μm.

Conventionally, as a manufacturing method of an SiC microtube, there is a method of hollowing a polycarbosilane fiber, which is a silicon-based polymer, with an electron beam. This is based on a method comprising the following steps.
1. A silicon polymer is spun into a fiber having a diameter of several tens of μm.

2. Irradiate ionizing radiation in air at room temperature to oxidize only the surface.
3. It heat-processes in inert gas, bridge | crosslinks an oxidation layer, and insolubilizes in a solvent.
4). The uncrosslinked portion inside the fiber is extracted with an organic solvent and hollowed out.

5. Ceramicize in an inert gas by heat treatment at 1000 ℃ or higher.
However, in the above method, it is possible to control the wall thickness of the tube by changing the dose rate and oxygen partial pressure in the radiation irradiation, but in the electron beam irradiation at room temperature, the temperature of the sample is changed by the energy of the electron beam. Since it rises, it is difficult to control the wall thickness of the tube to 10 μm or less.

The following is known as a document relating to the above method. That is, a method for producing a microceramic tube by irradiation of a silicon-based polymer (Patent Document 1), a method for producing a microceramic tube by exposing a silicon-based polymer to radiation (Patent Document 2), and a polymer precursor by radiation oxidation Improvement of the silicon carbide microtube (Non-patent Document 1), and a silicon carbide ceramic microtube (Non-patent Document 2) realized by an electron beam irradiation effect.
JP 2003-082532 A USP No. 6,780,370 Development of Silicon Carbide Micro Tube from Precursor Polymer by Radiation Oxidation, Masaki Sugimoto, Akira Idesaki, Shigeru Tanaka, and Kiyohito Okamura, Key Eng. Mater., 247, 133-136, (2003) Masato Yoshikawa, Masaki Sugimoto, "Convertech, 377" P56-60, (2004)

  As described above, at present, it is difficult to manufacture SiC microtubes by controlling the wall thickness to an arbitrary wall thickness of 10 μm or less, and industrially mass-produced SiC fibers with a diameter of 15 μm are used for applications. It is impossible to hollow by controlling to an appropriate wall thickness.

  An object of the present invention is to provide a method for producing a SiC microtube having a wall thickness of 2 to 10 μm by controlling the irradiation conditions of ionizing radiation. The inventors of the present invention determined that the thickness of the silicon-based polymer layer oxidized by ionizing radiation depends on the amount of active sites (radicals) generated by cutting the silicon polymer by ionizing radiation and diffusion from the surface of the silicon polymer. The present invention has been completed by paying attention to the fact that the amount of oxygen diffused can be controlled by the sample temperature at the time of ionizing radiation irradiation in relation to the amount of oxygen penetrating into the inside.

  This is based on the following principle. When the silicon polymer fiber is irradiated with radiation in the air, the active radicals uniformly generated in the fiber react with oxygen. When the dose rate of radiation is large, only the surface layer of the fiber is oxidized because the rate at which active radicals react with oxygen in the fiber surface layer is greater than the diffusion rate of oxygen from the surface to the inside of the fiber. At this time, if the sample at the time of irradiation is cooled, the diffusion rate of oxygen in the silicon polymer decreases, so the amount of oxygen that penetrates into the fiber by diffusion per unit time decreases, and all oxygen is activated closer to the surface layer. Since it reacts with radicals, the wall thickness corresponding to the oxidized portion is reduced.

  Therefore, in particular, the present invention oxidizes only the surface by irradiating ionizing radiation while cooling the silicon-based polymer fiber to a temperature of -40 to 0 ° C., and crosslinks the oxidized portion by heat treatment, and then the fiber with an organic solvent. The uncrosslinked part at the center is extracted to form a hollow fiber, which is fired in an inert gas, and has a wall thickness (tube thickness) of silicon carbide (SiC) micro with an arbitrary wall thickness of 2 to 10 μm. A method of manufacturing a tube.

  An SiC microtube having an outer diameter of 15 μm can be manufactured by controlling the polycarbosilane fiber having an outer diameter of 20 μm, which is a silicon-based polymer fiber mass-produced industrially, to an arbitrary wall thickness.

  In FIG. 1, an example of the manufacturing process of the micro ceramic tube using the radiation irradiation of this invention is shown. A raw material silicon polymer fiber is irradiated with an electron beam through a gas mixed with an inert gas and oxygen so that the partial pressure of oxygen is 0.5 to 50 kPa at a temperature of -40 to 0 ° C., and the surface layer is oxidized. At this time, the dose of the electron beam needs to be set in the range of 1 to 5 MGy, which is larger than the dose at which the silicon polymer is cross-linked by oxygen and smaller than the dose at which the fiber center is cross-linked by oxygen-free oxygen.

  The silicon polymer fiber oxidized only on the surface layer is heat-treated in an argon atmosphere or vacuum to crosslink the oxidized portion, thereby insolubilizing in the solvent. At this time, an appropriate temperature corresponding to the amount of oxygen introduced into the fiber is set in the range of 230 to 300 ° C. The hollowing treatment is performed by holding in an organic solvent such as cyclohexane or THF (tetrahydrofuran) in which the uncrosslinked silicon polymer is soluble. By heating to 1000 ° C or higher in an inert gas atmosphere, the silicon polymer is converted to a ceramic and converted to a SiC microtube.

Hereinafter, the present invention will be specifically described with reference to examples.
Polycarbosilane (PCS), a silicon polymer that is a raw material for SiC ceramics, is fiberized to an outer diameter of 20 μm. This fiber is placed on a sample stage that can be cooled by the heat of vaporization of liquefied carbon dioxide gas, placed in an electron beam irradiation container that can be replaced with gas, and a 2 MeV electron beam is passed through a mixed gas of helium / oxygen between 0.4 and 1.6. Irradiate to 2.4MGy at a dose rate of kGy / sec. After irradiation, the oxidized surface layer portion is crosslinked by heating in an inert gas or vacuum in the range of 200 to 300 ° C. and insolubilized in an organic solvent. At room temperature, the uncrosslinked portion at the center of the fiber is extracted with cyclohexane to form a hollow fiber. The obtained hollow fiber is fired at 1000 ° C. in argon to form a ceramic tube to obtain a SiC microtube. The outer diameter of the micro SiC tube thus obtained is about 15 μm, and its wall thickness is determined by temperature, oxygen partial pressure and electron beam dose rate as shown in FIG. 8 μm is the lower limit when irradiated at room temperature. On the other hand, when the electron beam is irradiated at −20 ° C., the wall thickness of the SiC microtube can be controlled within a range of 4 to 10 μm at an oxygen partial pressure of 20 kPa and 2 to 5 μm at an oxygen partial pressure of 10 kPa.

  That is, when an electron beam is irradiated at room temperature at an oxygen partial pressure of 20 kPa, as shown in the uppermost line graph, the average wall thickness of the SiC microtube is thick, and the wall thickness is about 8 μm, which is the lower limit. In addition, when an electron beam is irradiated at −20 ° C. at an oxygen partial pressure of 20 kPa, the average wall thickness of the SiC microtube is 4 to 10 μm as shown in the middle line graph. When the electron beam is irradiated at −20 ° C., the average wall thickness of the SiC microtube is 2 to 5 μm as shown in the bottom line graph.

Industrial applicability

  SiC synthesized from silicon-based polymers has an amorphous structure and has a function of selectively permeating hydrogen gas. When SiC microtubes are applied as gas separation filters, high efficiency is possible due to their large surface area, and application to heat and corrosion resistant gas separation filters such as thermochemical hydrogen production is expected.

It is a schematic diagram which shows an example of the manufacturing process of the ceramic tube by the cooling electron beam irradiation of this invention. It is an actual measurement result of the SiC microtube wall thickness synthesize | combined by this invention.

Claims (6)

While cooling the silicon-based polymer fiber to an arbitrary temperature within the range of −40 ° C. to 0 ° C. , the dose rate is 0.5 to 1.6 kGy / s, the dose at an oxygen partial pressure in the range of 0.5 to 50 kPa. Only the surface is oxidized by irradiating with ionizing radiation in the range of 1 to 5 MGy, and after the oxidized portion is crosslinked by heat treatment, the uncrosslinked portion at the center of the fiber is extracted and removed using an organic solvent to form a hollow fiber. A method in which this is fired in an inert gas to produce silicon carbide (SiC) microtubes having any wall thickness between 2 and 8 μm.   The method according to claim 1, wherein the silicon-based polymer is polycarbosilane, polytyranocarbosilane, polytitanocarbosilane, or a blend polymer of polycarbosilane and polyvinylsilane.   The method according to claim 1 or 2, wherein the wall thickness of the SiC microtube is controlled by temperature at the time of ionizing radiation irradiation.   The method according to claim 1 or 2, wherein the wall thickness of the SiC microtube is controlled by a dose of ionizing radiation.   The method according to claim 1 or 2, wherein the wall thickness of the SiC microtube is controlled by an oxygen partial pressure in an atmosphere at the time of irradiation with ionizing radiation.   The wall thickness of the SiC microtube is controlled by combining at least two of a temperature at the time of ionizing radiation irradiation, a dose of ionizing radiation, and an oxygen partial pressure in the atmosphere at the time of ionizing radiation irradiation. the method of.