KR20090110465A - A simple synthetic route of polycarbosilane using catalytic anodized metalic oxides - Google Patents

Abstract

PURPOSE: A synthesizing method of polycarbosilane with porous metal oxide as a catalyst is provided to synthesize the polycarbosilane without catalyst filtering process. CONSTITUTION: A synthesizing method of polycarbosilane with porous metal oxide comprises a step of molding the catalyst in the form of bulk, stirrer, cylinder or spring than contacting with a polymethylsalne. An inner wall of reactor which contacts with the polymethylsilane comprises a metal oxide which is anodic-oxidized. The porous metal oxid is selected from Ti, Al, Nb and W.

Description

A simple synthetic route of polycarbosilane using catalytic anodized metalic oxides

The present invention relates to a method for producing polycarbosilane, and more particularly, to a method for producing polycarbosilane which does not require a separate process of separating the catalyst after the catalytic conversion process from polydimethylsilane.

Polycarbosilane (PCS) is a type of polysilane (PS) and has a structure in which silicon and carbon atoms form a main chain, and improves the precursor or oxidation resistance and heat resistance of silicon carbide (SiC) continuous fibers. It is widely used as a precursor for SiC coating, SiC powder, SiC composite materials. However, due to the complex manufacturing process of the existing PCS precursor, the development and mass production thereof are slow, and thus, SiC commercialization in various fields is delayed. In particular, the production of SiC fiber through the synthesis of a radiation-capable PCS polymer has recently been in the spotlight as an extreme material for space, aviation, and nuclear fusion because it is very suitable for ultra-high temperature extreme environment that carbon fiber cannot.

The manufacture of spinnable PCS is very complex and is manufactured in the following way: (1) polydimethylsilane (PDMS) from dimethyldichlorosilane (DMDS) using desalination of alkali metals such as sodium. Synthesis, (2) synthesis of PCS from PDMS using (2) catalytic process, and (3) production of highly radioactive PCS through thermal polymerization (increase molecular weight).

Particularly, in the step (2), PCS production is very important. PDMS having a "Si-Si-Si-Si" backbone bond allows a methyl group (-CH2-) to enter between Si-Si using a catalyst (Kumada rearangement). After the catalytic process, the main backbone of the PCS becomes "Si-C-Si-C", and by heat treatment, a uniform SiC can be obtained.

As such, the PDMS-PCS catalytic conversion process is considered to be the most important process for the PCS synthesis with excellent radioactivity.

Yajima reported the preparation of polycarbosilane at atmospheric pressure using polyborodiphenylsiloxane as a catalyst (Nature Vol. 273 No. 15, 525-527), and Kurosaki Refractories Co. Ltd. .) Reported a method for synthesizing polycarbosilane at atmospheric pressure, 320 ° C. to 370 ° C. using a solid acid such as AlCl 3, ZrCl 2, VCl 3, SbCl 3 as a catalyst (US Pat. No. 4,590,253, Japanese Patent JP 87- 79228).

In addition, recently, a method of using zeolite as a catalyst for synthesizing polycarbosilane as a highly efficient and stable method has been reported (Korean Patent 10-0515239). However, this method has the disadvantage that the catalyst is expensive and it is not easy to separate the catalyst from the composite when using the nanopowder as the catalyst.

As described above, in the conventional catalytic conversion process, since the catalyst component is mostly left in the PCS prepared using the powdered catalyst, the catalyst must be separated by filtration, and the filtration process is more complicated than expected. In general, when the porous filter filter paper is used, the catalysts block the holes of the filter paper, which decreases the filter efficiency and causes a huge waste of time. In addition, if the polymer viscosity is large, it should be diluted appropriately with a solvent, and after completion of the catalyst filtration process, a process for removing the solvent is required.

On the other hand, there has been introduced a technique for removing the catalyst by centrifugation, the catalyst removal technology using centrifugation is not complete until now. As a result, existing catalysts have been an obstacle to mass production and commercialization of PCS due to the problem of removing them after the reaction.

In order to solve the above problems of the prior art, an object of the present invention is to provide a PCS manufacturing process that does not require a complicated process for removing the catalyst.

It is also an object of the present invention to provide a PCS manufacturing process capable of efficient conversion by providing a wide specific surface area for catalytic reactions.

It is also an object of the present invention to provide a method for producing SiC from PCS produced by the method described above.

In addition, an object of the present invention is to provide a member coated with SiC on the surface by using the PCS produced by the method described above.

In order to achieve the above technical problem, the present invention provides a method for synthesizing polycarbosilane using a porous metal oxide anodized from polydimethylsilane as a catalyst. In the present invention, the catalyst is preferably bulk.

In addition, the bulk catalyst may be molded into a stirrer to be in contact with the polydimethylsilane. In addition, the catalyst may be molded in a cylindrical shape and in contact with the polydimethylsilane. In addition, the catalyst may be molded in the form of a spring to be in contact with the polydimethylsilane. In addition, the inner wall of the reactor in contact with the polydimethylsilane may be an anodized metal oxide.

In the present invention, the anodized porous metal oxide may be an anodized oxide of at least one metal selected from the group consisting of Ti, Al, Nb, and W.

In addition, the present invention comprises the steps of spinning the PCS produced by the method described above to produce a PCS fiber; And it provides a method for producing a SiC fiber by heat-treating the PCS fibers.

In addition, the present invention comprises the steps of coating a PCS produced by the above-described method on the base material; And heat treating the base material to produce a SiC film on the surface of the base material.

SiC fiber, which is attracting attention as a next-generation new material, is an advanced material used in defense, space, aviation, and nuclear fusion. SiC manufacturing method In particular, SiC fiber produced by heat treatment from polycarbosilane precursor is a major material under control as a strategic material between countries. However, the process for producing polycarbon silane is a very difficult technique, and the manufacturing method is very limited and requires a catalytic process to obtain a good product. However, existing catalyst processes are extremely difficult to obtain pure PCS by using compound type or powder type catalysts, and additional catalyst filtration process has been a major obstacle to mass production by increasing costs.

Accordingly, the present invention has developed a process similar to the existing catalytic effect by using a new catalyst, that is, porous AMO (including AAO) and does not require a catalyst filtration process. This will revitalize the growing SiC market, and furthermore, powder and fiber SiC are expected to be applied to various industries.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The conversion of PDMS to PCS plays a large role in the surface acidity of conventional powdered zeolite catalysts (solid acid catalysts). That is, the catalytic conversion process takes place effectively when the surface metal ion site plays the same role as Lewis acid. The inventors have found that anodized metal oxides perform well as solid acids and are therefore suitable for PDMS-PCS catalytic conversion processes. Since the anodized metal oxide can be manufactured in various shapes, if a bulk anodized metal oxide catalyst is provided in the reaction, no special effort is required for the subsequent catalyst removal.

1 is a diagram schematically illustrating a process of synthesizing a PCS with a spring type AMO as an embodiment of the present invention.

Referring to the figure, the Al metal is molded in the form of a spring, for example, 0.3M oxalic acid (Oxalic acid), anodized at DC 40V to obtain anodized alumina porous body.

FIG. 2 is a photograph of the surface of an alumina porous body obtained by anodizing Al in FIG. 1. As shown, it can be seen that an alumina nanoporous spring having a plurality of nanopores formed on its surface can be fabricated. Here, the size of the nanopore was about 40-100 nm. In the present invention, 'nano porous body' refers to a porous material having a pore diameter of 1 μm or less and having a plurality of pores.

Referring back to FIG. 1, PCS may be prepared by placing a nanoporous spring prepared as described above in a reactor such as a stainless tube and contacting with PDMS.

3 is a graph of silicon NMR and GPC data, respectively, as a result of PCS analysis obtained in this manner. At this time, the reactor was placed in a furnace of 350-400 degrees and proceeded with the reaction. For comparison with the present invention, the case of using the AAO spring was used when the powder type ZSM-5 zeolite was used and the catalyst was not used. The experiment was performed after the same amount of PDMS was added to three samples in the case.

As shown in the NMR image of (a) of FIG. 3, all three samples show that PDMS is converted from PCS. However, as shown in the GPC results, most PCS without catalyst have a low molecular weight form. This shows that undesirable catalysts are made when no catalyst is used. However, zeolite and AAO show almost the same molecular weight distribution (average molecular weight: 950). As described above, ZSM-5 is known as a good catalyst in the PCS conversion process, and in contrast, it can be seen that the spring-type AAO catalyst has the same effect as the conventional zeolite catalyst (ZSM-5). However, in the present invention, since the PCS is obtained by removing the AAO spring from the reactor, a separate filtration process for separating the catalyst is unnecessary.

4 is a diagram showing another embodiment of the present invention.

Referring to FIG. 4, after Al was molded into a stirrer shape, an anodization was performed to prepare an AAO stirrer. The prepared AAO stirrer was mounted in the reactor. In addition, the cylindrical aluminum was anodized to prepare an AAO cylinder, which was then mounted on the wall of the reactor. In this embodiment, the reactor is controlled and monitored by a computer with a temperature and pressure controller. It is also equipped with a condenser to condense the gas phase and a nitrogen or argon gas reflux system.

After filling the reactor with 1 Kg of PDMS, the reaction vessel was heated to a temperature of 350 degrees with a heater on the wall of the reactor and reacted for 10 hours while maintaining the inside of the reactor in an inert atmosphere. At this time, the reaction was carried out while rotating the AAO stirrer. In this example, the catalyst fixation from PDMS to PCS occurs at the rotating AAO stirrer and cylindrical AAO walls.

After the reaction was completed, the liquid PCS was withdrawn to the lower drain of the reaction chamber. In this embodiment as well, no separate catalyst filtration process is required for the removal of the catalyst.

Subsequently, the liquid phase PCS was made into a spinable PCS (molecular weight of about 1500) through thermal polymerization at 400 ° C. for 10 hours, and then the PCS was spun by electrospinning. Figure 6 (a) shows a radioactive PCS photograph prepared using AAO. Figures 6 (b)-(d) show pictures of PCS fibers spun by electrospinning. The spun PCS fibers are continuous and very uniform within a few micrometer diameter range.

Spinning PCS produced through the above process can be produced by SiC fibers through a heat treatment and sintering process.

For example, the PCS fibers prepared in the above example were placed in an alumina crucible having a diameter of 10 mm and heated up to 200 degrees in an open electric furnace at 30 degrees per hour, followed by oxidative stabilization for 1 to 4 hours, and again in an alumina tubular furnace in which an argon atmosphere is maintained. After heating up to 12 hours to maintain 1 hour was converted to silicon carbide and recovered at room temperature. The obtained silicon carbide image was observed with a high magnification electron microscope to show a dense structure and no catalyst components were observed.

Although AAO has been described as an example of anodized metal oxide, the present invention can be applied to both anodized metal oxide (AMO). For example, oxidation of Ti, W, Nb and the like which can be anodized may be used as the catalyst of the present invention.

Moreover, although the spring, the stirrer, and the cylindrical cylinder were illustrated as the shape of the bulk catalyst material of this invention above, this invention is not limited to this. Those skilled in the art will be able to anodize at least a portion of the inner wall of the reactor and use it as a catalyst. Of course, in addition to those skilled in the art will be able to devise a variety of examples by changing or modifying the above-described embodiment, it will be included in the scope of the present invention as long as it falls within the scope of the technical idea of the present invention using a bulk catalyst. Anyone skilled in the art will know.

1 is a diagram schematically illustrating a method of synthesizing PCS using an anodized metal catalyst as an embodiment of the present invention.

FIG. 2 is an electron micrograph of the surface of the anodized AAO catalyst obtained in FIG. 1.

3 is a graph showing GPC data and NMR data of PCS synthesized using the apparatus of FIG. 1 according to an embodiment of the present invention.

4 is a diagram schematically illustrating a PCS synthesis method using an anodized metal oxide catalyst as another embodiment of the present invention.

FIG. 5 is an electron microscope photograph of PCS fibers obtained from the liquid PCS obtained in FIG. 4.

Claims (9)

A method for synthesizing polycarbosilane using a porous metal oxide anodized from polydimethylsilane as a catalyst. The method of claim 1, The catalyst is a polycarbosilane synthesis method, characterized in that the bulk. The method of claim 2, The catalyst is molded in the form of a stirrer polycarbosilane synthesis method, characterized in that the contact with the polydimethylsilane. The method of claim 2, Wherein said catalyst is shaped into a cylinder and is in contact with said polydimethylsilane. The method of claim 1, The catalyst is molded in the form of a spring polycarbosilane synthesis method, characterized in that in contact with the polydimethylsilane. The method of claim 2, And the inner wall of the reactor in contact with the polydimethylsilane comprises anodized metal oxide. The method of claim 1, A method for synthesizing polycarbosilane, characterized in that the anodized porous metal oxide is an anodized oxide of at least one metal selected from the group consisting of Ti, Al, Nb and W. Spinning PCS produced by the method of claim 1 to produce PCS fibers; And Heat treating the PCS fibers to produce SiC fibers. Coating the PCS prepared by the method of claim 1 on a base material; And Heat-treating the base material to produce a SiC coating on the surface of the base material.

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