JP4213612B2 - Method for producing porous structure - Google Patents

Description

  The present invention relates to a method for producing a porous structure having high strength and high rigidity.

  Since silicon carbide-based ceramics are lightweight and have excellent heat resistance, wear resistance, corrosion resistance, etc., in recent years, for example, high-temperature corrosion-resistant members, heater materials, wear-resistant members, as well as abrasives, grindstones, etc. Widely used in applications.

  Recently, research and development of heat-resistant lightweight porous ceramics has been conducted. For example, cordierite honeycomb ceramics having low thermal expansion used as a catalyst carrier has been obtained by a sintering method after extrusion and has been put to practical use. In the carbon system, there are wood ceramics using wood, which are inferior in oxidation resistance. In addition, as shown in JP-A-6-24859 and JP-A-6-24866, a synthetic resin foam having a three-dimensional network skeleton structure is immersed in a ceramic slurry and then dried and fired. A method for producing a ceramic porous body is known. The silicon carbide-based ceramic produced in this way is used as a filter for molten aluminum or the like. However, the porous ceramics according to the present method, even if the surplus slurry removing operation is performed, the surplus slurry remains, and the clogging is apt to occur and it is difficult to obtain a porous ceramic having a small pore diameter.

On the other hand, the present inventors have proposed, in Patent Document 1 and Patent Document 2, a method for producing a heat-resistant lightweight porous ceramic by a melt impregnation method and a heat-resistant lightweight porous ceramic structure. Usually, in the silicon melt impregnation method, since silicon is added from outside the system, the reaction increases in volume, and the dense amorphous carbon-only matrix resulting from the carbonization of the phenol resin hardly reacts with the molten silicon. However, in the manufacturing method shown in the above document, silicon carbide having good wettability with molten silicon produced by reaction sintering (volume reduction reaction) of a mixture of silicon powder and phenol resin, and a porous amorphous carbon matrix In this case, molten silicon easily penetrates and reacts. Thereby, a silicon carbide-based lightweight porous ceramic is obtained.
JP 2001-226174 A Japanese Patent Laid-Open No. 2003-119085

  However, in the manufacturing method described in Patent Document 1 or Patent Document 2, when the silicon is sufficiently impregnated, it is difficult to increase the content ratio of silicon carbide in the skeleton structure of the porous structure, and thus the matrix is high. It is difficult to produce a porous structure having rigidity and sufficient strength as a porous body.

  The present invention uses an organic sponge-like porous preform to which a metal powder is added, thereby increasing the proportion of high-rigidity ceramics in the skeleton, which is excellent in heat resistance and lightweight, while being porous. An object of the present invention is to provide a production method for producing a porous structure having sufficient strength and having a matrix having high rigidity.

  (1) In order to achieve the above object, the method for producing a porous structure according to the present invention is a slurry production for producing a slurry containing a resin or a combination of a resin and a carbon, metal powder, or ceramic powder. A slurry impregnation step of impregnating the slurry with an organic sponge-like porous preform containing a metal powder and removing unnecessary portions of the slurry; and A carbonization step in which carbonization is performed at 900 to 1350 ° C. in an active atmosphere, and the porous preform after carbonization is subjected to reaction sintering at a temperature of 1250 ° C. or higher in a vacuum or an inert atmosphere, and 1300 to 1800. And a sintering impregnation step of melt-impregnating a metal at a temperature of ° C.

  Thus, in the production method according to the present invention, the organic sponge-like porous preform contains the metal powder. Thereby, in the sintering impregnation step, it is possible to generate carbide ceramics having good wettability with the molten metal inside the skeleton part of the porous preform. Since a large amount of high-rigidity ceramics is contained inside the skeleton portion of the porous structure obtained as a result, the rigidity of the matrix can be improved while ensuring sufficient strength as the porous structure. Moreover, even if it is a complicated shape, the lightweight and heat-resistant porous structure which maintained the shape of the first porous preform can be manufactured easily. This porous structure can be used in many applications as a high temperature filter, a high temperature structural member, a heat insulating material, a molten metal filter material, a burner plate, a heater material, or a high temperature silencer.

    In addition, since the metal powder is contained inside the skeleton of the carbonized porous preform, the strength can be improved. As a result, the handleability of the porous preform after carbonization is improved.

  (2) Moreover, the manufacturing method of the porous structure which concerns on this invention is the slurry preparation process which produces the slurry containing resin or the combination of resin and carbon, silicon powder, or ceramic powder, silicon powder, Or an organic sponge-like porous material containing a powder of an alloy of silicon and at least one selected from magnesium, aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum and tungsten A slurry impregnation step of impregnating the porous preform with the slurry and removing unnecessary portions of the slurry, and carbon that carbonizes the porous preform after the slurry impregnation at 900 to 1350 ° C. in a vacuum or an inert atmosphere And the porous preform after carbonization is subjected to vacuum or Under an inert atmosphere, it is characterized in that it comprises reacted sintered at 1250 ° C. or higher, and sintering the impregnation step of melting impregnating the silicon at a temperature of from 1300 to 1800 ° C., the.

  Thus, in the manufacturing method according to the present invention, the organic sponge-like porous preform contains silicon powder or silicon alloy powder. Thereby, in the sintering impregnation step, it is possible to generate carbide ceramics having good wettability with the molten metal inside the skeleton part of the porous preform. Since a large amount of high-rigidity ceramics is contained inside the skeleton portion of the porous structure obtained as a result, the rigidity of the matrix can be improved while ensuring sufficient strength as the porous structure. Moreover, even if it is a complicated shape, the lightweight and heat-resistant porous structure which maintained the shape of the first porous preform can be manufactured easily. This porous structure can be used in many applications as a high temperature filter, a high temperature structural member, a heat insulating material, a molten metal filter material, a burner plate, a heater material, or a high temperature silencer.

  Further, since the silicon preform or silicon alloy powder is also contained inside the skeleton of the porous preform after carbonization, the strength can be improved. As a result, the handleability of the porous preform after carbonization is improved.

  (3) Moreover, the manufacturing method of the porous structure which concerns on this invention is characterized by the resin component mainly contained in the said porous preform being a urethane resin in the said slurry impregnation process.

  Since the urethane resin has elasticity, it is possible to facilitate the impregnation and removal of the slurry in the slurry impregnation step. In addition, familiarity with phenol resin and the like is good, and the slurry can be efficiently coated on the surface of the skeleton structure. As a result, a porous preform and further a porous structure having sufficient strength can be obtained.

  (4) Further, in the method for producing a porous structure according to the present invention, in the slurry impregnation step, the slurry impregnated in the porous preform contains at least one of a phenol resin, a furan resin, and an organometallic polymer. It is characterized by doing.

  Thereby, in a slurry impregnation process, a slurry with a high residual carbon ratio can be produced in a carbonization process. As a result, a porous preform and further a porous structure having sufficient strength can be obtained.

  According to the method for producing a porous structure according to the present invention, the strength and rigidity of the porous structure can be improved. Moreover, since the strength of the porous preform after carbonization can be improved, handling properties can be improved, and processing can be easily performed, a large-sized porous structure having a complicated shape can be easily manufactured.

  As a result of intensive research, the present inventor has obtained a silicon carbide-based porous structure with high strength and high rigidity easily while maintaining the shape of the skeleton part of the porous preform even if it has a complicated shape. It has been found that the body can be manufactured, and the present invention has been completed. Specifically, an organic sponge-like preform to which silicon powder is added is impregnated with silicon powder and resin, and porous silicon carbide and residual carbon parts are generated by a silicon carbide generating reaction accompanied by volume reduction. The porous skeleton portion is melt impregnated with silicon.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a porous structure 1 according to the present invention. FIG. 2 is an enlarged view of a cross section of the porous structure 1 according to the present invention. As shown in FIG. 2, the skeleton 2 has a plurality of branches from the nodes, and forms a three-dimensional network structure in which the branched ends are connected to branches from other nodes. The skeleton 2 is composed of a composite material of a metal silicon matrix and silicon carbide ceramic particles.

  Next, the manufacturing method of the porous structure 1 comprised as mentioned above is demonstrated. FIG. 3 is a flowchart showing a method for manufacturing the porous structure 1.

  Organic material containing silicon powder or an alloy powder of silicon and at least one selected from magnesium, aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum and tungsten in advance Prepare a sponge-like porous preform. A foam made of urethane resin having a cell structure of open cells by mixing polyol, polyisocyanate, foaming agent, foam stabilizer, catalyst, etc., and adding metal powder as a filler component. It is produced (step S1). In addition, it is also possible to manufacture by adding metal powder such as titanium, zirconium, and boron instead of silicon powder. The process of adding metal silicon powder will be described below.

  The organic sponge-like porous preform according to the present invention contains silicon powder. Thereby, in the sintering impregnation step, it is possible to generate carbide ceramics having good wettability with the molten metal inside the skeleton part of the porous preform. Since a large amount of high-rigidity ceramics is contained inside the skeleton portion of the porous structure obtained as a result, the rigidity of the matrix can be improved while ensuring sufficient strength as the porous structure. In addition, a lightweight and heat-resistant porous structure that maintains the shape of the first porous preform can be easily manufactured. This porous structure can be used in many applications as a high temperature filter, a high temperature structural member, a heat insulating material, a molten metal filter material, a burner plate, a heater material, or a high temperature silencer.

  Moreover, since the resin component mainly contained in the porous preform is a urethane resin, the slurry impregnation step can facilitate the impregnation and removal of the slurry. In addition, familiarity with phenol resin and the like is good, and the slurry can be efficiently coated on the surface of the skeleton structure. As a result, a porous preform and further a porous structure having sufficient strength can be obtained.

  The particle size of the silicon powder contained is preferably 50 μm or less, more preferably 20 μm or less. The volume content is preferably 2% or more and 40% or less. If it is 2% or less, the effect of addition is small, and if it is 40% or more, the formation of an organic sponge structure is inhibited.

  As a material constituting the skeleton part of the porous preform, a material capable of holding a slurry is desirable. Various resins such as urethane resin, melamine resin, phenol resin, furan resin, rubber sponge, or sponge-shaped Plastics and papers are suitable. These may be a mixture of two or more. The resin component is preferably mainly a urethane resin. “Mainly” means that the proportion of the resin component in terms of mass proportion is half or more.

  First, a slurry for impregnating the porous preform is prepared (step S2). Resins as a carbon source are dissolved in a solvent, and silicon powder is mixed. Preferred resins include phenolic resins, furan resins, organometallic polymers such as polycarbosilane, or sucrose. These resins may be used alone or in combination of two or more. In addition, it is effective to add an antifoaming agent from the viewpoint of suppressing the generation of bubbles in the slurry.

  Thus, since the slurry contains at least one of a phenol resin, a furan resin, and an organometallic polymer, a slurry having a high residual carbon ratio can be produced in the carbonization step in the slurry impregnation step described below. . As a result, a porous preform and further a porous structure having sufficient strength can be obtained.

  As the silicon powder, fine powder is suitable, and fine powder having an average particle diameter of 30 μm or less is particularly suitable. Those having a large particle diameter may be pulverized by a ball mill or the like. In place of silicon powder, powder of an alloy of at least one selected from magnesium, aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, or tungsten and silicon, or A mixture of them and silicon powder may be mixed into the slurry.

  Further, carbon powder, graphite powder, carbon black may be added as additives, and silicon carbide, silicon nitride, zirconia, zircon, alumina, silica, mullite, molybdenum disilicide, carbonization as aggregates or antioxidants. Boron, boron powder, etc. may be added to the slurry.

  The component ratio of the porous preform or slurry is preferably selected so that the atomic ratio of silicon to carbon in the porous preform after carbonization is Si / C = 0.05-4.

  As described above, after preparing the porous preform and the slurry, the porous preform is immersed in the slurry, impregnated with the slurry (step S3), and squeezed to such an extent that the slurry does not block the continuous pores. Is removed (step S4). The unnecessary amount of slurry refers to the amount of the slurry impregnated from the entire impregnated slurry so as not to block the continuous pores.

  The impregnation may be sufficiently applied to the skeleton of the porous preform instead of immersing the porous preform in the slurry. As a method for removing the slurry, various methods such as a method of sufficiently discharging the slurry by applying pressure to the structure and a method of discharging the slurry by centrifugal force are possible. Furthermore, in order to reduce clogging, it is also effective to add a step of removing the surface film-forming site by a method such as finally spraying compressed air or sticking with a stick having a sharp tip.

  After removing unnecessary portions of the slurry, the porous preform is dried at about 70 ° C. (step S5). The drying time is preferably about 12 hours.

  Next, the porous preform obtained by drying is carbonized at a temperature of about 900 to 1350 ° C. in an inert atmosphere such as vacuum or argon (step S6). In the porous preform as a carbonized composite obtained in this way, most of the urethane resin component of the skeleton part disappears due to thermal decomposition, but the skeleton part is formed by the carbon component and silicon powder by carbonization of the coated phenol resin. Maintains its original shape. In the inside of the skeleton, a carbon portion obtained by carbonization of a partially impregnated phenol resin and a silicon powder contained in advance remain, and a structure having appropriate voids is obtained. Moreover, the carbonized porous preform has a processable strength.

  Next, the carbonized porous preform is baked at a temperature of 1250 ° C. or higher in an inert atmosphere such as vacuum or argon (step S7), and the carbon and silicon are reacted to cause molten silicon and wettability. A good porous silicon carbide portion is formed in the skeleton of the structure. In this case, since this reaction is a volume reduction reaction, open pores resulting from the volume reduction reaction are generated. As a result, a porous preform having pores in the skeleton formed by silicon carbide and residual carbon or unreacted silicon is obtained.

Next, the porous preform as the sintered body is heated to a temperature of about 1300 to 1800 ° C. in a vacuum or in an inert atmosphere, and silicon is melted in the porous silicon carbide and carbon portions on the skeleton. Impregnation (step S8). As a result, the porous structure 1 according to the present invention is obtained. Silicon for melting and impregnation may be pure silicon metal, magnesium, aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, tungsten, etc., or an alloy of silicon, or those And a mixture of silicon and silicon.
In the above manufacturing method, the steps are described separately. However, the reactive sintering of silicon and carbon and the melt impregnation of silicon may be performed at the same time, and all heat treatment processes including carbonization are performed in the same furnace. It is possible to use a single temperature control program.

  Next, the method of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

  First, a urethane resin sponge containing silicon powder was produced as a porous preform. Specifically, a foam, a foam stabilizer, a catalyst and the like are mixed with a polyol and polyisocyanate as main components, and further, 15% by volume of silicon powder having a particle diameter of 20 μm or less is added as a filler component. Thus, a urethane resin sponge having an open cell structure was prepared. The size of the pores was 100 to 200 μm.

  Next, when the phenol resin is carbonized, the mixing amount of the phenol resin and the silicon powder is set so that the atomic ratio of carbon to silicon is 5: 4, and after mixing them, ethyl alcohol The phenol resin was dissolved in to prepare a slurry. Then, in order to make the particle size of silicon powder small, it mixed with the ball mill for 1 day.

  Next, the mixed slurry was impregnated into a polyurethane sponge and squeezed to such an extent that the slurry liquid did not block the continuous pores, and then dried. At this time, the sponge expanded about 15% in the axial direction.

Next, the dried sponge was baked and carbonized at 1000 ° C. for 1 hour in an argon atmosphere. The obtained carbonaceous porous body was subjected to reaction sintering and melt impregnation with silicon at 1450 ° C. for 1 hour in a vacuum to obtain a sponge-like porous structure 1. The sponge contracted during carbonization, and was slightly smaller with about 9% contraction in the axial direction than before carbonization. The obtained silicon carbide based porous structure 1 has the same porous structure as the sponge, has a pore diameter of 200 to 300 μm, an open porosity of 86%, a bulk density of 0.41 × 10 ³ kg / m ³ , and a true density of 2. It was 89 × 10 ³ kg / m ³ .

  First, a urethane resin sponge containing silicon powder was produced as a porous preform. Specifically, a foam, a foam stabilizer, a catalyst and the like are mixed with a polyol and polyisocyanate as main components, and further 20% by volume of silicon powder having a particle diameter of less than 20 μm is added as a filler component. Thus, a urethane resin sponge having an open cell structure was prepared. The pore size was 200 to 300 μm.

  Next, when the phenol resin is carbonized, the mixing amount of the phenol resin and silicon powder is set so that the atomic ratio of carbon to silicon is 5: 3, and after mixing them, ethyl alcohol The phenol resin was dissolved in to prepare a slurry. Thereafter, ball mill mixing was performed for 1 day in order to reduce the particle size of the silicon powder. The mixed slurry was impregnated into a polyurethane sponge, and the slurry was squeezed to such an extent that the continuous pores were not blocked, and then dried. At this time, the sponge expanded about 12% in the axial direction.

Next, the dried sponge was baked and carbonized at 1000 ° C. for 1 hour in an argon atmosphere. The sponge contracted during carbonization, and was slightly smaller with about 7% contraction in the axial direction than before carbonization. The obtained carbonaceous porous body was subjected to reaction sintering and silicon melt impregnation simultaneously in vacuum at 1450 ° C. for 1 hour to obtain a sponge-like silicon carbide based porous structure 1. The obtained silicon carbide based porous structure 1 has the same porous structure as the sponge, has a pore diameter of 200 to 300 μm, an open porosity of 90%, a bulk density of 0.30 × 10 ³ kg / m ³ , and a true density of 2 It was 91 × 10 ³ kg / m ³ .

(Comparative example)
A sponge to which no silicon powder was added was prepared, and using this sponge, slurry preparation, impregnation, carbonization, and silicon impregnation treatment were performed in the same manner as in Example 1. The obtained porous structure had an open porosity of 87%, a bulk density of 0.35 × 10 ³ kg / m ³ , and a true density of 2.70 × 10 ³ kg / m ³ . FIG. 4 is a table showing the physical properties of the porous structures according to Example 1, Example 2, and Comparative Example.

(Compressive strength, density measurement, stiffness calculation from density)
About the sample obtained by said each manufacturing method, the compressive strength of the porous body was measured. The rigidity of the skeleton was calculated from the true density assuming that the sample was composed of silicon and silicon carbide. The result is shown in FIG. The sample of Example 1 has a high true density and a rigidity value as high as 310 GPa. The compressive strength of the porous body is also high. The sample of Example 2 is a structure having a large sponge void and a large porosity, but it can be seen that the sample exhibits a relatively high compressive strength.

  Moreover, the photograph which observed the cross section of the frame | skeleton part of the obtained porous structure with the SEM electron microscope is shown in FIG. 5 and FIG. 5 shows a cross-section of the skeleton part 2 of the porous structure 1 according to Example 1, and FIG. 6 shows a SEM photograph of a cross-section of the skeleton part of the porous structure according to the comparative example. As shown in FIG. 5, the sample of Example 1 using a sponge to which silicon powder was added produced a large amount of silicon carbide 4 inside the skeleton structure, whereas a sponge to which no silicon powder was added. In the sample of the comparative example using No. 1, the surface has a large amount of silicon carbide 4, but the inside has a large amount of silicon 5.

1 is a perspective view of a porous structure according to the present invention. It is an enlarged view of the section of the porous structure concerning the present invention. It is a flowchart which shows the manufacturing method of the porous structure which concerns on this invention. It is a table | surface which shows the physical property of the porous structure which concerns on Example 1, Example 2, and a comparative example. 2 is a SEM photograph of a cross section of a skeleton part of a porous structure according to Example 1. It is a SEM photograph of the section of the frame part of the porous structure concerning a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous structure 2 Skeletal part 4 Silicon carbide 5 Silicon

Claims (4)

A slurry production step of producing a slurry containing a resin, or a combination of a resin and carbon, a metal powder, or a ceramic powder;
A slurry impregnation step of impregnating the slurry into an organic sponge-like porous preform containing metal powder, and removing unnecessary portions of the slurry;
A carbonization step of carbonizing the porous preform after slurry impregnation at 900 to 1350 ° C. in a vacuum or an inert atmosphere;
A sintering impregnation step in which the porous preform after carbonization is subjected to reactive sintering at a temperature of 1250 ° C. or higher in a vacuum or an inert atmosphere, and a metal is melted and impregnated at a temperature of 1300 to 1800 ° C. A method for producing a porous structure, comprising: A slurry production step for producing a slurry containing a resin or a combination of a resin and carbon, silicon powder, or ceramic powder;
Organic sponge containing silicon powder or powder of an alloy of silicon and at least one selected from magnesium, aluminum, titanium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum and tungsten A slurry impregnation step of impregnating the slurry with a slurry-like porous preform and removing unnecessary portions of the slurry;
A carbonization step of carbonizing the porous preform after slurry impregnation at 900 to 1350 ° C. in a vacuum or an inert atmosphere;
A sintering impregnation step in which the porous preform after carbonization is subjected to reaction sintering at a temperature of 1250 ° C. or higher in a vacuum or an inert atmosphere, and silicon is melt-impregnated at a temperature of 1300 to 1800 ° C. A method for producing a porous structure, comprising:   3. The method for producing a porous structure according to claim 1, wherein the resin component mainly contained in the porous preform is a urethane resin in the slurry impregnation step. The slurry impregnated in the porous preform in the slurry impregnation step contains at least one of a phenol resin, a furan resin, and an organometallic polymer, according to any one of claims 1 to 3. A method for producing a porous structure.

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