JP4641845B2 - Coated porous structure and method for producing coated porous structure - Google Patents

Description

  The present invention relates to a coated porous structure and a method for producing a coated porous structure.

  In recent years, porous structures containing ceramics have been studied. Among such porous structures, there are those having an isotropic and uniform three-dimensional network structure made of a tangible skeleton, in which silicon carbide or silicon is impregnated and dispersed ( For example, see Patent Literature 1 and Patent Literature 2).

Further, in a structure made of a ceramic porous body having a three-dimensional network structure having an internal communication space, the inner side of the skeleton lattice of the ceramic porous body is a non-oxide ceramic made of silicon carbide or the like, and the surface side is an oxide-based Some are made of ceramic (for example, see Patent Document 3).
JP 2000-109375 A Japanese Patent Laid-Open No. 2003-119085 JP 60-46980 A

  However, the porous structure described in Patent Document 1 or Patent Document 2 includes silicon in the skeleton, and when these porous structures are immersed in molten aluminum or the like, Silicon elutes. In that case, since aluminum mixes with aluminum and an alloy is produced, the purity of aluminum is lowered.

  Further, the porous body shown in Patent Document 3 has the surface of the skeleton lattice of the ceramic porous body formed of an oxide ceramic, but the oxide ceramic on the surface has wettability with a metal such as aluminum. Since it is high, it is not suitable for a protective film when immersed in a molten metal.

  The present invention has been made in view of such circumstances, and provides a coated porous structure and a method for producing a coated porous structure capable of suppressing elution of silicon in immersion in molten aluminum. To do.

  (1) In order to achieve the above object, the coated porous structure according to the present invention is substantially composed of silicon carbide, carbon, or a composite material composed of at least one of these and silicon, and is three-dimensional. A skeleton part that forms a simple network structure and a film that is substantially made of silicon nitride and covers the surface of the skeleton part.

  Thus, since the surface of the porous structure with a coating of the present invention is coated with a silicon nitride coating, the adhesion of the surface to the metal (wetting) is reduced, and the silicon is eluted into the molten metal. Can be reduced. For example, elution of silicon can be suppressed when immersed in a molten metal such as aluminum. Further, silicon is contained in the skeleton portion, and the strength of the skeleton portion is improved. Further, it can be used as a porous structure having extremely high heat resistance and thermal conductivity.

  (2) Moreover, it is suitable for the porous structure with a film that the diameter of the network formed by the network structure is 0.1 mm or more and 5 mm or less, and the porosity is 70% or more and 95% or less.

  Thus, since the porous structure with a coating of the present invention has a three-dimensional network structure with high void connectivity, it can also be applied to molten metal members such as filters and molten metal bubbling parts that require high strength. it can.

  (3) Moreover, as for the porous structure with a film, it is suitable for the film which coat | covers the surface of the said frame | skeleton part to have thickness of 0.1 micrometer or more and 25 micrometers or less.

  As described above, the porous structure with a coating according to the present invention has a thin coating covering the surface of the skeleton, so that the skeleton is kept thin and the coating is provided while maintaining the void connectivity. Thereby, the efficiency as a protective film which prevents elution of silicon can be improved.

  (4) Moreover, as for the porous structure with a film, it is suitable for the film which coat | covers the surface of the said frame | skeleton part to have a coverage of 50% or more.

  Thereby, when it immerses in the molten metal of aluminum, the elution amount of silicon can be suppressed to 1000 mg / kg or less. As a result, it is possible to prevent a decrease in the purity of aluminum when a porous structure with a coating is used as the molten metal member.

  (5) In addition, the method for manufacturing a coated porous structure according to the present invention includes a composite material substantially composed of silicon carbide and silicon, and melt-impregnated silicon into a porous structure having a three-dimensional network structure. And a nitriding treatment step of heating the porous structure in a nitrogen gas atmosphere and reacting silicon on the surface of the porous structure with nitrogen to form a silicon nitride film. It is a feature.

  As described above, in the production method of the present invention, the porous structure is heated in a nitrogen gas atmosphere, and the silicon on the surface of the porous structure is reacted with nitrogen to form a silicon nitride film. It is possible to produce a coated porous structure with low adhesion to the film. For example, it is possible to produce a coated porous structure that suppresses elution of silicon when immersed in a molten metal such as aluminum. In addition, the melt impregnation step of melt impregnating the porous structure with silicon impregnates the skeleton portion of the porous structure with silicon, thereby improving the strength of the skeleton portion. Further, it can be used as a porous structure having extremely high heat resistance and thermal conductivity.

  Also, in the nitriding treatment step, the silicon on the surface is nitrided by heating in a nitrogen gas atmosphere, so that the coating covering the surface of the skeleton part can be thinned, the skeleton part is kept thin, and the air gap is connected. A coating can be provided while maintaining. That is, the efficiency of the coating as a protective film is increased, and the mesh holes are not blocked by the coating.

  Since the reaction in the nitriding treatment process is a gas reaction by heated nitrogen, the reaction proceeds to the back of the fine three-dimensional structure, and at the same time, the reaction proceeds uniformly without blocking the hole. be able to.

  (6) Moreover, the manufacturing method of the porous structure with a film | membrane WHEREIN: It is suitable to heat at the temperature of 1100 degreeC or more and 1350 degrees C or less for 5 hours or more in the said nitriding treatment process.

  Thereby, the porous structure with a film which suppresses the elution amount of silicon to 1000 mg / kg or less when immersed in molten aluminum can be produced. Therefore, when the coated porous structure manufactured by this manufacturing process is used as a member immersed in the molten aluminum, a decrease in the purity of aluminum is prevented.

  According to the coated porous structure according to the present invention, since the surface is coated with the silicon nitride film, the adhesion of the surface to the metal (wetting) is lowered, and the silicon is eluted into the molten metal. Can be reduced. For example, elution of silicon can be suppressed when immersed in a molten metal such as aluminum. Further, silicon is contained in the skeleton portion, and the strength of the skeleton portion is improved. Further, it can be used as a porous structure having extremely high heat resistance and thermal conductivity.

  According to the porous structure with a coating film according to the present invention, since it has a three-dimensional network structure with high void connectivity, it can be applied to molten metal members such as filters and molten metal bubbling parts that require high strength. .

  According to the porous structure with a coating film according to the present invention, since the coating film covering the surface of the skeleton part is thin, the coating film is provided while keeping the skeleton part thin and maintaining the connectivity of the voids. Thereby, the efficiency as a protective film which prevents elution of silicon can be improved.

  With the coated porous structure according to the present invention, the amount of silicon eluted when immersed in a molten aluminum can be suppressed to 1000 mg / kg or less. As a result, it is possible to prevent a decrease in the purity of aluminum when a porous structure with a coating is used as the molten metal member.

  According to the method for manufacturing a coated porous structure according to the present invention, the porous structure is heated in a nitrogen gas atmosphere, and silicon on the surface of the porous structure is reacted with nitrogen to form a silicon nitride film. By forming it, it is possible to manufacture a porous structure with a coating having low adhesion to the metal on the surface. For example, it is possible to produce a coated porous structure that suppresses elution of silicon when immersed in a molten metal such as aluminum. In addition, the melt impregnation step of melt impregnating the porous structure with silicon impregnates the skeleton portion of the porous structure with silicon, thereby improving the strength of the skeleton portion. Further, it can be used as a porous structure having extremely high heat resistance and thermal conductivity.

  Also, in the nitriding treatment step, the silicon on the surface is nitrided by heating in a nitrogen gas atmosphere, so that the coating covering the surface of the skeleton part can be thinned, the skeleton part is kept thin, and the air gap is connected. A coating can be provided while maintaining. That is, the efficiency of the coating as a protective film is increased, and the mesh holes are not blocked by the coating.

  Since the reaction in the nitriding treatment process is a gas reaction by heated nitrogen, the reaction proceeds to the back of the fine three-dimensional structure, and at the same time, the reaction proceeds uniformly without blocking the hole. be able to.

  Moreover, according to the method for manufacturing a coated porous structure according to the present invention, it is possible to manufacture a coated porous structure that suppresses the elution amount of silicon to 1000 mg / kg or less when immersed in a molten aluminum. . Therefore, when the coated porous structure manufactured by this manufacturing process is used as a member immersed in the molten aluminum, a decrease in the purity of aluminum is prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a porous structure 1 with a coating, and FIG. 2 is an enlarged view of a part of the porous structure 1 with a coating. As shown in FIG. 2, the porous structure 1 has a three-dimensional network structure. The mesh has a plurality of branches from the nodes, and the branch destinations are connected to branches from other nodes.

  The mesh diameter and porosity can be arbitrarily set depending on the properties of the preform or slurry in the production process, but the mesh diameter is 0.1 mm to 5 mm and the porosity is 70% to 95%. Is preferred. If the mesh diameter is less than 0.1 mm, clogging occurs, making it difficult to use as a filter. Also, when used as a molten metal bubbling component, the gas pressure must be increased more than necessary, which is not suitable. On the other hand, if the mesh diameter is larger than 5 mm, the transmittance becomes too large to function as a filter. Moreover, even if it uses as a bubbling component of a molten metal, the effect of molten metal stirring becomes thin. When the porosity is less than 70%, the surface area of the network structure is decreased, and the function as a filter or a molten metal bubbling component is not achieved. On the other hand, if the porosity is greater than 95%, the strength of the filter or molten metal bubbling component is low. Since the porous structure 1 with a coating has such a three-dimensional network structure with high void connectivity, it can be applied to molten metal members such as filters and molten metal bubbling parts that require high strength.

  FIG. 3 is a scanning electron microscope (SEM) photograph of the surface P and the cross section Q of the coated porous structure 1. As shown in FIG. 3, the network structure of the porous structure 1 with a coating is formed by a skeleton 2 and a coating 3 that covers the skeleton 2. Fine irregularities are formed on the surface P of the network structure by the coating 3, and the convex portion of the coating 3 grows and the precipitated crystals 4 are partially generated. FIG. 3 shows a state in which the coating 3 covers the entire surface of the skeleton 2, although the thickness varies due to unevenness.

  The skeleton 2 is substantially composed of a composite material of a metal silicon matrix and silicon carbide ceramic particles. Carbon may remain as an impurity in the composite material. “Substantially” means that impurities are not considered. Since silicon is contained in the skeleton 2, the strength of the skeleton 2 is high, and it can be used for a filter or the like that requires strength. Further, since the skeleton 2 is composed of a composite material of silicon matrix and silicon carbide ceramic particles, the coated porous structure 1 is used as a porous structure having extremely high heat resistance and thermal conductivity. can do.

  The coating 3 is substantially made of silicon nitride. Thus, since the surface of the coated porous structure 1 is covered with the silicon nitride film 3 (including the precipitated crystals 4), the adhesion of the surface to the metal (wetting) is reduced, and the molten metal The elution of silicon into can be reduced. For example, elution of silicon into aluminum can be suppressed when immersed in a molten metal such as aluminum.

  As shown in FIG. 3, the coating 3 has a thickness of 0.1 μm or more and 25 μm or less. Thus, since the coating 3 covering the surface of the skeleton part 2 is thin, the coating is provided while maintaining the skeleton part thin and maintaining the connectivity of the gaps. Thereby, the efficiency as a protective film which prevents elution of silicon can be improved. Further, as shown in FIG. 3, the coating 3 covers about 50% or more of the surface of the skeleton 2. The surface covering state can be known by SEM photographs as shown in FIG. 3 or nitrogen analysis using EPMA. The thickness is obtained by analysis of the cross section of the three-dimensional skeleton, and the coverage is obtained by analysis of the surface of the three-dimensional skeleton.

  Next, the manufacturing method of the porous structure 1 comprised as mentioned above is demonstrated. FIG. 4 is a flowchart showing a method for manufacturing the coated porous structure 1.

  An organic sponge-like porous preform is prepared in advance. 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. The sponge mesh may be fine or coarse depending on the application.

  First, a slurry for impregnating the porous preform is prepared (step S1). Resins as a carbon source are dissolved in a solvent, and silicon powder is mixed. Preferred examples of the resin include an organometallic polymer such as a phenol resin, a furan resin, or polycarbosilane. These resins may be used alone or in combination of two or more. From the viewpoint of suppressing the generation of bubbles in the slurry, it is effective to add an antifoaming agent. In addition, polyester or paraffin powder, starch, or the like may be added to the slurry in order to adjust the presence or absence of voids and the size of the void diameter by changing the properties of the slurry to be applied or sprayed.

  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. Carbon powder, graphite powder, carbon black may be added as additives, and as an aggregate or antioxidant, silicon carbide, silicon nitride, zirconia, zircon, alumina, silica, mullite, molybdenum disilicide, boron carbide, Boron powder or the like 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 and impregnated with the slurry (step S2), and the slurry is squeezed to such an extent that it does not block the voids communicating with the mesh. Then, unnecessary portions of the slurry are removed (step S3). The unnecessary portion of the slurry refers to a portion of the entire impregnated slurry that is subtracted from the slurry that is left to the extent that the voids are not blocked.

  The slurry 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 S4). 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 S5). Thereby, the porous preform becomes a carbonized composite composed of carbon and silicon. Most of the urethane resin component in the skeleton of the porous preform disappears by thermal decomposition, but the sponge skeleton maintains its original shape due to the carbon component and silicon powder resulting from carbonization of the coated phenol resin. The skeleton part has a carbon part obtained by carbonization of a partially impregnated phenol resin and a silicon powder contained in advance, and has a structure having an appropriate void. The part where the voids are blocked by the applied or sprayed slurry is also thermally decomposed and carbonized in the same manner as the skeleton part. 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 S6), and carbon and silicon are reacted to cause molten silicon and wettability. A good porous silicon carbide portion is formed inside the skeleton. 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 minute pores is obtained by forming the skeleton portion with silicon carbide and residual carbon, or with unreacted silicon.

  Next, the porous preform as the sintered body is heated to a temperature of about 1300 to 1800 ° C. in a vacuum or an inert atmosphere, and the porous silicon carbide and carbon portions on the skeleton are melt-impregnated with silicon. (Step S7).

  Thereafter, the obtained porous structure is heated in a nitrogen gas atmosphere at 1200 ° C. to 1450 ° C., preferably 1300 to 1400 ° C., to convert the silicon in the three-dimensional network structure into silicon nitride (step S8). In this way, the film 3 is formed on the surface of the skeleton part 2 to obtain a porous structure 1 with a film. Thus, in the nitriding treatment step, the silicon on the surface is nitrided by heating in a nitrogen gas atmosphere, so that the coating covering the surface of the skeleton part 2 can be thinned, the skeleton part 2 is kept thin, The coating 3 can be provided while maintaining the connectivity. That is, the efficiency of the coating film 3 as a protective film can be increased, and the coating film 3 does not block the mesh holes. Since the reaction in the nitriding treatment process is a gas reaction by heated nitrogen, the reaction proceeds to the back of the fine three-dimensional structure, and at the same time, the reaction proceeds uniformly without blocking the hole. be able to.

  The temperature increase rate in this temperature range is related to the degree of conversion of silicon in the three-dimensional network structure to silicon nitride. The larger the temperature increase rate, the less silicon nitride is generated, and the lower the temperature increase rate, the silicon nitride generated. Will increase. For this reason, it is more preferable to stop the temperature increase in a more preferable temperature range of 1300 to 1400 ° C. and hold the temperature for a certain time. The holding time may be appropriately selected and determined according to the desired amount of silicon nitride produced, but is preferably 5 hours or longer. Thereby, when it immerses in the molten metal of aluminum, the elution amount of silicon can be suppressed to 1000 mg / kg or less. As a result, a decrease in the purity of aluminum can be prevented when the coated porous structure 1 is used as a molten metal member.

  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.

  A porous structure without a coating and a porous structure with a coating were prepared, and the weight change before and after the nitriding treatment was measured for the porous structure with a coating. Furthermore, the porous structure without a film and the porous structure with a film were each immersed in molten aluminum, and the amount of silicon eluted was measured. This will be specifically described below.

  First, the mixing ratio of the phenol resin and silicon powder was set so that the atomic ratio of carbon to silicon by carbonization of the phenol resin was 1: 1. Based on the set mixing ratio, the phenol resin was dissolved with ethyl alcohol, and silicon powder was blended therein to prepare a slurry. In order to reduce the silicon particle size contained in the prepared slurry, the slurry was mixed and ground in a ball mill for 1 day.

  After mixing and pulverizing, the resulting slurry was sufficiently impregnated with polyurethane sponge, and then squeezed to such an extent that the slurry did not block the void area, and the slurry was removed. A polyurethane sponge having a void area of 60 ± 10 cells / 25 mm was used.

  Next, after the sponge impregnated with the slurry was dried at room temperature, it was further sufficiently dried at 70 ° C. to remove volatile components such as ethanol. The preform obtained by drying was heated at 1000 ° C. for 1 hour under an inert atmosphere such as argon to carbonize the phenol resin component.

  Furthermore, this porous structure is fired in a vacuum at 1500 ° C. for 1 hour, subjected to reaction sintering and silicon melt impregnation at the same time, and is made of a composite material composed of silicon carbide ceramics and a metal silicon component ( Comparative Example 1) was obtained.

  A porous structure separately obtained by the same process is heated in a nitrogen gas atmosphere, and the temperature is raised from 1100 ° C. to 1350 ° C. over 5 hours (treatment time: 5 hours) to perform nitriding, with a coating A porous structure (Example 1) was obtained.

  Similarly, the separately obtained porous structure was elevated from 1100 ° C. to 1350 ° C. in a nitrogen gas atmosphere over 13 hours, 48 hours, and 140 hours (treatment times 13 hours, 48 hours, and 140 hours), respectively. Nitriding treatment was performed by heating to obtain porous structures with coating (Example 2, Example 3, and Example 4). About the sample (Example 1-Example 4) which performed nitriding treatment, the weight change before and behind nitriding treatment was measured.

  Next, the porous structure of Comparative Example 1 and the coated porous structure of Examples 1 to 4 were immersed in molten aluminum, and a silicon elution test was performed.

  First, 100 g of aluminum 11 (a reagent manufactured by Kanto Chemical Co., Inc., purity 99.5%) was inserted into a carbon crucible 10 having a volume of 270 ml, and the aluminum 11 was heated to 850 ° C. in an oxidizing atmosphere electric furnace and melted. A porous structure cut into 2 × 2 × 5 cm was inserted into molten aluminum 11 as shown in FIG. 5, and the crucible 10 was covered with an alumina lid 12 so as not to float, and heated for 24 hours. While the aluminum 11 was in a molten state, the entire crucible 10 was taken out from the furnace, and the porous structure was taken out immediately. Such treatment was performed on the porous structures of Comparative Example 1 and Examples 1 to 4, respectively.

  After the elution test, the aluminum 11 was cooled to room temperature and solidified, and the lump of aluminum 11 was taken out from the crucible 10. As shown in FIG. 6 (b), when the side of the aluminum 11 in contact with the bottom of the crucible 10 is the A side and the side facing the lid direction is the B side, the B side portion is first shown as shown by the broken line. Resected. The remaining A side portion was divided into four equal parts as shown in FIG. In this way, 10 g of the analytical sample 13 was obtained. In accordance with JIS H 1352: 1997 “Quantitative determination method of silicon in aluminum and aluminum alloy”, the analytical sample 13 was decomposed with an aqueous solution of sodium hydroxide, and then analyzed by ICP emission spectrometry. The mass of silicon was measured. Such measurement was performed on the aluminum 11 obtained for the porous structures of Comparative Example 1 and Examples 1 to 4, respectively. Moreover, it measured also about the aluminum which does not put a porous structure as a blank.

  In addition, when the surface of the solidified body of the aluminum 11 was observed, a clear discoloration seen as elution of silicon was observed at the bottom of the lump of the aluminum 11 into which the porous structure not nitrided was inserted. . Therefore, the sample was cut and subjected to analysis so that the discolored portion was divided into almost ¼.

  FIG. 8 is a table summarizing the measurement results of the weight change before and after the nitriding treatment and the amount of silicon eluted into the molten aluminum in the above test. The weight increase rate represents the ratio of the weight increased by the nitriding treatment with respect to the weight before treatment, and is calculated by the formula of (increased weight) / (weight before treatment) × 100. The nitriding reaction rate represents the ratio of the weight of silicon converted into silicon nitride by nitriding with respect to the total weight before the treatment, and (increased weight) / ((pre-treatment weight) × 0.5 X0.67)) It is calculated by the formula of x100. The silicon content is the weight of silicon contained per unit weight of aluminum used in the molten metal test. The silicon content analysis value of the reagent aluminum as a blank was 355 mg / kg. The amount of silicon elution is obtained by subtracting the weight of the blank from the silicon content of each sample.

  FIG. 9 is a graph showing the weight increase rate of the porous structure with respect to the treatment time of the nitriding treatment. It can be seen that as the treatment time increases, silicon on the surface of the porous structure is converted to silicon nitride, and the weight increases accordingly. It can also be seen that the silicon nitriding reaction is almost saturated after 140 hours of treatment.

  FIG. 10 is a graph showing the elution amount of silicon into molten aluminum with respect to the treatment time of nitriding treatment. The silicon elution amount of the porous structure (Comparative Example 1) that was not nitrided at all was 6805 mg / kg. On the other hand, the silicon elution amount of the sample treated for 5 hours (Example 1) is 945 mg / kg, and it can be seen that the elution amount is reduced to 1000 mg / kg or less. FIG. 11 is a graph showing the elution amount of silicon into the molten aluminum with respect to the weight increase rate of the porous structure. Although the weight increase rate was only 1.5% after the treatment for 5 hours, the elution amount of silicon was reduced to 1000 mg / kg or less, and a great effect was obtained as described above.

  Thus, from the tests described in the examples, it was demonstrated that the porous structure subjected to the nitriding treatment reduces the elution of silicon with respect to the molten aluminum. In addition, it was proved that a great effect was obtained when the treatment was performed for 5 hours or more and the weight increase rate by nitriding treatment was 1.5% or more.

It is a perspective view of the porous structure with a film concerning the present invention. It is an enlarged view of the porous structure with a film concerning the present invention. It is a SEM photograph of the porous structure with a film concerning the present invention. It is a flowchart which shows the manufacturing method of the porous structure with a film which concerns on this invention. It is sectional drawing which shows the state which immersed the porous structure with a film in the molten aluminum in the crucible. (A) It is a top view of the taken-out aluminum lump. (B) It is a side view of the taken-out aluminum lump. It is a perspective view of the sample for analysis. It is a table | surface which shows the test result of an Example. It is a graph which shows the weight increase rate of a porous structure with respect to processing time. It is a graph which shows the elution amount of the silicon | silicone to aluminum molten metal with respect to process time. It is a graph which shows the elution amount of the silicon | silicone to molten aluminum with respect to the weight increase rate of a porous structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous structure with film 2 Skeletal part 3 Film 4 Precipitated crystal

Claims (4)

A porous structure with a coating used for immersion in molten metal,
A skeleton part that is composed of a composite material substantially consisting of silicon carbide and silicon and forms a three-dimensional network structure;
A film that is substantially composed of silicon nitride and covers the surface of the skeleton ,
The diameter of the mesh formed by the mesh structure is 0.1 mm or more and 5 mm or less, and the porosity is 70% or more and 95% or less,
Coating, a coated porous structure characterized that you have had a thickness of 25μm or more 0.1μm covering the surface of the skeleton.   The coated porous structure according to claim 1, wherein the coating covering the surface of the skeleton has a coverage of 50% or more. A method for producing a coated porous structure used for immersion in molten metal,
An organic sponge-like porous preform is impregnated with a silicon powder slurry, unnecessary portions of the impregnated slurry are removed, and carbonized and fired in an inert atmosphere, thereby substantially consisting of silicon carbide and silicon. A preparation step of obtaining a porous structure composed of a composite material and having a three-dimensional network structure;
A melt impregnation step of silicon to melt impregnated into the porous structure,
The porous structure body melt-impregnated with silicon is heated in a nitrogen gas atmosphere, and the silicon on the surface of the porous structure body is reacted with nitrogen to form a silicon nitride film having a thickness of 0.1 μm or more and 25 μm or less. a nitriding step of forming, only including,
The melt impregnation step is to produce a coated porous structure having a network structure having a mesh diameter of 0.1 mm to 5 mm and a porosity of 70% to 95% in the porous structure. A method for producing a coated porous structure.   The method for producing a coated porous structure according to claim 3, wherein in the nitriding treatment step, heating is performed at a temperature of 1100 ° C. or more and 1350 ° C. or less for 5 hours or more.