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EP1296889A1 - Melange pouvant etre plastifie et procede d'utilisation dudit melange - Google Patents

Melange pouvant etre plastifie et procede d'utilisation dudit melange

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Publication number
EP1296889A1
EP1296889A1 EP01939384A EP01939384A EP1296889A1 EP 1296889 A1 EP1296889 A1 EP 1296889A1 EP 01939384 A EP01939384 A EP 01939384A EP 01939384 A EP01939384 A EP 01939384A EP 1296889 A1 EP1296889 A1 EP 1296889A1
Authority
EP
European Patent Office
Prior art keywords
mixture
silicon
weight
silicon carbide
filler
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01939384A
Other languages
German (de)
English (en)
Other versions
EP1296889A4 (fr
Inventor
Kishor P. Gadkaree
Joseph F. Mach
John L. Stempin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Corning Inc
Original Assignee
Corning Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/817,411 external-priority patent/US6555031B2/en
Application filed by Corning Inc filed Critical Corning Inc
Publication of EP1296889A1 publication Critical patent/EP1296889A1/fr
Publication of EP1296889A4 publication Critical patent/EP1296889A4/fr
Withdrawn legal-status Critical Current

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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
    • C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
    • C04B35/573—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide obtained by reaction sintering or recrystallisation
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    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • C04B35/62605—Treating the starting powders individually or as mixtures
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    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/34—Non-metal oxides, non-metal mixed oxides, or salts thereof that form the non-metal oxides upon heating, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
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    • C04B2235/3852—Nitrides, e.g. oxynitrides, carbonitrides, oxycarbonitrides, lithium nitride, magnesium nitride
    • C04B2235/3873—Silicon nitrides, e.g. silicon carbonitride, silicon oxynitride
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Definitions

  • the present invention relates to silicon carbide sintered bodies useful in the removal of diesel soot particles from the exhaust gas of diesel engines.
  • the invention more particularly relates to a method for producing the silicon carbide sintered bodies, in which a raw material batch of a carbon precursor and silicon metal powder is combined with a water-soluble thermoplastic binder, an inorganic filler and optionally an organic fibrous filler.
  • Silicon carbide honeycomb structures are desirable for industrial and automotive applications. Silicon carbide honeycomb structures are particularly useful because of the very high surface area to volume ratio and the low-pressure drops associated with such structures in applications where high flow rate streams are to be treated. The high surface area allows for high loading levels and hence longer life in filtration applications. Furthermore, the high chemical inertness, very high refractoriness, high thermal conductivity and thermal cycling resistance make such SiC honeycombs particularly desirable for many high temperature filtration applications. These silicon carbide honeycomb structures are particularly useful in diesel particulate filtration for use in the removal of soot particles from the exhaust gas of diesel engines.
  • the method for forming such silicon carbide honeycomb structures involves fabrication via the formation of a green body of fine particulate material, which is thereafter sintered.
  • the sintering is typically carried out at very high temperatures, normally greater than 2000°C, for long periods of time because of the diffusive processes involved.
  • Standard methods described in the literature typically involve extruding powdered silicon carbide with a thermoplastic binder, followed by burning off of the binder and thereafter sintering of the powder; see, e.g., US 5,914,187.
  • the drawback of the sintering method described is that very high temperatures (in excess of 2000°C) and long periods of "time at temperature” (6-10 hours) are needed for consolidation, making the process very expensive. Furthermore, large structures with uniform properties are difficult to form because the so-formed structure does not have sufficiently high strength after the binder is burned out (typically around 800°C), so as to be handled during the typical industrial process.
  • US Pat No. 5,853,444 discloses a method for the production of a porous permeable molded body made of silicon carbide.
  • the method disclosed therein involves utilizing a starting powder comprised of silicon, or a mixture of silicon with portions of silicon carbide and/or carbon.
  • the starting powder is thereafter combined with an organic binding agent capable of being coked.
  • This starting powder/binder mixture is then molded, specifically extruded, into a green body that is then subjected to an inert-gas atmosphere coking treatment.
  • the particular steps for the formation involve mixing together an inert solvent and a raw material batch comprising the following: (1) about 50-90%, by weight silicon carbide; (2) about 5.0 to about 50% graphite particles coated with a carbon precursor; (3) about 2 to about 20% of sintering aids; and, (4) about 0J5 to about 15% by weight temporary filler.
  • the method next involves drying the raw batch to evaporate the inert solvent and thereafter shaping the dried raw batch into a shaped body. After shaping the body into the desired shape, the method involves heating the shaped body at a temperature sufficient to carbonize the carbon precursor and volatilize the temporary filler thereby forming a matrix having interconnected pores; sufficient temperature disclosed for carbonizing the green body is 850°C.
  • the method for forming the self-sintered silicon carbide composite material involves sintering the shaped body to densify the matrix; sintering temperatures ranging from 1900 to 2500°C are disclosed.
  • Both the Maier and Pfaff methods described are capable of use in forming silicon carbide bodies, however the disadvantage of using each of these methods is that, like most standard SiC sintering processes, they require extraordinarily high sintering temperatures, typically in excess of 2000°C. Additionally, the Maier method results in the formation of very fragile after-carbonization structures, due to the very low carbon content material (i.e. starch or modified starch) used as the binder. Although the Pfaff method is suited to forming a graphite-containing silicon carbide, it is not suitable for the formation of ceramic bodies useful in filtration applications. Lastly, the batches disclosed in the Pfaff reference are not suitable for use in the extrusion process required for the formation of honeycomb structures.
  • US Pat No. 5,196,389 (Dubots) describes the formation of silicon carbide supports.
  • the method involves forming a plasticizable mixture of silicon powder, resin and carbon powder.
  • the mixture is thereafter shaped, preferably by extrusion, to form a green monolithic honeycomb structure suitable for use as the catalyst support. Heating of this green monolithic body in non-oxidizing atmosphere at a temperature of between 600 and 1000°C is continued for a period of time sufficient to carbonize all of the resin in the mixture/green body.
  • the green monolithic honeycomb body is sintered, in a non-oxidizing (or nitriding) atmosphere, at temperature of between 1350 and 1450°C for a period of between 1 to 2 hours.
  • Dubots discloses the use of carbon black as the major carbon source; i.e., very fine soot powders with high surface area. Typically, carbon does not bond to any binder very well, the result being that structures produced with carbon-based fillers are typically weak. Furthermore, when the carburetion is carried out at 1400°C, in order to form silicon carbide, the silicon powder has to melt and mix completely with the carbon. Discrete carbon particles make it difficult for this interaction to take place uniformly throughout the structure, thereby resulting in very small grained sintered SiC structures that are typically weak and non-uniform.
  • US Pat No. 5,217,930 discloses a porous refractory carbide with a skeleton of metal or metalloid refractory carbide for catalyst support.
  • the reference describes a method for the formation of silicon oxycarbide coated on metallic or SiC- type porous substrate. The method of forming this silicon oxycarbide material involves mixing an organic polymeric or polymerisable compound with metal powder and a solvent and thereafter curing the formed mass after removal the solvents.
  • Heat treating at 500-1000°C is then utilized for forming the porous skeleton; i.e., carbonization.
  • carbonization the structure is subjected to "activation” i.e., partial or controlled oxidation in presence of oxygen (500-900°C).
  • activation i.e., partial or controlled oxidation in presence of oxygen (500-900°C).
  • heat treatment in inert atmosphere, is carried out at temperature not exceeding 1400°C, preferably 1150-1250°C, to form an amorphous SiOxCy compound, while part of the structure forms silicon carbide.
  • the high viscosity of the resin utilized results in a high degree of oligomer reaction, thereby rendering the resin sparingly, if at all, soluble in water.
  • the resin cannot be diluted with water, thereby resulting in the severe splitting of walls, and in turn leading to the formation of weak silicon carbide honeycombs.
  • an object of the present invention is to provide, for a reduced sintering temperature process suitable for use in the formation of extruded thin-walled honeycomb silicon carbide structures.
  • the object of the present invention is directed at both a raw material batch mixture and a process for forming green and lowered-temperature sintered SiC honeycomb structures that exhibit with sufficient handling and so-formed strength.
  • the invention is directed at a plasticizable raw material batch mixture for forming a silicon carbide honeycomb structure, comprising the following components: (1) powdered silicon metal; (2) a carbon precursor comprising a water soluble crosslinking thermoset resin having a viscosity of less than about 1000 centipoise (cp), and preferably less than about 500 cp; (3) a powdered silicon- containing filler; and, (4) a water soluble thermoplastic binder.
  • the batch mixture can include either, or both, an organic fibrous filler and a pore forming filler comprising either a graphitic or a thermoplastic pore-forming filler.
  • the invention provides for a process for producing a silicon carbide honeycomb structure utilizing the inventive batch material.
  • the process involves the following steps: (1) mixing together selected raw materials to form the previously mentioned plasticizable raw material batch; (2) shaping the batch mixture to form a shaped green body, preferably involving extrusion to form a honeycomb structure; (3) drying and curing the green body; (4) heating the green body in a nitrogen atmosphere at a temperature sufficient to carbonize the resin; and, (5) sintering the green body at a temperature sufficient to convert the green body to a porous silicon carbide sintered body; preferably a temperature at least above 1400°C.
  • FIG. 1 is a scanning electromicrograph taken at 25x, of a sintered silicon carbide - honeycomb structure formed according to the process disclosed in the instant invention
  • FIG. 2 is a schematic flow-chart illustration of the process for producing a sintered silicon carbide graph according to the instant invention
  • FIG. 3 is a plot of the data of the X-ray analysis of the so-formed SiC honeycomb stracture of Example 1;
  • FIG. 4 is a scanning electromicrograph taken at 25x of the sintered silicon carbide structure formed using a phenolic resin exhibiting a viscosity of 2500 cp as detailed in Comparison Example 3.
  • This instant invention relates to a plasticizable batch mixture capable of being extruded into a silicon carbide green honeycomb body exhibiting surprisingly good strength; sufficient green strength to allow handling of the green honeycomb in a standard manufacturing process. Furthermore, this so-formed SiC honeycomb body formed from this inventive batch mixture can be dried, cured and sintered at temperatures as low as 1400°C to form a sintered SiC honeycomb structure possessing good strength.
  • the extrudable batch mixture for use in preparing a sintered silicon carbide honeycomb substrate comprises about 10-40%, by weight, finely powdered silicon metal; preferably about 15-30%.
  • the silicon powder should exhibit a small mean particle size; e.g., from about 0.2 micron to 50 microns, preferably 1-30 microns.
  • the surface area of the silicon powder may, in some instances, be more descriptive than particle size, and should range between about 0.5 to 10m 2 /g, preferably between about 1.0- 5.0 m 2 /g.
  • the silicon powder be comprised of a crystalline silicon powder. It has been found that the use of amorphous silicon metal powder in the subsequent formation process, as is standard in the prior art, results in an aqueous system that typically is subject to a reaction, and resultant foaming, between the silicon and water which is used as the preferred solvent for the resin. This foaming is particularly undesirable when forming honeycomb, or similar-type filtration structures, as it makes it particularly difficult to form structures exhibiting controlled wall uniformity, porosity and microstructure; i.e., difficulty in forming ceramic bodies exhibiting the narrowed pore size distribution desired for filtration applications. It has been surprisingly found that the use of powdered crystalline silicon does not result in presence of foaming reactions when utilized in an aqueous system.
  • the use of crystalline silicon powder allows use of water as the solvent and in the formation of an aqueous system.
  • the SiC formation process is much simpler, more economical, as water is an inexpensive solvent and requires no post formation handling or disposal of resultant water vapor.
  • the raw batch also contains about 10-40%, by weight, of a carbon precursor, specifically, a water soluble crosslinking thermoset resin having a viscosity of less than about 1000 centipoise (cp). It is necessary that the thermoset resin utilized also be a high carbon yield resin, and that it be utilized in an amount such that the resultant carbon to silicon ratio in the batch mixture is about 12:28 by weight; the stoichiometric ratio of Si-C needed for formation of silicon carbide.
  • Acceptable water-soluble crosslinking thermoset resins include phenolic resins, such as Phenolic resole liquid resin available from Georgia Pacific commercially sold as code GP510D34 RESI-SET.
  • Viscosity is an important feature of the thermoset resin utilized in the raw batch.
  • Phenolic resins are produced by a reaction of phenol and formaldehyde in a water solution while in the presence of an acid or base catalyst. As the reaction proceeds, oligomers are formed and the resin begins to precipitate. The longer the reaction is allowed to continue, the higher the oligomer molecular weight. Higher molecular weight oligomers have fewer reactive sites and lower water solubility. The viscosity of the resin thus indicates its oligomer reactivity and water solubility. Once the viscosity becomes very high, the resin completely precipitates out of the water.
  • the viscosity of the phenolic resin is thus very critical, since it will determine the reactivity of the resin with components, it's capability to be diluted and still form strong structure on cure, as well as carbonization tendency.
  • phenolic resin-containing honeycomb structures with fillers are preferably extruded, it is necessary to have the resin viscosity below the aforementioned level of 1000 cp.
  • liquid thermoset resin in the batch mixture intimately mixes with silicon powder to ultimately form, upon curing and carbonization steps of the process to be described later, a homogeneously and intimately mixed carbon/silicon structure. As such, the reaction between carbon and silicon that takes place during sintering does so uniformly, thereby resulting in a uniform SiC sintered structure.
  • Powdered silicon-containing fillers in an amount up to 60%, by weight, may also be included in the inventive batch mixture.
  • the main function of these fillers is to prevent excessive shrinkage of the green body during the carbonization and reactive consolidation/sintering steps.
  • Suitable silicon-containing fillers include silicon carbide, silicon nitride, mullite or other refractory materials.
  • the preferred particle size for the fillers is a mean particle size of between 0.5-50 ⁇ m, and more preferably 5-30 ⁇ m.
  • the surface area of the powders should be between OJand 5m 2 /g, and preferably 0.5- 1.5m 2 /g.
  • the batch may further optionally include up to about 15%, by weight, of an organic fibrous filler.
  • Suitable fibrous fillers include cotton fiber, cellulose fiber, wood fiber or crushed nut shells or other organic similar-type fibrous material, with cellulose fiber being the preferred filler.
  • the cellulose fiber is easily wetted, is flexible and helps knit the structure of the wall.
  • Suitable fibers exhibit a diameter of between 0J-50 ⁇ m, and preferably 1-20 ⁇ m.
  • the batch mixture contains about 2-10%, by weight of a water-soluble thermoplastic temporary binder.
  • Acceptable temporary binders include methylcellulose, hydroxypropyl methylcellulose, and combinations thereof.
  • Preferred sources of cellulose ethers and/or derivatives thereof, are Methocel A4M, F4M, and F240M from Dow Chemical Co.
  • Methocel A4M is a methylcellulose binder having a gel temperature of 50-55°C and gel strength of 5000 g/cm 2 (based on 2% solution at 65°C).
  • Methocel F4M and F240M are hydroxypropyl methylcellulose.
  • the inventive batch may include a pore-forming filler in an amount of up to 20%, by weight, specifically an organic filler, which does not leave any carbon residue after firing; suitable pore-formed fillers include either a graphitic or thermoplastic pore-forming filler.
  • Pore size and porosity amounts are important properties that must be controlled when forming a honeycomb structure for use in filtration applications. For applications such as diesel particulate filtration, for example, desired pore sizes range from 1- 30 microns.
  • FIG. 1 is an SEM of a formed SiC honeycomb wall section exhibiting the type/size of porosity that is desirable for diesel filtration applications. The utilization of pore forming fillers facilitates the formation of pores of desired size like that illustrated in FIG. 1.
  • the mean particle size and weight percent of graphite powder utilized determines the final porosity in the wall. It should be noted that the graphitic filler is not affected in any way during later-described cure, carbonization or reactive firing/sintering of the honeycomb structures. As such, any so- formed structure will require a post-sintering step to burn out graphite and leave porosity behind; e.g., the honeycombs can subjected to air firing at around 800°C to burn out graphite.
  • thermoplastic pore-forming filler will not require a post-sintering burn-out step as the filler burns out in nitrogen during the later-described carbonization with little or no carbon residue while still leaving behind the requisite porosity.
  • sintering aids such as boric oxide, aluminum oxide, silicon nitride, aluminum nitride, boron carbide, yttrium oxide or other rare earth oxides aluminum metal powders, as well as other standard sintering aids known in the art may be added to the batch.
  • the first step of the process involves mixing together the components of the aforementioned plasticizable raw batch.
  • the batch mixture should comprise the following: (a) about 10-40%, by weight, powdered silicon metal, preferably crystalline powdered silicon metal (b) about 10- 40%, by weight, of a water-soluble crosslinking thermoset resin having a viscosity of less than about 1000 centipoise (cp); and, (c) about 2-10%, by weight of a water soluble thermoplastic temporary binder.
  • the batch mixture can optionally include a surfactant, up to 60%, by weight, of powdered silicon-containing filler, up to about 15%, by weight, of an organic fibrous filler and a pore-forming filler comprising either a graphitic or a thermoplastic pore forming filler.
  • a surfactant up to 60%, by weight, of powdered silicon-containing filler, up to about 15%, by weight, of an organic fibrous filler and a pore-forming filler comprising either a graphitic or a thermoplastic pore forming filler.
  • the mixing preferably takes place in three stages.
  • the first stage the crystalline silicon metal powder is mixed with the required amount of the water-soluble resin.
  • the second stage or wetting stage of batch formation involves adding and dry mixing together the silicon metal powder-resin mixture and the remaining inorganic powder particles, i.e., the silicon containing powder filler, binder and optional surfactant, inorganic fibrous filler and pore forming filler, and thereafter adding the required amount of the solvent to form the wet batch.
  • This mixing and solvent addition is done in a standard mixer, for example a Littleford mixer.
  • the solvent typically water
  • the solvent is added in an amount that is less than is needed to plasticize the batch; typically the water is added as a superaddition, in amounts ranging from 5-25%, by weight, with levels ranging from 7-15%, by weight being preferred.
  • the water With water as the solvent, the water hydrates the binder and the powder particles.
  • the powder particles are coated and dispersed by the surfactant and solvent.
  • the plasticization takes place in the third stage.
  • the wet mix from the second stage is sheared in any suitable mixer (e.g., Littleford) in which the batch will be plasticized.
  • stirring together the powdered components in a suitable known manner, to prepare an intimate mixture of the inventive batch mixture capable of being formed into a SiC sintered body by, for example, by extrusion or molding.
  • the resulting stiff, uniform and extrudable batch mixture is then shaped into a green body by any known conventional ceramic forming process, such as, e.g., extrusion, injection molding, slip casting, centrifugal casting, pressure casting, dry pressing, etc.
  • extrusion through a die is preferable.
  • the so-formed stracture is then dried and cured by one of a variety of conventional techniques known to those skilled in the art, e.g., hot-air heating, microwave heating, and dielectric heating.
  • the green honeycomb structures are dried and cured for a period of 1 hour at temperatures of up between 90 to 150°C.
  • the resultant strength of these green, cured structures typically exceeds 10 ksi, though 5 ksi is sufficient.
  • the very strong green structures are then fired in nitrogen at temperatures of between 700-1000°C to carbonize the resin and to remove pore-forming fillers.
  • the green structure should be fired for a sufficient period of time so as to complete the reaction of the metal and carbon to form silicon carbide.
  • the carbonized structures are then fired at a temperature sufficient to complete the conversion to silicon carbide porous honeycombs; i.e., very strong monolithic structures of silicon carbide exhibiting crush strengths in excess of lOksi.
  • the firing is temperature range is between 1400 to about 1800°C; the resultant crystalline phase obtained by utilizing this firing temperature range is cubic silicon carbide. It is noted that, optionally the firing can be done at higher temperatures, up to 2400°C, if formation of the hexagonal or rhombic crystalline type of silicon carbide is desired.
  • the firing step can be carried out in a conventional batch or continuous furnace, wherein the shaped body is passed through the hot zone of the furnace at a rate to provide a prescribed residence time at the desired temperature.
  • the firing step accomplishes a "pressureless sintering" referred to herein simply as "sintering".
  • sintering or “pressureless sintering” it is meant that no mechanical pressure is applied to the object being fired or sintered to promote densification. Instead the object being sintered, usually in an inert container such as a graphite crucible, is maintained under an atmosphere of inert gas, a vacuum, or nitrogen; inert gasses include argon, helium and neon.
  • inert gasses include argon, carbon dioxide, carbon monoxide, helium, hydrogen, neon, and nitrogen and mixtures thereof.
  • nitrogen under sintering conditions, enters into, to some degree, the silicon carbide, it does so in sufficiently minor degree that the composition of the sintered ceramic body is not noticeably changed.
  • the firing can also be carried out under vacuum.
  • vacuum it is meant a practical vacuum of 1.0 torr or less.
  • Example 1 A plasticizable raw material batch mixture containing the following raw materials was mixed and mulled together with a 7%, by weight, superaddition of water:
  • Silicon carbide powder 0.6 ⁇ m 35.00
  • the mulled mixture was then extruded through a 200 cpsi die to obtain a honeycomb structure having a 2.5cm diameter and 30cm length.
  • the honeycomb shaped green stracture was then dried at 90°C for a period of 2 hours and then heated to 150°C to fully cure the phenole resin.
  • the cured honeycomb was very strong and rigid and exhibited a strength of in excess of lOksi.
  • the cured structure was thereafter heated to 900°C for a period of 2 hours in a nitrogen atmosphere to convert the resin to carbon.
  • the carbonized honeycomb structure was then heated, in a vacuum, to a temperature of 1500°C for one hour and thereafter cooled to room temperature.
  • the so-formed SiC honeycomb stracture was very strong, rigid and had the characteristic greenish color of silicon carbide.
  • Properties exhibited by the fully sintered SiC honeycomb stracture were as follows: 1) a microstructure comprising a 100% silicon carbide structure, with no trace of residual silicon or any other phase (an examination of the FIG. 3 X-ray plot reveals a nearly complete conversion to Silicon carbide for the so-formed honeycomb stracture); 2) a crush strength of about 12 ksi.
  • Example 2 A plasticizable raw material batch mixture containing the following raw materials was mixed and mulled together with a 6%, by weight, superaddition of water:
  • Silicon carbide powder 0.6 ⁇ m 25.00
  • Example 1 The process of example 1 was followed to form a sintered SiC honeycomb structure.
  • the so-formed SiC honeycomb stracture was very strong, rigid and had the characteristic greenish color of silicon carbide.
  • Properties exhibited by the fully sintered SiC honeycomb stracture were as follows: (1) a crush strength lOKsi; (2) X-ray data indicated complete conversion to silicon carbide, like Example 1 with no residual phases present.
  • Example 3 A plasticizable raw material batch mixture containing the following raw materials was mixed with a 7%, superaddition by weight, water and thereafter mulled together:
  • the mulled mixture was then extruded through a die to form a 200 cpsi honeycomb structure exhibiting a wall thickness of 20 mil.
  • the honeycomb shaped green structure was then dried at 90°C for a period of 2 hours and then heated to 150°C to fully cure the phenole resin; resulting in the crosslinking of the resin and stiffening of the structure.
  • the cured honeycomb was very strong and rigid and could be easily cut, cored drilled and handled without sufficient breakage problems.
  • the crush strength of the honeycomb was about lOKsi.
  • the cured structure was heated to 900°C, in a nitrogen atmosphere, for a period of 3 hours to convert the resin to carbon; i.e., carbonize the resin. Finally, the carbonized honeycomb structure was then heated, in a vacuum, to a temperature of 1500°C for one hour and thereafter cooled to room temperature.
  • Example 4 A plasticizable, extrudable raw material batch mixture containing the following raw materials was mixed with an 11.7%, by weight, superaddition of water and thereafter mulled together:
  • This batch was extruded, dried, cured, carbonized and fired at 1500°C in a similar manner as that described for Example 3.
  • the so-formed silicon carbide honeycomb structure was thereafter fired, in air at a temperature of 800°C to bum out the graphite, to obtain a SiC honeycomb structure exhibiting generally, uniform porosity, walls and exhibiting good strength.
  • the strength of the honeycomb was about 5Ksi, slightly lower than the ones obtained in examples 1,2 and 3.
  • Example 5 A plasticizable, extrudable raw material batch mixture containing the following raw materials was mixed with a 12.5%, by weight, superaddition of water and thereafter mulled together:
  • Silicon carbide powder ⁇ 0.6 ⁇ m
  • This batch was extruded, dried, cured, carbonized and fired at 1500°C in a similar manner as that described for Example 3, to obtain a strong porous SiC/Si 3 N 4 composite honeycomb structure.
  • Example 6 A plasticizable, extrudable raw material batch mixture containing the following raw materials was mixed with an 11.0%, by weight, superaddition of water and thereafter mulled together:
  • Methylcellulose binder 7.50
  • This batch was extruded, dried, cured, carbonized and fired at 1500°C in a similar manner as that described for Examples 1 and 2.
  • a honeycomb comprising dimensions, as described earlier was formed.
  • the so-formed sintered SiC honeycomb structure exhibited a porosity of about 48% with the pore averaging about 5 micron in size, and a crush strength of about 10 ksi similar to that exhibited by the earlier examples.
  • Example 7 A plasticizable, extrudable raw material batch mixture containing the following ' raw materials was mixed with a 10.0%, by weight, superaddition of water and thereafter mulled together:
  • Silicon carbide powder 10.0 ⁇ m 35.00
  • This batch was extruded, dried, cured, carbonized and fired at 1500°C in a similar manner as that described for Examples 1 and 2.
  • a honeycomb as described earlier was formed; the so-formed honeycomb exhibited a porosity of about 58% and a crush strength of 8ksi.
  • Comparison Example 1 Example 3 was substantially repeated, with the exception that the crystalline silicon powder was replaced with an amorphous silicon powder in the batch mixture.
  • foaming occurred, likely due to the interaction of the silicon with the aqueous phenolic resin.
  • the mixture was allowed to stand till the foaming reaction was minimized, and the mixture was thereafter extruded as above.
  • FoUowing extrusion the green body was dried in a manner as described above. During this drying step, however, this green stracture again exhibited periods of foaming resulting in a dried honeycomb body possessing undesirable non-uniformity in the honeycomb body cell walls.
  • Comparison Example 2 Example 3 was substantially repeated, with the exception that the phenolic resin utilized exhibited a viscosity of 2501 cp.
  • the resultant SiC honeycomb stracture exhibited severely distorted and split cell walls following the curing step;
  • FIG.4 is an SEM photograph taken at 25X of the walls of the so-formed honeycomb stracture.
  • the resin utilized in the inventive process should exhibit a viscosity of below about 1000 cp, preferably 500 cp.
  • Comparison Example 3 A plasticizable, extrudable raw material batch mixture containing the following raw materials was mixed with both 12.5 and 15%, by weight, superadditions of water and thereafter mulled together:
  • Comparison Example 3 was substantially repeated, with the exception that 6%, by weight, methyl cellulose binder and 1%, by weight SAN lubricant was added to the batch mixture. After mixing of the batch materials, the mixture was thereafter extraded as above; the resultant honeycomb was very fragile. Following extrusion, the green body was dried and subsequently carbonized at a temperature of 900°C. The dried and carbonized body was then fired in an Argon atmosphere at a temperature of 1500°C whereupon the honeycomb body completely disintegrated into a fine powder

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Abstract

Mélange par lot de matière première pouvant être plastifiée, pour former une structure en nid d'abeilles en carbure de silicium, qui contient les constituants suivants : (1) du silicium métal en poudre, (2) un précurseur de carbone comportant une résine thermodurcissable de réticulation hydrosoluble ayant une viscosité inférieure à environ 1.000 centipoises (cp) et de préférence inférieure à 500 cp, (3) une matière de charge contenant du silicium en poudre, et (4) un liant thermoplastique hydrosoluble. Eventuellement, ledit mélange par lot peut contenir une matière de charge fibreuse organique et / ou une matière de charge porogène qui est soit graphitique, soit thermoplastique. Dans un autre aspect, la présente invention concerne un procédé de production d'une structure en nid d'abeilles en carbure de silicium constituée de la matière en lot préparée selon la présente invention. Ledit procédé consiste à mélanger des matières premières sélectionnées pour former le lot de matière première pouvant être plastifiée mentionné et à conférer une forme au mélange en lot pour obtenir un corps vert façonné, de préférence par extrusion pour former une structure en nid d'abeilles, puis à sécher, cuire et fritter le corps vert à une température suffisante pour convertir le corps vert en un corps fritté en carbure de silicium poreux. De préférence, cette température est supérieure à environ 1.400 °C.
EP01939384A 2000-06-19 2001-05-23 Melange pouvant etre plastifie et procede d'utilisation dudit melange Withdrawn EP1296889A4 (fr)

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US59800800A 2000-06-19 2000-06-19
US598008 2000-06-19
US817411 2001-03-26
US09/817,411 US6555031B2 (en) 2000-06-19 2001-03-26 Process for producing silicon carbide bodies
PCT/US2001/016810 WO2001098207A1 (fr) 2000-06-19 2001-05-23 Melange pouvant etre plastifie et procede d'utilisation dudit melange

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US7759276B2 (en) 2004-07-23 2010-07-20 Helsa-Automotive Gmbh & Co. Kg Adsorptive formed body having an inorganic amorphous supporting structure, and process for the production thereof
EP1741685B1 (fr) 2005-07-05 2014-04-30 MANN+HUMMEL Innenraumfilter GmbH & Co. KG Corps formé céramique poreux contenant beta-SiC et son procédé de préparation.
EP1899280B1 (fr) 2005-07-05 2015-09-02 MANN+HUMMEL Innenraumfilter GmbH & Co. KG CORPS MOULE CERAMIQUE CONTENANT DU ß-SIC POREUX ET PRESENTANT UN REVETEMENT EN OXYDE D'ALUMINIUM ET PROCEDE POUR LE PRODUIRE
EP1741687B1 (fr) 2005-07-05 2011-10-12 MANN+HUMMEL Innenraumfilter GmbH & Co. KG Corps formé céramique poreux contenant ß-SiC et son procédé de préparation.
DE102006062140A1 (de) * 2006-12-22 2008-06-26 Dow Wolff Cellulosics Gmbh Celluloseetheradditive für die Extrusion keramischer Massen
US8097203B2 (en) * 2007-01-29 2012-01-17 Corning Incorporated Crosslinked green body articles and method of manufacturing porous ceramic articles therefrom
US7919040B2 (en) 2007-08-08 2011-04-05 Saint-Gobain Ceramics & Plastics, Inc. Method of preparing pressureless sintered, highly dense boron carbide materials
EP2365949A2 (fr) 2009-07-07 2011-09-21 Morgan Advanced Materials And Technology Inc. Article hybride céramique dure non oxyde ou oxyde/composite de céramique dure non oxyde ou oxyde
LU100801B1 (de) 2018-05-18 2019-11-21 Euro Composites Keramik-Wabenkörper für Leichtbaustrukturen und Herstellungsverfahren hierfür
DE102021128414A1 (de) 2021-11-01 2023-05-04 Nippon Kornmeyer Carbon Group Gmbh Verfahren zur Herstellung von karbonisierten oder graphitierten 3D-Gegenständen
CN120530012A (zh) 2023-01-24 2025-08-22 尼邦科恩迈尔特种石墨集团有限责任公司 通过3d打印制造石墨化的成形部件的方法
CN120136545B (zh) * 2025-05-15 2025-08-01 浙江金琨西立锆珠有限公司 一种氧化锆复合陶瓷微珠及其制备方法

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US4230651A (en) * 1977-07-18 1980-10-28 Ford Motor Company Method of fabricating a heat exchanger for Stirling engine
US4578363A (en) * 1984-01-23 1986-03-25 Kennecott Corporation Silicon carbide refractories having modified silicon nitride bond
FR2657603B1 (fr) * 1990-01-29 1993-07-09 Pechiney Electrometallurgie Procede d'obtention de corps solides poreux a base de carbure refractaire a l'aide de composes organiques et de metal ou metallouide.
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PT796830E (pt) * 1996-03-23 2003-01-31 Heimbach Gmbh Thomas Josef Artigo moldado poroso atravessavel assim como processo para a sua preparacao

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