Articles containing graphite composites

Abstract

A method of forming an article comprising a graphite-containing composite is disclosed. The article is suitable for containing or processing molten metal, such as aluminum. The method includes forming at least one granulated mixture by mixing at least carbon black, flake graphite, and needle coke with at least one resin, the at least one resin having a flow distance, as measured by ISO 8619:2003, of 20 mm to 150 mm. The method further includes forming the granulated mixture into a compact and sintering the compact.

Description

[Technical field]

[0001] The present disclosure relates to methods of forming articles comprising graphite-containing composites, and articles comprising graphite-containing composites. [Background technology]

[0002] Articles of manufacture used in molten metal processing, such as, for example, smelting vessels, transfer vessels, etc., have traditionally been made from cast iron, which results in heavy articles that absorb heat. Ceramic fiber fabric vacuum formed articles have been developed to overcome the problems associated with their cast iron counterparts. However, such ceramic fiber fabricated articles have difficulty meeting basic performance requirements. In recent years, reinforcing fiber materials have been developed as alternatives to cast iron and ceramic fiber vacuum formed articles. However, articles made from reinforcing fiber materials have high associated costs or poor quality. Thus, there is a need to provide articles of manufacture that can be used in molten metal applications, as well as other applications, that overcome the problems associated with cast iron articles, ceramic fiber vacuum articles, and articles containing reinforcing fiber materials. Summary of the Invention [Means for solving the problem]

[0003] The present application provides a method for forming an article comprising a graphite-containing composite, the article being suitable for containing or processing a molten metal, such as aluminum, comprising: (a) forming at least one granulation mixture by mixing at least carbon black, flake graphite, and needle coke with at least one resin, the resin having a flow distance of 20 mm to 150 mm as measured by ISO 8619:2003; (b) forming the at least one granulated mixture into at least one compact; (c) sintering at least one compact; Includes.

[0004] The present application provides a method for forming an article comprising a composite material including graphite suitable for containing or processing molten metal such as aluminum. Non-limiting examples of such articles include ladles, crucibles, filters, rotors and rotor subcomponents, continuous fiber fabrics, meshes, machined parts, and the like. The method of the present invention provides an article having a desired and controlled porosity and graphite orientation. Hereinafter, the terms "porosity" and "microporosity" have the same meaning and can be used interchangeably. The method of the present disclosure also enables the formation of an article having high strength (e.g., the composite material has a flexural strength of about 10 MPa to 25 MPa, or optionally more), and a non-wetting (i.e., non-stick) surface. These and other aspects of the present disclosure are now described in more detail. [Brief description of the drawings]

[0005] [Figure 1] 1 is a plot showing the particle size distribution of a granulated mixture according to the present disclosure before firing, and the pore size distribution of the part after firing. In some embodiments, as shown in FIG. 1 (see, for example, the far left side labeled "Granule Size in Graphite Mix"), the granulated mixture has a bimodal granule size distribution with a first set of granules having a granule size diameter of about 50 μm to about 100 μm and a second set of granules having a granule size diameter of about 110 μm to about 1000 μm. The first set of granules can comprise about 30% to about 60% by volume of the total granulated mixture, and the second set of granules can comprise about 20% to about 40% by volume of the total granulated mixture (as described elsewhere in this disclosure, the particle sizes expressed herein are D50 particle sizes, i.e., half of the particles are above the expressed value and the other half are below the expressed value). FIG. 1 also shows the pore size distribution of an exemplary granulated mixture after firing. [Diagram 2]1A and 1B are SEM images of a graphite composite structure according to an embodiment of the present disclosure, showing that the graphite in the composite structure is oriented graphite. 1B and 1C are SEM images showing a graphite composite prepared according to the present disclosure, including oriented graphite. The use of orientation in graphite is well known in the manufacture of crucibles as containers for molten metals. In some embodiments, the orientation of the graphite in such articles is achieved by roller forming or other similar techniques. In one embodiment, the orientation of the graphite is the result of the pattern or manner in which the 3D printer head moves as the article is 3D printed. In one embodiment, the orientation of the graphite is the result of the manner in which the granulated mixture is extruded through an extrusion head. In one embodiment, the orientation of the graphite is achieved by uniaxial pressing or isostatic pressing. In various embodiments, the presence of oriented graphite can result in superior resistance to metal attack and mechanical toughness. In some embodiments, the presence of oriented graphite further provides a potential route to improving the corrosion resistance of manufactured articles against flux, slag, and metal attack. In various embodiments, composites including oriented graphite may result in the formation of articles that exhibit superior corrosion resistance by forming such articles by methods that result in the formation of oriented graphite. [Diagram 3]FIG. 3 is an SEM image of a composite according to an embodiment of the present disclosure, where a clay, Al,Zn phosphate, is disposed adjacent to needle coke. FIG. 4 is an SEM image of a composite according to the present disclosure, including an aluminum-zinc phosphate ((Al,Zn)P) antioxidant (e.g., added as a first stage antioxidant and / or second stage antioxidant) disposed adjacent to needle coke. The SEM image shows that the addition of the antioxidant blocks the pores of the composite structure, as shown in FIG. 5. Of note is FIG. 4, which compares the pore size distribution of a base composite S1 according to the present disclosure with composites S2, S3, and S4 with various additives according to embodiments of the present disclosure. Base composite S1 was made from a granulated mixture of carbon black, flake graphite, needle coke, and binder only, composite S2 was made from a granulated mixture of carbon black, flake graphite, needle coke, binder, and (Al,Zn)P, composite S3 was made from a granulated mixture of carbon black, flake graphite, needle coke, binder, and (Al,Zn)P, calcined and infiltrated with siloxane, and composite S4 was made from carbon black, flake graphite, needle coke, binder, calcined and infiltrated with siloxane. Figure 4 shows that the addition of (Al,Zn)P to a granulated mixture of carbon black, flake graphite, needle coke, and binder results in pore blockage by the formation of glass (compare S1 with S2) or other similar glazing or glaze-like layers, and the density changes from 1.64 g / cm3 for S1 to 1.67 g / cm3 for S2. Figure 4 also shows that the infiltration of a granulated mixture of carbon black, flake graphite, needle coke, and binder with or without (Al,Zn)P with siloxane results in all or most of the remaining pores being blocked, with a concomitant change in density (compare S3 with S2, S1 with S4). [Figure 4] 1 is a plot comparing pore size distribution of a base composite according to the present disclosure with composites containing various additives according to embodiments of the present disclosure. [Diagram 5]1A and 1B are SEM images of a composite including a toughening / strength enhancing additive according to an embodiment of the present disclosure. 1A and 1B provide SEM images of a composite including a toughening / strength enhancing additive (e.g., carbon fiber bundles) according to an embodiment of the present disclosure. These SEM images show that the toughening / strength enhancing additive is well bonded to the matrix graphite. The oxidation package also ensures good bonding, and the siloxane infiltration further strengthens the bond. The carbon fiber bundles participate in the fracture process, providing long crack bridging and toughness enhancement. [Figure 6] 6 is an SEM image of a composite including a wear / corrosion resistant agent according to an embodiment of the present disclosure. FIG. 7 is an SEM image of a composite including a wear / corrosion resistant agent (e.g., zirconium oxide) according to an embodiment of the present disclosure. The addition of a wear / corrosion resistant agent (e.g., zirconium oxide) can react with the antioxidant to form erosion / oxidation resistant zircon (zirconium silicate, ZrSiO4) and / or ZrSi glass. [Figure 7] 7 is a plot showing pore size distribution for the composite shown in FIG. 6. [Figure 8] 1A and 1B are SEM images of composites including an insulating reinforcement agent according to an embodiment of the present disclosure. A shows that the insulating reinforcement agent is dispersed among the granules of the granulation mixture used to provide the composite, and B shows that the insulating reinforcement agent is located between the granules of the granulation mixture used to provide the composite. A shows that the insulating reinforcement agent is dispersed among the granules of the granulation mixture used to provide composite S5, and B shows that the insulating reinforcement agent is located between the granules of the granulation mixture used to provide composite S6. [Figure 9] FIG. 8B is a plot showing the pore size distribution of the composites shown in FIGS. 8A (S5) and 8B (S6). [Figure 10] 1 is a clear phase image of a composite including NiP according to an embodiment of the present disclosure. [Figure 11] 11 is a plot showing pore size distribution for the composite of FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] The present disclosure will now be described in more detail by referring to the following discussion and drawings related to the present disclosure. In the following description, numerous specific details, such as specific structures, components, materials, dimensions, processing steps, and techniques, are described to provide an understanding of various embodiments of the present disclosure. However, it will be apparent to those skilled in the art that various embodiments of the present disclosure may be practiced without these specific details. As used throughout this disclosure, the term "about" generally indicates no more than ±10%, ±5%, ±2%, ±1%, or ±0.5% from a numerical value. In this disclosure, when a range is expressed as a range from one numerical value to another numerical value (e.g., 20-40), the present disclosure contemplates any numerical value within that range (i.e., 22, 24, 26, 28.5, 31, 33.5, 35, 37.7, 39, or 40), or any amount bounded by either of two values ​​within that range (e.g., 28.5-35).

[0007] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising", as used herein, specify the presence of stated features, elements, steps, operations, components, and / or components, but do not exclude the presence or addition of one or more other features, elements, steps, operations, components, components, and / or groups thereof.

[0008] In the context of the present invention, the expression "at least one X" is intended to indicate one or more X. Mixtures of X can also be used for the purposes of the present invention.

[0009] The particle size provided herein can refer to the diameter when the particle is spherical or substantially spherical. When the particle deviates substantially from the spherical shape, the particle size is based on the equivalent diameter of the particle. As known in the art, the term "equivalent diameter" is used to express the size of an amorphous object by expressing the size of the object in terms of the diameter of a sphere having the same volume as the amorphous object. The particle size expressed herein is also the D50 particle size, i.e., half of the particles are above the expressed value, and the other half are below the expressed value.

[0010] According to the invention, the article is suitable for containing or processing molten metal. Non-limiting examples of such articles include rotors, ladles, filters, crucibles, or components thereof. The article is compatible with low and high pressure die casting using molten metal, such as molten aluminum.

[0011] The method of the present invention includes step (a) of forming at least one granulated mixture by mixing at least carbon black, flake graphite, and needle coke with at least one resin, the resin having a flow distance of 20 mm to 150 mm as measured by ISO 8619:2003. Unless otherwise stated, the flow distance was measured at 125°C.

[0012] As used herein, the term "granulated mixture" refers to a blended mixture including at least carbon black, flake graphite, and needle coke with at least one resin.

[0013] The inventors have surprisingly discovered that carbon black, flake graphite, and needle coke provide complementary shape profiles that result in high compaction when forming compacts from the granulated mixture. When the powders (i.e., carbon black, flake graphite, and needle coke) are mixed with resins that exhibit flow distances as described above, composites containing graphite are achieved that exhibit high performance in terms of porosity, density, surface roughness, strength, and wettability.

[0014] The inventors have discovered that the method of the invention provides a composite with a pore profile having a pore volume and pore size distribution such that at least 95% of the total pore volume is contained in pores with a diameter or equivalent diameter of less than 1 μm, and in a further or identical embodiment, at least 40% of the pore volume of pores with a diameter or equivalent diameter of less than 1 μm is contained in pores with a diameter or equivalent diameter of less than 0.1 μm. The fine pore profile formed in the composite as manufactured allows a significant reduction in the achievable surface roughness of the composite in the article. In the context of the invention, the pore profile (pore diameter) is understood as the porosity and was measured according to the ASTM C830-00 (2016) standard. The pore profile was measured by mercury (Hg) intrusion analysis. The equipment used to perform this analysis was an AutoPore V, micromeritrics®. The surface roughness R of the composite obtained from the method of the invention is a Regarding the above, the method of the present invention is to provide a surface roughness R between 3.2 μm and 0.025 μm. a where the surface roughness R a is as specified in the ISO 1302:1992 standard. The reduction of surface roughness also affects the adhesion forces (adhesion energy) or spreading forces (surface energy) and wetting forces (contact angle) that occur between the molten metal and the manufactured article. This has a significant impact on the performance of the manufactured article as a rotating body (e.g. rotor) or as a stationary part (e.g. crucible).

[0015] When an article (e.g., an article of manufacture) is produced from the method according to the invention, a substantially finished article having a non-wetting surface is obtained. By "substantially finished" it is meant that the article produced from the method of the present disclosure has dimensions (i.e., size and shape) that approximate (at least 90% or more) the desired dimensions (size and shape) of the finished product or article. By forming a substantially finished article, the manufacturing costs and time associated with producing the final product are significantly reduced.

[0016] "Non-wetting surface" refers to a surface that is wettable when the article made from the composite of the present disclosure is subjected to high pressure P 0 This means that the graphite article will not be infiltrated by molten / liquid metals, such as copper or aluminum, even if the graphite article is infiltrated by a sufficiently high pressure P 0 By applying capillary pressure P C This can be achieved by overcoming the C =-(2σ LV / r eff ) cosθ, where σ LV is the surface energy of the liquid, and r eff is the effective pore radius of the composite and θ is the contact angle of the pore walls. The effective pore radius of the composites of the present disclosure does not allow for infiltration of the molten metal due to capillary pressures that are too great. Advantageously, embodiments of the present disclosure provide little attack of the article by molten metal infiltrating through the pores, even after prolonged or repeated exposure to molten metal.

[0017] The mixing step (i.e., step (a) detailed above) can be carried out in various ways. For example, the granulation mixture of the present disclosure can be prepared by first adding carbon black, flake graphite, needle coke, optional one or more additives defined below, and resin. The addition of the various components / ingredients can be carried out in any order. For example, in one embodiment, the carbon black, flake graphite, needle coke, optional one or more additives are added before adding the resin. In another embodiment, the resin is added first, followed by the carbon black, flake graphite, and needle coke. The mixing can be carried out continuously during the addition of the various components / ingredients, or can be carried out intermittently during the addition of the various components / ingredients. The various components / ingredients used in providing the granulation mixture are in the amounts specified below.

[0018] During mixing, the powder particles (i.e., carbon black, flake graphite, and needle coke) are bound together by the resin, thereby forming granules. In this embodiment, mixing can also be referred to as granulation. Preferably, the granules can have a particle size of about 25 μm to about 4 mm, preferably about 70 μm to about 700 μm.

[0019] In another embodiment, the process according to the invention may further comprise a granulation step after the mixing step.

[0020] In one example, the mixing includes high shear mixing of the ingredients. In one embodiment where a high shear mixer is used in the mixing process, a resin can assist in forming agglomerates or coating the ingredients. The mixing parameters can be modified to increase or decrease the particle size and distribution of the granules as desired to optimize their use in subsequent processing steps. An example of a high shear mixer is an Eirich mixer, or the like. This mixing process forms the granular mixture of the present disclosure.

[0021] In some embodiments, the granulation mixture has a bimodal granule size distribution with a first set of granules having a granule size diameter of about 50 μm to about 100 μm and a second set of granules having a granule size diameter of about 110 μm to about 1000 μm. The first set of granules can comprise about 30% to about 60% by volume of the total granulation mixture, and the second set of granules can comprise about 20% to about 40% by volume of the total granulation mixture (as described elsewhere in this disclosure, the particle sizes expressed herein are D50 particle sizes, i.e., half of the particles are equal to or greater than the expressed value and the other half are equal to or less than the expressed value).

[0022] The various components (i.e., ingredients) that can be used in the granulation mixture of the present disclosure will now be described in more detail.

[0023] The carbon black that can be used in the granulation mixture of the present disclosure contains at least 99% by weight of carbon and has an ash content of 1% by weight or less. Typically, the carbon content in the carbon black that can be used in the present disclosure is about 99.5% by weight to about 100% by weight. The carbon black that can be used in the present application is spherical or substantially spherical, and may have some irregularities in shape that deviate from being completely spherical. The carbon black that can be used in the present disclosure has a particle size of about 10 μm to about 50 μm, preferably about 25 μm to about 40 μm.

[0024] Advantageously, carbon black is present in the granulation mixture in an amount equal to or greater than 2% by weight, preferably equal to or greater than 3% by weight and more preferably equal to or greater than 5% by weight relative to the total weight of the granulation mixture.

[0025] Preferably, the upper limit for the amount of carbon black in the granulated mixture is 15% by weight or less, preferably 10% by weight or less, more preferably 8% by weight or less, based on the total weight of the granulated mixture.

[0026] According to at least one embodiment, carbon black is present in the granulation mixture in an amount of about 5% to about 10% by weight, preferably about 5% to about 8% by weight, based on the total weight of the granulation mixture. Within the ranges presented in the present invention, the present disclosure contemplates the use of any numerical value within the range, or any amount bordering either of two numerical values. For example, the content of carbon black in the granulation mixture can be 5% by weight, 5.5% by weight, 6% by weight, 6.5% by weight, 7% by weight, 7.5% by weight, 8% by weight, 8.5% by weight, 9% by weight, 9.5% by weight, 10% by weight, or, for example, 5.5% to 8.5% by weight.

[0027] The needle coke that can be used in the granulation mixture of the present disclosure contains at least 99% carbon by weight and has a sulfur content of 1% by weight or less. Typically, the carbon content in the needle coke that can be used in the present disclosure is about 99.5% by weight to about 100% by weight. The needle coke that can be used in the granulation mixture of the present disclosure is an irregularly shaped needle coke. By "irregularly shaped needle coke" we mean one that has developed from (or has) a fibrous, cylindrical, or needle-like structure. The needle coke that can be used in the present disclosure has a particle size of about 10 μm to about 50 μm, with a particle size of about 25 μm to about 40 μm being more typical.

[0028] The inventors have determined that needle coke exhibits similar toughness and improved resistance to thermal shock compared to other types of carbon, such as chopped carbon fiber. The inventors have also determined that needle coke exhibits superior oxidation resistance compared to carbon fiber, and further, that the use of needle coke (as opposed to carbon fiber) provides superior surface smoothness in the graphite-containing composite formed upon firing of the compact to provide the graphite-containing composite. Thus, the use of needle coke improves the surface smoothness of the composite.

[0029] Advantageously, the needle coke is present in the granulated mixture in an amount equal to or greater than 0.5% by weight, preferably equal to or greater than 1% by weight, and more preferably equal to or greater than 2% by weight, relative to the total weight of the granulated mixture.

[0030] Preferably, the upper limit of the amount of needle coke in the granulated mixture is 7 wt. % or less, preferably 5 wt. % or less, more preferably 4 wt. % or less, based on the total weight of the granulated mixture.

[0031] In a preferred embodiment of the present invention, the needle coke is present in the granulation mixture in an amount of about 1% to about 5% by weight, preferably about 2% to about 4% by weight, based on the total weight of the granulation mixture.

[0032] The flake graphite usable in the granulation mixture of the present disclosure contains at least 95% carbon by weight and has an ash content of 1% by weight or less. Typically, the carbon content in the flake graphite usable in the present disclosure is about 95% by weight to about 99% by weight. The flake graphite usable in the present disclosure has a particle size of about 10 μm to about 500 μm, with a particle size of about 25 μm to about 40 μm being more typical. In one embodiment, the flake graphite usable in the granulation mixture of the present disclosure is a naturally occurring type of graphite, typically in the form of discrete flakes, which may include hexagonal crystals and may have some irregularity in shape that deviates from being perfectly hexagonal. In one embodiment, the flake graphite usable in the granulation mixture of the present disclosure has a distinct flake or plate-like morphology.

[0033] Advantageously, the flake graphite is present in the granulated mixture in an amount of at least 50% by weight, preferably at least 65% by weight, and more preferably at least 75% by weight, relative to the total weight of the granulated mixture.

[0034] Preferably, the upper limit of the amount of flake graphite in the granulated mixture is 90% by weight or less, preferably 85% by weight or less, more preferably 80% by weight or less, based on the total weight of the granulated mixture.

[0035] In a preferred embodiment of the present invention, the flake graphite is present in the granulated mixture in an amount of about 65% to about 85% by weight, preferably about 75% to about 80% by weight, based on the total weight of the granulated mixture.

[0036] In at least one embodiment, the approximately hexagonal crystal shape of flake graphite, the fibrous, cylindrical, acicular, or irregular shape of needle coke, and the substantially spherical shape of carbon black provide complementary shape profiles that result in a high degree of compaction when forming compacts from the granulated mixture.

[0037] Preferably, at least a portion of the carbon black has a generally spherical shape, preferably at least a portion of the needle coke has a generally cylindrical, fibrous, or acicular profile, and preferably at least a portion of the flake graphite has a generally hexagonal or triangular profile.

[0038] According to the present invention, the resin has a button flow distance of 20mm to 150mm as measured by ISO 8619:2003. A person skilled in the art will be able to select an appropriate resin to obtain the flow distance required by the present invention. The inventors have surprisingly found that the granulation mixture of the present disclosure, which includes a resin having a button flow distance of 20mm to 150mm as measured by ISO 8619:2003, reduces the complexity and steps in the mixing step compared to prior art binders.

[0039] Advantageously, the resin has a button flow distance, measured by ISO 8619:2003, of 20 mm or more, preferably 40 mm or more, more preferably 70 mm or more.

[0040] Preferably, the upper limit of the flow distance of the resin is 150 mm or less, preferably 70 mm or less, more preferably 40 mm or less, as measured by ISO 8619:2003.

[0041] In a preferred embodiment of the present invention, the resin has a button flow distance, measured by ISO 8619:2003, of 70 mm to 150 mm, preferably 40 mm to 70 mm, more preferably 20 mm to 40 mm.

[0042] In one embodiment of the method according to the present invention, the resin that may be used has a button flow distance of 70 mm to 150 mm as measured by ISO 8619:2003. Resins having such flow distances may be characterized herein as "low molecular weight resins". In another embodiment of the present disclosure, the resin that may be used in the present disclosure has a button flow distance of 40 mm to 70 mm as measured by ISO 8619:2003. Resins having such flow distances may be characterized herein as "medium molecular weight resins". In yet another embodiment of the present disclosure, the resin that may be used in the present disclosure has a button flow distance of 20 mm to 70 mm as measured by ISO 8619:2003. Resins having such flow distances may be characterized herein as "high molecular weight resins". In yet another embodiment of the present disclosure, any combination of low molecular weight resins, medium molecular weight resins, and high molecular weight resins may be used.

[0043] It should be noted that the type of resin (i.e., low molecular weight resin, medium molecular weight resin, high molecular weight resin, as defined above) can be selected to control the overall viscosity of the binder. Furthermore, it should be noted that the type of resin (i.e., low molecular weight resin, medium molecular weight resin, high molecular weight resin, as defined above) affects the strength of the pressed compact. For example, a high molecular weight resin, as defined herein, provides a pressed compact with the highest strength (flexural strength of 2 MPa or more), a medium molecular weight resin, as defined herein, provides a pressed compact with medium strength (flexural strength of 1 MPa to 2 MPa), and a low molecular weight resin, as defined herein, provides a pressed compact with the lowest strength (flexural strength of less than 1 MPa). The pressed compact represents the granulated mixture after molding and before firing.

[0044] It should be noted that the resin of the present disclosure aids in the granulation mixing step to form the granulation mixture. The organics of the resin are typically removed during the firing process.

[0045] Preferably, the resin is selected to have a viscosity of about 9000 cps to about 30,000,000 cps. More preferably, the resin is selected to have a viscosity of about 9000 cps to about 150,000 cps. Viscosity was measured at 25° C. unless otherwise noted.

[0046] Advantageously, the resin is present in the granulation mixture in an amount equal to or greater than 2% by weight, preferably equal to or greater than 4% by weight and more preferably equal to or greater than 6% by weight relative to the total weight of the granulation mixture.

[0047] Preferably, the upper limit for the amount of resin in the granulation mixture is 15% by weight or less, preferably 10% by weight or less, more preferably 8% by weight or less, based on the total weight of the granulation mixture.

[0048] In a preferred embodiment of the present invention, the resin is present in the granulation mixture in an amount of about 2% to about 10% by weight, preferably about 6% to about 8% by weight, based on the total weight of the granulation mixture.

[0049] In the context of the present invention, the resin can be in various physical states, preferably the resin is in a liquid state.

[0050] Preferably, the resin is a thermosetting resin.

[0051] The choice of resin is advantageously determined by having a high char yield after pyrolysis. Table 1 below lists typical char yields after pyrolysis of various carbon source materials. Preferably, the resin provides a high char yield after pyrolysis of 40% by weight or more, 50% by weight or more, 60% by weight or more.

[0052] [Table 1]

[0053] As one of ordinary skill in the art will appreciate, upon firing the compact to high temperatures, the amorphous carbon (i.e., the amorphous carbon resulting from the conversion of the resin when the compact is fired to provide a composite containing graphite) can further self-modify into other forms of carbon, such as, for example, crystallized carbon in the form of carbon nanotubes, graphene, and other similar materials.

[0054] Advantageously, the resin is selected from the group consisting of phenolic resins, cellulose-based derivatives, siloxane-modified resins, modified epoxy resins, polyimides, benzoxazines, or combinations thereof. Non-limiting examples of commercially available polyimides include ZT1000 [Polyimides], and Cornerstone (18C021). Non-limiting examples of commercially available benzoxazines include Huntsman (18B028). In some embodiments, the resin further comprises an additive such as carboa. More preferably, the resin is a phenolic resin. One advantage of using a phenolic resin is that up to 70% by weight of the phenolic resin can be converted to carbon in the form of amorphous carbon, for example, when the compact is fired to provide a composite containing graphite.

[0055] In a preferred embodiment of the present invention, the resin is formed by condensation of phenol or a phenol derivative with an aldehyde, particularly formaldehyde, in the presence of a catalyst. In one embodiment of the present disclosure, the phenolic resin usable in the present disclosure has a button flow distance of 70 mm to a maximum of 150 mm, as measured by ISO 8619:2003. Phenolic resins having such a flow distance may be characterized herein as "low molecular weight phenolic resins". In another embodiment of the present disclosure, the phenolic resin usable in the present disclosure has a button flow distance of 40 mm to 70 mm, as measured by ISO 8619:2003. Phenolic resins having such a flow distance may be characterized herein as "medium molecular weight phenolic resins". In yet another embodiment of the present disclosure, the phenolic resin usable in the present disclosure has a button flow distance of 20 mm to 70 mm, as measured by ISO 8619:2003. Phenolic resins having such a flow distance may be characterized herein as "high molecular weight phenolic resins". As an example, the phenolic resin that can be used in the present disclosure is a commercially available phenolic resin called Sumitomo XF3011P. In yet another embodiment of the present disclosure, the phenolic resin used is a liquid phenolic resin. In yet another embodiment of the present disclosure, any combination of low molecular weight phenolic resin, medium molecular weight phenolic resin, high molecular weight phenolic resin, or liquid phenolic resin can be used.

[0056] According to at least one embodiment, at least one solvent can be added to the resin to further improve the flowability and / or viscosity of the resin. In this embodiment, the resin can also be referred to as a binder, which is composed of at least one resin and at least one solvent. It is noted that the type of resin and the type of solvent can be selected to control the overall viscosity of the binder. According to at least one embodiment, the solvent comprises a dibasic acid ester. In one embodiment, the solvent is a carboxylic acid ester having the formula CH 3 O 2 C(CH 2 ) n CO 2 CH3 The dibasic ester may be an ester of a dicarboxylic acid having the formula: where n is equal to 2, 3, or 4. In some embodiments, the solvent used is an acetate ester. In further embodiments, the acetate ester is propylene glycol diacetate. Other solvents are possible and can be used with the resin as the binder of the present disclosure. According to one embodiment of the present disclosure, the resin and the solvent are present in the granulation mixture in a weight ratio of about 1:1 to about 6:1. According to another embodiment of the present disclosure, the resin and the solvent are present in the granulation mixture in a weight ratio of about 2:1 to about 4:1.

[0057] When the resin further comprises a solvent, the solvent is present in the granulation mixture in an amount of about 1% to about 5% by weight, preferably about 3% to about 4% by weight, based on the total weight of the granulation mixture.

[0058] In some embodiments, the resin of the granulation mixture further comprises an optional binder plasticizer. Thus, in some embodiments, the resin can further comprise a binder plasticizer, such as, for example, dextrin, propylene carbonate, stearic acid, oleic acid, glidol, and / or triacetin, while in other embodiments, no binder plasticizer is used.

[0059] In some embodiments, the granulation mixture of the present disclosure does not contain intentionally added water. In yet other embodiments, water can be included in the granulation mixture of the present disclosure. In some embodiments of the present disclosure, the granulation mixture has a moisture content of less than about 5.0 wt%, preferably 4.0 wt% or less, more preferably 3.0 wt% or less, based on the total weight of the granulation mixture. Advantageously, the granulation mixture has a moisture content of 0.5 wt% or more, preferably 1 wt% or more, more preferably 2.0 wt% or more, based on the total weight of the granulation mixture. In one embodiment, the moisture content in the granulation mixture is about 1.0 wt% to 4.0 wt% based on the total weight of the granulation mixture.

[0060] According to at least one embodiment, the carbon black, flake graphite, needle coke, and resin provide 100% of the total weight of the granulation mixture. In this embodiment, the granulation mixture is composed entirely of carbon black, flake graphite, needle coke, and resin, and no other components / additives are used in providing the granulation mixture. This embodiment can be advantageously used in the manufacture of articles where the presence of foreign matter other than carbon is undesirable, such as crucibles used in the manufacture of synthetic graphite.

[0061] In one embodiment, the granulation mixture comprises about 6%, 6.2%, 6.4%, 6.6%, 6.8%, 7%, 7.2%, 7.5%, or a range bounded by any two of the preceding values, of carbon black; about 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.5%, or a range bounded by any two of the preceding values, of needle cork; % by weight, about 78%, 78.2%, 78.4%, 78.6%, 78.8%, 79%, 79.2%, 79.5%, or within a range bounded by any two of the preceding values, of flake graphite, and about 7%, 7.2%, 7.4%, 7.6%, 7.8%, 8%, 8.2%, 8.4%, or within a range bounded by any two of the preceding values, of resin. When the granule further comprises about 3%, 3.2%, 3.4%, or 3.6% by weight of solvent, the granulation mixture further comprises about 3.8%, 4%, 4.2%, 4.5%, or within a range bounded by any two of the preceding values.

[0062] In another embodiment, the granulated mixture further comprises one or more of antioxidants, toughening / strength enhancing additives, anti-wear / anti-corrosion agents, thermal insulation enhancers, and transition metals selected from Groups 4 to 12 of the Periodic Table of the Elements. These additives can be in powder form or in granular form.

[0063] According to at least one embodiment, the granulation mixture further comprises about 5% to about 15% by weight, preferably about 8% to about 12% by weight, of an antioxidant, based on the total weight of the granulation mixture. According to at least one embodiment, the antioxidant comprises boron carbide, silicon carbide, aluminum-zinc phosphate, or any combination thereof.

[0064] The antioxidant serves to reduce oxidation of the resulting composite while simultaneously blocking pores and increasing the bulk density of the resulting composite. Exemplary antioxidants that may be present in the granulation mixture of the present disclosure include, but are not limited to, boron carbide, silicon carbide, bentonite, aluminum-zinc phosphate, or any combination thereof. In one embodiment, the antioxidant comprises a mixture of about 2% to about 7% by weight of boron carbide, about 1% to about 5% by weight of silicon carbide, about 0.25% to about 0.75% by weight of bentonite, and about 2% to about 5% by weight of aluminum-zinc phosphate, based on the total weight of the antioxidant.

[0065] In some embodiments where boron carbide is used as the antioxidant, the boron carbide is provided in the form of particulates having a particle size of less than about 50 μm, preferably having a particle size in the range of about 25 μm to about 40 μm. In some embodiments where silicon carbide is used as the antioxidant, the silicon carbide is provided in the form of particulates having a particle size of less than about 50 μm, preferably having a particle size in the range of about 20 μm to about 40 μm. In some embodiments where bentonite is used as the antioxidant, the bentonite is provided in the form of particulates having a particle size of less than about 10 μm, preferably having a particle size in the range of about 1 μm to about 7 μm. In various embodiments, the boron carbide, silicon carbide, and bentonite can be in the form of a powder or in the form of a granule.

[0066] In some embodiments, the antioxidant addition can be performed in two separate or different stages. In an embodiment where the antioxidant addition is performed in two stages, during the first of the two stages, the antioxidant of the first stage is added to the granulation mixture. The granulation mixture is then formed into a compact made of the granulation mixture. In the second of the two stages, the antioxidant of the second stage is applied to a part or all of the exposed surface of the compact, and the compact is then fired to obtain a composite made of graphite. In some embodiments, the antioxidant of the first stage added in the first stage is a different material compared to the antioxidant of the second stage added in the second stage. In some embodiments, the antioxidant of the first stage added in the first stage is the same material as the antioxidant of the second stage added in the second stage.

[0067] According to at least one embodiment, the granulation mixture further comprises a toughening / strength enhancing additive in an amount of about 1% to about 5% by weight, preferably about 2.5% to about 4.5% by weight, based on the total weight of the granulation mixture. According to at least one embodiment, the toughening / strength enhancing additive comprises carbon fiber, chopped carbon fiber bundles, basalt fiber bundles, alumina silicate fiber, chopped steel fiber, or any combination thereof.

[0068] The toughening / strength-enhancing additives serve to improve the toughness and / or strength of the resulting composite. Exemplary toughening / strength-enhancing additives that may be present in the granulation mixture of the present disclosure include, but are not limited to, carbon fiber, chopped carbon fiber bundles, basalt fiber bundles, alumina silicate fiber, chopped steel fiber, or any combination thereof. In some embodiments, the toughening / strength-enhancing additives include carbon fiber, chopped carbon fiber bundles, or combinations thereof, and such toughening / strength-enhancing additives improve the toughness of the resulting product made from the granulation mixture of the present application. In some embodiments, the toughening / strength-enhancing additives include basalt fiber, alumina silicate fiber, or combinations thereof, and such toughening / strength-enhancing additives improve the strength and reduce the thermal conductivity of the resulting product made from the granulation mixture of the present application. In some embodiments, the toughening / strength-enhancing additives include chopped steel fiber, and such toughening / strength-enhancing additives improve the strength and toughness of the resulting product made from the granulation mixture of the present application.

[0069] According to at least one embodiment, the granulation mixture further comprises about 1% to about 10% by weight, preferably about 4.5% to about 8.5% by weight, of an anti-wear / anti-corrosion agent, based on the total weight of the granulation mixture. According to at least one embodiment, the anti-wear / anti-corrosion agent comprises a metal oxide, a metal nitride, a metal boride, or any combination thereof.

[0070] The wear / corrosion resistant agent serves to increase the wear and / or reduce the erosion of the resulting composite. Exemplary wear / corrosion resistant agents that can be used herein include metal oxides (e.g., zirconium oxide, yttrium oxide, etc.), metal nitrides (e.g., boron nitride, aluminum nitride, silicon nitride, etc.), metal borides (e.g., titanium diboride, etc.), or combinations thereof. In some embodiments, zirconium oxide is used as the wear / corrosion resistant agent. In such embodiments, zirconium oxide can form in situ zirconium silicide or zirconium silicate, which can provide strong bonding, high oxygen resistance, high wear / corrosion resistance, and / or very fine pore profile. In such embodiments, zirconium oxide can form zirconium boride, which has very high wear / corrosion resistance. The anti-wear / anti-corrosion agents that can be used in the present disclosure are typically nanomicron sized powders having particle sizes less than about 40 μm, with particle sizes in the range of about 5 μm to about 25 μm being more typical.

[0071] According to at least one embodiment, the granulation mixture further comprises about 1% to about 5% by weight, preferably 2.5% to 4% by weight, of an insulating reinforcing agent, based on the total weight of the granulation mixture. These agents provide improved thermal insulation to the resulting composite. Exemplary insulating reinforcing agents that may be used in the present disclosure include, but are not limited to, colloidal silica shot, fibers, or mixtures thereof. According to at least one embodiment, the insulating reinforcing agent comprises a colloidal silica shot, fibers, or mixtures thereof. According to at least one embodiment, the insulating reinforcing agent comprises a mixture of sodium aluminosilicate shot and chopped silica fibers. According to at least one embodiment, optionally, the insulating reinforcing agent comprises colloidal silica shot, preferably alumino colloidal silicate shot, fibers, preferably a mixture of sodium and chopped silica fibers, or mixtures thereof. In such an embodiment, the mixture can include about 5% to about 50% by weight sodium aluminosilicate shot and about 20% to about 70% by weight chopped silica fibers, based on the total weight of the insulating reinforcement agent.

[0072] According to at least one embodiment, the granulation mixture further comprises about 1% to about 5% by weight, preferably about 2.5% to about 4% by weight, of a transition metal selected from Groups 4 to 12 of the Periodic Table of Elements, based on the total weight of the granulation mixture. The transition metal can be used to impart specific functionality, such as catalytic functionality, to the resulting composite. Examples of suitable transition metals that can be used in the present disclosure include, but are not limited to, iron, titanium, nickel, or combinations thereof.

[0073] In some embodiments, clay may also be present in the granulation mixture of the present disclosure. If clay is present, the clay is preferably present in an amount of about 0.25% to about 0.75% by weight, based on the total weight of the granulation mixture.

[0074] In embodiments where the mixing step provides a granulation and the granulation mixture includes a toughening / strength enhancing additive as defined above, an abrasion / corrosion resistance improving agent as defined above, an insulation improving agent as defined above, a transition metal as defined above, or any combination thereof, the additives can be disposed (dispersed) within the granules of the granulation mixture, or the additives can be disposed between the granules of the granulation mixture.

[0075] According to at least one embodiment, the granulated mixture as detailed above consists essentially of granules, and the toughening / strength enhancing additive, the wear / corrosion resistant agent, the insulation improver, the transition metal selected from Groups 4 to 12 of the Periodic Table of Elements, or any combination thereof, is disposed within the granules. According to at least one embodiment, the granulated mixture as detailed above consists essentially of granules, and the toughening / strength enhancing additive, the wear / corrosion resistant agent, the insulation improver, the transition metal selected from Groups 4 to 12 of the Periodic Table of Elements, or any combination thereof, is disposed between the granules of the granulated mixture.

[0076] In some embodiments of the present disclosure, the granulation mixture comprises about 5% to about 10% by weight of carbon black, about 65% to about 85% by weight of flake graphite, about 1% to about 5% by weight of needle coke, about 2% to about 10% by weight of phenolic resin, and about 1% to about 5% by weight of solvent. In yet other embodiments, the granulation mixture comprises about 5% to about 8% by weight of carbon black, about 75% to about 80% by weight of flake graphite, about 2% to about 4% by weight of needle coke, about 6% to about 8% by weight of phenolic resin, and about 3% to about 4% by weight of solvent. In the above ranges, the present disclosure contemplates the use of any number within the range or any amount bordering either of the two numbers. For example, the carbon black content in the granulation mixture can be 5 weight%, 5.5 weight%, 6 weight%, 6.5 weight%, 7 weight%, 7.5 weight%, 8 weight%, 8.5 weight%, 9 weight%, 9.5 weight%, 10 weight%, or, for example, 5.5 weight% to 8.5 weight%.

[0077] After forming the granulated mixture (i.e., step (a) detailed above), the granulated mixture is formed into a compact (i.e., step (b)), which can be referred to as a pressed compact. Forming includes, but is not limited to, isopressing (i.e., isostatic pressing), hydraulic pressing, extrusion, molding, 3D printing, and the like. In some embodiments, forming can be determined by the amount of resin present in the granulated mixture. For example, 4% to 8% by weight of resin in the granulated mixture is favorable for isopressing or hydraulic pressing, 8% to 12% by weight of resin is favorable for extrusion, and 12% to 17% by weight of resin is favorable for 3D printing. In some embodiments, forming the granulated mixture into a compact includes: machining or net shaping the granulated mixture to form a rotor component; forming the granulated mixture into a ladle; forming the granulated mixture to form a crucible; and extruding or 3D printing the granulated mixture to form a crucible. In one example, the granulated mixture can be subjected to isopressing using a molded polyurethane bag pressed onto a metal mandrel. The molded body can include any shape, including, for example, the shape of a rotor or rotor component, a ladle, a crucible, and a molten metal filter or filter component. In some embodiments, the molded body can be formed on a prefabricated structure, such as, for example, a steel mesh, a filter or filter component, a continuous carbon fabric, etc., prior to firing.

[0078] The present inventors have found that the method of the present invention achieves a compression molded product having a bending strength of about 1 MPa to about 5 MPa and a strength of about 1.5 g / cm 3 ~Approx. 1.7g / cm 3 and a compact density of about 0.5 g / cm 3 ~about 0.7g / cm 3It has been found that the present invention provides a compact having a powder packing density of 10 ...

[0079] Preferably, when the compaction is isopressing (i.e., isostatic pressing), during the mixing process (i.e., step (a) detailed above), the powder particles (i.e., carbon black, flake graphite, and needle coke) can be bound together by the resin, thereby forming granules. In this embodiment, the mixing can also be referred to as granulation.

[0080] In some embodiments, the shaped body may include a crucible shape, which is composed of a plurality of crucible rings that are stacked uniformly on top of each other to provide the crucible shape. The crucible ring is preferably obtained by net shaping the granulated mixture into a precise ring shape, or by shaping the granulated mixture into a large crucible shape, cutting the large crucible shape into a crucible ring, and machining the crucible ring. This shaping is particularly advantageous because it allows replacing parts of the crucible without the need to replace the entire crucible, thereby lengthening repair times, reducing costs, and improving overall efficiency.

[0081] In some embodiments, the compact can be cured before firing. Curing the compact before firing can cause crosslinking of the resin and improve the manipulation and handling of the compact before firing. Curing can be performed in air before firing. Curing can be performed at a single curing temperature or various curing temperatures can be used. In one embodiment of the present disclosure, curing is performed at a temperature of about 200°C to about 300°C for about 1 hour to about 5 hours. Other curing temperatures and / or times can be used in the present disclosure. Curing can be performed in any curing device commonly used in the art.

[0082] In some embodiments of the present disclosure, the compact may be subjected to a coating process, a glazing process, an impregnation process, an infiltration process, or any combination thereof, prior to firing. The coating process, the glazing process, the impregnation process, and / or the infiltration process may be performed directly on the compact, or such processes may be performed on a compact that has first been subjected to hardening.

[0083] When performing a coating process, at least a portion of the cured or uncured compact can be coated with any suitable coating material using known coating techniques, such as, for example, spraying, dipping, brushing, etc. In some embodiments, a silicon carbide (SiC), alumina, or alumina-titanate coating can be formed on at least a portion of the cured or uncured compact. In some embodiments, a boron nitride coating can be formed on at least a portion of the cured or uncured compact. The coating can modify the porosity and / or finish of the composite.

[0084] When performing the glazing process, at least a portion of the cured or uncured molded body can be glazed with any suitable glazing material using known glazing techniques, such as, for example, spraying, dipping, brushing, etc. As an example, a glazing material formulated from a frit-based composition can be used.

[0085] When the impregnation process is carried out, any known impregnation process can be used to impregnate at least a portion of the cured or uncured compact with a material, such as, for example, roller impregnation, cascade impregnation, dip impregnation, etc. In one example, the borax mixture can be impregnated into at least a portion of the cured and / or uncured compact before firing. In one embodiment, at least a portion of the compact composed of the granulation mixture is coated with an impregnation material (e.g., an antioxidant), and then the compact is fired, and the impregnation material (e.g., an antioxidant) is impregnated into the composite composed of graphite resulting from firing the compact.

[0086] When performing the infiltration process, at least a portion of the cured or uncured compact can be infiltrated with any suitable material using known infiltration techniques, such as, for example, injection, chemical vapor infiltration, etc. Preferably, at least a portion of the cured or uncured compact is infiltrated with a siloxane, a selected phosphate solution, or any combination thereof, before or after the firing step. In one example, a siloxane precursor, a selected phosphate solution, or any combination thereof, can be infiltrated into at least a portion of the compact before firing. In some embodiments, at least a portion of the composite is infiltrated with a siloxane, a selected phosphate solution, or any combination thereof, before or after the firing step. In one example, a siloxane precursor, a selected phosphate solution, or any combination thereof, can be infiltrated into at least a portion of the composite after firing. In one embodiment, at least a portion of the compact comprised of the granulated mixture is infiltrated with an infiltration material (e.g., an antioxidant) and then the compact is fired such that the infiltration material (e.g., an antioxidant) infiltrates the composite including graphite resulting from firing the compact.

[0087] The compact is then sintered to provide a composite comprising graphite (i.e., step (c)). Sintering of the compact comprising the granulated mixture of the present disclosure provides a composite comprising graphite. The composite may also be an article consisting of the composite. Alternatively, the composite may be further subjected to a manufacturing step to provide an article comprising the composite. The article may consist of a plurality of composites stacked together to provide the article. For example, if the article is a crucible, the crucible may consist of a plurality of crucible rings stacked uniformly on top of each other to provide the crucible. Alternatively or additionally, the composite may be subjected to a coating process, a glazing process, an impregnation process and / or an infiltration process to provide the article. Non-limiting examples of such articles include rotors, ladles, filters, and crucibles or components thereof.

[0088] The inventors have found that the method of the present invention provides composites containing graphite with improved properties, such as having a porosity of about 10% to about 25%. Also, the composites obtained by the process of the present invention have a porosity of about 1.6 g / cm. 3 ~Approx. 1.92g / cm 3 Advantageously, the composite has a total pore volume and pore size distribution, with at least 95% of the total pore volume being contained in pores having a diameter or equivalent diameter of less than 1 μm, and at least 40% of the pore volume of the pores having a diameter or equivalent diameter of less than 1 μm being contained in pores having a diameter or equivalent diameter of less than 0.1 μm. The micropore profile formed in the composite of the article of manufacture allows for a significant reduction in the achievable surface roughness of the composite of the article. The surface roughness R of the composite resulting from sintering of the compact is a Regarding roughness, ISO 1302:1992 specifies the method for expressing surface roughness. In fact, the average roughness (R a ) is often used as a measure of surface smoothness. The method of the present invention can produce surface roughness R between 3.2 μm and 0.025 μm. a It is possible to achieve a composite having a surface roughness R ais as specified in the ISO 1302:1992 standard. The reduction of surface roughness also affects the adhesion (adhesion energy) or spreading (surface energy) and wetting (contact angle) forces that occur between the molten metal and the manufactured article. This has a significant impact on the performance of the manufactured article as a rotating body (e.g. rotor) or as a stationary part (e.g. crucible).

[0089] Further, in accordance with the present invention, it is possible to provide an article (eg, an article of manufacture) that is a substantially final-form article and has a non-wetting surface, as described above.

[0090] The firing can be performed at a single firing temperature or various firing temperatures can be used. In one embodiment, the firing is performed at a temperature of about 800°C to about 1500°C. In one embodiment, the firing temperature is 800 to 1300°C. In one embodiment, the firing temperature is about 1250°C to about 1300°C, preferably about 1000°C to about 1250°C. In one embodiment, the firing temperature is about 1400°C to about 1500°C. In one embodiment, the firing temperature is about 1250°C. In one embodiment, the firing temperature is about 1050°C.

[0091] The firing time may vary depending on the temperature of the firing process and the exact composition of the compact. As an example, firing may be performed within a temperature range of about 1250°C to about 1500°C for 5 hours to 50 hours, including the time to ramp up to the peak temperature and hold time. Firing may be performed in a variety of ambient conditions, such as, for example, a reducing environment or a carbon environment, such as, for example, carbon monoxide. The carbon environment may be mixed with an inert carrier gas (i.e., helium, argon, and / or nitrogen).

[0092] Various firing profiles can be used in the present disclosure. In one embodiment, firing of glazed compacts can be carried out in a reducing atmosphere at a temperature of about 1250° C. to about 1300° C. In another embodiment, firing in air at a temperature of about 1000° C. to about 1250° C. can be used for glazed / coated compacts. In a further example, coated or uncoated compacts can be fired in a reducing environment at a temperature of about 1400° C. to about 1500° C.

[0093] In some embodiments, a calcination stage antioxidant (alternatively referred to herein as a second stage antioxidant) may be added to the molded article during the calcination process. Examples of calcination stage antioxidants that can be used in the present disclosure include, but are not limited to, bentonite, zinc phosphate, aluminum phosphate, aluminum-zinc phosphate, or combinations thereof. Calcination stage antioxidants can be added in amounts of about 1% to about 6% by weight, with a range of about 2% to about 4% by weight being more typical. In some embodiments, the calcination stage antioxidant is the only antioxidant present. In other embodiments, the calcination stage antioxidant is used with an antioxidant added to form the granulation mixture. In such an embodiment, the antioxidants added to form the granulation mixture may be referred to as a first stage antioxidant set, including boron carbide, silicon carbide, bentonite, aluminum-zinc phosphate, or any combination thereof, as defined above, while the calcination stage antioxidants may be referred to as a second stage antioxidant set, different from the first antioxidant set, including bentonite, zinc phosphate, aluminum phosphate, aluminum-zinc phosphate, or any combination thereof.

[0094] In various embodiments, sintering of a compact (comprising a granulated mixture of the present disclosure) provides a composite comprising graphite having a micropore profile in which at least 95% of the total pore volume is contained in pores having a diameter of less than 1 μm, and at least 40% of the pore volume of the pores having a diameter of less than 1 μm is contained in pores having a diameter of less than 0.1 μm. This micropore profile formed in the composite of the present disclosure provides excellent surface smoothness of the composite or an article formed from the composite. The surface roughness R of the composite resulting from sintering of the compact is a Regarding roughness, ISO 1302:1992 specifies the method for expressing surface roughness. In fact, the average roughness (R a ) is often used as a measure of surface smoothness.

[0095] In some embodiments of the present disclosure, the method of the present invention further comprises a step of coating, glazing, impregnation, infiltration, or any combination thereof, as described above, before or after the firing step. Preferably, when a coating step is provided, at least a part of the composite is coated with the coating. In other words, at least a part of the surface of the composite is coated with the coating. Advantageously, the coating is at least one selected from the group consisting of boron nitride, silicon carbide, alumina, or alumina titanate.

[0096] According to at least one embodiment, if an infiltration step is provided, at least a portion of the composite is infiltrated with a siloxane, a selected phosphate solution, or any combination thereof, before or after the firing step.

[0097] In another aspect of the present disclosure, a composite comprising graphite is provided. Additionally, an article comprising said composite comprising graphite is provided. As mentioned above, the composite may also be an article consisting of the composite. Alternatively, the composite may be further subjected to a manufacturing step to provide an article comprising the composite. Non-limiting examples of such articles include rotors, ladles, filters, and crucibles, or components thereof. In a preferred embodiment of the present invention, the article is a crucible, said crucible being composed of a plurality of crucible rings uniformly stacked on top of each other to provide the crucible. Alternatively or additionally, the composite may be further subjected to a coating process, a glazing process, an impregnation process, and / or an infiltration process to provide the article.

[0098] The composite has a total pore volume and a pore size distribution where at least 95% of the total pore volume is contained in pores having a diameter or equivalent diameter of less than 1 μm and at least 40% of the pore volume of the pores having a diameter or equivalent diameter of less than 1 μm is contained in pores having a diameter or equivalent diameter of less than 0.1 μm. Preferably, the composite has a total pore volume and a pore size distribution where at least 97% of the total pore volume is contained in pores having a diameter of less than 1 μm and at least 40% of the pore volume of the pores having a diameter of less than 1 μm is contained in pores having a diameter of less than 0.1 μm.

[0099] Such a pore profile can be seen on the right side of FIG. 1, entitled "Pore Size of Sintered Graphite Mix." The micropore profile created in the manufactured article composite allows for a significant reduction in the achievable surface roughness of the article composite. The reduction in surface roughness also affects the adhesion (adhesion energy) or spreading (surface energy) and wetting forces (contact angle) that occur between the molten metal and the manufactured article. This has a significant impact on the performance of the manufactured article as a rotating body (e.g., rotor) or as a stationary part (e.g., crucible).

[0100] Further, it is understood that all of the definitions and preferences set forth above apply equally to composites and articles that include graphite.

[0101] Preferably, the composite has a porosity of from about 10% to about 25%, more preferably from about 15% to about 20%.

[0102] Preferably, the composite has a density of about 1.6 g / cm 3 ~Approx. 1.92g / cm 3 , more preferably about 1.7 g / cm 3 ~Approx. 1.8g / cm 3 It has a bulk density of.

[0103] In some embodiments, the composites of the present disclosure have a microporosity of about 15% to about 20%, a microporosity of about 1.7 g / cm 3 ~Approx. 1.8g / cm 3 and a total pore volume and pore size distribution, wherein at least 97% of the total pore volume is contained in pores having a diameter less than 1 μm, and at least 40% of the pore volume of the pores having a diameter less than 1 μm is contained in pores having a diameter less than 0.1 μm.

[0104] Preferably, the composites of the present invention comprise graphite in an amount of at least 65 wt%, preferably at least 75 wt%, and more preferably at least 85 wt%, based on the total weight of the composite. In some embodiments, the composites of the present invention comprise graphite in an amount of about 65 wt% to about 85 wt%, preferably about 75 wt% to about 80 wt%, based on the total weight of the composite.

[0105] According to at least one embodiment, the composite has a surface roughness R between 3.2 μm and 0.025 μm. a and has a surface roughness R a as specified in the ISO 1302:1992 standard.

[0106] Table 2 below provides the equivalent values ​​of Ra and N numbers as defined by the ISO 1302:1992 standard. Table 2 also provides the Ra values ​​in microinches or μin., based on the ANSI B46.1 standard, which is optionally used in the United States.

[0107] [Table 2]

[0108] Below is a list of some exemplary N values ​​as defined by ISO 1302:1992: N=10 (N10=12.5 μm) indicates a rough cut with visible tool marks; N=8 (N8=3.2 μm) indicates a smooth machined surface; N=7 (N7=1.6 μm) indicates a static mating surface (or datum); N=6 (N6=0.8 μm) indicates a bearing surface; and N=1 (N1=0.025 μm) indicates a very fine lapped surface. In various embodiments, the composites of the present disclosure have a surface roughness (Ra) value between N=8 (N8=3.2 μm) and N=1 (N1=0.025 μm). In at least one embodiment, the “as pressed” surface finish of the composites of the present disclosure is between N=8 (3.2 μm) and N=1 (N1=0.025 μm). Stated another way, in at least one embodiment, the "as pressed" surface finish of the composite can range from N1 (very fine lapped surface) to N8 (smooth machined surface). In various embodiments, the composite can retain a polished mirror surface with the appropriate finish.

[0109] According to at least one embodiment, the composite has a flexural strength of about 10 MPa to 25 MPa, with a flexural strength of 12 MPa to 15 MPa being more preferred.

[0110] According to at least one embodiment, the graphite present in the composite is oriented graphite, where the graphite is oriented in a predetermined direction. In some embodiments, the orientation of the graphite in such articles is achieved by roller forming or other similar techniques. In one embodiment, the orientation of the graphite is the result of the pattern or manner in which the 3D printer head moves as the article is 3D printed. In one embodiment, the orientation of the graphite is the result of the manner in which the granulated mixture is extruded through an extrusion head. In one embodiment, the orientation of the graphite is achieved by uniaxial pressing or isostatic pressing. In various embodiments, the presence of oriented graphite can provide superior resistance to metal attack and mechanical toughness. In some embodiments, the presence of oriented graphite further provides a potential route to improve the corrosion resistance of manufactured articles against flux, slag, and metal attack. In various embodiments, composites containing oriented graphite can provide the formation of articles that exhibit superior corrosion resistance by forming such articles by methods that result in the formation of oriented graphite.

[0111] In various embodiments, the composite further comprises a non-wetting surface.

[0112] According to at least one embodiment, the composite is in a substantially finished shape.

[0113] In some embodiments, the carbon black, flake graphite, needle coke, and binder provide 100% of the total weight of the granulated mixture. In such embodiments, no other components (including the above-mentioned "additives") other than the carbon black, flake graphite, needle coke, and binder are present in the granulated mixture of the present disclosure. In such embodiments, when such a granulated mixture is formed into a compact composed of the granulated mixture and the compact is fired to provide a composite containing graphite, the resulting composite has a total carbon content of at least 99%.

[0114] According to at least one embodiment, the composite has pores larger than 0.005 μm that are blocked with antioxidants. According to at least one embodiment, the antioxidants in the article include a first set of antioxidants that include boron carbide, silicon carbide, aluminum-zinc phosphate, or any combination thereof, and a second set of antioxidants that are different from the first set of antioxidants and include zinc phosphate, aluminum phosphate, aluminum-zinc phosphate, or any combination thereof.

[0115] Preferably, at least a portion of the composite is further coated with a coating, in other words at least a portion of the surface of the composite is coated with a coating, advantageously the coating is at least one selected from the group consisting of boron nitride, silicon carbide, alumina or alumina titanate.

[0116] In some embodiments, the composite is infiltrated with a siloxane, a selected phosphate solution, or any combination thereof.

[0117] In one embodiment, a composite material comprising graphite is obtained by the method of the present invention. According to at least one embodiment, an article is obtained from the composite material as detailed above.

[0118] It should be noted that the pore sizes shown in Figures 1, 4, 7, 9, and 11 are based on mercury (Hg) porosimetry, as detailed above. EXAMPLES

[0119] Example 1: In this example, the granulation mixture consisted entirely of 88.0 wt.% natural flake graphite, 7.0 wt.% medium molecular weight phenolic resin powder, and 5.0 wt.% dibasic ester. The natural flake graphite and phenolic resin were combined in one hopper before being added to the mixer, and the dibasic ester was stored separately. The dry ingredients were added to the mixer and dry blended for approximately 2 minutes. After dry blending, the dibasic ester component was added and the mixer intensity was increased. The mixing process was continued for approximately 30-45 minutes until the granulation mixture was sufficiently granulated. The loose packing density of the granulation mixture was approximately 0.51 g / cm. 3 After cooling to room temperature, the granulated mixture was subjected to an isostatic press at approximately 5,000 psi. The pressed bodies had a compressibility of 1.6 g / cm. 3 The compact had a pressed density of 1000 and very low pressed strength. Increasing the phenolic resin and DBE resulted in a non-flowable powder that could not be easily formed into compacts. Nevertheless, the compact was cured at 200°C, but this only resulted in further weakening and eventual failure of the compact.

[0120] Example 2: In this example, the granulation mixture contained a combination of 76.0 wt% natural flake graphite, 7.5 wt% carbon black, 3.0 wt% needle coke, 7.5 wt% medium molecular weight phenolic resin powder, and 5.0 wt% dibasic ester. The dry ingredients were combined in one hopper before being added to the mixer, and the dibasic ester was stored separately. The dry ingredients were added to the mixer and dry blended for about 2 minutes. After dry blending, the dibasic ester was added and the mixer intensity was increased. The mixing process was carried out for about 30-45 minutes until the granulation mixture was sufficiently granulated. The loose packing density of the mixture was about 0.65 g / cm. 3 After cooling to room temperature, the mixture was subjected to an isostatic press at approximately 5,000 psi. The pressed bodies had a compressibility of 1.7 g / cm 3The compact had a pressed density of 1000 nm and a pressed strength that was easy to handle. After pressing, the compact was cured at 200° C. The curing process crosslinks the resin and further improves handling strength. The cured compact was exposed to a final firing cycle at 1200° C. for 4 hours. The resulting article contained a pore profile as disclosed in this disclosure. The surface roughness and profile were measured and are as disclosed in the preceding examples and figures, particularly Figures 2A and 2B.

[0121] Example 3: This example was carried out following the same process as Example 2, except that the pressed body was cured at 200° C., then infiltrated with a siloxane solution and / or a phosphate solution, and fired once at 1200° C. The resulting composite (article) exhibited a pore size distribution as shown in FIG.

[0122] Example 4: This example was carried out following the same process as Example 2, except that the calcined article was infiltrated with a siloxane and / or phosphate solution. After drying, the infiltrated article was calcined a second time at 1000° C. in a carbonaceous environment. The resulting composite (article) exhibited a pore size distribution as shown in FIG. 4. Referring to FIG. 3, an SEM image of a composite according to this example is shown, in which the clay and Al,Zn phosphates are disposed adjacent to the needle coke.

[0123] Applicant has noted that the infiltration treatment helps prevent oxidation of the carbon fibers during field use and also closes many of the coarse pores, thus resulting in an article having a high density.

[0124] Example 5: In this example, the granulation mixture contained a combination of 76.0 wt% natural flake graphite, 7.5 wt% carbon black, 3.0 wt% needle coke, and 13.0 wt% liquid medium molecular weight phenolic resin blend. The liquid phenolic resin was prepared by premixing the phenolic resin with a dibasic acid ester in a ratio of 70:30 or with ethylene glycol in a ratio of 55:45. The dry ingredients were combined in one hopper before being added to the mixer and dry blended in the mixer for about 2 minutes. After dry blending, the resin was added to the mixer and the mixer intensity was increased. The mixing process was carried out for about 30 to 45 minutes until the granulation mixture was sufficiently granulated. The loose packing density of the granulation mixture was about 0.65 g / cm. 3 After cooling to room temperature, the mixture was subjected to an isostatic press at approximately 5,000 psi. The pressed bodies had a compressibility of 1.7 g / cm 3 The compact had a pressed density of 1000 nm and a pressed strength that was easy to handle. After pressing, the compact was transferred to a kiln and cured at 200° C. The curing process crosslinks the resin and further improves handling strength. The cured compact was exposed to a final firing cycle at 1200° C. for 4 hours. The resulting article contained a pore profile as disclosed in this disclosure. Surface roughness and profile were measured and are as disclosed in the previous examples and figures.

[0125] Example 6: This example was carried out following the same process as Example 5, except that the pressed compact was infiltrated with a siloxane solution and / or a phosphate solution after curing at 200° C. and fired once at 1200° C. The resulting compact contained a pore profile as disclosed in this disclosure. Surface roughness and profile were measured and are as disclosed in this patent application.

[0126] Example 7: This example was carried out following the same process as Example 5, except that the fired article was infiltrated with a siloxane and / or phosphate solution. After drying, the infiltrated article was fired a second time at 1000° C. in a carbonaceous environment. Applicant noted that the infiltration treatment helps prevent oxidation of the carbon fibers during field use and also closes many of the coarse pores, thus resulting in an article with a higher density.

[0127] Example 8: In this example, the granulation mixture contained a combination of 70.0 wt% natural flake graphite, 6.0 wt% carbon black, and 2.0 wt% needle coke, 5.0 wt% boron carbide, 3.3 wt% silicon carbide, 7.0 wt% medium molecular weight phenolic resin powder, and 5.0 wt% dibasic acid ester. In this example, zirconia powder in an amount of 1.7 wt% was added to the dry ingredients. The dry ingredients were combined in one hopper before being added to the mixer, and the dibasic acid ester was stored separately. The dry ingredients were added to the mixer and dry blended for about 2 minutes. After dry blending, the dibasic acid ester was added to the mixer and the mixer intensity was increased. The mixing process was carried out for about 30 to 45 minutes until the granulation mixture was sufficiently granulated. The loose packing density of the mixture was about 0.68 g / cm. 3 After cooling to room temperature, the granulated mixture was subjected to an isostatic press at approximately 5,000 psi. The pressed compact had a compressibility of 1.75 g / cm. 3 The compact had a pressed density of 0.01 mm and a pressed strength that was easy to handle. After pressing, the compact was cured at 200° C. The curing process crosslinks the resin and further improves handling strength. The cured compact was exposed to a final firing cycle at 1200° C. for 4 hours. See FIG. 6, which is an SEM image of a composite with wear-resistant / erosion agent according to this example. The resulting article contained a pore profile as shown in FIG. 7. The inventors have discovered that the zirconia powder provides higher wear resistance to the resulting article.

[0128] Example 9: This example was carried out following the same process as Example 8, except that the pressed compact was infiltrated with a siloxane solution and / or a phosphate solution after curing at 200° C. and fired once at 1200° C. The resulting compact contained a pore profile as disclosed in this disclosure. Surface roughness and profile were measured and are as disclosed in the previous examples and figures.

[0129] Example 10: This example was carried out following the same process as Example 8, where the fired article was infiltrated with a siloxane and / or phosphate solution. After drying, the infiltrated article was fired a second time at 1000° C. in a carbonaceous environment.

[0130] Applicant has noted that the infiltration treatment helps prevent oxidation of the carbon fibers during field use and also closes many of the coarse pores, thus resulting in an article having a high density.

[0131] Example 11: In this example, the granulation mixture contained a combination of 70.0 wt% natural flake graphite, 6.0 wt% carbon black, and 2.0 wt% needle coke, 5.0 wt% boron carbide, 3.3 wt% silicon carbide, 7.0 wt% medium molecular weight phenolic resin powder, and 5.0 wt% dibasic acid ester. The dry ingredients were combined in one hopper before being added to the mixer, and the dibasic acid ester was stored separately. The dry ingredients were added to the mixer and dry blended for about 2 minutes. After dry blending, the dibasic acid ester was added to the mixer and the mixer intensity was increased. The mixing process was carried out for about 30-45 minutes until the granulation mixture was sufficiently granulated. An insulating aluminosilicate fiber was added in an amount of 1.7 wt% and mixing was continued for an additional 1-2 minutes. The loose packing density of the granulation mixture was about 0.63 g / cm. 3 After cooling to room temperature, the forged mixture was subjected to an isostatic press at approximately 5,000 psi. The pressed compact had a compressibility of 1.72 g / cm 3The compact had a pressed density of 0.01 mm and a pressed strength that was easy to handle. After pressing, the compact was cured at 200° C. The curing process crosslinks the phenolic resin and further increases the handling strength. The cured compact was exposed to a final firing cycle at 1200° C. for 4 hours. See Figures 8A and 8B, which show SEM images of the composite obtained according to this example. Figure 8A shows that the insulating reinforcement agent is dispersed in the granules of the granulation mixture used to provide the composite, and Figure 8B shows that the insulating reinforcement agent is located between the granules of the granulation mixture used to provide the composite. The pore size distribution of the composite is shown in Figure 9.

[0132] Example 12: This example was carried out following the same process as Example 11, except that the pressed compact was infiltrated with a siloxane solution and / or a phosphate solution after curing at 200° C. and fired once at 1200° C. The resulting compact contained a pore profile as disclosed in this disclosure. Surface roughness and profile were measured and are as disclosed in the previous examples and figures.

[0133] Example 13: This example was carried out following the same process as Example 11, except that the fired article was infiltrated with a siloxane and / or phosphate solution. After drying, the infiltrated article was fired a second time at 1000° C. in a carbonaceous environment.

[0134] Applicants have noted that the infiltration treatment closes many of the coarse pores, thus resulting in an article with increased density.

[0135] Example 14: In this example, the granulated mixture contained a combination of 70.0 wt% natural flake graphite, 6.0 wt% carbon black, and 2.0 wt% needle coke, 5.0 wt% boron carbide, 3.5 wt% silicon carbide, 7.0 wt% medium molecular weight phenolic resin powder, and 5.0 wt% dibasic ester. The dry ingredients were combined in one hopper before being added to the mixer, and the dibasic ester was stored separately. The dry ingredients were added to the mixer and dry blended for about 2 minutes. After dry blending, the dibasic ester was added to the mixer and the mixer intensity was increased. The blending process was carried out for about 30-45 minutes until the granulated mixture was sufficiently granulated. 1.5 wt% chopped carbon fiber bundles, 6 mm long and 3 mm wide, were added and mixing was continued for another 1-2 minutes. The loose packing density of the granulated mixture was about 0.63 g / cm. 3 After cooling to room temperature, the granulated mixture was subjected to an isostatic press at approximately 5,000 psi. The pressed compact had a compressibility of 1.72 g / cm. 3 The compact had a pressed density of 0.01 mm and a pressed strength that was easy to handle. After pressing, the compact was cured at 200° C. The curing process crosslinks the phenolic resin and further improves handling strength. The cured compact was exposed to a final firing cycle at 1200° C. for 4 hours. See FIGS. 5A and 5B, which show SEM images of a composite including a toughening / strength enhancing additive according to an embodiment of the present disclosure. Applicants have observed that both strength and toughness are improved compared to graphite articles that do not contain carbon fibers. The carbon fiber bundles are found to be strongly bonded to the graphite and are involved in the failure mechanism. Surface roughness and profile have been measured and are as disclosed in the previous examples and figures.

[0136] Example 15: This example was carried out according to the same process as Example 14, except that the pressed bodies were cured at 200°C, then infiltrated with a siloxane solution and / or a phosphate solution, and fired once at 1200°C.

[0137] Example 16: This example was carried out following the same process as Example 14, except that the fired article was infiltrated with a siloxane and / or phosphate solution. After drying, it was fired a second time at 1000° C. in a carbonaceous environment.

[0138] Applicant noted that the infiltration treatment is very important to prevent oxidation of the carbon fibers during field use. As reported in the previous examples, the infiltration treatment also blocked many of the coarse pores, thus resulting in an article with increased density.

[0139] While the present disclosure has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the present disclosure. It is therefore intended that the present disclosure not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.

Claims

1. A method for forming an article comprising a composite material containing graphite, wherein the article is suitable for containing or processing molten metal, and the method is (a) A step of forming at least one granulated mixture by mixing at least carbon black, flake graphite, and needle coke with at least one resin, wherein the at least one resin has a flow distance of 20 mm to 150 mm as measured by ISO 8619:2003, (b) The step of forming the at least one granulated mixture into at least one molded body, (c) The step of firing the at least one molded body, Methods that include...

2. With respect to the total weight of the granulated mixture, The carbon black is present in the granulated mixture in an amount of about 5% to about 10% by weight, preferably about 5% to about 8% by weight. The flake-like graphite is present in the granulated mixture in an amount of about 65% to about 85% by weight, preferably about 75% to about 80% by weight. The needle coke is present in the granulated mixture in an amount of about 1% to about 5% by weight, preferably about 2% to about 4% by weight, and The resin is present in the granulated mixture in an amount of about 2% to about 10% by weight, preferably about 6% to about 8% by weight. The method according to claim 1.

3. The method according to claim 1 or 2, wherein at least one solvent is added to the at least one resin to form at least one binder comprising the at least one resin and the at least one solvent.

4. The method according to claim 3, wherein the at least one solvent is present in the granulated mixture in an amount of about 1% to about 5% by weight, preferably about 3% to about 4% by weight, relative to the total weight of the granulated mixture.

5. The method according to claim 1 or 2, wherein at least the carbon black, the flake graphite, the needle coke, and the at least one resin constitute 100% of the total weight of the granulated mixture.

6. The method according to claim 1 or 2, wherein the at least one granulated mixture further comprises at least one antioxidant in an amount of about 5% to about 15% by weight, based on the total weight of the granulated mixture, and optionally the at least one antioxidant comprises boron carbide, silicon carbide, aluminum zinc phosphate, or any combination thereof.

7. The method according to claim 1 or 2, wherein the at least one granulated mixture further comprises at least one toughening / strengthening additive in an amount of about 1% to about 5% by weight relative to the total weight of the granulated mixture, and optionally the at least one toughening / strengthening additive comprises carbon fibers, chopped carbon fiber bundles, basalt fiber bundles, alumina silicate fibers, chopped steel fibers, or any combination thereof.

8. The method according to claim 1 or 2, wherein the granulated mixture further comprises at least one wear-resistant / corrosion-resistant agent in an amount of about 1% to about 10% by weight relative to the total weight of the granulated mixture, and optionally the at least one wear-resistant / corrosion-resistant agent comprises a metal oxide, a metal nitride, a metal boride, or any combination thereof.

9. The method according to claim 1 or 2, wherein the at least one granulated mixture further comprises about 1% to about 5% by weight of a thermal insulation reinforcing agent based on the total weight of the granulated mixture, and optionally the at least one thermal insulation reinforcing agent comprises colloidal silica shot, preferably aluminocolloidal silicate shot, fibers, preferably a mixture of sodium and chopped silica fibers, or a mixture thereof.

10. The method according to claim 1 or 2, wherein at least a portion of the composite material is impregnated with siloxane, a selected phosphate solution, or any combination thereof before or after the calcination step.

11. The method according to claim 1 or 2, wherein the resin is a phenolic resin, and optionally, the phenolic resin is a liquid phenolic resin.

12. An article comprising a graphite-containing composite material, wherein, in terms of total pore volume and pore size distribution measured according to the ASTM C830-00 (2016) standard, at least 95% of the total pore volume consists of pores with a diameter of less than 1 μm, and at least 40% of the pore volume of the pores with a diameter of less than 1 μm consists of pores with a diameter of less than 0.1 μm.

13. The composite material has a concentration of approximately 1.6 g / cm³. ３ ~Approx. 1.92g / cm ３ The article according to claim 12, having the density of

14. The article according to claim 12 or 13, wherein the composite material has 65% or more graphite.

15. The composite material has a surface roughness R between 3.2 μm and 0.025 μm. ａ It has the surface roughness R ａ The article according to claim 12 or 13, measured in accordance with the ISO 1302:1992 standard.

16. The article according to claim 12 or 13, wherein at least a portion of the composite material is further coated with a coating, the coating preferably being at least one selected from the group consisting of boron nitride, silicon carbide, alumina, or alumina titanate.

17. The article according to claim 12 or 13, wherein the article is a crucible, and the crucible is composed of a plurality of crucible rings stacked uniformly on top of each other to provide the crucible.

18. An article comprising a composite material containing graphite obtained by the method of claim 1 or 2.

19. The article according to claim 18, wherein the composite material has a total pore volume and pore size distribution measured in accordance with the ASTM C830-00 (2016) standard, wherein at least 95% of the total pore volume are pores with a diameter of less than 1 μm, and at least 40% of the pore volume of the pores with a diameter of less than 1 μm are pores with a diameter of less than 0.1 μm.

20. The article according to claim 18, wherein at least a portion of the composite material is further coated with a coating, the coating preferably being at least one selected from the group consisting of boron nitride, silicon carbide, alumina, or alumina titanate.

21. The article according to claim 18, wherein the article is a crucible, and the crucible is composed of a plurality of crucible rings stacked uniformly on top of each other to provide the crucible.

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