Ceramic disks and rods, methods for manufacturing them, and articles comprising them

Abstract

Disclosed herein is a dual density disk comprising a dense outer tube comprising alumina having a purity greater than 99% and a porous core comprising alumina of a density lower than that of the dense outer tube, wherein the porous core has an alumina purity greater than 99%. Also disclosed herein is a method comprising disposing a slurry comprising alumina powder and a pore former in the dense outer tube, heating the dense outer tube with the slurry disposed therein to a temperature of 300-600°C to activate the pore former, creating a porous core in the dense outer tube, and sintering the dense outer tube with the porous core in one or more stages at a temperature of 800-2000°C.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of priority to a provisional application filed on November 27, 2019, and assigned Serial No. 62 / 941,241. The entire contents of the foregoing provisional application are incorporated herein by reference.

Background Art

[0002] Ceramic disks and rods, methods of manufacturing them, and articles comprising them are disclosed herein. More specifically, alumina disks and rods having a high - density shell with a porous core are disclosed herein.

Summary of the Invention

[0003] A dual density disc comprising a high - density outer tube containing alumina having a purity greater than 96% and a porous core containing alumina having a density lower than the density of the high - density outer tube, wherein the porous core has an alumina purity greater than 99%, is disclosed herein.

[0004] Also disclosed herein is a method comprising disposing a slurry containing alumina powder and a pore - forming agent in the high - density outer tube, heating the high - density outer tube in which the slurry is disposed to a temperature of 300 - 600 °C to activate the pore - forming agent, creating a porous core in the high - density outer tube, and sintering the high - density outer tube having the porous core at a temperature of 800 °C to 2000 °C in one or more stages.

[0005] In an embodiment, a method for manufacturing an alumina disk includes disposing alumina powder in a high-density outer tube. No pore former and / or solvent is used in the powder. The high-density outer tube in which the alumina powder is disposed is placed therein at a temperature of 800 to 2000 °C in one or more steps. This creates a porous core in the high-density outer tube having a purity of greater than 99%. Both the porous core and the high-density outer tube have a purity of greater than 99%.

[0006] A dual-density disk comprising a high-density outer tube containing a first ceramic having a purity of greater than 96% and a porous core containing a second ceramic having a density lower than that of the high-density outer tube, wherein the porous core has a purity of greater than 99%, is disclosed herein. In an embodiment, the first ceramic may be the same as the second ceramic. In another embodiment, the first ceramic may be different from the second ceramic.

Brief Description of the Drawings

[0007]

Figure 1(A)

Figure 1(B)

Figure 2(A)

Figure 2(B)

Figure 3

Best Mode for Carrying Out the Invention

[0008] A ceramic disk or rod (hereinafter referred to as "disk") having a dual density, comprising a high-density shell used to provide a uniform gas flow for various applications in semiconductor manufacturing operations etc., and a porous core (of a lower density than the shell), is disclosed herein. The rod may be sliced into several smaller slices called disks. The disk has a high strength provided by a high-density ceramic shell (hereinafter referred to as the high-density shell). The high-density shell surrounds a mostly porous ceramic core (hereinafter referred to as the porous core) that enables a uniform gas flow during the manufacturing operation (such as the fabrication of semiconductor wafers). In addition, the disk contains a high-density ceramic shell with a purity of over 96%, thereby preventing contamination of semiconductor components during the manufacturing operation in which the ceramic disk is deployed. The porous core contacts the high-density outer tube (shell) on its inner surface, and the outer tube is in continuous contact with the porous core along the entire circumference of the porous core. In an embodiment, the porous core contains the same chemical composition as the high-density shell, except that the core is porous while the shell is high-density. The density of the shell is greater than the density of the porous core.

[0009] In another embodiment, the porous core contains a ceramic having a chemical composition different from that of the high-density shell. A dual-density disk is disclosed herein, comprising a high-density outer tube containing a first ceramic having a purity of over 96% and a porous core containing a second ceramic having a density lower than that of the high-density outer tube, wherein the porous core has a purity of over 99%. In an embodiment, the first ceramic may be the same as the second ceramic. In another embodiment, the first ceramic may be different from the second ceramic.

[0010] The ceramics used for the disk include metal oxides, carbides, oxycarbides, nitrides, oxynitrides, borides, borocarbides, boron nitrides, silicides, iodides, bromides, sulfides, selenides, tellurides, fluorides, or borosilicates. Suitable metals are aluminum, titanium, zirconium, silicon, cerium, etc., or combinations thereof.

[0011] In an embodiment, the ceramic is preferably a metal oxide. Preferred metal oxides are titania, silica, alumina, zirconia, ceria, etc., or combinations thereof. A preferred metal oxide for use in the disk is alumina. The articles and the manufacturing methods detailed below are directed to alumina disks, but they can equally well apply to any of the ceramics listed above. The listed temperatures and atmospheres for manufacturing the alumina disks below function equally well for any of the ceramics listed above, and thus there is no repetition of annealing temperature, sintering temperature, or atmosphere and pressure used to manufacture the ceramic disk.

[0012] Also disclosed herein is an alumina disk or rod (hereinafter referred to as a "disk") having a dual density, comprising a high-density shell used to provide a uniform gas flow for semiconductor manufacturing operations and a porous core (less dense than the shell). The rod can be sliced into several smaller slices called disks. The disk has high strength provided by the high-density shell. The high-density shell surrounds a mostly porous core that enables a uniform gas flow during manufacturing operations (for manufacturing semiconductors). Additionally, the disk contains alumina with a purity of over 96%, thereby preventing contamination of semiconductor components during manufacturing operations where the alumina disk is deployed. The porous core contacts the high-density outer tube (shell) on its inner surface, and the outer tube continuously contacts the porous core along the entire circumference of the porous core. This core-shell dual density structure provides radial hermiticity (i.e., prevents leakage from the sides of the porous body) and allows flow only through the longitudinal direction. Note that the outer shell is referred to herein as the "alumina shell", "alumina tube", "high-density shell", and "high-density outer tube".

[0013] Also disclosed herein is a method for manufacturing an alumina disk or rod. The method includes filling a high-density alumina tube with an alumina slurry. The alumina slurry contains (high-purity) alumina powder and a pore former. Then, the tube containing the slurry is fired to produce a porous core in the high-density alumina tube. Next, the alumina tube having the porous core can be subjected to finishing operations such as slicing, lapping, grinding, etc. to produce an alumina disk.

[0014] FIG. 1 shows a ceramic disk 100 comprising a ceramic shell 102 and a porous ceramic core 104 contained therein.

[0015] The ceramic tube (also referred to herein as the ceramic shell) used to manufacture the ceramic disk has an outer diameter (D o ) of 1.0 to 75 millimeters, preferably 3.5 millimeters to 12.6 millimeters and an inner diameter (D i ) of 0.8 to 70 millimeters, preferably 1.4 to 2.2 millimeters. These diameter dimensions also apply to the ceramic disks that can be obtained by slicing the ceramic tube. The ceramic tube has a length (L) of 1 millimeter to 120 millimeters, preferably 3.5 to 25.4 millimeters. The ceramic tube has a purity of more than 96%, preferably more than 99%, and a density (g / cm 3 ) of more than 3.0 to 3.95 grams per cubic centimeter. The dimensions shown in Figure 1 apply to an alumina tube with a high-density alumina shell and a porous alumina core.

[0016] The porous core is manufactured by filling the hollow central portion of the alumina tube with alumina slurry or powder and then heating the tube containing the slurry or powder to form an alumina disk. The slurry contains high-purity alumina powder, an optional solvent, and a pore former. These will be described in detail below.

[0017] The porous core can also be formed without using a pore former and a solvent. The particle size distribution can generate a porous core when sintering occurs. The adjacent portions of the particles undergo necking when bonding to each other to form the porous core.

[0018] Alumina powder having either a narrow particle size distribution or a wide particle size distribution is formed into a slurry having a solvent and a pore former. The alumina powder can have a particle size of 10 nanometers to 500 micrometers, preferably 100 nanometers to 150 micrometers, more preferably 150 nanometers to 100 micrometers. The alumina powder can have a unimodal distribution of particle size, or alternatively, can have a bimodal or more distribution of particle size.

[0019] The alumina powder also has a purity of greater than 99%, preferably greater than 99.3%. The alumina powder can be present in the slurry in an amount of 10 to 90% by weight, preferably 20 to 60% by weight, based on the total weight of the slurry.

[0020] The solvent is optional. The solvent used to form the slurry can include a polar solvent or a nonpolar solvent. The solvent can be protic or aprotic. Liquid aprotic polar solvents such as propylene carbonate, ethylene carbonate, butyrolactone, acetonitrile, benzonitrile, nitromethane, nitrobenzene, sulfolane, dimethylformamide, N-methylpyrrolidone, etc., or combinations thereof are generally desirable. Polar protic solvents such as water, methanol, acetonitrile, nitromethane, ethanol, propanol, isopropanol, butanol, or the like, but not limited thereto, or combinations thereof can be used. Other nonpolar solvents such as benzene, toluene, carbon tetrachloride, hexane, diethyl ether, tetrahydrofuran, etc., or combinations thereof can also be used. Suitable solvents are water, alcohol, or combinations thereof.

[0021] When present, the solvent can be used in an amount of 5 to 80% by weight, preferably 15 to 60% by weight, based on the total weight of the slurry.

[0022] The pore former is optional. The pore former may (or may not) be mixed into the slurry to facilitate the formation of the porous core in the alumina tube. As described above, the particle size distribution can result in the porosity present in the core (when no solvent or pore former is used in the slurry). The pore former can be a gas, a liquid, or a solid. In an embodiment, the pore former is an organic material that can decompose upon heating to a high temperature to release a gas. Examples of such pore formers include solids such as AIBN (azobisisobutyronitrile), an organic compound having the formula [(CH3)2C(CN)]2N2. It is a white powder and soluble in alcohol and common organic solvents.

[0023] In another embodiment, the pore former can be an organic polymer. The polymer is generally in powder form and is mixed with the alumina powder to form a mixture (or a slurry if a solvent is also used) that is then placed in the alumina tube. When the alumina tube is heated to a temperature of 300 - 600 °C, the polymer decomposes to facilitate the formation of pores in the alumina powder.

[0024] Organic polymers used in spaced features and / or surfaces can be selected from a wide variety of thermoplastic polymers, blends of thermoplastic polymers, thermosetting polymers, or blends of thermoplastic and thermosetting polymers. The organic polymer can also be a blend of a polymer, copolymer, terpolymer, or a combination containing at least one of the aforementioned organic polymers. The organic polymer can be an oligomer, homopolymer, copolymer, block copolymer, alternating block copolymer, random polymer, random copolymer, random block copolymer, graft copolymer, star block copolymer, dendrimer, polyelectrolyte (a polymer having several repeating groups containing an electrolyte), polyampholyte (a polyelectrolyte having both cationic and anionic repeating groups), ionomer, etc., or a combination containing at least one of the aforementioned organic polymers. The organic polymer has an average molecular weight of more than 10,000 grams per mole, preferably more than 20,000 g / mol, more preferably more than 50,000 g / mol.

[0025] Exemplary organic polymers include polyacetal, polyacrylic acid, polycarbonate, poly(meth)acrylate, polyalkyd, polystyrene, polyolefin, polyester, polyamide, polyaramid, polyamideimide, polyarylate, polyurethane, epoxy, phenolics, silicone, polyarylsulfone, polyethersulfone, polyphenylene sulfide, polysulfone, polyimide, polyetherimide, polytetrafluoroethylene, polyetherketone, polyetheretherketone, polyetherketoneketone, polybenzoxazole, polyoxadiazole, polybenzothiazinophenothiazine, polybenzothiazole, polypyrazinoquinoxaline, polypyromellitimide, polyguinoxaline, polybenzimidazole, polyoxindole, polyoxoisoindoline, polydioxoisoindoline, polytriazine, polypyridazine, polypiperazine, polypyridine, polypiperidine, polytriazole, polypyrazole, polycarborane, polyoxabicyclononane, polydibenzofuran, polyphthalide, polyacetal, polyanhydride, polyvinyl ether, polyvinyl thioether, polyvinyl alcohol, polyvinyl ketone, polyvinyl halide, polyvinyl nitrile, polyvinyl ester, polysulfonate, polysulfide, polythioester, polysulfone, polysulfonamide, polyurea, polyphosphazene, polysilazane, polypropylene, polyethylene, polyethylene terephthalate, polyvinylidene fluoride, polysiloxane, etc., or combinations thereof.

[0026] In another embodiment, the pore-forming agent can be a gas that is soluble in the solvent used in the alumina powder or slurry. The gas can then phase-separate from the slurry (by binodal decomposition when the pressure and / or temperature changes) to form a porous phase (pores) in the slurry. Examples of such gases include carbon dioxide, argon, hydrogen, nitrogen, or combinations thereof.

[0027] In yet another embodiment, a blowing agent such as chlorofluorocarbon, hydrochlorofluorocarbon (HCFC), and / or hydrofluorocarbon (HFC) can be used to form pores. Chlorofluorocarbon (CFC) is derived from methane and ethane, and these compounds have the formula CCl m F 4-m and C2Cl m F 6-m where m is non-zero. Hydrochlorofluorocarbon (HCFC) is also derived from methane and ethane, and these compounds have the formula CCl m F n H 4-m-n and C2Cl x F y H 6-x-y where m, n, x, and y are non-zero. Hydrofluorocarbon (HFC) can also be derived from methane, ethane, propane, and butane, and these compounds have the formulas CF m H 4-m , C2F m H 6-m , C3F m H 8-m , and C4F m H 10-m where m is non-zero.

[0028] The pore former can also be used in an amount of 5 to 50 wt%, preferably 10 to 50 wt%, based on the total weight of the slurry. Combinations of the aforementioned pore formers can also be used.

[0029] The slurry is prepared by mixing alumina powder, an optional solvent, and a pore former. The slurry is then introduced into the hollow center of the alumina tube. The slurry may or may not be consolidated.

[0030] The alumina tube containing the slurry is subjected to temperatures of 300 and 600 °C for a period of 10 minutes to 12 hours to form pores in the core of the alumina tube. This step promotes the activation of the pore-forming agent. The high temperature causes the pore-forming agent to decompose and release gas, which promotes pore formation in the core of the alumina tube.

[0031] The alumina tube containing porous alumina is then subjected to one or more sintering steps. In an embodiment, the first sintering step is carried out at a temperature of 800 to 1600 °C, in air, or in a controlled atmosphere. This first sintering step is optional and is carried out to improve handleability (i.e., to ensure that the porous core remains intact within a high-density alumina shell). The first sintering step is carried out in any of vacuum, air, oxygen, argon, nitrogen, natural gas, hydrogen, carbon dioxide, or combinations thereof, in a controlled pressure environment of vacuum, atmospheric pressure, and / or a pressure greater than atmospheric pressure.

[0032] The alumina tube having a porous core is then subjected to a second sintering step carried out at a temperature of 1500 and 2000 °C in any of vacuum, air, oxygen, argon, nitrogen, natural gas, hydrogen, carbon dioxide, or combinations thereof, to obtain an alumina disk having a porous center. The porous center contains continuous bubble pores that allow gas to flow through the alumina disk from one end to the other.

[0033] In an embodiment, a method for manufacturing an alumina disk includes disposing alumina powder in a high-density outer tube. No pore former and / or solvent is used in the powder. The high-density outer tube with the alumina powder disposed therein is sintered at a temperature of 800 to 2000 °C in one or more steps. The above two-step sintering process can also be used here. This creates a porous core in the high-density outer tube. The porous core is directly covalently bonded to the high-density outer tube. This creates a porous core in a high-density outer tube having a purity of greater than 99%. Both the porous core and the high-density outer tube have a porosity of greater than 99%. In other words, there is no adhesive or additive used to facilitate the bonding of the porous core to the high-density outer tube.

[0034] In both of the sintering methods disclosed above, the porous core has a higher purity than the high-density outer tube. This applies to all ceramic disks.

[0035] The sintered alumina disk is here a dual-density component having a first, higher-density shell and a second, lower-density core. The component may then or may not be subjected to further finishing operations. The alumina shell density is greater than the density of the porous alumina core. In an embodiment, the finishing operation can involve slicing the disk into several smaller disks. In another embodiment, the alumina disk can have features such as edges, steps, or radii (or multiple chamfers) that can be machined on the shell before the formation of the porous (interior), or after the formation of the pores. The porous portion within the outer alumina shell can be flashed with the shell wall by machining including milling. The outer diameter can be ground to the desired dimensions. The machining can be performed by using water-soluble cooling water to wash away any remaining machining impurities and ensure the high purity of the component.

[0036] The dual-density alumina disk allows fluid to flow from one side to the other and can be used as flow controllers and filters fabricated with various pore size distributions. High crushing strength due to the high-density alumina shell and high flow rates due to the porosity within the shell (formed without compaction) are important features of the dual-density component. The pore size is greater than 0.5 micrometers and can be controlled for flow control and filtration applications. A strong bond (via covalent and / or ionic bonds) between the porous alumina and the alumina tube (shell) is created during the sintering process.

[0037] The dual-density alumina disk complies with the cleanliness standards defined by the semiconductor industry. This is demonstrated by low particulate shedding under ultrasonic exposure in deionized water. The crushing strength of the dual-density alumina disk can exceed 20,000 pounds per square inch, and the crushing strength of the porous portion can exceed 1000 pounds per square inch, preferably 2000 pounds per square inch when tested as detailed below. The crushing strength and flow of gas within the pores depend on the initial particle size distribution of the alumina powder used, the amount of pore former in the blend (i.e., weight percent), and the sintering conditions. Furthermore, the flow increases with an increase in the inner diameter and a decrease in the length of the alumina disk. Flow rate, crushing strength (of the porous region within the high-density shell), and density data for dual-density disks obtained using different blend compositions are shown in Table 1 below. Table 1 contains exemplary data from the samples tested. The flow rate was determined at a gauge pressure of 30 pounds per square inch.

[0038]

Table 1

[0039] Table 1 shows the material composition of the porous core after sintering. The flow rate through the alumina disk can vary over a wide range depending on the application. It can be seen that the nitrogen flow rate through the alumina disk varies from 5,000 to 30,000 standard cubic centimeters per minute, preferably from 10,000 to 22,000 standard cubic centimeters per minute. The bulk density (apparent specific gravity) of the porous core varies from 1.00 to 2.50 g / cc, preferably from 1.05 to 1.30 g / cc, preferably from 1.08 to 1.27 g / cc, and the crushing strength within the alumina disk is 1,800 to 2,500 pounds per square inch. Figure 1(B) shows a cross-section of an alumina disk having a high-density skin and a porous core. In an embodiment, when present within the high-density outer tube, the porous core has a bulk density of 1.00 to 1.30 g / cc and a crushing strength of more than 2,000 pounds per square inch.

[0040] The porous core has a porosity of more than 30 volume percent, preferably more than 50 volume percent, preferably more than 70 volume percent, preferably more than 80 volume percent, more preferably more than 90 volume percent, based on the total volume of the core. The ceramic disk also exhibits radial hermeticity, i.e., it shows that when a fluid is transported through it, there is no leakage from the sides of the porous body. Thus, it is possible to flow only in the longitudinal direction (length L direction) (see Figure 1(A)).

[0041] Figures 2(A) and 2(B) show the porous regions of the alumina disk as seen in scanning electron microscope micrographs. Figure 2(A) shows the porous region at a low magnification, and Figure 2(B) shows the porous region at a high magnification.

[0042] Energy-dispersive X-ray analysis (EDAX) performed on the core indicates that it is of high purity (>99.3%). This can be seen in Figure 3, which shows a graph of the aluminum signal of the alumina disk. Figure 3 shows the EDAX spectrum of a double-density component indicating the presence of aluminum and oxygen as the only elements, which demonstrates the high purity of the double-density alumina disk. The porous section has a very high purity and is manufactured using alumina powder with a purity of over 99.9%, and the alumina tube (shell) has a purity of over 99.3%. The porous section is directly covalently bonded to the alumina tube (shell).

[0043] Test Method Porous Crushing Strength Test To reach the crushing strength of the porous core, a method has been developed to apply force independently only to the porous core, rather than applying force to both the porous core and the high-density shell. This method involves fixing the component to a device that allows a gauge pin with a diameter equal to that of the porous core to rest perpendicular to the surface of the porous core. The opening of this jig that houses the gauge pin is made 0.005 inches wider than the diameter of the gauge pin to minimize frictional force. In this device, the component is fixed such that the porous can be displaced when sufficient load is applied, while the shell is pinned to the inner surface of the device and cannot be displaced.

[0044] To test the crushing strength, the component is placed in the device and loaded into an MTS or Instron compression strength testing machine. The jig is placed on a flat and fixed bottom plate. The gauge pin is loaded on top of the jig. Then, the flat upper plate is set to displace downward at a speed of 0.001 inches / second, applying a load to the gauge pin and then to the component. The breakage of the component is recorded by the machine and characterized manually / visually by two breakage methods. The first breakage method involves extruding the porous from the shell. The second breakage mode involves crushing the porous material. Whichever breakage mode occurs first, the load in this breakage mode is converted to the compression strength.

[0045] Density determination test Shell: The outer diameter and length of the shell are dimensioned via the use of a drop gauge. The inner diameter is measured via imaging and analysis. The mass is recorded via the use of an analytical balance. The density is recorded as the measured mass divided by the calculated volume.

[0046] Porous core: Take the mass before and after processing the porosity. The difference between the measured mass of the shell only and the measured mass of the finished product (having the shell and the porous core) is converted to the mass of the porous core. Take the dimensions of the porous core. The drop gauge measures the length of the porous core and optical imaging provides the diameter. The density is taken as the differential mass divided by the calculated volume.

[0047] Shell + Porous: The finished product is dimensioned with a drop gauge. The mass is recorded via an analytical balance. The density of the bulk part is calculated as the measured mass with respect to the calculated volume.

[0048] The present invention has been described with reference to several embodiments, but it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its essential scope. Accordingly, the present invention is not limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present invention, but the present invention is intended to cover all embodiments within the scope of the appended claims.

Claims

1. A dual-density disk, comprising: A high-density outer tube containing alumina with a purity exceeding 96%; and A porous core containing alumina with a density lower than that of the high-density outer tube, wherein the porous core has an alumina purity exceeding 99%. When present within the high-density outer tube, the porous core has a bulk density of 1.00 to 2.5 g / cc and a crushing strength exceeding 2000 pounds per square inch.

2. The dual-density disk according to claim 1, wherein the porous core contacts the high-density outer tube on its inner surface, and the high-density outer tube is in continuous contact with the porous core along the entire circumference of the porous core.

3. The dual-density disk according to claim 1, wherein the nitrogen flow rate at a gauge pressure of 30 pounds per square inch in the dual-density disk varies from 5,000 to 30,000 standard cubic centimeters per minute.

4. The dual-density disk according to claim 1, having a radial hermeticity such that it does not leak from the side of the porous body and allows flow only in the longitudinal direction.

5. The dual-density disk according to claim 1, wherein the high-density outer tube has an outer diameter of 1 to 75 millimeters and an inner diameter of 0.8 to 70 millimeters.

6. The dual-density disk according to claim 1, wherein the high-density outer tube has an initial length of 1 to 120 millimeters.

7. The dual-density disk according to claim 1, wherein the porous core is manufactured from alumina powder having an initial purity exceeding 99%.

8. The dual-density disk according to claim 1, wherein the porous core is manufactured from alumina powder having an initial purity exceeding 99.3%.

9. A method, comprising: Placing a slurry containing alumina powder and a pore former in a high-density outer tube; Heating the high-density outer tube in which the slurry is placed to a temperature of 300 to 600 °C to activate the pore former; Forming a porous core in the high-density outer tube; and Sintering the high-density outer tube having the porous core at a temperature of 800 to 2000 °C in one or more steps.

10. The method according to claim 9, wherein the sintering operation is carried out in air, nitrogen, natural gas, argon, hydrogen, or a combination thereof. ​

11. The method according to claim 9, wherein the pore former is an organic pore former.

12. The method according to claim 9, wherein the slurry further contains a solvent.

13. The method according to claim 9, wherein the sintering is preceded by a first sintering step at a temperature of 1200 to 1600 °C.

14. The method according to claim 9, wherein the pore former is azobisisobutyronitrile.

15. The method according to claim 9, wherein the pore former is a gas soluble in the slurry.

16. The method according to claim 9, wherein the pore former is a liquid.

17. The method according to claim 9, wherein the pore former is an organic polymer.

18. The method according to claim 17, wherein the organic polymer is polyacetal, polyacrylic acid, polycarbonate, poly(meth)acrylate, polyalkyd, polystyrene, polyolefin, polyester, polyamide, polyaramide, polyamideimide, polyarylate, polyurethane, epoxy, phenols, polyarylsulfone, polyethersulfone, polyphenylene sulfide, polyimide, polyetherimide, polytetrafluoroethylene, polyetherketone, polyetheretherketone, polyetherketone, polybenzoxazole, polyoxadiazole, polybenzothiazinophenothiazine, polybenzothiazole, polypyrazinoquinoxaline, polypyromellitimide, polyquinoxaline, polybenzimidazole, polyoxindole, polyoxoisoindoline, polydioxoisoindoline, polytriazine, polypyridazine, polypiperazine, polypyridine, polypiperidine, polytriazole, polypyrazole, polycarborane, polyoxabicyclononane, polydibenzofuran, polyphthalide, polyacetal, polyanhydride, polyvinyl ether, polyvinyl thioether, polyvinyl alcohol, polyvinyl ketone, polyvinyl halide, polyvinyl nitrile, polyvinyl ester, polysulfonate, polysulfide, polythioester, polysulfone, polysulfonamide, polyurea, polyphosphazene, polysilazane, polyvinylidene fluoride, polysiloxane, or a combination thereof.

19. A method comprising: Placing alumina powder that does not contain a pore-forming agent in a high-density outer tube; Sintering the high-density outer tube in which the alumina powder is placed at a temperature of 800 to 2000 °C; Forming a porous core having a purity of more than 99% in the high-density outer tube, the method comprising.

20. The method according to claim 19, further comprising heating the high-density outer tube in which the alumina powder is placed to a temperature of 1200 to 1600 °C.

21. A dual-density disk, comprising: A high-density outer tube containing a first ceramic having a purity of more than 96%; A porous core containing a second ceramic having a density lower than that of the high-density outer tube, the porous core having a purity of more than 99%, the porous core; Comprising; When present in the high-density outer tube, the porous core has a bulk density of 1.00 to 2.5 g / cc and a crushing strength of more than 2000 pounds per square inch, the dual-density disk.

22. The dual-density disk according to claim 21, wherein the first ceramic is the same as the second ceramic.

23. The dual-density disk according to claim 21, wherein the first ceramic is different from the second ceramic.

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