Alumina ceramics composition for low-temperature sintering, manufacturing method therefor, and method for manufacturing alumina ceramics

Abstract

The present invention relates to a ceramics composition and a manufacturing method therefor and, more specifically, to an alumina ceramics composition for low-temperature sintering and a manufacturing method therefor. Provided according to the present invention is an alumina ceramics composition for low-temperature sintering, comprising: 90 to 92.9 wt% of alumina (Al2O3); 1 to 2 wt% of talc; 3 to 4 wt% of limestone; 3 to 4 wt% of clay; and 0.1 to 0.5 wt % of potassium oxide (K2O).

Description

Alumina ceramic composition for low-temperature sintering and method for manufacturing the same, and method for manufacturing alumina ceramics

[0001] The present invention relates to a ceramic composition and a method for manufacturing the same, and more specifically, to an alumina ceramic composition for low-temperature sintering and a method for manufacturing the same.

[0002] Alumina with an alumina content of about 95 weight percent (Grade 95 alumina) has excellent heat resistance, wear resistance, and insulation properties, so it is used in various industrial fields such as electronic components, insulators, wear-resistant parts, and structural materials for high-temperature environments. The remaining 5 weight percent of Grade 95 alumina may consist of oxides, impurities, and additives.

[0003] Grade 95 alumina is relatively inexpensive compared to high-purity alumina, but it still possesses excellent physical and chemical properties, so it is widely used in various applications. For example, it can be used as an insulator for electronic components, wear-resistant parts, high-temperature gas turbine parts, refractory materials, medical device parts, chemical equipment parts, etc.

[0004] General Grade 95 alumina is manufactured by sintering at high temperatures of approximately 1600 to 1650°C. Consequently, there are issues with high energy consumption and increased costs during the manufacturing process. Such high-temperature sintering extends process time and leads to reduced equipment durability and increased maintenance costs.

[0005] [Prior Art Literature]

[0006] (Patent Document 1) Korean Published Patent Application 10-2016-0102799

[0007] (Patent Document 2) Korean Published Patent Application 10-2012-0133235

[0008] The present invention aims to provide an alumina ceramic composition for low-temperature sintering, a method for manufacturing the same, and a method for manufacturing alumina ceramics using the alumina ceramic composition for low-temperature sintering.

[0009] To achieve the above-mentioned objective, according to the present invention, an alumina ceramic composition for low-temperature sintering is provided, comprising 90 to 92.9 wt% of alumina (Al2O3), 1 to 2 wt% of talc, 3 to 4 wt% of limestone, 3 to 4 wt% of clay, and 0.1 to 0.5 wt% of potassium oxide (K2O).

[0010] In addition, an alumina ceramic composition for low-temperature sintering is provided, further comprising, based on 100 parts by weight of solid content, 0.5 to 1.5 parts by weight of a dispersant, 0.1 to 0.5 parts by weight of an antifoaming agent, 1 to 3 parts by weight of a binder, 1 to 3 parts by weight of a release agent, and 2 to 4 parts by weight of a plasticizer.

[0011] In addition, according to the present invention, a method for manufacturing an alumina ceramic composition for low-temperature sintering is provided, comprising the step of preparing a slurry composition by mixing a solid content comprising 90 to 92.9 weight% of alumina (Al2O3), 1 to 2 weight% of talc, 3 to 4 weight% of limestone, 3 to 4 weight% of clay, and 0.1 to 0.5 weight% of potassium oxide (K2O), and, based on 100 weight parts of the solid content, 0.5 to 1.5 weight parts of a dispersant, 0.1 to 0.5 weight parts of an antifoaming agent, 1 to 3 weight parts of a binder, 1 to 3 weight parts of a release agent, and 2 to 4 weight parts of a plasticizer.

[0012] In addition, a method for manufacturing an alumina ceramic composition for low-temperature sintering is provided, wherein the particle size distribution of solid particles included in the slurry composition satisfies D50 3.5 ~ 4.0㎛ and D90 10.0㎛, and the viscosity of the slurry composition is 80 ~ 120cP.

[0013] In addition, a method for manufacturing an alumina ceramic composition for low-temperature sintering is provided, which further includes the step of spraying the above-mentioned slurry composition in the form of fine droplets and then drying it using a high-temperature gas to produce a powder.

[0014] In addition, a method for manufacturing an alumina ceramic composition for low-temperature sintering is provided, wherein the average particle size of the powder is 40 to 80 μm, the specific gravity is 1.14 to 1.34 g / cm³, the fluidity is 4.5 to 9.5 g / sec, and the moisture content is 0.2 to 0.6 weight%.

[0015] In addition, according to the present invention, a method for manufacturing alumina ceramics is provided, comprising the steps of: manufacturing a green molded body comprising a solid content including 90 to 92.9 wt% alumina (Al2O3), 1 to 2 wt% talc, 3 to 4 wt% limestone, 3 to 4 wt% clay, and 0.1 to 0.5 wt% potassium oxide (K2O); and, based on 100 wt% of the solid content, 0.5 to 1.5 wt% of a dispersant, 0.1 to 0.5 wt% of an antifoamer, 1 to 3 wt% of a binder, 1 to 3 wt% of a release agent, and 2 to 4 wt% of a plasticizer; a de-binding step of heat-treating the green molded body to remove components excluding the solid content; and a sintering step of sintering the molded body after the de-binding step to manufacture alumina ceramics.

[0016] In addition, a method for manufacturing alumina ceramics is provided, wherein the above-mentioned debinding step is a step of heat treatment in an oxidizing atmosphere containing water vapor.

[0017] In addition, a method for manufacturing alumina ceramics is provided, wherein an oxidizing atmosphere containing water vapor is obtained by introducing air or oxygen into a heat treatment furnace after passing it through a water bath in which water is stored.

[0018] In addition, a method for manufacturing alumina ceramics is provided, wherein the above-mentioned debinding step comprises a step of increasing the temperature to 600°C at a rate of 1 to 2°C per minute, a step of maintaining the temperature at 600°C for 30 minutes to 1 hour, a step of increasing the temperature to 1000°C at a rate of 3 to 4°C per minute, and a step of maintaining the temperature at 1000°C for 2 to 4 hours.

[0019] In addition, a method for manufacturing alumina ceramics is provided, wherein the sintering step is carried out for 1.5 to 5 hours in an oxidizing atmosphere at 1465℃ to 1495℃.

[0020] The alumina ceramic composition for low-temperature sintering according to the present invention has the advantage of a lower sintering temperature compared to conventional alumina ceramic compositions. In addition, the alumina ceramic manufactured using the alumina ceramic composition for low-temperature sintering according to the present invention has the advantage of excellent processability.

[0021] FIG. 1 is a flowchart of a method for manufacturing an alumina ceramic composition for low-temperature sintering according to an embodiment of the present invention.

[0022] FIG. 2 is a flowchart of a method for manufacturing alumina ceramics according to an embodiment of the present invention.

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. However, embodiments of the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shapes of elements in the drawings are exaggerated to emphasize clearer explanations, and elements indicated by the same reference numeral in the drawings represent the same elements.

[0024] FIG. 1 is a flowchart of a method for manufacturing an alumina ceramic composition for low-temperature sintering according to an embodiment of the present invention.

[0025] As illustrated in FIG. 1, a method for manufacturing an alumina ceramic composition for low-temperature sintering includes a slurry composition manufacturing step (S1), a spray drying step (S2), and a mixing step (S3). The embodiment illustrated in FIG. 1 relates to a method for manufacturing an alumina ceramic composition for low-temperature sintering in powder form. When manufacturing an alumina ceramic composition for low-temperature sintering in slurry form, the spray drying step (S2) and the mixing step (S3) may be omitted.

[0026] The alumina ceramic composition for low-temperature sintering of the present invention is a general term for the mixed state of materials required to manufacture alumina ceramic products through low-temperature sintering, and includes all of the following: a composition in the form of a slurry, a composition in the form of a powder, a green sheet manufactured using a slurry, a green molded body using a slurry or powder, etc.

[0027] First, the step of preparing the slurry composition (S1) will be explained.

[0028] A slurry composition refers to a mixture in which solid particles constituting alumina ceramics are dispersed in a liquid medium. The slurry composition can be used in a molding process or a powder manufacturing process.

[0029] The slurry composition preparation step (S1) may include a primary raw material mixing step (S11) and a secondary raw material mixing step (S12).

[0030] The first raw material mixing step (S11) is a step of mixing alumina (Al2O3), talc, limestone, clay, potassium oxide (K2O), water, a dispersant, and an antifoaming agent. This step can be carried out using various methods such as ball milling, attrition milling, planetary milling, and jet milling. The following description is based on ball milling.

[0031] First, each raw material is weighed according to the mixing ratio. It is preferable that the mixing ratio of solids is 90 to 92.9 wt% alumina (Al2O3), 1 to 2 wt% talc, 3 to 4 wt% limestone, 3 to 4 wt% clay, and 0.1 to 0.5 wt% potassium oxide (K2O).

[0032] Alumina is a key material that provides heat resistance, mechanical strength, corrosion resistance, and electrical insulation. High-purity alumina with a purity of 99.5% or higher can be used as a raw material.

[0033] Talc acts as a sintering aid. If talc is insufficient, the sintering temperature increases, and the density of the sintered body may decrease. Additionally, processability may be reduced. If the talc content is excessive, unnecessary phases may form, leading to a decrease in the uniformity and density of the sintered body. Furthermore, the material may be easily damaged during processing.

[0034] Limestone acts as a sintering aid, lowering the sintering temperature and promoting the sintering of alumina. If the limestone content is insufficient, the sintering temperature may rise and the sintering rate may slow down. Consequently, if sintering does not occur sufficiently, a sintered body with low density may be formed. Conversely, if there is too much limestone, an excessive liquid phase may form, preventing proper bonding between alumina particles during sintering. This not only reduces the mechanical strength of the product but can also cause excessive shrinkage or warping.

[0035] Clay acts as a binder, plasticizer, and sintering aid in ceramic compositions. It enhances the plasticity of ceramic raw materials, facilitating molding. Furthermore, clay strengthens the bonding between material particles during molding, helping to prevent damage to the molded body. In particular, it serves as a protective measure against cracking during the drying process. Additionally, clay lowers the sintering temperature and promotes the densification of the sintered ceramic body by facilitating the bonding between key components, such as alumina, during the process.

[0036] If the clay content is insufficient, plasticity decreases, making molding difficult. The molded body may easily break or deform, and the density may become uneven during compression molding. Cracks may easily occur in the molded body during drying, and the probability of cracking or deformation during firing increases. During sintering, insufficient bonding between raw material particles may result in the formation of a sintered body with many pores and low density.

[0037] Conversely, an excessive amount of clay can lead to excessive shrinkage during sintering. This can cause dimensional changes or warping of the sintered body, potentially distorting the shape of the final product. In particular, as clay content increases, moisture content rises and shrinkage during drying increases, posing a significant risk of deformation to the molded body. Furthermore, excessive clay content can cause the product to become too soft after sintering, potentially reducing mechanical strength. Additionally, since clay releases a large amount of gas during sintering, excessive pore formation may occur within the sintered body. This lowers the density of the sintered body and reduces its strength and durability.

[0038] Potassium oxide plays an important role as a sintering aid. During sintering, potassium oxide forms a glass phase, which strengthens the bonds between alumina particles. If it is insufficient, the sintering temperature may rise, and sintering may not proceed smoothly. Conversely, if it is included in excess, an excessive amount of glass phase may form during sintering, which can lead to a decrease in strength.

[0039] The mixing ratio of non-solids is preferably 0.5 to 1.5 parts by weight of dispersant and 0.1 to 0.5 parts by weight of defoamer based on 100 parts by weight of solids. The water content may vary depending on the application of the slurry. If used in a process such as slip casting, the water content can be adjusted so that the solid content is 40 to 50% by weight; if used in a spray drying or tape casting process, the water content can be adjusted so that the solid content is 50 to 60% by weight; and if used in a process such as compression molding or extrusion molding, the water content can be adjusted so that the solid content is 60 to 70% by weight.

[0040] Dispersants adsorb onto the surface of particles to impart a charge or cause electrostatic repulsion between particles, thereby preventing the particles from clumping together and allowing them to be uniformly dispersed. This maintains the stability of the slurry and enables the particles to be uniformly distributed.

[0041] Antifoaming agents prevent foam from forming in the slurry or quickly remove foam that has already formed.

[0042] The measured raw materials can be fed directly into the ball mill for mixing, or they can be mixed in advance using a pre-mixer before being fed into the ball mill.

[0043] A ball mill consists of a cylindrical drum and balls contained within it. As the drum rotates, the balls are pulled upward by rotational force and fall downward due to gravity. During this process, grinding occurs as the balls collide with the raw materials. The materials are ground or mixed through friction and impact between the balls and the raw materials.

[0044] The inner surface of the drum may be covered with an alumina liner of 95% or higher purity. The liner protects the inner wall of the drum and prevents contamination of the raw material.

[0045] Press-formed alumina balls with a diameter of about 40 mm and a purity of 92% or higher can be used.

[0046] It is preferable that the rotational speed of the ball mill be 24 to 32 rpm, and the ball milling time be 16 to 18 hours.

[0047] When the first raw material mixing step (S11) is completed, a slurry composition in which the raw materials are homogeneously mixed can be obtained.

[0048] Next, the second raw material mixing step (S12) is described. The second raw material mixing step (S12) is a step of further mixing by adding a binder, a release agent, and a plasticizer to the slurry composition that has undergone the first raw material mixing step (S11).

[0049] The second raw material mixing step (S12) can be carried out in the same ball mill after the first raw material mixing step (S11) is completed.

[0050] In this step (S12), a binder, a release agent, and a plasticizer are added to the slurry composition of the previous step (S11). Based on 100 parts by weight of solid content, 1 to 3 parts by weight of binder, 1 to 3 parts by weight of release agent, and 2 to 4 parts by weight of plasticizer are added.

[0051] Although all components, including the binder, can be added to the ball mill at once without distinguishing between the first and second stages of raw material mixing, it is preferable to add the binder later to ensure uniformity of mixing. If the binder is added at the beginning, the raw material particles may clump together, and mixing may be difficult due to excessively high viscosity.

[0052] In this step (S12), the binder can be added all at once, but it is preferable to add it in small increments.

[0053] Binders play a role in maintaining the strength and shape of the molded body and improving its processability. Suitable binders include polyvinyl alcohol (PVA) and carboxymethylcellulose (CMC). If the amount of binder is too small, the molded body may easily break or deform during molding; conversely, if the amount is too large, numerous pores may form after firing, resulting in a lower density of the sintered body. If the binder is not completely removed during the de-binder process, it may oxidize during firing, forming a reducing atmosphere that hinders the sintering of alumina.

[0054] A release agent (or lubricant) is a substance that reduces friction between the molded body and the mold during the molding process and helps the molded body separate easily from the mold.

[0055] Plasticizers penetrate between raw material particles, weakening the bonds between them and imparting flexibility to the material. This allows the molded body to deform easily under external pressure, enabling it to be formed into more complex shapes.

[0056] Ball milling can be performed for about 2 hours in the second raw material mixing step (S12).

[0057] It is preferable that the particle size distribution of solid particles included in the slurry composition that has undergone the second raw material mixing step (S12) satisfies D50 3.5 to 4.0 μm and D90 10.0 μm. It is preferable that the viscosity be 80 to 120 cP. The ball milling time in the second raw material mixing step (S12) can be adjusted to satisfy these conditions. The viscosity can also be adjusted through the content of the binder and plasticizer.

[0058] When the second raw material mixing step (S12) is completed, a degassing process to remove bubbles in the slurry composition may be additionally performed as needed. The degassing process may be carried out by methods such as vacuum degassing, stirring degassing, thermal degassing, centrifugal degassing, and pressure degassing.

[0059] The spray drying step (S2) is a step of drying the slurry composition to obtain fine powder. That is, it is a step of removing water, which is a solvent, from the low-temperature sintering alumina ceramic composition in slurry form to transform it into a low-temperature sintering alumina ceramic composition in powder form.

[0060] Spray drying is a process of producing powder by spraying a slurry composition in the form of fine droplets (liquid droplets) and then drying it using high-temperature gas.

[0061] In this step (S2), the slurry composition prepared in step S1 is sprayed in the form of fine droplets through a nozzle or atomizer. During this process, the slurry composition is sprayed like a fine mist, and the size of the droplets is controlled according to the type of atomizer. The size of the droplets is an important factor in determining the particle size distribution of the powder being manufactured. Drying begins as the sprayed droplets come into contact with high-temperature air or gas. The high-temperature air is maintained at approximately 150 to 300°C. In this high-temperature environment, the water, which is the solvent in the slurry composition, evaporates rapidly. The powder is separated from the air along the airflow through a cyclone separator or a filter system.

[0062] It is preferable that the average particle size of the powder produced through this step (S2) is 40 to 80㎛, the specific gravity is 1.14 to 1.34 g / cm³, the fluidity is 4.5 to 9.5 g / sec, and the moisture content is 0.2 to 0.6 weight%.

[0063] Next, the mixing step (S3) is described.

[0064] In this step (S3), the manufactured powder is mixed using a mixing device, for example, a V mixer. This step (S3) serves to increase the uniformity of the powder. This step may be carried out for about 15 to 30 minutes. After this step (S3), a homogeneous powder form of an alumina ceramic composition for low-temperature sintering can be obtained.

[0065] This powder-form alumina ceramic composition for low-temperature sintering can be used for other forms of alumina ceramic compositions for low-temperature sintering, such as in the manufacture of green molded bodies.

[0066] FIG. 2 is a flowchart of a method for manufacturing alumina ceramics according to an embodiment of the present invention. As shown in FIG. 2, the method for manufacturing alumina ceramics according to an embodiment of the present invention includes a step of manufacturing a green molded body (S101), a debinding step (S102), and a sintering step (S103).

[0067] First, the step (S101) of manufacturing a green molded body is described.

[0068] This step may be a step of manufacturing a green molded body using a powder-form alumina ceramic composition for low-temperature sintering, prepared by the method for manufacturing the alumina ceramic composition for low-temperature sintering shown in FIG. 1.

[0069] A green molded material can be manufactured by applying pressure after introducing a powdered alumina ceramic composition for low-temperature sintering into a mold. Pressure molding methods include vertical pressure molding, which applies pressure from the top and bottom of the mold using a mechanical or hydraulic press, or hot or cold isostatic pressing, which applies uniform pressure from multiple directions using a fluid.

[0070] In addition, if a green molded body in the form of a plate or sheet is required, a green sheet can be manufactured by a tape casting method using a slurry composition, and after separating the green sheet from the tape, the green sheet can be laminated to a desired thickness and then compressed to manufacture the green molded body.

[0071] Next, the removal binder step (S102) is described.

[0072] This step (S102) is a step for removing organic materials such as dispersants, defoamers, binders, lubricants, and plasticizers contained within the green molded body. These organic materials serve to bind raw material particles so that the green molded body can maintain its shape, but they must be removed before final sintering. If organic materials remain during the sintering stage, they decompose by combining with oxygen, forming a reducing atmosphere, which can reduce the sintering density.

[0073] This step (S102) can be carried out using a batch or continuous heat treatment furnace. The debinding step can be carried out in an oxidizing atmosphere, for example, in air.

[0074] This step (S102) may include a step of gradually increasing the temperature to 600°C at a rate of 1 to 2°C per minute, a step of maintaining the temperature at 600°C for 30 minutes to 1 hour, a step of increasing the temperature to 1000°C by increasing the rate of increase to 3 to 4°C per minute, and a step of maintaining the temperature at 1000°C for 2 to 4 hours. Most organic matter is removed during the step of maintaining at 600°C, and residual carbon is removed during the step of maintaining at 1000°C.

[0075] This step (S102) may be carried out in an atmosphere containing steam. An atmosphere containing steam can be obtained by passing air or oxygen through a water tank containing water and then introducing it into a continuous or batch heat treatment furnace.

[0076] The water bath is a constant temperature water bath that maintains a constant water temperature. Gas supplied through an inlet formed at the bottom of the water bath creates bubbles, passes through the water stored in the bath, is discharged through an outlet formed at the top of the water bath, and is then supplied into the interior of the heat treatment furnace through an atmosphere gas supply pipe. At this time, it is necessary to heat the atmosphere gas supply pipe with a heater to prevent condensation of water vapor. The amount of water vapor contained in the gas passing through the water bath increases as the temperature of the water stored in the bath increases.

[0077] Steam is particularly advantageous for effectively removing residual carbon that may remain inside molded greens as organic matter decomposes. Using steam effectively removes residual carbon not only from the surface of the molded green but also from within.

[0078] Next, the sintering step (S103) is described.

[0079] This step (S103) can be carried out following the debinding step in the heat treatment furnace where the debinding step (S102) was carried out. This step (S103) can be carried out for 1.5 to 5 hours in an oxidizing atmosphere of 1465°C to 1495°C, which is about 100°C lower than the sintering temperature of a typical Grade 95 alumina.

[0080] It is preferable that the density of the alumina ceramic sintered body obtained in this step (S103) be 3.65 g / cm³ or higher.

[0081] The debinding step (S102) and the sintering step (103) may be carried out in separate heat treatment furnaces. Although carrying them out separately has the disadvantage that the process becomes more complex and the molded body weakened after debinding may break during transport, it has the advantage of preventing the gas generated during the debinding step (S102) from being completely removed and affecting the sintering step (103).

[0082] Although the present invention has been described above, the scope of protection of the present invention is limited only by the matters described in the claims, and a person skilled in the art may modify and change the technical concept of the present invention in various forms. Accordingly, such modifications and changes will fall within the scope of protection of the present invention insofar as they are obvious to a person skilled in the art.

Claims

1. Alumina ceramic composition for low-temperature sintering comprising 90 to 92.9 wt% alumina (Al2O3), 1 to 2 wt% talc, 3 to 4 wt% limestone, 3 to 4 wt% clay, and 0.1 to 0.5 wt% potassium oxide (K2O).

2. In Paragraph 1, A low-temperature sintering alumina ceramic composition further comprising, based on 100 parts by weight of solid content, 0.5 to 1.5 parts by weight of a dispersant, 0.1 to 0.5 parts by weight of an antifoaming agent, 1 to 3 parts by weight of a binder, 1 to 3 parts by weight of a release agent, and 2 to 4 parts by weight of a plasticizer.

3. A method for manufacturing an alumina ceramic composition for low-temperature sintering, A solid content comprising 90 to 92.9 wt% alumina (Al2O3), 1 to 2 wt% talc, 3 to 4 wt% limestone, 3 to 4 wt% clay, and 0.1 to 0.5 wt% potassium oxide (K2O), and A method for preparing an alumina ceramic composition for low-temperature sintering, comprising the step of preparing a slurry composition by mixing 0.5 to 1.5 parts by weight of a dispersant, 0.1 to 0.5 parts by weight of an antifoaming agent, 1 to 3 parts by weight of a binder, 1 to 3 parts by weight of a release agent, and 2 to 4 parts by weight of a plasticizer, based on 100 parts by weight of solid content.

4. In Paragraph 3, The particle size distribution of the solid particles included in the above slurry composition satisfies D50 3.5 ~ 4.0㎛ and D90 10.0㎛, and A method for preparing an alumina ceramic composition for low-temperature sintering, wherein the viscosity of the above slurry composition is 80 to 120 cP.

5. In Paragraph 3, A method for manufacturing an alumina ceramic composition for low-temperature sintering, further comprising the step of spraying the above slurry composition in the form of fine droplets and then drying it using a high-temperature gas to produce a powder.

6. In Paragraph 5, A method for manufacturing a low-temperature sintering alumina ceramic composition having an average particle size of 40 to 80 μm, a specific gravity of 1.14 to 1.34 g / cm³, a fluidity of 4.5 to 9.5 g / sec, and a moisture content of 0.2 to 0.6 wt% of the above powder.

7. A method for manufacturing alumina ceramics, A step of manufacturing a green molded body comprising a solid content comprising 90 to 92.9 wt% alumina (Al2O3), 1 to 2 wt% talc, 3 to 4 wt% limestone, 3 to 4 wt% clay, and 0.1 to 0.5 wt% potassium oxide (K2O), and, based on 100 wt% of the solid content, 0.5 to 1.5 wt% of a dispersant, 0.1 to 0.5 wt% of an antifoamer, 1 to 3 wt% of a binder, 1 to 3 wt% of a release agent, and 2 to 4 wt% of a plasticizer. A debinding step in which the above green molded body is heat-treated to remove components excluding the solid components, and A method for manufacturing alumina ceramics comprising a sintering step of sintering a molded body that has undergone a debinding step to produce alumina ceramics.

8. In Paragraph 7, The above-mentioned binder step is, A method for manufacturing alumina ceramics, comprising a step of heat treatment in an oxidizing atmosphere containing water vapor.

9. In Paragraph 8, A method for manufacturing alumina ceramics by introducing an oxidation atmosphere containing water vapor into a heat treatment furnace after passing air or oxygen through a water bath in which water is stored.

10. In Paragraph 8, The above-mentioned binder step is, A step of increasing the temperature to 600℃ at a rate of 1 to 2℃ per minute, and A step of maintaining at 600℃ for 30 minutes to 1 hour, and A step of increasing the temperature to 1000℃ at a rate of 3 to 4℃ per minute, and A method for manufacturing alumina ceramics comprising the step of maintaining at 1000℃ for 2 to 4 hours.

11. In Paragraph 8, A method for manufacturing alumina ceramics in which the above sintering step is carried out for 1.5 to 5 hours in an oxidizing atmosphere at 1465℃ to 1495℃.

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