99 alumina structural ceramics and methods for making the same

Abstract

The application provides a 99 alumina structural ceramic, and solves the problems of performance reduction of ceramic products, high cost, and large loss of kiln and kiln furniture caused by high-temperature sintering. The 99 alumina structural ceramic comprises the following raw materials: alumina, magnesium oxide, silicon oxide and rare earth oxide; the alumina comprises flaky alumina, and the content of the flaky alumina is greater than 0 and less than or equal to 20% based on the total mass of the 99 alumina structural ceramic raw materials. The cooperation between the above 99 alumina structural ceramic raw materials is beneficial to reducing the sintering temperature to reduce the cost and the loss of the kiln and the kiln furniture; and the obtained 99 alumina structural ceramic product has high fracture toughness and strength.

Description

Technical Field

[0001] This application relates to the field of ceramic technology, specifically to a 99% alumina structural ceramic and its preparation method. Background Technology

[0002] Currently, 99% alumina structural ceramics typically require sintering at relatively high temperatures (≥1750℃). High-temperature sintering can lead to grain growth, resulting in a decline in the performance of ceramic products. Furthermore, excessively high sintering temperatures result in higher energy costs and greater wear and tear on kilns and kiln furniture. Summary of the Invention

[0003] In view of this, the present application provides a 99% alumina structural ceramic, which solves the problems of decreased ceramic product performance, high cost, and large wear and tear on kilns and kiln furniture caused by high-temperature sintering.

[0004] The first aspect of this application provides a 99% alumina structural ceramic, which comprises the following raw materials:

[0005] Aluminum oxide, magnesium oxide, silicon oxide, and rare earth oxides;

[0006] Alumina includes lamellar alumina, and based on the total mass of 99% alumina structural ceramic raw materials, the content of lamellar alumina is greater than 0 and less than or equal to 20%.

[0007] Furthermore, based on the total mass of the 99% alumina structural ceramic raw material, the content of lamellar alumina is 13-17%, preferably 15%.

[0008] Furthermore, the particle size of the flake-shaped alumina is 1–2 μm;

[0009] Preferably, the height-to-length ratio of the sheet-like alumina is 1:(8-12).

[0010] Furthermore, rare earth oxides include lanthanum oxide and yttrium oxide.

[0011] Furthermore, alumina comprises bulk alumina and lamellar alumina, and 99% alumina structural ceramics comprise the following raw materials by mass percentage:

[0012] The main component is 79-94% alumina, 5-20% lamellar alumina, 0.2-0.4% magnesium oxide, 0.2-0.4% silicon oxide, 0.1-0.3% lanthanum oxide, and 0.1-0.3% yttrium oxide.

[0013] Preferably, the 99% alumina structural ceramic comprises the following raw materials in weight percentages: 84% main alumina, 15% lamellar alumina, 0.3% magnesium oxide, 0.3% silicon oxide, 0.2% lanthanum oxide, and 0.2% yttrium oxide.

[0014] A second aspect of this application provides a method for preparing the above-mentioned 99% alumina structural ceramic, the method comprising:

[0015] Alumina, magnesium oxide, silicon oxide and rare earth oxides are mixed and sintered to obtain 99 alumina structure ceramics.

[0016] Alumina includes lamellar alumina, and based on the total mass of 99% alumina structural ceramic raw materials, the content of lamellar alumina is greater than 0 and less than or equal to 20%.

[0017] Furthermore, the mixture of alumina, magnesium oxide, silicon oxide, and rare earth oxides is sintered, including:

[0018] Alumina, magnesium oxide, silicon oxide and rare earth oxides were mixed and then ball-milled to obtain a mixture;

[0019] The mixture is dried and granulated to obtain granulated powder;

[0020] The granulated powder was sintered to obtain 99% alumina structural ceramic.

[0021] Furthermore, the rare earth mixture includes lanthanum oxide and yttrium oxide, and the mixture of aluminum oxide, magnesium oxide, silicon oxide and rare earth oxides is subjected to ball milling, including:

[0022] Alumina, magnesium oxide, silicon oxide, lanthanum oxide and yttrium oxide are mixed and then ball-milled.

[0023] Preferably, alumina, magnesium oxide, silicon oxide, lanthanum oxide, and yttrium oxide are mixed with a solvent, a first dispersant, and a binder before being ball-milled.

[0024] Preferably, the solvent accounts for 45-55% of the total mass of the 99% alumina structural ceramic raw material;

[0025] Preferably, the mass of the first dispersant accounts for 0.5 to 1.5% of the total mass of the 99 alumina structural ceramic raw material;

[0026] Preferably, the mass of the binder accounts for 0.2 to 0.4% of the total mass of the 99 alumina structural ceramic raw material;

[0027] Preferably, the ball milling treatment time is 45–55 hours;

[0028] Preferably, the first dispersant comprises ammonium polyacrylate at a concentration of 14-16% and / or sodium polyacrylate at a concentration of 14-16%, and / or the binder comprises PVA.

[0029] Furthermore, after drying and granulating the mixture, and before sintering the granulated powder, the process also includes:

[0030] The granulated powder is subjected to aging and molding processes in sequence.

[0031] Preferably, the moisture content of the granulated powder is 0.4-0.6%;

[0032] Preferably, the aging process takes more than 18 hours;

[0033] Preferably, the molding process includes applying a unidirectional pressure of 140–160 MPa to the aged granulated powder;

[0034] Preferably, drying and granulating the mixture includes spray granulation;

[0035] Preferably, the sintering temperature is 1560–1590℃, the heating rate is 2–5℃ / min, and the holding time is 2–4h.

[0036] Furthermore, after ball milling the mixture of alumina, magnesium oxide, silicon oxide and rare earth oxides, and before drying and granulating the mixture, the method further includes: adding a second dispersant to the mixture, wherein the mass of the second dispersant accounts for 0.4 to 0.6% of the mass of the mixture;

[0037] Preferably, the second dispersant comprises ammonium polyacrylate at a concentration of 14-16%.

[0038] In the 99% alumina structural ceramic raw material of this application, magnesium oxide, alumina, and silicon oxide form a ternary liquid phase system of MgO-Al2O3-SiO2, while rare earth oxides form a solid phase system. The MgO-Al2O3-SiO2 ternary liquid phase system has a low eutectic temperature. During sintering, the liquid phase wets the solid phase system, and the rare earth oxides are free between the alumina particles. The large ion effect of the rare earth oxide solid solution hinders the abnormal growth of alumina grains, which is conducive to the escape of pores from the inside of the grains, making the pores smaller or eliminated. This is beneficial to improving the strength of the 99% alumina structural ceramic product, while also helping to reduce the sintering temperature to reduce costs and wear and tear on the kiln and kiln furniture. Using lamellar alumina raw material can deflect cracks generated during sintering, consume crack propagation energy to hinder crack propagation, and turn some intergranular fracture into transgranular fracture, further increasing energy loss and effectively improving the fracture toughness of the 99% alumina structural ceramic product. In addition, the MgO-Al2O3-SiO2 ternary liquid phase system can effectively wet and fill the gaps caused by the lamellar alumina, avoiding the influence of vacancies on the properties of the ceramic itself and increasing the strength of 99 alumina structural ceramics. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the process of sintering alumina, magnesium oxide, silicon oxide and rare earth oxides in related technologies.

[0040] Figure 2 The image shows a SEM image of the cross-section of the 99% alumina structure ceramic in Example 1.

[0041] Figure 3 The image shows the SEM image of the cross-section of the alumina ceramic in Comparative Example 4. Detailed Implementation

[0042] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0043] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In some instances, methods and means well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0044] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0045] Furthermore, the terms "first" and "second" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0046] The strong chemical bonds in Al2O3 necessitate sintering at very high temperatures (typically 1750℃). However, the resulting high temperatures lead to grain growth problems, resulting in ceramic products with poor performance and high production costs. To reduce production costs and achieve densified sintering to improve ceramic performance, the sintering temperature needs to be lowered. Currently, appropriate additives are typically added to the ceramic raw materials before sintering; however, these additives do not effectively improve the fracture toughness of the ceramic products.

[0047] Based on this, the first aspect of this application provides a 99% alumina structural ceramic, which comprises the following raw materials:

[0048] Aluminum oxide, magnesium oxide, silicon oxide, and rare earth oxides;

[0049] Alumina includes lamellar alumina, and based on the total mass of 99% alumina structural ceramic raw materials, the content of lamellar alumina is greater than 0 and less than or equal to 20%.

[0050] In the 99% alumina structural ceramic raw material of this application, magnesium oxide, alumina, and silicon oxide form a ternary liquid phase system of MgO-Al2O3-SiO2, while rare earth oxides form a solid phase system. The MgO-Al2O3-SiO2 ternary liquid phase system has a low eutectic temperature. During sintering, the liquid phase wets the solid phase system, and the rare earth oxides are free between the alumina particles. The large ion effect of the rare earth oxide solid solution hinders the abnormal growth of alumina grains, which is conducive to the escape of pores from the inside of the grains, making the pores smaller or eliminated. This is beneficial to improving the strength of the 99% alumina structural ceramic product, while also helping to reduce the sintering temperature to reduce costs and wear and tear on the kiln and kiln furniture. Using lamellar alumina raw material can deflect cracks generated during sintering, consume crack propagation energy to hinder crack propagation, and turn some intergranular fracture into transgranular fracture, reducing energy concentration and effectively improving the fracture toughness of the 99% alumina structural ceramic product. In addition, the MgO-Al2O3-SiO2 ternary liquid phase system can effectively wet and fill the gaps caused by the lamellar alumina, avoiding the influence of vacancies on the properties of the ceramic itself and increasing the strength of 99 alumina structural ceramics.

[0051] Compared to the content of lamellar alumina in this application, when the content of lamellar alumina accounts for more than 20% of the total mass of 99% alumina structural ceramic raw materials, a large number of vacancies are generated inside the ceramic, which prevents the liquid phase from completely filling them, ultimately affecting the product performance.

[0052] It should be noted that alumina includes bulk alumina and flake alumina. Bulk alumina includes industrial alumina with an average particle size of about 1 micrometer or α-alumina powder with an average particle size of about 1 micrometer.

[0053] In a preferred embodiment, based on the total mass of the 99% alumina structural ceramic raw material, the content of lamellar alumina is 13-17%, preferably 15%. This results in better energy dissipation and inhibition of crack propagation during sintering, and further improves the fracture toughness of the 99% alumina structural ceramic product.

[0054] In one embodiment, the particle size of the lamellar alumina is 1–2 μm. In a preferred embodiment, the particle size of the lamellar alumina is 1 μm. Therefore, lamellar alumina of this size allows for easier and more uniform mixing of the raw material components, resulting in better matching and avoiding the problem of large vacancies caused by large-sized lamellar alumina, leading to insufficient liquid phase filling. Compared to the aforementioned particle size of lamellar alumina, when the particle size is greater than 2 μm, the large-sized lamellar alumina creates large vacancies that the liquid phase system cannot fill, resulting in poor performance of the 99% alumina structural ceramic; when the particle size is less than 1 μm, the cost of lamellar alumina is high, which is not conducive to large-scale applications.

[0055] It should be noted that the particle size of flake alumina refers to the maximum distance between any two points on the surface of flake alumina.

[0056] In a preferred embodiment, the height-to-length ratio of the sheet-like alumina is 1:(8-12), for example, 1:8, 1:9, 1:10, 1:11, or 1:12. Therefore, the sheet-like alumina has a suitable size and is more effective at filling the voids created inside the ceramic.

[0057] It should be noted that the height-to-length ratio of sheet alumina refers to the thickness of the sheet alumina as the height, and the longest side of the cross-section perpendicular to the thickness as the length. For example, the cross-section perpendicular to the thickness is a square, and the side length of the square is the length; or, for example, the cross-section perpendicular to the thickness is a rectangle, and the longer side of the rectangle is the length.

[0058] In one embodiment, the rare earth oxides include lanthanum oxide and yttrium oxide. This results in a better large-ion effect in the dual rare earth oxide solid solution, which better hinders abnormal grain growth in alumina and reduces the firing temperature. Conversely, if other rare earth oxides, such as neodymium oxide, are used, the product color may change significantly or become uneven, leading to decreased customer acceptance.

[0059] In one embodiment, the alumina comprises a bulk alumina and lamellar alumina, and the 99 alumina structural ceramic comprises the following raw materials in weight percentages: 79-94% bulk alumina, 5-20% lamellar alumina, 0.2-0.4% magnesium oxide, 0.2-0.4% silicon oxide, 0.1-0.3% lanthanum oxide, and 0.1-0.3% yttrium oxide.

[0060] In a preferred embodiment, the 99% alumina structural ceramic comprises the following raw materials by mass percentage: 84% main alumina, 15% lamellar alumina, 0.3% magnesium oxide, 0.3% silicon oxide, 0.2% lanthanum oxide, and 0.2% yttrium oxide. This results in a better ratio of magnesium oxide, alumina, and silicon oxide, leading to the lowest melting point of the 99% alumina structural ceramic, which is beneficial for subsequent sintering. Furthermore, the sintered ceramic structure has smaller grains, resulting in optimal ceramic performance. Additionally, the lower sintering temperature also helps save costs and is suitable for large-scale production.

[0061] The second aspect of this application provides a method for preparing the above-mentioned 99% alumina structural ceramic, the method comprising: mixing alumina, magnesium oxide, silicon oxide and rare earth oxide and then sintering to obtain 99% alumina structural ceramic; the alumina includes lamellar alumina, and based on the total mass of the 99% alumina structural ceramic raw materials, the content of lamellar alumina is greater than 0 and less than or equal to 20%.

[0062] In one embodiment, a schematic diagram of the process of sintering a mixture of alumina, magnesium oxide, silicon oxide, and rare earth oxides is shown below. Figure 1 The process of sintering a mixture of alumina, magnesium oxide, silicon oxide, and rare earth oxides includes:

[0063] S100: A mixture of aluminum oxide, magnesium oxide, silicon oxide and rare earth oxides is ball-milled to obtain a mixture.

[0064] In one embodiment, the rare earth mixture includes lanthanum oxide and yttrium oxide. The ball milling process involves mixing aluminum oxide, magnesium oxide, silicon oxide, and rare earth oxides, and then performing a ball milling process.

[0065] In one embodiment, aluminum oxide, magnesium oxide, silicon oxide, lanthanum oxide, and yttrium oxide are mixed with a solvent, a first dispersant, and a binder before being ball-milled.

[0066] In one embodiment, the solvent accounts for 45-55% of the total mass of the 99% alumina structural ceramic raw material; the first dispersant accounts for 0.5-1.5% of the total mass of the 99% alumina structural ceramic raw material; and the binder accounts for 0.2-0.4% of the total mass of the 99% alumina structural ceramic raw material.

[0067] In one embodiment, the ball milling time is 45–55 hours; the first dispersant comprises ammonium polyacrylate at a concentration of 14–16% and / or sodium polyacrylate at a concentration of 14–16%; the binder comprises PVA (polyvinyl alcohol). Thus, the powder does not settle during the ball milling process, resulting in a homogeneous colloid product.

[0068] S200: The mixture is dried and granulated to obtain granulated powder.

[0069] In one embodiment, after ball milling the mixture of alumina, magnesium oxide, silicon oxide, and rare earth oxides, and before drying and granulating the mixture, the method further includes adding a second dispersant to the mixture, wherein the mass of the second dispersant accounts for 0.4 to 0.6% of the mass of the mixture. This adjusts the flowability of the mixture, facilitating uniform drying.

[0070] In one embodiment, the second dispersant comprises ammonium polyacrylate at a concentration of 14 to 16%, such as ammonium polyacrylate at a concentration of 14%, 15%, or 16%.

[0071] In one embodiment, after drying and granulating the mixture and before sintering the granulated powder, the process further includes: sequentially aging and molding the granulated powder; the moisture content of the granulated powder is 0.4–0.6%; and the aging time is greater than 18 hours. Thus, ensuring a moisture content of 0.4–0.6% (mass fraction) in the granulated powder after granulation enhances its plasticity, and aging for more than 18 hours promotes uniform moisture content among the granulated powder particles, resulting in a product with better consistency.

[0072] It should be noted that aging treatment refers to leaving the granulated powder for a certain period of time.

[0073] In one embodiment, drying and granulating the mixture includes spray granulation. In one specific embodiment, the granulated powder particles obtained after spray granulation are required to pass through a 60-mesh stainless steel sieve, but not a 300-mesh stainless steel sieve. Excessively large granulated powder particles will result in numerous pores in the product, while excessively small granulated powder particles will cause the ceramic product to be prone to cracking and deformation.

[0074] In one embodiment, the molding process includes applying a unidirectional pressure of 140–160 MPa (e.g., 140 MPa, 150 MPa, or 160 MPa) to the aged granulated powder. In a specific embodiment, a release agent with a mass fraction of 0.3% is added to the aged granulated powder before the molding process to prevent the molded product from sticking to the mold.

[0075] S300: The granulated powder is sintered to obtain 99% alumina structural ceramic.

[0076] In one embodiment, the sintering temperature is 1560–1590°C (e.g., 1560°C, 1570°C, 1580°C, or 1590°C), the heating rate is 2–5°C / min (e.g., 3°C / min, 4°C / min, or 5°C / min), and the holding time is 2–4 hours (e.g., 2 hours, 3 hours, or 4 hours). This results in a suitable sintering temperature, which helps save costs and reduces wear and tear on the kiln and kiln furniture. Within the above sintering temperature and time range, auxiliary components such as solvents, dispersants, and binders can be completely removed, resulting in smaller internal ceramic grains and better performance of the 99% alumina structure ceramic. However, with the above heating rate, if the heating rate exceeds 5°C / min, the excessively rapid firing rate can lead to problems such as cracking in the ceramic product. If the heating rate is below 25°C / min, the internal ceramic grains are larger, reducing product quality. Compared to the sintering time and sintering temperature mentioned above, if the sintering time is too long or the sintering temperature is too high, the internal grains of the ceramic will be larger, reducing product quality; if the sintering time is too short or the sintering temperature is too low, the ceramic will not be fully sintered, resulting in poor product quality.

[0077] It should be noted that the main alumina source is wide-ranging, as long as it meets the requirements. For example, the main alumina source can be Henan Tianma New Materials' CC series special ceramic ultrafine activated α-alumina, German Martin's α-alumina, or Henan Jiyuan Brothers' α-alumina.

[0078] The present application will be further described below with reference to specific embodiments. It should be noted that the following embodiments are only used to explain the present application and should not be construed as limiting the present application.

[0079] It should be noted that, unless otherwise specified, in the following examples and comparative examples, a Mastersizer 3000 laser particle size analyzer was used to observe the particle size and distribution of the slurry; the basket method was used to measure the bulk density of the ceramic products; the four-point bending method was used to measure the flexural strength of the ceramic products; and the indentation method specified in GB / T 37900-2019 was used to measure the fracture toughness of the ceramic products.

[0080] Example 1

[0081] 99% alumina structural ceramics comprise the following raw materials by weight percentage:

[0082] The alumina content is 94%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 5% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, with a height-to-length ratio of 1:10.

[0083] The preparation steps of 99% alumina structural ceramics are as follows:

[0084] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the 99% alumina structural ceramic raw material; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the 99% alumina structural ceramic raw material; and the binder PVA accounts for 0.3% of the total mass of the 99% alumina structural ceramic raw material.

[0085] The first step is to add all the above raw materials, dispersants, binders and solvents into a ball mill and ball mill for 48 hours to ensure that all components are fully mixed and homogeneous.

[0086] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0087] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0088] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0089] Fifth step: Pour the granulated powder into a metal mold, with a unidirectional pressure of 150 MPa;

[0090] Step 6: High-temperature firing, sintering temperature is 1580℃, and holding temperature for 2 hours.

[0091] The SEM (scanning electron microscope) image of the cross-section of the 99% alumina structural ceramic obtained in this embodiment is shown below. Figure 2 As shown.

[0092] Example 2

[0093] 99% alumina structural ceramics comprise the following raw materials by weight percentage:

[0094] The alumina content is 89%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 10% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, with a height-to-length ratio of 1:10.

[0095] The preparation steps of 99% alumina structural ceramics are as follows:

[0096] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the 99% alumina structural ceramic raw material; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the 99% alumina structural ceramic raw material; and the binder PVA accounts for 0.3% of the total mass of the 99% alumina structural ceramic raw material.

[0097] The first step is to add all the above raw materials, dispersants, binders and solvents into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0098] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0099] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0100] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0101] Fifth step: Pour the granulated powder into the metal mold, with a unidirectional pressure of 150 MPa;

[0102] Step 6: High-temperature firing, sintering temperature is 1580℃, and holding temperature for 2 hours.

[0103] Example 3

[0104] 99% alumina structural ceramics comprise the following raw materials by weight percentage:

[0105] The alumina content is 84%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 15% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, with a height-to-length ratio of 1:10.

[0106] The preparation steps of 99% alumina structural ceramics are as follows:

[0107] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the 99% alumina structural ceramic raw material; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the 99% alumina structural ceramic raw material; and the binder PVA accounts for 0.3% of the total mass of the 99% alumina structural ceramic raw material.

[0108] The first step is to add all the above raw materials, dispersants, binders and solvents into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0109] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0110] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0111] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0112] Fifth step: Pour the granulated powder into the metal mold, with a unidirectional pressure of 150 MPa;

[0113] Step 6: High-temperature firing, sintering temperature is 1580℃, and holding temperature for 2 hours.

[0114] Example 4

[0115] 99% alumina structural ceramics comprise the following raw materials by weight percentage:

[0116] The alumina content is 79%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 20% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, with a height-to-length ratio of 1:10.

[0117] The preparation steps of 99% alumina structural ceramics are as follows:

[0118] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the 99% alumina structural ceramic raw material; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the 99% alumina structural ceramic raw material; and the binder PVA accounts for 0.3% of the total mass of the 99% alumina structural ceramic raw material.

[0119] The first step is to add all the above raw materials, dispersants, binders and solvents into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0120] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0121] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0122] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0123] Fifth step: Pour the granulated powder into a metal mold, with a unidirectional pressure of 150 MPa;

[0124] Step 6: High-temperature firing, with a sintering temperature of 1580℃ and a holding time of 2 hours.

[0125] Example 5

[0126] In this embodiment, the 99% alumina structural ceramic comprises the following raw materials by mass percentage:

[0127] The alumina content is 94%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 5% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide; the flake alumina particle size is 3 micrometers, with a height-to-length ratio of 1:10.

[0128] The preparation method of 99% alumina structural ceramics is basically the same as in Example 1.

[0129] Example 6

[0130] In this embodiment, the 99% alumina structural ceramic comprises the following raw materials by mass percentage:

[0131] The alumina content is 94%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 5% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% neodymium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, with a height-to-length ratio of 1:10.

[0132] The preparation method of 99% alumina structural ceramics is basically the same as in Example 1.

[0133] Example 7

[0134] In this embodiment, the 99% alumina structural ceramic comprises the following raw materials by mass percentage:

[0135] The alumina content is 94.2%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 5% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, and 0.3% silicon oxide; the flake alumina has a particle size of 1 micrometer and a height-to-length ratio of 1:10.

[0136] The preparation method of 99% alumina structural ceramics is basically the same as in Example 1.

[0137] Example 8

[0138] In this embodiment, the 99% alumina structural ceramic comprises the following raw materials by mass percentage:

[0139] The alumina content is 94.2%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, which contains 5% flake alumina, 0.2% yttrium oxide, 0.3% magnesium oxide, and 0.3% silicon oxide; the flake alumina has a particle size of 1 micrometer and a height-to-length ratio of 1:10.

[0140] The preparation method of 99% alumina structural ceramics is basically the same as in Example 1.

[0141] Example 9

[0142] In this embodiment, the 99% alumina structural ceramic comprises the following raw materials by mass percentage:

[0143] The alumina content is 94.2%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, which contains 5% flake alumina, 0.2% neodymium oxide, 0.3% magnesium oxide, and 0.3% silicon oxide; the flake alumina has a particle size of 1 micrometer and a height-to-length ratio of 1:10.

[0144] The preparation method of 99% alumina structural ceramics is basically the same as in Example 1.

[0145] Comparative Example 1

[0146] Alumina ceramics comprise the following raw materials by weight percentage:

[0147] The alumina content is 99%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide.

[0148] The preparation steps of alumina ceramics are as follows:

[0149] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the alumina ceramic raw materials; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the alumina ceramic raw materials; and the binder PVA accounts for 0.3% of the total mass of the alumina ceramic raw materials.

[0150] The first step is to add the above raw materials, dispersant, binder and solvent into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0151] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0152] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0153] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0154] Fifth step: Pour the granulated powder into a metal mold, with a unidirectional pressure of 150 MPa;

[0155] Step 6: High-temperature firing, with a sintering temperature of 1580℃ and a holding time of 2 hours.

[0156] Comparative Example 2

[0157] Alumina ceramics comprise the following raw materials by weight percentage:

[0158] The alumina content is 99.2%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 0.2% lanthanum oxide, 0.2% magnesium oxide, 0.2% yttrium oxide, and 0.2% silicon oxide.

[0159] The preparation steps of alumina ceramics are as follows:

[0160] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the alumina ceramic raw materials; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the alumina ceramic raw materials; and the binder PVA accounts for 0.3% of the total mass of the alumina ceramic raw materials.

[0161] The first step is to add the above raw materials, dispersant, binder and solvent into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0162] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0163] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0164] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0165] Fifth step: Pour the granulated powder into a metal mold, with a unidirectional pressure of 150 MPa;

[0166] Step 6: High-temperature firing, with a sintering temperature of 1580℃ and a holding time of 2 hours.

[0167] Comparative Example 3

[0168] Alumina ceramics comprise the following raw materials by weight percentage:

[0169] The alumina content is 99.5%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 0.1% lanthanum oxide, 0.2% magnesium oxide, 0.1% yttrium oxide, and 0.1% silicon oxide.

[0170] The preparation steps of alumina ceramics are as follows:

[0171] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the alumina ceramic raw materials; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the alumina ceramic raw materials; and the binder PVA accounts for 0.3% of the total mass of the alumina ceramic raw materials.

[0172] The first step is to add the above raw materials, dispersant, binder and solvent into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0173] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0174] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0175] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0176] Fifth step: Pour the granulated powder into a metal mold, with a unidirectional pressure of 150 MPa;

[0177] Step 6: High-temperature firing, with a sintering temperature of 1580℃ and a holding time of 2 hours.

[0178] Comparative Example 4

[0179] Alumina ceramics comprise the following raw materials by weight percentage:

[0180] 100% alumina, using Henan Tianma New Materials CC series special ceramic ultrafine active α-alumina.

[0181] The preparation steps of alumina ceramics are as follows:

[0182] The preparation process requires solvents, dispersants, and binders. The solvent (deionized water) accounts for 50% of the total mass of the alumina ceramic raw materials; the dispersant ammonium polyacrylate accounts for 1% of the total mass of the alumina ceramic raw materials; and the binder PVA accounts for 0.3% of the total mass of the alumina ceramic raw materials.

[0183] The first step is to add alumina, dispersant, binder and solvent into a ball mill and ball mill for 48 hours to ensure that the components are fully mixed and uniform.

[0184] The second step is to pour the ball-milled slurry into the mixing tank to ensure the uniformity of the slurry;

[0185] The third step is spray granulation, which requires the moisture content of the granulated powder to be approximately 0.5%.

[0186] The fourth step is to put the granulated powder into the silo and age it for more than 18 hours;

[0187] Fifth step: Pour the granulated powder into a metal mold, with a unidirectional pressure of 150 MPa;

[0188] Step 6: High-temperature firing, with a sintering temperature of 1580℃ and a holding time of 2 hours.

[0189] The SEM image of the cross-section of the alumina ceramic obtained in this embodiment is shown below. Figure 3 As shown.

[0190] Comparative Example 5

[0191] Alumina ceramics comprise the following raw materials by weight percentage:

[0192] The alumina content is 74%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 25% flake alumina, 0.2% lanthanum oxide, 0.3% magnesium oxide, 0.2% yttrium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, with a height-to-length ratio of 1:10.

[0193] The preparation method of alumina ceramics is basically the same as in Example 1.

[0194] Comparative Example 6

[0195] Alumina ceramics comprise the following raw materials by weight percentage:

[0196] The alumina content is 94.4%, using the CC series special ceramic ultrafine active α-alumina from Henan Tianma New Materials, with 5% flake alumina, 0.3% magnesium oxide, and 0.3% silicon oxide; the flake alumina particle size is 1 micrometer, and the height-to-length ratio is 1:10.

[0197] The preparation method of alumina ceramics is basically the same as in Example 1.

[0198] The particle size, density, fracture toughness, and flexural strength of the ceramic products obtained in Examples 1-9 and Comparative Examples 1-6 are shown in Table 1 below:

[0199] Table 1

[0200]

[0201]

[0202] By comparing Examples 1-4 and Comparative Example 1, it can be seen that lamellar alumina can significantly increase the strength and fracture toughness of 99 alumina structural ceramics. Among them, the sample of Example 3 has the best performance. Specifically, the lamellar alumina can cause crack propagation during the fracture process.

[0203] Comparing Examples 1-3, it was found that the liquid phase could fill the gaps caused by the flake alumina, specifically, the density did not decrease and the product performance was significantly improved. Comparing Example 4 with Examples 1-3, it was found that a large amount of flake alumina would lead to a decrease in the density of the product, specifically, an increase in pores. The liquid phase components could not completely fill the gaps, and the pores had a fatal impact on the product performance.

[0204] Comparison of Comparative Examples 1 and 2-3 shows that fluctuations in the content of inorganic additives (including silicon oxide, lanthanum oxide, and yttrium oxide) affect the density and strength of alumina ceramics. Specifically, firstly, a decrease in the amount of inorganic additives leads to an increase in firing temperature; secondly, a decrease in the liquid phase results in more pronounced grain growth, leading to more closed pores. Porosity is the main reason for the decrease in ceramic density and strength.

[0205] Comparisons of Examples 1, 2, 3 and 4 show that the addition of inorganic additives can effectively reduce the firing temperature and increase the strength.

[0206] A comparison of Example 1 with Comparative Examples 1 and 4 shows that adding flake alumina can significantly reduce the firing temperature, increase strength, and improve fracture toughness.

[0207] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0208] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A 99% alumina structural ceramic, characterized in that, It is composed of the following raw materials: Aluminum oxide, magnesium oxide, silicon oxide, and rare earth oxides; The alumina comprises bulk alumina and lamellar alumina, and based on the total mass of the 99 alumina structural ceramic raw material, the content of the lamellar alumina is 15%; the particle size of the lamellar alumina is 1~2μm; and the height-to-length ratio of the lamellar alumina is 1:(8~12). The rare earth oxides include lanthanum oxide and yttrium oxide.

2. The 99% alumina structural ceramic according to claim 1, characterized in that, The 99% alumina structural ceramic comprises the following raw materials by mass percentage: The main body contains 84% ​​alumina, the flake alumina contains 15%, the magnesium oxide contains 0.2-0.4%, the silicon oxide contains 0.2-0.4%, the lanthanum oxide contains 0.1-0.3%, and the yttrium oxide contains 0.1-0.3%.

3. The 99% alumina structural ceramic according to claim 1, characterized in that, The 99% alumina structural ceramic comprises the following raw materials in weight percentages: 84% main alumina, 15% lamellar alumina, 0.3% magnesium oxide, 0.3% silicon oxide, 0.2% lanthanum oxide, and 0.2% yttrium oxide.

4. A method for preparing 99% alumina structural ceramic according to any one of claims 1 to 3, characterized in that, include: Alumina, magnesium oxide, silicon oxide and rare earth oxides are mixed and sintered to obtain the 99 alumina structure ceramic. The alumina comprises bulk alumina and lamellar alumina, and based on the total mass of the 99 alumina structural ceramic raw material, the content of the lamellar alumina is 15%. The rare earth oxides include lanthanum oxide and yttrium oxide.

5. The method for preparing 99% alumina structural ceramics according to claim 4, characterized in that, The process of mixing alumina, magnesium oxide, silicon oxide, and rare earth oxides and then sintering them includes: The alumina, magnesium oxide, silicon oxide and rare earth oxide are mixed and then ball-milled to obtain a mixture; The mixture is dried and granulated to obtain granulated powder; The granulated powder is sintered to obtain the 99 alumina structural ceramic.

6. The method for preparing 99% alumina structural ceramic according to claim 5, characterized in that, The alumina, magnesium oxide, silicon oxide, lanthanum oxide, and yttrium oxide are mixed with a solvent, a first dispersant, and a binder, and then subjected to ball milling.

7. The method for preparing 99% alumina structural ceramic according to claim 6, characterized in that, The solvent accounts for 45-55% of the total mass of the 99 alumina structural ceramic raw material.

8. The method for preparing 99% alumina structural ceramics according to claim 6, characterized in that, The mass of the first dispersant accounts for 0.5 to 1.5% of the total mass of the 99 alumina structural ceramic raw material.

9. The method for preparing 99% alumina structural ceramic according to claim 6, characterized in that, The mass of the binder accounts for 0.2 to 0.4% of the total mass of the 99% alumina structural ceramic raw material.

10. The method for preparing 99% alumina structural ceramic according to claim 6, characterized in that, The ball milling process takes 45 to 55 hours.

11. The method for preparing 99% alumina structural ceramic according to claim 6, characterized in that, The first dispersant comprises ammonium polyacrylate at a concentration of 14-16% and / or sodium polyacrylate at a concentration of 14-16%, and the binder comprises PVA.

12. The method for preparing 99% alumina structural ceramic according to any one of claims 5 to 11, characterized in that, After drying and granulating the mixture and before sintering the granulated powder, the process further includes: The granulated powder is subjected to aging and molding processes in sequence.

13. The method for preparing 99% alumina structural ceramic according to claim 12, characterized in that, The moisture content of the granulated powder is 0.4~0.6%.

14. The method for preparing 99% alumina structural ceramic according to claim 12, characterized in that, The aging process takes more than 18 hours.

15. The method for preparing 99% alumina structural ceramic according to claim 12, characterized in that, The molding process includes applying a unidirectional pressure of 140-160 MPa to the granulated powder after aging treatment.

16. The method for preparing 99% alumina structural ceramic according to claim 12, characterized in that, Drying and granulating the mixture includes spray granulation.

17. The method for preparing 99% alumina structural ceramic according to claim 5, characterized in that, The sintering temperature is 1560~1590℃, the heating rate is 2~5℃ / min, and the holding time is 2~4h.

18. The method for preparing 99% alumina structural ceramic according to any one of claims 5 to 11, characterized in that, After ball milling the mixture of alumina, magnesium oxide, silicon oxide and rare earth oxide, and before drying and granulating the mixture, the method further includes adding a second dispersant to the mixture, wherein the mass of the second dispersant accounts for 0.4 to 0.6% of the mass of the mixture.

19. The method for preparing 99% alumina structural ceramic according to claim 18, characterized in that, The second dispersant comprises ammonium polyacrylate at a concentration of 14-16%.

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