A method for producing a high-purity alumina fiber-reinforced alumina composite

Abstract

The application discloses a preparation method of high-purity alumina fiber reinforced alumina composite material, which comprises the following steps: adding short-cut alumina fibers into water, adding a small amount of acid, and using high-purity alumina balls for rolling grinding; then adding high-purity nano-alumina dispersion liquid, continuously adding aluminum sol, fully dispersing the mixture, and performing spray drying to obtain alumina fiber reinforced alumina composite powder; the composite powder is subjected to dry pressing and isostatic pressing, and then ceramic balls with a diameter of 5-30 mm are prepared; and finally, high-temperature sintering is performed. The fiber powder is a fiber under a microscope and a powder under a macroscopic view, is more easily formed into a ball, and has a greatly increased toughness after use; the nano-alumina powder has excellent sintering activity, can be sintered at a lower temperature, and has better toughness because alumina grains are not easily grown; the aluminum sol has low-temperature sintering property, can bond the powder and the fiber, and finally generates alumina after high-temperature sintering, and has no impurities and high yield.

Description

Technical Field

[0001] This invention relates to the field of alumina composite ceramic sphere technology, and more specifically to a method for preparing a high-purity alumina fiber-reinforced alumina composite material. Background Technology

[0002] Alumina ceramic balls are a common grinding medium widely used in the mining, ceramics, and new energy fields. There are various methods for their preparation, such as dry pressing, isostatic pressing, rolling, titration, emulsion, flame method, and plasma method. Different methods are required to prepare alumina ceramic balls with different diameter requirements, but balls prepared by all methods must possess common characteristics: wear resistance and non-breakability.

[0003] Ordinary alumina ceramic balls, when supplemented with sintering aids or reinforcing phases such as magnesium oxide and zirconium oxide, exhibit relatively high wear resistance. High-purity alumina balls, however, cannot contain additives, are relatively brittle, have poor toughness, and consequently, poor wear resistance. Currently, the preparation or use of high-purity nano-alumina necessitates the use of high-purity ceramic balls as grinding media. The wear resistance of these ceramic balls significantly impacts the powder's properties; therefore, it is essential to improve the toughness and wear resistance of the ceramic balls.

[0004] Alumina fiber, as a reinforcing agent, has been widely used in the aerospace field to improve the wear resistance of ceramics. This composite material often uses continuous or chopped fibers as reinforcement. The preparation of this composite material is costly, time-consuming, and involves complex operating conditions, resulting in high costs. It is generally used for large structural components and has not yet been applied to the preparation of ceramic spheres.

[0005] Therefore, in order to solve the above problems, the present invention is thus developed. Summary of the Invention

[0006] In view of at least one of the above-mentioned technical problems, the purpose of this invention is to provide a method for preparing high-purity alumina fiber-reinforced alumina composite material.

[0007] The technical solution of this invention is:

[0008] The purpose of this invention is to provide a method for preparing high-purity alumina fiber-reinforced alumina composite material, comprising the following steps:

[0009] Short-cut alumina fibers are added to water, along with a small amount of acid, and then rolled using high-purity alumina balls.

[0010] Then, high-purity nano-alumina dispersion is added, followed by aluminum sol. After the mixture is fully dispersed, it is spray-dried to obtain alumina fiber-reinforced alumina composite powder. The composite powder is then dry-pressed and isostatically pressed to prepare ceramic balls of 5-30 mm. The ceramic balls are then sintered at high temperature to finally obtain the high-purity alumina fiber-reinforced alumina composite material.

[0011] Preferably, the chopped alumina fiber has an alumina content of 99% and a length of 3-5 cm.

[0012] Preferably, the mass ratio of the chopped alumina fibers to water is 2:8-5:5.

[0013] Preferably, the high-purity nano-alumina dispersion has a solid content of 30%-70%, an alumina particle size D50 of 100nm-500nm, and a purity higher than 99.9%.

[0014] Preferably, the aluminum sol has a purity higher than 99.9%, a particle size of 10nm-100nm, and accounts for 5%-10% of the total mass.

[0015] Preferably, the alumina powder and the chopped alumina fibers in the high-purity nano-alumina dispersion account for 30%-50% of the total mass, and the ratio of the chopped alumina fibers to the alumina powder in the high-purity nano-alumina dispersion is 1:1-1:3.

[0016] Preferably, the high-temperature sintering temperature is 1100℃-1400℃.

[0017] Preferably, the acid is a sulfur-free and / or halogen-free acid, and the amount of acid is based on the system pH value reaching 4.

[0018] Preferably, the acid is nitric acid, acetic acid, or lactic acid.

[0019] Preferably, the tumbling time is 2h-48h.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] This invention discloses a method for preparing high-purity alumina fiber-reinforced alumina composite material. To reduce the preparation time and cost of the composite material, this invention uses chopped alumina fibers, which are ground into powder. Using fiber powder, the fibers remain fibrous at the microscopic level, providing reinforcement. Furthermore, the powder is easier to mix with alumina powder, and the interfacial bonding is easier to handle. In contrast, existing technologies that directly use chopped alumina fibers for reinforcement face greater difficulties in interfacial bonding and molding. The preparation method of this invention significantly reduces preparation time and cost, and does not add other oxides such as magnesium oxide or zirconium oxide, nor sintering aids, resulting in higher purity and the absence of other impurities. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0023] Figure 1 This is the state of the ceramic spheres prepared in Example 1 under a microscope;

[0024] Figure 2 This is the state of the short-cut alumina fibers after they were ground into powder in Example 1, as shown under SEM.

[0025] Figure 3 This is a SEM image of the nano-alumina powder in the high-purity nano-alumina dispersion used in Example 1. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0027] A method for preparing a high-purity alumina fiber-reinforced alumina composite material according to an embodiment of the present invention, see [link to relevant documentation]. Figures 1 to 3 Short-cut alumina fibers (3cm-5cm) with an alumina content of 99% were used. These fibers were added to water with a small amount of acid and then tumbled using high-purity alumina balls for 2-48 hours. The mass ratio of the short-cut alumina fibers to water was 2:8-5:5. A high-purity nano-alumina dispersion with a solid content of 30%-70% was then added to the mixture of the tumbled alumina fibers and water. The alumina particle size D... 50The particle size is 100nm-500nm, and the purity is higher than 99.9%. Alumina sol with a purity higher than 99.9% and a particle size of 10nm-100nm is added, making the aluminum sol account for 5%-10% of the total mass. Alumina powder (alumina powder in high-purity nano alumina dispersion, the same below) and fiber powder (formed by tumbling short alumina fibers, the same below) account for 30%-50% of the total mass, and the ratio of fiber to alumina powder is 1:1-1:3. After the above mixture is fully dispersed, it is spray-dried to obtain an alumina fiber-reinforced alumina composite powder. The powder is then dry-pressed and isostatically pressed to prepare ceramic balls with a particle size of 5nm-30mm. The ceramic balls are then sintered at a high temperature of 1100℃-1400℃ to finally obtain alumina fiber-reinforced alumina ceramic balls, which is the alumina fiber-reinforced alumina composite material of the present invention.

[0028] According to some preferred embodiments of the present invention, the acid added to the chopped alumina fibers before tumbling is intended to improve the dispersion of the chopped alumina fibers with the high-purity nano-alumina dispersion and to enhance the gel-sol state of the alumina sol. More preferably, to ensure better dispersion and gel-sol state, the amount of acid in the embodiments of the present invention is based on a system pH of 4. The applicant has found that dispersion effects are less pronounced at pH values ​​higher or lower than 4 compared to pH 4. Even more preferably, to ensure the high purity of the final composite material, the acid added to the chopped alumina fibers before tumbling should preferably be a sulfur- and / or halogen-free acid, such as nitric acid, acetic acid, or lactic acid. Such acids do not introduce new impurities, which is beneficial to the purity of the final alumina fiber-reinforced alumina composite material.

[0029] In summary, compared with ordinary ceramic balls, the composite material obtained in this embodiment of the invention, i.e., ceramic balls, uses chopped alumina fiber powder as toughening agent, which significantly increases the toughness of the final ceramic balls. The main reason why ceramic balls are not wear-resistant is their insufficient toughness, and the fragments are easily detached during impact. Using chopped alumina fibers can solve this problem. At the same time, nano-alumina powder has excellent sintering activity, allowing for sintering at lower temperatures. The alumina grains are less likely to grow, resulting in better toughness. Alumina sol acts as a binder, possessing low-temperature sintering properties, and simultaneously binds the powder and chopped alumina fibers together. Finally, high-temperature sintering generates alumina again, free of impurities, resulting in a high ceramic yield. The chopped alumina fibers are ground into powder in a ball mill. At the microscopic level, they are fibers, providing toughening; at the macroscopic level, they are powders, which are easier to combine with the powder in the high-purity nano-alumina dispersion, making it easier to form spheres. Example 1

[0030] Short-cut alumina fibers (3cm-5cm) with an alumina content of 99% were used. These fibers were added to water with a small amount of nitric acid and milled using high-purity alumina balls for 24 hours. The fiber-to-water mass ratio was 1:3. A high-purity nano-alumina dispersion (50% solids, 100nm D50, and over 99.9% purity) was added to the fiber-water mixture. Alumina sol (over 99.9% purity, 50nm particle size) was also added, resulting in an alumina sol comprising 5% of the total mass, and alumina powder and fibers comprising 50% of the total mass, with a fiber-to-alumina powder ratio of 1:3. After thorough dispersion, the mixture was spray-dried to obtain an alumina fiber-reinforced alumina composite powder. This powder was then dry-pressed and isostatically pressed to prepare 8mm ceramic balls. These balls were sintered at 1200℃ to obtain alumina fiber-reinforced alumina ceramic balls. Figure 1 As shown, its true density is 3.88 g / cm³. 3 The ball was self-milled in a planetary ball mill at 200 rpm in water for 24 hours with a loss of only 0.5%. Example 2

[0031] Short-cut alumina fibers (3cm-5cm) with an alumina content of 99% were used. These fibers were added to water with a small amount of nitric acid. The fibers were not ground into powder; instead, they were directly mixed with water to form a 1:3 fiber-to-water mixture. A high-purity nano-alumina dispersion (50% solids, 100nm D50, and over 99.9% purity) was added. Alumina sol (over 99.9% purity, 50nm particle size) was also added, resulting in a mixture where the alumina sol comprised 5% of the total mass, and the alumina powder and fibers comprised 50%, with a fiber-to-alumina powder ratio of 1:3. After thorough dispersion and drying, an alumina fiber-reinforced alumina composite powder was obtained. This powder was then dry-pressed and isostatically pressed to prepare 8mm ceramic spheres. These spheres were sintered at 1200℃ to obtain alumina fiber-reinforced alumina ceramic spheres. However, the true density of these spheres was only 3.7g / cm³. 3 The ball was self-milled in a planetary ball mill at 200 rpm in water for 24 hours, resulting in a loss of up to 22%. This indicates that if the alumina fibers are not ground into powder, the interfacial bonding between the fibers and the high-purity nano-alumina powder is poor, making molding relatively difficult and the prepared ceramic balls difficult to sinter. Example 3

[0032] A high-purity nano-alumina dispersion was used as the sole source of alumina powder. This dispersion had a solid content of 50%, an alumina particle size (D50) of 100 nm, and a purity higher than 99.9%. Alumina sol, also with a purity higher than 99.9% and a particle size of 50 nm, was added, bringing the sol's total mass to 5%. After thorough dispersion and drying, an alumina fiber-reinforced alumina composite powder was obtained. This powder was then dry-pressed and isostatically pressed to prepare 8 mm ceramic spheres. These spheres were sintered at 1200℃ to obtain alumina fiber-reinforced alumina ceramic spheres. However, the true density of these spheres was only 3.88 g / cm³. 3 The ball was self-milled in a planetary ball mill at 200 rpm in water for 24 hours, and the loss was as high as 5%. This indicates that although the density can be achieved by using only alumina sintered balls without adding alumina fiber powder as toughening, the toughness is poor and the wear is high.

[0033] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for preparing a high-purity alumina fiber-reinforced alumina composite material, characterized in that, Includes the following steps: Short alumina fibers with a length of 3-5cm are added to water, along with a small amount of acid, and then tumbled using high-purity alumina balls. Then, a high-purity nano-alumina dispersion is added, wherein the ratio of the chopped alumina fibers to the alumina powder in the high-purity nano-alumina dispersion is 1:1-1:

3. Alumina sol is then added to fully disperse the mixture. After spray drying, alumina fiber-reinforced alumina composite powder is obtained. The composite powder is then dry-pressed and isostatically pressed to prepare ceramic balls of 5-30 mm. The ceramic balls are then sintered at high temperature to finally obtain the high-purity alumina fiber-reinforced alumina composite material.

2. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The chopped alumina fibers contain 99% alumina.

3. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The mass ratio of the chopped alumina fibers to water is 2:8-5:

5.

4. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The high-purity nano-alumina dispersion has a solid content of 30%-70% and an alumina particle size D. 50 The wavelength range is 100nm-500nm, and the purity is higher than 99.9%.

5. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The aluminum sol has a purity of over 99.9% and a particle size of 10nm-100nm, and the aluminum sol accounts for 5%-10% of the total mass.

6. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The alumina powder and the short-cut alumina fibers in the high-purity nano-alumina dispersion account for 30%-50% of the total mass.

7. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The high-temperature sintering temperature is 1100℃-1400℃.

8. The method for preparing high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The acid is a sulfur-free and / or halogen-free acid, and the amount of acid is based on the system pH value reaching 4.

9. A method for preparing a high-purity alumina fiber-reinforced alumina composite material according to claim 1 or 8, characterized in that, The acid mentioned is nitric acid, acetic acid, or lactic acid.

10. The method for preparing a high-purity alumina fiber-reinforced alumina composite material according to claim 1, characterized in that, The tumbling time is 2h-48h.

Images