Alumina ceramic and its preparation method and application

Abstract

The present invention discloses an alumina ceramic, a preparation method thereof, and an application thereof. The present invention provides a preparation method of an alumina ceramic, comprising the following steps: (1) preparing raw materials according to a ratio based on the moisture content of alumina raw powder; (2) preparing a slurry by a first ball milling and a second ball milling to obtain a mixed slurry; (3) granulating the mixed slurry after adjusting the pH value, and dry-forming the slurry to obtain an alumina ceramic green body; (4) machining the alumina ceramic green body obtained in step (3) into a designed shape, and then transferring the green body to a high-temperature sintering furnace for sintering, and cooling the furnace to obtain the alumina ceramic. The present invention utilizes a dry forming and sintering process to prepare the alumina ceramic, thereby achieving an alumina ceramic product with good porcelain body density and flexural strength, thereby ensuring the quality of the alumina ceramic product.

Description

Technical Field

[0001] This invention relates to the field of alumina ceramics technology, specifically to an alumina ceramic, its preparation method, and its application. Background Art

[0002] Alumina ceramics are ceramic materials with alumina (Al2O3) as the main component. Due to their advantages such as high mechanical strength, high hardness, and good wear resistance, they are widely used in industries such as electronics, electrical machinery, chemical industry, textile industry, medical industry, automotive industry, metallurgy, and aerospace industry.

[0003] Currently, existing technologies for producing high-performance alumina ceramics involve preparing a mixed slurry from high-purity alumina powder, followed by ball milling, spray granulation, dry pressing, and sintering to obtain the final alumina ceramic product. A key characteristic of alumina ceramics is that their electromechanical properties improve with increasing alumina content. However, this improvement is accompanied by higher firing temperatures, posing challenges to the sintering process. Therefore, the key to producing high-performance alumina ceramics lies in the research of high-performance alumina granulated powder and a suitable sintering scheme. However, existing technologies produce alumina ceramics with poor body density and flexural strength, severely impacting product quality. Therefore, there is an urgent need to develop a sintering process for alumina ceramics with good body density and flexural strength, aiming to achieve high-performance alumina ceramics and lay a solid foundation for accelerating domestic production. Summary of the Invention

[0004] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide an alumina ceramic, its preparation method, and its application. This invention provides a method for preparing alumina ceramic, utilizing dry forming and sintering processes to achieve good ceramic density and flexural strength, thereby ensuring the quality of the alumina ceramic product.

[0005] This invention provides a method for preparing alumina ceramics, characterized by comprising the following steps:

[0006] (1) Test the moisture content of alumina powder and prepare raw materials according to the ratio based on the moisture content: the solid content of alumina powder is 65-80% by mass percentage, and the remainder is pure water;

[0007] (2) Slurry preparation: The weighed alumina powder and pure water from step (1) are placed into a ball mill jar, and an appropriate amount of dispersant and alumina grinding balls are added to the ball mill jar. The first ball milling is carried out for t1 of 14-24 hours. Then, an appropriate amount of defoamer, lubricant and binder are added to the ball mill jar after the first ball milling, and the second ball milling is carried out for t2 of 1 hour to obtain a mixed slurry.

[0008] (3) Preparation of alumina ceramic green body: Add an appropriate amount of acidic solution to the mixed slurry in step (2) and stir to adjust the pH value of the mixed slurry to 8.0-9.0; then granulate and dry form the mixed slurry after pH adjustment to obtain alumina ceramic green body;

[0009] (4) The alumina ceramic green body obtained in step (3) is machined into the designed shape and then transferred to a high-temperature sintering furnace for sintering. After cooling in the furnace, the alumina ceramic is obtained.

[0010] Preferably, in step (4), the sintering process in the high-temperature sintering furnace includes the following steps:

[0011] S1: The heating rate V1 is 1-2℃ / min, and the temperature is raised to T1 at 600℃;

[0012] S2: The heating rate V2 is 2-4℃ / min, the temperature rises to T2 is 1620-1650℃, and the holding time t4 is 2-4h.

[0013] Preferably, in step (3), the dry molding adopts cold isostatic pressing (CIP) or dry bag isostatic pressing (DIP), the pressure P is 120-150MPa, and the holding time t3 is 10-60s.

[0014] Preferably, in step (3), granulation is carried out by spray granulation drying to obtain granulated powder. The inlet temperature of the spray dryer is 170℃-180℃, the outlet temperature is 90℃-95℃, the rotation speed of the atomizing disc is 11000rpm-12000rpm, and the particle size of the granulated powder obtained by granulation is 30-60μm.

[0015] Preferably, in step (3), the acidic solution is an oxalic acid solution with a concentration of 4.7%.

[0016] Preferably, in step (2), the alumina grinding balls are selected with a purity of 99.9%, and the mass ratio of 5mm grinding balls to 10mm grinding balls to 20mm grinding balls is 12:2:1, with a material-to-ball ratio of 1:2.

[0017] Preferably, in step (2), the dispersant is added at a ratio of 0.7-0.8% of the mass of the alumina powder.

[0018] Preferably, in step (2), the defoamer is added at a ratio of 0.02-0.035% of the mass of the alumina powder, the lubricant is added at a ratio of 0.5-1.67% of the mass of the alumina powder, and the binder is added at a ratio of 4.0-5.5% of the mass of the alumina powder.

[0019] Furthermore, the present invention provides an alumina ceramic prepared by the aforementioned method.

[0020] The alumina ceramic in this invention has high flexural strength and high Vickers hardness, which can meet the mechanical performance requirements of structural ceramics, especially the application requirements of mechanical parts, particularly the requirements of mechanical support components.

[0021] Furthermore, the present invention also provides the application of the aforementioned alumina ceramic in mechanical parts.

[0022] The present invention has the following beneficial effects:

[0023] (1) In this technical solution, as the solid content of alumina powder increases, the viscosity of the mixed slurry also gradually increases; although the viscosity of the mixed slurry reaches 295.6 MPa·s when the solid content of alumina powder is 80%, it can still ensure that it maintains normal flow in the subsequent granulation process.

[0024] (2) The loose packing density of granulated powder gradually increases with the increase of the solid content of alumina powder. When the loose packing density of granulated powder is high, it indicates that the gap between granulated powder particles is small, which helps to improve the filling effect of powder, so that the powder can better fill the container and the filling process is more compact.

[0025] (3) The flowability of granulated powder gradually decreases as the solid content of alumina powder increases. The smaller the value of the flowability of granulated powder, the better its flowability. The better the flowability, the better the spherical structure of the powder.

[0026] (4) Particle morphology and surface roughness of alumina granulated powder: Particles are spherical or nearly spherical. When flowing, more particles roll, and the friction between particles is small, so the fluidity is good. The better the spherical structure of alumina granulated powder, the more compact the regularly shaped particles will be, and the higher the loose density will be. Attached Figure Description

[0027] Figure 1 Electron microscope images of the alumina granulated powder in Examples 1-4;

[0028] Figure 2 Images of machined alumina ceramic green bodies from Examples 1-4;

[0029] Figure 3 The images show the sintered alumina ceramics from Examples 1-4. Detailed Implementation

[0030] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0031] Examples 1-4

[0032] The preparation method of alumina ceramics provided in Examples 1-4 of this invention is shown in Table 1.

[0033] A method for preparing alumina ceramics includes the following steps:

[0034] (1) Test the moisture content of alumina powder and prepare raw materials according to the ratio based on the moisture content: the solid content of alumina powder is 65-80% by mass percentage, and the remainder is pure water;

[0035] (2) Slurry preparation: The weighed alumina powder and pure water from step (1) are placed into a ball mill jar, and an appropriate amount of dispersant and alumina grinding balls are added to the ball mill jar. The first ball milling is carried out for t1 of 14-24 hours. The dispersant is added at a ratio of 0.7-0.8% of the mass of the alumina powder. The alumina grinding balls are selected with a purity of 99.9% (mass of 5mm grinding balls: mass of 10mm grinding balls: mass of 20mm grinding balls = 12:2:1), and the material-to-ball ratio is 1:2. Then, an appropriate amount of defoamer, lubricant and binder are added to the ball mill jar after the first ball milling, and the second ball milling is carried out for t2 of 1 hour to obtain a mixed slurry. The defoamer is added at a ratio of 0.02-0.035% of the mass of the alumina powder, the lubricant is added at a ratio of 0.5-1.67% of the mass of the alumina powder, and the binder is added at a ratio of 4.0-5.5% of the mass of the alumina powder.

[0036] (3) Preparation of alumina ceramic green body: Add an appropriate amount of 4.7% oxalic acid solution to the mixed slurry in step (2) and stir to adjust the pH value of the mixed slurry to 8.0-9.0; then granulate the mixed slurry after pH adjustment and dry molding to obtain alumina ceramic green body; granulation is carried out by spray granulation and drying to obtain granulated powder. The inlet temperature of the spray dryer is 170℃-180℃, the outlet temperature is 90℃-95℃, the atomizing disc speed is 11000rpm-12000rpm, and the particle size of the granulated powder obtained by granulation is 30-60μm; among which, the dry molding adopts cold isostatic pressing (CIP) or dry bag isostatic pressing (DIP), the pressure P is 120-150MPa, and the holding time t3 is 10-60s; the cold isostatic pressing equipment and the dry bag isostatic pressing equipment are existing technologies and will not be described in detail here;

[0037] (4) The alumina ceramic green body obtained in step (3) is machined into the designed shape and then transferred to a high-temperature sintering furnace for sintering. After cooling in the furnace, the alumina ceramic is obtained. The sintering process in the high-temperature sintering furnace includes the following steps:

[0038] S1: The heating rate V1 is 1-2℃ / min, and the temperature is raised to 600℃ at T1; when the temperature is between room temperature and 100℃, the alumina ceramic green body is drained in the furnace; when the temperature is between 300℃ and 600℃, the alumina ceramic green body is debonded in the furnace (that is, the binder in the alumina ceramic green body is decomposed and discharged).

[0039] S2: The heating rate V2 is 2-4℃ / min, the temperature rises to T2 is 1620-1650℃, and the holding time t4 is 2-4h.

[0040] In the above-mentioned method for preparing alumina ceramics, the binder is selected from methylcellulose, oleic acid, paraffin wax, boric acid, glycerin and polyvinyl alcohol; the dispersant is selected from ammonium carboxylate, acrylic resin and ammonium acrylate; the lubricant is stearic acid emulsion; and the defoamer is tributyl phosphate.

[0041] Table 1

[0042]

[0043] In Example 1, the dispersant was added at a ratio of 0.8% of the mass of the alumina powder, the defoamer was added at a ratio of 0.02% of the mass of the alumina powder, the lubricant was added at a ratio of 0.5% of the mass of the alumina powder, and the binder was added at a ratio of 4.0% of the mass of the alumina powder.

[0044] In Example 2, the dispersant was added at a ratio of 0.7% of the mass of the alumina powder, the defoamer was added at a ratio of 0.028% of the mass of the alumina powder, the lubricant was added at a ratio of 1.67% of the mass of the alumina powder, and the binder was added at a ratio of 5.5% of the mass of the alumina powder.

[0045] In Example 3, the dispersant was added at a ratio of 0.7% of the mass of the alumina powder, the defoamer was added at a ratio of 0.032% of the mass of the alumina powder, the lubricant was added at a ratio of 1.67% of the mass of the alumina powder, and the binder was added at a ratio of 5.5% of the mass of the alumina powder.

[0046] In Example 4, the dispersant was added at a ratio of 0.7% of the mass of the alumina powder, the defoamer was added at a ratio of 0.035% of the mass of the alumina powder, the lubricant was added at a ratio of 1.67% of the mass of the alumina powder, and the binder was added at a ratio of 5.5% of the mass of the alumina powder.

[0047] Performance testing

[0048] Testing standards:

[0049] (1) The viscosity of the mixed slurry shall be determined in accordance with the standard operating procedure of the viscometer.

[0050] (2) The loose packing density of granulated powder shall be performed in accordance with the standard operating procedure of Hall flow meter.

[0051] (3) The flowability of granulated powder shall be performed in accordance with the standard operating procedure of Hall flow meter.

[0052] (4) The density of the porcelain body shall be in accordance with GB / T5593-1996.

[0053] (5) Flexural strength shall be in accordance with GB / T5593-1996.

[0054] (6) Vickers hardness is measured using a Vickers hardness tester and the indentation method. The hardness value is calculated based on the load borne by the unit area of ​​the indentation. Five points are taken and the average value is calculated.

[0055] Test results: The performance test results are shown in Table 2.

[0056] Table 2

[0057]

[0058] As can be seen from Examples 1-4, the viscosity of the mixed slurry gradually increases with the increase of the solid content of the alumina powder. Although the viscosity of the mixed slurry reaches 295.6 MPa·s when the solid content of the alumina powder is 80%, it can still ensure that it maintains normal flow in the subsequent granulation process.

[0059] As can be seen from Examples 1-4, the loose packing density of the granulated powder gradually increases with the increase of the solid content of the alumina raw powder. When the loose packing density of the granulated powder is high, it indicates that the gaps between the granulated powder particles are small, which helps to improve the filling effect of the powder, so that the powder can better fill the container and the filling process is more compact.

[0060] As can be seen from Examples 1-4, the flowability of granulated powder gradually decreases with the increase of solid content of alumina raw powder. The smaller the value of flowability of granulated powder, the better its flowability, and the better the flowability, the better the spherical structure of the powder.

[0061] like Figure 1 As shown, Figure 1 (a) Figure 1 (b) Figure 1 (c) and Figure 1 (d) Electron microscope images of the alumina granulated powders corresponding to Examples 1-4, respectively; observation Figure 1(a) It can be seen that the alumina granulated powder in Example 1 has a mushroom-shaped morphology, accompanied by some irregular shapes, and even shows adhesion and breakage; observation Figure 1 (b) It can be seen that the alumina granulated powder in Example 2 has an apple-shaped morphology, but some irregular shapes and breakage still occur; observation Figure 1 (c) It can be seen that the alumina granulated powder in Example 3 has an apple-shaped morphology, which is consistent with... Figure 1 (a) and Figure 1 (b) Compared to the previous method, the overall morphology of alumina granulated powder was significantly improved; observation Figure 1 (d) It can be seen that the alumina granulated powder in Example 4 has a morphology that is close to spherical and has a regular apple shape, exhibiting an excellent spherical structure. The particle morphology and surface roughness of the alumina granulated powder are spherical or nearly spherical. When flowing, more particles roll, and the friction between particles is small, so the flowability is good. The better the spherical structure of the alumina granulated powder, the denser the regularly shaped particles will be, and the higher the loose density will be. This is consistent with the loose density test results and flowability test results in Table 2.

[0062] As shown in Examples 1-4, with the increase of the solid content of the alumina powder and the corresponding preparation process, the density, flexural strength, and Vickers hardness of the alumina ceramic gradually increase. When the solid content of the alumina powder is 65-80%, its ceramic density can reach 3.85-3.94 g / cm³. 3 Its flexural strength can reach 385-429 MPa, and its Vickers hardness can reach 1745.83-1977.13 HV; when the solid content of the alumina powder is 80%, its ceramic density can reach 3.94 g / cm³. 3 The flexural strength can reach 429 MPa, and the Vickers hardness can reach 1977.13 HV. It is not difficult to see that the alumina ceramic prepared by the method of this application has excellent ceramic density, flexural strength, and Vickers hardness, realizing the development of high-performance alumina ceramics and laying a good foundation for accelerating the localization of production.

[0063] like Figure 2 As shown, the alumina ceramic green bodies of Examples 1-4 were formed by cold isostatic pressing and machined, respectively. Their surfaces are smooth, and no powder loss was observed, indicating that the alumina ceramic green bodies formed by cold isostatic pressing in Examples 1-4 possess good machinability. Figure 3As shown, the alumina ceramics after sintering in Examples 1-4 have smooth surfaces and exhibit a pale yellow color, indicating that the sintering process is good and the alumina ceramics are of good quality. Therefore, in the preparation method of this application, by optimizing the material formulation and process parameters, high-performance alumina ceramic granules with excellent spherical structure, excellent bulk density, and excellent flowability were obtained; and then, through the improved sintering process, high-performance alumina ceramics with excellent product quality were prepared.

[0064] It should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing alumina ceramics, characterized in that, Includes the following steps: S1. Test the moisture content of the alumina powder; S2. Based on the moisture content of the alumina powder, prepare the raw materials according to the following proportions: The solid content of the alumina powder is 80% by mass percentage, with the remainder being pure water; the dispersant is added at 0.7% of the alumina powder mass, the tributyl phosphate at 0.035% of the alumina powder mass, the stearic acid emulsion at 1.67% of the alumina powder mass, and the binder at 5.5% of the alumina powder mass. S3. Add the weighed alumina powder and pure water to the ball mill jar, and add the weighed dispersant and an appropriate amount of alumina grinding balls to the ball mill jar. Perform the first ball milling for t1, which is 14-24 hours. S4. After the first ball milling is completed, put the weighed tributyl phosphate, stearic acid emulsion and binder into the ball milling jar after the first ball milling, and perform a second ball milling for t2 of 1 hour to obtain a mixed slurry. S5. Add an appropriate amount of acidic solution to the mixed slurry and stir to adjust the pH value of the mixed slurry to 8.0-9.0; S6. The pH-adjusted mixed slurry is granulated, and the granulation is carried out by spray granulation drying to obtain granulated powder. The inlet temperature of the spray dryer is 170℃-180℃, the outlet temperature is 90℃-95℃, the atomizing disc speed is 11000rpm-12000rpm, and the particle size of the granulated powder obtained by granulation is 30-60μm. The morphology of the granulated powder is a regular apple shape that tends to be spherical. S7. The granulated powder is dry-formed to obtain alumina ceramic green body; S8. The alumina ceramic green body is machined into the designed shape, then transferred to a high-temperature sintering furnace for sintering, and cooled with the furnace to obtain alumina ceramic.

2. The method for preparing alumina ceramics according to claim 1, characterized in that, In step S8, the sintering process in the high-temperature sintering furnace includes the following steps: S801: The heating rate V1 is 1-2℃ / min, and the temperature is raised to T1 at 600℃; S802: The heating rate V2 is 2-4℃ / min, the temperature rises to T2 is 1620-1650℃, and the holding time t4 is 2-4h.

3. The method for preparing alumina ceramics according to claim 1, characterized in that: In step S7, the dry molding process adopts cold isostatic pressing (CIP) or dry bag isostatic pressing (DIP), with a pressure P of 120-150MPa and a holding time t3 of 10-60s.

4. The method for preparing alumina ceramics according to claim 1, characterized in that: In step S6, granulation is carried out by spray granulation drying to obtain granulated powder. The inlet temperature of the spray dryer is 170℃-180℃, the outlet temperature is 90℃-95℃, the atomizing disc speed is 11000rpm-12000rpm, and the particle size of the granulated powder obtained by granulation is 30-60μm.

5. The method for preparing alumina ceramics according to claim 1, characterized in that: In step S5, the acidic solution is an oxalic acid solution with a concentration of 4.7%.

6. The method for preparing alumina ceramics according to claim 1, characterized in that: In step S3, the alumina grinding balls are selected with a purity of 99.9%, and the mass ratio of 5mm grinding balls to 10mm grinding balls to 20mm grinding balls is 12:2:1, with a material-to-ball ratio of 1:

2.

7. An alumina ceramic prepared by the method for preparing alumina ceramic according to any one of claims 1-6.

8. An application of the alumina ceramic as described in claim 7 in mechanical parts.

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