Alumina ceramic and preparation method thereof

Abstract

The invention relates to the technical field of ceramic materials, in particular to aluminum oxide ceramic and a preparation method thereof. The aluminum oxide ceramic provided by the invention is prepared by drying a ceramic biscuit and then carrying out air pressure sintering, the ceramic biscuit is prepared by pressing alumina powder with D50 of 0.35 to 0.45 [mu] m; the initial vacuum degree of air pressure sintering is within 10 Pa, the temperature rise rate of sintering is 2-3 DEG C / min, and the highest sintering temperature does not exceed 1600 DEG C; after the temperature is increased to the highest sintering temperature, the pressure is increased to 2-3 MPa, and heat preservation is conducted for 1-2 h. Compared with the alumina ceramic prepared under the traditional oxidation pressureless sintering condition, the alumina ceramic provided by the invention is higher in compactness, higher in volume density and better in mechanical property, the bending strength is improved by 41.6%, the alumina ceramic can be used in worse working conditions, and the alumina ceramic has the characteristic of longer service life.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and in particular to an alumina ceramic and a preparation method thereof. Background Art

[0002] Alumina ceramics, a ceramic material primarily composed of aluminum oxide (Al2O3), exhibit excellent conductivity, mechanical strength, and high-temperature resistance. They are widely used in a variety of fields, including electronic component manufacturing, aerospace, biomedicine, and the automotive industry, and their applications are continuously expanding with technological advancements. However, in some extreme conditions, such as those requiring more stringent mechanical and wear resistance requirements, alumina sintered in traditional oxidizing environments is insufficient. Developing alumina ceramic materials and preparation processes with improved performance is of great significance.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an alumina ceramic and a preparation method thereof.

[0005] Specifically, the technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention provides a method for preparing alumina ceramics, comprising the following steps: drying the ceramic green body and then sintering it under gas pressure; the ceramic green body is pressed by alumina powder with D50 = 0.35-0.45 μm; the initial vacuum degree of the gas pressure sintering is within 10 Pa, the sintering heating rate is 2-3°C / min, and the maximum sintering temperature does not exceed 1600°C; after heating to the maximum sintering temperature, pressurizing to 2-3 MPa and keeping warm for 1-2 hours.

[0007] Preferably, the pressing method of the ceramic green body comprises the steps of compression molding, vacuum packaging, isostatic pressing and drying in sequence.

[0008] Preferably, the pressure of the compression mold is 8-12 MPa.

[0009] Preferably, the isostatic pressing method is: pressurizing to 160-200 MPa and maintaining the pressure for 2-5 minutes.

[0010] Preferably, the drying condition parameters are 80-120° C., 15-30 h.

[0011] Preferably, after the temperature is raised to the maximum sintering temperature, nitrogen is filled and pressurized.

[0012] Preferably, after keeping the temperature for 1-2 hours, the heating is stopped and the temperature is naturally lowered to below 100° C. to obtain a sintered ceramic blank.

[0013] In a more specific embodiment, the method provided by the present invention includes the following steps: loading alumina powder into a steel mold and pressing the mold at 8-12 MPa; then loading it into a vacuum packaging bag; then placing it into an isostatic press and pressurizing it to 160-200 MPa, maintaining the pressure for 2-5 minutes; then placing it into an 80-120°C oven for drying for 15-30 hours; then loading it into a gas pressure sintering furnace, evacuating the vacuum, and when the vacuum reaches within 10 Pa, starting the heating process and maintaining the temperature at a rate of 2-3°C / min; when the maximum sintering temperature of 1500-1550°C is reached, turning off the vacuum pump and adding nitrogen to make the air pressure reach 2-3 MPa; keeping the highest temperature for 1-2 hours, stopping heating, and cooling with the furnace; when the furnace temperature drops below 100°C, opening the furnace and taking out the sintered ceramic blank.

[0014] In a second aspect, the present invention provides an alumina ceramic prepared by the aforementioned method for preparing the alumina ceramic.

[0015] Beneficial effects:

[0016] The present invention provides an alumina ceramic and a preparation method thereof. The alumina ceramic provided by the present invention is obtained by drying a ceramic blank and then gas pressure sintering the ceramic blank; the ceramic blank is pressed from alumina powder with D50=0.35-0.45μm; the initial vacuum degree of the gas pressure sintering is within 10Pa, the sintering heating rate is 2-3℃ / min, and the maximum sintering temperature does not exceed 1600℃; after heating to the maximum sintering temperature, the pressure is increased to 2-3MPa and kept warm for 1-2h. Compared with alumina ceramics prepared under traditional oxidation pressureless sintering conditions, the alumina ceramic provided by the present invention has higher density, higher volume density, better mechanical properties, and a 41.6% increase in bending strength. It can meet the needs of use in more severe working conditions and has the characteristics of longer service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be described below.

[0018] Figure 1 This is a production process flow chart of the alumina ceramics of the present invention. DETAILED DESCRIPTION

[0019] The present invention provides a novel alumina (99.5% density) ceramic and its preparation method. The preparation method improves its density and mechanical properties by controlling the pressure and atmosphere during the sintering process. The density of existing alumina ceramics is generally around 98% (corresponding to a volume density of 3.93±0.02g / cm 3), with flexural strength generally below 500 MPa. Compared to alumina ceramics produced using traditional pressureless oxidative sintering, the present invention offers higher density, higher bulk density, and superior mechanical properties. Its flexural strength is increased by 41.6%, enabling it to withstand harsher operating conditions and extending its service life. Furthermore, the present invention eliminates the need for additional sintering aids and introduces no contaminants during the preparation process, maintaining a high-purity alumina ceramic material. Furthermore, the present invention offers the advantage of high production efficiency.

[0020] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0021] The endpoints and any values ​​of the ranges disclosed in this specification are not limited to the exact ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0022] In the description of this specification, the reference terms "one embodiment", "some embodiments", "specific implementation methods", or "some specific implementation methods" and the like mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiments of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0023] Unless otherwise specified, the materials and reagents used in the following examples are all commercially available. Experimental methods without specific conditions specified in the examples are generally performed under conventional conditions or the conditions recommended by the manufacturer.

[0024] Example 1

[0025] This embodiment provides a novel alumina ceramic. The preparation method of the novel alumina ceramic provided in this embodiment is as follows:

[0026] (1) Alumina powder with a purity of 99.9% and a D50 of 0.4 μm was placed in a steel mold and pressed at a pressure of 10 MPa to obtain an alumina blank.

[0027] (2) Place the alumina blank into a vacuum packaging bag and evacuate the bag.

[0028] (3) Place the vacuumed blank into the isostatic press, start the cold isostatic press, increase the pressure to 180 MPa, and maintain the pressure for 3 minutes.

[0029] (4) Take out the isostatically pressed ceramic blank, put it into an oven, and dry it at 100°C for 20 hours.

[0030] (5) The dried ceramic green body is placed into a gas pressure sintering furnace.

[0031] (6) Open the gas pressure sintering furnace and draw a vacuum. When the vacuum degree reaches within 10 Pa, start the heating process and keep the temperature rising at a rate of 2.5 ° C per minute.

[0032] (7) When the maximum sintering temperature of 1525°C is reached, the vacuum pump is turned off and nitrogen is added to bring the pressure to 2.5 MPa.

[0033] (8) After keeping the highest temperature for 1.5 hours, stop heating and let the furnace cool.

[0034] (9) When the furnace temperature drops below 100°C, open the furnace and take out the sintered ceramic blank.

[0035] (10) Detect the density of the ceramic blank and process it into test bars.

[0036] Example 2

[0037] This embodiment provides a novel alumina ceramic. The preparation method of the novel alumina ceramic provided in this embodiment is as follows:

[0038] (1) Alumina powder with a purity of 99.9% and a D50 of 0.4 μm was placed in a steel mold and pressed at a pressure of 10 MPa to obtain an alumina blank.

[0039] (2) Place the alumina blank into a vacuum packaging bag and evacuate the bag.

[0040] (3) Place the vacuumed blank into the isostatic press, start the cold isostatic press, increase the pressure to 160 MPa, and maintain the pressure for 3 minutes.

[0041] (4) Take out the isostatically pressed ceramic blank, put it into an oven, and dry it at 100°C for 20 hours.

[0042] (5) The dried ceramic green body is placed into a gas pressure sintering furnace.

[0043] (6) Start the gas pressure sintering furnace and evacuate the air. When the vacuum degree reaches less than 10 Pa, start the heating process and keep the temperature rising at a rate of 2°C per minute.

[0044] (7) When the maximum sintering temperature of 1500°C is reached, the vacuum pump is turned off and nitrogen is added to bring the pressure to 2 MPa.

[0045] (8) After keeping the highest temperature for 1 hour, stop heating and let the furnace cool.

[0046] (9) When the furnace temperature drops below 100°C, open the furnace and take out the sintered ceramic blank.

[0047] (10) Detect the density of the ceramic blank and process it into test bars.

[0048] Example 3

[0049] This embodiment provides a novel alumina ceramic. The preparation method of the novel alumina ceramic provided in this embodiment is as follows:

[0050] (1) Alumina powder with a purity of 99.9% and a D50 of 0.4 μm was placed in a steel mold and pressed at a pressure of 10 MPa to obtain an alumina blank.

[0051] (2) Place the alumina blank into a vacuum packaging bag and evacuate the bag.

[0052] (3) Place the vacuumed blank into the isostatic press, start the cold isostatic press, increase the pressure to 200 MPa, and maintain the pressure for 3 minutes.

[0053] (4) Take out the isostatically pressed ceramic blank, put it into an oven, and dry it at 100°C for 20 hours.

[0054] (5) The dried ceramic green body is placed into a gas pressure sintering furnace.

[0055] (6) Start the gas pressure sintering furnace and evacuate the air. When the vacuum degree reaches within 10 Pa, start the heating process and keep the temperature rising at a rate of 3°C per minute.

[0056] (7) When the maximum sintering temperature of 1550°C is reached, the vacuum pump is turned off and nitrogen is added to bring the pressure to 3 MPa.

[0057] (8) After keeping the highest temperature for 2 hours, stop heating and let the furnace cool.

[0058] (9) When the furnace temperature drops below 100°C, open the furnace and take out the sintered ceramic blank.

[0059] (10) Detect the density of the ceramic blank and process it into test bars.

[0060] Example 4

[0061] This example compares the bulk density (GB / T25995-2010 "Test method for density and apparent porosity of fine ceramics"), flexural strength (GB / T6569-2006 "Test method for flexural strength of fine ceramics"), and crushing value (Shanghai Panlian Technology Co., Ltd., material load test report, model: TYE100A flexural and compression testing machine) of alumina ceramics prepared by different sintering methods.

[0062] The results are shown in Tables 1 to 3. The atmospheric pressure sintering method specifically comprises: dry pressing preforming, cold isostatic pressing at 200 MPa for 3 minutes, placing the cold isostatically pressed green body in a muffle furnace, uniformly heating it to a sintering temperature of 1550±10°C, and holding it for 2 hours; the gas pressure sintering method is the same as in Example 1.

[0063] Table 1 Bulk density (g / cm 3 )

[0064]

[0065]

[0066] From the data in Table 1, it can be seen that the bulk density of pressureless sintering is 3.937 g / cm 3 The sample sintered at normal pressure was sintered again according to the method of the present invention, and the bulk density was increased to 3.966 g / cm 3 , the increase ratio is 0.74%; if after forming, directly according to the sintering method of the present invention using a single gas pressure sintering, the bulk density can be increased to 3.978g / cm 3 Compared with pressureless sintering, the improvement is as high as 1.04%.

[0067] Table 2 Bending strength (N / mm 2 )

[0068] Group Atmospheric pressure sintering Atmospheric pressure sintering followed by gas pressure sintering Direct gas pressure sintering 1 357 414 502 2 378 427 540 3 360 404 552 4 365 445 527 5 / 421 539 6 / 449 525 7 / / 524 8 / / 472 9 / / 493 10 / / 499 average value 365 427 517

[0069] From the data in Table 2, it can be seen that the average bending strength of pressureless sintering is 365N / mm 2 The sample sintered at normal pressure is sintered again by the method of the present invention, which can increase its bending strength to 427N / mm 2 , the improvement ratio is 16.98%; if the molding is done and then sintered once with gas pressure, the bending strength can be increased to 517N / mm 2 Compared with pressureless sintering, the improvement is as high as 41.6%.

[0070] Table 3 Crushing value (KN)

[0071]

[0072]

[0073] From the data in Table 3, it can be seen that the crushing value of the gas pressure sintering in this experiment is improved by 11.01%.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing alumina ceramics, characterized in that: The method comprises the following steps: drying a ceramic green body and then sintering it under gas pressure; pressing the ceramic green body with alumina powder having a D50 of 0.35-0.45 μm; the initial vacuum degree of the gas pressure sintering is within 10 Pa, the sintering heating rate is 2-3°C / min, and the maximum sintering temperature does not exceed 1600°C; after heating to the maximum sintering temperature, pressurizing to 2-3 MPa and keeping the temperature for 1-2 hours.

2. The method for preparing alumina ceramics according to claim 1, wherein: The ceramic green body pressing method comprises the steps of pressing, vacuum packaging, isostatic pressing and drying in sequence.

3. The method for preparing alumina ceramics according to claim 2, wherein: The pressure of the compression mold is 8-12 MPa.

4. The method for preparing alumina ceramics according to claim 2, wherein: The isostatic pressing method is: pressurizing to 160-200 MPa and maintaining the pressure for 2-5 minutes.

5. The method for preparing alumina ceramics according to claim 2, wherein: The drying conditions are 80-120° C. for 15-30 hours.

6. The method for preparing alumina ceramics according to claim 1, wherein: After heating to the highest sintering temperature, nitrogen is filled and pressurized.

7. The method for preparing alumina ceramics according to claim 1, wherein: After keeping warm for 1-2 hours, stop heating and cool naturally to below 100°C to obtain a sintered ceramic blank.

8. The method for preparing alumina ceramics according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: loading alumina powder into a steel mold, pressing the mold at 8-12 MPa; loading the powder into a vacuum packaging bag; loading the powder into an isostatic press and pressurizing the powder to 160-200 MPa, maintaining the pressure for 2-5 minutes; loading the powder into an 80-120 DEG C oven for drying for 15-30 hours; loading the powder into a gas pressure sintering furnace, evacuating the powder, and starting the heating process when the vacuum degree reaches within 10 Pa, and maintaining the temperature at a rate of 2-3 DEG C / min; when the maximum sintering temperature of 1500-1550 DEG C is reached, turning off the vacuum pump, adding nitrogen, and raising the pressure to 2-3 MPa; maintaining the maximum temperature for 1-2 hours, stopping the heating, and cooling the powder along with the furnace; and when the furnace temperature drops below 100 DEG C, opening the furnace and taking out the sintered ceramic blank.

9. Alumina ceramics prepared by the method for preparing alumina ceramics according to any one of claims 1 to 8.

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