A method for preparing high-transparency AlON ceramic by high-temperature instant liquid-phase pressureless sintering

Abstract

This invention relates to the field of transparent ceramic preparation technology, and discloses a method for preparing high-transparency AlON ceramics by high-temperature instantaneous liquid-phase pressureless sintering. It includes the following steps: using pure-phase AlON powder as raw material, adding sintering aids, and ball milling to obtain D... 50 AlON powder with a particle size of 3.5-1.5 μm was dry-pressed to obtain an AlON green body. The AlON green body was heated to the pressureless sintering temperature T1 at a heating rate v1 and held for t1 time under a flowing nitrogen atmosphere; then heated to the instantaneous liquidus temperature T2 at a heating rate v2 and held for 0-10 min; and finally cooled to the pressureless sintering temperature T1 at a cooling rate v3 and held for t2 time to obtain AlON ceramics. Among these conditions, 5℃ / min≤v1≤15℃ / min, 2℃ / min≤v2≤4℃ / min, 2℃ / min≤v3≤4℃ / min; 1900℃≤T1≤2000℃, 2030℃≤T2≤2060℃; 2h≤t1+t2≤6h, and t1>t2≥0. The method provided by this invention uses a transient liquid phase process, which solves the problems of low density and poor light transmittance caused by dry pressing and pressureless sintering of coarse AlON powder, and has high practical application value.

Description

Technical Field

[0001] This invention relates to the field of transparent ceramic preparation technology, and more specifically, to a method for preparing high-transparency AlON ceramics by high-temperature instantaneous liquid-phase pressureless sintering. Background Technology

[0002] In the preparation of AlON transparent ceramics, sintering technology is a crucial factor affecting their performance. The main sintering technologies for AlON transparent ceramics include pressureless sintering, hot pressing, spark plasma sintering, and hot isostatic pressing. Pressureless sintering technology has advantages such as simple process, low cost, and applicability to large-size sample preparation, and is widely used in the preparation of AlON transparent ceramics.

[0003] Pressureless sintering requires prolonged ball milling to refine AlON powder, thereby improving its sintering activity. However, this process is inefficient and prone to introducing impurities. Furthermore, the finer the AlON powder particles, the easier it is for the AlON phase to decompose during the AlON ceramic sintering process, generating α-Al₂O₃ and AlN phases. These AlON phases are then re-solution-synthesized later, which can easily lead to AlON particle agglomeration and coarsening. This solid-solution synthesis can result in uneven phase composition in the sample, negatively impacting the optical properties of transparent AlON ceramics.

[0004] Molding is one of the key steps in the preparation of transparent AlON ceramics. Currently, the preparation of transparent AlON ceramics generally adopts the low-cost dry molding method (dry pressing), which has several problems such as low green body density, low strength, simple shape, and difficulty in scaling up the size. In addition, the green bodies prepared by unidirectional or bidirectional pressure methods also have the problem of poor uniformity. For the molding of coarse-grained (micron-sized) AlON, wet molding is usually used.

[0005] Therefore, it is necessary to develop a method for preparing high-transparency AlON ceramics using coarse-particle AlON powder as raw material and employing low-cost dry pressing and pressureless sintering technology. Summary of the Invention

[0006] To address the problems in existing AlON transparent ceramic pressureless sintering processes, such as the need to refine AlON powder and the resulting AlON phase decomposition and resynthesis during heating, leading to AlON particle agglomeration and coarsening, this invention provides a method for preparing high-transparency AlON ceramics through high-temperature instantaneous liquid-phase pressureless sintering. Utilizing the characteristic that coarse-particle AlON powder is not easily decomposed at high temperatures, this invention employs dry pressing, pressureless sintering, and instantaneous liquid-phase processes to prepare AlON ceramics with high transparency.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing high-transparency AlON ceramics by high-temperature instantaneous liquid-phase pressureless sintering includes the following steps:

[0009] D was prepared by ball milling pure phase AlON powder as raw material, with the addition of sintering aids. 50 AlON powder with a particle size of 3.5-1.5 μm was dry-pressed to obtain AlON green body; AlON green body was heated to pressureless sintering temperature T1 and held at t1 time under flowing nitrogen environment at heating rate v1; heated to instantaneous liquidus temperature T2 and held at 0-10 min at heating rate v2; cooled to pressureless sintering temperature T1 and held at t2 time at cooling rate v3 to obtain AlON ceramic;

[0010] Among them, 5℃ / min≤v1≤15℃ / min, 2℃ / min≤v2≤4℃ / min, 2℃ / min≤v3≤4℃ / min; 1900℃≤T1≤2000℃, 2030℃≤T2≤2060℃; 2h≤t1+t2≤6h, and t1>t2≥0.

[0011] Furthermore, the sintering aid is a commonly used aid in the art, for example, it can be a single dopant of yttrium oxide or a combination of magnesium oxide, yttrium oxide and lanthanum oxide, and its dosage is 0.1-0.5 wt% of AlON powder.

[0012] Furthermore, the ball milling equipment is not limited; for example, it can be a polyurethane ball milling jar.

[0013] Furthermore, when the ball milling equipment is a polyurethane ball milling jar, the ball milling specifically involves using silicon nitride as the ball milling medium and anhydrous ethanol as the solvent, and milling at 250 rpm for 6-24 hours.

[0014] It should be noted that there is no limit to the amount of anhydrous ethanol used during ball milling; it is sufficient that it serves to aid the milling process.

[0015] Furthermore, the dry pressing process specifically involves: loading the ball-milled AlON powder into a steel mold and pressing it unidirectionally into an AlON blank under a pressure of 30-70 MPa.

[0016] Furthermore, it also includes: pressureless sintering and transient liquid phase sintering under a positive pressure of 2.0-4.0 kPa.

[0017] Furthermore, the pressureless sintering equipment is a commonly used pressureless sintering equipment, such as a vertical graphite high-temperature atmosphere furnace.

[0018] In this invention, coarse-grained AlON powder is used as raw material. Based on the mass transfer-promoting properties of ceramic liquid-phase sintering and the existence of a liquid-solid coexistence region of AlON in the Al2O3-AlN phase diagram, a sintering process of pressureless sintering followed by high-temperature instantaneous liquid-phase treatment is employed to prepare AlON transparent ceramics. Utilizing the characteristic that coarse-grained AlON powder is not prone to decomposition, the negative impacts of decomposition leading to α-Al2O3 and AlN are eliminated. Based on the densification achieved through pressureless sintering, a suitable amount of liquid phase is provided through high-temperature instantaneous liquid-phase treatment to promote mass transfer, further eliminating residual porosity in the sintered body and improving the optical transmittance of the final AlON transparent ceramic.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The method provided by this invention can effectively promote the densification process of AlON ceramics by simply using high-temperature instantaneous liquid phase treatment during pressureless sintering. It overcomes the defect of insufficient driving force when using coarse-sized AlON powder in pressureless sintering technology. Compared with traditional pressureless sintering technology, it can achieve the preparation of AlON transparent ceramics with high optical transmittance. When the pressureless sintering holding time is the same, high-temperature instantaneous liquid phase treatment can increase the maximum infrared transmittance by 15%-51%.

[0021] The AlON powder used in this invention only requires simple ball milling and does not require a long and complex ball milling and refining process. This can effectively reduce the risk of impurity introduction, has low requirements for ball milling equipment, and can achieve high-temperature instantaneous liquid phase process by relying on low-cost pressureless sintering equipment. It is suitable for industrial production and has high application value. Attached Figure Description

[0022] Figure 1 The images show SEM (a) and PSD (b) images of AlON powder after ball milling.

[0023] Figure 2 The XRD pattern of the sample in Example 1 was obtained when it was heated at 1400℃-1900℃ for 5 min.

[0024] Figure 3 Optical transmittance curves and physical images of AlON transparent ceramics prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0025] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0027] As an example, the AlON powder prepared in the following embodiments and comparative examples was prepared using the following method: pure phase AlON powder was used as raw material, 0.2 wt% nano Y2O3 was added as a sintering aid, a polyurethane ball mill jar was used, silicon nitride was used as the ball milling medium, anhydrous ethanol was used as the solvent, and the mixture was ball-milled at 250 rpm for 12 h to obtain D. 50 AlON powder with a particle size of 2.54 μm. Its microstructure (SEM) and particle size distribution (PSD) images are shown below. Figure 1 As shown.

[0028] Example 1

[0029] AlON powder, after being ball-milled and crushed, was loaded into a steel mold and unidirectionally pressed into an AlON green body under a pressure of 50 MPa. The resulting AlON green body was then placed in a boron nitride crucible and placed in a vertical graphite high-temperature atmosphere furnace. Under a flowing nitrogen atmosphere and a positive pressure of 2.0-4.0 kPa, the following steps were performed: First, the temperature was increased to 2000℃ at 10℃ / min and held for 5 h; second, the temperature was increased to 2050℃ at 3℃ / min and held for 5 min; third, the temperature was decreased to 2000℃ at 3℃ / min and held for 1 h, yielding an AlON transparent ceramic sample. The XRD patterns of the sample during the heating process (1400-1900℃ for 5 min) are shown below. Figure 2 As shown, a small amount of α-Al2O3 appears only at 1500-1600℃ during the heating process, and α-Al2O3 disappears at 1700℃. Therefore, the negative effects of AlON decomposition producing α-Al2O3 and AlN can be significantly eliminated.

[0030] The prepared AlON transparent ceramic sample was polished to 2 mm on both sides, and its maximum infrared transmittance was measured to be 83.9%. The actual sample and transmittance are shown in the image below. Figure 3 As shown.

[0031] Example 2

[0032] AlON powder, after being ball-milled and crushed, was loaded into a steel mold and unidirectionally pressed into an AlON green body under a pressure of 50 MPa. The obtained AlON green body was then placed in a boron nitride crucible and placed in a vertical graphite high-temperature atmosphere furnace. Under a flowing nitrogen atmosphere and a positive pressure of 2.0-4.0 kPa, the following steps were performed: First, the temperature was increased to 2000℃ at 10℃ / min and held for 5 h; second, the temperature was increased to 2040℃ at 3℃ / min and held for 5 min; third, the temperature was decreased to 2000℃ at 3℃ / min and held for 1 h, thus obtaining an AlON transparent ceramic sample.

[0033] The prepared AlON transparent ceramic sample was polished to 2 mm on both sides, and its maximum infrared transmittance was measured to be 81.8%. The actual sample and transmittance are shown in the image below. Figure 3 As shown.

[0034] Example 3

[0035] AlON powder, after being ball-milled and crushed, was loaded into a steel mold and unidirectionally pressed into an AlON green body under a pressure of 50 MPa. The obtained AlON green body was then placed in a boron nitride crucible and placed in a vertical graphite high-temperature atmosphere furnace. Under a flowing nitrogen atmosphere and a positive pressure of 2.0-4.0 kPa, the following steps were performed: First, the temperature was increased to 2000℃ at 10℃ / min and held for 1 hour; second, the temperature was increased to 2050℃ at 3℃ / min and held for 5 minutes; third, the temperature was decreased to 2000℃ at 3℃ / min and held for 1 hour, thus obtaining an AlON transparent ceramic sample.

[0036] The prepared AlON transparent ceramic sample was polished to 2 mm on both sides, and its maximum infrared transmittance was measured to be 76.6%. The actual sample and transmittance are shown in the image below. Figure 3 As shown.

[0037] Comparative Example 1

[0038] AlON powder, after being ball-milled and crushed, was loaded into a steel mold and unidirectionally pressed into an AlON green body under a pressure of 50 MPa. The obtained AlON green body was then placed in a boron nitride crucible and placed in a vertical graphite high-temperature atmosphere furnace. Under a flowing nitrogen atmosphere and a positive pressure of 2.0-4.0 kPa, the temperature was directly increased to 2000℃ at a rate of 10℃ / min and held for 6 hours to obtain an AlON transparent ceramic sample.

[0039] The prepared AlON transparent ceramic sample was polished to 2 mm on both sides, and its maximum infrared transmittance was measured to be 72.4%. The actual sample and transmittance are shown in the image below. Figure 3 As shown.

[0040] Comparative Example 2

[0041] AlON powder, after being ball-milled and crushed, was loaded into a steel mold and unidirectionally pressed into an AlON green body under a pressure of 50 MPa. The obtained AlON green body was then placed in a boron nitride crucible and placed in a vertical graphite high-temperature atmosphere furnace. Under a flowing nitrogen atmosphere and a positive pressure of 2.0-4.0 kPa, the temperature was directly increased to 2000℃ at a rate of 10℃ / min and held for 2 hours to obtain an AlON transparent ceramic sample.

[0042] The prepared AlON transparent ceramic sample was polished to 2 mm on both sides, and its maximum infrared transmittance was measured to be 50.6%. The actual sample and transmittance are shown in the image below. Figure 3 As shown.

[0043] Comparative Example 3

[0044] AlON powder, after being ball-milled and crushed, was loaded into a steel mold and unidirectionally pressed into an AlON green body under a pressure of 50 MPa. The obtained AlON green body was then placed in a boron nitride crucible and placed in a vertical graphite high-temperature atmosphere furnace. Under a flowing nitrogen atmosphere and a positive pressure of 2.0-4.0 kPa, the following steps were performed: First, the temperature was increased to 2000℃ at 10℃ / min and held for 5 h; second, the temperature was increased to 2070℃ at 3℃ / min and held for 5 min; third, the temperature was decreased to 2000℃ at 3℃ / min and held for 1 h, thus obtaining an AlON transparent ceramic sample.

[0045] The prepared AlON transparent ceramic sample was polished to 2 mm on both sides, and its maximum infrared transmittance was measured to be 58.2%. The actual sample and transmittance diagram are shown below. Figure 3 As shown.

[0046] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0047] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing high-transparency AlON ceramics by high-temperature instantaneous liquid-phase pressureless sintering, characterized in that, Includes the following steps: D was prepared by ball milling pure phase AlON powder as raw material, with the addition of sintering aids. 50 AlON powder with a particle size of 3.5-1.5 μm was dry-pressed to obtain AlON preforms; the AlON preforms were then heated at a rate of [missing information] in a flowing nitrogen atmosphere. v 1 Heat to pressureless sintering temperature T 1 Insulation t 1 time; heating rate v 2 Heating to instantaneous liquidus temperature T 2 Hold at the temperature for 0-10 minutes, not zero; at the cooling rate v 3 Cool down to pressureless sintering temperature T 1 Insulation t 2 Time, and AlON ceramics are produced; Among them, 5 ℃ / min≤ v 1 ≤15 ℃ / min, 2 ℃ / min≤ v 2 ≤4 ℃ / min, 2 ℃ / min≤ v 3 ≤4 ℃ / min; 1900 ℃≤ T 1 ≤2000 ℃, 2030 ℃≤ T 2 ≤2060 ℃; 2 h≤ t 1 + t 2 ≤6 h, and t 1 > t 2 ≥0.

2. The method according to claim 1, characterized in that, The sintering aid is a single-doped yttrium oxide or a combination of magnesia oxide, yttrium oxide and lanthanum oxide, and its dosage is 0.1-0.5 wt% of AlON powder.

3. The method according to claim 1, characterized in that, The ball milling process specifically involves using a polyurethane ball milling jar, silicon nitride as the milling medium, anhydrous ethanol as the solvent, and milling at 250 rpm for 6-24 hours.

4. The method according to claim 1, characterized in that, The dry pressing process specifically involves: loading the ball-milled AlON powder into a steel mold and pressing it unidirectionally into an AlON blank under a pressure of 30-70 MPa.

5. The method according to claim 1, characterized in that, Also includes: Pressureless sintering and transient liquid phase are carried out under a positive pressure of 2.0-4.0 kPa.

6. The method according to claim 5, characterized in that, The pressureless sintering and instantaneous liquid phase are carried out in a vertical graphite high-temperature atmosphere furnace.

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