ALUMINUM OXYNITRIDE POWDER, DIRECT NITRIDATION HIGH-PRESSURE SYNTHESIS METHOD AND APPLICATION THEREOF

Abstract

Aluminum oxynitride (AlON) powder, a synthesis method thereof by direct nitridation under high pressure and use thereof, which belongs to the field of ceramic powder are presented. In the method, pure-phase AlON powder is synthesized by direct nitridation under high pressure with aluminum powder and alumina powder as starting materials. The powder has a spherical-like morphology, with a particle size ranging from 5 μm to 15 μm. The powder has good dispersibility and uniformity, and higher sintering activity. AlON transparent ceramic (1.2 mm thick) prepared from the AlON powder has a linear transmittance of more than 84%. The batch yield is on kilogram-scale; therefore, the method is suitable for large-scale production of the AlON powder.

Claims

1. A preparation method of AlON powder, characterized in that the method comprises the following step: synthesizing pure-phase AlON powder by direct nitridation under high pressure with aluminum powder and alumina powder as starting materials.

2. The method according to claim 1, characterized in that the high pressure refers to a pressure of gas in the direct nitridation system of 1-3 MPa, such as 1.5-2.5 MPa.

3. The method according to claim 1, characterized in that the preparation method comprises the following steps: (1) mixing: mixing the aluminum powder, the alumina powder and an organic solvent homogeneously; (2) drying: removing the organic solvent from the mixture obtained in step (1), drying and sieving to obtain a mixed powder; (3) loading: placing the mixed powder obtained in step (2) in a pressure sintering furnace, and introducing nitrogen to increase the pressure; and (4) calcination: after the loading is completed, calcining the mixed powder to obtain the AlON powder.

4. The method according to claim 3, characterized in that in step (1), the organic solvent is at least one of absolute ethanol, diethyl ether, acetone and petroleum ether; preferably, the organic solvent is absolute ethanol; preferably, in step (1), the mass of the organic solvent is 1-3 times, such as 1.5-2.5 times the sum of the masses of the alumina powder and the aluminum powder; preferably, in step (1), the mixing is mechanical stirring, preferably mechanical stirring for 1-4 h.

5. The method according to claim 1, characterized in that the alumina powder is selected from at least one of α-alumina powder and γ-alumina powder; preferably, the alumina powder has a particle size of no more than 80 μm, preferably no more than 60 more preferably no more than 35 and still more preferably no more than 10 μm; preferably, the alumina powder has a purity of more than 99.9%; preferably, the aluminum powder has a particle size of no more than 80 preferably no more than more preferably no more than 35 and still more preferably no more than 10 μm; preferably, the aluminum powder has a purity of more than 99.9%; preferably, the amount of the alumina powder and the aluminum powder is calculated based on the stoichiometric ratio of the AlON phase.

6. The method according to claim 3, characterized in that removing the organic solvent in step (2) is removing the organic solvent by rotary evaporation; preferably, drying in step (2) is vacuum drying; preferably, sieving in step (2) is performed using a 100-mesh sieve; preferably, the mass of the Al powder in the mixed powder in step (2) and step (3) is 27-33 mol %, such as 28-32 mol %, based on the molar percentage of AlN in the AlON phase.

7. The method according to claim 3, characterized in that step (3) comprises the following steps: placing the mixed powder obtained in step (2) in crucibles, placing the crucibles in a pressure sintering furnace, and introducing nitrogen to increase the pressure; preferably, in step (3), the amount of the mixed powder loaded is 0.3-0.7, such as ½ to ⅔ of the capacity of the crucible; preferably, in step (3), the crucibles are stacked, preferably stacked in a staggered manner; preferably, in step (3), the mixed powder is placed in a plurality of crucibles, and the crucibles are stacked in a staggered manner in the pressure sintering furnace; preferably, in step (3), the furnace is at a vacuum degree of no less than 10′ Pa at room temperature before the nitrogen is introduced; preferably, in step (3), the nitrogen has a purity of no less than 99.9%; preferably, in step (3), the nitrogen is introduced until the pressure sintering furnace has an internal gas pressure of 1-3 MPa, such as 1.5-2.5 MPa; preferably, in step (4), the calcination is performed at 1700-1800° C., such as 1720-1780° C.; preferably, in step (4), the calcination is performed for 1-3 h, such as 1.2-2.8 h; preferably, in step (4), after the calcination is completed, the temperature is lowered to 900-1100° C., and the pressure is relieved to allow further cooling; preferably, in step (4), the furnace is heated and/or cooled at a rate of 5-12° C./min, preferably 8-10° C./min; preferably, step (4) comprises: under the nitrogen pressure in step (4), heating to 1700-1800° C. for calcination for 1-3 h, then lowering the temperature to 900-1100° C., and gradually relieving the pressure until the furnace is cooled to room temperature.

8. AlON powder, characterized in that the AlON powder has a purity of at least 99.9%, preferably, the AlON powder has a nitrogen content of 3.8-4.94%, preferably 4.35-4.90%; preferably, the AlON powder has a particle size of 5-15 μm, such as 7-12 μm; preferably, the AlON powder is spherical-like, or spherical; preferably, the AlON powder has an XRD spectrum substantially as shown in FIG. 1; preferably, the AlON powder has an SEM morphology substantially as shown in FIG. 2; preferably, the AlON powder is prepared by the method according to claim 1.

9. A method for preparing an AlON ceramic, comprising: sintering the AlON powder according to claim 8.

10. AlON ceramic, prepared from a starting material containing the AlON powder according to claim 8, wherein preferably, the AlON ceramic has a linear transmittance of more than 80%, such as more than 84%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] FIG. 1 is an XRD spectrum of the AlON powder synthesized in Example 1;

[0052] FIG. 2 is an SEM image of the AlON powder synthesized in Example 1;

[0053] FIG. 3 is an SEM image of the AlON powder synthesized under normal pressure in Comparative Example;

[0054] FIG. 4 is a photograph of transparent ceramic samples prepared in Example 3 and Comparative Example.

DETAILED DESCRIPTION

[0055] The technical solution of the present disclosure will be further illustrated in detail with reference to the following specific examples. It should be understood that the following examples are merely exemplary illustration and explanation of the present disclosure, and should not be construed as limiting the protection scope of the present disclosure. All techniques implemented based on the aforementioned content of the present disclosure are encompassed within the protection scope of the present disclosure.

[0056] Unless otherwise specified, the starting materials and reagents used in the following examples are all commercially available products or can be prepared by known methods. In the examples, X-ray diffraction pattern analysis was performed using an X-ray diffraction analyzer (Miniflex-600, Rigaku, Japan).

[0057] In the examples, the linear transmittance of AlON transparent ceramic was measured using an ultraviolet-visible-near infrared spectrophotometer (Lambda950, Perkin Elmer, USA).

[0058] In the examples, scanning electron microscopy (SEM) was performed using a scanning electron microscope (SU-8010, Hitachi, Japan).

Example 1: Synthesis of AlON Powder by Direct Nitridation Under High Pressure

[0059] (1) Mixing: the amount of alumina powder and aluminum powder was calculated based on the stoichiometric ratio of the AlON phase; α-alumina powder (with a particle size of 0.5 μm) and aluminum powder (with a particle size of 2 μm) were weighed as desired into the same polytetrafluoroethylene plastic vessel, and absolute ethanol was added in an amount 2 times the sum of the masses of the alumina powder and the aluminum powder, followed by mixing by mechanical stirring.

[0060] (2) Drying: the ceramic slurry homogeneously mixed in step (1) was placed in a round-bottom flask, then evaporated in a rotary evaporator to remove the organic solvent, dried in a vacuum dryer at 60° C. for 4 h, and sieved with a 100-mesh sieve to obtain mixed powder of the alumina powder and the aluminum powder, wherein the mass of the aluminum powder was 30 mol % based on the molar percentage of AlN in the AlON phase.

[0061] (3) Loading: the mixed powder obtained in step (2) was placed in cylindrical boron nitride crucibles, each of which was loaded with the mixed powder at a height of ⅔ of the capacity of the boron nitride crucible; four crucibles were sequentially stacked in a staggered manner and placed in a pressure sintering furnace, which was then slowly vacuumized and was charged with high-purity nitrogen until the pressure reached 1.2 MPa.

[0062] (4) Calcination: the pressure sintering furnace was heated at a rate of 10° C./min to 1750° C. for calcination for 2 h, and then cooled to 1000° C. at a rate of 8° C./min; the pressure was gradually relieved until the furnace cooled to room temperature to obtain AlON powder. As shown in FIG. 1, the obtained product was pure-phase AlON powder as identified by X-ray diffraction analysis. The AlON powder had a purity of 99.9%, and a nitrogen content of 4.56%. As shown in FIG. 2, the AlON powder was spherical-like, with a particle size of 5-15 μm.

Example 2

[0063] This example is substantially the same as Example 1, except that:

[0064] (3) Loading: the mixed powder obtained in step (2) was placed in cylindrical boron nitride crucibles, each of which was loaded with the mixed powder at a height of ½ of the capacity of the boron nitride crucible; four crucibles were sequentially stacked in a staggered manner and placed in a pressure sintering furnace, which was then slowly vacuumized and was charged with high-purity nitrogen until the pressure reached 2.5 MPa.

[0065] (4) Calcination: the pressure sintering furnace was heated at a rate of 15° C./min to 1750° C. for calcination for 3 h, and then cooled to 1000° C. at a rate of 10° C./min, and the pressure was gradually relieved until the furnace cooled to room temperature to obtain AlON powder.

[0066] The AlON powder had a purity of 99.9%, and a nitrogen content of 4.89%.

Example 3: Preparation of AlON Transparent Ceramic Sample

[0067] (1) Ball-milling: the AlON powder prepared in Example 1 was sieved with a 100-mesh nylon sieve; 40 g of the sieved powder, 0.2 wt % yttrium oxide and 0.1 wt % magnesium oxide were weighed and placed in a nylon ball-milling tank; with alumina used as the ball-milling medium and absolute ethanol used as the dispersion medium, the mixture was ball-milled in a planetary ball mill at 250 r/min for 24 h.

[0068] (2) Drying and shaping: the AlON ceramic powder slurry obtained in step (1) was dried in a vacuum dryer at 60° C. for 6 h, sieved with a 150-mesh nylon sieve, and dry-pressed and cold isostatic-pressed on a hydraulic press machine and a cold isostatic press machine under the pressures of 20 Mpa and 200 Mpa respectively to obtain AlON ceramic biscuit.

[0069] (3) Sintering: the AlON biscuit obtained in step (2) was loaded in a boron nitride crucible, which was then placed in a carbon tube sintering furnace; after the furnace was vacuumized to 10.sup.−3 Pa at room temperature, the extraction valve was closed, and high-purity nitrogen was introduced into the furnace; when the nitrogen pressure was slightly positive, the outlet valve was opened to adjust the nitrogen flow rate to be 0.3 L/min; under the condition of flowing nitrogen, the furnace was heated to 1640° C. at a rate of 10° C./min, and then heated to 1830° C. at a rate of 6° C./min, and maintained at this temperature for 6 h; after the sintering was completed, the furnace was cooled to 900° C., and then the power was turned off to allow further cooling; AlON transparent ceramic was obtained.

[0070] (4) Post-treatment: the AlON transparent ceramic obtained in step (3) was ground and polished on both sides to obtain the AlON transparent ceramic.

[0071] The obtained sample was pure-phase AlON as identified by X-ray diffraction and ultraviolet-visible-near infrared spectrophotometer, with a linear transmittance of more than 84%, suggesting a transparent ceramic (as shown in (a) in FIG. 4).

Comparative Example

[0072] This example differed from Example 1 in that: the mixed powder obtained in step (2) was loaded in a boron nitride crucible, which was then placed in a carbon tube sintering furnace; after the furnace was vacuumized to 10.sup.−3 Pa at room temperature, the extraction valve was closed, and high-purity nitrogen was introduced into the furnace; when the nitrogen pressure was slightly positive, the outlet valve was opened to adjust the nitrogen flow rate to be 0.3 L/min; under the condition of flowing nitrogen, the furnace was heated to 1750° C. at a rate of 10° C./min and maintained at this temperature for 3 h; after the calcination was completed, the furnace was cooled to 900° C. at a rate of 8° C./min, and then the power was turned off to allow further cooling; AlON powder was obtained. The AlON powder had a purity of 98.9%, and a nitrogen content of 4.32%.

[0073] The preparation process of the corresponding transparent ceramic sample was the same as that of Example 3.

[0074] As shown in (b) in FIG. 4, the ceramic sample prepared in this comparative example is a translucent AlON ceramic, with a linear transmittance of less than 10%.

[0075] As shown in FIG. 3, the AlON powder synthesized by direct nitridation had irregular morphology accompanied with agglomeration, and it had a large particle size and low sintering activity.

[0076] The embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the above embodiments. Any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.