METHOD FOR PREPARING A SPHERICAL ALN GRANULE

Abstract

A method for preparing a spherical aluminum nitride granule includes (A) providing an aluminum oxide powder and a resin, followed by dissolving the aluminum oxide powder and the resin in a solvent to form a mixed slurry; (B) performing spray drying on the mixed slurry to form a spherical granule; (C) performing carbonization on the spherical granule in an inert atmosphere to form a carbonized spherical granule; (D) performing carbothermic reduction on the carbonized spherical granule in a nitrogen atmosphere to form a spherical aluminum nitride granule; (E) performing a densification sintering thermal treatment continuously on the spherical aluminum nitride granule in a nitrogen atmosphere; and (F) performing decarbonization on the densified spherical aluminum nitride granule in a nitrogen atmosphere to form densified spherical aluminum nitride sintered particles of tens of micrometers. Accordingly, the manufacturing process is simple and energy-saving.

Claims

1. A method for preparing a spherical aluminum nitride granule, comprising the steps of: (A) providing an aluminum oxide powder and a resin, followed by dissolving the aluminum oxide powder and the resin in a solvent to form a mixed slurry; (B) performing spray drying on the mixed slurry to form a spherical granule; (C) performing carbonization on the spherical granule in an inert atmosphere to form a carbonized spherical granule; (D) performing carbothermic reduction on the carbonized spherical granule in a nitrogen atmosphere to form a spherical aluminum nitride granule; (E) performing a densification sintering thermal treatment continuously on the spherical aluminum nitride granule in a nitrogen atmosphere; and (F) performing in a nitrogen atmosphere decarbonization on the spherical aluminum nitride granule which has undergone the densification sintering thermal treatment; wherein a weight ratio of the aluminum oxide powder to the resin is 1:0.52.0; wherein the carbothermic reduction in the step (D) is performed at 1500 C.1600 C.; wherein a sintering temperature of the step (E) is 1750 C.1850 C.

2. The method for preparing a spherical aluminum nitride granule according to claim 1, wherein a crystal structure of the aluminum oxide powder comprises one selected from the group consisting of -aluminum oxide phase, -aluminum oxide phase, -aluminum oxide phase, and a combination thereof.

3. The method for preparing a spherical aluminum nitride granule according to claim 1, wherein the resin is one of phenol resin, epoxy resin, formaldehyde urea resin, polymethylmethacrylate, polytetrafluoroethylene, and melamine-formaldehyde resin.

4. The method for preparing a spherical aluminum nitride granule according to claim 1, wherein the solvent is one of water, methanol, ethanol, isopropanol, n-butanol, and acetone aqueous solution.

5. (canceled)

6. The method for preparing a spherical aluminum nitride granule according to claim 1, wherein, the step (A) entails one of stirring and ball milling.

7. The method for preparing a spherical aluminum nitride granule according to claim 1, wherein, the carbonization in the step (C) is performed at 700 C.900 C.

8. (canceled)

9. (canceled)

10. The method for preparing a spherical aluminum nitride granule according to claim 1, wherein the nitrogen atmosphere of the step (D) and step (E) is one of pure nitrogen gas, a mixture of nitrogen gas and hydrogen gas, and a mixture of nitrogen gas and ammonia gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a flowchart of a method for preparing a spherical aluminum nitride granule according to the present invention;

[0016] FIG. 2 is an SEM picture taken of spray-dried spherical granules according to an embodiment of the present invention;

[0017] FIG. 3 is an SEM picture taken of carbonized spherical granules according to an embodiment of the present invention;

[0018] FIG. 4 is an SEM picture taken of spherical aluminum nitride granules which have undergone carbothermic reduction according to an embodiment of the present invention;

[0019] FIG. 5 are graphs of spherical aluminum nitride granules which have undergone carbothermic reduction and imaged by X-ray according to an embodiment of the present invention; and

[0020] FIG. 6 are SEM pictures taken of densified spherical aluminum nitride sintered particles according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The implementation of the present invention is illustrated with specific embodiments. By making reference to the disclosure contained in the specification, persons skilled in the art can easily accomplish the advantages and effects of the present invention.

[0022] A method for preparing a spherical aluminum nitride granule according to the present invention involves covering uniformly the surfaces of aluminum oxide powders with a carbon-containing resin by spray drying, performing primary carbonization on the granules, mixing the carbonized granules uniformly, allowing the mixed carbonized granules to undergo carbothermic reduction at 1500 C.1700 C. so as to form a spherical aluminum nitride granule, allowing the granule to undergo a densification sintering thermal treatment at a high temperature of 1750 C.1850 C., and allowing the sintered granule to undergo decarbonization in an oxygen-containing environment, thereby preparing densified spherical aluminum nitride sintered particles. During the carbothermic reduction, the resin, which covers aluminum oxide powder surfaces and is carbonized, functions as a reducing agent for reducing aluminum oxide in a nitrogen atmosphere, and thus the products of reduction, namely aluminum and nitrogen gas, react to produce aluminum nitride granules. Furthermore, the method for preparing a spherical aluminum nitride granule according to the present invention includes a sintering heat treatment which enhances the densification of the aluminum nitride granules but reduces the specific surface area thereof, thereby preparing densified spherical aluminum nitride particles.

[0023] Referring to FIG. 1, there is shown a flowchart of a method for preparing a spherical aluminum nitride granule according to the present invention. As shown in the diagram, the present invention provides a method for preparing a spherical aluminum nitride granule, comprises the steps of: (A) providing an aluminum oxide powder and a resin, followed by dissolving the aluminum oxide powder and the resin in a solvent to form a mixed slurry (S101); (B) performing spray drying on the mixed slurry to form a spherical granule (S102); (C) performing carbonization on the spherical granule in an inert atmosphere to form a carbonized spherical granule (S103); (D) performing carbothermic reduction on the carbonized spherical granule in a nitrogen atmosphere to form a spherical aluminum nitride granule (S104); (E) performing a densification sintering thermal treatment continuously on the spherical aluminum nitride granule in a nitrogen atmosphere (S105); and (F) performing in a nitrogen atmosphere decarbonization on the spherical aluminum nitride granule which has undergone the densification sintering thermal treatment to form a densified spherical aluminum nitride sintered particles (S106).

[0024] The crystal structure of the aluminum oxide powder is -aluminum oxide phase, -aluminum oxide phase, -aluminum oxide phase, or a combination thereof. The resin is phenol resin, epoxy resin, formaldehyde urea resin, polymethylmethacrylate, polytetrafluoroethylene, melamine-formaldehyde resin. The solvent is water, methanol, ethanol, isopropanol, n-butanol, or acetone aqueous solution. Regarding mixing raw materials, the weight ratio of the aluminum oxide powder to the resin is 1:0.52.0. The raw materials are mixed by stirring or ball milling.

Embodiment 1

[0025] 100 g of aluminum oxide powders are placed in 1000 mL of ethanol to form a disperse solution. 50 g of phenol resin is dissolved in 1000 mL of ethanol to form a resin solution. Then, the two aforesaid solutions are uniformly mixed to form mixed slurry. Afterward, the mixed slurry undergoes spray drying with an atomizer at a rotation speed of 10000 rpm to form spherical granules. Referring to FIG. 2, there is shown an SEM picture taken of spray-dried spherical granules according to an embodiment of the present invention. As shown in the diagram, the powders undergo spray drying to become spherical granules of tens of micrometers, that is, an average particle diameter D.sub.50 of 40.74 m, as measured with a laser particle diameter analyzer. Afterward, the spherical granules thus produced are placed in a boron nitride crucible (BN crucible), and then the spherical granules undergo carbonization in a high-temperature furnace with a nitrogen gas atmosphere at 800 C. for 1 hour to form carbonized spherical granule. Referring to FIG. 3, there is shown an SEM picture taken of carbonized spherical granules according to an embodiment of the present invention. The carbonized spherical granules are heated to raise its temperature at a speed of 5 C./min and eventually stays at 1600 C. for 7 hours; afterward, the carbonized spherical granules undergo carbothermic reduction in a high-temperature furnace with a nitrogen gas or nitrogen-hydrogen mixture atmosphere to form a spherical aluminum nitride granule. Referring to FIG. 4, there is shown an SEM picture taken of spherical aluminum nitride granules which have undergone carbothermic reduction according to an embodiment of the present invention. As shown in the diagram, after undergoing carbothermic reduction, the granules look spherical. Referring to FIG. 5, there are shown graphs of spherical aluminum nitride granules which have undergone carbothermic reduction with an aluminum oxide to phenol resin weight ratio of 1:0.5 and imaged by X-ray according to an embodiment of the present invention. As shown in the diagram, the granules thus prepared manifest a single pure phase of aluminum nitride, thereby confirming that the preparation of a spherical aluminum nitride granule is done. Afterward, the spherical aluminum nitride granules undergo a densification sintering thermal treatment in a high-temperature furnace at 1850 C. for 5 hours. Eventually, the densified spherical aluminum nitride granules undergo decarbonization in the air at 650 C. for 10 hours to produce densified spherical aluminum nitride sintered particles. Referring to FIG. 6, there are shown SEM pictures taken of densified spherical aluminum nitride sintered particles according to an embodiment of the present invention. As shown in the diagrams, after undergoing decarbonization, the spherical aluminum nitride particles look uniformly spherical. The granules have an average particle diameter D.sub.50 of 29.74 m and sphericality D.sub.S/D.sub.L (short diameter to long diameter ratio) greater than 0.85. Furthermore, the Brunauer-Emmett-Teller (BET) specific surface area of the granules is evaluated by gas adsorption technique and determined to be 0.16 m.sup.2/g, showing that the densified spherical aluminum nitride sintered particles are already satisfactorily prepared.

Embodiment 2

[0026] 100 g of aluminum oxide powders are placed in 1000 mL of ethanol to form a disperse solution. 60 g of phenol resin is dissolved in 1000 mL of ethanol to form a resin solution. Afterward, the two aforesaid solutions are uniformly mixed to form mixed slurry. Afterward, the mixed slurry undergoes spray drying with an atomizer at a rotation speed of 10000 rpm to form spherical granules with an average particle diameter D.sub.50 of 39.54 m, as measured with a laser particle diameter analyzer. Afterward, the spherical granules thus produced are placed in a boron nitride crucible (BN crucible), and then the spherical granules undergo carbonization in a high-temperature furnace with nitrogen gas atmosphere at 800 C. for 2 hours to form carbonized spherical granules. The carbonized spherical granules are heated to raise its temperature at a speed of 5 C./min and eventually stays at 1600 C. for 7 hours; afterward, the carbonized spherical granules undergo carbothermic reduction in a high-temperature furnace with a nitrogen gas or nitrogen-hydrogen mixture atmosphere to form a spherical aluminum nitride granule. Referring to FIG. 5, there are shown graphs of spherical aluminum nitride granules which have undergone carbothermic reduction and imaged by X-ray according to an embodiment of the present invention. In embodiment 2, the aluminum oxide to phenol resin weight ratio is 1:0.6. As shown in the diagram, the granules thus prepared manifest a single pure phase of aluminum nitride, thereby confirming that the preparation of a spherical aluminum nitride granule is done. Afterward, the spherical aluminum nitride granules undergo a densification sintering thermal treatment in a high-temperature furnace at 1830 C. for 7 hours. Eventually, the densified spherical aluminum nitride granules undergo decarbonization in the air at 580 C. for 5 hours to produce densified spherical aluminum nitride sintered particles. The average particle diameter D.sub.50 of the granules is assessed with a laser particle diameter analyzer and determined to be 28.25 m, and sphericality D.sub.S/D.sub.L (short diameter to long diameter ratio) of the granules is found to be greater than 0.85. Furthermore, the BET specific surface area of the granules is evaluated by gas adsorption technique and determined to be 0.19 m.sup.2/g, showing that the densified spherical aluminum nitride sintered particles are already satisfactorily prepared.

Embodiment 3

[0027] 100 g of aluminum oxide powders are placed in 1000 mL of ethanol to form a disperse solution. 70 g of phenol resin is dissolved in 1000 mL of ethanol to form a resin solution. Afterward, the two aforesaid solutions are uniformly mixed to form mixed slurry. Afterward, the mixed slurry undergoes spray drying with an atomizer at a rotation speed of 12000 rpm to form spherical granules with an average particle diameter D.sub.50 of 37.24 m, as measured with a laser particle diameter analyzer. Afterward, the spherical granules thus produced are placed in a boron nitride crucible (BN crucible), and then the spherical granules undergo carbonization in a high-temperature furnace with nitrogen gas atmosphere at 800 C. for 4 hours to form carbonized spherical granules. The carbonized spherical granules are heated to raise its temperature at a speed of 5 C./min and eventually stays at 1600 C. for 7 hours; afterward, the carbonized spherical granules undergo carbothermic reduction in a high-temperature furnace with a nitrogen gas or nitrogen-hydrogen mixture atmosphere to form a spherical aluminum nitride granule. Referring to FIG. 5, there are shown graphs of spherical aluminum nitride granules which have undergone carbothermic reduction and imaged by X-ray according to an embodiment of the present invention. In embodiment 3, the aluminum oxide to phenol resin weight ratio is 1:0.7. As shown in the diagram, the granules thus prepared manifest a single pure phase of aluminum nitride, thereby confirming that the preparation of a spherical aluminum nitride granule is done. Afterward, the spherical aluminum nitride granules undergo a densification sintering thermal treatment in a high-temperature furnace at 1800 C. for 10 hours. Eventually, the densified spherical aluminum nitride granules undergo decarbonization in the air at 580 C. for 3 hours to produce densified spherical aluminum nitride sintered particles. The average particle diameter D.sub.50 of the granules is assessed with a laser particle diameter analyzer and determined to be 27.68 m, and sphericality D.sub.S/D.sub.L (short diameter to long diameter ratio) of the granules is found to be greater than 0.85. Furthermore, the BET specific surface area of the granules is evaluated by gas adsorption technique and determined to be 0.23 m.sup.2/g, showing that the densified spherical aluminum nitride sintered particles are already satisfactorily prepared.

[0028] Unlike conventional carbothermic reduction, the method of the present invention is characterized in that: carbon-containing resin substitutes for carbon black systems such that aluminum nitride granules in a pure phase can be synthesized at 1600 C.; it dispenses with an additional slurry adjusting step and process environment; given a temperature-raising process, densified spherical aluminum nitride particles of a high density but low surface area are prepared. Hence, the method of the present invention features a simple process flow, incurs low production costs, dispenses with extra additives, and reduces consumption of carbon-containing raw materials greatly. The method of the present invention is further characterized in that aluminum oxide powder surfaces are uniformly covered with the carbon-containing resin by spray drying, and the powders are uniformly mixed as a result of primary carbonization, so as to greatly lower the carbothermic reduction temperature, thereby bring economic benefits, effectuating energy saving, and opening up to wide applications.

[0029] Although the present invention is disclosed above by embodiments, the embodiments are not restrictive of the present invention. Any persons skilled in the art can make some changes and modifications to the embodiments without departing from the spirit and scope of the present invention. Accordingly, the legal protection for the present invention should be defined by the appended claims.