WO2016114413A1

WO2016114413A1 - Manufacturing method for aluminum nitride whisker

Info

Publication number: WO2016114413A1
Application number: PCT/KR2015/000306
Authority: WO
Inventors: Woosik JUNG; Hosung CHOI; Kwanghyun RYU; Wonsik Kim; Sungkook Kim
Original assignee: Ltc Co., Ltd; Industry-Academic Cooperation Foundation, Yeungnam University
Priority date: 2015-01-12
Filing date: 2015-01-13
Publication date: 2016-07-21
Also published as: KR20160086648A

Abstract

The present invention relates to a manufacturing method for an aluminum nitride whisker, and more particularly, to a manufacturing method for an aluminum nitride whisker, the method including: forming a mixture by mixing an aluminum supply source with a carbon supply source; and reduction-nitriding the aluminum supply source to be an aluminum nitride whisker by reacting the mixture under nitriding atmosphere, in which the carbon supply source contains an activator having a predetermined content.

Description

MANUFACTURING METHOD FOR ALUMINUM NITRIDE WHISKER

The present invention relates to a manufacture of aluminum nitride (AIN), and more particularly, to a manufacturing method for an aluminum nitride whisker.

Recently, weight reduction, thinning, miniaturization and multi-functionalization have been demanded for electronic devices used in the automobile and electrical and electronics fields and the like. As these electronic devices have been highly integrated, more heat is generated. Since this heat not only lowers the function of devices, but also causes malfunction of the peripheral devices, deterioration of a board, and the like, there have been much interest and many studies on the technology of controlling heat. In particular, a high heat dissipation circuit board material may use thermal conductivity of a base metal board, and thus is advantageous in manufacturing a part such as a power device or an LED module, which consumes high power and generates high heat.

As a heat dissipation material, a composite material, in which high thermal conductivity filler materials such as a carbon or ceramic material and a polymer material are mixed, is used. The composite material may impart characteristics of metal and ceramic materials while maintaining easy processability, low costs, weight reduction, diversity of product forms, and the like, which are advantages of a polymer material in the related art. Further, the reason why a composite material is used is that a high heat conductivity filler material has excellent heat conductivity but no adhesion strength, whereas a polymer material has excellent adhesion strength but low heat conductivity. Accordingly, in order to achieve high heat conductivity of a polymer composite material, a filler which may shorten a heat transfer path is needed in a large amount, and in this case, there occur some problems in that processing conditions become difficult and physical properties of a product deteriorate. In order to shorten the heat transfer path of the heat dissipation material as described above, may studies have been actively conducted on developing a filler with a higher thermal conductivity, increasing a particle diameter of a filler, or modifying the shape or the like, in addition to studies on increasing the packing ratio of a filler.

Aluminum nitride has 10 times higher theoretical heat conductivity than that of alumina, and is excellent in electric insulation. In addition, the thermal expansion coefficient of aluminum nitride is smaller than that of alumina, and similar to that of silicon. Furthermore, aluminum nitride has excellent mechanical strength, and thus, is a material which is suitable for securing durability of a semiconductor device, and is expected to be applied as a heat dissipation material.

Recently, attempts to manufacture the aluminum nitride whiskers have been made in which the whisker has a high aspect ratio of long axis to short axis (that is, a value calculated by dividing long axis by short axis), for example, 3 or more in the form of wire or fiber as a form having anisotropy in a shape to use aluminum nitride as a heat dissipation filler. Representative examples of a method of synthesizing the aluminum nitride whisker include a direct nitridation method, a chemical vapor phase reaction method, a sublimation-condensation method using a temperature gradient, a carbothermal reduction-nitridation method, and the like. Among them, a high-quality whisker may be obtained by the direct nitridation method, the sublimation-condensation method, and the chemical vapor phase reaction method, but a starting material is expensive or the configuration of devices is complicated, so that there is a problem in that these methods are not suitable for mass production. The carbothermal reduction-nitridation method is a method of economically producing aluminum nitride, but in general, the shape of aluminum nitride is similar to that of aluminum oxide which is a starting raw material, so that when a typical aluminum oxide powder having an approximately spherical shape is used as a starting raw material, there is a problem in that an aluminum nitride whisker having a high aspect ratio in the form of wire may not be manufactured.

The present invention has been made in an effort to provide a method which may economically manufacture an aluminum nitride whisker by using a carbothermal reduction-nitridation method. However, this problem is illustrative only, but the scope of the present invention is not limited thereby.

An embodiment of the present invention provides a manufacturing method for an aluminum nitride whisker, the method including: forming a mixture by mixing an aluminum supply source with a carbon supply source; and reduction-nitriding the aluminum supply source to be an aluminum nitride whisker by reacting the mixture under nitriding atmosphere. In this case, the carbon supply source may contain an activator.

The activator may have a content in a range of 500 ppm to 25,000 ppm in the carbon supply source.

The activator may include at least one selected from iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), manganese (Mn), molybdenum (Mo), niobium (Nb), and copper (Cu).

The aluminum supply source may include an aluminum oxide, or a hydrate which may be converted into an aluminum oxide by heating. Specifically, the aluminum supply source may include one selected from α-alumina, δ-alumina, γ-alumina, boehmite, diaspore, and aluminum hydroxide (Al(OH)₃).

The aluminum supply source may include a powder having an aspect ratio of 3 or more.

The nitriding atmosphere may include a reaction gas atmosphere including nitrogen, ammonia, or a cyanide compound. The nitriding atmosphere may further include a hydrogen (H₂)gas in addition to the reaction gas. The cyanide compound may include at least one selected from, for example, acetonitrile, propanonitrile, benzonitrile, and hydrogen cyanide.

The carbon supply source may include at least one selected from graphite, activated carbon, carbon nanotube (CNT), carbon nanofiber (CNF), carbon black, graphene, and fullerene.

Meanwhile, the method may further include: calcining and removing the remaining carbon after performing the reduction-nitriding of the aluminum supply source to be an aluminum nitride whisker.

The reduction-nitriding may be performed at a temperature of 1,300℃ to 1,700℃.

According to an embodiment of the present invention configured as described above, a manufacturing method for the aluminum nitride whisker may be implemented. The aluminum nitride whisker has low electron affinity and high thermal conductivity so that startup time, fastness properties, and durability are significantly enhanced when the aluminum nitride whisker is utilized for a product such as a semiconductor. Furthermore, when the aluminum nitride whisker is used as a heat dissipation material, heat dissipation characteristics are enhanced because the heat transfer path is shortened. It is natural that the scope of the present invention is not limited by this effect.

FIG. 1 is a flowchart schematically illustrating a manufacturing method for an aluminum nitride whisker according to an embodiment of the present invention.

FIG. 2 is a configuration view exemplarily illustrating an apparatus for manufacturing an aluminum nitride whisker according to an embodiment of the present invention.

FIGS. 3 and 4 are Raman spectroscopic analysis and X-ray diffraction analysis results of the aluminum nitride whisker manufactured according to embodiments of the present invention, respectively.

FIG. 5 is a result of aluminum nitride whiskers manufactured according to the Examples and Comparative Examples of the present invention observed by an electron microscope.

Hereinafter, embodiments of the present invention will be described in detail as follows with reference to the accompanying drawings. However, the present invention is not limited to embodiments to be disclosed below, but may be implemented as various forms different from each other, and the following embodiments are provided to make the disclosure of the present invention complete and to completely inform a person with ordinary skill in the art of the scope of the present invention. Further, in the drawings, sizes of elements may be exaggerated or reduced for convenience of explanation.

Referring to FIG. 1, a manufacturing method for an aluminum nitride whisker according to an embodiment of the present invention includes mixing an aluminum supply source with a carbon supply source (S100), and preparing the aluminum nitride whisker by reacting the mixture under nitriding atmosphere (S200). Calcining and removing carbon, which is additionally remaining (S300), may be further performed after the preparing of the aluminum nitride whisker (S200) is completed.

The aluminum supply source may include aluminum oxide (Al₂O₃,alumina) as a starting material for the aluminum nitride whisker. For example, the aluminum oxide may include all of the alumina having a crystal structure of α, γ, θ, δ, η, κ, χ, and the like. As another example, the aluminum supply source may include an alumina hydrate, such as boehmite, diaspore and aluminum hydroxide (Al(OH)₃),which is dehydrated and transferred by heating,and in which a portion thereof is finally transferred to alumina.

The aluminum supply source may include, for example, a powder form, and may have a shape such as a sphere, a fiber, a plate and a cylinder without particularly limiting the shape. According to an embodiment of the present invention, it is possible to manufacture an aluminum nitride whisker regardless of the shape of an aluminum supply source. For example, even though an α-alumina having an aspect ratio of less than 3 is used as an aluminum supply source, it is possible to manufacture an aluminum nitride whisker having an aspect ratio much higher than 3 in the form of wire. Further, as the aluminum supply source, for example, the particle diameter is not particularly limited, but an aluminum supply source having a particle diameter of 5 ㎛ or less may be used.

The carbon supply source is a material which supplies carbon used in a reduction-nitridation reaction, and may include at least one selected from, for example, graphite, activated carbon, carbon nanotube (CNT), carbon nanofiber (CNF), carbon black, graphene, and fullerene. In addition, the carbon supply source may include, for example, a powder form, and the particle diameter is not particularly limited, but a carbon supply source having a particle diameter of 300 ㎛ or less may be used.

In particular, the carbon supply source contains an activator as a configuration element. The activator is, for example, an element which facilitates aluminum nitride to be grown in the form of a whisker in a process in which aluminum oxide is reduced into aluminum by carbon, and then again reacted with nitrogen to become aluminum nitride. The activator includes a metal component, and may be one or more selected from, for example, iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), manganese (Mn), molybdenum (Mo), niobium (Nb), and copper (Cu). The activator is present inside the carbon supply source, and is judged to be evaporated in a reaction process at high temperature and released from a carbon supply source and contributes to a process in which aluminum nitride is produced in a form of a whisker and grown.

In the mixing of the aluminum supply source with the carbon supply source, for example, both a wet mixing method and a dry mixing method may be used. In the wet mixing method, the aluminum supply source and the carbon supply source may be mixed by using a solvent such as water, methanol, ethanol, isopropyl alcohol, acetone, toluene and xylene. The solvent is removed from a slurry which is implemented by uniform mixing, and the slurry is subjected to a drying process. Examples of the dry mixing method include a simple mixing method using a mixer and an impeller, and a method using a ball mill may also be used.

A mixture of the aluminum supply source and the carbon supply source is introduced into a predetermined reaction furnace, and then is reacted under nitriding atmosphere. The nitriding atmosphere may be, for example, formed by introducing a gas including nitrogen (N₂),ammonia(NH₃),or a cyanide compound into a reaction furnace. The cyanide compound may include at least one selected from, for example, acetonitrile, propanonitrile, benzonitrile, and hydrogen cyanide. The nitrogen supply source is preferably a gas state, but is not particularly limited.

The temperature of the nitriding atmosphere may be in a temperature range of 1,300℃ to 1,700℃, rigorously 1,500℃ to 1,700℃, and more rigorously 1,500℃ to 1,650℃. When the temperature of the nitriding atmosphere is too low, the reduction-nitridation reaction is slow, and abnormal aluminum nitride may be formed. Furthermore, when the temperature of the nitriding atmosphere is too high, the reduction-nitridation reaction occurs too quickly, thereby lowering the purity, and as a result, aluminum nitride in a fine powder form is formed, thereby making it difficult to form a whisker shape.

The time of the nitriding atmosphere may be in a range of 3 hours to 10 hours. When the time of the nitriding atmosphere is too short, the reduction-nitridation reaction does not sufficiently occur, and when the time is too long, abnormal aluminum nitride is easily formed. Further, the flow rate of the nitriding atmosphere is preferably, for example, 150 mL/min to 250 mL/min.

When the mixture is reacted under the nitriding atmosphere, a nitride aluminum whisker in the form of a wire, which is significantly different from a sphere in terms of aspect ratio, is produced by an activator contained in the carbon supply source even though a powder in the form of a sphere in the aluminum supply source has a spherical form. In this case, the amount of the aluminum nitride whisker produced shows a tendency to be increased as the content of the activator included in a carbon supply source is increased.

When the carbon supply source is remaining after the reaction is completed, the carbon supply source may be subjected to a decarbonizing process of calcining and removing the remaining carbon supply source. In the calcining of the remaining carbon, for example, heat treatment may be performed under air atmosphere to oxidize and remove carbon. The time for calcining the remaining carbon is usually limited by the amount of remaining carbon, and the amount of remaining carbon is limited by the amount of carbon supply source added and the addition ratio. For example, when the amount of carbon supply source added is large or the addition ratio is high, the time for the remaining carbon to be calcined is prolonged.

The aluminum nitride whisker of the present invention as described above has low electron affinity and high thermal conductivity, so that startup time, fastness properties, and durability are significantly enhanced when the aluminum nitride whisker is utilized for a device such as a semiconductor. Further, when the aluminum nitride whisker is used as a filler of a heat dissipation material, a heat transfer path may be shortened without increasing the packing ratio of the filler.

FIG. 2 is a configuration view exemplarily illustrating an apparatus 100 for manufacturing an aluminum nitride whisker according to an embodiment of the present invention. Referring to FIG. 2, the apparatus 100 for manufacturing the aluminum nitride whisker has a shape of a box-type nitridation furnace (110, furnace shell). The box-type nitridation furnace 110 includes a gas supply line 120 for supplying nitrogen, ammonia or a cyanide compound in order to form a nitriding atmosphere, and a gas exhaust line 130 for discharging carbon dioxide or carbon monoxide produced in a reduction-nitridation reaction. A reaction vessel 150 may be disposed inside the box-type nitridation furnace 110. The reaction vessel may include an alumina boat, a graphite boat, and the like. A mixture 160 of mixing an aluminum supply source with a carbon supply source may be provided to the reaction vessel 150. Further, a heater 140 is disposed on an outer circumferential surface of the box-type nitridation furnace 100, and thus, may supply heat inside the box-type nitridation furnace 100. When the heater 140 forms a high-temperature atmosphere in the boxy-type nitridation furnace 100, the mixture 160 may be subjected to reduction-nitridation reaction to implement the aluminum nitride whisker according to an embodiment of the present invention.

Hereinafter, experimental examples will be provided in order to help understand the present invention. However, the following experimental examples described below are only for helping to understand the present invention, and the present invention is not limited by the experimental examples below.

Experimental Example 1)

5.00 g of an α-alumina powder which is an aluminum supply source was mixed with 2.00 g of a carbon black powder which is a carbon supply source, and the mixture was placed in an alumina boat which is a reaction vessel and introduced into a box-type nitridation furnace illustrated in FIG. 2. In this case, 500 ppm of iron (Fe) was included as an activator in carbon black. The reaction was performed at 1,600℃ under a nitrogen atmosphere (flow rate: 200 mL/min) for 5 hours, and after the reaction was completed, the remaining carbon was calcined and removed in the air for 1 hour.

Experimental Example 2)

The experiment was performed in the same manner as in Experimental Example 1 as described above, except that the content of iron (Fe) contained in carbon black was 25,000 ppm.

Comparative Example 1)

The experiment was performed in the same manner as in Experimental Example 1 as described above, except that a carbon black powder containing no iron was used. In this case, the carbon black powder containing no iron was a carbon black powder obtained by immersing a commercially available carbon black powder in a concentrated hydrochloric acid solution for 1 week and dissolving iron components.

Comparative Example 2)

The experiment was performed in the same manner as in Experimental Example 1 as described above, except that a carbon black powder containing no iron was used, and 1 mg of a nano iron powder was further added to the mixture of an α-alumina powder and a black carbon powder.

In order to confirm the manufactured aluminum nitride, the sample was analyzed by a Raman spectroscopic analysis apparatus and an X-ray diffraction analysis apparatus, and as a result of the analysis, it could be confirmed that aluminum nitride was produced. Representatively, analysis results of Example 1 are illustrated in FIGS. 3 and 4.

FIG. 3 is an analysis result of the Raman spectroscopic analysis apparatus, and as illustrated, peaks detected all correspond to the peaks of the aluminum nitride. Meanwhile, the X-ray diffraction peaks of FIG. 4 were all the peaks of the aluminum nitride.

FIG. 5 is a result of aluminum nitrides manufactured according to the Examples of the present invention observed by a scanning electron microscope (SEM). FIGS. 5(a) and (b) are an observation result of aluminum nitride manufactured by Comparative Examples 1 and 2, respectively, and FIGS. 5(c) and (d) are an observation result of aluminum nitride manufactured by Experimental Examples 1 and 2, respectively.

Referring to FIGS. 5(c) and (d), it can be seen that an aluminum nitride whisker in the form of a wire was formed together with an aluminum nitride powder having an approximately spherical shape. Further, in Example 2 in which the content of iron, which is an activator, was higher, it can be confirmed that the aluminum nitride whisker was formed in a larger amount.

Meanwhile, referring to FIG. 5(a), it can be seen that when no iron was contained in carbon black, the whisker was not formed at all. Furthermore, referring to FIG. 5(b), when iron which is an activator was separately added, unlike Examples 1 and 2, whiskers were slightly produced, but the amount of whiskers produced was significantly smaller than those of Examples 1 and 2.

From these results, in manufacturing an aluminum nitride whisker by a carbothermal reduction-nitridation method, the activator needs to be certainly supplied, and it can be seen that it was more effective only when the activator is supplied while being contained in a carbon supply source rather than being separately provided. It is inferred that this is associated with the distribution of the activator before the aluminum nitride whisker was produced. That is, in consideration of the reaction temperature at which the aluminum nitride was formed, the added activator is expected to be evaporated in a reaction of producing the aluminum nitride, and in this case, the evaporated activator provided while being contained in the carbon supply source is expected to be brought in contact with an aluminum supply source, for example, aluminum oxide in a more uniform and wider area than the activator provided separately from the carbon supply source. For this reason, it is interpreted that the probability of forming the aluminum nitride whisker is high.

The present invention has been described with reference to the embodiments illustrated in the drawings, but the embodiments are illustrative only, and it would be appreciated by those skilled in the art that various modifications and other equivalent embodiments may be made. Therefore, the true technical scope of the present invention needs to be defined by the technical spirit of the appended claims.

Claims

A manufacturing method for an aluminum nitride whisker, the method comprising:

forming a mixture by mixing an aluminum supply source with a carbon supply source; and

reduction-nitriding the aluminum supply source to be an aluminum nitride whisker by reacting the mixture under a nitriding atmosphere,

wherein the carbon supply source contains an activator.
The method of claim 1, wherein the activator has a content in a range of 500 ppm to 25,000 ppm in the carbon supply source.
The method of claim 1, wherein the activator comprises at least one selected from iron (Fe), nickel (Ni), magnesium (Mg), cobalt (Co), manganese (Mn), molybdenum (Mo), niobium (Nb), and copper (Cu).
The method of claim 1, wherein the aluminum supply source comprises an aluminum oxide, or a hydrate which is capable of being converted into an aluminum oxide by heating.
The method of claim 4, wherein the aluminum supply source comprises one selected from α-alumina, δ-alumina, γ-alumina, boehmite, diaspore, and aluminum hydroxide (Al(OH)₃).
The method of claim 1, wherein the aluminum supply source comprises a powder having an aspect ratio of 3 or more.
The method of claim 1, wherein the nitriding atmosphere comprises a reaction gas atmosphere comprising nitrogen, ammonia, or a cyanide compound.
The method of claim 7, further comprising hydrogen (H₂) in addition to the reaction gas.
The method of claim 7, wherein the cyanide compound comprises at least one selected from acetonitrile, propanonitrile, benzonitrile, and hydrogen cyanide.
The method of claim 1, wherein the carbon supply source comprises at least one selected from graphite, activated carbon, carbon nanotube (CNT), carbon nanofiber (CNF), carbon black, graphene, and fullerene.
The method of claim 1, further comprising: calcining and removing the remaining carbon after performing the reduction-nitriding of the aluminum supply source to be an aluminum nitride whisker.
The method of claim 1, wherein the reduction-nitriding is performed at a temperature of 1,300℃ to 1,700℃.