KR20080065159A - Aluminum nitride nanopowders prepared by using melamine and the fabrication method thereof - Google Patents

Abstract

Aluminum nitride nanopowders prepared by adding melamine and a preparation method of the aluminum nitride nanopowders are provided to synthesize aluminum nitride nanopowders which are more efficient in solving non-economic efficiencies such as high reaction temperatures and long reaction times that are problems of an existing synthetic method. A preparation method of an aluminum nitride nanopowder comprises: a first step of mixing a boehmite(AlOOH) powder, a carbon-containing powder, and a powder containing carbon and nitrogen; a second step of charging the mixed powder into a furnace; a third step of primarily heating the furnace under a hydrogen gas or nitrogen-containing gas atmosphere, thereby decomposing the boehmite powder to form aluminum oxide(Al2O3) that is reducible at low temperatures as an intermediate; and a fourth step of secondly heating the furnace at a temperature higher than that in the first heating process under an ammonia gas or nitrogen gas atmosphere, thereby reacting the intermediate with a carbon component and a nitrogen component to reduce the intermediate and nitride aluminum at the same time. The preparation method further comprises the step of maintaining temperature of the resulting material at a final process temperature for 1 to 5 hours after performing the second heating process of the fourth step. Further, a mixing ratio of the boehmite(AlOOH) powder, the powder containing carbon and nitrogen and the carbon-containing powder is 1.00:0.36:0.20 to 1.00:5.35:3.00.

Description

Aluminum nitride nano powder manufactured using melamine and a method of manufacturing the same {ALUMINUM NITRIDE NANOPOWDERS PREPARED BY USING MELAMINE AND THE FABRICATION METHOD THEREOF}

1 is a flow chart showing a manufacturing process of the aluminum nitride nano powder of the present invention,

Figure 2 shows the X-ray diffraction curve of the aluminum nitride powder synthesized by the production method of the present invention,

3 is a TEM photograph of aluminum nitride powder synthesized by the production method of the present invention.

The present invention relates to an aluminum nitride powder having excellent sinterability using melamine and a method for manufacturing the same, and more particularly, to a method for producing aluminum nitride nano powder having low cohesion and excellent crystallinity at low cost.

Aluminum nitride is a compound in which aluminum is combined with nitrogen and is referred to as AlN. Aluminum nitride is much more thermally conductive than other ceramic materials (320 W / mK) and is very chemically stable. In addition, aluminum nitride is an electrically insulator. In particular, the thermal expansion coefficient of aluminum nitride is similar to that of silicon (4.3 × 10 ⁻⁶ / K) (IV Nicolaescu et al., J. Am. Ceram . Soc ., 77 , p2265, 1994). Because of this feature, aluminum nitride is attracting attention as the most promising heat dissipation material that can solve the thermal problem that is becoming a problem in various silicon semiconductor devices or large-scale high-power electronic devices that are rapidly increasing in density and increasing in output.

Aluminum nitride, which is used as a heat dissipation material, is a sintered compact mainly obtained by densifying powdered aluminum nitride at high temperature. Therefore, the heat dissipation characteristics of aluminum nitride are determined according to the physical properties of the final sintered compact, so that the degree of densification (sintering) should be high and there should be few components such as oxygen and carbon that adversely affect the heat transfer characteristics. These properties required for the sintered body require not only control of the sintering process but also strict control of the powder properties that are the raw materials of the sintering process (PM Lundquist et al. ", Appl. Phys. Lett ., 65 , p1085, 1994; Y. Baik et al.," Aluminum nitride: processing and applications ", Key Eng . Mater., 533 , pp 122-124, 1996).

There are several methods for producing aluminum nitride powder, and two commonly used methods. The first method is a method of directly nitriding aluminum, which is a method of directly nitriding aluminum powder by reacting it in a nitrogen or ammonia atmosphere at a high temperature of 800 ° C. or higher as shown in the following formula.

2Al + N ₂ → 2AlN (nitrogen atmosphere)

Al + N ⁺ → AlN (ammonia atmosphere)

In the case of directly nitriding aluminum on a metal, aluminum nitride, which is highly agglomerated, is formed because the melting point of aluminum is 660 ° C., which is significantly lower than the nitriding temperature. This aluminum nitride is ground to produce aluminum nitride powder (Yu Qiu et al., "Nitridation reaction of aluminum powder in flowing ammonia", J. European Ceram . Soc ., 23 , p2015, 2003; Qinghong Zhang et al., "Synthesis of nanocrystalline aluminum nitride by nitridation of δ-Al ₂ O ₃ nanoparticles in flowing ammonia", J. Am. Ceram. Soc ., 89 , p415, 2006; JM Haussonne et al., "A new synthesis process for AlN" , Am. Ceram . Soc . Bull., 72 , p84, 1993).

The second method is a method in which alumina powder, which is aluminum oxide, is mixed with a carbon raw material powder, and then heated in a nitrogen-containing atmosphere at high temperature to induce carbon heat reduction and nitriding the reduced aluminum.

Al ₂ O ₃ + 3C → 2Al + 3CO

2Al + N ₂ (or 2N ⁺ ) → 2AlN

In order to induce a carbon heat reduction reaction, a very long processing time of about 7 to 48 hours is required along with a high temperature of about 1400 to 1850 ° C. Occasionally, hydrocarbon gas is used instead of carbon powder as a carbon source. Some of the carbon components remaining after the carbon heat reduction reaction are heated at 600 to 900 ° C. in the air to oxidize and remove the carbon components. At this time, the aluminum nitride powder (primarily the powder surface) may be partially oxidized while the carbon component is removed by heating in the air. By this method, aluminum nitride powders having an average diameter of about 2 μm can be produced (JC Kuang et al., “Formation and characterization of cubic AlN crystalline in a carbothermal reduction reaction”, Mater. Lett ., 59 , p2006, 2005; T. Suehiro et al., "Synthesis and sintering properties of aluminum nitride nanopowder prepared by the gas-reduction-nitridation method", Nanotechnology , 14 , p487, 2003; T. Yamakawa et al., "Synthesis of AlN powder from Al (OH) ₃ by reduction-nitridation in a mixture NH ₃ -C ₃ H ₈ gas ", J. European Ceram . Soc ., 26 , p2413, 2006).

In addition to the above two methods, there may be a method of manufacturing various aluminum nitride powders, but there is a problem in efficiency (economical efficiency) for mass production. Conventional aluminum nitride powder production methods including the above two methods are unsuitable for producing fine aluminum nitride powder having a diameter of 2 μm or less, particularly an aluminum nitride powder having a nanometer size (about 100 nanometers or less). In order to lower the sintering temperature of the aluminum nitride powder requiring a high temperature of about 1700 ~ 2100 ℃ it is necessary to reduce the size of the aluminum nitride powder.

There has also been a study on the effects of addition of glucose or starch on the aluminum nitride synthesis, but the study is also conducted at 1400-1500 ℃, and the manufacturing process is complicated by using combustion aids (JC). kuang et al., "Influence of processing parameters on synthesis of nano-sized AlN powders", J. Crystal Growth., 236 , p12, 2004).

On the other hand, by applying melamine on aluminum flakes, a study of generating AlN through the SHS process in a vacuum atmosphere was in progress. However, it is virtually economical and has not been studied on nanopowders (GunChoo Sim, "Synthesis of AlN in Low Pressure Nitrogen Atmosphere Using Melamine as an Additive", KIGAM Bulletin ., 8 , p37, 2004).

Therefore, the conventional aluminum nitride synthesis method has a problem that it is uneconomical, such as high reaction temperature, long reaction time. Accordingly, the present inventors have invented a method for producing aluminum nitride nanopowders having low cohesion and excellent crystallinity using melamine at low cost.

An object of the present invention is to provide an aluminum nitride divided powder prepared by adding melamine and a method for preparing the same, and to solve the problems of the conventional synthesis method, such as high reaction temperature and long reaction time, which are more economical. The purpose is to synthesize efficient aluminum nitride nanopowders.

In order to achieve the above object, the present invention provides a method for producing aluminum nitride nanopowder using melamine as follows:

A first step of mixing boehmite (AlOOH) powder, carbon-containing powder, and powder containing both carbon and nitrogen; A second step of charging the mixed powder into a furnace; A third step of decomposing boehmite powder by primary heating the furnace in a hydrogen gas or nitrogen containing gas atmosphere to form aluminum oxide which can be reduced at low temperatures as an intermediate product; And a fourth step in which the intermediate is reacted with a carbon component to nitrate aluminum simultaneously with reduction by heating the furnace at a temperature higher than the first heating step in the third step under an ammonia and nitrogen atmosphere.

Here, the method may further include maintaining a temperature for 1 to 5 hours at the final process temperature after the second heating.

At this time, the primary heating is preferably made until it is 900 ℃.

In addition, the secondary heating is preferably made within a temperature range of 900 to 1400 ℃.

In addition, the primary heating is performed under a hydrogen gas or nitrogen gas atmosphere, and the secondary heating is performed under pure nitrogen gas or pure ammonia gas atmosphere, or an atmosphere in which ammonia gas is mixed with the gas used in the primary heating step. It can also be done under.

Alternatively, both the first heating step and the second heating step may use pure ammonia gas or mixed ammonia gas, but may use a method of increasing the flow rate of ammonia gas in the second heating step than in the first heating step.

In addition, the weight mixing ratio of the boehmite powder, the powder containing both carbon and nitrogen, and the carbon-containing powder is preferably in the range of 1.00: 0.36: 0.20 to 1.00: 5.35: 3.00.

In addition, the boehmite powder, the powder containing both the carbon and nitrogen, and the mixed powder during the mixing of the carbon-containing powder may be wet milled.

On the other hand, aluminum nitride powder according to another aspect of the present invention for achieving the above object is characterized in that the average diameter is 100 nanometer or less.

Hereinafter, the present invention will be described in detail.

In the present invention, a reaction scheme for synthesizing aluminum nitride is as follows.

(1) 6AlOOH → 3Al ₂ O ₃ + 3H ₂ O

(2) 3Al ₂ O ₃ + C ₃ H ₆ N ₆ + 6C-> 2AlN + 9CO + 2H ₂

(1)-(2) 6AlOOH + C ₃ H ₆ N ₆ + 6C-> 6AlN + 9CO + 2H ₂ + 3H ₂ O

To synthesize aluminum nitride, a boehmite powder, a powder containing both carbon and nitrogen, and a carbon containing powder are mixed. The boehmite (AlOOH) is used as a raw material for providing an aluminum component, and carbon-containing powders such as graphite, activated carbon or carbon black powder are used as raw materials for carbon thermal reduction, Carbon black powder is used.

In addition, melamine, urea, ammonium nitrate, ammonium chloride and the like (compound including ammonium group) may be used as the powder containing both carbon and nitrogen, and melamine powder is preferably used. This melamine has a nitrogen component and a carbon component, and is used as a raw material for carbon heat reduction and nitriding. Therefore, melamine contains both carbon for reduction and nitrogen for nitriding, so that aluminum nitride can be produced more economically than the synthesis of aluminum nitride using only boehmite powder and carbon-containing powder. In addition, it replaces the non-contact space by the low depth permeability due to the fast flow, which is a disadvantage of the gas reaction, with solid melamine to compensate for the disadvantage of the gas reaction and secures the expandability of the large area. Is present in the presence of a more favorable reduction and at the same time the use of ammonia supply of melamine leads to a relatively reduced use of ammonia. In addition, the amount of excess carbon lost by the production of hydrocarbons by the reaction of ammonia and carbon can be reduced, and the yield of products can be improved, which has the advantage of mass production of aluminum nitride more economically.

In order to uniformly mix very fine boehmite powder, nano-size carbon black powder and melamine, ethanol is added and mechanical grinding using milling is performed. Meanwhile, the weight mixing ratio of the boehmite powder, the melamine powder and the carbon black is controlled in the range of 1.00: 0.36: 0.20 to 1.00: 5.35: 3.00 so that the precursor particles of aluminum nitride may not be in contact with each other before or during the reaction. Mix and adjust the proportion of melamine.

Thereafter, the above-mentioned uniformly mixed powder is dried and charged in a crucible to a furnace. Boehmite is decomposed by primary heating to 900 ° C. while maintaining the atmosphere of the furnace with hydrogen or nitrogen to form aluminum oxide (Al ₂ O ₃ ) which can be reduced at low temperatures as an intermediate. Thereafter, by heating the furnace secondly within a temperature range of 900 to 1200 ° C., which is lower than conventional temperature, under nitrogen atmosphere or ammonia gas atmosphere, the intermediate product reacts with the carbon component to nitrate the reduced and reduced aluminum (see FIG. 1). ).

Boehmite is generally decomposed during heating to form alumina and water as in the following formula.

2AlOOH → Al ₂ O ₃ + H ₂ O

The key point of the present invention is that alumina (Al ₂ O ₃ ) formed as a result of the above decomposition reaction is chemically and thermally very stable, making subsequent carbon reduction process difficult and requiring a very high temperature for reduction. In the intermediate product stage, which is a step before aluminum oxide formed when the mite is decomposed, it is combined with a carbon component so that it is reduced at low temperature and immediately nitrided. That is, atomic nitrogen (N ^{3 −} ) and hydrogen (H ⁺ ) generated in the decomposition of highly active intermediates and ammonia gas are allowed to react directly. In addition, since the nitrogen and carbon generated in the melamine helps to reduce and nitrate, the reaction can be brought more advantageously.

In the case of the primary heating it is heated to 900 ° C under a hydrogen gas or nitrogen gas atmosphere, and in the case of the secondary heating at 900 ° C the atmosphere using pure nitrogen gas, or replaced with pure ammonia gas or used in the primary heating step The heating is continued to the final process temperature (1400 ° C. or less) under an atmosphere of ammonia gas mixed with the gas. Alternatively, pure ammonia gas or mixed ammonia gas may be used in both the first heating step and the second heating step, but the flow rate of the ammonia gas may be lowered in the first heating step and the flow rate may be increased in the second heating step.

It is then maintained at the final process temperature for 1-5 hours to promote complete nitriding and crystallinity. The carbon component remaining after the reaction is removed in the form of methane gas (CH ₄ ) or carbon monoxide (CO) by heating in decomposed ammonia gas or air.

The aluminum nitride powder prepared according to the present invention has an average diameter of 100 nanometers, preferably 50 nanometers or less, and has excellent crystallinity and very low cohesion. Fig. 2, which shows the result of X-ray diffraction analysis of the crystalline phase of the powder, shows that the powder does not contain other crystal components and is composed of single-phase pure aluminum nitride. It can be seen from the transmission electron microscope (TEM) observation picture of FIG. 3 that the manufactured aluminum nitride powder particles have a substantially constant size and shape, and the aggregation between the powder particles is not severe.

The yield of the product relative to the amount of reactants is increased by 100% compared to the experiments using only conventional carbon. When 1 g of the mixture was tested, it was confirmed that 0.1 g of AlN was used when only carbon powder was used and 0.2 g of AlN was used when melamine was used together. In other words, by using melamine, the yield is improved by 100%.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are only examples of the present invention, and the scope of the present invention is not limited thereto.

Example  One. Bohemite According to the mixing ratio of, melamine and carbon black Aluminum nitride  Generation rate

The effect of the mixing ratio of boehmite, melamine and carbon black on the production rate of aluminum nitride was examined.

The mixing ratio of boehmite, melamine and carbon black is varied as a weight fraction in the range of 1.00: 0.36: 0.20 to 1.00: 1.78: 1.00, and 0.5 g of the mixture is blown for 3 hours at 1100 DEG C while blowing ammonia gas at a rate of 3 L / min. After treating for X-ray diffraction, the synthesized aluminum nitride powder was observed by TEM.

As a result, aluminum nitride began to form under the condition that the mixing ratio of boehmite, melamine and carbon black was 1.00: 0.36: 0.20, and the amount of aluminum nitride produced was linearly increased as the mixing ratio of carbon black and melamine increased. Pure aluminum nitride was obtained for the mixing ratio of 1.00: 1.48: 0.80. The X-ray diffraction curve of the aluminum nitride nanopowder thus obtained is shown in FIG. 2, and the TEM photograph of the synthesized powder is shown in FIG. 3.

Example  2. Inflow of nitrogen gas Aluminum nitride  Impact on generation

The mixing ratio of melamine and carbon black was further increased than in the case of Example 1, and production of aluminum nitride was observed when nitrogen gas was introduced.

The mixture ratio of boehmite, melamine and carbon black was adjusted to 1.00: 0.36: 0.20 to 1.00: 5.35: 3.00, charged with 0.5 g of the mixture, and treated for 3 hours while maintaining the nitrogen flow rate at 1 l / min at 1100 ° C. It was.

X-ray diffraction analysis showed that the ratio of the intensity of the γ-Al ₂ O ₃ (220) plane to the strength of the AlN (100) plane on the hexagonal system was 1 when synthesized in a nitrogen atmosphere. In case of synthesis in the ammonia atmosphere instead of nitrogen, it was found to be 6.147. Synthesis in an ammonia atmosphere has been shown to be more advantageous than synthesis in a nitrogen atmosphere.

Example  3. Growth and Aggregation of Particles According to Reaction Temperature

Charge the mixing ratio of boehmite, melamine and carbon black to 1.00: 1.48: 0.80 to charge 10 g of the mixture, keep the ammonia at 4 L / min and perform experiments at 1100 and 1150 ° C to increase the reaction temperature The effect was observed.

As a result of the experiment, it was observed that the BET surface area was 96 m ² / g at 1100 ° C and 46 m ² / g at 1150 ° C.

Example  4. AlN  Of the mixture on the synthesis Charge  Relationship to Ammonia Flow

The effect of the amount charged with the mixture of boehmite, melamine and carbon black on the flow rate was observed.

In the synthetic experiment where the mixing ratio of boehmite, melamine and carbon black was fixed at 1.00: 1.48: 0.80 and kept at 1100 ° C for 3 hours, when 5 g of mixed powder was charged, 20 g of mixed powder was charged at 3 slm of ammonia flow rate. Pure AlN was obtained at an ammonia flow rate of 5 slm.

As a result, it was found that the reaction proceeded completely only by increasing the flow rate as the amount of the mixture increased. This means that when only carbon powder is used, 7 g of mixed powder is charged and ammonia flow rate is 5 slm condition, and when treated at 1100 ° C. for 3 hours, the required ammonia flow rate is lower than in the 2006 patent filed by the inventors of pure AlN.

As described above, the present invention relates to an aluminum nitride nanopowder using melamine and a method for manufacturing the same, which uses aluminum, which is a low-cost boehmite powder, carbon black powder, and melamine as raw materials, to produce aluminum nitride using only existing carbon. The use of significantly less carbon than that and the addition of melamine, which can supply nitrogen components, reduces the use of expensive ammonia and significantly lowers the cost of manufacturing aluminum nitride due to the low reaction temperature and shortened reaction time. The price competitiveness of the product can be strengthened.

In addition, by lowering the particle size of the aluminum nitride powder produced by the method of the present invention to the nanometer level and reducing the cohesion between particles to improve the formability, it is possible to significantly improve the sinterability compared to the conventional powder for semiconductor devices or high power electronics Various applications are expected as thermal management materials (parts) for devices. In addition, it is possible to apply to non-aqueous nano-fluid with improved thermal conductivity because of excellent dispersibility.

Claims (11)

A first step of mixing boehmite (AlOOH) powder, carbon-containing powder, and powder containing carbon and nitrogen together; A second step of charging the mixed powder into a furnace; A third step of decomposing boehmite powder by primary heating the furnace in a hydrogen gas or nitrogen-containing gas atmosphere to form aluminum oxide (Al ₂ O ₃ ) capable of reduction at low temperature as an intermediate product; And And a fourth step of heating the furnace at a temperature higher than the first heating step in an ammonia gas atmosphere or a nitrogen gas atmosphere to react with the carbon component and the nitrogen component to nitrate aluminum simultaneously with reduction. Method for producing an aluminum nitride nano powder characterized in that. The method of claim 1, further comprising maintaining the temperature for 1 to 5 hours at the final process temperature after the second heating in the fourth step. The method of claim 1, wherein the first heating in the third step is made until 900 ℃. The method of claim 1, wherein the second heating in the fourth step is a method for producing aluminum nitride nanopowder, characterized in that made in the temperature range of 900 to 1400 ℃. The method of claim 1, wherein the first heating in the third step is performed under a hydrogen gas or nitrogen gas atmosphere, and the second heating in the fourth step is performed under a pure ammonia gas atmosphere or a nitrogen atmosphere, or the first heating. A process for producing aluminum nitride nanopowders, characterized in that the mixture is made under an atmosphere in which ammonia gas is mixed with the gas used in the heating step. The method of claim 1, wherein pure ammonia gas or mixed ammonia gas is used for both the primary heating in the third step and the secondary heating in the fourth step, but the ammonia is lower than in the primary heating in the secondary heating. The manufacturing method of the aluminum nitride powder which raises the flow volume of gas. According to claim 1, The boehmite powder, the powder containing carbon and nitrogen together, and the weight mixing ratio of the carbon-containing powder is in the range of 1.00: 0.36: 0.20 ~ 1.00: 5.35: 3.00 aluminum nitride nano Method for producing a powder. The method of claim 1, wherein the mixed powder is wet milled when the boehmite powder, the powder containing carbon and nitrogen, and the carbon-containing powder are mixed. The method of claim 1, wherein the carbon-containing powder is carbon black powder. The method of claim 1, wherein the powder containing both carbon and nitrogen is melamine powder production method. An aluminum nitride nanopowder manufactured by the method of any one of claims 1 to 9 and having an average diameter of 100 nanometers or less.

Images