KR101442646B1 - Manufacturing method of aluminium nitride powder - Google Patents

Abstract

The present invention relates to a method for producing a solid-gel mixture, comprising the steps of mixing an alumina (Al ₂ O ₃ ) powder and a liquid phenol resin to form a precursor solution in which the alumina powder is dispersed in the phenol resin, Forming a precursor powder by pulverizing the solid-gel mixture; and heat-treating the precursor powder at a temperature of 1600 to 1800 占 폚 with flowing a gas containing nitrogen to synthesize aluminum nitride (AlN) To a process for producing an aluminum nitride powder. According to the present invention, it is possible to synthesize an aluminum nitride powder even at a relatively low temperature, to produce an AlN powder having a plate-like structure with a simple manufacturing process and high reproducibility.

Description

[0001] Manufacturing method of aluminum nitride powder [0002]

More particularly, the present invention relates to a method for producing an aluminum nitride powder, and more particularly, to a method for producing an aluminum nitride powder, which comprises mixing an aluminum oxide powder and a liquid phenol resin to form a solid-gel mixture, pulverizing the solid- To a method of synthesizing aluminum nitride powder under a nitrogen atmosphere by a carbothermal reduction nitriding method.

Since microelectronic devices are in the trend of using high power consumption and high frequencies, it is very important to emit heat generated from electronic products such as light emitting diodes (hereinafter referred to as "LEDs") and highly integrated memory chips .

The most common problem in LEDs is the gradual decrease in output and the decrease in efficiency due to the increase in temperature due to heat generation. With the development of high-power LEDs, junction temperature is known to reach 90-100 ° C compared to previous electronic devices. These harsh thermal stresses are the main cause of deterioration of light output, and LEDs that are exposed to outside air used for traffic signals and automobile signals are vulnerable to changes in the external environment. Accordingly, attempts have been made to extend the lifetime of the LED by solving the heat dissipation problem.

Heat dissipation is regarded as a very important design element for improving the lifetime and performance of electronic products. It is very important to achieve high heat dissipation in terms of cost efficiency such as performance stability, reliability, and price / performance for commercialization and popularization . Therefore, a lot of polymer-ceramic composites are used in the packaging of LED and microchip. In the packaging of semiconductor chips, epoxy is mainly used as a packaging material. However, since the polymer has a polymer chain bonded thereto, the polymer composite material filled with a ceramic filler such as silica, aluminum oxide, aluminum nitride or boron nitride is usually used because it has a thermal conductivity of 1 W / mK or less have.

Ceramics are compounds composed of ions and covalent bonds of positive and negative ions, including metal oxides, nitrides, carbides, borides and the like. Aluminum nitride is a typical crystalline phase of w-AlN on Wurtzite, and has a wide band gap of 6.2 eV, which has a potential application market as an ultraviolet light-emitting device.

Aluminum nitride was first discovered by F. Bregler in 1862 and first synthesized in 1877 by JW Mallet. However, by the mid-1980s, it had a relatively high thermal conductivity, and at the same time, it had insulation performance, which was first applied to microelectronics. Polycrystalline aluminum nitride represents the thermal conductivity of ^{70~210 W · m -1 · K -1} , the single crystal has a thermal conductivity of 285W · m ^-1 · K ^-1. Because of its high thermal conductivity and high electrical insulation, AlN is an interesting material as a radiator plate for many electronic products.

AlN is a semiconductive material with a wide bandgap energy of 6.2 eV and has high electrical resistivity (10 ¹³ Ω cm), low dielectric constant (8.8 at 1 MHz) and low thermal expansion coefficient (similar to silicon, 4.7 × 10 ^-6 K ^-1 ). The sintered AlN substrate is used as a radiator plate material.

Anisotropic ceramic materials with high aspect ratios such as nanorods, nanotubes, and nanosheets are known to have high thermal conductivity. For example, anisotropic BN sheet composites are known to exhibit higher thermal conductivity than AlN composites. The BN composite has a value of 1.2 W / mK whereas the AlN composite has a value of 0.6 W / mK. This is because the plate-like BN particles have better filler filling and are oriented in the in-plane direction to improve the heat radiation performance in the in-plane direction of the composite material I think.

Since the heat dissipation performance is greatly affected by the shape of the filler, it is necessary to quantify the aspect ratio referred to as the shape factor. Thermal conductivity is reported to vary with shape parameters. In addition to the shape factor, the particle size also affects the thermal conductivity because it is involved in the packing rate of the filler, the contact area between the filler and the polymer matrix, the interface characteristics, and the heat conduction path. Therefore, controlling the shape of the particles and controlling the aspect ratio of the particles are important factors in improving the thermal conductivity of the composite material.

A method for the synthesis of AlN is a method of directly nitriding the Al metal particles under a nitrogen atmosphere and the ammonium, Al ₂ O _{3 2} -CN system is the Al ₂ O ₃ in the _{Al 2 O 3 -NH 3 -C 3} H 8 system Carbothermal reduction, vapor phase synthesis, plasma synthesis, self-propagating high temperature synthesis, and the like.

Direct nitriding and carbonitriding are used as a method for commercializing aluminum nitride. The AlN powder synthesized by the carbonization heat reduction method has advantages in high purity, sinterability and stability against humidity. The disadvantages are that it is difficult to uniformly mix the starting materials, the production cost is high due to the high synthesis temperature, and that high purity Al ₂ O ₃ and high purity carbon are required. Silverman synthesized AlN by starting from the uniform dispersion of colloidal aluminum oxide in the polymer for uniform mixing (Silverman LD, J. Adv. Ceram. Mater, 3 [4], 418-419 Hashimoto synthesized using an aluminum complex and glucose (Hashimoto N, Yoden H, Nomura K, J. Am. Ceram. Soc., 74 [6], 1282-1286 (1991) ). Their results report that mixing of starting materials affects reaction temperature and reaction results. Therefore, selection and homogeneous mixing of starting materials is an important factor for synthesizing high quality AlN.

Silverman L D, J. Adv. Ceram. Mater, 3 [4], 418-419 (1988) Hashimoto N, Yoden H, Nomura K, J. Am. Ceram. Soc., 74 [6], 1282-1286 (1991)

A problem to be solved by the present invention is to provide a method for producing aluminum nitride powder capable of synthesizing aluminum nitride powder even at a relatively low temperature, simplifying the manufacturing process, exhibiting high reproducibility, and also capable of synthesizing AlN powder having a plate- .

(A) mixing a powder of alumina (Al ₂ O ₃ ) with a liquid phenol resin to form a precursor solution in which the alumina powder is dispersed in the phenol resin; (b) (C) forming a precursor powder by pulverizing the solid-gel mixture; and (d) drying the precursor powder at a temperature of 1600 to 1800 占 폚 while flowing a gas containing nitrogen And then heat-treating the aluminum nitride to synthesize aluminum nitride (AlN).

In step (a), cobalt sulfide may be further mixed with the catalyst or the flux.

The alumina powder and the cobalt sulfide are preferably mixed in a molar ratio of 1: 0.0001 to 0.01.

The halide may be further mixed with the flux in the step (a).

The halide may be composed of at least one material selected from NaCl, KCl, NH ₄ Cl and NH ₄ F, and the alumina powder and the halide are mixed in a molar ratio of 1: 0.0001 to 0.01.

The alumina powder may be a powder made of spherical or plate-like? -Al ₂ O ₃ .

In the step (d), the nitrogen-containing gas is preferably flowed at a flow rate of 0.5 to 5 L / min.

The liquid phenol resin may be a solution in which a phenol resin of the resole type is mixed with an alcohol solvent.

According to the present invention, a solid-gel mixture is formed by mixing an aluminum oxide powder and a liquid phenol resin, and the solid-gel mixture is pulverized to form a precursor powder, followed by carbothermal reduction nitrification under a nitrogen atmosphere A high purity aluminum nitride powder can be synthesized.

According to the present invention, an aluminum nitride powder can be synthesized even at a relatively low temperature, and the manufacturing process is simple and the reproducibility is high.

When cobalt sulfide is used as a catalyst or a flux and heat treatment is performed at a temperature lower than 1800 ° C., since AlN synthesized according to the present invention has a plate-like particle structure, it is preferable to use a plate-like AlN having a high aspect ratio (AlN) having a spherical particle structure can be filled more filler, and the orientation can be made in an in-plane direction so that the in-plane direction of the composite material The heat radiation performance can be improved.

FIG. 1 is a graph showing the result of thermogravimetric analysis of a solid-gel mixture formed according to Example 1. FIG.
2 is an X-ray diffraction (XRD) pattern showing the crystalline phase of the product synthesized at 1300 to 1800 캜 for 2 hours under a nitrogen gas flow according to Example 1. Fig.
3 is a graph showing the effect of the synthesis temperature on the conversion of? -Al ₂ O ₃ to AlN.
4 is a graph showing the relationship between the natural logarithmic reaction constant (lnk) and 1 / T, which determines the activation energies of h-AlN, c-AlN and AlN.
FIG. 5A is an FE-SEM (field emission scanning electron microscope) image of the product synthesized at 1600 ° C. according to Example 1, FIG. 5B is an FE-SEM image of the product synthesized at 1650 ° C., FIG. 5D is an FE-SEM image of the synthesized product, and FIG. 5D is an FE-SEM image of the product synthesized at 1800.degree.
FIG. 6 is a graph showing the particle size of a product synthesized at 1600 to 1800 ° C. according to Example 1. FIG.
7 is a graph showing the XRD pattern of a product obtained by reacting cobalt sulfide as a catalyst or a flux at 1700 캜 for 2 hours according to Example 2 and the XRD pattern of a product obtained by using a catalyst or a flux at 1700 캜 ≪ / RTI > for 2 hours.
FIG. 8A is an FE-SEM image of a product obtained by reacting at 1700 ° C. for 2 hours in the case of not using a catalyst or a flux, FIG. 8B is an FE-SEM image of a product obtained by using cobalt sulfide as a catalyst or flux according to Example 2 at 1700 ° C. The FE-SEM image of the product obtained by reaction for 2 hours.
9 is an X-ray diffraction pattern of a product obtained by reacting cobalt sulfide as a catalyst or a flux at 1200 to 1800 ° C for 2 hours.
FIG. 10 is a graph showing the reaction rate (%) of Al ₂ O ₃ and the formation rate (%) of h-AlN and c-AlN according to the synthesis temperature.
11A is an FE-SEM image of a product obtained by reacting cobalt sulfide as a catalyst or a flux at 1600 DEG C for 2 hours under a nitrogen gas flow according to Example 2, and FIG. 11B is an FE-SEM image of a product obtained under a nitrogen gas flow FIG. 11C is an FE-SEM image of a product obtained by reacting cobalt sulfide as a catalyst or flux at 1650 ° C for 2 hours, and FIG. 11C is a FE-SEM image of a product obtained by using cobalt sulfide as a catalyst or flux under a nitrogen gas flow at 1700 ° C. Fig. 11D is an FE-SEM image of the product obtained by reacting cobalt sulfide as a catalyst or flux for 2 hours at 1800 DEG C under nitrogen gas flow according to Example 2. Fig. to be.
12 is a graph showing the aspect ratio (d / t) of the sheet-like AlN particles
13 is a graph showing the particle size of the product according to the synthesis temperature.
14 is an X-ray diffraction pattern of a product obtained by reacting at 1700 캜 for 2 hours while changing the flow rate of nitrogen to 1 to 4 L / min according to Example 2. Fig.
15 is a graph showing the reaction rate (%) of h-AlN and c-AlN according to the amount of nitrogen flow in the product obtained by reacting at 1700 ° C for 2 hours according to Example 2. Fig.
16A is an FE-SEM image of a product obtained by reacting cobalt sulfide as a catalyst or flux at 1700 캜 for 2 hours in a nitrogen flow rate of 1 L / min according to Example 2. Fig. 16 FIG. 16C is an FE-SEM image of a product obtained by reacting cobalt sulfide as a flow amount at 1700 ° C for 2 hours using a catalyst or a flux, and FIG. 16c is an FE-SEM image of a product obtained by using cobalt sulfide as a catalyst or flux at a flow rate of 3 L / 16D shows the FE-SEM image of the product obtained by reacting cobalt sulfide with cobalt sulfide as a catalyst or flux for 2 hours at 1700 ° C in a nitrogen flow rate of 4 L / min. Image.
17 is a graph showing the aspect ratio according to the amount of nitrogen flow of the product obtained by reacting at 1700 캜 for 2 hours according to Example 2. Fig.
18 is a graph showing the particle size according to the amount of nitrogen flow of the product obtained by reacting at 1700 캜 for 2 hours according to Example 2. Fig.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the following embodiments are provided so that those skilled in the art will be able to fully understand the present invention, and that various modifications may be made without departing from the scope of the present invention. It is not.

Recently, high temperature conductive composites have become increasingly important materials for high power consumption and miniaturization of computer central processing unit (CPU), semiconductor chip, and light emitting diode. In electronic packaging, heat dissipation is important not only in terms of product life, but also in performance and reliability. In order to obtain a high heat dissipation performance, it is necessary to add a high thermal conductive filler, and a lot of studies have been made on ceramic fillers such as boron nitride and aluminum nitride.

Aluminum nitride is stable at high temperatures in an inert atmosphere and melts at about 2800 ° C. In vacuum, AlN begins to decompose at around 1800 ℃. In air, the surface begins to oxidize at 700 ° C or higher, and even at room temperature, surface oxidation occurs, and the thickness of the surface oxide layer is about 5 to 10 nm. This oxide layer protects aluminum nitride up to 1370 ° C, and above this temperature the bulk begins to oxidize. Aluminum nitride is stable in a hydrogen and carbon dioxide atmosphere up to 980 ° C. Aluminum nitride is slowly dissolved by the acid through the grain boundaries, and in the strong bases, aluminum nitride is eroded through the grain boundaries. Aluminum nitride is slowly hydrated in water and is resistant to erosion from the molten salt of the major part in chlorides and the like.

Similar to alumina and beryllium oxide, aluminum nitride is also applied to electronic products by applying metal electrodes.

At present, AlN is considered to be used as an ultraviolet LED as a material to replace LED using gallium nitride. In 2006, low efficiency LEDs were released at 210nm. The bandgap of the AlN single crystal was measured to be 6.2 eV, and light of a wavelength of 200 nm could be emitted in principle.

Optoelectronic devices, dielectric layers in optical storage media, substrates requiring high thermal conductivity, and chip carriers.

The aluminum nitride epitaxial crystal growth is formed on the silicon wafer due to the piezoelectric properties of AlN and is used as a surface acoustic sensor. It is rare to reliably form such an AlN thin film.

In general, AlN is widely used as a sintered substrate, and is also applied to a polymer composite. In the case of polymer composites, it is necessary to increase the content of AlN in order to obtain high thermal conductivity. Many researchers are trying to disperse more ceramic fillers in the polymer matrix. The high content of dispersed AlN forms a heat conduction path and exhibits high thermal conductivity characteristics.

Method for synthesizing the AlN is how to reduce the metal Al directly in a nitrogen atmosphere and aluminum, Al ₂ O ₃ system is -CN _{2 Al 2 O 3 -NH 3 -C 3} H 8 system carbonization heat the Al ₂ O ₃ on the reduction A vapor phase synthesis method, a plasma method, a magnetization thermal method, and the like. Two commercially available methods are direct nitriding and carbonitriding.

In the present invention, an effective method of synthesizing aluminum nitride powder by solid-gel mixing, which is a method of uniformly mixing aluminum oxide with phenol resin, is proposed.

In addition, the present invention is intended to suggest a method for synthesizing plate-shaped AlN powder.

Hereinafter, a method of manufacturing an aluminum nitride powder according to a preferred embodiment of the present invention will be described.

Alumina (Al ₂ O ₃ ) powder and a liquid phenol resin are mixed to form a precursor solution in which the alumina powder is dispersed in the phenol resin.

At this time, cobalt sulphide may be further mixed with a catalyst or a flux, and the alumina powder and the cobalt sulphide are preferably mixed in a molar ratio of 1: 0.0001 to 0.01.

Further, a halide may be further mixed with the flux. The halide may be composed of at least one material selected from NaCl, KCl, NH ₄ Cl and NH ₄ F, and the alumina powder and the halide are mixed in a molar ratio of 1: 0.0001 to 0.01.

The alumina powder may be a powder made of spherical or plate-like? -Al ₂ O ₃ . The liquid phenol resin may be a solution in which a resole type phenol resin is mixed with an alcohol solvent such as methanol. The alumina powder may be pulverized such as ball milling to be pulverized. The smaller the particle size of the alumina powder is, the smaller the particle size of the synthesized aluminum nitride powder is. Due to the use of liquid phenolic resin, phenol resin and alumina powder can be mixed uniformly and sufficient reduction and nitrification reaction can occur even at low synthesis temperature. During the nitridation reaction, the alumina oxide is uniformly distributed in the carbon matrix (phenol resin), and the carbonization is caused by the dehydration and decomposition of the phenol resin, whereby the carbon and the aluminum oxide are uniformly contacted. In the present invention, liquid phenol resin is used as a carbon source to sufficiently uniformly mix alumina (aluminum oxide) as a starting material, and alumina and carbon source are uniformly mixed, It can happen.

The precursor solution is dried to form a solid-gel mixture. The drying is preferably performed at a temperature higher than the boiling point of the solvent used in the liquid phenol resin (for example, 80 to 180 DEG C) for 10 minutes to 48 hours. When the precursor solution is dried, the solvent is evaporated off, the alumina powder forms a solid component, and the phenol resin forms a gel component to form a solid-gel mixture in the form of a solid.

The solid-gel mixture is pulverized to form a precursor powder. Grading the solid-gel mixture will result in a powdered precursor.

The precursor powder thus obtained is placed in a crucible, the crucible is charged into a furnace, and then heat treatment is performed at 1600 to 1800 ° C while flowing a gas containing nitrogen to synthesize aluminum nitride (AlN) powder. The nitrogen-containing gas is preferably flowed at a flow rate of 0.5 to 5 L / min. The heat treatment is preferably performed for about 10 to 48 hours. By appropriately adjusting the temperature of the heat treatment and the heat treatment time, an aluminum nitride powder having a desired particle size and a desired shape (spherical or plate-like structure) can be formed.

According to the present invention, by dispersing aluminum oxide in phenol resin, aluminum nitride powder can be efficiently synthesized by solid-gel mixing, which is a method of uniform mixing. By heat treatment (annealing), the phenol resin is decomposed and carbonized, whereby it is possible to uniformly mix aluminum oxide and carbon and synthesize more uniform AlN. The thus synthesized aluminum nitride powder has a crystal phase changed by Al ₂ O ₃ and AlN depending on temperature, AlN on cubic phase, AlN on hexagonal phase and AlN on hexagonal phase. AlN is on the cubic 250~600 W · m ^-1 · K ^- are known to exhibit greater thermal conductivity than AlN on the hexagonal to ^one.

Further, according to the present invention, plate-shaped AlN powder can be synthesized. It is expected that plate-like AlN having a high aspect ratio will exhibit a higher thermal conductivity when synthesizing a composite material, and it is necessary to synthesize plate-shaped AlN.

In the embodiments of the present invention described below, the plate-shaped AlN was synthesized by a carbonization thermal reduction nitridation method in which a solid-gel mixture in which plate-shaped aluminum oxide and phenol resin were mixed. At this time, cobalt sulfide was used as a catalyst or flux, and it was examined how this affects the formation of plate-like AlN. In addition, the influence of the catalyst temperature, the synthesis temperature and the flow rate of nitrogen gas on the crystallinity, aspect ratio, particle size and shape were investigated.

In order to improve the efficiency of synthesis of aluminum nitride using a solid-gel mixture as a precursor, the molar ratio of C / Al ₂ O ₃ = 3 (0.05 mol of phenol resin and 0.1 mol of Al ₂ O ₃ were mixed And C / Al ₂ O ₃ is converted to ₃ in terms of molar ratio of carbon (C) and Al ₂ O ₃ ), mixed with aluminum oxide powder using phenol resin as a precursor of carbon (C) Aluminum nitride powders were synthesized under nitrogen atmosphere by carbothermal reduction. The reaction temperature, decomposition of phenol resin, reduction of aluminum oxide and reaction rate to aluminum nitride were studied. In the case of synthesizing aluminum nitride using phenol resin, it is possible to efficiently reduce and nitrify aluminum oxide powder by coating aluminum oxide powder with phenol resin and then converting it into carbon by annealing and calcining treatment.

In order to improve the heat dissipation performance of the heat-dissipating composite material in order to dissipate heat of the electronic device, flat plate-shaped ceramic particles are dispersed in the polymer matrix. Flat plate-shaped ceramic particles have a high aspect ratio. Flat plate-shaped ceramic particles improve filler filling and networking between particles, which improves the heat dissipation performance of the composite material in the in-plane direction. .

In the present invention, a study is made on how to add a catalyst such as cobalt sulfide or a flux to form plate-shaped aluminum nitride when nitrogen is flowed at 1200 to 1800 ° C using plate-shaped aluminum oxide particles as a raw material. . In this case, it was possible to form plate-shaped aluminum nitride having a length (or diameter) ratio of particles to thickness, that is, an aspect ratio of about 10 to 20.

Hereinafter, embodiments according to the present invention will be specifically shown, and the present invention is not limited to the following embodiments.

≪ Example 1 >

Aluminum nitride powders were synthesized from a solid - gel mixture of aluminum oxide - phenol resin by carbothermal reduction nitridation method.

Specific experimental methods are as follows.

As the starting material, α-Al ₂ O ₃ powder of alpha (α) phase and resol type phenol resin (Kangnam Chemical) diluted in 50% methanol (solvent) as supplied by Kodell were used . 0.1 mol of? -Alumina powder and 0.05 mol of phenol resin were mixed, and the mixed solution was a form in which alumina powder was dispersed in liquid phenolic resin.

The solid-gel mixture was obtained by drying at 110 DEG C to remove the solvent. This solid-gel mixture is a dark brown substance, which is ground to produce a precursor powder. When this solid-gel mixture is subjected to mass thermal analysis, 80% of the phenol resin decomposes at 800 ° C or less as shown in FIG. Then, the aluminum oxide powder is dispersed in carbon (C).

AlN synthesis was carried out in a graphite furnace in order to cause a carbonization thermal reduction nitrification reaction. The precursor powder was charged into a furnace in a graphite crucible, and the furnace was evacuated before being heated, then filled with nitrogen gas and then heated. While the nitrogen gas was flowing, the precursor powder was subjected to AlN synthesis for 2 hours while changing the reaction temperature at 1300 to 1800 ° C.

The purity of the nitrogen gas was 5 N and the flow rate of the nitrogen gas was 1 L / min. The XRD-6000 diffractometer (XRD-6000 diffractometer with CuK _alpha radiation (XRD)) was used for the analysis of the crystal phase. , RIGAKU) were observed. The shapes of powders synthesized by FE-SEM (Field Emission Scanning Electron Microscope, JSM-6700F, JEOL, Japan) were observed. The particle size distribution of AlN was analyzed by laser particle size analyzer (LPSA).

Resol type phenol resins are crosslinked by methylene (-CH ₂ -), forming cresol and forming phenol and xylenol. With increasing temperature, the (= CH-) bond decreases and the diphenol ether increases.

As shown in FIG. 1, five decomposition steps of the aluminum oxide-phenol resin mixture can be observed at 600 ° C. or less.

Referring to FIG. 1, a mass reduction of 0.4% occurs in the region I at 20-150 ° C, which is expected to be due to evaporation of residual water or solvent. A mass reduction of 2.1% in Region II occurs at 150-250 ° C, which is believed to be related to the formation of a cresol by the decomposition of methylene bridges. Above 250 ° C, decomposition of the phenolic resin begins to take place, and the (= CH-) group from the cresol and xylenol decomposes between 250 and 400 ° C (region III). In the region IV of 400 to 600 ° C, a mass reduction of 10% takes place, which is believed to be the decomposition of phenol resin, ie decomposition of (-OH) and (= CH) from phenol to carbonization. The carbon around the alumina gradually decomposes at 600-1,300 ° C in the region V and the alumina surface is reduced, and nitridation takes place at 1300 ° C or higher (region VI).

2 is an X-ray diffraction pattern showing the crystal phase of the product obtained by synthesizing at 1300 to 1800 캜 for 2 hours under a nitrogen gas flow according to Example 1. Fig.

Referring to FIG. 2, the sample (product) synthesized at 1300 ° C is? -Al ₂ O ₃ Only crystalline phase appeared, and as shown in Fig. 1, the mass reduction of 8.5% is thought to be due to carbonization heat reduction.

[Reaction Scheme 1]

Al ₂ O ₃ (s) + 2 C (s)? Al ₂ O + ₂ CO (g)

[Reaction Scheme 2]

Al ₂ O (g) + solid surface → Al ₂ O (s)

For samples synthesized at 1400 ° C, weak h-AlN was detected with α-Al ₂ O _3, and at 1400 ° C or higher, the mass rapidly decreased, and it is believed that the nitridation reaction starts to occur at 1400 ° C. h-AlN appears to be caused by the following reaction.

[Reaction Scheme 3]

Al ₂ O (s) + N ₂ (g) + CO (g)? Al ₇ O ₉ N (s) + CO ₂ (g)

[Reaction Scheme 4]

Al ₇ O ₉ N (s) + N ₂ (g) + CO (g)? AlN (hexagonal) (s) + CO ₂

According to Reaction Schemes 1 to 4, Reaction Scheme 5 is obtained.

[Reaction Scheme 5]

Al ₂ O ₃ (s) + N ₂ (g) + _{3 C} (s)? ₂ AlN (hexagonal) (s)

When the reaction temperature is increased from 1400 ° C to 1650 ° C, it can be seen that the h-AlN peak is increased. At 1650 ° C, h-AlN is the main crystal phase, but a-Al ₂ O ₃ is slightly remained. In 1700~1800 ℃ c-AlN phase appears, α-Al ₂ O ₃ phase completely disappeared. It can be seen that the crystal phase of cubic AlN crystal phase is an intermediate phase and the crystal is completely transformed to h-AlN at 1800 ° C.

Figure 3 shows the effect of the synthesis temperature on the conversion of alpha -Al ₂ O ₃ to AlN.

Referring to FIG. 3, the nitridation reaction takes place in three steps at 1300 to 1800 ° C. It can be seen that the alumina is stable at 1300 ° C, and below 1300 ° C is too low to cause reduction and nitrification. In the alumina-carbon black system, in order to completely convert alumina to aluminum nitride, the reaction should be carried out at 1800 ° C for 5 hours. However, when the reaction was carried out using a solid-gel mixture, alumina was completely converted to aluminum nitride at a lower temperature of 1700 ° C for 2 hours. It is considered that sufficient reaction occurs at a lower temperature since the starting materials are uniformly mixed. In the present invention, liquid phenol resin is used as a carbon source, and the aluminum oxide and carbon are uniformly mixed with the starting material aluminum oxide, so that the reduction and nitridation reaction occur even at a lower temperature . That is, during the nitriding reaction, the alumina oxide is uniformly distributed in the carbon matrix (phenol resin), and the carbonization is caused by the dehydration and decomposition of the phenol resin, whereby the carbon and the aluminum oxide are uniformly contacted.

Aluminum oxide crystals exist only in region I, and at 1400 to 1650 ° C in region II, h-AlN increases sharply and the amount of -Al ₂ O ₃ sharply decreases. The c-AlN phase appears in the region of 1650 ~ 1700 ℃ and its amount decreases with increasing temperature. That is, it can be seen that c-AlN is an unstable intermediate phase. At 1700 ℃, the ratio of h-AlN to c-AlN was 59% and 41%, respectively, and the amount of c-AlN decreased to 31% at 1800 ℃.

In the Arrhenius equation, the dependence of the reaction constant k on the temperature T and the activation energy E _a of the chemical reaction is summarized as follows.

[Equation 1]

Where A is a constant, E _a is the activation energy for the reaction, R is the gas constant, and T is the absolute temperature. Equation (1) can be expressed by the following equation.

&Quot; (2) "

In FIG. 4, the nitridation reaction constant k can be calculated from FIG. The relationship between the natural logarithmic reaction constant (lnk) and 1 / T is shown in Fig. 4 and Table 1 to determine the activation energies of h-AlN, c-AlN and AlN.

1300 ^o C 1400 ^o C 1600 ^o C 1650 ^o C 1700 ^o C 1800 ^o C Crystal phase (%) Al ₂ O ₃ 100 87 36 31 0 0 h-AlN 0 13 64 69 58 64 c-AlN 0 0 0 0 42 36 E _a
(kJ / mol) AlN -206 -80
-8
- 91 h-AlN c-AlN Crystal size (탆) - 0.85 0.75 0.7

The activation energy of the AlN in the 1300~1650 ℃ was -206kJmol ^{-1, -1} was -80kJmol in 1700~1800 ℃. However, at 1700 ~ 1800 ℃, the activation energy for h-AlN was -8kJmol- ¹ and for c-AlN was 91kJmol- ¹ . Along with the increase in temperature, the conversion from c-AlN to h-AlN was found to continue.

5A is an image of a field emission scanning electron microscope (FE-SEM) image of a product synthesized at 1600 ° C. according to Example 1, and FIG. 5B is an FE image of a product synthesized at 1650 ° C. Fig. 5C is an FE-SEM image of the product synthesized at 1700 DEG C, and Fig. 5D is an FE-SEM image of the product synthesized at 1800 DEG C. Fig. FIG. 6 is a graph showing the particle size of a product synthesized at 1600 to 1800 ° C. according to Example 1. FIG.

Referring to Figures 5A-6, it can be seen that the particle size decreases with increasing temperature, which has been shown to decrease from 0.85 탆 to 0.7 탆. Along with the reduction of α-Al ₂ O ₃ , oxygen ions diffuse from the inside to the outside, and nitrogen is diffused into the inside along with nitriding, so the size of the particles seems to decrease with increasing temperature.

As we have seen, hexagonal and cubic aluminum nitride (AlN) grains were successfully synthesized by solid-gel mixture formation and carbonization thermal reduction nitridation. At this time, when the molar ratio of C / Al ₂ O ₃ = 3 (0.05 mol of phenol resin and 0.1 mol of Al ₂ O ₃ is mixed and converted into the molar ratio of carbon (C) to Al ₂ O ₃ , C / Al ₂ O ₃ is 3 To form a precursor powder. The result is an α-Al ₂ O ₃ solid showed that the reduction and nitrification of the AlN at a relatively low temperature by being uniformly mixed with the gel precursor takes place. The conversion of α-Al ₂ O ₃ to AlN completely took place at 1700 ° C. because phenol resin, which is the starting material, was uniformly mixed and carbonized with aluminum oxide to uniformly mix carbon and aluminum oxide, It is thought that this is happening. It can be seen that h-AlN and c-AlN coexist at 1700 ° C and 1800 ° C, and c-AlN appears to be a metastable phase. Above 1800 ℃, c-AlN disappears and is converted to h-AlN. There are three areas: at less than 1400 ° C, aluminum oxide is predominant (Region I), h-AlN begins to form at 1400-1650 ° C (Region II) and at 1700-1800 ° C aluminum oxide is completely A transition occurs (region III). In region II, the activation energy is -206 kJ / mol and in region III is -80 kJ / mol, where c-AlN is 91 kJ / mol. Here, phenol resin is a good carbon source for synthesizing AlN, which makes it possible to synthesize AlN at a low temperature.

≪ Example 2 >

Anisotropic plate - like AlN powders were synthesized.

Specific experimental methods are as follows.

Plate-shaped alumina (α-Al ₂ O ₃ ) provided by Kodell as a starting material and phenol resin of a resole type diluted in 50% methanol provided by Kangnam Chemical were used. At this time, cobalt sulfate was added as a catalyst or flux. 0.1 mol of flaky alumina was mixed with 0.05 mol of phenol resin and dried at 110 캜 to remove the solvent to obtain a solid-gel mixture. The solid-gel mixture was ground to produce precursor powder. AlN synthesis was carried out in a graphite furnace in order to cause a carbonization thermal reduction nitrification reaction. 0.2 mmol of cobalt sulfide was added in comparison with 0.1 mol of alumina (1.0 mmol of cobalt sulfide was added to Al). The precursor powder was charged into a furnace in a graphite crucible, and the furnace was evacuated before being heated, then filled with nitrogen gas and then heated. While the nitrogen gas was flowing, the precursor powder was subjected to AlN synthesis for 2 hours while changing the reaction temperature at 1200 to 1800 ° C.

And the crystal phase and shape of the product (reactant) were observed while reacting at 1200 to 1800 ° C for 2 hours. The crystal phase of the reaction product was observed using an X-ray diffractometer of Rigaku Co., and the shape of the crystal was observed with an FE-SEM (JSM-6700F, JEOL, Japan) of JEOL. The particle size was observed using a Brookfield Laser Particle Analyzer.

7 is a graph showing the XRD pattern of a product obtained by reacting cobalt sulfide as a catalyst or a flux at 1700 캜 for 2 hours according to Example 2 and the XRD pattern of a product obtained by using a catalyst or a flux at 1700 캜 ≪ / RTI > for 2 hours. The use of cobalt sulfide (cobalt sulfide) as a catalyst or flux is shown in FIG. 7 as 'with catalyst' and the absence of catalyst or flux is shown as 'without catalyst' in FIG.

Referring to FIG. 7, in the case of using cobalt sulfide and the case of using cobalt sulfide, the XRD patterns of the two products were found to contain both h-AlN and c-AlN.

FIG. 8A shows an FE-SEM image of a product obtained by reacting at 1700 ° C for 2 hours in the case of not using a catalyst, and FIG. 8B shows an FE-SEM image of the product obtained by using cobalt sulfide as a catalyst or flux according to Example 2 at 1700 ° C. SEM image of the product obtained by reaction for 2 hours.

8A and 8B, it can be seen that when the cobalt sulfide is not used, the particles have a spherical shape. On the other hand, when cobalt sulfide is used as a catalyst or a flux, It can be seen that much remains. Although the particles of the platelets are not uniform, the diameter of the platelets is in the range of 10 to 13 mu m. It is believed that cobalt sulfide plays a role in maintaining the plate morphology, but the exact mechanism is unknown. It is considered that cobalt sulphide plays a role like flux or to maintain the plate shape by lowering the energy at the interface in the reaction of aluminum oxide and carbon. Even in the growth of a single crystal, when a halide such as NaCl, KCl, NH ₄ Cl, or NH ₄ F is used as a flux, the shape of a single crystal can be synthesized at a lower temperature. Likewise, cobalt sulfide acts as a flux and can be considered to maintain the crystal form of aluminum nitride produced in a plate form.

The X-ray diffraction pattern of the product obtained by reacting cobalt sulfide as a catalyst or a flux at 1200 to 1800 ° C for 2 hours is shown in FIG.

Referring to FIG. 9, only α-Al ₂ O ₃ phase is observed at 1200 ° C., and only aluminum oxide and amorphous carbon are present at this time. At 1300 ℃, carbon is oxidized and CO gas is generated and blown, and aluminum oxide starts to be reduced.

[Reaction Scheme 6]

Al ₂ O ₃ (s) + 2 C (s)? Al ₂ O + ₂ CO (g)

[Reaction Scheme 7]

Al ₂ O (g) + solid surface → Al ₂ O (s)

Aluminum oxide reduced with the increase of temperature can be considered to react with nitrogen gas and carbon monoxide to form oxynitride and finally to aluminum nitride.

[Reaction Scheme 8]

Al ₂ O (s) + N _{2 (} g) + CO (g)? Al ₇ O ₉ N (s) + CO _{2 (} g)

[Reaction Scheme 9]

Al ₇ O ₉ N (s) + N _{2 (} g) + CO (g)? AlN (hexagonal) (s) + CO ₂

The final reaction is summarized as follows.

Al ₂ O ₃ (s) + N _{2 (} g) + _{3 C} (s)? ₂ AlN (hexagonal) (s)

AlN peak intensity of at 1300~1650 ℃ is was found to increase with an increase in temperature, but the main crystal phase is h-AlN in _{1650 ℃, α-Al 2 O} 3 can be seen that there are remaining. In 1700~1800 ℃ cubic phase AlN (c-AlN) will co-exist with the h-AlN, however, α-Al ₂ O ₃ was found completely disappeared.

FIG. 10 shows the conversion ratio of? -Al ₂ O ₃ to AlN phase based on the AlN phase in the X-ray diffraction pattern. The reaction rate was calculated as follows.

&Quot; (3) "

&Quot; (4) "

&Quot; (5) "

,

,

는 각각 큐빅 AlN, 헥사고날 AlN, α-Al₂O₃ 상의 전체 피크의 총면적을 나타낸다. Here, R ₁ , R ₂ and R ₃ are cubic AlN, hexagonal AIN, α-Al ₂ O ₃ Lt; / RTI >

,

,

Are each cubic AlN, hexagonal AlN, α-Al ₂ O ₃ Lt; / RTI >

As shown in FIG. 10, the nitridation reaction takes place in three stages at 1200 to 1800 ° C. In the first step, Al ₂ O ₃ Phase is a stable region, and the temperature is too low to cause reduction and nitridation reaction of aluminum oxide at 1200 ° C. In general, the reaction between aluminum oxide and carbon black requires a reaction at 1800 ° C for 5 hours in order for reduction and nitridation reaction to take place completely. However, it has been possible to cause reduction and nitridation reactions at lower temperatures by mixing the starting materials more evenly by uniformly mixing the phenolic resin with the aluminum oxide in liquid form and carbonizing it. It is considered that as the nitridation reaction progresses, alumina uniformly dispersed in the carbon matrix can be more easily converted to aluminum nitride by reduction and nitrification reaction. The h-AlN phase grows gradually through the generation of h-AlN and the stronger peak at 1300-1650 ° C, which is the region II, and instead, α-Al ₂ O ₃ The prize seems to be shrinking. At 1700-1800 ° C, there is a region where h-AlN and c-AlN coexist, and c-AlN decreases with increasing temperature. Moreover, when cobalt sulfide is added, c-AlN appears to be more stable (compare Fig. 3 and Fig. 10). When cobalt sulfide was added, the amount of c-AlN increased from about 42% to 52% (see FIG. 10 and Table 2).

Table 2 below shows the crystal phase (%), morphology, and aspect ratio (d / t) of the particle size and crystal size of the product synthesized from the precursor using cobalt sulphide as a catalyst or flux according to the synthesis temperature.

1200 ^o C 1300 ^o C 1400 ^o C 1600 ^o C 1650 ^o C 1700 ^o C 1800 ^o C Crystal phase (%) Al ₂ O ₃ 100 80.27 78.1 48.17 41.94 0 0 h-AlN 0 19.73 21.9 51.83 58.06 52.4 46.8 c-AlN 0 0 0 0 0 41.94 53.2 Shape Flake Flake Flake Flake Flake Flake Particle Particle Particle Particle Particle Particle Particle The aspect ratio (d / t) of the plate- - - - 8.87-21.23 8.45 - 14.34 3.86 - 9 One Particle size of AlN (nm) - - - 318.5-
353.81 555.26-
673.71 556.17-
703.26 402.54-
509.27

11A to 11D are FE-SEM images of products obtained by reacting at 1600 to 1800 DEG C for 2 hours while flowing nitrogen gas. 11A is an FE-SEM image of a product obtained by reacting cobalt sulfide as a catalyst or a flux at 1600 DEG C for 2 hours under a nitrogen gas flow according to Example 2, and FIG. 11B is an FE-SEM image of a product obtained under a nitrogen gas flow FIG. 11C is an FE-SEM image of a product obtained by reacting cobalt sulfide as a catalyst or flux at 1650 ° C for 2 hours, and FIG. 11C is a FE-SEM image of a product obtained by using cobalt sulfide as a catalyst or flux under a nitrogen gas flow at 1700 ° C. Fig. 11D is an FE-SEM image of the product obtained by reacting cobalt sulfide as a catalyst or flux for 2 hours at 1800 DEG C under nitrogen gas flow according to Example 2. Fig. to be.

Referring to FIGS. 11A to 11D, it can be seen that the reaction temperature influences the particle size and formation of the product. The products synthesized at 1600 ℃ and 1700 ℃ were found to have both plate - like particles and spherical particles. However, spherical particles were mainly present at 1800 ℃.

12 shows the length and the thickness ratio, that is, the aspect ratio (d / t), of the plate-shaped AlN particles.

Referring to FIG. 12, it can be seen that as the reaction temperature increases, the aspect ratio decreases greatly. As shown in Table 2, the aspect ratios are in the range of 8.87 to 21.23, 8.4 to 14.34, 3.88 to 9, and about 1 at 1600, 1650, 1700, and 1800 ° C, respectively.

Further, as shown in Fig. 13, the size of the spherical particles increases with increasing temperature from 337 nm to 630 nm at 1600 to 1700 ° C. 13 is a graph showing the particle size of the product according to the synthesis temperature.

Referring to FIG. 13, it can be seen that the particle size sharply decreases with an increase in temperature at 1700 to 1800 ° C. The product synthesized at 1800 ℃ had spherical particles and a particle size of 456nm. As described above, in the process of reducing and nitriding Al ₂ O ₃ , oxygen ions diffuse out from the inside of the particle, and nitrogen ions are converted into aluminum nitride crystals through diffusion from the outside to the inside, Is considered to maintain the plate shape because it acts as a flux and the reduction and nitridation reaction speed is fast due to the increase of the temperature, so it can be seen that the aluminum nitride is formed thermodynamically stable. However, it was possible to form a desired plate-like aluminum nitride at 1700 ° C.

14 shows an X-ray diffraction pattern of a product obtained by reacting at 1700 캜 for 2 hours while changing the flow rate of nitrogen to 1 to 4 L / min according to Example 2. Fig.

Referring to FIG. 14, it was found that AlN on cubic and AlN on hexagonal phase coexisted, and cubic phase decreased with increasing temperature. It can be seen that the cubic phase decreases sharply even when the flow rate of nitrogen is increased.

15 is a graph showing the reaction rate (%) of h-AlN and c-AlN according to the amount of nitrogen flow in the product obtained by reacting at 1700 ° C for 2 hours according to Example 2. Fig.

Referring to FIG. 15, when the reaction rate of each phase is examined with respect to the amount of nitrogen flow, the amount of h-AlN increases as the amount of nitrogen flow increases, and the amount of c-AlN as a cubic phase decreases.

16A to 16D are FE-SEM images of the product obtained by reacting at 1700 ° C for 2 hours with different amounts of nitrogen flow according to Example 2. FIG. FIG. 16A is an FE-SEM image of a product obtained by reacting cobalt sulfide with a nitrogen flow rate of 1 L / min as a catalyst or flux at 1700 ° C for 2 hours, and FIG. 16B shows an FE-SEM image of a product obtained by reacting cobalt sulfide FIG. 16C is an FE-SEM image of a product obtained by reacting at 1700.degree. C. for 2 hours using a catalyst or a flux as a catalyst or a flux; And FIG. 16D is an FE-SEM image of the product obtained by reacting cobalt sulfide with cobalt sulfide as a catalyst or flux at 1700 ° C. for 2 hours in a nitrogen flow rate of 4 L / min. 17 is a graph showing the aspect ratio according to the amount of nitrogen flow of the product obtained by reacting at 1700 캜 for 2 hours according to Example 2. Fig. 18 is a graph showing the particle size according to the amount of nitrogen flow of the product obtained by reacting at 1700 캜 for 2 hours according to Example 2. Fig. Table 3 below shows the crystallinity (%), morphology, and aspect ratio (d / t) of the particle size and crystal size of the product synthesized from the precursor using cobalt sulfide as a catalyst or flux according to the amount of nitrogen flow .

1 L / min 2 L / min 3 L / min 4 L / min Crystal phase (%) h-AlN 52.29 53.87 42.41 61.1 c-AlN 47.5 46.13 57.59 38.9 Morphology Flake Flake - - Particle Particle Particle Particle The aspect ratio (d / t) of the plate- 3.86 ~ 9 10.64-13.35 One One AlN particle size (nm) 630-703 682-803 378-538 393-533

Referring to FIGS. 16A to 18 and Table 3, the shape of AlN is influenced by the flow amount of nitrogen. As shown in FIG. 17, when the reaction is performed at a flow rate of 2 L / min, the aspect ratio exhibits the greatest value, , Respectively. When the amount of nitrogen is increased, the shape of the plate-like particles is broken and converted into more stable spherical particles. It can be seen that the particle size also shows the same tendency in Fig. That is, as the particle size increased from 1 L / min to 2 L / min, the particle size slightly increased and then decreased.

As described above, it was possible to synthesize anisotropic, sheet-like aluminum nitride (AlN) by using α-Al ₂ O ₃ phase and phenol resin as precursors and using cobalt sulfide as a catalyst and flux. When cobalt sulfide is added and the molar ratio of C / Al ₂ O ₃ = 3 (0.05 mol of phenol resin and 0.1 mol of Al ₂ O ₃ is mixed and converted into the molar ratio of carbon (C) to Al ₂ O ₃ , C / Al ₂ O < ₃ > is 3) was produced by carbonization thermal reduction nitrification in a graphite furnace to give a precursor of a solid-gel mixture. At this time, cobalt sulfide was found to play a very important role in the formation of plate-like aluminum nitride. Spherical aluminum nitride was produced in the absence of cobalt sulphide. Platinum-form aluminum nitride having an aspect ratio of about 10 could be produced by reacting cobalt sulfide at 1700 ° C for 2 hours.

In addition, cobalt sulfide was found to form relatively high cubic alumina aluminum compared to the case without it.

In addition, the shape of aluminum nitride is related to the amount of nitrogen flow. When the amount of nitrogen is larger than 2 L / min, the particle size is larger and the plate shape is maintained better. appear.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, This is possible.

Claims (8)

(a) mixing an alumina (Al ₂ O ₃ ) powder and a liquid phenol resin to form a precursor solution in which the alumina powder is dispersed in the phenol resin;
(b) drying the precursor solution to form a solid-gel mixture;
(c) pulverizing the solid-gel mixture to form a precursor powder; And
(d) synthesizing aluminum nitride (AlN) by heat-treating the precursor powder at 1600 to 1800 캜 while flowing a gas containing nitrogen,
Wherein the cobalt sulfide is further mixed with the catalyst or the flux in the step (a).
delete The method according to claim 1, wherein the alumina powder and the cobalt sulfide are mixed in a molar ratio of 1: 0.0001 to 0.01.
(a) mixing an alumina (Al ₂ O ₃ ) powder and a liquid phenol resin to form a precursor solution in which the alumina powder is dispersed in the phenol resin;
(b) drying the precursor solution to form a solid-gel mixture;
(c) pulverizing the solid-gel mixture to form a precursor powder; And
(d) synthesizing aluminum nitride (AlN) by heat-treating the precursor powder at 1600 to 1800 캜 while flowing a gas containing nitrogen,
In the step (a), the halide is further mixed with the flux,
Wherein the halide is composed of at least one material selected from the group consisting of NaCl, KCl, NH ₄ Cl and NH ₄ F.
5. The method according to claim 4, wherein the alumina powder and the halide are mixed in a molar ratio of 1: 0.0001 to 0.01.
The method for producing an aluminum nitride powder according to claim 1, wherein the alumina powder is a powder made of spherical or plate-like? -Al ₂ O ₃ .
The method according to claim 1, wherein the nitrogen-containing gas is flowed at a flow rate of 0.5 to 5 L / min in the step (d).
The method according to claim 1, wherein the liquid phenol resin is a solution in which an alcohol solvent and a phenol resin of a resole type are mixed.

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