JP2005008432A - Method of manufacturing aluminum nitride particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture aluminum nitride superfine particle with high purity. <P>SOLUTION: The superhigh purity aluminum nitride superfine particle is manufactured by blowing gaseous ammonia to a gaseous mixture comprising nitrogen and aluminum vapor being at a temperature ranging from a temperature at which aluminum nitride starts to be formed to a temperature at which the formation of the aluminum nitride is completely finished so as to lower the temperature at which the formation of the aluminum nitride is completely finished while keeping the temperature higher than the condensation temperature of aluminum and passing the resultant produced particle through ethanol. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing aluminum nitride particles. More specifically, the present invention relates to a method for producing ultrafine aluminum nitride particles with high purity.
[0002]
[Prior art]
Aluminum nitride (also referred to as AlN) has features such as high thermal conductivity and high electrical insulation, and is used as a material for high heat dissipation control boards in electronic equipment and electrical insulation materials in energy conversion equipment. The In particular, ultrafine particles of aluminum nitride (generally particles having a particle size of about 100 nm or less) have high activity due to their large surface area, and can reduce the sintering temperature during the production of an AlN sintered body, thus simplifying the sintering apparatus. In addition, when AlN ultrafine particles are filled in an organic material such as an epoxy resin (so-called “nanocomposite”), the mechanical strength and thermal properties are reduced due to the relaxation effect of concentrated stress. It is highly useful because it can be expected to improve.
[0003]
Conventionally, a method for producing aluminum nitride ultrafine particles from metal aluminum powder using an arc plasma reactor has been proposed (Non-Patent Document 1). In this prior art, the plasma gas is based on argon (Ar) as a base and hydrogen (H ₂ ) And nitrogen (N ₂ ) Mixed gas (Ar: about 200 L (liter) / min (minute), H ₂ : About 5 L / min, N ₂ : About 5 L / min), a transitional arc plasma is generated, and the metal aluminum powder (0.9 to 1.6 g / min) is heated and evaporated using the plasma as a heating source. Hydrogen (H ₂ ) Based on ammonia (NH ₃ ) Mixed gas (H ₂ : About 80 to 100 L / min, NH ₃ : 0 to about 20 L / min, H ₂ And NH ₃ Are sprayed at 100 L / min) to obtain AlN ultrafine particles.
[0004]
Patent Document 1 discloses a method of synthesizing aluminum nitride by a high frequency induction thermal plasma method using a mixed gas of argon, nitrogen, hydrogen and ammonia and aluminum powder as raw materials. In the example of Patent Document 1, a mixed gas of argon (40 L / min) and nitrogen (10 L / min) is used as a plasma gas, hydrogen (5 L / min or less) is used as a particle size control gas, and ammonia ( A mixed gas of 20 L / min or less and hydrogen (20 L / min or less) is used, respectively, and aluminum powder (100 g / min) is introduced into the plasma. The flow rate ratio of ammonia / hydrogen in the reaction gas is 0.1. It is described that a nitriding rate of 100% can be obtained in the range of ˜70.
[0005]
In Patent Documents 2 and 3, there is a method of increasing the purity of aluminum nitride by heat-treating mixed powder of aluminum nitride and aluminum in nitrogen or a mixed gas of nitrogen and inert gas to nitride the surface of aluminum. It is disclosed.
[0006]
[Non-Patent Document 1]
Kikukawa, Makino: "Material synthesis by arc plasma reactor with secondary anode (2nd report) -Synthesis of AlN ultrafine particles from Al metal powder-" Pollution Resources Institute Vocabulary, Vol. 20, no. 1, 19 (1990)
[Patent Document 1]
No. 6-49566
[Patent Document 2]
JP-A-62-282635
[Patent Document 3]
JP-A-2-102110
[0007]
[Problems to be solved by the invention]
However, AlN purity is not quantified in Non-Patent Document 1, but judging from the XRD result indicated by Table 1 in the same document, it seems that the purity of aluminum nitride is about 70% by mass even when the purity is high. This is because in the manufacturing method of Non-Patent Document 1, the kind of plasma gas or reaction / quenching gas or the temperature condition for blowing reaction / quenching gas is not appropriate. Condensation causes a substantial amount of aluminum to be mixed in the manufactured particles. As a result, the purity of aluminum nitride is necessary for practical use (for example, high heat dissipation control board materials and electrical insulating materials) (manufacturing) It seems that the amount of aluminum nitride particles in the particles is much lower than about 96% by mass).
[0008]
Further, Patent Document 1 does not show temperature conditions for blowing reaction / quenching gas. A complex reaction occurs in a plasma in which multiple types of gas are mixed, and the start temperature and completion temperature of aluminum nitride generation and the condensation temperature of aluminum depend on the set conditions (gas type, Al to gas molar ratio, pressure). Change. Therefore, when the capacity of the production apparatus is increased and the above setting conditions are changed, unreacted aluminum is condensed without sufficiently producing AlN, and a considerable amount of aluminum is mixed in the produced particles. Therefore, it seems difficult to obtain high-purity aluminum nitride particles.
[0009]
Furthermore, it is difficult for the high frequency induction thermal plasma used in Patent Document 1 to increase the capacity of a device including a power source, and the plasma tends to become unstable when raw materials are injected into the plasma. There is a problem that it is difficult to drive.
[0010]
Moreover, the argon gas used as the base of the plasma gas in Non-Patent Document 1 and Patent Document 1 is expensive, and there is a problem that the operating cost is increased. Furthermore, although hydrogen is used for the quenching gas in Non-Patent Document 1 and Patent Document 1, a gas having a hydrogen concentration of 4% by volume or more needs to be handled as an explosive / flammable gas. For this reason, it is necessary to make the plasma furnace itself and its peripheral equipment explosion-proof, and to install hydrogen detectors at a number of locations, which increases the equipment cost.
[0011]
In addition, since both of the techniques of Patent Documents 2 and 3 are methods for nitriding only the surface of the aluminum powder, the inside of the aluminum powder cannot be nitrided, leaving metal aluminum, and the purity of the aluminum nitride is still real. Does not satisfy the purity required for industrial use. Furthermore, since the productivity of high-purity aluminum nitride ultrafine particles is low as described above, there is a problem that the manufacturing cost is extremely high.
[0012]
Accordingly, an object of the present invention is to provide a method capable of producing aluminum nitride ultrafine particles with high purity.
[0013]
[Means for Solving the Problems]
In order to achieve this object, the inventors of the present application have conducted various experiments and intensive studies. As a result, by selecting the type of gas used for producing aluminum nitride and the temperature conditions for blowing the gas, ultrafine aluminum nitride particles having a purity higher than that of the conventional method are obtained. It came to know that can be manufactured. The method for producing aluminum nitride particles according to claim 1 is based on such knowledge, and ammonia gas is blown into a mixed gas composed of nitrogen and aluminum vapor.
[0014]
Therefore, by using a mixed gas composed of nitrogen and aluminum vapor, the formation reaction of aluminum nitride starts from a higher temperature state, so that the conversion rate from aluminum to aluminum nitride can be increased. And the condensation temperature of aluminum can be lowered | hung by using ammonia as a reaction gas (nitrogen source) which accelerates | stimulates the production | generation reaction of aluminum nitride, and as a quenching gas for obtaining the ultrafine particle of aluminum nitride. Thereby, condensation of unreacted aluminum can be prevented and mixing of metal aluminum can be prevented. In other words, by using a mixed gas composed of nitrogen and aluminum vapor and using ammonia as a reaction / quenching gas blown into the mixed gas, a temperature range necessary for producing aluminum nitride from aluminum is obtained. Can be expanded. Thereby, ultra-fine aluminum nitride particles with high purity (for example, the amount of aluminum nitride particles in the manufactured particles is 90% by mass or more) can be obtained.
[0015]
The invention according to claim 2 is the method for producing aluminum nitride particles according to claim 1, wherein a temperature at which the nitrogen and aluminum in the mixed gas react to start producing aluminum nitride and a temperature at which the production is completed. The ammonia gas is blown into the mixed gas in the temperature range between and.
[0016]
The temperature range between the production start temperature and the production completion temperature of aluminum nitride is a temperature range where the production reaction of aluminum nitride proceeds actively, and ammonia can be easily produced by blowing ammonia as a nitrogen source into this temperature range. It decomposes to generate nitrogen atoms (N), and the conversion rate from aluminum to aluminum nitride can be increased. As a result, high-purity aluminum nitride ultrafine particles can be obtained. Here, the production start temperature and the production completion temperature of aluminum nitride can be calculated, for example, by chemical equilibrium calculation in a case where aluminum is mixed in an atmosphere of nitrogen gas, the reaction field pressure is 50 kPa, and aluminum and nitrogen gas. Is 1:50, the AlN generation start temperature is about 2100 ° C., and the AlN generation completion temperature is about 1700 ° C. In addition, when the pressure is 10 to 100 kPa and the mole number of nitrogen gas is 10 to 100 mol with respect to 1 mol of aluminum, the upper limit of the AlN generation start temperature is about 2200 ° C., and the lower limit of the AlN generation completion temperature is about 1500 ° C.
[0017]
The invention according to claim 3 is the method for producing aluminum nitride particles according to claim 2, wherein the temperature of the mixed gas remains higher than the condensation temperature of unreacted aluminum in the mixed gas. The ammonia gas is blown in such a manner that the temperature is lowered to a temperature at which the generation of is completed.
[0018]
In order to set the conversion rate from aluminum to aluminum nitride to 100%, it is necessary to lower the temperature from the AlN production start temperature to the AlN production completion temperature. On the other hand, if the AlN formation reaction is not sufficiently advanced, rapid cooling is performed, and if the unreacted aluminum vapor remains and the temperature is below the condensation temperature of aluminum, a solid metal aluminum is produced, and the generated particles Al powder is mixed in and the purity of AlN is lowered. The condensation temperature of aluminum greatly varies depending on the proportion of unreacted aluminum (Al unreacted rate). Therefore, ammonia gas, which is a reaction / quenching gas, is blown into the mixed gas of nitrogen and aluminum vapor in the temperature range between the AlN generation start temperature and the AlN generation completion temperature, and the temperature of the mixed gas is made to react with aluminum and nitrogen. The temperature is lowered to the AlN generation completion temperature while keeping the temperature below the condensation temperature of aluminum corresponding to the Al unreacted rate at this time. This can be realized, for example, by adjusting the position where the ammonia gas is blown, the flow rate or temperature of the blown ammonia gas, and the like. Thereby, condensation of unreacted aluminum vapor | steam can be prevented and it can prevent that metallic aluminum mixes in manufacture particle | grains. In order to obtain AlN ultrafine particles, it is preferable to prevent the growth of AlN particles by rapidly cooling immediately after the conversion rate from aluminum to aluminum nitride reaches almost 100%.
[0019]
According to a fourth aspect of the present invention, there is provided a method for producing aluminum nitride particles, wherein particles in which aluminum nitride particles and metal aluminum particles are mixed are passed through ethanol. Therefore, a chemical reaction does not occur between aluminum nitride (AlN) and ethanol, but a chemical reaction occurs between metal aluminum (Al) and ethanol, and as a result, ethoxide is generated. That is, only metallic aluminum is captured by ethanol, and the particles that have passed through ethanol are only aluminum nitride particles. Thereby, the metal aluminum powder in the manufactured particles is removed, and aluminum nitride ultrafine particles with higher purity (for example, the amount of aluminum nitride particles in the manufactured particles is 99% by mass or more) can be manufactured.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.
[0021]
1 to 3 show an embodiment of the method for producing aluminum nitride particles of the present invention. In this method for producing aluminum nitride particles, ammonia gas is blown into a mixed gas composed of nitrogen and aluminum vapor.
[0022]
“Temperature range necessary for producing aluminum nitride (AlN) from aluminum (also referred to as Al)” is a temperature region where aluminum nitride is produced and is equal to or higher than the condensation temperature of unreacted aluminum. ,is required. Therefore, the inventors of the present application have identified nitrogen gas (N ₂ Also written. ) Or ammonia gas (NH ₃ Also written. The chemical equilibrium calculation of the field where aluminum was mixed in the atmosphere was performed to calculate the formation temperature of aluminum nitride and the condensation temperature of unreacted aluminum (metallic aluminum). FIG. 1 shows an example of the result calculated by the above chemical equilibrium calculation. The pressure is 50 kPa, Al and atmospheric gas (N ₂ Or NH ₃ ) Molar ratio was 1:50.
[0023]
The curves A and A ′ on the left in FIG. 1 represent the formation temperature of aluminum nitride, and correspond to the left vertical axis (conversion rate from Al to AlN [%]). In addition, upper right curves B and B ′ in the figure represent the condensation temperature of unreacted aluminum and correspond to the right vertical axis (Al unreacted rate [%]). In addition, the solid curves A and B in FIG. ₂ The dashed curves A ′ and B ′ show the case where the atmospheric gas is NH ₃ Shows the case.
[0024]
Curves A and A ′ in FIG. 1 show the relationship between the temperature and the AlN conversion rate obtained by chemical equilibrium calculation based on the temperature. From the results of FIG. 1, the gas species is nitrogen (N ₂ ), The gas species is ammonia (NH ₃ ), The AlN generation start temperature (the temperature at which the conversion rate from Al to AlN starts to increase from 0% in the left-upward curves A and A ′) becomes higher, that is, the AlN generation reaction from a higher temperature state. It turns out that occurs. Further, from the results of FIG. 1, the gas species is ammonia (NH ₃ ) Is nitrogen (N ₂ It can be seen that the condensation temperature of the unreacted aluminum is lower than in the case of). Gas type is NH ₃ In the case of NH, the reason why the AlN formation start temperature and the condensation temperature of unreacted aluminum are reduced is NH. ₃ Decomposition of N ₂ , H ₂ This is thought to be because the partial pressure of Al was relatively low.
[0025]
Therefore, by using a mixed gas composed of nitrogen and aluminum vapor, an AlN generation reaction can be caused from a higher temperature range, and the conversion rate from Al to AlN can be increased. And by using ammonia as a reaction gas (nitrogen source) for promoting the AlN formation reaction and as a quenching gas for obtaining ultrafine particles of aluminum nitride, the condensation temperature of aluminum is lowered, thereby Condensation can be prevented, and mixing of metal aluminum can be prevented. In other words, by using a mixed gas composed of nitrogen and aluminum vapor and using ammonia as a reaction / quenching gas blown into the mixed gas, a temperature range necessary for producing aluminum nitride from aluminum is obtained. Can be expanded. Thereby, ultra-fine aluminum nitride particles with high purity (for example, the amount of aluminum nitride particles in the manufactured particles is 90% by mass or more) can be obtained.
[0026]
Here, for the production of aluminum nitride particles, it is preferable to use arc plasma. Arc plasma has the feature that it is ultra-high temperature (for example, about 10000 ° C.) and can extend the high-temperature region, and it becomes possible to continuously produce a large amount of aluminum nitride ultrafine particles, which in turn has been extremely expensive. This is because the cost can be expected to be reduced. Also, unlike the high-frequency induction thermal plasma method, it is easy to increase the capacity of the device including the power source, and further, when the raw material is injected into the plasma, the plasma is stable and easy to operate continuously. There are also advantages. For example, in this embodiment, nitrogen gas (N) is used as plasma gas (also referred to as torch gas or Al carrier gas). ₂ ) To generate an arc plasma, inject metal aluminum (aluminum powder) from the upstream or upper side of the plasma, heat and evaporate the metal aluminum using the plasma as a heating source, and create a mixed gas composed of nitrogen and aluminum vapor. Then, ammonia gas is sprayed as a cooling / reaction gas on the mixed gas downstream or below the plasma to produce ultrafine aluminum nitride particles.
[0027]
Here, with respect to the mixed gas composed of nitrogen and aluminum vapor, the timing of injecting the ammonia gas is that the temperature of the mixed gas is “nitrogen atoms (also referred to as N)” and aluminum (Al) react and nitride. It is preferably in the “temperature range between the temperature at which aluminum starts to be generated (AlN generation start temperature) and the temperature at which the generation is completed (AlN generation completion temperature)”. Gas type is N ₂ The reaction field pressure is 50 kPa, Al and N ₂ In the example of FIG. 1 where the gas molar ratio is 1:50, the AlN generation start temperature is about 2100 ° C., and the AlN generation completion temperature is about 1700 ° C. That is, in the example of FIG. 1, it is preferable to blow ammonia gas into a portion of the mixed gas composed of nitrogen and aluminum vapor at a temperature of 1700 ° C. to 2100 ° C.
[0028]
The temperature range between the production start temperature and the production completion temperature of AlN is a temperature range in which the production reaction of aluminum nitride proceeds actively. By blowing ammonia as a nitrogen source into this temperature range, the condensation temperature of aluminum And the unreacted aluminum is prevented from condensing, and the blown ammonia is easily decomposed to generate nitrogen atoms (N), thereby further increasing the conversion rate from Al to AlN (approximately 100%). it can. Although the AlN production start temperature and production completion temperature vary depending on the reaction field pressure and the molar ratio of Al to the atmospheric gas, theoretical values can be calculated by chemical equilibrium calculation. For example, when the pressure is changed to 10 to 100 kPa and the number of moles of atmospheric gas relative to 1 mol of aluminum is changed to 10 to 100 mol, the upper limit of the AlN generation start temperature is about 2200 ° C., and the lower limit of the AlN generation completion temperature is about 1500 ° C. there were.
[0029]
Here, in order to set the conversion rate to AlN to 100%, it is necessary to lower the temperature from the AlN production start temperature to the AlN production completion temperature, but the relationship between the time required for the AlN production reaction and the cooling rate. Therefore, if the rapid cooling is performed in a state where the AlN production reaction has not sufficiently progressed, there are cases where the unreacted Al vapor remains and the temperature is below the condensation temperature of Al. In this case, a solid (powder) of metal Al is generated, and even if ammonia gas is blown in, the solid Al powder does not react, and the Al powder is mixed with the generated particles and the purity of AlN is lowered. For this reason, in order to increase the AlN purity, it is cooled slowly until Al vapor and N sufficiently react to ensure sufficient AlN generation reaction time (residence time) so as not to leave unreacted Al vapor. There is a need to. For example, when the conditions shown in FIG. 1 are satisfied, the temperature is gradually lowered from a temperature range of 1700 ° C. to 2100 ° C. by blowing ammonia gas so as to maintain a temperature range of 1200 to 1600 ° C., for example. This is a temperature range where unreacted Al is still condensed at 1200 to 1600 ° C. even when the AlN production reaction proceeds smoothly and the AlN purity is as high as about 90% by mass, for example. This is necessary. On the other hand, if the cooling is continued as it is, the AlN particles frequently grow repeatedly with repeated collisions, and ultrafine particles cannot be obtained. For this reason, in order to obtain AlN ultrafine particles, it is necessary to rapidly cool immediately after the conversion rate from Al to AlN becomes almost 100%.
[0030]
As shown in FIG. 1, the condensation temperature of Al varies greatly depending on the proportion of unreacted Al. From the above, in order to obtain high-purity AlN from Al vapor, N in the temperature range between the AlN generation start temperature (for example, about 2100 ° C.) and the AlN generation completion temperature (for example, about 1700 ° C.). ₂ -NH reacts with Al vapor mixed gas-quenching gas ₃ The temperature of the mixed gas is lowered to the AlN generation completion temperature while keeping the temperature of the mixed gas not lower than the condensation temperature of Al corresponding to the Al unreacted rate at this time. is important. Therefore, for example, in this embodiment, the temperature of the mixed gas of nitrogen and aluminum vapor is lowered to a temperature at which the formation of aluminum nitride is completed while the temperature is higher than the condensation temperature of unreacted aluminum contained in the mixed gas. I am trying to blow ammonia gas. This can be realized, for example, by adjusting the position where the ammonia gas is blown, the flow rate or temperature of the blown ammonia gas, and the like. In order to obtain AlN ultrafine particles, it is preferable to prevent the growth of AlN particles by rapidly cooling immediately after the conversion rate from aluminum to aluminum nitride reaches almost 100%.
[0031]
FIG. 2 shows an example of an apparatus for producing aluminum nitride particles using arc plasma. This manufacturing apparatus 1 includes a cathode 2 and a plasma torch 3 to which a plasma gas is supplied, an anode 5 for generating a transfer type DC arc plasma 4 between the cathode 2, and the cathode 2 and the anode 5. A recovery cylinder 7 provided downstream of the arc plasma 4 generated between them and having a reaction / quenching gas outlet 6, and a chamber 9 that supports the plasma torch 3, the anode 5 and the recovery cylinder 7 and forms a closed chamber. And a vacuum pump 10 connected to the recovery cylinder 7 by a gas flow pipe 8. Further, for example, in the manufacturing apparatus 1 of the present embodiment, an ethanol-containing tank 11 and a filter 12 are interposed between the recovery cylinder 7 and the vacuum pump 10.
[0032]
The cathode 2 is made of, for example, tungsten containing pipe-like lanthanum oxide. The anode 5 is made of, for example, bar-shaped graphite. Further, the plasma torch 3 is, for example, a movable type (see arrow C in FIG. 2) so that the distance between the cathode 2 and the anode 5 can be adjusted. The metal aluminum powder as a raw material is conveyed to plasma gas (nitrogen) and introduced into the pipe-like cathode 2. Reference numeral 13 in FIG. 2 represents the flow of plasma gas, and reference numeral 14 represents the flow of metal aluminum powder. Thereby, metallic aluminum powder is injected in the axial direction of the arc plasma 4 generated between the cathode 2 and the anode 5. The current, length, and the like of the arc plasma 4 are set so that the entire amount of Al powder evaporates in the plasma 4. All the Al powder evaporates in the plasma 4 at an extremely high temperature (for example, about 10000 ° C.), so that N in the downstream portion of the plasma 4 (near the anode 5) ₂ And Al vapor mixture gas is generated. Since the vicinity of the anode 5 is the terminal portion of the plasma 4, N ₂ -The temperature of the Al vapor mixed gas is about 5000 ° C. N ₂ -As the Al vapor mixed gas further proceeds downstream, the temperature of the spot decreases from 5000 ° C to about 1000 ° C. An annular outlet 6 for reaction / quenching gas (ammonia) is provided on the inner periphery of the front end portion of the recovery cylinder 7. Reference numeral 15 in FIG. 2 represents the flow of reaction / quenching gas. The collection cylinder 7 is movable (see arrow D in FIG. 2), for example, so that the distance between the tip of the collection cylinder 7 (reaction / quenching gas outlet 6) and the anode 5 can be adjusted. By changing the position of the collection cylinder 7, the temperature of the reaction / quenching gas blowing site, the AlN generation reaction time (the reaction time between Al and N), and the like can be controlled. The closer the collection cylinder 7 is to the anode 5, the higher the temperature at the location where the reaction / quenching gas is blown, and the shorter the AlN generation reaction time. On the other hand, the farther the collection cylinder 7 is from the anode 5, the lower the temperature of the reaction / quenching gas blowing portion and the longer the AlN production reaction time.
[0033]
With the above structure, ammonia gas is blown into a mixed gas composed of nitrogen and aluminum vapor, and high purity aluminum nitride ultrafine particles (for example, the amount of aluminum nitride particles in the manufactured particles is 90% by mass or more) are produced. Is done. Further, the gas that has passed through the recovery cylinder 7 is exhausted from the vacuum pump 10 through the ethanol-containing tank 11 and the filter 12. Reference numeral 16 in FIG. 2 represents the flow of exhaust gas. A chemical reaction does not occur between aluminum nitride (AlN) and ethanol, but a chemical reaction occurs between metal aluminum (Al) and ethanol, resulting in the production of ethoxide. That is, only metallic aluminum is captured by ethanol, and the particles that have passed through ethanol are only aluminum nitride particles. Thereby, by passing the production particles through ethanol, the metal aluminum powder in the production particles is removed, and ultra-fine aluminum nitride particles with higher purity (for example, the amount of aluminum nitride particles in the production particles is 99% by mass or more) are produced. it can. In addition, although illustration is abbreviate | omitted, you may further provide a tank with water as an exhaust gas purification apparatus. Since water absorbs ammonia very well, ammonia can be removed from the exhaust gas by bubbling the exhaust gas here. Since impurities in the gas may become impurities in the manufactured particles, it is desirable that the purity of nitrogen and ammonia gas is higher.
[0034]
【Example】
<Example 1>
Aluminum nitride ultrafine particles were actually produced using the apparatus 1 shown in FIG. The metal aluminum powder used as a raw material was a powder (Al-At-350, average particle size of about 20 μm, shape: spindle shape) manufactured by Fukuda Metal Foil Powder Industry. The arc current was constant at 140 A, and the plasma length was constant at 75 mm. The distance between the anode 5 and the tip of the collecting cylinder 7 was fixed to 75 mm so as to ensure the reaction time between Al and N. The temperature at the point where the reaction / quenching gas was blown was about 1300 ° C. The plasma gas is nitrogen (N ₂ The purity was 99.9% by volume or more), and the flow rate was 10 L / min inside the pipe-shaped cathode 2 and 10 L / min around the pipe-shaped cathode 2. The reaction / quenching gas is ammonia (NH) at room temperature (around 20 ° C). ₃ , Purity 99.9% by volume or more), and the flow rate was 20 L / min. Al powder was supplied to the inside of the pipe-like cathode 2, and the supply amount was constant at 0.5 g / min. The pressure in the chamber 9 was approximately 30 to 50 kPa.
[0035]
When the powder (particles) adhering to the tip of the collection cylinder 7 (see reference numeral 17 in FIG. 2) was collected, it was confirmed to be aluminum nitride ultrafine particles (average particle size of about 30 nm) having a purity of about 90% by mass. . Furthermore, when powder (particles) that passed through the ethanol-containing tank 11 and adhered to the filter 12 was collected, it was confirmed that the particles were ultrafine aluminum nitride particles (average particle size of about 30 nm) having a purity of 99% by mass or more.
[0036]
Although the temperature of the reaction / quenching gas blowing portion in this example was as low as about 1300 ° C., the AlN purity was relatively high as about 90% by mass. This is because the reaction of Al and N proceeds in a high-temperature space (about 1500 to 5000 ° C.) between the anode 5 and the tip of the recovery cylinder 7 that is upstream of the recovery cylinder 7, and directly above the front end of the recovery cylinder 7 And some NH ₃ Therefore, it is considered that the condensation temperature of Al decreased and AlN purity increased. If the position of the recovery cylinder 7 is further closer to the anode 5, the temperature of the reaction / quenching gas blowing point is set to a temperature range between the AlN generation start temperature (about 2100 ° C) and the AlN generation completion temperature (about 1700 ° C). Since it can be set, there is a possibility that higher-purity AlN ultrafine particles can be obtained.
[0037]
<Example 2>
The apparatus 1 shown in FIG. 2 is used to produce aluminum nitride ultrafine particles by changing the plasma gas or reaction / quenching gas to 100% nitrogen gas, 100% ammonia gas, mixed gas of 50% by volume of nitrogen and 50% by volume of ammonia. The AlN purity of the particles produced in each case was examined. The other conditions were the same as in Example 1. The results are shown in FIG. In the figure, the Δ mark plot and the curve indicated by symbol E represent the plasma gas, and the circle mark plot and the curve indicated by symbol F in the figure represent the reaction / quenching gas. From FIG. 3, it can be confirmed that the plasma gas is higher in AlN purity when it contains only nitrogen and does not contain ammonia. Further, it can be confirmed that the reaction / quenching gas does not contain nitrogen and contains only ammonia, and the AlN purity becomes higher.
[0038]
As described above, according to the present invention, ultrafine aluminum nitride particles, which are highly functional materials having features such as high thermal conductivity and high electrical insulation, can be produced with extremely high purity. Aluminum nitride ultrafine particles can be used as a material for high heat dissipation control substrates and electrical insulating materials in energy conversion equipment, and can greatly contribute to the downsizing and high efficiency of electronic equipment and energy conversion equipment.
[0039]
Also, by using only nitrogen gas as the plasma gas, the operating cost is lower than when using a conventional plasma gas based on a relatively expensive argon gas. Further, by using only ammonia gas as the reaction / quenching gas, the equipment cost can be reduced as compared with the case of using the conventional quenching gas based on hydrogen. Since hydrogen has a low molecular weight, it easily leaks, and gas with a hydrogen concentration of 4% by volume or more must be handled as an explosive / flammable gas. Although it is necessary to make it and its peripheral equipment explosion-proof and install hydrogen detectors at many locations, such measures are not necessary when using ammonia gas. NH ₃ The thermal conductivity of H is H ₂ Is equivalent to that of NH ₃ It is thought that there is sufficient quenching effect by itself.
[0040]
The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in order to ensure sufficient AlN generation reaction time so that unreacted Al does not remain, and to cool rapidly immediately after the conversion rate from Al to AlN becomes almost 100%, blowing in ammonia gas (For example, a relatively high temperature ammonia gas is blown as a reaction gas (nitrogen source) in the upper stage and a relatively low temperature ammonia gas is blown as a cooling gas in the lower stage), or the Al vapor-containing gas is kept at a substantially constant temperature. A heating device for holding may be separately provided on the downstream side of the arc plasma 4.
[0041]
【The invention's effect】
As apparent from the above description, according to the method for producing aluminum nitride particles according to claim 1, since ammonia gas is blown into the mixed gas composed of nitrogen and aluminum vapor, aluminum nitride is generated from aluminum. Therefore, it is possible to expand the temperature range necessary for the production, and to obtain aluminum nitride ultrafine particles with high purity (for example, the amount of aluminum nitride particles in the produced particles is 90 mass% or more).
[0042]
Furthermore, according to the method for producing aluminum nitride particles according to claim 2, since ammonia gas is blown into the mixed gas in the temperature region where the formation reaction of aluminum nitride actively proceeds, the conversion rate from Al to AlN can be increased. As a result, high-purity aluminum nitride ultrafine particles can be obtained.
[0043]
Furthermore, according to the method for producing aluminum nitride particles according to claim 3, ammonia is used so that the temperature of the mixed gas is lowered to a temperature at which the formation of aluminum nitride is completed while being higher than the condensation temperature of unreacted aluminum. Since gas is blown in, it can prevent that unreacted Al vapor | steam condenses and metal aluminum mixes in manufacture particle | grains.
[0044]
Furthermore, according to the method for producing aluminum nitride particles according to claim 4, since the produced particles are passed through ethanol, the metal aluminum powder in the produced particles is removed, and the purity is higher (for example, the amount of aluminum nitride particles in the produced particles). Is 99% by mass or more).
[Brief description of the drawings]
FIG. 1 is a graph showing an example of the formation temperature of aluminum nitride and the condensation temperature of unreacted aluminum.
FIG. 2 is a schematic configuration diagram showing an example of an apparatus for producing aluminum nitride particles.
FIG. 3 is a graph showing changes in the purity of aluminum nitride when the components of plasma gas and reaction / cooling gas are changed.
[Explanation of symbols]
1 Aluminum nitride particle production equipment
2 Cathode
3 Plasma torch
4 Arc plasma
5 Anode
6 Reaction / cooling gas outlet
7 collection cylinder
8 Gas distribution pipe
9 chambers
10 Vacuum pump
11 Ethanol tank
12 Filter
13 Flow of nitrogen gas
14 Flow of metal aluminum powder
15 Flow of ammonia gas
16 Flow of exhaust gas

Claims (4)

A method for producing aluminum nitride particles, wherein ammonia gas is blown into a mixed gas comprising nitrogen and aluminum vapor. The ammonia gas is blown into the mixed gas in a temperature range between a temperature at which the nitrogen and aluminum in the mixed gas react to start generating aluminum nitride and a temperature at which the generation is completed. The method for producing aluminum nitride particles according to claim 1. The ammonia gas is blown so that the temperature of the mixed gas is lowered to a temperature at which the formation of aluminum nitride is completed while the temperature of the mixed gas remains higher than the condensation temperature of unreacted aluminum in the mixed gas. The method for producing aluminum nitride particles according to claim 2. A method for producing aluminum nitride particles, comprising passing particles containing aluminum nitride particles and metal aluminum particles through ethanol.

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