JP6796385B2 - Manufacturing method of AlN whiskers - Google Patents

Description

The present invention relates to a method for producing an AlN whisker to which a combustion synthesis method is applied, and an AlN whisker.

As a conventional method for producing an AlN whisker, Patent Document 1 discloses a production method for producing an AlN whisker by reducing alumina in a nitrogen atmosphere at 1800 ° C. to 2000 ° C. using carbon. The manufacturing method in Patent Document 1 is carried out by a semi-continuous operation of a horizontal furnace provided with a graphite heating device. Then, a graphite container charged with a mixture of alumina, carbon, and carbonyl iron as a growth activator is periodically supplied through the above furnace. Further, Patent Document 2, a metallic Al powder and the like in the following vacuum 5.0Torr was heated to five hundred and forty to six hundred and fifty ° C., at a pressurized atmosphere of _{N 2} gas while maintaining the temperature, direct nitriding A method for producing an AlN whiskers by law is disclosed. Further, in Patent Document 3, an alumina boat is filled with a material containing Al—Ti—Si as a main component, which is heated and melted at 1500 ° C. to 1800 ° C., and a direct nitriding method is used in a nitrogen atmosphere. A method for producing AlN whiskers on the surface of a material is disclosed.

Japanese Unexamined Patent Publication No. 9-118598 Japanese Unexamined Patent Publication No. 11-139814 Japanese Unexamined Patent Publication No. 2014-73951

However, in the method for producing AlN whiskers disclosed in Patent Document 1, carbon and carbonyl iron are added to the raw materials as reducing agents. Therefore, there is a problem that impurities such as carbon and iron and unreacted alumina remain inside the generated AlN whiskers. As a result, the thermal conductivity and insulating properties of the AlN whiskers were inferior, and a treatment for removing these unreacted substances and impurities was required. Further, in Patent Document 1, high energy is required to cause a reduction reaction, and specifically, it is necessary to treat at a very high temperature of 1800 ° C. to 2000 ° C. by external heating. Therefore, there is a problem in terms of energy cost.

Further, also in the method for producing AlN whiskers described in Patent Documents 2 and 3, AlN whiskers are produced by external heating. Therefore, as in Patent Document 1, there is a problem in terms of energy cost. Further, in the method by external heating described in Patent Documents 2 and 3, it takes time to raise and lower the temperature of the furnace, and a holding time for growing the AlN whiskers is also required. As a result, the cycle time required for manufacturing the AlN whiskers became long, and the productivity of the AlN whiskers decreased.

Therefore, the present invention has been made in view of the above problems, and it has made it possible to manufacture a high-purity AlN whisker by a simple method in a short time, energy saving, and at low cost as compared with the conventional case. An object of the present invention is to provide a method for manufacturing a whisker and an AlN whisker.

In the method for producing an AlN whisker of the present invention, a combustion synthesis reaction is carried out in a nitrogen atmosphere using a raw material containing Al and NH ₄ Cl, and the decomposition gas of NH ₄ Cl is discharged by the heat of combustion. , AlN whiskers are produced by the combustion synthesis reaction.

In the present invention, it is preferable to form the AlN whiskers in layers on the surface layer of the composite of the raw materials.

The method for producing an AlN whisker of the present invention is to produce an AlN whisker by a combustion synthesis reaction from a raw material containing Al and NH ₄ Cl of 0.5% by mass or more and 5% by mass or less in a nitrogen atmosphere. It is characterized by .

The method for producing an AlN whisker of the present invention is to produce an AlN whisker by a combustion synthesis reaction from a raw material containing Al and AlN as a diluent of 10% by mass or more and 40% by mass or less in a nitrogen atmosphere. It is characterized by .

Method of manufacturing AlN whiskers of the invention, under a nitrogen atmosphere, and Al, from the raw materials containing _Y 2 _{O 3} of 5 wt% or less than 0.5 wt%, the AlN whiskers, produced by combustion synthesis reaction It is characterized by that .

In the method for producing an AlN whisker of the present invention, an AlN whisker is produced by a combustion synthesis reaction from a raw material containing Al and Al ₂ O ₃ of 0.2% by mass or more and 2% by mass or less in a nitrogen atmosphere. It is characterized by that .

According to the present invention, by producing an AlN whisker by applying a combustion synthesis method, it is possible to produce an AlN whisker in a short time with energy saving without requiring external heating. Moreover, since carbon, iron, and the like are not added to the raw material, the possibility of contamination of the AlN whiskers with impurities that lower the insulating property and thermal conductivity is suppressed. Therefore, a high quality AlN whiskers can be manufactured.

It is a flowchart which shows the manufacturing method of the AlN whisker in embodiment of this invention. It is a schematic diagram which shows the raw material arrangement in a crucible. It is a schematic diagram which shows the layered AlN whiskers in embodiment of this invention, and the AlN whisker sheet formed by die-cutting an AlN whiskers. It is a spectrum figure which shows the analysis result of XRD of the AlN whiskers of this Example. It is a photograph which shows the image taken by the scanning electron microscope.

Hereinafter, one embodiment of the present invention (hereinafter, abbreviated as “embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

AlN whiskers have high thermal conductivity, excellent insulating properties, and are preferably used as resin encapsulants because of their high aspect ratio.

The method for producing an AlN whisker in the embodiment of the present invention is an application of combustion synthesis. The combustion synthesis method is a method of producing a compound by utilizing the heat of formation generated during a chemical reaction of a substance, and is an energy-saving process that does not require external heating. In addition, it has a high-temperature high-speed reaction and a quenching action, and can produce a compound in a short time. In this embodiment, since it is a combustion synthesis between a solid (Al) and a gas (nitrogen gas), it belongs to a part of the direct nitriding method.

According to the method for producing an AlN whisker of the present embodiment, when a raw material containing Al as a main component is burned, AlN gas ejected from the inside of the composite is rapidly cooled on the surface layer of the composite to quench AlN. It enables the whiskers to grow layered on the surface of the composite.

The mechanism of the combustion synthesis reaction will be described below. First, a raw material containing Al as a main component is filled in a crucible made of graphite, for example. Here, the amount of Al in the raw material is not limited, but occupies 50% by mass or more as the main component. Then, the crucible is installed in the combustion synthesis furnace with the carbon foil for ignition in contact with a part of the raw material. The inside of the furnace is degassed to a predetermined pressure, and then nitrogen substitution is performed to create a nitrogen-pressurized atmosphere.

Subsequently, the carbon foil is energized until the raw material is ignited, and the combustion synthesis reaction of Al and nitrogen gas in the raw material is started. The reaction formula of the combustion synthesis reaction is 2Al + N ₂ → AlN. At this time, since the combustion wave of the combustion synthesis reaction proceeds at a speed of, for example, about 10 mm / sec, the synthesis reaction is completed in a short time, for example, about several minutes (specifically, about 3 to 5 minutes). ..

The formation of AlN whiskers is carried out at the same time as the combustion synthesis reaction. The internal temperature of the raw material during combustion reaches, for example, about 1900 to 2000 ° C., and Al exists inside the raw material in an Al gas state.

In the present embodiment, it is preferable to add NH ₄ Cl as an auxiliary agent to the raw material. As a result, NH ₄ Cl becomes a decomposition gas of NH ₃ and HCl due to the heat of combustion, and is discharged to the surface layer of the composite. This decomposed gas becomes a carrier of Al gas inside the composite and releases Al gas from the surface layer of the composite. The released Al gas is rapidly cooled with a nitriding reaction, and AlN whiskers are formed on the surface layer of the composite. In the present embodiment, it is preferable to add a small amount of Y ₂ O ₃ or Al ₂ O ₃ as a growth activator to the raw material in order to increase the amount of AlN whiskers produced.

Then, in the present embodiment, as the final form, AlN whiskers can be formed in layers on the surface layer of the composite. Therefore, the recovery efficiency of AlN whiskers can be made very high. Here, "layered" refers to a sheet shape having a thickness in almost the entire surface layer of the composite.

In the present embodiment, as described above, direct nitriding from Al is possible by producing AlN whiskers using the combustion synthesis method. Since carbon and iron are not used as a reducing agent, the possibility of impurities that reduce thermal conductivity and insulation is suppressed inside the AlN whiskers, making it possible to obtain high-quality AlN whiskers. Become. In addition, it does not require external heating, can be synthesized in a short time, has high production efficiency, can be produced with energy saving, and is excellent in economy.

Subsequently, the manufacturing process of the AlN whiskers in the present embodiment will be described in detail. First, as shown in step ST1 of FIG. 1, raw materials are prepared. In the present embodiment, it is preferable to use Al-AlN-NH ₄ Cl-Y ₂ O _3- Al ₂ O ₃ as a raw material containing Al as a main component. That is, it is preferable that the raw material does not substantially contain components other than these components. "Substantially" means that it does not exclude the inclusion of other components / elements that are inevitably mixed. These components are dry-mixed, for example, in an alumina ball mill.

In the present embodiment, the average particle size of each component contained in the raw material is not limited. However, as an example, Al has an average particle size D50 = 1 to 20 μm, AlN has an average particle size D50 = 0.5 to 6 μm, and NH ₄ Cl has an average particle size D50 = 0. .5 to ₂ mm, Y ₂ O ₃ has an average particle size D50 = 0.2 to 5 μm, and Al ₂ O ₃ has an average particle size D50 = 0.5 to 4 μm. The particle size distribution was measured by a laser scattering method (using a laser diffraction type particle size distribution measuring device HORIBA LA-950). “D50” indicates a particle size in which the cumulative number is 50% of the total number of particles.

Further, in the present embodiment, it is preferable to add AlN as a diluent in the range of 10% by mass or more and 40% by mass or less in the raw material. As a result, as shown in the experimental results described later, the combustion temperature can be raised and the unreacted amount of Al can be reduced. Further, it is preferable to add NH ₄ Cl as a synthetic auxiliary agent in the raw material in the range of 0.5% by mass or more and 5% by mass or less. Further, it is preferable to add Y ₂ O ₃ as a growth active material in the raw material in the range of 0.5% by mass or more and 5% by mass or less. Further, it is preferable to add Al ₂ O ₃ as a growth active material in the raw material in the range of 0.2% by mass or more and 2% by mass or less. By adding the addition amounts of NH ₄ Cl, Y ₂ O ₃ and Al ₂ O ₃ within the above range, the amount of AlN whiskers produced can be appropriately increased as shown in the experimental results described later. ..

Subsequently, the raw material is installed (filled) in the crucible (step ST2 in FIG. 1). The method of installing the raw material in the crucible will be described with reference to FIG. Reference numeral 1 shown in FIG. 1 is a crucible made of graphite (hereinafter referred to as graphite crucible 1). However, in the present embodiment, the present invention is not limited to graphite, and may be formed of a material other than graphite, such as BN, Al ₂ O ₃ , Al N, and Si ₃ N ₄ .

As shown in FIG. 2, AlN powder 2 is spread on the bottom surface of the graphite crucible 1. The particle size and layer thickness of the AlN bed powder 2 are not limited, but for example, the average particle size D50 is about 4 to 20 μm, and the layer thickness is 5 mm or more. The reason for spreading the AlN bed powder 2 in this way is to block the heat of reaction of the raw material 3 and prevent the generation of carbon from the graphite crucible 1 due to the heat.

Subsequently, the raw material 3 is placed on the AlN bedding powder 2. At this time, the layer thickness of the raw material 3 is not limited, but the layer thickness is preferably in the range of 5 mm or more and 20 mm or less, and more preferably 5 mm or more and 10 mm or less. When the layer thickness is thinner than 5 mm, the amount of heat of the composite is low and the amount of AlN gas generated is small, so that the amount of AlN whiskers produced is reduced. If it is thicker than 20 mm, the amount of heat of the composite is large, the surface temperature of the composite becomes too high, the formation of AlN whiskers nuclei is inhibited, and the amount of AlN whiskers produced decreases. Further, as shown in FIG. 2, in order to prevent the influence of heat during the combustion reaction, it is preferable to leave a space of 1 mm or more between each side surface of the raw material 3 and the graphite crucible 1.

Next, the graphite crucible 1 for which the installation (filling) of the raw material 3 is completed is installed in the combustion synthesis furnace. Then, as shown in FIG. 2, the surface of the raw material 3 is brought into contact with the carbon foil 4 for ignition. Then, the carbon felt lid 5 is installed on the graphite crucible 1. By covering the upper surface of the graphite crucible 1 with the carbon felt lid 5 in this way, it is possible to prevent the AlN gas from diffusing into the atmosphere inside the furnace and increase the amount of AlN whiskers produced. In the present embodiment, the material of the lid is not limited to carbon felt, and for example, an Al ₂ O ₃ fiber composition having some air permeability can be used as the lid.

It is preferable that the combustion synthesis furnace to be used has a mechanism for keeping the set pressurized atmosphere constant and has a configuration capable of performing vacuum replacement. Further, it is desirable that the combustion synthesis furnace has a cooling jacket and a chiller for cooling the atmosphere inside the furnace, and the temperature inside the furnace can be maintained at 25 ° C. or lower.

The inside of the furnace is degassed to a predetermined pressure, and then nitrogen substitution is performed to create a nitrogen-pressurized atmosphere (step ST3 in FIG. 1). Here, the depressurization is not limited, but for example, it is 100 Pa or less, preferably 50 Pa to 20 Pa, and more preferably 5 Pa or less. Further, although the pressing force of the nitrogen pressurized atmosphere is not limited, it is, for example, 0.2 MPa to 30 MPa, preferably 0.7 MPa or more.

Then, using a cooling mechanism, cooling is performed until the temperature inside the furnace becomes, for example, 25 ° C. or lower (step ST4 in FIG. 1). Subsequently, the carbon foil 4 is energized (but not limited to, for example, 50 to 200 V) until the raw material is ignited to start combustion synthesis (step ST5 in FIG. 1). As described above, the synthetic reaction is completed in a short time of, for example, about several minutes (specifically, about 3 to 5 minutes).

As described above, in this embodiment, the rapid reaction and the quenching action, which are one of the features of the combustion synthesis method, are used, and the gas pressure and the atmospheric temperature are important factors. The gas pressure is the pressing force in the nitrogen-pressurized atmosphere described above, and the combustion temperature can be raised by increasing the pressure, and as a result, the amount of Al gas generated can be increased. Further, as the atmosphere density increases, the heat dissipation is improved, and by keeping the atmosphere temperature (the above-mentioned cooling temperature in the furnace) low, the quenching action can be promoted and the amount of AlN whiskers produced can be increased.

After the combustion is completed, the inside of the furnace is returned to the atmospheric pressure, and the graphite crucible 1 is taken out from the combustion synthesis furnace. As shown in FIG. 3A, the generated AlN whiskers exist in a layered state (AlN whisker layer 7) on the surface layer of the composite body 6 formed by burning the raw material 3, and the AlN whiskers layer 7 is formed from the composite surface layer. By peeling it off, it can be easily recovered (step ST6 in FIG. 1).

As described above, in the present embodiment, the layered AlN whiskers can be obtained by applying the combustion synthesis method.

The AlN whiskers are not in a fixed crystal direction but are randomly entangled to form a fibrous layer. The layer thickness is not limited, but is, for example, about 0.2 to 1 mm.

Then, by die-cutting or cutting the AlN whisker layer 7, an AlN whisker sheet 8 having an arbitrary shape as shown in FIG. 3B can be obtained (step ST7 in FIG. 1). The AlN whisker sheet 8 is useful for a heat conductive member (for example, a high heat conductive composite by impregnation with a resin), a heat resistant member (for example, a heat resistant filter), a catalyst member (for example, a catalyst carrier material), and the like.

As described in detail above, the present embodiment is a method for producing an AlN whisker by applying a combustion synthesis method in which a synthesis reaction proceeds by self-generated heat. According to this embodiment, it is possible to generate AlN whiskers in a short time with energy saving without requiring external heating. In addition, AlN whiskers can be produced without the need for special materials, and can be produced with high production efficiency and low cost. In addition, since carbon and iron are not added to the raw material, there is a low possibility that impurities that lower the insulating property and thermal conductivity will be mixed in the generated AlN whiskers, and it is possible to manufacture high-quality AlN whiskers. is there.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples carried out to clarify the effects of the present invention. The present invention is not limited to the following examples.

In the following, the appropriate range of the amount of diluent (AlN) added, the amount of NH ₄ Cl added, the amount of Y ₂ O ₃ added, and the amount of Al ₂ O ₃ added contained in the Al raw material are determined by experiments. It was.

In the experiment, the total amount of raw materials was 80 g. The mixing was carried out in a mortar. However, it may be done with a ball mill. The Al powder used in the experiment has an average particle size of 3 μm manufactured by the Institute of High Purity Chemistry, the AlN powder is H grade (average particle size 1 μm) manufactured by Tokuyama, and NH ₄ Cl is genuine chemical. The particle size of the product is about 1 mm, Y ₂ O ₃ is D50 ≤ 3 μm of Nippon Ittorium, and Al ₂ O ₃ is α-Al ₂ O _{3 of} high-purity chemicals (average particle size is). It was 1 μm).

The above raw materials were placed in a graphite crucible in the state shown in FIG. 1, and combustion synthesis was carried out with the gas pressure of the combustion synthesis furnace set to 0.95 MPa.

(Dilution rate experiment)
First, in the experiment, in order to measure the dilution ratio, a plurality of raw materials having different dilution ratios were prepared by changing the mixing ratio of Al and AlN, and the unreacted amount of Al and the combustion temperature were measured using each raw material. The experimental results are shown in Table 1 below.

The numerical value in the "dilution rate" column indicates the mass% of AlN in the raw material. The unreacted amount was measured by quantitative analysis by X-ray analysis.

As shown in Table 1, it was found that as the dilution ratio increased, the unreacted amount of Al decreased and the combustion temperature decreased.

In order to obtain an efficient combustion synthesis reaction, the range of the preferable addition amount of AlN was set to 10% by mass or more and 40% by mass or less, which has a high combustion temperature and a small amount of unreacted Al.

(Experiment on the amount of NH ₄ Cl added)
Subsequently, the AlN fixed at 30 wt%, a plurality of raw material addition amount of _NH 4 Cl is composed of different _Al-AlN-NH 4 Cl was prepared, using each starting material, the amount of AlN whiskers, and, The combustion temperature was measured. The experimental results are shown in Table 2 below.

As shown in Table 2, it was found that when the amount of NH ₄ Cl added was increased to 4% by mass, the amount of AlN whiskers produced increased and the combustion temperature decreased. Further, when the addition amount of NH ₄ Cl was 6% by mass, self-propagation did not occur and AlN whiskers could not be obtained appropriately.

Based on Table 2, the preferable range of the addition amount of NH ₄ Cl was set to 0.5% by mass or more and 5% by mass. Further, a more preferable range was set to 1% by mass or more and 5% by mass or less.

(Experiment on the amount of Y ₂ O ₃ added)
Subsequently, AlN was fixed at 30% by mass and NH ₄ Cl was fixed at 4% by mass, and a plurality of raw materials composed of Al-AlN-NH ₄ Cl-Y ₂ O ₃ having different amounts of Y ₂ O ₃ added were prepared. The amount of AlN whisker produced was measured using each raw material. The experimental results are shown in Table 3 below.

As shown in Table 3, it was found that the amount of AlN whiskers produced could be increased by increasing the amount of Y ₂ O ₃ added from 1% by mass to 4% by mass. When the amount of Y ₂ O ₃ added is 5% by mass, the amount of Y ₂ O ₃ produced is larger than that of 1% by mass, but AlN whiskers are produced as compared with the case of 2% by mass to 4% by mass. It was found that the amount of production was reduced.

According to Table 3, the preferable range of the addition amount of Y ₂ O ₃ was set to 0.5% by mass or more and 5% by mass or less. Further, a more preferable range was set to 1% by mass or more and 5% by mass or less. A more preferable range was 2% by mass or more and 4% by mass or less.

(Experiment on the amount of Al ₂ O ₃ added)
Subsequently, the AlN 30 wt%, 4 _wt% of _NH 4 _Cl, Y 2 _{O 3} was fixed to 2 _{wt%, Al 2 O Al-AlN} -NH 4 that the amount is different _{3 Cl-Y} 2 _{O 3} A plurality of raw materials composed of −Al ₂ O ₃ were prepared, and the amount of AlN whisker produced was measured using each raw material. The experimental results are shown in Table 4 below.

As shown in Table 4, it was found that 300 mg or more of AlN whiskers can be obtained by setting the addition amount of Al ₂ O ₃ in the range of 0.5% by mass to 2% by mass. When the amount of Al ₂ O ₃ added was 2.5% by mass, self-propagation did not occur and AlN whiskers could not be obtained properly.

According to Table 4, the preferable range of the addition amount of Al ₂ O ₃ was set to 0.2% by mass or more and 2% by mass or less. Further, a more preferable range was set to 0.5% by mass or more and 1.5% by mass or less.

(XRD analysis result)
Subsequently, the AlN whiskers obtained in this example were analyzed by XRD (X-Ray Diffraction). Here, the raw material of the AlN whiskers to be analyzed is Al-AlN (30% by mass) -NH ₄ Cl (4% by mass) -Y ₂ O ₃ (2% by mass) -Al ₂ O ₃ (1% by mass). , The gas pressure of the combustion synthesis furnace was set to 0.95 MPa. The XRD analysis result is shown in FIG.

Results were examined by XRD analysis, most of the product is AlN composition, impurities _{(carbides, Y 2 O 3, Al 2} O 3) was not detected. Although it contained a small amount of unreacted Al, it became AlN by performing heat treatment for about 1 hour in a nitrogen atmosphere at 800 to 1000 ° C. Can be done.

(Scanning electron microscope image)
FIG. 5 is a photograph showing an image taken by a scanning electron microscope. As shown in FIG. 5, the AlN whiskers produced in this example (the same as those used in the experiment of FIG. 4) have different characteristics from the AlN whiskers produced by the prior art with directional crystals. I understand. That is, as shown in FIG. 5, the direction of crystal growth of the AlN whiskers was random. Then, the AlN whiskers could be formed in layers.

The AlN whiskers produced in the present invention are fibrous with random crystal growth directions, and are useful for high heat conductive fillers and the like used as resin encapsulants. Also. Since the AlN whiskers can be formed in layers, an AlN whiskers sheet having an arbitrary shape can be obtained by die cutting or cutting. The AlN whisker sheet can be preferably applied to a high thermal conductive composite impregnated with a resin, a heat resistant filter, a catalyst carrier material, and the like.

1 Graphite crucible 2 AlN bedding powder 3 Raw material 4 Carbon foil 5 Carbon felt lid 6 Composite 7 AlN whisker layer 8 AlN whisker sheet

Claims (6)

Using a raw material containing Al and _NH 4 Cl, under a nitrogen atmosphere, subjected to combustion synthesis reaction, by the heat during combustion, is discharged decomposition gas _NH 4 Cl, the AlN whiskers, by the combustion synthesis reaction A method for producing an AlN whisker, which comprises producing. A method for producing an AlN whisker, which comprises producing an AlN whisker from a raw material containing Al and NH ₄ Cl of 0.5% by mass or more and 5% by mass or less under a nitrogen atmosphere by a combustion synthesis reaction. A method for producing an AlN whisker, which comprises producing an AlN whisker from a raw material containing Al and AlN as a diluent of 10% by mass or more and 40% by mass or less in a nitrogen atmosphere by a combustion synthesis reaction. Under a nitrogen atmosphere, Al and, from the raw materials containing _Y 2 _{O 3} of 5 wt% or less than 0.5 wt%, the AlN whiskers method of AlN whiskers and generating by combustion synthesis reaction .. A method for producing an AlN whisker, which comprises producing an AlN whisker from a raw material containing Al and Al ₂ O ₃ of 0.2% by mass or more and 2% by mass or less in a nitrogen atmosphere by a combustion synthesis reaction. .. The method for producing an AlN whisker according to any one of claims 1 to 5 , wherein the AlN whiskers are formed in layers on the surface layer of the composite of the raw material.