JPWO2019180937A1 - Aluminum nitride particles - Google Patents

Abstract

Disclosed are aluminum nitride particles used as a raw material for an aluminum nitride sintered body. The aluminum nitride particles have the same crystal orientation in the particles, are plate-shaped, and have holes on the surface.

Description

The present specification discloses techniques relating to aluminum nitride particles. In particular, the present specification discloses techniques relating to aluminum nitride particles used as a raw material for an aluminum nitride sintered body.

Flat plate aluminum nitride particles are disclosed in WO2014 / 123247A1 (hereinafter referred to as Patent Document 1). Patent Document 1 discloses aluminum nitride particles having a plane length L of 3 to 110 μm and a thickness direction length D of 2 to 45 μm. The aluminum nitride particles of Patent Document 1 are used as a heat conductive filler added to a resin or as a raw material for a high-strength aluminum nitride sintered body.

As described above, the aluminum nitride particles of Patent Document 1 are used as a heat conductive filler added to the resin or as a raw material for a high-strength aluminum nitride sintered body. Therefore, the aluminum nitride particles of Patent Document 1 are not required to have transparency in the aluminum nitride sintered body even when used as a raw material for the aluminum nitride sintered body. The present inventors have started research on producing a highly transparent aluminum nitride sintered body using aluminum nitride particles. However, as a result of the research by the present inventors, it has been found that it is difficult to produce a highly transparent aluminum nitride sintered body with the conventional aluminum nitride particles. That is, it was found that new aluminum nitride particles different from the conventional ones are required to obtain a highly transparent aluminum nitride sintered body. The present specification provides aluminum nitride particles that can be suitably used as a raw material for a highly transparent aluminum nitride sintered body.

The present specification discloses aluminum nitride particles used as a raw material for an aluminum nitride sintered body. The aluminum nitride particles may have uniform crystal orientations in the particles, may be plate-shaped, and may have pores on the surface. The "surface of the aluminum nitride particles" is the surface having the largest area among the constituent surfaces of the aluminum nitride particles, and means the end surface in the thickness direction. Further, for convenience, "front surface" and "back surface" may be distinguished from each other, but unless it is necessary to distinguish between the two, the expression "front surface" means both "front surface" and "back surface".

In order to increase the transparency of the aluminum nitride sintered body, it is necessary to promote the sintering of the aluminum nitride particles and increase the density of the aluminum nitride sintered body (reduce the pores remaining inside). When the size of the aluminum nitride particles is reduced, the length of the contact interface edge of each particle (the length of the edge of the portion where the particles are in contact with each other) is increased, and sintering is facilitated. This is because the sintering proceeds from the contact interface edge of each particle. Therefore, even with conventional aluminum nitride particles, it is possible to facilitate sintering by selecting the particle size (using small-sized aluminum nitride particles). However, when small-sized aluminum nitride particles are used, even if the particles are flat plates (particles having a high aspect ratio in the plane direction and the thickness direction), the crystal orientation of each particle is aligned and the molded body (molding before firing). The body) becomes difficult to produce, and the process of producing the molded body before firing becomes complicated. If the crystal orientation of the pre-firing molded product is disturbed, the crystal orientation of the aluminum nitride sintered body is also disturbed, and the transparency is lowered.

Since the aluminum nitride particles are provided with holes on the surface, non-contact portions can be provided on the surfaces of other aluminum nitride particles that are in contact with each other. That is, by providing holes on the surface, it is possible to secure a long contact interface end. Therefore, even if a large size aluminum nitride particle is used, the sintering of the aluminum nitride particle is promoted, and an aluminum nitride sintered body having high transparency can be obtained. Since large-sized aluminum nitride particles can be used as the aluminum nitride particles, the crystal orientation of the particles can be easily aligned in the step of producing the pre-baked molded product. In addition, in the step of producing the molded product before firing, it is possible to suppress the aggregation of particles. By using the aluminum nitride particles, it is possible to produce an aluminum nitride sintered body having high crystal axis orientation and high transparency.

In the aluminum nitride particles, the holes provided on the surface may be through holes. That is, in the aluminum nitride particles, the holes may be through holes extending from the front surface to the back surface instead of non-penetrating dents. A long contact interface edge can be secured on both the front surface and the back surface, and sintering can be further promoted.

Further, the aluminum nitride particles may be provided with a plurality of holes (non-through holes, through holes). By having a plurality of pores, it is possible to secure a long contact interface edge on the particle surface.

In the aluminum nitride particles, the diameter of the maximum circle that can be formed in the region where no pores exist on the surface may be 0.1 or more and 0.9 or less with respect to the maximum length in the plane direction on the surface. When the ratio of the above lengths is less than 0.1, the particle strength becomes low, and it becomes difficult to obtain a good aluminum nitride sintered body. On the other hand, when the ratio of the above lengths exceeds 0.9, it becomes difficult to obtain the effect of providing holes. That is, when the above ratio exceeds 0.9, the range where the pores do not exist becomes too wide, and the region where the contact interface edge does not exist on the particle surface (the region where the non-contact portion does not exist) becomes too wide, and sintering is promoted. It becomes difficult to obtain the effect of making it.

In the aluminum nitride particles, the total area of the pores on the surface may be 0.01 or more and 1.5 or less with respect to the total area of the region where the pores do not exist. More specifically, when the total area of the non-perforated portion of the surface is S1 and the total area of the holes is S2, 0.01 ≦ (S2 / S1) ≦ 1.5. You may be satisfied.

The surface state of the aluminum nitride particles is schematically shown. The figure for demonstrating the hole provided in the aluminum nitride particle is shown. The figure for demonstrating the advantage of the aluminum nitride particle having a plurality of pores is shown. The molded product before firing is schematically shown. A summary of the examples is shown.

Hereinafter, embodiments of the techniques disclosed in the present specification will be described.

This specification discloses aluminum nitride particles used as a raw material for an aluminum nitride sintered body. In the production of the aluminum nitride sintered body, first, a pre-baked molded product having a predetermined size is molded using the aluminum nitride particles. The pre-firing molded product is formed by, for example, applying and drying a slurry containing aluminum nitride particles on the film, laminating the molded product peeled off from the film so as to have a predetermined thickness, and pressing with hydrostatic pressure. After degreasing the molding aid added when molding the molded product, aluminum nitride is sintered and particle-grown by firing at a predetermined temperature while pressurizing the molded product before firing, resulting in high density (fewer pores). ) Form a primary sintered body of aluminum nitride. Then, the aluminum nitride primary sintered body is secondarily fired in a non-pressurized state to remove the sintering aid, and an aluminum nitride sintered body is obtained. The aluminum nitride particles can be produced by heating a raw material containing aluminum oxide and a carbon source in an atmosphere containing a nitrogen source. Specifically, the aluminum nitride particles are produced by the reaction represented by the following formula (1).
Al ₂ O ₃ + 3C + N ₂ → 2AlN + 3CO ... (1)

(Raw material containing aluminum oxide)
The raw material containing aluminum oxide may contain aluminum oxide in the raw material, may be aluminum oxide alone (excluding unavoidable impurities) containing no other substance, or may contain other substances in the raw material. You may. For example, the raw material containing aluminum oxide may contain 70% by mass or more of aluminum oxide, 80% by mass or more of aluminum oxide, and 90% by mass or more of aluminum oxide in the raw material. It may contain 95% by mass or more of aluminum oxide. The crystal structure of aluminum oxide may be α-type, γ-type, θ-type, η-type, κ-type, χ-type, etc., and may be α-type or γ-type in particular. In particular, good reactivity can be obtained by using α-alumina, γ-alumina, boehmite or the like as aluminum oxide. Hereinafter, the "raw material containing aluminum oxide" is simply referred to as an aluminum oxide raw material.

(Shape of aluminum oxide raw material)
The shape of the aluminum oxide raw material may be plate-like and may have a high aspect ratio. The aspect ratio may be 3 or more, 5 or more, 10 or more, 20 or more, 30 or more, 50 or more, 70 or more. It may be 100 or more, and may be 120 or more. Although it depends on the intended use of the aluminum nitride particles, the aluminum nitride particles having a high aspect ratio can be obtained by using the aluminum oxide raw material having a high aspect ratio (aspect ratio of 3 or more). Plate-shaped and high-aspect ratio aluminum nitride particles can be oriented by using a doctor blade or the like, and products that require control of the crystal axis direction (crystal orientation) (for example, a highly transparent aluminum nitride sintered body). ) Can be suitably used as a raw material.

The size of the aluminum oxide raw material may have a plane length L of 0.2 μm or more, 0.6 μm or more, 2 μm or more, 5 μm or more, and 10 μm or more. It may be 15 μm or more. Further, the length L in the plane direction may be 50 μm or less, 20 μm or less, 18 μm or less, and 15 μm or less. Further, the length D in the thickness direction may be 0.05 μm or more, 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, 0.8 μm or more. You may. Further, the length D in the thickness direction may be 2 μm or less, 1.5 μm or less, or 1.0 μm or less. The size of the aluminum oxide raw material is reflected in the size of the aluminum nitride particles after synthesis. Therefore, the size of the aluminum oxide raw material can be appropriately selected according to the intended use of the aluminum nitride particles. The aspect ratio is indicated by (length L in the plane direction / length D in the thickness direction).

(Carbon source)
The carbon source is used as a reducing agent for aluminum oxide. The carbon source may be one that can come into contact with the aluminum oxide raw material in an environment in which aluminum nitride particles are synthesized (aluminum oxide is heated). For example, the carbon source may be a solid mixed with the aluminum oxide raw material. Alternatively, the carbon source may be a carbide gas supplied in an environment for synthesizing aluminum nitride particles (in a synthetic atmosphere). Alternatively, the carbon source may be a carbon component that comes into contact with the aluminum oxide raw material in a synthetic atmosphere, such as a container for accommodating the aluminum oxide raw material and a jig arranged in the container.

Carbon black, graphite, or the like can be used as the solid carbon source to be mixed with the aluminum oxide raw material. As the carbon black, carbon black, acetylene black or the like obtained by the furnace method, the channel method or the like can be used. The particle size of carbon black is not particularly limited, but may be 0.001 to 200 μm. An organic compound may be used as a solid carbon source to be mixed with the aluminum oxide raw material. For example, as a carbon source, synthetic resin condensates such as phenol resin, melamine resin, epoxy resin and furanphenol resin, hydrocarbon compounds such as pitch and tar, and organic compounds such as cellulose, sucrose, polyvinylidene chloride and polyphenylene are used. You may. Among the above-mentioned solid carbon sources, carbon black is particularly useful from the viewpoint of good reactivity.

When mixing the aluminum oxide raw material and the solid carbon source, a solvent such as water, methanol, ethanol, isopropyl alcohol, acetone, toluene, or xylene may be used for mixing. The contact state between the aluminum oxide raw material and the carbon source can be improved. After mixing, the mixed raw material may be dried using an evaporator or the like.

As the carbide gas, linear hydrocarbons such as methane, ethane, propane, butane and ethylene, alcohols such as methanol, ethanol and propanol, aromatic hydrocarbons such as benzene and naphthalene can be used. Linear hydrocarbons are particularly useful because of their ease of thermal decomposition. By using the hydrocarbon gas as the carbon source, the aluminum oxide raw material and the carbon source come into good contact with each other, and the production time of the aluminum nitride particles can be shortened. As the carbide gas, fluoride such as fluorocarbon (CF ₄ ) and fluorinated hydrocarbon (CH ₃ F ₄ ) can also be used.

(Nitrogen source)
As the nitrogen source, nitrogen gas, ammonia gas, and a mixed gas thereof can be used. Ammonia gas is particularly useful as a nitrogen source because it is inexpensive and easy to handle. Further, by using ammonia gas as the nitrogen source, the reactivity can be improved and the production time of the aluminum nitride particles can be shortened.

The supply amount of the nitrogen source to the aluminum oxide raw material may be 1 to 6 L / min. The smaller the supply amount of the nitrogen source, the larger the speed difference of the reduction nitriding reaction between the surface and the inside of the aluminum oxide, and the more easily the pores are formed on the surface of the aluminum nitride particles. Specifically, as the supply amount of the nitrogen source decreases, the phenomenon that the internal nitriding is delayed with respect to the nitriding of the surface of aluminum oxide becomes remarkable. In this case, when the gas generated when the inside of aluminum oxide is nitrided is released to the outside, holes are formed on the surface of aluminum oxide (aluminum nitride).

(Nitriding temperature)
The nitriding temperature (holding temperature) may be 1450 ° C. or higher and 1900 ° C. or lower. The nitriding temperature may be 1450 ° C. or higher, 1500 ° C. or higher, or 1600 ° C. or higher. By setting the nitriding temperature to 1450 ° C. or higher, it is possible to prolong the production time and prevent the residual unreacted aluminum oxide. Further, by setting the nitriding temperature to 1450 ° C. or higher, inconsistency in crystal orientation can be prevented. Further, from the viewpoint of suppressing the energy cost, the nitriding temperature may be 1800 ° C. or lower, or 1700 ° C. or lower. If the nitriding temperature exceeds 1800 ° C., sintering may occur inside the aluminum nitride particles, and a phenomenon that the pores are closed may occur. The nitriding time (retention time) may be 3 hours or more, 5 hours or more, or 8 hours or more from the viewpoint of preventing the residual of unreacted aluminum oxide. Further, the nitriding time may be 20 hours or less, 15 hours or less, or 10 hours or less from an industrial point of view.

The rate of temperature rise from the temperature at which the reduction nitriding reaction of aluminum oxide starts (900 ° C.) to the nitriding temperature may be 5 to 200 ° C./hr. The rate of temperature rise up to 900 ° C. may be the same as or different from the rate of temperature rise from 900 ° C. to the nitriding temperature. For example, the heating rate from room temperature to 900 ° C. may be faster than the heating rate from 900 ° C. to the nitriding time. The time required for producing the aluminum nitride particles (specifically, the time for reaching 900 ° C.) can be shortened.

(Post-heat treatment)
After synthesizing the aluminum nitride particles, the carbon may be removed by heating (heat treatment) in an air or oxygen atmosphere to remove carbon remaining in the obtained aluminum nitride particles. This heat treatment is particularly useful when the carbon source is a solid mixed with the aluminum oxide raw material. The post-heat treatment temperature may be 500 ° C. or higher, 600 ° C. or higher, or 700 ° C. or higher from the viewpoint of reliably removing residual carbon. Further, the post-heat treatment temperature may be 900 ° C. or lower, or 800 ° C. or lower, from the viewpoint of suppressing oxidation of the surface of the aluminum nitride particles. The post-heat treatment time can be appropriately selected according to the post-heat treatment temperature, but may be, for example, 3 hours or more.

(Shape of aluminum nitride particles)
The aluminum nitride particles may have the same crystal orientation. If the crystal orientations of the aluminum nitride particles are aligned, the crystal orientations of the aluminum nitride sintered body can be aligned by regularly arranging the aluminum nitride particles in the premolded body. By aligning the crystal orientations of the aluminum nitride sintered body, a highly transparent aluminum nitride sintered body can be obtained. In other words, if the crystal orientations of the aluminum nitride particles are not aligned, even if the aluminum nitride particles are regularly arranged in the pre-baked molded body, the crystal orientations of the aluminum nitride sintered body are not aligned and the transparency is lowered. The c-axis of the aluminum nitride crystal may appear on the particle surface (the surface having the largest area among the surfaces constituting the particles). That is, the c-axis may extend in the thickness direction of the aluminum nitride particles (direction substantially orthogonal to the particle surface). Whether or not the crystal orientations are aligned is determined by mapping the electronic image obtained by a scanning electron microscope (SEM) for each crystal orientation by the backscatter diffraction method (EBSD: Electron BackScatter Diffraction). It may be determined based on the ratio of a specific crystal orientation to the total. For example, the front surface (or back surface) of aluminum nitride particles is mapped for each crystal orientation using EBSD, the ratio (area ratio) of the (001) plane to the whole is calculated, and the state where the area ratio is 80% or more is ". It may be judged that the crystal orientations are aligned. "

The aluminum nitride particles may be plate-shaped and have an aspect ratio (L / D) of 3 or more. That is, the ratio of the plane length (maximum length of the front and back surfaces) L and the thickness direction length (length in the direction connecting the front and back surfaces) D of the plate-shaped aluminum nitride particles may be 3 or more. The length D in the thickness direction may be the length (that is, the thickness) of the portion where the distance between the planes is minimized when the aluminum nitride particles are sandwiched between a pair of parallel planes. The shape of the front and back surfaces may be a polygon such as a hexagon. When the aspect ratio is 3 or more, the aluminum nitride particles are regularly arranged in the molded body before firing (the aluminum nitride particles are oriented), and the crystal orientation of the aluminum nitride sintered body after firing is easily aligned.

The plane length (longitudinal size) L of the aluminum nitride particles may be 0.6 μm or more, 1 μm or more, 1.5 μm or more, or 2 μm or more. If the plane length L of the aluminum nitride particles is too small, the particles may aggregate with each other and a highly oriented (highly oriented crystal axis) aluminum nitride sintered body may not be obtained. The plane length L of the aluminum nitride particles may be 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less. If the plane length L of the aluminum nitride particles is too large, it becomes difficult for sintering to occur when the aluminum nitride sintered body is manufactured, and the density of the aluminum nitride sintered body (relative density with respect to the theoretical density) may decrease. is there. When the density of the aluminum nitride sintered body decreases, pores remain inside the aluminum nitride sintered body, and the transparency of the aluminum nitride sintered body decreases. When the length L of the aluminum nitride particles in the plane direction is within the above range (0.6 to 25 μm), a highly oriented and highly transparent aluminum nitride sintered body can be produced. The transparency of the aluminum nitride sintered body can be evaluated by irradiating the aluminum nitride sintered body with light (laser) having a specific wavelength and the linear transmittance of the light.

The thickness direction length (short direction size) D of the aluminum nitride particles may be 0.05 μm or more. If the length D of the aluminum nitride particles in the thickness direction is less than 0.05 μm, the shape of the aluminum nitride particles may be deformed when the aluminum nitride sintered body is manufactured, for example, in the process of mixing the raw materials. When the molded product before firing is formed due to the collapse of the particle shape, the degree of orientation of the aluminum nitride particles may decrease. The length D of the aluminum nitride particles in the thickness direction may be 0.1 μm or more, 0.3 μm or more, 0.5 μm or more, or 0.8 μm or more.

Further, the length D of the aluminum nitride particles in the thickness direction may be 2 μm or less, 1.5 μm or less, 1 μm or less, or 0.5 μm or less. If the length D of the aluminum nitride particles in the thickness direction is too large, for example, when adjusting the thickness of the pre-baked molded body using a doctor blade or the like, the shear stress applied to the aluminum nitride particles from the blade is applied to the side surface of the particles (parallel to the thickness direction). The proportion of the aluminum nitride particles received increases, and the arrangement of the aluminum nitride particles may be disturbed. Further, if the length D of the aluminum nitride particles in the thickness direction is too large, the aspect ratio is lowered as a result, and it becomes difficult for the aluminum nitride particles to be regularly arranged. When the length D of the aluminum nitride particles in the thickness direction is within the above range (0.05 to 2 μm), an aluminum nitride sintered body having high orientation and high transparency can be produced.

Holes may be formed on the front surface and / or the back surface of the aluminum nitride particles. By providing holes on the surface of the aluminum nitride particles, a portion (non-contact portion) that does not come into contact with other aluminum nitride particles can be provided on the front surface (back surface) of the aluminum nitride particles. As a result, the contact interface edge of the aluminum nitride particles can be secured for a long time, and the sintering of the aluminum nitride particles can be easily promoted. Further, since the holes are provided, it is possible to suppress agglomeration of particles when adjusting the thickness of the molded product before firing using a doctor blade or the like. Hereinafter, the holes provided in the aluminum nitride particles will be described with reference to the drawings.

FIG. 1 schematically shows the surface (c-plane) of the aluminum nitride particles 10. Holes 2 are provided on the surface of the aluminum nitride particles 10. The number of holes 2 may be plural as shown in FIG. 1 (A), or may be singular (1) as shown in FIG. 1 (B). As described above, the number of holes 2 can be adjusted by changing the supply amount of the nitrogen source. The size of the hole 2 is not particularly limited, but may be 0.1 to 5 μm.

When the total area of the portion of the surface of the aluminum nitride particles 10 where the holes 2 are not provided is S1 and the total area of the holes 2 is S2, the area ratio α (α = S2 / S1) of the holes 2 is 0. It may be 0.01 or more, 0.05 or more, 0.1 or more, 0.3 or more, 0.5 or more, 0.7 or more. You may. Further, the area ratio α may be 1.5 or less, 1.3 or less, 1.2 or less, 1.0 or less, 0.9 or less. May be good. If the area ratio α is too small (the ratio of the holes 2 is too low), it becomes difficult to secure a long contact interface edge on the surface of the aluminum nitride particles 10, and a good (highly transparent) aluminum nitride sintered body is obtained. It becomes difficult to obtain. On the other hand, if the area ratio α is too large (the ratio of the holes 2 is too high), the strength of the aluminum nitride particles 10 decreases, and it becomes difficult to maintain the shape of the aluminum nitride particles 10. It should be noted that adjusting the area ratio α of the holes 2 to an appropriate value has a greater contribution to improving the transparency of the aluminum nitride sintered body than adjusting the size of the holes 2. Further, it is easier to adjust the area ratio α by adjusting the number of holes 2 than by adjusting the size of the holes 2.

Further, when the maximum length in the plane direction on the surface of the aluminum nitride particles 10 is 10a and the diameter of the maximum circle 6 created in the region where the holes 2 do not exist is 6r in diameter, the length ratio β ( β = diameter 6r / length 10a) may be 0.1 or more, 0.2 or more, 0.3 or more, and 0.5 or more. Further, the length ratio β may be 0.9 or less, 0.8 or less, or 0.7 or less. When the length ratio β becomes too large, the region where the pores 2 do not exist increases on the surface of the aluminum nitride particles 10 (see comparison between FIGS. 1A and 1B). As a result, on the surface of the aluminum nitride particles 10, the region that is not in contact with the other aluminum nitride particles is reduced (the region that is in contact with the other aluminum nitride particles is widened), and the region where the contact interface edge does not exist on the surface. Is widened, and it becomes difficult to obtain the effect of promoting sintering. On the other hand, if the length ratio β becomes too large, the strength of the aluminum nitride particles 10 decreases, and it becomes difficult to maintain the shape of the aluminum nitride particles 10. The length ratio β can be adjusted by adjusting the position of the holes 2 on the surface of the aluminum nitride particles 10, adjusting the size of the holes 2, and adjusting the number of the holes 2. The position and size of the hole 2 is difficult to adjust. Therefore, the length ratio β is preferably adjusted by changing the number of holes 2. From this, it is preferable that the number of holes 2 is a plurality.

The hole 2 may have a bottomed form (dent 2a) as shown in FIG. 2 (A), or may be a through hole 2b as shown in FIG. 2 (B). Alternatively, one aluminum nitride particle 10 may have both a recess 2a and a through hole 2b. In both FIGS. 2 (A) and 2 (B), two holes 2 are provided on the front surface and the back surface. However, FIG. 2 (A) has four holes 2 (dents 2a), and FIG. 2 (A) has two holes 2 (through holes 2b). That is, if the holes 2 provided on the surface of the aluminum nitride particles 10 are through holes 2b, many holes can be provided on the front surface (and the back surface) with a small number of holes.

As described above, the number of holes 2 is preferably a plurality. As shown in FIG. 3, if the number of holes 2 is plural, one large aluminum nitride particle 10 can be regarded as an aggregate of a plurality of small aluminum nitride particles 10a, 10b, 10c. FIG. 3 shows that the nearby holes 2 are connected by a virtual line, and one aluminum nitride particle 10 is divided into three aluminum nitride particles 10a, 10b, and 10c.

FIG. 4 shows a pre-baked molded product 12 in which aluminum nitride particles 10 are laminated. When the aluminum nitride particles 10 are laminated, a part of the front surface (or back surface) of the aluminum nitride particles 10 faces the holes 2 of the other aluminum nitride particles 10. As a result, a portion (a portion exposed to the hole 2) that is not in contact with the other aluminum nitride particles 10 is formed on the front surface (or back surface) of the aluminum nitride particles 10. That is, the contact interface end 8 is formed on the surface of the aluminum nitride particles 10. For example, focusing on the aluminum nitride particles 10a and 10b in FIG. 4, if the holes 2 do not exist, the contact edge 8 is a portion where the outer edge of the aluminum nitride particles 10a and 10b and the surface of the aluminum nitride particles 10a and 10b are in contact with each other. Only (contact interface end 8a). However, by providing the holes 2, the contact interface end 8b is formed, and the contact interface end of the aluminum nitride particles 10a and 10b becomes long. The firing (grain growth) of the aluminum nitride particles 10 proceeds from the contact interface end 8. By providing the holes in the aluminum nitride particles 10, the length of the contact interface end 8 is increased and firing is promoted. If the hole 2 is a through hole 2a, the length of the contact interface end 8 is further increased, and firing is further promoted.

The specific surface area of the aluminum nitride particles may be 0.4 m ² / g or more, 1 m ² / g or more, 2 m ² / g or more, and 3.5 m ² / g or more. It may be 5 m ² / g or more, and may be 8 m ² / g or more. If the specific surface area is too small, it becomes difficult for the aluminum nitride particles to be sintered during firing, and a high-density aluminum nitride sintered body may not be obtained. The specific surface area may be 16 m ² / g or less, 13 m ² / g or less, or 10 m ² / g or less. If the specific surface area is too large, the aluminum nitride particles tend to aggregate, and the aluminum nitride particles cannot be arranged in a high orientation in the premolded body, and an aluminum nitride sintered body having a uniform crystal orientation cannot be obtained. There is. Further, if the specific surface area is too large, for example, when molding the pre-firing molded body using a doctor blade or the like, the shear stress applied from the blade to the aluminum nitride particles becomes small, and the arrangement of the aluminum nitride particles may be disturbed. .. When the specific surface area of the aluminum nitride particles is within the above range (0.4 to 16 μm), a highly oriented pre-firing molded product can be molded, and by firing the pre-firing molded product, high density and transparency can be obtained. It is possible to produce a high-quality aluminum nitride sintered body.

(Impurity concentration)
The amount of impurities (impurity metal, oxygen, etc.) contained in the aluminum nitride particles is preferably small. Specifically, the impurity metal may be 0.2 wt% or less, 0.1 wt% or less, 0.07 wt% or less, or 0.05 wt% or less. Further, the oxygen content may be 2 wt% or less, 1.5 wt% or less, 1 wt% or less, or 0.9 wt% or less. As the concentration of impurities in the aluminum nitride particles increases, the concentration of impurities contained in the aluminum nitride sintered body also increases. When the concentration of impurities in the aluminum nitride sintered body becomes high, the transparency of the aluminum nitride sintered body may decrease (the linear transmittance decreases), or the thermal conductivity may decrease. When the impurity concentration in the aluminum nitride particles is within the above range (impurity metal 0.2 wt% or less, oxygen content 2 wt% or less), a highly transparent aluminum nitride sintered body can be produced.

(Manufacturing of aluminum nitride sintered body)
The aluminum nitride sintered body is manufactured by molding a slurry-like raw material containing aluminum nitride particles into a sheet, laminating the sheet-shaped molded bodies to form a pre-baked molded body, and then performing primary firing and secondary firing. be able to. As the slurry-like raw material, a mixed raw material is prepared by mixing aluminum nitride particles with an auxiliary agent such as calcium carbonate, yttria, or a Ca—Al—O-based firing aid, and the mixed raw material is mixed with a binder, a plasticizer, a dispersant, or the like. Can be added to produce. As the binder, polyvinyl butyral (product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) can be used. As the plasticizer, di (2-ethylhexyl) phthalate (manufactured by Kurogane Kasei Co., Ltd.) can be used. Sorbitan trioleate (Leodor SP-O30, manufactured by Kao Corporation) can be used as the dispersant, 2-ethylhexanol, xylene, 1-butanol, a mixture thereof, or the like can be used as the dispersion medium. In addition, granular aluminum nitride particles of 0.1 to 2 μm may be added to the slurry-like raw material. Commercially available aluminum nitride particles can be used, and examples thereof include commercially available aluminum nitride powder (manufactured by Tokuyama Corporation, F grade, average particle size 1.2 μm). The sheet molded body can be molded by using, for example, the doctor blade method. The temperature of the primary firing and the secondary firing can be 140 to 2100 ° C. Further, the primary firing can be performed in a state where the pre-baking molded body (laminated body for firing) is pressurized. The aluminum nitride particles grow by the primary firing, and the auxiliary agent remaining in the aluminum nitride sintered body after the primary firing can be removed by the secondary firing.

(Characteristics of aluminum nitride sintered body)
The c-plane orientation of the aluminum nitride sintered body (the c-axis orientation of the aluminum nitride crystals constituting the aluminum nitride sintered body) may be 95% or more, 97% or more, and 100. May be%. The relative density of the aluminum nitride sintered body may be 99% or more, 99.8% or more, or 100%. The concentration of the impurity metal contained in the aluminum nitride particles may be 0.04 wt% or less. The oxygen concentration contained in the aluminum nitride particles may be 0.6 wt% or less. Further, the linear transmittance of the aluminum nitride sintered body may be 30% or more, 60% or more, or 65% or more when using light having a wavelength of 450 nm.

Hereinafter, examples of the aluminum nitride particles and the aluminum nitride sintered body manufactured by using the aluminum nitride particles will be shown. It should be noted that the examples shown below are for explaining the disclosure of the present specification, and do not limit the disclosure of the present specification.

(Example 1: Production of aluminum nitride particles)
First, plate-shaped aluminum oxide 100 g, carbon black (Mitsubishi Chemical Co., Ltd.) 50 g, alumina boulder (φ2 mm) 1000 g, and IPA (isopropyl alcohol: Tokuyama Co., Ltd., Tokuso IPA) 350 mL were mixed at 30 rpm for 240 minutes. , A mixture was obtained. As the aluminum oxide, one having an average particle size (length in the plane direction) of 10 μm, an average thickness (length in the thickness direction) of 0.5 μm, and an aspect ratio of 20 was used. Alumina boulders were removed from the resulting mixture and the mixture was dried using a rotary evaporator. Then, the remaining mixture was lightly crushed in a mortar (the agglomerated particles were separated with a relatively weak force), and 150 g of the carbon crucible was filled. Then, the crucible filled with the mixture was placed in a heating furnace, and the temperature was raised to 1600 ° C. at a heating rate of 50 ° C./hr under the flow of nitrogen gas at 3 L / min and maintained at 1600 ° C. for 20 hours. After the heating was completed, the sample was naturally cooled, the sample was taken out from the crucible, and heat-treated (post-heat-treated) at 650 ° C. for 10 hr in an oxidizing atmosphere using a muffle furnace to obtain plate-shaped aluminum nitride particles. The post-heat treatment was performed to remove carbon remaining in the sample.

(Evaluation of aluminum nitride particles)
The obtained aluminum nitride particles were evaluated for particle shape, crystal orientation, and surface condition (presence or absence of pores). The evaluation result is shown in FIG.

(Particle shape)
As for the shape of the aluminum nitride particles, the obtained aluminum nitride particles were photographed at 1000 to 2000 times using SEM (JSM-6390 manufactured by JEOL Ltd.), and 30 particles were randomly selected from the photographed images. It was selected and the length in the plane direction (particle size) and the length in the thickness direction were measured. Further, the aspect ratio (L / D) was calculated from the length L (μm) in the surface direction and the length D (μm) in the thickness direction. As shown in FIG. 5, the shape of the obtained aluminum nitride particles was almost the same as that of the raw material (aluminum oxide).

(Crystal orientation)
The crystal orientation was evaluated using an EBSD (Aztec HKL manufactured by Oxford Instruments Co., Ltd.) attached to the SEM. The crystal orientation was evaluated on the front surface or the back surface of the aluminum nitride particles, where no pores were formed. That is, the crystal morphology was evaluated on the surface (front surface or back surface) orthogonal to the thickness direction of the aluminum nitride particles and having the largest area among the surfaces constituting the aluminum nitride particles. Specifically, of the front surface (or back surface) of the aluminum nitride particles, the portion where no pores are formed is mapped for each crystal orientation, the ratio (area ratio) of the (001) plane to the whole is calculated, and the crystal is formed. It was judged whether or not the directions were aligned. When the area ratio is 80% or more, it is determined that the crystal orientations are aligned, and when it is less than 80%, it is determined that the crystal orientations are not aligned. In FIG. 5, “◯” is attached when the crystal orientations are aligned, and “x” is attached when the crystal orientations are not aligned. As shown in FIG. 5, the crystal orientations of the obtained aluminum nitride particles were aligned.

(Surface condition)
As for the surface condition of the aluminum nitride particles, the obtained aluminum nitride particles were photographed by SEM (manufactured by JEOL Ltd., JSM-6390) at a magnification of 1000 to 2000, and 30 particles were randomly obtained from the photographed images. Was selected and evaluated. Specifically, the presence or absence of holes, the type of holes (dents or through holes), the number of holes (one or more), and the maximum diameter of the maximum circle created in the area where no holes exist in the plane direction. The ratio to the length (length ratio β) and the ratio of the total area of the holes to the total area of the area where the holes did not exist (area ratio α) were evaluated. The presence or absence of holes and the number of holes were visually evaluated. In addition, the types of holes (dents, through holes) were also determined from the images taken by SEM. If the hole is a through hole, an SEM sample table is confirmed in the hole. For the area ratio α, the area S of the surface of the aluminum nitride particles and the total area S2 of the holes are calculated from the captured image, and the total area S1 of the region where the holes do not exist is calculated from the result (S1 = S-S2). , Area ratio α = S2 / S1 was calculated. Regarding the length ratio β, as described in FIG. 1, the plane length 10a (maximum length) of the aluminum nitride particles was measured, and a maximum circle 6 having no holes was created on the surface of the aluminum nitride particles. The diameter 6r of the maximum circle 6 was obtained, and the length ratio β = 6r / 10a was calculated. As shown in FIG. 5, the aluminum nitride particles have a plurality of through holes, and the results of the length ratio β: 0.30 and the area ratio α: 0.32 were obtained.

(Manufacturing of aluminum nitride sintered body)
A method for producing an aluminum nitride sintered body using the obtained aluminum nitride particles will be described. First, a method for synthesizing an auxiliary agent (Ca—Al—O-based firing auxiliary agent) used when sintering an aluminum nitride sintered body will be described. The auxiliary agent is mixed with the aluminum nitride particles and fired together with the aluminum nitride particles.

(Synthesis of auxiliary agent)
Calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., Silver-W) 47 g, γ-alumina (manufactured by Daimei Chemical Industry Co., Ltd., TM-300D) 24 g, alumina boulder (φ15 mm) 1000 g, IPA (manufactured by Tokuyama Co., Ltd., Tokuso) 125 mL of IPA) was pulverized and mixed at 110 rpm for 120 minutes to obtain a mixture. Alumina boulders were then removed from the mixture and the resulting mixture was dried using a rotary evaporator. 70 g of the mixture was filled in an alumina crucible. Then, the crucible filled with the mixture was placed in a heating furnace, the temperature was raised to 1250 ° C. at a heating rate of 200 ° C./hr in the air, and the temperature was maintained at 1250 ° C. for 3 hours. After the heating was completed, the mixture was naturally cooled and the mixture (auxiliary agent) was taken out from the crucible.

(Adjustment of raw materials for synthesis)
Next, a step of adjusting the raw material using the above-mentioned auxiliary agent will be described. To the above-mentioned aluminum nitride particles, 4.8 parts by mass of an auxiliary agent (Ca—Al—O-based auxiliary agent) was added, and the total amount was weighed to 20 g. This mixture, 300 g of alumina boulder (φ15 mm), and 60 mL of IPA (Tokuyama IPA, manufactured by Tokuyama Corporation) were mixed at 30 rpm for 240 minutes. Alumina boulders were removed from the obtained mixture, and the mixture was dried using a rotary evaporator to obtain a raw material for synthesis.

(Creation of molded product before firing)
2. 7.8 parts by mass of polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., product number BM-2) as a binder and di (2-ethylhexyl) phthalate (manufactured by Kurogane Kasei) as a plasticizer with respect to 100 parts by mass of the above synthetic raw material. 9 parts by mass, 2 parts by mass of sorbitan trioleate (manufactured by Kao, Leodor SP-O30) as a dispersant, and 2-ethylhexanol as a dispersion medium were added and mixed to prepare a raw material slurry. The amount of the dispersion medium added was adjusted so that the slurry viscosity was 20000 cP. The obtained raw material slurry was molded on a PET film by the doctor blade method. By using the doctor blade method, a raw material slurry is formed on the PET film so that the plate surface (c surface) of the aluminum nitride particles is aligned with the surface of the PET film. The thickness of the slurry was adjusted so that the thickness after drying was 30 μm. Through the above steps, a sheet-shaped tape molded product was obtained. The obtained tape molded body was cut into a circle having a diameter of 20 mm, and then 120 circular tape molded bodies were laminated to obtain a pre-baked molded body. The obtained pre-baked molded product was placed on an aluminum plate having a thickness of 10 mm and then placed in a vacuum package to evacuate the inside. Then, the vacuum package was hydrostatically pressed at 100 kgf / cm ² in warm water at 85 ° C. to obtain a disk-shaped pre-calcined molded product (laminated product for firing).

(Primary firing)
Next, the pre-baked molded product was placed in a degreasing furnace and degreased at 600 ° C. for 10 hours. Then, it was fired at 1900 ° C. for 10 hours under the condition of a surface pressure of 200 kgf / cm ² , and then the temperature was lowered to room temperature to obtain an aluminum nitride primary sintered body. The pressurizing direction at the time of hot pressing was the laminating direction of the molded product before firing (the direction substantially orthogonal to the surface of the tape molded product). The pressurization was maintained until the temperature dropped to room temperature. By the primary firing, the aluminum nitride particles constituting the pre-calcined molded body grow into grains, and the pores in the molded body disappear, so that the aluminum nitride primary sintered body having a high density (relative density) can be obtained.

(Secondary firing)
The surface of the aluminum nitride primary sintered body was ground to prepare a sample having a diameter of 20 mm and a thickness of 0.7 mm. This sample was placed on a plate made of aluminum nitride, the inside of the heating furnace was set to a nitrogen atmosphere, and the sample was fired at a firing temperature of 1900 ° C. for 75 hours to obtain an aluminum nitride sintered body. By the secondary firing, the auxiliary agent (auxiliary agent used at the time of sintering) remaining in the aluminum nitride primary sintered body is removed, and a transparent aluminum nitride sintered body is obtained.

(Evaluation of aluminum nitride sintered body)
The c-plane orientation (c-axis orientation), relative density, and linear transmittance of the obtained aluminum nitride sintered body were evaluated. The evaluation result is shown in FIG.

(C-plane orientation)
After polishing the surface of the aluminum nitride sintered body, the polished surface was irradiated with X-rays and the degree of c-plane orientation was measured. Specifically, using an XRD device (RINT-TTR III manufactured by Rigaku Co., Ltd.), the XRD profile was measured in the range of 2θ = 20 to 70 ° under the conditions of a voltage of 50 kV and a current of 300 mA using CuKα rays. .. The c-plane orientation (f) was calculated by the lot-gering method. Specifically, it was calculated by substituting the results P and P ₀ obtained by the following equations (3) and (4) into the equation (2). In the formula, P is a value obtained from the XRD measurement of the obtained aluminum nitride sintered body, and P ₀ is a value calculated from standard aluminum nitride (JCPDS card No. 076-0566). In addition, (100), (002), (101), (102), (110), (103) were used as (hkl).
f = {(P−P ₀ ) / (1-P ₀ )} × 100 ... (2)
P ₀ = ΣI ₀ (002) / ΣI ₀ (hkl) ... (3)
P = ΣI (002) / ΣI (hkl) ... (4)

(Relative density)
For the relative density, the bulk density was measured by the method described in JIS R1634, and the value with respect to the theoretical density (3.260) was calculated.

(Linear transmittance)
The sintered aluminum nitride sintered body is cut to a size of φ10 mm, and four aluminum nitride sintered bodies are placed on the outer peripheral portion of an alumina platen (φ68 mm) at equal intervals (aluminum nitride adjacent to the center of the platen). It was fixed (so that the angle formed by the sintered body was 90 °), polished by a copper wrapping machine on which a slurry containing diamond abrasive grains having a particle size of 9 μm and 3 μm was dropped, and further, a slurry containing colloidal silica was dropped. Polished on a buffing machine for 300 minutes. Then, the polished sample having a thickness of φ10 mm × 0.3 mm was washed with ion-exchanged water, acetone, and ethanol in this order for 3 minutes each, and then linear transmittance at a wavelength of 450 nm using a spectrophotometer (Perkin Elmer, Lambda900). Was measured.

As shown in FIG. 5, as a result of producing an aluminum nitride sintered body using the aluminum nitride particles obtained in this example, the c-plane orientation degree is 98.5%, the relative density is 99.9%, and the linear transmittance is 67. % Aluminum nitride sintered body was obtained.

(Examples 2 and 3)
Aluminum nitride particles and an aluminum nitride sintered body were produced by the same production method as in Example 1. Therefore, as shown in FIG. 5, the shape, crystal orientation, presence / absence of pores, type of pores, number of pores, and area ratio α of the aluminum nitride particles were the same as those in Example 1. However, in Examples 2 and 3, the holes were unevenly distributed as compared with Example 1, and the length ratio β was larger than that of Example 1. Therefore, although the characteristics (c-plane orientation, relative density, linear transmittance) of the aluminum nitride sintered body were good, the results were slightly lower than those of the aluminum nitride sintered body of Example 1. This result indicates that if the length ratio β becomes too large, it becomes difficult to obtain the effect of promoting the sintering of the aluminum nitride particles.

(Examples 4 to 8)
Aluminum nitride particles were produced by the same method as in Example 1 except that the flow rate of nitrogen gas was changed by using aluminum oxide of the same size as in Example 1, and the obtained aluminum nitride particles were used to produce aluminum nitride. A sintered body was manufactured. Moreover, the obtained aluminum nitride particles and the aluminum nitride sintered body were evaluated in the same manner as in Example 1. In Examples 4 and 5, the flow rate of nitrogen gas was 6 L / min (more than in Example 1), and in Example 6, the flow rate of nitrogen gas was 5 L / min (more than in Example 1). In No. 7, the flow rate of nitrogen gas was 2 L / min (less than in Example 1), and in Example 8, the flow rate of nitrogen gas was 1 L / min (less than in Example 1).

As shown in FIG. 5, the aluminum nitride particles of Examples 4 to 9 had the same results as those of Example 1 in terms of particle shape and crystal orientation. However, in Examples 4 and 5, the number of holes was one, and in particular, in Example 4, through holes were not formed and only dents were formed. Further, since the number of holes in Examples 4 and 5 was smaller than that in Example 1, the length ratio β was larger and the area ratio α was smaller than in Example 1. Although the aluminum nitride sintered bodies of Examples 4 and 5 obtained sufficient levels of characteristics, the results were slightly lower than those of the aluminum nitride sintered bodies of Example 1. This result indicates that if the area ratio α becomes too small, it becomes difficult to obtain the effect of promoting the sintering of the aluminum nitride particles. Comparing Examples 4 and 5, the aluminum nitride sintered in Example 5 in which the through hole was formed was compared with Example 4 in which the through hole was not formed (the depression was formed). The characteristics of the body were good. The aluminum nitride particles of Examples 4 and 5 have the same surface state except for the types of holes (through holes, dents). This result shows that the effect of promoting the sintering of the aluminum nitride particles is more likely to be obtained by providing the through holes in the aluminum nitride particles than by providing the recesses.

Although the aluminum nitride particles of Example 6 had a plurality of through holes formed, the area ratio α was smaller than that of Example 1. The aluminum nitride sintered body of Example 6 had slightly lower characteristics than that of Example 1, but the same level of characteristics as that of Example 1 was obtained. The aluminum nitride particles of Example 7 had the same shape, crystal orientation, and surface state of the aluminum nitride particles, except that the area ratio α was higher than that of Example 1. The characteristics of the aluminum nitride sintered body of Example 7 were better than those of Example 1 in all of the c-plane orientation, the relative density, and the linear transmittance. In addition, the characteristics of the aluminum nitride sintered body of Example 8 were also better than those of Example 1 in all of the c-plane orientation, the relative density, and the linear transmittance. This result indicates that the contact interface edge became longer and sintering was promoted by increasing the area ratio α.

(Examples 9 to 11)
Aluminum nitride particles and an aluminum nitride sintered body were produced by the same production method as in Example 1 except that aluminum oxide having a size different from that of Example 1 was used. In Example 9, the plane length L and the thickness direction length D are different from those of Example 1, and the aspect ratio is the same as that of Example 1. Specifically, in Example 9, the length L in the surface direction and the length D in the thickness direction are smaller than those in Example 1. Further, in Example 10, the length L in the surface direction is smaller than that in Example 1, and the length D in the thickness direction is the same as that in Example 1. Therefore, the aspect ratio of Example 10 is smaller than that of Example 1. The aspect ratio of the tenth embodiment is the same as that of the first embodiment, but the length L in the plane direction and the length D in the thickness direction are larger than those in the first embodiment. The shape of the obtained aluminum nitride particles was almost the same as that of the raw material aluminum oxide. In addition, the crystal orientations were the same in all of Examples 9 to 11, and the surface state was the same as that of Example 1. Moreover, the characteristics (c-plane orientation, relative density, linear transmittance) of the aluminum nitride sintered body were all good. The aluminum nitride sintered body of Example 9 had a better relative density than that of Example 1. The aluminum nitride sintered body of Example 10 had a better relative density than that of Example 1. The aluminum nitride sintered body of Example 11 had a better c-plane orientation than that of Example 1. This result shows that by adjusting the surface state of the aluminum nitride particles, an aluminum nitride sintered body having good characteristics can be obtained even if the particle size (particle shape) changes.

(Comparative Example 1)
A production method similar to that of Example 11 (that is, Example), except that aluminum oxide having the same size as that of Example 11 was used and the flow rate of nitrogen gas was set to 10 L / min (more than that of Examples 1 to 11). Aluminum nitride particles and an aluminum nitride sintered body were produced by the same production method as in 1. The aluminum nitride particles of Comparative Example 1 had the same crystal orientation, but no pores were formed on the surface. The aluminum nitride sintered body of Comparative Example 1 had lower results than all of Examples 1 to 10 in all characteristics. This result shows that the characteristics of the aluminum nitride sintered body can be improved by providing holes on the surface of the aluminum nitride particles (Examples 1 to 10).

(Comparative Example 2)
Aluminum nitride particles and an aluminum nitride sintered body were produced by the same production method as in Example 1 except that the nitriding temperature was set to 1440 ° C. using aluminum oxide of the same size as in Example 1. The surface condition of the aluminum nitride particles of Comparative Example 2 was the same as that of Example 1, but the nitriding temperature was too low and the crystal orientation was inconsistent. That is, the aluminum nitride particles of Comparative Example 2 did not have the same crystal orientation. Therefore, the aluminum nitride sintered body of Comparative Example 2 had the same relative density as that of Example 1, but the c-plane orientation was low and the linear transmittance was also low.

(Comparative Example 3)
Aluminum nitride particles and an aluminum nitride sintered body were produced by the same production method as in Example 1 using non-plate-shaped aluminum oxide (aspect ratio 2). Although the particle shape of the aluminum nitride of Comparative Example 3 was not plate-like, the crystal orientations were the same and the surface condition was the same as that of Example 1. The aluminum nitride sintered body of Comparative Example 3 had the same relative density as that of Example 1, but the c-axis orientation was low and the linear transmittance was low. The reason is that the crystal orientations of the aluminum nitride particles are not aligned because the aspect ratio is small (not plate-shaped) when the aluminum nitride particles are laminated to prepare a pre-baked molded product.

Although the embodiments of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above. In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques illustrated in the present specification or drawings achieve a plurality of objectives at the same time, and achieving one of the objectives itself has technical usefulness.

Claims (5)

Aluminum nitride particles used as a raw material for an aluminum nitride sintered body.
The crystal orientations within the particles are aligned,
It is plate-shaped and
Aluminum nitride particles having holes on the surface. The aluminum nitride particle according to claim 1, wherein the hole is a through hole. The aluminum nitride particle according to claim 1 or 2, wherein a plurality of the holes are provided. According to any one of claims 1 to 3, the diameter of the maximum circle created in the region where the holes do not exist on the surface is 0.1 or more and 0.9 or less with respect to the maximum length in the surface direction on the surface. The aluminum nitride particles described. The aluminum nitride particle according to any one of claims 1 to 4, wherein the total area of the pores on the surface is 0.01 or more and 1.5 or less with respect to the total area of the region where the pores do not exist.

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