JPH0517190B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing an aluminum nitride sintered body having high purity, high density, and particularly excellent thermal conductivity. [Prior art and problems to be solved by the invention] Aluminum nitride sintered bodies have recently attracted particular attention as an insulator that has excellent physical properties such as heat resistance, corrosion resistance, and strength, as well as high thermal conductivity. It is a substance. In the case of pressureless sintering, the aluminum nitride sintered body is usually obtained by firing a mixed powder of aluminum nitride powder and a sintering aid. However, the aluminum nitride sintered body thus obtained contains about several percent of impurities derived from the sintering aid. Therefore, the influence of these impurities, especially the diffusion and solid solution of impurities into the crystal grains of the sintered body structure, exists to a greater or lesser extent, and the inherent excellent properties of aluminum nitride sintered bodies, such as high thermal conductivity, are It was difficult to obtain an aluminum nitride sintered body having the above-mentioned properties. [Means for Solving the Problems] In view of the above-mentioned problems, the present inventors have attempted to obtain an aluminum nitride sintered body that has the inherent excellent properties of an aluminum nitride sintered body, particularly high thermal conductivity. We have been conducting intensive research to achieve this goal. As a result, when sintering aluminum nitride powder using a relatively large amount of sintering aid required for sintering aluminum nitride powder, it has become possible to use a combination of two specific sintering aids. It has thus been found that the amount of sintering aid contained in the sintered body becomes extremely small, and the oxygen content in the sintered body also becomes extremely small.
We discovered that because the amount of sintering aid and oxygen content are small, an aluminum nitride sintered body with excellent properties, especially high thermal conductivity, can be obtained, and this book is based on this research. The invention was completed. That is, the present invention provides a method for producing an aluminum nitride sintered body by sintering a mixed powder of aluminum nitride powder and a sintering aid, in which particles having an average particle size of 3 μm or less and 5 μm or less are used as the aluminum nitride powder. (A) using aluminum nitride powder containing 80% by volume or more, an oxygen content of 3% by weight or less, and a cationic impurity content of 0.5% by weight or less, and as a sintering aid, (A) yttrium; , an oxygen-containing compound of at least one metal selected from the group consisting of lanthanum group metals and alkaline earth metals; and (B) an oxygen-containing compound of at least one metal selected from the group consisting of yttrium and lanthanum group metals. This is a method for producing an aluminum nitride sintered body characterized by using a halide. Considering that the aluminum nitride powder used in the present invention can be densified well during sintering and obtain a sintered body with high thermal conductivity, the average particle size is 3 μm.
It is preferable to use an aluminum nitride powder containing particles of 5 μm or less at a ratio of 80% by volume or more, an oxygen content of 3% by weight or less, and a cationic impurity content of 0.5% by weight or less. The average particle size referred to here is not the average value of the particle size of primary particles calculated from photographs taken with a scanning electron microscope of powder, but rather the average particle size of secondary particles as measured by a sedimentation-type particle size distribution analyzer. Refers to the average size of aggregated particles. One of the features of the present invention is that, as a sintering aid, (A) an oxygen-containing compound (hereinafter referred to as a sintering aid) of at least one metal selected from the group consisting of yttrium, lanthanum group metals, and alkaline earth metals; (A) and (B) a halide of at least one metal selected from the group consisting of yttrium and lanthanum group metals (hereinafter referred to as sintering aid (B)). Among the above sintering aids (A), when the sintering aids made of yttrium and lanthanum group metals are mixed with aluminum nitride powder and fired alone, they do not volatilize and remain in the aluminum nitride sintered body. remain. However, when the above-mentioned sintering aid (B) is coexisting, not only the sintering aid (A) but also the sintering aid (B) is volatilized, and the resultant aluminum nitride sintered body is The amount of sintering aid remaining is extremely smaller than the amount of sintering aids (A) and (B) added before firing. Usually, the amount of the sintering aid remaining in the sintered body is 1/2 or less of the added amount, sometimes 1/5 or less, and even 1/10 or less.
Additionally, compared to when sintering aids (A) and (B) were mixed with aluminum nitride powder alone and fired, surprisingly, sintering aids (A) and (B) were simultaneously nitrided. The thermal conductivity of the sintered body obtained by mixing it with aluminum powder and firing it is extremely high. In the metal oxygen-containing compound of the sintering aid (A),
Yttrium, lanthanum group metals, and alkaline earth metals can be used without particular limitation. For example, yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb). ,
Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu), Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr) and barium (Ba) can both be used. Especially for industrial purposes, Y, La, Ce,
Pr, Nd, Sm, Eu, Gd, Dy, Ca, Sr, Ba, etc. are preferably used. Moreover, as these oxygen-containing compounds, compounds in which oxygen atoms are bonded and contained are employed without any restrictions. Also,
The above-mentioned oxygen-containing compounds also include compounds that become oxides under the sintering conditions when a mixed powder of aluminum nitride powder and a sintering aid is sintered. As the oxygen-containing compound used in the present invention, not only oxides but also nitrates, carbonates, oxalates, sulfates, hydroxides, and the like are preferably used. Further, the other sintering aid (B) used in the present invention is a halide of at least one metal selected from the group consisting of yttrium and lanthanum group metals. The above-mentioned yttrium and lanthanum group metals are not particularly limited, and the above-mentioned metal elements can be used. Especially industrially Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy
etc. are preferably used. Further, as these halides, fluoride, chloride, bromide, iodide, etc. can be used without any restriction. In particular, fluorides, bromides, iodides, etc. are preferably used industrially. Specific examples of yttrium and lanthanum group metal halides that are preferably used in the present invention include yttrium fluoride, lanthanum fluoride, cerium fluoride, praseodymium fluoride, neodymium fluoride, samarium fluoride, and fluoride. Europium, gadolinium fluoride, dysprosium fluoride, yttrium bromide, lanthanum bromide, cerium bromide, praseodymium bromide, neodymium bromide, samarium bromide, europium bromide, gadolinium bromide, dysprosium bromide, yttrium iodide,
Examples include lanthanum iodide, cerium iodide, praseodymium iodide, neodymium iodide, samarium iodide, europium iodide, gadolinium iodide, and dysprosium iodide. Among these, fluorides are preferably used because the resulting aluminum nitride sintered body has better thermal conductivity. The amounts of the sintering aids (A) and (B) used in the present invention vary depending on the properties required of the sintered body and cannot be absolutely limited, but generally aluminum nitride powder, sintering aids The amount contained in the mixed powder of (A) and sintering aid (B) is 0.02 to 5% by weight in terms of oxide in the case of sintering aid (A), and 0.02 to 5% by weight in terms of oxide for sintering aid (B). 0.02~10 for
It is preferable to select the amount within a range of % by weight. As long as the amounts of sintering aids (A) and (B) added are within the above range, the ratio of these amounts is not limited at all, but the amount of sintering aids remaining after sintering and the content of the sintered body may In order to reduce the oxygen content of Preferably, the range is within the range. The mixing of the aluminum nitride powder and the sintering aid in the present invention is not particularly limited, and may be dry or wet mixing. A particularly preferred embodiment is wet mixing, ie mixing in the wet state using a liquid dispersion medium. The liquid dispersion medium is not particularly limited, and commonly used water, alcoholic hydrocarbons, or a mixture thereof is preferably used. In particular, the most suitable method for industrial use is
These are lower alcohols having 4 or less carbon atoms, such as methanol, ethanol, butanol. Further, the wet mixing device used for mixing the raw materials is not particularly limited and any known device may be used, but it is preferable to select one that does not generate impurity components due to the materials. For example, the material may be aluminum nitride itself, a plastic material such as polyethylene, polyurethane, nylon, or a material coated with these materials. Furthermore, aluminum nitride powder, sintering aid (A)
The mixing order of the sintering aid (B) and the sintering aid (B) is not particularly limited. A method of preparing and mixing one component is adopted. However, in order to uniformly disperse and mix small amounts of two types of powder into the aluminum nitride powder, which is the main component, first mix the sintering aid (A) and the sintering aid (B). A method of later preparing and mixing the mixture and aluminum nitride powder is preferably employed. Specific aspects of firing in the present invention include:
The mixed powder obtained by adding the sintering aid (A) and the sintering aid (B) to the aluminum nitride powder is formed by an appropriate molding method, such as a dry press method, a rubber press, an extrusion method, an injection method, a doctor blade sheet molding method. After molding it into the desired shape, use a suitable crucible,
Place on top of pod wood, etc., and fire at high temperature under a non-oxidizing atmosphere of vacuum or atmospheric pressure, such as an atmosphere of nitrogen gas, helium gas, argon gas, etc., or under nitrogen gas pressure of about 2 to 100 atmospheres. There are several methods. Alternatively, directly add the mixed powder to
A method of firing at high temperature under a non-oxidizing atmosphere of vacuum or atmospheric pressure, or under nitrogen gas pressure of about 2 to 100 atmospheres while applying a mechanical pressure of about 500 kg/cm ² is adopted. The firing temperature is 1700 to 2100°C in a non-oxidizing atmosphere at vacuum or atmospheric pressure, preferably
A temperature of 1750~2050℃ is preferably adopted, and a temperature of 2~100℃ is preferably adopted.
Under atmospheric pressure of nitrogen gas, a temperature of 1700 to 2400°C, preferably 1750 to 2300°C is suitably employed.
Note that the temperature in the present invention is a value that is compensated to indicate the gas temperature within the graphite crucible by measuring the surface of the graphite crucible containing the mixed powder with a radiation thermometer. In the present invention, in order to make the resulting aluminum nitride sintered body highly thermally conductive and dense, the average heating rate in the temperature range of at least 1300 to 1700°C is set at 1°C/1°C during firing. min~40℃/
It is preferable to set it in the range of min. 5 to 30 more
It is more preferable to raise the temperature within a range of °C/min. The above average temperature increase rate is based on the added sintering aid (A)
There is an optimal range depending on the type and amount of (B) and (B), so it may be determined appropriately depending on the sintering aid. In determining the heating rate, it is important to select heating conditions that will not cause excessive evaporation of the sintering aid during the heating process, and will ensure that as little of the sintering aid component remains after sintering. That's a thing. As for the method of raising the temperature,
Although it is industrially preferable to set a single temperature increase rate in the range of 1300 to 1700°C, it is also possible to select a temperature increase program with a two-stage or three-stage rate gradient. The rate of temperature increase until reaching 1300°C and the rate of temperature increase when it is necessary to increase the temperature from 1700°C to the firing temperature are not particularly limited, and any rate of temperature increase may be used. However, in consideration of the density and thermal conductivity of the obtained sintered body, it is preferable that the average temperature increase rate described above is maintained even in the temperature range of 1200 to 1300°C. Further, industrially, it is preferable to maintain a single average heating rate over the entire temperature range up to the firing temperature. After the temperature has been raised in this manner, it is then preferably fired at a firing temperature of 1700 to 2400°C. Firing time varies depending on firing temperature, type and amount of sintering aid, and average heating rate, but is usually 10 minutes to 20 minutes.
Selected from a time range. (Effect) The aluminum nitride sintered body obtained by the method of the present invention does not contain any sintered material after sintering, despite the addition of several weight percent of sintering aid necessary for sintering aluminum nitride powder. The amount of the auxiliary agent is extremely small, being 1/2 or less, preferably 1/5 or less, and more preferably 1/10 or less of the added amount. That is, the amount of the sintering aid remaining in the aluminum nitride sintered body is 0.5% by weight or less for each of the sintering aids (A) and (B), in some cases 0.3% by weight or less, and even 0.1% by weight. % or less. Furthermore, according to the method of the present invention, in addition to the sintering aid, the oxygen content of the sintered body is also reduced. That is, the oxygen content in the sintered body is less than 1/2 of the total amount of oxygen derived from the aluminum nitride powder and the sintering aid.
It further decreased to less than 1/5, and further decreased to less than 0.5% by weight.
It is 0.2% by weight or less. As described above, the aluminum nitride sintered body obtained by the method of the present invention has extremely good thermal conductivity because it contains a small amount of sintering aid and oxygen.
Usually, a sintered body with high thermal conductivity of 150 w/m·k or more, preferably 160 w/m·k or more, can be obtained. Furthermore, depending on the firing conditions,
It is possible to obtain a sintered body with extremely excellent thermal conductivity of 170w/m・k or more. Furthermore, an aluminum nitride sintered body having excellent translucency can also be obtained. That is, in the Lambert-Beer equation, 6μ
A sintered body having a respiration coefficient of 60 cm ^-1 or less for light with a wavelength of m can be obtained. Of course, the aluminum nitride sintered body obtained by the method of the present invention is a dense sintered body with a sintered density of 3.2 g/cm ³ or more. The present invention, which provides a method for manufacturing an aluminum nitride sintered body exhibiting excellent properties as described above, is extremely important industrially as a method for providing a new material, and has high value. Example 1 1.0% by weight of CaO powder and 2.0% by weight of YF ₃ powder were added to aluminum nitride powder with an average particle size of 1.42 μm and 87% by weight of 3 μm or less and the composition shown in Table 1, and the powder was homogenized in ethanol. mixed with. After drying the mixture, about 1.0g of it was heated using a mold with an inner diameter of 15mm.
A powder compact having a density of 1.62 g/cm ^{3 was produced by uniaxial pressing at a pressure of Kg/cm 2 and} then rubber pressing at a pressure of 1500 Kg/cm ² . This compact was placed in a graphite crucible coated with boron nitride powder,
The temperature was raised to 1100°C in 40 minutes in nitrogen at 1 atm, then the temperature was raised from 1100°C to 1800°C at a rate of 10°C/min, and held at 1800°C for 10 hours. The density of the obtained sintered body was 3.25 g/cm ³ . This sintered body was ground to a thickness of 3 mm and then injected using the laser flashing method.
-Thermal conductivity measured by non-contact method using Sb infrared sensor was 230W/m・k at room temperature, 100℃
At 205W/m・k, we obtained a value of 180W/m・k at 200℃. The oxygen content of this sintered body was measured by activation analysis and was found to be 0.08% by weight. Furthermore, the sintered body is melted with an alkali, and the sintered body is melted with an alkali.
Ca, Y, Mg, Cr, Si, Zn, Fe, Cu, Mn, Ni,
The contents of Ti and Co were measured using inductively coupled plasma emission spectroscopy and were converted into concentrations in the sintered body: Ca=510ppm, Y=590ppm, Mg<5ppm,
Cr＜10ppm, Si＝97ppm, Zn＜10ppm, Fe＜
10ppm, Cu<10ppm, Mn<5ppm, Ni=19ppm,
Ti < 10 ppm, Co < 10 ppm, and the total content of 10 elements other than Ca and Y added as sintering aids was 186 ppm or less. Another sintered body sintered in the same manner as above is 0.5mm
When we measured the light transmittance of a material that had been ground to a thickness of 100 μm and mirror-polished on both sides, we obtained a linear transmittance of 34% for a wavelength of 5.5 μm. Table 1 Amminium nitride powder analysis values AlN content 98.0% Element Content Mg <5ppm Cr <10〃 Si 27〃 Zn <10〃 Fe 13〃 Cu <5〃 Mn <5〃 Ni <10〃 Ti <5〃 Co < 5 64.8% N 33.5 O 1.0 C 0.05 Example 2 The same aluminum nitride powder used in Example 1, various types of sintering aids (A), and sintering aids
Table 2 shows the results of pressureless sintering of (B) in which YF ₃ was added and mixed in the same manner as in Example 1. Thermal conductivity measurements were carried out in the same manner as in Example 1 on a sample ground to a thickness of 3 mm. No.9, No.
10 is a comparative example.

[Table] Example 3 The heating rate of the same aluminum nitride powder used in Example 1 with CaO as the sintering aid (A) and YF ₃ as the sintering aid (B) added and mixed. Table 3 shows the results of pressureless sintering performed in the same manner as in Example 1, except for various changes. Thermal conductivity measurements were carried out in the same manner as in Example 1 on a sample ground to a thickness of 3 mm.

[Table] Example 4 The same aluminum nitride powder used in Example 1 was mixed with various types of sintering aids (A) and sintering aids (B). Table 4 shows the results of pressureless sintering in the same manner. Thermal conductivity measurements were carried out in the same manner as in Example 1 on a sample ground to a thickness of 3 mm.

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Claims (1)

[Claims] 1. In a method for producing an aluminum nitride sintered body by sintering a mixed powder of aluminum nitride powder and a sintering aid, the aluminum nitride powder has an average particle size of 3 μm or less and 5 μm or less. particles of 80% by volume
(A) Yttrium, a lanthanum group metal; and (B) a halide of at least one metal selected from the group consisting of yttrium and lanthanum group metals. A method for producing an aluminum nitride sintered body, characterized by: