JPH0468262B2 - - 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 comparative example with a large amount of sintering aid required for sintering aluminum nitride powder, we found that it was 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: (A) yttrium, a lanthanum group metal; and (B) at least one metal selected from the group consisting of yttrium, lanthanum group metals, and alkaline earth metals. This is a method for producing an aluminum nitride sintered body, characterized by using a halide of the present invention. The aluminum nitride powder used in the present invention is not particularly limited, and any known aluminum nitride powder can be used. In order to achieve good densification during sintering and obtain a sintered body with high thermal conductivity, it is recommended that particles with an average particle diameter of 3 μm or less and 5 μm or less be contained at a ratio of 80% or more by volume, and oxygen-containing It is preferable to use aluminum nitride powder containing 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. The greatest feature of the present invention is that (A) a carbide or nitride of at least one metal selected from the group consisting of yttrium, lanthanum group metals, and alkaline earth metals (hereinafter referred to as a sintering aid) is used as a sintering aid; Agent (A)
and (B) a halide of at least one metal selected from the group consisting of yttrium, lanthanum group metals, and alkaline earth metals (hereinafter referred to as sintering aid (B)). When the above-mentioned sintering aids (A) and (B) are coexisted, both of the sintering aids (A) and (B) volatilize, resulting in sintering in the aluminum nitride sintered body. The remaining amount of the auxiliary agent is extremely smaller than the amount of the sintering auxiliary agents (A) and (B) added before sintering. 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 alone with aluminum nitride powder and fired, surprisingly, sintering aid (A)
The thermal conductivity of the sintered body obtained by simultaneously mixing and firing aluminum nitride powder and (B) is extremely high. The sintering aid (A) used in the present invention is a carbide or nitride of an alkaline earth metal such as magnesium, calcium, strontium, or barium, or a rare earth metal such as yttrium or a lanthanum group metal.
These sintering aids have the effect of improving the thermal conductivity of the obtained aluminum nitride sintered body. As carbides of these metals, compounds known as acetylides are usually used without particular limitation. Carbides particularly preferably used in the present invention include, for example, MgC ₂ , CaC ₂ , SrC ₂ , BaC ₂ , YC ₂ ,
Examples include LaC ₂ , CeC ₂ , PrC ₂ , NdC ₂ and SmC ₂ . Furthermore, specific examples of the metal nitrides preferably used in the present invention are as follows. Mg ₃ N ₂ , Ca ₃ N ₂ , Sr ₃ N ₂ , Ba ₃ N ₂ , YN,
Examples include LaN, CeN, PrN, NdN, ErN, etc. The sintering aid (B) used in the present invention is yttrium,
It is a halide of at least one metal selected from the group consisting of lanthanum group metals and alkaline earth metals. 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), itterbium (Yb) , lutetium (Lu), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba) can all be used. Especially industrially, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy,
Ca, Sr, Ba, etc. are preferably used. In addition, these halides include 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, lanthanum group metal, and alkaline earth metal halides preferably used in the present invention include yttrium fluoride, lanthanum fluoride, cerium fluoride, praseodymium fluoride, neodymium fluoride, samarium fluoride, europium fluoride, gadolinium fluoride,
Dysprosium fluoride, yttrium bromide, lanthanum bromide, cerium bromide, praseodymium bromide, neodymium bromide, samarium bromide, europium bromide, gadolinium bromide, dysprosium bromide, yttrium iodide, lanthanum iodide, iodide Cerium, praseodymium iodide, neodymium iodide, samarium iodide, europium iodide, gadolinium iodide, dysprosium iodide, calcium fluoride, barium fluoride, strontium fluoride, calcium bromide, barium bromide, strontium bromide, Calcium iodide, barium iodide,
Examples include strontium 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 the case of sintering aid (A), preferably 0.1 to 4% by weight, In the case of (B), it is preferable to select the amount within the range of 0.02 to 10% by weight, preferably 0.1 to 6% by weight. As long as the amounts of sintering aids (A) and (B) 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 oxygen in the sintered body In order to reduce the content, it is suitable that the weight ratio of sintering aid (A) to sintering aid (B) is in the range of 1/10 to 5, preferably 1/5 to 3. . The mixing of the aluminum nitride powder and the sintering aid in the present invention is not particularly limited, and may be dry mixing 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. Particularly suitable 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 limited to aluminum nitride itself, plastic materials such as polyethylene, polyurethane, nylon, or materials 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 aluminum nitride powder, which is the main component, first mix the sintering aid (A) and the sintering aid (B), and then A method of 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, for example, under 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 of 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,
It is industrially preferable to set a single temperature increase rate in the range of 1300 to 1700°C, or 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 1,700 to 2,400°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, in some cases, 0.3% by weight or less as the metal of each of the sintering aids (A) and (B). It is 0.1% by weight or less. Furthermore, according to the method of the 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,
A sintered body having an absorption coefficient of 60 cm ^-1 or less for light with a wavelength of 6 μm 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% by weight of CaC ₂ and 2% by weight of YF ₃ were added to aluminum nitride powder with an average particle size of 1.42 μm and 3 μm or less accounting for 87% by weight and having the composition shown in Table 1,
Mixed homogeneously in ethanol. After drying the mixture, approximately 1.0g of it was molded into a mold with an inner diameter of 15mm to give a weight of 200Kg/cm ²
A powder molded body having a density of 1.60 g/cm 3 was produced by uniaxial pressing at a pressure of 1,500 kg/cm ² and then by rubber pressing at a pressure of 1,500 kg/cm ² . This compact was placed in a graphite crucible coated with boron nitride powder, heated to 1100°C in 40 minutes in 1 atm nitrogen, and then heated to 1100°C.
The temperature was increased from 1800℃ at a rate of 15℃/min.
It was held at 1800°C for 10 hours. The density of the obtained sintered body was 3.26 g/cm ³ . This sintered body was ground to a thickness of 3 mm, and its thermal conductivity was measured by a non-contact method using a 1n-Sb infrared sensor using a laser flash method, and a value of 203 w/m·k was obtained. The oxygen content of this sintered body was measured by activation analysis and was found to be 0.03% 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 respective contents of Ti and Co were measured using inductively coupled plasma emission spectroscopy and were converted into concentrations in the sintered body.Ca=210ppm, Y=320ppm, Mg<5ppm,
Cr＜10ppm, Si＝89ppm, Zn＜10ppm, Fe＜
10ppm, Cu<10ppm, Mn<5ppm, Ni=19ppm,
Ti = 14 ppm, Co < 10 ppm, and the total content of 10 elements added as sintering aids, excluding Ca and Y, was 182 ppm or less. Another sintered body sintered in the same manner was ground to a thickness of 0.5 mm, and both sides were polished to a mirror finish.The light transmittance was measured at 31 at a wavelength of 5.5 μm.
% in-line transmittance was obtained. For comparison, only 1% by weight of CaC ₂ was added to the powder shown in Table 1, and a sintered body was synthesized in exactly the same manner. The density of this sintered body is 3.23 g/ ^cm3 , and the thermal conductivity of this sintered body is ground to a thickness of 3 mm and measured by a non-contact method using an In-Sb infrared sensor using the laser flash method. As a result, it was 130w/m・
The value of k was obtained.

【table】

[Table] Example 2 The same AlN powder used in Example 1 was mixed with 1% by weight of various carbides and nitrides as a sintering aid (A) and _{2% of YF 3} as a sintering aid (B). % by weight were added and mixed and fired in the same manner as in Example 1 to obtain an atmospheric pressure sintered body. These sintered bodies were ground to a thickness of 3 mm, and their thermal conductivities were measured in a non-contact manner using an In-Sb infrared sensor using a laser flash method. The results are shown in Table 2.

[Table] Example 3 The same AlN powder used in Example 1 was mixed with various types of carbides and nitrides as a sintering aid (A) and various types of nitrides as a sintering aid (B). A halide was added and mixed, and the mixture was fired in the same manner as in Example 1 to obtain an atmospheric pressure sintered body. These sintered bodies were ground to a thickness of 3 mm, and the thermal conductivity was measured in the same manner as in Example 1. The results are shown in Table 3.

[Table] Example 4 The same AlN powder used in Example 1,
CaC ₂ and YF ₃ were added and mixed and fired in the same manner as in Example 1, varying the heating rate to obtain an atmospheric pressure sintered body. These sintered bodies were ground to a thickness of 3 mm, and the thermal conductivity was measured in the same manner as in Example 1. The results are shown in Table 4.

【table】

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, as the sintering aid, (A) yttrium, lanthanum group A carbide or nitride of at least one metal selected from the group consisting of metals and alkaline earth metals, and (B) at least one metal selected from the group consisting of yttrium, lanthanum group metals, and alkaline earth metals. A method for producing an aluminum nitride sintered body, characterized by using a halide.