JP2846375B2 - Aluminum nitride powder and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aluminum nitride powder having excellent hydrolysis resistance and a method for producing the same.

[Conventional technology]

BACKGROUND ART Aluminum nitride powder has been attracting attention because of its high thermal conductivity and insulation properties, being used for semiconductor substrate materials, heat sinks, and other high-temperature structural materials. There are mainly two types of industrial mass production methods of aluminum nitride powder. That is, a method in which metallic aluminum powder is heated and nitrided in a nitrogen or ammonia atmosphere (direct nitridation method), and a method in which a mixture of alumina and carbon is heated in a nitrogen or ammonia atmosphere to reduce and nitride alumina (reduced nitriding method) ). Although the direct nitridation method may be more advantageous in terms of production cost, in the case of the direct nitridation method, the surface of the obtained aluminum nitride powder is active and easily reacts with moisture in the air as shown in the following equation. Ammonia is generated as the oxygen content increases.

AIN + 3H ₂ O → Al (OH) ₃ + NH ₃ Such an increase in the amount of oxygen significantly impairs the original high thermal conductivity of aluminum nitride, and the generated ammonia deteriorates the working environment.

Therefore, conventionally, measures against the above-mentioned problems have been taken, such as storing nitrogen nitride powder by enclosing nitrogen gas in a closed container and adjusting the humidity of the handling atmosphere.

Recently, a method of improving the hydrolysis resistance by coating the surface of an aluminum nitride powder with an organic substance (JP-A-63-22)
No. 5,507), but the organic substances on the surface often have an adverse effect depending on the intended use. For example, phenomena such as incompatibility with the organic binder used at the time of molding and the carbon content remaining in a small amount at the time of firing occur.

Furthermore, the oxidation reaction of aluminum nitride is activated in air or in an inert gas containing oxygen.
A method has also been proposed in which a heat treatment is performed at a temperature of not less than ° C. to form an oxide film on the surface of the aluminum nitride powder to stabilize it (Japanese Patent Laid-Open No. 1-141811). However, in this method, through the pulverization process, in the case of aluminum nitride powder by the direct nitridation method having many active points on the surface, the difference in the formation rate of the oxide film layer occurs due to the difference in the partial activity of the surface, and one There are portions where the oxide film layer is sufficiently formed and portions where the oxide film layer is not formed also on the particles. Therefore, when the oxide film layer is formed in an inert gas containing oxygen, if the heat treatment is carried out under the condition where the effect can be sufficiently obtained, the oxygen content of the entire aluminum nitride powder becomes very large, and as a result, the hydrolysis resistance is lowered. Even though the properties improved, the thermal conductivity had to be greatly reduced.

[Problems to be solved by the invention]

An object of the present invention is to make aluminum nitride powder obtained by a direct nitriding method stable against water and moisture in air without impairing its sinterability and high thermal conductivity.

[Means for solving the problem]

That is, the present invention is an aluminum nitride powder and a method for producing the same having the following gist.

1. Aluminum nitride powder obtained by directly nitriding metallic aluminum, and having a specific surface area of 3 m ² / g or more, a carbon content of 0.2 wt% or less, an oxygen content of 2.0 wt% or less, and a temperature of 30 ° C. An aluminum nitride powder characterized in that the oxygen content after standing in air at 95% relative humidity for 24 hours is 1.25 times or less the oxygen content before standing.

2. Specific surface area obtained by directly nitriding metallic aluminum
3m ² / g or more, carbon content 0.2% by weight or less, oxygen content 2.0
Weight percent or less of nitrogen aluminum powder with an oxygen concentration of 20
2. The method for producing aluminum nitride powder according to claim 1, wherein the heat treatment is performed at a temperature of 500 to 1000 [deg.] C. in an inert gas atmosphere of not more than 00 ppm.

3. The specific surface area obtained by directly nitriding metallic aluminum
3m ² / g or more, carbon content 0.2% by weight or less, oxygen content 2.0
2. The aluminum nitride powder according to claim 1, wherein the aluminum nitride powder having a concentration of not more than 20% by weight is heat-treated at a temperature of 500 to 1000 ° C. in an inert gas atmosphere containing 20% by volume or less of CO ₂ . Production method.

 Hereinafter, the present invention will be described in more detail.

First, in the present invention, the reason why the present invention is limited to the aluminum nitride powder obtained by the direct nitridation method is that the direct nitridation method is advantageous in terms of cost because it can be produced on a large scale.

In the present invention, the specific surface area by the BET method is 3 m ² / g
The above and the carbon content is limited to 0.2% by weight or less
This is because the sinterability of the aluminum nitride powder is not impaired, and the reason why the oxygen content is set to 2.0% by weight or less is that the thermal conductivity is not significantly reduced.

Further, in the present invention, the aluminum content is limited to aluminum nitride powder having a temperature of 30 ° C. and an oxygen content after standing for 24 hours in air at a relative humidity of 95% is not more than 1.25 times the oxygen content before standing, This is because, in the case of aluminum nitride powder having a value exceeding 1.25 times, physical properties are severely degraded in handling in a high-temperature and high-humidity atmosphere such as in summer, and high thermal conductivity cannot be stably obtained.

To obtain the aluminum nitride powder of the present invention, for example, the invention described in claim 2 or 3 described below may be used.

(Invention of Claim 2) The present invention provides an aluminum nitride powder obtained by a direct nitriding method having good sinterability and thermal conductivity, that is, a specific surface area of at least 3 m ² / g obtained by directly nitriding metallic aluminum, In order to improve the hydrolysis resistance of an aluminum nitride powder having a carbon content of 0.2% by weight or less and an oxygen content of 2.0% by weight or less on an industrial scale, this aluminum nitride powder was prepared at an oxygen concentration of 2000%.
The heat treatment is performed at a temperature of 500 to 1000 ° C. in an inert gas atmosphere of ppm or less.

In the present invention, the reason why the aluminum nitride powder having the above properties is used as a raw material is as described above. Aluminum nitride powder having such physical properties,
For example, a metal aluminum powder of 44 μm or less under a nitrogen atmosphere or an inert gas atmosphere containing ammonia, 1200 ~
It can be obtained by pulverizing an ingot of aluminum nitride obtained by heating and nitriding at a temperature of 1500 ° C.

In the present invention, the oxygen concentration of the heat treatment atmosphere is 2000 pp
m (excluding “0”), preferably limited to 100 to 2000 ppm, because if it exceeds 2000 ppm, the oxygen content of the aluminum nitride powder after treatment exceeds 2.0% by weight, resulting in good hydrolysis resistance This is because, even if it can be obtained, the thermal conductivity is remarkably reduced and is not practical. Further, when the treatment temperature is lower than 500 ° C., the oxidation reaction of the aluminum nitride powder becomes difficult to occur, and the effect of forming a dense and thin oxide film on the surface to improve the hydrolysis resistance is reduced. On the other hand, when the processing temperature exceeds 1000 ° C., the reaction occurs too rapidly, and the oxygen amount increases even in a very short processing time.
It is difficult to control the amount to less than 10% by weight, and fine powders are aggregated to deteriorate sinterability. The processing time is preferably within 12 hours.

Examples of the type of the inert gas include nitrogen, argon, helium, and a mixed gas thereof. It is desirable that the processing furnace does not contain carbon. For example, a tubular furnace made of quartz glass or alumina, or a heating furnace that does not use carbon as a heat insulating material or a heating element is used.

(Invention of Claim 3) The present invention relates to a method of preparing the aluminum nitride powder described in the invention of claim 2 under an inert gas atmosphere containing 20% or less of CO ₂ at a temperature of 500 to 1000 ° C. Heat treatment is performed.

 The reaction formula in the present invention is as follows.

2AIN + CO ₂ → Al ₂ O ₃ + 3CO + 2N ₂ This reaction is less likely to occur than the reaction between aluminum nitride and oxygen as in the second aspect of the present invention, and the reaction proceeds slowly. Therefore, in the invention according to claim 2, carbon is used for forming a surface oxide film of the aluminum nitride powder, and strict control of 2,000 ppm or less is required. In contrast, the present invention has an advantage that control can be performed on the order of%. .

In the present invention, the CO ₂ concentration in the heat treatment atmosphere is limited to 20% by volume or less (excluding “0”), preferably 1 to 20%. When the CO ₂ concentration exceeds 20%, the oxygen content is reduced to 2.0% by weight or less. This is because it is difficult to suppress, and the treatment temperature at that time is set to 500 to 1000 ° C, the above reaction becomes difficult to occur below 500 ° C, and the reaction becomes active when it exceeds 1000 ° C. This is because it becomes difficult to suppress the oxygen content after the treatment to 2.0% by weight or less. The processing time, the type of the inert gas, and the processing furnace are as described in the second aspect of the present invention.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Production of raw aluminum nitride powder
By heating at a temperature of 00 ° C., an aluminum nitride ingot was synthesized and pulverized with a ball mill to produce various raw material aluminum nitride powders shown in Table 1. The carbon content of the aluminum nitride powder was adjusted by introducing methane into the atmosphere during the synthesis of the ingot, and the specific surface area was adjusted by the pulverization time. The oxygen content changed in proportion to the specific surface area.

Table 1 shows the measurement results of the specific surface area, carbon content and oxygen content of the various aluminum nitride powder raw materials obtained as described above.

Examples 1 to 8 Comparative Examples 1 to 7 Various aluminum nitride powder raw materials produced as described above were subjected to a heat treatment under the conditions shown in Table 1, and the specific surface area, carbon content, and the like of the aluminum nitride powder obtained thereby were obtained. Oxygen content and temperature 30 ° C, relative humidity 95% in air
The amount of increase in oxygen when left for 24 hours was measured.

Furthermore, the sinterability and thermal conductivity of the heat-treated aluminum nitride powder obtained above were measured.

 Table 1 shows the results.

 In addition, the above-mentioned physical property measurement was performed as follows.

(1) Specific surface area; measured by the BET one-point method.

(2) Carbon content: measured by a LECO CS-344 C / S simultaneous analyzer.

(3) Oxygen content; measured using a TC-136 O / N simultaneous analyzer from LECO.

(4) Oxygen increase; aluminum nitride powder on watch glass
3 g was weighed, and after standing for 24 hours in an incubator in which the atmosphere (air) was adjusted to 30 ° C. and the relative humidity was 95%, the oxygen content was measured, and the magnification relative to before the standing was calculated.

(5) Sintering property: 5% by weight of Y ₂ O _{3 is} added to form a pellet, which is fired at a temperature of 1900 ° C. for 2 hours in a nitrogen atmosphere to obtain a sintered body, and a relative density is measured by an Archimedes method. did.

(6) Thermal conductivity: 5% by weight of Y ₂ O _{3 is} added to form a pellet, which is fired in nitrogen at 1900 ° C. for 2 hours to obtain a sintered body.
Its thermal conductivity was measured by the laser flash method.

[Effect of the Invention] Since the aluminum nitride powder of the present invention has a thin oxide film layer formed on its surface, its hydrolysis resistance is dramatically improved,
Moreover, it is possible to obtain a sintered body having excellent sinterability and high thermal conductivity.

Further, the method for producing the aluminum nitride powder of the present invention,
An aluminum nitride powder having the above characteristics can be efficiently produced on an industrial scale.

Claims (3)

(57) [Claims] 1. An aluminum powder obtained by directly nitriding metallic aluminum, having a specific surface area of 3 m ² / g or more, a carbon content of 0.2 wt% or less, an oxygen content of 2.0 wt% or less, and a temperature. An aluminum nitride powder characterized in that the oxygen content after standing in air at 30 ° C. and 90% relative humidity for 24 hours is not more than 1.25 times the oxygen content before standing. 2. An aluminum nitride powder having a specific surface area of not less than 3 m ² / g, a carbon content of not more than 0.2% by weight and an oxygen content of not more than 2.0% by weight obtained by directly nitriding metallic aluminum,
The method for producing aluminum nitride powder according to claim 1, wherein the heat treatment is performed at a temperature of 500 to 1000 ° C in an inert gas atmosphere having an oxygen concentration of 2000 ppm or less (excluding 0). 3. An aluminum nitride powder having a specific surface area of 3 m ² / g or more, a carbon content of 0.2 wt% or less, and an oxygen content of 2.0 wt% or less obtained by directly nitriding metallic aluminum,
2. The method for producing aluminum nitride powder according to claim 1, wherein the heat treatment is performed at a temperature of 500 to 1000 [deg.] C. in an inert gas atmosphere containing CO2 at a concentration of 20% by volume or less (excluding 0).