JPH0459609A - Production of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To readily obtain aluminum nitride powder having a fine particle diameter and sharp particle size distribution by mixing an Al-containing compound which is an alpha-alumina precursor with a reducing substance and burning the resultant mixture in a nitrogen compound-containing nonoxidizing atmosphere in specific two stages. CONSTITUTION:An aluminum-containing compound such as gamma-alumina, aluminum hydroxide, basic aluminum chloride or basic aluminum lactate having properties of transforming into alpha-alumina is prepared. The resultant aluminum-containing compound is subsequently mixed with a substance (e.g. carbon or methyl cellulose) having reducing properties at a burning temperature. The obtained mixed powder is then primarily burned in a nitrogen compound-containing nonoxidizing atmosphere (e.g. nitrogen gas) to provide burned powder containing crystals of the alpha-alumina existing in the powder. The burned powder is further secondarily burned at a higher temperature than the primary burning temperature in the similar atmosphere to afford the objective aluminum nitride powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a method for producing aluminum nitride powder used for producing, for example, electrically insulating ceramic substrates.

[Prior Art] As semiconductor devices become more highly integrated and have more power, electrical insulating materials with good heat dissipation properties are required. Various ceramic substrates having high thermal conductivity have been proposed to meet this requirement. Among these, ceramic substrates made of aluminum nitride are being put into practical use because they are excellent in terms of thermal conductivity, thermal expansion, electrical insulation, etc.

At that time, since aluminum nitride powder, which is a raw material, is difficult to sinter, there was a problem in that a high temperature was required for sintering in order to obtain an aluminum nitride substrate with high thermal conductivity. In order to obtain aluminum nitride substrates with high thermal conductivity by firing at low temperatures, it is effective to use aluminum nitride powder with a small particle size and sharp particle size distribution as a raw material. It is sought after as a raw material.

Conventionally, aluminum nitride powder has been produced by a direct nitriding method in which metal aluminum is fired in a nitrogen or ammonia gas stream, a carbon reduction method in which a mixture of alumina and carbon powder is fired in a nitrogen atmosphere, and the like.

It is difficult to obtain aluminum nitride powder with a small particle size and a sharp particle size distribution by sintering metal aluminum using the direct nitriding method. When trying to manufacture a substrate, there was a problem that it was not economical because sintering required high temperatures. In an attempt to improve this, when the obtained aluminum nitride powder is pulverized, there is a problem that impurities are mixed in during the pulverization process, resulting in a decrease in the thermal conductivity of the aluminum nitride substrate obtained by sintering. Ta.

On the other hand, in the alumina carbon reduction method, in order to obtain aluminum nitride powder with a small particle size and sharp particle size distribution, the raw material alumina needs to be small in particle size and sharp in particle size distribution. However, there was a problem in that producing such alumina powder required a very complicated process.

[Problem to be Solved by the Invention 1] The present invention has been made to solve the above-mentioned drawbacks, and provides a manufacturing method that can easily obtain aluminum nitride powder with a small particle size and a sharp particle size distribution. There is a particular thing.

[Means for Solving the Problems] The present invention provides raw material powder containing an aluminum-containing compound having the property of transforming into α-alumina and a substance having reducing properties at a firing temperature in a non-oxidizing atmosphere containing a nitrogen compound. The first firing is performed to obtain a fired powder containing α-alumina crystals, and the fired powder is then heated in a non-oxidizing atmosphere containing nitrogen compounds at a temperature higher than the first firing point. This is a method for producing aluminum nitride powder, which is characterized by performing secondary firing.

The present invention will be explained in detail below.

The aluminum-containing compound used in the present invention, which has the property of transforming into α-alumina, transforms into α-alumina by firing, and the aluminum-containing compounds include γ, χ
, δ, θ, or ρ type alumina, aluminum hydroxide, or preferably water-soluble aluminum compounds are useful.

Examples of the water-soluble aluminum compounds include aluminum polynuclear complexes such as basic aluminum chloride, basic aluminum lactate, basic aluminum sulfate, and basic aluminum nitrate. These water-soluble aluminum compounds have reducing properties at the firing temperature in a water/8 liquid state! !
If it is mixed with 7J quality, it can be mixed more uniformly, and as a result, when it is transformed into α-alumina, it is possible to obtain a state in which α-alumina crystals are more uniformly dispersed.

In the present invention, a raw material powder is obtained by mixing the aluminum-containing compound and a substance that has reducibility at the firing temperature. Substances that have reducing properties at this firing temperature include various carbon compounds and carbon, but among these, water-soluble carbon compounds can be mixed more uniformly with aluminum-containing compounds by using them as a 7-volume solution of water. It is useful because it has the advantage of being able to Examples of the water-soluble carbon compound having reducibility at this firing temperature include, but are not limited to, methylcellulose, polyethylene oxide, polyvinyl alcohol, sugars such as glucose, and lignin.

In addition, if the substance that has reducibility at the firing temperature is a compound containing carbon and nitrogen in its molecules, such as urea or guanidine, or a mixture of a carbon-containing compound and a nitrogen-containing compound such as ammonium chloride, higher purity nitriding can be achieved. Effective for making aluminum powder.

The mixture of the above-mentioned aluminum-containing compound and a substance having reducibility at the firing temperature is dried as necessary. This drying temperature is not particularly limited, but is 150"C to 20"C.
0'C is preferred.

When pulverizing the above mixture, more uniform mixing can be achieved if the pulverization is performed by mechanical impact. The method of applying mechanical impact is not particularly limited, but vibration milling or moisture permeable ball milling is suitable.

Next, the above mixed powder is first fired in a non-oxidizing atmosphere containing nitrogen element to obtain a fired powder in which α-alumina microcrystals are uniformly contained. Here, the non-oxidizing atmosphere containing nitrogen element may be an atmosphere of non-oxidizing gas containing nitrogen gas, ammonia gas, or any of these, and may include nitrogen gas, ammonia gas, or argon containing any of these. Inert gases such as and carbon monoxide gas can also be used.

The α-alumina crystals formed here act as the nucleus of the aluminum nitride powder that is to be obtained in the end, so the nitride crystals with a sharp particle size distribution can be uniformly incorporated as microcrystals in the powder. Effective for obtaining aluminum powder.

Normally, a firing temperature of 1200°C or higher is required for the transformation to α-alumina, but according to the present invention, since the aluminum compound is uniformly dispersed, α-alumina can be converted to α-alumina by firing at a low temperature of 1000°C or lower. May contain microcrystals. The temperature of this first firing is preferably 700°C to 1200°C, more preferably 700°C to 1000°C. 7
Below 00℃, the transition to α~alumina is difficult to occur, and 1
When the temperature exceeds 200°C, a nitriding reaction occurs, inhibiting the growth of α-alumina crystals, and as a result, aluminum nitride powder with a large particle size is produced, resulting in the problem that the particle size distribution of the obtained aluminum nitride powder becomes broad. .

There are no particular restrictions on the firing equipment that performs the primary firing, but if the residence time is short, the firing temperature should be set to 1.
It is desirable to set the temperature as high as 000° C. to 1200° C., and as low as 800° C. to 100° C. for devices with long residence times.

Next, the fired powder containing α-alumina microcrystals is subjected to a second firing in a non-oxidizing atmosphere containing nitrogen at a temperature higher than the first firing temperature, preferably at a temperature of 1500°C to 1700°C. to obtain aluminum nitride powder. In this case, the non-oxidizing atmosphere containing nitrogen element is the same as in the first firing.

If there is residual carbon in the aluminum nitride powder after the secondary firing, the residual carbon can be removed by heat treatment in an oxidizing atmosphere at 600'C to 800'C.

In addition, in the manufacturing method of the present invention, in addition to the above-mentioned steps, various steps used in the manufacturing of ordinary ceramic powders can be added as necessary.

The present invention will be explained below using examples.

[Example] Examples 1 to 3 The aluminum-containing compounds shown in Table 1 and carbon were mixed so that the carbon to aluminum ratio C/AIV (element blend molar ratio) was 4.0. . Vibratory milling was performed using a nylon pot and nylon-coated balls for 2 to 24 hours to apply mechanical shock to the mixed raw materials.

The obtained powder was first fired in a haunch furnace at 800°C in a nitrogen gas stream for 4 hours.

The obtained powder was fired for a second time in a haunch furnace at 1600"C in a nitrogen gas stream for 4 hours to obtain aluminum nitride powder.

Furthermore, the obtained aluminum nitride powder was added to the air at 65%
A heating oxidation treatment was performed at 0° C. for 1 hour to remove residual carbon.

Table 1 shows the measurement results of the average particle size and purity of the obtained aluminum nitride powder. Further, FIGS. 1 to 31 show graphs of the particle size distribution of the aluminum nitride powders obtained in Examples 1 to 3, respectively.

In Figures 1, 2, and 3, the vertical axes are percentages (unit: 2%)
The horizontal axis indicates the particle size (unit: μm). The same applies to the vertical and horizontal axes in the following figures.

Comparative example 1 Carbon to aluminum ratio C/Af (element blending molar ratio)
Aluminum hydroxide and carbon were mixed so that the carbon was 4.0. Vibratory milling was performed using a nylon pot and nylon coated balls for 2 to 24 hours to impart mechanical shock to the mixed raw materials. The obtained powder was fired in a hatch furnace at 1600° C. for 4 hours in a nitrogen gas stream to obtain aluminum nitride powder.

Furthermore, the obtained aluminum nitride powder was added to the air at 65%
A heating oxidation treatment was performed at 0'C for 1 hour to remove residual carbon.

The results of measuring the average particle diameter and purity of the obtained aluminum nitride powder are shown in Table 1, and a graph of the particle size distribution is shown in FIG.

Incidentally, a graph of the particle size distribution of aluminum hydroxide used in Example 1 and Comparative Example 1 is shown in FIG.

Examples 4 to 8 Water-soluble aluminum compounds and water-soluble carbon compounds or carbon shown in Table 2 were blended so that the carbon to aluminum ratio C/AN (element blend molar ratio) was 3.0. Water 78a was prepared.

As water-soluble aluminum compounds, basic aluminum chloride (aluminum content in terms of alumina is 50% by weight) and basic aluminum lactate (aluminum content in terms of alumina is 35% by weight) manufactured by Tamoto Kagaku Co., Ltd. Using.

Glucose and methylcellulose were used as water-soluble carbon compounds.

After drying this aqueous solution with a spray dryer, it was subjected to vibration mill pulverization for 2 hours using an alumina porcelain pot and an alumina ball. The obtained powder was first fired in a hatch furnace at 800° C. for 4 hours in a nitrogen gas stream.

The obtained powder was subjected to secondary firing in a hatch furnace at 1600° C. for 4 hours in a nitrogen gas stream to obtain aluminum nitride powder.

Furthermore, the obtained aluminum nitride powder was added to the air at 65%
0°C T: Heat oxidation treatment was performed for 1 hour to remove residual carbon.

Table 2 shows the measurement results of the average particle size and purity of the obtained aluminum nitride powder. Further, FIGS. 6 to 10 show graphs of the particle size distribution of the aluminum nitride powders obtained in Examples 4 to 8, respectively.

Comparative example 2 Carbon to aluminum ratio C/Af (element blending molar ratio)
An aqueous solution containing the same basic aluminum chloride and glucose as that used in Example 4 was prepared so that the ratio was 3.0.

After drying this aqueous solution with a spray dryer, it was subjected to vibration mill pulverization for 2 hours using an alumina porcelain pot and an alumina ball. The obtained powder was fired in a patch furnace at 1600'C in a nitrogen gas stream for 4 hours to obtain aluminum nitride powder.

The results of measuring the average particle size and purity of the obtained aluminum nitride powder are shown in Table 2, and a graph of the particle size distribution is shown in FIG.

1. Effects of the Invention] According to the present invention, aluminum nitride powder having a small particle size and a soyral particle size distribution can be easily produced.

[Brief explanation of drawings]

Figures 1 to 3 are graphs showing the particle size distribution of the aluminum nitride powders of Examples 1 to 3, respectively, the fourth box is a graph showing the particle size distribution of the aluminum nitride powder of Comparative Example I, and Figure 5 is a graph showing the particle size distribution of the aluminum nitride powder of Comparative Example I. are graphs showing the particle size distribution of aluminum hydroxide used in Example 1 and Comparative Example 1, and FIGS. 6 to 1O are graphs showing the particle size distribution of aluminum nitride powder in Examples 4 to 8, respectively. FIG. 11 is a graph showing the particle size distribution of aluminum nitride powder of Comparative Example 2.

Claims (14)

[Claims] (1) A raw material powder containing an aluminum-containing compound that has the property of transforming into α-alumina and a substance that has reducing properties at the firing temperature is first fired in a non-oxidizing atmosphere containing a nitrogen compound, and then The method is characterized in that a fired powder containing α-alumina crystals is obtained, and then this fired powder is subjected to a second firing in a non-oxidizing atmosphere containing a nitrogen compound at a temperature higher than the first firing temperature. Method for producing aluminum nitride powder. (2) The method for producing aluminum nitride powder according to claim 1, wherein the aluminum-containing compound is any one of γ, χ, δ, θ, κ, or ρ type alumina. (3) The method for producing aluminum nitride powder according to claim 1, wherein the aluminum-containing compound is aluminum hydroxide. (4) The method for producing aluminum nitride powder according to claim 1, wherein the aluminum-containing compound is water-soluble. (5) The aluminum nitride powder according to claim 4, which contains at least one of basic aluminum chloride, basic aluminum lactate, basic aluminum sulfate, and basic aluminum nitrate as the water-soluble aluminum-containing compound. manufacturing method. (6) Production of aluminum nitride powder according to claim 4 or 5, characterized in that the above-mentioned water-soluble aluminum-containing compound is mixed in the form of an aqueous solution with a substance that has reducing properties at the firing temperature. Method. (7) The method for producing aluminum nitride powder according to any one of claims 1 to 6, wherein the substance having reducibility at the above firing temperature is carbon. (8) The method for producing aluminum nitride powder according to any one of claims 1 to 6, wherein the substance having reducibility at the above firing temperature is a water-soluble carbon compound. (9) The method for producing aluminum nitride powder according to claim 8, wherein the water-soluble carbon compound is any one of methylcellulose, polyethylene oxide, polyvinyl alcohol, saccharide, or lignin. (10) The method for producing aluminum nitride powder according to claim 8 or 9, characterized in that the above-mentioned water-soluble carbon compound is mixed with an aluminum-containing compound in the form of an aqueous solution. (11) Claims 1 to 3, characterized in that the substance that has reducibility at the above firing temperature is a compound containing carbon and nitrogen in the molecule, or a mixture of a carbon-containing compound and a nitrogen-containing compound. 6. A method for producing aluminum nitride powder according to any one of Item 6. (12) The method according to any one of claims 1 to 11, characterized in that the raw material containing the aluminum-containing compound and a substance having reducibility at the firing temperature is pulverized by mechanical impact. Method for producing aluminum nitride powder. (13) When the raw material powder containing the above-mentioned aluminum-containing compound and a substance that has reducibility at the firing temperature is first fired to incorporate α-alumina into the powder, the firing temperature is 120°C.
13. The method for producing aluminum nitride powder according to any one of claims 1 to 12, characterized in that the temperature is 0°C or lower. (14) The non-oxidizing atmosphere containing nitrogen element is an atmosphere of nitrogen gas, ammonia gas, or argon gas or carbon monoxide gas containing any of these. Method for producing aluminum nitride powder.