JP2008120636A - Water-resistant aluminum nitride powder and method for producing granules containing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum nitride powder and granules having excellent water-resistance, which are obtained without using an organic solvent because there is a problem of safety such as inflammability or toxicity after drying in a conventional production method of the water-resistant aluminum nitride powder using an organic solvent. <P>SOLUTION: A method for producing the water-resistant aluminum nitride powder or granules containing the water-resistant aluminum nitride includes a process for treating an aluminum nitride powder with an aqueous solution of a dicarboxylic acid. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aluminum nitride powder excellent in water resistance and a method for producing granules containing the same.

  Aluminum nitride is known as a substance having excellent thermal conductivity, mechanical strength, and electrical insulation, and is being used in various fields such as structural materials and functional materials. When used in these applications, granular materials mixed with a sintering aid are preferred. However, at the same time, the aluminum nitride powder has a problem that it is easily hydrolyzed.

Therefore, studies have been made to impart water resistance to aluminum nitride powder. For example, it is known that aluminum nitride is surface treated using dodecanedioic acid as a surface treating agent (Patent Document 1).
JP-A-6-345538

  In the method described in Patent Document 1, isopropyl alcohol, which is an organic solvent, is used as a dispersion medium when mixing dodecanedioic acid and aluminum nitride. However, the use of an organic solvent may cause safety problems such as flammability and toxicity after drying.

  Then, an object of this invention is to provide the aluminum nitride powder and granule which have the outstanding water resistance, without using an organic solvent.

  As a result of intensive studies, the present inventors have found that an aluminum nitride powder having water resistance can be obtained even when water is used as a dispersion medium, and the present invention has been completed. That is, this invention is a manufacturing method of the granule containing the water-resistant aluminum nitride powder or water-resistant aluminum nitride including the process of processing aluminum nitride powder with the aqueous solution of dicarboxylic acid.

  According to the present invention, an aluminum nitride powder having excellent water resistance or a granule containing the same can be produced without using an organic solvent, which is extremely valuable industrially.

Hereinafter, the present invention will be described in detail.
The production method of the present invention includes a step of treating aluminum nitride powder with an aqueous solution of dicarboxylic acid.

  The aluminum nitride powder used in the present invention is not limited by the production method, and a commonly used aluminum nitride powder can be used. For example, an aluminum nitride powder produced by reacting an alkylaluminum with ammonia and then heating it, an alumina reduction method in which a mixture of alumina and carbon is heated in nitrogen, a direct nitridation method in which aluminum and nitrogen are reacted, etc. Either can be used suitably.

  In the production method of the present invention, the aluminum nitride powder is treated with an aqueous solution of dicarboxylic acid. By treating with an aqueous solution, water-resistant aluminum nitride powder can be obtained without causing safety problems such as flammability and toxicity due to organic solvents. The dicarboxylic acid used here may be water-soluble. Preferred dicarboxylic acids include lower dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, and oxalic acid is particularly preferred.

  The present inventors have experimentally confirmed that performances such as high temperature water resistance and long time water resistance can be imparted to aluminum nitride by the production method of the present invention. The details of this mechanism are unknown, but by treating with an aqueous solution of dicarboxylic acid, a hardly soluble dicarboxylate is formed on the surface of the aluminum nitride powder, and drying this results in thermal decomposition of the dicarboxylate. At the same time, it can be assumed that a dense aluminum oxide layer is formed on the surface of the aluminum nitride powder.

The amount of oxalic acid dissolved in the aqueous solution is preferably in the range of 1 × 10 ⁻⁶ to 1 × 10 ⁻⁴ mol / m ² per surface area of the aluminum nitride powder. The range is more preferably 2 × 10 ^{−6 to} 5 × 10 ⁻⁵ mol / m ² , and particularly preferably 3 × 10 ⁻⁶ to 8 × 10 ⁻⁵ mol / m ² . When the amount of oxalic acid per surface area of the aluminum nitride powder is within this range, good water resistance can be obtained, and furthermore, the oxygen content in the aluminum nitride powder does not become too high. The thermal conductivity, which is a characteristic, is also favorable and preferable.

  The water resistant aluminum nitride powder obtained by the present invention preferably contains aluminum oxide in the range of 0.1 to 10% by weight, more preferably 0.2 to 8% by weight, particularly preferably 0.3 to 5% by weight. In the range of. When the aluminum oxide content of the water-resistant aluminum nitride powder is within this range, good water resistance can be obtained, and furthermore, the oxygen content in the aluminum nitride powder does not become too high. The thermal conductivity, which is a characteristic, is also favorable and preferable.

  The content of aluminum oxide in the water-resistant aluminum nitride can be measured by fluorescent X-rays. Quantitative analysis of oxygen can be performed with fluorescent X-rays, and the obtained amount of oxygen can be obtained.

  Although the usage-amount of the oxalic acid solution with respect to aluminum nitride powder does not have a restriction | limiting in particular, The range of 25-200 mass parts is preferable with respect to 100 mass parts of aluminum nitride powder, and it is still more preferable that it is 30-100 mass parts. By setting it in this range, the aluminum nitride powder can be uniformly mixed with the oxalic acid aqueous solution, which is preferable.

  The temperature at which the aluminum nitride powder is treated with the oxalic acid aqueous solution is preferably in the range of 0 to 70 ° C, and more preferably in the range of 18 to 50 ° C. By setting it within this range, the aluminum nitride powder and the aqueous oxalic acid solution react quickly, and further, no impurities are mixed from the processing vessel, and the thermal conductivity, which is the original characteristic of aluminum nitride, is favorable.

  The time for treating the aluminum nitride powder with the oxalic acid aqueous solution is not generally determined depending on the concentration of oxalic acid, the amount used, the temperature, etc., but is preferably 5 to 120 minutes, more preferably 10 to 60 minutes.

  The aluminum nitride slurry treated with the dicarboxylic acid aqueous solution can be dried as it is. For drying, a method of transferring the slurry to a vat and drying with a drier, a method of spray drying using a spray dryer, or the like can be used. When drying with a drier, the slurry can be dried at 80-300 ° C. for 3-15 hours. As the dryer used, a hot air dryer, a steam dryer or the like can be used. Since the dried cake may be agglomerated, it can be pulverized after drying. For the pulverization, a jet mill, a sample mill, a ball mill or the like can be used. In addition, this grinding | pulverization is making a secondary particle into a primary particle, and it is preferable not to destroy a coating | coated surface.

  Moreover, in order to obtain granular dry powder, it can be dried with a spray dryer. A spray dryer can produce spherical granules by spraying with an atomizer called an atomizer and air-drying. The gas temperature on the supply side that generates the airflow can be set to 150 to 200 ° C. and dried instantaneously.

  Granular aluminum nitride is used as a raw material for materials such as sintered plates and spherical fillers by sintering at high temperatures. In order to perform this sintering quickly and with low energy, a sintering aid is used. Therefore, these sintering aids can be added to the slurry in advance and dried with a spray dryer to produce granules.

  Hereinafter, the present invention will be described by way of examples.

<Measurement of aluminum oxide content>
In this example, the content of aluminum oxide was determined as follows. A fully automatic fluorescent X-ray diffraction apparatus 3070 manufactured by Rigaku Corporation was used, and RX-35 was used as a spectroscopic crystal. A calibration curve was created by measuring the oxygen peak at 2θ = 52.61 using known oxygen content data. Thereafter, a sample of aluminum nitride was measured, and the amount of oxygen was determined from this calibration curve.

<Water resistance test of aluminum nitride>
1 g of granules containing aluminum nitride powder or aluminum nitride was dispersed in 100 g of pure water at 60 ° C. This dispersion was maintained at 60 ° C., and the change in pH was measured over time.

(Example 1)
After mixing 500 L of pure water and 10 g of oxalic acid dihydrate in a glass container having a capacity of 5 L to prepare an aqueous oxalic acid solution, 1 kg of aluminum nitride powder having a specific surface area of 10 m ² / g is added to the aqueous oxalic acid solution to prepare an aqueous solution. The mixture was dispersed therein and stirred at a treatment temperature of 30 ° C. for 30 minutes.
The amount of oxalic acid at this time was 8 × 10 ⁻⁶ mol / m ² per surface area of the aluminum nitride powder. Next, this slurry was dried at 120 ° C. with a hot air dryer for 5 hours, dried, and then pulverized with a jet mill to obtain a water-resistant aluminum nitride powder. Table 1 shows the results of the water resistance test of the water resistant aluminum nitride powder.
Further, this water-resistant aluminum nitride powder was press-molded, sintered at 1700 ° C. in an N ₂ atmosphere furnace, and the thermal conductivity was measured and found to be 170 W / k · m.

(Examples 2 to 6)
The same procedure as in Example 1 was conducted except that the amounts of aluminum nitride powder and oxalic acid dihydrate used were changed to the amounts shown in Table 1. The results are shown in Table 1.

(Example 7)
After mixing 900 L of pure water and 10 g of oxalic acid dihydrate in a 5 L glass container to prepare an oxalic acid aqueous solution, 1 kg of aluminum nitride powder having an average particle diameter of 1 μm is dispersed in this oxalic acid aqueous solution, and the processing temperature Stir processing was performed at 30 ° C. for 30 minutes. Next, this slurry was spray-dried with a spray dryer. The temperature of the hot air on the supply side of the spray dryer was 200 ° C. The results are shown in Table 1.

(Example 8)
After mixing 900 L of pure water and 10 g of oxalic acid dihydrate in a glass container with a capacity of 5 L to prepare an oxalic acid aqueous solution, 1 kg of aluminum nitride powder having an average particle diameter of 1 μm is dispersed in the oxalic acid aqueous solution, followed by treatment. Stirring was performed at a temperature of 30 ° C. for 20 minutes. Next, 3 g of Y ₂ O ₃ (Wako Pure Chemicals Grade 1 Reagent) and 3.5 g of CaCO ₃ (Wako Pure Chemicals Grade 1 Reagent) were added to this slurry, and further stirred for 10 minutes. To this slurry, 100 g of a 10% aqueous solution of polyvinyl alcohol was added, and after slowly stirring for 1 minute, it was spray-dried with a spray dryer. The temperature of the hot air on the supply side of the spray dryer was 200 ° C. Table 1 shows the results of the water resistance test of the obtained granules containing aluminum nitride.
The obtained granule has an average particle size of 50 μm. If this granule is used as a raw material and fired at 1500 to 2000 ° C., a spherical sintered filler can be produced. Moreover, if this granule is pressure-molded and fired at 1500 to 2000 ° C., a sintered plate can be produced.

(Comparative Example 1)
Using 1 g of aluminum nitride used in Example 1, a water resistance test was conducted in the same manner as in Example 1. As a result, as shown in Table 1, the pH value exceeded 9 after 5 minutes. At the same time, an ammonia odor was generated. This indicates that aluminum nitride is hydrolyzed.

Claims (4)

A method for producing granules comprising water-resistant aluminum nitride powder or water-resistant aluminum nitride, comprising a step of treating the aluminum nitride powder with an aqueous solution of dicarboxylic acid. The production method according to claim 1, wherein the dicarboxylic acid is oxalic acid. The amount (mol) of oxalic acid contained in the treatment solution is 1 × 10 ⁻⁶ to 1 × 10 ⁻⁴ mol / m ² with respect to the surface area (m ² ) of the aluminum nitride powder. 2. The production method according to 2. A granule containing water-resistant aluminum nitride powder or water-resistant aluminum nitride produced by the method according to any one of claims 1 to 3 and containing 0.1 to 10% by mass of aluminum oxide.