JPS62278110A - Production of high-purity aluminum nitride - Google Patents

Abstract

PURPOSE:To produce the titled AlN having excellent thermal conductivity and containing little residual oxygen, by heating a powdery mixture of Al2O3 and carbon in N2 atmosphere and heating the resultant AlN powder containing residual carbon powder by high-frequency dielectric heating. CONSTITUTION:A mixture of Al2O3 powder and carbon powder is heated in an N2 atmosphere to obtain AlN powder 2 containing residual carbon powder. The AlN powder 2 is charged into a decarbonization furnace 1 wound with a work coil 3, a mixed gas of N2 and O2 is introduced into the furnace 1 via a gas inlet 10 opened at one end of the coil 3 and the gas is exhausted from the other end by a vacuum pump. At the same time, the powder is heated by high-frequency dielectric heating using a high-frequency oscillator 5, a directional coupler 6 and a matching box 4. The excess carbon can be oxidized and evaporated from the powder by this process while suppressing the surface oxidation of the AlN powder.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing aluminum nitride powder used as a raw material for high thermal conductivity ceramics.

[Conventional technology]

Aluminum nitride (AtN) has excellent properties as a highly thermally conductive ceramic.

Generally, the following method is used to produce ALN powder.

(1) Direct nitriding method 2 of At At+N2→2 AtN (2) Reductive nitriding method of At203 (S@rp@ni method) At
203+N2+3 C→2 AAN + 3 C0The above direct nitriding method (1) has a simple reaction formula and has great advantages in terms of process, but it is difficult to sufficiently nitride the inside of kl'ALN It is difficult to achieve high purity, and contamination with impurities cannot be avoided. Furthermore, if a large amount of impurities are mixed in, it will be difficult to obtain the high thermal conductivity inherent to AtN, and the characteristics will also deteriorate.

The reduction nitriding method (2) has a large effect on the purity of the ALN powder depending on the purity of the alumina powder (At2o3) and carbon powder (C), but it is relatively easy to produce high purity At203 powder and C powder. High purity AtN
I can get it. Also, when this tN powder is sintered into a formed body, it is possible to obtain a product with high properties.

However, in the reductive nitriding method, j) ALN powder can be obtained by heating a mixed powder in which At203 powder and C powder are well dispersed at 1550°C or higher for about 5 hours in a nitrogen atmosphere. After the nitriding treatment, carbon added in excess for the purpose of reaction remains, so this carbon must be removed in order to obtain AΔ of high purity. The removal method is to remove carbon by heating it to about 600° to 700°C in a dry air atmosphere to oxidize and vaporize it, but the problem with the decarburization process is that it is not only the residual carbon powder. This is because the surface of the ALN powder is oxidized and the amount of residual oxygen increases.

Although the amount of residual oxygen in AtN produced by direct nitriding is smaller than that produced by AtN produced by reduction nitriding, the molar concentration reaches approximately 1.

It is known that the amount of residual oxygen has a significant effect as a factor that inhibits the high thermal conductivity of AΔ. Therefore, in order to improve the high thermal conductivity, it is necessary to reduce the amount of residual oxygen. There was a need for improvements in the decarburization process in the method.

[Problem that the invention seeks to solve]

The present invention was developed as a result of intensive research in view of the current situation.
The purpose is to suppress the surface oxidation of AtN in the decarburization step in the reduction nitriding method (5erpek method) of No. 203, reduce the amount of residual oxygen, and improve the associated properties, especially the thermal conductivity.

[Failure to solve the problem]

The method of the present invention uses aluminum oxide powder by reducing nitriding method.
In a method of producing high purity aluminum nitride powder,
A crude aluminum nitride powder obtained by heating a mixed powder of aluminum oxide powder and carbon powder in a nitrogen atmosphere is heated by high frequency dielectric to suppress surface oxidation of the aluminum nitride powder, and remove excess carbon by oxidizing and vaporizing it. It is characterized by:

In the method of the present invention, A& powder and C powder are mixed in the crude aluminum nitride after reduction nitridation. Here A
Comparing the electrical characteristics of tN and C, ALN is an insulator;
C is classified as a conductor, and AtN' in particular has an inductive loss (
tan δ = 5 to 10 × 10 ) and a low dielectric constant, making it a material that is difficult to dielectrically heat. On the other hand, C powder is a conductor and can be heated by induction if it is a continuous body, but the continuity of the 6 eddy current is lost in the powder, and heating using eddy current loss, that is, induction heating, is not effective.

In other words, the C powder starts to behave like a dielectric rather than like a conductor, and a state is reached where high-frequency dielectric heating is appropriate instead of low-frequency induction heating.

Therefore, by dielectrically heating a mixture of AtN powder and residual carbon powder, the residual carbon is selectively heated while the AtN powder is hardly heated. Although the AtN powder is slightly heated by heat conduction from the residual carbon powder, the rate at which the AtN powder is heated is extremely small compared to the conventional method in which the whole is heated by an electric furnace. Therefore, by performing such high-frequency dielectric heating, when decarburizing in an oxidizing atmosphere such as dry air, the residual carbon powder will be removed. Oxidation can be suppressed. Note that residual carbon powder oxidizes to carbon monoxide (CO) or carbon dioxide (
C02) and dissipates.

Regarding the processing time, since the reflected power of the high frequency oscillator increases as the amount of carbon decreases, it can be used as a monitor to confirm that decarburization has been completed. In other words, since it is easy for radio waves to pick up on the current of carbon powder, when the carbon powder decreases through oxidation and vaporization, radio waves pick up K<. In other words, the impedance of aluminum nitride powder mixed with residual carbon after nitriding treatment is eliminated The processing time can be monitored by utilizing the phenomenon that the power that can be supplied decreases if the oscillation state of the power supply is constant because the power increases with the coal time.

Next, the present invention will be specifically explained with reference to Examples.

Example (1) Adjusted powder 200I (C/At
203 (weight ratio: 0.45) was subjected to reduction-nitriding treatment at 1575° C. for 5 hours to obtain ALN powder (adjusted powder after nitriding treatment) containing residual carbon. Next, the obtained adjustment plug was decarburized using a high-frequency heating decarburization apparatus shown in FIG. That is, the regulating plug 2 after the nitriding treatment is placed in the decarburization furnace 1 around which the work coil 3 is wound, and a mixed gas of nitrogen 2 SLM and oxygen 600 accm is introduced from the gas inlet 10 at one end of the 3, and the other end is While evacuating with a vacuum pump, a 13.56 MHz radio frequency oscillator 5 was used as a heating power source to increase the surface temperature of the regulating valve 2 to 750 MHz.
C. (measured with a pyrometer) while controlling the power of the oscillator 5 for 8 hours to obtain A4N powder.

In addition, 4 is a matching box, 6 is a directional coupler, and 7 is a matching box.
is the incident reflection output monitor. In addition, the power supplied to the decarburization furnace was 3.5 kW in steady state.

The amount of residual oxygen in the A powder obtained after the decarburization treatment was measured using an inert gas melting/thermal conductivity method.

Next, these AtN powders were added with YF'3 (At
4% by weight of N powder) was added and sintered under normal pressure at 1850°C for 2 hours to create an AtN substrate with a diameter of 10 m and a thickness of 2 m, and the thermal diffusivity was measured using the laser flash method. The thermal conductivity was calculated.

The obtained characteristic results are summarized in Table 1.

Examples (2) to (5) Example (2) is shown in FIG. 2, Example (3) is shown in FIG. 3, Example (4) is shown in FIG. 4, and Example (5) is shown in FIG.
), each decarburization treatment apparatus as shown in FIG. )
Under the same conditions as above, decarburization treatment was performed for 8 hours while supplying gas from the gas inlet 10 and controlling the respective supplied power to maintain the surface temperature of the AtN powder 2 at 750°C.

The obtained AtN powder after decarburization treatment was used to evaluate the same characteristics as in Example (]), and the results are shown in Table 1.

In the decarburization apparatus shown in FIGS. 2 to 5, 8 and 8' are electrodes, 9 is a power supply unit, 11 is a planter, 112 is a perforated waveguide, 13 is a matching box, 14 is a dummy load, and 15 is a Isolator, 16 magnetron, 17 waveguide, 1
8 is a cavity resonator, and 19 is a coaxial tube.

Comparative Example In order to compare with the method of the present invention, AtN powder mixed with residual carbon prepared by the same method as in Example (1) was used in Example (1).
75 using an electric furnace while supplying gas under the same conditions as
The treatment was carried out for 8 hours while maintaining the temperature at 0°C to obtain AtN powder with a conventional force cQ''.
), and the results are shown in Table 1.

〔effect〕

As detailed above, according to the method of the present invention, surface oxidation of AtN powder can be suppressed, and high-purity AtN powder with an extremely small amount of residual oxygen can be obtained. It has conductivity and is extremely useful industrially.

[Brief explanation of drawings]

1 to 5 are schematic explanatory diagrams showing an example of a decarburization treatment apparatus using high-frequency dielectric heating for producing high-purity aluminum nitride by the method of the present invention. Note that Figures 1 to 3 use a radio frequency oscillator.
4 and 5 use a microwave oscillator. 1... Decarburization furnace, 2... Adjusted powder after nitriding treatment, 3...
・Work coil, 4... matching? x, 5...
・Radio frequency oscillator, 6,6'... directional coupler,
7... Incident/reflected output monitor, 8, 8'... Electrode, 9... Power supply unit, 10... Gas inlet, 1... Granger, 12... Hole waveguide tube, 13.
... Matching device, 14... Dummy load, 15... Isolator, 16... Magnetron, 17... Waveguide, 18... Cavity resonator, 19... Coaxial tube. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] In a method for producing high-purity aluminum nitride by reducing aluminum oxide and nitriding, aluminum nitride powder mixed with residual carbon powder obtained by heating a mixed powder of aluminum oxide powder and carbon powder in a nitrogen atmosphere is heated by high-frequency dielectric heating. A method for producing high-purity aluminum nitride, which comprises removing excess carbon by oxidizing and vaporizing it while suppressing surface oxidation of the aluminum nitride powder.