JPH0519484B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention uses high-frequency induction thermal plasma to synthesize a fine mixed powder of aluminum nitride and aluminum carbide by nitriding and carbonizing metal aluminum using argon, nitrogen, ammonia, and methane as raw material gases. It is about law. (Prior Art) Aluminum nitride has excellent insulating properties and good thermal conductivity, so it has become increasingly important as a material for heat dissipation substrates for electronic circuits in recent years. However, aluminum nitride is a material that is difficult to sinter, and at present, sufficiently dense sintered bodies can only be obtained at temperatures above 1800°C and by hot pressing. To solve this problem, the raw material aluminum nitride
It is necessary to micronize to 0.3 μm or less. Therefore, the present inventors used high-frequency induction thermal plasma to produce metal aluminum, argon, and nitrogen as raw materials.
By using hydrogen and ammonia, we succeeded in synthesizing fine aluminum nitride powder with a particle size of less than 0.1 μm. Furthermore, this fine aluminum nitride powder can be sintered at a lower temperature than before, and has extremely high practical value. On the other hand, it is known that the properties of aluminum nitride sintered bodies, including thermal conductivity, are significantly reduced by the presence of impurities, especially oxygen. The surface of aluminum nitride powder is covered with oxides due to oxygen and moisture in the atmosphere. This oxide reacts with aluminum nitride during sintering to produce oxynitride, which deteriorates the properties of the sintered body. Therefore, how to remove impurity oxygen from aluminum nitride has become an important issue. Conventionally, in order to remove oxygen from aluminum nitride, several weight percent of additives such as yttrium oxide and calcium oxide were mixed with aluminum nitride powder, and the oxygen in aluminum nitride was removed during sintering.
A method is used in which it is precipitated at grain boundaries in the form of YAG (yttrium aluminum garnet) or the like. (Problems to be solved by the invention) Although it is possible to generate oxynitrides in a sintered body using the method described above, a new process of mixing aluminum nitride and additives is possible. There is a risk that impurities may be mixed in during mixing. Furthermore, if the particle sizes of the aluminum nitride powder and additives are different, it is not only difficult to mix them uniformly, but also the contact between the aluminum nitride powder and the additives is insufficient, resulting in the addition of more than the necessary amount of additives. There is a problem that makes it necessary to use it.
Considering that the presence of impurities deteriorates the properties of the sintered body, the amount of additives must be kept to the minimum necessary amount. The purpose of the present invention is to eliminate the drawbacks of using additives as described above, and by simultaneously synthesizing aluminum nitride and additives by high-frequency induction thermal plasma method, additives with the same particle size can be uniformly mixed. An object of the present invention is to provide a method for synthesizing a mixed fine powder of aluminum nitride and aluminum carbide. (Means for Solving the Problem) The present invention uses methane in addition to metallic aluminum, argon, nitrogen, hydrogen, and ammonia as raw materials in a method for synthesizing fine powder of aluminum nitride by high-frequency induction thermal plasma method. This method is characterized by synthesizing a fine mixed powder of aluminum nitride and aluminum carbide. (Function) In the present invention, metal aluminum is nitrided and carburized in a high-temperature region of plasma, and aluminum nitride and aluminum carbide are mixed in a gaseous state. Obtainable. Therefore, processes such as mixing additives before sintering are unnecessary, and problems caused by the difference in particle size between aluminum nitride powder and additives can also be solved. (Example) Next, an example of the present invention will be described. FIG. 1 shows a high frequency induction thermal plasma device used in the present invention. After evacuating the quartz plasma generating tube 2 and the reaction vessel 9 using the exhaust device 12, argon gas is introduced through the gas supply port 4. High frequency coil 1
When a high frequency wave is applied to the argon, electrodeless discharge occurs in the argon, and a plasma flame 5 is generated. When plasma is generated, nitrogen, hydrogen, ammonia and methane mixed by the gas mixer 13 are introduced from the mixed gas inlet 8. Furthermore, metal aluminum powder is supplied to the raw material supply port 14.
Input more. The conditions for metal aluminum and gas used in the present invention are as follows. Metal aluminum (99.9%, 30 mesh or less)
…5g/min Argon (99.99%)…30/min Nitrogen (99.99%)…10/min Hydrogen (99.99%)…5/min Ammonia (99.99%)…15/min Methane (99.99%)…0 to 10/min The aluminum introduced into the plasma is evaporated by the high temperature of the plasma, most of it is nitrided in the reaction vessel 9, and some of it is carbonized by methane. The produced aluminum nitride and aluminum carbide are mixed in a gaseous state, and are condensed and pulverized while being conveyed to the powder collector 10 by the exhaust device 11. The obtained fine powder is a mixed powder of aluminum nitride and aluminum carbide, and its particle size is
It was 0.2 μm or less. Furthermore, when the powders were sintered at a temperature of 1400 to 1800°C in a nitrogen stream, they were densified to more than 90% of the theoretical density, and X-ray diffraction revealed that the sintered bodies contained The phase indicated by the circle was confirmed.

[Table] Also, as shown in Table 1 and Figure 2, the thermal conductivity of the sintered body increases rapidly when the amount of aluminum carbide is 1% by weight or more, but it reverses when the amount of aluminum carbide exceeds 10% by weight. decreased. Therefore, the aluminum carbide contained in the mixed fine powder is preferably in the range of 1.0 to 10 weight percent. (Effects of the Invention) As described above, according to the present invention, aluminum carbide fine powder can be uniformly mixed by using aluminum, argon, nitrogen, hydrogen, ammonia, and methane as raw materials using the high-frequency induction thermal plasma method. The practical value of this method is extremely great because it enables the synthesis of aluminum nitride fine powder and solves the conventional problems of particle size and mixing of additives at the same time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a high frequency induction plasma device used in the present invention. FIG. 2 is a diagram showing the relationship between the proportion of aluminum carbide contained in the mixed fine powder and the thermal conductivity of the sintered body thereof. In FIG. 1, 1...high frequency coil, 2...quartz plasma generation tube, 3...cooling water inlet, 4...plasma gas supply port, 5...plasma generation section, 6...hydrogen gas inlet, 7...cooling water outlet, 8 , 8'... Mixed gas inlet, 9... Reaction vessel, 10... Powder collector, 11... Exhaust device, 12... Vacuum exhaust device, 13... Gas mixer, 14... Raw material supply port.

Claims (1)

[Claims] 1. A method for synthesizing aluminum nitride using high-frequency induction thermal plasma, which uses argon as a plasma generation gas, a mixed gas of nitrogen, hydrogen, ammonia and methane as a reaction gas, and introduces aluminum powder into the plasma. A method for synthesizing a mixed fine powder of aluminum nitride and aluminum carbide.