CN1216010C - Method for Synthesizing Ultrafine Aluminum Nitride by Self-propagation - Google Patents

Abstract

The present invention provides a self-propagating high-temperature synthesized superfine AlN ceramic powder and AlN base multiphase ceramic powder. The preparation method of the AlN powder comprises the following steps of: 50-90wt% of Al powder and 10-50wt% of AlN powder; the density of the biscuit is 35-60%, and the nitrogen pressure is 1-30 MPa. For AlN/ZrN/Al₃The Zr complex phase ceramic powder comprises 0-40wt% of AlN powder, 0-30wt% of ZrN powder, 10-85wt% of Al powder and 30-70wt% of Zr powder according to the component ratio of original reactant powder, wherein the density of a biscuit is 35-50%, and the nitrogen pressure of SHS reaction is 1-30 MPa. For AlN/ZrN complex phase ceramic powder, the composition ratio of the original reactant powder is 70-80wt% of Zr powder and 20-30wt% of AlN powder, the density of the biscuit is 35-50%, and the nitrogen pressure of the SHS reaction is 1-30 MPa. The original mixture ratio of the AlN-SiC solid solution reactant is that Si and C are 0-85atm%, Al is 15-100atm%, atm% is atomic percent, and the pressure of nitrogen is 1-30 MPa.

Description

Method for Synthesizing Ultrafine Aluminum Nitride by Self-propagation

Technical field:

The invention relates to a class of ultrafine AlN ceramic powder and AlN-based multiphase ceramic powder prepared by a self-propagating high-temperature synthesis (SHS) method.

Background technique

Since the former Soviet scholars A.G.Merzhanov and I.P.Borovinskaya discovered the SHS phenomenon in 1967, SHS has been one of the most active research directions in the field of materials science and engineering. Its basic features are: using externally provided necessary energy to induce a local chemical reaction in a highly exothermic chemical reaction system (this process is called ignition), forming a chemical reaction front (that is, a combustion wave), after which the chemical reaction releases heat by itself. With the support, continue to move forward, showing that the combustion wave spreads throughout the reaction system, and finally synthesizes materials. The most prominent advantages of the SHS synthesis process are energy saving, simple process, and high purity of the compound. So far, more than 500 kinds of products have been produced by SHS technology. However, these products mainly rely on solid-solid reaction, while the combustion synthesis of gas-solid system, the reaction is carried out by gas phase and solid phase reaction under high pressure conditions, the lack of gas in the pores will affect the complete reaction, and the melting of the solid phase will hinder infiltration of gas. Its reaction mechanism is more complex, and the process is difficult to control.

Aluminum nitride has low density, high thermal conductivity, low dielectric constant, high resistivity, thermal expansion coefficient matching silicon, and excellent thermal shock resistance. It is not only used as the preferred substrate and packaging material for VLSI, And with the continuous improvement of its performance, it also has a good application prospect as a structural ceramic. However, the traditional method of preparing AlN needs to be carried out under high-temperature heating conditions, which has a long cycle, high energy consumption, and high powder cost, which seriously limits the popularization and application of AlN. SHS synthesis of aluminum nitride is a promising low-cost preparation technology because of its low energy consumption, rapid reaction, high product purity and low cost. However, due to some basic theoretical and technical problems have not been well resolved, the process of combustion synthesis of AlN has not yet been applied on a large scale. Now my country, Russia, the United States, Japan, South Korea and other countries are making great efforts to solve the problem of SHS synthesis of AlN.

International patents involving combustion synthesis of ultrafine AlN ceramic powders and AlN-based composite ceramic powders include the Japanese patent "Preparation of BN, AlN and Si ₃ N ₄ by Combustion Synthesis" (JP2000264608) filed by Yamada Osamu. However, the synthetic sample weight of this patent is very small, and it is ignited with a laser, and the cost is very high. The US patent "Preparation Method of Aluminum Nitride" (US5846508) applied by Taiwan Yu Wen-Liang et al. This patent uses ammonium halide as a nitrogen source, and the weight of the synthesized sample is very small, which cannot realize large-scale or even large-scale production.

Invention content:

The invention controls the reaction temperature and pressure, and adds appropriate diluent, and synthesizes a complete large-size AlN billet (φ120mm) by SHS technology, and prepares ultra-fine AlN ceramic powder and AlN-based multiphase ceramic powder.

For the preparation of AlN (aluminum nitride) powder, the composition ratio of the original reactant is: 50-90wt% Al powder and 10-50wt% AlN powder, wt% is weight percent; the density of green body is 35-60 %, nitrogen pressure 1-30MPa.

For the AlN/ZrN/Al ₃ Zr composite ceramic powder, the composition ratio of the original reactant powder is 0-40wt% AlN powder, 0-30wt% ZrN powder, 10-85wt% Al powder and 30-70wt% % Zr powder, the density of the green body is 35-50%, and the nitrogen pressure of the SHS reaction is 1-30MPa.

For the AlN/ZrN composite ceramic powder, the composition ratio of the original reactant powder is 70-80wt% Zr powder and 20-30wt% AlN powder, the density of the green body is 35-50%, and the nitrogen pressure of the SHS reaction 1-30MPa.

The original ratio of the reactants of the AlN-SiC solid solution is 0-85 atm% for Si and C, 15-100 atm% for Al, the atm% is atomic percentage, and the pressure of nitrogen is 1-30MPa.

The principles and advantages of this method are briefly described as follows:

Recent studies have shown that due to its superior mechanical properties, AlN can be used as an important component of cermets and composite ceramics, and is expected to be widely used in structural ceramic materials. The technological process is as follows: (1) powder is prepared according to the specified ratio, (2) ball milled for 6 hours, (3) powder is dried, passed through a 100-mesh sieve and (4) powder is put into a combustion chamber and ignited.

Due to the low melting point of metal aluminum, melting and agglomeration will occur during the combustion process, which hinders the penetration of nitrogen, so increasing the pressure of nitrogen, adding AlN diluent to Al powder, and reducing the density of the green body, in order to improve the permeability of nitrogen, is to improve The key to the degree of nitriding of Al powder. At the same time, the size of the sample has an important influence on the combustion process of SHS AlN. The large-size sample has an obvious secondary nitriding peak during the combustion process, and the combustion behavior of different parts of the large-size sample itself is different under different green densities and nitrogen pressures. different characteristics under different conditions. As a structural ceramic, aluminum nitride has the disadvantage of low mechanical strength. Therefore, using the advantages of AlN ceramics and avoiding its disadvantages, a multi-phase composite material is designed on the basis of aluminum nitride to obtain multiple superimposed advantages of performance. In the Al-Zr-N system, AlN/ZrN composite ceramics combine the superior mechanical properties of AlN and ZrN; at the same time, Al ₃ Zr phases appear under low nitrogen pressure conditions, and Al ₃ Zr phases are mostly distributed in At the grain boundaries of AlN and ZrN, it plays the role of the binder phase, and the simultaneous densification that is difficult to achieve in the gas-solid system is achieved during the SHS synthesis.

As an important structural ceramic material, silicon carbide has a high degree of covalent bonding characteristics. At present, silicon carbide-based ceramic materials are used in heat engines, high-temperature environments and chemical and chemical industries because of their high hardness, wear resistance and chemical stability. research applications in other fields. α-SiC(2H) and AlN have similar structures, and have great similarities in valence and unit cell parameters. The similar structure and high temperature performance of the two means that the composite material of the two is of great help to the improvement of the material performance. The SHS process has opened up the application prospect of low-cost preparation of high-purity AlN-SiC solid solution.

Description of drawings:

Accompanying drawing 1 is the structure schematic diagram of the SHS reaction combustion chamber of the present invention, in the figure ignition wire 1, reactant body 2, thermocouple 3 for temperature measurement, sample stage 4.

Detailed ways:

Example 1: Synthesis of ultrafine aluminum nitride powder by SHS

The purity of the aluminum powder used in the experiment is greater than 99%, and the particle size is 250-300 mesh; the purity of AlN is 99.4%, and the particle size is less than 300 mesh. Reactant content: Al is 80wt%, AlN is 20wt%. In order to prevent the hydrolysis of AlN, use acetone as the medium, ball mill in an agate jar for 6 hours, dry in the air, loosely pack in the combustion chamber, or press into a certain powder with a limit mold, powder and loose reactants The diameter is 120mm. Ignited under a nitrogen pressure of 7MPa, the prepared aluminum nitride is completely nitrided, with a specific surface of 2-6m ² /g and an equivalent particle size of 0.3-0.9μm.

Example 2: Synthesis of AlN/ZrN/Al ₃ Zr composite ceramic powder by SHS

The properties of Al and AlN powder in the original reactant are the same as in Example 1. The purity of Zr powder is greater than 98%, and the particle size is less than 200 mesh.

The composition ratio of the powder is 31wt% AlN powder, 15.8wt% Al powder and 53.2wt% Zr powder, the density of the green body is 45%, the nitrogen pressure of the SHS reaction is 5MPa, and the obtained product is AlN/ZrN/ _Al3 Zr multiphase ceramic powder, the particle size is between 2-5μm.

Example 3: Synthesis of AlN/ZrN composite ceramic powder by SHS

The properties of Al and AlN powder in the original reactant are the same as in Example 1. The purity of ZrN powder is greater than 98%, and the particle size is less than 300 mesh.

The composition ratio of the powder is 80wt% Al powder and 20wt% ZrN powder, the density of the green body is 45%, the nitrogen pressure of the SHS reaction is 5MPa, and the obtained product is an AlN/ZrN composite ceramic powder with a particle size of 2- Between 5μm.

Example 4: Synthesis of AlN-SiC solid solution by SHS

The properties of Al and AlN powder in the original reactant are the same as in Example 1. The purity of Si powder and C powder is greater than 98%, and the particle size is less than 200 mesh.

The original ratio of the reactants of the AlN-SiC solid solution is 50 atm% for Si and C, 50 atm% for Al, and the pressure of nitrogen is 5MPa. The properties of the prepared AlN-SiC solid solution after hot pressing and sintering are: flexural strength 510MPa, HRA=93, K _IC =6.21MPa·m ^1/2 .

Claims (1)

1, the method for the synthetic AlN powder of a kind of self propagating high temperature is characterized in that: AlN powder synthetic, and the primitive reaction thing is made up of Al powder and AlN powder, and its composition proportion is: the Al powder of 50-90wt% and the AlN powder of 10-50wt%; The density of biscuit is 35-60%, and wt% is weight percentage; Its technical process is: by specifying proportioning preparation, ball milling, dry, sieve, pine is loaded in the combustion chamber or is molded into certain powder base with spacing, lights under the nitrogen pressure of 5-7Mpa with powder.

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