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Aluminum nitride ceramic high temperature sintering design and verification, sintering temperature range (1200℃~1900℃) requirements, the best sintering temperature of 1600℃, reached 1600℃, oxidation r

2025-02-22

1, Term definition

Aluminum nitride

CAS: 24304-00-5

Chemical formula: AlN

Properties

Aluminum nitride has hexagonal crystal structure and belongs to wurtzite type. Its pure form is blue-white, but in practice, it usually appears gray or off-white. The material has a relative density of 3.26 and a Mohs hardness of 9. In the temperature range of 25℃ to 600℃, its thermal expansion coefficient is 4.84×10⁻⁶ K⁻¹. When the temperature is 200℃, the thermal conductivity is 30 W/(m·K), the resistivity is 2×10¹¹Ω·cm (25℃), and the dielectric constant is 8.15. Aluminum nitride exhibits high strength at room temperature, and its strength decreases relatively slowly as the temperature increases. It has excellent thermal conductivity and small coefficient of thermal expansion, and is an excellent heat-resistant impact material. In addition, aluminum nitride also has excellent thermal shock resistance. Its thermal conductivity is 2 to 3 times that of alumina (Al₂O₃), and its strength is even higher than that of alumina during hot pressing. Aluminum nitride has good corrosion resistance to aluminum and other molten metals, gallium arsenide and other substances, especially for molten aluminum liquid, showing excellent corrosion resistance. At the same time, it also has excellent electrical insulation and dielectric properties. However, the high temperature oxidation resistance of aluminum nitride is poor, it is easy to absorb moisture and hydrolysis in the atmospheric environment, and once it is in contact with wet air, water or aqueous liquid, it will produce heat and nitrogen, and quickly decompose. The substance will decompose at 2516 ° C, has a high thermal hardness, and will not soften or deform even before the decomposition temperature. Aluminum nitride can remain stable at temperatures up to 2200 ° C. Its strength is higher at room temperature, and its strength decreases slowly with the increase of temperature.

Characteristic

It has a high thermal conductivity of about 320 W/(m·K), similar to BeO and SiC, and more than 5 times that of Al₂O₃. The thermal expansion coefficient is 4.5×10⁻⁶℃, which is consistent with Si (3.5~4×10⁻⁶℃) and GaAs (6×10⁻⁶℃). It has excellent electrical properties, including dielectric constant, dielectric loss, bulk resistivity and dielectric strength. The mechanical properties are excellent, the folding strength is higher than Al₂O₃ and BeO ceramics, and can be prepared by atmospheric pressure sintering process. It can be produced by casting process and is a promising substrate and packaging material for high power integrated circuits.

Application:

Aluminum nitride ceramics belong to a new type of ceramic material in the field of high and new technology. Aluminum nitride substrate not only has very high thermal conductivity, but also has non-toxicity, good corrosion resistance, high temperature resistance and excellent thermochemical stability. These characteristics make it an ideal packaging material, heat dissipation material, circuit components and interconnect carrier for large-scale integrated circuits, semiconductor module circuits and high-power devices. In addition, aluminum nitride ceramics are also excellent additives to improve the thermal conductivity and mechanical properties of polymer materials. In other applications, aluminum nitride ceramics can be used in crucbles for melting non-ferrous metals and semiconductor materials gallium arsenide, protective tubes for thermocouples, high-temperature insulating components, microwave dielectric materials, high-temperature and corrosion-resistant structural ceramics, and transparent aluminum nitride microwave ceramic products. It can also be used as a raw material for the production of high thermal conductivity ceramics and a filling material for resins. As an electrical insulator, aluminum nitride has good dielectric properties. The aluminum nitride coating on the surface of gallium arsenide can effectively prevent it from being affected by ion implantation during the annealing process.

2 Preparation process of aluminum nitride powder

2.1 Direct nitriding method

Direct nitriding method is to place aluminum powder in high temperature nitrogen atmosphere, so that aluminum powder and nitrogen directly react to produce aluminum nitride powder. The chemical reaction equation is 2Al(s)+N2(g)→2AlN(s), and the reaction temperature is usually between 800 ° C and 1200 ° C.

2.2. Carbothermic reduction method:

After evenly mixing Al₂O₃ with C, they are heated in a nitrogen atmosphere so that Al₂ ₃ is first reduced and then reacts with N₂ to form AlN. The chemical reaction equation is: Al2O3(s)+3C(s)+N2(g)→2AlN(s)+3CO(g). Advantages: wide source of raw materials, simple process; The produced powder has high purity, small particle size and uniform distribution. Disadvantages: long synthesis time, high nitriding temperature; After the reaction, the excess carbon needs to be decarbonized, which increases the production cost.

2.3 High-energy ball milling method

High-energy ball milling method is in the atmosphere of nitrogen or ammonia, using the rotation or vibration of the ball mill, so that the hard ball to alumina or aluminum powder and other raw materials for strong impact, grinding and stirring, so as to achieve direct nitriding into aluminum nitride powder. Advantages: simple equipment, short process flow, high production efficiency. Disadvantages: the nitriding reaction is difficult to be completely carried out, and impurities are easy to be introduced in the ball milling process, affecting the quality of the powder.

2.4. High temperature self-propagating synthesis

High temperature self-propagating synthesis is a derivative of the direct nitriding method. The Al powder is ignited in high-pressure nitrogen, and the heat generated by the Al and N₂ reaction is used to maintain the reaction until the reaction is complete. The chemical reaction equation is 2Al(s)+N2(g)→2AlN(s).

2.5. In situ autoreactive synthesis method The principle of in situ autoreactive synthesis method is similar to the direct nitriding method, and the alloy formed by aluminum and other metals is the raw material. Other metals in the alloy are melted at high temperatures and react with nitrogen to form metal nitrides, and then metal Al replaces the metal in the nitride to form AlN.

2.6 Plasma chemical synthesis method

Plasma chemical synthesis method is to use DC arc plasma generator or high-frequency plasma generator to transport Al powder to the plasma flame zone. Under the action of high temperature of flame, the powder quickly melts and volatilizes, and quickly reacts with nitrogen ions to form AlN powder.

2.7 Chemical vapor precipitation method

Chemical vapor precipitation method is to raise the reaction temperature to much higher than the theoretical reaction temperature, so that the reaction product vapor form a high supersaturated vapor pressure, so as to automatically condense into crystal nuclei, and gradually aggregate into particles.

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