The average particle size of aluminum powder produced by atomization method is in micron level, which is difficult to meet the requirements of ultrafine powder nanometer level. With the development of science and technology, ultrafine aluminum powder is widely used. For example, rocket solid propellant, coating materials of thermal spraying composite materials, aluminum nitride, etc., require that the particle size of aluminum powder reach the standard of nanometer level.
If the aluminum is gasified in vacuum or inert gas, the molecular size of the gas is calculated by angstroms (1 = 10-10m). In the process of condensation, controlling the size of the crystal nucleus, the nanometer powder can be obtained.
The model of ultrafine particles was prepared by gas evaporation.
The melting point of aluminum is 660.452 ℃, the boiling point is 2520 ℃, and aluminum is very easy to combine with oxygen at a higher temperature to release a large amount of heat, resulting in Al2O3. Therefore, aluminum powder cannot be generated in the aerobic environment, and aluminum can only be evaporated in the vacuum or inert gas environment.
Saturated vapor pressure of pure aluminum:
Evaporation rate of aluminum:
Aluminum vapor condenses into powder
To prepare ultrafine powder, aluminum vapor should be condensed into solid powder instead of liquid. The condensation temperature is set below the melting point of aluminum, increasing the degree of supercooling, forming homogeneous nucleation as far as possible, and falling to a colder place. During the falling process, the powder does not grow much, so nanometer aluminum powder can be obtained.
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