Pure metal iron is silvery white, and iron powder is black, which is an optical problem. Because the surface area of iron powder is small, there is no fixed geometry, and the crystal structure of iron block is geometry, so iron block absorbs part of visible light, and reflects the other part of visible light mirror, showing white; the light that iron powder does not absorb is diffusely reflected, which can enter the human eye There's less light, so it's black.

A particle aggregate of iron with a size of less than 1 mm. Color: black. It is the main raw material of powder metallurgy. According to the particle size, it is usually divided into five grades: coarse powder, medium powder, fine powder, fine powder and ultra-fine powder. Iron powder with particle size of 150-500 μ m is coarse powder, medium powder with particle size of 44-150 μ m, fine powder with particle size of 10-44 μ m, extremely fine powder with particle size of 0.5-10 μ m and ultra-fine powder with particle size of less than 0.5 μ M. Generally, the powder that can pass 325 target sieve, i.e. the particle size is less than 44 μ m, is called sub sieve powder. If a higher precision sieve is to be carried out, only air flow classification equipment can be used, but for some easily oxidized iron powder, only jzdf nitrogen protection classifier can be used. Iron powder mainly includes reduced iron powder and atomized iron powder, which are named after different production methods.

A particle aggregate of iron with a size of less than 1 mm. Color: black. It is the main raw material of powder metallurgy....