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普通粉末与超细粉末普通粉末就是所谓松散的,可用筛分分开的粉末。最细筛为400目孔径,约37μm。通常,我们把粒度为1μm以下的粉末称为超细粉末。烟囱的煤灰就是碳的超细粉,金属的超细粉与它相似。当粒度r变小时,则各粒子所受的重力随r~3成比例的变小,然而各粒子间的粘结面积仅随r~2减少。当粒度在某个界限以下,则表面粘结力大于重力,即便有轻微的振动颗粒也不分离。这个性质不是由于潮湿的缘故而是因为原来的表面力存在一定的差别,这是超细粉的通性。像煤灰那样的轻漂状超细粉不能用筛分就是由于这个原因。松装比重随粒度变小而减少,100nm粒度的松装比重是真比重的1/10,10nm粒度
Ordinary powder and ultrafine powder Ordinary powder is the so-called loose, can be used to separate the powder sieve. The finest sieve is 400 mesh aperture, about 37μm. In general, we call the powder with a particle size of 1 μm or less as an ultra-fine powder. Chimney coal ash is carbon ultra-fine powder, metal and its similar ultra-fine powder. When the particle size r becomes smaller, the gravitational force of each particle becomes smaller in proportion to r ~ 3, but the adhesion area between the particles decreases only with r ~ 2. When the particle size is below a certain limit, the surface adhesion is greater than the gravitational force, and the particles are not separated even with slight vibration. This property is not due to wetness but because of the original surface force there is a certain difference, which is the generality of ultrafine powder. It is for this reason that light-drift ultra-fine powders such as soot can not be sieved. Loaded with the proportion of loose and smaller particle size decreases, 100nm particle size of the loose proportion is the true proportion of 1/10, 10nm granularity