ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collision from the balls of small size how the milling will produce the compound
is only due to high pressure or else?
You mean difference between attritor (http://www.attritor.in/attritor_working.html) and normal ball mill (https://en.wikipedia.org/wiki/Ball_mill)?
There is no fundamental difference, only the attritor with the same mass of equal balls grinds 5-10 times faster. Seen from the other side, only small attritors exist, and the large ball mills are anyway more efficient than small attritors. From a purely economic point of view, the attritors have little meaning, ball mills are cheaper, wear not so fast and can be very large.
As for the energy of the grinding, this question is not so easy. Kinetic energy of the balls depends not only on its velocity, but also on its mass. Attritors work with small balls and are therefore only suitable for fine grinding. On the other hand, ball mills work, as well as with small balls and with large balls, can also be used for coarse-grained powders (small and fast balls of attritors do not have enough kinetic energy for crushing coarse particles).
High energy ball milling process was developed by Benjamin and his coworkers at the International Nickel Company in the late of 1960. This process, termed mechanical alloying, could successfully produce fine, uniform dispersions of oxide particles (Al2O3, Y2O3, ThO2) in nickel-base superalloys that could not be made by more conventional powder metallurgy methods. Their innovation has changed the traditional method in which production of materials is carried out by high temperature synthesis. Besides materials synthesis, high-energy ball milling is a way of modifying the conditions in which chemical reactions usually take place either by changing the reactivity of as-milled solids (mechanical activation — increasing reaction rates, lowering reaction temperature of the ground powders)—or by inducing chemical reactions during milling (mechanochemistry). It is, furthermore, a way of inducing phase transformations in starting powders whose particles have all the same chemical composition: amorphization or polymorphic transformations of compounds, disordering of ordered alloys, etc.
http://www.understandingnano.com/nanomaterial-synthesis-ball-milling.html
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