Biomedical Engineering Reference
In-Depth Information
Figure 4.3
Steal vial for SPEX mill.
4.1.1.2 Nanoprocessing
Five major processing methods can be employed during milling
of materials in high-energy ball mills: (i) high energy ball milling
(HEBM), (ii) mechanical alloying (MA), (iii) mechanochemical
activation synthesis (MCAS), (iv) mechanochemical synthesis (MCS),
and (v) mechanical amorphization (MAM) [54].
High-energy ball milling is nanotechnology top down approach
for the synthesis of nanoparticles. In the HEBM process, brute force is
applied to material, whether it is a metal, a pre-alloyed intermetallic,
or a solid chemical (stoichiometric) compound. Short milling times
can break thin chemically passive surface coatings (e.g., surface
oxides) and expose fresh, clean chemically active metallic surface.
Such milling can also introduce defects into solid compounds. It
results in an increased chemical activity of milled media toward
both gasses and chemical reactions in solutions and electrolytes.
This process is often termed mechanochemical activation synthesis.
A process wherein mixture of elemental metal powders, or
powders of metal and nonmetal are milled long enough to trigger
alloying of elemental powders in a solid-state process is termed
mechanical alloying. Since substantial rearrangement of chemical
species must take place during alloying, the latter requires long times
of milling, usually more than twice the time needed for preparation
of nanopowders by mechanical milling. Even longer milling results
in the term, mechanical amorphization of a crystalline solid.
