Biomedical Engineering Reference
In-Depth Information
In the 1960s and 1970s, metallic nanopowders for magnetic
recording tapes were developed. The irst nano-size metallic
materials were produced in 1960 by the application of rapid
quenching
process with the cooling rate of 10
6
K s
-1
by Pol Duvez
and coworkers [30]. Using a quench technique capable of cooling
metal/alloy melts to ambient temperatures with such extraordinary
cooling rates, the process of nucleation and growth was kinetically
bypassed to yield a coniguration of frozen liquid or amorphous
metal. The nanoalloys with nanometric grains were processed by
low-temperature annealing of amorphous alloy [12]. Additionally,
in 1972 a new rapid quenching process of melt spinning
was used
to spin the irst nonocrystalline ferrous and ferromagnetic metal
ribbons (Fe
80
B
20
) [10]. The outstanding physical and chemical
properties of these materials were the direct consequence of the
lack of structural crystalline long-range order and the presence
of short-range order. It is important to mention that many, if not
all of these amorphous alloys, i.e., metallic glasses, when carefully
annealed at low temperatures change to nanostructure alloy phases.
Those were the irst nanomaterials.
They were produced in the
form of thin ribbons via rapid solidiication processing of melt
alloys. They allowed controlled exploration of physical, chemical,
mechanical, and other properties as arising from nanostructures.
At this time, scientists and engineers became refocused from well-
ordered crystalline materials to disordered and nanocrystalline
phases. Gleiter observed that nanometer-size crystalline materials
being polycrystals with very small crystallite sizes of about 2-10 nm
in diameter are composed of randomly oriented high-angle grain
boundaries [18].
The irst such nanocrystalline phases
came from Gleiter research
group around 1984 by evaporation of the material in a high-purity
inert gas atmosphere followed by condensation and compaction in
ultrahigh vacuum [5].
The percentage of metal atoms on the surface
of grain increases from a few percent in a 100 nm particle to about
90% in a 1 nm crystallite [19, 43]. As above, these materials should
be attractive for the development of engineering materials with an
outstanding combination of properties or novel properties. In the
meantime, among materials that became studied were nanophases
produced by mechanical alloying [4, 7, 47].
Nanomaterials continue to attract a great deal of attention
because of their potential impact on an incredibly wide range of
