Page 232 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 8.8 Nanomaterials

they have certain properties that are often superior to traditional and commercially
available materials. These characteristics include high strength, hardness, ductility,
toughness, wear resistance and corrosion resistance, suitable for structural (load
bearing) and nonstructural applications in combination with unique electrical, mag-
netic, thermal, and optical properties.
The composition of a nanomaterial can be any combination of chemical ele-
ments. Among the more important compositions are carbides, oxides, nitrides, metals
and alloys, organic polymers, semiconductors, and various composites. Nanometal-
polymer hybrid nanomaterials are also being developed for very lightweight compo-
nents. Recent investigations include the development of nanopaper, produced from
wood pulp with fibers rearranged into an entangled porous mesh, resulting in very
high strength and toughness.
Synthesis methods include inert-gas condensation, sputtering, plasma synthe-
sis, electrode position, sol-gel synthesis, and mechanical alloying or ball milling.
Synthesized powders are consolidated into bulk materials by various techniques,
including compaction and sintering. Nanoparticles have a very high surface-area-
to-volume ratio, thus affecting their behavior in processes such as diffusion and
agglomeration. Because the synthesis of nanomaterials is done at atomic levels, their
purity (on the order of 99.9999%), their homogeneity, and the uniformity of their
microstructure are highly controlled. As a result, their mechanical, electrical, mag-
netic, optical, and chemical properties also can be controlled precisely. Control of
impurities in nanomaterials produced remains a challenging field. Nanoparticles
may also be coated for specific purposes.

Applications of Nanomaterials. The unique properties of nanomaterials enable
manufacturing of products that are strong, light, and more efficient. The following
are some current and potential applications for nanomaterials:

a. Cutting tools and inserts made of nanocrystalline carbides and other ceramics.
b. Nanophase ceramics that are ductile and machinable.
c. Powders for powder-metallurgy processing.
d. Carbon nanotubes have been used in specialty bicycle frames, baseball bats,
and tennis racquets. (See also Section 8.6.2.)
e. Next-generation computer chips using nanocrystalline starting materials
with very high purity, better thermal conductivity, and more durable inter-
connections.
f. Flat-panel displays for laptop computers and televisions, made by synthesizing
nanocrystalline phosphorus to improve screen resolution.
g. Spark-plug electrodes, igniters and fuels for rockets, medical implants, high-
sensitivity sensors, catalysts for elimination of pollutants, high-power magnets,
and high-energy-density batteries.
h. Switches, valves, motor, and pumps.
i. Coatings made of nanomaterials are being investigated for improved wear,
abrasion, corrosion resistance and thermal insulation; nanocrystalline materi-
als; nanophase materials because of their lower thermal conductivity.

Because nanomaterials are very expensive to produce and process into products,
their cost-effectiveness is under continued study.

Health Hazards. Because of their small size, nanoparticles can present health haz-
ards by virtue of their absoption through the skin, lungs, or the digestive tracl<.
They can also penetrate human cells. There is increasing evidence that nanoparticles