Page 233 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

2 I2 Chapter 8 Ceramics, Graphite, Diamond, and Nanomaterials: Structure, General Properties, and Applications

can pollute air, water, and the ground. Consequently, there is growing research on
the risks of nanoparticles to humans and the environment.

SUMMARY

Ceramics, glasses, and various forms of carbon are of major importance in engi-
neering applications and in manufacturing processes. Ceramics, which are com-
pounds of metallic and nonmetallic elements, generally are characterized by high
hardness, high compressive strength, high elastic modulus, low thermal expansion,
high temperature resistance, good chemical inertness, low density, and low ther-
mal and electrical conductivity. On the other hand, they are brittle and have low
toughness. Nanophase ceramics have better properties than common ceramics.
Porosity in ceramics has important effects on their properties.
Ceramics generally are categorized as either traditional or industrial (or high-
tech) ceramics; the latter are particularly attractive for applications such as en-
gine components, cutting tools, and components requiring resistance against
wear and corrosion. Ceramics of importance in design and manufacturing are the
oxide ceramics (alumina and zirconia), tungsten and silicon carbides, nitrides,
and cermets.
Glasses are supercooled liquids and are available in a wide variety of composi-
tions and of mechanical, physical, and optical properties. Glass ceramics are pre-
dominantly crystalline in structure and have properties that are more desirable
than those of glasses.
Glass in bulk form has relatively low strength, but glasses can be strengthened by
thermal and chemical treatments in order to obtain high strength and toughness.
Glass fibers are used widely as a reinforcing material in composite materials, such
as in fiber-reinforced plastics.
Graphite, fullerenes, carbon nanotubes, and diamond are forms of carbon that
display unique combinations of properties. These materials have several estab-
lished and emerging applications in engineering and manufacturing. Graphite has
high-temperature and electrical applications; graphite fibers are used to reinforce
plastics and other composite materials.
Diamonds (both natural and synthetic) are used as cutting tools for fine machin-
ing operations, as dies for thin-wire drawing, and as abrasives for grinding
wheels. Diamond-like carbon has applications as a coating material giving im-
proved wear resistance.
Nanomaterials in various shapes are a more recent development, with physical,
mechanical, optical, chemical, and thermal properties allowing their unique appli-
cations. Carbon nanotubes are of continued research interest, particularly because
of their relevance to nanoscale electrical and electromechanical systems.

KEY TERMS

Alumina Carbides Carbon nanotubes Clay
Bioceramics Carbon Ceramics Devitrification
Buckyballs Carbon foam Cermets Diamond