A low magnification
SEM micrograph of an advanced ceramic material. The properties of ceramics make fracturing an important inspection method.
A ceramic material is an inorganic, non-metallic, often crystalline oxide, nitride or carbide material. Some elements, such as
carbon or
silicon, may be considered ceramics. Ceramic materials are brittle, hard, strong in compression, weak in
shearing
and tension. They withstand chemical erosion that occurs in other
materials subjected to acidic or caustic environments. Ceramics
generally can withstand very high temperatures, such as temperatures
that range from 1,000 °C to 1,600 °C (1,800 °F to 3,000 °F). A
glass is often not understood as a ceramic because of its
amorphous
(noncrystalline) character. However, glassmaking involves several steps
of the ceramic process and its mechanical properties are similar to
ceramic materials.
Traditional ceramic raw materials include clay minerals such as
kaolinite, whereas more recent materials include aluminium oxide, more commonly known as
alumina. The modern ceramic materials, which are classified as advanced ceramics, include
silicon carbide and
tungsten carbide.
Both are valued for their abrasion resistance, and hence find use in
applications such as the wear plates of crushing equipment in mining
operations. Advanced ceramics are also used in the medicine, electrical
and electronics
industries.
Crystalline ceramics
Crystalline ceramic materials are not amenable to a great range of
processing. Methods for dealing with them tend to fall into one of two
categories – either make the ceramic in the desired shape, by reaction
in situ, or by "forming" powders into the desired shape, and then
sintering to form a solid body.
Ceramic forming techniques include shaping by hand (sometimes including a rotation process called "throwing"),
slip casting,
tape casting (used for making very thin ceramic capacitors, e.g.),
injection molding, dry pressing, and other variations. Details of these processes are described in the two books listed below.
A few methods use a hybrid between the two approaches.
Noncrystalline cera mics
Noncrystalline ceramics, being glass, tend to be formed from melts.
The glass is shaped when either fully molten, by casting, or when in a
state of toffee-like viscosity, by methods such as blowing into a mold.
If later heat treatments cause this glass to become partly crystalline,
the resulting material is known as a glass-ceramic, widely used as
cook-top and also as a glass composite material for nuclear waste
disposal.
No comments:
Post a Comment