Ceramics
Glass, tiles, pottery, porcelain,
bricks, cement, diamond and graphite - you can probably see from this short
list that "ceramics" is a very broad term and one of them is that you
have a hard time defining.
From a chemical point of view, we
define ceramics in terms of what they are not. So you will find most science
textbooks and dictionaries that tell you ceramics are nonmetallic and inorganic
substances (not metals or based on carbon compounds); In other words, ceramic
is when we remove metals and organic materials (e.g. wood, plastic, rubber and
a thing that was alive).
Some books try to define ceramics
as a "refractory" material, which is a technical, literary science
term that means it is able to withstand the daily pressures of temperature, and
salts, and normal wear-tears. It is often easy to define materials in terms of
their properties (for example, how bad they are when we heat them, how much
electricity goes through them or soaks them in water). But once you start doing
that things can get confusing. For example, graphite is considered a ceramic
because it is nonmetallic and inorganic, yet (more than most ceramics) it is
softer, more easily worn, and a better conductor of electricity so if you just
look at the properties of graphite, you will not consider it ceramic at all.
Diamond is also ceramic for the same reason; its properties may not be much
different than graphite, but they are similar to other ceramics.
Types of Ceramics
People first made pottery, glass
and brick are some of the oldest man-made materials thousands of years ago and
we are still designing new ceramic materials - catalytic converters for today's
cars and high-temperature superconductors for tomorrow's computers.
General-purpose ceramics, such as brick and glass, and modern engineered
ceramics have many differences between ceramics, such as filtering soot from a
truck's dirty diesel engine, or for a specific purpose.
Traditional Ceramics
Bricks, pottery, glass,
porcelain, tiles, cement and concrete are our classic, time-tested ceramics.
Although their overall use is different, we can still consider them for a
general purpose. We can keep them in or out of our homes; Walls, floors or
ceilings, and we can stick the glass in our windows or hang it on the screen of
the smartphone - we can even drink champagne from it. Ceramics like these are
ancient materials - as our ancestors may have known - gradually found more and
more use as they have been worn for centuries.
Advanced Engineering Ceramics
In contrast, advanced ceramics
have been engineered for very specific applications mostly in the early 20th
century. For example, silicon nitrides and tungsten carbides are designed to
make exceptionally rigid, high-performance devices - although they have other
uses. Most modern engineered ceramics are metal oxides, carbides, and nitrides,
meaning compounds formed by combining metal atoms with oxygen, carbon, or
nitrogen atoms. So, for example, we have tungsten carbide, silicon carbide and
boron nitride, which are rigid, cutting-tooling ceramics; Aluminum oxide
(alumina) and silicon dioxide are used to make integrated circuits
("microchips"); and lithium-silicon oxide is used to make
heat-protective nose cones on space rockets. High-temperature superconductors
are made from crystals of yttrium, barium, copper and oxygen.
Not all high-tech ceramic
materials are simple compounds. There are some composite materials, which form
a kind of background material called ceramic matrix, which is reinforced with
fibers of another material (often carbon fiber or sometimes completely
different ceramic fibers). Materials like these are known as ceramic matrix
composites (CMCs). Examples include silicon carbide fibers in the silicon
carbide matrix with boron nitride in their interface - a material used in
sophisticated gas-turbine jet engines.
Properties of Ceramics
The most important common
property of ceramics is that they are resistant, they are a rough and tangled
material that will withstand the right amount of abuse under extremely normal
and unusual conditions.
·
High melting points (i.e. they are heat
resistant).
·
Great rigidity and strength.
·
Considerable durability (they are long lasting
and tough to wear).
·
Low electrical and thermal conductivity (they
are good insulators).
·
Chemical inertia (they are unpleasant with other
chemicals).
·
Most ceramics are also non-magnetic materials,
although ferrites (iron-based ceramics) make excellent magnets (because of
their iron content).
These are useful points, but, if
you think about traditional ceramics like glass or porcelain, you may also see
a big flaw: they can be fragile and brittle and if you leave them they will
crack or break (subject to "mechanical shock") or suddenly Change
their temperature ("thermal shock").
Read More Articles: Most Important Applications of Ceramic
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