A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent
cooling.
Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous.
Because most common ceramics are crystalline, the definition of ceramic is often restricted
to inorganic crystalline materials, as opposed to the noncrystalline glasses, a distinction
followed here.
The earliest ceramics made by humans were pottery objects, including 27,000 year old
figurines, made from clay, either by itself or mixed with other materials, hardened in
fire.
Later ceramics were glazed and fired to create a colored, smooth surface.
Ceramics now include domestic, industrial and building products and a wide range of
ceramic art.
In the 20th century, new ceramic materials were developed for use in advanced ceramic
engineering; for example, in semiconductors.
The word "ceramic" comes from the Greek word κεραμικός, "of pottery" or "for pottery",
from κέραμος, "potter's clay, tile, pottery".
The earliest known mention of the root "ceram-" is the Mycenaean Greek ke-ra-me-we, "workers
of ceramics", written in Linear B syllabic script.
"Ceramic" may be used as an adjective describing a material, product or process; or as a singular
noun, or, more commonly, as a plural noun, "ceramics".
Types of ceramic product For convenience, ceramic products are usually
divided into four sectors; these are shown below with some examples:
Structural, including bricks, pipes, floor and roof tiles
Refractories, such as kiln linings, gas fire radiants, steel and glass making crucibles
White wares, including tableware, cookware, wall tiles, pottery products and sanitary
ware Technical, is also known as engineering, advanced,
special, and in Japan, fine ceramics.
Such items include tiles used in the Space Shuttle program, gas burner nozzles, ballistic
protection, nuclear fuel uranium oxide pellets, biomedical implants, coatings of jet engine
turbine blades, ceramic disk brake, missile nose cones, bearing,etc.
Frequently, the raw materials do not include clays.
Examples of white ware ceramics
Earthenware, which is often made from clay, quartz and feldspar.
Stoneware Porcelain, which is often made from kaolin
Bone china Classification of technical ceramics
Technical ceramics can also be classified into three distinct material categories:
Oxides: alumina, beryllia, ceria, zirconia Nonoxides: carbide, boride, nitride, silicide
Composite materials: particulate reinforced, fiber reinforced, combinations of oxides and
nonoxides.
Each one of these classes can develop unique material properties because ceramics tend
to be crystalline.
Other applications of ceramics Knife blades: the blade of a ceramic knife
will stay sharp for much longer than that of a steel knife, although it is more brittle
and can snap from a fall onto a hard surface.
Ceramic brake disks for vehicles are resistant to abrasion at high temperatures.
Advanced composite ceramic and metal matrices have been designed for most modern armoured
fighting vehicles because they offer superior penetrating resistance against shaped charges
and kinetic energy penetrators.
Ceramics such as alumina and boron carbide have been used in ballistic armored vests
to repel large-caliber rifle fire.
Such plates are known commonly as small arms protective inserts, or SAPIs.
Similar material is used to protect the cockpits of some military airplanes, because of the
low weight of the material.
Ceramics can be used in place of steel for ball bearings.
Their higher hardness means they are much less susceptible to wear and typically last
for triple the lifetime of a steel part.
They also deform less under load, meaning they have less contact with the bearing retainer
walls and can roll faster.
In very high speed applications, heat from friction during rolling can cause problems
for metal bearings, which are reduced by the use of ceramics.
Ceramics are also more chemically resistant and can be used in wet environments where
steel bearings would rust.
In some cases, their electricity-insulating properties may also be valuable in bearings.
Two drawbacks to ceramic bearings are a significantly higher cost and susceptibility to damage under
shock loads.
In the early 1980s, Toyota researched production of an adiabatic engine using ceramic components
in the hot gas area.
The ceramics would have allowed temperatures of over 3000°F. The expected advantages would
have been lighter materials and a smaller cooling system, leading to a major weight
reduction.
The expected increase of fuel efficiency of the engine could not be verified experimentally;
it was found that the heat transfer on the hot ceramic cylinder walls was higher than
the transfer to a cooler metal wall as the cooler gas film on the metal surface works
as a thermal insulator.
Thus, despite all of these desirable properties, such engines have not succeeded in production
because of costs for the ceramic components and the limited advantages.
Such engines are possible in laboratory settings, but mass production is not feasible with current
technology.
Work is being done in developing ceramic parts for gas turbine engines.
Currently, even blades made of advanced metal alloys used in the engines' hot section require
cooling and careful limiting of operating temperatures.
Turbine engines made with ceramics could operate more efficiently, giving aircraft greater
range and payload for a set amount of fuel.
Recent advances have been made in ceramics which include bioceramics, such as dental
implants and synthetic bones.
Hydroxyapatite, the natural mineral component of bone, has been made synthetically from
a number of biological and chemical sources and can be formed into ceramic materials.
Orthopedic implants coated with these materials bond readily to bone and other tissues in
the body without rejection or inflammatory reactions so are of great interest for gene
delivery and tissue engineering scaffolds.
Most hydroxyapatite ceramics are very porous and lack mechanical strength, and are used
to coat metal orthopedic devices to aid in forming a bond to bone or as bone fillers.
They are also used as fillers for orthopedic plastic screws to aid in reducing the inflammation
and increase absorption of these plastic materials.
Work is being done to make strong, fully dense nanocrystalline hydroxyapatite ceramic materials
for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials
with a synthetic, but naturally occurring, bone mineral.
Ultimately, these ceramic materials may be used as bone replacements or with the incorporation
of protein collagens, synthetic bones.
High-tech ceramic is used in watchmaking for producing watch cases.
The material is valued by watchmakers for its light weight, scratch resistance, durability
and smooth touch.
IWC is one of the brands that initiated the use of ceramic in watchmaking.
The case of the IWC 2007 Top Gun edition of the Pilot's Watch double chronograph is crafted
in black ceramic.
Types of ceramic material
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. A glass is often not understood as a ceramic because of its
amorphous 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, slip casting, tape casting, 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 ceramics 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.
Ceramics in archaeology Ceramic artifacts have an important role in
archaeology for understanding the culture, technology and behavior of peoples of the
past.
They are among the most common artifacts to be found at an archaeological site, generally
in the form of small fragments of broken pottery called sherds.
Processing of collected sherds can be consistent with two main types of analysis: technical
and traditional.
Traditional analysis involves sorting ceramic artifacts, sherds and larger fragments into
specific types based on style, composition, manufacturing and morphology.
By creating these typologies it is possible to distinguish between different cultural
styles, the purpose of the ceramic and technological state of the people among other conclusions.
In addition, by looking at stylistic changes of ceramics over time is it possible to separate
the ceramics into distinct diagnostic groups.
A comparison of ceramic artifacts with known dated assemblages allows for a chronological
assignment of these pieces.
The technical approach to ceramic analysis involves a finer examination of the composition
of ceramic artifacts and sherds to determine the source of the material and through this
the possible manufacturing site.
Key criteria are the composition of the clay and the temper used in the manufacture of
the article under study: temper is a material added to the clay during the initial production
stage, and it is used to aid the subsequent drying process.
Types of temper include shell pieces, granite fragments and ground sherd pieces called 'grog'.
Temper is usually identified by microscopic examination of the temper material.
Clay identification is determined by a process of refiring the ceramic, and assigning a color
to it using Munsell Soil Color notation.
By estimating both the clay and temper compositions, and locating a region where both are known
to occur, an assignment of the material source can be made.
From the source assignment of the artifact further investigations can be made into the
site of manufacture.
See also Ceramic chemistry
Ceramic materials Ceramic engineering
Ceramic matrix composite Ceramic art
Pottery Potter's wheel
References
Further Reading Guy, John.
Guy, John, ed.
Oriental trade ceramics in South-East Asia, ninth to sixteenth centuries: with a catalogue
of Chinese, Vietnamese and Thai wares in Australian collections.
Oxford University Press.
Retrieved 24 April 2014.
External links Dolni Vestonice Venus- Oldest known Ceramic
statuette of a nude female figure dated to 29 000 – 25 000 BP (Gravettian industry.
Czech Republic How pottery is made
How sanitaryware is made World renowned ceramics collections at Stoke-on-Trent
Museum Click on Quick Links in the right-hand column to view examples.
The Gardiner Museum – The only museum in Canada entirely devoted to ceramics
Introduction, Scientific Principles, Properties and Processing of Ceramics
Advanced Ceramics – The Evolution, Classification, Properties, Production, Firing, Finishing
and Design of Advanced Ceramics Cerame-Unie, aisbl – The European Ceramic
Industry Association