Dictionary
an artifact made of hard brittle material produced from nonmetallic minerals by firing at high temperatures of or relating to or made from a ceramic "a ceramic dish"
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Wikipedia
The word '' ceramic'' is derived from the Greek language Greek word !Κερα&m u;εικ&omicr on;ς? (-keramos- the name of a suburb of Athens)The term covers inorganic non-metallic materials whose formation is due to the action of heat. Up until the 1950s or so, the most important of these were the traditional clays, made into pottery, bricks, tiles and the like, along with cements and glass. The traditional crafts are described in the article on pottery. A composite material of ceramic and metal is known as cermet.The Venus of Dolni Vestonice is the oldest known ceramic in the world. Historically, ceramic products have been hard, porous and brittle. The study of ceramics consists to a large extent of methods to mitigate these problems, and accentuate the strengths of the materials, as well as to offer up unusual uses for these materials.
Classifications of technical ceramics - Technical Ceramics can also be classified into three distinct material categories: Oxides: Alumina, zirconia Non-oxides: Carbides, borides, nitrides, silicides Composites: Particulate reinforced, combinations of oxides and non-oxides.Each one of these classes can develop unique material properties
Examples of ceramic materials - Barium titanate (often mixed with strontium titanate) displays ferroelectricity, meaning that its mechanical, electrical, and thermal responses are coupled to one another and also history-dependent. It is widely used in electromechanical transducers, ceramic capacitors, and Ferroelectric RAMdata storage elements. crystalliteGrain boundary phenomena in these materials can give rise to positive temperature coefficientPTC behavior for heating elements.Boron carbide (boron!B4carbo nC), which is used in some helicopter and tank vehicle armourarmor.Boron_nitride is structurally isoelectronic to carbon and takes on similar physical forms: a graphite-like one used as a lubricant, and a diamond-like one used as an abrasive.Bricks (mostly aluminium silicates), used for construction.ferrite (magnet)Ferrite (iron!Fe3O< ;sub>4),? which is ferrimagnetismferrimagnetic and is used in the core of electrical transformers and magnetic core memory.Lead zirconate titanate is another ferroelectric material.Magnesium diboride (magnesiumMgboronB2), which is an unconventional superconductor.Silicon carbide (siliconSicarbonC), which is used as a susceptor in microwave furnaces, a commonly used abrasive, and as a refraction (metallurgy)refractory material.Silicon nitride (silicon!Si3nitr ogenN4), which is used as an abrasive powder.Steatite is used as an electrical insulator.Uranium oxide (uraniumUO2), used as nuclear fuelfuel in nuclear reactors.Yttrium barium copper oxide (yttriumYbarium!Ba2copp er!Cu3oxyg enO7-x), a high temperature Superconductivitysuperconductor.Zinc oxide (zincZnoxygenO), which is a semiconductor, and used in the construction of varistors.Zirconia, which in pure form undergoes many phase (matter)phase changes between room temperature and practical sintering temperatures, can be chemically "stabilized" in several different forms. Its high oxygen ion conductivity recommends it for use in fuel cells. In another variant, metastable structures can impart transformation toughened ceramicstransformation toughening for mechanical applications; most ceramic knife blades are made of this material.
Properties of ceramics -
Mechanical properties - Ceramic materials are usually ionic bondionic or covalently-bonded materials, and can be crystalline or amorphous solidamorphous. A material held together by either type of bond will tend to Fracture#Brittle fracturefracture before any plastic deformation takes place, which results in poor toughness in these materials. Additionally, because these materials tend to be porous, the pores and other microscopic imperfections act as Stress concentrationstress concentrators, decreasing the toughness further, and reducing the tensile strength. These combine to give catastrophic failures, as opposed to the normally much more gentle failure modes of metals.These materials do show plasticity (physics)plastic deformation. However, due to the rigid structure of the crystalline materials, there are very few available slip systems for dislocations to move, and so they deform very slowly. With the non-crystalline (glassy) materials, Viscosityviscous flow is the dominant source of plastic deformation, and is also very slow. It is therefore neglected in many applications of ceramic materials.
Electrical properties -
Semiconductivity - There are a number of ceramics that are semiconductors. Most of these are transition metal oxides that are II-VI semiconductors, such as zinc oxide.Whilst there is talk of making blue LEDs from zinc oxide, ceramicists are most interested in the electrical properties that show grain boundary effects.One of the most widely used of these is the varistor. These are devices that exhibit the unusual property of negative resistance. Once the voltage across the device reaches a certain threshold, there is a Electrical breakdownbreakdown of the electrical structure in the vicinity of the grain boundarygrain boundaries, which results in its electrical resistance dropping from several megaohms down to a few hundred ohms. The major advantage of these is that they can dissipate a lot of energy, and they self reset — after the voltage across the device drops below the threshold, its resistance returns to being high. This makes them ideal for Surge protectorsurge-protection applications. As there is control over the threshold voltage and energy tolerance, they find use in all sorts of applications. The best demonstration of their ability can be found in electrical substations, where they are employed to protect the infrastructure from lightning strikes. They have rapid response, are low maintenance, and do not appreciably degrade from use, making them virtually ideal devices for this application.Semiconducting ceramics are also employed as gas sensors. When various gases are passed over a polycrystalline ceramic, its electrical resistance changes. With tuning to the possible gas mixtures, very inexpensive devices can be produced.
Superconductivity - Under some conditions, such as extremely low temperature, some ceramics exhibit superconductivity. The exact reason for this is not known, but there are two major families of superconducting ceramics.
Ferroelectricity and subsets - Piezoelectricity, a link between electrical and mechanical response, is exhibited by a large number of ceramic materials, including the quartz resonators used as to crystal oscillatormeasure time watches and other electronics. Such devices use both properties of piezoelectrics, using electricity to produce a mechanical motion (powering the device) and then using this mechanical motion to produce electricity (generating a signal). The unit of time measured is the natural interval required for electricity to be converted into mechanical energy and back again.The piezoelectric effect is generally stronger in materials that also exhibit pyroelectricity, and all pyroelectric materials are also piezoelectric. These materials can be used to interconvert between thermal, mechanical, and/or electrical energy; for instance, after synthesis in a furnace, a pyroelectric crystal allowed to cool under no applied stress generally builds up a static charge of thousands of volts. Such materials are used in motion sensors, where the tiny rise in temperature from a warm body entering the room is enough to produce a measurable voltage in the crystal.In turn, pyroelectricity is seen most strongly in materials which also display the ferroelectric effect, in which a stable electric dipole can be oriented or reversed by applying an electrostatic field. Pyroelectricity is also a necessary consequence of ferroelectricity. This can be used to store information in ferroelectric capacitors, elements of ferroelectric RAM.The most common such materials are lead zirconate titanate and barium titanate. Aside from the uses mentioned above, their strong piezoelectric response is exploited in the design of high-frequency loudspeakers, transducers for sonar, and actuators for atomic force microscopeatomic force and scanning tunneling microscopes.
Positive thermal coefficient - Increases in temperature can cause crystallitegrain boundaries to suddenly become insulating in some semiconducting ceramic materials, mostly mixtures of heavy metalsheavy metal titanates. The critical transition temperature can be adjusted over a wide range by variations in chemistry. In such materials, current will pass through the material until joule heating brings it to the transition temperature, at which point the circuit will be broken and current flow will cease. Such ceramics are used as self-controlled heating elements in, for example, the rear-window defrost circuits of most automobiles.At the transition temperature, the material's dielectric response becomes theoretically infinite. While a lack of temperature control would rule out any practical use of the material near its critical temperature, the dielectric effect remains exceptionally strong even at much higher temperatures. Titanates with critical temperatures far below room temperature have become synonymous with "ceramic" in the context of ceramic capacitors for just this reason.
Processing of ceramic materials - Non-crystalline ceramics, being glasses, 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 to a mould. If later heat-treatments cause this class to become partly crystalline, the resulting material is known as a glass-ceramic.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. A few methods use a hybrid between the two approaches.
In situ manufacturing - The most common use of this method is in the production of cement and concrete. Here, the dehydrated powders are mixed with water. This starts hydration reactions, which result in long, interlocking crystals forming around the aggregates. Over time, these result in a solid ceramic.The biggest problem with this method is that most reactions are so fast that good mixing is not possible, which tends to prevent large-scale construction. However, small-scale systems can be made by deposition techniques, where the various materials are introduced above a substrate, and react and form the ceramic on the substrate. This borrows techniques from the semiconductor industry, such as Chemical vapor depositionchemical vapour deposition, and is very useful for coatings.These tend to produce very dense ceramics, but do so slowly.
Sintering-based methods - The principles of sintering-based methods is simple. Once a roughly held together object (called a "green body") is made, it is baked in a kiln, where diffusion processes cause the green body to shrink. The pores in the object close up, resulting in a denser, stronger product. The firing is done at a temperature below the melting point of the ceramic. There is virtually always some porosity left, but the real advantage of this method is that the green body can be produced in any way imaginable, and still be sintered. This makes it a very versatile route. There are thousands of possible refinements of this process. Some of the most common involve pressing the green body to give the densification a head start and reduce the sintering time needed. Sometimes organic binder (material)binders such as polyvinyl alcohol are added to hold the green body together; these burn out during the firing (at 200-350°C). Sometimes organic lubricants are added during pressing to increase densification. It is not uncommon to combine these, and add binders and lubricants to a powder, then press. (The formulation of these organic chemical additives is an art in itself. This is particularly important in the manufacture of high performance ceramics such as those used by the billions for electronics, in capacitors, inductors, sensors, etc. The specialized formulations most commonly used in electronics are detailed in the book "Tape Casting," by R.E. Mistler, et al., Amer. Ceramic Soc. Westerville, - Ohio, 2000.) A comprehensive book on the subject, for mechanical as well as electronics applications, is "Organic Additives and Ceramic Processing," by D. J. Shanefield, Kluwer Publishers Boston, 1996.A slurry can be used in place of a powder, and then cast into a desired shape, dried and then sintered. Indeed, traditional pottery is done with this type of method, using a plastic mixture worked with the hands.If a mixture of different materials is used together in a ceramic, the sintering temperature is sometimes above the melting point of one minor component - a ''liquid phase'' sintering. This results in shorter sintering times compared to solid state sintering.
Other applications of ceramics - A couple of decades ago, Toyota researched production of an adiabatic ceramic engine which can run at a temperature of over 6000 °F (3300 °C). Ceramic engines do not require a cooling system and hence allow a major weight reduction and therefore greater fuel efficiency. Fuel efficiency of the engine is also higher at high temperature.In a conventional metallic engine, much of the energy released from the fuel must be dissipated as waste heat in order to prevent a meltdown of the metallic parts.Despite all of these desirable properties, such engines are not in production because the manufacturing of ceramic parts in the requisite precision and durability is difficult. Imperfection in the ceramic leads to cracks, which can lead to potentially dangerous equipment failure. Such engines are possible in laboratory settings, but mass-production is infeasible with current technology.Work is being done in developing ceramic parts for gas turbine heat engineengines. Currently, even blades made of superalloyadvanced 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.Since the late 1990s highly specialized ceramics, usually based on boron carbide, formed into plates and lined with DyneemaSpectra, have been used in bulletproof vestballistic armored vests to repel large-caliber rifle fire. Such plates are known commonly as small-arms protective inserts (SAPI). Very similar technology is used for armoring of cockpits of some military airplanes, because of the low weight of the material.Recently, there have been advances in ceramics which include bio-ceramics, such as dental implants and synthetic bones. Hydroxyapatite, the natural mineral componet of bone, has been made synthetically from a number of biological and chemical sources and can be formed into ceramic materials. Orthopedic implants made from these materials bond ready to bone and other tissues in the body without rejection or inflammatory reactions. Because of this, they 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 absorbtion of these plastic materials. Work is being done to make strong-fully dense nano crystalline Hydroxapatite ceramic materials for orthopedic weight bearing devices, replacing foreign metal and plastic orthopedic materials with a synthetic natural bone mineral. Ultimately these ceramic materials may be used as bone replacements or with the incorperation of protein collagens, synthetic bones.Wiktionary
See also - Ceramic forming techniques
External links - azom.com - Advanced Ceramics – The Evolution, Classification, Properties, Production, Firing, Finishing and Design of Advanced Ceramics !Category:MaterialsCategory:Pot teryCategory:Ceramicsbg:К ;ерам& #1080;каca:Ceràmi cacs:Keramicada:Keramikde:Kera mikel:Κεραμικά? !Υλικάes:Cerámicafr:Céra miqueja:セラӣ 1;ックスms:S eramiknl:Keramiekno:Keramikkru :Кера& #1084;икаpl: Ceramikapt:Cerâmicasv:Keramik th:เซรามิกzh: 8518;瓷he:קר מיקה DEBUG REDIRECT (ceramics)
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Luxury goods for the table
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European Tile Specialists
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The Ceramic Art of Regina Heinz
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Eda Easton - Sculptures and Paintings
Sculpture, paintings and drawings by the American artist Eda Easton. Her classical European education is reflected in the figurative nature of much of her work and in the style of her abstract pieces.
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Linda Agar-Hendrix
Columbine Beads represents the work of American artist, Linda Agar-Hendrix whose work has progressed from hand-woven textiles to raku beads and associated jewelry to ceramic sculpture. Her floral imagery has remained a constant with her recent sculptural pieces focusing on the idea of growth and discovery. The use of low-fire glazes on red clay gives added dimension and texture to her pieces, while white porcelain series illustrates crisp line and smooth surfaces.
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Iznik Classics
Iznik ceramics reached their zenith in the 16th century. The technique used to make the Iznik ceramics was lost to mankind for over one hundred years. After many years of research and experiments, some of these masters have been successful in reproducing the ceramics and ceramics of past ages which are an important part of the Turkish cultural heritage. It is our aim to provide the continuity of this art form and share its beauty with all people today.
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Gifts From A Distance
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American Ceramic Society's Web Site
ACerS, an international association that provides the latest technical, scientific and educational information to its Members and others in the ceramics and related materials field, structures its services, staff and capabilities to meet the needs of the ceramics community, related fields, and the general public.
http://www.acers.org/
Ceramic Bulletin
Magazine covering ceramic technology, engineering and manufacturing. Includes selections from the current print issue and breaking news.
http://www.ceramicbulletin.org/
Ceramic Industry
Site offers news and research articles to the ceramic industry, updated monthly.
http://www.ceramicindustry.com/
Journal of the Americam Society
Journal concerning ceramic materials.
http://www.ceramicjournal.org/
Korff Ceramic Originals
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