What is a Ceramic ? Ceramics are classified as inorganic and nonmetallic materials that are essential to our daily lifestyle. Ceramic and materials engineers are the people who design the processes in which these products can be made, create new types of ceramic products, and find different uses for ceramic products in everyday life. Ceramics are all around us. This category of materials includes things like tile, bricks, plates, glass, and toilets. Ceramics can be found in products like watches (quartz tuning forks-the time keeping devices in watches), snow skies (piezoelectric-ceramics that stress when a voltage is applied to them), automobiles (sparkplugs and ceramic engine parts found in racecars), and phone lines. They can also be found on space shuttles, appliances (enamel coatings), and airplanes (nose cones). Depending on their method of formation, ceramics can be dense or lightweight. Typically, they will demonstrate excellent strength and hardness properties; however, they are often brittle in nature. Ceramics can also be formed to serve as electrically conductive materials, objects allowing electricity to pass through their mass, or insulators, materials preventing the flow of electricity.

Some ceramics, like superconductors, also display magnetic properties. Ceramics are generally made by taking mixtures of clay, earthen elements, powders, and water and shaping them into desired forms. Once the ceramic has been shaped, it is fired in a high temperature oven known as a kiln. Often, ceramics are covered in decorative, waterproof, paint-like substances known as glazes. What are Ceramic Materials and Their Uses? What are Ceramic Materials and Their Uses? written by: Senadheera Jayakody • edited by: Lamar Stonecypher • updated: 11/21/2009 Ceramics are typically hard and chemically stable materials with valuable applications. Traditional and advanced are the main types of ceramics, and the advanced ceramics industry is a rapidly growing industry with important functional applications. slide 1 of 7 Introduction to Ceramics Ceramics are special materials with many applications in almost all the engineering disciplines. But their importance has often been underestimated due to the fact that many people believe that ceramics are all about pottery and tiles. Today's ceramics industry is one of most rapidly advancing concerns in many parts of the world including USA, where the advanced ceramic market is over 13 billion US dollars.

Ceramic industry began to expand as a modern industry with the attribution of new techniques and knowledge gained in the 1970s. Since then it has also been one of most competitive industries in the market. slide 2 of 7 Ceramic Materials Ceramic materials are special because of their properties. They typically possess high melting points, low electrical and thermal conductivity values, and high compressive strengths. Also they are generally hard and brittle with very good chemical and thermal stability. Ceramic materials can be categorized as traditional ceramics and advanced ceramics. Ceramic materials like clay are categorized as traditional ceramics and normally they are made of clay, silica, and feldspar. As its name suggests, traditional ceramics are not supposed to meet rigid specific properties after their production, so cheap technologies are utilized for most of the production processes. slide 3 of 7 Traditional Ceramics Ball clay, China clay, Feldspar, Silica, Dolomite, Talc, Calcite and Nepheline are the common materials used for most of the ceramic products. Each raw material contributes a certain property such as dry strength, plasticity, shrinkage, etc. to the ceramic body. Therefore, by careful selection of materials, desired properties are acquired for the final output.

Powder preparation is a major consideration in the ceramic industry. Surface area, particle size and distribution, particle shape, density, etc. each have their own effect on production. Powder has to be prepared to meet required particle size, particle shape, and other requirements for a particular industry. Milling is done to get the desired particle size. Unlike in the ,advanced ceramics industry the purity of ceramic powder is not an issue in traditional ceramics. The traditional ceramics industry originated long ago. Even thousands of years ago it was a well established practice in many parts of the world. Today there are many divisions of this industry. Pottery, tableware, sanitaryware, tiles, structural clay products, refractories, blocks, and electrical porcelain are some of the products of traditional ceramics. slide 4 of 7 Advanced Ceramics Advanced ceramics are special type of ceramics used mainly for electrical, electronic, optical, and magnetic applications. This sector is different from traditional ceramics due to the fact that ceramic powder preparation is quite important. Advanced production techniques are employed to assure that the produced ceramic powders possess sufficient purity.

Generally chemical reactions are used to produce the ceramic powder such as Sol-gel processing and liquid-gas reactions like NH3 gas and SiCl4 liquid to produce Si3N4. Many of these methods are very costly. Therefore, powder preparation is always a cost factor in the advanced ceramics industry. slide 5 of 7 Applications of Advanced Ceramics In electronic and electrical industries advanced ceramic materials like Barium Titanate (BaTiO3), piezoelectric materials and semiconductor materials are heavily used for producing ceramic capacitors, vibratos, temperature sensors, oscillators, etc. Ceramics used for this type of applications are called functional ceramics. Specific properties of advanced ceramic materials are utilized for their industrial applications. Ferroelectricity is such property in materials like Lead Zirconate Titanate, Lead Titanate, Barium Titanate, etc. Ferroelectric materials have two properties. One is there should be a spontaneous polarization and the other is the polarization should be able to reorient. This property is used to produce applications like sensors, pumps, sonar, microphones, etc. slide 6 of 7 There are a number of other applications that are found in the other areas too.

Magnetic ceramics are another type of advanced ceramic material that is used for the production of antennas and inductors. Bioceramics like Alumina with high density and purity is used to dental implants. Eye glasses, chemical ware, and the replacement of hips and knees, etc. are some of the applications of bioceramic materials. slide 7 of 7 Although traditional ceramics have been in use in ancient civilizations, advanced ceramics is a recently developed field. But they have some extremely important functions and have already shown a rapid growth. Both of these ceramic materials posses significant importance for the industry and it can be expected that the best is yet to come especially in the field of advanced ceramics. ◄ ● ● ● ● ● ● ● ► How ceramic tile is made - material, manufacture, making, used, processing, dimensions, composition, steps Ceramic Tile Background Wall and floor tile used for interior and exterior decoration belongs to a class of ceramics known as whitewares. The production of tile dates back to ancient times and peoples, including the Egyptians, the Babylonians, and the Assyrians. For instance, the Step Pyramid for the Pharoah Djoser, built in ancient Egypt around 2600 B.C. , contained colorful glazed tile.

Later, ceramic tile was manufactured in virtually every major European country and in the United States. By the beginning of the twentieth century, tile was manufactured on an industrial scale. The invention of the tunnel kiln around 1910 increased the automation of tile manufacture. Today, tile manufacture is highly automated. The American National Standards Institute separates tiles into several classifications. Ceramic mosaic tile may be either porcelain or of natural clay composition of size less than 39 cm2 (6 in.2). Decorative wall tile is glazed tile with a thin body used for interior decoration of residential walls. Paver tile is glazed or unglazed porcelain or natural clay tile of size 39 cm2 (6 in.2) or more. Porcelain tile is ceramic mosaic tile or paver tile that is made by a certain method called dry pressing. Quarry tile is glazed or unglazed tile of the same size as paver tile, but made by a different forming method. Europe, Latin America, and the Far East are the largest producers of tile, with Italy the leader at 16.6 million ft.2/day as of 1989.

Following Italy (at 24.6 percent of the world market) are Spain (12.6 percent), Brazil and Germany (both at 11.2 percent), and the United States (4.5 percent). The total market for floor and wall tile in 1990 according to one estimate was $2.4 billion. The United States has approximately 100 plants that manufacture ceramic tile, which shipped about 507 million ft.2 in 1990 according to the U.S. Department of Commerce. U.S. imports, by volume, accounted for approximately 60 percent of consumption in 1990, valued at around $500 million. Italy accounts for almost half of all imports, with Mexico and Spain following. U.S. exports have seen some growth, from $12 million in 1988 to about $20 million in 1990. Because the tile industry is a relatively mature market and dependent on the building industry, growth will be slow. The United States Department of Commerce estimates a three to four percent increase in tile consumption over the next five years.

Another economic analysis predicts that 494 million ft.2 will be shipped in 1992, a growth of about 4 percent from the previous year. Some tile manufacturers are a bit more optimistic; an American Ceramic Society survey showed an average growth of around 36 percent per manufacturer over the next five years. Raw Materials The raw materials used to form tile consist of clay minerals mined from the earth's crust, natural minerals such as feldspar that are used to lower the firing temperature, and chemical additives required for the shaping process. The minerals are often refined or beneficiated near the mine before shipment to the ceramic plant. The raw materials must be pulverized and classified according to particle size. Primary crushers are used to reduce large lumps of material. Either a jaw crusher or gyratory crusher is used, which operate using a horizontal The initial step in ceramic tile manufacture involves mixing the ingredients. Sometimes, water is then added and the ingredients are wet milled or ground in a ball mill. If wet milling is used, the excess water is removed using filter pressing followed by spray drying. The resulting powder is then pressed into the desired tile body shape. squeezing motion between steel plates or rotating motion between steel cones, respectively.

Secondary crushing reduces smaller lumps to particles. Hammer or muller mills are often used. A muller mill uses steel wheels in a shallow rotating pan, while a hammer mill uses rapidly moving steel hammers to crush the material. Roller or cone type crushers can also be used. A third particle size reduction step may be necessary. Tumbling types of mills are used in combination with grinding media. One of the most common types of such mills is the ball mill, which consists of large rotating cylinders partially filled with spherical grinding media. Screens are used to separate out particles in a specific size range. They operate in a sloped position and are vibrated mechanically or electromechanically to improve material flow. Screens are classified according to mesh number, which is the number of openings per lineal inch of screen surface. The higher the mesh number, the smaller the opening size. A glaze is a glass material designed to melt onto the surface of the tile during firing, and which then adheres to the tile surface during cooling. Glazes are used to provide moisture resistance and decoration, as they can be colored or can produce special textures. The Manufacturing Process Once the raw materials are processed, a number of steps take place to obtain the finished product.

These steps include batching, mixing and grinding, spray-drying, forming, drying, glazing, and firing. Many of these steps are now accomplished using automated equipment. Batching 1 For many ceramic products, including tile, the body composition is determined by the amount and type of raw materials. The raw materials also determine the color of the tile body, which can be red or white in color, depending on the amount of iron-containing raw materials used. Therefore, it is important to mix the right amounts together to achieve the desired properties. Batch calculations are thus required, which must take into consideration both physical properties and chemical compositions of the raw materials. Once the appropriate weight of each raw material is determined, the raw materials must be mixed together. Mixing and grinding 2 Once the ingredients are weighed, they are added together into a shell mixer, ribbon mixer, or intensive mixer. A shell mixer consists of two cylinders joined into a V, which rotates to tumble and mix the material. A ribbon mixer uses helical vanes, and an intensive mixer uses rapidly revolving plows. This step further grinds the ingredients, resulting in a finer particle size that improves the subsequent forming process (see step #4 below).

Sometimes it is necessary to add water to improve the mixing of a multiple-ingredient batch as well as to achieve fine grinding. This process is called wet milling and is often performed using a ball mill. The resulting water-filled mixture is called a slurry or slip. The water is then removed from the slurry by filter pressing (which removes 40-50 percent of the moisture), followed by dry milling. Spray drying 3 If wet milling is first used, the excess water is usually removed via spray drying. This involves pumping the slurry to an atomizer consisting of a rapidly rotating disk or nozzle. Droplets of the slip are dried as they are heated by a rising hot air column, forming small, free flowing granules that result in a powder suitable for forming. Tile bodies can also be prepared by dry grinding followed by granulation. Granulation uses a machine in which the mixture of previously dry-ground material is mixed with water in order to form the particles into granules, which again form a powder ready for forming. Forming 4 Most tile is formed by dry pressing. In this method, the free flowing powder—containing organic binder or a low percentage of moisture—flows from a hopper into the forming die.

The material is compressed in a steel cavity by steel plungers and is then ejected by the bottom plunger. Automated presses are used with operating pressures as high as 2,500 tons. Several other methods are also used where the tile body is in a wetter, more moldable form. Extrusion plus punching is used to produce irregularly shaped tile and thinner tile faster and more economically. This involves compacting a plastic mass in a high-pressure cylinder and forcing the material to flow out of the cylinder into short slugs. These slugs are then punched into one or more tiles using hydraulic or pneumatic punching presses. Ram pressing is often used for heavily profiled tiles. With this method, extruded slugs of the tile body are pressed between two halves of a hard or porous mold mounted in a hydraulic press. The formed part is removed by first applying vacuum to the top half of the mold to free the part from the bottom half, followed by forcing air through the top half to free the top part. Excess material must be removed from the part and additional finishing may be needed. Another process, called pressure glazing, has recently been developed.

This process combines glazing and shaping simultaneously by pressing the glaze (in spray-dried powder form) directly in the die filled with the tile body powder. Advantages include the elimination of glazing lines, as well as the glazing waste material (called sludge) that is produced with the conventional method. Drying 5 Ceramic tile usually must be dried (at high relative humidity) after forming, especially if a wet method is used. Drying, which can take several days, removes the water at a slow enough rate to prevent shrinkage cracks. Continuous or tunnel driers are used that are heated using gas or oil, infrared lamps, or microwave energy. Infrared drying is better suited for thin tile, whereas microwave drying works better for thicker tile. Another method, impulse drying, uses pulses of hot air flowing in the transverse direction instead of continuously in the material flow direction. Glazing 6 To prepare the glaze, similar methods are used as for the tile body. After a batch formulation is calculated, the raw materials are weighed, mixed and dry or wet milled. The milled glazes are then applied using one of the many methods available.

In centrifugal glazing or discing, the glaze is fed through a rotating disc that flings or throws the glaze onto the tile. In the bell/waterfall method, a stream of glaze falls onto the tile as it passes on a conveyor underneath. Sometimes, the glaze is simply sprayed on. For multiple glaze applications, screen printing on, under, or between tile that have been wet glazed is used. In this process, glaze is forced through a screen by a rubber squeegee or other device. Dry glazing is also being used. This involves the application of powders, crushed frits (glass materials), and granulated glazes onto a wet-glazed tile surface. After firing, the glaze particles melt into each other to produce a surface like granite. Firing 7 After glazing, the tile must be heated intensely to strengthen it and give it the desired porosity. Two types of ovens, or After forming, the file is dried slowly (for several days) and at high humidity, to prevent cracking and shrinkage. Next, the glaze is applied, and then the tile is fired in a furnace or kiln.

Although some types of tile require a two-step firing process, wet-milled tile is fired only once, at temperatures of 2,000 degrees Fahrenheit or more. After firing, the tile is packaged and shipped. kilns, are used for firing tile. Wall tile, or tile that is prepared by dry grinding instead of wet milling (see #2 and #3 above), usually requires a two-step process. In this process, the tile goes through a low-temperature firing called bisque firing before glazing. This step removes the volatiles from the material and most or all of the shrinkage. The body and glaze are then fired together in a process called glost firing. Both firing processes take place in a tunnel or continuous kiln, which consists of a chamber through which the ware is slowly moved on a conveyor on refractory batts—shelves built of materials that are resistant to high temperatures—or in containers called saggers. Firing in a tunnel kiln can take two to three days, with firing temperatures around 2,372 degrees Fahrenheit (1,300 degrees Celsius). For tile that only requires a single firing—usually tile that is prepared by wet milling—roller kilns are generally used.

These kilns move the wares on a roller conveyor and do not require kiln furnitures such as batts or saggers. Firing times in roller kilns can be as low as 60 minutes, with firing temperatures around 2,102 degrees Fahrenheit (1,150 degrees Celsius) or more. 8 After firing and testing, the tile is ready to be packaged and shipped. Byproducts A variety of pollutants are generated during the various manufacturing steps; these emissions must be controlled to meet air control standards. Among the pollutants produced in tile manufacture are fluorine and lead compounds, which are produced during firing and glazing. Lead compounds have been significantly reduced with the recent development of no-lead or low-lead glazes. Fluorine emissions can be controlled with scrubbers, devices that basically spray the gases with water to remove harmful pollutants. They can also be controlled with dry processes, such as fabric filters coated with lime. This lime can then be recycled as a raw material for future tile. The tile industry is also developing processes to recycle wastewater and sludge produced during milling, glazing, and spray-drying.

Already some plants recycle the excess powder generated during dry-pressing as well as the overspray produced during glazing. Waste glaze and rejected tile are also returned to the body preparation process for reuse. Quality Control Most tile manufacturers now use statistical process control (SPC) for each step of the manufacturing process. Many also work closely with their raw material suppliers to ensure that specifications are met before the material is used. Statistical process control consists of charts that are used to monitor various processing parameters, such as particle size, milling time, drying temperature and time, compaction pressure, dimensions after pressing, density, firing temperature and time, and the like. These charts identify problems with equipment, out of spec conditions, and help to improve yields before the final product is finished. The final product must meet certain specifications regarding physical and chemical properties. These properties are determined by standard tests established by the American Society of Testing and Materials (ASTM). Properties measured include mechanical strength, abrasion resistance, chemical resistance, water absorption, dimensional stability, frost resistance, and linear coefficient of thermal expansion. More recently, the slip resistance, which can be determined by measuring the coefficient of friction, has become a concern.

However, no standard has yet been established because other factors (such as proper floor design and care) can make results meaningless. The Future In order to maintain market growth, tile manufacturers will concentrate on developing and promoting new tile products, including modular or cladding tile, larger-sized tile, slip- and abrasion-resistant tile, and tile with a polished, granite or marble finish. This is being accomplished through the development of different body formulations, new glazes, and glaze applications, and by new and improved processing equipment and techniques. Automation will continue to play an important role in an effort to increase production, lower costs, and improve quality. In addition, changes in production technology due to environmental and energy resource issues will continue. Where To Learn More Books Bender, W. and F. Handle, eds. Brick and Tile Making: Procedures and Operating Practices in the Heavy Clay Industries. Bauverlag GmbH, 1982. Jones, J. T. and M. F. Berard. Ceramics: Industrial Processing and Testing. Iowa State University Press, 1972. Pellacani, G. and T. Manfredini. Engineered Materials Handbook. ASM International, 1991, pp.

925-929. Periodicals Burzacchini, B. "Technical Developments in Ceramic Tile Glazes and Related Applications," American Ceramic Society Bulletin. March, 1991, pp. 394-403. Fugmann, K. "Rapid Changes in Tile Technology," Tile & Brick International. March, 1991, pp. 165-166. Gehringer, George. "Tile Glossary: A Guide to Techniques and Surface Designs," American Ceramic Society Bulletin. December, 1990, pp. 1950-1952. Geiger, Greg. "Developments in the Tile Industry," American Ceramic Society Bulletin. December, 1991, pp. 1879-1885. — L. S. Millberg How porcelain is made - material, making, used, processing, parts, components, composition, steps Porcelain Background The term porcelain refers to a wide range of ceramic products that have been baked at high temperatures to achieve vitreous, or glassy, qualities such as translucence and low porosity.

Among the most familiar porcelain goods are table and decorative china, chemical ware, dental crowns, and electrical insulators. Usually white or off-white, porcelain comes in both glazed and unglazed varieties, with bisque, fired at a high temperature, representing the most popular unglazed variety. Although porcelain is frequently used as a synonym for china, the two are not identical. They resemble one another in that both are vitreous wares of extremely low porosity, and both can be glazed or unglazed. However, china, also known as soft-paste or tender porcelain, is softer: it can be cut with a file, while porcelain cannot. This difference is due to the higher temperatures at which true porcelain is fired, 2,650 degrees Fahrenheit (1,454 degrees Celsius) compared to 2,200 degrees Fahrenheit (1,204 degrees Celsius) for china. Due to its greater hardness, porcelain has some medical and industrial applications which china, limited to domestic and artistic use, does not. Moreover, whereas porcelain is always translucent, china is opaque.

Hard-paste or "true" porcelain originated in China during the T'ang dynasty (618-907 A.D.); however, high quality porcelain comparable to modern wares did not develop until the Yuan dynasty (1279-1368 A.D.). Early Chinese porcelain consisted of kaolin (china clay) and pegmatite, a coarse type of granite. Porcelain was unknown to European potters prior to the importation of Chinese wares during the Middle Ages. Europeans tried to duplicate Chinese porcelain, but, unable to analyze its chemical composition, they could imitate only its appearance. After mixing glass with tin oxide to render it opaque, European craftspeople tried combining clay and ground glass. These alternatives became known as soft-paste, glassy, or artificial porcelains. However, because they were softer than genuine porcelain, as well as expensive to produce, efforts to develop true porcelain continued. In 1707 two Germans named Ehrenfried Walter von Tschimhaus and Johann Friedrich Bottger succeeded by combining clay with ground feldspar instead of the ground glass previously used.

Later in the eighteenth century the English further improved upon the recipe for porcelain when they invented bone china by adding ash from cattle bones to clay, feldspar, and quartz. Although bone china is fired at lower temperatures than true porcelain, the bone ash enables it to become translucent nonetheless. Because it is also easier to make, harder to chip, and stronger than hard porcelain, bone china has become the most popular type of porcelain in the United States and Britain (European consumers continue to favor hard porcelain). Raw Materials The primary components of porcelain are clays, feldspar or flint, and silica, all characterized by small particle size. To create different types of porcelain, craftspeople combine these raw materials in varying proportions until they obtain the desired green (unfired) and fired properties. Although the composition of clay varies depending upon where it is extracted and how it To make porcelain, the raw materials—such as clay, felspar, and silica—are first crushed using jaw crushers, hammer mills, and ball mills. After cleaning to remove improperly sized materials, the mixture is subjected to one of four forming processes—soft plastic forming, stiff plastic forming, pressing, or casting—depending on the type of ware being produced.

The ware then undergoes a preliminary firing step, bisque-firing. is treated, all clays vitrify (develop glassy qualities), only at extremely high temperatures unless they are mixed with materials whose vitrification threshold is lower. Unlike glass, however, clay is refractory, meaning that it holds its shape when it is heated. In effect, porcelain combines glass's low porosity with clay's ability to retain its shape when heated, making it both easy to form and ideal for domestic use. The principal clays used to make porcelain are china clay and ball clay, which consist mostly of kaolinate, a hydrous aluminum silicate. Feldspar, a mineral comprising mostly aluminum silicate, and flint, a type of hard quartz, function as fluxes in the porcelain body or mixture. Fluxes reduce the temperature at which liquid glass forms during firing to between 1,835 and 2,375 degrees Fahrenheit (1,000 and 1,300 degrees Celsius). This liquid phase binds the grains of the body together. Silica is a compound of oxygen and silicon, the two most abundant elements in the earth's crust.

Its resemblance to glass is visible in quartz (its crystalline form), opal (its amorphous form), and sand (its impure form). Silica is the most common filler used to facilitate forming and firing of the body, as well as to improve the properties of the finished product. Porcelain may also contain alumina, a compound of aluminum and oxygen, or low-alkali containing bodies, such as steatite, better known as soapstone. The Manufacturing Process After the raw materials are selected and the desired amounts weighed, they go through a series of preparation steps. First, they are crushed and purified. Next, they are mixed together before being subjected to one of four forming processes—soft plastic forming, stiff plastic forming, pressing, or casting; the choice depends upon the type of ware being produced. After the porcelain has been formed, it is subjected to a final purification process, bisque-firing, before being glazed. Glaze is a layer of decorative glass applied to and fired onto a ceramic body. The final manufacturing phase is firing, a heating step that takes place in a type of oven called a kiln.

Crushing the raw materials 1 First, the raw material particles are reduced to the desired size, which involves using a variety of equipment during several crushing and grinding steps. Primary crushing is done in jaw crushers which use swinging metal jaws. Secondary crushing reduces particles to 0.1 inch (.25 centimeter) or less in diameter by using mullers (steel-tired wheels) or hammer mills, rapidly moving steel hammers. For fine grinding, craftspeople use ball mills that consist of large rotating cylinders partially filled with steel or ceramic grinding media of spherical shape. Cleaning and mixing 2 The ingredients are passed through a series of screens to remove any under- or over-sized materials. Screens, usually operated in a sloped position, are vibrated mechanically or electromechanically to improve flow. If the body is to be formed wet, the ingredients are then combined with water to produce the desired consistency. Magnetic filtration is then used to remove iron from the slurries, as these watery mixtures of insoluble material are called. Because iron occurs so pervasively in most clays and will impart After bisque firing, the porcelain wares are put through a glazing operation, which applies the proper coating.

The glaze can be applied by painting, dipping, pouring, or spraying. Finally, the ware undergoes a firing step in an oven or kiln. After cooling, the porcelain ware is complete. an undesirable reddish hue to the body if it oxidizes, removing it prior to firing is essential. If the body is to be formed dry, shell mixers, ribbon mixers, or intensive mixers are typically used. Forming the body 3 Next, the body of the porcelain is formed. This can be done using one of four methods, depending on the type of ware being produced: soft plastic forming, where the clay is shaped by manual molding, wheel throwing, jiggering, or ram pressing. In wheel throwing, a potter places the desired amount of body on a wheel and shapes it while the wheel turns. In jiggering, the clay is put on a horizontal plaster mold of the desired shape; that mold shapes one side of the clay, while a heated die is brought down from above to shape the other side. In ram pressing, the clay is put between two plaster molds, which shape it while forcing the water out.

The mold is then separated by applying vacuum to the upper half of the mold and pressure to the lower half of the mold. Pressure is then applied to the upper half to free the formed body. stiff plastic forming, which is used to shape less plastic bodies. The body is forced through a steel die to produce a column of uniform girth. This is either cut into the desired length or used as a blank for other forming operations. pressing, which is used to compact and shape dry bodies in a rigid die or flexible mold. There are several types of pressing, based on the direction of pressure. Uniaxial pressing describes the process of applying pressure from only one direction, whereas isostatic pressing entails applying pressure equally from all sides. slip casting, in which a slurry is poured into a porous mold. The liquid is filtered out through the mold, leaving a layer of solid porcelain body. Water continues to drain out of the cast layer, until the layer becomes rigid and can be removed from the mold. If the excess fluid is not drained from the mold and the entire material is allowed to solidify, the process is known as solid casting.

Bisque-firing 4 After being formed, the porcelain parts are generally bisque-fired, which entails heating them at a relatively low temperature to vaporize volatile contaminants and minimize shrinkage during firing. Glazing 5 After the raw materials for the glaze have been ground they are mixed with water. Like the body slurry, the glaze slurry is screened and passed through magnetic filters to remove contaminants. It is then applied to the ware by means of painting, pouring, dipping, or spraying. Different types of glazes can be produced by varying the proportions of the constituent ingredients, such as alumina, silica, and calcia. For example, increasing the alumina and decreasing the silica produces a matte glaze. Firing 6 Firing is a further heating step that can be done in one of two types of oven, or kiln. A periodic kiln consists of a single, refractory-lined, sealed chamber with burner ports and flues (or electric heating elements). It can fire only one batch of ware at a time, but it is more flexible since the firing cycle can be adjusted for each product. A tunnel kiln is a refractory chamber several hundred feet or more in length.

It maintains certain temperature zones continuously, with the ware being pushed from one zone to another. Typically, the ware will enter a preheating zone and move through a central firing zone before leaving the kiln via a cooling zone. This type of kiln is usually more economical and energy efficient than a periodic kiln. 7 During the firing process, a variety of reactions take place. First, carbon-based impurities burn out, chemical water evolves (at 215 to 395 degrees Fahrenheit or 100 to 200 degrees Celsius), and carbonates and sulfates begin to decompose (at 755 to 1,295 degrees Fahrenheit or 400 to 700 degrees Celsius). Gases are produced that must escape from the ware. On further heating, some of the minerals break down into other phases, and the fluxes present (feldspar and flint) react with the decomposing minerals to form liquid glasses (at 1,295 to 2,015 degrees Fahrenheit or 700 to 1,100 degrees Celsius). These glass phases are necessary for shrinking and bonding the grains.

After the desired density is achieved (greater than 2,195 degrees Fahrenheit or 1,200 degrees Celsius), the ware is cooled, which causes the liquid glass to solidify, thereby forming a strong bond between the remaining crystalline grains. After cooling, the porcelain is complete. Quality Control The character of the raw materials is important in maintaining quality during the manufacturing process. The chemical composition, mineral phase, particle size distribution, and colloidal surface area affect the fired and unfired properties of the porcelain. With unfired body, the properties evaluated include viscosity, plasticity, shrinkage, and strength. With fired porcelain, strength, porosity, color, and thermal expansion are measured. Many of these properties are monitored and controlled during manufacturing using statistical methods. Both the raw materials and the process parameters (milling time and forming pressure, for example) can be adjusted to achieve desired quality. The Future High-quality porcelain art and dinnerware will continue to enhance the culture. Improvements in manufacturing will continue to increase both productivity and energy efficiency. For instance, a German kiln manufacturer has developed a prefabricated tunnel kiln for fast firing high-quality porcelain in less than 5 hours.

Firing is achieved by partly reducing atmosphere at a maximum firing temperature of 2,555 degrees Fahrenheit (1,400 degrees Celsius). The kiln uses high-velocity burners and an automatic control system, producing 23,000 pounds (11,500 kilograms) of porcelain in 24 hours. Manufacturers of porcelain products may also have to increase their recycling efforts, due to the increase in environmental regulations. Though unfired scrap is easily recycled, fired scrap poses a problem: mechanically strong and therefore hard to break down, it is usually dumped into landfills. However, preliminary research has shown that fired scrap can be reused after thermal quenching (where the scrap is reheated and then quickly cooled), which makes it weaker and easier to break down. The scrap can then be used as a raw material. Porcelain appears to be playing a more important role in technical applications. Recent patents have been issued to Japanese and American companies in the area of electrical insulators and dental prostheses. NGK Insulators, Ltd., a Japanese manufacturer, has developed high-strength porcelain for electrical insulators, whereas Murata Manufacturing Co. has developed low-temperature-sintering porcelain components for electronic applications.

Where To Learn More Books Campbell, James E. The Art and Architecture Information Guide Series, vol. 7: Pottery and Ceramics, A Guide to Infonnation Sources. Gale Research, 1978. Camusso, Lorenzo, ed. Ceramics of the World: From Four Thousand B.C. Ceramics - their properties, manufacture, and everyday uses Ceramics Tweet by Chris Woodford . Last updated: June 18, 2016. The major periods of civilization, such as the Stone Age and Bronze Age, were named for the materials that dominated them, and it may seem surprising that there has never been a "Ceramics Age." Yet almost any age might have qualified for this title. Archeologists have found evidence of primitive ceramic manufacture dating back to around 24,000 B.C.E., but those most modern of materials, the silicon chip and the catalytic converter , are also examples of ceramics. The modern era is as much a ceramics age as any other. Let's find out more about ceramics and how they work! Photo: A ceramic Percy Pig piggy bank.

It started life as a soft piece of clay molded to shape, fired hard in a pottery kiln, then painted with bright colors. What are ceramics? Photo: Porcelain plates are very familiar examples of ceramics, but there are other, much more surprising uses of ceramics too. Ceramics once referred purely to pottery and to articles made by firing materials extracted from Earth. Today, the term has a much broader definition. Ceramics are generally thought of as inorganic and nonmetallic solids with a range of useful properties, including very high hardness and strength, extremely high melting points, and good electrical and thermal insulation . The best-known ceramics are pottery, glass , brick , porcelain, and cement. But the general definition of a ceramic—a nonmetallic and inorganic solid—is so broad that it covers a much wider range of materials. At one end of the scale, ceramics include simple materials such as graphite and diamond, made up from different crystalline arrangements of the element carbon. But at the other end of the scale, complex crystals of yttrium, barium, copper , and oxygen make up the advanced ceramics used in so-called high-temperature superconductors (materials with almost no electrical resistance ). Most ceramics fall somewhere between these extremes.

Many are metal oxides, crystalline compounds of a metal element and oxygen. Others are silicides, borides, carbides, and nitrides, respectively made from silicon, boron, carbon, and nitrogen. Some of the most advanced ceramic materials are combinations of ceramics and other materials known as ceramic matrix composites (CMCs). Properties of ceramics Ceramics are best known as brittle solids particularly suited for withstanding high temperatures but, in fact, the different materials used in ceramics can give them a wide range of properties. The classic properties of ceramics include durability, strength and brittleness, high electrical and thermal resistance, and an ability to withstand the damaging effects of acids, oxygen, and other chemicals because of their inertness (chemical unreactivity). But not all ceramics behave in this way. For example, graphite is a very soft ceramic and conducts electricity well, whereas diamond is a very good conductor of heat . Ceramics called ferrites are particularly good conductors of electricity and superconductors have almost no electrical resistance at all. Ceramic matrix composites, made by embedding fibers of a strengthening material in what is known as a ceramic matrix, are not at all brittle.

Photo: Silicon and carbon fuse to form silicon carbide power (left), which can be made into a hard and hard-wearing ceramic called silicon carbide that can survive high temperatures. It has many applications, from drills and cutting tools to components (middle, right) that can withstand high temperatures in gas-turbine engines that would melt ordinary metal parts. Ceramic components are also used in ordinary car engines for the same reason. Picture by Warren Gretz courtesy of US Department of Energy/National Renewable Energy Laboratory (NREL) (picture id 6307388). The properties of a particular ceramic depend not just on the materials from which it is made but also on the way they are joined together—in other words, on its crystalline structure. Diamond is strong because all of its carbon atoms are bonded tightly to other carbon atoms. Graphite (such as that used in pencil "leads") shears because it is made up from different layers. Although the carbon atoms are tightly bonded within a given layer, the different layers are held together only by much weaker bonds. China clay (also called kaolin) behaves in a similar way to graphite, with its constituent aluminum , silicon, oxygen, and hydrogen atoms tightly bonded into flat sheets.

But the weak bonds between those sheets are easily broken when water surrounds them and it is this that makes wet clay so easy to mold. When china clay is fired, heat removes the water, and the chemicals inside the clay rearrange themselves into crystals of aluminum silicate tightly bonded by silicate glass, which is overall very much stronger. How ceramics are made Photo: Ceramic floor tiles get their hardness and durability from being fired. Picture by Michael Sandberg courtesy of US Navy . Firing is the process by which ceramics have traditionally been made; indeed, the word "ceramic" can be traced back to a Sanskrit word meaning "to burn." Simple ceramics such as bricks and certain types of glass are still made by processes that would be recognized by people who lived thousands of years ago. Just as in ancient times, today's pottery is made by digging clay from the ground, mixing it with water to make it flexible, shaping it on a wheel or in a mold, and then firing it in a kiln. Some of today's processes are more sophisticated than the techniques of past times.

Machines have long been used in processes such as extrusion (forcing a material into shape by squeezing it like toothpaste through a shaped tool), jiggering (laying the material automatically into a rotating mold), or hot pressing (forcing a powdered form of the ceramic into a mold then simultaneously heating it and pressing it to fuse the material into shape). The latest industrial ceramics sometimes demand more advanced production processes. Extremely tough ceramics made of silicon nitride are made by a method called reaction bonding. This involves forming silicon powder into the desired shape then heating it with nitrogen gas. Because the silicon powder already occupies the same volume as the finished product, grains of silicon nitride can form only by fusing together tightly. Types of clay and their common ceramic uses The US Geological Survey lists six types of clay mined in the United States: common clay, kaolin (China clay), bentonite, ball clay, fuller's Earth, and fire clay, and each has a number of different uses: Common clay is mostly used for bricks, cement, and aggregate. Kaolin is widely used for making glossy paper. Bentonite has a variety of industrial uses, including drilling mud and foundary sand, and is also found in household products that absorb pet waste.

Ball clay is a high quality clay prized for its use in ceramics, sanitaryware, and wall and floor tiles. Fuller's Earth is also used for pet-waste products. Fire clay is used in refractory (high-temperature) bricks and cement. The world of modern ceramics Photo: Toilets are still largely made from ceramics (though the lid and seat are typically made of plastic or wood). It is difficult to think of an area of modern life that has not been touched by ceramics. Our homes are made from brick walls, held together by cement made from calcium silicates, and glass windows, also made from silica. Inside, the walls are plastered with ceramic gypsum, porcelain bathrooms are decorated with tiles made of clay and talc, and kitchens stacked with pottery and glass have decorative ceramic floor tiles. Clay pipes link our homes to the sewage system and ceramic insulators are essential in connecting them to the electricity grid .

Back inside the house, that electricity flows through television sets that contain more ceramic insulators, components such as capacitors and resistors made from ceramics, computers based on silicon chips, magnetic ceramics used in the electric motors of appliances such as vacuum cleaners and food blenders, and piezoelectric ceramics used in tiny headphones and loudspeakers . Telephone calls and cable television signals may be piped to the home through glass fibers , while other kinds of glass fibers keep heat inside the walls and the roof. That heat may itself be provided by a heated ceramic filament, just as lighting comes from glass bulbs or fluorescent tubes . But ceramics have not just proved useful in everyday situations. The properties of advanced ceramics have made them important for some much more extraordinary applications. For example, the toughened silicon carbide used in hip replacements is designed to be porous so that it stimulates natural bone growth and tissue formation around the artificial joint. Ceramic engine components are used in "lean burn" car engines that combust fuel more cleanly. Catalytic converters , which convert air pollution into less harmful gases, are made from light but strong aluminosilicate ceramics that can withstand the high temperatures generated in car exhausts.

The latest generation of lightweight, deep-sea submersibles are being built not from steel , like their predecessors, but from ceramics originally made for defense purposes. One of the most innovative uses of ceramics is a new kind of paint made from a piezoelectric ceramic. Like other piezoelectric materials, this produces a tiny electric current when it undergoes stresses and strains and its Japanese inventors believe it could be used to detect metal failures or even earthquakes . Ceramics in action! Space Shuttle When NASA's Space Shuttle returned from space, thousands of heat-resistant tiles protected its exterior from overheating due to friction generated by Earth's atmosphere. The now-retired Shuttle used different tiles made from carbon, ceramics, and silica composites. But future reusable space planes are expected to use a new, slimline ceramic material made from hafnium and zirconium metals that will enable it to be both more aerodynamic and withstand temperatures up to 4300°F (2400°C). Picture courtesy of NASA on the Commons .

Superconductors Superconductors —materials that have practically no electrical resistance—were discovered in 1911, but found few practical applications because they became superconducting only at temperatures close to absolute zero (–459.67°F or –273.15°C). But in the 1980s, scientists invented new types of ceramic superconductors that showed superconductivity at temperatures as high as –292°F (–180°C). High-temperature superconductors such as this are expected to find many new applications, including high-speed, magnetic levitation (" maglev ") trains and super-fast computers. Maglev train picture courtesy of US Department of Energy. Electrical insulators Familiar insulators such as rubber and plastic are relatively poor conductors, but they will conduct electricity if extremely large voltages are placed across them. This makes them unsuitable for use in high-power applications, such as in electrical generators , and transformers . Ceramics made from alumina ( aluminum oxide) and porcelain are widely used in insulators that protect electrical equipment outdoors. Ceramics have been used as the insulation in automobile sparking plugs since the early 20th century.

Power plant picture courtesy of US Department of Energy.

Question: Ceramic items are made from what material?
Answer: China