CERAMICSA ceramic is an inorganic, nonmetallic solid comprising metal, nonmetal or metalloid atoms primarily held in ionic and covalent bonds. The crystallinity of ceramic materials ranges from highly oriented to semi-crystalline, and often completely amorphous (e.g., glasses). Varying crystallinity and electron consumption in the ionic and covalent bonds cause most ceramic materials to be good thermal and electrical insulators and extensively researched in ceramic engineering. Nevertheless, with such a large range of possible options for the composition/structure of a ceramic (e.g. nearly all of the elements, nearly all types of bonding, and all levels of crystallinity), the breadth of the subject is vast, and identifiable attributes (e.g. hardness, toughness, electrical conductivity, etc.) are hard to specify for the group as a whole.However, generalities such as high melting temperature, high hardness, poor conductivity, highmoduli of elasticity, chemical resistance and low ductility are the norm,[1]with known exceptions to each of these rules (e.g.piezoelectric ceramics,glass transitiontemp,superconductive ceramics, etc...). Many composites, such asfiberglassandcarbon fiber, while containing ceramic materials, are not considered to be part of the ceramic family.The word "ceramic" comes from theGreekword (keramikos), "of pottery" or "for pottery",from (keramos), "potter's clay, tile, pottery". The word "ceramic" may be used as an adjective to describe a material, product or process; or it may be used as a noun, either singular, or more commonly, as the plural noun "ceramics".The earliest ceramics made by humans werepotteryobjects, including27,000 year oldfigurines, made fromclay, either by itself or mixed with other materials likesilica, hardened,sintered, in fire. Later ceramics wereglazedand fired to create smooth, colored surfaces, decreasingporositythrough the use of glassy, amorphous ceramic coatings on top of the crystalline ceramic substrates. Ceramics now include domestic, industrial and building products, as well as a wide range ofceramic art. In the 20th century, newceramic materialswere developed for use in advanced ceramic engineering; for example (e.g.semiconductors).

Properties These materials are insulator of heat and electricity and more resistance to high temperature. These materials are stronger than that of metals because of their covalent and ionic bonding. These materials are less density it means they are lighter than metals. The inability of slip of ceramic materials can cause more difficult in the processing and performance. Some oxide of ceramic show magnetic behaviors such as Fe3O4. Low toughness and ductility They are brittle materials. hard, wear-resistant, refractory, nonmagnetic, oxidation resistant, prone to thermal shock, and Chemically stable.

Ceramics used for engineering applications, can be divided into two groups: Traditional ceramic materials Advanced ceramic materialsTraditional Ceramics Made from three basic components: clay, silica (flint), and feldspar. The clay in traditional ceramics provides workability of the material before firing hardens it and constitutes the major body material. The silica has a high melting temperature and is the refractory component of traditional ceramics. Potash feldspar, has a low melting temperature and makes a glass when the ceramic mix is fired. It bonds the refractory components together.

Advanced Ceramics Advanced ceramics are ideally suited for industrial applications that provide a physical interface between different components due to their ability to withstand high temperatures, vibration and mechanical shock. A type of ceramic exhibiting a high degree of industrial efficiency. A type of ceramic used in specialized, recently developed applications. Advanced ceramics often have simple chemical compositions, but they are difficult to manufacture.

History of CeramicsArcheologists have uncovered human-made ceramics that date back to at least 24,000 BC. These ceramics were found in Czechoslovakia and were in the form of animal and human figurines, slabs, and balls. These ceramics were made of animal fat and bone mixed with bone ash and a fine claylike material. After forming, the ceramics were fired at temperatures between 500-800C in domed and horseshoe shaped kilns partially dug into the ground with loess walls. While it is not clear what these ceramics were used for, it is not thought to have been a utilitarian one. The first use of functional pottery vessels is thought to be in 9,000 BC. These vessels were most likely used to hold and store grain and other foods.

It is thought that ancient glass manufacture is closely related to pottery making, which flourished in Upper Egypt about 8,000 BC. While firing pottery, the presence of calcium oxide (CaO) containing sand combined with soda and the overheating of the pottery kiln may have resulted in a colored glaze on the ceramic pot. Experts believe that it was not until 1,500 BC that glass was produced independently of ceramics and fashioned into separate items.

Since these ancient times, the technology and applications of ceramics (including glass) has steadily increased. We often take for granted the major role that ceramics have played in the progress of humankind.

Ceramic Crystal Structure Broader range on chemical composition than metals with more complicated structures contains at least 2 and often 3 or more atoms usually compounds between metallic ions (e.g. Fe, NI, Al) -called cations - and non-metallic ions (e.g. O, N, Cl) -called anions Bonding will usually have some covalent character but is usually mostly ionicProcessing of CeramicsThe figure shows general process flow diagram for ceramic products manufacturing.The basic steps include raw material procurement, beneficiation, mixing, forming, green machining, drying, presinter thermal processing, glazing, firing, final processing, and packaging. 1. Raw Material Procurement -To begin the process, raw materials are transported and stored at the manufacturing facility. The raw materials used in the manufacture of ceramics range from relatively impure clay materials mined from natural deposits to ultrahigh purity powders prepared by chemical synthesis. Naturally occurring raw materials used to manufacture ceramics include silica, sand, quartz, flint, silicates, and aluminosilicates. Raw Materials Clay Minerals Talc and Related Minerals Silica, Sand and Silicate Minerals Feldspars and related minerals. Important Characteristics of Clays in Ceramic Bodies Clays have the ability to form clay-water composition and to maintain their shape and strength during drying and firing They fuse over a temperature range depending on their composition in such a way as to become dense and strong without losing their shape Talc and Related Minerals Talc is a hydrous magnesium silicate which has a layer structure similar to that of the clay minerals. It is an important ceramic raw material for the manufacture of electrical and electronic components Silica and Silicate Minerals Silica is a major ingredient in glass, glazes, enamels, refractories, abrasives, and whiteware compositions. It is widely used because it is inexpensive, hard, chemically stable Feldspars and Related Minerals Feldspar are anhydrous aluminosilicates containing K+, Na+, and Ca2.; they are present in virtually all igneous rocks. Most production comes from pegmatites which are coarsely crystalline rock formed in the later stages of crystallization of a magma

2. Beneficiation -The next step in the process is beneficiation. Although chemically synthesized ceramic powders also require some beneficiation, the focus of this discussion is on the processes for beneficiating naturally occurring raw materials. The basic beneficiation processes include comminution, purification, sizing, classification, calcining, liquid dispersion, and granulation. Naturally occurring raw materials often undergo some beneficiation at the mining site or at an intermediate processing facility prior to being transported to the ceramic manufacturing facility. Comminution- entails reducing the particle size of the raw material by crushing, grinding, and milling or fine grinding. The purpose of comminution is to liberate impurities, break up aggregates, modify particle morphology and size distribution, facilitate mixing and forming, and produce a more reactive material for firing. Primary crushing generally reduces material up to 0.3 meter (m) (1 foot [ft]) in diameter down to 1 centimeter (cm) (0.40 inch [in.]) in diameter. Secondary crushing reduces particle size down to approximately 1 millimeter (mm) (0.04 in.) in diameter. Fine grinding or milling reduces the particle size down to as low as 1.0 micrometer (m) (4 x 10-5 in.) in diameter. Ball mills are the most commonly used piece of equipment for milling. However, vibratory mills, attrition mills, and fluid energy mills also are used. Crushing and grinding typically are dry processes; milling may be a wet or dry process. In wet milling, water or alcohol commonly is used as the milling liquid. Purification- Several procedures are used to purify the ceramic material. Water soluble impurities can be removed by washing with deionized or distilled water and filtering, and organic solvents may be used for removing water-insoluble impurities. Acid leaching sometimes is employed to remove metal contaminants. Magnetic separation is used to extract magnetic impurities from either dry powders or wet slurries. Froth flotation also is used to separate undesirable materials.Sizing and classification separate the material into size ranges. Sizing is most often accomplished using fixed or vibrating screens. Dry screening can be used to sizes down to 44 m(0.0017 in., 325 mesh). Dry forced-air sieving and sonic sizing can be used to size dry powders down to 37 m (0.0015 in., 400 mesh), and wet sieving can be used for particles down to 25 m (0.00098 in., 500 mesh). Air classifiers generally are effective in the range of 420 m to 37 m (0.017 to 0.0015 in., 40 to 400 mesh). However, special air classifiers are available for isolating particles down to 10 m (0.00039 in.).Calcining- consists of heating a ceramic material to a temperature well below its melting point to liberate undesirable gases or other material and to bring about structural transformation to produce the desired composition and phase product. Calcining typically is carried out in rotary calciners,heated fluidized beds, or by heating a static bed of ceramic powder in a refractory crucible.Liquid dispersion of ceramic powders sometimes is used to make slurries. Slurry processing facilitates mixing and minimizes particle agglomeration. The primary disadvantage of slurry processing is that the liquid must be removed prior to firing the ceramic.Granulation- Dry powders often are granulated to improve flow, handling, packing, and compaction. Granulation is accomplished by direct mixing, which consists of introducing a binder solution during powder mixing, or by spray drying. Spray dryers generally are gas-fired and operate at temperatures of 110 to 130C (230 to 270F).Mixing - The purpose of mixing or blunging is to combine the constituents of a ceramic powder to produce a more chemically and physically homogenous material for forming. Pug mills often are used for mixing ceramic materials. Several processing aids may be added to the ceramic mix during the mixing stage. Binders and plasticizers are used in dry powder and plastic forming; in slurry processing, deflocculants, surfactants, and antifoaming agents are added to improve processing. Liquids also are added in plastic and slurry processing.Binders are polymers or colloids that are used to impart strength to green or unfired ceramic bodies. For dry forming and extrusion, binders amount to 3 percent by weight of the ceramic mixture.Plasticizers and lubricants are used with some types of binders. Plasticizers increase the flexibility of the ceramic mix. Lubricants lower frictional forces between particles and reduce wear on equipment.Water is the most commonly used liquid in plastic and slurry processing. Organic liquids such as alcohols may also be used in some cases. Deflocculants also are used in slurry processing to improvedispersion and dispersion stability. Surfactants are used in slurry processing to aid dispersion, and antifoams are used to remove trapped gas bubbles from the slurry.3. Forming - In the forming step, dry powders, plastic bodies, pastes, or slurries are consolidated and molded to produce a cohesive body of the desired shape and size. Dry forming consists of the simultaneous compacting and shaping of dry ceramic powders in a rigid die or flexible mold. Dry forming can be accomplished by dry pressing, isostatic compaction, and vibratory compaction.Plastic molding is accomplished by extrusion, jiggering, or powder injection molding. Extrusion is used in manufacturing structural clay products and some refractory products. Jiggering is widely used in the manufacture of small, simple, axially symmetrical whiteware ceramic such as cookware, fine china, and electrical porcelain. Powder injection molding is used for making small complex shapes.Paste forming consists of applying a thick film of ceramic paste on a substrate. Ceramic pastes are used for decorating ceramic tableware, and forming capacitors and dielectric layers on rigid substrates for microelectronics.

Ingredients of Ceramic Paste for Shaping - Clay (hydrous aluminum silicates) - usually the main ingredient because of ideal forming characteristics when mixed with water- Water creates clay-water mixture with suitable plasticity for shaping- Nonplastic raw materials, such as alumina and silica - reduce shrinkage in drying and firing but also reduce plasticity of the mixture during forming- Other ingredients, such as fluxes that melt (vitrify) during firing and promote sintering, and wetting agents to improve mixing of ingredients Slip Casting This is whereslip, liquidclay, is poured into aplastermould. The water in the slip is drawn out of the slip, leaving an inside layer of solid clay. When this is thick enough, the excess slip can be removed from the mould. When dry, the solid clay can then also be removed. The slip used in slip casting is often liquified with a substance that reduces the need for additional water to soften the slip; this prevents excessive shrinkage which occurs when a piece containing a lot of water dries.

4. Green Machining- After forming, the ceramic shape often is machined to eliminate rough surfaces and seams or to modify the shape. The methods used to machine green ceramics include surface grinding to smooth surfaces, blanking and punching to cut the shape and create holes or cavities, and laminating for multilayer ceramics.

5. Drying - After forming, ceramics must be dried. Drying must be carefully controlled to strike a balance between minimizing drying time and avoiding differential shrinkage, warping, and distortion. The most commonly used method of drying ceramics is by convection, in which heated air is circulated around the ceramics. Air drying often is performed in tunnel kilns, which typically use heat recovered from the cooling zone of the kiln. Periodic kilns or dryers operating in batch mode also are used. Convection drying also is carried out in divided tunnel dryers, which include separate sections with independent temperature and humidity controls. An alternative to air drying is radiation drying in which microwave or infrared radiation is used to enhance drying.

6. Presinter Thermal Processing - Prior to firing, ceramics often are heat-treated at temperatures well below firing temperatures. The purpose of this thermal processing is to provide additional drying, to vaporize or decompose organic additives and other impurities, and to remove residual, crystalline, and chemically bound water. Presinter thermal processing can be applied as a separate step, which is referred to as bisque firing, or by gradually raising and holding the temperature in several stages.7. Glazing- For traditional ceramics, glaze coatings often are applied to dried or bisque-fired ceramic ware prior to sintering. Glazes consist primarily of oxides and can be classified as raw glazes or frit glazes. Application of a ceramic surface coating to make the piece more impervious to water and enhance its appearance. The application of glassy coatings on ceramic wares to give them decorative finishes and to make them impervious to moisture. Glazes mature at temperatures of 600 to 1500C (1110 to 2730F).

8. Firing - Firing is the process by which ceramics are thermally consolidated into a dense, cohesive body comprised of fine, uniform grains. This process also is referred to as sintering or densification.Parameters that affect firing include firing temperature, time, pressure, and atmosphere. A short firing time results in a product that is porous and has a low density; A short to intermediate firing time results in fine-grained (i. e., having particles not larger than 0.2 millimeters), high-strength products; And long firing times result in a coarse-grained products that are more creep resistant.Applying pressure decreases firing time and makes it possible to fire materials that are difficult to fire using conventional methods. Oxidizing or inert atmospheres are used to fire oxide ceramics to avoid reducing transition metals and degrading the finish of the product.In addition to conventional firing, other methods used include pressure firing, hot forging, plasma firing, microwave firing, and infrared firing. The following paragraphs describe conventional and pressure firing, which are the methods used often.Tunnel kilns generally have separate zones for cooling, firing, and preheating or drying. The most commonly used tunnel kiln design is the roller hearth (roller) kiln. In conventional firing, tunnel kilns generally are fired with gas, oil, coal, or wood. Following firing and cooling, ceramics are sometimes refired after the application of decals, paint, or ink.Advanced ceramics often are fired in electric resistance-heated furnaces with controlled atmospheres. For some products, separate furnaces may be needed to eliminate organic lubricants and binders prior to firing.Ceramic products also are manufactured by pressure firing, which is similar to the forming process of dry pressing except that the pressing is conducted at the firing temperature. Because of its higher costs, pressure firing is usually reserved for manufacturing ceramics that are difficult to fire to high density by conventional firing.9. Final Processing - Following firing, some ceramic products are processed further to enhance their characteristics or to meet dimensional tolerances. Ceramics can be machined by abrasive grinding, chemical polishing, electrical discharge machining, or laser machining. Annealing at high temperature, followed by gradual cooling can relieve internal stresses within the ceramic and surface stresses due to machining. In addition, surface coatings are applied to many fired ceramics. Surface coatings are applied to traditional clay ceramics to create a stronger, impermeable surface and for decoration.Coatings also may be applied to improve strength, and resistance to abrasion and corrosion. Coatings can be applied dry, as slurries, by spraying, or by vapor deposition.

Factors Affecting the Ceramic Process Oxidation Decomposition Reactions Phase Transformations Trapped Gases Non uniform Mixing Over firing Hot Pressing Firing Shrinkage Warping

Application of Traditional Ceramics White Wares Made from components of clay, silica, and feldspar for which the composition is controlled.Example: Electrical porcelain Dinner china Sanitary ware Structural Clay Products Made of natural clay, which contains all three basic components.Example: Building brick Sewer pipe Drain tile Roofing tile Floor tile

Abrassives is a material, often amineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away a material often meanspolishingit to gain a smooth, reflective surface which can also involve roughening as in satin, matte or beaded finishes Refractories 3 is one that retains its strength at hightemperature Example: kilnlinings gas fire radiants glass making crucibles

Application of Advanced Ceramics Electroceramics Itis a class ofceramicmaterials used primarily for their electrical properties.Further classified to: Dielectric ceramics- are capable of storing large amounts of electrical charge in relatively small volumes.- Is an electrical insulator that can be polarized by an applied electric field.- Dielectric materials can be solids, liquids, or gases. - Solid dielectrics are perhaps the most commonly used dielectrics in electrical engineering, and many solids are very good insulators.

Fast ion conductor ceramics- are solids in which ions are highly mobile. These materials are important in the area of solid-state ionics, and are also known as solid electrolytes and superionic conductors. - These materials are useful in batteries and various sensors. Fast ion conductors are used primarily in solid oxide fuel cells. Piezoelectric and ferroelectric ceramics- Piezoelectric ceramic materials are categorized as functional ceramics. - In sensors they make it possible to convert forces, pressures and accelerations into electrical signals, and in sonic and ultrasonic transducers and actuators they convert electric voltages into vibrations or deformations. Magnetic Ceramics- Are made of ferrites, which are crystalline minerals composed of iron oxide in combination with some other metal. Optical Ceramics- Arepolycrystallinematerials produced through controlled crystallization of base glass.

Advance Structural Ceramics

Nuclear CeramicsCeramic materials employed in the generation ofnuclear powerand in the disposal of radioactive nuclear wastes.

Bioceramics Ceramic products or components employed in medical and dental applications, mainly as implants andreplacements.

Tribological Ceramics

Also calledwear-resistant ceramics, ceramic materials that are resistant to friction and wear. They are employed in a variety of industrial and domestic applications, including mineral processing and metallurgy.

Automotive Ceramics

Advanced ceramic materials that are made into components forautomobiles. Examples include spark plug insulators, catalysts and catalyst supports for emission control devices, and sensors of various kinds.

Glass is actually a type of ceramic.The word Ceramic can be used to describe a number of materials, including: glass, enamel, concrete, cement, pottery, brick, porcelain, and chinaware.Glass is a special type of ceramic, in that it has no crystalline structure, and is classed as an amorphous solid, meaning there is no long-range order of the positioning of its molecules.Summary1. Glass can be called as a type of ceramic.2. Glass is known to be non-crystalline. Ceramics may be crystalline or partly crystalline.3. Glass is also transparent, which means light passes through it. Ceramics may be opaque, which means it does not allow light to pass through it.4. The history of glass dates back to 3500 BC in Mesopotamia. The term Glass was first developed during the late Roman empire. Ceramics comes from Greek word keramikos, which means pottery and keramos, which means potters clay.5. A glass kiln will have heating elements on the top whereas a ceramic kiln will have heating elements on the sides.6. When comparing the two in terms of the price, ceramics is a bit costlier than glass.