Chapter 13 Engineering Materials

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Glass ceramic

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A fine-grained crystalline ceramic materialformed as a glass and subsequently crystallized.

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crystallization

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The process in which a glass(noncrystalline or vitreous solid) transforms into a crystallinesolid.

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nucleating agent (frequently titanium dioxide)

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is oftenadded to the glass to promote crystallization.

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Glass ceramic

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The most common uses for these materials areas ovenware, tableware, oven windows, andrange tops—primarily because of their strengthand excellent resistance to thermal shock.

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clay

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One of the most widely used ceramic rawmaterials

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Structural clay products

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includebuilding bricks, tiles, and sewer pipes—applications inwhich structural integrity is important

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Structural clay products

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Ceramic products made principally ofclay and used in applications in which structural integrity isimportant (e.g., bricks, tiles, pipes).

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whitewares

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become white after the high-temperaturefiring. Included in this group are porcelain, pottery,tableware, china, and plumbing fixtures (sanitary ware).

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refractory

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A metal or ceramic that may be exposed to extremelyhigh temperatures without deteriorating rapidly orwithout melting.

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bricks

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most common form of refractory material

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fireclayrefractories

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The primary ingredients for the these are high-purity fireclays, alumina andsilica mixtures usually containing between 25 and45 wt% alumina.

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Fireclay bricks

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used principally in furnaceconstruction, to confine hot atmospheres, andto thermally insulate structural members fromexcessive temperatures.

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silica/acid refractories

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These materials, wellknown for their high-temperature load-bearingcapacity, are commonly used in the archedroofs of steel- and glass-making furnaces; forthese applications, temperatures as high as1650°C (3000°F) may be realized.

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basic refractories

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The refractories that are rich in periclase,or magnesia (MgO) are termed this

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special refractories

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Included in this group are alumina, silica, magnesia, beryllia(BeO), zirconia (ZrO2), and mullite (3Al2O3–2SiO2).

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Siliconcarbide

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has been used for electrical resistance heatingelements, as a crucible material, and in internal furnacecomponents

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Abrasive ceramics

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are used to wear, grind, or cutaway other material, which necessarily is softer

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coated abrasive

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are those in which anabrasive powder is coated on some type of paperor cloth material; sandpaper is probably the mostfamiliar example.

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cement

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A substance (often a ceramic) that by chemical reactionbinds particulate aggregates into a cohesive structure.With hydraulic cements the chemical reaction is one of hydration,involving water

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calcination

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A high-temperature reaction by which one solidmaterial dissociates to form a gas and another solid. It is onestep in the production of cement

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Portland cement

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termed a hydraulic cement because itshardness develops by chemical reactions with water

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High-pressure high-temperature (HPHT) techniques

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to produce syntheticdiamonds that were developed beginning in the mid-1950s.

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graphite

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highlyanisotropic—property values depend on crystallographicdirection along which they are measured.

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graphitic carbonfibers

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properties of graphite include goodchemical stability at elevated temperatures and innon oxidizing atmospheres, high resistance to thermalshock, high adsorption of gases, and good machinability.

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Hybrid graphitic

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turbostratic fibers, composedof regions of both structure types, may also be synthesized.

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turbostratic carbon

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a more disorderedstructure results when, during fabrication, graphene sheets becomerandomly folded, tilted, and crumpled to form this

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pyrolytic carbon

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used extensively asa biomaterial because of its biocompatibility with somebody tissues ---- isotropic

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Graphitic fibers

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typically have higher elastic moduli thanturbostratic fibers, whereas turbostratic fibers tend to be stronger.

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adv. ceramics

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include materials used inmicroelectromechanical systemsas well as the nanocarbons(fullerenes, carbon nanotubes,and graphene).

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Microelectromechanical systems (abbreviated MEMS)

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areminiature ―smart‖ systems consisting of a multitude ofmechanical devices that are integrated with large numbers ofelectrical elements on a substrate of silicon

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micosensors

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collect environmental information by measuring mechanical,thermal, chemical, optical, and/or magnetic phenomena.

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microactuator devices

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devices that perform such responses aspositioning, moving, pumping, regulating, and filtering.

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nanocarbons

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have novel and exceptional properties,are currently being used in some cutting-edgetechnologies, and will certainly play an important rolein future high-tech applications.

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fullerenes, carbonnanotubes, and graphene

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Three nanocarbonsthat belong to nanocarbons are

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buckminsterfullerene, (orbuckyball for short)

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The material composed ofC60 molecules is known as

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fullerene

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is usedto denote the class of materials that are composed of thistype of molecule.

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fullerite

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In the solid state, the C60 units form a crystalline structure and packtogether in a facecentered cubic array. What is this material?

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Carbon Nanotubes

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Its structure consists of a singlesheet of graphite (i.e., graphene) that is rolled into atube

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Bulknanotubes

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are currently being used as reinforcements in polymermatrixnanocomposites to improve not only mechanical strength, butalso thermal and electrical properties.

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Graphene

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the newest member of the nanocarbons,is a single-atomic-layer of graphite, composed ofhexagonally sp2 bonded carbon atoms

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glass transition temperature (Tg)

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The temperature at which,upon cooling, a noncrystalline ceramic or polymer transformsfrom a supercooled liquid into a rigid glass.

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melting

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the glass is fluid enough to be considered a liquid --- viscosityis 10 Pa.s (100 P)

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working point

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the glass is easily deformed at this viscosity. viscosity is103 Pa.s (104 P);

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softening point

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The maximum temperature at which aglass piece may be handled without permanent deformation;this corresponds to a viscosity of approximately 4 x 10^6 Pa.s(4 x 107 P)

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annealing point

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The temperature at which residualstresses in a glass are eliminated within about 15 min; thiscorresponds to a glass viscosity of about 10^12 Pa.s(1013 P);

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strain point

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corresponds to the temperature at which the viscositybecomes 3 x 1013 Pa.s (3 x 1014 P); for temperatures below this point, fracture will occur before the onset of plastic deformation.

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glass

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produced by heating the raw materials to anelevated temperature above which melting occurs.

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homogeneity

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achieved by complete melting andmixing of the raw ingredients

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porosity

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results fromsmall gas bubbles that are produced;

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Pressing i

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is used in the fabrication of relatively thick-walledpieces such as plates and dishes

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parison

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formed by mechanical pressing in a mold from a raw gob of glass

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drawing/casting

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is used to form long glass pieces such assheet, rod, tubing, and fibers, which have a constant crosssection.

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sheet glass

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it was produced bycasting (or drawing) the glass into a plate shape, grindingboth faces to make them flat and parallel, and finally,polishing the faces to make the sheet transparent—aprocedure that was relatively expensive.

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fibers

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formed by drawing themolten glass through many small orifices at the chamberbase

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thermal stress

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A residual stress introduced within a body resultingfrom a change in temperature.

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thermal shock

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The fracture of a brittle material as a result ofstresses introduced by a rapid temperature change.

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thermal tempering

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Increasing the strength of a glass piece bythe introduction of residual compressive stresses within theouter surface using an appropriate heat treatment.

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hydroplasticity

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a condition when water is added to clay, they become veryplastic

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clay

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are aluminosilicates, being composed ofalumina (Al2O3) and silica (SiO2), that containchemically bound water.

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Clay, Flint (Quartz), Flux (Feldspar)

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General Composition of Clay Products

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Hydroplastic Forming

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The molding or shaping of clay-basedceramics that have been made plastic and pliable by addingwater

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slip casting

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A forming technique used for some ceramic materials.A slip, or suspension of solid particles in water, is pouredinto a porous mold. A solid layer forms on the inside wall aswater is absorbed by the mold, leaving a shell (or ultimately asolid piece) having the shape of the mold

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green ceramic body

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a term that refers to a body that has beenformed and dried but not fired

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drying

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is a process of water removal.

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Vitrification

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the gradual formation of a liquid glass that flows intoand fills some of the pore volume.

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Vitrification

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During firing of a ceramic body, the formation ofa liquid phase that, upon cooling, becomes a glass-bondingmatrix.

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powder pressing

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used to fabricateboth clay and nonclay compositions,including electronic and magneticceramics as well as some refractorybrick products

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Uniaxial Pressing

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the powder is compacted ina metal die by pressure that is applied in asingle direction.

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Isostatic Pressing

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the powdered material iscontained in a rubber envelope and thepressure is applied by a fluid, isostatically (i.e., ithas the same mag-nitude in all directions).

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Hot Pressing

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the powder pressing and heattreatment are performed simultaneously—thepowder aggregate is compacted at an elevatedtemperature

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Sintering

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the process by which there is acoalescence of the powder particles into a moredense mass

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tape casting

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thin sheets of a flexibletape are produced by means of a castingprocess.

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tape casting

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widely used in theproduction of ceramic substrates thatare used for integrated circuits and formultilayered capacitors.