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Tulane - Chemical Engineering Glossary Category: Sciences > Chemical Engineering Date & country: 13/09/2007, USA Words: 180

Impact Energy
a measure of the energy absorbed during the fracture of a specimen of standard dimensions and geometry when subjected to very rapid (impact) loading. Charpy and Izod impact tests are used to measure this parameter, which is important in assessing the ductile-to-brittle transition behavior of a material.

Index of Refraction
see Refractive Index

Instrinsic Semiconductor
a semiconductor material for which the electrical behavior is characteristic of the pure material.

Insulator (electrical)
a nonmetallic material that has filled valence band at 0 K and a relatively wide energy band gap.

Intermetallic
a compound of two metals that has a distinct chemical formula. The bonds in intermetallic compounds are often partly ionic.

Invariant Point
a point on a binary phase diagram at which three phases are in equilibrium.

Isotactic
a type of polymer chain configuration wherein all side groups are positioned on the same side of the chain molecule.

Isotope
atoms of the same element having the different masses.

Izod Impact Test
one of two tests that may be used to measure the impact energy of standard notched specimen.

Laser
an acronym for light amplification by stimulated emission of radiation.

Lattice
the regular geometrical arrangement of points in crystal space.

Lattice Parameter
the combination of unit cell edge lengths and interaxial angles that defines the unit cell geometry.

Lever Rule
mathematical expression whereby the relative phase amounts in a two-phase alloy at equilibrium my be computed.

Macromolecule
a huge molecule made up of thousands of atoms.

Magnetic Field Strength
the intensity of an externally applied magnetic field.

Magnetic Induction
see Magnetic Flux Density

Magnetic Susceptibility
the proportionality constant between the magnetization M and the magnetic field strength H.

Magnetization
the total magnetic moment per unit volume of material. Also, a measure of the contribution to the magnetic flux by some material within an H field.

Martensite
a metastable Fe-C composition consisting of supersaturated carbon in iron that is the product of a diffusionless (athermal) transformation from austenite.

Matrix
the body constituent of a composite or two-phase alloy that completely surrounds the dispersed phase and gives the body its bulk form.

Melting Point
the temperature at which a solid substance changes to a liquid state.

Mer
the group of atoms that constitutes a polymer chain repeat unit.

Metal
the electroposite elements and alloys based on these elements.

Metastable
nonequilibrium state that may persist for a very long time.

Microstructure
the structural features of an alloy that are subject to observation under a microscope.

Miller Indices
a set of three integers that designate crystallographic planes, as determined from reciprocals of fractional axial intercepts.

Miller-Bravis Indices
a set of four integers that designate crystallographic planes in hexagonal crystals.

Mixed Dislocation
a dislocationthat has both and screw components.

Modulus of Elasticity
the ratio of stress to strain for a material under perfectly elastic deformation.

Monomer
a molecule consisting of a single mer.

MOSFET
Metal-oxide-silicon field effect transistor, an integrated circuit element.

Network Polymer
a polymer composed of trifunctional mer units that form three-dimensional molecules.

Noncrystalline
the solid state wherein there is no long-range atomic order. Sometimes used synonymously with the terms amorphous, glassy and vitreous.

Nucleation
the initial stage in a phase transformation. It is evidenced by the formation of small particles (nuclei) of the new phase, which are capable of growing.

Octahedral position
the void space among closed-packed, hard sphere atoms or ions for which there are six nearest neighbors. An octahedron (double pyramid) is curcumscribed by lines constructed from centers of adjacent spheres.

p-type Semiconductor
a semiconductor for which the predominant charge carriers responsible for electrical conduction are holes. Normally, acceptor impurity atoms give rise to the excess holes.

Paramagnetism
a relatively weak form of magnetism that results from the independent alignment of atomic dipoles (magnetic) with an applied magnetic field.

Pearlite
a two-phase microstructure found in some steels and cast irons. It results from the transformation of austenite of eutectoid compositions and consists of alternating layers of alpha-ferrite and cementite.

Permittivity
the proportionality constant between the dielectric displacement D and the electric field E.

Phase
a homogeneous region of matter.

Phase Diagram
a graphical representation of the relationships between environmental constraints, composition, and regions of phase stability, ordinarily under conditions of equilibrium.

Phase Transformation
a change in the number and/or character of the phases that constitute the microstructure of an alloy.

Phonon
a single quantum of vibrational or elastic energy.

Photon
a quantum unit of electromagnetic energy.

Piezoelectric
a dielectric material in which polarization is induced by the application of external forces.

Planck's Constant
a universal constant that has a value of 6.63 x 10-34 J.

Plastic
a solid material in the primary ingredient of which is an organic polymer of high molecular wight.

Plastic Deformation
deformation that is permanent or nonrecoverable after release of the applied load.

Plasticizer
a low molecular weight polymer additive that enhances flexibility and workability and reduces stiffness and brittleness.

Point Defect
a crystalline defect associated with one or, at most, several atomic sites.

Poisson's Ratio
for elastic deformation, the negative ratio of lateral and axial strains that result from an applied axial stress.

Polar Molecule
a molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions.

Polarization (electronic)
for an atom, the displacement of the center of the negatively charged electron cloud relative to the positive nucleus, which is induced by an electric field.

Polarization (ionic)
polarization as a result of the displacement of anions and cations in opposite directions.

Polarization (orientation)
polarization resulting from the alignment (by rotation) of permanent electric dipole moments with an applied electric field.

Polycrystalline
referring to crystalline materials that are composed of more than one crystal or grain.

Polymer
a solid, nonmetallic (normally organic) compound of high molecular weight the structure of which is composed of small repeat (or mer) units.

Polymorphism
the ability of a solid material to exist in more than one form or crystal structure.

Precipitation Hardening
hardening and strengthening of a metal alloy by extremely small and uniformly dispersed particles that precipitate from a supersaturated solid solution.

Prepreg
continuous fiber reinforcement pre-impregnated with a polymer resin which is then partially cured.

Primary Bond
interatomic bonds that are relatively strong and for which bonding energies are relatively large.

Proportional Limit
the point on a stress-strain curve at which the straight line proportionality between stress and strain ceases.

Random Copolymer
a polymer in which two different mer units are randomly distributed along the molecular chain.

Recrystallization
the formation of a new set of strain-free grains within a previously cold-worked material; normally an annealing heat treatment is necessary.

Reflection
deflection of a light beam at the interface between two media.

Refraction
bending of a light beam upon passing from one medium into another.

Refractive Index
the ratio of the velocity of light in a vacuum to the velocity of light in some medium.

Refractory
a metal or ceramic that may be exposed to extremely high temperatures without deteriorating rapidly or without melting.

Relative Magnetic Permeability
the ratio of the magnetic permeability of some medium to that of a vacuum.

Resistivity
the reciprocal of electrical conductivity, and a measure of a material's resistance to the passage of electric current.

Rupture
failure that is accompanied by significant plastic deformation.

Technical Ceramic
a ceramic that exhibits a high degree of industrial efficiency through carefully designed microstructures and superb dimensional precision.

Unit Cell
the basic structural unit of a crystal structure.

Vacancy
a normally occupied lattice site from which an atom or ion is missing.

van der Waals Bond
a secondary interatomic bond between adjacent molecular dipoles, which may be permanent or induced.

Viscoelasticity
a type of deformation exhibiting the mechanical characteristics of viscous flow and elastic deformation.

Viscosity
the ratio of the magnitude of an applied shear stress to the velocity gradient that it produces.

Vulcanization
nonreversible chemical reaction involving sulfur or other suitable agent wherein cross-links are formed between molecular chains in rubber materials.

Yield Strength
the stress required to produce a very slight yet specified amount of plastic strain.

Young's Modulus
see Modulus of Elasticity the ratio of stress to strain when deformation is totally elastic.