Materials

Atactic

Atactic

A type of polymer chain configuration (stereoisomer) in which side groups are randomly positioned on one side of the chain or the other.

Bifunctional

Designates monomers that may react to form two covalent bonds with other monomers to create a two-dimensional chainlike molecular structure.

Branched Polymer

A polymer having a molecular structure of secondary chains that extend from the primary main chains.

Crosslinked Polymer

A polymer in which adjacent linear molecular chains are joined at various positions by covalent bonds.

Crystalline

The state of a solid material characterized by a periodic and repeating three-dimensional array of atoms, ions, or molecules.

Isomerism

The phenomenon by which two or more polymer molecules or repeat units have the same composition but different structural arrangements and properties.

Isotactic

A type of polymer chain configuration (stereoisomer) in which all side groups are positioned on the same side of the chain molecule.

Linear Polymer

A polymer produced from bifunctional monomers in which each polymer molecule consists of repeat units joined end to end in a single chain.

Monomer

A stable molecule from which a polymer is synthesized.

Network Polymer

A polymer produced from multifunctional monomers having three or more active covalent bonds, resulting in the formation of three-dimensional molecules.

Polymer

A compound of high molecular weight (normally organic), the structure of which is composed of chains of small repeat units.

Syndiotactic

A type of polymer chain configuration (stereoisomer) in which side groups regularly alternate positions on opposite sides of the chain.

Thermoplastic polymer

A semicrystalline polymeric material that softens when heated and hardens upon cooling. While in the softened state, articles may be formed by molding or extrusion.

Thermosetting polymer

A polymeric material that, once having been cured (or hardened) by a chemical reaction, will not soften or melt when subsequently heated.

Trifunctional

Designating monomers that may react to form three covalent bonds with other monomers.

Alloy

A metallic substance that is composed of two or more elements.

Atom Percent

A concentration specification on the basis of the number of moles (or atoms) of a particular element relative to the total number of moles (or atoms) of all elements within an alloy.

Composition

The relative content of a particular element or constituent (i) within an alloy, usually expressed in weight percent or atom percent.

Edge Dislocation

A linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra half-plane of atoms within a crystal. The Burgers vector is perpendicular to the dislocation line.

Frenkel Defect

In an ionic solid, a cation-vacancy and cation-interstitial pair.

Interstitial Solid Solution

A solid solution in which relatively small solute atoms occupy interstitial positions between the solvent or host atoms.

Microstructure

The structural features of an alloy (e.g., grain and phase structure) subject to observation under a microscope.

Point Defect

A crystalline defect associated with one or, at most, several atomic sites.

Schottky Defect

In an ionic solid, a defect consisting of a cation-vacancy and anion-vacancy pair.

Self-Interstitial

A host atom or ion positioned on an interstitial lattice site.

Solid Solution

A homogeneous crystalline phase that contains two or more chemical species. Both substitutional and interstitial solid solutions are possible.

Solute

One component or element of a solution present in a minor concentration. It is dissolved in the solvent.

Solvent

The component of a solution present in the greatest amount. It is the component that dissolves a solute.

Substitutional Solid Solution

A solid solution in which the solute atoms replace or substitute for the host atoms.

Vacancy

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

Weight Percent

A concentration specification on the basis of weight (or mass) of a particular element relative to the total alloy weight (or mass).

Activation Energy

The energy required to initiate a reaction, such as diffusion.

Carburizing

The process by which the surface carbon concentration of a ferrous alloy is increased by diffusion from the surrounding environment.

Diffusion

Mass transport by atomic motion.

Diffusion Coefficient

The constant of proportionality between the diffusion flux and the concentration gradient in Fick’s first law. Its magnitude is indicative of the rate of atomic diffusion.

Interdiffusion

Diffusion of atoms of one metal into another metal.

Interstitial Diffusion

A diffusion mechanism by which atomic motion is from interstitial site to interstitial site.

Nonsteady-state Diffusion

The diffusion condition for which there is some net accumulation or depletion of diffusing species. The diffusion flux is dependent on time.

Self-Diffusion

Atomic migration in pure metals.

Vacancy Diffusion

The diffusion mechanism in which net atomic migration is from a lattice site to an adjacent vacancy.

Cold Working

The plastic deformation of a metal at a temperature below that at which it recrystallizes.

Grain Growth

The increase in average grain size of a polycrystalline material; for most materials, an elevated-temperature heat treatment is necessary.

Recovery

The relief of some of the internal strain energy of a previously cold-worked metal, usually by heat treatment.

Recystallization

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

Recrystallization Temperature

For a particular alloy, the minimum temperature at which complete recrystallization occurs within approximately 1 h.

Slip

Plastic deformation as the result of dislocation motion; also, the shear displacement of two adjacent planes of atoms.

Solid-Solution Strengthening

Hardening and strengthening of metals that result from alloying in which a solid solution is formed. The presence of impurity atoms restricts dislocation mobility.

Strain Hardening

The increase in hardness and strength of a ductile metal as it is plastically deformed below its recrystallization temperature.

Vulcanization

A nonreversible chemical reaction involving sulfur or another suitable agent in which crosslinks are formed between molecular chains in rubber materials. The rubber’s modulus of elasticity and strength are enhanced.