Material Science Exam 1 Uiowa

Crystalline

Material in which the atoms are situated in a repeating or periodic array over large atomic distances

Crystal structure

Manner in which atoms, ions, or molecules are spatially arranged

Face-centered cubic (FCC)

Has atoms located at each of the corners and the centers of all cube faces

Coordination number

Number of nearest-neighbor or touching atoms

Atomic packing factor (APF)

Sum of sphere volumes of all atoms within a cell divided by the until cell volume

Body-centered cubic (BCC)

Has eight corner atoms and a single atom in the middle

Hexagonal close-packed (HCP)

Has top and bottom faces of the unit cell that consist of six atoms that form a hexagon and surround a single atom

Cations

Positively charged because they have given up their valence electrons

Anions

Negatively charged because they received valence electrons

Polymorphism

When metals or nonmetals have more than one crystal structure

Allotropy

Elemental solid condition

- crystal structure depends on both the temperature and pressure (external)

Lattice parameters

The parameters in which unit cell geometry is defined

Crystal system

Seven possible combinations

-cubic, tetragonal, hexagonal, orthorhombic, rhombohedral (trigonal), monoclinic, triclinic

Family of directions

Group of directors that are all crystallographically equivalent

Single crystal

When the periodic and repeated arrangement of atoms is perfect or extends throughout the entirety of the specimen without interruption

Anisotropy

When the physical properties of single crystals of some substances depend on the crystallographic direction in which measurements are taken

Isotrophic

Substances in which measure properties are independent of the direction of measurement

Diffractiuon

Occurs when a wave encounters a series of regularly spaced obstacles that are capable of scattering the wave and have spacing that are comparable in magnitude to the wavelength

Bragg's Law

Magnitude of the distance between two adjacent and parallel planes of atoms is a function of miller indices

Noncrystalline

Solids that lack a systematic and regular arrangement of atoms over relatively large atomic distances

Amorphous

Means "without form"

Unsaturated

Molecules that have double and triple covalent bonds

Saturated

Has all single bonds

Macromolecules

Polymers alternate name due to their size

Repeat units

Structural entities that long molecules are composed of

Polymer

Means "many Mers"

Monomer

Refers to the small molecule from which a polymer is synthesized

Homopolymer

When all the repeating units along a chain are the same type

Copolymer

Composed of two or more different repeat units

Bifunctional monomers

Form a two-dimensional chain like molecular structure

Functionality

The number of bonds a polymer can form

Degree of polymerization

Another way to express average chain size

Linear polymers

Those in which the repeat units are joined together end to end in single chains

Branched polymers

Polymers that are synthesized in which side-branch chains are connected to the main ones

Cross-linked polymers

Adjacent linear chains that are joined one another at various positions by covalent bonds

Network polymers

Multifunctional monomers forming three or more active covalent bonds that make three-dimensional networks

Stereoisomerism

Denotes the situation in which atoms are in the same order but differ in their spatial arrangements

Isotactic configuration

When all of the R groups are situated on the same side of the chain

Syndiotactic configuration

When all of the R groups alternate sides of the chain

Atactic configuration

Random positioning of the R group

Cis structure

CH3 and H atom are on the same side of the double bond

Trans structure

CH3 and H on different side of the double bond

Random copolymer

Two different units randomly dispersed along the chain

Alternating copolymer

Two repeat units alternate chain positions

Block copolymer

Identical repeat units clustered in blocks along the chain

Graft polymer

Homopolymer side branches of one type may be grafted to homopolymer main chains that are composed of a different repeat unit

Polymer crystallinity

The packing of molecular chains to produce an ordered atomic array

Crystallites

Small crystalline regions that make up semicrystalline polymers

Chain-folded model

Molecular chains within each platelet fold back and forth on themselves

Spherulite

Bulk polymers that crystallized from a melt are semicrystalline and form this structure

Point defects

Associated with one or two atomic positions

Linear defects

One dimensional

Self-interstital

Atom from the crystal that is crowded in an interstitial site

-small void space that under ordinary circumstances is not occupied

Defect structure

Often used to designate the types and concentrations of atomic defects in ceramics

Electroneutrality

State that exists when there are equal numbers of positive and negative charges from the ions

Frenkel defect

Defect that involves a cation-vacancy and a cation-interstitial pair

Schottky defect

Found in AX materials and is a cation vacancy-anion vacancy pair