Material Science Exam 1

Valence Electrons

Electrons that occupy the outermost shell.

Ionic Bonding

Bonding found in metallic and nonmetallic elements that make ions then bond to acheive inert states.

Covalent Bonding

"Sharing of Electrons." Mainly attributed to nonmetallic elements.

Metallic Bonding

"Sea of Electrons." Found in metals and alloys, in this bond type electrons move freely throughout the metal.

Van der Waals Bonding

This type of bonding arises from atomic or molecular dipoles. Ex. Hydrogen bonding (Secondary Bond).

Polar Molecules

Permanent dipole moments existing in certain asymmetrical arrangement of positively and negatively charged regions.

Mole

6.022 x 10^23. A "chemists dozen"

Unit Cell

In crystal structures, the repeated entity that is repeated throughout the structure.

Crystal Structure

The manner in which atoms, ions, or molecules are spatially arranged.

Crystal System

Most metals exhibit one of these three simple crystal structures.

Lattice

A three-dimensional array of points coinciding with atom positions.

Atomic Packing Factor

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

Body Centered Cubic

Atoms at eight corners with one atom in the middle of the cube.

Hexagonal Close-Packed

Unit cell with hexagonal base.

Face Centered Cubic

Atoms at eight corners with six atoms in the middle on all six faces.

Coordination Number

The number of neighbor or touching atoms to the unit cell structure.

Linear Atomic Density

Number of atoms per unit length whose centers lie on the particular plane.

Planar Atomic Density

Number of atoms per unit area that are centered on the particular plane.

Alloy

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

Point Defect

Defects that are associated with one or two atomic positions; include vacancies and self-interstitials.

Vacancy

Normally occupied from which an atom is missing.

Solid Solution

May form when impurity atoms are added to a solid, in which case the original crystal structure is retained and no new phases are formed.

Solute

Lesser amount in a solution.

Solvent

Greater amount in a solution.

Self-interstitial

Atom crowded into an interstitial site, that under normal circumstances normally isn't occupied.

Substitutional Solid Solution

Impurity atoms substitute for host atoms in this solution.

Interstitial Solid Solution

Form for relatively small impurity atoms that occupy interstitial sites among the host atoms.

Dislocations

One-dimensional crystalline defects of which there are two pure types: edge and screw.

Anisotropic

Not Isotropic, directionally dependent.

Isotropic

Equal properties, in all orientations/directions. Metals generally have this property.

Crystalline

The atoms are situated in a repeating or periodic array over large atomic distances. Upon solidification, the atoms will postion themselves in a repetitive three dimensional pattern.

Polycrystaline

Isotropic, this solid is a collection of many small crystals or grains.

Grain

small crystal.

Grain Size

often determined when the properties of a polycrystalline material are under consideration.

Grain Boundary

A boundary separating two small grains having different crystallographic orientations.

Twin

Special type of grain boundary across which there is a specific mirror lattice symmetry.