Materials Science and Engineering Ch 1, 2, and 3

Material Classifications

Metals, Ceramics, Polymers, Composites, Advanced Materials

What are metals?

composed of one or more metallic elements, extracted from ores, often mixed with non-metallic elements, arranged in orderly manner, Non-localized electrons - great conductors.

What are ceramics?

compounds between metallic and non-metallic elements. Relatively stiff, strong, very hard, very brittle, and susceptible to fracture

What are polymers?

plastics or rubbers, usually organic compounds based on C, H, and non-metallic elements. Very large molecular structure that is often chainlike with a C backbone.

What are composites?

Compound of two or more individual materials.

What are the three primary interatomic bonds?

Ionic bonds, covalent bonds, and metallic bonds.

What are ionic bonds?

Atoms of metallic elements easily give up electrons to non-metallic elements. Non-directional bonds. Found in compounds of metallic and non-metallic elements. (Hard, brittle, and good insulators)

What is covalent bonding?

Stable electron configuration is achieved by sharing electrons. Bonds between two atoms with similar electronegativity (close on periodic table). Directional bonds. May be very strong or very weak. (Electrical insulators, some are semi conductors)

What is metallic bonding?

Valence electrons do not belong to a particular atom. Non-directional bonds. Net positive charge core, electron cloud where all electrons are free to move around the material. Bonds within all metals and their alloys. (Conductors [thermal and electrical] and ductile)

What is van der waals bonding?

Weak compared to primary bonds. Dipoles are created by the separation of positive and negative portions of an atom.

What are the 3 types of metallic crystal structures

Face-centered cubic (FCC), Body-centered cubic (BCC), Hexagonal close packed (HCP).

Face centered cubic properties

a=2Rsqrt(2), Coordination number: 12, Atomic Packing Factor: 0.74 (Highest possible APF)

Body centered Cubic Properties

a=4R/sqrt(3), Coordination number: 8, Atomic packing factor: 0.68

Hexagonal close packed

a=2R, c/a=1.633, Coordination number: 12, Atomic packing factor: 0.74

Polymorphism/Allotropy

two or more distinct crystal structures for the same material

Single Crystal

when all the repeat units are arranged perfectly without any interruption over a large atomic length. Long range order (no grain boundaries).

Polycrystalline Materials

Most materials are made of a collection of small crystals/grains. small crystals in random orientations and crystals grow and impinge one another. Long range order.

Non-crystalline solids

no regular arrangement of atoms or molecules, short range order but not long range

High bond energy

high melting point, high stiffness, low coefficient of thermal expansion.

Interatomic spacing

The equilibrium spacing between the centers of two atoms.