Midterm 1(materials science)

Electron Energy States

Electrons occupy the lowest available energy state, with each state holding a maximum of 2 electrons with opposite spins.

Valence Electrons

Electrons that determine chemical, electrical, thermal, and optical properties of an atom.

Electropositive Elements

Elements that readily give up electrons to become positive ions.

Electronegative Elements

Elements that readily acquire electrons to become negative ions.

Coefficient of Thermal Expansion (α)

α is larger if the modulus of elasticity (E0) is smaller.

Melting Temperature (Tm)

Tm is larger if the modulus of elasticity (E0) is larger.

Primary Interatomic Bonding

Bonding characterized by strong attractions and valence electron exchange, e.g., ionic, covalent, metallic.

Secondary Interatomic Bonding

Bonding associated with attractions between molecules without electron transfer, such as dipole bonds.

Crystalline Materials

Materials with atoms packed in periodic, 3D arrays, typical of metals and ceramics.

Noncrystalline (Amorphous) Materials

Materials with no periodic atomic packing, often resulting from complex structures and rapid cooling.

Simple Cubic Structure (SC)

Rare structure with one complete atom per unit cell, exemplified by Polonium (Po).

Body-Centered Cubic (BCC)

Structure where atoms touch along cube diagonals, containing 2 full volume of atoms per unit cell.

Face-Centered Cubic (FCC)

Structure where atoms touch along the face diagonals, common in metals such as Al, Cu, and Au.

Anisotropic Properties

Properties that vary with direction in single crystals.

Isotropic Properties

Properties that do not vary with direction in polycrystalline materials.

Solidification Process

Occurs in two steps: nuclei formation and growth into crystals.

Point Defects

Defects in crystal structures such as vacancies and interstitials.

Dislocations

Line defects that cause movement between crystal planes leading to permanent deformation.

Edge Dislocation

A dislocation featuring an extra half-plane of atoms; moves under shear stress.

Screw Dislocation

A dislocation that forms a spiral ramp due to shear deformation.

Burger’s Vector

A measure of lattice distortion associated with dislocations.

Diffusion

Mass transport in materials by atomic motion, occurring through mechanisms like vacancy and interstitial diffusion.

Self-Diffusion

Migration of atoms within an elemental solid.

Interdiffusion

Migration of atoms from high concentration to low concentration in alloys.

Vacancy Diffusion

Atoms exchange with vacancies, relevant for substitutional impurity atoms.

Interstitial Diffusion

Movement of smaller atoms between atomic sites in solids.

Case Hardening

Process to diffuse carbon atoms into surface iron atoms for increased hardness.