MTL200 - All in One Midterm Prep

What are the three primary material eras?

Stone Age, Bronze Age, Iron Age

What are the four levels of Material Structures?

Subatomic Structures, Atomic Structures, Micro structures, Macro structures

What are the three basic materials?

Metals, Ceramics and Polymers

Advanced Materials

semiconductors, biomaterials, smart materials, nanomaterials

atomic number

the number of protons in the nucleus of an atom, usually equals the number of neutrons

Isotope

Atoms of the same element that have different numbers of neutrons

formula for atomic mass

Atomic Number + Neutrons

mole

the SI base unit used to measure the amount of a substance 6.022 x 10^23

Bohr's Atomic Model

Atoms have levels surrounding the nucleus where electrons are found. Levels can hold different amounts of electrons depending on their distance from the nucleus.

Wave-Mechanical Model [Schrodinger's Model]

Modern model of the atom, atoms have electrons in "orbitals" that are like clouds around the nucleus

Quantum Numbers

A set of four numbers that specify the properties of atomic orbitals and the properties of electrons in orbitals

Principal Quantum Number (s)

symbolized by n, indicates the main energy level/shell occupied by the electron. N is the row in the periodic table

Secondary Quantum Number

symbol \= l; tells which sublevel the electron is on and determines the shape of the orbital; sublevels are repetitively numbered and also lettered

Valence Electrons

The electrons in the outermost shell, which participate in the bonding between atoms.

Pauli Exclusion Principle

An atomic orbital may describe at most two electrons, each with opposite spin direction

Bonding Energy

The energy required to separate two atoms that are chemically bonded to each other to an infinite distance

What does a column group represent in a periodic table?

Similar valence electron configurations/structure and chemical/physical properties

Electropositive Elements

The elements have a tendency to release valence electrons (metals) and have a low electronegativity

Electronegative Elements

The elements having a tendency to accept valence electrons (non-metals) and have a high electronegativity. [MC]

What is the general trend on the periodic table for increasing the Electronegativity?

The electronegativity usually increases from left to right and bottom to top. [MC]

Ionic Bonding and Directonality

Chemical bonding that results from the electrical attraction between cations and anions. Electron is given. Non-directional

Covalent Bonding and Directionality

Covalent Bonding happens when electrons are shared between two atoms and they have a similar electronegativity.

Covalend Bonds are directional

Metallic Bonding and Directionality

In a metallic bond, the valence electrons are not bound to a particular electron and can flow throughout the metal.

Metallic Bonds are non-directional.

Dipole

created by equal but opposite charges that are separated by a short distance

Fluctuating Induced Dipole Bonds

a fluctuating induced dipole bonds is a temporary bond due to some atomic vibrations or motion.

Polar Molecule Induced Dipole Bonds

A polar molecule induced bond happens when two polar molecules are attracted to their opposite sides. [Water Molecule]

Hydrogen Bonds - Permanent Dipole Bonds

Hydrogen has some very strong bonds to other atoms such as Cl, F.

Crystalline Material

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

Unit Cell

a basic structural unit of a crystal structure, defined in terms of geometry and atom positions within a parallelepiped volume.

FCC Number of Atoms, Coordination Number and APF

4 atoms in Unit Cell

12 Coordination Number

APF is 0.74 or 74%

BCC Number of Atoms, Coordination Number and APF

2 atoms in Unit Cell

8 Coordination Number

APF is 0.68 or 68%

HCP Number of Atoms, Coordination Number and APF

6 atoms in Unit Cell

12 Coordination Number

APF is 0.74 or 74%

For BCC, the relation between the atomic radius and unit cell length

a\=4R/sqrt(3)

For FCC, the relation between the atomic radius and unit cell length

a \= 2Rsqrt(2)

Polymorphism

The phenomenon of a solid material to exist in more than one form of crystal structure.

Allotropy

Polymorphism but in Elements.

Linear Density Formula

Number of Atoms in a Direction Vector/Length of Direction Vector

Planar Density Formula

Number of Atoms centered on a Plane / Area of Plane

HCP Closest Packed Plane and Stacking Pattern

(0001) and ABABAB...

FCC Closest Packed Plane and Stacking Pattern

(111) and ABCABCABC...

single crystal

A crystalline solid for which the periodic and repeated atomic pattern extends throughout its entirety without interruption.

Polycrystalline

Crystalline materials composed of more than one crystal or grain.

Anisotropy

Exhibiting different values of a property in different crystallographic directions. (Greater Electrical Conductivity in a Certain Plane)

Isotropy

having the same properties in all directions

Bragg's Law

nλ\=2dsinθ--\> fundamental equation of diffraction. It states that diffraction occurs at specific values of , where is determined by the wavelength of the radiation and the interplanar spacing

What is the diffraction angle?

The diffraction angle is 2θ, so theta is half the diffraction angle.

d_hkl formula

Sufficient Conditions for Diffraction in FCC and BCC

FCC: h,k and l must all be odd

BCC: h + k + l \= even

Two types of Point Defects

Self-Interstitial and Vacancies

self-interstitial

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

vacancy

unfilled position; unoccupied apartment or room

Solid Solution

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

alloy

A mixture of two or more metals

Two types of Solid Solution

Substitutional and Interstitial

Factors affecting the Solubility of Substitutional Solid Solutions

1. Atomic Size

2. Crystal Structure

3. Electronegativity Factor

4. Valence

Weight Percentage

C1 \= m1/(m1+m2)

Atom Percentage

C1' \= (n_m1)/(n_m1+n_m2)

What is a dislocation?

a linear or one-dimensional defect around which some of the atoms are misaligned.

Burgers vector

A vector that denotes the magnitude and direction of lattice distortion associated with a dislocation.

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.

screw dislocation

A linear crystalline defect associated with the lattice distortion created when normally parallel planes are joined together to form a helical ramp. The Burgers vector is parallel to the dislocation line.

External Surface - Interfacial Defect

Surface Atoms aren't bonded to the maximum number of atoms and thus can be broken off easier.

Grain Boundaries - Interfacial Defect

The angle difference between grain boundaries can affect the hardness of the material. Higher angles between the alignment of boundaries can create harder to move grains.

Phase boundaries - Interfacial Defect

Different phases can have different properties in a multi phase material

Twin Boundaries

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

grain size

The average grain diameter as determined from a random cross section.

ASTM grain size number

A measure of the size of the grains in a crystalline material obtained by counting the number of grains per square inch at a magnification of 100

Diffusion

Movement of molecules from an area of higher concentration to an area of lower concentration.

Interdiffusion

diffusion of atoms of one metal into another metal

Self diffusion

atomic migration in pure metals, from higher concentration to lower concentration regions.

Two key conditions for Atoms to migrate

1. An empty adjacent site

2. Sufficient energy to break bonds.

vacancy diffusion

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

interstitial diffusion

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

diffusion flux

The quantity of mass diffusing through and perpendicular to a unit cross-sectional area of material per unit time.

steady-state diffusion

The diffusion condition for where the diffusion flux is independent of time

What is the driving force of steady-state diffusion?

The concentration gradient.

Components

A chemical consituent of an alloy either pure metal or compound.

System

A specific body of material under consideration or a series of possible alloys. Consisting of the same components (Pb-Sn Systems)

Solubility Limits

The max concentration of solute that may be added without forming a new phase.

Phase

A homogeneous portion in a system having uniform physical & chemical characteristics

What are the 4 characteristicts of a mictorstructure

1. \# of Phase

2. Phase Composition

3. Relative Amount

4. Distribution

The major factors affecting the structure

1. Alloying Elements

2. Their Composition

3. Heat Treatment