MSE 2101 Quiz 1/Exam 1
edge (line) dislocation
- slip plane along edge dislocation line - shear stress τ moves in the same direction as the dislocation line - increase shear stress: can push/pull material to a certain extent without permanent deformation, making the material stronger - if shear stress is too much --> permanent deformation
Impurity point defects
1. Substitutional (Al-Cu) - Cu has similar size, same valence, and same crystal structure as Al 2. Interstitial - fills the voids between host atoms of the crystalline structure
Atomic Packing Factor (APF)
the volume of solid divided by the volume of the unit cell Ex. FCC: Vf = (16/3)piR^3 / 16√2*R^3
coordination number
the number of anions that surround each cation in a crystal
amorphous
noncrystalline, shapeless, without definite form - ex. glass
theoretical and bulk density
p(th) = nA/VcNa p(bulk) = real density of a component of substance - bulk density is always less than theoretical density -- vacancies -- crystals (voids between packed grains)
close-packed structures
A crystal of a single atom type in which the spherical atoms are packed as tightly as possible, giving an APF of 0.74 - FCC
Body Centered Cubic (BCC)
A cubic structure in which atoms are located in the corners of the unit cell plus one in the center of the cubic unit cell. - no atoms in faces - less stable than FCC but more than simple cubic - 2 atoms per unit cell (8*1/8 + 1) - side length a = 4R/√3 - volume V = a^3 = 64R^3 / 3√3
Miller Indices
A shorthand for expressing directions and planes in crystals. - Notation: (1 1 1) - where the plane hits the *axes*
Simple Cubic
A unit cell that consists of a cube with one atom at each corner - 1/8 of an atom at each corner --> 1 total atom per unit cell - very open, unstable - a = 2R - V = 8R^3
Group IIA
Alkaline earth metals (Ca, Ba, Mg, Sr)
Group IA
Alkaline metals (Li, Na, K)
modified silica (SiO2) glass
As more Na2O is added: - 3D silica network breaks - melting temperature decreases - static viscosity decreases (thinner glass) - workability (ease of shaping) increases - glass stability (how stable is the glass state?) decreases --> wants to crystallize more
Group VIIA
Halogens (F, Cl, Br, I)
fractional concentration of vacancies
Nv/N = e^(-Qv / KT) - Nv = equilibrium # of vacancies/m^3 at temp T (in K) - N = # of lattice sites/m^3 - N = Na*p / A (p is density) - Qv = activation energy for vacancy formation per atom (eV/atom) - K = Boltzmann's constant Nv/N = e^(-Qv / (K*Na)T) for per mole
Bohr Atom Model
Principal quantum number n, secondary quantum number l, spin (+/-). ex. 2p6 (2 = n, p = l, spin --> how electrons fill up orbitals)
Grain boundaries
The boundaries between crystals (grains) in a polycrystalline material. - the orientation of the grains defines the strength of the material - bunch of grains oriented differently (their [1 0 0] is different) -- any edge of a cube is [1 0 0]
Face Centered Cubic (FCC)
a cubic structure in which atoms are at the corners and an atom is on each cube face of the unit cell - most stable - 4 atoms per unit cell (8x1/8 + 6x1/2) - close-packed structure - 8 tetrahedral voids (1 per corner) - 4 octahedral voids (1/4 at each edge and 1 in center --> 1/4 * 12 + 1 = 4) - side length a = 2R√2 - volume V = 16√2*R^3
Electronegativity (Xa)
an element's tendency to attract electrons and is equal to IP + EA
% Ionic Character
depends on Xa - Xb %IC = [ 1 - e^(-0.25*(Xa-Xb)^2) ] x 100%
covalent bonding
electron sharing (CH4)
ionic bonding
electrostatic attraction/repulsion (Na+Cl-)
Electron affinity (EA)
energy released from the atom when an electron condenses (goes back) into the atom (<0)
Ionization potential (IP)
energy required to extract one electron from an atom (>0)
metallic bonding
free electron cloud with positive atomic cores
Voids
if top layer has one void, layer below has other type of void (octa, tetra)
van der waals bonding
instantaneous molecular dipoles - force between layers of carbon in graphite
Arrhenius plot
ln(Nv/N) = (-Qv/R)*(1/T) lnY = K*(1/T)