Exam #1 MSE 250

Engine turbine blades are made stronger and lighter by fabricating them with single crystal ____ that is oriented along the _____ direction for ____ _____

Nickel; [110]; Close packed; FCC

Atomic packing factor is?

The fraction of the unit cell volume occupied by atoms

Atomic Packing factor eqn?

#* (4/3) *pi *R³ / a_o ³ = APF

where a_{o is the} length of a unit cell, to get R to come out relate the two along the contiguous direction (whichever direction the atoms always touch)

APF eqn in words?

(Volume of atoms in unit cell/ volume of a unit cell)=

atom*volume of atom/ a_o ³=

Coordination Number

the number of nearest-neighbor atoms touching/surrounding one atom in the unit cell

A Grain is…

A single crystal in a polycrystalline metal or ceramic

Simple Cubic?

SC or Primitive (P), 1 lattice point per cell, atoms are only sitting on the corners

Body Centered Cubic?

I or BCC, 2 lattice points per unit cell, 1 point sitting in the middle

Face Centered Cubic

(F), 4 lattice points per unit cell, corners and each face

Base Centered

2 lattice points per unit cell, one on each base and 1 per corner (C)

How many types of unit cells?

4

How many crystal systems?

7: Cubic, Hexagonal, Tetragonal, Monoclinic, Orthorhombic, Triclinic, Trigonal

How many Bravais Lattices?

14, the 14 different ways lattice points can be arranged in 3d space while maintaining symmetry

Lattice Parameter?

a_o for our class, a=b=c= a_o the unit cell lengths

Crystal STRUCTURE is?

Crystal Lattice + Basis

Theoretical Mass Density?

#atoms * (atomic weight/avogadro’s) / Volume unit cell

volume = a_o³ for cubic

Avogadros number?

6.022×10²³

Theoretical Number Density?

#atoms/ volume unit cell

Volume unit cell for a cubic?

a_o^³

Polymorphism

1 material can exist in 2 or more crystal structures, also known as allotropic or polymorphic

Anisotropic?

a material has different properties depending on which direction u measure from

ex) Iron has 273 Gpa along the diagonal and 125 Gpa along the edge.

Metals and their packing?

Closed packed and heavy atomic weight

Ceramics and their packing?

lower packing than metals

Polymers and their packing?

Low packing factor and lighter elements

Which crystal system has P, I and F?

Cubic

Which Crystal system has P and I?

Tetragonal

Which Crystal System has P, I, F, C?

Orthorhombic, remember I is body centered cubic

Which Crystal system has P and C?

Monoclinic

Which crystal systems only have primitive?

Hexagonal, Triclinic, Trigonal

The deeper the atomic bonding potential well….

the stronger the bond is.

Deepest to shallowest potential wells

Ionic, Covalent, Metallic, Van der Waals

The bottom of the well is what?

When T= 0k, absolute zero

As you go further up the well, what increases?

Mean interatomic distance because temperature is increasing, and average oscillation amplitude as well. The atoms are getting further and further apart

(wider well= more space)

If melting temperature is larger so is…

E, young’s modulus

If the Coeff of thermal expansion is larger?

Young’s is smaller

Polymers have?

Van der waals and 1D covalent bonds, Low Bond energy, low Tm, Low E, higher alpha

Metals have?

Metallic bonding, higher bond energy, higher Tm, higher E, moderately low alpha

Ceramics have?

Ionic and Covalent, High bond energy, high E, high Tm, lower alpha

Ionic Bonding

Strong attractive coulombic force between adjacent cations and anions, due to TRANSFER of electrons

-occurs between far apart elements

-electronegativity greater than 1.7

Covalent bonding

Sharing electrons between neighboring atoms

-0.4 - 1.7 Polar covalent

-Less than 0.4 nonpolar covalent

Metallic Bonding

Strong attractive force due to a ‘sea’ of delocalized electrons around cation cores

-deeper in the periodic table the stronger these bonds become (more dEN)

Van der waals bonding?

weak attractive force between molecules from weak coulombic attraction due to temporary or permanent dipoles.

Weight percent?

mass of atoms in sample/ total mass * 100

Atomic percent?

#atoms in the sample/ total # of atoms *100

wt% —→ at%

Divide by atomic weight

at%——→ wt%

Multiply by atomic weight

Amorphous Ceramic?

Glass, short range periodicity- no long range crystal structure

NO ORDER

Crystalline Ceramic?

Quartz, long range periodicity

Polycrystalline

Has a grains, lots of composite crystal orientations, isotropic