Materials Test 1

Materials Test 1

1. Chemical Bonding

   • Metallic Bonding
     • delocalized electrons
     • Atoms are spherical
     • no directional bonding constraints
     • CN is determined by size of atoms
     • allows for contact welding
   • Covalent Bonding
     • bonds formed by sharing outer s and p orbitals or sp^3 orbitals
     • very directional
     • high electron density between atom centers
     • Electrons are held in narrow energy levels
     • CN is fixed by number of bonding orbitals and shape of orbitals
     • electrons are shared
   • Ionic Bonding
     • strong absorption in the infrared
     • transparent in visible spectrum
     • high hardness, strength, and MP
     • Complete Outer Shell
     • CN controlled by geometry or radius ratio
     • Coulombic forces of attraction/repulsion determine bond length

2. Properties of Engineering Materials

   • Metals
     • opaque
     • ductile
     • tough
     • good conductors
     • reflective
   • Ceramics
     • cheap
     • translucent
     • poor conductors
     • refractory
     • strong/brittle
     • good insulator
   • Polymers
     • weak
     • low melting point
     • easy to form
     • expensive raw materials
     • transparent/translucent

3. Potential Well Concept

   • Elastic Modulus: E
     • steep, narrow-large E
     • broad, shallow-small E
     • objects resistance to being plastically deformed
     • the slope of a stress-strain curve
     • Stress(o)/strain(e)
       • stress=Force/area
     • Force*Length/(A*change in Length)
   • deep well-high bonding energy, high melting point
   • Thermal expansion-amplitude of vibration

4. Pauling's rules of crystal chemistry

   • Geometry or radius ratio determines the packing of anions around a central cation
     • sum of atomic radii determines cation-anion distance
     • r+/r- determines CN
   • Electrical neutrality must be preserved
     • CN=cations around an anion
   • Polyhedra are shared at corners, seldom at edges, and almost never at faces
   • # of essentially different constituents tend to be small

5. Crystallography

   • Bravais Space Lattice
     • 14 different verifiable ways to build lattice in 3-D
       • 3 ways to create
         • translation of lattice points
         • symmetry elements
           • Center of Symmetry
             • inversion/reflection in point
           • Mirror Symmetry
             • reflection in a plane
           • Rotational symmetry
             • rotation about axis
           • Structures
             • Cubic: 4(3 fold)
             • Hexagonal:1(6 fold)
             • Rhombic:1(3 fold)
             • Tetragonal: 1(4 fold)
             • Orthorhombic: 3(2 fold)
             • Monoclinic:1 (2 fold)
             • Triclinic: none
         • Coordination number
     • Simple Cubic
       • CN=6
       • a=2r
       • 8 fold interstial in center
     • BCC
       • CN=8
       • r=sqrt(3)*a/4
       • 6 fold interstitial in face centers
     • FCC
       • CN=12
       • r=sqrt(2)*a/4
       • 6 Fold Inter (edge corners)
       • 4 fold Inter(corners)
     • HCP
       • CN=12
       • 6 fold inter
       • 4 fold inter(corners)
   • Unit Cell
     • smallest unit of volume that permits identical cells to be stacked together to fill al space
     • Miller Indices
     • Braggs Law
       • gamma=2*dhkl*sin(theta)
   • Defects
     • 0-D: point Defects
       • vacancy concentration highest at the melting point
     • 1-D: line defects
       • Dislocations
         • Edge
         • Screw
         • Formation
           • Collapse of thermal vacancies
           • Frank-Reed Source(2 pinning sites)
           • Growth Defects
           • Mechanical Stress
         • Dislocation Climb
           • movement of dislocations out of glide planes by interaction with vacancies
         • Interactions
           • Annihilation
           • Pinning
           • large atoms collect in strain area
           • small atoms collect in compression
     • 2-D
       • grain boundaries
       • Twinning
     • 3-D
       • porosity

6. Mechanical Properties of Materials

   • elastic deformation is reversible
   • plastic deformation happens when stress is sufficient enough to permanently deform the metal
   • Yield Strength(O)
     • elastic becomes plastic at this point
   • Ultimate Tensile Strength
     • The maximum amount of stress a material can withstand before breaking
     • highest point on Y axis of Stress Strain curve
   • Stored Elastic Energy
     • Area under stress strain graph up to the yield stress
   • toughness
     • area under the curve

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