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38 Cards in this Set
- Front
- Back
Chemical bonds |
Form by interactions between the valence electrons |
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Ionic bonding |
Transfer of electrons, non directional, hard but brittle, resistant to degradation, bad conductors. Ex. Ceramic (alumina, calcium phosphate) |
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Covalent bonding |
Sharing electrons, only non metals, directionality by geometry of sub shells, flexible —> easily deformed, not good conductors
Ex. Polymers (polyethylene) |
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Metallic Bonding |
All electropositive, want to give up e-, valence electrons are floating around, conductive, easily formed and processed, susceptible to corrosion
Ex. Stainless steel, cobalt chrome, titanium and alloys |
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Forces between atoms are determined by ____ and ____ |
Charge and distance |
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Bonding energy |
Energy needed to separate the two atoms |
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Higher bond energies = _______ melting temps |
Higher |
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The steeper the force curve, the _______ the material |
The greater the force needed to change interatomic distance, stuff the material |
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Hydrogen bonding |
Electrostatic interaction between polar molecules |
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_______ are crystalline materials |
Metals and ceramics |
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Crystalline material |
Any material that has long-range orderly arrangement of atoms/ions that can be described by a unit cell |
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Unit cell |
Smallest repeating unit |
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Atomic hard sphere model |
Each atom is a hard sphere with a fixed volume |
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Simple cubic |
One atom located at each corner of the unit cell |
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Atomic packing factor |
Volume fraction occupied by atoms
APF = volume of atoms in a unit cell / tot unit cell volume |
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Body centered cubic |
Additional atom in center of cube Ex. Iron, chromium |
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Face centered cubic |
Atom at the center of each face, APF highest of all struct
Ex. Aluminum, copper, gold, lead, platinum |
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Coordination number |
Number of nearest neighbors |
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Linear Density Equation |
LD = number of atoms centered on a direction vector / length of the vector |
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Planar Density Equation |
PD = number of atoms centered on a plane / area of plane |
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Coordination number |
Number of nearest neighbors of opposite charge |
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Point defect: vacancy |
Missing atom in structure (extra space) |
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Point defect: interstitials |
Extra atom in structure (crowding) |
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Rules of solubility of metals |
1. Atomic radii of solvent & solute must be similar (<15% diff) 2. Solute and solvent have identical crystal structures 3. Metal prefers to dissolve into solution with higher valency (number of valence electrons) over a solution with low valency 4. Solute and solvent have similar electronegativities |
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Which element is usually interstitial |
Carbon |
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Shottky defect |
Vacancy in both cation and anion to maintain neutrality |
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Frenkel defect |
Vacancy and interstitial pair created to maintain electroneutrality |
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Diffusion in gas/liquid |
Occurs by random motion |
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Diffusion in solids |
Occurs by jumping into neighboring lattice points/positions |
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Vacancy diffusion |
Atom jumps to neighboring position with a vacancy |
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Interstitial diffusion |
Interstitial atom jumps to nearby interstitial site |
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Which is faster? Vacancy or interstitial and why? |
Interstitial because doesn’t require existence of vacancy |
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Diffusivity depends on |
Temperature and activation energy |
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The larger the activation energy, the _____ the diffusion coefficient |
Smaller |
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The higher the temp, the _______ the diffusion coefficient |
Higher |
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Flux |
Rate of change in mass or number of atoms across an area over a given time |
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At a steady state, flux _______ it is _____ |
Doesn’t change with time, constant |
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Conservation of mass |
Rate of change in concentration in the box is equal to the flux into the box minus the flux out of the box |