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106 Cards in this Set
- Front
- Back
- 3rd side (hint)
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electronegative
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elements that tend to receive electrons during chemical reactions
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electropositive
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elements that tend to give up an electron
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Bonding force=
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bonding force= F{attractive} + F{repulsive}
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Attractive force
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tendency of atoms to achieve noble gas configuration
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Repulsive force
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inner, fully occupied electron shells cannot overlap (Pauli's priniciple)
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Bonding energy is...
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energy required to break atoms apart
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Bonding Energy = E(r) =
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Bonding energy= E(r) = E{attractive} + E{repulsive}
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generic bonding potential
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chart with bonding energy; repulsive energy on top, attractive energy on bottom; lowest bonding energy is where the bond will occur in nature
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High bonding energy = high E (o)
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closer atoms will be to each other, shorter the bond length will be, stronger the bond
ex: solids, hard, high melting temperatures, low thermal expansion coefficient |
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small r (distance between atoms)
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repulsive force is dominating
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large r (distance between atoms)
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attractive force is dominating
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Why is it important to know where energy is minimum?
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Everything in nature goes towards minimum energy
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electronegativity
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tendency to acquire electrons
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Primary bonds
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strong, determined by valence electrons (main bonds you know)
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ionic bonding
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-TRANSFER of valence electrons; metal + nonmetal; Large difference in electronegativity required; occurs between + and - ions
-LARGE bond energy **NON-DIRECTIONAL** |
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Covalent bonds
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atoms achieve noble gas configuration by SHARING VALENCE ELECTRONS; involves hybridization (mixing of orbitals)
**DIRECTIONAL** |
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Metallic Bonds
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valence electrons are being shared among all atoms in material; free electron gas= electron and thermal conductivity
**NON-DIRECTIONAL** |
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Which bonds are directional and which are nondirectional?
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Ionic and Metallic= non-directional
Covalent= directional |
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Secondary Bonds
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involve all electrons, not just valence; WEAK
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Van-der-Waal interactions
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induced dipolar interactions due to fluctuations in electron cloud, ACTIVE FOR ALL MOLECULES/ATOMS
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Permanent Dipole
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if covalent bonds form between atoms of distinct electronegativity, permanent dipole moments occur (depending on symmetry of molecules)
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Z
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atomic number
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atomic number
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corresponds to number of protons in nucleus for natural elements
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isotopes
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nuclei with same atomic number "Z" but different number of neutrons
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amu
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atomic mass unit
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Atomic mass unit (amu)
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a unit of mass used to express atomic and molecular weights; = (1/12)*mass of C-12
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Avogadro's number
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= 6.02 x 10^23 (1/mol)
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Schrodinger's wave-mechanical model of atoms
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wave particle duality of electrons
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quantum numbers
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Qn; characterize the electronic structure of atoms; nlms
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https://o.quizlet.com/Ud4mtzEtQFdybA3uGGEAEw_m.jpg
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primary/principle quantum number (n)
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corresponds with primary energy level (Bohr energy level)
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secondary quantum number (l)
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describes the shape of subshells (orbitals) that exist in the primary energy level
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tertiary (magnetic) quantum numbers (m)
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describes the number of orbitals and their orientation within a subshell
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electron configuration
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describes the distribution of electrons among the available states
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four components of the disciplines of material science engineering?
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processing-->structure-->properties-->performance
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Structure of a material is based off...?
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how it was processed
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function of a material's properties tells us its...?
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performance
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Materials Science
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investigation of the relationship between structures and properties of materials
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Materials Engineering
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designing/engineering of material structures to meet certain property requirements (material selection/processing)
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metals
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-moderate melting temperature
-moderate bond energy -moderate coefficient of thermal expansion |
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ceramics
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high melting temperature
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crystal structure
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regular, periodic arrangement of atoms
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crystalline solids represent atoms/ions as...?
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represents atoms/ions as "hard spheres"
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Unit Cell (UC)
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smallest repeat unit that allows to reproduce the positions of all atoms by translating UC integer multiples along its edges;
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lattice
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a discrete but infinite regular arrangement of points (lattice sites) in a vector space
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3 types of crystal structures of metals
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1. face-centered cubic
2. body-centered cubic 3. hexagonal close-packed |
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Coordinate number (CN) of crystal structure
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number of nearest neighbors
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Atomic Packing fraction (APF)
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(volume of atoms/UC) / (volume of UC)
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Face-centered cubic (FCC)
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atoms are located at corners and face-center of cubical UC
ex: Al, Au, Cu, Pb |
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atomic radius of FCC (a)
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a= (4R) / (sqrt 2)
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# of atoms in UC of FCC
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4
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Coordinate # (CN) of FCC
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12
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Atomic Packing Fraction (APF) of FCC
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0.74
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Body-Centered Cubic (BCC)
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cubic UC; atoms at corners & center of cube; atoms connect along body diagonal
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atomic radius of BCC (a=)
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a= (4R) / (sqrt 3)
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# of atoms per UC of BCC
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2
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Coordinate number (CN) of BCC
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8
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atomic packing fraction (APF) of BCC
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0.68
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Hexagonal Close Packed (HCP)
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UC has hexagonal symmetry; atoms are in each corner, center of top & bottom face, plus 3 atoms inside UC
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density (p) =
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=Mass/volume
= [(# of atoms/UC)(atomic weight)]/[(volume of UC)(Avogadro's #)] = (m*A)/(Vuc*Nav) |
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polymorphism
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metals/nonmetals having more than one crystal structure
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allotropy
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polymorphism in elemental metals
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crystal structures
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grouping scheme of possible UC structures depending on symmetry
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There are __ combinations of lattice parameters that can form a periodic structure(BRAVAIS systems)
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There are SEVEN combinations of lattice parameters that can form a periodic structure
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high symmetry constituents (spheres) will often form...
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high symmetry constituents will often form high symmetry structures
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metals have the crystal structure of:
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cubic, hexagonal
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proteins/ polymers have the crystal structure of:
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monoclinic, triclinic
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crystallographic point coordinates
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identifies coordinates of a point within the coordinate system that is spanned by UC edges
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Orientation of crystallographic plane is indicated by ______
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MILLER indeces (h k l) **NO COMMAS
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for crystallographic planes, assume:
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assume the plane passes through one corner of UC that is NOT the origin
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family of equivalent planes
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set of planes with equivalent atomic packing {h k l}
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linear density (LD)
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(# of atoms along direction vector)/(length of vector)
[LD]= 1/length |
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planar density (PD)
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(# atoms centered on plane)/(area of plane)
[PD]=1/area |
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polycrystallinity
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material made up of distinct grains with equal crystal structure but different orientation
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defect
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lattice imperfection with at least one dimension on atomic scale
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3 types of defects
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point defect, one-dimensional, two-dimensional
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point defect
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vacancy, self-interstitial, & impurity atoms
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one-dimensional
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dislocations
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two-dimensional
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grain boundaries, external surfaces, (phase boundary)
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vacancy
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empty lattice site
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driving force for vacancies
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increase in entropy
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There is an equilibrium number of ________ that exists in materials
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There is an equilibrium number of defects that exists in materials
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Boltzman Equations describes number of _______
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Boltzman equation= number of vacancies
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Boltzman equation
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N(vacancies)=N(total)*e^-[delta Q/[k(B)*T]]
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Boltzman equation: delta Q=
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energy penalty associated with creating the defect
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Boltzman equation: k(B)
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Boltzman constant= 1.38 * 10^-23 J/K
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Boltzman Equation: T
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T=absolute temperature
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Boltzman Equation: k(B)T
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k(B)T= thermal energy (vibrations)
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Self-Interstitial Defect
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when an atom is displaced into interstitial space
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Self-Interstitial defects cause large _____________ for disturbing lattice
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Self-interstitial defects cause large ENERGY PENALTY for distorting lattice***energy penalty for self-inter>>energy penalty for vacancy
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Impurity atoms
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always present, distribute throughout a material
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Two possibilities for how impurity atoms can distribute in a material:
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solid solution or phase separation
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solid solution
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uniform distribution of 2nd component atoms in host lattice (in the solution, solvent is majority component, solute is minority)
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phase separation
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clustering of 2nd component atoms to form a new phase
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miscibility
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ability for two solids to be partially or completely soluble in each other
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Substitutional Solid Solution
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Solvent atoms are replaced by solute atoms; Perfect miscibility in substitutional solid solutions
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What do Hume Rothery Rules do?
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describe the conditions under which an element could dissolve in a metal, forming a solid solution
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What are the Hume Rothery Rules?
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1.) similar atomic size (size must differ by <15%)
2.) equal crystal structure in element pure state 3.) similar electronegativity 4.) better solubility with increasing atomic number |
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Interstitial Solid Solutions
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solid fills interstitial regions in solvent lattice; only when r(solute) << r(solvent);
typically limited to small solute concentrations due to lattice distortions |
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Line defects-- dislocations
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1D defects around which the lattice is distorted
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2 types of dislocation:
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edge dislocation & screw dislocation
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edge dislocation
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line defect that centers along the edge of an extra half-plane of atoms that has been inserted into the crystal
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screw dislocation
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line along the center of a helical path that is traced by atomic planes about the dislocation direction
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general properties of dislocations
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in reality often mixed type, lattice around dislocations is distorted (gives rise to stress/strain fields), amplitude of distortion decreases with increasing distance from dislocation
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Burger's Vector
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describes the magnitude and direction of lattice distortion associated with dislocation
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edge dislocation is ____ to dislocation direction
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edge location is NORMAL to dislocation direction
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screw dislocation is _______ to dislocation direction
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screw dislocation is PARALLEL to dislocation direction
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