35 terms

Materials Science Chapter 5

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alloy
a metallic substance that is composed of two or more elements
atom percent
concentration specification on the basis of the number of moles or atoms of a particular element relative to the total number of moles or atoms of all elements within an allow
atomic vibration
vibration of an atom about its normal position in a substance
Boltzmann's constant
1.38 x 10^-23 J/atomk or 8.62 x 10^-5 eV/atomk
Burgers vector
a vector that denotes the magnitude and direction of lattice distortion associated with a dislocation
composition
relative content of a particular element or constituent within an alloy
defect structure
kinds and concentrations of vacancies and interstitials in a ceramic compound
dislocation line
line that extends along the end of the extra half plane of atoms for an edge dislocation and along the center of the spiral of a screw dislocation
edge dislocation
a linear crystalline defect associated with the lattice distortion produced in the vicinity of the end of an extra hard plane of atoms within a crystal. Burgers vector is perpendicular to the dislocation line
electroneutrality
state of having exactly the same numbers of positive and negative electrical charges
Frenkel defect
in an ionic solid, a cation-vacancy and cation-interstitial pair
grain size
average grain diameter as determined from a random cross section
imperfection
deviation from perfection. You probably have a lot.
interstitial solid solution
solid solution in which relatively small solute atoms occupy interstitial positions between the solvent or host atoms. Impurity must fit interstitial site; less densely packed structures have ore room for interstices; charge balance must be maintained in ionic materials; chemical affinity; covalent materials don't work with this
microstructure
structural features of an alloy subject to observation under a microscope
mixed dislocation
a dislocation that has both edge and screw dislocation
point defect
crystalline defect associated with one or several atomic sites
Schottky defect
in an ionic solid, a defect consisting of a cation-vacancy and anion-vacancy pair
screw dislocation
linear crystalline defect associated with the lattice distortion created when normally parallel planes are joined together to form a helical ramp. The Burgers vector is parallel to the dislocation line.
self-interstitial
host atom or ion positioned on an interstitial lattice site
solid solution
homogeneous crystalline phase that contains two or more chemical species.
solute
one component or element of a solution present in a minor concentration. Dissolved in solvent.
solvent
component of a solution present in the greatest amount Component that dissolves a solute.
stoichiometry
for ionic compounds, the state of having exactly the ratio of cations to anions specified by the chemical formula
-when compound is not defined by formula it is nonstoichiometric
substitutional solid solution
a solid solution in which the solute atoms replace or substitute for the host atoms. Difference in radius < 15%, large difference fields lattice distortion --> new phase; crystal structure must be the same; electronegativity should be similar or else favor compound formation; metals are more likely to dissolve in another metal of higher valency than one of lower valency, in ionic materials different valences require compensating defects, in covalent materials they must satisfy discrete, directional bonds
vacancy
a normally occupied lattice site from which an atom or ion is missing
weight percent
a concentration specification on the basis of weight or mass of a particular element relative to the total alloy weight or mass
equilibrium concentration
http://images.slideplayer.com/26/8285293/slides/slide_6.jpg
See notes to get Q
extrinsic
control concentration via processing, composition
aliovalent
having different valency from host
dopants
intentional impurities, added at low concentration to control behavior; substitutional
grain boundary
boundary between crystals produced by solidification process or crystallization of thin films/glasses; have a change in crystal orientation across them; impede dislocation motion , scatter electrons/phonons; have higher energy than that of crystals (internal surface)
phase boundary
boundary between two regions of different phases
Nv (number of vacancies)
Nexp(-Qv/KT) where Qv is heat of formation of vacancy, k is a constant, N-8x10^28 atoms/m^3, T is temp Nv/N is vacancy concentration
hume rothery rules
rules for solid solution formations, when solute atoms are added to host materials, (whether or not another type of atom can replace an atom there)
1. atomic size factor... less than 15% difference
2. crystal structure... same type
3. electronegativity...close
4. valences
when these conditions are satisfied, a substitution can occur, if the first condition results in the solute atoms being much smaller than the host atoms, they may be placed in interstitial positions to form interstitial impurity atoms
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