Chp. 6 Summary Flashcards
Point defects are those associated with
one or two atomics positions (vacancies and self-interstitials.
With regard to atomic point defects in ceramics,
interstitials and vacancies for each anion and cation type are possible
Defects sometimes occur in pair, like
Frenkel and Schottky defects, in order to mantain charge neutrality
A stoichiometric ceramic is one in which the
ratio of cations to anions is the same as predicted by the chemical formula
Nonstoichiometric materials are possible when
one of the ions exist in more than one ionic state
Addition of impurity atoms result because of
the formation of substitutional or interstitial solid solutions.
For substitutional solid solutions, an
impurity atom will substitute for host atoms.
A solid solution may form when
impurity atoms are added to a solid
For substitutional solid solutions,
apreciable solubility is possible only when atomic diameters and electronegativities for both atoms are similar.
Although point defects in polymers are different than in metals and ceramiccs,
vacancies, interstitial atoms, and impurity atoms exist in all crystalline regions.
Disclocations are
one-dimentional crystalline defects (edge & screw)
Edge dislocations may be thought of in terms of
the lattice distortion along the end of an extra-plane of atoms
Screw dislocation is
achelical planar ramp
Burgers Vector specify the
magnitude and direction of lattice distortion associated with a disclocation
Orientation for Burgers Vector
- perpendicular for edge
- paraller for screw
- neither for mixed
