Chapter 2 - Crystal Structure Flashcards
What does manufacturability depend on?
Crystal structure
Why do we use Zircaloy as fuel cladding?
Because of limited swelling due to underlying crystal lattice structure
What are metallic glasses?
metals without a crystal structure
What is the unit cell?
The smalles unit translation of space lattice that reproduces a macroscopic crystal
What are cubic crystals characterized by?
The number of lattice sites per unit cell
What are close packed planes?
The planes containing the highest atom density
What are close packed directions?
direction of smalles atomic separation
How do we determine the crystal strucutre?
X-ray spectroscopy
How do we specify planes and indices?
With millers notations
What crystalline structure is circonium?
HPC
What are ionic solids?
solids formed from electro-negative and -positive elements (cations and anions).
Name some examples of ionic solids in nuclear?
UO2 B4C
How are ionic solids sub-lattices represented?
mixture of simple lattices formed by the elements
What is the usual structure for MX solids?
The NaCl and the CsCl structure
What is the usual structure for MX2 solids?
box withing box
What are point deffects?
- Vacancy
- SIA
- Interstitial Solute
- Subtitutional Solute
Name the three type of mixed crystals?
substitutional random
substitutional ordered
interstitial
What determines solid solution or precipitation?
The hume rothery rules
What are the hume rothery rules?
Atom radius not more than 15%
Similar crystal structure
Small electro negativity difference
Number of valence electrons should be similar
What is the electronegativity?
Chemical potential of an element. It describes the tendency of a material to attract electrons.
What is the principal product of neutron irradiation of the structural metals in LWR?
highly non-equilibrium concentrations of vacancies and self-interstitials in equal numbers
What is the effect of a vacancy in the nearby atoms?
Attractive force of neighboring atoms into vacancy creates a tensile stress (strain) field which is elastic isotropic.
What is the equilibrium vacancy fraction a function of (#/atom sites)?
The gibs free energy of vacancies and the temperature. X = exp(-G/RT)
What does the gibs free energy of vacancies depends on?
Entropy, temperature and enthalpy. G=H-TS=E+pV-TS