Elemental & Metallic Solids

Elemental & Metallic Solids

Nv= nexp (-Qv/ RT)

nv: number of vacancies/cm3
n: number of atoms/cm3
Qv: activation energy required to produce vacancies – J/mol
R: gas constant
T: Temperature – K
Origin of vacancies in elemental & metallic solids: thermal excitation; aka "intrinsic vacancies"

Effect of Heat Treatment

- Vacancy concentration after furnace cooling
- Vacancy concentration after quenching
- Comparison of electrical resistivity between furnace cooled and quenched Cu wires
- Comparison of yield strength between furnace cooled and quenched Cu wires
- Comparison of diffusivity (of other species) between furnace cooled and quenched Cu wires

Vacancies in Ionic Solids-2

-  Vacancies are created when "solutes" dissolve in "solvent"
-  Vacancy concentration dependent on solute concentration
-  Cations dissolve into cation sites
-  Anions dissolve into anion sites
-  Vacancies are distinguished as:
-  Cation vacancies, and
-  Anion vacancies
-  Charge neutrality must be maintained 
-  Vacancies created as a result of solute dissolution are called "extrinsic vacancies"

Substitutional Defects - 1

-  What is a substitutional defect?
-  Examples of substitutionals
-  Hume-Rothery Rules
-  Size ratio
-  Electronegativity difference
-  Valence difference
-  Crystal structure difference

Franky L. Duque Ayala
15.990.445
CRF
http://www.sjsu.edu/faculty/selvaduray/page/mate115/Defects%20in%20Solids.pdf

---

Connect to the next generation of MSN Messenger  Get it now!