Crystalline Defects

Porosity

• Volume fraction of a solid that is empty

• 0= no pores

• 1= barely empty space

Defects

• Point defect (zero D): singular atom

• Liine defect (1D): line of atoms

• planar defect (2D): plane of atoms

• Bulk defects (3D)

Point Defect

• Vacancy: an atom missing

• Interstitial: atom is not where it normally belongs

• More vacancy, more entropy

• Higher temperature= higher vacancies

Line defects

• Dislocation in missing/extra half plane

  • Affects electrical conductivity

  • Unstable

  • Disappear at high temperatures

Planar defects

• Solids are polycrystalline: multiple different crystalline regions

• Grain boundary: transition from 1 grain to another

• Grain boundaries impact mechanical properties

Bulk Defects

• Voids (e.g casting)

• Porosity (e.g 3D printing)

• Cracks

• Fracture toughness is very sensitive to bulk defects