Crystal Defects Flashcards
What are the types of linear defects?
Edge Dislocation
Screw Dislocation
What is an edge dislocation?
When a extra row of atoms inserts itself in crystal matrix
Consider the magnitude and direction of atomic displacement
What is a screw dislocation?
part of the material shifts
caused by shear forces
Burger’s vector is parallel to the dislocation
What is a mixed defect?
When edge and screw dislocations exist at the same time in the same material
What process causes dislocations?
Slipping
Describe surfaces as a planar defect.
atoms at the surface are not bonded to maximum number of nearest neighbors
contain more free energy
Describe grain boundaries as a planar defect.
atoms at edges do not often contain maximum number of nearest neighbors
larger grain = lower interfacial energy
What are volume defects?
regions in which long range order of crystal is lost
How are precipitates a volume defect?
clusters or substitutional or interstitial impurities
How are voids a volume defect?
three dimensional aggregates of vacancies
What do porous materials have?
voids
How can you create pores?
Chemically: salt, gelatin, wax, gases
Mechanically: etch, print, weave, spin
What is burger’s vector?
variable (b): it represents the magnitude and direction of the lattice distortion resulting from a dislocation in a crystal lattice
