Mats Lecture 19 Flashcards
Imperfections of Solids
What do we characterize defects by?
Their geometry
What are the categories of defects?
-Point defects
-Line defects
-Planar defects
What are examples of point defects?
-vacancies
-impurities
What are examples of line defects?
-Dislocations
What are examples of Planar defects?
-Grain boundaries
What are Point Defects?
-are localized disruptions in perfect atomic or ionic arrangement in a crystalline structure, which involve several atoms or ions
How are point defects introduced? List the different ways
When there is a movement of atoms or ions when they gain energy by:
-heating
-processing of the material
-intentional or unintentional introduction of impurities
How is a vacancy produced?
-When an atom or an ion is missing from its normal site in a crystal structure
When are vacancies introduced into metals and alloys?
-Introduced during solidifications:
-at high temperatures
-or as a consequence of radiation damage
How is an interstitial defect formed?
-Formed when an extra atom or ion is inserted into the crystal structure at a normally unoccupied position
What happens to the surrounding regions of where interstitial defects form?
-The surrounding crystal region is compressed and distorted
How is an interstitial defect different from vacancies?
-The number of interstitial atoms or ions stay constant even when temperature is changed
How are substitutional defects introduced?
-When one atom or ion is replaced by a different type of atom or ion
Where are substitution atoms or ions found?
-They occupy normal lattice sites
What is the definition of impurities?
-normally are elements or compounds that are present from raw materials or processing
