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
What is the definition of Dopents?
elements or compounds that are deliberately added in known concentrations at specific locations in the microstructure with an intended beneficial effect on properties or processing
True or false. Are dislocations present in all materials, including ceramics and polymers
True
