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今日上mech3110所學


Point defects are the smallest one
More at high T responsible for movement
These are from lattice vacancy
Atoms need it to move cause closely packed


Impurity may cause it too
Purposely in raw materials


There's interstitial too
Which is any atom in place where atoms not supposed to be
Mechanically important
Like the smaller carbon ones in steel


There are also line defects too
1D defect but it looks like 2D
As there are perfect unit cells, one distorted for difference between two parts


Mediates mechanical deforms
Bonds move like plastics deform


Surface defects most common
Cause surface boundary between material and environment
Reactions start, atoms behave differently
New functions cause *nano ones unique


The atoms have surface stress to get closer
Those matter materials have different properties
Interface same impacts between two different phases, like Cu and Al


Grain boundaries have 2 regions of same phase but different orientations so no cell
Bonds weaker, smaller effects on
Properties than surface, like polycrystals


Some solids are amorphous
Just like glass, some polymers, their structures look like a liquid
When compressed, or closely packed, atoms need to move a lot of space


Atoms may deviate 
From crystal structure or composition of material
So it is defected, in 1 2 or 3D
Responsible for different properties


They're not perfect


*Nano ones:  Nanomaterials.



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