Siphamandla Mtem | Nelson Mandela Metropolitan University (original) (raw)
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Mech 221 lecture 7/2 There is no such thing as a perfect crystal! • Thermodynamically " impossibl... more Mech 221 lecture 7/2 There is no such thing as a perfect crystal! • Thermodynamically " impossible " • " defects " lower the energy of a crystal & make it more stable • always have vacancies and impurities, to some extent Defect does not necessarily imply a bad thing • addition of C to Fe to make steel • addition of Cu to Ni to make thermocouple wires • addition of Ge to Si to make thermoelectric materials • addition of Cr to Fe for corrosion resistance • introduction of grain boundaries to strengthen materials …… and so on " Defect " (in this context) can be either desirable or undesirable. In general, a defect simply refers to a disruption in the crystalline order of an otherwise periodic material.
Mech 221 lecture 7/2 There is no such thing as a perfect crystal! • Thermodynamically " impossibl... more Mech 221 lecture 7/2 There is no such thing as a perfect crystal! • Thermodynamically " impossible " • " defects " lower the energy of a crystal & make it more stable • always have vacancies and impurities, to some extent Defect does not necessarily imply a bad thing • addition of C to Fe to make steel • addition of Cu to Ni to make thermocouple wires • addition of Ge to Si to make thermoelectric materials • addition of Cr to Fe for corrosion resistance • introduction of grain boundaries to strengthen materials …… and so on " Defect " (in this context) can be either desirable or undesirable. In general, a defect simply refers to a disruption in the crystalline order of an otherwise periodic material.