材料科學(xué)基礎(chǔ)英文版課件_(12)-全文預(yù)覽
【正文】 tion – leading to an increase of entropy (randomness) –free energy decrease At a given temperature, there must be a concentration of point defects at which the free energy of the system has a minimum value. Why there is a thermal equilibrium concentration for vacancies or interstitials (selfinterstitials) Point Defects – Point Defects in Metals (3) Derivation of equilibrium vacancy concentration where ?Hv is the increase in enthalpy per mole of vacancies introduced (the vacancy formation energy) The increase in enthalpy for introducing Xv mole of vacancies in one mole of material (Xv: the mole fraction of vacancies): The increase in entropy: where ?Sv is the increase in thermal entropy per mole of vacancies introduced The increase in the free energy of the system due to the vacancy formation: ?G = ?H T ?S Point Defects – Point Defects in Metals (4) The molar free energy of the crystal containing Xv mole of vacancies: where GA is the molar free energy of the vacancyfree crystal The equilibrium concentration of vacancies can be calculated by the condition: Point Defects – Point Defects in Metals (5) Or (?G = ?H T ?S) is in units of the mole fraction and can
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