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Size Effect on the Elasticity and Thermal Stability of Nanomaterials

Author: LiuXinJuan
Tutor: SunChangQing
School: Xiangtan University
Course: Materials Physics and Chemistry
Keywords: Nanomaterials Bond-breaking theory Size effect Elasticity Low melting point
CLC: TB383.1
Type: Master's thesis
Year: 2010
Downloads: 66
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Abstract


Microscopic first-principles molecular dynamics, and macroscopic continuum mechanics at the nano-scale range, were encountered in the analysis of of nanomaterials elastic and thermal stability of the size effect of varying degrees of difficulty and challenge. Therefore, there is an urgent need to find new theoretical model prediction and analysis of nanomaterials Young's modulus increased melting point lowering the novel phenomenon, and to reveal the intrinsic physical mechanism. Due to the interaction between a large number of low ligand surface atoms of nanomaterials performance is completely different from the isolated atoms and block material. This thesis explores several typical nanomaterials such as ZnO, TiO 2 , Ag, Au, and elastic and thermal stability of the size effect. Specific work and conclusions are summarized as follows: from local key average approximate point of departure to explore the dependence of the elastic properties of semiconductor ZnO nanostructures size, found that: (i) Young's modulus is proportional to the energy density; (ii) Yang 's modulus with the changes in the size, only there is a tendency, i.e., Young's modulus increases with the reduction in size of; (iii) a specific surface area dominated the change trend of the size effect; only the most outer layer of atoms in the (iv) nano materials play a leading role in the size effect of the Young's modulus, the keys of the central atom keep the bulk value, has no effect on the size of the effect of the Young's modulus; (v) nano materials low ligand atoms keys shorter to strong resulting in increased energy density is the main reason for the increase of the Young's modulus. The same time, the bond-breaking theory also good forecast and analysis of the the TiO 2 , Ag, Au nanomaterials elastic properties of the size effect. 2 from the surface atomic binding energy of the perspective of the low melting point of Ag, Au and other metal nanomaterials phenomenon found: the nanomaterials low ligand surface atom bond length shorter; keys can enhance; combination of atoms reduced, which is the main reason for the decrease of the melting point of the lead nanomaterials. Meanwhile, the bond-breaking theory is also very good prediction and analysis of Pb, In, Bi phenomenon of the low melting point of the metal nanomaterials. The theoretical and experimental consistency proved the key of low coordination atoms shorter, leading to increased energy density between atoms combine to reduce, which dominates the size effect of nanomaterials elastic and thermal stability. The broken bonds theory is to study the size effect of nanomaterials elastic properties and thermal stability of the effective ways to connect the macro-theoretical methods and the bridge of the microscopic theory.

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