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The Evolvement and Characterization of Low Dimension Materials Induced by Interface

Author: ZhaoMing
Tutor: JiangQing
School: Jilin University
Course: Materials Science
Keywords: Nanocrystals Melting temperature Size dependence Interfacial stress Interfacial energy Hall-Petch relationship Monatomic Al-Si alloy Alkali metal halides
CLC: TB39
Type: PhD thesis
Year: 2004
Downloads: 239
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Abstract

The people are very concerned about the performance changes, which depends on the microstructure is determined by the chemical composition and atomic structure of solid material in the size of the one-dimensional, two-dimensional and three-dimensional direction in the range of mechanics, physics and chemistry of the solid material. When one or more of these parameters change or atomic structure deviates from the equilibrium conditions or their size is reduced to nano size and dimension is less than three-dimensional, the mechanical, electronics, magnetic, optical, catalytic and thermodynamic and other properties with traditional bulk material will undergo remarkable changes. Surface and interface material physical and chemical properties of two-dimensional region of space mutation, many important material physical and chemical processes that occur at surfaces and interfaces first, at the same time a lot of the material's physical and chemical phenomena associated with material surfaces and interfaces, When the material enters the nanometer size range, the size of the change is essentially at the same time is also introducing more interface leading to a series of changes, such as melting temperature, mechanical properties and interface characterization. A lot of damage and failure of the material originated in the first surface and interface. The microscopic structure of the study surfaces and interfaces and the interaction with the surroundings, as well as physical and chemical phenomena related to surfaces and interfaces, change the interfacial properties of the surface of the material, and the material properties of the control of the material surface and the interface of the physical and chemical processes undoubtedly is crucial. This article studied the melting temperature of the nanocrystals, mechanical properties, single-atom chain formation, the interface stress and interface morphology. Summarized in the system on the basis of the melting temperature of the model of the size dependent on the application of the low-dimensional crystals of the various types, as well as different dimensions, the effects of melting and surface melting of the low-dimensional in crystals in the different dimensions, as well as the entropy of fusion, and melting enthalpy thermodynamic model to determine a unified no free parameters. The predicted results are in good agreement with experimental data. Surface melting temperature T _sm (D) function of the size effect is significantly weaker than the the ordinary melting temperature T _m (D) function. This difference is only about the size of the C _pm S _m the eleventh. Melting the surface of the drive force is much smaller than the melting driving force. H _m (D) the size-dependent than T _m (D) The sizes stronger dependence, because H _m (D) is T _m (D) and S _{the product of the m} (D), while T _m (D) and S _{m (D), another Jilin University doctoral thesis are size dependent. The model predictions and experimental results consistently show that the size dependence of the melting is a thermodynamic transition. Hm (D) increase or decrease in physical nature the nanocrystals the inner surface of the free surface and bound cases, the changes in its size dependent stronger than or weaker than the change in internal energy of the liquid. So make Hm (D) are respectively less than or greater than Hm (advised Second, the melting temperature of introduction of the Hall Petch relationship, the coefficients C 'and KCT', studied the influence of the melting temperature on the Hall Petch relationship With crystal particle size decreases, the melting temperature of the nano-crystals decreases when the grain size is reduced to the range of about 15 30 nm, traditional Hall Petch relationship will lapse as the square root of the grain size when the yield strength or hardness countdown function, there is a great value of the AMA, the range that the grain boundary sliding in the process during the deformation by dislocation movement becomes. i.e. as the grain size D decreases to a certain range, occurrence of grain boundary weakening leaving G (D) value decreased gradually. this value is dependent on a large bulk crystal melting braised Hm. Hm and the deformation temperature a few are two basic parameters affecting the yield stress size dependent. several usually at room temperature and therefore have a higher melting baking Hm material AMA larger, the corresponding D Shan x a, the / '2 also smaller. be understood that when D decreases, with higher Hm material the grain boundary has a higher strength, the opposite materials Hm The smaller occurred in the larger D is the softening of the grain boundary. discusses traditional Hall Petch relationship the effective size of the range by a corrected Hall Petch relationship results show that the function of a (D) of the repair ended pairs metal elements Cu, Fe, Ni, Pd, and zn alloy N Bu P Compound Nizr: and TiO: Prediction and experimental results coincide. three, according to the definition of the surface stress and its relationship with the surface energy and Lap} ace a Young equation is derived to the surface of the stress formula and size-dependent model of the solid-liquid interfacial energy. surface stress is intrinsic, does not depend on the crystal size varies; interfacial energy with the goods body size decreases reduced model predicted values ??are in good agreement with the available experimental results and computer simulation results the model is applied to the ion products body has been decided to have the the Nacl alkali metal halide (100) surface stress still and solid-liquid The interfacial energy (Y) model. Ah predicted value is consistent with the principles of thermodynamics, the the model predictive NaCl structure an alkali metal halide (100) crystal plane plant value obtained by the theoretical calculation values ??match, the material forming a single atom chain general Mechanical Analysis in accordance with a large bulk crystal dislocations Peierls stress and single-atom chain (MC) theoretical fracture ratio of the shear stress discussed under tensile stress material forming a single atomic chain trend found that the metal element having a face-centered cubic structure having a good single-atom chain forming ability. V determines the size of a single atom corresponding to the formation of chains in a metal element of the face-centered cubic trends. This is because such a metal element minimal elastic energy reserves and can withstand the maximum plastic deformation of the face-centered cubic metal elements Poisson's ratio v size Shun Jilin University Doctoral Dissertation sequence predicted single-atom chain forming ability of these elements, with the experimental and theoretical results consistent with Au as a single-atom chain forming one of the elements does have this characteristic. for Pt, Pd and Pb because they are in a face-centered cubic metal element having the second largest v values, so the presence of forming a single atomic chain the opportunity., using high-resolution transmission electron microscopy to observe the rapid cooling of Al-Si alloy AI / Si interface morphology silicon nanoparticles embedded in the aluminum matrix grainy and rod-like particulate Al / Si interface mainly chaotic arrangement, the rod-like AI / Si interface is basically the face of half of the close-packed plane of Sites of relationship from thermodynamic and mechanical considerations, interface morphology and the size of the nanocrystals linked with close-packed results found that, as long as the size of the nanocrystals are sufficiently small, even if the interface strain of 1/4, the silicon nanocrystals can still total aluminum substantially semi?}

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