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Introduction

Urgency of a theme of the dissertation. The urgency atomisticheskogo modelling nanochastits and nanosistem, including the structural transfomations induced by change of temperature, is caused by that corresponding experimental researches, as a rule are inconvenient and expensive.

Prognostichesky possibilities of theoretical approaches to studying nanochastits and nanosistem also are limited. It does actual application of methods atomisticheskogo modelling, first of all, - molekuljarnoyodinamicheskogo (MD) modelling for research of structural transfomations in nanochastitsah, including the structural transfomations interpreted as fusion and crystallisation. From the fundamental point of view the urgency of researches on a dissertation theme is defined by that interpretation of structural transfomations in nanochastitsah as phase changes demands an additional substantiation, including borders of applicability of concepts and concepts of classical thermodynamics at transferring to nanosistemam. In particular, laws and mechanisms of a hysteresis of fusion-crystallisation though it is quite clear are not found out to the full, that presence of such hysteresis testifies to nonequilibrium character of processes of fusion and crystallisation nanochastits. Remains opened and a question on, whether there can be a fusion-crystallisation hysteresis completely eliminated or, at least, essentially reduced. From the applied point of view, the knowledge of laws of fusion and crystallisation nanochastits, including kinetic aspects of these processes, is necessary for working out of scientifically proved approaches nanotehnologii, connected with reception and application nanochastits and nanostruktur.

Degree of a readiness of a theme of the dissertation. Dimensional dependence of melting point nanochastits various metals was investigated earlier with use atomisticheskogo modelling. At the same time, dimensional dependence of crystallisation temperature, fusion and crystallisation mechanisms nanochastits, and also kinetic aspects of the specified phase changes are investigated in ready smaller degree.

Objects and objects of research. As the basic object of research will act mezoskopicheskie metal nanochastitsy, first of all - nanochastitsy transitive metals: Ni, Co, Cu, Au, Ag. Besides, in work were modelled nanochastitsy Al and Pb. The choice mezoskopicheskih metal nanochastits as the basic object of research is caused both prospects of their practical application, and presence reliable parametrizatsy two alternative types of multipartial potentials: potential of strong communication (PSS) and the potentials answering to a method of diped atom (MPA). Under mezoskopicheskimi we understand nanochastitsy, containing from several hundreds to several hundreds thousand atoms. Unlike small metal nanoklasterov, containing to 100 atoms, application to mezoskopicheskim nanochastitsam methods ab initio is represented inconvenient. As the additional objects of research chosen for finding-out of degree of influence of the nature of a chemical bond on fusion and crystallisation nanochastits, acted molecular (lennard-dzhonsovskie) nanochastitsy and nanochastitsy Si, answering to a covalent bonding. For demonstration of influence of dimensional dependence of melting point singl-component nanochastits on processes in binary nanochastitsah and modelling nanosistemah as objects of research acted also: 1) systems from two nanochastits, for which the coalescence phenomena (for nanokapel) and sintering (for solid nanochastits) are characteristic; 2) binary nanochastitsy in which the phenomena of segregation and destruction of bimetallic structures "kernel-cover" are observed; 3) systems “nanochastitsa -
Solid even surface ”in which the wetting phenomena are observed, including - wetting in solidity; 4) nanorelef a metal surface. Nanosistemy were not the basic objects of research in the yielded work, and corresponding results should be considered as an illustration of a role of dimensional dependence of melting point and influence of a substrate on gauged values of melting point.

The basic object of research is dimensional dependence of thermodynamic characteristics nanochastits, including kinetic aspects of this dependence. In particular, dimensional dependences of melting points and crystallisations, enthalpies of fusion and crystallisation, enthalpies of evaporation and sublimation mean. The basic attention is given finding-out of influence of speed of change of temperature on dimensional dependences specified above thermodynamic characteristics nanochastits.

The work purpose: finding-out of thermodynamic and kinetic laws of fusion and crystallisation nanochastits, working out and realisation thermodynamic and kinetic (diffusive) approaches to registration of melting point and other thermodynamic characteristics nanochastits in MD experiments.

For object in view achievement following primary goals of research were put:

1. MD researches of dimensional dependences of melting points and crystallisation, and also enthalpies of phase changes of 1 sort in nanochastitsah with use of two alternative variants of a thermodynamic campaign: in the conditions of a hysteresis of fusion - of crystallisation and by a relaxation nanochastits at the fixed temperatures (the quasistatic approach);

2. Finding-out of influence of heat rates and cooling on a fusion and crystallisation hysteresis, including their influence on melting points and the crystallisations registered in MD experiments;

3. MD researches of behaviour of heat capacity nanochastits in a melting point vicinity;

4. Working out and realisation of the kinetic (diffusive) approach to a melting point finding nanochastits on temperature dependence of factor of self-diffusion;

5. Finding-out of degree of influence of the nature of a chemical bond in nanochastitsah on dimensional dependence of melting point;

6. MD research of temperature effect of fusion and its dimensional dependence on the phenomena in nanochastitsah and nanosistemah, including segregatsionnye the phenomena in binary nanochastitsah, coalescence nanokapel and sintering solid nanochastits, wetting on nanomasshtabah and degradation nanorelefa a solid surface.

Scientific novelty of work.

As a result of the made researches following new results have been received:

1. For the first time besides melting point Tmи of crystallisation temperature Tc which are registered in the conditions of a fusion-crystallisation hysteresis, i.e. are obviously nonequilibrium, dimensional dependences of equilibrium temperature of fusion Tm which was by a relaxation nanochastits at the fixed temperatures are found and analysed. As a result of the carried out comparative research of dimensional dependences Tm, Tcи Tmq^для nanochastits Cu, Au, Ag, Ni, Co and Pb it is shown, that Tc

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A source: Talyzin Igor Vladimirovich. MOLECULAR DYNAMIC INVESTIGATION OF THERMODYNAMIC AND KINETIC ASPECTS OF MELTING AND CRYSTALLIZATION OF METAL NANOPARTICLES. DISSERTATION on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2019. 2019

More on topic Introduction:

  1. in introduction
  2. INTRODUCTION
  3. INTRODUCTION
  4. 10.1. Introduction
  5. INTRODUCTION
  6. approbation and introduction of results.
  7. Introduction
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  10. INTRODUCTION
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  12. Introduction
  13. INTRODUCTION
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  15. PRACTICAL INTRODUCTION OF RESULTS OF WORK
  16. 5. Attention strengthening to questions of legal introduction.
  17. Introduction
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  19. Introduction