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THE WORK GENERAL CHARACTERISTIC

Urgency of a theme of the dissertation. Experimental researches nanochastits and nanosistem, including the structural transfomations proceeding in them induced by change of temperature, as a rule are inconvenient and expensive, and prognosticheskie possibilities of theoretical approaches to their studying also are limited.

All it does actual application of methods atomisticheskogo modelling, first of all, - molekuljarno-dynamic (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 and specification of borders of applicability of concepts and concepts of classical thermodynamics 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 corresponding processes. Remains opened and the question on in what degree a fusion-crystallisation hysteresis can be reduced or is completely eliminated. From the applied point of view, the knowledge of laws of fusion and crystallisation nanochastits, including their kinetic aspects, is necessary for working out of scientifically proved approaches nanotehnologii, connected with reception and application nanochastits, nanostruktur and nanostrukturirovannyh materials.

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 acted mezoskopicheskie metal nanochastitsy, first of all - nanochastitsy transitive metals: Ni, Co, Cu, Au, Ag. Were besides, modelled nanochastitsy Al and Pb. The choice of objects 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 500 to several hundreds thousand atoms. Unlike small metal nanoklasterov, containing to 100 atoms, application to mezoskopicheskim nanochastitsam methods ab initio is 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 as an example of covalent system.
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-firm even surface” in which the wetting phenomena are observed, including - wetting in solidity; 4) nanorelef a metal surface. At the same time, 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.

The basic object of research were dimensional dependences of thermodynamic characteristics nanochastits, including kinetic aspects of these dependences. First of all, 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 kinetic laws of fusion and crystallisation nanochastits, working out and realisation of thermodynamic and kinetic approaches to a finding 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 research of dimensional dependences of melting points and

Crystallisations, 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 fusion - hysteresis

Crystallisations (dynamic variant) and by a relaxation nanochastits at the fixed temperatures (a quasistatic variant);

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 research of behaviour of heat capacity nanochastits in a melting point vicinity;

4. Working out and realisation of the kinetic 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 Tt and crystallisation temperatures of the Hardware which are registered in the conditions of a fusion-crystallisation hysteresis, i.e. are obviously nonequilibrium, dimensional dependences of equilibrium temperature of fusion Tm^le q\which are found and analysed was by a relaxation nanochastits at the fixed temperatures. As a result of the carried out comparative research of dimensional dependences Tt, the Hardware and Tm^e qдля nanochastits Cu, Au, Ag, Ni, Co and Pb is shown, chtot

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A source: Talyzin Igor Vladimirovich. MOLECULAR DYNAMIC INVESTIGATION OF THERMODYNAMIC AND KINETIC ASPECTS OF MELTING AND CRYSTALLIZATION OF METAL NANOPARTICLES. ABSTRACT of dissertation for the degree of candidate of physical and mathematical sciences. Tver - 2019. 2019

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