SVIBOR - Project code: 1-03-313


Strossmayerov trg 4, HR - 10000 ZAGREB
tel.: +385 1 459 44 44, fax: +385 1 459 44 69


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Project code: 1-03-313


Main researcher: RUBČIĆ, ANTUN (41584)

Type of research: basic
Duration from: 06/30/92. to 12/31/96.

Papers on project (total): 2
Institution name: Prirodoslovno-matematički fakultet, Prirodoslovni odjeli, Zagreb (119)
Department/Institute: Department of Physics
Address: Bijenička c. 32
City: 10000 - Zagreb, Croatia
Phone: 385 (0)1 4555 730
Fax: 385 (0)1 432 525
Fax: 385 (0)1 432 525

Summary: The project anticipates an investigation of various mechanisms of the phase transition solid-to-liquid. Structural properties of the solid and liquid phase will be simulated by computer using the methods of Monte Carlo and molecular dynamics. Thermodynamic parameters will be determined by the methods of statistical mechanics and numerically during the simulation; also by an analysis of the existing experimental data and the results of theoretical approaches. Only relatively simple substances will be studied like the condensed noble gases, metals, simplest substances with ionic bonding and homologous series of n-aliphatic paraffins, alcohols and acids. Special attention will be focused to an analysis of some important parameters at melting, as for example, the change of volume, enthalpy, conformation of molecules, electrical resistivity etc. The purpose of that is to find the microstructure processes which lead a crystal structure of the long range order to the liquid phase with short range order. In the period including the year 1994. and 1995. we have cinsidered stability of the gravitaionally-bound many-bpdy systems. It was a departure from the project, but the importance of the problem strongly suggested this investigation. Particularly, we foccused our attention to the Solar system, i.e. to the distribution of planetary orbits and orbits of major satellites. We have abondoned the traditional Titius-Bode law and applied the new parabolic law. This law gives a new insight into regularity of orbital radii and discovers some important properties of the Solar system.The results are published in the journal Fizika B (1995) and exposed on the Symposium: Contributions to the development of croatian programm of physics.

Keywords: Structural-thermodynamic processes, phase transition solid-to-liquid, melting, mechanism of melting, solid-liquid interface, density profile, pair correlation function, coordination number, volume change at melting, entropy, conformation of molecules, electrical resistivity, cohesion energy, condensed noble gases, metals, n-aliphatic paraffins, computer simulation. Solar system, planetary distances, satellite systems, parabolic law, angular momentum.

Research goals: The aim of the project is a determination of the mechanism of melting for some simple substances like metals, alkali halides and some inorganic and organic compounds, on the basis of a calculated structural-thermodynamic parameters of solid and liquid phase in the vicinity of melting.The investigation should be later extended to the substances with complex rigid molecules and flexible ones. On the basis of experimental data for volume and enthalpy change at melting, conformational changes of molecules in a liquid, and with the help of phonon spectra of both phases, it is possible in principle estimate the entropy of transition. Entropy may be summed as the contributions of several mechanisms i.e. that of the disordering and that of the volume change. Both contributions may be further broken to the basic inter-molecular and to the intra-molecular ones, the latter being possibly much larger due to the conformational changes. We have reached some results in that direction, but it is necessary to extend the treatment to more general cases. This approach is by its character semiempirical one, because it is related to experimental data and various correlations. But, there is also a theoretical approach of statistical mechanics as a part of the project. With computer simulation of a definite system of particles, it is possible to determine the microstructure and behaviour of particles in solid or liquid phase. The dynamics of particles at the interface of two phases is of particular interest. In that purpose we have considered a Lennard-Jones liquid near a hard wall, and we hope to extend similar calculations to more realistic systems with the application to the melting. An additional problem is an analysis of the gravitationally-bound many-bodz systems, with an application to the Solar system. Investigation of astronomical data, in the aim of finding the laws for angular momenta of planets and major satellites and also of the distribution of orbital radii, has given the interesting results, which are already published. Further research is in a course.

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Last update: 10/09/95