IVESTIGATION OF STRUCTURAL-THERMODYNAMIC PROCESSES AT MELTING
Main researcher
: RUBČIĆ, ANTUN (41584) Assistants
BATURIĆ-RUBČIĆ, JASNA (2533)
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
Communication
E-mail: rubcic@phy.hr
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. Other information about the project.