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Пятница, 19.04.2024, 16:02 Приветствую Вас Гость | Регистрация | Вход |
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Welcome to website of Dr. Aram Shirinyan | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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SCIENTIFIC ACHIEVEMENTS1. The discovery a new fundamental effect in multicomponent
nanoscaled systems related to their phase diagrams:
the solubility curves in contrast to ones in bulk materials
do not correspond to the condition of thermodynamic equilibrium
and show only the beginning and the end of phase transformation.
For example, solidus and liquidus curves in commonly accepted meaning of terms
do not correlate to thermodynamic equilibrium.
It is shown the "loop-like split path" of an equilibrium
temperature-composition diagram for solidus and liquidus
shifted in comparison to bulk infinite system.
2. The construction of the size-dependent solubility curves
and the solubility diagram of isolated nanosized Cu-Ni particle
and the demonstration of the decrease and narrowing and
vanishing of the two-phase zone.
3. The reconsideration of such basic concepts as
phase diagram, solubility curve, etc.
The well-known concept of equilibrium state diagram has to be revised,
due to the fact that the amount of matter is limited in a nanosystem.
4. The introduction of the concept of "critical supersaturation"
and prediction of the "split of the binodal curve"
on the phase temperature-composition diagrams based on depletion effect
- for the decomposition of supersaturated nanoalloys
taking into account the number of coexisting solid phases
and the compositional redistribution during the phase transitions.
5. The demonstration of the size-dependent "thermodynamic” hysteresis
for the volume fraction of the new phase in nanopowder
under the thermal cycling as the function of the temperature
and different phase transition mechanisms.
It is shown that the thermal "thermodynamic” hysteresis arises
due to the asymmetry of transforming paths of the nanosystem
with respect to the initial conditions,
kinetic constraints on the transition modes, different probabilities
of forth and back transitions and multiple states
separated by different energy barriers.
It is argued that in nanosystems it is required to differentiate
the "kinetic” hysteresis and "thermodynamic” hysteresis
in the first order phase transition.
6. First demonstration of fundamental effect of the superposition
of "kinetic” hysteresis and "thermodynamic” hysteresis
leading to the size-independent hysteresis of first order phase transition
in nanomaterials for wide range of sizes and parameters.
[Physics and Chemistry of Solid State, 2010, 11, 49;
Doctorate thesis for scientific degree of doctor
of physical and mathematical sciences by speciality
01.04.07 – solid state physics, Kiev National University, 2012, 368p].
7. The introduction of the notions of size-dependent ‘superheating limit’
and ‘supercooling limit’ and discovery the logarithmic correlations
for them as functions of nanosizes and temperature change rates.
The description of the evolution of a transforming metal
nanoparticle ensemble subjected to a temperature cycling
with constant rates of temperature change.
8. Demonstration of a size-induced thermal hysteresis
in first order phase transitions and the invention of using
of such hysteresis for the achievement of an alternative method
of information (nonmagnetic) recording
in present-day and future technologies.
9. First demonstration of concentration ‘self-saturation’ effect in kinetics
of phase separation of metastable mulicomponent alloy
under the constant external conditions: at the end of the intermediate stage
there takes place the "inverse behavior" of basic characteristics
- the decrease of the mean size, critical size,
and volume fraction of the new phase and the increase
of the mole fraction of the component building the phase.
The self-saturation effect can be considered as one of the simple criteria
of the start of coalescence stage.
10. A suggestion and thermodynamic validation the atomic hypothesis
related to the size dependence of the atom-atom interaction energy:
the nearest interactions and coordinated actions of atoms in the nanomaterial
will be different depending on the size of a nanomaterial.
Solid nanofilms of monoatomic metallic systems having an fcc structure
are simulated by the molecular-statics method
with the Morse and Sutton-Chen potentials.
Bulletin of Kiev National University, Physical and Mathematical Series, 2011, 13, 34].
11. Theoretical validation of the size dependence
of diffusion coefficient of atoms in nanomaterials
based on microscopic and phenomenological points of view.
The result has been applied for the reactive diffusion problem
of new nanosized phase growth kinetics in а binary diffusion couple.
Depending on the type of diffusion coefficient dependence
on the size of new nanophase layer
the phase formation rate exponent can change nonmonotonically.
Physics and Chemistry of Solid State, 2011, 12, 32].
12. The development of the techniques of the thermodynamic calculations
and designing temperature-composition diagrams of binary metallic nanophases
based on the size dependence for potential energy of the interaction
between neighbour atoms in nanomaterials at zero temperatures.
13. The introduction of a notion "mesoentropy” in a thermodynamics
of a new phase formation in the supersaturated binary solid solution,
taking into account the depletion of the solution and
the space distribution of new phase nuclei.
It is shown the principal possibility of obtaining
of the size distribution function for the new phase nuclei
in the framework of a general variation procedure
of the optimal crossover point determination
for the first order phase transition,
assigning the Gibbs free energy functional.
14. The demonstration the competitive nucleation and growth
of two intermediate phases in nanovolumes
taking into account the mole fraction depletion
of the parent phase and yielding situations:
(i) total prohibition of separation,
(ii) formation and total stabilization of metastable phase instead of a stable one,
(iii) relative stabilization of metastable phase with the temporary delay
of its transformation into the stable phase,
(iv) formation and growth of stable phase
when the metastable phase does not appear at all,
(v) formation and growth of stable phase via the metastable phase.
This was applied to the coherent precipitation of metastable
Al3Li ordered phase in supersaturated solid solution Al(Li).
15. The demonstration of the size-induced "freezing effect”
in separation kinetics for the isolated nanoparticle
with a coating shell of the third atoms
by means of Monte-Carlo sampling and Ising-type model,
where the species exchange positions due to vacancy mechanism:
the rate of relaxation process depends on the size of a nanosystem.
Depending on the shell properties, the nucleation of a new phase
may be either heterogeneous (on the external surface)
or homogeneous (in the core of the particle).
Doctorate thesis for scientific degree
of doctor of physical and mathematical sciences
by speciality 01.04.07 – solid state physics,
Kiev National University, 2012, 368p].
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