Abstract: The present paper deals with the application of the transient techniques for
thermophysical analysis of the structural changes in materials. The technique has been applied for
study of equilibrium transitions as well as for kinetic transitions. A special methodology has been
developed to study kinetic transitions like crystallization, melting, etc. in a “pseudo-equilibrium
states” by the help of porous structures. The paper includes three different issues: the transient
methods for measuring thermodynamic and transport parameters, data analysis and application of
the pulse transient method for measurements of materials in thermodynamic equilibrium, pseudoequilibrium
and in non-equilibrium (quasi-equilibrium) states. Equilibrium transitions in CsPbCl3
and CsPbBr3 single crystals, kinetic transitions of freezing and thawing water in porous stones and
non-equilibriums states in E-glass and Al2O3 ceramics during sintering have been studied.
Abstract: Numerous solid-state transformations occur in metal iodides. These transformations can
be classified into three categories: polymorphic transformations, polytypic transitions and molecular
solids. Many of the modifications of metal iodides involve metastable phases transforming into
stable phases. Revisions to the In-I and Th-I phase diagrams are made based on data found in the
Abstract: A new characterization method, "Macroscopic Composition Gradient (MCG) Method" is
proposed to investigate the phase transformations near the phase boundaries, such as the solubility
limit, order/disorder line and so on. Since the macroscopic composition gradient in the alloy is
prepared so as to step over the phase boundary, the morphological transition of critical phenomena
at the phase boundary can be observed by means of analytical transmission electron microscopy.
By utilizing this method, the critical minimum size of stable precipitate in the vicinity of edge of
miscibility gap is experimentally determined for the Ni3Si in Ni-Si, Ni3Al in Ni-Al, Cu4Ti in Cu-Ti
and Co in Cu-Co binary alloy systems. The results are as follows: The critical nucleus size shows a
steep increase up to several tens of nm in a very narrow composition range less than 0.3at% from
the phase boundary. The Gibbs-Thomson relation and the conventional nucleation theory
statistically rationalize such the composition dependence of nucleus size change. However, the
nucleus formation is kinetically never rationalized by the conventional nucleation theories. The
phase decomposition of supersaturated solid solution progresses by a mechanism of spinodal phase
decomposition, even in the composition range near the solubility limit, i.e. a so-called Nucleation-
Growth region. Such the phase decomposition behavior is never rationalized by the Boltzmann-
Gibbs free energy, which is based on the extensive entropy. The experimental facts obtained here
are explained by Tsallis's non-extensive entropy.
It should be noted that the present experiments can systematically be conducted in the
composition range very near the solubility limit where they has hardly been examined in the past.
The MCG method proposed here is considered to open a new way to investigate the microstructure
evaluation, particularly for the critical phenomena near the phase boundary.
Abstract: The response of the relative resistivity changes to the isochronal annealing was measured in
MgSc, MgScMn and MgYNdScMn alloys. The derivatives of the annealing curves were fitted by
Gaussian functions to determine and separate the temperature ranges of the phase transformations
taking place. The Austin-Rickett kinetics is argued to justify this procedure for diffusion driven
transformations. TEM observation verified the conclusions drawn from the procedure.
Abstract: Hydrogen is suggested as a promising fuel of the near future for the utilization in
automotive and mobile applications. Therefore, safe and effective hydrogen storage systems need to
be developed. One of the possibilities, suitable especially for mobile applications, is the storage of
hydrogen in the form of light-metal hydrides. In this work we studied microstructure and hydrogen
absorption and desorption kinetics in selected Mg-Ni alloys. Hydrogen saturation was carried out by
the cathodic polarization in alkaline water-based solution. It was confirmed that hydrogen could be
stored in the Mg2Ni intermetallic phase forming Mg2NiH0.3 phase using this technology. MgH2
hydride is also formed when the temperature of 90 °C is applied. The total content of hydrogen in
the material after saturation is approx. 0.7 wt. % according to the thermogravimetry analysis. This
low value is caused probably by the surface oxidation, blocking further hydrogen diffusion. Thermal
hydrogen desorption tests showed that the Mg2NiH0.3 phase is able to release hydrogen even at
temperatures lower than 100 °C.
Abstract: Kinetics of hydrogen desorption from Mg2NiH4 was studied. Experimental material was
prepared by two techniques – by melting and casting and by ball-milling and compacting into
pellets. Experimental materials were hydrogen charged at elevated temperature and pressure. The
pellets were charged in two different regimes resulting in structures with high fraction of twinned
low-temperature phase LT2 and with low fraction of LT2. It was made an attempt to measure
diffusion coefficients of hydrogen and its temperature dependence both in high-temperature (HT)
and in low-temperature (LT) phases of Mg2NiH4. The measurement was carried out in temperature
interval from 449 K to 576 K by the volumetric method. It was found that the LT2 slows-down the
desorption rate considerably.
Abstract: Specific phase transitions to the compound-like impurity nanosegregation structures at
dislocations and grain boundaries in metals and their influence on diffusion-assisted processes are
considered, mainly, on the basis of the thermodynamic analysis of the related experimental data.
The following systems and aspects are in detail considered: (1) the hydride-like nanosegregation of
hydrogen at dislocations and grain boundaries in palladium and their influence on the apparent
characteristics of hydrogen solubility and diffusivity in palladium; (2) the physics of the anomalous
characteristics of diffusion of Fe and other transition impurities in crystalline Al at elevated
temperatures, the role of the compound-like nanosegregation (CLNS) of Fe and the others at
dislocations and grain boundaries in Al, analysis of the Mössbauer and diffusion data on CLNS of
Fe at grain boundaries and dislocations in Al; (3) some new physical aspects of internal oxidation
and nitridation of metals (for Cu-0.3%Fe alloy/Cu2O surface layer, and for (Ni-5%Cr) alloy / N2
gas), the role of the compound-like impurity nanosegregation at dislocations and grain boundaries,
study results on the deviations from the classical theories predictions and their interpretation. The
possibility is considered of nanotechnology applications of the study results for creation of
nanostructured metals with compound-like nanosegregation structures at grain boundaries, in order
to obtain specific physical and mechanical properties of such a cellural-type nanocomposites. In
particular, it can be complex hydride-like, carbide-like, nitride-like, carbide-nitride-like, oxide-like
or intermetallide-like nanosegregation structures at grain boundaries of nanostructured metals.
Abstract: The mechanisms of formation of activated states upon diffusion of impurity interstitial
atoms in metals have been identified, which allows formulation of the theoretical criterion for
reliability of corresponding experimental data. This criterion is valid for almost all experimental
results gained using precise techniques for bcc, fcc, and hcp metals. In case of hydrogen, oxygen,
and nitrogen, most adequate are the models of potential diffusion barrier that are based on the
elasticity theory. For carbon and boron, a less energy-taking mechanism is realized which involves
the electron system rearrangement in a crystal during the diffusion jump. The accuracy of the
theoretical criterion is in line with the capacities of modern precision techniques.
Abstract: The possibilities of Fisher’s model development and generalization are considered, as this
model in its classical form contradicts some experimental results. Particularly, it does not explain
such a phenomenon, observed in Mössbauer studies, as the transfer of grain-boundary diffusing
atoms into near-boundary crystallite areas at temperatures when the volume diffusion is admittedly
frozen. Different models explaining this phenomenon are briefly reviewed, the greatest attention
being paid to a model accounting for the presence of equilibrium-composition near-boundary layers.
It is demonstrated that based on the results of grain boundaries investigations one can conclude that
at relatively low temperatures (< 0.35 – 0.40 Tm) the diffusant pumping from a grain boundary
proceeds much faster than volume diffusion, and possible reasons for that are considered.