Time filter

Source Type

Golovchak R.,Lehigh University | Golovchak R.,Lviv Institute of Materials | Kozdras A.,University of Opole | Balitska V.,Lviv Institute of Materials | And 3 more authors.
Journal of Physics Condensed Matter | Year: 2012

The long-term kinetics of physical ageing at ambient temperature is studied in Se-rich As-Se glasses using the conventional differential scanning calorimetry technique. It is analysed through the changes in the structural relaxation parameters occurring during the glass-to-supercooled liquid transition in the heating mode. Along with the time dependences of the glass transition temperature (Tg) and partial area (A) under the endothermic relaxation peak, the enthalpy losses (ΔH) and calculated fictive temperature (TF) are analysed as key parameters, characterizing the kinetics of physical ageing. The latter is shown to have step-wise character, revealing some kinds of subsequent plateaus and steep regions. A phenomenological description of physical ageing in the investigated glasses is proposed on the basis of an alignment-shrinkage mechanism and first-order kinetic equations. © 2012 IOP Publishing Ltd.

Balitska V.,Lviv Institute of Materials | Balitska V.,Lviv State University of Vital Activity Safety | Golovchak R.,Austin Peay State University | Kozdras A.,University of Opole | And 2 more authors.
Physica B: Condensed Matter | Year: 2014

Sigmoid behavior of natural physical ageing in glassy As 10Se90 reveals multi-step-wise growing kinetics of enthalpy losses. Phenomenological description of this kinetics can be adequately developed in terms of first-order relaxation processes, tending atomic structure from initial towards more thermodynamically equilibrium state. This kinetics is shown to obey characteristic stretched exponential behavior originated from a number of growing steps, attributed to the interconnected processes of chalcogen chain alignment and cooperative shrinkage of glass network. © 2013 Published by Elsevier B.V.

Balitskii A.,NASU Karpenko Physico Mechanical Institute | Balitskii A.,West Pomeranian University of Technology | Semerak M.,Lviv State University of Vital Activity Safety | Balitska W.,Lviv State University of Vital Activity Safety | And 2 more authors.
Solid State Phenomena | Year: 2015

It is experimentally established that air-tested samples of degraded material showed tooth flow that disappears for tests in hydrogen. The main feature inherent in the studied materials are metastable and presence of more or less pronounced time- and temperature-dependent processes of structural relaxation, which reduces the total free energy of a thermodynamic system. The values of fracture toughness minimize the square deviation of experimentally obtained values drift from the theoretical curve corresponding to the exponential relaxation function. © (2015) Trans Tech Publications, Switzerland.

Noshchenko G.V.,Ukrainian National University of Forestry and Wood Technology | Mykhalichko B.M.,Lviv State University of Vital Activity Safety | Davydov V.N.,Ivan Franko National University of Lviv
Russian Journal of Inorganic Chemistry | Year: 2012

The first mononuclear π-complex of copper(I) chloride with monosubstituted alkyne of the for- mula [(C 9H 16NH 2(OH)C=CH)CuCl 2] was obtained in the system CuCl-HCl-H 2O- (C 9H 16NH 2(OH)C=CH) C l (C 9H 16 (OH)C=CH is the 4-ethynyl-4-hydroxy- 2,2,6,6-tetramethylpiperi- dinium cation) and studied by single-crystal X-ray and X-ray powder diffraction. The crystals are monoclinic: a = 16.868(8) Å, b = 13.177(8) Å, c = 13.32(1) Å, γ = 103.50(4)°, space group P2 1/b, Z = 8. The structure of the complex contains two crystallographically independent zwitterionic entities of the formula [(C 9H 16NH 2(OH)C=CH)CuCl 2], which result from π-coordination of the potential π-bidentate bond C=C of the organic cation to one Cu(I) atom of the inorganic anion . The distances Cu-m (m is the mid- point of the C=C bond) are 1.91(2) Å. Along with weak intermolecular hydrogen bonds =CH⋯Cl and intramolecular contacts OH⋯Cl, the structure is stabilized by a directed ionic interaction through strong NH⋯Cl bonds. © Pleiades Publishing, Ltd., 2012.

Balitska V.,Lviv State University of Vital Activity Safety | Golovchak R.,Lehigh University | Shpotyuk O.,Lviv Institute of Materials
Solid State Phenomena | Year: 2013

Phenomenological description of below-Tg structural relaxation in network glass formers known also as long-term natural physical ageing is developed on the basis of the first-order kinetics. This kinetics in binary arsenic selenides was shown to obey a character stretched exponentional behavior being treated as sequence of aligning-shrinkage stages throughout the glassy matrix. © (2013) Trans Tech Publications, Switzerland.

Shpotyuk O.,Lviv Institute of Materials | Shpotyuk O.,Jan Dlugosz University in Czestochowa | Balitska V.,Lviv Institute of Materials | Balitska V.,Lviv State University of Vital Activity Safety | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

Mixed Ni-Co-Cu oxymanganospinels of Cu 0.1Ni 0.8Co 0.2Mn 1.9O 4 composition with improved functional reliability are first developed for possible application as high-precise NTC thermistors. It is established the amount of additional rock-salt NiO phase in these ceramics, which was not externally introduced at the initial stages of ceramics processing, but extracted during sintering route occurs a decisive role to inhibit the parasitic degradation caused by thermal storage at the elevated temperatures. This effect is well revealed only in ceramics having a character fine-grain microstructure obtained due to injection of small amount of thermally transferred energy, while structural monolithization caused by great value of thermally transferred energy into ceramics bulk reveals an opposite influence. The fact, the ceramics with fine-grain microstructure and large content of rock-salt NiO extractions demonstrate the best suitability for stretched-exponential relaxation kinetics (the most appropriate one for describing degradation kinetics in structurally dispersive solids like ceramics) serves as additional confirmation to the above conclusion. © 2010 Elsevier B.V. All rights reserved.

Balitska V.O.,Lviv State University of Vital Activity Safety | Balitska V.O.,Lviv Institute of Materials | Iovu M.S.,Institute of Applied Physics | Shpotyuk O.I.,Lviv Institute of Materials | Shpotyuk O.I.,Jan Dlugosz University in Czestochowa
Journal of Non-Crystalline Solids | Year: 2013

The governed kinetics describing in-situ photodarkening in amorphous As100-xSex films of different compositions (x = 40, 50, 60) and thicknesses (0.54-2.04 μm) were analyzed within stretched exponential parameterization algorithm. It was found that this kinetics strongly depended on penetration depth of pumping light. In case of films thicker than penetration depth, the governed kinetics attained a character stretched exponential behavior, while in thinner films (with thickness less than penetration depth) the stretched exponential relaxation tented towards single exponential one. These peculiarities were described in terms of photon-assisted site switching facilitating percolative growth of atomic clusters in the ground state activated under the influence of absorbed pumping light. © 2013 Elsevier B.V. All rights reserved.

Shpotyuk O.,Dlugosz University of Czestochowa | Shpotyuk O.,Vlokh Institute for Physical Optics | Kozdras A.,Opole University of Technology | Balitska V.,Lviv State University of Vital Activity Safety | Golovchak R.,Austin Peay State University
Journal of Non-Crystalline Solids | Year: 2016

Compositional features of enthalpy losses ΔH(t) caused by long-term physical aging at normal conditions are studied at the example of Se-rich chalcogenide glasses As20Se80, As30Se70 and Ge5Se95 obeying "chain-crossing" structural model. The observed relaxation kinetics in general are described by a stretched exponential behavior, but can be also parameterized in terms of multi-step single exponential decays. Microstructural mechanism of natural physical aging in the studied glasses is explained by accepting their structural-topological specificity with a decisive role of preferential chemical environment around Se atoms. The characteristic time constants of aging are shown to increase in more topologically constrained structural fragments capable to relaxation. Independent relaxation stages originated from different chemical environments in As10Se90 and Ge5Se95 glasses allow observation of plateau-like behavior. However, plateaus are found to be smoothed in As20Se80 glass because of overlap of different structural complexes responsible for relaxation. © 2016 Elsevier B.V. All rights reserved.

Golovchak R.,Austin Peay State University | Kozdras A.,Opole University of Technology | Shpotyuk O.,Jan Dlugosz University in Czestochowa | Shpotyuk O.,Vlokh Institute of Physical Optics | Balitska V.,Lviv State University of Vital Activity Safety
Journal of Physics Condensed Matter | Year: 2016

Kinetics of physical aging at different temperatures is studied in situ in arsenic selenide glasses using high-precision differential scanning calorimetry technique. A well-expressed step-like behaviour in the enthalpy recovery kinetics is recorded for low aging temperatures. These fine features disappear when the aging temperature (T a) approaches the glass transition temperature (T g). The overall kinetics is described by stretched exponential function with stretching exponent close to 3/5 at T a > ∼0.95 T g almost independent on glass composition, and 3/7 when the aging temperature drops to ∼0.9 T g. These values are consistent with the prediction of Phillips' diffusion-to-traps model. Further decrease in aging temperature to ∼0.85 T g leads to the appearance of step-like behaviour and stretching exponent of 1/3 for the overall kinetics, which is the limiting value predicted by random walk on the fractal model. Such behavior is explained as crossover from homogeneous cooperative relaxation of non-percolating structural units to high-dimensional fractal relaxation within hierarchically-arranged two-stage physical aging model. © 2016 IOP Publishing Ltd.

Vakal S.,Sumy State Scientific Research Institute of Fertilizers and Pegments | Karpovych E.,Sumy State Scientific Research Institute of Fertilizers and Pegments | Malyovannyi M.,Lviv Polytechnic | Stokalyuk O.,Lviv State University of Vital Activity Safety
Chemistry and Chemical Technology | Year: 2014

Technological aspects of ammophos production using Algerian phosphorites as a raw material have been investigated. The necessity of increased consumption of sulphuric acid during the Algerian phosporites processing compared with apatite processing has been grounded. The dependence of pH solution on NH3:H3PO4 molar ratio has been determined during neutralization of extraction phosphoric acid prepared from Algerian phosphorites. The necessity of acid solution deeper neutralization in the technology of extraction phosphoric acid production has been proved. The boundary drying temperature of ammonia pulp has been determined. The relation between ammonium nitrogen and drying time has been specified. © Vakal S., Karpovych E., Malyovannyi M., Stokalyuk O., 2014.

Loading Lviv State University of Vital Activity Safety collaborators
Loading Lviv State University of Vital Activity Safety collaborators