G. Kopitsa - Academia.edu (original) (raw)
Papers by G. Kopitsa
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2014
This study is devoted to investigation of the micro and mesostructure (including fractal proper t... more This study is devoted to investigation of the micro and mesostructure (including fractal proper ties) of porous zirconia glasses synthesized by precipitation from zirconium n propoxide solutions in the presence of different hydrolyzing agent (H 2 O) quantities at different temperatures. Analysis of small angle neutron, ultra small angle neutron and X ray scattering, scanning electron microscopy allows concluding that the synthesized glasses are complex systems with a three level hierarchical fractal structure. It is revealed that both the temperature of synthesis and the H 2 O concentration in the initial solution significantly affect the structural characteristics of the glasses.
Journal of Solid State Chemistry, 2013
We report a detailed study of structural and chemical transformations of amorphous hydrous zircon... more We report a detailed study of structural and chemical transformations of amorphous hydrous zirconia into sulfated zirconia-based superacid catalysts. Precipitation pH is shown to be the key factor governing structure, composition and properties of amorphous sulfated zirconia gels and nanocrystalline sulfated zirconia. Increase in precipitation pH leads to substantial increase of surface fractal dimension (up to $ 2.7) of amorphous sulfated zirconia gels, and consequently to increase in specific surface area (up to $ 80 m 2 /g) and simultaneously to decrease in sulfate content and total acidity of zirconia catalysts. Complete conversion of hexene-1 over as synthesized sulfated zirconia catalysts was observed even under ambient conditions.
Journal of Physics: Conference Series, 2012
We report structural changes in amorphous hydrated zirconia caused by high intensity ultrasonic t... more We report structural changes in amorphous hydrated zirconia caused by high intensity ultrasonic treatment studied by means of small-angle neutron scattering (SANS) and X-ray diffraction (XRD). It was established that sonication affects the mesostructure of ZrO 2 ×xH 2 O gels (i.e. decreases their homogeneity, increases surface fractal dimension and the size of monomer particles). Ultrasound induced structural changes in hydrated zirconia governs its thermal behaviour, namely decreases the rate of tetragonal to monoclinic zirconia phase transition.
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques, 2019
The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at differe... more The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at different stages of heat treatment are determined by small-angle neutron scattering. Particles of amorphous zirconium dioxide, which form mass fractals with the dimension D v = 2.21, are rearranged into surface fractals with a surface dimension of D s = 2.52 upon annealing at a temperature of 400°C or higher. In the resulting system, a shell with a fractal structure is formed over a dense core (a cluster of nanoparticles of zirconium dioxide with a constant density). Transformation of the fractal system from a mass fractal into a surface one is characterized by the appearance of a core, and its growth is due to the crystallization of hydrated zirconia particles at high temperatures. A model for the formation of a fractal particle, implying the existence of a core-shell surface fractal system, is proposed. The characteristic radius of ZrO 2 nanoparticles increases from 14 to 200 Å with an increase in the annealing temperature from 400 to 600°C.
The theoretical studies [1- 3] have shown that the orbital part of the magnetic scattering amplit... more The theoretical studies [1- 3] have shown that the orbital part of the magnetic scattering amplitude con-tains the term, which is singular at q 0 and gives rise the small-angle neutron scattering on the conduction electrons in metals:, (1) where r = e2/mc2 = 5.410-13 cm and =-1.91 is the neutron g-factor; q is the momentum transfer and p is the electron momentum. It was also shown [1 – 3] that in metals the scattering cross section is proportional to (m/M)2, where m is the effective mass of the electrons (carriers) and M is the mass of the neutron. For ordinary metals this factor is of order 10-5- 10-6 and the neutron-electron scattering is negligibly small. However for some heavy-fermion substances m ~ 100me [4] and (m/M)2 ~ 10-2. In such cases the neutron-carrier scattering could be observed if one takes into account that the static cross section d()/d is proportional to --1 for 2E >> T and T/( 2E) for T>>2E, where << 1 is the scattering angle and E is the neutro...
Russian Journal of Inorganic Chemistry
A method was developed for the low-temperature sol–gel synthesis of one of the most popular compo... more A method was developed for the low-temperature sol–gel synthesis of one of the most popular components of functional and structural materials—nanostructured yttrium aluminum garnet Y3Al5O12—using precursors from the class of alkoxoacetylacetonates produced from the corresponding acetylacetonates. It was determined that increasing duration of heat treatment of yttrium-aluminum-containing xerogen in air to 6 h reduces the crystallization temperature of the Y3Al5O12 phase from 920–930 to 750–800°C, which was confirmed by IR spectroscopy and X-ray powder diffraction analysis. The microstructure of nanocrystalline yttrium aluminum garnet obtained at 800°С was studied; it was found that the size of crystallites is 30–40 nm, the size of particles is 30–50 nm, and the size of pores is 20–30 nm. Small-angle neutron scattering demonstrated that, in the powders synthesized at 700–800°C, there is structural ordering of the short-range type, whereas in the nanocrystalline samples heat-treated at a higher temperature (850°С), there is no such ordering.
Lecture Notes in Earth System Sciences, 2019
Morphologically simple and microbially dominated ecosystems termed “biofilms” have existed on Ear... more Morphologically simple and microbially dominated ecosystems termed “biofilms” have existed on Earth for a long period of biosphere evolution. A model biofilm combining one heterotroph and one phototroph component was used in a laboratory experiment to simulate biogenic weathering with two different specimens of basic rock samples from the soil profiles. The rocks fragments from the regions of cold environments of Eurasia, where abiotic physical processes, including rock disintegration initiated by freezing–thawing cycles, represent the most probable scenario of rock weathering, were subjected to biological colonization. The rock fragments were represented by dolerite and metagabbro amphibolites. Polished sections of the rock samples were inoculated with the model microbiological consortium of the oligotrophic fungus and the phototrophic cyanobacteria (biofilm). After 3 month runtime of the experiment the progress of rock weathering was derived from the growth of the biofilm on the r...
where r = e2/mc2 = 5.410-13 cm and = -1.91 is the neutron g-factor; q is the momentum trans... more where r = e2/mc2 = 5.410-13 cm and = -1.91 is the neutron g-factor; q is the momentum transfer and p is the electron momentum. It was also shown [1 – 3] that in metals the scattering cross section is proportional to (m/M)2, where m is the effective mass of the electrons (carriers) and M is the mass of the neutron. For ordinary metals this factor is of order 10-5 10-6 and the neutron-electron scattering is negligibly small. However for some heavy-fermion substances m ~ 100me [4] and (m/M)2 ~ 10-2. In such cases the neutron-carrier scattering could be observed if one takes into account that the static cross section d()/d is proportional to --1 for 2E >> T and T/( 2E) for T >>2E, where << 1 is the scattering angle and E is the neutron energy. The crossover from one regime to another is observed at qc= ksin(T/2E). In this work [5], small-angle neutron scattering experiments were carried out with CeRu2Si2 single crystal in order to directly observe SANS ...
The mesostructure of segmented poly(urethane imide) containing 4–10 wt % CoFe 2 O 4 or Al 3 Fe 5 ... more The mesostructure of segmented poly(urethane imide) containing 4–10 wt % CoFe 2 O 4 or Al 3 Fe 5 O 12 nanoparticles was experimentally studied by small-angle polarized neutron scattering, which can analyze the nuclear and magnetic subsystems of the obtained composites. The transformation of the domain structure of the magnetic elastomers based on poly(urethane imide) was investigated at various concentrations, chemical compositions, and localizations of ferrite nanoparticles in polymer chains. The dynamics of the change in the segmental mobility of soft blocks during heating of samples was characterized by magnetic–nuclear interference scattering. The experiments detected changes in the supramolecular structure of the multiblock copolymer, which depended on the percentage and type of nanoparticles. The correlation radii were determined in the magnetic subsystem of ferrite nanoparticles embedded in hard aromatic blocks of poly(urethane imide) as nodes of intermolecular crosslinkers a...
Russian Journal of Inorganic Chemistry
Structural analysis in the range of characteristic sizes from 1 nm to ~1.5 µm was performed for S... more Structural analysis in the range of characteristic sizes from 1 nm to ~1.5 µm was performed for SiO2–TiO2 aerogels prepared in supercritical CO2, isopropanol, hexafluoroisopropanol, or methyl-tert-butyl ether using small-angle X-ray scattering and neutron scattering complementary methods. A two-level model that accounts for scattering by individual inhomogeneities and their aggregates, which have fractal properties, satisfactorily describes the aerogel structures over the entire range of scales. It is shown for the first time that the titania concentration is the key factor in the small-angle neutron and X-ray scattering by SiO2–TiO2 aerogels. The phase composition of an aerogel does not significantly affect the aerogel structure in the range of scales from 1 nm to ~1.5 µm, as probed by small-angle X-ray and neutron scattering.
Nanosystems: Physics, Chemistry, Mathematics
Functional nanomaterials based on transition metal oxides are often used for the manufacture of s... more Functional nanomaterials based on transition metal oxides are often used for the manufacture of supercapacitors and batteries, due to their special redox properties. The nanosized transition metal oxides used as the electrode material in some cases exhibit abnormally high values of capacitance and energy density. In this regard, it is important to understand what structural features of the nanomaterial determine the electrochemical characteristics of an electronic device. For this purpose, ceria nanorods and nanocubes were specifically synthesized under hydrothermal conditions at elevated pressure (15 MPa), different alkali contents, and two temperature regimes (100 and 180 • C). The obtained CeO 2 nanostructures were characterized using the methods of X-ray diffraction, transmission electron microscopy, and low-temperature nitrogen adsorption. The electrochemical properties of ceria nanostructures were investigated in 1 M Na 2 SO 4 water electrolyte. The influence of the structural and surface characteristics of the synthesized nanorods and nanocubes on their charge storage ability is discussed. It was shown that CeO 2 in the form of nanocubes demonstrate higher specific capacitance in comparison with nanorods, which makes them more attractive for application in supercapacitors with neutral electrolytes.
Glass Physics and Chemistry
This work describes the preparation of an organic-inorganic composite and the study of its charac... more This work describes the preparation of an organic-inorganic composite and the study of its characteristics. Particles of core (BaTiO3)–shell (SiO2–CoFe2O4) type were used as inorganic composite. These inorganic particles are used for the preparation of composites based on poly(vinyl alcohol) cyanoethyl ether synthesized in an external direct magnetic field. It is determined that the dielectric permittivity of the composites formed in an external magnetic field at the optimal content of the magnetic phase (concentration of CoFe2O4 = 20.3%) is four times as large (ε = 460 at the frequency f = 1000 Hz) as that of analogous composites formed without a magnetic field.
Inorganic Materials
SiO2-based aerogels have been produced be removing a solvent (ethanol or hexafluoroisopropanol) f... more SiO2-based aerogels have been produced be removing a solvent (ethanol or hexafluoroisopropanol) from lyogels both above and below the critical temperature of the alcohols (in the range 210–260 and 160–220°C, respectively). The resultant materials have been characterized by low-temperature nitrogen adsorption measurements, X-ray diffraction, thermal analysis, scanning electron microscopy, X-ray microanalysis, and small-angle and ultrasmall-angle neutron scattering. The results demonstrate that removing the solvent 20–30°C below the critical temperature of the solvent yields silica that is characterized by higher specific porosity and has the same or a larger specific surface area in comparison with the aerogels produced by drying under supercritical conditions. The nature of the solvent used and the solvent removal temperature influence the size and aggregation behavior of primary clusters and the cluster aggregate size in the aerogels.
Russian Journal of Inorganic Chemistry
The structure of SiO2-based materials obtained by hydrolysis of tetraethoxysilane and subsequent ... more The structure of SiO2-based materials obtained by hydrolysis of tetraethoxysilane and subsequent drying of SiO2 lyogels at temperatures from 85 to 265°C has been analyzed in detail. It has been found that drying conditions have no marked effect on the specific surface area of SiO2, which constitutes ~1000 m2/g in all cases. Average pore size and specific pore volume monotonically increase with drying temperature, the contribution of large mesopores (>20 nm) into total material porosity rises at high drying temperature. Drying temperature has a considerable effect on the degree and character of individual SiO2 particles aggregation.
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2016
Acta Physica Polonica A, 2015
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2014
This study is devoted to investigation of the micro and mesostructure (including fractal proper t... more This study is devoted to investigation of the micro and mesostructure (including fractal proper ties) of porous zirconia glasses synthesized by precipitation from zirconium n propoxide solutions in the presence of different hydrolyzing agent (H 2 O) quantities at different temperatures. Analysis of small angle neutron, ultra small angle neutron and X ray scattering, scanning electron microscopy allows concluding that the synthesized glasses are complex systems with a three level hierarchical fractal structure. It is revealed that both the temperature of synthesis and the H 2 O concentration in the initial solution significantly affect the structural characteristics of the glasses.
Journal of Solid State Chemistry, 2013
We report a detailed study of structural and chemical transformations of amorphous hydrous zircon... more We report a detailed study of structural and chemical transformations of amorphous hydrous zirconia into sulfated zirconia-based superacid catalysts. Precipitation pH is shown to be the key factor governing structure, composition and properties of amorphous sulfated zirconia gels and nanocrystalline sulfated zirconia. Increase in precipitation pH leads to substantial increase of surface fractal dimension (up to $ 2.7) of amorphous sulfated zirconia gels, and consequently to increase in specific surface area (up to $ 80 m 2 /g) and simultaneously to decrease in sulfate content and total acidity of zirconia catalysts. Complete conversion of hexene-1 over as synthesized sulfated zirconia catalysts was observed even under ambient conditions.
Journal of Physics: Conference Series, 2012
We report structural changes in amorphous hydrated zirconia caused by high intensity ultrasonic t... more We report structural changes in amorphous hydrated zirconia caused by high intensity ultrasonic treatment studied by means of small-angle neutron scattering (SANS) and X-ray diffraction (XRD). It was established that sonication affects the mesostructure of ZrO 2 ×xH 2 O gels (i.e. decreases their homogeneity, increases surface fractal dimension and the size of monomer particles). Ultrasound induced structural changes in hydrated zirconia governs its thermal behaviour, namely decreases the rate of tetragonal to monoclinic zirconia phase transition.
Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques, 2019
The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at differe... more The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at different stages of heat treatment are determined by small-angle neutron scattering. Particles of amorphous zirconium dioxide, which form mass fractals with the dimension D v = 2.21, are rearranged into surface fractals with a surface dimension of D s = 2.52 upon annealing at a temperature of 400°C or higher. In the resulting system, a shell with a fractal structure is formed over a dense core (a cluster of nanoparticles of zirconium dioxide with a constant density). Transformation of the fractal system from a mass fractal into a surface one is characterized by the appearance of a core, and its growth is due to the crystallization of hydrated zirconia particles at high temperatures. A model for the formation of a fractal particle, implying the existence of a core-shell surface fractal system, is proposed. The characteristic radius of ZrO 2 nanoparticles increases from 14 to 200 Å with an increase in the annealing temperature from 400 to 600°C.
The theoretical studies [1- 3] have shown that the orbital part of the magnetic scattering amplit... more The theoretical studies [1- 3] have shown that the orbital part of the magnetic scattering amplitude con-tains the term, which is singular at q 0 and gives rise the small-angle neutron scattering on the conduction electrons in metals:, (1) where r = e2/mc2 = 5.410-13 cm and =-1.91 is the neutron g-factor; q is the momentum transfer and p is the electron momentum. It was also shown [1 – 3] that in metals the scattering cross section is proportional to (m/M)2, where m is the effective mass of the electrons (carriers) and M is the mass of the neutron. For ordinary metals this factor is of order 10-5- 10-6 and the neutron-electron scattering is negligibly small. However for some heavy-fermion substances m ~ 100me [4] and (m/M)2 ~ 10-2. In such cases the neutron-carrier scattering could be observed if one takes into account that the static cross section d()/d is proportional to --1 for 2E >> T and T/( 2E) for T>>2E, where << 1 is the scattering angle and E is the neutro...
Russian Journal of Inorganic Chemistry
A method was developed for the low-temperature sol–gel synthesis of one of the most popular compo... more A method was developed for the low-temperature sol–gel synthesis of one of the most popular components of functional and structural materials—nanostructured yttrium aluminum garnet Y3Al5O12—using precursors from the class of alkoxoacetylacetonates produced from the corresponding acetylacetonates. It was determined that increasing duration of heat treatment of yttrium-aluminum-containing xerogen in air to 6 h reduces the crystallization temperature of the Y3Al5O12 phase from 920–930 to 750–800°C, which was confirmed by IR spectroscopy and X-ray powder diffraction analysis. The microstructure of nanocrystalline yttrium aluminum garnet obtained at 800°С was studied; it was found that the size of crystallites is 30–40 nm, the size of particles is 30–50 nm, and the size of pores is 20–30 nm. Small-angle neutron scattering demonstrated that, in the powders synthesized at 700–800°C, there is structural ordering of the short-range type, whereas in the nanocrystalline samples heat-treated at a higher temperature (850°С), there is no such ordering.
Lecture Notes in Earth System Sciences, 2019
Morphologically simple and microbially dominated ecosystems termed “biofilms” have existed on Ear... more Morphologically simple and microbially dominated ecosystems termed “biofilms” have existed on Earth for a long period of biosphere evolution. A model biofilm combining one heterotroph and one phototroph component was used in a laboratory experiment to simulate biogenic weathering with two different specimens of basic rock samples from the soil profiles. The rocks fragments from the regions of cold environments of Eurasia, where abiotic physical processes, including rock disintegration initiated by freezing–thawing cycles, represent the most probable scenario of rock weathering, were subjected to biological colonization. The rock fragments were represented by dolerite and metagabbro amphibolites. Polished sections of the rock samples were inoculated with the model microbiological consortium of the oligotrophic fungus and the phototrophic cyanobacteria (biofilm). After 3 month runtime of the experiment the progress of rock weathering was derived from the growth of the biofilm on the r...
where r = e2/mc2 = 5.410-13 cm and = -1.91 is the neutron g-factor; q is the momentum trans... more where r = e2/mc2 = 5.410-13 cm and = -1.91 is the neutron g-factor; q is the momentum transfer and p is the electron momentum. It was also shown [1 – 3] that in metals the scattering cross section is proportional to (m/M)2, where m is the effective mass of the electrons (carriers) and M is the mass of the neutron. For ordinary metals this factor is of order 10-5 10-6 and the neutron-electron scattering is negligibly small. However for some heavy-fermion substances m ~ 100me [4] and (m/M)2 ~ 10-2. In such cases the neutron-carrier scattering could be observed if one takes into account that the static cross section d()/d is proportional to --1 for 2E >> T and T/( 2E) for T >>2E, where << 1 is the scattering angle and E is the neutron energy. The crossover from one regime to another is observed at qc= ksin(T/2E). In this work [5], small-angle neutron scattering experiments were carried out with CeRu2Si2 single crystal in order to directly observe SANS ...
The mesostructure of segmented poly(urethane imide) containing 4–10 wt % CoFe 2 O 4 or Al 3 Fe 5 ... more The mesostructure of segmented poly(urethane imide) containing 4–10 wt % CoFe 2 O 4 or Al 3 Fe 5 O 12 nanoparticles was experimentally studied by small-angle polarized neutron scattering, which can analyze the nuclear and magnetic subsystems of the obtained composites. The transformation of the domain structure of the magnetic elastomers based on poly(urethane imide) was investigated at various concentrations, chemical compositions, and localizations of ferrite nanoparticles in polymer chains. The dynamics of the change in the segmental mobility of soft blocks during heating of samples was characterized by magnetic–nuclear interference scattering. The experiments detected changes in the supramolecular structure of the multiblock copolymer, which depended on the percentage and type of nanoparticles. The correlation radii were determined in the magnetic subsystem of ferrite nanoparticles embedded in hard aromatic blocks of poly(urethane imide) as nodes of intermolecular crosslinkers a...
Russian Journal of Inorganic Chemistry
Structural analysis in the range of characteristic sizes from 1 nm to ~1.5 µm was performed for S... more Structural analysis in the range of characteristic sizes from 1 nm to ~1.5 µm was performed for SiO2–TiO2 aerogels prepared in supercritical CO2, isopropanol, hexafluoroisopropanol, or methyl-tert-butyl ether using small-angle X-ray scattering and neutron scattering complementary methods. A two-level model that accounts for scattering by individual inhomogeneities and their aggregates, which have fractal properties, satisfactorily describes the aerogel structures over the entire range of scales. It is shown for the first time that the titania concentration is the key factor in the small-angle neutron and X-ray scattering by SiO2–TiO2 aerogels. The phase composition of an aerogel does not significantly affect the aerogel structure in the range of scales from 1 nm to ~1.5 µm, as probed by small-angle X-ray and neutron scattering.
Nanosystems: Physics, Chemistry, Mathematics
Functional nanomaterials based on transition metal oxides are often used for the manufacture of s... more Functional nanomaterials based on transition metal oxides are often used for the manufacture of supercapacitors and batteries, due to their special redox properties. The nanosized transition metal oxides used as the electrode material in some cases exhibit abnormally high values of capacitance and energy density. In this regard, it is important to understand what structural features of the nanomaterial determine the electrochemical characteristics of an electronic device. For this purpose, ceria nanorods and nanocubes were specifically synthesized under hydrothermal conditions at elevated pressure (15 MPa), different alkali contents, and two temperature regimes (100 and 180 • C). The obtained CeO 2 nanostructures were characterized using the methods of X-ray diffraction, transmission electron microscopy, and low-temperature nitrogen adsorption. The electrochemical properties of ceria nanostructures were investigated in 1 M Na 2 SO 4 water electrolyte. The influence of the structural and surface characteristics of the synthesized nanorods and nanocubes on their charge storage ability is discussed. It was shown that CeO 2 in the form of nanocubes demonstrate higher specific capacitance in comparison with nanorods, which makes them more attractive for application in supercapacitors with neutral electrolytes.
Glass Physics and Chemistry
This work describes the preparation of an organic-inorganic composite and the study of its charac... more This work describes the preparation of an organic-inorganic composite and the study of its characteristics. Particles of core (BaTiO3)–shell (SiO2–CoFe2O4) type were used as inorganic composite. These inorganic particles are used for the preparation of composites based on poly(vinyl alcohol) cyanoethyl ether synthesized in an external direct magnetic field. It is determined that the dielectric permittivity of the composites formed in an external magnetic field at the optimal content of the magnetic phase (concentration of CoFe2O4 = 20.3%) is four times as large (ε = 460 at the frequency f = 1000 Hz) as that of analogous composites formed without a magnetic field.
Inorganic Materials
SiO2-based aerogels have been produced be removing a solvent (ethanol or hexafluoroisopropanol) f... more SiO2-based aerogels have been produced be removing a solvent (ethanol or hexafluoroisopropanol) from lyogels both above and below the critical temperature of the alcohols (in the range 210–260 and 160–220°C, respectively). The resultant materials have been characterized by low-temperature nitrogen adsorption measurements, X-ray diffraction, thermal analysis, scanning electron microscopy, X-ray microanalysis, and small-angle and ultrasmall-angle neutron scattering. The results demonstrate that removing the solvent 20–30°C below the critical temperature of the solvent yields silica that is characterized by higher specific porosity and has the same or a larger specific surface area in comparison with the aerogels produced by drying under supercritical conditions. The nature of the solvent used and the solvent removal temperature influence the size and aggregation behavior of primary clusters and the cluster aggregate size in the aerogels.
Russian Journal of Inorganic Chemistry
The structure of SiO2-based materials obtained by hydrolysis of tetraethoxysilane and subsequent ... more The structure of SiO2-based materials obtained by hydrolysis of tetraethoxysilane and subsequent drying of SiO2 lyogels at temperatures from 85 to 265°C has been analyzed in detail. It has been found that drying conditions have no marked effect on the specific surface area of SiO2, which constitutes ~1000 m2/g in all cases. Average pore size and specific pore volume monotonically increase with drying temperature, the contribution of large mesopores (>20 nm) into total material porosity rises at high drying temperature. Drying temperature has a considerable effect on the degree and character of individual SiO2 particles aggregation.
Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2016
Acta Physica Polonica A, 2015