Tony Spassov - Profile on Academia.edu (original) (raw)
Papers by Tony Spassov
Materials
Composites based on Mg2Ni with 5% activated carbon from apricot stones (ACAP) have been prepared ... more Composites based on Mg2Ni with 5% activated carbon from apricot stones (ACAP) have been prepared by ball milling and subsequent annealing in hydrogen atmosphere. The purpose of the primary metal (Mg, Ni, and V) milling was to reduce the particle size and achieve a good contact between them, without forming intermetallic compounds. During hydriding/dehydriding at 300 °C the amount of the Mg2Ni phase progressively increased, and after 10 cycles about 50% Mg2(Ni,V) was achieved. The hydrogenation produced mainly Mg2NiH4, but small amounts of MgH2 and VHx were also detected in the powder mixture. Relatively high hydrogen storage capacity and fast hydriding/dehydriding kinetics of the Mg2.1Ni0.7V0.3—5 wt.% ACAP composite were determined both from hydrogen gas phase and electrochemically.
Facile preparation of edelweiss-like ZnO microparticles with strong UV-violet emission
Vacuum
Bulk Amorphous Foam of (Pd48Cu20Ni6Sb26)96Zr4 Alloy
Hierarchical CuO microparticles constructed via underwater Leidenfrost process and their Fenton-like catalytic activity
Materials Letters
Inclusion complexes of ibuprofen and β-cyclodextrin: Supramolecular structure and stability
Journal of Molecular Structure
Novel spherical simonkolleite nanoparticles and their promotional effect on the thermal decomposition of ammonium perchlorate
Vacuum
Metals
The thermal properties of a Pd40Ni40Si20 glassy alloy with the largest supercooled liquid region ... more The thermal properties of a Pd40Ni40Si20 glassy alloy with the largest supercooled liquid region among the glassy alloys containing Si as a metalloid element are studied using static and dynamic measurement methods. The relatively wide supercooled liquid region of 45 K, defined by the temperature interval between the glass transition temperature (Tg) and the onset temperature of crystallization (Tx), and the viscosity of the supercooled liquid, varying from 2.7 × 1010 to 3.2 × 1011 Pa·s, make this glass suitable for the introduction of controlled pores by a viscous flow in the temperature range Tg~Tx. The obtained activation energy for crystallization, 272 ± 19 kJ/mol, is slightly higher than that of Tg (228 ± 11 kJ/mol), indicating the dominant contribution of the atomic transport barrier in the overall energy barrier for crystallization.
Microstructural and morphological investigations on Mg-Nb2O5-CNT nanocomposites processed by high-pressure torsion for hydrogen storage applications
International Journal of Hydrogen Energy
Ammonia-evaporation-induced construction of three-dimensional NiO/g-C 3 N 4 composite with enhanced adsorption and visible light-driven photocatalytic performance
Superlattices and Microstructures
Journal of Nanomaterials
A series of AB5-type alloys with different particle and grain size were characterized electrochem... more A series of AB5-type alloys with different particle and grain size were characterized electrochemically as materials for negative electrodes in Ni-MH batteries. Besides, the effect of alloy composition on the discharge capacity and cycle life was studied. Ball milling under hydrogen atmosphere was applied to reduce significantly the grain size of the alloys and to avoid the initial activation at the electrochemical charge/discharge cycling. The alloy morphology and microstructure after different mechanical treatments were characterized by XRD and SEM. The best effect in respect of discharge capacity and cycle life was achieved for the materials milled for 5 h under hydrogen atmosphere.
Preparation and Characterization of Amorphous and Nanocrystalline Palladium Alloys
Engineering Sciences
Journal of Cereal Science
Amylose-LPC inclusion complexes are acquired by a novel mechanochemical method and by hydrotherma... more Amylose-LPC inclusion complexes are acquired by a novel mechanochemical method and by hydrothermal method. The new synthetic method includes mechanical milling of suspension of LPC and starch under controlled conditions. Both methods applied resulted in similar microstructure of the complexes, studied by x-ray diffraction (XRD). Furthermore, Solid-state 13 C NMR spectroscopy and differential scanning calorimetry (DSC) also confirm the efficient complexation by the new approach.
Micron (Oxford, England : 1993), Jan 18, 2016
This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch prec... more This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch precursors treated with H2SO4 and HNO3 and finally annealed at 1000°C and 2000°C. Our experimental investigations combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and micro-spot near-edge X-ray absorption fine structure (μ-NEXAFS) spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of the carbon foams. The high-resolution microscopy data indicate the formation of carbonaceous amorphous microspheres (average diameters of 0.28±0.01μm) embedded in the partially graphitized carbon foam matrix at 1000°C. The microspheres are enriched with sp-bonded species and their microstructural characteristics depend on the reagent (nitric vs. sulfuric acid) used for pitch treatment. A complete chemical transformation ...
Grain Growth Kinetics in Nanocrystalline ZR-Based Alloys
Key Engineering Materials, 1993
J Alloys Compounds, 2002
Oxidation of a rapidly solidified Mg-Ni-Y alloy was studied in a wide temperature range in air by... more Oxidation of a rapidly solidified Mg-Ni-Y alloy was studied in a wide temperature range in air by means of TG, DSC, XRD, TEM, SEM / EDAX. The alloy was in different microstructural states and with a different phase composition depending on the temperature of oxidation. The oxidation kinetics have been found to obey different laws (linear, logarithmic, parabolic) at the different temperatures. At low temperatures of oxidation (200-3508C) the alloy oxidizes slowly with linear kinetic law. In the temperature range of 350-4308C generally a logarithmic model describes best the experimental kinetic data, as the initial stage of oxidation follows also a linear kinetic equation. At temperatures above 4308C a parabolic law is valid. During further increase of the temperature, again a linear kinetic law was followed due to partial cracking of the oxide film. The rate constants, activation energies and pre-exponential factors were also derived. The products of oxidation, the morphology and microstructure of the oxide film, alloy matrix and oxide / alloy matrix interface were investigated. The phase composition and microstructure of the metal matrix do not differ very much from those resulting after annealing in a protective argon atmosphere. Grain growth proceeds with a low rate even after long term annealing at temperatures of about 400-4508C. It was found that the oxide film consists of MgO and MgNiO and traces of yttrium oxides. The outer layer of the scale is 2 nanocrystalline. At the oxide / alloy matrix interface dense coarse crystals with most probable composition Mg Y were observed. The 24 5 microscopic observations as well as the kinetic results indicate that the oxide film in Mg Ni Y works successfully as a protective layer 87 12 1 at temperatures up to 500-5208C, retarding the oxygen transport in the scale and to the oxide / metal interface.
J Therm Anal Calorim, 2009
Hydrogen sorption properties and some corresponding changes in the crystallization of amorphous T... more Hydrogen sorption properties and some corresponding changes in the crystallization of amorphous TM 33 Zr 67 (TM=Fe, Co, Ni) alloys have been investigated. Relatively large amount of hydrogen was found to dissolve into the amorphous alloys during electrochemical hydrogen charging. The microstructural evolution during annealing of H-charged Ni 33 Zr 67 was studied as well. The weaker bonded hydrogen desorbs in a large temperature range (440-625 K) before the crystallization of the amorphous alloys to start. A hydride phase (ZrH 2) was found to form during annealing the H-charged amorphous Ni 33 Zr 67 alloy. During heating at constant heating rate the hydride decomposes at about 715 K and formation of Zr 2 Ni immediately takes place. The final microstructure of the Zr 2 Ni, crystallized from the H-charged matrix, is noticeably finer compared to the material crystallized from the H-free amorphous alloy, most probably due to the higher temperature of Zr 2 Ni formation in the H-charged amorphous alloy than in the H-free sample.
Electrochemical hydriding of nanocrystalline TiFe alloys
Journal of Applied Electrochemistry, Mar 27, 2007
Nanocrystalline TiFe alloys with different morphology and microstructure were synthesized by mech... more Nanocrystalline TiFe alloys with different morphology and microstructure were synthesized by mechanical alloying from the elemental powders with varied milling time. The particle morphology distinctly changes from globular to slaty between the 10th and 15th h of milling and then becomes spherical again after 30 h. The average particle size decreases continuously with milling time from about 50 μm (10 h milling) to 1–2 μm
Microstructure, microhardness and corrosion behavior of rapidly solidified magnesium based Mg-Ni-(Y, MM) alloys
Zeitschrift Fur Metallkunde, 2000
Nanocrystalline Mg-Ni-Based Hydrogen Storage Alloys Produced by Nanocrystallization
Journal of Metastable and Nanocrystalline Materials, Mar 31, 1999
?lectrochemical hydriding/dehydriding of nanocrystalline Mg2-x Sn x Ni (x�=�0, 0.1, 0.3)
J Appl Electrochem, 2008
Materials
Composites based on Mg2Ni with 5% activated carbon from apricot stones (ACAP) have been prepared ... more Composites based on Mg2Ni with 5% activated carbon from apricot stones (ACAP) have been prepared by ball milling and subsequent annealing in hydrogen atmosphere. The purpose of the primary metal (Mg, Ni, and V) milling was to reduce the particle size and achieve a good contact between them, without forming intermetallic compounds. During hydriding/dehydriding at 300 °C the amount of the Mg2Ni phase progressively increased, and after 10 cycles about 50% Mg2(Ni,V) was achieved. The hydrogenation produced mainly Mg2NiH4, but small amounts of MgH2 and VHx were also detected in the powder mixture. Relatively high hydrogen storage capacity and fast hydriding/dehydriding kinetics of the Mg2.1Ni0.7V0.3—5 wt.% ACAP composite were determined both from hydrogen gas phase and electrochemically.
Facile preparation of edelweiss-like ZnO microparticles with strong UV-violet emission
Vacuum
Bulk Amorphous Foam of (Pd48Cu20Ni6Sb26)96Zr4 Alloy
Hierarchical CuO microparticles constructed via underwater Leidenfrost process and their Fenton-like catalytic activity
Materials Letters
Inclusion complexes of ibuprofen and β-cyclodextrin: Supramolecular structure and stability
Journal of Molecular Structure
Novel spherical simonkolleite nanoparticles and their promotional effect on the thermal decomposition of ammonium perchlorate
Vacuum
Metals
The thermal properties of a Pd40Ni40Si20 glassy alloy with the largest supercooled liquid region ... more The thermal properties of a Pd40Ni40Si20 glassy alloy with the largest supercooled liquid region among the glassy alloys containing Si as a metalloid element are studied using static and dynamic measurement methods. The relatively wide supercooled liquid region of 45 K, defined by the temperature interval between the glass transition temperature (Tg) and the onset temperature of crystallization (Tx), and the viscosity of the supercooled liquid, varying from 2.7 × 1010 to 3.2 × 1011 Pa·s, make this glass suitable for the introduction of controlled pores by a viscous flow in the temperature range Tg~Tx. The obtained activation energy for crystallization, 272 ± 19 kJ/mol, is slightly higher than that of Tg (228 ± 11 kJ/mol), indicating the dominant contribution of the atomic transport barrier in the overall energy barrier for crystallization.
Microstructural and morphological investigations on Mg-Nb2O5-CNT nanocomposites processed by high-pressure torsion for hydrogen storage applications
International Journal of Hydrogen Energy
Ammonia-evaporation-induced construction of three-dimensional NiO/g-C 3 N 4 composite with enhanced adsorption and visible light-driven photocatalytic performance
Superlattices and Microstructures
Journal of Nanomaterials
A series of AB5-type alloys with different particle and grain size were characterized electrochem... more A series of AB5-type alloys with different particle and grain size were characterized electrochemically as materials for negative electrodes in Ni-MH batteries. Besides, the effect of alloy composition on the discharge capacity and cycle life was studied. Ball milling under hydrogen atmosphere was applied to reduce significantly the grain size of the alloys and to avoid the initial activation at the electrochemical charge/discharge cycling. The alloy morphology and microstructure after different mechanical treatments were characterized by XRD and SEM. The best effect in respect of discharge capacity and cycle life was achieved for the materials milled for 5 h under hydrogen atmosphere.
Preparation and Characterization of Amorphous and Nanocrystalline Palladium Alloys
Engineering Sciences
Journal of Cereal Science
Amylose-LPC inclusion complexes are acquired by a novel mechanochemical method and by hydrotherma... more Amylose-LPC inclusion complexes are acquired by a novel mechanochemical method and by hydrothermal method. The new synthetic method includes mechanical milling of suspension of LPC and starch under controlled conditions. Both methods applied resulted in similar microstructure of the complexes, studied by x-ray diffraction (XRD). Furthermore, Solid-state 13 C NMR spectroscopy and differential scanning calorimetry (DSC) also confirm the efficient complexation by the new approach.
Micron (Oxford, England : 1993), Jan 18, 2016
This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch prec... more This work reports the microstructural evaluation of carbon foams derived from coal-tar pitch precursors treated with H2SO4 and HNO3 and finally annealed at 1000°C and 2000°C. Our experimental investigations combine scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) imaging, X-ray photoelectron spectroscopy (XPS) and micro-spot near-edge X-ray absorption fine structure (μ-NEXAFS) spectroscopy. This set of complementary techniques provides detailed structural and chemical information of the surface and the bulk of the carbon foams. The high-resolution microscopy data indicate the formation of carbonaceous amorphous microspheres (average diameters of 0.28±0.01μm) embedded in the partially graphitized carbon foam matrix at 1000°C. The microspheres are enriched with sp-bonded species and their microstructural characteristics depend on the reagent (nitric vs. sulfuric acid) used for pitch treatment. A complete chemical transformation ...
Grain Growth Kinetics in Nanocrystalline ZR-Based Alloys
Key Engineering Materials, 1993
J Alloys Compounds, 2002
Oxidation of a rapidly solidified Mg-Ni-Y alloy was studied in a wide temperature range in air by... more Oxidation of a rapidly solidified Mg-Ni-Y alloy was studied in a wide temperature range in air by means of TG, DSC, XRD, TEM, SEM / EDAX. The alloy was in different microstructural states and with a different phase composition depending on the temperature of oxidation. The oxidation kinetics have been found to obey different laws (linear, logarithmic, parabolic) at the different temperatures. At low temperatures of oxidation (200-3508C) the alloy oxidizes slowly with linear kinetic law. In the temperature range of 350-4308C generally a logarithmic model describes best the experimental kinetic data, as the initial stage of oxidation follows also a linear kinetic equation. At temperatures above 4308C a parabolic law is valid. During further increase of the temperature, again a linear kinetic law was followed due to partial cracking of the oxide film. The rate constants, activation energies and pre-exponential factors were also derived. The products of oxidation, the morphology and microstructure of the oxide film, alloy matrix and oxide / alloy matrix interface were investigated. The phase composition and microstructure of the metal matrix do not differ very much from those resulting after annealing in a protective argon atmosphere. Grain growth proceeds with a low rate even after long term annealing at temperatures of about 400-4508C. It was found that the oxide film consists of MgO and MgNiO and traces of yttrium oxides. The outer layer of the scale is 2 nanocrystalline. At the oxide / alloy matrix interface dense coarse crystals with most probable composition Mg Y were observed. The 24 5 microscopic observations as well as the kinetic results indicate that the oxide film in Mg Ni Y works successfully as a protective layer 87 12 1 at temperatures up to 500-5208C, retarding the oxygen transport in the scale and to the oxide / metal interface.
J Therm Anal Calorim, 2009
Hydrogen sorption properties and some corresponding changes in the crystallization of amorphous T... more Hydrogen sorption properties and some corresponding changes in the crystallization of amorphous TM 33 Zr 67 (TM=Fe, Co, Ni) alloys have been investigated. Relatively large amount of hydrogen was found to dissolve into the amorphous alloys during electrochemical hydrogen charging. The microstructural evolution during annealing of H-charged Ni 33 Zr 67 was studied as well. The weaker bonded hydrogen desorbs in a large temperature range (440-625 K) before the crystallization of the amorphous alloys to start. A hydride phase (ZrH 2) was found to form during annealing the H-charged amorphous Ni 33 Zr 67 alloy. During heating at constant heating rate the hydride decomposes at about 715 K and formation of Zr 2 Ni immediately takes place. The final microstructure of the Zr 2 Ni, crystallized from the H-charged matrix, is noticeably finer compared to the material crystallized from the H-free amorphous alloy, most probably due to the higher temperature of Zr 2 Ni formation in the H-charged amorphous alloy than in the H-free sample.
Electrochemical hydriding of nanocrystalline TiFe alloys
Journal of Applied Electrochemistry, Mar 27, 2007
Nanocrystalline TiFe alloys with different morphology and microstructure were synthesized by mech... more Nanocrystalline TiFe alloys with different morphology and microstructure were synthesized by mechanical alloying from the elemental powders with varied milling time. The particle morphology distinctly changes from globular to slaty between the 10th and 15th h of milling and then becomes spherical again after 30 h. The average particle size decreases continuously with milling time from about 50 μm (10 h milling) to 1–2 μm
Microstructure, microhardness and corrosion behavior of rapidly solidified magnesium based Mg-Ni-(Y, MM) alloys
Zeitschrift Fur Metallkunde, 2000
Nanocrystalline Mg-Ni-Based Hydrogen Storage Alloys Produced by Nanocrystallization
Journal of Metastable and Nanocrystalline Materials, Mar 31, 1999
?lectrochemical hydriding/dehydriding of nanocrystalline Mg2-x Sn x Ni (x�=�0, 0.1, 0.3)
J Appl Electrochem, 2008