Crystallization process of amorphous Fe 81 B 13 Si 4 C 2 alloy manifested as a slightly asymmetri... more Crystallization process of amorphous Fe 81 B 13 Si 4 C 2 alloy manifested as a slightly asymmetrical exother-mic peak in temperature range 770–820 K of differential scanning calorimetry (DSC) curves. Complex crystallization DSC peak was deconvoluted into three steps corresponding to formation of-Fe(Si), Fe 3 B and Fe 2 B crystalline phases. Fe 2 B phase is formed from the amorphous matrix, while metastable Fe 3 B decomposes, providing constituents for subsequent formation of Fe 2 B phase. Examination of mechanism and kinetics of each individual step of crystallization yielded similar values of kinetic triplets, indicating similar crystallization mechanism for all individual phases, which was subsequently discussed using the values of Avrami exponents of individual crystallization steps. Both the range of and changes in values of the local Avrami exponent suggested the appearance of impingement, which precluded full applicability of JMA equation, and mixed nucleation type with accelerating nucleation for crystallization of all phases. Position of the transformation-rate maxima of individual crystallization steps indicates that anisotropic growth is the prevailing type of impingement. Estimation of lifetime showed very high stability of the alloy against crystallization at room temperature, with exponential decline in lifetime with temperature increase.
The influence of thermal treatment on functional properties of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous... more The influence of thermal treatment on functional properties of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous alloy was investigated, showing the change that resulted from thermally induced structural transformations. Thermal history of the sample was found to have a significant effect on magnetic properties. Structural transformations were identified using DSC and thermomagnetic curve and characterized using Möss-bauer spectroscopy and X-ray diffraction. Further investigation of magnetic and electrical properties of the alloy showed that structural relaxation prior to crystallization affected both magnetic susceptibility and electrical resistivity of the alloy, leading to an increase in both. This was caused by a confluence of stress relieving and a decrease in number of defects and an increase in free volume in the alloy sample, not only enabling greater mobility of magnetic domain walls, but also decreasing electron density of states at the Fermi level. Annealing at temperatures below crystallization caused an increase in magnetic susceptibility of the alloy at room temperature, however, a shift in Curie temperature was not observed. The alloy also exhibits a wide supercooled liquid region before crystallization, where its functional properties remained relatively constant, exhibiting the low values of both magnetic susceptibility and electrical conductivity.
DSC and thermomagnetic measurements of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous alloy investigated in 2... more DSC and thermomagnetic measurements of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous alloy investigated in 298e973 K temperature range show that alloy remains amorphous up to around 773 K, when it undergoes multi-step structural transformation. As thermomagnetic measurements provided more complete information , the alloy ribbon was successively annealed at temperatures chosen on the basis of these measurements and its microstructure was investigated after each annealing cycle using X-ray diffraction and SEM. XRD and microstructural analysis of the as-prepared and the annealed sample showed there is no difference between shiny and matte side of the ribbon. Two stable, a-Fe(Si) and Fe 2 B, and one metastable, Fe 3 B, crystalline phases were identified after annealing. Microstructural analysis showed that Fe 3 B probably acts as an intermediate in the formation of Fe 2 B, which formed later than the other two phases. Si and B in the alloy show a tendency to separate into different phases, exhibiting complementary fluctuations in concentration in chemical depth profile. Analysis of microstructure, combined with chemical composition, showed that after the final annealing at 973 K, alloy ribbon is composed of interdispersed nanocrystals of a-Fe(Si) and Fe 2 B less than 90 nm in size, with no observable larger domains of either phase.
Keywords: A. magnetic intermetallics B. mechanical properties at ambient temperature D. microstru... more Keywords: A. magnetic intermetallics B. mechanical properties at ambient temperature D. microstructure F. diffraction a b s t r a c t Correlation between hardness of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy and thermally induced structural transformations has been investigated by measuring microhardness in a series of samples heated at different temperatures from 25 to 1000 C. The alloy has a relatively high hardness in the amorphous state, due to its chemical composition involving silicon, boron and carbon. As the alloy begins to crystallize , microhardness increased and reached a plateau in 500e650 C temperature region, due to formation composite structure involving the small nanocrystals of a-Fe(Si) and Fe 2 B phases dispersed in the amorphous matrix. After treatment at higher temperatures, the nanocomposite structure is replaced by a more granulated structure, leading to decline in microhardness.
Thermally induced structural transformations of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy have bee... more Thermally induced structural transformations of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy have been characterized in terms of both thermodynamic and kinetic parameters of individual processes. The crystallization of the alloy occurs in temperature region around 500 • C with primary crystallization of stable-Fe(Si) and Fe 2 B and metastable Fe 3 B phase, followed by transformation of Fe 3 B to Fe 2 B. The latter process exhibits the lowest values of apparent activation energy and change in Gibbs free energy of activated complex, as well as negative value of change in entropy of activated complex, indicating that this corresponds to transformation of one crystalline phase to another, making it the least complex of the four processes. Another set of transformations occurs around 700 • C, where two consecutive processes are observed: phase transformation of-Fe(Si) to 1-Fe(Si) and subsequent transformation of a portion of 1-Fe(Si) to Fe 2 B. The consecutive nature of these processes is indicated by the fact that the first process exhibits significantly higher values of apparent activation energy and changes in Gibbs free energy and entropy of activated complex.
The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B ... more The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B 13 C 2 alloy after thermal treatment at different temperatures from 298 K to 973 K (25 °C to 700 °C) was studied. The as-prepared alloy ribbon containing a small amount of crystalline phases, as well as domains of short-range crystalline ordering embedded in the amorphous matrix, exhibits unexpectedly high microhardness, mostly due to its composition. After thermal treatment above 723 K (450 °C), the alloy samples begin to crystallize, creating a nanocomposite structure involving nanocrystals embedded in an amorphous matrix, leading to an increase in microhardness. Further growth of the nanocrystals, as the heating temperature was increased to 973 K (700 °C), caused the change from nanocomposite structure into a more granulated and porous structure, with a dominant type of interface changing from amorphous/ crystal to crystal/crystal, leading to a decrease in microhardness.
As a result of the preparation process of Fe 81 Si 4 B 13 C 2 amorphous alloy ribbon, a differenc... more As a result of the preparation process of Fe 81 Si 4 B 13 C 2 amorphous alloy ribbon, a difference has been observed between the opposite sides of the ribbon in microstructure and surface morphology. Influence of these differences on thermally induced structural transformations was studied. Thermal treatment below 600 • C had a significant influence on the evolution of the microstructure, as well as phase composition of individual sides of the ribbon. Treatment at higher temperatures caused the microstructural differences between two sides to decrease significantly. Phase composition of the alloy samples showed the opposite trend: the differences observed were the greatest in the fully crystallized alloy, after treatment at 700 • C. These differences are the result of different numbers of nucleation sites for Fe 2 B phase on respective sides of the ribbon, leading to 30% difference in its content on different sides in the fully crystallized alloy.
Izvod Ispitana je kristalizacija amorfne legure Fe 75 Ni 2 Si 8 B 13 C 2 i njen uticaj na mehanič... more Izvod Ispitana je kristalizacija amorfne legure Fe 75 Ni 2 Si 8 B 13 C 2 i njen uticaj na mehanička i fizička svojstva legure. DSC merenja su pokazala da je amorfna legura stabilna do oko 500 °C, kada počinje stupnjeviti proces kristalizacije. Termomagnetna merenja su pokazala da, pored kristalizacije, legura prolazi i kroz druge procese transformacije pre i posle kristalizacije. Uticaj svih strukturnih transformacija na funkcionalna svojstva legure je ispitan merenjem magnetnog momenta, magnetne susceptibilnosti, električne otpornosti i mikrotvrdoće na uzorcima legure odgrevanim na različitim temperaturama, kao i, gde je bilo moguće, pra-ćenjem promene ovih svojstava sa temperaturom. Mikrostukturne promene su paralelno praćene Mössbauer-ovom spektroskopijom, SEM-om i difraktometrijom X-zraka.
Hydrothermally synthesized one-dimensional and two-dimensional nanocrystals of VO 2 undergo phase... more Hydrothermally synthesized one-dimensional and two-dimensional nanocrystals of VO 2 undergo phase transition around 65 o C, where temperature and mechanism of phase transition are dependent on dimensionality of nanocrystals. Both nanocrystalline samples exhibit depression of phase transition temperature compared to the bulk material, the magnitude of which depends on the dimensionality of the nanocrystal. One-dimensional nanoribbons exhibit lower phase transition temperature and higher values of apparent activation energy than two-dimensional nanosheets. The phase transition exhibits as a complex process with somewhat lower value of enthalpy than the phase transition in the bulk, probably due to higher proportion of surface atoms in the nanocrystals. High values of apparent activation energy indicate that individual steps of the phase transition involve simultaneous movement of large groups of atoms, as expected for single-domain nanocrystalline materials.
5 Binuclear [Ni 2 (en) 2 (H 2 O) 6 (pyr)]·4H 2 O complex undergoes dehydration in 325-400 K tempe... more 5 Binuclear [Ni 2 (en) 2 (H 2 O) 6 (pyr)]·4H 2 O complex undergoes dehydration in 325-400 K temperature region, which is accompanied by polymerization. Polymerized product is characterized by chelate coordination of carboxylate group to Ni, as identified by vibrational spectroscopy. XRD and spectroscopic measurements suggest that the resulting dehydration product is two-dimensional layered polymer with weak interconnectivity between the polymer layers. A combination of experimental measurements and DFT 10 calculations was used to identify two reaction mechanisms, as well as the factors determining the change from one mechanism to the other. Reaction mechanism changes with increase in the heating rate, due to slow diffusion of released water inhibiting the polymerization. Polymerization occurs in parallel with dehydration at lower heating rates, while it follows dehydration at higher heating rates, leading to an increase in overall enthalpy of the reaction of around 50 kJmol −1 and decrease in crystallinity of the 15 polymeric product. Determined isokinetic temperature of the dehydration reaction corresponds to the vibrational frequency of Ni−OH 2 bond.
The coordination polymer [Cd(N-Boc-gly) 2 (H 2 O) 2 ] n undergoes thermally induced degradation i... more The coordination polymer [Cd(N-Boc-gly) 2 (H 2 O) 2 ] n undergoes thermally induced degradation in temperature region between 60 and 900 o C. Kinetic parameters were determined for dehydration (63-123 o C) and further degradation processes (123-461 o C) using different isoconversional and non-isoconversional methods. Due to appearance of kinetic " compensation effect " , isokinetic temperatures were determined for individual degradation processes and correlated with resonant vibrational frequencies ascribed to Cd-OH 2 coordination bond, Cd-O (O from N-Boc-glyH ligand) coordination bond and CO covalent bond.
A Zn(II) complex with N-benzyloxycarbo-nylglycinato ligands was studied by non-isothermal methods... more A Zn(II) complex with N-benzyloxycarbo-nylglycinato ligands was studied by non-isothermal methods, in particular Kissinger–Akahira–Sunose's method, and further analysis of these results was performed by Vyazovkin's algorithm and an artificial compensation effect. Density functional theory calculations of thermodynamic quantities were performed, and results obtained by both methods are consistent, thus clarifying the mechanism of this very interesting multi-step degradation.
Reversible 3D to 2D framework topochemical transformation on dehydration around 365 K. Resulting ... more Reversible 3D to 2D framework topochemical transformation on dehydration around 365 K. Resulting polymer exhibits 2D layered structure with weak interlayer connectivity. Dehydration is fully reversible in saturated water vapor at room temperature. Further degradation around 570 K yields 2D polymer without interlayer connectivity. 2D polymer exhibits conjugated electronic system.
Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate... more Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO 2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re = Yb, Gd and Sm) were added to ceria in total concentration of x = 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.
The effect of yttria additive on the thermal shock behavior of magnesium aluminate spinel has bee... more The effect of yttria additive on the thermal shock behavior of magnesium aluminate spinel has been investigated. As a starting material we used spinel (MgAl 2 O 4 ) obtained by the modified glycine nitrate procedure (MGNP). Sintered products were characterized in terms of phase analysis, densities, thermal shock, monitoring the damaged surface area in the refractory specimen during thermal shock and ultrasonic determination of the Dynamic Young modulus of elasticity. It was found that a new phase between yttria and alumina is formed, which improved thermal shock properties of the spinel refractories. Also densification of samples is enhanced by yttria addition.
Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate... more Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO 2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re = Yb, Gd and Sm) were added to ceria in total concentration of x = 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.
Development of dielectric materials for microwave frequencies is increasing with rapid progress i... more Development of dielectric materials for microwave frequencies is increasing with rapid progress in mobile and satellite communications systems, where zinc titanates have found application due to their semi-conducting and dielectric properties. Mechanical activation by grinding is a well-known method and common part of the powder preparation route in the field of ceramics. The aim of this work is investigation of the influence of experimental conditions for mechanochemical synthesis of zinc orthotitanate. Starting powder mixtures of ZnO and TiO 2 , in the molar ratio that is in accordance with the stoichiometry of zinc titanate spinel type Zn 2 TiO 4 , were mechanically activated using a high-energy planetary ball mill. The process of mechanical activation was performed during different time intervals from 0 to 300 minutes. Microstructure characterization was determined by X-ray diffraction analysis and scanning electron microscopy. Also, the specific surface area (SSA) of powders samples was measured by a nitrogen gas sorption analyzer using the BET method. The very first traces of zinc titanate are detectable after only 5 minutes of activation. The most interesting occurrence during the mechanical method of activation is that we have an almost pure phase after 90 minutes.
Journal of Pharmaceutical and Biomedical Analysis, 2001
A multifactor optimisation technique is successfully applied to develop a new HPLC method in whic... more A multifactor optimisation technique is successfully applied to develop a new HPLC method in which methyldopa, hydrochlorothiazide and amiloride were analysed and determined on a C18 column with detection at 286 nm. The optimal conditions of HPLC separation were determined with the aid of the response surface diagram -'window diagram'. The effect of simultaneously varying the pH, proportion aqueous acetic acidum and methanol in the mobile phase were studied to optimise the separation. The mobile phase composition that provides an acceptable resolution methyldopa, hydrochlorothiazide and amiloride in a short elution time is water-methanol (75:25) and pH 3.60. The k' values for methyldopa, hydrochlorothiazide and amiloride after optimisation were 1.40, 2.50 and 5.33, respectively. Relative retention (h) for ratio hydrochlorothiazide/methyldopa and amiloride/hydrochlorothiazide were 1.767 and 2.159, respectively. Correlation coefficients of the calibration curves for all analytes were greater than 0.995 and the R.S.D. values for the slope and the intercept with respect to the linearity were less than 2%. A method is applied for the quantitative analysis of Alatan ® tablets (Lek-Ljubljana). The powdered tablets are extracted with methanol, containing caffeine as the internal standard and assayed by comparison of peak areas after liquid chromatography. The high recovery (for all analytes about 100%) and the low R.S.D. ( B 2%) confirm good precision and reproducibility of the chromatographic method.
... IZVOD SINTEZA I KARAKTERIZACIJA FACIJALNOG I MERIDIJALNOG IZOMERA uns-cis-(ETILENDIAMIN-N,N&#... more ... IZVOD SINTEZA I KARAKTERIZACIJA FACIJALNOG I MERIDIJALNOG IZOMERA uns-cis-(ETILENDIAMIN-N,N'-DI-3-PROPIONATO)(S-ARGININ)KOBALT(III)-HLORIDA DIHIDRATAVESNA M. \INOVI] i TIBOR J. SABO Hemijski ... 4. JI Legg and DW Cooke, BE Douglas, Inorg. ...
Crystallization process of amorphous Fe 81 B 13 Si 4 C 2 alloy manifested as a slightly asymmetri... more Crystallization process of amorphous Fe 81 B 13 Si 4 C 2 alloy manifested as a slightly asymmetrical exother-mic peak in temperature range 770–820 K of differential scanning calorimetry (DSC) curves. Complex crystallization DSC peak was deconvoluted into three steps corresponding to formation of-Fe(Si), Fe 3 B and Fe 2 B crystalline phases. Fe 2 B phase is formed from the amorphous matrix, while metastable Fe 3 B decomposes, providing constituents for subsequent formation of Fe 2 B phase. Examination of mechanism and kinetics of each individual step of crystallization yielded similar values of kinetic triplets, indicating similar crystallization mechanism for all individual phases, which was subsequently discussed using the values of Avrami exponents of individual crystallization steps. Both the range of and changes in values of the local Avrami exponent suggested the appearance of impingement, which precluded full applicability of JMA equation, and mixed nucleation type with accelerating nucleation for crystallization of all phases. Position of the transformation-rate maxima of individual crystallization steps indicates that anisotropic growth is the prevailing type of impingement. Estimation of lifetime showed very high stability of the alloy against crystallization at room temperature, with exponential decline in lifetime with temperature increase.
The influence of thermal treatment on functional properties of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous... more The influence of thermal treatment on functional properties of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous alloy was investigated, showing the change that resulted from thermally induced structural transformations. Thermal history of the sample was found to have a significant effect on magnetic properties. Structural transformations were identified using DSC and thermomagnetic curve and characterized using Möss-bauer spectroscopy and X-ray diffraction. Further investigation of magnetic and electrical properties of the alloy showed that structural relaxation prior to crystallization affected both magnetic susceptibility and electrical resistivity of the alloy, leading to an increase in both. This was caused by a confluence of stress relieving and a decrease in number of defects and an increase in free volume in the alloy sample, not only enabling greater mobility of magnetic domain walls, but also decreasing electron density of states at the Fermi level. Annealing at temperatures below crystallization caused an increase in magnetic susceptibility of the alloy at room temperature, however, a shift in Curie temperature was not observed. The alloy also exhibits a wide supercooled liquid region before crystallization, where its functional properties remained relatively constant, exhibiting the low values of both magnetic susceptibility and electrical conductivity.
DSC and thermomagnetic measurements of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous alloy investigated in 2... more DSC and thermomagnetic measurements of Fe 75 Ni 2 Si 8 B 13 C 2 amorphous alloy investigated in 298e973 K temperature range show that alloy remains amorphous up to around 773 K, when it undergoes multi-step structural transformation. As thermomagnetic measurements provided more complete information , the alloy ribbon was successively annealed at temperatures chosen on the basis of these measurements and its microstructure was investigated after each annealing cycle using X-ray diffraction and SEM. XRD and microstructural analysis of the as-prepared and the annealed sample showed there is no difference between shiny and matte side of the ribbon. Two stable, a-Fe(Si) and Fe 2 B, and one metastable, Fe 3 B, crystalline phases were identified after annealing. Microstructural analysis showed that Fe 3 B probably acts as an intermediate in the formation of Fe 2 B, which formed later than the other two phases. Si and B in the alloy show a tendency to separate into different phases, exhibiting complementary fluctuations in concentration in chemical depth profile. Analysis of microstructure, combined with chemical composition, showed that after the final annealing at 973 K, alloy ribbon is composed of interdispersed nanocrystals of a-Fe(Si) and Fe 2 B less than 90 nm in size, with no observable larger domains of either phase.
Keywords: A. magnetic intermetallics B. mechanical properties at ambient temperature D. microstru... more Keywords: A. magnetic intermetallics B. mechanical properties at ambient temperature D. microstructure F. diffraction a b s t r a c t Correlation between hardness of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy and thermally induced structural transformations has been investigated by measuring microhardness in a series of samples heated at different temperatures from 25 to 1000 C. The alloy has a relatively high hardness in the amorphous state, due to its chemical composition involving silicon, boron and carbon. As the alloy begins to crystallize , microhardness increased and reached a plateau in 500e650 C temperature region, due to formation composite structure involving the small nanocrystals of a-Fe(Si) and Fe 2 B phases dispersed in the amorphous matrix. After treatment at higher temperatures, the nanocomposite structure is replaced by a more granulated structure, leading to decline in microhardness.
Thermally induced structural transformations of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy have bee... more Thermally induced structural transformations of amorphous Fe 75 Ni 2 Si 8 B 13 C 2 alloy have been characterized in terms of both thermodynamic and kinetic parameters of individual processes. The crystallization of the alloy occurs in temperature region around 500 • C with primary crystallization of stable-Fe(Si) and Fe 2 B and metastable Fe 3 B phase, followed by transformation of Fe 3 B to Fe 2 B. The latter process exhibits the lowest values of apparent activation energy and change in Gibbs free energy of activated complex, as well as negative value of change in entropy of activated complex, indicating that this corresponds to transformation of one crystalline phase to another, making it the least complex of the four processes. Another set of transformations occurs around 700 • C, where two consecutive processes are observed: phase transformation of-Fe(Si) to 1-Fe(Si) and subsequent transformation of a portion of 1-Fe(Si) to Fe 2 B. The consecutive nature of these processes is indicated by the fact that the first process exhibits significantly higher values of apparent activation energy and changes in Gibbs free energy and entropy of activated complex.
The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B ... more The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B 13 C 2 alloy after thermal treatment at different temperatures from 298 K to 973 K (25 °C to 700 °C) was studied. The as-prepared alloy ribbon containing a small amount of crystalline phases, as well as domains of short-range crystalline ordering embedded in the amorphous matrix, exhibits unexpectedly high microhardness, mostly due to its composition. After thermal treatment above 723 K (450 °C), the alloy samples begin to crystallize, creating a nanocomposite structure involving nanocrystals embedded in an amorphous matrix, leading to an increase in microhardness. Further growth of the nanocrystals, as the heating temperature was increased to 973 K (700 °C), caused the change from nanocomposite structure into a more granulated and porous structure, with a dominant type of interface changing from amorphous/ crystal to crystal/crystal, leading to a decrease in microhardness.
As a result of the preparation process of Fe 81 Si 4 B 13 C 2 amorphous alloy ribbon, a differenc... more As a result of the preparation process of Fe 81 Si 4 B 13 C 2 amorphous alloy ribbon, a difference has been observed between the opposite sides of the ribbon in microstructure and surface morphology. Influence of these differences on thermally induced structural transformations was studied. Thermal treatment below 600 • C had a significant influence on the evolution of the microstructure, as well as phase composition of individual sides of the ribbon. Treatment at higher temperatures caused the microstructural differences between two sides to decrease significantly. Phase composition of the alloy samples showed the opposite trend: the differences observed were the greatest in the fully crystallized alloy, after treatment at 700 • C. These differences are the result of different numbers of nucleation sites for Fe 2 B phase on respective sides of the ribbon, leading to 30% difference in its content on different sides in the fully crystallized alloy.
Izvod Ispitana je kristalizacija amorfne legure Fe 75 Ni 2 Si 8 B 13 C 2 i njen uticaj na mehanič... more Izvod Ispitana je kristalizacija amorfne legure Fe 75 Ni 2 Si 8 B 13 C 2 i njen uticaj na mehanička i fizička svojstva legure. DSC merenja su pokazala da je amorfna legura stabilna do oko 500 °C, kada počinje stupnjeviti proces kristalizacije. Termomagnetna merenja su pokazala da, pored kristalizacije, legura prolazi i kroz druge procese transformacije pre i posle kristalizacije. Uticaj svih strukturnih transformacija na funkcionalna svojstva legure je ispitan merenjem magnetnog momenta, magnetne susceptibilnosti, električne otpornosti i mikrotvrdoće na uzorcima legure odgrevanim na različitim temperaturama, kao i, gde je bilo moguće, pra-ćenjem promene ovih svojstava sa temperaturom. Mikrostukturne promene su paralelno praćene Mössbauer-ovom spektroskopijom, SEM-om i difraktometrijom X-zraka.
Hydrothermally synthesized one-dimensional and two-dimensional nanocrystals of VO 2 undergo phase... more Hydrothermally synthesized one-dimensional and two-dimensional nanocrystals of VO 2 undergo phase transition around 65 o C, where temperature and mechanism of phase transition are dependent on dimensionality of nanocrystals. Both nanocrystalline samples exhibit depression of phase transition temperature compared to the bulk material, the magnitude of which depends on the dimensionality of the nanocrystal. One-dimensional nanoribbons exhibit lower phase transition temperature and higher values of apparent activation energy than two-dimensional nanosheets. The phase transition exhibits as a complex process with somewhat lower value of enthalpy than the phase transition in the bulk, probably due to higher proportion of surface atoms in the nanocrystals. High values of apparent activation energy indicate that individual steps of the phase transition involve simultaneous movement of large groups of atoms, as expected for single-domain nanocrystalline materials.
5 Binuclear [Ni 2 (en) 2 (H 2 O) 6 (pyr)]·4H 2 O complex undergoes dehydration in 325-400 K tempe... more 5 Binuclear [Ni 2 (en) 2 (H 2 O) 6 (pyr)]·4H 2 O complex undergoes dehydration in 325-400 K temperature region, which is accompanied by polymerization. Polymerized product is characterized by chelate coordination of carboxylate group to Ni, as identified by vibrational spectroscopy. XRD and spectroscopic measurements suggest that the resulting dehydration product is two-dimensional layered polymer with weak interconnectivity between the polymer layers. A combination of experimental measurements and DFT 10 calculations was used to identify two reaction mechanisms, as well as the factors determining the change from one mechanism to the other. Reaction mechanism changes with increase in the heating rate, due to slow diffusion of released water inhibiting the polymerization. Polymerization occurs in parallel with dehydration at lower heating rates, while it follows dehydration at higher heating rates, leading to an increase in overall enthalpy of the reaction of around 50 kJmol −1 and decrease in crystallinity of the 15 polymeric product. Determined isokinetic temperature of the dehydration reaction corresponds to the vibrational frequency of Ni−OH 2 bond.
The coordination polymer [Cd(N-Boc-gly) 2 (H 2 O) 2 ] n undergoes thermally induced degradation i... more The coordination polymer [Cd(N-Boc-gly) 2 (H 2 O) 2 ] n undergoes thermally induced degradation in temperature region between 60 and 900 o C. Kinetic parameters were determined for dehydration (63-123 o C) and further degradation processes (123-461 o C) using different isoconversional and non-isoconversional methods. Due to appearance of kinetic " compensation effect " , isokinetic temperatures were determined for individual degradation processes and correlated with resonant vibrational frequencies ascribed to Cd-OH 2 coordination bond, Cd-O (O from N-Boc-glyH ligand) coordination bond and CO covalent bond.
A Zn(II) complex with N-benzyloxycarbo-nylglycinato ligands was studied by non-isothermal methods... more A Zn(II) complex with N-benzyloxycarbo-nylglycinato ligands was studied by non-isothermal methods, in particular Kissinger–Akahira–Sunose's method, and further analysis of these results was performed by Vyazovkin's algorithm and an artificial compensation effect. Density functional theory calculations of thermodynamic quantities were performed, and results obtained by both methods are consistent, thus clarifying the mechanism of this very interesting multi-step degradation.
Reversible 3D to 2D framework topochemical transformation on dehydration around 365 K. Resulting ... more Reversible 3D to 2D framework topochemical transformation on dehydration around 365 K. Resulting polymer exhibits 2D layered structure with weak interlayer connectivity. Dehydration is fully reversible in saturated water vapor at room temperature. Further degradation around 570 K yields 2D polymer without interlayer connectivity. 2D polymer exhibits conjugated electronic system.
Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate... more Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO 2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re = Yb, Gd and Sm) were added to ceria in total concentration of x = 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.
The effect of yttria additive on the thermal shock behavior of magnesium aluminate spinel has bee... more The effect of yttria additive on the thermal shock behavior of magnesium aluminate spinel has been investigated. As a starting material we used spinel (MgAl 2 O 4 ) obtained by the modified glycine nitrate procedure (MGNP). Sintered products were characterized in terms of phase analysis, densities, thermal shock, monitoring the damaged surface area in the refractory specimen during thermal shock and ultrasonic determination of the Dynamic Young modulus of elasticity. It was found that a new phase between yttria and alumina is formed, which improved thermal shock properties of the spinel refractories. Also densification of samples is enhanced by yttria addition.
Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate... more Nanometric powders of solid solutions of cerium oxide were obtained by a modified glycine nitrate procedure. Solid solutions of the host compound CeO 2 with one or more dopants in the lattice were synthesized. Rare earth cations (Re = Yb, Gd and Sm) were added to ceria in total concentration of x = 0.2 that was kept constant. The criterion in doping was to keep the value of lattice parameter of ceria unchanged. The lattice parameters were calculated by using the model that takes into account the existence of oxygen vacancies in the structure.
Development of dielectric materials for microwave frequencies is increasing with rapid progress i... more Development of dielectric materials for microwave frequencies is increasing with rapid progress in mobile and satellite communications systems, where zinc titanates have found application due to their semi-conducting and dielectric properties. Mechanical activation by grinding is a well-known method and common part of the powder preparation route in the field of ceramics. The aim of this work is investigation of the influence of experimental conditions for mechanochemical synthesis of zinc orthotitanate. Starting powder mixtures of ZnO and TiO 2 , in the molar ratio that is in accordance with the stoichiometry of zinc titanate spinel type Zn 2 TiO 4 , were mechanically activated using a high-energy planetary ball mill. The process of mechanical activation was performed during different time intervals from 0 to 300 minutes. Microstructure characterization was determined by X-ray diffraction analysis and scanning electron microscopy. Also, the specific surface area (SSA) of powders samples was measured by a nitrogen gas sorption analyzer using the BET method. The very first traces of zinc titanate are detectable after only 5 minutes of activation. The most interesting occurrence during the mechanical method of activation is that we have an almost pure phase after 90 minutes.
Journal of Pharmaceutical and Biomedical Analysis, 2001
A multifactor optimisation technique is successfully applied to develop a new HPLC method in whic... more A multifactor optimisation technique is successfully applied to develop a new HPLC method in which methyldopa, hydrochlorothiazide and amiloride were analysed and determined on a C18 column with detection at 286 nm. The optimal conditions of HPLC separation were determined with the aid of the response surface diagram -'window diagram'. The effect of simultaneously varying the pH, proportion aqueous acetic acidum and methanol in the mobile phase were studied to optimise the separation. The mobile phase composition that provides an acceptable resolution methyldopa, hydrochlorothiazide and amiloride in a short elution time is water-methanol (75:25) and pH 3.60. The k' values for methyldopa, hydrochlorothiazide and amiloride after optimisation were 1.40, 2.50 and 5.33, respectively. Relative retention (h) for ratio hydrochlorothiazide/methyldopa and amiloride/hydrochlorothiazide were 1.767 and 2.159, respectively. Correlation coefficients of the calibration curves for all analytes were greater than 0.995 and the R.S.D. values for the slope and the intercept with respect to the linearity were less than 2%. A method is applied for the quantitative analysis of Alatan ® tablets (Lek-Ljubljana). The powdered tablets are extracted with methanol, containing caffeine as the internal standard and assayed by comparison of peak areas after liquid chromatography. The high recovery (for all analytes about 100%) and the low R.S.D. ( B 2%) confirm good precision and reproducibility of the chromatographic method.
... IZVOD SINTEZA I KARAKTERIZACIJA FACIJALNOG I MERIDIJALNOG IZOMERA uns-cis-(ETILENDIAMIN-N,N&#... more ... IZVOD SINTEZA I KARAKTERIZACIJA FACIJALNOG I MERIDIJALNOG IZOMERA uns-cis-(ETILENDIAMIN-N,N'-DI-3-PROPIONATO)(S-ARGININ)KOBALT(III)-HLORIDA DIHIDRATAVESNA M. \INOVI] i TIBOR J. SABO Hemijski ... 4. JI Legg and DW Cooke, BE Douglas, Inorg. ...
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