DSpace Repository :: Browsing by Author "Dimitriev Y."

Browsing by Author "Dimitriev Y."

Now showing 1 - 20 of 21

A study of the effect of citric acid on the crystallinity of ZnO/TiO2 nanopowders
(2013-12-17) Shalaby A.; Bachvarova-Nedelcheva A.; Iordanova R.; Dimitriev Y.
It is well known that the citric acid is used as a chelating agent which forms poly (basic acid) chelates with the metal cations in a nano-powder synthesis route. The aim of this investigation is to study the influence of the citric acid on the crystallization process in obtaining ZnO/TiO2 nano-composites. Samples have been synthesized by the aqueous sol-gel method applying two different schemes with and without citric acid, respectively. Several compositions containing different TiO2 (10, 90 mol %) and ZnO (10, 90 mol %) amounts were investigated. The as-prepared powders were calcinated from 100 to 500°C. The phase formation and structural transformation at every step of the synthesis route were followed by X-ray phase analysis and IR spectroscopy and the obtained results were compared.
Chemical and technological characterization of medieval glass bracelets from South-East Bulgaria
(2014-01-01) Georgieva R.; Detcheva A.; Dimitriev Y.
The present paper deals with chemical and physicochemical characterization of seven glass fragments of medieval glass bracelets from South-East Bulgaria. Samples were investigated by Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and differential thermal analysis (DTA). Gravimetric chemical analysis was used for silica assessment. Flame photometry was applied to determine sodium and potassium content while aluminium, calcium and magnesium were determined by flame atomic absorption spectrometry after dissolution using a mixture of acids. All investigated artefacts are soda-lime-silica glasses and when produced two different recipe norms were used. Important technological parameters of glass manufacturing were determined and discussed. This investigation throws light on the technological development and production of glass during medieval times. ©Versita Sp. z o.o.
Chemical and technological characterization of medieval glass bracelets from South-East Bulgaria
(2014-01-01) Georgieva R.; Detcheva A.; Dimitriev Y.
The present paper deals with chemical and physicochemical characterization of seven glass fragments of medieval glass bracelets from South-East Bulgaria. Samples were investigated by Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and differential thermal analysis (DTA). Gravimetric chemical analysis was used for silica assessment. Flame photometry was applied to determine sodium and potassium content while aluminium, calcium and magnesium were determined by flame atomic absorption spectrometry after dissolution using a mixture of acids. All investigated artefacts are soda-lime-silica glasses and when produced two different recipe norms were used. Important technological parameters of glass manufacturing were determined and discussed. This investigation throws light on the technological development and production of glass during medieval times. ©Versita Sp. z o.o.
Combustion gel method for synthesis of nanosized ZnO/TiO2 powders
(2013-05-21) Gegova R.; Dimitriev Y.; Bachvarova-Nedelcheva A.; Iordanova R.; Loukanov A.; Iliev T.
Nanosized powders in the ZnO-TiO2 system were synthesized by combustion gel method using different precursors: Zn(NO3)2.6H2O, Ti(OC2H5)4 and Ti(OC4H9)4. During the combustion process only one phase, ZnO was obtained. The phase formation and structural transformation at every step of routes for the synthesis were followed by XRD and IR analysis. Our previous investigation in the same system, applying the hydrolytic sol-gel method showed that the type of precursor and the order of adding the components influenced on the microstructure of the final product in the ZnO-TiO2 system, which was proved also in this study. The obtained powders possess photocatalytical activity against organic dye (Malachite green) in the UV and Vis region.
Eu3+ doped glasses in the Bi2O3-B2O3-WO3-Al2O3 system
(2015-01-01) Aleksandrov L.; Iordanova R.; Khanna A.; Georgiev N.; Dimitriev Y.
The structure of many Eu3+ doped Bi2O3-B2O3-WO3-Al2O3 glasses of a different composition is studied using infrared spectroscopic technique (IR). It is found that distorted BiO6 (of a band at 480 cm-1), BO3 (of bands at 1390, 1230, 620 cm-1), BO4 (of a band at 1020 cm-1) and WO4 polyhedra (of a band at 880 cm-1) are the main building units forming the amorphous networks. WO6 groups exist in the glass network of a high WO3 content (of bands at 880 cm-1, 620 cm-1, and a shoulder at 670 cm-1). WO3 does not stimulate formation of BO4 structural units. According to the differential thermal analysis (DTA) the glass transition temperature (Tg) of the investigated glasses is situated in the range of 400°C - 485°C. The DTA curves of all glasses show two exothermic peaks corresponding to the formation of two crystal phases. Photoluminescence emissions due to the 4f transitions 5D0→7Fj (j=0-4) of Eu3+ ions are observed. The addition of WO3 to the glass compositions decreases the emission intensity of investigated glasses.
Glass formation and structure of glasses in the ZnO-WO3-La2O3-Al2O3 system
(2015-01-01) Ataalla M.; Milanova M.; Aleksandrov L.; Iordanova R.; Staneva A.; Dimitriev Y.
The glass formation region in the section 90(xZnO.yWO3.zLa2O3).10Al2O3 of a constant Al2O3 content of 10 mol % and varying amounts of WO3, ZnO and Nd2O3 from ZnO-WO3-La2O3-Al2O3 system is determined by the melt quenching technique (with cooling rates of 10 Ks-1 - 102 Ks-1). The glasses are obtained from compositions of a high WO3 content (60 mol % - 75 mol %). The amorphous state of the samples is verified by X-ray diffraction (XRD). The thermal parameters of the investigated glasses are obtained by differential thermal analysis (DTA). The glass transition temperature (Tx) is in the range 440°C - 510°C, while the crystallization temperature (Tg) varies from 520°C to 650°C. The glasses are characterized by a good thermal stability in respect to crystallization. ΔT varies in the range of 60°C - 135°C (ΔT = Tx-Tg). The glasses structure is studied by IR spectroscopy. It is established that the amorphous network is built up mainly by WO6 octahedra connected through W-O-W bridges.
Growing Oriented Layers of Bi4Ti3O12 in Bi2O3/TiO2/SiO2/Nd2O3/Al2O3 Glass-Ceramics by Melt Quenching
(2018-12-01) Wisniewski W.; Slavov S.; Rüssel C.; Dimitriev Y.
A glass melt with the composition 24Bi2O3/40TiO2/10SiO2/10Nd2O3/16 Al2O3 was prepared and rapidly quenched between two copper blocks (sample A). A part of this glass was subsequently crystallised at 800 °C for 8 h (sample B). For the preparation of another two samples, the melt was slowly cooled on a cooper plate (sample C) or cast into a graphite mould and subsequently thermally treated at 300 °C for 3 h (sample D). As shown by X-ray diffraction (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) measurements, the rapidly cooled samples contained notable amounts of uncrystallised glassy phase next to the Aurivillius phase Bi4Ti3O12. The latter occurred in higher concentrations in all other samples and formed oriented layers. Minor concentrations of Bi2Al4O9 and Al2O3 were also detected in the microstructure.
Growing Oriented Layers of Bi4Ti3O12 in Bi2O3/TiO2/SiO2/Nd2O3/Al2O3 Glass-Ceramics by Melt Quenching
(2018-12-01) Wisniewski W.; Slavov S.; Rüssel C.; Dimitriev Y.
A glass melt with the composition 24Bi2O3/40TiO2/10SiO2/10Nd2O3/16 Al2O3 was prepared and rapidly quenched between two copper blocks (sample A). A part of this glass was subsequently crystallised at 800 °C for 8 h (sample B). For the preparation of another two samples, the melt was slowly cooled on a cooper plate (sample C) or cast into a graphite mould and subsequently thermally treated at 300 °C for 3 h (sample D). As shown by X-ray diffraction (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray spectroscopy (EDXS) and electron backscatter diffraction (EBSD) measurements, the rapidly cooled samples contained notable amounts of uncrystallised glassy phase next to the Aurivillius phase Bi4Ti3O12. The latter occurred in higher concentrations in all other samples and formed oriented layers. Minor concentrations of Bi2Al4O9 and Al2O3 were also detected in the microstructure.
Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics
(2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.
We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics
(2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.
We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
Photocatalytic properties of ZnO/TiO2 powders obtained via combustion gel method
(2013-03-01) Bachvarova-Nedelcheva A.; Iordanova R.; Stoyanova A.; Gegova R.; Dimitriev Y.; Loukanov A.
The present study is a continuation of our previous investigations on the ZnO-TiO2 system. By applying different sol-gel methods we proved that the type of precursor and the order of adding the components influence the microstructure of the final product. This study focuses on the combustion sol-gel synthesis and photocatalytic properties of nanosized (∼7-20 nm) ZnO-TiO2 powders. The photocatalytic tests were performed toward two model organic dyes, Malachite Green and Reactive Black 5, in the UV and Vis region. For synthesis of ZnO/TiO2 powders, different precursors such as Zn(NO3)2·6H2O, Zn(CH 3COO)2·2H2O, Ti(OC2H 5)4 and Ti(OC4H9)4 were used. During the combustion process various phases (ZnO, TiO2 - anatase and rutile, ZnTiO3) were obtained. The structure and morphology of the resulting particles were characterized by XRD and SEM analysis. All samples exhibited a good photocatalytic activity in both UV and Vis regions. © 2012 Versita Warsaw and Springer-Verlag Wien.
Photocatalytic properties of ZnO/TiO2 powders obtained via combustion gel method
(2013-03-01) Bachvarova-Nedelcheva A.; Iordanova R.; Stoyanova A.; Gegova R.; Dimitriev Y.; Loukanov A.
The present study is a continuation of our previous investigations on the ZnO-TiO2 system. By applying different sol-gel methods we proved that the type of precursor and the order of adding the components influence the microstructure of the final product. This study focuses on the combustion sol-gel synthesis and photocatalytic properties of nanosized (∼7-20 nm) ZnO-TiO2 powders. The photocatalytic tests were performed toward two model organic dyes, Malachite Green and Reactive Black 5, in the UV and Vis region. For synthesis of ZnO/TiO2 powders, different precursors such as Zn(NO3)2·6H2O, Zn(CH 3COO)2·2H2O, Ti(OC2H 5)4 and Ti(OC4H9)4 were used. During the combustion process various phases (ZnO, TiO2 - anatase and rutile, ZnTiO3) were obtained. The structure and morphology of the resulting particles were characterized by XRD and SEM analysis. All samples exhibited a good photocatalytic activity in both UV and Vis regions. © 2012 Versita Warsaw and Springer-Verlag Wien.
Preparation and characterization of a zinc oxide nanopowder supported onto inorganic clay
(2016-01-01) Hassan M.; Afify A.S.; Ataalla M.; Mohammed A.; Staneva A.; Dimitriev Y.; Tulliani J.M.
Zinc oxide nanoparticles are obtained by a wet chemical method using zinc sulphate as a raw material. Doping sepiolite, micro-fibrous inorganic clay, with ZnO after precipitation under basic conditions and subsequent thermal treatment is investigated as both materials are abundant. They are used for the development of humidity and gas sensors of great environmental importance. The particle size distribution, the morphology and the composition of the powder samples are characterized by X-Ray diffraction accompanied by Field Emission Scanning Electron Microscopy and High Resolution-Transmission Electron Microscopy techniques. The data obtained confirm the formation of zinc oxide nanoparticles of a size of 10 nm on the modified sepiolite grains.
Structure of zinc phosphate glasses of 75 and 80 mole% ZnO content studied by X-ray diffraction and reverse Monte Carlo simulations
(2005-01-01) Hoppe U.; Dimitriev Y.; Jóvari P.
X-Ray diffraction, using high-energy photons from a synchrotron, was used to extend the investigation of (ZnO)x(P2O 5)1-x glasses to samples of ZnO content close to x = 0.8 which were obtained by roller-quenching. The isolated PO4 tetrahedra are surrounded by ZnO polyhedra, where Zn-O coordination numbers of ∼ 4.5 are determined. The small increase of NZnO ∼ 4 at metaphosphate composition (x = 0.5) to ∼ 4.5 is not sufficient to explain the strong increase of the packing density beyond the minimum at x = 0.5. The medium-range order was analyzed on the basis of partial SPP(Q) and S ZnZn(Q) factors obtained from Reverse Monte Carlo simulations of glasses with 0 ≤ x ≤ 0.8. The positions of the first peaks in these factors, the number densities of P and Zn atoms and knowledge of definite P-P and Zn-Zn distances were used to check the applicability of simple models such as the dense packing of uniform P- and Zn-centered spherical environments for glasses with x = 0.8 and 0.5, the packing of corrugated sheets for vitreous P2O5 and the packing of phosphate chains for Zn metaphosphate glass. © 2005 Verlag der Zeitschrift für Naturforschung, Tübingen.
Structure of zinc phosphate glasses of 75 and 80 mole% ZnO content studied by X-ray diffraction and reverse Monte Carlo simulations
(2005-01-01) Hoppe U.; Dimitriev Y.; Jóvari P.
X-Ray diffraction, using high-energy photons from a synchrotron, was used to extend the investigation of (ZnO)x(P2O 5)1-x glasses to samples of ZnO content close to x = 0.8 which were obtained by roller-quenching. The isolated PO4 tetrahedra are surrounded by ZnO polyhedra, where Zn-O coordination numbers of ∼ 4.5 are determined. The small increase of NZnO ∼ 4 at metaphosphate composition (x = 0.5) to ∼ 4.5 is not sufficient to explain the strong increase of the packing density beyond the minimum at x = 0.5. The medium-range order was analyzed on the basis of partial SPP(Q) and S ZnZn(Q) factors obtained from Reverse Monte Carlo simulations of glasses with 0 ≤ x ≤ 0.8. The positions of the first peaks in these factors, the number densities of P and Zn atoms and knowledge of definite P-P and Zn-Zn distances were used to check the applicability of simple models such as the dense packing of uniform P- and Zn-centered spherical environments for glasses with x = 0.8 and 0.5, the packing of corrugated sheets for vitreous P2O5 and the packing of phosphate chains for Zn metaphosphate glass. © 2005 Verlag der Zeitschrift für Naturforschung, Tübingen.
Synthesis and characterization of glass doped reduced graphene oxide
(2015-01-01) Shalaby A.; Aleksandrov L.; Iordanova R.; Staneva A.; Dimitriev Y.
Graphene is very attractive material which has high conductivity and good electrical properties. By using glass as a matrix to incorporate the graphene, it is possible to improve the conductivity and the electrical properties of the glass. In our previous study we synthesized composite material by adding of reduced graphene oxide (RGO) to silica. In this work we continue our experiments to synthesize a composite material on a glass basis in the PbO-ZnO-B2O3 system. The differential thermal analysis of the present glass showed that the glass transition temperature (Tg) is situated at ca 415°C. The synthesized glass was doped with 20 % of reduced graphene oxide (RGO). A mixture of glass with RGO was heated at different temperature values for different time taking into consideration the glass transition temperature. The characterization is performed by X-ray phase analysis, DTA and SEM analysis. It was found according to the XRD results that graphene was kept inside the glass matrix till 600°C.
Synthesis of amorphous and crystalline LaBWO6 using mechanochemical activation
(2015-01-01) Gancheva M.; Aleksandrov L.; Iordanova R.; Dimitriev Y.
This article presents data referring to the mechanochemical activated synthesis of amorphous and crystalline LaBWO6. A stoichiometric mixture of La2O3, B2O3 and WO3 of a 1:1:2 molar ratio was subjected to intense mechanical treatment in air using a planetary ball mill (Fritsch - Premium line - Pulversette No. 7). The obtained samples were analyzed by XRD, DTA, IR and UV-Vis spectroscopy. The process of mechanochemical amorphization was accomplished within 20 h at a milling speed of 500 rpm at room temperature. An additional heat-treatment of the mechanochemically obtained amorphous phase was carried out in order to obtain single crystal LaBWO6 phase. The short range order of the amorphous network was defined by BO3, BO4 and WO4 structural units. Glassy LaBWO6 was obtained by us with the application of the melt quenching method prior to these experiments. The infrared and optical spectra showed that WO4 units were more distorted in the structure of the glassy LaBWO6 when compared to those of both amorphous phases. The crystallization of LaBWO6 was achieved after thermal treatment at 690°C of the mechanochemically obtained amorphous and glass composition.
Synthesis of doped bismuth titanate ceramics with Nd2O3 and SiO2 and their electrical properties
(2013-05-21) Slavov S.; Krapchanska M.; Kashchieva E.; Parvanov S.; Dimitriev Y.
Bismuth-titanate ceramics containing SiO2 and Nd2O3 as additives are synthesized by melt quenching method in the system Bi2O3-TiO2-Nd2O3-SiO2 at temperature range 1260 - 1500oC. The phase composition of the obtained materials is determined by X-ray diffraction analysis and energy dispersive spectroscopy. Using scanning electron microscopy different microstructures are observed in the samples depending on the composition. The addition of SiO2 and Nd2O3 allows controlling the crystallization, glass formation ability, melting temperature and Curie temperature. Different values of conductivity, dielectric losses and relative permittivity are obtained depending on the composition. Measurements of the electrical conductivity, capacitance and dielectric losses of selected samples are performed by DC resistible bridge and digital capacity meter (with frequency of 1 kHz) using two-terminal method and a suitable sample holder with graphite electrodes. It is established that all investigated samples are dielectric materials with conductivity between 10-9 and 10-13 (O cm)-1 at room temperature, dielectric permittivity from 1000 to 3000 and dielectric losses tgd between 0,0002 and 0,1.
Synthesis, structure and optical properties of TiO2/TeO2/MnOm (M = Zn, B) gels: A comparison
(2015-01-01) Gegova R.; Iordanova R.; Bachvarova-Nedelcheva A.; Dimitriev Y.
We report in this study the preparation of gels of a nominal composition 50TiO2-25TeO2-25MnOm (M = Zn, B) and our attempt to verify the oxide components behaviour using Ti butoxide, Te (VI) acid, Zn acetate and boric acid as precursors. The phase and structural transformations of the prepared gels upon heat treatment in the temperature range of 200 °C - 700°C are thoroughly studied. The powdered samples still contain organics at 200°C as verified by XRD. Composites containing an amorphous phase along with different crystalline phases (elementary Te, α-TeO2, TiO2 (anatase), ZnTeO3 and TiTe3O8) are formed with temperature increase (above 300°C). The IR results obtained show that the amorphous phases (300 °C - 400°C) of the composite materials consist of TiO6, TeO4, ZnO4, BO3 and BO4 units in different ratio depending on the composition. The UV-Vis spectra of the gels prepared exhibit a red shift of the cut-off compared to pure Ti butoxide gel behavior.
The effect of Nd substitution on the glass forming ability and thermal properties in the system Bi2O3-TiO2-SiO2
(2015-01-01) Slavov S.; Kashchieva E.; Parvanov S.; Dimitriev Y.
The paper reports data on glass formation in wider concentration ranges. The samples amorphous nature is characterized by x-ray diffraction analysis, their thermal characteristics and stability are determined by differential thermal analysis (DTA), while the transmission and absorption characteristics outlined are investigated by ultraviolet-visible spectroscopy (UV-Vis). SiO2 content increase leads to a shift of the absorption border to lower wavelengths. The experimental results show that it is possible to obtain low-melting glasses containing 5 mol % - 20 mol % SiO2 and 30 mol % - 63 mol % Bi2O3 with the synthesis technique applied. Substitution of Bi2O3 with Nd2O3 up to 10 mol% leads to the preparation of a complex multicomponent glasses and glass-crystalline materials of high thermal stability.

Browsing by Author "Dimitriev Y."

Results Per Page

Sort Options