Browsing by Author "Jordanov V."

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    Glass Formation and Properties of Multicomponent Glasses of the As2Se3-Ag2Te-GeTe System
    (2024-01-01) Karadashka I.; Ivanova V.; Jordanov V.; Karadjova V.
    Chalcogenide alloys of As2Se3-Ag2Te-GeTe were synthesized using the melt-quenching technique. By the visual and XRD analyses, the state of obtaining alloys was proven (glass, crystalline, glass + crystalline), and the glass formation region in the system was established. The thermal characteristics of some samples were determined—temperatures of glass transition (Tg); crystallization (Tcr); and melting (Tm). The basic physicochemical parameters, such as density (d) and Vickers microhardness (HV), were measured. Compactness (C), as well as some thermomechanical characteristics, such as module of elasticity (E), volume (Vh), and formation energy (Eh) of micro-voids, were calculated, and the influence of the composition on these characteristics was investigated. The addition of silver telluride resulted in a decrease in Tg and HV values and an increase in d and Vh values. No thermochemical effects of crystallization or melting were detected in some of the alloys. The obtained results were in agreement with the available literature data for similar systems.
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    In vitro bioactivity of 70 wt.% SiO2 - 30 wt.% CaO sol-gel glass, doped with 1, 3 and 5 wt.% NbF5
    (2012-02-01) Radev L.; Hristova K.; Jordanov V.; Fernandes M.; Salvado I.
    The 70SiO2-30CaO (wt.%) sol-gel glasses doped with 1, 3 and 5 NbF5 (wt.%) were prepared via polystep sol-gel route. The synthesized glasses were characterized by XRD, FTIR and SEM. Changes in 1.5 SBF solutions were measured by ICP-AES. XRD of the glasses stabilized at 700°C for 6 hours proved the presence of niocalite. FTIR was consistent with XRD data. The in vitro bioactivity study of all glasses prepared were carried out by soaking in 1.5 simulated body fluid (1.5 SBF) at 37°C for 6 and 12 days in static conditions. The FTIR reveals the formation of A-type and B-type carbonate containing hydroxyapatite (CO3HA) layer. Changes in 1.5 SBF solutions, after 6 days of soaking, show that the Ca concentration increased significantly, compared to the initial Ca content in the 1.5 SBF solution before in vitro test. After 12 days of immersion, the Ca concentration decreased, i.e., the formation of HA phase consumed Ca from 1.5 SBF solution. For all soaking times, the concentration of P is much lower than that the used 1.5 SBF. Based on these results we suggest that Ca and P play an active role in the future of the glasses. SEM depicts that the different morphology of hydroxyapatite can be formed as a function of soaking time. © 2011 Versita Warsaw and Springer-Verlag Wien.
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    PREPARATION AND PROPERTIES OF BULK AMORPHOUS CHALCOGENIDES OF THE A2Se3 - GeTe - CdTe SYSTEM
    (2022-01-01) Karadashka I.; Aljihmani L.; Jordanov V.
    Bulk amorphous chalcogenides from the As2Se3 - GeTe - CdTe system were studied. The alloys were prepared using the method of multi-step direct mono-temperature synthesis and characterized with the help of visual analysis and X-ray powder diffraction (XRD). The region of glass formation was outlined. Some physicochemical properties of the samples as microhardness, density, and characteristic temperatures, were determined. Compactness (C), modulus of elasticity (E), minimal volume of micro-voids (Vh), and energy of their formation (Eh) were calculated. The composition dependence of these parameters was discussed.