Browsing by Author "Ivanova D."

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    Atomic Layer Deposition Titanium Oxide Coating for C-Rate Improvement of Li-Ion Cathodes
    (2024-02-01) Olkhovskii D.; Ivanova D.; Chernyavsky V.; Vishniakov P.; Nazarov D.; Ezhov I.; Yafarova L.; Peng S.; Maximov M.
    Highlights NCM111 coating with titanium oxide films obtained by the atomic layer deposition; Study of the binder heat-treatment effect on the cathode performance; The importance of selecting the protective coating synthesis temperature; Modified cathode’s capacity preservation improvement with increasing current.
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    Combining IEC 61499 and ISA S88 for batch control
    (2009-01-01) Ivanova D.; Batchkova I.; Panjaitan S.; Wagner F.; Frey G.
    Modeling of batch process control over several hierarchical layers is proposed in ISA S88, independently of a concrete implementation. IEC 61499, describes models to implement distributed control systems. This contribution proposes to combine the concepts of ISA S88 for hierarchical design with the models of IEC 61499 for distributed implementation. To formally describe and analyze the control sequences, Signal Interpreted Petri Nets are utilized. From the verified description, the implementation is derived using pre-defined IEC 61499 function blocks either by hierarchical aggregation of the blocks or by using a scheduler. The scheduler approach allows re-configuration of the sequences without altering the implemented controller. The proposed approach offers analyzable formal models, re-usable basic components, and re-configurable distributed implementation. © 2009 IFAC.
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    Flavonoids Extraction Kinetics, Antimicrobial Activity and Radical Scavenging Potential of Bulgarian Woundwort (Solidago virgaurea L.)
    (2022-02-01) Yaneva Z.; Simeonov E.; Rusenova N.; Ivanova D.; Nikolova G.; Karamalakova Y.; Chilev C.; Beev G.
    The medicinal plant woundwort (Solidago virgaurea L.) characterizes by diuretic, antimutagenic, anti-inflammatory activity and it has been applied for urinary tract, nephrolithiasis and prostate disorders treatment. The aim of the present study was to analyze the extraction kinetics of catechin, epigallocatechin and quercetin from Bulgarian woundwort extracts, to assess the antibacterial potential of the medicinal plant extracts against four bacterial strains (Staphylococcus aureus ATCC25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Bacillus cereus), their antioxidant capacity and radical scavenging potential. The concentrations of the flavonoids in the extracts obtained at different extraction conditions (solvent, temperature, extraction time) were determined by newly-developed by the scientific team RP-HPLC-PDA methodologies. The agar well diffusion method was applied to evaluate the antibacterial activity of the plant extracts. The 70% EtOH extracts at 20◦C displayed significantly higher antibacterial activity against the foodborne pathogenic bacteria S. aureus and P. aeruginosa as compared to the 70% and 98% EtOH extracts at 30◦C and 20◦C, respectively. The medicinal plant exhibited satisfactory antioxidant potential and radical-scavenging activity.
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    Ftir spectroscopy method for investigation of Co-Ni nanoparticle nanosurface phenomena
    (2017-01-01) Zahariev I.; Piskin M.; Karaduman E.; Ivanova D.; Markova I.; Fachikov L.
    The Co-Ni nanoparticles examined are synthesized through a borohydride reduction with NaBH4 in aqueous solutions of chloride salts containing a different ratio of Co and Ni (1:1, 4:1 and 1:4, correspondingly) and also in the course of a template synthesis with graphite as a support in presence of β-cyclodextrin. The morphology, the elemental and phase composition of the synthesized Co-Ni nanoparticles are studied by SEM, EDS and XRD analyses. FTIR spectroscopy investigations carried out provide to elucidate the atom /molecule groups formed in the Co-Ni nanoparticles and their carbon-containing nanocomposites. The different shape and position of the bands of absorption at the relevant wavenumber [cm-1] identify the mode of vibrations (symmetric and asymmetric stretching and bending vibrations) of the created chemical bonds arising at the nanoparticle surface such as C-OH, CO-OH, C-H2, C=O, BO3, BO4, free OH, H-OH (H2O), CoO, NiO. The FTIR spectra reported illustrate also the effect of the different Co:Ni ratios studied and that of the support used. The data obtained show that FTIR spectroscopy is a sensitive method suitable for studying Co-Ni nanoparticles and their carbon-containing nanocomposites surface phenomena.
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    Newly Synthesized Lignin Microparticles as Bioinspired Oral Drug-Delivery Vehicles: Flavonoid-Carrier Potential and In Vitro Radical-Scavenging Activity
    (2023-04-01) Ivanova D.; Toneva M.; Simeonov E.; Nikolova B.; Semkova S.; Antov G.; Yaneva Z.
    The aim of the present study was to synthesize lignin microparticles, to evaluate their physicochemical, spectral, morphological and structural characteristics, to examine their encapsulation and in vitro release potential and behaviour towards the flavonoid morin in simulated physiological medium and to assess the in vitro radical-scavenging potential of the morin-loaded lignin microcarrier systems. The physicochemical, structural and morphological characteristics of alkali lignin, lignin particles (LP) and morin-encapsulated lignin microparticles (LMP) were determined based on particle size distribution, SEM, UV/Vis spectrophotometric, FTIR and potentiometric titration analyses. The encapsulation efficiency of LMP was 98.1%. The FTIR analyses proved that morin was successfully encapsulated in the LP without unexpected chemical reactions between the flavonoid and the heteropolymer. The in vitro release performance of the microcarrier system was successfully mathematically described by Korsmeyer–Peppas and the sigmoidal models outlining the general role of diffusion during the initial stages of the in vitro release process in simulated gastric fluid (SGF), and the predominant contribution of biopolymer relaxation and erosion was determined in simulated intestinal medium (SIF). The higher radical-scavenging potential of LMP, as compared to that of LP, was proven via DPPH and ABTS assays. The synthesis of lignin microcarriers not only provides a facile approach for the utilization of the heteropolymer but also determines its potential for the design of drug-delivery matrices.
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    Organic/inorganic bioactive materials part II: In vitro bioactivity of Collagen-Calcium Phosphate Silicate/Wollastonite hybrids
    (2009-10-19) Radev L.; Hristov V.; Samuneva B.; Ivanova D.
    In the present study, novel hybrid materials of Collagen (C) and Calcium Phosphate Silicate/Wollastonite (CPS/W) were synthesized. The CPS/W ceramic was prepared via polystep sol-gel method. The dissolution test of CPS/W ceramic was filled with TRIS-HCl buffer. FTIR depicts that hydroxyl carbonate apatite (OHCO3HA) was observed after 3 days of immersion in TRIS-HCl buffer. Biohybrids of C-CPS/W were produced from diluted hydrochloric acid collagen type I and ceramic powder with different ratios of C and CPS/W equal to 25:75 and 75:25 wt.%. The synthesized hybrids were characterized by FTIR, XRD and SEM. FTIR depicts a ``red shift`` if amide I could be attributed to the fact that the collagen prefers to chelate Ca2+ from partial dissolution of CPS/W ceramic. The growth of B-type carbonate containing hydroxyapatite (B-CO3HA) on the C-CPS/W hybrids soaked in 1.5SBF was observed. The negatively charged carboxylate groups from the collagen may be responsible for hydroxyapatite (HA) deposition. This fact was confirmed by the ``red shift`` of carboxylate groups of collagen in FTIR spectra. The formation of HA was observed by FTIR, XRD and SEM. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2009.
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    Phosphating of Carbon Steels in Solutions Containing Zinc and Zinc-Manganese Phosphates
    (2018-06-12) Ivanova D.
    The formation of phosphating coatings on carbon steels by novel baths containing zinc and zinc-manganese phosphates has been investigated. By gravimetric, chemical, electrochemical and physical methods are determined the characteristics of preparations (density, pH, conductivity, total and free acidity) and those of the produced coatings (thickness, phase and chemical compositions, structure, protection ability). The concentration range has been varied from 5 to 20% vol., while the temperature effects have been studied in the range from 20 to 80°C. The thicknesses of the coatings and the amount of the substrate dissolved have been determined. It is proved that Mn-phosphate decreases the coating thickness for all working solution concentrations and temperatures, at the same time increases the mass of dissolved metal of the substrate. The results obtained indicate that the coatings developed in zinc and manganese baths contain the following phases: hopeite, phosphophyllite, quasihopeite, strunzite and mixtures of them.
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    Phosphatizing of mild steel in zinc-manganese-nickel phosphates in different correlations
    (2019-01-01) Ivanova D.
    In this investigation three type phosphating concentrates containing zinc, manganese and nickel phosphates in different ratios have been studied. Gravimetric, chemical, electrochemical and physical methods were used to determine the main characteristics of the concentrates and obtained phosphate coatings. The results indicate that the coatings formed in KAF-622 are thicker, while those obtained in other concentrates are practically all the same. The phosphate coatings contain mainly hopeite and less phosphophyllite. Irrespective of modification the correlation of metal phosphates in the concentrates the coatings obtained have homogeneous structures with well defined habits of the crystals. All coatings formed in phosphate concentrates possess a good resistance in a model 3.5 % NaCl corrosion solution.
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    SEM and EDX Study of Stainless Steels, Suggested as Human Body Implants
    (2018-06-12) Simitchiiska R.; Ivanova D.; Fachikov L.
    The most important requirement for any material used as an implant is to be biocompatible and not to cause undesirable effects in the human body. Corrosion of implants is included in the topic of biocompatibility because it is a determining factor in their sustainability and seamless fulfillment of their functional purpose. The work presents the results obtained in the comparative study of two austenitic stainless steels (Cr18Ni9 and Cr18Mn12N) in two models of artificial saliva, accepted as environments for testing the corrosion behavior of materials for these aims. The nature of the corrosion attack, the composition of the corrosion products at 37°C and the pH 5.5 and pH 6.75 of the model media were determined using physical methods such as SEM and EDX of investigation and analysis. It was found that Cr18Mn12N steel (0.61 % N), exhibits higher corrosion resistance.
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    Spectroscopic study of the template synthesized intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles with a carbon support
    (2018-01-01) Markova I.; Piskin M.; Zahariev I.; Ivanova D.; Fachikov L.; Christoforou E.
    Intermetallic (Co-Sn, Ni-Sn, Co-Ni) nanoparticles are synthesized through a borohydride reduction in a mixture of aqueous solutions of CoCl2.6H2O, NiCl2.6H2O and SnCl2.2H2O salts at room temperature applying a template technique. A carbon support is used. As a result nanocomposite materials are obtained in situ. The ratio of the metallic components is chosen on the ground of the phase diagrams of the relevant binary (Co-Sn, Ni-Sn, Co-Ni) systems: Co:Sn = 35:65, Ni:Sn = 45:55, Co:Ni = 50:50. Graphite and carbon powders are used as a carbon support. To avoid the nanoparticle's aggregation β-cyclodextrin is added to the reaction solutions. EDS and XPS investigation methods are applied to study the surface composition of the synthesized intermetallic nanoparticles and their carbon nanocomposites. A particle's morphology is typical for the alloyed materials. The nanoparticles are characterized by a relatively high specific surface area. Both the elemental and phase composition of the investigated particles and their carbon composites do not alter with the change of the carbon support. They depend only on the ratio between the respective metal components set in the starting reaction solutions according to the phase diagrams of the corresponding binary systems. The studies conducted on the intermetallic nanoparticles synthesized with various carriers demonstrate that they are suitable to be used as catalysts, electrode materials in Li-ion batteries and as magnetic materials for biomedical applications.