Papers by Bilyana Kostova
ORGANIZED BY THE HELLENIC PHYSICAL SOCIETY WITH THE COOPERATION OF THE PHYSICS DEPARTMENTS OF GREEK UNIVERSITIES: 7th International Conference of the Balkan Physical Union, 2010
ABSTRACT
Different types of isomorphic substitutions in the apatite structure are well known, as the subst... more Different types of isomorphic substitutions in the apatite structure are well known, as the substitution of PO 4 by CO 3-ion is the most common. This specifies the existence of various members of the apatite isomorphic series. Carbonate-hydroxyl-flour apatite sample (B-type with Ca/P ratio >1.67) from Tunisia sedimentary phosphorite ore deposit are investigated. The high energy milling is an environmentally friendly technological alternative for ore processing, to the conventional acid leaching methods. The high energy milling creates defects in the apatite structure with simultaneous accumulation of mechanic energy. The impact of the mechanical forces over the solids is mostly revealed through the changes of the quantities being related to the energetic stability and reactivity of the solid phase. Under high energy milling process the isomorphic substitution increases mainly of on the account of CO 2 and partly of water vapor. Thermal with gas-mass analysis in the temperature interval 600-900 °С in air medium has been used to evaluate the achieved effect of the high energy milling on the positional redistribution of CO 3-ions and the structural phasetransformations occurring in the investigated sample. The experimental analysis shows liberation of CO 3-ions in three temperature stages with varying mass losses. Peaks intensities are determined from the high energy milling effect, the high temperature heating and the gas medium during the measurements.
Zenodo (CERN European Organization for Nuclear Research), Apr 27, 2023
This work deals with Roman and Late Antique bricks and roof tiles from eight archaeological sites... more This work deals with Roman and Late Antique bricks and roof tiles from eight archaeological sites in Southeast Bulgaria. The samples' study was through X-ray fluorescence, powder X-ray diffraction, Fourier transform infrared, and thermal analysis, supported by macro and micro observations. The results indicate the successful combination of the experimental methods to determine with great accuracy the mineral composition and type of the raw clay (regarding the content of carbonate phases), the firing technology, and some findings of high ceramic quality and durability over time. This work shows that the clay type (calcareous type-carbonate-rich clay or non-calcareous type-carbonate-poor clay) cannot be determined by using chemical analysis only. The clay type determination is only possible by combination with thermal analysis in the case of ceramic firing below the calcite decarbonation temperature and by taking into account only the CaO amount included in the clay as calcite, which is calculated from the measured mass loss of calcite decarbonation. The results prove that for a more precise determination of the ceramic firing temperature range, it is necessary to use not only the phase composition (mineral-thermometers), but also the structural features of minerals determined by Fourier transform infrared and thermal analyses. The results evidence the use of identical ceramic manufacturing technologies in the entire geographical area during the Roman and Late Antique periods and a clear perspective for future investigation. They also complement the known archaeological background by interpreting people's knowledge continuity from the Roman age to Late Antiquity and giving insight into their economic and cultural life, based on the ceramic experimental investigations. KEYWORDS: Late Antique and Roman ceramic tiles and bricks, thermal analysis, phase analysis, chemical analysis 2 B. KOSTOVA et al.
IOP conference series, Feb 1, 2023
The analysis, characterization, and comparison of modern and ancient mortars provide fundamental ... more The analysis, characterization, and comparison of modern and ancient mortars provide fundamental (by tracing the change in the raw materials and recipes used from the past to the present) and practical (obtaining modern mortars compatible with the ancient) knowledge. This work aimed to characterize modern and ancient mortars by investigating their phase composition, binder-to-aggregate ratio, hydraulicity, and hygroscopic properties. The used methods for analyses were powder X-ray diffraction, Fourier transforms infrared spectroscopy, and thermal analysis. A modern mortar (sample A) preparation was with a binder of white Portland cement and an aggregate of river sand. Ancient mortar samples (sample B - cocciopesto and sample C - lime mortar) collection were from Bulgarian archaeological sites allocated within the Roman period. The results define investigated sample A as pozzolanic mortar with hygroscopic properties, sample B - as hydraulic lime mortar with hygroscopic properties, and sample C – as lime mortar without any hygroscopic properties. Obtained results with these, achieved for phase composition and binder-to-aggregate ratio, show that modern mortar is not compatible with the Romans and is not suitable for reconstruction and conservation of masonry from these archaeological sites.
Optical Materials, 2011
Crystals of BSO doped with Se in two different concentrations (BSO:Se(I) and BSO:Se(II)) were gro... more Crystals of BSO doped with Se in two different concentrations (BSO:Se(I) and BSO:Se(II)) were grown by the Czochralski method. It is established that doping with Se is accompanied with preferential absorption of Fe from the melt. According to the in-depth chemical analysis, it is assumed that the doping Se ions enter the tetrahedral positions by means of the substitution of
IOP Conference Series: Materials Science and Engineering
The object of the study is cement compositions based on white Portland cement, characterized by a... more The object of the study is cement compositions based on white Portland cement, characterized by a high content of marble powder and a low water-to-cement ratio. The samples were prepared with different concentrations of the components, affecting their densities and strengths determined at 28 days or 120 days of curing. The IR spectroscopy and scanning electron microscopy supplement the thermal analysis (heating rate of 10°C/min in the temperature range of 20-1200°C). This work aimed to characterize cement mortars by powder X-ray diffraction (PXRD) and thermal (TG-DTG-DSC) analysis up to 1200°C. The study obtained data on phase composition, binder-to-aggregate and water-to-cement ratio, and spectroscopic and thermal properties of cement mortars. As a result of the study, an increase in the decomposition temperatures of composites with marble powder was found. Substitution of a part of the Portland cement clinker with a marble powder leads to the formation of carbo-sulpho-aluminates.
Annual of Natural Sciences Department
The aim of this paper is to promote thermal analysis as a method for the study of archaeological ... more The aim of this paper is to promote thermal analysis as a method for the study of archaeological ceramics. In order to achieve this goal, the nature of the thermal methods (thermal processes, types of thermal methods and their application) is described. Specific experimental measurements by simultaneous TG/DTG-DSC analysis of ceramic archaeological artifacts are also presented.
A route was created and tested for the tourists regarding alternative geological tourism in the I... more A route was created and tested for the tourists regarding alternative geological tourism in the Iskar gorge. The papperwork shows that the resources make the Svoge municipal a region with a great potential for development of geotourism. The geological tourism could become very popular for the amatures. The combining of geological and cultural objects increases the touristic interest to this product. Геоложки туризъм по Искърски пролом, България Биляна Костова, Ралица Берберова Нов български университет, департамент "Природни науки" РЕЗЮМЕ Създаден е и е тестван туристически продукт (маршрут) за алтернативен геоложки туризъм в Искърския пролом. Работата показва, че ресурсите в района определят община Своге като място с изключителен потенциал за развитието на геоложки туризъм, който може да добие голяма популярност сред непрофесионалисти в сферата на геологията, като съчетанието на геоложки с културно-исторически обекти увеличава интереса към изготвения продукт. Ключови думи...
Materials Today Communications, 2021
The major issue studied in this paper is a natural mineral aggregate of quartz, calcite, and fluo... more The major issue studied in this paper is a natural mineral aggregate of quartz, calcite, and fluorapatite (the raw material originated from Bulgaria) before and after high energy milling and thermal treatment, in the order to investigate the properties of natural CaO-SiO 2-P 2 O 5 ceramic system. The activation effects are monitored by chemical analysis, X-ray powder diffraction, Fourier transformed infrared spectroscopy, and Thermal analysis (TG/DTG). The activation effect study shows: (i) change of chemical bond strength; (ii) deformation of structural polyhedrons with the formation of new isomorphic phases; (iii) the prolonged time of HEM activation leads to lower raw mineral stability and to the formation of new phases; iv) increased SiO 2 reactivity resulting in solid-phase crystallization. The obtained results can be used in the study of ceramic and cement materials (ancient and modern), soil conditioners, etc.
Annual of Natural Sciences Department, 2021
The official data of the Executive Environment Agency (ExEA) for the contents of SO2, NO2, fine a... more The official data of the Executive Environment Agency (ExEA) for the contents of SO2, NO2, fine air particles, O3, CO and C6H6 in the atmospheric air on the territory of Sofia for a 12-year period (2007 – 2018) are analyzed. The trends in their seasonal and annual changes defining the air quality in the urban environment are outlined.
Journal of Crystallization Process and Technology, 2014
Specimens of Bi12SiO20 (BSO) crystals oriented along , and were examined by electron diffraction ... more Specimens of Bi12SiO20 (BSO) crystals oriented along , and were examined by electron diffraction and various two- and three-dimensional defects were characterized. Low- angle misoriented sub-grains were found along the [001] and the [111] zone axes. The observed weak reflections elongation along and is attributed to some kind of stacking faults lying in planes perpendicular to these directions. We discuss a complex image of the electron diffraction patterns observed along the [011] zone axis and conclude that these patterns are caused by a second-phase inclusion consisting of BSO, meta-stable phase Bi2SiO5 and SiO2.
Crystals of Bi12SiO20 doped with Se (BSO:Se) are grown by the Czochralski method. The measured co... more Crystals of Bi12SiO20 doped with Se (BSO:Se) are grown by the Czochralski method. The measured concentration of Se is 1.75×1018 N/cm-3 and an additional increase of the Fe concentration from 1.9×1018 N/cm-3 (undoped Bi12SiO20) to 6.4×1018 N/cm-3 (BSO:Se) is also detected. The lattice parameter of BSO:Se is 10.096 A˚. It is assumed that the doping takes place in the tetrahedral positions by replacement of 3Si4+ ions by (Se6++2Fe3+) ions. The doping is found to cause an increase of the absorption coefficient practically in the entire spectral interval (1.4-3.1 eV) studied by optical absorption spectroscopy. Such an effect is typical for all Fe-doped Bi12SiO20 crystals. The weak bands situated in the 1.4-2.1 eV spectral range should be attributed to crystal-field induced transitions of Fe3+ as well as of other uncontrolled impurities as Cr4+, Ni2+ and Co2+.
Journal of Physics: Conference Series, 2010
Bi 12 SiO 20 are widely used in optical devices, spatial-time light modulators and as holographic... more Bi 12 SiO 20 are widely used in optical devices, spatial-time light modulators and as holographic media depending on their properties in a wide spectral range. This work deals with the optical absorption coefficient of pure and doped Bi 12 SiO 20 (BSO) crystals measured in the energy region l.5-3.2 eV and generalise our already published and new experimental data on crystals doped with Al, P, Cr, Mn, Fe, Co, Ni, Cu, Se, Ru. It is shown that such doping affects differently the optical absorption in both the near-fundamental-edge shoulder (3.2-2.2 eV) and on impurity levels in the band gap (2.2-1.5 eV). The main factors determining the absorption are concentration and segregation coefficient, electro-negativity of the doping ion and its difference from that of oxygen (DEN), the oxidation states, possible coordination and corresponding ionic radius. The role of some of these factors to the spectral dependence of the optical absorption of BSO is discussed from the view point of a suitable doping of BSO to obtain and modify the optical transparency.
IOP Conference Series: Materials Science and Engineering, 2010
View the article online for updates and enhancements. You may also like Comparison of the photoch... more View the article online for updates and enhancements. You may also like Comparison of the photochromic behaviour of dyes in solution and on polyester fabric applied by supercritical carbon dioxide M T Abate, S Seipel, M Viková et al.-Raman spectroscopy of bismuth silicon oxide single crystals grown by the Czochralski technique Z Lazarevi, S Kosti, V Radojevi et al.-Fluorescent photochromes of diarylethene series: synthesis and properties V Z Shirinian, D V Lonshakov, A G Lvov et al.
Crystals
The production and trade of metals was the foundation of the economic wealth of many regions in t... more The production and trade of metals was the foundation of the economic wealth of many regions in the world, which makes the study of ancient metallurgical slags of primary importance. This type of study is relatively new for Bulgaria, where research in the field started in the late 1960s with chemical analysis of copper ore, slags, tools and finished goods from the ancient copper mine in the Ay-bunar area. Iron is one of the most commonly found elements in the earth’s crust and its deposits are widespread, including on Bulgaria’s territory. To this day, however, the study of iron slags from Bulgarian sites through chemical and phase analysis has almost never been explored. The application of these methods allows for the determination of the technology of the ancient metallurgical process. This study investigates iron slags from two Bulgarian archaeological sites, situated in close proximity to the Sarnevets hematite ore deposit, Sarnena Sredna Gora mountain. The ore bodies of the dep...
Journal of Thermal Analysis and Calorimetry
Annual of Natural Sciences Department, 2021
The main objective of this paper is to present the fieldwork results ofarchaeological and geologi... more The main objective of this paper is to present the fieldwork results ofarchaeological and geological investigations in the area of Hadjiyska river and the southern slopesof Eminska Stara Planina in Bulgaria. The area of interest is home to a large number ofarcheological findings dating back from the Late Antiquity (4-6th c.) and the Middle Ages (7-18thc.), and fewer from older periods (prehistorical, Thracian and Roman periods). Geologicalobservations show presence of alluvial, prolluvial-delluvial, and prolluvial hollocen sediments.Combining the results of archaeological and geological research allowed for (i) the verification ofthe hypothesis that older archaeological objects are covered by accumulated sediments, and (ii) anattempt to look into the livelihood in the area.
ISSN:0016-7037ISSN:1872-953
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Papers by Bilyana Kostova