Nadia Petrova
Verified @mail.bg
Bulgarian Academy of Sciences, Institute of Mineralogy and Crystallography
RESEARCH INTERESTS
Thermal analyses, mineralogy
Scopus Publications
Scopus Publications
Rositsa Nikolova, Vladislav Kostov-Kytin, Nadia Petrova, Krasimir Kossev, Rositsa Titorenkova, and Gergana Velyanova
MDPI AG
Urea complexes of magnesium sulfate have been intensively studied due to their application in many areas of life, including agricultural chemistry, pharmacy, medicine, etc. The aim of this study is to add new knowledge about the trends and consistencies in the preparation procedures of MgSO4·nOC(NH2)2·mH2O phases. A set of analytical methods was used to characterize their structure, thermal and spectroscopic properties. The conditions for obtaining the three complexes in pure form were specified and the crystal structures of MgSO4·OC(NH2)2·2H2O and MgSO4·OC(NH2)2·3H2O were determined. The spectroscopic data of the considered compounds were analysed with respect to their structural and chemical properties. Thermal analyses showed that both the melting point and the urea decomposition temperature depend on the OC(NH2)2: H2O ratio in the octahedral environment of the magnesium ion in the studied structures.
Tsveta Stanimirova, Rositsa Nikolova, and Nadia Petrova
MDPI AG
A theoretical model of the crystal structure of the newly obtained compound Zn4(OH)6SO4·2–2.25H2O based on the compilation of the crystal–chemical properties of two known zinc-hydroxy-sulfate phases—mineral namuwite and hemihydrate—is proposed. The single XRD data confirmed the model and determined the structure, with a trigonal symmetry SG of P-3, the unit cell with a = 8.3418(15) Å and c = 17.595(7) Å, and a cell volume of 1060.3(6) Å3, with Z = 2. The results show that the Zn4(OH)6SO4·2–2.5H2O crystal structure consists of an alternating paired octahedral–tetrahedral doubly decorated hydroxide layer with cationic vacancies and an aqueous interlayer.
A Stoyanova-Ivanova, V Mihaylov, V Georgiev, M Georgieva, V Petrov, L Andreeva, N Petrova, and V Mikli
IOP Publishing
Abstract The Bio-active™ archwires are the latest generation multi-force orthodontic archwires made of a Ni-Ti alloy. It is of particular importance to orthodontists to know what their composition and structural characteristics are so that they can determine which one is suitable for a given stage of orthodontic treatment. The aim of this work is to characterize as-received Bio-active™ archwires, consisting of three segments (anterior, bicuspid and posterior), by determining their physicochemical properties. Laser-induced breakdown spectroscopy (LIBS) was used to determine the elemental composition in the three different segments of the archwires, along with X-ray diffraction analysis (XRD), scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and differential scanning calorimetry (DSC). A LIBS and EDX analysis of the elemental composition showed that nickel (55wt.%) and titanium (45wt.%) are the main elements, and in some segments Fe and Cr registered as trace elements. A XRD analysis, at room temperature, showed two similar peaks, characteristic of a Ni-Ti alloy, proof that the archwire is an austenite phase. The DSC data was obtained by measuring the Af temperatures for each segment (heated up to +80°C and cooled down to -80°C), showing that they can be classified as martensite-active wires (heat-activated). Based on that a recommendation can be made to cool down the unused, as-received archwires before clinical use to ensure that they will fit in the brackets easier. On the surface of the as-received archwires small grains can be seen from the SEM micrographs. The obtained results provide orthodontists important information regarding the physicochemical properties of the as-received Bio-active™ archwires. The results can also serve as a foundation for future research on the elemental composition and morphology of clinically applied Bio-active™ archwires.
Stanislav Ferdov, Boris Shivachev, Nikola Drenchev, Konstantin Hadjiivanov, Svetlana Simova, Rositsa Titorenkova, Nadia Petrova, Mihail Tarassov, and Rositsa Nikolova
Elsevier BV
Angelina Stoyanova-Ivanova, Mirela Georgieva, Valeri Petrov, Jorge N. R. Martins, Laura Andreeva, Alexander Petkov, Nadia Petrova, and Velizar Georgiev
MDPI AG
Multiforce nickel–titanium (NiTi) orthodontic archwires release progressively increasing forces in a front-to-back direction along their length. The properties of NiTi orthodontic archwires depend on the correlation and characteristics of their microstructural phases (austenite, martensite and the intermediate R-phase). From a clinical and manufacturing point of view, the determination of the austenite finish (Af) temperature is of the greatest importance, as in the austenitic phase, the alloy is most stable and exhibits the final workable form. The main purpose of using multiforce orthodontic archwires is to decrease the intensity of the applied forces to the teeth with a small root surface area, such as the lower central incisors, and also provide forces high enough to move the molars. With the optimally dosed forces of multiforce orthodontic archwires in the frontal, premolar and molar segments, the feeling of pain can be reduced. This will contribute to the greater cooperation of the patient, which is of utmost importance to achieve optimal results. The aim of this research was to determine the Af temperature at each segment of as-received and retrieved Bio-Active® and TriTanium® archwires with dimensions of 0.016 × 0.022 inches, investigated by the differential scanning calorimetry (DSC) method. A classical Kruskal–Wallis one-way ANOVA test and multi-variance comparison based on the ANOVA test statistic using the Bonferroni corrected Mann–Whitney test for multiple comparisons were used. The incisor, premolar and molar segments have different Af temperatures, and they decrease from the anterior to posterior so that the posterior segment has the lowest Af. Bio-Active® and TriTanium® with dimensions of 0.016 × 0.022 inches can be used as first leveling archwires by additional cooling and are not recommended for use on patients with mouth breathing.
Rositsa P. Nikolova, Nadia L. Petrova, Zlatka G. Delcheva, Liliya V. Tsvetanova, Tsveta Stanimirova, and Iskra Piroeva
Springer Science and Business Media LLC
Louiza Dimowa, Nadia Petrova, Yana Tzvetanova, Ognyan Petrov, and Iskra Piroeva
MDPI AG
The structural features and the thermal behavior of natural, Na-, Ca-, K-, Mg-, and Cd-exchanged clinoptilolite from the Beli Plast deposit (Bulgaria) were studied. Purified clinoptilolite sample was preliminary prepared and ion-exchanged at 100 °C for six days. DSC-TG analyses were performed for all studied forms. The effects in the DSC curves show differences with temperature due to release of weakly bound H2O molecules and strongly bound ones. The endotherm minima temperatures were between 78 and 115 °C decreasing in the sequence K- < Na- < Natural- < Ca- ≤ Mg- < Cd-clinoptilolite. The hydrate complexes around the exchanged cations also influenced the DSC curves. The cation-coordinating H2O molecules and the non-coordinating ones were determined by XRD structural refinement for all exchanged samples. The H2O molecules of the cation–hydrate complexes are released at higher temperatures than weakly bound ones and affected the DSC curves differently. The structural adjustments made by the Rietveld method, as well as the applied EDS analyzes for the chemical composition of the samples, allowed us to correlate these data to the thermal characteristics of the studied clinoptilolite samples.
Constanze Rösche, Naemi Waeselmann, Nadia Petrova, Thomas Malcherek, Jochen Schlüter, and Boriana Mihailova
Springer Science and Business Media LLC
AbstractUnderstanding the thermal behaviour of iron-containing amphiboles (AB2C5T8O22W2, C5 = M(1)2 M(2)2 M(3)) at atomic-level scale may have important implications in several fields, including metamorphic petrology, geophysics, and environmental sciences. Here, the thermally induced oxidation and decomposition of actinolite are studied by in situ high-temperature Raman spectroscopy and complementary thermogravimetric/mass-spectrometry analyses as well as X-ray diffraction of the products of amphibole decomposition. The effect of CFe2+ on dehydrogenation/dehydroxylation is followed by comparing the results on actinolite with those for tremolite. We show that mobile charge carriers, namely polarons (conduction electrons coupled to FeO6 phonons) and H+ cations, exist in actinolite at elevated temperatures ~ 1150–1250 K. The temperature-induced actinolite breakdown is a multistep process, involving (i) delocalization of e− from CFe2+ as well as of H+ from hydroxyl groups shared by Fe-containing M(1)M(1)M(3) species, which, however, remain in the crystal bulk; (ii) dehydrogenation and ejection of e− between 1250 and 1350 K, where actinolite can be considered as “oxo-actinolite”, as H+ also from hydroxyl groups next to M(1,3)(MgMgMg) configurations become delocalized and mostly remain in the crystal bulk; (iii) complete dehydroxylation and consequent structure collapse above 1350 K, forming an Fe3+-bearing defect-rich augitic pyroxene. The dehydrogenation of tremolite occurs at 1400 K, triggering immediately a disintegration of the silicate double-chain into single SiO4-chains and followed by a rearrangement of the amphibole octahedral strips and BCa2+ cations into pyroxene-type octahedral sheets at 1450 K. The result of tremolite decomposition is also a single-phase defect-rich clinopyroxene with an intermediate composition on the diopside–clinoenstatite join.
Ivelina Georgieva, Krasimir Kossev, Rositsa Titorenkova, Nadia Petrova, Tsvetan Zahariev, and Rositsa Nikolova
Elsevier BV
Stanislav V. Vassilev, Christina G. Vassileva, and Nadia L. Petrova
Elsevier BV
V. Nikolov, R. Nikolova, N. Petrova, I. Koseva, and N. Kuvandjiev
Elsevier BV
Stanislav Ferdov, Boris Shivachev, Rositsa Titorenkova, Nadia Petrova, Mihail Tarassov, and Rositsa Nikolova
Royal Society of Chemistry (RSC)
This work reports the synthesis and characterization of novel zeolite-like indium silicate MS-2 (Minho-Sofia, solid number 2).
Stanislav V. Vassilev, Christina G. Vassileva, and Nadia L. Petrova
Elsevier BV
Stanislav V. Vassilev, Christina G. Vassileva, and Nadia L. Petrova
American Chemical Society (ACS)
Short-term stored, long-term stored, and weathered biomass ashes (BAs) produced from eight biomass varieties were studied to define their composition, mineral carbonation, and CO2 capture and storage (CCS) potential by a combination of methods. Most of these BAs are highly enriched in alkaline-earth and alkaline oxides, and the minerals responsible for CCS in them include carbonates such as calcite, kalicinite, and fairchildite, and to a lesser extent, butschliite and baylissite. These minerals are a result of reactions between alkaline-earth and alkaline oxyhydroxides in BA and flue CO2 gas during biomass combustion and atmospheric CO2 during BA storage and weathering. The mineral composition of the short-term stored, long-term stored, and weathered BAs is similar; however, there are increased proportions of carbonates and especially bicarbonates in the long-term stored BAs and particularly weathered BAs. The carbonation of BAs based on the measurement of CO2 volatilization determined in fixed temperature ranges is approximately 1–27% (mean 11%) for short-term stored BAs, 2–33% (mean 18%) for long-term stored BAs, and 2–34% (mean 22%) for weathered BAs. Hence, biomass has some extra CCS potential because of sequestration of atmospheric CO2 in BA, and the forthcoming industrial bioenergy production in a sustainable way can contribute for decreasing CO2 emissions and can reduce the use of costly CCS technologies.
Stanislav Ferdov, Armandina M. L. Lopes, João P. Araujo, Boris Shivachev, Rositsa Titorenkova, Nadia Petrova, and Rosica Nikolova
American Chemical Society (ACS)
Small-pore iron silicate MS-1 (Minho-Sofia, solid number 1) with a 3D porous system, an analogue of the rare mineral imandrite, has been synthesized and characterized. This material is the lowest framework density iron silicate, one of the most siliceous (Si/Fe = 6) iron silicates, the first iron cyclosilicate achieved at hydrothermal conditions, and the only synthetic iron-based member of the lovozerite mineral group.
K. Kosev, N. Petrova, I. Georgieva, R. Titorenkova, and R. Nikolova
Elsevier BV
Zlatka Delcheva, Tsveta Stanimirova, Nadia Petrova, and Elena Tacheva
Springer Science and Business Media LLC
A new compound, NaZn4(OH)6(SO4)Br·6H2O named “Br-gordaite”, was obtained by mixing of ZnO with a solution of ZnSO4 and NaBr. The Br− ion occupies the Cl− ion tetrahedral position of the brucite-like layer of the gordaite structure without any other changes relating to the structure and chemical composition. The thermal decomposition of the new phase was studied by DSC–TG(DTG)–MS in regard to the thermal events and mass loss during volatile releasing, while phase composition and chemical composition of the initial and heating products were studied by XRD and SEM–EDAX, respectively. All processes are endothermic: (1) dehydration (20–185 °C), (2) dehydroxylation (185–320 °C), (3) evolving of bromine (400–600 °C) and (4) evolving of SO3 (770–1165 °C). One-stage releasing of bromine from the “Br-gordaite” was observed at 400–600 °C. Bromine-containing intermediate crystalline phases were not detected by XRD during the “Br-gordaite” decomposition. The presence of bromine in the solid residue at 340 °C was established by chemical analysis, while after 600 °C the bromine was no longer present. The final products of the thermal decomposition of “Br-gordaite” are ZnO and traces of Na2Zn(SO4)2. The thermal behavior and the obtained thermal decomposition products of the “Br-gordaite” were compared with other minerals with Zn octahedral–tetrahedral hydroxide layer.
Ekaterina Karteva, Neshka Manchorova, Nadia Petrova, Zhelyazko Damyanov, and Stoyan Vladimirov
IOS Press
BACKGROUND
Human dentin is a highly calcified tissue of mesenchymal origin with a heterogeneous structure. Its morphology is constantly remodelled throughout the life span of the tooth, as well as under the influence of external stimuli.
OBJECTIVE
The aim of the present study was to obtain information about the thermal changes in the crown and root dentin specimens of vital and devitalized teeth.
METHODS
The investigated samples were divided into 6 groups, depending on the patients' age and dentin location (crown, root). An additional group of endodontically treated teeth was created. The methods of choice were were combined thermal analysis (DTA-TG(DTG)-MS and gas chromatography-mass spectrometry.
RESULTS
After heating up to 1200 °C, endo- and exothermal effects were observed. The effects' dynamic was the same for all samples. The differences were in the samples' weight after the experiment, with root dentin showing the greatest mass loss percentage.
CONCLUSIONS
The observed mass loss differences could be attributed to the presence of impurities in the dentin, as well as alterations in the collagen matrix. Ageing and endodontic treatment could catalyse the accumulation of such changes and affect the microstructure of the mineralized tissue.
Georgi Kirov, Nadia Petrova, and Tsveta Stanimirova
Informa UK Limited
ABSTRACT The mixing of dehydrated zeolites with product particles leads to drying of the product, owing to the decrease in relative humidity of the environment and increase the temperature of the mixture, due to the release of adsorption heat. The analysis of the conventional one-stage contact drying process showed a significant mismatching in the water states of the product and the zeolite during drying. A two-stage drying process is proposed for harmonization of the water state of both product and sorbent. The significant advantage of the two-stage drying over one-stage regarding the degree of drying of the product, the utilization of the zeolite adsorption capacity and the duration of the process were experimentally confirmed.
Velichka Andonova, Petya Peneva, George S Georgiev, Vencislava T Toncheva, Elisaveta Apostolova, Zhivko Peychev, Stela Dimitrova, Mariana Katsarova, Nadia Petrova, and Margarita Kassarova
Informa UK Limited
The purpose of the study was to investigate the stability and biopharmaceutical characteristics of ketoprofen, loaded in polymeric carriers, which were included into a bigel in a semisolid dosage form. The polymer carriers with in situ-included ketoprofen were obtained by emulsifier-free emulsion polymerization of the monomers in aqueous medium or a solution of the polymers used. The morphological characteristics of the carriers, the in vitro release and the photochemical stability of ketoprofen were evaluated. The model with optimal characteristics was included in a bigel formulation. The bigel was characterized in terms of pH, rheological behavior, spreadability, and in vitro drug release. Acute skin toxicity, antinociceptive activity, anti-inflammatory activity, and antihyperalgesic effects of the prepared bigel with ketoprofen-loaded polymer carrier were evaluated. The carriers of ketoprofen were characterized by a high yield and drug loading. The particle size distribution varied widely according to the polymer used, and a sustained release was provided for up to 6 hours. The polymer mixture poly(vinyl acetate) and hydroxypropyl cellulose as a drug carrier, alone or included in the bigel composition, improved the photostability of the drug compared with unprotected ketoprofen. The bigel with ketoprofen-loaded particles provided sustained release of the drug and had optimal rheological parameters. In vivo experiments on the bigel showed no skin inflammation or irritation. Four hours after its application, a well-defined analgesic, anti-inflammatory, and antihyperalgesic effect was registered. The polymer mixture of poly(vinyl acetate) and hydroxypropyl cellulose as a carrier of ketoprofen and the bigel in which it was included provided an enhanced photostability and sustained drug release.
I. Koseva, V. Nikolov, N. Petrova, P. Tzvetkov, and M. Marychev
Elsevier BV