Browsing by Author "Gugov I."
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Item Crystallization behaviour of the systems Na2O/BaO/TiO2/SiO2/B2O3/Al2O3 and Na2O/BaO/TiO2/SiO2/B2O3/Fe2O3/Al2O3(2015-01-01) Harizanova R.; Mazhdrakova A.; Vladislavova L.; Avdeev G.; Bocker C.; Gugov I.; Rüssel C.This work reports data on the synthesis of glasses in three selected compositions of each of the systems Na2O/BaO/ TiO2/SiO2/B2O3/Al2O3 and Na2O/BaO/TiO2/SiO2/B2O3/Fe2O3/Al2O3 and the preparation of glass-ceramics by applying appropriate time-temperature regimes. Crystallization of a large volume fraction of cubic BaTiO3 is observed in both systems. The phase compositions of the obtained annealed specimens are investigated by x-ray diffraction, while the microstructure of the obtained glass-ceramics is studied by optical and scanning electron microscopy. The barium titanate crystals in the samples containing iron have a size varying from ca 100 nm to some hundreds of nm. They form interconnected structures which tend to grow further for all temperature-time schedules applied. The microstructure of the annealed samples containing no iron, as proved by optical and electron scanning microscopy, is characterized by barium titanate crystals of a size of some micrometers which are uniformly dispersed in the amorphous matrix. They start to grow independently and tend to merge upon longer annealing times.Item Electron microscopy investigation of the microstructure and elemental composition of barium titanate precipitated in oxide glasses(2018-01-01) Harizanova R.; Vladislavova L.; Avdeev G.; Bocker C.; Gugov I.; Rüssel C.The present work reports on the synthesis of glasses for two different ratios of alumina to sodium oxide in compositions of the system Na2O/Al2O3/BaO/TiO2/B2O3/SiO2 with addition of Fe2O3. Barium titanate-based glass-ceramics of different average crystallite sizes, depending on the ratio Na/Al-oxides, are precipitated after appropriate thermal treatment of the glasses prepared. The phase composition analyses performed by X-ray diffraction show the formation of cubic barium titanate, BaTiO3 as a main phase and also, some BaTi0.75Fe0.25O2.888. Additional crystalline phases, such as nepheline, NaAlSiO4 appear in the course of thermal treatments at higher temperatures and longer annealing times. The scanning electron micrographs of the prepared glass-ceramics verify the presence of interconnected spherulitic structures, which correspond to barium titanate crystals and which start to grow with crystallization time increase. The morphology of the spherulitic crystals is elucidated by means of transmission electron microscopy. The elemental analysis carried out by TEM verifies the precipitation of two main crystalline phases - barium titanate and barium titanium iron oxide.Item IR-SPECTROSCOPY, THERMOPHYSICAL AND MECHANICAL PROPERTIES OF GLASSES IN THE SYSTEM Na2O/BaO/TiO2/B2O3/SiO2/Al2O3(2023-01-01) Harizanova R.; Gaydarov V.; Gugov I.; Zamfirova G.; Mihailova I.; Pernikov M.; Rüssel C.Glasses with the compositions (23.1-x)Na2O/23.1BaO/23TiO2/9.8B2O3/21SiO2/xAl2O3 x = 3, 7, 11 and 15 mol% were melted using a traditional melt-quenching technique. The thermophysical properties of the obtained glasses, i.e., glass transition temperature, Tg, and crystallization peak maximum temperature, Tc, were determined by differential scanning calorimetry and showed that the increasing alumina concentration leads to an increase of both the Tg and Tc values, while the difference Tg-Tc, used as a glass stability criterium, changes in the opposite manner, being highest for the glass with 3 mol % Al2O3 and smallest for the composition with 15 mol % Al2O3. The structure of the prepared series of glasses was studied by infrared spectroscopy and showed that the main structural units present are isolated and interconnected SiO4 tetrahedra. Both BO4 and BO3 structural units, which number initially increases with the increasing alumina concentration and then starts to decrease, are also present. The conducted depth-sensing indentation on the obtained glasses allowed to determine mechanical properties such as universal (HMV) and indentation (Hit) hardness, elastic modulus and elastic part of indentation work. The change of the Na2O/Al2O3 ratio resulted in increasing HMV and Hit up to 11 mol% Al2O3 and then a slight decrease of the respective parameters was observed.Item Prof. Christian Rüssel - always one step ahead and in search of something new in glass science(2015-01-01) Harizanova R.; Gugov I.The 18th Conference on Glass and Ceramics is dedicated to Prof. Christian Rüssel for his outstanding contributions to glass science and technology. Due to his close connections to Bulgarian scientists from Bulgarian Academy of Sciences and University of Chemical Technology and Metallurgy he was awarded the title Dr. h. c. of the University of Chemical Technology and Metallurgy on September 29th, 2014, while on October 7th, 2014 he received the Golden Band Honorary Medal ``Prof. Marin Drinov`` from the Bulgarian Academy of Sciences. Christian Rüssel was born on the 1st of August, 1952 in Nürnberg. He obtained his diploma in Chemistry in 1980. He is married to his wife Angela, who is also an engineer in glass and ceramics. He has a daughter Kathrin and two grandchildren, Clara and Johann. Between 1980 and 1992 C. Rüssel gathered tremendous scientific experience by successively joining the Institute of Physical and Theoretical Chemistry, Erlangen University, the Fraunhofer Institute of Solar Energy, Freiburg and the Faculty of Engineering, Department of Materials Science, Erlangen. In 1992, he headed the Otto-Schott-Institut for Glass Chemistry, Jena where he organized four Otto Schott Colloquia. He was an active member of the management of the Friedrich Schiller University working as Dean of the Faculty of Chemistry and Geoscience (1996-1997) and Vice Rector of Research (2002-2004). His versatile investigations encompass novel and intriguing topics: electrochemistry of polyvalent metal ions in glass melts; energy storage oriented glass-ceramics by extrusion or electrochemically induced nucleation; nano-sized glass ceramics and self-constraint crystallization; electron backscatter diffraction studies of surface crystallization of glass; high temperature spectroscopy of redox pairs in glass; synthesis of nanocrystalline glass ceramics of advanced thermomechanical and optical properties.