8th International Materials Science Conference HighMatTech-2023
October 2-6, 2023 Kyiv, Ukraine
Ceramics and Glasses
Head:
Dr.Sc., Professor Tetiana Prikhna
Head of the Department of High Pressure Technologies, Functional Ceramic Composites and Dispersed Superhard MaterialsV. Bakul Institute for Superhard Materials of the National Academy of Sciences of UkraineUkraine
Prikhna Tetyana Oleksiivna, Academician of the National Academy of Sciences of Ukraine, Doctor of Technical Sciences (Full), Professor, Academician of the World Academy of Ceramics (WAC), Academician of the Euro-Mediterranean Academy of Arts and Sciences (EMAAS), Head of the Department of High Pressure Technologies, Functional Ceramic Composites and Dispersed Superhard Materials of the V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine (ISM NAS of Ukraine), Professor of the Chair of Chemistry of the Kyiv National University of Construction and Architecture (KNUCA), Member of the Scientific Council of the National Research Foundation of Ukraine (NFDU), Member of the National Agency for Quality Assurance in Higher Education (NAQA).
The main research activity of T.O. Prikhna connected with the development of new ceramic materials having the necessary set of physicochemical characteristics – their synthesis, sintering, study of structure, properties and practical application. Over the years under her leadership and with her direct participation, a number of materials with a unique set of functional characteristics have been developed and researched, including high-temperature superconductors in the form of massive blocks, wires, thin films and Josephson junctions, materials based on MAX phases in the form of massive materials and coatings, single crystals of aluminum dodecaborides, massive materials based on refractory and shock-wave-resistant borides, carbides, nitrides and silicides, as well as nano- and micropowders of metals and their oxides and carbides, heavy and hard alloys made by electroerosive dispersion method. In her scientific works Prikhna TO studies the regularities of consolidation and synthesis of ceramic materials in a wide range of pressures and temperatures, using high quasi-hydrostatic pressures transmitted through solid media, isostatic gas pressures, hot pressing, spark plasma sintering, pressureless and vacuum sintering, magnetron and vacuum-arc evaporation methods. She specializes in the study of the structure of materials by scanning electron microscopy and Auger spectroscopy, as well as a comprehensive study of superconducting, electromagnetic, mechanical properties, chemical and mechanical resistance in reducing and oxidizing media in a wide range of temperatures.
Keynote speaker:
Dr. Branko Matovic
Director of the Center for Excellence for the Synthesis, Processing and Characterization of Materials at Extreme Conditions
Institute for Nuclear Cciences Vinca, Belgrade University
Dr. Branko Matovic is Professor and Scientific Advisor and he also serves as Director of the Center for Excellence for the Synthesis, Processing and Characterization of Materials at Extreme Conditions. He received Dr. Rer. Nat. degree from the Max Planck Institute, Stuttgart, Germany. He is engaged in research that requires an interdisciplinary approach; ie. basic and applied research in the border area of basic sciences (chemistry, physics, biology) and engineering. experimental and computational investigations of materials obtained or operated under extreme conditions. The emphasis is on the innovative materials processed and/or exploited at high pressures, under high magnetic and electric fields, over a wide range of temperatures, radiation conditions, corrosive environments, under extreme mechanical loads and non-equilibrium thermodynamic conditions. He is currently acting as editor-in-chief of Journal of Innovative Materials in Extreme Conditions.
Speakers:
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H3-DC1711 |
The effect of ZrO₂ concentration on the optical properties of Y₂O₃ transparent ceramics Dariia Chernomorets1,2, Jan Hostaša2, Laura Esposito2 1Institute for Single Crystals of NAS of Ukraine Good optical and mechanical properties and thermochemical stability allow using optical Y₂O₃ ceramics for different applications. However, the process of obtaining this material is challenging due to the high melting point of Y₂O₃, and, therefore, sintering aids are used to reduce the sintering temperature and promote densification during the process [1]. For the presented work ZrO₂ was chosen, since it is one of the common sintering aids for producing Y₂O₃ ceramics [2]. The aim of the study is to establish the optimal concentration of ZrO₂ for obtaining transparent Y₂O₃ ceramics. The concentration of ZrO₂ varied in the range of 0–11 mol%. Transparent optical ceramics Y₂O₃:Zr⁴⁺ were obtained from a stoichiometric mixture of powders by uniaxial pressing followed by CIP (cold isostatic pressing) and vacuum sintering at 1735°C for 22 hours. The dependence of the optical characteristics of transparent Y₂O₃ ceramics on the concentration of ZrO₂ was investigated. It was established that 7 mol% is the optimal concentration that allows obtaining yttrium ceramics of the highest optical quality. This sample is characterized by full densification (100% of the theoretical value), homogeneous microstructure without defects, such as pores or secondary phases, and mean grain size of about 4.8 μm. The optical transmittance of this sample reached 80.2% at 1100 nm. When no sintering aid was used, significant grain growth was observed (about 14 μm) and the formation of almost opaque ceramics with a transmittance of 7.2% at 1100 nm. An increase in the concentration of ZrO₂ up to 7 mol% leads to an increase in optical transmittance. With the subsequent addition of a sintering aid, the optical properties of ceramics deteriorate slightly. At the same time, it is worth noting that the presence of secondary phases is not observed even at 11 mol% of ZrO₂. This indicates that for the studied composition range, a solid solution of ZrO₂ in Y₂O₃ is obtained without reaching the solubility limit.
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Dariia Chernomorets |
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H3-RY1355 |
Infrared transparent ceramics of complex architecture for extreme operating conditions Roman Yavetskiy, Olexandra Kryzhanovska, Nadiia Safronova, Dariia Chernomorets, Oxana Matvienko, Serhii Parkhomenko, Andrii Doroshenko, Ihor Vorona, Anton Balabanov, Arsenii Timoshenko Institute for Single Crystals of NAS of Ukraine Creating new transparent windows for modern infrared (IR) optics working in aggressive conditions is an urgent task of materials science. Such materials require high transparency, low emissivity, high thermomechanical stability. Existing materials meet the needs of optical quality, but most of them do not have sufficient thermomechanical properties. Composite nanoceramics are potentially able to combine high optical quality with extremely high heat resistance. Nanoceramics in Y2O3–MgO system are considered as promising optical materials for IR range due to excellent transparency, improved thermal shock resistance and mechanical strength. This work aims to study obtaining peculiarities of IR-transparent ceramics of complex architecture based on Y2O3–MgO system.
Y2O3 ceramics have been synthesized by reactive sintering method. The effects of starting materials, mesostructure of green bodies and processing conditions on the properties of Y2O3 ceramics were studied. Y2O3 ceramic samples of complex geometry were produced by slip casting. Influence of dispersant type and their concentration on Y2O3 suspensions stability was investigated. Rheological properties of Y2O3 slips were studied. Microstructure, optical properties and mechanical characteristics of hemispherical samples were determined.
50:50 vol.% Y2O3–MgO composite nanoceramics were produced using nitrate-glycine method and spark plasma sintering. Effect of heat treatment conditions on structural and morphological characteristics of Y2O3–MgO nanopowders was investigated. Influence of spark plasma sintering parameters of Y2O3–MgO nanopowders and ceramics properties were studied. Morphology, microhardness and IR-transmittance of Y2O3–MgO nanocomposites were determined. Hemispherical green body was obtained by slip casting. Effect of solid loading, dispersant type and its concentration on stability and rheological properties of aqueous Y2O3–MgO suspensions was investigated in details.
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Roman Yavetskiy |
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H3-OB1453 |
AlMgB14-related orthorhombic boron carbide phases from first principles: structure and mechanical properties Oleksiy Bystrenko1,2, Jingxian Zhang2,3, Dong Fangdong4, Xiaoguang Li2,3, Weiyu Tang2,3, Kaiqing Zhang2,3, Jianjun Liu2,3 1Frantsevich Institute for problems of materials science, National Academy of Sciences, Kiev, Ukraine We theoretically examine the effects produced by replacing interlayer boron-boron bonds in AlMgB14-related boron network by carbon-carbon bonds on its structure and mechanical properties. The equilibrium structure, elastic constants, Vickers hardness and shear strength are evaluated by means of first principle computer simulations on the basis of density functional theory by employing ultrasoft and PAW pseudopotentials with the use of GGA approximation. The obtained results support the conclusions of Ref. [1] concerning the importance of interlayer bonds in AlMgB14-related boron network for mechanical properties of compounds with related structure.
The results of simulations suggest a possibility of existence of a number of new orthorhombic boron carbide phases with enhanced mechanical properties with the theoretically predicted Young’s modulus of 550-620 GPa and intrinsic hardness of 43-50 GPa.
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Oleksiy Bystrenko |
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H3-TP3074 |
Structure, mechanical characteristics and high temperature stability of sintered under high and by hot pressing ZrB2- and HfB2– based materials without and with SiC and Si3N4 additions Tetiana Prikhna1, Anastasiya Lokatkina1, Pavlo Barvitskyi1, Myroslav Karpets2, Viktor Moshchil1, Semyon Ponomarov3, Johen Werner4, Bernd Büchner4, Richard Haber5, Zeynep Ayguzer Yasar5, Branko Matovich6, Robert Kluge4, Anatoly Bondar7, Olexander Borymskyi1, Leonid Devin1 1V. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine The study of the structure, mechanical characteristics and high temperature stability in vacuum and in air (DTA and TG measurements) of sintered under high quasiisostatic pressure (at
4.1 GPa) and by hot pressing (at 30 MPa) ZrB2 - and HfB2 – based materials without and with SiC and Si3N4 additions showed that the use of high pressures at comparatively low temperatures (1800oC) and short sintering time (8 min) makes it possible to obtain mentioned materials with improved mechanical properties as compared to all other known methods. The stability in vacuum of pure ZrB2 and HfB2 occurred to be essentially higher than that of the materials with SiC additions (the beginning of melting of the materials with additions observed at 2150-2160°C, while the materials without them did not melt up to 2970°C). The composite material prepared from HfB2 -30 wt.% SiC mixture demonstrated mechanical characteristics (density =6.21 g/cm 3, microhardness Hv(9.8 N) =38.1±1.4 GPa, H V (49 N) = 27.7±0.24 GPa, HV (98 N)=26.3±2.03 and fracture toughness K 1C (9.8 N) = 8.2±0.2, MH•m 0.5 , K 1C (49 H)=6.8±0.6 MH•m 0.5 , K 1C (98 N) = 6.4 ±0.11 MH•m 0.5 ) which are essentially higher than that of pure HfB2 sintered in the same conditions (=10.79 g/cm 3 , Hv(9.8 N)=21.3±0.84 GPa, HV (49 N)=19.3±1.34 GPa, HV (98 N)=19.2±0.5 and fracture toughness K 1C (49 N)=7.2±0.9 MH•m 0.5 , K 1C (98 N)=5.7 ±0.3 MN•m 0.5 , Young modulus E=984 GPa, Poisson ratio µ=0.146). The mechanical characteristics of high pressure sintered material from ZrB 2 +20 wt.% SiC (=5.04 g/cm 3 , Hv(9.8 N)=24.2±1.0 GPa, H V (49 N)= 17.6±0.7, H V (98 N)=16.73±1.1 GPa, K 1C (49 N)=7.21±1.55 MH•m 0.5 , K 1C (98 N)=6.2 ±1.24 MH•m 0.5 , E=386 GPa, µ=0.093) are higher than that sintered by hot pressing at 30 MPa, 1900 o C for 1 h from ZrB 2 +30 wt.% SiC (=5.25 g/cm 3 , Hv(9.8 N)=22.95±1.0 GPa, K 1C (9.8 H)=3.44±0.22 MH•m 0.5 ). The formation of solid solutions in the case of SiC additions to ZrB2 and HfB2 was confirmed by Auger quantitative analysis and Auger mapping.
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Pavlo Barvitskyi |
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H3-NU1224 |
Phase transformations during heat treatment of germanium-doped hydroxyapatite and their influence on physico-chemical and biological properties Nataliia Ulianchych1, Sergey Firstov1, Volodymyr Kolomiiets’1, Oksana Koriak1, Larysa Strilets1, Mykhailo Rublenko2, Tetiana Todosiuk2 1Frantsevich Institute for Problems of Materials Sciences of National Academy of Sciences of Ukraine The application of calcium phosphate ceramics (CPC) for bone repair is limited by its low bioactivity, which can be improved by the Ge-doping, which is a biologically active microelement. There is almost no published data on Ge doping effect on the properties of CPCs. In the current study, the Ge doping of hydroxyapatite (HAP) was carried out during the synthesis from solutions of calcium and phosphate salts via the introduction of 1.0 and 1.5wt% of Ge– metaphosphate colloidal solution. The material's structure, phase composition, solubility, and adsorption activity were determined.
The phase composition of HAP doped with 1.0 wt%Ge after annealing at T=800ºС is as follows: HAP–45%; α-tricalcium phosphate (TCP)–55%. The distinguishing feature of this process is the formation of the α-TCP phase, which is stable at T~1125ºС and has a higher solubility instead of β-TCP, which is stable at 800ºС. Annealing at 1200ºС leads to the formation of HAP–6%, β-TCP–55%, and α-TCP–39%, which are also atypical phase changes during annealing for TCP. The phase composition of HAP doped with 1.5 wt%Ge annealed at 800ºС was as follows: HAP–57%; α-TCP–10%; β-TCP–33%. That is too difficult to simultaneously obtain three biocompatible phases, with different solubility of each phase and due to the optimal structure formation, this leads to enhanced bioactivity. Changes in the phase composition of synthesized materials caused changes in solubility and adsorption activity, which were reported to be higher than in Si-doped HAP.
In vivo, studies of 1.0 wt% Ge-doped HAP on rabbit bones showed the significant osteoinductive properties of the material, manifested radiologically and macro-morphologically by dynamic phenomena of osteointegration and early remodeling of bone tissue. It was confirmed histomorphologically that the formation of ‘bone regenerate’ is significantly accelerating and have better quality if compared with Si-doped HAP.
The Ge-doped HAP shows the enhanced bioactivity of CPC.
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Nataliia Ulianchych |
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H3-LK1250 |
Effect of Mn doping on structural and optical properties of (Zn,Mg)O ceramics Iryna Markevich1, Tetyana Stara1, Yuliia Polishchuk1, Semyon Ponomaryov1, Kostiantin Kozoriz1, Oleksandr Melnichuk2, Lyudmyla Melnichuk2, Nadiia Korsunska1, Lyudmyla Borkovska1, Larysa Khomenkova1,3 1V. Lashkaryov Institute of Semiconductor Physics at the National Academy of Sciences of Ukraine Manganese-related luminescence has been reported for Mn-doped ZnS and ZnSe. Contrary to ZnS and ZnSe, ZnO is more attractive as a non-toxic and environmentally friendly material. Due to the large exciton binding energy (60 meV), ZnO demonstrates bright, room-temperature UV emission. In addition, ZnO shows visible emission whose intensity and spectrum can be controlled by certain treatments and by doping with different impurities. However, Mn doping causes the dramatic quenching of intrinsic ZnO luminescence, and, in contrast to ZnS:Mn and ZnSe:Mn, this quenching is not accompanied by an appearance of Mn-related emission.
To clarify this issue, in the present work the ZnO was doped with Mn and Mg simultaneously. The use of magnesium permitted the formation of Zn1-xMgxO solid solution with a bandgap larger than that of ZnO. The Zn1-xMgxO samples with [Mn]=0.1at% were prepared by sintering at 900-1200 C for 3 hours in the air and their structural, electric and optical properties were studied by XRD, EPR, diffuse reflectance, photocurrent and photoluminescence methods.
It was observed that (Zn,Mg)O:Mn alloys are dominated with wurtzite phase for x<0.25. The largest band gap was found to be Eg = 3.65 eV. Optical absorption and photocurrent spectra exhibit broad unstructured bands originating from the photoionization of MnZn2+ ions. They demonstrate the same onset at 2.16 eV which is blue-shifted with respect to ZnO:Mn one (set at 2.0 eV). Thus, MnZn energy level in wurtzite alloy is settled at 2.16eV below conduction band bottom. However, the excited states of MnZn2+ ions, including the lowest one, are still located in conduction band, which implies the absence of the MnZn2+ luminescence. It was concluded that a further increase of the bandgap of Zn1-xMgxO wurtzite alloys is desirable. It is assumed that achieving a bandgap larger than 4 eV will permit to shift down the lowest excited state of MnZn2+ ions inside the bandgap and achieve the Mn-related light emission.
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Larysa Khomenkova |
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H3-OV1525 |
Machine Learning assisted structure optimization and mechanical properties assessment of Si-doped boron carbide Oleksandr Vasiliev, Vladyslav Bilyi, Valerii Bekenev, Valerii Kartuzov Frantsevich Institute for Problems of Materials Science NAS of Ukraine In the recent decade, the possibility of improving boron carbide's performance at high-velocity impact with silicon doping received significant attention. While some optimistic results were achieved in experiment, several DFT studies found no improvement of the target properties, leaving the mechanism of improvement unclear. In this work, we used Machine Learning approaches to take a closer look at possible ground states in the system in an attempt to elucidate the mechanism. We trained high-precision Machine Learning interatomic potentials model (MLP) for the B₁₃₋ₓC₂Siₓ (x≤1) system with the NequIP package [1] using in-house DFT training data derived from the refined structure [2]. The model was further used in a simulated annealing algorithm to find optimal positions of Si atoms in angular chains in 2×2×2 and 4×4×4 supercells. The optimization results indicate that the dopant atoms tend to arrange themselves in parallel planes of the \{$1\bar{1}00$\} family with the closest atoms displaced in opposite directions. Such configuration has the lowest energy in the Si containing system. The MLP was also used in a hybrid DFT-ML procedure to assess the elastic moduli of the ground state. The resulting bulk modulus is virtually the same as that for boron carbide and shear and Young's moduli are up to 7 and 6% higher respectively. Thus, incorporation of Si and subsequent structural adjustments potentially have positive influence on the mechanical properties, which is rather small to be responsible for significant improvement. Further DFT studies of B₁₂C-C-C and B₁₂C^Si^C behavior under extreme uniaxial strain in direction parallel to the chain suggest that the middle carbon in the undoped boron carbide can temporarily change its chemical identity, possibly causing a "chemical lock" of the deformation. No changes are expected for the silicon containing chains, and the structure can freely recuperate to the initial when the strain is released.
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Oleksandr Vasiliev |
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Poster session Important.session is online-only and include 5 min presentation in the common conference room and 1 hour of discussion in individual rooms (Zoom) |
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H3-AG2356 |
Influence of Lead Oxide Addition on the Electrical Characteristics of Tin Oxide Based Ceramic Varistors Alexei Gaponov Oles Honchar Dnipro National University, Ukraine The ceramic varistors are often used to protect electronic devices from overvoltage. One of this is SnO2 - Co3O4 - Nb2O5 - Cr2O3 ceramics which has high nonlinear current-voltage characteristics. This ceramics must have low breakdown electric field and low leakage current (low-field electrical conductivity) for varistor application. For this purpose we decided to add the oxide PbO to the SnO2-based ceramics. In this investigation the electrical properties of (99.4-x) SnO2 - x PbO - 0.5 Co3O4 - 0.05 Nb2O5 - 0.05 Cr2O3 ceramics (x = 0, 0.1, 0.5, 0.7, 2, 4 and 8 mol.%) are studied. The samples were obtained by traditional technology. The axial pressure was 45 MPa, the sintered temperatures were 1050, 1150, 1250 and 1350C (1 hour) and the Ag-electrodes prepared at 800C (10 min) were used. The studied ceramics consists of SnO2 grains and Pb-rich secondary phases at the grain boundaries. They influence on the shrinkage of samples which is increasing from 1.6% for the sample without PbO addition sintered at 1050C to 11.3% for the sample with 8 mol.% PbO addition sintered at 1350C. The Pb-rich secondary phases are also responsible for the low breakdown electric field of varistors. We received the minimal value 1.3 kV/cm for the sample with 2 mol.% PbO addition sintered at 1350C (cf. 3.1 kV/cm for samples without PbO addition). The investigated varistors have a high value of nonlinearity coefficient 24 - 25 for the samples with 0.5 and 0.7 mol.% PbO additions sintered at 1150 and 1250C. Such samples have low values of low-field electrical conductivity 7.4 - 27 pS/cm (cf. 120 - 310 pS/cm for samples without PbO addititon). These parameters are explained by the high Shottky type potential barriers (0.9 - 1.1 eV) on the SnO2 grain boundaries. Thus, the low leakage current and the low breakdown voltage can be received with adding PbO oxide to SnO2-based varistors. Optimal concentrations of PbO addition are 0.5 - 0.7 mol.% and optimal sintered temperatures are 1150 - 1250C.
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Alexei Gaponov |
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H3-SK1252 |
Synthesis of alkaline nitride glasses and their physical and chemical properties Eugen Pashchenko, Denys Savchenko, Svitlana Kukharenko, Sergiy Skorokhod, Roman Kurganov Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine We introduced nitrogen into the molecular glasses mesh in order to obtain microporous binders with high adhesion to the synthetic diamond surface and optimal physical and mechanical properties for creating abrasive composites with advantage in the processes of precision grinding of complex profiled products. This is the combination of a significant volumetric content of micron-diameter spherical cavities, as well as high physical and mechanical properties like nonporous high-melting glasses.
Oxynitride glasses in the Si–Zr–Na–Li–K–B–O–N system were produced by incorporating Si3N4 into the glass structure. This system is an oxynitride analogue of the widely known alkali-resistant (AR) glass. Batches of glasses containing from 1 to 5 at. % of nitrogen were produced.
Oxynitride glass analogues with a high zirconium content can be produced with the addition of Si3N4 and the use of a remelting stage. A significant increase in properties is observed with the introduction a few atomic percentages of nitrogen. Oxynitride glasses have demonstrated both increased chemical resistance and reduced deposition at the material-lubricant-coolant interface in strong alkaline environments under harsh aging conditions. The combination of improved initial strength and increased chemical resistance opens up significant potential for the use them in tooling composites.
The developed technology of nitride glass synthesis and the creation of highly effective diamond-containing composites based on them opens up the possibility of producing elite grinding wheels for especially responsible conditions of application combining extremely high dimensional stability, close to the stability of wheels on metal binders, with high cutting capacity of polymer and ceramic binders.
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Denys Savchenko |
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H3-VG1222 |
Study of silicon carbide and silicon nitride ceramics by the method of acoustic emission Victor Goncharuk, Irina Goncharova, Vadim Tsyvilitsin, Mykola Iefimov Frantsevich Institute for Problems of Materials Science, NASU, Ukraine The method of acoustic emission (AE) has recently been increasingly used in science and technology, due to the fact that the processes of deformation and destruction serve as sources of AE, the signals of which can provide detailed information about these processes. AE in a material can be caused by such internal sources as sliding, twinning, phase transformations, cracking, and friction processes. In this work, reaction-sintered silicon carbide materials (SCM) with different ratios of fractions of the initial SiC were studied: M5 monofraction with an initial particle size of d<SiC> = 5 μm (SCM-1) and polyfractional composition 40%M100 + 40%M28 + 20%M10 (SCM-2). These materials are also known as self-bonded silicon carbide (SCC) and in addition to SiC they contain 10-12% free silicon. Also investigated: reaction-sintered silicon nitride ceramics (RSNC) with an initial particle size of d<Si3N4> = 3-5 μm and a hot-pressed composite Si3N4+5%Y2O3+2%Al2O3+(0-50%)TiN(HPNC+TiN) with an initial particle size of d<Si3N4> = 1 µm, d<TiN> = 3-6 µm. In this work, the AE method was used to study the main mechanical characteristic of ceramic materials - the 3-point bending strength σr. Two methods have been proposed for estimating the bending strength: 1 - by the magnitude of the total AE amplitude; 2 - by the transition stress from discrete to continuous AE. Some advantage of the second method is a relatively low stress during preloading of a controlled sample σ = 0.8σr, while in the first method σ = (0.5-0.7)σr. However, when using both methods, preloading did not negatively affect the bending strength of the material. The average estimation error according to the proposed methods does not exceed 3%, which is about 5-6 times more precisely, than in the traditional assessment (≈20%) of the bending strength by the average sample value.
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Victor Goncharuk |
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H3-MZ1221 |
Mechanical and dielectric properties of ceramics based on Si3N4 produced by spark plasma sintering Maryna Zamula, Valerii Kolesnichenko, Nadiya Tyschenko, Oleksandr Shyrokov, Artur Stepanenko, Hanna Borodianska, Andriy Ragulya Institute for Problems of Materials Science National Academy of Sciences of Ukraine Due to its mechanical properties at room and high temperatures, the dense Si3N4 ceramic is a candidate for radio-transparent materials operating under extreme conditions. BN, which has a lower density and lower permittivity than Si3N4, can be a candidate for reducing permeability[1,2]. The work is devoted to the study of the influence of oxide additives on the α→β phase transformation in Si3N4 under spark plasma sintering (SPS) conditions and the study of mechanical and dielectric properties. SPS of Si3N4–Y2O3, Si3N4–Y2O3–SiO2, and Si3N4–Y2O3–BN was carried out in a heating rate of 50 K/min and a pressure of 35 MPa. It was established that the complex addition of Y2O3-SiO2 contributes to the formation of a significant amount of liquid phase and ensures compaction by rearranging Si3N4 nanoparticles under pressure. The slower consolidation of ceramics, with the addition of only Y2O3, is explained by the local interaction of Y2O3 and SiO2, which is manifested on the surface of Si3N4 particles. It was found that during SPS, for complete densification of Si3N4, 5 min of exposure at 1800°C is required for Si3N4–Y2O3–SiO2 and more than 30 min for Si3N4–Y2O3. Si3N4–Y2O3 and Si3N4–Y2O3–SiO2 composites showed flexural strengths of ~860 and 910MPa at room temperature and a gradual decrease in flexural strength to ~200MPa with temperature up to 1400°C. The resulting strength at room and elevated temperatures, HV of ~15GPa and 16GPa, and fracture toughness of ~7.5 MPa·m1/2 meet the current level of requirements for this ceramic. The Si3N4–Y2O3–BN composite shows ~30% lower mechanical properties compared to Si3N4–Y2O3, which can be explained by the presence of graphite-like BN, which has significantly lower hardness. The results of radio frequency measurements of composites based on Si3N4 showed that the addition of 10% BN reduces the dielectric constant of the Si3N4–Y2O3–BN composite by ~0.5. In addition, a residual porosity of ~10% further reduces the dielectric constant by ~1.
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Maryna Zamula |
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H3-VN2117 |
3D printing of the ceramic materials based on Mo₀.₉Cr₀.₁Si₂ by Robocasting technique Vladyslav Naumenko, Ostap Zgalat-Lozynskyy, Dmytro Zyatkevych Institute for Problems of Material Science, National Academy of Sciences of Ukraine To obtain products of complex shape by from high-melting point materials using traditional technology are quite difficulty. This problem can be solved via utilization of additive technologies (AM). One of them could be used for forming of workpieces of complex shape is Robocasting. Research shows that this method is promising for the formation of bioceramics, but for refractory compounds, such works are few [1]. The purpose of this work is to study the peculiarities of the formation of the structure and shape of a 3D printed product by Robocasting depending on various printing and processing parameters. Mo0.9Cr0.1Si2 solid solution powder was used as the starting material. To prepare the paste, the powder was mixed with a solution of synthetic rubber in gasoline. Robocasting studies were performed on 3D printers ZMorph 2 with a ceramic module and an Ender 5 with a Stoneflower clay module. The optimal composition of the prepared paste was 62.5 wt.% powder and 37.5 wt.% binder. The influence of 3D printing parameters on the quality of obtained samples was investigated. The dependence of the sample surface roughness from the size of the powder in paste was established. Submicron powder allows one to get a smoother, non-porous surface of the printed sample. The printed samples were heat treated for 2h at 400 ⁰С to remove the plasticizer and sintered at 1400 ⁰С for 1h. After sintering, the density of the samples was 4.38 g/cm³, which corresponds to a relative density of 70%. The relatively high porosity of the samples could be related with delamination of layers during thermal treatment and sintering of the samples. This indicates the need for a comprehensive approach to obtaining products using the Robocasting from pastes formation to development of regimes for heat treatment and consolidation.
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Vladyslav Naumenko |
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H3-ID2129 |
Scale particles from rocks - fillers for polymer composite materials Iryna Diduk, Olga Jashchenko, Kateryna Krasnikova Institute for Problems of Materials Science of NAS of Ukraine An alternative to fibrous fillers in the production of engineering composite materials are reinforcing dispersed fillers. In this work, an attempt was made to use scaly materials based on raw materials from rocks (basalt). Fillers with scaly-shaped particles are a special class of fillers for various types of compositions. Features of the structure allow them to be easily crushed or split to minimum sizes. The structure of the scale and obtaining a relief pattern of the image was carried out by the method of microscopy. When performing the work, methods of physical and chemical analysis of inorganic substances, methods of control of composite materials in accordance with the requirements of regulatory documentation were used. The resulting scale contains particles of various shapes (spherical, prismatic, lamellar or scaly, fibrous or needle-like) with a thickness of 1.0 to 4.5 μm and a size of 0.1 to 5.0 mm. In its original state, the basalt flake has a glassy structure, with a relatively smooth surface, but with some defects in the form of unmelted inclusions and submicrocracks. During the heat treatment of basalt scales, the ratio of iron oxide content changes significantly, the transition of FeO to Fe2O3 occurs at a temperature of 450-900 oC and higher. Heat treatment affects the appearance of a crystalline phase, which causes an increase in the density of the material by (10-20)%. A clear increase in density begins after a temperature of 450°С, and at a temperature ≥ (900 – 1000)°С it increases from 2.85 g/cm3 in the initial state to 3.04 - 3.08 g/cm3. Depending on the temperature and exposure time, the scale samples differ in their characteristics and color scheme.
The advantage of scales is the positive effect of the orientation of its particles when processing filled compositions. It can be assumed that the correct combination of scales and rock fibers will provide a better combination of strength, stiffness and impact strength of the filled compositions.
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Iryna Diduk |
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H3-IH9494 |
Increased wear resistance of end seal rings due to the use of improved ceramic material based on silicon carbide Ihor Hnylytsia Ivano-Frankivsk National Technical University of Oil and Gas, Ukraine In recent years, much attention has been paid to the development of new and improvement of existing materials in the C / SiC, SiC / SiC system. One of the promising areas for improving the properties of silicon carbide ceramics is the use of nanosized additives. The initial charge of silicon carbide powder, graphite powder in the amount of 12% and nano-sized additives of silicon and chromium carbides with a size of 30 nm in the amount of 1-8% was mixed in two conical mixers. A plasticizer (12% solution of bakelite in ethyl alcohol) was added to the prepared charge, dried and pressed in a mold with a moving matrix at a pressure of 200 kg/cm2. When the optimal pressure was exceeded, cracks were observed due to the elastic aftereffect. Pressed blanks were dried in a drying cabinet at a temperature of 150-180 0C for 8 hours to polymerize bakelite. Sintering was carried out in a vacuum induction furnace for 60 minutes at a temperature of 2000-2100 0С. The criteria for assessing the effect of nano-sized additives depend on the initial structure of the material, the features of the structural components and their relative arrangement. It is difficult and not always possible to assess such an effect from images of the structure. For materials based on self-bonded silicon carbide, the amount and nature of the placement of the intergranular phase, which is formed from free silicon and everything dissolved in it, has a significant impact on the structure and properties. An increase in the amount of the intergranular phase disrupts the integrity of the framework of silicon carbide particles, reduces the number of contacts between them and leads to a decrease in the hardness and crack resistance of the material. Known results indicate that reducing the amount of intergranular phase and reducing the number of contacts (bridges) between separate areas of free silicon is possible due to the use of nanosized additives. The density of the samples without nanosized additives was obtained at the level of 3.04-3.06 g/cm3. When using nanosized additives, there is a complex nature of the dependence of density on the content of additives. For samples of all compositions, the minimum density at the level of 2.7-2.8 g/cm3 was obtained at a content of 3-4% nanopowders and an increase of almost 3.1 g/cm3 (for SiC additives) at a content of 6% nanosized additives. With increasing content of nanosized additives, the density of all obtained samples was less than 2.7 g/cm3. In result we can talk about the positive effect of nanosized additives of silicon carbide and chromium carbide in the amount about 5% on the formation of the structure and properties of silicon carbide based materials. Field tests of the manufactured rings showed that the characteristics of silicon carbide end seal rings with nano-sized additives are 10-15% higher than the material without additives.
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Ihor Hnylytsia |
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H3-GO1610 |
On the methodology of generalization of knowledge about the structure formation of ceramic materials to implement it in technology Galyna Oleynik, Andrii Kotko I.M. Frantsevych Institute for Problems of Material Sciences NAS of Ukraine One of the new approaches to the development of ceramic materials is the design of microstructure. Previously, we have proposed a concept of such a design on the basis of the assembly of material with pre-planned elements of microstructure that determine the formation of its required service properties. Generalization and systematization of relevant information along are urgent tasks for the implementation of the accumulated knowledge on the structure formation of materials in the technology of their production and the development of new materials. In this report, an approach is proposed to generalize the relevant information in order to use it in both the control of service properties of known materials and the development of new ones. As the basic structural component of any ceramic material is a grain, it is logical to classify ceramic materials by the characteristics of both the grain structure of materials and the elements of the grain substructure. Important characteristics of grains are size, crystal morphology, composition, character of spatial distribution, and the structural state of intergranular and interphase (in composites) boundaries. Elements of the grain substructure are dislocation subboundaries, stacking defects, growth twins, deformation twins, inversion twins, domains, interfacial boundaries with inclusions of other phases, and pores of different crystal morphology. Each ofthem can be classified according tothe structural mechanisms of their formation. The generalized knowledge about the structure formation of ceramic materials can be used for introducing it into the improvement of known technologies and the development of new ones based on the knowledge. On the example of SiC ceramics, an algorithm for microstructural design of a material for constuctive purposes is proposed. The main components for the microstructural design of this material are identified.
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Galyna Oleynik |
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H3-GO1659 |
Structure formation of ultradispersed detonation diamond Galyna Oleynik, Andrii Kotko, Yurii Solonin I.M. Frantsevych Institute for Problems of Material Sciences NAS of Ukraine Ultradispersed diamond (UDD) obtained by detonation synthesis is a unique powder material. This is due to such characteristics as the size of nanoparticles (3-10 nm) and the presence of particles of anomalous size (much larger than the above: from hundreds of nm to tens of µm). Despite the fact that UDD was synthesized in the world in the early 80s of the last century, the mechanism of its formation has not yet been established. The purpose of this work is to determine the nature of the basic characteristics of UDD: the mechanism of formation of UDD as a substance from the initial structural state and the mechanisms of formation of powder structure components. The research was carried out by TEM combined with microdiffraction. There were studied UDD, the diamonds of dynamic synthesis and static synthesis. It was established that flat particles of the above types of diamond are characterized by a rail substructure, which is formed as a result of the martensitic transformation of graphite in to a diamond of hexagonal and cubic modifications. That is the rail substructure is a diagnostic indicator of such a transformation. Thus, it can be reliablystated that the formation of UDD stems from graphite. It was determined that the rail substructure in all of the diamonds is qualitatively similar. Rails based on the lonsdaleite contain basal packing defects, while two-phase rails contain defects of the lonsdaleite phase and streaks of the cubic phase with twins. In the rails, a phase transformation occurs with the orientation ratio (111)a||(001)l, [110]a||[1120]l, which initiates mechanical stress leading to the destruction of the rails. At the stage of the phase transformation, particles of anomalous sizes are formed. This proces sis provided by two mechanisms: (i) homoepitaxial сoalescence of nanoparticles during contacts of rails and (ii) in groups of randomly distributed particles processes characteristic for the sintering of loose powders take place: the zonal formation of coarse particles.
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Galyna Oleynik |
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H3-AG2282 |
Influence of lead oxide addition on the electrical characteristics of tin oxide dased ceramic varistors Alexei Gaponov Oles Honchar Dnipro National University, Ukraine The ceramic varistors are often used to protect electronic devices from overvoltage. One of this is SnO2 - Co3O4 - Nb2O5 - Cr2O3 ceramics which has high nonlinear current-voltage characteristics. This ceramics must have low breakdown electric field and low leakage current (low-field electrical conductivity) for varistor application. For this purpose we decided to add the oxide PbO to the SnO2-based ceramics.
In this investigation the electrical properties of (99.4-x) SnO2 - x PbO - 0.5 Co3O4 - 0.05 Nb2O5 - 0.05 Cr2O3 ceramics (x = 0, 0.1, 0.5, 0.7, 2, 4 and 8 mol.%) are studied. The samples were obtained by traditional technology. The axial pressure was 45 MPa, the sintered temperatures were 1050, 1150, 1250 and 1350C (1 hour) and the Ag-electrodes prepared at 800C (10 min) were used.
The studied ceramics consists of SnO2 grains and Pb-rich secondary phases at the grain boundaries. They influence on the shrinkage of samples which is increasing from 1.6% for the sample without PbO addition sintered at 1050C to 11.3% for the sample with 8 mol.% PbO addition sintered at 1350C. The Pb-rich secondary phases are also responsible for the low breakdown electric field of varistors. We received the minimal value 1.3 kV/cm for the sample with 2 mol.% PbO addition sintered at 1350C (cf. 3.1 kV/cm for samples without PbO addition).
The investigated varistors have a high value of nonlinearity coefficient 24 - 25 for the samples with 0.5 and 0.7 mol.% PbO additions sintered at 1150 and 1250C. Such samples have low values of low-field electrical conductivity 7.4 - 27 pS/cm (cf. 120 - 310 pS/cm for samples without PbO addititon). These parameters are explained by the high Shottky type potential barriers (0.9 - 1.1 eV) on the SnO2 grain boundaries.
Thus, the low leakage current and the low breakdown voltage can be received with adding PbO oxide to SnO2-based varistors. Optimal concentrations of PbO addition are 0.5 - 0.7 mol.% and optimal sintered temperatures are 1150 - 1250C.
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Alexei Gaponov |
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H3-ID1515 |
Glass and fibers based on silicate-hafnium and silicate-boron-hafnium systems Iryna Diduk, Yurii Chuvashov, Olga Jashchenko, Nataliya Koshelenko Institute for Problems of Materials Science of NAS of Ukraine Availability and cheapness of rocks made it possible to use them to obtain fibers and products based on them. The use of natural raw materials makes it possible to produce environmentally friendly materials resistant to atmospheric influences and aggressive environments. At the present time, special interest is shown in the production of radiation-protective compositions for special applications. Investigation of glass formation and fiber formation in silicate-boron-hafnium systems, namely rocks (andesite-basalts) plus HfO2; andesite-basalts plus HfO2–В2О3 are carried out in this research. The influence of individual components of the initial components on the properties of melts, glasses and fibers was determined by selecting raw materials, studying the compositions and physicochemical properties of multicomponent systems. Melts and glasses were produced in laboratory high-temperature furnaces, and the processes of fiber formation were studied on a universal high-temperature single-filament laboratory stand. For andesite-basalt modified 0.5; 1.0; 1.5% (wt.) HfO2 melting temperature range is 1165-1400 oС, for 2.0; 5.0; 6.0% (wt.) HfO2 – 1165-1450 oС. Melts are characterized by a smooth, shiny surface with a visible metallic luster. The microstructure of glass with hafnium additives from 0.5 to 6% (wt.) differs from the microstructure of the original glass from andesite-basalt by the presence of more pronounced liquation zones. The melt with 6% (wt.) HfO2 has a high viscosity, which does not allow obtaining an amorphous state by the quenching method. To reduce the viscosity of the melt, 5% (wt.) B2O3 was additionally introduced. The melt modified with HfO2and B2O3, 6 and 5% (wt.), respectively, has close values of the temperature dependence of viscosity relative to the initial melt from andesite-basalt in the temperature range of 1250-1450 °C. Laboratory samples of continuous fibers from modified melts were produced. The temperature range of fiber formation was 70oС.
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Iryna Diduk |
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H3-ID1956 |
The influence of aluminum oxide on the physical and mechanical properties of silicate fibers Yurii Chuvashov, Olga Yashchenko, Iryna Diduk, Nataliya Koshelenko Institute for Problems of Materials Science of NAS of Ukraine Volcanic rocks, as a complex silicate system consisting of oxides of alkaline and alkaline earth metals, are characterized by a wide diversity of oxides in their composition, including aluminum oxides. The study of the effect of aluminum oxides was carried out on specially prepared samples from the raw materials of natural silicate systems of the main composition (rocks of the basalt type), melts, glass and fibers. Fibers from raw materials from different deposits, obtained under the same conditions of formation, almost do not differ in strength. However, glasses with a larger total amount of Al2O3, SiO2, Fe2O3, TiO2 oxides have a positive effect on fiber strength due to strong bonds in the Al – O, Si – O, Si – O – Fe system. At the same time, aluminum oxide has a pronounced effect on the strength indicators, which is due to both the high strength of the Al-O bond and the formation of the alumino-silica structural frame of the glass. It has been studied that in glasses and fibers with an increase in the content of aluminum oxide, an increase in the glass transition temperature and an increase in the temperature of the upper limit of crystallization are observed. With a high content of aluminum oxide, the crystallization of basalt glass and fibers with increasing temperature occurs with the formation of aluminous magnetite (magnetite containing more than 15% Al2O3); growth of augite crystals (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 and, subsequently, with the formation of Ca[Al2Si2O8] anorthite. At a low content of aluminum oxide, crystallization takes place with the formation of augite (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. The temperature interval for the production of continuous fibers and their diameter was (1380-1450) oC and (9-15) microns, respectively; coarse fibers - (1300-1400) oC and (180-400) microns. The strength of the fibers is related to the scale factor, because the larger the diameter and length of the fibers, the lower their strength.
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Iryna Diduk |
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H3-DK2014 |
Preparation of Ti3SiC2 MAX phases using high-energy ball milling of the initial components in a planetary mill Maria Savyak, Dmytro Korablov, Alla Коpаn, Yuriy Solonin Frantsevich Institute for Problems of Materials Science, NAS of Ukraine Layered ternary carbides (MAX phases) are large collection of oxygen-free ceramic materials exhibit a unique combination of properties characteristic of both metals and ceramics. MAX phases are hard materials which are metallically conductive and thermally conductive. Such materials have low density, Young’s modulus values on the order of 300 GPa, excellent corrosion resistance in aggressive liquid media, resistance to high temperature oxidation and has high melting point. Among the many MAX-phases synthesized to date, the greatest interest from the standpoint of the level of their properties represents such material based on titanium as Ti3SiC2.
Synthesis of MAX phases is carried out mainly by methods of hot isostatic pressing, spark plasma sintering and by the method of self-propagating high-temperature synthesis (SHS). These processes are quite complex, can be difficult and non-technological. In order to obtain MXenes it is desirable to synthesize MAX phases in the form of a dispersed powder to improve etching of A-element layers. Herein, the preparation of Ti3SiC2 MAX phases using high-energy milling of the initial components in a planetary mill has been studied with a view to improve the quality and purity of resultant MXene.
In the present investigation the milling of reactants was performed in argon atmosphere in a planetary mill AIR-015M. The phase composition of the samples was examined by XRD using a diffractometer "DRON 3" (Cu Kα radiation).
The effect of the content of the mixture components, its purity, the energy intensity of the mill (rotation speed, ball-to-powder ratio) and the milling time on the formation, in particular on the purity of Ti3SiC2 phase has been studied by numerous experiments. It is shown that in the 3Ti–Si–2C systems Ti3SiC2 MAX phase with a small amount of TiC, TiSi2, Ti5Si3 impurities can be formed as a result of the reaction of mechanically activated self-propagating synthesis.
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Dmytro Korablov |
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H3-SL1034 |
Phase diagram of the Fe7Se8–Bi2Se3 system Serhii Lakiza, Kingshuk Bandopadhyay, Krzysztof Markus, Yaroslav Korol Center of Excellence in Nanophotonics, Advanced Materials and New Technologies Based on Crystal Growth, Warsaw, Poland The three-dimensional (3D) topological insulators (TIs) have been of increasing theoretical and experimental interest due to their topologically protected surface states. As the electron’s spin and momentum on the surface of a TI are essentially interlocked, it has become a source of new physics and advanced spintronic devices. To achieve that, there has been intense interest in TI-based heterostructures with different magnetic materials like ferromagnetic, antiferromagnetic, superconductor, etc. Iron-chalcogenides have recently attracted great interest due to the recent discovery of superconductivity in Fe1-xSe-based compounds. Among them, Fe7Se8 single crystals, due to their high iron concentration, are characterized by the high magnetic ordering temperatures (Néel temperature ~450 K). Fe7Se8 has a simple NiAs-type structure with filled layers of a chalcogenide, with hexagonal packing, alternate with metal layers with vacancies. The magnetic moments of iron ions are ferromagnetically ordered within layers, but the coupling between adjacent layers is antiferromagnetic. The presence of vacancies (due to intrinsic non-stoichiometry) in each second layer leads to the appearance of resulting magnetization and ferrimagnetism.
We present phase diagram of the Fe7Se8+Bi2Se3 system. Phase diagram of this system is of simple eutectic type. Coordinates of eutectic point were determined as 80 mol.% Bi2Se3 and 671 °C. Solubility on the base of components is less than 1 mol. %. An eutectic phase Bi2Se3 forms matrix, phase Fe7Se8 – armature. The Bi2Se3 is a leading (seeding) phase, Fe7Se8 - leaded phase. The eutectic Fe7Se8+Bi2Se3 is of a honeycomb type, as far as leading phase Bi2Se3 forms an eutectic matrix.
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Serhii Lakiza |
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H3-VB1448 |
Structural and mechanical properties of SiC-rich by-products of the metal grade Si (MG-Si) process Vira Bovda1,2, Thomas Hafner1, Joans Hafner1, Frank Kimm1, Oleksandr Bovda3, Oleksandr Kuprin3, Anatoliy Pikalov3, Viktoria Podhurska4, Bohdan Vasyliv4, Ihor Vorona5 1MFG Metall- und Ferrolegierungsgesellschaft mbH, Germany The metallurgical grade silicon (MG-Si) has continued to attract much attention as a primary material for photovoltaics, metallurgy, silicones industries etc. The production of MG-Si in submerged electric arc furnaces is accompanied by high-energy consumption and significant carbon and environmental footprint. The traditional solid by-products of the MG-Si process are dross, silica dust, fines and slag. Additionally, dozens of tons of mechanically stable bulk slag are generated inside the Si furnace within its standard life cycle. One of the main components of Si/FeSi furnace slag is silicon carbide (SiC). SiC-rich composites were found in diverse forms and quantities, from loose condensates to sintered crust on the furnace floor that might obstruct the tapping of the liquid Si metal. SiC-rich composites resemble the ceramic materials with a 3D skeleton architecture of hard SiC grains filled with silicone and slag phases.
In this paper, system studies were conducted to assess the correlation between microstructure and mechanical properties of SiC-rich composites produced from the bulk SiC-rich furnace slag by traditional stone and ceramic machining technologies. Macroscopically uniform samples with an area of 50x50mm were composed of coarse monocrystalline SiC grains soaked with Si-rich and glassy cristobalite phases. Dense bulk samples (ρ=3.1 g/cm3) possessed moderate flexural strength in the range of 50-106 MPa and high compression strength of 750 MPa. The fracture mechanism and thermal behaviour of coarse-grained SiC-rich composites was discussed. Despite inhomogeneous macro and microstructure, mechanical and thermal properties of bulk samples are superior to the traditionally produced siliconised SiSiC ceramics. It opens up new opportunity for the circular economy and value-added recycling of the Si/FeSi industries’ wastes.
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Vira Bovda |
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H3-VB1220 |
Ground states in B4C-Al system Oleksandr Vasiliev1, Vladyslav Bilyi1,2, Yaroslav Zaulychnyy2, Valerii Kartuzov1 1Frantsevich Institute for Problems of Materials Science NAS of Ukraine In the last decade, scientists have tried to improve the high-speed impact behavior of boron carbide by doping with silicon and aluminum. The aim of this work is to determine the structure and energies of the ground states in the B4C-Al system and to evaluate their relative stability.We considered the following structures (B₁₂)C^Al^C, (B₁₂)C-Al-C, (B₁₁C)C^Al^C, (B₁₁Al)C-B-C, where aluminum was substituted either into the intercosahedral chain, with or without changing the chain configuration to an angular one, or into a boron carbide icosahedron. The structures were built using the Python ASE library and in-house specialized programs. Parameters of the DFT calculation for the Quantum Espresso software package were chosen to ensure that the total energy converged within 1 meV/atom. The atomic positions and lattice parameters of all structures were optimized with a convergence thresholds of 1.4⋅10⁵ eV on energy and 2.57⋅10² eV/Å on atomic forces. For the optimized configurations the enthalpies of formation were calculated as the difference between the total energy of the structure and total energies of the simple substances and relative stability of the configurations was estimated from their values.(B₁₁Al)C-B-C has a positive formation energy and therefore does not exist. (B₁₁C)C^Al^C has two non-equivalent states with negative but relatively high energy, so it is unlikely to exist. B₁₂C-Al-C configuration has a negative formation energy close to that of B₁₂C-C-C-C and may exist in the material, but it is metastable and readily transforms into an angular configuration. (B₁₂)C^Al^C configuration has 6 degenerate ground states lying in the (0002) plane of a hexagonal prototype cell on a circle with a radius of approximately 1 Å from the center of the intercosahedral chain. This configuration has the lowest energy among all the tested structures, making it the most likely product of boron carbide doping with aluminum.
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Vladyslav Bilyi |
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E-mail: conference@umrs.org.ua