SiO2 System Research Articles

Phase equilibria and thermodynamic modelling of the PbO–ZnO-“CuO0.5”-SiO2 system

The phase equilibria of the PbO–ZnO-“CuO0.5“- SiO2 system were studied as part of the investigation of the 19-component PbO–ZnO–Cu2O–FeO–Fe2O3–CaO–SiO2–Al2O3–MgO–S-(As, Sn, Sb, Bi, Ag, Au, Ni, Cr, Co as minor elements) slag/matte/metal/speiss/gas system in support of the development and optimization of pyrometallurgical processes. In the experimental study, samples were equilibrated at high temperatures, then quenched, and the lead, zinc, copper and silicon concentration in the phases were directly measured by electron probe X-ray microanalysis (EPMA). The cristobalite (SiO2) primary phase field of the PbO–SiO2 system was experimentally studied between 1575 and 1717 °C. The massicot (PbO), zincite ((Zn,Cu)O), cuprite (Cu2O), copper plumbite (Cu2PbO2) and Pb2SiO4 primary phase fields of the PbO-“CuO0.5”-SiO2, PbO–ZnO-“CuO0.5” and PbO–ZnO–SiO2 systems were studied between 664 and 1100 °C. The cuprite (Cu2O), willemite ((Zn,Cu)2SiO4), larsenite (PbZnSiO4) and melilite (Pb2ZnSi2O4) secondary phase fields of the PbO–ZnO-“CuO0.5”-SiO2 system in equilibrium with metal and tridymite/quartz (SiO2) or zincite ((Zn,Cu)O) were studied between 745 and 1100 °C. The zincite ((Zn,Cu)O), tenorite ((Cu,Zn)O) and willemite ((Zn,Cu)2SiO4) solid solutions in equilibrium with air or pure O2 at 1 atm were studied between 900 and 1100 °C. Using the FactSage thermodynamic calculation software, a self-consistent set of parameters based on the Modified Quasichemical Model (MQM) were developed to describe the newly obtained and existing experimental data.

ANTIBACTERIAL PROPERTIES OF BOROSILICATE ENAMEL WITH NANOSCALE ZINC OXIDE PARTICLES

Glass-enamel coatings have been modified with nanosized particles, which expands the scope of their application and is a promising direction. It has been established that the introduction of nanosized zinc oxide in the amount of 0.5 wt. % into the composition of the enamel of the Na2O–B2O3–TiO2–SiO2 system imparts antibacterial properties to the coating against gram-positive and gram-negative bacteria. The meaning of the index of antibacterial activity of the surface of the enamel increases on average five times more in relation to Escherichia coli (E. coli) and six times more in relation to Staphylococcus aureus (St. aureus) compared with a control sample that does not contain zinc oxide.

Liquid–Crystal Structure Inheritance in Machine Learning Potentials for Network-Forming Systems

It has been studied whether machine learning interatomic potentials parameterized with only disordered configurations corresponding to liquid can describe the properties of crystalline phases and predict their structure. The study has been performed for a network-forming system SiO2, which has numerous polymorphic phases significantly different in structure and density. Using only high-temperature disordered configurations, a machine learning interatomic potential based on artificial neural networks (DeePMD model) has been parameterized. The potential reproduces well ab initio dependences of the energy on the volume and the vibrational density of states for all considered tetra- and octahedral crystalline phases of SiO2. Furthermore, the combination of the evolutionary algorithm and the developed DeePMD potential has made it possible to reproduce the really observed crystalline structures of SiO2. Such a good liquid–crystal portability of the machine learning interatomic potential opens prospects for the simulation of the structure and properties of new systems for which experimental information on crystalline phases is absent.

STUDY OF TECHNOLOGICAL PARAMETERS OF OBTAINING CELSIANE AND SLAWSONITE CERAMICS USING SINGLE-STAGE TECHNOLOGY

On the basis of the RO–Al2O3–SiO2 system, radiotransparent ceramic materials of cordierite, celsian, and anorthite composition, which have low dielectric characteristics, are obtained. These requirements are met by one of the main phases of the BaO–Al2O3–SiO2 system – celsian (BaAl2Si2O8), the melting point of which is 1740 °C, and the beginning of active phase formation occurs at a processing temperature of 1300 °C, as well as one of the main phases of the SrO–Al2O3–SiO2 is slavsonite (SrAl2Si2O8), which undergoes congruent melting at a temperature of 1765 °C, and the beginning of active phase formation occurs at a processing temperature of 1400 °C. The purpose of the work is to study the technological parameters of obtaining celsian and slavsonite ceramics by one-stage technology. According to the subsolidus structure of the three-component system RO–Al2O3–SiO2 (RO = ВаО, SrO), it is advisable to synthesize the necessary phases from pure raw materials and, taking into account the presence of impurities that impair the dielectric characteristics, the synthesis of the necessary crystalline phases is carried out from technical raw materials. Figurative points of the compositions of the selected compounds correspond to their stoichiometric composition (for slavsonite, wt. %: SrO – 31,99; Al2O3 – 30,93; SiO2 – 37,08; for celsian, wt. %: BaO – 40,85; Al2O3 – 27,17; SiO2 – 31,98). It was established that the physical characteristics of the obtained samples improve with an increase in the firing temperature by 100 °C, but they are far from the desired level. The dielectric characteristics of the obtained materials are within the requirements for radio-transparent materials. Taking into account the investigated physical properties and the obtained radiographs of fired samples in order to obtain a densely sintered material, it was decided to investigate model compositions with the addition of intensifying additives and to study their influence on the properties of fired samples

Thermodynamic analysis of processes in the high-temperature polycomponent Fe–Y–Si–O–C system

In the production of low-carbon and high-quality steels, it is recommended to use special complex alloys of rare earth metals for deoxidation, microalloying and modification. To elucidate the mechanism of action of each of the components of the alloy, it is necessary to differentiate the action of each individual element. Yttrium is usually classified as a rare earth metal, but its deoxidizing and modifying ability deficiency studies. The use of yttrium applica-tion is known to increase in density, ductility, scale resistance, resistance to high-temperature corrosion of steel, effec-tively affects the shape, size and distribution of non-metallic inclusions. This paper consider the interaction of yttrium, silicon, and carbon with oxygen dissolved in liquid iron. Nonmetallic inclusions formed in this case can be identified on the state diagram of the FeO–Y2O3–SiO2 oxide system. This diagram is absent in the literature; therefore, it was mod-eled on the basis of the available binary phase diagrams of the FeO–Y2O3, FeO–SiO2, and Y2O3–SiO2 systems. Com-plex deoxidation by yttrium and silicon is possible only at yttrium concentrations in liquid iron less than 0.0001% (ox-ide melt or yttrium silicates are formed as non-metallic inclusions). If the concentration of yttrium is higher than this value, then it is the only deoxidizer. In the presence of carbon, liquid non-metallic inclusions can form in a very narrow range of liquid metal compositions, and the main oxide non-metallic inclusion is yttrium oxide. At yttrium concentra-tions below 0.0001% and silicon concentrations up to 1%, only carbon is the deoxidizer. Taking into account the previ-ously studied Fe–Y–Me–O–C (Me–Ca, Mg, Al, Cr) systems, a thermodynamic data base was created for designing the compositions of complex yttrium-containing ligatures.

Modification of Quartz Ceramics by Applying a Sol-Gel Composition of MgO–Al2O3–ZrO2–SiO2 System

Modification of Quartz Ceramics by Applying a Sol-Gel Composition of MgO–Al2O3–ZrO2–SiO2 System

Vaporization and the Thermodynamic Properties of the SrO–Al2O3–SiO2 System

Vaporization and the Thermodynamic Properties of the SrO–Al2O3–SiO2 System

Structural Features of K2O-SiO2 Melts: Modeling and High-Temperature Experiments

Despite numerous investigations, the thermodynamic properties of potassium silicates remain apparently contradictory. In situ experiments are complicated by the unstable behavior of a K2O–SiO2 melt in the region of compositions with a high potassium oxide content. In this paper, we study the structure of melts by the method of physicochemical modeling, taking into account the results of high-temperature Raman spectroscopy. To do this, the Raman spectra were curve-fitted, taking into account the second coordination sphere of silicon atoms. From the interpretation of the spectra of K2O–SiO2 glasses and melts having a K2O content of up to 55 mol.%, quantitative characteristics of the system were obtained. Since available information on the thermodynamic properties of potassium silicates is known to be contradictory, coordinated thermodynamic characteristics of potassium silicates, some of which were evaluated, were used as input data for modeling. Structural modeling of glasses and melts of the K2O–SiO2 system was carried out across a range of compositions up to 60 mol.% potassium oxide. The database of structural units of melts of the potassium silicate system, updated according to experimental data, will find practical application in chemistry, geochemistry and engineering fields.

Криохимический синтез порошков трикальцийфосфата и смешанных натрийсодержащих силикофосфатов и фосфатогерманатов для формирования биокерамики методом стереолитографической 3D-печати

Synthesis of chemically homogeneous fine powders based on glaserite-like phases in the CaO – Na2O – P2O5 – SiO2 (GeO2) systems by the cryochemical method, including rapid freezing of the total salt solution, sublimation ice removal, and subsequent thermolysis of the dehydrated salt precursor, is considered. The complex chemical composition of the powders is required to create bioceramics with improved osteoplastic characteristics. The paper presents the results of the synthesis of powders with submicron granulometry from solutions with different anionic composition; the behavior of such powders in the sintering process is described.

Determination of hyper-parameters in the atomic descriptors for efficient and robust molecular dynamics simulations with machine learning forces.

The atomic descriptors used in machine learning to predict forces are often high dimensional. In general, by retrieving a significant amount of structural information from these descriptors, accurate force predictions can be achieved. On the other hand, to acquire higher robustness for transferability without overfitting, sufficient reduction of descriptors should be necessary. In this study, we propose a method to automatically determine hyperparameters in the atomic descriptors, aiming to obtain accurate machine learning forces while using a small number of descriptors. Our method focuses on identifying an appropriate threshold cut-off for the variance value of the descriptor components. To demonstrate the effectiveness of our method, we apply it to crystalline, liquid, and amorphous structures in SiO2, SiGe, and Si systems. By using both conventional two-body descriptors and our introduced split-type three-body descriptors, we demonstrate that our method can provide machine learning forces that enable efficient and robust molecular dynamics simulations.

Vaporization and the Thermodynamic Properties of the SrO–Al2O3–SiO2 System

Vaporization and thermodynamic properties of the SrO–Al2O3–SiO2 system are studied by high-temperature differential mass spectrometry in the concentration range from 90 to 10 mol % of SrO and the molar ratio of x(Al2O3)/x(SiO2) = 1.5. The samples are evaporated from Knudsen effusion cell made of tungsten. The partial pressures of the molecular forms of the vapor, the activities of the condensed phase components, the Gibbs energies, and the excess Gibbs energies are determined. It is established that the studied system is characterized by a slight negative deviation from the ideal behavior. For mullite (Al6Si2O13) the value of the standard enthalpy of formation is determined. The melting points of the synthesized samples are established by high-temperature microscopy.

PHASE TRANSFORMATIONS UNDER THE ACTION OF FEMTOSECOND PULSES IN THE GLASS-CERAMIC OF ZnO–MgO–Al2O3–SiO2 SYSTEM

The effect of femtosecond laser micro-treatment in thermal and non-thermal modes on the structure of transparent glass-ceramic based on the ZnO–MgO–Al2O3–SiO2 system, characterized by increased mechanical strength and hardness, is investigated. The amorphization of nanoscale ganite (ZnAl2O4) crystals, which occurs under the irradiation of laser pulses, is confirmed by the results of electron microscopy and electron diffraction. Quantitative phase microscopy was used to evaluate changes in the refractive index in individual tracks written by a laser beam. At the repetition frequency of 10 kHz in non-thermal mode, complete amorphization of the crystal phases in volume glass-ceramic sample leads to an increase of the refractive index by the value ?n = 0.0007 in the laser processing area. The results obtained expand the potential applications of transparent glass-ceramics with increased mechanical properties and open up the possibility of forming channel waveguides in their volume by direct laserwriting.

Determining patterns in the formation of cordierite phase during the synthesis of density-sintered low-temperature ceramics based on glasses of the MgO–Al2O3–SiO2 system

The search for effective modifiers of the structure of densely baked cordierite ceramics to reduce the firing temperature is a relevant task but typically requires a large amount of experimental research. The object of this study is the reaction of the formation of the cordierite phase with the participation of glass components of the eutectic compositions of the MgO– Al2O3–SiO2 system under low-temperature firing conditions. In this case, thermodynamic analysis was used as a tool to assess the probability of chemical reactions. Thermodynamic analysis can significantly reduce the volume of the experimental sample. This paper reports the results of theoretical and experimental studies into the features of the course of chemical reactions with the participation of glass components of eutectic compositions of the MgO–Al2O3–SiO2 system. It was revealed that once the stoichiometric ratio is maintained, the resulting product of the interaction between the components of eutectic glasses of the MgO–Al2O3–SiO2 system with charging components is cordierite. Changes in the mineralogical composition of cordierite compositions depending on the firing temperature have been determined. The formation of the cordierite phase is preceded by the process of transformation of meta kaolinite Al2O3·2SiO2, which is a product of kaolin dehydration, into mullite 3Al2O3·2SiO2. Subsequently, the formation of cordierite (in addition to crystallizing directly from eutectic glasses) occurs with the participation of the mullite phase. The formation of the cordierite phase occurs in several stages and is completed at a temperature of 1300 °C. The established features of the reactions of cordierite formation make it possible to determine the most optimal compositions for glasses of the MgO–Al2O3–SiO2 system to obtain low-temperature cordierite ceramics with a high degree of sintering. At the same time, it is also possible to control the phase composition of ceramics and its properties

Effect of TiO2 on crystallization and mechanical properties of MgO–Al2O3–SiO2 glasses containing P2O5

MgO–Al2O3–SiO2 glass-ceramics have been widely used in military, industrial, and construction applications. The nucleating agent is one of the most important factors in the production of glass-ceramics as it can control the crystallization temperature or the grain size. In this study, we investigated the effect of replacing P2O5 with different amounts of TiO2 on the crystallization, structure, and mechanical properties of an MgO–Al2O3–SiO2 system. The crystallization and microstructure were investigated by differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were investigated by measuring the Vickers hardness, Young's modulus, and fracture toughness. The results showed that adding TiO2 favored the precipitation of fine grains and significantly increased the Vickers hardness, Young's modulus, and fracture toughness of the glasses. Introducing an appropriate amount of TiO2 can make a glass structure more compact, promote crystallization, and improve the mechanical properties of MgO–Al2O3–SiO2 glass-ceramics.

Formation pathways of endogenous slag in typical charges of cohesive zone

The diffusion behaviour of oxides in FeO·2CaO·SiO2 (FC2S) systems was systematically analysed using slag compositions at different temperatures, and the formation pathway of an endogenous slag in the pellet and sinter of the cohesive zone was determined. The FeO-CaO-Al2O3-SiO2 endogenous slag proved to be the dominant slag phase because of a stronger diffusion capacity of Al3+ than Mg2+ and the less destructive effect of Al3+ diffusion on the original system. The enhanced effect of CaO and FeO on ion diffusion in the systems containing MgO resulted in a more pronounced diffusion of MgO and Al2O3 into the FC2S system at 1200 °C. The formation of the endogenous slag in the pellet and sinter was also established, which confirmed the rationality of the selection of the slag phase formation path. The endogenous slag-phase formation pathway also explained the nature of the cohesive zone.

GLASS FILLERS BASED ON THE SrO–Al2O3–B2O3–SiO2 SYSTEM FOR DENTAL COMPOSITES

Dental composite ?lling materials based on glass in the SrO–Al2O3–B2O3–SiO2 system was obtained. The glass filler meets the modern level of requirements for filling materials, and is characterized by high chemical resistance to water, acids and alkalis (class I), high transparency (more than 80 %), consistency with the polymer matrix according to CTE while maintaining of an acceptable melting temperature and no tendency to crystallization. It is shown that the developed glass filler provides a high level of biomedical, operational and functional properties of a dental composite based on it and competitiveness with respect to popular foreign analogue materials.

Preparation and characterization of a novel luminescence nano-sillenite (Bi12SiO20) glass ceramic within Bi2O3–ZnO–SiO2 system

Bismuth silicate with sillenite structure (Bi12SiO20) nanophase was prepared via melt–quenching technique in the Bi2O3–ZnO–SiO2 glass system. The effect of replacement ZnO by Bi2O3 was studied. Their thermal behavior showed the change of glass transition temperature (Tg) from 577 °C in the Bi2O3-free glass to 438 °C in ZnO-free glass. In addition, the crystallization temperatures were not only changed from two to one peak, but also decreased from 927 to 476 °C in the same order. According to the heat treatment regimes, willemite, sillenite, tetragonal Bi2O3, cubic Bi2O3 and traces of ZnO were crystallized with different ratios depending on the change in composition and temperature. Sillenite was enhanced with increase heat treatment temperature and/or Bi2O3 additions. Heat treatment at 650 °C/10 h revealed the best regime, where higher degree of crystallization was achieved. The microstructure at 700 ℃/30 min showed nano-scale oriented parallel rod crystals with hexagonal making at their end, whereas clusters of irregular nano-size crystals was appeared at 650 °C/10 h. Transmission spectra of the glasses in UV–Vis–midIR region were increased with Bi2O3 addition reaching 74% in 100B. Photoluminescence properties of both glasses and their corresponding glass–ceramics showed luminescence nature since the blue and green colors were clearly appeared. Calculation of optical bandgap (Eopt) revealed 3.2–2.19 eV with increasing Bi2O3; these values are located in the semiconducting range. The prepared samples can be utilized in electro-optical instruments, also the high transmission in mid-IR nominate it for IR transmitting windows.

Exothermic synthesis of ceramic materials based on the system Zn2SiO4‒RO (R ― Ba, Sr)‒Al2O3‒SiO2

The synthesis of ceramic materials in the Zn2SiO4‒RO (R ― Ba, Sr)‒Al2O3‒SiO2 system was carried out using the technology of exothermic synthesis from solutions including zinc, barium and strontium nitrates, silica and organic reducing agent (glycine and carbamide). It is shown that the implementation of an exothermic process followed by calcination at a temperature of 1000 °C contributes to the formation of crystalline phases of willemite (Zn2SiO4), barium aluminosilicates (BaAl2Si2O8) and strontium (SrAl2Si2O8). The dependence of the quantitative phase composition and parameters of the elementary cells of the crystalline phases is established. Sintering of synthesized materials occurs at a temperature of 1275 °C. The dielectric permittivity of sintered materials is 5,33‒6,06 and the tangent of the dielectric loss angle is 1,5·10‒3‒3,16·10‒3 at a frequency of 1 MHz, the minimum values correspond to ceramics based on the Zn2SiO4‒BaAl2Si2O8‒SrAl2Si2O8 triple system. Ill. 5. Ref. 19. Tab. 2.

Low-temperature crystallization and microwave dielectric properties of forsterite generated in MgO–SiO2 system following LiF addition

The crystallization and microwave dielectric properties of forsterite (Mg2SiO4) produced in (1-x)2MgO–SiO2(MS)-xLiF mixtures were characterized. High-temperature XRPD for a 0.91MS-0.09LiF specimen indicated the crystallization of forsterite above 800 °C, although MgSiO3, MgO and SiO2 were also detected due to the short heating duration. The XRPD patterns for (1-x)MS-xLiF ceramics sintered at 900 °C for 4 h in a covered crucible demonstrated the formation of forsterite as a single phase in compositions having x values less than 0.08. The activation energy for the crystallization fraction of forsterite was estimated from the DTA curves by using Kissinger-Akahira-Sunose method and decreased from 1382.4 to 474.0 kJ/mol, suggesting that the LiF addition enhances the nucleation and crystallization of forsterite. Refinement of the crystal structures of the (1-x)MS-xLiF ceramics by Rietveld analysis showed that the patterns acquired from samples having x values of 0.03–0.08 corresponded to a forsterite single phase with a decrease in the lattice parameters, confirming the substitution of Li and F for Mg and O in the forsterite. 7Li and 19F solid-state NMR spectroscopy analyses also confirmed the presence of 7Li and 19F signals for the sintered ceramics. The Q・f values for the ceramics increased from 22,800 to 104,800 GHz as x was increased to 0.08, due to the improvement in the crystallinity of forsterite. Although a near zero TCf value was achieved by CaTiO3 addition for (1-y)(0.92MS-0.08LiF)-yCaTiO3 ceramics at y = 0.10 (εr = 8.2, Q・f = 25,050 GHz, TCf = −5 ppm/°C), the Q・f values were drastically decreased due to the lower crystallinity of the forsterite and the presence of SiO2 and Li2MgSiO4 as secondary phases.

Effect of a Ca-rich environment on the reaction process of the MgO-activated SiO2 system

The mechanism of the effect of a Ca-rich environment on the reaction process and the molecular structure of the magnesium oxide (MgO)-activated SiO2 reaction product are described in this research. In the experimental study, MgO, silica fume, and calcium oxide (CaO) were used as raw materials to prepare a calcium-magnesium coupling excited SiO2 system with different Ca:Mg molar ratios. The samples were characterized by X-ray diffraction, thermogravimetry/derivative thermogravimetry, inductively coupled plasma mass spectroscopy, transmission electron microscopy, and 29Si nuclear magnetic resonance. A higher Ca:Mg molar ratio (above 0.179:1) inhibited magnesium silicate hydrate gel formation, while a lower ratio (less than 0.09:1) promoted magnesium silicate hydrate gel formation. The amount of Ca2+ and Mg2+ presented in the pore solution in the Ca-rich environment was not sufficient to react with silicate ions (H2SiO2− 4 and H3SiO− 4) to form gel, leading to surplus SiO2. Changes in the Ca2+ concentration in the pore solution affected Mg2+ and silicate ions behavior. The hydration of low amounts of CaO provided ionization products of Ca2+ and OH− ions, MgO and CaO were hydrolyzed, and less ionized OH− was consumed by silicate ions. The hydration and ionization of MgO increased the Mg2+ concentration, while the silicate ions concentration decreased. However, excess OH− ions produced by hydration and ionization with high amounts of CaO exhibited opposite effects, subsequently impacting the calcium–magnesium coupling excited SiO2 system. Thermodynamic calculations revealed that the magnesium silicate hydrate gel was more stable than the calcium silicate hydrate gel, and the influence of various Ca-rich environments on the MgO-activated SiO2 reaction process was further studied.