Multicomponent Melts Research Articles

Density and thermal expansion of borate and borosilicate glass-forming melts

Density, molar volume and thermal expansion of borate and borosilicate melts are properties that significantly affect the process of forming composite coatings by slip-firing technology. Based on experimental data on the density of glass-forming melts, adequate generalizing mathematical models have been developed by using the method of multiple correlation; these models describe the dependence of the molar volume (VT) of alkaline borate, alkaline silicate and multicomponent melts on their oxide composition and temperature with a standard deviation of (0.22–0.27) cm3 mol–1. The regression equation has the following general form: VT=A(xi)–B(xi)/T, where xi is the content of an oxide, T is the temperature, subscript "i" stands for the number of an oxide concerned. The changes in volumetric coefficient of thermal expansion (CTE) of the molten glasses are analyzed as functions of both temperature and chemical composition. It should be noted that borate melts in comparison with silicate ones have much higher values of CTE. The highest value of CTE of experimental melts is observed at glass transition temperatures (Tg). An increase in the temperature above Tg contributes to a significant decrease in CTE. An increase in the content of alkali metal oxides in most glass-forming melts results in an increase in the values of CTE.

Electroseparation of uranium from lanthanides (La, Ce, Pr, Nd and Sm) on liquid gallium electrode

The aim of this work is to explore the electroseparation of uranium from lanthanides (La, Ce, Pr, Nd and Sm) on a liquid gallium electrode. Cyclic voltammetric results showed that in multi-component melt systems (U/Nd, U/La-Ce-Nd, and U/La-Ce-Pr-Nd-Sm), the reduction potentials of each lanthanides on the Ga cathode are identical and cannot be distinguished and resolved. The peak potential differences between the lanthanides and uranium are all at about 250 mV. The practical electroseparations in U/Nd, U/La-Ce-Nd and U/La-Ce-Pr-Nd-Sm systems were carried out by applying different electrochemical techniques as galvanostatic, potentiostatic and current pulse electrolysis. After electrolysis, the ICP-AES technique was used to determine the composition of molten salt and alloy deposits, and the actual separations factor of U over lanthanides in these multi-component systems were calculated and compared. The results showed that the separation factors of U/La and U/Sm can be both up to 1000, whilst that of U/Nd is relatively low with an average value of about 350. In addition, the separation factor obtained by the current pulse electrolysis is larger than that of galvanostatic and potentiostatic method, and the potentiostatic electrolysis provides the lowest one.

On the Theory of Directional Solidification in the Presence of a Mushy Zone

A model is developed for the directional solidification of a binary melt with a two-phase zone (mushy zone), where the fraction of the liquid phase is described by a space–time scaling relation. Self-similar variables are introduced and the interphase boundary growth is inversely proportional to the square root of time. The mathematical model of the process is reformulated using self-similar variables. Exact self-similar solutions of heat-and-mass transfer equations are determined in the presence of two mobile phase-transition boundaries, namely, solid–mushy zone and mushy zone–liquid ones. The temperature and impurity concentration distributions in the solid phase, the mushy zone, and the melt are found as integral expressions. A decrease in the dimensionless cooled-boundary temperature leads to an increase in the solidification rate and the fraction of the liquid phase. The solidification rate, the parabolic growth constants, and the fraction of the liquid phase at the solid–mushy zone boundary are determined depending on the scaling parameter and the thermophysical constants of the solidifying melt. The positions of the solid–mushy zone and mushy zone–binary melt phase transition boundaries are found. The dependences of the solidification rate (inversely proportional to the square root of time) are analyzed. The scaling parameter significantly is shown to substantially affect the solidification rate and the fraction of the liquid phase in the phase transformation region. The developed model and the method of its solution can be generalized to the case of directional solidification of multicomponent melts in the presence of several phase transformation regions (e.g., main and cotectic two-phase zones during the solidification of three-component melts).

Modeling the viscosity of silicate melts containing Fe oxide: Fe saturation condition

Our recently developed model for the viscosity of silicate melts is applied to describe and predict the viscosities of oxide melts containing iron oxide. In the present study, the viscosity experimental data under the reduced atmosphere, which is Fe saturation condition were critically reviewed and three pairs of adjustable model parameters related to ‘FeO’ were optimized to best reproduce all experimental data in the FeO–SiO2–Al2O3–CaO–MgO–Na2O–MnO–Ti2O3–TiO2 system. The viscosities of a wide compositional and temperature range of binary, ternary and multicomponent melts were well reproduced by the present model within the scatter of experimental data.

Detection of the liquid–liquid transitions in superalloys melts upon overheating and relaxation by the electromagnetic method

Among numerous melt structure model representations, the most relevant for liquid heat-resistant nickel alloys description is the quasicrystalline model of a microinhomogeneous structure, in which it is assumed that multicomponent nickel melts consist of clusters and intercluster space. Clusters inherit the short-range order of the atomic structure from various phases of the initial solid metal crystalline structure. Heating the melt to a certain temperature and/or increasing a period of its isothermal holding at constant pressure led to a second-order phase liquid–liquid phase transition (LLT). As a result, atomic associations that are more balanced and uniformly distributed over the melt volume are formed. Structural changes in nickel superalloy melts are irreversible and have a significant effect on the formation of the structure and properties of a solid metal during crystallization. Structural LLT changes in multicomponent nickel melts are the basis for a scientific substantiation of the technological modes of smelting, which contributes to an improvement in the technological properties of melts, a reduction of metallurgical defects, a rational use of expensive elements and foundry waste, as well as a significant improvement in the quality of metal products. This work is devoted to the experimental determination of the LLT transition in superalloy melts by the noninvasive electromagnetic method.

Modeling the viscosity of silicate melts containing Fe oxide: FeO/Fe2O3 containing system

In the present study, the viscosity experimental data for the FetO-containing silicate melts under oxidation atmosphere, which Fe3+ and Fe2+ co-exist were critically evaluated and model parameters related to Fe2O3 were optimized to best reproduce all reliable experimental viscosity data. The charge compensation effect on the viscosity for the systems containing Fe2O3 was modeled with the Gibbs energies for LiFe, NaFe, KFe and CaFe2 “associate species” formation. The viscosities of a wide compositional and temperature range of binary, ternary and multicomponent melts containing Fe2O3–FeO–SiO2–Al2O3–CaO–MgO–Li2O–Na2O–K2O–MnO–Ti2O3–TiO2 were well reproduced by the present model within the scatter of experimental data.

Nanocrystalline Soft Magnetic Iron-Based Materials from Liquid State to Ready Product.

The review is devoted to the analysis of physical processes occurring at different stages of production and application of nanocrystalline soft magnetic materials based on Fe–Si–B doped with various chemical elements. The temperature dependences of the kinematic viscosity showed that above a critical temperature, the viscosity of multicomponent melts at the cooling stage does not coincide with the viscosity at the heating stage. Above the critical temperature, the structure of the melt is more homogeneous, the amorphous precursor from such a melt has greater plasticity and enthalpy of crystallization and, after nanocrystallization, the material has a higher permeability. The most effective inhibitor elements are insoluble in α-Fe and form a smoothed peak of heat release during crystallization. On the other hand, the finest nanograins and the highest permeability are achieved at a narrow high-temperature peak of heat release. The cluster magnetic structure of a nanocrystalline material is the cause of magnetic inhomogeneity, which affects the shape of the magnetic hysteresis loop and core losses.

МОДЕЛЬНЕ ПРОГНОЗУВАННЯ ФІЗИКО-ХІМІЧНИХ І ТЕПЛОФІЗИЧНИХ ХАРАКТЕРИСТИК НОВИХ ВИДІВ МАРГАНЦЕВМІСНИХ (Mn-50-60%) ФЕРОСПЛАВІВ

The aim of the work is to implement a new approach to the description of physicochemical and thermophysical characteristics of low-melting manganese-containing ferroalloys (in the range of concentrations of Mn 50-60%, Si 3-8%, C 2.5-6%) during deoxidation and alloying of metal melt. The proposed approach is focused on the development of methods and criteria for the quantitative assessment and accounting of microhomogeneity of multicomponent metal melts, which include ferroalloys. This approach makes it possible to predict such important characteristics as melting temperature, density, heat capacity, heat of fusion, thermal conductivity, resistivity, temperature coefficient, which will expand the understanding of melting processes and assimilation of ferroalloy elements. The method of solving regularity modeling problems developed at the Iron and Steel Institute of the National Academy of Sciences of Ukraine, which is based on the original concept of directed chemical bonding of interaction processes in melts and solutions, developed by E.V. Prikhodko. To assess and take into account the influence of microhomogeneity of the structure of metal melts of ferroalloy production, the method of calculating criteria (ΔZY and Δd), which characterize the degree of difference between electronic and structural state of the melt (as a chemically unified system) from the mechanical mixture of their initial components. Using these criteria and the available experimental data, which acted as reference points, the calculated values of the consumer properties of manganese-containing ferroalloys, which differ from standard brands in the direction of increasing the silicon content and decreasing manganese. On the basis of new results of calculation of a complex of physical and thermophysical properties the estimation of efficiency of use of ferroalloys is carried out. The fundamental possibility of graphical dependences «property-parameter» to determine the boundary conditions for choosing the optimal composition of new types of ferroalloys, purposefully control the physicochemical state of the iron-carbon melt and, accordingly, to influence the properties of the finished metal.

Thermodynamic Modeling of Iron and Nickel Reduction from B2O3-CaO-FeO-NiO Melts


 
 
 At present, during solving theoretical and applied problems of metallurgical technologies improving, thermodynamic modeling (TDM) methods are widely used to calculate multicomponent and multiphase systems. However, existing methodology TДM are intended for the balance analysis in the ”closed” systems. The authors of [9] proposed a technique that allows, using TDMs, to describe metal reduction processes during gas bubbling of multicomponent oxide melts in approximation to “open” real systems. The applicability of the methods is estimated using the example of joint Nickel and Iron reduction modeling in the B2O3-CaO-FeO-NiO system by Carbon monoxide for ”open” and ”closed” systems. The data obtained comparison for ”open” and ”closed” systems show that the consecutive output of products (gas and metal) from working medium promotes achievement of the best parameters for Nickel extraction to alloy and to its residual content in oxide melt. Using this technique, the TДM process of joint reduction of Nickel and Iron in system B2O3-CaO-FeO-NiO by Carbon monoxide in ”open” system was undertaken at various temperatures in the 1273-1773K interval.
 Keywords: thermodynamic modeling, ”closed” system, ”open” system, joint reduction, Carbon monoxide, oxide melt, gas bubbling
 
 

Nonequilibrium Molecular Conformations in Polymer Self-Consistent Field Theory

The morphology of a multicomponent polymer melt within self-consistent field theory (SCFT) is completely characterized by the spatial density distribution of the components. SCFT therefore assumes ...

Detection of the LLT in Superalloys Melts Upon Overheating and Relaxation by the Electromagnetic Method

Among numerous melt structure model representations, the most relevant for liquid heat-resistant nickel alloys description is the quasicrystalline model of microinhomogeneous structure, in which it is assumed that multicomponent nickel melts consist of clusters and intercluster space. Clusters inherit the short-range order of the atomic structure from various phases of the initial solid metal crystalline structure. Heating the melt to a certain temperature and/or increasing a period of its isothermal holding at constant pressure leads to a second-order phase LLT transition. As a result, atomic associations which are more balanced and uniformly distributed over the melt volume are formed. Structural changes in nickel superalloy melts are irreversible and have a significant effect on the formation of the structure and properties of a solid metal during crystallization. Structural LLT changes in multicomponent nickel melts are the basis for the scientific substantiation of technological modes of smelting, which contribute to improving the technological properties of melts, reducing metallurgical defects, the rational use of expensive elements and foundry waste, as well as, a significant improvement in the quality of metal products. This work is devoted to the experimental determination of the LLT transition in superalloy melts by the noninvasive electromagnetic method.

Studies of amorphous-siliceous rocks of the Republic of Kazakhstan as mineral raw materials in the formation of the porous structure of heat-insulating foam glass

Foam glass is known mainly as a cellular thermal insulation material obtained by sintering a mixture of glass powder and a blowing agent followed by annealing of the foam material. This article explores the possibility of producing heat-insulating foam glass directly from widely available amorphous-siliceous natural flasks, eliminating economically disadvantageous and energy-intensive processes of cooking and granulation of special multicomponent glass melt from the scheme of traditional technology.

Unravelling the effect of nano-heterogeneity on the viscosity of silicate melts: Implications for glass manufacturing and volcanic eruptions

Traditionally depicted as homogeneous materials, manmade and volcanic glasses are often subjected to nanostructuration during demixing and crystallization of their parental melt. While the controlled formation of nanocrystals has been exploited for decades in the industrial production of glass-ceramics to obtain materials with superior properties, nano-heterogeneities have been recently recognized in volcanic products erupted explosively. Here, a multi-pronged approach is adopted to highlight how the emergence of nano-heterogeneities exerts a previously unexplored influence on the viscosity of multicomponent silicate melts. Calorimetry and viscometry provide evidence of how the formation of TiO2- and FeO-bearing nanocrystals increases the effective viscosity of suspensions. Raman spectroscopy and transmission electron microscopy allow the correlation between the increase in viscosity and the degree of sample modification. This study has implications for glass and glass-ceramics manufacturing and for the development of better numerical models of volcanic eruptions, which are key for the operational assessment of volcanic risk.

The Resonant Principle of Nanomaterial Synthesis from Aqueous Solutions and Molten Electrolytes

The possibility of applying the resonance principle of matter synthesis to complex multicomponent systems, namely, aqueous solutions and electrolyte melts, has been demonstrated for the first time. The interaction of $${\text{WO}}_{4}^{{2 - }}$$ , $${\text{MoO}}_{4}^{{2 - }}$$ , $${\text{NbF}}_{7}^{{2 - }}$$ , $${\text{TaF}}_{7}^{{2 - }}$$ , and $${\text{TiF}}_{6}^{{2 - }}$$ anions with alkali and alkaline-earth metal cations (Li+, Ca2+, and Mg2+) in aqueous solutions and electrolyte melts (in particular, in melts of fluorides and chlorides of alkali metals) was studied. The correspondence between the resonant frequencies of the components of selected electrolytes was revealed, and this enabled the elucidation of complexation principles in the systems studied. Resonance has been demonstrated for the energies of the molecular orbitals, rather than for the frequencies only. Analysis of the energies of molecular orbitals revealed the correspondence of the highest occupied molecular orbitals of some reagents to the lowest unoccupied molecular orbitals of other reagents. This result is consistent with the frequency resonance of the electrolyte components. Information on the frequency spectra of multicomponent systems at the advanced modern theoretical level enables the selection of electrolyte composition to actually steer the synthesis of the required substance in a predetermined direction without conducting preliminary experiments. The results of our studies of the resonance principle of obtaining certain substances are unique and have no analogs worldwide. This opens up the prospects for the purposeful creation of conditions for controlling the processes of producing matter with desired properties.

Dissolution kinetics of arbitrarily-shaped alumina in oxide melt: An integration of phase-field modelling and real-time observation study

Abstract A feasibility study of utilizing a phase-field model considering the convection effect is performed in this work to investigate the dissolution kinetics of arbitrarily-shaped alumina particle in the oxide melt. The established model has been benchmarked by high temperature confocal laser scanning microscope (HT-CLSM) to observe the polycrystalline sapphire dissolution in multicomponent oxide melt. The effects of alumina morphology and temperature on the dissolution kinetics were studied quantitatively. It is for the first time found that the dissolution of irregular alumina particle in oxide melt shows a double-fold smooth anisotropy behavior. The dissolution rate of alumina particle is governed by the interface interactions rather than the self-diffusion of dissolved component in oxide melt. Increasing the temperature, the interfacial mobility coefficient increases, and the effect of alumina particle shape on the dissolution rate decreases. The temperature variation has a minor influence on the shape evolution of alumina during dissolution process. The convection intensity affects both the dissolution rate and shape evolution of alumina particle. An increased convection intensity increases the dissolution rate. As the convection partially affects the contact area of alumina particle with oxide melt, a decreased alumina particle curvature increases the dissolution rate. When the convection affects the whole contact area of alumina particle with oxide melt, the contact area plays an important role on the dissolution rate. The obtained methodology can be applied to investigate a general dissolution phenomenon in the high temperature oxide melt in materials science.

Ab initio molecular dynamics and high-dimensional neural network potential study of VZrNbHfTa melt

The structural and dynamics properties of melts are directly related to their solidification processes, and consequently to the properties of as-cast solid alloys. Ab initio molecular dynamics (AIMD) is a powerful tool that can study both of these factors. However, the main disadvantage of this method is its low performance which is critical for simulation of the multicomponent liquids. At the same time the atomistic simulation of multicomponent liquids has found its application for prediction of the formation of high-entropy alloys—a novel class of materials with enhanced mechanical properties. An effective method to solve the problem of AIMD low performance may be the design of pair or many-body potentials for classical molecular dynamics. One of the promising approaches is high-dimensional neural networks—the method of constructing many-body potentials for classical molecular dynamics from ab initio data. Thus, in this work, the high-dimensional neural network potential for multicomponent liquid VZrNbHfTa melt was constructed. The structure of this melt obtained by AIMD and high-dimensional neural network potential was compared by analyzing partial radial distribution functions. Dynamics of the melt obtained by both methods was also compared analyzing velocity autocorrelation functions and mean-square displacement for each type of atom in multicomponent VZrNbHfTa melt. It was shown that structure and dynamics are reproduced well by high-dimensional neural network potential (HDNNP). Some differences between HDNNP- and AIMD-obtained structure and dynamics are explained by finite-size effect and lack of statistics in AIMD simulation along with inherent errors in energy and force estimations made by high-dimensional neural network potentials. Analysis of melt structure via partial radial distribution functions and chemical short range order parameters led to the conclusion that vanadium atoms are repulsed from all the atoms of another type in liquid VZrNbHfTa system, which lowers the probability of single phase disordered solid solution formation. Diffusivity in multicomponent melt was found to decrease with increasing mass and size of an atom.

A practical method to account for random phase approximation effects on the dynamic scattering of multi-component polymer systems.

Investigations of polymer systems that rely on the interpretation of dynamical scattering results as, e.g., the structure factor S(Q, t) of single chains or chain sections may require the inclusion of effects, as described within the framework of the random phase approximation (RPA) for polymers. To do this in practice for the dynamic part of S(Q, t) beyond the initial slope is a challenge. Here, we present a method (and software) that allows a straightforward assessment of dynamical RPA effects and inclusion of these in the process/procedures of model fitting. Examples of applications to the interpretation of neutron spin-echo data multi-component polymer melts are shown.

Simulation of crystal growth in multicomponent metastable alloys

A method for predicting the regularities of crystal growth from metastable melts has been developed. The process of crystal growth from a multicomponent melt is described by the methods of nonequilibrium thermodynamics, taking into account the mutual influence of thermal and diffusion processes. The application of a new variational approach to the constructed system of equations made it possible to obtain expressions of the crystal growth rate from a multicomponent melt convenient for practical calculations. The obtained technique allowed us to analyze the features of crystal growth at high rate of crystallization front, which leads to “impurity capture” effect – deviation from equilibrium conditions at the phase interface. The developed mathematical model makes it possible to calculate the growth rate of new phase particles and to estimate the effect of metastable effects on deviation of the components’ concentration at surface of the growing crystal from equilibrium values. Thus, using the obtained method, a “metastable” phase diagram of the system under study can be constructed. The developed approach is applied to the calculation of growth of α-Fe(Si) nanocrystals during annealing of amorphous alloy Fe73,5 Cu1 Nb3 Si13,5B9. The calculation results were compared with the results of the experiment on the alloy primary crystallization. It is shown that the concentration of Fe at the surface of the growing crystal does not significantly deviate from the equilibrium values. On the other hand, silicon atoms are captured by the crystallization front, silicon concentration at the surface of the growing nanocrystal deviates significantly from equilibrium values. The calculation has shown that after the initial crystallization of the amorphous phase, occurring at a temperature of 400 – 450 °C, the deviation of silicon concentration from equilibrium value is about 2 %, while this equilibrium value is about 13.3 %.

Thermodynamic Regularities of Nuclei Growth during Crystallization of Metastable Alloys

The process of crystal growth in a metastable multicomponent melt has a high speed of the solidification front, which captures atoms of some other components. As a result of such a growth, at the surface of the growing crystal the effect of “impurity capture” is observed, and the concentrations of components significantly deviate from the local equilibrium. Under such conditions, the conventional physico-chemical methods for description of processes at the interfacial surface become inapplicable. Therefore, a new variational approach was applied for an integrated description of diffusion and thermal processes at the phase interface. The growth rate of crystal nucleus in a metastable melt was obtained, using the methods of non-equilibrium thermodynamics. The developed approach allows estimation of the degree of metastable effects influence on a crystal growth rate.

Effect of straining flow on growth of columnar crystal in ternary undercooled melt

As an important microstructure, columnar crystal growth technology, especially the growth technology of single columnar crystal plays an important role in improving the performances of semiconductor, optical devices and other related products. In many practical applications, because the alloy is composed of multi-component and there is inevitably flow in the melt, it is necessary to study the growth of columnar crystals in multi-component melt with flow separately. The growth of columnar crystal in a ternary undercooled melt subjected to straining flow under non-isothermal conditions is studied, and the approximate analytical expression for growth morphology of columnar crystal is given by using asymptotic method. It can be seen from the expression that straining flow is an important reason for irregular columnar crystal. When analyzing the effect of straining flow on the growth of columnar crystal in ternary melt, it is found that the incoming flow accelerates the growth velocity of the interface, while the outgoing straining flow reduces the growth velocity of the interface, namely, the straining flow makes the interface of columnar crystal deformed. At the same time, it is found that the interface deformation becomes more intense with the increase of flow velocity. The above conclusion can also be applied to the effect of straining flow on the interface morphology of columnar crystal in pure melt and binary melt. The comparison of the effects of straining flow on the interface of columnar crystal among pure melt, binary melt and ternary melt, shows that the interface morphology of columnar crystal in dilute alloy melt is more affected by straining flow than in the pure melt, but the more components are more easily affected by flow. However, the number of components in melt is not a decisive factor for the change of interface morphology of the columnar crystal, but the constitutional undercooling is an important factor for determining the interface morphology of multicomponent alloy. According to the conclusion of this paper, the influence of straining flow on the interface morphology of columnar crystal growth can be quantitatively predicted, which provides the necessary theoretical guidance in accurately controlling the interface morphology in the future.