Melt Structure Research Articles

Atomistic Mechanism Underlying Nucleation in Al–Cu Alloys with Different Compositions and Cooling Rates

Nucleation, significantly influenced by local structures in metallic melts, is crucial for controlling the microstructure of solidified materials. However, the connection between local atomic struc...

Buoyancy and Structure of Volatile-Rich Silicate Melts.

The early Earth was marked by at least one global magma ocean. Melt buoyancy played a major role for its evolution. Here we model the composition of the magma ocean using a six‐component pyrolite melt, to which we add volatiles in the form of carbon as molecular CO or CO2 and hydrogen as molecular H2O or through substitution for magnesium. We compute the density relations from first‐principles molecular dynamics simulations. We find that the addition of volatiles renders all the melts more buoyant compared to the reference volatile‐free pyrolite. The effect is pressure dependent, largest at the surface, decreasing to about 20 GPa, and remaining roughly constant to 135 GPa. The increased buoyancy would have enhanced convection and turbulence, and thus promoted the chemical exchanges of the magma ocean with the early atmosphere. We determine the partial molar volume of both H2O and CO2 throughout the magma ocean conditions. We find a pronounced dependence with temperature at low pressures, whereas at megabar pressures the partial molar volumes are independent of temperature. At all pressures, the polymerization of the silicate melt is strongly affected by the amount of oxygen added to the system while being only weakly affected by the specific type of volatile added.

MODEL REPRESENTATIONS OF THE MELTS STRUCTURE DESCRIPTION BY THE MODEL OF HARD SPHERES

In the article the optimization of the oil and gas enterprise, a complex process both from the technological and from the economic point of view is investigated. It is noted that today the development of methods of mathematical modeling of physical processes, for example, in oil fields on the basis of theoretical research and modern computer technology is absolutely relevant
 One of the ways is to create new or improve existing mathematical models of processes occurring in oil and gas reservoirs, and calculate on their basis the characteristics of the process that optimize production. From this perspective, the study appears particularly relevant liquids in a narrow, purely physical and chemical aspects – namely melt.
 Various fluid models have been proposed to describe the equilibrium and kinetic properties of liquids (melts), as well as to interpret experimental results. Model representations are also used in solving integrodifferential equations that relate distribution functions to interaction potentials. It is noted that integrodifferential equations are a powerful mathematical algorithm for describing inhomogeneous dynamic models, but they depend directly on the efficiency of software that implements the proposed models.
 The model of hard spheres as simple fluid model proposed use. The reasons that allow you to choose this model as optimal were defined. Namely: the presence of analytical expression for the structural factor; application to describe the electronic and atomic properties of melts. The optimal methods for obtaining optimal values for the theoretical calculation of the structural factor of the proposed model were determined.
 As a result of the analysis of existence of correspondence between the calculated and experimental structural factors it is established. This led to the conclusion that the possibility of applying the model of rigid to calculate the equilibrium and kinetic properties of melts exists. It is determined that the model of rigid spheres could be used as an approximation to describe the structure of both one-component and multicomponential melts (liquids).

Higher-order structure of polymer melt described by persistent homology

The optimal method of the polymer Materials Informatics (MI) has not been developed because the amorphous nature of the higher-order structure affects these properties. We have now tried to develop the polymer MI’s descriptor of the higher-order structure using persistent homology as the topological method. We have experimentally studied the influence of the MD simulation cell size as the higher-order structure of the polymer on its electrical properties important for a soft material sensor or actuator device. The all-atom MD simulation of the polymer has been calculated and the obtained atomic coordinate has been analyzed by the persistent homology. The change in the higher-order structure by different cell size simulations affects the dielectric constant, although these changes are not described by a radial distribution function (RDF). On the other hand, using the 2nd order persistent diagram (PD), it was found that when the cell size is small, the island-shaped distribution become smoother as the cell size increased. There is the same tendency for the condition of change in the monomer ratio, the polymer chain length or temperature. As a result, the persistent homology may express the higher-order structure generated by the MD simulation as a descriptor of the polymer MI.

Performance and transition mechanism from acidity to basicity of amphoteric oxides (Al2O3 and B2O3) in SiO2–CaO–Al2O3–B2O3 system: A molecular dynamics study

Amphoteric oxides (Al2O3 and B2O3) represent opposite effects on the structure and properties of silicate melts in different conditions, while the understanding about the transition from acidity to basicity is far from complete. Molecular dynamics simulation was adopted in the present study to investigate the performance and acidity-basicity transformation of Al2O3 and B2O3 in the SiO2–CaO–Al2O3–B2O3 system. The results showed that, different from Ca2+ ions, excessive Al3+ or B3+ ions tend to destroy the bridge oxygen structures, showing the function of basic oxide. This is similar to the behavior of Ca2+ ions and other basicity ions. It was found that, on the one hand, B3+ ions tend to form [BO3]3- planar triangular structures with the increase of B3+ ions contents, on the other hand, B3+ ions could reduce the stability of Si–O bonds. Therefore, B3+ ions could make the system structure less stable, which is the reason why the B2O3 is a kind of active agent. In addition, because of the significant differences in lattice energy and atomic structure between Al2O3 and B2O3, the effects of Al2O3 and B2O3 on the thermodynamic properties of silicate melts are quite different.

From melt to crystals: The effects of cooling on Fe[sbnd]Ti oxide nanolites crystallisation and melt polymerisation at oxidising conditions

The state and properties of magma are crucial controls on the eruptive behaviour of volcanic systems. Nowhere is the importance of the link between the state and properties more dramatically expressed than in the rheology of multiphase magmatic systems, and it is magma rheology in turn that exerts a primary control on eruption style. Magmas ascending to shallow levels are subjected to decompression that leads to volatile loss and melt viscosity increase as well as the nucleation and growth of microlites and nanolites. Yet the effects of nanolites on magma rheology have only been investigated to date in a reconnaissance fashion. In order to better constrain the influence of cooling on FeTi oxide nanolite crystallisation and silicate melt structure, we conducted magma cooling experiments at controlled cooling rates of 0.1 − 50 K min−1. All experiments were run in air at 1 bar on a Fe-rich rhyolitic magma at superliquidus starting conditions. We analysed the resultant glasses via micro-Raman spectrometry to monitor the structural changes in the melt induced during the transition from a crystal-free melt to a nanolite-bearing magma, as well as the process of nanolite crystallisation itself. The Raman spectral data indicate that nanolite formation together with a concomitant increase in melt polymerisation occur at cooling rates of 0.5 K min−1 or less. The timescales for nanolite formation are estimated to be on the order of 104s for both dynamic crystallisation and isothermal crystallisation. Our experimental results, obtained at oxidising conditions and slow cooling rates, provide insights into the formation of FeTi oxide nanolites and structural changes of silicate melts that can also be observed and are expected in equivalent natural volcanic systems. The higher degree of melt polymerisation and the higher load of crystals both due to the formation of nanolites in Fe-rich rhyolites are likely to cause increases in the magma viscosity. In addition the nanolites likely provide sites for heterogeneous bubble nucleation in these degassing magmas. Taken together these effects may have the potential to shift shallow magmas from an effusive eruption style into conditions favourable for an explosive eruption.

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.

Lithium Borates from the Glass to the Melt: A Temperature-Induced Structural Transformation Viewed from the Boron and Oxygen Atoms.

A multiedge study of the local structure of lithium borate glasses and melts has been carried out using X-ray Raman scattering (XRS) as a function of temperature. Thanks to a wide range of compositions, from pure B2O3 up to the metaborate composition, we are able to finely interpret the modifications of the local environment of both the boron and oxygen atoms in terms of boron coordination number, formation of nonbridging oxygens (NBOs), and polymerization degree of the borate framework as a function of temperature and composition. A temperature-induced [4]B to [3]B conversion is observed above the glass transition temperature (Tg) from the glass to the melt from the triborate composition up to the metaborate composition. Two distinct melt structures are reported: a well-polymerized borate network-with few NBOs-below the triborate composition and a depolymerized borate network above the diborate composition with a rapid increase of the number of NBOs when Li2O is added. These two structurally distinct melts allow explaining the two dynamic regimes observed for lithium ion diffusion.

Rigidity theory of glass: Determining the onset temperature of topological constraints by molecular dynamics

Topological constraint theory has been extensively used to describe how the composition and structure of glasses and glass-forming melts control their properties. This approach relies on an accurate enumeration of the topological constraints acting in the atomic network. Such direct enumeration is challenging since constraints can be active or thermally-broken depending on temperature. Here, based on molecular dynamics simulations, we present a generic method aiming to predict the onset temperature below which constraints become active. We illustrate this method by considering the example of a series of binary calcium silicate glasses. We find that inter-polytope angular bond-bending constraints are associated with a lower onset temperature than intra-polytope angular constraints. Based on this, we show that the differing values of these two onset temperatures largely govern the glasses’ fictive temperature.

In situ pair distribution function analysis of crystallizing Fe-silicate melts

The structures of a series of Na2O–FeO–Fe2O3–SiO2 melts with Si/Fe = 1, 2, or 3 have been characterized via synchrotron X-ray total scattering using aerodynamic levitation, a containerless technique, paired with laser heating. The melt structure has been simulated using empirical potential structure refinement (EPSR) based on X-ray scattering data and molecular dynamics (MD) simulations with effective partial charge potentials. Pair distribution functions and coordination numbers of cations in the melt were obtained from the data refinement and from the MD simulations. Iron redox and accompanying density were modeled for each composition assuming either (1) oxidized (all Fe3+) or (2) reduced (some Fe2+) to the level predicted for the Ar levitator environment from a literature model. The actual redox of the melts appears to be intermediate, with some Fe2+ but not as much as assumed from the literature model of redox. Comparison of EPSR and MD models at the same redox conditions indicates generally good agreement, and precise values of coordination numbers depend sensitively on the assumptions for cutoff lengths. Stepwise cooling of each melt in the series resulted in formation of magnetite on the free surface of the sample, but no silica-containing crystalline phases were observed. This study provides a comprehensive assessment of coupled factors (composition, redox, density) needed to assess high-temperature in situ structural measurements of simplified iron silicates.

Effect of fluorine on surface tension of CaO-SiO2-Al2O3-Na2O-CaF2 mold flux

The surface tension of mold flux is an important parameter for controlling the quality of continuous billet, affected deeply by the compositions of mold flux and temperature, andclosed related with the structure of mold flux. In the present study, the effect of CaF2and temperature on the surface tension of CaO-SiO2-Al2O3-Na2O-CaF2 mold flux melts is investigated by the pulling cylinder method; furthermore, the structure of melts is determined by FT-IR spectroscopy to analyze the change mechanism of surface tension. The results indicate that the variation of surface tension is in accord with that of structure of melts. The surface tension of melt decreases with the increase of CaF2 mass fraction, and this tendency becomes more apparent at higher temperature. The FT-IR spectra show thatboth the amount of Obandthe degree of structural polymerization of melts decrease as the CaF2 content increases. This is because the Si-Ob bonds in the [SiO4]-tetrahedrons are broken by F− and transformed into Si-F bonds, and the silicon-oxygen anions with more complex structure were depolymerized into silicon-oxygen anions containing fluorine with simpler structure, resulting in an increase of Si-F saturated bonds on the melt surface, and thusreducing the surface tension of melts.

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.

ДО ВИБОРУ РАЦІОНАЛЬНИХ СКЛАДІВ ШЛАКІВ ТА ШЛАКОУТВОРЮЮЧИХ СУМІШЕЙ ПРИ ВИРОБНИЦТВІ ЧАВУНУ ТА СТАЛІ

When solving the problem of choosing the rational chemical composition of metallurgical slags and mixtures, it is important to study their properties (viscosity, melting point, electrical conductivity, surface tension, etc.). According to scientific studies, the physicochemical properties of slag and aluminosilicate melts (including their viscosity and electrical conductivity) depend on the chemical composition of the system and temperature and reflect structural changes in the melt. The properties of slag melts are well explained by the ion theory according to which the viscosity is determined by the structure of polymer ions (SixOyz- anions), and the electrical conductivity by mobile ions by cations and/or anions (Ca2+, Mg2+, O2-, F-, and etc.). Increasing the temperature of the slag melt weakens the bonds of its structural particles (ions and/or their groups) is an important and necessary condition for improving the efficiency of heat and mass transfer processes in the system "metal-slag". The study of the relationship between viscosity and electrical conductivity and the development of criteria for assessing the structure of the slag melt, the establishment of a rational chemical composition for specific technological conditions of the smelting process of cast iron or steel is of great scientific and practical importance. The relationship between the viscosity and electrical conductivity of different oxide systems has been studied and the activation energies of viscosity (Eη) and electrical conductivity (Eχ) have been calculated. A criterion is proposed, the ratio n = Еη/Еχ, which varies in the regions: Еη>Еχ = n >1, Еη<Еχ = n <1 and Еη≈Еχ = n≈1, which indicate the presence of three structural regions: heterogeneous (Еη > Еχ = n> 1), homogeneous (Еη <Еχ = n <1) and equilibrium state of the melt (Еη≈Еχ = n≈1). The performed research has expanded the scientific ideas about the structure of slag melts, and the proposed criterion allows the choice of rational compositions of slags and mixtures in the production of iron and steel

The structure of metallic melts in eutectic alloys based on the Wulff cluster model: theory meets experiment.

In the present work, the Wulff cluster model, which has been proved to be successful for pure metals and homogeneous alloys, has been extended to eutectic alloys (Ag-Cu and Al-Si). In our model, the shapes of the clusters in melts were determined by the interfacial energy calculated by density functional theory (DFT) of different facet families based on Wulff theory. The cluster size was given by the pair distribution function (PDF) g(r), which was converted from experimental high-temperature X-ray diffraction (HTXRD). The simulated XRD curves in the high temperature region were in good agreement with the experimental results. For the Al-Si alloy, a deviation of the intensity and position of the second peak near the eutectic temperature was observed. The simulated results after structure and composition modification corresponded to the experimental ones. It indicates that the deviation is mainly related to the significant change of the cluster size during Si clusters' growth processes before nucleation. Differently, there are no such nucleation processes at temperatures near the eutectic point due to the relatively high nucleation barriers of the two components in the Ag-Cu alloy.

Intrinsic structure and dynamics of monolayer ring polymer melts.

We present the general structural and dynamical characteristics of flexible ring polymers in narrowly confined two-dimensional (2D) melt systems using atomistic molecular dynamics simulations. The results are further analyzed via direct comparison with the 2D linear analogue as well as the three-dimensional (3D) ring and linear melt systems. It is observed that dimensional restriction in 2D confined systems results in an increase in the intrinsic chain stiffness of the ring polymer. Fundamentally, this arises from an entropic penalty on polymer chains along with a reduction in the available chain configuration states in phase space and spatial choices for individual segmental walks. This feature in combination with the intermolecular interactions between neighboring ring chains leads to an overall extended interpenetrated chain configuration for the 2D ring melt. In contrast to the generally large differences in structural and dynamical properties between ring and linear polymers in 3D melt systems, relatively similar local-to-global chain structures and dynamics are observed for the 2D ring and linear melts. This is attributed to the general structural similarity (i.e., extended double-stranded chain conformations), the less effective role of the chain ends, and the absence of complex topological constraints between chains (i.e., interchain entanglement and mutual ring threading) in the 2D confined systems compared with the corresponding 3D bulk systems.

Electrical Conductivity, Liquidus Temperatures and Raman Spectra of YbCl3–KCl–Yb2O3 and YbCl3–KCl–NaCl–Yb2O3 Systems

The electrical conductivity of 0.507KCl–0.493YbCl3 and 0.5YbCl3–0.25KCl–0.25NaCl chloride melts with the ytterbium oxide (Yb2O3) additions ranging from 0 to 3.15 mol% was measured depending on both the temperature and concentration of Yb2O3. The liquidus temperatures of the studied systems containing from 0 to 3.35 mol.% Yb2O3 were determined by DSC method and the electrical conductivity measurements. The Yb2O3 additions increase the liquidus temperatures of the systems under study. The high-temperature Raman spectra of chloride (YbCl3–KCl–NaCl) and oxide-chloride (YbCl3–KCl–NaCl–Yb2O3) melts were recorded. In the oxide-chloride melt an additional band was detected in the region of 460 cm−1 corresponding to stretching-vibrations of the Yb–O bond in [OYb3Cln] oxychloride associates. There was no evidence of vibrational bands related to ytterbium oxide. Such changes in the Raman spectrum points to the dissociation of ytterbium oxide and modifications to the local structure of the chloride melt.

РОЗВИТОК АЛГОРИТМУ ОПИСУ МІЖАТОМНОЇ ВЗАЄМОДІЇ В РОЗПЛАВАХ НА ОСНОВІ ЗАЛІЗА З АТОМАМИ ВПРОВАДЖЕННЯ

The aim of this work is to develop an algorithm for calculating the parameters of interatomic interaction in melts in the presence of introduction atoms. Along with high-cost research methods, which make it possible to obtain temperature and concentration dependences of the structure-sensitive properties of melts (density, viscosity, electrical resistance, etc.), and with diffraction methods of research (X-ray, electron and neutronography using synchrotron or magnetic-brake, X-ray radiation) theoretical research (using computer modeling methods) is less expensive and complements other research methods. Conducting a short analysis of aspects of modern quasicrystallinic theories of the structure of metallic melts. Since the proposition that liquid metal materials have a hereditary structure of their crystalline state, an analysis of the concepts of interstitial atoms (hydrogen, oxygen, nitrogen, boron, carbon) for iron-based melts is made. The proposed structures of unit cells for hydrides, oxides, nitrides, borides and cementite of iron-containing melts. The existing methodology was developed by the employees of the ISI NASU on the basis of the concept of directed chemical bonding, which assumes the structure of the structure of metal melts with the composition of various atoms by the type of substitution. The internuclear distance and other integral and portion parameters are calculated using the system of equations for pair interactions of different and identical atoms in the unit cell of the structure in the first coordination (short-range order) and second (long-range order of their arrangement) spheres. The need arose to introduce an additional (third) coordination sphere of interaction for ordering interstitial atoms in iron-based melts. A method of theoretical assessment has been developed and the expediency of taking into account the differences from the existing concepts (according to the theory of Ye.V. Prikhodko) on the structure formation of metal melts with intrusion elements for further modeling of alloying and microalloying processes is shown. An algorithm for recalculating the parameters of interatomic interaction is proposed. The expediency is confirmed by an increase in the accuracy of the ratio of calculated and experimental data on the mechanical properties of steels for welding purposes.

On the importance of mathematical calculations in the study of structure characteristics and the physical and mechanical properties of 30XGSA steel, smelted on a different charge

The article considers the influence of the quality of the initial charge on the structure and physical and mechanical properties of the structural medium-alloy steel 30KhGSA. It was found that the 30KhGSA steel (smelters No. 3-4) cast in cast-iron molds (ingot weight 2.6 t) has a significant chemical heterogeneity and liquation in carbon and the main alloying elements (Cr and Mn), and in the melting on the semi-product of the boiling slag layer, the liquation is more pronounced. Starting from the tempering temperature of 500∘C, the structure of both melts (the fluidized slag layer and the ordinary metallized charge) becomes more uniform and the mechanical properties are aligned. Microstructural studies have established that with an increase in the annealing temperature at a single exposure, the chemical inhomogeneity decreases, but not significantly. Starting from 1000 ∘C, when the annealing temperature increases, the steel grain diversity and the growth of austenitic grains appear, especially in the melting on the semi-product of the boiling slag layer. Different grain sizes adversely affect the mechanical properties of steel: grain enlargement reduces the resistance of steel to brittle fracture, worsens the service characteristics of the metal. Elimination of chemical and structural heterogeneity can be achieved by conducting a ho-mogenizing annealing (annealing at 950 ∘C for 8 hours). An increase in the annealing temperature leads to an intensive grain growth, especially in steel smelted on the original charge. It is shown that 30XGSA steel, which is melted on a semi-product of a boiling slag layer, in an improved state with equal hardness and strength characteristics, has increased plastic properties and especially impact strength in comparison with steel on a conventional metallized charge. Apparently, this should also determine the higher operating characteristics of steel obtained with the use of pure primary charge.

ON THE STRUCTURE OF EUTECTIC SYSTEMS MELTINGS: THEORETICAL ASPECTS OF MODEL REPRESENTATION OF THE LIQUID STRUCTURE DESCRIPTION

In the offered article theoretical researches of eutectic systems are systematized, connection of results of these researches with model representation of the description of structure of a liquid for the purpose of the further practical realization is allocated. This study is relevant because there is no generalized and systematic information on the study of the structure of melts of eutectic systems. On the one hand, this is due to certain contradictions in some studies. However, the main problem is the ambiguity and inconsistency of interpretation of the results of studies of the structure of melts. The authors note that in solving problems related to the nature of the liquid state, of particular interest is the study of the structure of two-component melts, which form in the solid state phase equilibrium diagrams of the eutectic type. The term eutectic means "most fusible" and is used to describe an isothermal reversible reaction in which a liquid decomposes into two or more solid phases during cooling. It is proposed to make judgments about the structure of metal melts of eutectic systems according to the type of liquidus line of the phase equilibrium diagram. To do this, all eutectic systems are divided into: systems with a smooth liquidus line without an inflection point in either the pre-eutectic or the supereutectic region (NI); systems with an inflection point on one branch of the liquidus line; systems with an inflection point on both branches of the liquidus line; systems with a eutectic point near the zero concentration of one of the components and an inflection point on the liquidus line (0% SI). Based on the generalized and systematized results of theoretical and experimental studies, it is proved that eutectic systems are polygenic systems that have a wide range of interactions between particles and, accordingly, have a short-range structure. This information can make it possible to unambiguously interpret the results of diffraction studies and physicochemical analysis data to create a model representation of the description of the structure of the liquid (melt).

Boron coordination and B/Si ordering controls over equilibrium boron isotope fractionation among minerals, melts, and fluids

The high mobility of boron during fluid-rock interaction makes it an effective tracer for the sources of magmatic and metamorphic fluids, as recorded in minerals such as tourmaline and muscovite. Although advances have been made in quantifying the fractionation of boron isotopes among different phases, boron isotope fractionation in complex silicate melts remains poorly understood. Here, we propose appropriate models for the BO3 and BO4 units in silicate melts covering a wide range of chemical compositions and boron coordination structures in silicate magmas, and report the results of a theoretical investigation of boron isotope fractionation among silicate melt, minerals and fluids using a first principles theoretical approach. A comparison of measured and calculated α factors in mineral-melt and fluid-melt systems shows good agreement, suggesting the applicability of a simplified treatment of boron coordination structures in silicate melt. The results of this study show that the proportion of trigonal/tetrahedral coordinated boron and the B/Si ordering in silicate tetrahedral layers control the boron isotope fractionation among different phases, and that the effect of chemical composition is minor (less than 2‰ at 600 K). The temperature-dependent boron isotope fractionations are described as 1000lnαmica-basic fluid = 0.8–2.4 × (1000/T) - 0.8 × (1000/T)2, 1000lnαmica-acidic fluid = 7.0–14.0 × (1000/T) - 1.2 × (1000/T)2 and 1000lnαmica-tur = 1.9–5.4 × (1000/T) -3.4 × (1000/T)2 (T is temperature in Kelvins). At magmatic temperatures, ∆11B values between mineral/fluid and melt also vary with the proportion of the BO4 unit in the melt. This study underpins the applicability of the white mica-tourmaline geothermometers and boron isotopes for fluid source identification, and also offers an explanation of boron isotope fractionation in systems that contain complex silicate melts.