Oxide-fluoride Melts Research Articles

Influence of alloying parameters on the structure and properties of AK-6 aluminium alloy

This work is devoted to the study of the effect of zirconium addition and crystallization rate on the structure and properties of industrial aluminium alloys. Experimental alloying of the AK6 alloy was performed. The required amount of Al-Zr-10 alloy (10 wt. % Zr) was added at a temperature of 900 °C until the zirconium content in the target alloy reached 0.1; 0.3; 0.5 wt. %. According to the results of scanning electron microscopy and X-ray diffraction analysis, the main proportion of zirconium in the initial alloy was represented by intermetallic compounds of predominantly Al3Zr composition and sizes from 5 to 50 μm. Values of microhardness measured after direct alloying of high-purity aluminum with zirconium by the electrolysis of oxide-fluoride melts demonstrate that at a zirconium content of 0.4 wt. %, the microhardness of the alloy increases by 1.5 times and continues to grow as the zirconium content increases. Based on the results of structural analysis, it was found that the average grain size of the aluminium alloy decreased by 4–5 times even at a Zr content of 0.1 wt. %. When studying the properties of the obtained samples, it was found that the addition of zirconium to the AK6 alloy does not affect its hardness, in contrast to high-purity aluminium, which is presumably due to the more pronounced influence of other components and the absence of an additive effect of zirconium on the alloy hardness. Accelerated cooling of the alloy to 103 K/s without zirconium additives has a similar effect of grain reduction, and also increases the microhardness of the alloy by 10 HB according to Brinell. A study of the combined effect of zirconium addition and accelerated cooling shows the additive effect of grinding by more than 25 times, while individual grains do not exceed 5 microns in size. The absence of intermetallic compounds in the obtained samples of the AK6 alloy after modification with the Al-Zr alloy indicates that the phase composition of the initial Al-Zr alloy does not affect the properties of the target alloys.

Comparative analysis of modern methods of production of Al – Zr ligatures

A brief overview of modern industrial and experimental methods for the synthesis of aluminozirconium ligatures is performed. The basic regularities of the proceeding processes, and also properties of the obtained ligatures are considered, technical and economic indicators and prospects of development of the considered technologies are estimated. The comparative estimation of key parameters of the most promising technologies for industrial application is carried out, the influence of temperature, a mode of synthesis and a kind of initial raw materials on profitability of the process is estimated. Aluminothermic and electrolytic methods of ligature synthesis are considered in more detail, the views of other authors on the kinetics of ongoing processes are taken into account, and an overview of the influence of electrolyte composition and electrolysis mode on the structure and properties of produced alloys is presented. It has been shown that, depending on the method, in a wide temperature range (80 – 1000 oC), Al – Zr master alloy with a zirconium content up to 57 wt.% can be obtained. However, all existing methods for the production of Al – Zr master alloys have significant drawbacks, which lead to the relatively high cost of the master alloys, the presence of hazard waste and low production efficiency. It is concluded that along with the current methods of direct fusion of metals and aluminothermic synthesis, it is promising to obtain ligatures by electrolysis of oxide-fluoride melts KF – NaF – AlF3 using zirconium oxide as the main metalcontaining raw material. The results of experimental testing of a new method for obtaining Al – Zr master alloys via electrolysis of oxide-fluoride melts are presented. It has been established that the developed technology makes it possible to maximize the extraction of zirconium from the oxide, to continuously obtain master alloys with a high zirconium content, excluding the accumulation of unclaimed waste. The study was performed with the financial support of the Russian Foundation for Basic Research within the research project No. 19-33-90144.

MOLECULAR DYNAMIC SIMULATION OF THE MELT OF OXIDE-FLUORIDE INDUSTRIAL SLAG-FORMING MIXTURE

The paper discusses the results of molecular dynamic simulation of a melt of the multicomponent oxide-fluoride system CaO – SiO2 – – Al2O3 – MgO – Na2O – K2O – CaF2 – FeO, corresponding to composition of industrial slag-forming mixture (SFM) used in steel casting for slag targeting in the mold of a continuous casting machine (in wt %: 35.35 % SiO2 , 30.79 % CaO, 8.58 % Al2O3 , 1.26 % MgO, 13.73 % CaF2 , 7.57 % Na2O, 0.88 % K2O, and 1.82 % FeO). These concentrations were converted to mole fractions, and the number of ions was calculated for each of the components in the model. An eightcomponent oxide-fluoride melt containing 2003 ions in the main cube with a side length of 31.01 Å was simulated under periodic boundary conditions at an experimentally determined solidification onset temperature of 1257 K at constant volume. Coulomb interaction was taken into account by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7,608·10–14 s is the internal unit of time. The melt density was taken to be 3.04 g/cm3 based on our experimental data. The interparticle interaction potentials were chosen in the Born–Mayer form. Based on the simulation results, the structure of subcrystalline groups of atoms present in the melt at the temperature of solidification onset was determined. A discussion of the simulation results and their comparison with the literature data was held. It is shown that the computer model allows one to obtain a fairly realistic picture of atomic structure of the slag melt, indicating that the main structural component of all silicate systems is silicon-oxygen tetrahedron. Tetrahedra in silicates are either in the form of structural units isolated from each other, or, connecting together through peaks, they form complex anions. It is consistent with the theory of slag melts. Molecular-dynamic simulation allows one to obtain adequate information on structure of the melt of a certain chemical composition.

Molecular–Dynamic Simulation of the Melt of an Industrial Oxide–Fluoride Mold Flux

Abstract—The paper discusses the results of molecular–dynamic simulation of a melt of the multicomponent oxide–fluoride CaO–SiO2–Al2O3–MgO–Na2O–K2O–CaF2–FeO system that corresponds to the composition of an industrial mold flux (MF) used in steel casting for slag targeting in the mold of a continuous casting machine as: (wt %) 35.35% SiO2, 30.79% CaO, 8.58% Al2O3, 1.26% MgO, 13.73% CaF2, 7.57% Na2O, 0.88% K2O, and 1.82% FeO. These concentrations were converted to mole fractions and the number of ions was calculated for each of the components in the model. An eight-component oxide–fluoride melt containing 2003 ions in the main cube with an edge length of 31.01 A was simulated under periodic boundary conditions at an experimentally determined solidification onset temperature of 1257 K at a constant volume. The Coulomb interaction was considered by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7.608 × 10–14 s is the internal unit of time. The melt density was taken as 3.04 g/cm3 based on experimental data obtained by the authors. The interparticle interaction potentials were chosen in the Born–Mayer form. Based on the simulation results, the structure of subcrystalline groups of atoms present in the melt at the temperature of solidification onset was determined. A discussion of the simulation results and their comparison with the literature data was held. It is shown that the computer model allows one to obtain a fairly realistic picture of the atomic structure of the slag melt, which indicates that the basic structural component of all silicate systems is silicon–oxygen tetrahedron. Tetrahedra in silicates either are in the form of structural units isolated from each other or, being connected together through vertices, form complex anions, which is consistent with the theory of slag melts. Molecular–dynamic simulation allows one to obtain adequate information on the structure of a melt of a certain chemical composition.

Mathematic simulation of atomic structure of multicomponent oxide-fluoride melt for continuous casting machines

Determination of relation between oxides melts properties, based on silicates and calcium alum-silicates and magnesium and their chemical composition and structure is an important condition to provide a rational slag mode in a continuous casting machines mold. A mathematical simulation of slag melts and casting powders accomplished. The oxide-fluoride system was chosen for the simulation, for which the structure after solidification was determined by experiment. Results of molecular-dynamic simulation of CaO–SiO2–Al2O3–MgO–Na2O–K2O–CaF2–FeO system, correspondent to industrial casting powders composition, used during steel casting for slag formation in a CCM mold (35.35 % SiO2; 30.79 % CaO; 8.58 % Al2O3; 1.26 % MgO; 13.73 % CaF2; 7.57 % Na2O; 0.88 % K2O; 1.82 % FeO). Taking into account the concentration, a re-calculation was accomplished to mole shares and correspondent number of ions in the model for each component calculated. Simulation of the 8-component oxide-fluoride melt with 2003 ions size in the main cube (a side length of 31.01 Å) was accomplished at the experimentally determined temperature of solidification onset (1257 K) under periodic boundary conditions and fixed volume. The Coulomb interaction was taken into account by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7,608×10–14 sec is the internal unit of time. The melt density was taken as 3.04 g/cm3 based on the experimental data. The inter-particle interaction potentials were chosen in the Born–Mayer form. According to the simulation results, the structure of sub-crystalline groups of atoms present in the melt at the temperature of the onset of solidification was determined. A discussion of the simulation results and their comparison with the literature data presented.

Computer simulation of the structure of multicomponent oxide-fluoride melts

Based on the experimental data on the density, the molecular dynamics simulation of multicomponent oxidefluoride melts was first carried out in the ionic bond model approximation: SiO2-CaO-Al2O3-MgO-CaF2- Na2O-K2O-FeO. The results are discussed and compared with the experimental and calculated data. An increased diffusion mobility of fluorine ions as well as ions of alkali metals in comparison with other elements has been revealed. It is shown that the computer model allows obtaining adequate information about the structure of the melt of a certain chemical composition, as well as a fairly realistic picture of the atomic structure of the slag melt, which, according to the main parameters, agrees well with the data of the diffraction experiment.

Computer Simulation of the Structure of Multicomponent Oxide–Fluoride Melts

Computer Simulation of the Structure of Multicomponent Oxide–Fluoride Melts

Extraction of Scandium and Zirconium from Their Oxides during the Electrolysis of Oxide–Fluoride Melts

The main features of scandium and zirconium extraction from their oxides to aluminum during the aluminothermic and electrolytic preparation of Al–Sc and Al–Zr alloys and master alloys in the KF–AlF3, NaF–AlF3, and KF–NaF–AlF3 oxide–fluoride melts with Sc2O3 and ZrO2 additives are studied. The influence of the melt composition and temperature, the synthesis time, the contents of oxides Sc2O3 and ZrO2 in the melts, the mechanical stirring of aluminum, and the cathodic current density on the contents of scandium and zirconium in aluminum and on their extraction from the oxides is determined. The average values of scandium and zirconium extraction are 20–75 and 40–100%, respectively, depending on the synthesis parameters. The electrolytic decomposition of the oxides in the KF–AlF3, NaF–AlF3, and KF–NaF–AlF3 melts results in the enhancement of scandium and zirconium extraction to aluminum. The parameters of the preparation of Al–Sc and Al–Zr alloys and master alloys with the scandium content to 10 wt % and zirconium content to 15 wt % during the electrolysis of oxide–fluoride melts are chosen as a result of the results obtained.

Surface tension of a titanium-containing oxide–fluoride melt calculated by the polymer theory

The surface tension of an aluminum–calcium oxide–fluoride melt is calculated using the polymer theory. It is shown that, at 15 mol % titanium oxide in the melt, aluminum–fluorine–oxygen complexes mainly form. When the titanium oxide content increases further, these complexes disappear and are partly replaced by titanium–oxygen TiO 4 4- and Ti2O 7 6- anions and titanium–fluorine–oxygen groups.

Evaluating Composition Dependence in Surface Tension of Si–Ca–Na–O–F Reciprocal Oxide–fluoride Melts

Evaluating Composition Dependence in Surface Tension of Si–Ca–Na–O–F Reciprocal Oxide–fluoride Melts

THE EFFECT OF TITANIUM AND MOLYBDENUM OXIDES ON THE SURFACE AND VOLUME PROPERTIES OF OXIDE-FLUORIDE SLAGS

The effect of titanium and molybdenum oxides on the surface tension and the density of the Al2O3–CaO–CaF2 melt has been investigated. The addition of 4–25 mol.% TiO2 and 2,8 mol.% MoO3 to the oxide-fluoride melt at temperatures of 1773–1923 K results to surface tension reduction and density increase. Upon adding titanium and molybdenum, the investigated oxide-fluoride slags show complexing properties; the dimensions and morphology of the structural units are determined.

Physical-Chemical Properties of Potassium Cryolite-Based Melts Containing KBF4

Recent developments in the field of low-temperature aluminum electrolysis utilizing oxygen-evolving inert anodes prove the efficiency of potassium cryolite-based electrolytes. Such electrolytes give an opportunity to perform electrolysis at temperature below 800 °C. The potassium cryolite-based electrolytes can be used as prospective media for other electrochemical and chemical technological processes including aluminum alloys production. However, the introduction to the electrolytic bath the metal-containing additives along with alumina can result in electrolysis violation. It is a consequence of significant change in electrolyte properties with varied composition. In present work the KBF4impact on the physical-chemical properties of the potassium cryolite-based melts was studied.Liquidus temperature, electrical conductivity, density, alumina solubility in the KF-AlF3 and KF-NaF(15.9 mol%)-AlF3 molten mixtures containing KBF4 were determined. Cryolite ratio (CR), the ratio between molar concentrations of the alkali metal fluoride and aluminum fluoride (CR=NMF/NAlF3), was varied from 1.3 to 1.5. It should be mentioned that the cryolite ratio for the mixed KF-NaF-AlF3 cryolite melts was calculated as CR=(NKF+NNaF)/NAlF3. Elemental composition of the molten mixtures being studied was controlled by ICP analysis and X-ray fluorescence spectroscopy on XRF-1800 (Shimadzu).The liquidus temperature of the cryolite melts was measured by the specially developed thermal analysis technique. The data obtained in the KF-AlF3-KBF4 and KF-NaF(15.9 mol%)-AlF3-KBF4 systems showed that the liquidus temperature rises with the KBF4 content. It should be noted that the NaF, LiF, and CaF2, potential additives to the electrolyte for low-temperature electrolysis, being added to the KF-AlF3 melts with low CR, impact the liquidus temperature the same manner as KBF4.The alumina additions to the potassium cryolite-based melts decrease the liquidus temperature as it is shown in Fig.1. The quasi-binary “cryolite mixture”– alumina phase diagrams are simple eutectics. The KBF4 presence in the KF-NaF-AlF3-Al2O3 electrolytes shifts the eutectic point to the right and increases the alumina solubility in these melts. The eutectic points were found equal to 759 and 761°C at the Al2O3 content 4 and 5 mol%, respectively, in the [KF-NaF(15.9mol%)-AlF3+KBF4 (3mol%)]-Al2O3 and [KF-NaF(15.9 mol%)-AlF3+KBF4(5 mol%)]-Al2O3 mixtures with CR=1.3. The Al2O3addition of 6 mol% to the both electrolytes results in significant rise of the liquidus. The bend point on the cooling curves corresponding to the temperature of primary crystallization was not detected because the beginning temperature of the cooling process in these tests was below the liquidus. The presence of not dissolved deposit at the bottom of crucible at 850 °C was also confirmed by visual observation.The original technique to study the electrical conductivity of aggressive fluoride and oxide-fluoride melts was developed. It consists in combination of two types cells: capillary (BN) and with parallel electrodes (Mo). The resistivity of electrolyte was measured by means of impedancemeter (Zahner electrik IM6E) in a frequency range from 100 Hz to 1 MHz using a signal with amplitude 5 mV/s. The electrical conductivity of the potassium and potassium-sodium cryolites was measured in the capillary-type cell whereas the electrical conductivity of electrolytes with KBF4 and Al2O3additions was studied in the cell with parallel electrodes. The temperature dependence of a cell constant was taken into account that made the electrical conductivity measurements more accurate in a wide temperature range.The density of cryolite melts was measured using the Archimedean method. A platinum sphere suspended with platinum wire and attached to an electronic balance unit (Mettler AT20) was immersed into the electrolyte located in the glassy carbon crucible. The measurements were performed in the temperature range 700-800 °C. The temperature dependence of the Pt sphere volume was considered and determined in the calibration test with FLiNaK (eutectic). The density of the KF-AlF3-KBF4 melts decreases with increasing the KBF4 content. So, the addition of the KBF4 3 mol% reduces the density of the molten mixture on about 5%.

Effect of zirconium and molybdenum oxides on the surface and volume properties of an aluminocalcium oxide-fluoride melt

The effect of additions of zirconium and molybdenum oxides on the surface tension and density of oxide-fluoride slags is studied by the method of the maximum pressure in a gas bubble. The obtained experimental and calculated results reveal a complex-forming character of the behavior of zirconium and molybdenum in oxide-fluoride slag melts, and they are used to estimate the sizes of the structural units present in the surface layer of the slags.

Effect of titanium and molybdenum oxides on viscosity and electrical conductivity of oxide-fluoride slags

The effect of additives of titanium and molybdenum oxides on the viscosity and electrical conductivity of the Al2O3-CaO-CaF2 oxide-fluoride slag melts at 1750–1950 K is investigated by vibration viscosimetry and the ac bridge method. Crystallization intervals are established depending on the variation in the TiO2 and MoO3 concentrations in the melts from 0 to 25%, and it is revealed that the majority charge carriers are calcium and fluorine ions. These data indicate the complex-forming character of the behavior of Ti and Mo in aluminum-calcium oxide-fluoride melts.

Effect of titanium dioxide on the surface tension and density of an aluminocalcium oxide-fluoride melt

The effect of titanium oxides on the surface tension and density of an Al2O3-CaO-CaF2 melt is studied. At 1773–1923 K, an addition of 4–25 mol % TiO2 to an oxide-fluoride melt decreases the surface tension and increases the density. The complexation properties of titanium in the oxide-fluoride slags are revealed, and the size and character of the structural units are determined.

Electrochemical reduction of niobium from oxide-fluoride melts upon electroslag melting

Some regularities of electrochemical reduction of niobium from oxide-fluoride melts upon electroslag melting (ESM) have been established for various electrical regimes. It has been found that the use of an asymmetric electric current during ESM substantially improves the technological parameters of the electrolysis process. Based on the experimental data obtained, a special program has been developed for correcting the electrical regime of melting depending on the Nb2O5 content in the oxide-fluoride melt, which permits one to obtain a desired niobium concentration in the metal ingot.

Electrical conductivity of niobium-containing oxide-fluoride melts

The effect of Nb2O5 on electrical conductivity of metals based on CaF2 and CaF2-30% Al2O3 at T = 1500–1900 K in an oxidizing atmosphere is investigated using an ac bridge at the frequency 5 kHz. It is found that, as the Nb2O5 concentration increases from 0 to 25%, the electrical conductivity of the melts decreases, while the activation energy of electrical conductivity increases monotonically. The data obtained agree with viscosity investigations and indicate that niobium is the complexing agent in oxide-fluoride melts.

Viscosity of niobium-containing oxide-fluoride melts

Influence of Nb2O5 on viscosity of the CaF2-based and CaF2-30% Al2O3-based melts was investigated using a vibration viscosimetry method in the range 1523–1873 K. It is found that viscosity of the melts rise and the crystallization range shifts to lower temperatures as the Nb2O5 concentration increases from 0 to 25 wt %. The activation energy of viscous flow increases from 34 to 110 kJ mol−1 and from 56 to 148 kJ mol−1 for the CaF2-based and CaF2-30% Al2O3-based melts, respectively. The obtained data indicate the complexing behavior of niobium in the oxide-fluoride melts.

Effect of niobium-containing additions on the viscosity and electrical conductivity of oxide-fluoride melts

An oscillatory viscometer and ac 5-kHz bridge are used to measure the viscosity and electrical conductivity (at 1450–1600°C) of two types of slag melts based on CaF2(ANF-1P flux) and on the CaF2-30% Al2O3 system (ANF-6 flux) with additions (to 35%) of one of the following three types of niobium-containing compounds: Nb2O5 (extrapure grade), Nb2O5 (commercial purity), and a niobium concentrate (about 70% Nb2O5). An addition of the niobium-containing compounds to the fluxes is found to increase the viscosity, to increase the solidification range, and to decrease the electrical conductivities of the melts. In this case, the activation energies of viscous flow (34–148 kJ/mol) and conduction (22–100 kJ/mol) increase monotonically, which indicates polymerization of the melts.