Liquid Magnesium Research Articles

Numerical simulation of heat transfer in the cooling channel of a titanium apparatus

Numerical modeling of thermophysical processes in the air cooling channel of the titanium sponge reduction reactor is performed. The cooling channel is an area bounded by a retort filled with liquid magnesium and a wall on which heating elements are mounted. Air flows inside the channel, cooling the retort. A mathematical model is constructed based on unsteady Navier-Stokes equations in axisymmetric formulation using a k −ω SST turbulence model. The model takes into account the radiation heat transfer between the retort and reactor walls. Two variants of thermal boundary conditions are considered. The temperature conditions of the retort wall have been calculated, and the profiles of the heat transfer coefficient along the retort wall for a wide interval of airflow rates have been obtained. It is shown that temperature distributions along the retort are not uniform and strongly depend both on external boundary conditions and on cooling intensity. Heat transfer coefficient distributions from its outer wall for different retort heating conditions are plotted, and an empirical formula for calculating the profile of this coefficient is proposed.

A model to predict the recovery of cobalt and copper from liquid magnesium distillation

A model to depict that it is possible to separate solid cobalt and copper from liquid Mg-Co-Cu mixtures is presented. The model aims to demonstrate how the application of solution thermodynamics concepts can help in depicting real processes.

Direct Strip Casting of Magnesium

AbstractA new interest in magnesium alloys has arisen since lightweight constructions have become more and more attractive. Products that are currently available are mostly cast, forged, and extruded. A cost-effective production of sheet metals will render new perspectives in the design of lightweight constructions [1, 2].The development of new casting technologies like thin slab casting or strip casting with an in-line rolling process is expected to result in a shorter processing time featuring a high potential of saving energy, time, and cost [3, 4, 5, 6, 7, 8, 9]. Particular attention is paid to the casting process parameters such as casting speed and solidification speed. This article deals with some aspects of a magnesium-adapted singlebelt caster. Results of casting experiments and material examination are shown as well as some advices given concerning safety and handling of liquid magnesium [10].

Численное моделирование конвекции жидкого магния в аппарате восстановления титана с учетом эффективных граничных условий

We investigate the numerical problem of conjugate heat exchange between liquid magnesium, a steel retort, and the air-cooling zone of the titanium sponge reduction reactor furnace at the initial stages of production. The uneven distribution of heat fluxes on the side surface of the retort significantly affects the formation of convective turbulent flow inside the apparatus. The accurate consideration of thermal boundary conditions will make it possible to adequately solve the problem of heat and mass transfer in the reactor without using model representations of heat flows on the boundaries of the retort. The problem was solved in the axisymmetric nonstationary formulation using the k-ω SST turbulence model. In the numerical simulation, two conceptual solutions of the problem were implemented. The first one involves the end-to-end calculation in the framework of the coupled heat and mass transfer problem, with the calculations performed in all parts of the titanium reduction apparatus and thermal boundary conditions set on its outer boundaries. The second model relies on an effective thermal boundary condition that is applied to the outer boundary of the retort and excludes calculations in the cooling channel when investigating magnesium convection. The first model, due to its greater completeness, is more accurate, but requires considerable computational resources and time. The model with an effective thermal boundary condition, provided that the coefficients in it are selected appropriately, gives results qualitatively and quantitatively close to those obtained through end-to-end calculations. At the same time, such a model is more economical. The paper evaluates the possibility of applying an effective boundary condition. Convective flows of molten magnesium in the retort under different modes of blowing and heating have been studied. The influence of the radiation part of the heat flow on the formation of convective currents is shown.

Influence of B4C on mechanical properties of AZ91 magnesium matrix composites

In this research, the impact of Boron Carbide on AZ91 Magnesium alloy composite mechanical and tribological behaviour. AZ91 Magnesium Alloy Particulate-reinforced composites were made by mounting the wetting problem between B4C and liquid magnesium metal. K2TiF6 was added as a flux. Subsequently, T6 thermal treatment was conducted for the magnesium B4C composites thus produced. The magnesium alloy matrix AZ91 composite was tested for hardness, compression and flexural strength. The results of testing showed a greater hardness of the composites compared to the base alloy due to the increased ceramic phase.

Influence of Dysprosium Compounds on the Extraction Behavior of Dy from Nd-Dy-Fe-B Magnet Using Liquid Magnesium

During the liquid metal extraction reaction between a Nd-Dy-Fe-B magnet and liquid Mg, Nd rapidly diffuses out of the magnet, whereas Dy is not extracted due to the reaction with the matrix and the formation of Dy2Fe17 phase. In addition, theDy2O3 phase exists at the grain boundaries. Until now, only the effect of the Dy2O3 phase on the extraction of Dy has been reported. In this study, the effect of the Dy2Fe17 phase on the extraction of Dy from the Nd-Dy-Fe-B magnet was investigated in liquid Mg. The formation of the Dy2Fe17 phase during the reaction between Mg and matrix (RE2Fe14B) was first examined using a thermodynamical approach and confirmed by microstructural analysis. It was observed that Dy extraction was dominated by Dy2Fe17 phase decomposition from 3 h to 24 h, followed by Dy2O3 phase dominant reaction with Mg. Comparing the activities of the Dy2Fe17 phase and the Dy2O3 phase, the reaction of Dy2Fe17 is dominant, as compared to the Dy2O3 phase. Finally, at 48 h, the high Dy extraction percentage of 93% was achieved. As a result, in was concluded that the Dy2Fe17 phase acts as an obstacle in the extraction of Dy. In the future, if research to control the Dy2Fe17 phase proceeds, it will be of great importance to advance the recycling of Dy.

Structure Analysis of Amorphous and Liquid Magnesium Silicate

We use the Oganov potentials and period boundary condition to perform molecular dynamics simulation of amorphous and liquid Mg2SiO4 systems under pressures 0 GPa and 40 GPa. We clarify structure of amorphous Mg2SiO4 at 0 and 40 GPa and compared with the one of Mg2SiO4 at liquid state. Especially, the origin of sub-peaks in radial distribution function of O-O, Si-Si and Mg-Mg pairs is explained clearly. The change of radial distribution functions, coordination number and the number of all types of bonds including the corner-, edge- and face-sharing bonds is also discussed in detail in this paper.

Solubilities of Nickel, Iron, and Chromium in Liquid Magnesium in the Presence of Austenitic Stainless Steel

Steel containers and instruments are used to hold and transport Mg melts. Thus, quantitative analysis of the dissolution of metallic elements from the steel materials into the liquid Mg is important for controlling the impurities in processes such as Mg alloy production and Ti smelting. When austenitic stainless steels containing Cr and Ni come in contact with a Mg or Mg alloy melt, a large amount of Ni and limited amounts of Fe and Cr dissolve into the melt. In this study, the composition of a Mg-Ni-based melt in equilibrium with SUS316 was investigated to determine the maximum amounts of impurities dissolved from SUS316 into the liquid Mg. Mg-Ni melts of different compositions were held in a closed crucible of SUS316 at 1073 K (800 °C) to 1273 K (1000 °C), and the compositions of the inner wall of the crucible and the Mg-Ni alloy were evaluated after quenching. Subsequently, the relationships between the solubility limit of element i (i: Ni, Fe, and Cr) in liquid Mg with the coexistence of SUS316, $$ C_{{{\text{sol}},{i}}}^{*} $$ (mass pct), and the temperature, T (K), were determined: $$ \log \,(C_{{{\text{sol}},{\text{Ni}}}}^{*} ) = {{ - 1.40 \times 10^{3} }}/{T} + 2.57 \, ( \pm \,0.12), $$ $$ \log \,(C_{{{\text{sol}},{\text{Fe}}}}^{*} ) = - {{5.20 \times 10^{3} }}/{T} + 3.93 \, ( \pm \,0.16),\;{\text{and}} $$ $$ \log \,(C_{{{\text{sol}},{\text{Cr}}}}^{*} ) = - {{5.96 \times 10^{3} }}/{T} + 3.80 \, ( \pm \,0.05). $$ These solubility limits were compared with those estimated based on the available thermodynamic data for the SUS316 and Mg-i binary systems. The validity of the obtained data and the reliability of the previously reported thermodynamic data were also discussed.

Influence of Complexing Additives on the Reversible Deposition/Dissolution of Magnesium in an Ionic Liquid

AbstractAiming at a fundamental understanding of the synergistic effects of different additives on the electrochemical Mg deposition/dissolution in an ionic liquid, we have systematically investigated these processes in a combined electrochemical and theoretical study, using 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMP‐TFSI) as the solvent and a cyclic ether (18‐crown‐6) and magnesium borohydride as additives. Both crown ether and BH4− improve Mg deposition, its reversibility, and cycling stability. The combined presence of both additives and their concentration relative to that of Mg2+ are decisive for more facile and reversible Mg deposition/dissolution. These results and those of quantum chemical calculations indicate that 18‐crown‐6 can partly displace TFSI− from its direct coordination to Mg2+. Furthermore, the interaction between Mg2+ and directly coordinated TFSI− is weakened by coordination with 18‐crown‐6, preventing its Mg+‐induced decomposition. Finally, Mg deposition is improved by the weaker overall coordination upon Mg2+ reduction to Mg+.

Моделирование тепловых режимов в канале воздушного охлаждения аппарата восстановления титана

Numerical modeling of thermophysical processes in the air cooling channel of titanium sponge reduction apparatus is performed. The cooling channel is an area bounded by a retort filled with liquid magnesium and the apparatus wall, on which heating elements are mounted. Air flows inside the channel, cooling the retort. A mathematical model is constructed based on unsteady Navier-Stokes equations in axisymmetric formulation using a k-ω SST turbulence model. The model takes into account the radiation heat transfer between the retort and reactor walls. Four variants of thermal boundary conditions are considered. The aim of this work is to create a mathematical model of conjugate heat transfer in an air channel. Based on this model, the temperature conditions of the retort wall are calculated and the profiles of the heat transfer coefficient along the retort wall for a wide interval of air flow rates are obtained. It is shown that temperature distributions along the retort are heterogeneous and strongly depend both on external boundary conditions and on the cooling intensity. Heat transfer coefficient distributions from its outer wall for different retort heating conditions are plotted and an empirical formula for calculating the profile of this coefficient is proposed.

Structural and calorimetric studies of magnesium-rich Mg-Pd alloys

Despite the fact that the affinities of both palladium and magnesium with hydrogen have been studied for many years, information about magnesium-palladium alloys is still incomplete. Although palladium is an extremely expensive metal and magnesium palladium alloys will likely never applied as solid-state hydrogen storage materials, the interaction of these alloys with hydrogen may be useful for broadening knowledge or finding applications as hydrogen splitters, catalysts, and hydrogen sensors. In this work, two types of calorimetric techniques were applied to measure the thermodynamic properties of magnesium-rich alloys from the Mg-Pd system (containing 97.7; 85.4; 80.6; 79.9; 72.3; 70.7; 64.5 at% of Mg respectively). The solution calorimetric method was used to determine the heat of solution of liquid magnesium and palladium in liquid tin. Additionally, the standard enthalpies of formation of six alloys corresponding to the intermetallic phases of the Mg-rich region were measured. These alloys were prepared from pure Mg and Pd, which were melted in a glove box filled with high purity argon, with a very low concentration of impurities. All the obtained alloys were structurally analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDS) methods. Moreover, DSC studies were used to determine the transformation temperatures in the Mg-rich region. The values of the standard formation enthalpy of the studied alloys were determined to be −27.3 ± 0.8 kJ/mol at., −33.4 ± 0.9 kJ/mol at., −35.2 ± 1.4 kJ/mol at., −44.2 ± 0.9 kJ/mol at., −46.0 ± 0.7 kJ/mol at., and −54.3 ± 2.3 kJ/mol at. These values were compared with the data calculated using the Miedema model, as well as with existing literature data for the Mg6Pd and Mg5Pd2 phases.

Modeling of Liquid Magnesium Turbulent Convection in a Titanium Reduction Apparatus Using the RANS and LES Approaches

Abstract—This study focuses on turbulent convection of molten magnesium in a titanium reduction reactor. The reactor retort is a cylindrical vessel with a radius of 0.75 m and a height of 4 m, which contains liquid magnesium at a temperature of 850°C. During a process that lasts for more than 2 days, significant temperature gradients occur in the reduction apparatus due to an exothermic chemical reaction on the metal surface and simultaneous cooling of the side wall of the retort and heating of its bottom. Temperature gradients cause convective flows inside the reactor, which in turn significantly affect the formation of the titanium block. The mathematical model of convective flows in the reactor is based on the equations of thermogravitational convection for a single-phase medium in the Boussinesq approximation. We consider the possibility of modeling turbulent convective flows in a titanium reduction reactor using RANS (Reynolds-averaged Navier–Stokes equations) k–e and k–ω SST (Shear Stress Transport) models. The results of simulations performed with the k–ω SST model on relatively coarse grids (0.825 million finite volumes) are shown to qualitatively and quantitatively agree with the results of LES simulations on fine grids (3.7 million finite volumes). However, the k–e model does not always produce acceptable results. RANS simulations produce average velocity and temperature fields with averaging times much longer than those possible in LES simulations. Several different configurations of heating and cooling of the apparatus were examined, including those that were previously unstudied. It has been found that using the k–ω SST model allows simulation of flow dynamics taking into account changes in the heating and cooling conditions of the apparatus during the entire process and identification of single- and double-vortex large-scale flows in the retort, as well as the transition between them, so the degree of convection influence on the reaction can be assessed.

Analytical investigation of magnesium aerosol combustion based on the asymptotic model of flame structure

Due to shortage and environmental pollution of fossil fuels and environment-dependent production of renewable energies, the metal fuels are promising candidates for alternative energy sources. In this study, the micron-sized magnesium particles are considered as energy carrier and the flame propagation of lean premixed magnesium-air combustion is investigated under zero gravity condition. To analyze dust cloud combustion, an asymptotic model of flame structure is proposed. According to the combustion behavior of single particle, the flame structure consists of four different zones including preheat, liquid magnesium, vaporized magnesium and post-flame zones in which the melting, vaporization and flame occur instantaneously. Afterwards, the non-dimensional forms of governing equations including mass, energy and gaseous fuel mass fraction conservations and the appropriate boundary conditions are derived and analytically solved. Subsequently, as the important achievements of the present study, the explicit formulas are obtained for flame velocity, location and temperature. Eventually, the effects of involved parameters on combustion characteristics are examined. The results indicate that as the particle diameter enhances from 15 to 60 µm, the flame front moves to a place 2.5 times farther away. The flame temperature increases linearly with concentration, while it decreases with the inverse of square of the diameter.

Open Porous α + β Titanium Alloy by Liquid Metal Dealloying for Biomedical Applications

Open porous dendrite-reinforced TiMo alloy was synthesized by liquid metal dealloying of the precursor Ti47.5Mo2.5Cu50 (at.%) alloy in liquid magnesium (Mg). The porous TiMo alloy consists of α-titanium and β-titanium phases and possesses a complex microstructure. The microstructure consists of micrometer scale β-titanium dendrites surrounded by submicrometer scale α-titanium ligaments. Due to the dendrite-reinforced microstructure, the porous TiMo alloy possesses relatively high yield strength value of up to 180 MPa combined with high deformability probed under compression loading. At the same time, the elastic modulus of the porous TiMo alloy (below 10 GPa) is in the range of that found for human bone. This mechanical behavior along with the open porous structure is attractive for biomedical applications and suggests opportunities for using the porous TiMo alloy in implant applications.

Nanoporous High-Entropy Alloy by Liquid Metal Dealloying

High-entropy nanomaterials possessing high accessible surface areas have demonstrated outstanding catalytic performance, beating that found for noble metals. In this communication, we report about the synthesis of a new, nanoporous, high-entropy alloy (HEA) possessing open porosity. The nanoporous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%) was fabricated from a precursor (TaMoNbV)25Ni75 alloy (at%) by liquid metal dealloying using liquid magnesium (Mg). Directly after dealloying, the bicontinuous nanocomposite consisting of a Mg-rich phase and a phase with a bulk-centered cubic (bcc) structure was formed. The Mg-rich phase was removed with a 3M aqueous solution of nitric acid to obtain the open, porous, high-entropy Ta19.1Mo20.5Nb22.9V30Ni7.5 alloy (at%). The ligament size of this nanoporous HEA is about 69 ± 9 nm, indicating the high surface area in this material.

Bonding effect of liquid magnesium with open-celled carbon foam in interpenetrating phase composite

Abstract The issue of bonding formation in liquid metal/open-celled carbon foam (Cof) systems was examined, taking into account the practical aspects of the synthesis of a new type of Mg-C metal material composite. The problem is complex due to the strong oxidation and intense evaporation of liquid magnesium, as well as the 3D geometry of the carbon component, where metal transport occurred through the foam cells’ windows. Laboratory experiments performed at 700°C in ceramic crucibles showed that spontaneous carbon foam infiltration by liquid metal is impossible under the applied conditions, either in an air atmosphere coupled with flux protection or under argon protection. Comparative tests performed in a UHV chamber filled with static pure Ar by a sessile drop method, coupled with non-contact heating and capillary purification at a test temperature of 700°C directly in the UHV chamber, showed non-wetting behavior of the Mg/Cof couple with a correspondingly high contact angle of about 135°. The graphite capillary was then moved down, the liquid drop being slightly pressed into the foam, but these changes did not induce effective foam penetration. Despite the short contact time for the sessile drop test under an argon atmosphere, SEM+WDS analysis of the solidified Mg/Cof couple revealed the formation of an MgO interlayer at the interface, with a thickness of approx. 1 µm. The experimentally demonstrated presence of oxygen in the carbon foam sample, both before and after its contact with magnesium, points to oxide-type bonding being established between Mg and Cof. This observation is in a good agreement with previous reports on the interface characterization of magnesium matrix composites reinforced with glassy carbon materials and carbon fibers by stir casting and pressure infiltration. Based on the findings of this study, a general structural scheme of the bonding process between carbon foam and liquid magnesium, as an important stage in the syntheses of Mg-C composites, was proposed.

Surface Functionalization of Biomedical Ti-6Al-7Nb Alloy by Liquid Metal Dealloying

Surface functionalization is an effective approach to change the surface properties of a material to achieve a specific goal such as improving the biocompatibility of the material. Here, the surface of the commercial biomedical Ti-6Al-7Nb alloy was functionalized through synthesizing of a porous surface layer by liquid metal dealloying (LMD). During LMD, the Ti-6Al-7Nb alloy is immersed in liquid magnesium (Mg) and both materials react with each other. Particularly, aluminum (Al) is selectively dissolved from the Ti-6Al-7Nb alloy into liquid Mg while titanium (Ti) and niobium (Nb) diffuse along the metal/liquid interface to form a porous structure. We demonstrate that the porous surface layer in the Ti-6Al-7Nb alloy can be successfully tailored by LMD. Furthermore, the concentration of harmful Al in this porous layer is reduced by about 48% (from 5.62 ± 0.11 wt.% to 2.95 ± 0.05 wt.%) after 30 min of dealloying at 1150 K. The properties of the porous layer (e.g., layer thickness) can be tuned by varying the dealloying conditions. In-vitro tests suggest improved bone formation on the functionalized porous surface of the Ti-6Al-7Nb alloy.

Tantalum network nanoparticles from a Ta2O5+kMg system by liquid magnesium controlled combustion

In this study, tantalum network nanoparticles are prepared from a Ta2O5+kMg system via a liquid magnesium-controlled combustion reaction. Super-stoichiometric amounts of magnesium are used in the preparation of a reaction mixture to produce a liquid magnesium pool capable of lowering the combustion temperature and leading to the formation of Ta network structures. The heat transfer kinetics from the hot reaction zone of ‘cold’ Mg particles is determined using heat transfer-coupled fluid dynamics simulation software. The formation of network structures is characterized through SEM, TEM, XRD, and BET analysis techniques. The mechanism of network formation is explained based on solid particle collisions in liquid media. Our method is able to produce Ta network structures in which the size of individual particles ranges between 50 and 700 nm.

Combustion synthesis of hexagonal boron nitride nanoplates with high aspect ratio

High crystalline hexagonal boron nitride nanoplates with high aspect ratio of ~400 have been synthesized by combustion synthesis method through magnesiothermic reduction reaction between B2O3 and Mg in N2 pressure. The synthesized hexagonal boron nitride nanoplates were about 50 nm in thickness and larger than 20 μm in lateral size. The six-fold symmetric spots electron diffraction pattern of transmission electron microscopy shows that the nanoplate is well crystallized. Hexagonal boron nitride nanoplates grow via an Oswald ripening process and have larger lateral size when it was prepared with larger magnesium particles. High temperature liquid magnesium provides an important environment for the growth and crystallization of boron nitride. This work provides an effective way to achieve low-cost and large-scale preparation of high-quality boron nitride nanoplates.

Squeeze Cast Mg-Zn Alloys for Bioapplications: Tensile Properties and Microstructure

In the past, Mg-Zn alloys prepared by a two-step manufacturing process of casting plus extrusion have been demonstrated to be a good candidate for biodegradable applications. But, studies on fabricating of Mg-Zn alloys with a single step process of squeeze casting capable of producing porosity-free Mg alloys, which can reduce the cost, are limited. In the present work, Zinc (Zn) addition varying from 1.0 up to 10.0 wt. % was introduced into liquid magnesium. The alloyed liquid was squeeze cast under an applied pressure of 90 MPa. The results of mechanical testing on the squeeze cast Mg-Zn alloys shows that Zn is an effective additive for enhancing their mechanical properties, specifically, tensile and yield strengths at room temperature, but reducing the elongation. While the Zn addition rises from 1.0 to 10.0 wt.%, the ultimate tensile and yield strengths increases to 181.0 MPa and 105.0 MPa from 140.7 MPa and 39.3 MPa, while the elongation-to-failure (ef) decreases to 3.7% from 6.2%, respectively. The reveal of the as-cast grain structure by an optical microscope (OM) indicates that the high Zn content reduces grain sizes considerably. The microstructures analyzed by a scanning electron microscope (SEM) with the energy dispersive spectroscopy (EDS) show that the secondary MgZn phase forms once Zn is introduced in sufficient amount. The grain refinement and the massive presence of the secondary MgZn phase at the boundaries of the refined grains should be responsible to the enhancement of the strengths and the reduction in the elongation. The developed pressurized casting without employing secondary manufacturing processes such as extrusion or heat treatment exhibits its advantages to enhance the mechanical properties of the Mg alloys with high Zn content over conventional fabrication processes, since high Zn-containing Mg alloys have a long freezing range and tend to form microshrinkage porosity.