Simultaneous Solidification Research Articles

Образование глобальной Азиатской изотопной термальной аномалии (ASITA) в зарождающейся системе Земля–Луна: Мегаимпакт или фрагментация газопылевого облака?

A review of lunar studies is given that indicate the isotope crisis of the Earth mega-impact hypothesis and the removal of emerging contradictions by a competing model of the origin of the Earth-Moon binary system from a gas-dust cloud. The simultaneous solidification of the magma ocean of the Moon with the solidification of the magma ocean in the global ASITA heterogeneity of the Earth 4.54–4.44 billion years ago is substantiated. From the model of the Earth–Moon binary system, the solidification of the ASITA magma ocean is assumed to precede the solidification of the rest of the Earth. It is concluded that the Earth's crust consolidated at different times after the solidification of the magma ocean: in ASITA – 4.31 billion years ago and in the rest of the Earth – with a delay of up to 3.82 billion years ago.

Microstructure of a modulated Ti-6Al-4V – Cu alloy fabricated via in situ alloying in laser powder bed fusion

In this work, Ti-6Al-4V was in situ alloyed with 15 wt% Cu using laser powder bed fusion (LPBF) to investigate the influence of the eutectoid alloying element Cu on microstructural features. The chemical inhomogeneities owing to in situ alloying are used to allow simultaneous solidification of differently composed material.After LPBF, the matrix material consists of metastable, equiaxed β-Ti and Ti2Cu precipitates. Cu stabilizes β-Ti, and the unique solidification conditions with high thermal supercooling cause the equiaxed grain morphology and the formation of Ti2Cu precipitates. Inclusions, assigned incompletely melted Ti-6Al-4V powder particles, consist of α’/α-Ti. In the transition zone between β-Ti and α’/α-Ti, orthorhombic α’’ is found as nano-sized crystals. For the first time, β-stabilization across a wide area through Cu with a composition of Ti76.2Al5.7V3.2Cu14.9 and the formation of α’’ with the composition of Ti80.2Al5.4V3.3Cu11.1 is shown. It is demonstrated that Cu is a very versatile alloying element in Ti-6Al-4V, significantly impacting microstructural development. Hence LPBF in situ alloying allows more than one alloy composition to be investigated for microstructural features in a single experiment, which could be an interesting approach to alloy development.

Droplet impact-induced molten pool dynamics and particle migration patterns during TIG-assisted droplet deposition manufacturing of SiC particle-reinforced Al–Si alloy

A three-dimensional droplet-pool coupled model with dispersed phase was developed to simulate the TIG-assisted droplet deposition manufacturing (DDM) of silicon carbide (SiC) particle-reinforced aluminum (Al) matrix composites (AMCs), which was employed to calculate the surface morphology of the deposited layer, the thermal-flow fields and the distribution state of reinforcing particles in the molten pool. The cross-section profile of a single-track SiC-reinforced AMC deposit and the distribution state of reinforcements were examined and compared with the findings predicted by simulation, a good agreement was achieved. It is found that the falling Al droplet produces an obvious crater on the curved surface of molten pool. The viscous damping and simultaneous solidification are the main factors that dissipate the kinetic energy of the droplet. In addition, we discuss quantitatively how impact-induced thermodynamic within molten pool can change the migration behaviors and the distribution state of SiC reinforcement. The heterogeneous distribution of reinforcement particles can be attributed to the thermocapillary micro-convection and the velocity difference in the spreading and recoiling stages.

Synthesis of inherently helical nanofibers: Effects of solidification of electrified jet during electrospinning

AbstractIn this paper, a helical fiber was fabricated through electrospinning by increasing the vapor pressure of the solvent, increasing the conductivity of the polymer solution and forming an uneven electrical field distribution around the jet. Fiber morphology during electrospinning of a dielectric polymer solution was observed to dramatically change from straight to helical due to rapid solidification of the jet as vapor pressure of the solvent increased. A similar effect was observed with conductive solutions prepared by adding large amounts of metal ion to the polymer solution. The addition of metal ion induced strong electrical stresses, causing the electrified jet to rapidly solidify in the early stage of electrospinning. Simulations revealed that the jet near the nozzle tip was subject to a strong electrical field due to increased charge density. The thickness of the emerging fiber was rapidly reduced with fast and simultaneous solidification, resulting in helical nanofibers. In addition, by using the asymmetric spinnerets, an uneven electric field distribution around jet was generated, maximizing the fiber curvature and increasing the helical fiber ratio.

Droplet Impact-Induced Molten Pool Dynamics and Particle Migration Patterns During TIG-Assisted Droplet Deposition Manufacturing of SiC Particle-Reinforced Al-Si Alloy

A three-dimensional droplet-pool coupled model with dispersed phase (solid SiC particles) was developed to simulate TIG-assisted droplet deposition manufacturing (DDM) of silicon carbide particle-reinforced aluminum matrix composites (AMCs), which was employed to calculate the surface morphology of the deposited layer, the thermal-flow fields and the distribution state of reinforcing particles in the molten pool. The cross-section profile of a single-track SiC-reinforced AMC deposit and the distribution state of reinforcement were examined and compared with the findings predicted by simulation, a good agreement was achieved. It is found that the impacting droplet including the SiC reinforcement creates an obvious crater within the molten pool. The viscous damping and simultaneous solidification are the main factors that dissipate the kinetic energy of the droplet. In addition, we discuss quantitatively how impact-induced thermodynamic within molten pool can change the migration behavior and distribution state of SiC reinforcement. The non-homogeneous distribution of the particles can be attributed to the thermocapillary micro-convection and the velocity difference in the spreading and recoiling stages.

Regional temperature control in ceramic injection moulding: An approach based on cooling rate optimisation

The injection moulding of ceramic components with uneven wall thickness presents challenges due to differential cooling rates developing in the injected parts, which cause premature solidification of the feedstock at thin features and lead to detrimental defects, worsening in components from green to sintered states. To cope with this, suitable mould thermal control approaches have to be selected and validated, as current control methods are based on the achievement of a uniform cavity surface temperature, which is not tailored to such complex geometries. In this work, a novel thermal control system is proposed, based on regional mould temperatures, implemented with the use of Peltier modules, which locally and independently heat and cool different cavity features according to their thickness. The regional temperature profiles are optimised over time with the use of a coupled Finite Element - Particle Swarm Optimisation (FE-PSO), to achieve uniform cooling rates throughout the moulded components. The performance of this approach is compared to both constant ambient mould temperature and Rapid Heat Cycle Moulding (RHCM) techniques, which instead aim at achieving uniform temperatures throughout the mould cavity surface. Results show that the novel proposed method, based on regional temperature control and uniform cooling rates, promotes the simultaneous solidification of features with a 10-times difference in surface-to-volume ratio. Due to this, in terms of components quality, the novel method brings the advantages of higher dimensional control and reduction of differential shrinkage compared to the other analysed approaches, thus increasing the capability to use injection moulding to manufacture ceramic components characterised by non-uniform wall thickness.

Core-shell microstructure simultaneous solidification mechanism of Cr(III), Mn(IV), Ni(II) and Pb(II) in glass-ceramics

Glass-ceramics with crystal-coated glass phase microstructure were designed and prepared using the method of base-glass surface crystallization to simultaneously solidify multiple heavy metal ions (Cr3+, Ni2+, Mn4+ and Pb2+). Cr2O3 and PbO had opposite effects on the surface crystallization of the base glass, promoting and inhibiting it, respectively, when their concentrations were increased from 0.1 to 0.9 wt.%. This then affected their resistance to leaching of heavy metal. When the mass ratio of Na2O/SiO2 was increased from 0.08 to 0.20, the effect of PbO on inhibiting surface crystallization was weakened. The distribution of Cr3+, Ni2+, Mn4+ was inhomogeneous, and the concentrations of the ions were the highest at the glass phase-crystal interface and lowest in the wollastonite (CaSiO3) crystals.However, the concentration of Pb2+ at the interface decreased and the content of Pb2+ in the crystal gradually increased. The leaching test results showed that the leached concentrations of Cr3+, Mn4+, Ni2+, Pb2+ are all on the order of 10−2 mg/L.

Microstructure evolution during dendrite coarsening in an isothermal environment: 3-D cellular automaton modeling and experiments

Microstructure evolution of columnar dendrites during isothermal coarsening is simulated by a three-dimensional (3-D) cellular automaton (CA) model. The 3-D CA model incorporates the thermodynamics, and kinetics aspects influenced by the factors of temperature, composition, and interfacial weighted mean curvature. After quantitative validation through grid independence test and the liquid pool migration problem, the 3-D CA model is applied to simulate the dendrite coarsening phenomena caused by the simultaneous melting and solidification for a SCN-2.0 wt.% ACE alloy in an isothermal environment. Several typical features of dendrite coarsening occurring in the 3-D space are reproduced by the CA model, including melting of tertiary and small secondary branches, interdendritic groove base advancement, and coalescence of neighboring dendrite arms. The simulated dendritic microstructure compares well with the in situ experimental observation. Besides, the simulated specific surface area of the solid/liquid interface decreases with time following a power-law relation with an exponent of 1/3. The simulated distribution curve of the interfacial weighted mean curvatures becomes narrower with time, and the peak gradually shifts to zero, showing that the S/L interface is flattened during the isothermal dendrite coarsening. The average thickness of the primary dendrite arm and the secondary dendrite arm spacing (λ2) are found to increase with time, and the third power of λ2 shows a nearly linear relationship with time. The CA model not only visualizes morphological evolution of the dendrite arms, but also provides insight into the complex interaction among local melting/solidification, solute diffusion, and variation of weighted mean curvature in the 3-D space.

Structures for Heat Treatment Assembled from Cast Elements

Various types of technological equipment individually designed for operation in pit and elevator heat treatment furnaces aredescribed in this article. A common characteristic of these structures is that they are composed of several or several dozen thin--walled elements of various shapes and sizes, gravity cast in sand moulds from creep-resistant alloys (austenitic Cr-Ni/Ni-Crcast steel and cast nickel alloys). The design of the castings requires the development of a manufacturing technology that caneffectively use the principle of the simultaneous solidification of all components. Properly designed equipment should have minimumweight, maximum strength, and maximum loading capacity combined with adequate durability and reliability. Two designsof the equipment for the heat treatment of steel parts were presented. Both designs, as well as their individual components, weredescribed in detail and illustrated. The main task of the equipment is to form the charge in the furnace and transport this chargeboth inside and outside the furnace. The first design is the design of an equipment for the heat treatment of large ring-shapedparts. The second design is the design of an equipment, whose structure can be modified using various repeatable components. Asa result of these modifications, different variants of the equipment are obtained, allowing for the heat treatment of five differenttypes of the shafts characterized by different shapes and sizes. The study is of an application nature. It is addressed to engineeringand technical staff dealing with both the design and operation of heat treatment furnaces.

Glass-ceramics microstructure formation mechanism for simultaneous solidification of chromium and nickel from disassembled waste battery and chromium slag

A new method to solidify Cr(VI), Cr(III), and Ni(II) simultaneously by using a glass-ceramics microstructure was used. For a crystallization temperature of 870 °C, base glass (air cooling) with a mass ratio of CaO / SiO2 (R(C/S)) of 6/16, 10/16 precipitated a CaNiSi2O6 crystalline phase that could not solidify Ni(II) stably, and with an increase in R(C/S), the CaNiSi2O6 crystal precipitation tendency increased. When R(C/S) = 6/16, the crystallization temperature was 760 °C and spinel that was enriched in chromium and nickel formed preferentially during the inhibition of CaNiSi2O6 formation, indicating that lowering R(C/S) can inhibit the formation of CaNiSi2O6. Cr and Ni were mostly solidified in spinel, some of them enter augite (Ca (Mg, Fe, Al) (Si, Al)2O6) phases, a few of them were distributed in the glass matrix. The results of toxic leaching showed that the leached concentration of total Cr and Ni2+ in spinel glass-ceramics were 0 ppm and 0.07 ppm respectively, and the spinel glass-ceramics for simultaneous solidification of Cr(VI), Cr(III) and Ni(II) had excellent curing effect.

Stabilization and solidification of arsenic and iron contaminated canola meal biochar using chemically modified phosphate binders

Adsorption is a widely used process for removal of heavy metals, but the management of spent adsorbent containing concentrated amounts of heavy metals is a problem due to potential risk of groundwater contamination from leaching of heavy metals. Generally, cementitious binder and additives are used for stabilization and solidification treatment, however heavy metals tend to leach from such matrices. Therefore, this research investigated the effectiveness of chemically modified phosphate biochar (CMPB) composite for the simultaneous solidification and stabilization of arsenic (As) and iron (Fe) contaminated canola meal biochar. Results showed that the performance of spent biochar added CMPB composites was significantly better than the pure composites (without biochar) due to filling of inter-aggregate pores using biochar and availability of sufficient amount of MgKPO4 for binding of biochar particles. Moreover, leaching test and risk assessment studies indicated that there is no potential adverse effect as the concentrations of As and Fe in TCLP leachate were well below the Universal Treatment Standard (UTS) in optimized CMPB composites. In conclusion, chemically modified phosphate binders were found effective in stabilization and solidification of As and Fe contaminated biochar into thermodynamically stable material with high immobilization capacity and low leachability.

A facile Solvent/Nonsolvent Preparation of Sintering‐Resistant MgO/CaO Composites for High‐Temperature CO2 Capture

AbstractFor CaO‐based high‐temperature CO2 sorbents, excellent cyclic stability is highly desired for its practical applications. Among all techniques, preparation of CaO‐based composites is one of the most widely accepted strategies, and the mixing status between CaO and the inert supporting material is crucial for its anti‐sintering property. This work provides a new strategy for preparing nanometrically dispersed MgO/CaO composites with significantly improved cyclic stability. The so called solvent/nonsolvent synthesis method can endow a simultaneous solidification of Ca and Mg and result in a nano‐meter level mixing of CaO and MgO. The optimized sorbent Mg/Ca‐0.2 retained 95.3 % (13.45 mmol g−1) of its initial capacity after 7 cycles, while the control CaAc2−CaO only retained 52.9 % (8.67 mmol g−1) of its initial capacity. The addition of MgO also increase the CO2 sorption and desorption kinetics after several cycles. We believe that this new and facile solvent/nonsolvent synthesis method is also promising for the preparation of other highly mixed metal oxides.

Solidification of welded SiC–ZrB2–ZrC ceramics

AbstractA silicon carbide‐based ceramic, containing 50 vol% SiC, 35 vol% ZrB2, and 15 vol% ZrC was plasma arc welded to produce continuous fusion joints with varying penetration depth. The parent material was preheated to 1450°C and arc welding was successfully implemented for joining of the parent material. A current of 138 A, plasma flow rate of ~1 L/min or ~0.5 L/min, and welding speed of ~8 cm/min were utilized for repeated joining, with full penetration fusion zones along the entire length of the joints. Solidification was determined to occur through the crystallization of β‐SiC (3C), then the simultaneous solidification of SiC and ZrB2, and lastly through the simultaneous solidification of SiC, ZrB2, and ZrC through a ternary eutectic reaction. The ternary eutectic composition was determined to be 35.3 ± 2.2 vol% SiC, 39.3 ± 3.8 vol% ZrB2, and 25.4 ± 3.0 vol% ZrC. A dual fusion zone microstructure was always observed due to convective melt pool mixing. The SiC content at the edge of the fusion zone was 57 vol%, while SiC content at the center of the fusion zone was 42 vol% although the overall SiC content was still nominally 50 vol% throughout the entire fusion zone.

Interaction of local solidification and remelting during dendrite coarsening - modeling and comparison with experiments

The microstructural evolution of dendrite coarsening during isothermal holding is simulated using a quantitative cellular automaton (CA) model involving the mechanisms of both solidification and melting. The present model encompasses the essential aspects of thermodynamics and kinetics, particularly the evolution/influence of composition, temperature, and curvature, leading to valid simulations of simultaneous solidification and melting. Model validation is performed through a comparison of the CA simulations with analytical predictions for a liquid pool migrating in the mushy zone of a SCN–0.3 wt.% ACE alloy due to temperature gradient zone melting. The model is applied to simulate the microstructural evolution of columnar dendrites of a SCN–2.0 wt.% ACE alloy during isothermal holding in a mushy zone. The simulation results are compared with those of a previous CA model that does not include the melting mechanism under otherwise identical conditions. The role of melting for dendrite coarsening is quantified, showing how the melting influences the coarsening process. The present model effectively reproduces the typical dendrite coarsening features as observed in experiments reported in the literature. The simulations reveal how local solidification and melting stimulate each other through the complicated interactions between phase transformation, interface shape variation, and solute diffusion.

Development of the models for advection-diffusion of eroded concrete into debris and concrete volume reduction in molten core-concrete interactions

ABSTRACTModels for the three-dimensional (3D) advection, diffusion, and volume reduction of eroded concrete into molten core are being developed. As part of the assessment of the reactor interior at TEPCO's Fukushima Daiichi Nuclear Power Plant, analytical models of molten core–concrete interaction (MCCI) to predict locations and condition of molten core (debris) have been improved in the debris spreading analysis (DSA) module of the severe accident analysis code SAMPSON. In addition to the primary model for 3D natural convection with simultaneous spreading, melting, and solidification in an open space, the analysis model to treat phenomena in a closed space, such as debris eroding laterally under concrete floors at the bottom of the sump pits, had been improved. This modeling with practical applicability is referred to as the full-3D MCCI model. This paper presents modeling of the advection and diffusion of eroded concrete into debris melt and calculation processes that were installed for simulating volume reduction when concrete decomposed. They were developed and incorporated into the full-3D MCCI model. The advanced DSA module with the models noted above was validated using MCCI test data. The calculated erosion rates agreed with the test data within a margin of about 16%.

Effect of Final EMS on Shrinkage Cavity of Bloom

Final EMS parameters in the continuous bloom casting have been optimized by experimental and simulated researches. Simulation results show that the temperature gradient in the molten melt can be decreased and simultaneous solidification can be obtained with the final EMS. When the current is 600 A and frequency is 6 Hz, the maximum temperature gap between the inside and the brim of the melt bottom is 1.79 °C, which is 49.3% of that without EMS. Processing parameters are rectified based on the research results, the number of the shrinkage cavities is limited and the maximum diameter of the cavity is decreased.

Cocrystallization of Max-Phases in the Ti–Al–C System

The structure and phase transformations in the Ti–Al–C system were studied by X-ray diffraction, differential thermal analysis, and scanning electron microscopy, including energy-dispersive X-ray spectroscopy and electron backscatter diffraction on samples obtained by arc melting and annealing at high temperatures. The ternary system has a cocrystallization region for the two MAX-phases, N and H. The Ti41.5Al38.5C20 samples contain three phases at all experimental temperatures (from 650 to 1660°C): Ti3AlC2 (N-phase of Ti3SiC2 type), Ti2AlC (H, Cr2AlC type), and binary intermetallic TiAl3 (e, its own crystal type). The morphology of the as-cast alloy and annealed samples (at temperatures above and below the solidus temperature, 1660 and 1250°C, respectively) shows that invariant solidification at 1405°C (solidus temperature) precedes the univariant simultaneous solidification of N- and H-phases, i.e. both MAX-phases separating from the melt.

Simultaneous solidification of potassium and phosphorus using rice straw charcoal and saturated phosphorus adsorbent

Phosphorus (P) ore is an expensive and limited resource that will be depleted in a few decades if the current global consumption rate continues. Japan, one of the most developed countries in the world, relies completely on imported phosphate rock for P. Potassium (K) ore, which is equally important for continuous development, is also becoming increasingly expensive. The recovery of P and K is therefore important for continuous and sustainable development. In this study, concentrated P (obtained from eluent) and K (obtained through alkali leaching of rice straw charcoal) were recovered as potassium magnesium phosphate (PMP) through the controlled addition of magnesium (Mg). A PMP crystal was produced when an equimolar (with respect to P) Mg solution was added to the leaching solution (rich in P and K) at a pH range of 11–12. Thus, the production of PMP in a crystalline form demonstrates the huge scope for the recycling of limited resources.

Getting in shape: Molten wax drop deformation and solidification at an immiscible liquid interface

The controlled production of non-spherical shaped particles is important for many applications such as food processing, consumer goods, adsorbents, drug delivery, and optical sensing. In this paper, we investigated the deformation and simultaneous solidification of millimeter size molten wax drops as they impacted an immiscible liquid interface of higher density. By varying initial temperature and viscoelasticity of the molten drop, drop size, impact velocity, viscosity and temperature of the bath fluid, and the interfacial tension between the molten wax and bath fluid, spherical molten wax drops impinged on a cooling water bath and were arrested into non-spherical solidified particles in the form of ellipsoid, mushroom, disc, and flake-like shapes. We constructed cursory phase diagrams for the various particle shapes generated over a range of Weber, Capillary, Reynolds, and Stefan numbers, governed by the interfacial, inertial, viscous, and thermal effects. We solved a simplified heat transfer problem to estimate the time required to initiate the solidification at the interface of a spherical molten wax droplet and cooling aqueous bath after impact. By correlating this time with the molten wax drop deformation history captured from high speed imaging experiments, we elucidate the delicate balance of interfacial, inertial, viscous, and thermal forces that determine the final morphology of wax particles.

Microsphere-assisted Fabrication of Ultra-high Aspect-ratio PDMS Micropillars for Bio-inspired Acoustic Sensing

ABSTRACTWe developed a new soft-lithographic fabrication technique which enables the realization of high aspect-ratio PDMS micropillars. The key enabling factor is the adoption of the direct drawing technique incorporated with the in situ heating for simultaneous hardening and solidification of the PDMS micropillars. In addition, our technique allows self-aligned installation of highly reflective microspheres at the tips of the micropillars. Using the transparent PDMS micropillar as a flexible waveguide and the microsphere as a self-aligned reflector, we transformed the microsphere-tipped PDMS micropillars into all optically interrogated acoustic sensors inspired by the cricket’s filiform hairs and successfully demonstrated the sensing capability.