Molten Droplets Research Articles

Cr(VI) formation in ferrochrome-smelter dusts

Dusts generated during ferrochrome smelting in a pilot-scale DC arc furnace were sampled from the furnace freeboard and from the off-gas handling stream (cyclone and baghouse). The dusts comprise fine-grained feed material (chromite, flux, and reductant); compositionally heterogeneous, glassy micro-spherules, interpreted as gas condensates and/or aerosolized melt droplets; and trace amounts of ferrochrome. Synchrotron-based micro-X-ray-fluorescence and micro-X-ray absorption near-edge structure around the chromium (Cr) K-edge was used to identify the distribution and speciation of Cr in dust particulates from the freeboard and the cyclone. The dust samples contain Cr in multiple oxidation states, including Cr(0) (hosted by ferrochrome), Cr(III), and Cr(VI). The majority of Cr occurs as Cr(III) in chromite. In both the furnace-freeboard and the cyclone dusts, Cr(VI) was consistently associated with the Si-Ca-Mg-rich micro-spherules. A major finding of this study is that Cr oxidation and Cr(VI) formation can occur in aerosolized dusts within the closed DC-arc furnace during ferrochrome smelting under conditions that are deemed to be essentially reducing. The association of Cr(VI) with the micro-spherules forwards the hypothesis that the high temperature of the furnace off-gasses and the flux composition influence the likelihood of Cr(VI) formation within a closed furnace under open-bath smelting conditions.

One-step and green synthesis of a bio-based high-efficiency flame retardant for poly (lactic acid)

The synthesis of bio-based high-efficiency flame retardants in accordance with green and facile method is critical yet very challenging for bioplastics, e.g., poly (lactic acid) (PLA). In this study, a bio-based flame retardant named as PF is synthesized by the reaction between phytic acid (PA) and furfurylamine (FA) in water. PF improves the flame retardancy of PLA at low addition. For instance, PLA composite containing only 2 wt% PF passes a UL-94 V-0 classification, and that containing 4 wt% PF exhibits a limiting oxygen index (LOI) of 28.5%, which is 46.2% higher than that of pure PLA. PF slightly reduces the peak heat release rate (PHRR) and total heat release (THR) of PLA in cone calorimeter test (CCT). In detail, 4 wt% PF reduces the PHRR from 362.2 kW/m2 to 332.7 kW/m2 by 8%. Additionally, PLA/PF composite is comparable to the neat PLA in terms of mechanical properties and thermal stability when a UL-94 V-0 rating is achieved. The flame-retardant mechanism analyses demonstrate that PF takes action in both gaseous and condensed phases. It is proposed that PF accelerates the generation of melting droplets to take away heat, suppresses the release of combustible gases and improves the compactness of char layer during combustion. This study provides a green and facile strategy to create bio-based high-efficiency flame retardants for the preparation of fire-safe bioplastics holding a promising future in the industry.

Electro spark coating of AlCoCrFeNi high entropy alloy on AISI410 stainless steel

AlCoCrFeNi high entropy alloy (HEA) was coated on AISI410 stainless steel through the electro spark deposition. Fine melt droplets in the arc-zone led to fine dendrites in the coating. Coated phase contained body centered cubic with a minor fraction of face centered cubic phase. Constituent elements from HEA were diffused in the substrate and led to solid solution strengthening at the interface. Threefold increase in the microhardness (to 907 ± 17 HV) was achieved after coating, compared to steel. HEA coated pin exhibits very good wear resistance.

On the phenomena of partial crystallization of highly undercooled magnesium silicate molten droplets

The present work reports real-time observations of the phenomena of partial crystallization of one of the glass-forming materials, namely enstatite (MgSiO3) from its supercooled liquid droplet. Initially, the molten droplet has been held under purely non-contact conditions using the aerodynamic levitation technique. The desired levels of undercooling have been achieved by deliberately making the levitated molten droplet touch a thin molybdenum wire and hence to initiate heterogeneous nucleation from the point of contact. Influence of thermal parameters like undercooling, cooling rates and recalescence on the process of crystallization is investigated. To understand and report the morphological properties and extent of crystallinity, the solidified enstatite samples have been characterized using optical/scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively, which confirmed the formation of partially crystallized enstatite spherules and fully glass spherules. XRD showed sharp peaks of enstatite, which confirm crystallinity and a halo profile confirms the amorphous phase of enstatite. Based on the observations of several experiments, we propose the effect of thermal parameters such as levels of undercooling and recalescence on the partial crystallization, as well as partial glass formation from the initially molten droplets of enstatite composition.

Urea Melt Marbles Developed by Enwrapping Urea Melt Droplets with Superhydrophobic Particles: Preparation, Properties, and Application in Large Urea Granule Production

AbstractUrea melt droplets (UMDs) spontaneously spheronize and form large urea granules after condensation on superhydrophobic surfaces without dust generation. However, they break and coalesce when colliding with each other; moreover, they adhere to the surface and form tails when rolling. These problems limit the practicality of the process using UMDs for large urea granulation directly. Urea melt marbles (UMMs) are introduced to overcome these drawbacks by enwrapping UMDs with superhydrophobic polytetrafluoroethylene (PTFE) powder, thus enhancing the elasticity and maintaining the sphericity. A premixing–melting process is developed to obtain UMMs and lower the PTFE powder consumption to half of that required in the traditional liquid marble preparation. The best determined elasticity modulus of UMMs reaches 44.9 ± 3.6 Pa, and the sphericity is 0.9992. No adhering or tailing occurs during rolling granulation. Large urea granules obtained through UMMs meet all requirements for the commercial urea products and exhibit additional advantages of protection against moisture and slow release of fertilizer.

Peritectic minerals record partial melting of the deeply subducted continental crust in the Sulu orogen

AbstractThe deeply subducted continental crust commonly undergoes partial melting during its exhumation from mantle to crustal depths. Peritectic minerals are commonly produced during decompressional melting, providing an important record of the timing, P–T conditions, and mechanisms of crustal anatexis in continental subduction zones. A combined study of petrography, mineral inclusions, mineral major and trace element compositions, phase equilibrium modelling, zircon and titanite U–Pb dating, and zircon Hf–O isotopes was carried out to characterize peritectic minerals in ultrahigh‐pressure (UHP) metamorphic gneisses from the Sulu orogen, China. Field and petrographic observations reveal that the crustal anatexis was extensive and is recorded by folded leucosomes, corroded phengite relicts, cuspate K‐feldspar and quartz, pseudomorphs of melt films along grain boundaries, and multiphase crystal inclusions in zircon, garnet, and phengite. The multiphase crystal inclusions represent the crystallized product of anatectic melt droplets trapped in the peritectic zircon and garnet as well as the residual UHP phengite. The peritectic origin of both zircon and garnet is identified by their compositional characteristics, and the peritectic origin of garnet is further supported by phase equilibrium modelling which shows an increase in garnet contents as partial melting proceeds. The modelled phase diagrams also indicate that the two peritectic minerals were produced through two episodes of phengite dehydration melting. The first occurred at 237 ± 3 Ma under P–T conditions of ≥2.6 GPa and 810–880°C, corresponding to thermobaric ratios of ~312–338℃/GPa. The second took place at 222 ± 2 Ma under P–T conditions of 1.5–2.1 GPa and 730–760℃, corresponding to thermobaric ratios of 362–487℃/GPa. In comparison to peak UHP metamorphic P–T conditions of 2.8–4.0 GPa and 720–870℃ for thermobaric ratios of 218–257℃/GPa, it appears that the decompressional melting is associated with an increase in thermal gradients during the exhumation in the different stages. Whereas the first is caused by decompression during initial exhumation of the deeply subducted continental crust, the second is caused by decompression during relamination of the UHP slices into the collision‐thickened orogenic lower crust. Peritectic amphibole and titanite were also recognized by comparing their petrographic textures with natural samples and experimental products. They were produced through water‐fluxed melting at 217 ± 3 Ma under lower P–T conditions, suggesting the liberation of aqueous fluids from the underlying exhuming UHP rocks. All of the peritectic minerals generally show compositional inheritance from their precursor minerals. Nevertheless, they commonly underwent dissolution when anatectic P–T conditions deviate significantly from those of peritectic reactions. This is indicated by the dissolution of peritectic zircon and garnet and by the occurrence of anhedral and embayed peritectic amphibole. As a consequence, the behaviour of peritectic minerals provides a snapshot of crustal anatexis for geochemical differentiation in collisional orogens.

Effect of different excitation currents on droplet transfer and weld formation of Al-Mg-Si alloy CMT MIX + Synchropulse welded joint

In this paper, the droplet transfer behavior, molten pool flow and weld formation of Al-Mg-Si alloy CMT MIX + Synchropulse welded joint under different excitation currents were studied. The external magnetic field (EMF) can effectively suppress the porosity and macroscopic pore (＞200 μm), especially at 20 A and 30 A excitation currents level. The EMF significantly reduces the droplet size (0 A → 20 A, 1.6 mm → 1.4 mm), which reduces the droplet heat and the impact force on the molten pool. The EMF changes the impact position of the molten droplet on the molten pool, making the temperature distribution on both sides of the molten pool inconsistent, which finally leads to asymmetrical weld cross-sectional morphology.

Pyroxenite-hosted chalcopyrites from Sung Valley, Meghalaya, NE India: implications for the formation of both high- and low-temperature sulfides in plume-derived magma

Abstract Sulfides play a crucial role in the distribution of chalcophile elements in the Earth's mantle. In this work, combined petrography and mineral chemistry of sulfide and diopside in a pyroxenite from an ultramafic–alkaline–carbonatite complex of NE India, related to the Kerguelen plume, was carried out and a considerably high sulfur concentration in the parental melt of the pyroxenite was obtained. Two types of sulfide, with similar compositions, were detected in pyroxenite: Type A are multifaceted polygons, elliptical and spherical in shape, occurring as poikilitic inclusions in diopside; and Type B are intergranular sulfides of irregular shapes in silicate grains. These sulfides are often partially replaced by magnetite. Mineral chemistry suggests that both types of sulfide are products of re-equilibration of high-temperature monosulfide solid solution and represent a low-temperature ( c. 400°C) mineral phase of the Cu–Fe–S system. Petrographical features suggest that the sulfides were separated as immiscible melt droplets at the time of sulfur saturation and fractionation of diopside in the coexisting silicate magma. Our study implicates that both high- and low-temperature sulfides can form in the plume-associated ultramafic rocks.

Macroscopic Orientation Domains Grown via Aerodynamic Levitation: A Path toward Single Crystals

Powder pellets of ca. 30 mg with the mol % composition 0.61Ga2O30.39La2O3 are levitated in a gas stream and melted using a pair of CO2 lasers. The levitating melt droplets crystallize to form La2Ga3O7.5 or LaGaO3 after the lasers are turned off. The microstructure of cross sections prepared from them is analyzed using scanning electron microscopy and electron backscatter diffraction. One of the beads containing La2Ga3O7.5 shows a fully crystallized, polycrystalline microstructure, whereas the other broke apart during cooling, and its cross section shows only a single orientation domain which is more than 7 mm2 in area. Solid-state 71Ga NMR spectroscopy was applied to this sample and showed that it was not a single crystal but contains only about 3 orientation domains. The bead containing LaGaO3 showed dendritic growth originating from multiple nuclei. Although a single crystal was not achieved by the applied experiments so far, a detailed correlation of measured cooling curves with the observed microstructures enables devising steps along the path toward single crystal production in future experiments.

Effects of porosity on drug release kinetics of swellable and erodible porous pharmaceutical solid dosage forms fabricated by hot melt droplet deposition 3D printing

3D printing has the unique ability to produce porous pharmaceutical solid dosage forms on-demand. Although using porosity to alter drug release kinetics has been proposed in the literature, the effects of porosity on the swellable and erodible porous solid dosage forms have not been explored. This study used a model formulation containing hypromellose acetate succinate (HPMCAS), polyethylene oxide (PEO) and paracetamol and a newly developed hot melt droplet deposition 3D printing method, Arburg plastic free-forming (APF), to examine the porosity effects on in vitro drug release. This is the first study reporting the use of APF on 3D printing porous pharmaceutical tablets. With the unique pellet feeding mechanism of APF, it is important to explore its potential applications in pharmaceutical additive manufacturing. The pores were created by altering the infill percentages (%) of the APF printing between 20 and 100% to generate porous tablets. The printing quality of these porous tablets was examined. The APF printed formulation swelled in pH 1.2 HCl and eroded in pH 6.8 PBS. During the dissolution at pH 1.2, the swelling of the printing pathway led to the gradual decreases in the open pore area and complete closure of pores for the tablets with high infills. In pH 6.8 buffer media, the direct correlation between drug release rate and infills was observed for the tablets printed with infill at and less than 60%. The results revealed that drug release kinetics were controlled by the complex interplay of the porosity and dynamic changes of the tablets caused by swelling and erosion. It also implied the potential impact of fluid hydrodynamics on the in vitro data collection and interpretation of porous solids.

The use of ultrasound to produce metallic powder in the plasma discharge electrolyte

In this work, a new process of plasma-electrolyte sputtering under the action of ultrasonic vibration is proposed, which makes it possible to obtain a finely dispersed metal powder with an average particle diameter of about 100 μm. The process involves irradiation with a high-power continuous laser on a consumable metal substrate vibrating at an ultrasonic frequency. The burning of a gas discharge around the vibrating electrode causes the surface to melt and small droplets are ejected. Preliminary results of spraying stainless steel 12X18H9T with a discharge power of 800 W and an ultrasonic vibration frequency of 20 kHz are presented. Vibration displacement does not significantly affect average particle size and size distribution according to capillary wave spray theory. The microstructure of the larger atomized particles exhibits a fine dendritic structure on the surface and shrinkage porosity at the center of the particles, indicating multiple surface nucleation for solidification.

In situ Si isotope and chemical constraints on formation and processing of chondrules in the Allende meteorite

Chondrules in undifferentiated meteorites are former silicate melt droplets of variable texture and composition. Although widely studied, the chondrule formation mechanisms and conditions that explain all properties of chondrules are yet to be identified. To further constrain the processes that affected chondrules in the solar nebula and on the meteorite parent body, we determined in situ Si isotope ratios and major and trace element compositions of minerals in chondrules of variable types and sizes from the Allende CV3 chondrite.The δ30Si in chondrule minerals ranges from −1.28 ± 0.19 to 0.55 ± 0.20‰ (2SE). The δ30Si in chondrules shows no direct relationship with chondrule sizes or with distance between core and rim. Barred olivine-rich chondrules record the highest δ30Si, likely because of faster cooling and less interaction with isotopically light nebular gas. Type I non-porphyritic and some porphyritic chondrules show overall higher δ30Si compared to type II porphyritic chondrules. Furthermore, Mg-rich olivine and Mg-rich pyroxene have systematically higher δ30Si compared to Fe-rich olivine and Fe-rich pyroxene.The variable δ30Si of type I chondrule silicates (Mg-rich) compared to type II chondrule silicates (Fe-rich) may be explained by variable interaction of chondrule silicates with the nebular gas in the solar nebula. We envision a combination of equilibrium and kinetic isotope fractionation of Si between nebular gas and Fe-poor silicates (such as forsterite, anorthite, enstatite and mesostasis) and Fe-rich olivine and orthopyroxene. Petrographic evidence suggests that the enrichment of Fe in some highly altered porphyritic chondrules and at chondrule rims was likely caused by hydrothermal alteration on the parent body. Therefore, the correlation of Fe and δ30Si of the chondrule minerals might serve as an indicator for the extent of further secondary processing of some chondrule minerals. The sum of these observations suggests that the formation and alteration of type II chondrules occurred by oxidation of originally reduced, metal-rich type I chondrules, both in the solar nebula and later on the meteorite parent body. Remaining 30Si depleted gas contributed to the isotopic composition of matrix silicates. The evidence favours the formation of chondrules and matrix of the Allende meteorite in nebular settings rather than by asteroid impacts.

Preparation of phytic acid‐based green intumescent flame retardant and its application in PLA nonwovens

AbstractAs a bio‐based and biodegradable textile, poly (lactic acid) (PLA) nonwovens are an important supplement for nature cotton, flax, and silk. This work concentrated on improving the flame retardancy of PLA nonwovens by introducing a novel eco‐friendly flame retardant (TPA), which was synthesized from phytic acid and tris(hydroxymethyl)methyl aminomethane. The structure, composition, and properties of TPA were fully characterized, and the results showed that TPA owned excellent thermal expansion performance. The flame retardancy of PLA nonwovens was efficiently improved by the presence of TPA. For PLA/23%TPA sample, the molten droplet was inhibited and the damaged area was decreased by 71.8%. The LOI value was increased from 18.0% of control PLA to 26.5%, and the peak heat release rate (pHRR) and total heat release rate (THR) were decreased by 30.2% and 29.0%, respectively. Besides, TG analysis confirmed a great char‐forming capability of the treated fabrics with the residue amount increasing from 1.8 to 11.6 wt% at 800°C. TPA released vapor, phosphorus radicals into the gas phase, and also promoted to form a compact char barrier in the condensed phase, which enhanced the carbonization and flame retardancy of PLA nonwovens. To our best knowledge, our work is one of the few studies focused on the flame retardancy of bio‐based PLA nonwovens.

Інертні гази та утворення пор в гранулах жароміцних сплавів

An integrated approach to the generalization and analysis of scientific and technical literature in the direction of improving the technological processes of spraying metal melts used a comprehensive approach The processing and analysis of experimental data for the determination of argon at different stages of heat-resistant alloy production were performed. Micro structural analysis of nickel-based heat-resistant alloys obtained by gas and centrifugal spraying was performed. A significant increase in the mass fraction of argon in the melt is shown when held in a furnace before gas or centrifugal spraying, the absence of capture of inert gas by sprayed liquid particles during centrifugal spraying is shown, unlike the process of gas spraying, it is shown. The results of the study indicate the absence of "dissolution" of Ar or a mixture of Ar-He in the liquid or solid state at argon levels up to 1 • 10-4% of the mass. It is established that centrifugal spraying of metal melts allows obtaining compact powders with small particle size distribution at relatively low energy consumption. It is also noted that argon is captured by the metal only in the process of moving on the disk, and not due to the weak dynamic gas interaction directly on the melt droplets. Hence, its amount in the metal increases after the argon’s injection into the furnace chamber and at the subsequent centrifugal spraying does not change, in comparison with gas spraying. A technological possibility has been found to significantly reduce the amount of gas pores and the mass fraction of inert gas in nickel-based heat-resistant alloys. Nickel-based heat-resistant alloys obtained by the method of gas and centrifugal spraying make it possible to improve the quality of products for the aviation industry, their reliability when operating in extreme conditions. Keywords: gas spraying, centrifugal spraying, heat-resistant alloy, argon, helium, pore formation.

High frame rate emission spectroscopy for ablation tests in plasma wind tunnel.

This article describes a novel high frame rate emission spectroscopy setup developed for measurements in high enthalpy flow fields. The optical setup and the associated hardware arrangements are described in detail followed by test case data to demonstrate the capability of recording spectral images at 1 kHz frame rate. The new system is based on a classical Czerny-Turner spectrograph but with a particular setup for high frame rate detection using a Generation II intensifier coupled with a high-speed camera. The high frame rate spectral images acquired enable, for the first time, investigation of the spatial distribution and temporal tracking and evolution of molten droplets of an ablating sample. In this paper, an example is shown from ablating meteorite samples tested in a high enthalpy plasma flow field corresponding to a flight scenario at an altitude of 80 km. This new instrumental configuration allows emission spectroscopic analysis of transient phenomena simulated in the high enthalpy ground test facilities with kHz resolution. The particular feature of this system is the ability to measure very faint spectral lines at high temporal and spatial resolution.

A numerical analysis on molten droplet hydrodynamics in sodium pool

The risk and consequences of vapor explosion during severe accidents are among the most critical safety problems to be considered in next-generation sodium-cooled fast reactors. The melt of the core material (corium) may be produced in the event of inadequate core cooling and/or during Loss of Coolant Accident (LOCA) leading to Core Disruptive Accident (CDA). Corium displacement can then lead to powerful fuel-coolant interactions (FCIs). One of the consequences of this molten corium-coolant interaction is that vapor formation and hence explosion may occur. Due to the problem complexity, only hydrodynamic effects of the multiphase system of a single-droplet vapor explosion phenomenon, without heat transfer, is considered. The present study focuses on simulating a molten droplet pre-conditioning (deformation before breakup) through the early stages of the molten fuel coolant interaction. In order to efficiently capture the melt-sodium interfaces and predict droplet behavior with appropriate mass conservation, calculations were conducted using the CFD code of STAR CCM+ for several melt coolant two-phase system configurations. The results demonstrate that the melt properties and velocity are the dominant factors on the melt droplet pre-conditioning behavior.

Numerical Simulation of Laminar-Turbulent Transition in Magnetohydrodynamic Convection in an Electromagnetically Levitated Molten Droplet of Cu-Co Alloys Under a Static Magnetic Field

Numerical Simulation of Laminar-Turbulent Transition in Magnetohydrodynamic Convection in an Electromagnetically Levitated Molten Droplet of Cu-Co Alloys Under a Static Magnetic Field

1,6-hexanediol rapidly immobilizes and condenses chromatin in living human cells.

Liquid droplets formed inside the cell by liquid-liquid phase separation maintain membrane-less condensates/bodies (or compartments). These droplets are important for concentrating certain molecules and facilitating spatiotemporal regulation of cellular functions. 1,6-hexanediol (1,6-HD), an aliphatic alcohol, inhibits weak hydrophobic protein-protein/protein-RNA interactions required for the droplet formation (droplet melting activity) and is used here to elucidate the formation process of cytoplasmic/nuclear condensates/bodies. However, the effect of 1,6-HD on chromatin in living cells remains unclear. We found that 1,6-HD drastically suppresses chromatin motion and hyper-condenses chromatin in human cells by using live-cell single-nucleosome imaging, which detects changes in the state of chromatin. These effects were enhanced in a dose-dependent manner. Chromatin was "frozen" by 5%, or higher, concentrations of 1,6-HD. 1,6-HD greatly facilitated cation-dependent chromatin condensation in vitro. This 1,6-HD action is distinct from its melting activity of liquid droplets. Alcohols, such as 1,6-HD, appear to remove water molecules around chromatin and locally condense chromatin. Therefore, liquid droplet results obtained using 1,6-HD should be carefully interpreted or reconsidered when these droplets are associated with chromatin.

Research on Melt Wettability Measurements Under Microgravity

Wetting and the interaction between liquid and solid phases are significantly affected by gravity. In recent years, Chinese scientists have carried out wettability experiments in space, but the limitations of experimental facilities have hindered their ability to carry out in-situ observations of the dynamic process of wettability in space. The future Chinese space station will provide a platform for real-time observation of the melt wettability in space. To study the wettability of melt under microgravity, a research method for real-time observation on orbit is proposed. The change in the image contour is determined on the basis of Hu moments, according to changes in the image, to control the acquisition frame rate. This can greatly reduce the memory required to store the images. At the same time, the proposed method uses the binarization method to process the images, and then performs target searching and positioning. Furthermore, it uses the Canny multi-level edge detection operator to extract the target contour. The Young-Laplace equation is used to fit the contour of the droplet. Finally, it obtains the surface tension and contact angle of the melt droplet in real time. The experimental results show that the data storage capacity can be reduced by 90% nearly using this method, and the change in the contact angle and surface tension in the melting process can be obtained in real time.

Synergistically Optimized Thermoelectric and Mechanical Properties in p‐Type BiSbTe by a Microdroplet Deposition Technique

Bismuth telluride is widely used in thermoelectric cooling, but the commercial zone‐melting materials suffer the poor mechanical property and dramatically decrease thermoelectric performance at intermediate temperature. Herein, a low‐cost and high‐efficiency preparation technique named microdroplet deposition is demonstrated to synergistically improve the thermoelectric and mechanical properties of Bi0.48Sb1.52Te3 alloy. It is found that a weakly preferred alignment with fine grains occurs during the molten droplets flattening and stacking processes. Although the obtained power factor is not further improved, the corresponding κl is significantly suppressed due to the increased interfacial thermal resistance between flakes by the micropores and dense grain boundaries. Consequently, a peak ZT of 1.12 and a Vickers hardness of 0.60 GPa are simultaneously achieved in the microdroplet‐deposited sample.