Melt Drop Research Articles

Research on Gas-Assisted Extrusion of Elastic Material Round-Tube for Flexible Robot Body.

The flexible robot is widely used in a variety of fields such as medical treatment, rescue and disaster relief, industry, and agriculture. Using elastic materials to prepare flexible robot body structures is the core of the study of flexible robots. Due to the small selection of materials, single preparation method, and long fabrication time, in this study, a new method of gas-assisted extrusion (GAE) of elastic material round-tube for flexible robot body was proposed, and the numerical simulation of GAE was carried out with nonsilicone elastic material round-tube under different viscosities. The results showed that with the change of viscosity, the velocity, pressure drop, and shear rate of melt in all directions change accordingly. When the viscosity is too small or too large, it is easy to bring negative effects on the GAE process of elastic materials. TPE and TPU were completely plasticized in the GAE, and the surface of the extruded elastic products was smooth and straight, with full gloss. Therefore, in the preparation of the flexible robot body, nonsilicone elastic materials and GAE forming methods can be considered.

Capillarity interaction of NiTi melt with crucible oxides

The interaction of nitinol melt with Al2O3, ZrO2, BeO and Y2O3 oxides used as crucible materials has been studied. Capillary interaction has been monitored directly using the method of sessile drop with video and thermal imaging in 10−3torr vacuum at 1350 °C. Nitinol melt drops have been formed in a high-density graphite dispenseror directly on the substrate surface. The contact angleson the surface of polished oxides have been obtained. The contact angles established within 30 s increase in the sequence Al2O3, ZrO2, BeO and Y2O3 from 30° to 70°. The corrosion resistance of the oxides has been studied for cross-sections using scanning electron microscopy with energy dispersion analysis. The phase composition at the ceramic/melt boundary has been studied using transmission electron microscopy. Thermodynamic analysis of melt chemical interaction with oxides has been conducted within equilibrium concentration calculation.

Influence of environmental pressure on the energy coupling and droplet transition behavior in laser welding with filler wire

The influence of environmental pressure on droplet behavior and weld formation in laser welding with filler wire for 304 stainless steel was investigated and the energy coupling behavior was analyzed. As ambient pressure increases from 5 kPa to 700 kPa, the weld depth decreases by 77 %, the variance of the weld width increases approximately 5 times, and the continuity of the weld surface formation deteriorates. During the welding process, a high-speed camera was employed to observe the melt pool, plasma, and melt drop transition behavior. With an increase in the ambient pressure followed by an increase in the metal evaporation temperature, the effects of shielding of the plasma and its internal metal vapor particles on the laser beam lead to a reduction in the depth of the melt. The inverse bremsstrahlung absorption of laser by plasma increased by approximately 36.3 times at 700 kPa compared with that at atmospheric pressure. The number of metal vapor particles at 700 kPa is approximately 3.58 times higher than that at 101 kPa, and the average particle diameter is approximately 0.4 times higher, causing enhanced absorption of laser light by the metal vapor particles. An increase in gas density at elevated ambient pressures resulted in a significant increase in the resistance to droplet descent and decrease in the drive force, leading to an increase in the droplet transition period. This change shifts from a liquid bridge transition to a particle transition, which is the main cause of the deterioration of weld surface formation at high pressures.

Sensitivity analysis of simulated premixed layer and vapour explosion in stratified configuration

Experiments of fuel–coolant interaction in stratified geometry at the PULiMS and SES (KTH, Sweden) test facilities resulted in spontaneous steam explosions. Prior to the explosion, a premixed layer of ejected melt drops in the water layer was observed in the experiments. Based on the experimental and analytical knowledge, we have recently developed a model for premixed layer formation in the Fuel-Coolant Interaction code MC3D and applied it to estimate steam explosion energetics.In the paper, a sensitivity study of this model is performed on the three main uncertain parameters of the premixed layer formation model, which define the melt fragmentation rate, the size of the ejected melt drops and the ejected melt drop velocity. The analysis is performed against the SES S1 and the PULiMS E6 experimental results. The chosen tests were selected as in both of them the same material was used, the geometry was similar, and both of them resulted in a spontaneous steam explosion. The effects can be observed in all the performed analyses and they are consistent in simulations of both experiments, affecting the premixed layer height as well as the explosion strength and duration. Some uncertainty of the experimental results is assessed, with the main limitation related to the visual observations. The combination of both analyses provides us with the assessment of future work necessity and prioritization.The presented sensitivity analysis of the premixed layer formation model enables a more reliable assessment of the stratified vapour explosion risk and its uncertainty in nuclear power plants and other industries.

A late Eocene lamprophyre-carbonatite association in the SE Tibetan Plateau: Rapid basalt-induced H2O-saturated partial melting of the upper crust

Abstract The processes by which lamprophyres and associated carbonatites are generated remain subject to debate. The Wase Basin on the SE Tibetan Plateau contains trachytes, rhyolites, and minor carbonatites that were emplaced at 37–36 Ma. Coeval lamprophyre dikes are widespread in the adjacent regions. Geochemically and petrographically, both the extrusive trachytes and dikes can be classified as lamprophyre. The numerous millimete r-sized SiO2-rich and calcite-rich ocelli that occur within the trachytes and dikes are solidified pseudomorphs of felsic and calcic melt drops, respectively. These ocelli combined with inherited granitic zircons suggest magma mixing between the calcic melt or felsic melt and basaltic melt. Petrographic evidence, mineral compositions, and zircon textures and U-Pb ages (827–682 Ma) suggest that the felsic melt and the calcic melt were generated by rapid H2O-saturated partial melting of Neoproterozoic granite and limestone, respectively, at >800 °C and <2 kbar, according to available experimental data. These melts were separated from each other and were stored at upper crustal depths, forming a zone of transient magma lenses or parcels. Melts mixed when an ascending basaltic magma intersected this zone. Reaction between the basaltic melt and the calcic melt occurred when they mixed, which formed clinopyroxene of predominantly diop side-hedenbergite solid solution. The observed heterogeneity of the upper crust combined with the variable degrees of magma mixing account for the great chemical diversity of the lamprophyres of SE Tibet. This model sheds new light on the petrogenesis of other lamprophyre-carbonatite associat ions elsewhere.

Low temperature multi-catalytic growth and growth mechanism of carbon nanotubes on carbon fiber surfaces

In order to reduce the etching effect of the catalysts to carbon fibers caused by high temperature during the chemical vapor deposition (CVD) process, four multi-element catalysts, Fe–Co, Fe–Ni, Co–Ni and Fe–Co–Ni, were used to realize the low temperature growth of carbon nanotubes (CNTs) on carbon fibers at 350 °C–400 °C. The results show that the growth state of CNTs has a great relationship with the type of catalysts. The catalytic efficiency of Fe–Co catalysts is low, but the graphitization degree of CNTs is relatively high. The Fe–Co–Ni catalysts has high catalytic efficiency but low graphitization degree of CNTs. The tensile strength of carbon fiber/CNTs reinforcements prepared by Fe–Ni catalysts at 400 °C is the highest, reaching 3.99 GPa, which is 11.14% higher than that of desized fiber. The melt drop phenomenon of the catalysts was found by TEM, indicating the formation of the liquid phase catalysts during the growth of CNTs. This phenomenon can change the diffusion mode of carbon atoms in the catalyst and significantly reduce the growth activation energy of CNTs, so that CNTs can grow at lower temperatures. Based on the detailed analysis of the CVD process, a low temperature growth model of CNTs on carbon fibers was proposed.

A long-lived mafic magma reservoir: Zircon evidence from a hornblende peridotite in the Hida Belt, Japan

Abstract Zircon geochronology has contributed to our understanding of the longevity of transcrustal magmatic systems; however, most studies focus on zircon records from felsic rocks due to the restricted occurrence of zircon in mafic-ultramafic rocks. We present U–Pb age, geochemical, and Hf–O isotope data for zircons from a hornblendite peridotite in the Hida Belt, Japan, that offers a unique opportunity to investigate the lifetime of a long-lived mafic plumbing system in an arc setting. We found two zircon U–Pb age clusters: an incompatible element-rich cluster at 196 Ma and an incompatible element-poor cluster at 186 Ma. Their homogeneous isotopic signatures (δ18O = 7.7‰ ± 0.8‰, εHf = 10.3‰ ± 1.7‰) indicate the same magma source despite the 10 m.y. age gap. These two clusters are explained by different zircon formation mechanisms that differ depending on whether or not zircon saturation requires differentiated melt with high SiO2. The enriched older zircons formed by local zircon saturation at the mafic melt-olivine interface, whereas the younger depleted zircons precipitated from the last drop of interstitial felsic melt co-existing with hornblendes. Our finding substantiates the longevity of mafic systems at lower crusts, which sustain transcrustal magma systems and crustal evolution.

On a mathematical model of the cooling and crystallization of metal drops during centrifugal granulation

A mathematical model has been developed for the crystallization of aluminum alloy granules under cooling conditions in an aqueous and water-steam media. The practical significance of the mathematical model lies in predicting the average value of the dendritic parameter of the obtained granules depending on the granulation method, the characteristics of the granulation process and the size of the obtained granules. The average value of the dendritic parameter makes it possible to predict the fineness of the granule structure and, consequently, the mechanical properties of the granular material. The mathematical model makes it possible to determine the speed of a melt drop in an aqueous media and takes into account the presence of a steam jacket effect, i.e., a vapor layer that appears between a crystallizing drop and an aqueous media, which significantly reduces the intensity of heat removal and the rate of crystallization. The application of the mathematical model was tested on the obtaining of granules of high-alloyed aluminum alloys (alloys D1 and D16 of the Al–Cu–Mg system, alloys V95 and V96Ts of the Al–Zn–Mg–Cu system), made by centrifugal spraying of the melt from a perforated rotating crucible and drip method during cooling in an aqueous media. The cooling rate and the crystallization rate of the granules obtained in real experiments were determined by measuring the dendritic parameter of the material structure. The mathematical model showed a high convergence of the simulation results and of real experiments of aluminum alloy granulation.

Study on rheological behavior of polystyrene‐polyisoprene‐polystyrene around viscous flow transformation: Effect of polystyrene block content and molecular weight

AbstractThe flow behavior of triblock copolymer polystyrene‐polyisoprene‐polystyrene (SIS) was different below and above the viscous flow transition temperature (Tf). The study investigated the relationship between molecular structure (molecular weight and polystyrene block content) and the macroscopic rheological properties of SIS melt around Tf via capillary rheometer. The results indicated that below the Tf, shear viscosity of SIS melt was controlled by the polystyrene (PS) block content. On the other hand, above the Tf, shear viscosity was controlled by molecular weight. The rheological phenomena were explained based on the state change of the PS domains below and above Tf. The effect of PS block content on the viscous flow activation energy (Eη) and pressure drop of SIS melt was also investigated.

Визуализация процессов, происходящих при самопроизвольном триггеринге парового взрыва

The vapor explosion process is an explosive increase in the volume of vapor, accompanied by a sharp rise in pressure when a hot melt enters a cold liquid medium with a temperature above its limiting superheat temperature. This phenomenon incurs the threat of great destruction and human casualties in certain types of accidents in the nuclear, metallurgical, pulp and paper industries. Nevertheless, there are still many insufficiently studied aspects of this phenomenon, one of which is the initiation (triggering) of the process. There are a number of logically fairly consistent descriptions of the processes occurring at a given stage of a vapor explosion. However, almost all of them are based on experiments carried out with external (forced) triggering. The article describes the data obtained during spontaneous triggering, i.e. under conditions much closer to reality. In this paper, using high-speed video recording (with a frame rate of up to 180 kHz and an exposure time of up to 2 μs), the first visualization of the processes occurring during spontaneous triggering of a vapor explosion on molten NaCl salt drops in distilled water subcooled to saturation temperature is presented. It is shown that when several drops of the NaCl melt interact with water, the micro vapor explosion that occurred on one drop, with an interval of several tens of microseconds, causes explosive vaporization on neighboring drops as well. Thus, the logical descriptions of the processes received instrumental confirmation.

Improving the properties of nickel/graphene oxide coated copper plate by changing the electroplating process conditions

One of the attractive ways to improve the mechanical properties and prevent damage to the surface of the copper plate is to create a nickel/graphene coating on it. In this work, the effect of bath type and process conditions on mechanical and wettability properties of nickel/graphene oxide coated copper plate via electroplating, has been investigated. Ultrasonic stirring of the bath with a power of 200 W increased the hardness of the coating to 747 Vickers and the wetting angle with molten steel to 125° by uniformly distributing the graphene oxide layers among the nickel grains and preventing the growth of the grains. By using a chloride bath instead of a Watts bath, due to the adhesion and delamination mechanism, a slight weight loss occurred in the pin-on-disk wear test. The coating obtained by electroplating in a chloride bath containing 20 cc of colloidal graphene oxide had a structure with a thickness of 12–15 μm consisting of large and compact masses of cauliflower with a uniform distribution of graphene layers. This sample shown a contact angle of 130° with the surface tension of 25 × 10−6 N/m to the aluminum melt drop and a 135° and 120 × 10−6 N/m to the steel melt drop.

Energetics of oxidation and formation of uranium monocarbide

To enable better implementation of uranium monocarbide (UC) as an advanced nuclear fuel for future high-temperature reactors, it is essential to have a thorough knowledge of its thermal and thermodynamic properties under reactor operational conditions. In this work, we studied thermal bulk oxidation of UC by simultaneous thermal analysis consisting of thermogravimetric analysis – differential scanning calorimetry coupled with evolved gas mass spectrometry (TGA-DSC-MS), and we examined the thermodynamic stability of UC using high temperature oxide melt drop solution calorimetry. In air, our studied UC sample (which contains ∼5 mol% UO2) was found to undergo a step-wise thermal oxidation process consisting of consecutive oxidations and thermal decomposition reactions: 0.95UC·0.05UO2→ UO3·0.29(CxOy) + 0.66CO2 → UO3·0.20(CxOy) + 0.09CO2 → UO3·0.03(CxOy) + 0.17CO2 → U3O8 + 0.03CO2 + 0.166O2. DSC was further used to determine the enthalpies of reactions associated with this series of oxidation reactions. Synchrotron X-ray diffraction (XRD) and extended X-ray absorption spectroscopy (EXAFS) were performed to characterize both the long- and short-range structures of UC. The standard enthalpy of formation (ΔH°f) of UC was determined to be –50.7 ± 10.8 kJ/mol·atom, in good agreement with previous values measured by bomb calorimetry. Lastly, the enthalpic landscape of U-C compounds, including UC, U2C3, and α-UC1.94, were established based on the enthalpy normalized per mole atom, which suggests that U-C phases are thermodynamically stable at lower C/U ratios.

Modelling and simulating of premixed layer in stratified fuel coolant configuration

A hypothetical severe accident in a nuclear power plant can lead to significant core damage, including melting of the core. The interaction between the molten core and the coolant water is known as a fuel–coolant interaction. One of the consequences can be a rapid transfer of a significant part of the molten corium thermal energy to the coolant in a time scale smaller than the characteristic time of the pressure relief of the created and expanding vapour. Such a phenomenon is known as a vapour explosion. Given possibly a large amount of thermal energy, initially stored in the liquid corium melt at about 3000 K, and pressure peaks of the order of 100 MPa, vapour explosion can be a credible threat to the structures, systems and components inside the reactor containment. It can also threaten the integrity of the reactor containment itself, which would lead to the release of radioactive material into the environment and threaten the general public safety. In analyses of severe accidents in nuclear power plants, a fuel–coolant interaction was mostly addressed in a geometry of a melt jet poured into a coolant pool. Based on some experimental and analytical work from the past a geometry with a continuous layer of melt under a layer of water, called stratified configuration, was believed to be incapable of producing energetic fuel–coolant interaction of sufficient magnitude to likely fail the containment. However, the results from recent experiments performed at the PULiMS and SES facilities (KTH, Sweden) with corium simulants materials contradict this hypothesis. In some of the tests, a premixing layer of ejected melt drops in water was clearly visible and was followed by strong spontaneous vapour explosions.The purpose of our research is to improve the knowledge, understanding and modelling of the fuel–coolant interaction and vapour explosion in stratified configuration. Based on the past experimental and analytical research, mechanisms for the premixed layer formation are identified and a model for the melt-coolant premixed layer formation in stratified configuration is presented. The analyses on the PULiMS and SES experimental results demonstrate the model’s capability to describe the premixed layer formation.

Анализ особенностей процессов теплообмена при кристаллизации гранул алюминиевых сплавов в водной и водно-паровой среде

The result analysis of the created mathematical model application of a detailed change in the temperature field and analysis of phase transitions during cooling and crystallization of a melt drop under cooling conditions in an aqueous and water-vapor medium have been carried out. The presented mathematical model allows one not only to determine the temperature fields in the body of a drop or a granule, but also determines the speed of movement of a drop in the coolant at any given time, determines the intensity of heat removal, the cooling rate and the rate of crystallization of the melt at different points in the volume. All this, in the end, makes possible to predict the size of dendrites, properties and phase composition of material of the obtained granules. The mathematical model was tested in the process of granulation of high-doped aluminum alloys (alloys D1 and D16 of the Al—Cu—Mg system, alloys B95 and B96C of the Al—Zn—Mg—Cu system) obtained by the centrifugal melt spraying method and the drip method during cooling in an aqueous medium. The crystallization rate in full-scale samples was measured on the basis of the method of analysis of the dendritic parameter of the material structure. The mathematical model showed a high degree of convergence between the results of simulation modeling and the results of real experiments for obtaining granules. In particular, the model showed fairly accurate results for the formation of granules at ultra-high crystallization rates, in the absence of a «steam jacket», namely, a steam layer arising between the body of the granule and the coolant that prevents the intensity of heat removal, and is an obstacle to increasing the crystallization rate due to a lower thermal conductivity of water vapor.

Simulation of deformation and growth during surfacing of aluminum bronze nanograins

In additive manufacturing, it is important to determine the technological and structural factors that control the crystallization process and specify the required structure of the product. The crystallization structure is affected by the parameters of the starting material and the crystallization conditions. Using the orientation of the grains of the substrate, which is formed after electron-beam surfacing of aluminum bronze, the modeling parameters were set by the molecular dynamics simulation. The process of deformation of three adjacent grains under constrained conditions and structural changes in the process of interaction with a melt drop and subsequent crystallization were considered. An analysis of grain deformation made it possible to reveal the role of geometric shear stress concentrators and to determine the significance of constrained conditions for deformation of polycrystal grains. It has been established that under the influence of a drop of melt, stacking faults are the least thermally stable, and twins are the most stable. The crystallographic orientation of the crystallizing grains coincides with the orientation of the substrate grains. During crystallization, columnar grains continue to grow, in which stacking faults and twins are formed.

Toward a deep understanding of the difference between isotactic and syndiotactic polypropylene on the fire performance and degradation behavior

This work investigated the difference in flame retardancy and degradation behavior of polypropylene (PP) composites with different configurations. The piperazine pyrophosphate (PAPP) was combined with melamine polyphosphate (MPP) to construct an intumescent flame retardant system, before incorporating into the PP system by melt blending. It showed that by the introduction of equal amounts of flame retardant, isotactic polypropylene composites (iPP-IFR) can achieve better flame retardancy with a desirable UL-94 V-0 rating, whereas syndiotactic polypropylene (sPP-IFR) shows poor fire performance. Melt index tests show that sPP-IFR sample is easy to flow and prone to melt drops. Differential scanning calorimetry results show that iPP-IFR has a higher degree of crystallinity. The thermogravimetric infrared coupling results show that sPP-IFR produces more small molecule hydrocarbon gases during combustion, making the system more difficult to achieve satisfied flame retardancy. The burning properties of iPP-IFR have been proven to be somewhat better compared to that of sPP-IFR, and sPP is more difficult for flame retardant modification.

Influence of arc mode on the microstructure and mechanical properties of 5356 aluminum alloy fabricated by wire arc additive manufacturing

In this paper, two arc modes of gas shielded metal arc welding (GMAW), a new pulsed mode (microMIG) and a non-pulsed mode (microMIG-CC), were used to melt ER5356 aluminum alloy wire for thin-wall fabrication. The influence of both arc modes on the melt–drop transition pattern, thin–wall properties, porosity, microstructure and mechanical properties was investigated at the same heat input. The microMIG mode adds SKS-based current time based on conventional pulsed GMAW for short-circuiting the transition, which leads to a faster spread of melt pool temperature. The rapid cooling of the melt pool contributed to the increase of grain nucleation rate and inhibited grain growth, resulting in smaller grain size in the microMIG mode specimens. In addition, the low porosity of microMIG specimens is attributed to the high voltage of the micro-MIG mode resulting in an unfocused heat source, which leads to a shallow penetration depth of the specimens and a reduced hydrogen escape distance. Compared with the microMIG-CC mode, the microMIG mode specimens have smaller grain size and lower porosity, therefore higher tensile strength is obtained. The isotropic property of thin walls is due to the existence of equiaxed grains and the random distribution of grain orientation. However, the aggregation of dislocations and the increase of precipitates make microMIG-CC have higher hardness. Overall, the mechanical properties of the thin wall specimens of WAAM 5356 aluminum alloy are higher than those of the as-cast specimens.

Hydrogen on softening-melting and slag forming behavior under the operation of blast furnace with iron coke charging

The effect on the slag formation behavior in the softening melting zone of a hydrogen-rich blast furnace is investigated by charging iron coke to the iron ore and controlling different volume fractions of hydrogen. The reduction mechanism of iron coke to iron ore under hydrogen-rich conditions is expounded that iron coke and hydrogen increase the concentration of CO around iron ore and promote its further reduction. The participation of iron coke and hydrogen promotes that FeO is reduced to Fe in iron ore, which prompts the production of high melting point substances in slag. The melting point of slag iron increases the melting start temperature. Hydrogen and iron coke promote the carburization of dripping iron so that molten iron drips quickly, which narrows the melting drop interval. From the perspective of the maximum pressure difference and the comprehensive permeability S value, the blast furnace permeability will be improved.

Energetics of oxidation and formation of uranium mononitride

Uranium mononitride (UN) is an advanced nuclear fuel currently being considered for use in several generation IV fast and thermal neutron spectrum core designs, with additional applications to thermal and electric nuclear propulsion reactors. To better understand the thermal behavior and thermodynamic stability of UN, we investigated the bulk thermal oxidation process and thermochemical reactions, including the enthalpy of oxidation and standard enthalpy of formation, by conducting thermalgravimetric analysis – differential scanning calorimetry coupled with mass spectrometry (TGA-DSC-MS), and high temperature transposed temperature drop and oxide melt drop solution calorimetry. The bulk oxidation of UN (containing a small amount of α-UN1.5+x) in air was found to follow a step-wise process characterized by consecutive oxidative reactions UN-UN1.5+x-UO2 → UO2-UO3Nk → UO3Nk → UO3 → U3O8. TGA results support that the UO2 – U2N3+x passivating layer delays the onset of rapid bulk oxidation of UN in air up to 662 K. Synchrotron X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) analyses were performed to characterize UN and its final oxidized product. The standard enthalpy of formation (ΔH°f) of UN was determined to be –144.4 ± 5.9 kJ/mol·atom, in good agreement with previously determined values from Pt encapsulation and bomb calorimetric experiments. Lastly, a negative linear correlation between ΔH°f and the N/U molar ratio was established based on the thermochemical data obtained in this work and previously reported enthalpies of formations of β-UN1.5-x and α-UN1.5+x.

Synthesis of aluminum-magnesian ceramics MgAl<sub>2</sub>O<sub>3</sub> in thermal plasma environment

A search for new methods for the synthesis of magnesium-aluminum ceramics is currently an urgent task for the refractory, metallurgical, and optical industries. The paper presents the experimental results of the magnesium-aluminum spinel MgAl2O3 synthesis in the thermal plasma. The samples are synthesized from natural materials such as magnesite MgCO3 and boehmite γ-AlO(OH) in the stoichiometric ratio Al2O3/MgO = 2.53. It is shown that the optimum conditions for the ceramic sample synthesis include 100 A current strength, 90 V voltage, 1 g/s gas rate, 30 s melting time. In these conditions, the formation of a hemispherical melt drop is observed, which confirms a complete melting of the initial components. The density of the crystallized sample is 3.5 g/cm3. The synthesized ceramic matrix is characterized by a high concentration of the stoichiometric phase MgAl2O4. At the same time, for 2θ = 29.4° and 30.8°, the reflection splits, thereby indicating to the nonstoichiometric spinel (Mg, Al)Al2O4 of variable composition. The ceramic matrix morphology represents prismatic grains 30–60 µm in size connected by fibers with a diameter of 1–3 µm.