Melting Layer Research Articles

Features of ablation and modification of Al<sub>2</sub>O<sub>3</sub>‒TiC ceramic surface structure during two-coordinate pulsed laser treatment

The main regularities of influence of two-coordinate pulsed laser treatment parameters on processes of ablation and structural modification of Al2O3‒TiC ceramics were established. The ambiguous influence of laser treatment parameters mode on the intensity of the ablation process was revealed. It was shown that structural modification nature is determined by parallel processes of fragmentation, melting and fusion of original ceramics grains and defective surface layer with the formation of new elements was established. The influence of laser treatment parameters mode on nature of structural modification is manifested through the size and number of newly formed elements of surface structure.

Magnetotelluric Imaging of the Lithospheric Structure of the Southern Oklahoma Aulacogen: Evidence for Long‐Term Weakening Caused by Rifting

AbstractMagnetotelluric data were used to study the lithosphere structure of the Southern Oklahoma Aulacogen (SOA). Inversion of the data revealed two low resistivity anomalies beneath the SOA. The first is located in the depth range 0–90 km in the crust and upper lithospheric mantle. The second extends from a depth 100 km to the base of the lithospheric mantle and extends away from the SOA to the ends of the profile. The cause of low resistivity anomalies is discussed in relation to the tectonic evolution of the region and recent laboratory experiments on rock conductivity. The first anomaly is attributed to the combination of (a) water present in mantle minerals and (b) the formation of hydrous mineral phases by interactions between a plume and the lithosphere during rifting. Grain size reduction and fabric alignment from deformation during the Ancestral Rocky Mountain (ARM) orogeny may have also contributed to the low resistivity. This enrichment phase may have mechanically weakened the lithosphere and allowed deformation to occur during the ARM orogeny. The low resistivity of the deeper anomaly is attributed to a fluorine‐enriched phlogopite layer that is also coincident with an observed seismic mid‐lithosphere discontinuity (MLD). A lithosphere keel of mantle minerals enriched in water underlies this layer and may have formed by accretion of the plume head to the lower lithosphere after rifting, which also rethickened the lithosphere to its present‐day depths. The MLD may then reflect a melt layer along a paleo lithosphere‐asthenosphere boundary entombed during the accretion.

Quality Evaluation of Hot Melt Welding of Plastic Pipes

In this paper, aiming at the welding quality problems of plastic pipes, finite element analysis method was used to evaluate the quality of welded joints through temperature, melting layer and stress. The results showed that: the crystallization degree and heat transfer distance of the welded surface and its heat-affected zone were different, resulting in different properties of welded joints. Stress stabilization will increase polymer apparent viscosity and reduce melt flow capacity, thus reducing residual stress.

Peak-ring magnetism: Rock and mineral magnetic properties of the Chicxulub impact crater

The Chicxulub impact event at ca. 66 Ma left in its wake the only complex crater on Earth with a preserved peak ring, characterized by a well-developed magnetic anomaly low. To date, little is known about its magnetic properties. The joint Integrated Ocean Drilling Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drill core M0077A revealed that the peak ring consists of uplifted and strongly deformed granitoid basement rocks overlain by a 130-m-thick impact melt and suevite layer. Pre- and postimpact hydrothermal systems affected this basement with maximum temperatures up to 450 °C. We used microscopy, mineral chemistry, temperature-dependent magnetic susceptibility, and hysteresis properties to characterize the magnetic mineralogy of pre-, syn-, and postimpact rocks. Compared to its amount of pure, stoichiometric shocked magnetite, the granitoid basement shows low magnetic susceptibility, which is in line with earlier experimental studies indicating that shock reduces magnetic susceptibility. Cation-substituted magnetite with varying compositions in the melt rocks carries a higher induced and remanent magnetization compared to the basement. In the granitoid basement, magnetite was partially oxidized to hematite by a pre-impact hydrothermal event, but at lithological contacts with high-temperature impact melt rock, this hematite was locally retransformed back to magnetite. Elsewhere in the granitoid basement, the temperature reached in the hydrothermal system was too low for hematite retransformation. It was also too low to anneal all the lattice defects in the shocked magnetite, which likely occurs above 540 °C. The presence of shocked magnetite in the granitoid basement well explains the magnetic anomaly low due to its unusually low induced magnetization.

Experimental Study on the Interaction of an Impulse Water Jet with Molten Metal

The impingement of a short-duration water jet on a pool of molten Rose’s metal is studied experimentally herein. Short-duration water jet impacting on the free surface of a molten metal pool with a temperature of 300 °C are generated with a pneumatic water delivery system, with two-camera high-speed video registration. A total of 14 experimental series, each containing 5 repeated tests, are performed for a water volume of 0.2–1 mL and a jet impact velocity of 4.1–9.0 m/s. The cavity development in the melt layer is studied, with the main stages described herein. Despite the significantly higher density of melt in comparison with water, the cavity can reach the melt pool bottom; furthermore, its further collapse results in the formation of a central jet rising to the height of a few centimeters. The maximum height of the central jet is shown to depend linearly on the total momentum of the water jet, and a semi-logarithmic correlation is found for the maximum diameter of the cavity. Repeatability analysis is performed within each experimental series, and the relative standard deviation for the melt splash height is shown to be from 8.8% to 26.8%. The effects of the pool depth, the vessel shape, and the water temperature are weaker in the range of the experimental parameters used here.

Morphological structure of the Pb island films melted on the Ta layer surface

An effective way to create self-organizing arrays of metal particles is to melt thin layers of substance on a poorly wetted surface. Such arrays may improve the technological properties of functional structures, and are themselves functional elements of modern devices and systems. During the melting of a solid layer on a poorly wetted substrate, an array of spherical particles is formed, which are evenly distributed over the surface of the substrate. The distribution of particles by size is determined by the thickness of the fusible layer and conditions of the deposition. The location of islands, formed after the melting of vapour-crystal deposited solid films, is determined primarily by the initial stages of de-wetting, when the thin continuous film starts to decay while remaining in solid state. This work studied self-organizing processes during the melting of Pb films deposited on a Ta substrate. The films were deposited on glass plates in a high vacuum and then after deposition were heated to a temperature slightly above the Pb melting point. After the heat treatment the samples were removed from the vacuum chamber and examined using SEM microscopy and EDS analysis. It was discovered that arrays of spherical particles are formed during the melting of micron-thick Pb films. The histograms of the size distribution of such particles are quite wide and can be represented as bimodal with partially overlapping maxima. This can be explained by active coalescence processes in thicker samples. This study demonstrated that small temperature gradients can cause noticeable kinetic effects that allow separate particles to move macroscopic distances and capture the surrounding substance. The study also estimated the energy associated with the optimization of the morphological structure of vacuum condensate and which is a physical factor of de-wetting.

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

The failure mechanism of plasma-facing components (PFCs) under extreme plasma conditions relevant for fusion reactors were investigated. Here, edge-localized mode (ELM)-like transient thermal shock irradiation experiments were performed on tungsten and molybdenum using compressed plasma flow, and combined with thermal–mechanical analysis by means of finite element simulations to discuss the grain structure evolution, cracking behavior and variations of hardness. When ELM-like thermal shock irradiation was sufficient to melt tungsten and molybdenum, a submicron-sized cellular sub-grain structure was created on their surface due to the high temperature gradient of the molten layer under the effect of Bénard–Marangoni instability. Rapid directional solidification from the bottom of the molten layer to the surface induced the formation of columnar grains dominated by the <200> orientation. While the formation of cellular sub-grains increased hardness, the thermal effect of irradiation and the formation of columnar grains led to softening. The high thermal stress induced by the ELM-like thermal shock produced macro-cracks and micro-cracks on the surface of tungsten and only micro-cracks on the surface of molybdenum. Macro-cracks were generated due to the intrinsic brittleness of tungsten. As a result of stress evolution, longitudinal macro-cracks extending perpendicular to the surface experienced transverse transformation within the material. Micro-cracks formed due to the embrittlement of the re-solidification zone, and their width increased with the melting depth. These results help us to understand failure mechanisms in PFCs under extreme operating conditions and are valuable for developing future fusion reactors.

Quantification of supplied laser energy and its relationship with powder melting process in PBF-LB/P using near-infrared laser

This study discusses the quantitative understanding of the laser input energy considering the optical properties and its effect on the melting process of powder materials in PBF-LB/P using a near-infrared laser. With the increased use of near-infrared lasers for PBF-LB/P in recent years, the influence of the input energy loss due to transmission and reflection on the powder melting process must be considered. Therefore, the modified energy melt ratio (Modified EMR), which is the ratio of the input energy to the energy required to melt the powder material, was proposed as a new energy supply index in this study. The energy absorbed by the powder layer was estimated from the transmission and diffuse reflection properties obtained in a previous study and the specular reflection properties obtained in this study. The powder layer thickness was determined by considering the consolidation of the powder layer, which affected the optical properties. The parts were fabricated with various optical properties, powder bed temperatures, and input energies to evaluate part density, which is closely related to the melting process. Compared to conventional indices, such as the energy density or EMR, the relationship between the Modified EMR and part density was more consistent, regardless of the optical properties and powder bed temperature. This study also investigated the effect of the laser heating of the layer below the powder layer on the melting process of the powder layer. The optical properties of a thin plate simulating the underlying layer were obtained, and the temperature increase in the underlying layer was determined from the known transmittance of the powder layer. It was concluded that heating the underlying layer does not accelerate the melting of the powder layer even at low powder bed temperatures, which require the highest laser energy for melting the powder material.

Precipitation Microphysics of Locally-Originated Typhoons in the South China Sea Based on GPM Satellite Observations

Locally-originated typhoons in the South China Sea (SCS) are characterized by long duration, complex track, and high probability of landfall, which tend to cause severe wind, rainstorm, and flood disasters in coastal regions. Therefore, it is of great significance to conduct research on typhoon precipitation microphysics in the SCS. Using GPM satellite observations, the precipitation microphysics of typhoons in the SCS are analyzed by combining case and statistical studies. The precipitation of Typhoon Ewiniar (2018) in the SCS is found to be highly asymmetric. In the eyewall, the updraft is strong, the coalescence process of particles is distinct, and the precipitation is mainly concentrated in large raindrops. In the outer rainbands, the “bright-band” of melting layer is distinct, the melting of ice particles and the evaporation of raindrops are distinct, and there exist a few large raindrops in the precipitation. Overall, the heavy precipitation of typhoons in the SCS is composed of higher concentration of smaller raindrops than that in the western Pacific (WP), leading to a more “oceanic deep convective” feature of typhoons in the SCS. While the heavy precipitation of typhoons in the SCS is both larger in drop size and number concentration than that in the North Indian Ocean (NIO), leading to more abundant rainwater of typhoons in the SCS. For the relatively weak precipitation (R &lt; 10 mm h−1), the liquid water path (LWP) of typhoons in the SCS is higher than that of the NIO, while the ice water path (IWP) of the locally-originated typhoons in the SCS is lower than that of the WP. For the heavy precipitation (R ≥ 10 mm h−1), the LWP and IWP of typhoons in the SCS are significantly higher than those in the WP and NIO.

Granitoids indicating moderate to high heat production associated with oceanic subduction system in the NE Tibetan Plateau

Regional heat flow provides a direct surface indication of the thermal state and energy balance of the lithosphere. Heat flux in the Tibetan Plateau remains poorly studied due to the lack of adequate information on heat flow. In this study, we investigated granitoids from the Gonghe-Guide district located in the NE Tibetan Plateau, which have important significance as hot and dry rocks with potential for geothermal resources. Samples from granitoid rocks as well as felsic dikes were collected from this area, and their geochemical data were combined with regional geophysical and drilling core data to evaluate a high-heat-flow anomaly. Our data show that granitoid rocks, including granodiorite, monzogranite, and syenogranite, crystallized at ca. 253−240 Ma, while felsic dikes formed ca. 230 Ma. The former were emplaced during the oceanic subduction process, whereas the latter formed in the syncollisional stage associated with the closure of the paleo-Zongwulong Ocean. Geochemically, these granitoid rocks are metaluminous to slightly peraluminous, with an average differentiation index (DI) value of 80, and they are classified as weakly to moderately fractionated I-type granites. The felsic dikes are peraluminous with high DI values (average of 95), typical of highly fractionated I-type granites. In terms of their high K and especially U and Th abundances, the calculated radioactive heat generation produced by the granodiorite, monzogranite, syenogranite, and felsic dikes is 1.85, 2.91, 6.85, and 3.02 μW/m3, respectively. Their moderate to high heat production generates a local heat-flow anomaly of 14.8−22.2 mW/m2 above the regional value of subduction zones, accounting for 11%−18% of the total regional heat flow. In combination with regional magnetotelluric data, the high-heat-flow anomaly may be attributed to an additional heat-flow contribution from a partial melt layer beneath this region. Furthermore, there is a significant positive correlation between the radioactive heat generation and magmatic fractionation, indicating that the enrichments of heat-producing elements are controlled by fractional crystallization and subsequently source composition. The granitoid rocks with high heat generation correspond to the large-scale intermediate-felsic magmatism during the subduction stage. We propose a model wherein a continuous subduction process during the closure of the paleo-Zongwulong Ocean and protracted cooling and crystallization processes resulted in the enrichment in heat-producing elements.

Modelling the effects of areal capacity on mass transport in liquid metal batteries

Liquid metal batteries (LMBs) are formed from three molten layers, and the interaction of thermal, compositional and electromagnetic forces influences their performance and stability. The coupled behaviour of these forces in LMBs remains uncharacterised, so in this study, a three-layer numerical model was developed to investigate this interaction in lab-scale to grid-scale batteries; areal capacities 0.9–7.5 Ah/cm2. Thermal convection was modelled first, and Rayleigh-Bénard convection, a flow observed in the anode, only developed in batteries larger than current grid-scale batteries. Electro-vortex flow was introduced and found to suppress thermal convection in the anode and electrolyte layers. Thermally stratifying temperature gradients in the cathode had some effect on electro-vortex flow, but compositional effects from mass transport were dominant. Finally, a background magnetic field was used to induce swirl flow, and the coupled effects of this flow with thermal gradients was studied. Swirl flow also suppressed thermal convection, and stratifying temperature gradients had little effect on the flow; however, compositional gradients in the cathode decelerated the poloidal velocity of swirl flow during discharge. These results show that electromagnetic flows are dominant in LMBs, and mixing compositional gradients in the cathodes of large areal capacity batteries remains a challenge in the field.

Underlying Microphysical Processes in the Melting Layer during Moderate Precipitation: Evidence from Ground-Based Data

Abstract We performed a detailed analysis of ground-based data to investigate changes in the morphological properties and particle size distribution of precipitation particles as they fall through the melting layer (ML). In July 2013, we started continuous precipitation monitoring in Sapporo (Japan) with a two-dimensional video disdrometer, an electrical balance–type snow gauge, and an X-band marine radar. We used data collected from 0943 to 1040 Japan standard time (JST) 10 March 2015 for analysis, when the bright band progressively descended to the ground surface and precipitation intensity was moderate and approximately steady (∼10 mm h−1). We found that the aggregation of aggregates in the upper half of the ML did not necessarily result in large raindrops. Almost all of the snow particles with a melted diameter (Dm) ≥ 4 mm broke up before they melted into raindrops of equivalent size. The apparent one-to-one relationship between melting snow particles and raindrops held for particles with 2 &lt; Dm &lt; 3 mm. Most small raindrops were generated by the successive breakup of melting particles in the lower half of the ML.

Ablation behavior of La2O3 modified C/C–ZrC composites fabricated by precursor infiltration and pyrolysis

La2O3 modified C/C–ZrC composites were produced by precursor infiltration and pyrolysis (PIP) technique, and the ablation resistance was tested in plasma flame at 1700 and 2400 °C. Results displayed that the density of the composites was ∼1.90 g/cm3, and ZrC and La2O3 were uniformly distributed in them. At 2400 °C, the linear and mass ablation rates of La2O3 modified C/C–ZrC composites were 8.89 ± 0.82 μm/s and 0.21 ± 0.01 mg/s, respectively. The positive effect of La2O3 was to promote the liquid phase sintering of ZrO2, which was helpful to promote the formation of an inlaid La–Zr–O molten layer that acted as a protective barrier. At 1700 °C, the composites exhibited minimal linear and mass ablation rates of 0.41 ± 0.14 μm/s and 0.04 ± 0.01 mg/s, respectively. At this temperature, La2O3 promoted the solid phase sintering of ZrO2 to form an intact La–Zr–O particle-stacked layer, and the intact oxide layer positively protected the composites.

Numerical simulation and analysis of contact erosion by high-current and low-voltage air arc considering the movement of arc

When a low-voltage circuit breaker (LVCB) breaks a high current, the contact erosion caused by the arc greatly reduces the LVCB’s breaking performance and service lifetime. Therefore, this paper uses AgW alloy contacts as a research object, which are commonly used for breaking high currents, and establishes a contact erosion model for an LVCB with a breaking current of 14 kA. The model considers the energy balance of a contact surface and uses a solidification and melting model and a dynamic mesh model to deal with the phase transition problem of the contact material and introduces the arc movement into this model. Using this model, the contact melting and evaporation width, erosion depth, erosion rate, and erosion mass are calculated when Ag and AgW30 and AgW70 alloys are used as contact materials. The influence of W-content on the erosion characteristics of a contact is analyzed. The results show that, although the introduction of element W significantly reduces the erosion mass, it advances the time when the melting point and boiling point are reached. The position, width, and depth of the melting pool and melting layer thickness change with the movement of the arc. In the process of contact erosion considering the movement of the arc, the introduction of W element will increase the width of the molten pool and the solidification time of the molten material. Especially when the mass percentage of element W in the contact material reached 70%, the solidification time of the molten material greatly increased, which weakened the welding resistance of the contact.

Purification of monoethylene glycol by melt crystallization

Separation of glycols with close boiling points and relatively high viscosity at their melting point is a challenge in the production of high purity products downstream of biorefinery processes. In this work, the efficiency of the layer melt crystallization process with acetone as the assisting solvent was evaluated for a mixture of monoethylene glycol and 1,2-pentanediol. Solid-liquid equilibrium was measured and modelled with the NRTL and modified UNIFAC group-contribution models to evaluate the thermodynamic driving force of crystallization. Layer melt crystallization was conducted to determine the effect of solvent composition on purity, distribution coefficient of impurity, crystal growth rate, and yield at different operating conditions. Addition of the solvent altered the thermodynamics and kinetics of crystallization, thereby altering the purity level of the final product. An effective distribution coefficient of impurity between 0.1 and 0.6 in one-step crystallization was obtained, depending on the solvent composition and the applied operating conditions.

Purity-Targeted Prediction of the Cooling Profile in Layer Melt Crystallization via Thermal Approximation

Purity-Targeted Prediction of the Cooling Profile in Layer Melt Crystallization via Thermal Approximation

Performance and analysis of key factors on the design of melt crystallization‐based separation process

AbstractThis study combines theoretical models with experiments to analyze the impurity migration mechanism and obtain the key factors of separation optimization for the design of layer melt crystallization. The fractal slice model was used to explore pore structure formation and calculate the heat properties of the crystal layer. It was found that the fractal characteristics approached the features of Euclidean geometry with increasing porosity, and the thermal conductivity showed a linear decrease with the porosity. Three kinetic models were established based on the temperature difference to reveal quantitative correlations with the degree of supercooling (or superheating). The effects of the pore structure, kinetic behavior, and sweating intensity on the separation process are highlighted. Finally, this work analyzed the important roles of kinetic factors and impurity migration distribution, where a qualitative analysis revealed that the kinetic effect was important in impurity migration in the sweating process.

Fiber laser cutting study on ternary NiTiV shape memory alloy

ABSTRACT Shape memory alloys (SMA) made of nickel–titanium (NiTi) have grown in popularity because of their functionality and mechanical qualities. Vanadium (V) was added as an alloying element to the regular binary NiTi shape memory alloy for enhancement of its ability to retain memory at high temperatures. In this research, the machined surface roughness (Ra) and material removal rate (MRR) of fiber-laser cutting of Ni50Ti48V2 SMA were investigated using Box-Behnken design (BBD) experimentation. The surface characteristics in terms of Ra decreased by 57.79% while cutting speed and laser power decreased and the frequency level gradually increased. The microhardness was high due to the resolidified molten layer on the machined surface. A surface morphology study indicated the formation of debris and striations due to the flow of nitrogen gas. DSC analysis reveals a minimal variation in the shape memory property even after laser machining.

Fractal model-based crystal pillar structure simulation and mechanism analysis of impurity migration process in layer melt crystallization

Layer melt crystallization (LMC) is regarded as a green purification technique and is widespread in the separation of isomers. Based on the highly efficient separation, this work combined the experiments and models to explore the crystal pillar structure and impurity migration. Firstly, we established the crystallization process kinetic model to reveal the crystal growth rules and pointed out the correlations of growth rate and supercooling degree. Then the fractal porous model was used to analyze the crystal pillar structure, where the fractal characteristics tended to the Euclidean geometric features with porosity increase in both crystallization and sweating processes. Next, we simulated the melt seepage rate through the pore channel, where the modeling results showed high consistency with the experiments. Finally, the effects of pore structure, kinetics, and sweating intensity on the separation and impurity migration in both crystallization and sweating processes were revealed, to guide the technical design.

Transportation and deformation of high-speed aluminum nanoparticles in inert gas with molecular dynamics study

In addition to complex deformation, high-speed nanoparticles in gas are also accompanied by significant size and interfacial effects. In this work, we simulate the transportation behavior of high-speed aluminum nanoparticles in helium gas with the classical molecular dynamics method. The evolution of aerothermodynamic quantities of solid particles and liquid particles is revealed, and different temperature rise effects are found. Furthermore, the melting of aluminum particles induced by high aerodynamic drag force is discovered, and the melting threshold conditions are proposed. In low-density (0.002 g/cm3) and high-density (0.02 g/cm3) gas, the initial velocity at which particles start to melt is 6 and 4 km/s, respectively. During the deformation of solid particles, the evolution of dislocation motion is discussed, and the evolution of the development characteristics of the molten layer is given. During the deformation of the liquid particles, vibration deformation and bag deformation modes are observed. The threshold conditions for deformation mode transitions are also given. Only in high-density gas, bag deformation occurs when the initial velocity of particles (D &amp;gt; 5 nm) exceeds 6 km/s. The local mechanical quantity of gas is used to explain the variation of the drag force of the particles. Moreover, the drag force model is corrected according to temperature and deformation effects. Within a certain period, the model results overestimate the drag force, and the error with the simulation results is about 25%. This provides a model reference for high-speed nanoparticle dynamics and two-phase flow problems.