Two-stage Melting Research Articles

Two-Stage Melting of Near-Symmetric Random Poly[(butylene succinate)-ran-(butylene adipate)] Copolyesters

Two-Stage Melting of Near-Symmetric Random Poly[(butylene succinate)-<i>ran</i>-(butylene adipate)] Copolyesters

Evaluation of plume-induced continental crust growth rate in early Earth: Insight from integrated petrological-thermo-mechanical modeling

The origin of Earth’s felsic continental crust remains a mystery. The generation of felsic continental crust requires a two-stage partial melting from original mantle sources. There are two hypotheses for the continental crust generation in the early Earth. One is the subduction-related magmatism, e.g., island arcs, which produces intermediate to felsic magma that constitutes the early buoyant continental crust. The other is the magmatism induced by the mantle plume that creates thick basaltic crust and finally the continental crust. However, there is controversy about the origin of plate tectonics, which is an obstacle for simply applying the subduction-induced model in the early Earth. On the other hand, the efficiency of mantle plume-induced continental crust growth remains unknown. In this study, we develop a new numerical model, integrating the petrological-thermo-mechanical model with melt migration and crystallization, to evaluate the efficiency of continental crust production by mantle plumes in Earth’s history. Our results indicate that mantle plumes are considerably more effective for continental crust generation in the hot early Earth than that in the present Earth. The contribution of plume-induced continental crust growth may be greatly promoted by the possible high frequency of mantle plume generation in the early Earth than the present.

The influence of deformation affected region on microstructure and mechanical property of 316L fabricated by hybrid additive-subtractive manufacturing

The hybrid of additive manufacturing and subtractive manufacturing is promising in producing high-quality and high-accuracy parts made of hard-to-machine metallic materials with complex geometries. However, few studies have been conducted to analyze the influence of responses from subtractive manufacturing, especially the plastic deformation region induced by mechanical cutting, on the following additive manufacturing processes. This paper comprehensively investigates the impact of finishing milling on the mechanical properties and quality of 316L fabricated by hybrid additive-subtractive manufacturing. The whole manufacturing process consisted of a two-stage micro selective laser melting μSLM process with three scanning speeds and one finishing milling process. Typical machining responses including phase, cutting force, surface roughness at different manufacturing stages were analyzed; the mechanisms of how the deformation-affected region induced in subtractive manufacturing process affects the microstructure, hardness, and mechanical properties after the second-stage additive manufacturing were explored. Fine grains were formed after the second-stage μSLM in the connected region, because of the lower G/R ratio and the higher G × R value, whereas the hardness in this region was lower than the bulk material consisting of coarse grains, caused by the thermal softening effect induced in mechanical cutting. The elongation rate was increased due to the existence of the grain-boundary-rich connected region.

Effect of composition and architecture on the thermodynamic behavior of AuCu nanoparticles.

The chemical and physical properties of nanomaterials ultimately rely on their crystal structures, chemical compositions and distributions. In this paper, a series of AuCu bimetallic nanoparticles with well-defined architectures and variable compositions has been addressed to explore their thermal stability and thermally driven behavior by molecular dynamics simulations. By combination of energy and Lindemann criteria, the solid-liquid transition and its critical temperature were accurately identified. Meanwhile, atomic diffusion, bond order, and particle morphology were examined to shed light on thermodynamic evolution of the particles. Our results reveal that composition-dependent melting point of AuCu nanoparticles significantly departs from the Vegard's law prediction. Especially, chemically disordered (ordered) alloy nanoparticles exhibited markedly low (high) melting points in comparison with their unary counterparts, which should be attributed to enhancing (decreasing) atomic diffusivity in alloys. Furthermore, core-shell structures and heterostructures demonstrated a mode transition between the ordinary melting and the two-stage melting with varying Au content. AuCu alloyed nanoparticles presented the evolution tendency of chemical ordering from disorder to order before melting and then to disorder during melting. Additionally, as the temperature increases, the shape transformation was observed in AuCu nanoparticles with heterostructure or L10 structure owing to the difference in thermal expansion coefficients of elements and/or of crystalline orientations. Our findings advance the fundamental understanding on thermodynamic behavior and stability of metallic nanoparticles, offering theoretical insights for design and application of nanosized particles with tunable properties.

High temperature interfacial dynamics in Nickel coated Aluminum nanoparticles

Molecular dynamics simulations are used to investigate the thermal stability of Al-Ni core–shell nanoparticles (NP) with different core sizes and shell thicknesses. Our study reveals that a distinct two-stage melting occurs during the continuous heating of bimetallic NPs. Unlike previous studies for single NP, where melting start from the outer surface and gradually encompass the core of the material, our result clearly indicates the interface dominated melting phenomena. It is evidenced in our analysis through microstructure, coordination number, and Lindemann index, that this interface dominated phenomena does not alter with decreased shell thickness. We estimate that the interfacial misfit, and bond energy orders (Ni-Al, Al-Al, and Al-Al) are the sources of such premelting phenomena to be nucleated at the interface. This study provides a fundamental perspective on the melting behavior of bimetallic nanoparticles and can be extended towards multimetallic NPs at the atomic level.

Anisotropic Melting of Frustrated Ising Antiferromagnets.

Magnetic frustrations and dimensionality play an important role in determining the nature of the magnetic long-range order and how it melts at temperatures above the ordering transition T_{N}. In this Letter, we use large-scale MonteCarlo simulations to study these phenomena in a class of frustrated Ising spin models in two spatial dimensions. We find that the melting of the magnetic long-range order into an isotropic gaslike paramagnet proceeds via an intermediate stage where the classical spins remain anisotropically correlated. This correlated paramagnet exists in a temperature range T_{N}<T<T^{*}, whose width increases as magnetic frustrations grow. This intermediate phase is typically characterized by short-range correlations; however, the two-dimensional nature of the model allows for an additional exotic feature-formation of an incommensurate liquidlike phase with algebraically decaying spin correlations. The two-stage melting of magnetic order is generic and pertinent to many frustrated quasi-2D magnets with large (essentially classical) spins.

Two-stage melting of an intercomponent Potts long-range order in two dimensions

The interplay of topology and competing interactions can induce enriched phases and phase transitions at finite temperatures. We consider a weakly coupled two-dimensional hexatic-nematic XY model with a relative ${Z}_{3}$ Potts degrees of freedom, and apply the matrix product state method to solve this model rigorously. Since the partition function is expressed as a product of two-legged one-dimensional transfer matrix operator, an entanglement entropy of the eigenstate corresponding to the maximal eigenvalue of this transfer operator can be used as a stringent criterion to determine various phase transitions precisely. At low temperatures, the intercomponent ${Z}_{3}$ Potts long-range order (LRO) exists, indicating that the hexatic and nematic fields are locked together and their respective vortices exhibit quasi-LRO. In the hexatic regime, below the BKT transition of the hexatic vortices, the intercomponent ${Z}_{3}$ Potts LRO appears, accompanying the binding of nematic vortices. In the nematic regime, however, the intercomponent ${Z}_{3}$ Potts LRO undergoes a two-stage melting process. An intermediate Potts liquid phase emerges between the Potts ordered and disordered phases, characterized by an algebraic correlation with formation of charge-neutral pairs of both hexatic and nematic vortices. These two-stage phase transitions are associated with the proliferation of the domain walls and vortices of the relative ${Z}_{3}$ Potts variable, respectively. Our results thus provide a prototype example of two-stage melting of a two-dimensional LRO driven by multiple topological defects.

Interaction of MnTOEtPyP4 porphyrin with DNA

The binding of water-soluble meso-tetra-(4N-oxyethylpyridyl) porphyrin (H2TOEtPyP4) and its manganese (III) derivative (MnTOEtPyP4) with calf thymus DNA have been quantitatively studied using UV/Vis spectrophotometry, Circular Dichroism (CD), thermal melting curves and viscometry. The results show, that porphyrins interact with DNA via one binding mode at low relative concentrations (r) and two binding modes at high values of r. The binding constant (Kb ) and stoichiometry (n) were determined from binding isotherms for both porphyrin–DNA complexes. The thermal melting analysis indicates that the double-helical structure of DNA molecules is stabilizing in presence of studied porphyrins. At certain concentrations of porphyrin, two-stage melting curves were observed, which indicates the existence of two different binding modes. Obtained results show that MnTOEtPyP4 associates with DNA duplex via outside binding mode. Communicated by Ramaswamy H. Sarma

Melting and Crystallization Features of CsPbBr3 Perovskite

The all-inorganic perovskite cesium lead bromide (CsPbBr3) has attracted considerable attention as a promising material for optoelectronics and high-energy radiation detectors. In order to obtain a bulk single crystal from a melt, it is crucial to understand the peculiarities of melting and crystallization processes. Here, the solid–liquid and liquid–solid phase transitions were studied by differential thermal analysis at different heating/cooling rates (0.1, 1, 3, 5, and 10 °C/min). A two-stage melting mechanism of CsPbBr3 perovskite was proposed. The critical maximal sample temperature (Tcritical) was determined for each heating rate. If the sample was heated to a temperature below Tcritical, the crystallization occurred at a temperature higher than the melting point. Contrarily, if the sample was heated to a temperature higher than this critical value, the melt crystallization occurred with supercooling. We believe that such crystallization features are closely related to the melt structure, which changes during the sample heating. The activation energies of melting and crystallization processes of CsPbBr3 were determined to be 1846 and 1940 kJ/mol, respectively. For the first time, this study demonstrates the impact of heating and cooling conditions on the melting and crystallization processes of the bulk CsPbBr3. It is significant for gaining a fundamental understanding of the crystal growth and fabrication of high-quality monocrystalline materials.

Synthesis of Large Amounts of Volatile Element-Bearing Silicate Glasses Using a Two-Stage Melting Process

Synthesis of Large Amounts of Volatile Element-Bearing Silicate Glasses Using a Two-Stage Melting Process

How atoms of polycrystalline Nb20.6Mo21.7Ta15.6W21.1V21.0 refractory high-entropy alloys rearrange during the melting process

The melting mechanism of single crystal and polycrystalline Nb20.6Mo21.7Ta15.6W21.1V21.0 refractory high entropy alloys (RHEAs) were investigated by the molecular dynamics (MD) simulation using the second-nearest neighbor modified embedded-atom method (2NN MEAM) potential. For the single crystal RHEA, the density profile displays an abrupt drop from 11.25 to 11.00 g/cm3 at temperatures from 2910 to 2940 K, indicating all atoms begin significant local structural rearrangement. For polycrystalline RHEAs, a two-stage melting process is found. In the first melting stage, the melting of the grain boundary (GB) regions firstly occurs at the pre-melting temperature, which is relatively lower than the corresponding system-melting point. At the pre-melting temperature, most GB atoms have enough kinetic energies to leave their equilibrium positions, and then gradually induce the rearrangement of grain atoms close to GB. In the second melting stage at the melting point, most grain atoms have enough kinetic energies to rearrange, resulting in the chemical short-ranged order changes of all pairs.

Decoupled Zn-Sr-Nd isotopic composition of continental intraplate basalts caused by two-stage melting process

Ocean island basalts (OIBs) with Zn isotopic ratios higher than the normal mantle (δ66Zn = 0.17 ± 0.08‰) or mid-ocean ridge basalts (MORBs; δ66Zn = 0.27 ± 0.06‰) generally also have an enriched Sr-Nd isotopic signature, suggesting carbonate-bearing eclogites, whose protolith is inferred to be subducting altered oceanic crust, in their mantle source. On the contrary, continental intraplate basalts with high δ66Zn usually show depleted Sr-Nd isotopic signatures (i.e., decoupled Zn-Sr-Nd isotopic composition). To elucidate the origin of the decoupled Zn-Sr-Nd isotopic composition in continental intraplate basalts, we report the discovery of both coupled and decoupled Zn-Sr-Nd isotopic data for a suite of Cenozoic continental intraplate basalts from the Zhejiang province, Southeast China. These basalts display clear spatial and temporal geochemical variations, with early-stage inland low-silica samples presenting moderately enriched Sr-Nd isotopic signatures and high δ66Zn (coupled Zn-Sr-Nd isotopic composition, similar to OIBs), and later-stage coastal high-silica samples that display a pronounced δ66Zn decrease with increasing SiO2 and 87Sr/86Sr and with decreasing alkali contents and 143Nd/144Nd (decoupled Zn-Sr-Nd isotopic composition). The early-stage basalts with coupled high Zn-Sr-Nd isotopic signatures are also more enriched in incompatible elements than any other basalts from eastern China reported so far. We explain the spatial and temporal geochemical variations of these basalts as the result of two main melting events: 1) the low-silica early-stage magmatism mostly occurs inland and results from high-pressure partial melting of a carbonated eclogite-bearing asthenospheric mantle. Because of the presence of a thick lithosphere limits the melting of the depleted mantle component, the signature of the Zn-Sr-Nd isotopically enriched, and more fusible carbonated eclogite is preserved. 2) At the later stage, magmatism mostly occurs on the coast where the subcontinental lithosphere is thinner. Hence, decompression melting progresses to shallower depth, resulting in an increase of the contribution from the depleted peridotite matrix and a dilution of the signal from the isotopically enriched fusible component. Further upwelling and in-situ melting at the base of the subduction-modified sub-continental lithospheric mantle (SCLM) explains both the decoupled Zn-Sr-Nd isotopic signature of the coastal basalts and their major and trace element variability. We further propose that decompression melting is driven by small-scale convection resulting from variations of lithospheric thickness. Our data highlight the importance of dynamic melting of carbonated eclogite-bearing asthenosphere and subsequent lithospheric melting in preservation and destruction of the coupled enriched Zn-Sr-Nd isotopic signature of carbonated eclogite component and generation of the apparent decoupled Zn-Sr-Nd isotopic signal commonly observed in continental intraplate basalts.

Molecular Dynamics Investigation on Thermal Stability and Shape Evolution of Pd-Au Heterostructured Nanorods: Implications for Catalysis

Heterogeneous nanostructures have attracted tremendous interest because of their exceptional properties and promising applications in extensive fields. In this work, we employed molecular dynamics (MD) simulations to investigate thermally driven structural and shape evolutions of Pd-Au heterostructured nanorods consisting of hexagonal close-packed (hcp) Pd-core/Au-shell structures in the middle and face-centered cubic (fcc) Au terminated at both ends (referred to as fcc-2H-fcc Pd@Au nanorods). Our results reveal that these nanorods exhibit a two-stage melting mode, that is, melting initiates at both ends of the nanorods and extends to the middle with increasing temperature. Moreover, specific thermodynamic behaviors are associated with the core size. With the lowering core size, the difference in the melting points between the core and the shell in the nanorods decreases accordingly, and the two-stage melting characteristic tends to be obscure. During heating, these nanorods experience a significant shrinkage after the melting of Au at both ends, forming a liquid-like shell/solid-core structure prior to the overall melting. However, two-stage melting is absent in fcc-2H-fcc Au nanorods. These results extend the fundamental understanding of the thermal stability of metallic heterostructured nanorods and provide a theoretical reference for the design and application of one-dimensional metallic heterostructures.

Coexistence of two types of Late Paleocene adakitic granitoid, Soursat complex, NW Iran

Late Neoproterozoic basement of the Soursat complex to the southeast of Shahin-Dej, NW Iran, spans an area wider than 100 km2 and is cut by Paleogene monzonite and granodiorite bodies. Zircon U-Pb dating yields monzonite and granodiorite crystallization ages of 54.7 ± 3.8 Ma and 57.7 ± 2.9 Ma, respectively. The monzonite group has relatively high MgO (2.40–7.01 wt%), Cr (37.5–233 ppm) and Ni (30.6–177 ppm), and high Sr/Y (103−132) and La/Yb (68.0–102) similar to low silica-adakites (LSA). The granodiorite group has low MgO (<1 wt%), Ni (<10 ppm) and Cr (<33 ppm), and high Sr/Y (192–361) and La/Yb (37.3–156) ratios, and are consistent as high silica-adakites (HSA). The monzonite and granodiorite have 87Sr/86Sr(i) values of 0.7045 to 0.7047 and 0.7053 to 0.7058, and εNd(t) values of +1.1 to +1.8 and − 1.9 to −0.8, respectively. The differing chemical compositions and Sr-Nd isotope ratios of these two groups of coeval adakites suggest different sources. Upon consideration of the geodynamic evolution of NW-Iran during the Cenozoic, we infer a two-stage melting process. LSA melts were first produced due to partial melting of delaminated lithosphere and then modified by fractional crystallization in the lower crust. Subsequently, HSA melts were generated during partial melting of lower crustal mafic segments in the hot root zone.

Origin of the Middle Paleoproterozoic Tiksheozero Ultramafic-Alkaline-Carbonatite Complex, NE Fennoscandian Shield: Evidence from Geochemical and Isotope Sr-Nd-Hf-Pb-Os Data

This article reports new geochemical, Sr-Nd-Hf-Pb and Re-Os data on the rocks of the Middle Paleoproterozoic (1.99 Ga) Tiksheozero ultramafic-alkaline-carbonatite complex confined to the northeastern margin of the Karelian Craton. We focus on the poorly studied silicate rocks. Based on petrographic and geochemical research, the silicate rocks are subdivided into two groups: an ultramafic-mafic series depleted in REE, and other incompatible elements and an alkaline series enriched in these elements. Isotope studies showed that all rocks have juvenile isotope signatures and were likely derived from a primitive OIB-type mantle source with possible contributions of the subcontinental lithospheric mantle (SCLM). Insignificant crustal contamination is recorded by Pb and Os isotopic compositions. The incompatible element enrichment in the alkaline rocks and depletion in ultramafic-mafic rocks of the mildly alkaline series with allowance for insignificant crustal contamination confirm their derivation from different primary melts. However, a narrow range of Sr, Nd, Hf, and Pb isotope compositions and compact clusters in 207Pb/204Pb-206Pb/204Pb, Nd-87Sr/86Sr and Hf-Nd isotope diagrams indicate their origination from a common mantle source. A model of subsequent two-stage melting is being most consistent with the geochemical data for this complex.

Laser-induced melting of two-dimensional dusty plasma system in RF discharge

We present a detailed analysis of experimental study, which shows clear evidence of a two-stage melting process of a quasi-two-dimensional dusty plasma system in a high-frequency gas discharge. We accurately calculated global parameters of the orientational and translational order, as well as their susceptibilities to determine two critical points, related to “solid-to-hexatic” and “hexatic-to-liquid” phase transitions. The nature of the emerging defects and changes in their mutual concentration, in addition to the estimate of core energy of free dislocations also counts in favor of the formation of an intermediate hexatic phase. These results are fully consistent with the Berezinsky–Kosterlitz–Thouless theory.

Melt extraction and reaction in the forearc mantle: Constraints from trace elements and isotope geochemistry of ultra-refractory peridotites of the New Caledonia Peridotite Nappe

The forearc mantle has generally experienced high degrees of partial melting and pervasive melt-rock reactions. Large ultramafic massifs of the New Caledonia ophiolite (Peridotite Nappe) provide opportunities for studying processes within the forearc mantle. Samples of harzburgite, dunite and websterite from three massifs (i.e., Me Maoya, Ouassë Bay, Massif du Sud) have been selected in this study. The peridotites have low contents of Al2O3 (0.10–0.78 wt%) and CaO (0.21–0.58 wt%), but high olivine Fo (90.8–92.5) and spinel Cr# (0.55–0.74) values. This indicates that they have experienced high degrees of partial melting, resulting in the complete consumption of primary clinopyroxene. Trace elements of orthopyroxenes have been measured to constrain the evolution of the New Caledonia harzburgites. Results show that orthopyroxenes have low contents of heavy rare earth element (HREE); their Yb contents are 0.04–0.39 times of chondrites, which can be modeled by ~25–30% of fractional melting of a depleted MORB mantle (DMM) source. The orthopyroxenes also show variable enrichment of light and middle rare earth elements (LREEs and MREEs) and large ion lithophile elements (LILEs), implying late-stage metasomatism. The websterites have high CaO (9.02–9.75 wt%) but low Al2O3 (1.59–1.60 wt%) contents. They have depleted Sr-Nd-Hf isotope compositions similar to that of New Caledonia CE-boninites and plot within the MORB field. Both websterites and dunites have 187Os/188Os ratios (0.12348–0.13067) comparable to that of abyssal peridotites and the New Caledonia harzburgites (0.1203–0.1534). Geochemical compositions and modeling of whole-rock and minerals of harzburgites, dunites and websterites suggest that the New Caledonia peridotites have experienced at least two-stage partial melting and reactions with various migrating melts. Moreover, we also demonstrated that trace element of orthopyroxenes can be applied to discriminate ultra-refractory harzburgites from different tectonic settings.

Atomic-scale insights into structural and thermodynamic stability of spherical Al@Ni and Ni@Al core–shell nanoparticles

Atomic-scale comprehension of structure and thermodynamic stability of metallic core–shell nanoparticles is important for viewpoints of both their synthesis and applications. Thermodynamic and structural properties of Al@Ni and Ni@Al core–shell nanoparticles are investigated at various temperatures by using molecular dynamics (MD) simulations within the interactions defined by the many-body embedded atom model (EAM). The sizes of Al@Ni core–shell nanoparticles and their pure counterparts are chosen as two different values of about 5 nm and 10 nm in this study. MD method is used to calculate the total energy, one-body particle density, radial distribution function, and heat capacity to estimate the melting temperatures of the core–shell systems considered in the present study. Our estimated melting temperatures of core–shell nanoparticles are also verified by doing common neighbor analysis (CNA). MD study shows that a distinct two-stage melting takes place during the heating of the Al@Ni core–shell nanoparticles, although their melting mechanism has started from surface into interior. It is reported that the width of the melting temperature of the core–shell nanoparticles is dependent not only on the bulk melting points of their pure metals but also on the ratio of the shell thickness and the core size of the nanoparticles.

Role of topological defects in the two-stage melting and elastic behavior of active Brownian particles

We find that crystalline states of repulsive active Brownian particles at high activity melt into a hexatic state but this transition is not driven by an unbinding of bound dislocation pairs as suggested by the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory. Upon reducing the density, the crystalline state melts into a high-density hexatic state devoid of any defects. Decreasing the density further, the dislocations proliferate and introduce plasticity in the system, nevertheless maintaining the hexatic state, but eventually melting into a fluid state. Remarkably, the elastic constants of active solids are equal to those of their passive counterparts, as the swim contribution to the stress tensor is negligible in the solid state. The sole effect of activity is that the stable solid regime shifts to higher densities. Furthermore, discontinuities in the elastic constants as a function of density correspond to changes in the defect concentrations rather than to the solid-hexatic transition.

Multi-stage evolution of forearc mantle peridotites of Kağızman Ophiolite (Ağrı-eastern Anatolia)

The Kağızman Ophiolite, constituting the easternmost part of Tethys ophiolites in Anatolia, is located on the İzmir-Ankara-Erzincan ophiolitic belt. Ophiolitic rocks include a range of mantle peridotites, gabbros, pillow basalts and isolated sheeted dykes. The studied mantle peridotites are investigated with regard to geochemical and petrographical characteristics. MgO content of peridotites varies from 41.24 to 45.63 wt % while that of Al2O3 is in the range of 0.20–0.32 wt % indicating a high partial melting degree. Highly depleted mantle peridotites represent residues of primitive mantle formed by 17–23% melting. Whole rock trace element patterns point to variable partial melting conditions. Petrographical and geochemical results reveal that mantle peridotites of Kağızman Ophiolite are the residues of two-stage partial melting process. The first melting (consuming) stage occurred in a mid-ocean ridge setting which was later metasomatized in a subduction zone by interaction between peridotites and fluids derived from the subducted crust. According to all data, these rocks are hypothesized as forearc peridotites affected by high degree partial melting.