Equilibrium Melting Research Articles

Unveiling relaxation and crystal nucleation interplay in supercooled germanium liquid

A well-designed study of the relationship between crystal nucleation and relaxation in supercooled liquids could clarify some critical issues in condensed matter science. In this article, we dwell on the kinetic spinodal temperature, TKS – where the times of first critical nucleus formation and structural relaxation curves cross over – and the Kauzmann temperature, TK – where the entropy of the supercooled liquid and crystal equalize. Germanium liquid was used as a model system, for which a reliable Stillinger-Weber potential and crystal nucleation kinetics are available. Using molecular dynamics (MD) simulations, we obtained the self-diffusion coefficient, D(T), and the shear viscosity, η(T), down to T=0.7·Tm, where Tm is the equilibrium melting temperature. In this way, three relaxation times were determined in the supercooled liquid: (i) via the shear viscosity, τη; (ii) the incoherent intermediate scattering function, τα; and (iii) the self-diffusion coefficient, τD. We found that τα(T)≈τD(T) and τη(T)<τα(T), corroborating the findings of recent experimental and computational studies conducted with other four substances. Hence, the viscosity only gives a lower bound to the intrinsic structural relaxation times,τα(T). We also compared the MD values of the atomic transport coefficient across the supercooled liquid/critical nucleus interface, D*, with those obtained by the classical nucleation theory (CNT) and found that the activation energies of D(T), η(T), and D*(T) are similar. The birth times of the first critical crystal nucleus at steady-state conditions, τ1(T), obtained in our previous study for the same material, were extrapolated to lower temperatures using the CNT for different sample sizes. We found that τ1(T) is much longer than the nucleation time-lags, confirming the establishment of the steady-state nucleation regime. A relevant finding is that the τα(T) and τ1(T) curves indeed cross over, confirming the existence of a kinetic spinodal for this liquid. Finally, we demonstrate that if the Kauzmann temperature existed for germanium, it would be located well below the TKS; hence, crystallization would intervene in the cooling path before the supercooled germanium liquid could reach TK, thus averting the entropy paradox, posed by Kauzmann in 1948. These findings shed light on several fundamental questions related to supercooled liquids.

Ni self-diffusion in glass forming Pd–Ni–S melts

The Ni self-diffusion in glass forming Pd40Ni40S20, Pd37Ni37S26 and Pd31Ni42S27 melts was probed by incoherent, quasielastic neutron scattering over a temperature range between 773 and 1023 K. The Ni self-diffusion coefficients are on a 10−10 m2 s−1–10−9 m2 s−1 scale and barely change with composition. Each composition exhibits an Arrhenius-type temperature dependence of the Ni self-diffusion coefficients, which results in activation energies ranging from E A = 348 ± 16 meV for Pd40Ni40S20 to E A = 387 ± 6 meV for Pd37Ni37S26. The structural relaxation shows a stretched exponential behavior even far above the liquidus temperatures. In addition, the viscosity of the Pd37Ni37S26 melt was measured under reduced gravity conditions. The diffusion calculated from the viscosity reveals a significant deviation from the measured Ni self-diffusion by a factor between 4 and 8. This may indicate a dynamic decoupling between the atoms within the Pd–Ni–S equilibrium melts.

Silicone/fluorine‐functionalized flow modifier with low surface energy for improving interfaces in highly filled composites

Highly filled composites have received the urgent demands in various areas (i.e., electrical and thermal conductive materials) due to their many advantages (i.e., low cost and high comprehensive performance). However, it is challenging to simultaneously improve the processability and toughness of highly filled composites by adding a small amount of flow modifier. In this work, for the first time, a novel silicone/fluorine‐functionalized flow modifier (Si-DPF) with low surface energy is synthesized and incorporated into a highly filled magnesium hydroxide/linear low-density polyethylene (MH/LLDPE) composite (80:20 by weight) to simultaneously improve the processability, toughness and flame retardancy. The results show that Si-DPF is dominantly located at the interface between the MH particles and LLDPE matrix to form a core-shell structure, leading to the relatively homogeneous dispersion of the MH particles. The melt equilibrium torque of the MH/LLDPE composite is decreased by 48.9%, the notched impact strength is increased by more than 4 times, and the area under the stress-strain curves is increased by more than 9 times at 5 wt% loading of Si-DPF. Additionally, the corresponding limited oxygen index (LOI) value is increased to 63.8%. This work provides a facile and effective strategy to simultaneously enhance the processability, toughness and flame retardancy of highly filled polymer-based composites by only one kind of multi-functional flow modifier.

Chemical Modification of Poly(butylene trans-1,4-cyclohexanedicarboxylate) by Camphor: A New Example of Bio-Based Polyesters for Sustainable Food Packaging.

Among the several actions contributing to the development of a sustainable society, there is the eco-design of new plastic materials with zero environmental impact but that are possibly characterized by properties comparable to those of the traditional fossil-based plastics. This action is particularly urgent for food packaging sector, which involves large volumes of plastic products that quickly become waste. This work aims to contribute to the achievement of this important goal, proposing new bio-based cycloaliphatic polymers based on trans-1,4-cyclohexanedicarboxylic acid and containing different amount of camphoric acid (from 0 to 15 mol %), a cheap and bio-based building block. Such chemical modification was conducted in the melt by avoiding the use of solvents. The so-obtained polymers were processed in the form of films by compression molding. Afterwards, the new and successfully synthesized random copolymers were characterized by molecular (NMR spectroscopy and GPC analysis), thermal (DSC and TGA analyses), diffractometric (wide angle X-ray scattering), mechanical (through tensile tests), and O2 and CO2 barrier point of view together with the parent homopolymer. The article aims to relate the results obtained with the amount of camphoric moiety introduced and to present, the different microstructure in the copolymers in more detail; indeed, in these samples, a different crystalline form developed (the so-called β-PBCE). This latter form was the kinetically favored and less packed one, as proven by the lower equilibrium melting temperature determined for the first time by Baur’s equation.

Major and Trace Element Compositions of Basaltic Lavas From Western Margin of Central Main Ethiopian Rift: Enriched Asthenosphere vs. Mantle Plume Contribution

Major and trace element data are presented for basaltic lavas from western rift margin of central main Ethiopian rift located at Kella area to investigate the processes involved in the petrogenesis of the erupted magmas and the nature of mantle source compositions. Kella area is composed of Quaternary (<1.6 Ma), Miocene (10.6-8.3 Ma) and Oligocene basalts (30-29 Ma) ranging from alkaline to tholeiitic in composition. The geochemical variations of basaltic samples from Kella area exhibit two compositionally distinct basaltic groups. The Oligocene tholeiitic basalts display low MgO (5.29-6.11 wt.%), TiO2 (2.15-2.47 wt.%), P2O5 (0.28-0.34 wt.%), and high ratio of CaO/Al2O3 (0.68-0.72) and La/Nb (0.89-1.10). Whereas Quaternary and Miocene alkaline basalts display high MgO (7.40-8.86 wt.%), TiO2 (2.4-2.53 wt.%), P2O5 (0.44-0.52 wt.%) and low ratio of CaO/Al2O (0.62-0.66) and La/Nb (0.71-0.76). The contrasting incompatible element ratios (e.g., K/Nb, La/Nb, Rb/Zr and Zr/Nb) between tholeiite and alkaline basalts reflect differences in their mantle sources. Major and trace element variations, therefore, reflect the involvement of two geochemically distinct mantle sources in the petrogenesis of Kella basaltic lavas: i) the Oligocene tholeiite basaltic melts derived from enriched asthenosphere mantle source (E-MORB) and ii) the Miocene and Quaternary alkali basaltic melts show close similarity with ocean island basalts (OIBs) geochemistry, and this end member ascribed to the arrival of Afar plume head. The geochemical modeling reveals that the Oligocene tholeiite basaltic melts produced by equilibrium melting with 3-5 % degree of partial melting in spinel lherzolite mantle source, whereas the alkali basalts are produced with ~2% degree of partial melting within spinel-garnet lherzolite transition zone mantle sources.

Peculiar self‐nucleation behavior of a polybutene‐1/ethylene random copolymer

The self-nucleation behavior of a polybutene-1/ethylene random copolymer, P(B1-ran-E), which undergoes a complex crystal-crystal transition behavior, has been studied in detail. Similar to PE random copolymers, this material shows a strong melt memory effect even above equilibrium melting point of PB-1 homopolymer. Different polymorphic forms can be obtained when P(B1-ran-E) is cooled from different self-nucleation domains. The trigonal form I′ could only be nucleated in the presence of remaining form I crystals via self-seeding, while the melt memory in Domain IIa could only act as self-nuclei for kinetically favored form II. Furthermore, observations from optical microscopy illustrated that melt memory is able to enhance nucleation density but it does not affect the spherulitic growth rate.

ReversePetrogen: A Multiphase Dry Reverse Fractional Crystallization‐Mantle Melting Thermobarometer Applied to 13,589 Mid‐Ocean Ridge Basalt Glasses

AbstractWe present a new algorithm, ReversePetrogen (RevPet), to infer mantle melting conditions (pressure, temperature, source composition) using evolved basalts that have experienced multiphase fractional crystallization. RevPet measures and minimizes the compositional distance between experimentally predicted phase saturation boundaries and an erupted basalt and the more primitive liquids that return it to a primary melt. We use RevPet to investigate mantle melting conditions at mid‐ocean ridges (MORs) using a global data set of 13,589 basaltic glasses. We find that their average apparent mantle potential temperature (TP*) is 1322°C ± 56°C with melting pressures of 13.0 ± 5 kbars. Inferring the true initial (pre‐melted) TP from TP* requires knowing the style and degree of melting of the input basalts. If MORB glasses were entirely produced by near‐fractional melting of a homogenous source, they would record the cooling of the mantle during melting from an initial TP = ∼1380°C (ΔTP = 0°C) down to TP = ∼1270°C. If, instead, they were all fully pooled near‐fractional melts of the same source, they would record variations in ambient MOR TP from ∼1300°C to 1450°C (ΔTP = 150°C). However, because MOR basalts are thought to be both near‐fractional and variably pooled melts of variable sources, MOR TP must be intermediate between these two extremes. Our best estimate, consistent with MOR crustal thickness, is that ambient MOR TP is homogenous (∼1350°C–1400°C) except near hotspots where TP reaches ∼1600°C. Some primitive glasses found near slow‐spreading ridges and back‐arcs record very low temperatures (TP* &lt; 1250°C) and pressures of melting (&lt;10 kbar) and reflect mantle cooling during melting and melt equilibration in the mantle lithosphere.

Kinetics of solid-liquid interface motion in molecular dynamics and phase-field models: crystallization of chromium and silicon.

The results of molecular dynamics (MD) simulations of the crystallization process in one-component materials and solid solution alloys reveal a complex temperature dependence of the velocity of the crystal-liquid interface featuring an increase up to a maximum at 10-30% undercooling below the equilibrium melting temperature followed by a gradual decrease of the velocity at deeper levels of undercooling. At the qualitative level, such non-monotonous behaviour of the crystallization front velocity is consistent with the diffusion-controlled crystallization process described by the Wilson-Frenkel model, where the almost linear increase of the interface velocity in the vicinity of melting temperature is defined by the growth of the thermodynamic driving force for the phase transformation, while the decrease in atomic mobility with further increase of the undercooling drives the velocity through the maximum and into a gradual decrease at lower temperatures. At the quantitative level, however, the diffusional model fails to describe the results of MD simulations in the whole range of temperatures with a single set of parameters for some of the model materials. The limited ability of the existing theoretical models to adequately describe the MD results is illustrated in the present work for two materials, chromium and silicon. It is also demonstrated that the MD results can be well described by the solution following from the hodograph equation, previously found from the kinetic phase-field model (kinetic PFM) in the sharp interface limit. The ability of the hodograph equation to describe the predictions of MD simulation in the whole range of temperatures is related to the introduction of slow (phase field) and fast (gradient flow) variables into the original kinetic PFM from which the hodograph equation is obtained. The slow phase-field variable is responsible for the description of data at small undercoolings and the fast gradient flow variable accounts for local non-equilibrium effects at high undercoolings. The introduction of these two types of variables makes the solution of the hodograph equation sufficiently flexible for a reliable description of all nonlinearities of the kinetic curves predicted in MD simulations of Cr and Si. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

Analysis of non-isothermal polymer crystallization at constant scan rates based on the Avrami model

When polymer crystallization is initiated by an instantaneous athermal nucleation and controlled by two-dimensional secondary nucleation on the growth face, for crystallization from the melt upon cooling at a constant scan rate β, an analysis based on the Avrami model reveals that a plot of β/(ΔTpeak)2=β/(TM0−Tpeak)2, in which Tpeak represents the peak temperature of crystallization rate and TM0 the equilibrium melting point, is nearly equivalent to that of the inverse of crystallization half-time τ1/2 and peak time τpeak, which are obtained from isothermal crystallization and used as a measure of crystal growth rate. Therefore, a plot of β/(ΔTpeak)2 against Tpeak at different scan rates can be utilized to examine the temperature dependence of the crystal growth rate in the same way as that of τ1/2 and τpeak obtained under isothermal conditions at different temperatures. The applicability was confirmed via numerical calculations and experiments using poly(vinylidene fluoride) and poly(butylene terephthalate). The agreement of the temperature dependence estimated by the plot of β/(ΔTpeak)2 was much better than that of β/(Tpeak)2 used in the well-known Kissinger plot.

Phase equilibria modeling of anatexis during ultra-high temperature metamorphism of the crust

Ultra-high temperature (UHT) granulite-facies metamorphism is commonly identified in Mg–Al-rich rocks. Many such lithologies are thought to be metasedimentary rocks based on the presence of detrital zircon. However, whether a metasedimentary protolith is required to form diagnostic mineral assemblages and how much melt is lost during burial and heating to reach UHT conditions varies significantly according to the prograde pressure–temperature path. In this study, integrated thermodynamic modeling, accessory mineral modeling, and trace element modeling has been conducted on an average metapelite composition and average mid-ocean ridge basalt (MORB) composition under open-system conditions. The results show at least three and two melt loss events occur before reaching UHT conditions in initially water-saturated pelitic and basaltic rocks, respectively. Around 22–27 vol% S-type granite and 12–17 vol% I-type granite would be produced during these evolutions, respectively. Melt extraction leads to an increase of Al and Mg in metapelite residua. Mineral assemblage sapphirine + quartz is then allowed to form at higher grades; however, metabasalt does not form these UHT diagnostic assemblages, regardless of the amount of melt lost. During equilibrium melting, crustal differentiation induced by UHT metamorphism would significantly reduce the amount of heat-producing elements (HPEs) in the melt-depleted residuum, which progressively decreases a rock's heat production capacity. In reality, however, new monazite grains likely form during peak metamorphism and some monazite grains would be shielded by porphyroblasts, resulting in an increase of Th in the residua during heating. Even so, we suggest the efficiency of heat production would still decrease, given the heat production rate of Th is much lower than U. Considering some granitic rocks with relatively high heat production are emplaced into the granulite terrane, we suggest that radioactive heat production may be a contributing driving force for UHT metamorphism; however, it is not sufficient. Most heat required to generate UHT granulites must come from hybrid sources, such as advected heat from the mantle, conducted heat from nearby magmatic intrusions, radioactive heat production, and ductile shear deformation.

Sunda arc mantle source \u03b418O value revealed by intracrystal isotope analysis

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) δ18O values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30 km at Merapi to ≤20 km at Agung. Here we show that mean clinopyroxene δ18O values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt δ18O values of 5.7 ‰ (±0.2 1 SD) indistinguishable from the δ18O range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member.

Surface Crystal Nucleation and Growth in Poly (ε-caprolactone): Atomic Force Microscopy Combined with Fast Scanning Chip Calorimetry.

By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was placed on the active/heatable area of the FSC chip, melted, and then rapidly cooled to 330 K, which is 13 K below the equilibrium melting temperature. Subsequent isothermal crystallization at this temperature was initiated by a soft-tapping AFM-tip nucleation event. Crystallization starting at such surface nucleus led to formation of a single spherulite within the FSC sample, as concluded from the radial symmetry of the observed morphology. The observed growth rate in the sub-micron thin FSC sample, nucleated at its surface, was found being much higher than in the case of bulk crystallization, emphasizing a different growth mechanism. Moreover, distinct banding/ring-like structures are observed, with the band period being less than 1 µm. After crystallization, the sample was melted for gaining information about the achieved crystallinity and the temperature range of melting, both being similar compared to much slower bulk crystallization at the same temperature but for a much longer time.

Stereocomplex- and homo-crystallization behavior, polymorphism, and thermal properties of enantiomeric random copolymers of l- and d-lactic acids from the melt

Enantiomeric stereo random copolymers (SRCs), l-lactic acid-rich poly (lactic acid)s (L -PLAs) and d-lactic acid-rich poly (lactic acid)s (D-PLAs) with major monomer unit fraction down to 85% were synthesized from mixtures of l- and d-lactic acids and their stereocomplex (SC)- and homo-crystallization from the melt were investigated. The obtained results were compared with those previously reported for enantiomeric SRCs,l-lactide-rich poly (l-lactide-co-d-lactide)s and d-lactide-rich poly (l-lactide-co-d-lactide)s synthesized from l- and d-lactides (lactic acid cyclic dimers). Homo-crystallization of L-PLAs occurred for major monomer unit fraction (MMUF) = 96.6–100% and major monomer unit sequence length (MMUSL) = 29.4–63.8 monomer units. The crystalline form transition from δ to α occurred in L-PLAs with MMUF = 98.2 and 100% (MMUSL = 55.6 and 63.8 monomer units) between Tc = 90 and 100 °C and Tc = 100 and 110 °C, respectively, whereas only α-form formation took place in L-PLA with MMUF = 96.6% (MMUSL = 29.4 monomer units). The homo-crystallizability and δ-form crystallizability of L-PLAs and l-lactide-rich poly (l-lactide-co-d-lactide)s were determined by MMUSL rather than MMUF. SC crystallization occurred in L-PLA/D-PLA blends for wider MMUF = 84.4–100% (MMUSL = 6.4–56.4 monomer units) compared to that of homo-crystallization of unblended specimens, i.e., SC crystallization widened crystallizable MMUF and MMUSL ranges. The SC crystallizability was determined by not only MMUF or MMUSL but also by other factors, in contrast with the homo- and δ-form crystallizability. The interplanar distance values of L-PLA decreased with an increase in Tc and transition from δ-form to α-form, whereas those of SC crystallites for L-PLA/D-PLA blends remained unchanged for Tc range of 100–180 °C. It is interesting to note that the incorporated d-monomer units at ca. 3% caused compact packing of L-PLA chains in α-form. The equilibrium melting temperature (Tm0) values of SC crystallites [Tm0(S)] decreased with decreasing MMUF or MMUSL. The Tm0 of homo-crystallites [Tm0(H)] and Tm0(S) were lower for PLAs with lactic acid monomers than those with lactide monomers, when compared at the similar MMUF values. Tm0(H) and Tm0(S) values were determined by MMUSL not by MMUF. In summary, MMUSL was found to play a critical role to determine the crystallizability of unblended L-PLAs and the Tm0 values of unblended L-PLAs and L-PLA/D-PLA blends.

Geochemical, Sr-Nd isotopic and U-Pb zircon study of 1.88 Ga gabbro-wehrlite from north-eastern Singhbhum Craton, India: Vestiges of Precambrian oceanic crust?

Dismembered, kilometer-scale slices of gabbroid and serpentinized wehrlite rocks are found emplaced within metapelites of Chaibasa Formation, belonging to the North Singhbhum Mobile Belt, Singhbhum Craton, India. Zircon grains from the gabbroid body yield an average U-Pb crystallization age of 1881.1 ± 8.4 Ma. The undeformed gabbroid body exhibits modal and cryptic layering, and both units exhibit cumulate texture. The presence of dismembered cumulate and layered mafic–ultramafic rocks within a mobile belt assemblage is enigmatic and has potentially far-reaching implications. The gabbroid rocks are moderately evolved with Mg# (100 Mg/Mg + Fe) ranging from 48 to 63, low alkali, TiO2, U, Th, Zr, and high Al2O3, Pb, Ba, Rb, with unfractionated rare earth elements patterns. The serpentinized wehrlite (Mg# 65–71) hosts secondary minerals (clinopyroxene rims, amphibole blebs and interstitial Mg-chlorite) and has LREE enriched rare earth element patterns, which suggest complex fluid-rock interaction history. The gabbroid rocks have 87Sr/86Sr(t) 0.70600–0.71099, 143Nd/144Nd(t) 0.510130–0.510294, and ƐNd(t) 1.8 to −1.4. The serpentinized wehrlite displays extreme enrichment with 87Sr/86Sr(t) 0.71045–0.72640, 143Nd/144Nd(t) 0.509120–0.509706, and almost upper crust-like ƐNd(t) of −9.7 to −21.2. The cumulate nature of the mafic–ultramafic rocks with other petrographical and geochemical evidences suggest formation in a magma chamber. Additionally, their field characteristics, stratigraphic constraints and E-MORB like character of calculated equilibrium melts of the gabbroid rocks, indicates affinity towards formation in an oceanic magma chamber and possible emplacement by obduction. Mineral chemistry, whole-rock geochemistry and clinopyroxene trace elements of the serpentinized wehrlite reveal progressive fluid-rock interaction from very high-temperature to low-temperature regimes, and deep crustal affinity of the modeled metasomatic fluid. Isotopic character of the gabbroid rocks can be explained by 30%-50% mixing between a depleted and an enriched domain in the lithospheric mantle, whereas isotopic nature of the wehrlite has been perturbed by the prolonged metasomatic event. Their occurrence within the Chaibasa intra-continental rift basin indicates rift-drift transition and formation of incipient oceanic crust at 1.88 Ga. A 1.86 Ga orogenic event caused closure of the basin and obduction of these remnant oceanic fragments onto the mobile belt assemblage. This is the first discovery of oceanic crustal fragments in Singhbhum Craton, which fits into the model of rift-dominated tectonics, widespread continental amalgamation, and ophiolite emplacement during the Columbia supercontinent cycle in Paleoproterozoic.

The overall crystallization behavior of polyethylene/wax blends as phase change materials for thermal energy storage: A mini review

AbstractThis review paper deals with the overall crystallization behavior of polyethylene/wax blends as phase change materials (PCMs) for thermal energy storage with the determination of their thermal properties. The addition of molten wax to the polyethylenes decreases the crystallization and melting temperatures of the blends. However, incorporating fillers to the polyethylene/wax blends can either decrease or increase the crystallization and melting temperatures of the composites depending on the filler type. The normalized enthalpy values of linear low‐density polyethylene showed no significant change when increasing the wax content. On the contrary, the normalized enthalpy values of the wax in the blends were lesser than that of pure wax and increased with increasing wax content. Since the wax in the blend had a lower crystallinity compared to pure wax, this influences its effectiveness as a PCM for thermal energy storage. The effect of different polyethylenes on the wax morphology gave rise to enhance phase separation when wax was blended to high‐density polyethylene as compared to the other polyethylenes. On the contrary, the effect of various waxes on the morphology of polyethylene resulted in different morphologies due to the molecular weight of the wax used and the structure of the polyethylene chain. The addition of fillers to the polyethylene (PE)/wax samples resulted in enhanced phase separation. The overall isothermal crystallization rate and the equilibrium melting temperature of PEs in the PEs/wax blends were depressed by wax addition due to the wax dilution effect.

Shock-induced melting of two-dimensional Yukawa systems from TH−PH Hugoniot curves

The TH−PH Hugoniot curves of compressional shocks in 2D Yukawa systems are derived from the combination of the Rankine–Hugoniot relation around the shock front and the universal relationship for the temperature in the postshock region. From the equation of state of 2D Yukawa liquids, the equilibrium melting curve for 2D Yukawa systems is derived using the two variables of the temperature T and the pressure P. It is found that the obtained TH−PH Hugoniot curves are intercepted by the equilibrium melting curve, indicating the existence of shock-induced phase transition at these crossing points. To confirm this prediction, molecular dynamical simulations of 2D Yukawa systems of κ=0.75 for the conditions around the crossing point are performed. In the postshock region, the calculated various diagnostics of static structural measures, like the Voronoi diagram, the defect ratio, the probability distribution of the shape factors ξ, the pair correlation function g(r), and the static structure factor S(q), suggest that, for our studied system, the shock-induced melting happens when the compressional speed of the boundary is 0.212a0ωpd&amp;lt;vleft&amp;lt;0.283a0ωpd, the same as the prediction from the crossing point.

The petrology of a hazardous volcano: Calbuco (Central Southern Volcanic Zone, Chile)

The recurrent explosive eruptions of Calbuco (Andean Southern Volcanic Zone (SVZ)) threat a rapidly expanding touristic and economic region of Chile. Providing tighter constraints on its magmatic system is therefore important for better monitoring its activity. Calbuco is also distinguished by hornblende-bearing assemblages that contrast with the anhydrous parageneses of most Central SVZ volcanoes. Here we build on previous work to propose a detailed petrological model of the magmatic system beneath Calbuco. Geochemical data acquired on a hundred samples collected in the four units of the volcano show no secular compositional change indicating a steady magmatic system since ~ 300 ka. A tholeiitic Al2O3-rich (20 wt. %) basalt (Mg# = 0.59) is the parent magma of a differentiation trend straddling the tholeiitic/calc-alkaline fields and displaying a narrow compositional Daly gap. Amphibole crystallization was enabled by the higher H2O content of the basalt (3–3.5 wt. % H2O at 50 wt. % SiO2) compared to neighboring volcanoes. This characteristic is inherited from the primary mantle melt and possibly results from a lower degree of partial melting induced by the mantle wedge thermal structure. Although macrocrysts are not all in chemical equilibrium with their host rocks and were thus presumably unlocked from the zoned crystal mush and transported in the carrier melt, the bulk-rock trend follows both experimental liquid lines of descent and the chemical trend of calculated melts in equilibrium with amphibole (AEMs). These contradictory observations can be reconciled if minerals are transported in near cotectic proportions. The AEMs overlap the Daly gap revealing that the missing liquid compositions were present in the storage region. Geothermobarometers all indicate that the chemical diversity from basalt to dacite was acquired at a shallow depth (210–460 MPa). We suggest that differentiation from the primary magma to the parental basalt took place either in the same storage region or at the MOHO.

Synthesis and characterization of bio‐based polyesters derived from 1,10‐decanediol

AbstractTwo kinds of bio‐based polyesters were synthesized from 1,10‐decanediol (DD), dimethyl terephthalate (DMT) or 2,6‐naphthalene dicarboxylic acid (NDCA). Chemical structure, thermal properties and crystal structures, tensile properties and rheological properties were investigated. The glass transition temperature and melting temperature of poly(decamethylene 2,6‐naphthalate) (PDN) are higher than that of poly(decamethylene terephthalate) (PDT). Differential scanning calorimetry and wide‐angle X‐ray diffraction results suggested that PDT and PDN were semi‐crystalline polymers. Equilibrium melting points of PDT and PDN were 129.5°C and 167.1°C, respectively. Compared with PDT, PDN exhibited the higher tensile strength (36.8 MPa) and lower elongation at break (224%) and the complex viscosity of PDN is more sensitive to temperature and oscillation frequency. Compared with the current available bio‐based plastic poly(butylene succinate) (PBS), PDT and PDN exhibit higher melting temperature, faster crystallization rate and comparable tensile properties.

Cr-poor and Cr-rich clinopyroxene and garnet megacrysts from southern African Group 1 and Group 2 kimberlites: Clues to megacryst origins and their relationship to kimberlites

Controversies surround the origin of kimberlite megacrysts, including whether and how they are genetically related to their host kimberlites, the relationship between the Cr-poor and Cr-rich suites and the dominant processes responsible for elemental and isotopic variations of megacrysts from a given kimberlite. We present new in-situ major and trace element and Sr isotopic results for clinoyroxene and garnet megacrysts from four southern African kimberlites: Colossus and Orapa (Group 1 kimberlites on the Zimbabwe craton), and Kalkput and Bellsbank (Group 2 kimberlites on the western Kaapvaal craton), that include both Cr-poor and Cr-rich megacryst varieties. Cr-poor megacrysts are present at Colossus, Orapa and Kalkput and the data exhibit tight, well-defined trends on major element diagrams as well as incompatible and rare earth element abundances similar to those previously reported for Cr-poor megacrysts. Cr-rich megacrysts, which are also present at Orapa and are the only variety present at Bellsbank, generally have higher Mg# values, lack well-defined major element trends and show stronger incompatible element enrichments as well as more radiogenic 87Sr/86Sri ratios than Cr-poor megacrysts from the same kimberlite group. Thermobarometry indicates that the Cr-poor megacrysts equilibrated at temperatures of ≈1200 to 1450 °C and pressures of 4.5 to 7.5 GPa. Cr-rich megacrysts, in contrast, extend to temperatures and pressures as low as 700 °C and 3 GPa, respectively. This indicates that, in the studied suites, Cr-poor megacrysts equilibrated at high temperatures in the lower lithosphere (>135 km), whereas Cr-rich megacrysts typically equilibrated at lower temperatures and pressures. Within the Cr-poor megacrysts from Group 1 and Group 2 kimberlites, there is a clear correspondence between kimberlite group, diagnostic incompatible element ratios (e.g., Nb/La) and Sr isotope ratios that parallel the differences noted between whole-rock Group 1 and Group 2 kimberlites. In the case of Cr-poor megacrysts, similar calculated melt compositions in equilibrium with garnet and clinopyroxene from the same kimberlite were obtained using recent high-pressure mineral‑carbonated melt partition coefficients. This suggests formation in conditions close to trace element equilibrium, and is consistent with crystallization from primitive melts with kimberlite-like trace element compositions. In the case of Cr-rich megacrysts, differences in the compositions of melts in equilibrium with clinopyroxene and garnet tend to be larger, and melts in equilibrium with Cr-rich clinopyroxene tend to show significantly greater incompatible element enrichments than those of estimated near-primary kimberlite melts. This could be due to the different behaviour of clinopyroxene and garnet during metasomatic melt-rock interaction, but the apparent disequilibrium between clinopyroxene and garnet could also be due to some of the Cr-rich megacrysts actually being peridotitic xenocrysts. We propose a model for the origin of southern African megacrysts in which carbonated protokimberlite melts formed stockwork-like bodies of variable size in the deep lithosphere (>130 km), which fed networks of melt-filled veins extending into the surrounding and overlying mantle. Crystallization of larger melt bodies resulted in megacryst assemblages dominated by Cr-poor megacrysts, and the incompatible element and isotopic characteristics of these dominantly reflect those of the protokimberlite melt. In contrast, crystallization of smaller melt bodies and their vein networks resulted in megacryst assemblages dominated by Cr-rich megacrysts, which formed as a result of extensive assimilation and metasomatic melt-rock interaction between protokimberlite and peridotite wallrock at low melt/rock ratios, particularly in the middle to shallow lithosphere where pre-existing potassic metasomatic heterogeneities are prevalent. The Cr-rich nature and enrichments in incompatible elements and radiogenic Sr in the Cr-rich megacrysts reflect extensive interaction of their parental magmas with this metasomatized peridotite.

Ring-banded spherulites in polylactide and its blends

In this paper the influence of different aspects of crystallization process on the formation of ring-banded spherulites and the transition between banded and non-banded structures in polylactide was analyzed. Based on the measurements using the differential scanning calorimetry (DSC) and polarized optical microscopy (POM), it was found that the banding phenomenon of spherulites in polylactide and its blends with triethyl citrate (TEC) exclusively depends on the degree of supercooling (ΔT). In the work, for the first time, the equilibrium melting point (Tm0) of polylactide was correlated with the isothermal crystallization temperature (Tic) in the context of banded spherulites formation. To determine the Tm0 of polylactide blends, due to the possibility of modifier migration towards the sample surface, a correction of the methodology was proposed. It has been shown that ΔT necessary to initiate the growth of spherulites with a ring pattern in polylactide ranges from 46 to 56 °C. The inclusion of TEC into polylactide matrix shifts the Tic range in which banded spherulites appear towards lower values, but does not change the required value of supercooling degree. A direct correlation between the band space of the ring-banded spherulites and the degree of supercooling was also demonstrated.