Peritectic Melting Research Articles

Forsteritic olivine in EH (enstatite) chondrite meteorites: A record of nebular, metamorphic, and crystal‐lattice diffusion effects

AbstractThe occurrence of forsteritic olivine in EH enstatite chondrites is indicative of bulk disequilibrium. In MgO‐rich magmatic systems, forsterite can either crystallize as a liquidus phase or be produced during peritectic melting of enstatite. Because diffusion of divalent cations through forsterite is relatively rapid, it records peak melting (i.e., chondrule‐forming events) and is also sensitive to subsequent metamorphism in the EH chondrite parent body. Here, we report the major and minor element geochemistry of olivine in EH chondrites across petrologic types 3 and 4. In all cases, olivine meets the technical definition of forsterite (>90 mole% Mg2SiO4). For unequilibrated EH chondrites, minor elements identify CaO‐Al2O3‐TiO2‐rich (refractory forsterite), MnO‐rich (“LIME” forsterite), and FeO‐bearing (forsteritic olivine) endmember components, the latter with Cr2O3‐rich and Cr2O3‐poor varieties. At higher petrologic type, minor element concentrations become restricted and compositions approach pure forsterite, while grain sizes reduce strongly with peak metamorphic temperatures. These changes reflect diffusive equilibration with enstatitic groundmass and dissolution reaction with free silica. The global geochemical distribution of forsteritic olivine in EH chondrites is, perhaps unexpectedly, more similar to those in low‐FeO type I chondrules and associated objects in carbonaceous chondrites (CCs), rather than equivalent objects in ordinary (H, L, LL), low‐FeO (or HH), or Kakangari (K) chondrites. Among achondrites, there is similarity between pure forsterite in aubrites and EH4 chondrites arising due to subsolidus equilibration in both settings, while Cr2O3‐poor forsteritic olivine in EH3 and CCs is similar to magnesian xenocrystic olivine in angrites. This might reflect CaO‐rich and SiO2‐poor magmatic sources across multiple early solar system reservoirs.

New insights into phase equilibria of the SnTe–Bi2Te3 pseudo-binary system: Synthesis and crystal structure of new tetradymite-type compound Sn3Bi2Te6

The phase relationship in the SnTe–Bi2Te3 pseudo-binary system has been reinvestigated experimentally by means of powder X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX) techniques to obtain a better description of the phase diagram. The new version of the phase diagram differs from previous versions. The formation of a total of 5 tetradymite-type ternary compounds has been experimentally confirmed, including 4 compounds mentioned in the literature and, for the first time, a new compound Sn3Bi2Te6. The newly revealed phase was determined to be a rhombohedral structure (space group R-3m, No. 164, lattice parameters: а = b = 4.40935 Å, c = 63.8370 Å in hexagonal representation) based on the powder XRD data and melts with solid-phase reaction, while other re-confirmed ternary compounds have peritectic melting character. Furthermore, the solid solubility of starting binary compounds SnTe and Bi2Te3 is established to be ∼12 and 9 mol % at 450 °C, respectively. A eutectic temperature of 575 °C was observed at a composition of ∼85 mol% Bi2Te3. The current updated version of the phase diagram can provide the essential information for alloying strategies and guide the designing of the Sn–Bi–Te-based high-performance functional materials.

Partial Melting under Shallow-Crustal Conditions: A Study of the Pleistocene Caldera Eruption of Mendeleev Volcano, Southern Kuril Island Arc

Abstract The southern part of the Kuril Island Arc is one of the world’s most active modern volcanic zones, with widespread felsic caldera volcanism, but it has been less well studied compared with other arcs. The Mendeleev caldera-forming eruption (40 ka) on Kunashir Island, southern Kurils, is one of the most explosive Pleistocene eruptions to have occurred in this region. This study aimed to establish the origin and storage conditions of magma preceding the Pleistocene caldera eruption of Mendeleev volcano. Mineralogical and melt inclusion analyses reveal that the primary melts had felsic compositions and that the early stage of magmatic evolution involved amphibole breakdown into a two-pyroxene, plagioclase, and Fe–Ti oxide assemblage under pressure–temperature conditions of 107–314 MPa and 807–932°C. The caldera-forming products are represented by dacitic pumice composed of plagioclase + augite + hypersthene+ quartz + Fe–Ti oxides and melt with uniform low-K rhyolite composition. Pre-eruptive magma was stored in a reservoir at 77–195 MPa (3.0–7.6 km depth) and 830–890°C under H2O-saturated conditions. The mechanism of magmatic evolution implies the following two-step scenario: (1) generation of magma by the partial melting of an amphibole-bearing substrate accompanied by the formation of early Mg-rich clino- and orthopyroxene, plagioclase, Fe–Ti oxides, and peritectic rhyolitic melt; and (2) crystallization of late plagioclase and quartz directly from these partial melts. Local or regional extension during the Pleistocene, accompanied by increasing heat flow in the supra-subduction mantle, generated an active mafic intrusion into the upper crust. This process was accompanied by abundant subaerial eruptions of basaltic volcanoes and could have caused intense heating and partial melting of upper-crustal rocks. Our results indicate that the partial melting of amphibole-bearing substrates in island arcs may serve as a universal mechanism for the generation of silicic magmas during powerful caldera eruptions in young island arcs.

Phase diagram of the semiconductor GaSb–ferromagnet GaMn system

In this work we report the results of complex studies of basic properties and phase equilibria in GaSb–GaMn system within wide composition range. Investigated alloys were synthesized using regimes with relatively low crystallization speed, which resulted in a formation of stable monoclinic modification of GaMn, as suggested by the X-ray diffraction data analysis. The latter also suggested the negligible role of mutual solubility of components in agreement with spatial distribution of elements in studied alloys determined using energy dispersive X-ray spectroscopy. Combination of microstructural data and results of differential thermal analysis reveals the eutectic character of interaction in GaSb–GaMn system with eutectic composition corresponding to 45 mol.% of GaMn and melting temperature of 609 °C. This temperature is substantially lower than reported values of peritectic melting temperature of GaMn, which suggests the possibility of stabilizing hard ferromagnetic L10-GaMn modification in GaSb–GaMn system without substantial deterioration of crystal quality typical for GaMn compounds.

Structural, thermal and superconducting properties of Ag2O-doped YBa2Cu3O7-x composite materials

A composite material with superconducting properties, consisting of YBa2Cu3O7-x doped with Ag2O, was obtained after 233 h of sintering at 960 °C and followed by a special cooling program in oxygen atmosphere. Preferential orientation of YBa2Cu3O7-x (YBCO-123) crystallites was evidenced through X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Small increase of c parameter for orthorhombic YBCO-123 crystalline unit cell together with a slight decrease of oxygen content (7-x) versus Ag content, were encountered. The dimensions of YBCO-123 crystallites are dependent on Ag content. Thermogravimetric analysis (TGA) during heating in flowing air atmosphere from room temperature (RT) to 1100 °C, showed that total mass loss is depending on Ag content. The cooling (from 1100 °C to RT, in air atmosphere) endows optimal oxygen accumulation only for 0 and 5 wt% Ag, while final masses for 10 and 20 wt% of Ag content, are more than 10% less. Differential scanning calorimetry (DSC) showed peritectic melting points for YBa2Cu3O7-x dependent on Ag percentage. DSC graphics also highlighted the endothermic effects: silver melting; melting and decomposition of Ag2O (in 225.81–345.12 °C temperature range) only for 10 and 20 wt%, but completely missing in the case of 5 wt% Ag content. We concluded that some of Cu sites from YBCO-123 superconductor were substituted by Ag ions. Quasi de Almeida-Thouless lines in the range of magnetic field amplitudes from 0.4 to 800 A/m, in the temperature range from 77 K to RT, were also investigated. Two cases are found concerning intergranular critical currents (Jci): depinning mechanism available for 5 wt% Ag content; the decoupling mechanism for 10, and 20 wt% Ag content.

Cretaceous thermal evolution of the closing Neo-Tethyan realm revealed by multi-method petrochronology

A Cretaceous paleo-accretionary wedge, the Ashin Complex, now exposed along the Zagros suture zone in southern Iran, exhibits mafic, metasedimentary and ultramafic lithologies. Field, geochemical and petrological observations point to an anomalous high-temperature event that gave rise to the formation of peritectic (trondhjemitic) melts associated with restitic garnet-bearing amphibolites. Lu-Hf isotopic dating of centimetre-sized garnet in amphibolite-facies metasediments yielded a crystallization age of 113.10 ± 0.36 Ma, possibly representing the age of prograde to near-peak metamorphic conditions. SHRIMP U-Th-Pb zircon dating from trondhjemitic leucosomes yields crystallization ages of 104 ± 1 Ma, interpreted as the age of the temperature peak, which occurred in the upper amphibolite-facies (c. 650–680 °C at 1.1–1.3 GPa), according to thermodynamic modelling and Ti-in-zircon thermometry. Rutile crystals from two leucosomes yield Zr-in-rutile temperatures in the range of 580–640 °C and a LA-ICP-MS U-Pb age range from 85 to 112 Ma, interpreted as a consequence of partial re-equilibration during incipient cooling. A late static recrystallization event is indicated by the presence of sodic-calcic clinopyroxene, sodic amphibole, Si-rich phengite, titanite overgrowths after rutile and lawsonite within former leucosomes and late fractures. This mineral assemblage is a typical blueschist-facies (high pressure-low temperature) paragenesis and is interpreted as reflecting long-term isobaric cooling that occurred until the end of the Cretaceous as a consequence of increasing slab thermal age. This first report of a melting event in the Zagros paleo-accretionary wedge reveals the presence of a transient, abnormally high thermal gradient of c. 18 °C/km that occurred at c. 105–113 Ma. We speculate that this could be explained by the subduction of a thermal anomaly such as a seamount chain, a transform fault system or, more likely, a spreading ridge under the southern Iranian margin. Indeed, paleogeographic reconstructions of the Tethyan realm suggest the entrance of the Northern Tethyan basin ridge into the subduction zone shortly after 120 Ma.

Solid-liquid equilibria in the Bi-Ca-Co-O system

Thermodynamic properties of the quaternary phases in the Bi-Ca-Co-O system, namely those of oxide melt and the misfit bismuth calcium cobaltite, Bi1.85Ca2Co1.7O7.4−δ, were assessed based on the knowledge of phase diagrams of the respective ternary sub-systems and the heat capacity, variable oxygen content and melting behavior of the misfit phase. The isothermal and isoactivity sections of the phase diagram, projections of the liquidus surface at fixed activity of oxygen and pO2 vs. T diagram for a fixed ratio of metal elements were constructed using FactSage program. The variable oxygen stoichiometry of the misfit phase derived from thermogravimetry was described in terms of simple point defect model obtaining a fair agreement with experiment and extrapolating the oxygen content to different values of pO2 and T even above the peritectic melting.

Inverse-Doped Melt-Textured Gd1212 Superconductors Samples: Normal State Raman Characterisation Study

Gd1212 (GdSr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RuCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8-y</sub> ) is a superconductor, isostructural to Y123 (YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> ), whose high interest is due to the coexistence of superconducting and magnetic ordered phases in the same unit cell. Up to now the best superconducting properties for Gd1212 have been achieved by TSG (Top-Seeded Melt-Textured growth), a well-known technique used to grow high quality samples from High Temperature Superconductors characterized by a peritectic melting reaction. Due to the relevant production of liquid during the melting of Y123-like materials, the standard TSG procedure involves the addition of secondary phases in the starting powders mixture, generally the peritectic solid phase or one of its precursors, to enhance the structural stability of pellets during the process. This practice also provides additional pinning centers in the final samples, improving their Superconducting features. Unfortunately, Gd1212 peritectic reaction produces an insufficient amount of liquid phase, so preventing from obtaining wide crystallographic domains, and the addition of the peritectic solid phase Gd1210 (GdSr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> RuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ), although beneficial on the superconducting properties, even worsen this problem. In this work we tried to grow larger Gd1212 domains by inverting the usual approach: i.e., by adding in the precursor powders some peritectic liquid phase (CuO) instead of Gd1210. Anyway, previous analyses suggested us that the chemistry of Gd1212 melting may change for excess CuO mixtures. We have characterized the obtained samples by means of Raman spectroscopy and mapping, data were compared with those of Gd1210-doped and pure Gd1212 samples, results confirm our hypothesis of different melting reaction for CuO rich samples.

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

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

Li4(OH)3Br-Based Shape Stabilized Composites for High-Temperature TES Applications: Selection of the Most Convenient Supporting Material.

Peritectic compound Li4(OH)3Br has been recently proposed as phase change material (PCM) for thermal energy storage (TES) applications at approx. 300 °C Compared to competitor PCM materials (e.g., sodium nitrate), the main assets of this compound are high volumetric latent heat storage capacity (>140 kWh/m3) and very low volume changes (<3%) during peritectic reaction and melting. The objective of the present work was to find proper supporting materials able to shape stabilize Li4(OH)3Br during the formation of the melt and after its complete melting, avoiding any leakage and thus obtaining a composite apparently always in the solid state during the charge and discharge of the TES material. Micro-nanoparticles of MgO, Fe2O3, CuO, SiO2 and Al2O3 have been considered as candidate supporting materials combined with the cold-compression route for shape-stabilized composites preparation. The work carried out allowed for the identification of the most promising composite based on MgO nanoparticles through a deep experimental analysis and characterization, including chemical compatibility tests, anti-leakage performance evaluation, structural and thermodynamic properties analysis and preliminary cycling stability study.

Peritectic Melting of Mica in Fault‐Related Pseudotachylite Melts and Potassium Mass Balance as an Indicator of Fluid‐Absent Source Conditions.

AbstractPseudotachylites are generally considered to be produced by flash melting of the most fusible minerals, with compositions often dominated by biotite mica. We present phase fraction calculations for 237 pseudotachylite analyses from 28 localities spanning a range of host rock compositions from granites to peridotites. Pseudotachylite matrix compositions cannot be reproduced by a simple linear mixture of the minerals in their host rocks and commonly show a potassium deficit in pseudotachylites which contain significant contributions from biotite or muscovite. This is strongly indicative of peritectic melting of mica under fluid‐absent conditions. Occasionally, a negative contribution from an aluminosilicate phase is required but with a positive contribution from potassium feldspar. This is most consistent with peritectic melting of micas under fluid present conditions. The present data therefore suggest that, while fluid absent flash melting might be the most common mode of formation of pseudotachylite, in some instances pseudotachylites can be produced in the presence of a free fluid. Potassium mass balance of pseudotachylites might therefore be a diagnostic indicator of fluid‐absent conditions in their source regions during seismogenic rupture. We give some examples of observational evidence of peritectic liquidus phases in pseudotachylites and suggest that the significance of these phases might have been overlooked in previous studies.

Polymorphism and surface diversity arising from stress-induced transformations – the case of multicomponent forms of carbamazepine

Stress-induced transformations of labile multicomponent organic solids may have a significant impact on industrial manufacturing processes, for example, in the pharmaceutical field. This study considers 15 carbamazepine (CBZ) multicomponent crystal forms, with the aim of identifying the structural and surface features that drive the outcome of thermal stress-induced transformations. Analysis of the crystal structures, and specifically the degree of similarity with the CBZ polymorphs produced by desolvation-like processes, identifies some degree of correlation between structural features. In particular, mutually exclusive supramolecular motifs identified previously within CBZ crystal structures are frequently (but not invariably) preserved, and thereby provide some indication of the anticipated polymorphic outcome. This is broadly consistent with established models relating reactant and product crystal phases. Some of the CBZ multicomponent materials show surface modifications indicative of the formation of a liquid intermediate phase, which provides an alternative dissolution/recrystallization mechanism and different polymorphic outcomes compared to the direct solid–solid transformation pathway. Other cases show intermediates of varying stoichiometry and instances of chemical decomposition. Hence, the product of thermal decomposition is frequently affected by the physical properties of the coformer, such as boiling point and reactivity. This can lead to a dependence on experimental conditions, especially when events such as recrystallization, chemical decomposition of the coformer, solubilization and peritectic melting occur concomitantly. This study highlights that the overall picture is complex, even within this series of closely related materials.

The role of melting on the geochemical evolution and isotopic variability of an anatectic complex in the Iberian Variscides

The genesis and evolution of migmatite-granite terranes usually involve several complex petrological and geochemical processes that leave their imprint on elemental and isotopic signatures. In this paper, we assess the role of melting reactions on the genesis of the variscan Figueira de Castelo Rodrigo-Lumbrales Anatectic Complex (FCR-LAC) in the Central Iberian Zone that culminated in the generation of abundant S-type granites. At odds with the proposed for several anatectic complexes elsewhere, here we demonstrate that no isotopic (Sr-Nd-Hf-Pb) disequilibrium occurred in the FCR-LAC, either in the transitions from metatexites to diatexites nor to granites. However, variable contribution of the source minerals generated batches of melts characterized by distinct parent/daughter ratios, which explain the significant heterogeneity of present-day isotopic signatures. While Rb/Sr ratios and the Pb budget of the successively generated lithotypes were mainly controlled by major minerals such as muscovite, K-feldspar and plagioclase, the accessory phases played a major control on the Sm/Nd and Lu/Hf ratios. Our study also demonstrates the existence of two distinct diatexite groups produced by different melting reactions. Type-1 diatexites, having high Rb contents and fractionated HREE, are geochemically akin to the associated S-type granites. They were produced by dehydration-melting of muscovite with production of peritectic K-feldspar, sillimanite and melt. The less abundant type-2 diatexites required influx of external fluids for melting, which consumed more plagioclase than muscovite.Isotopic data reveal the existence of two groups with distinct initial compositions (εNd320 = −5.05 to −6.03 and εHf320 = −3.42 to −4.45 vs. εNd320 = −7.30 to −8.89 and εHf320 = −6.45 to −8.47), both composed of metatexites, diatexites and granites, due to source heterogeneity. The main source of the anatectic complex was the metasedimentary Neoproterozoic – lower Cambrian Douro-Beiras Supergroup, with minor contribution of Ordovician, Ollo de Sapo magmatic rocks.

Superheating nature coupled with Mg‐doping effect of high thermal stable NdBa2Cu3O7‐δ film

AbstractNdBa2Cu3O7‐δ thin film deposited on a MgO substrate has been verified to remain solid above its peritectic melting temperature (Tp). Such a superheating nature is attributed to its low energy surface and epitaxial interface with substrate. Here, combining superheating nature with doping effect, we report a novel structure, Mg‐doped NdBa2Cu3O7‐δ film with YBa2Cu3O7‐δ buffer layer for the first time. Remarkably, this film presents a higher thermal stability level than heretofore possible when acting as a seed for preparing SmBa2Cu3O7‐δ bulks by melt growth, enduring a temperature of 1128°C, 43 K above its Tp for 1 hour. The utilization of such a high Tmax in melt growth is beneficial to the fabrication of large‐sized and high‐performance bulk in terms of effectively broadening the growth window and suppressing the heterogeneous nucleation. More importantly, some high thermal stability required technological applications, such as batch growth and failed bulk recycling, are likely to be realized by this novel Mg‐doped NdBa2Cu3O7‐δ film seed. Finally, we show how the observed metastable phase is linked to the distinctive film architecture.

Identification of growth mechanisms in metamorphic garnet by high-resolution trace element mapping with LA-ICP-TOFMS

Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major elements, zoning in trace elements can provide a wealth of information to document the changing conditions of garnet growth and modification. However, mapping trace elements at low concentrations, over large areas and with high resolution has remained a major challenge. We present a comprehensive investigation of the TE distribution in garnet from three Alpine samples that underwent a complex evolution at different metamorphic conditions. The TE distribution in garnet grains is mapped in 2D in thin section with a novel approach using laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) to achieve a lateral resolution of 5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g. Comparison with major element zoning measured by electron probe microanalysis and trace elements measured by conventional LA-ICPMS spot analysis testifies to the accuracy of the measurements. Garnet in an amphibolite-facies metapelite from Campolungo, Central Alps, that recorded metamorphism to 600 °C preserves Y + REE trace element zoning that closely matches that of Ca. In this sample, there is no notable diffusive modification for trace elements. Y + REE zoning is dominated by Rayleigh fractionation in the core and by the sporadic breakdown of accessory phases producing annuli in the rim of the garnet. A granulite-facies garnet from Malenco, Eastern Central Alps, formed during subsolidus heating, followed by peritectic melting reactions up to temperatures of 800–850 °C. Major and trace element zoning are decoupled indicating diffusional resetting of major elements, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle may be related to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y + REE) in the melt. Diffusion of Y + HREE at the core–mantle boundary occurred over a length scale of ~ 200 µm. Garnet in an eclogite from the Sesia Zone, Western Alps (P ~ 2 GPa, T ~ 600 °C), displays pronounced fluid-related veinlets, visible in FeO, MgO and MnO, which cross-cut the primary growth zoning. Surprisingly, complex Y + REE and Cr zoning is not affected by the veinlets, indicating that they did not form by a crack-seal mechanism but are rather related to a selective replacement process. The trace element maps provide a detailed insight into the growth and modification of garnet and thus allow assessment of equilibrium versus disequilibrium processes, and assist in determination of P–T conditions, garnet dating, diffusion modelling as well as documenting fluid-induced modifications.

DTA-TG Analysis of Gd0.95La0.05Ba1.95Sr0.05Cu3Oy Compounds

The sintering temperature is played a vital role in the evolution of phase structure, microstructure, and the properties of the superconductor. In this study, the Gd0.9La0.1Ba1.95Sr0.05Cu3O7-d phase compound has been synthesized by the wet method using HNO3 as a solvent. The samples were divided into two groups. The first sample was calcined at 400 °C for 2 hours + 500 °C for 2 hours + 600 °C for 6 hours. The second sample treated by the same process and then continued by heating at 900 °C for 15 minutes. The effect of the calcination temperature for the synthesis of Gd0.9La0.1Ba1.95Sr0.05Cu3O7-d bulks was investigated using the DTA-TG method. The results showed that the optimum reaction temperature for the formation of Gd0.9La0.1Ba1.95Sr0.05Cu3O7-d phase was 938 °C. The additional heating temperature e.g. 900 °C for 15 minutes on the calcination process can reduce the optimum formation temperature of Gd0.9La0.1Ba1.95Sr0.05Cu3O7-d compounds by 20 °C. The peritectic melting reaction temperatures of the sample without the addition of heating and with the addition of heating at temperature 900 °C for 15 minutes are 1032°C and 1035°C, respectively. The melting temperatures of both samples are 1164 °C and 1200 °C.

Inhomogeneity of SmBCO bulk superconductors grown in air

The local superconducting properties and microstructure of SmBCO bulk single-grain superconductors with the addition of different quantities of BaO2 were studied. The single-grain bulk SmBCO superconductors were fabricated via the top-seeded melt growth process in air. Increasing transition temperature, critical current density and the narrowing superconducting transition width were observed with BaO2 addition. It was shown that the transition temperature and critical current density depend on the distance from the seed. Microstructural analysis showed that the reaction of Ba with the supporting ZrO2 bars is responsible for the gradient of Ba concentration in the peritectic melt, and consequent changes in Sm/Ba substitution in the Sm123 crystal lattice lead to the inhomogeneity of local superconducting properties.

Evolution of a bicontinuous structure in peritectic melting: The simplest form of dealloying

Materials with two interpenetrating phases often exhibit excellent mechanical and physical properties, and can be used as precursors for the production of porous materials that have many practical applications. Such bicontinuous structures can be generated by liquid metal dealloying, followed by quenching. However, this procedure is neither efficient nor cost-effective, because it requires a sizeable liquid-metal corrosion reservoir and long-range mass transport that restricts sample size and synthesis rate. In this paper, we propose a mechanism that generates bicontinuous structures by simple thermal treatments. By heating a TiAg intermetallic compound to above its peritectic temperature, we demonstrate that it decomposes into solid Ti and liquid Ag that interpenetrate at the micrometer scale. The resulting structure can be quenched to room temperature. In this case, peritectic melting proceeds by cooperative growth of solid Ti and liquid Ag into a solid TiAg compound. The behavior of structural evolution resembles the process of dealloying, particularly liquid metal dealloying, except that corrosion media and long-range diffusion are no longer required. Our findings suggest that the directional transition from a solid to another solid and a fluid phase, instead of ``selective etching,'' might be responsible for the evolution of a bicontinuous structure in all dealloying processes. This study also provides a versatile metallurgical route to generate bicontinuous solid/solid or solid/liquid structures and hierarchical nanoporous structures in many materials for mechanical and functional applications.

The dual origin of I-type granites: the contribution from experiments

Abstract New laboratory experiments using granulite xenoliths support a dual origin for I-type granites as primary and secondary. Primary I-type granites represent fractionated liquids from intermediate magma systems of broadly andesitic composition. Fluid-fluxed melting of igneous rocks that resided in the continental crust generates secondary I-type granites. The former are directly related to subduction, with Cordilleran batholiths as the most characteristic examples. Experiments with lower crust granulite sources, in the presence of water, show that amphibole is formed by a water-fluxed peritectic rehydration melting reaction . Entrainment of only 10% of restites composed of amphibole, pyroxene, plagioclase and magnetite, is sufficient to account for discrepancies in aluminium saturation index and maficity in secondary I-type granites. Lower crust granulite xenoliths, attached to a sanukitoid containing 6 wt% water, have been used in two-layer capsules to test fluid-fluxed melting reactions as the origin of secondary I-type granites. It is proposed that sanukitoid magmas act as water donors that trigger extensive melting of the lower crust, giving rise to granodioritic liquids. Because primary granites are related to coeval subduction, and secondary ones are crustal melts from older subduction-related rocks, the distinction between both I-types is essential in tectonic reconstructions of ancient orogenic belts.

Thermal reactivity of YBa2Cu3O7-δ with Al2O3 addition in air atmosphere

The high–temperature thermal reactivity of YBa2Cu3O7-δ (Y123) compound with Al2O3 addition (0.5–10 wt%) was investigated and the thermal processes were described. Experimentally obtained results showed that Al2O3 firstly reacted with Y123 at temperatures far below the peritectic melting point of Y123. During this solid state reaction Al partially diffused into Y123 and formed a solid solution. Also, the formation of Al-rich complex oxides, mainly with barium, and basic secondary phases as Y2BaCuO5 and CuO, was observed with increasing Al2O3 content. The formation of additional secondary phases with Al2O3 provoked their reactivity with Y123 or between themselves. After increasing the temperature of the powder mixtures above the peritectic melting point of Y123 it was found that Al was incorporated in Y123 at higher concentrations than during the solid state reaction. The reason for that could be a partial or full dissolution of Al-rich complex oxides formed at lower temperatures which in turn increased the source of Al for the incorporation in Y123.The thermal behaviour of powder mixtures was investigated with the help of simultaneous differential thermal analysis and thermogravimetry. Morphology and microstructure were examined using powder X-ray diffraction and scanning electron microscopy in combination with energy dispersive X-ray spectroscopy.