Peritectic Phase Research Articles

Formation of late Miocene silicic volcanic rocks in the central Tibetan Plateau by crustal anatexis of granulites

Partial melting of granulites generates melts, which causes the modification of continental crust. However, the detailed mechanisms of this partial melting and related magmatic processes are debated. In this study, we investigated how crustal melting of granulites generated late Miocene (ca. 6.0 Ma) silicic volcanic rocks in the Chibuzhangcuo area of the Qiangtang Block, Tibet. Various peritectic textures (e.g., quartz inclusions in clinopyroxene and fluorhydroxyl phlogopite) suggest that the pyroxenes were derived from a residual granulite phase and peritectic reactions, and were then entrained into the partial melts. The F-rich mica, granulite mineral assemblages, and high titanomagnetite–ilmenite (811–975 °C) and zircon saturation (836–867 °C) temperatures indicate the silicic magmas were high-temperature and water-poor. The geochemical and isotopic compositions of the silicic volcanic rocks are similar to those of middle–lower crustal intermediate–mafic granulite xenoliths in Cenozoic volcanic rocks in the Qiangtang Block. We suggest that these volcanic rocks were generated by partial melting of hydrous mineral-bearing granulites, triggered by an underlying thermal anomaly associated with the high crustal heat-flow of the central Tibetan Plateau. This work indicates that the occurrence of restitic hydrous mineral and perturbation of thermal anomaly are the primary conditions to cause the partial melting of granulite. As the melting went on, the residual granulite phase and peritectic minerals were likely to be preferentially entrained into the melt due to the erosion effect caused by the continued melt flow at the sites of melting.

On the microstructure of as-cast Zn-based ternary alloy

There are limited investigations of the alloys that involve peritectic reactions, due to its complexity. In the present study, casting experiments in a steel mold of square section were carried out in order to show a formal characterization of a zinc-based ternary alloy that has a complex microstructure. The results obtained confirm that instead of the typical structure of primary phase surrounded by peritectic phase on Zn-Ag peritectic systems, a AgZn dendritic phase, a mixture of two solid solutions (η-Zn and AgZn3), precipitates, and a eutectic-like lamellar structures with atomic ratio of Zn/Ag/Mg ~95/3/2 were observed.

Peritectic-eutectic transformation of intermetallic in Zn alloy: Effects of Mn on the microstructure, strength and ductility

Zn alloy containing peritectic intermetallic compound usually has fine grains, so they show relatively high strength. But the intermetallic compound is coarse, which is blamed for the brittleness. In this work, a strategy to transform the peritectic intermetallic phase of Zn-Fe alloy into eutectic intermetallic phase is proposed by adding Mn. In detail, Mn co-precipitates with Fe and Zn to form a (Fe, Mn)Zn13 phase, which provides nucleation substrate and increase the nucleation rate of the MnZn13 eutectic phase because of their low interatomic and interplanar spacing misfit according to the edge-to-edge matching model. The intermetallic compound formed via eutectic reaction is finer than that formed by peritectic reaction. Results show that the intermetallic in Zn-Fe-Mn is refined by 79% compared with that of Zn-Fe. Moreover, the MnZn13 phase forms a semi-coherent interface with negligible lattice misfit (0.09%) in (01¯11¯) orientation with Zn matrix, which is believed to decrease the intergranular fracture ratio. Consequently, Zn-Fe-Mn alloy has a compression yield strength, ultimate tensile strength and elongation of 135.98 MPa, 226.8 MPa, and 15.9%, respectively, which are 28%, 25% and 87% higher than those of Zn-Fe alloy. The strength is improved by dislocation shearing: lattice dislocations cut precipitates to advance through the alloy. The ductility is improved by significantly refined Zn grains, smaller second phase particles and their semi-coherent interfaces with the matrix.

Morphologies of intermetallic compound phases in Sn-Cu and Sn-Co peritectic alloys during directional solidification

The morphologies of intermetallic phases (IMCs) during directional solidification of the Sn-Cu (L+Cu3Sn→Cu6Sn5) and Sn-Co (L+CoSn→CoSn2) peritectic systems were analyzed. The primary Cu3Sn and peritectic Cu6Sn5 phases in Sn-Cu alloy are IMCs whose solubility ranges are narrow, while both the primary CoSn and peritectic CoSn2 phases in Sn-Co alloy are IMCs whose solubility ranges are nil in equilibrium condition. The experimental results before acid corrosion shows that the dendritic morphology of both the Cu6Sn5 and CoSn2 phases can be observed. The investigation on the local dendritic morphology after deep acid corrosion shows that these dendrites are composed of small sub-structures with faceted feature. Faceted growth of the primary Cu3Sn and CoSn phases is also confirmed, and a faceted to non-faceted transition in their morphologies is observed with increasing growth velocities. Further analysis shows that the dendritic morphology is formed in the solidified phases whose solubility range is larger during peritectic solidification.

Metastable coupled growth kinetics between primary and peritectic intermetallic compounds within the liquid Mo-37 wt% Co refractory alloy

The metastable coupled growth between primary σ-Mo3Co2 and peritectic ε-Co7Mo6 phases for hypoperitectic Mo-37 wt% Co refractory alloy was investigated by electromagnetic levitation (EML) and drop tube (DT) methods. The highest alloy undercooling attained 261 K (0.14 TL) under EML conditions, which reached up to 311 K (0.17 TL) in DT experiments. At small undercoolings, the typical peritectic solidification prevailed and the corresponding double recalescence processes were in-situ recorded for levitated alloys. In this case, the primary σ-Mo3Co2 phase preferentially nucleated from liquid alloy and its growth velocity monotonously increased as a power function with the rise of undercooling. When the liquid undercooling increased beyond the threshold of 162 K, the competitive nucleation between σ-Mo3Co2 and ε-Co7Mo6 compounds was facilitated, leading to a novel lamellar eutectic-like microstructure for peritectic-type alloys. Meanwhile, the measured growth velocity exhibited a sudden drop at first and then slightly increased with the bulk undercooling. Once the alloy undercooling exceeded 295 K (D = 226 µm), only the metastable coupled growth mechanism could occur within the liquid alloy. The final microstructure of hypoperitectic Mo-37 wt% Co alloy even transformed from lamellar to anomalous eutectic-like morphology in a sufficiently undercooled state. Furthermore, as the undercooling increased, the random orientation relationship between σ-Mo3Co2 and ε-Co7Mo6 phases in typical peritectic solidification mode was replaced by the parallel orientation, i.e. {111}σ//{101̅0}ε for metastable coupled growth mechanism.

A kinetic transition from peritectic crystallization to amorphous solidification of rapidly quenched refractory Nb-Ni alloy

In this study, the kinetic transition of solidification modes for refractory peritectic Nb54Ni46 alloy was revealed using melting spinning experiments combined with molecular dynamics (MD) simulation and classical nucleation theory. This begins with a shift from the usual peritectic solidification to the direct precipitation of the peritectic Nb7Ni6 phase when the roller speed reaches 10 m/s. Once the roller speed exceeds 20 m/s, the nucleation of the Nb7Ni6 phase is suppressed and the amorphous phase forms. The high-resolution transmission electron microscopy images indicate that the stacking fault and twining model of the peritectic Nb7Ni6 phase are {101¯2}/<1¯011> with a misorientation angle of 35.65°. The results of an individual local crystallization zone in amorphous matrix imply that the chemically disordered crystalline structure is more likely to form during the early stages of nucleation and growth, whereas the chemically ordered crystalline structure may evolve during the growth of the complex intermetallic compound Nb7Ni6 phase. Furthermore, the MD simulation of the glass transition temperature agrees well with the experiment, and the Voronoi polyhedron analysis suggests that the Ni-centered 〈0,0,12,0〉, 〈0,2,8,2〉 as well as Nb-centered 〈0,1,10,4〉 icosahedron-like clusters and their medium-range ordered structures play an important role in the formation of amorphous Nb54Ni46 alloy. In addition, the predictions made using classical nucleation theory and the time-temperature-transformation diagram propose that the phase selection rules are consistent with the experimental results as the undercooling and cooling rate increase, with the critical cooling rate for the formation of amorphous phase determined to be 1.71 × 107 K/s.

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 equilibrium in Fe-Co alloys

Abstract Recent results of directional solidification experiments with Fe–Co alloys were not consistent with the presently accepted peritectic phase diagram. Therefore, the Fe-rich part of this phase diagram was re-examined. High-temperature gradient plane front solidification was carried out at a low velocity. After quenching of the specimen from the peritectic temperature, the compositions of the phases close to the solid/liquid interface were determined through electron probe microanalysis. Using these results together with previously published phase diagram information, an improved phase diagram is proposed with the peritectic equilibrium at T p = 1774 K, C δ = 17.7, C γ = 18.1 and C L = 19.5 at.% Co.

Simulation of the Peritectic Phase Transition in Fe-C Alloys.

In this work, a multi-phase cellular automaton (CA) model is extended for the quantitative simulation of peritectic phase transition. First, the effects of cooling rate/supersaturation and temperature on the peritectic transformation kinetics in Fe-C alloys are investigated by utilizing the present CA model. The CA simulations show that supersaturations in the parent phases (liquid and δ-ferrite) increase the L/γ interface growth velocity remarkably, but tinily for the δ/γ interface migration velocity. There exists a transition supersaturation for isothermal transformations, at which the growth rates of the two interfaces are equal. The transition supersaturation is found to increase with decreasing temperature. Microstructural evolution at different cooling rates during peritectic transformation is simulated using the experimental conditions. At low cooling rates, the δ/γ interface propagates at a higher velocity than the L/γ interface. At high cooling rates, however, the γ-phase grows more into the L-phase with a cellular morphology. Then, the proposed CA model is applied to simulate the microstructural evolution during peritectic reaction. It is observed that the γ-phase propagates along the L/δ interface and finally encircles the δ-phase. Meanwhile, the intervenient γ-phase grows in thickness through peritectic transformation. The CA simulations are compared reasonably well with the experimental data and analytical calculations.

Crystal orientation induced by high magnetic fields during peritectic reaction of alloys

Using Tb0.27Dy0.73Fe1.95 as a model alloy, we generate (Tb, Dy)Fe2 and (Tb, Dy)Fe3 phases with preferred orientations. We study the mechanism that determines the preferred crystal orientation of a peritectic alloy under high magnetic fields. Adjusting the preparation parameters yields four Tb0.27Dy0.73Fe1.95 alloys with respective 〈110〉, 〈111〉, 〈112〉, and 〈113〉 directions of the peritectic (Tb, Dy)Fe2 phase parallel to the high magnetic field. The 〈112¯0〉, 〈0001〉, 〈101¯0〉, and 〈101¯3¯〉 directions of the corresponding primary (Tb, Dy)Fe3 phase are parallel to the magnetic field. We deduce the orientation relationships (1¯11)//(0001) and [110]//[112¯0] for the (Tb, Dy)Fe3 and (Tb, Dy)Fe2 phases. The growth velocity and high magnetic field do not change the orientation relationships of these two phases. The high magnetic field induces the rotation of the primary (Tb, Dy)Fe3 phase and then affects the orientation of the peritectic (Tb, Dy)Fe2 phase. Magnetic torque induces stacking of the {0001} plane perpendicular to the magnetic field, meaning the c-axis of the primary (Tb, Dy)Fe3 phase aligns parallel to the field. At this time, the {111} plane of the (Tb, Dy)Fe2 phase grows perpendicular to the magnetic field, as reflected in the preferred orientation of the (Tb, Dy)Fe2 phase along the 〈111〉 direction.

Study of Crack Sensitivity of Peritectic Steels

By comprehensively considering both the high temperature mechanical properties and peritectic transformation during peritectic steel solidification, the strain εCth is proposed to evaluate the crack sensitivity of peritectic steels produced in the brittle temperature range in the present work. The zero ductility temperature (ZDT) and the zero strength temperature (ZST) of Fe–C–0.32Si–1.6Mn–0.01P–0.015S steel under nonequilibrium conditions by taking the effect of the peritectic transformation on the solute segregation into account were calculated by the CK microsegregation model (Clyne–Kurz model) and were compared with the measured data. The comparison results show that this model can well simulate the nonequilibrium solidification process of peritectic steel. Then, based on the calculation of the CK microsegregation model, the strain during the peritectic phase transformation in the brittle temperature range (ZDT &lt; TB &lt; LIT) was calculated under nonequilibrium conditions. The results show that the calculated strain is in good agreement with the actual statistical longitudinal crack data indicating that the strain can therefore be used to predict the crack sensitivity of peritectic steels effectively.

Analysis on phase nucleation in Sn-Ni peritectic alloy combining confocal laser scanning in-situ observation and differential scanning calorimetry

The analysis of the phase nucleation requires not only the in-situ images but also the accurate nucleation information. Thus, the nucleation of both the primary Ni3Sn2 and peritectic Ni3Sn4 phases were studied during peritectic solidification of Sn-Ni alloy using the high temperature confocal laser scanning microscope (HT-CLSM) and differential scanning calorimetry (DSC). The results by both methods confirm that the nucleation undercooling ∆T of the solid phases decrease with increasing cooling rates, which is demonstrated to be caused by higher concentration difference at larger cooling rates. Besides, the freezing range of the alloy is also found to decrease with the increase in cooling rate. However, the nucleation undercooling of the peritectic Ni3Sn4 phase determined by HT-CLSM is larger than that by DSC at each cooling rate. This is attributed to the slower capture of peritectic reaction when using HT-CLSM. Furthermore, the nucleation of peritectic Ni3Sn4 phase is confirmed to be controlled by the heterogeneous nucleation on primary Ni3Sn2 phase by comparison between the HT-CLSM observation and DSC result. In addition, the wetting angles for heterogeneous nucleation of both phases which are important parameters in analyzing the nucleation of solid phases were determined through the entropy of solidification data from the DSC results. The smaller wetting angle of peritectic Ni3Sn4 phase as compared with that of the primary Ni3Sn2 phase further proving the smaller nucleation undercooling of Ni3Sn4 phase during solidification.

Rare elements enrichment in crustal peraluminous magmas: insights from partial melting experiments

Experiments were conducted to explore the behavior of Li, Rb, Nb, Sn, Cs, Ta, W during crustal melting and test the anatectic origin of rare metal-bearing peraluminous granites such as rare metal granites (RMGs). The experiments were performed under fluid-absent conditions at 800 and 850 °C, 400 MPa and moderately reducing fO2 (ΔFMQ = − 0.5 to − 0.8). Starting materials were cores of several millimetres drilled from two natural rocks, a biotite-rich paragneiss (Pg) and a muscovite-rich orthogneiss (Og) enriched in Li, Be, Sn, Cs, W. Both protoliths produced small melt fractions from 8 to 20% vol. Melt distributions were either homogeneously distributed at grain boundaries in the Pg or preferentially associated with muscovite reaction zones in the Og. In the Pg at 800 °C, melting is mainly fluid present, driven by interstitial water at grain boundaries. At 850 °C, biotite dehydration-melting produces peritectic orthopyroxene, hercynitic spinel, ilmenite and alkali feldspar in addition to melt. In the Og, muscovite dehydration-melting generates melt plus peritectic biotite, hercynitic spinel, ilmenite, Al silicates and alkali feldspar. Experimental glasses are nearly homogeneous, silica rich, peraluminous and leucogranitic and their major element compositions differ only little between the two protoliths. In contrast, the trace element concentrations vary as a consequence of chemical and textural heterogeneities in our starting materials. Compared with source rocks, the Og glasses are enriched in Rb, Nb, Ta, W and depleted in Li, Cs and the Pg are enriched in Li, Rb, Cs, W and depleted in Nb, Ta. Mass-balance calculations indicate that during muscovite dehydration-melting, Li, Cs and Rb partition into the melt; whereas Nb, Ta and W are preferentially incorporated in peritectic phases. Li and Cs also partition toward the melt during biotite dehydration-melting. The partitioning behavior of trace elements during crustal melting is a function of the melting reaction and partition coefficients between melt, residual and peritectic phases. Experimental glasses are similar to peraluminous muscovite granites but fail to reproduce RMG compositions. Alternatives to mica dehydration-melting such as fluid-present and residual source melting emphasize the difficulties with an origin of RMGs by purely anatectic processes. Crystallization differentiation might have to be combined with mica dehydration-melting to explain the distinctive geochemical features of RMGs.

Variscan intracrustal recycling by melting of Carboniferous arc-like igneous protoliths (Évora Massif, Iberian Variscan belt)

Abstract Bulk rock geochemistry and sensitive high-resolution ion microprobe zircon geochronology of igneous and metaigneous rocks of the Évora gneiss dome, located to the north of the reworked Rheic Ocean suture zone in the southwest Iberian Variscan belt, reveal a succession of magmatic and melting events lasting ~30 m.y. between ca. 341–314 Ma. The study of detailed field relationships of orthomigmatites (i.e., migmatites from igneous protoliths) and host granitic rocks proved to be crucial to reconstruct the complex sequence of tectono-thermal events of the Évora gneiss dome. The older igneous protoliths, with marked geochemical arc-like signatures, are represented by 338 ± 3 Ma tonalites and 336 ± 3 Ma diorites. These tonalites and diorites appear as mesosomes of igneous orthomigmatites containing new melts (leucosomes) of monzogranite composition and silica-poor trondhjemites formed in a melting episode at 329 ± 4/6 to 327 ± 3 Ma. The absence of peritectic phases (e.g., pyroxene), together with shearing associated with migmatization, imply the existence of water-rich fluids during melting of the older igneous rocks of the Évora gneiss dome. This melting event is coeval with the second magmatic event of the Évora gneiss dome represented by the neighboring Pavia pluton. A porphyritic monzogranite dated at 314 ± 4 Ma defines a later magmatic event. The porphyritic monzogranite encloses large blocks of the orthomigmatites and contains magmatic mafic enclaves (autoliths) dated at 337 ± 4 Ma that are ~23 m.y. older than the host rock. All studied rocks of the Évora gneiss dome show arc-like, calc-alkaline geochemical signatures. Our results support recycling of intermediate-mafic plutonic rocks, representing the root of an early magmatic arc that formed at the time of Gondwana-Laurussia convergence (after the closure of the Rheic Ocean) and coeval subduction of the Paleotethys. A geodynamic model involving ridge subduction is proposed to explain the Early Carboniferous intra-orogenic crustal extension, dome formation, exhumation of high-grade rocks, compositional variations of magmatism and formation of new granitic magmatism in which, arc-like signatures were inherited from the crustal source.

Influence of B contents on the microstructure, fracture toughness and oxidation resistance of Mo-Si-B alloys

The Mo-10Si-(0, 5, 10, 15)B (at.%) alloys located in Moss (Mo solid solution) +Mo3Si +T2 (Mo5SiB2) region were prepared by arc melting. The effect of B content on the microstructure, microhardness, fracture toughness and oxidation resistance of the alloys was studied. In the Mo-10Si alloy, there are primary Moss and peritectic Mo3Si phases. With the addition of B, (Moss + T2) binary and (Moss + T2 + Mo3Si) ternary eutectics emerge in Mo-10Si-(5, 10)B alloys. For Mo-10Si-15B alloy, primary Moss disappears and the microstructure is only composed of binary and ternary eutectics. With the increase of B content, the proportion and grain size of Moss decrease. The microhardness of alloys increases with the increase of B content due to the increasing intermetallics. The fracture toughness of alloys decreases obviously in single-edge notched three-point bending testing (SENB) and the fracture mode transforms from transgranular fracture to intergranular fracture because of the refinement of Moss. In the high-temperature oxidation test at 1250 °C, the oxidation weight loss of the alloys decreases with the addition of B due to the densification of the borosilicate layer.

Peritectic phase formation kinetics of directionally solidifying Sn-Cu alloys within a broad growth rate regime

Previous studies have shown that the peritectic transformation may not occur and, depending on the cooling rate, the peritectic phase can nucleate and grow directly from the melt. This study investigates the effect of growth rate (pull rate) on a peritectic alloy via in-situ directional solidification, in particular where rapid solidification dramatically alters the microstructure, whereby only the peritectic phase nucleates directly from the liquid. The phase formation events occurring during the directional solidification of a Sn-Cu peritectic alloy were studied, confirming that growth rate has a critical effect on the phase selection of the Sn-10 wt %Cu alloy. Over the range of growth rates studied, competitive nucleation between the pro-peritectic Cu3Sn phase and the peritectic Cu6Sn5 phase occurs, and beyond a critical growth rate, nucleation of the Cu3Sn phase does not occur and the Cu6Sn5 phase nucleates preferentially from the metastable liquid. Phase competition in peritectic alloys is of interest from not only a fundamental perspective but also from a practical viewpoint allowing for unique microstructure design. This work presents for the first time the in-situ directional solidification of a Sn-Cu alloy that involves an equilibrium peritectic reaction and shows the effect of growth rate on phase selection. Furthermore, this study has confirmed that the peritectic transformation does not occur in the investigated Sn-Cu alloy for the range of conditions examined.

Multiphase Field Modeling of Dendritic Solidification of Low-Carbon Steel with Peritectic Phase Transition

In the present study, an improved multiphase field model with taking into consideration the S/L interface anisotropy is proposed to simulate the dendritic growth with peritectic transition of low-carbon steel, and a new random heterogeneous nucleation method is proposed to treat the γ phase nucleation during the peritectic solidification process. The γ phase growth around the dendrite (the single dendrite and polycrystalline ferrite) and the subsequent peritectic transformation during the peritectic solidification are simulated. The results show that when the temperature reaches the γ phase nucleation temperature, γ nuclei suddenly nucleate at the δ/L interface, and laterally grow with the movement of L/γ/δ triple point around the δ/L interface of δ dendrite. After the δ dendrite is fully wrapped by the continuous intervening γ phase, the γ phase continues to grow with direct phase transformation from both δ phase and liquid phase. With the increase of melt undercooling, more δ phase and liquid phase are consumed to form γ phase, and the intervening γ phase between the δ dendrite and liquid phase becomes more and more thick, but the δ dendrite arm becomes more and more thin. During the dendritic solidification process, the solute would be rejected from dendrite trunk with the dendritic growth and enriched at the dendrite boundary, especially at the dendrite root. The solute enrichment at the dendrite root would inhibit the γ phase growth at the dendrite root and thus the thickness of intervening γ phase at the dendrite root is thinnest around the dendrite. Moreover, the solute concentration in γ phase is among the δ phase and liquid phase, because the carbon solubility in γ phase is higher than that in δ phase, but lower than that in liquid phase.

Genetic relations between enclaves and their host granitoids from Doumer Island, northern Antarctic Peninsula: Evidence from mineral chemistry, Sr–Nd and Li isotopes

Dark enclaves in the late Paleocene granitoids of Doumer Island, northern Antarctic Peninsula, were examined by field investigations, zircon U–Pb geochronology, mineral chemistry, whole-rock major- and trace-elements, and Sr-Nd-Li isotopes to elucidate their origins and genetic relationships with host granitoids. The enclaves and host granitoids have similar zircon U–Pb ages of 54.6–55.7 Ma and indistinguishable Nd–Sr isotopes of εNd(t) = 4.7–6.1, ISr = 0.7036–0.7039, indicating a cogenetic relationship. A pyroxene-dioritic enclave (WA16–06-3) is a cognate restite with peritectic phases that resulted from amphibole-dehydration melting at temperatures above 800 °C and at low-P (7–10 kbar). Two other enclaves (WA16–07-2 and WA15–27-3) are fragments of the chilled margins of the conduits entrained in the later insurgent felsic magma. The flat, right-leaning REE patterns are accompanied by positive Eu anomalies (Eu/Eu* = 1.07–1.16) in the dark enclaves and negative Eu anomalies (Eu/Eu* = 0.72–0.88) in the host intrusions. The accumulation of restitic plagioclase and peritectic pyroxene could have induced the positive Eu anomalies in the dark enclaves. The P–T conditions estimated from cummingtonite rims on pyroxene in the pyroxene-dioritic enclave suggest near-isothermal decompression in an environment of fast exhumation. Enclave WA16–07-2 is part of an intense swarm of enclaves near the pluton margin, and crystallized from a less evolved melt that was mechanically eroded by the host magma, indicating a transient state of magma flow. The dioritic enclaves were transported in the form of ductile crystal–melt mushes that were rotated in the insurgent viscous granitoid magma. The enclaves become rounder and sparser towards the interior of the host pluton. Dehydration melting of metabasalt could have produced these melts that are rich in δ7Li while leaving a lighter δ7Li pyroxene-rich residue at the source. The underlying cause of these events was the retreat of the subducting proto-Pacific (Phoenix) oceanic slab beneath the western Antarctic Peninsula that triggered melting of asthenospheric mantle, with basaltic magma underplating and melting a juvenile metabasaltic lower crust.

Reactive structure materials

The effectiveness of lethal weapons is predominantly dependent on the overpressure generated and blast effect. Reactive structure materials (RSM) can be made of either metal-polymer mixtures or represent intermetallic phases. An example for a metal-polymer mixture is the system PTFE/W/Cu/Pb which shows higher penetration depth compared to the original PTFE/Al liner. The intermetallic phases (alloys) ZrW2 and HfW2 discussed in this review are very promising materials for use as reactive structure materials (RSMs). Both compounds have been shown to possess remarkable properties such as high melting temperatures, high densities, high hardness and high ignition energies on burning in air. The heats of combustion as well as the combustion temperatures have been calculated using the EXPLO5 code (version V6.05.02). ZrW2 and HfW2 can be prepared by melting the constituent elements in an arc-furnace. By cooling through peritectic phase lines above approximately 2000°C, samples of the nominal 1:2 composition were obtained as pure products (consisting of two phases, of which approximately 95% adopts the MgCu2 type structure and 5% the W structure). Both intermetallic phases are very dense and hard alloys which burn at a crash in air in a strong exothermic ignition reaction. Both intermetallic phases (alloys), ZrW2 and HfW2, are non-toxic.

Peritectic Formation and Phase Stability of the Icosahedral Quasicystal i-GdCd and Its Ternary Variants with Zn, Mg, and Y

Stable binary icosahedral quasicrystals (i-QCs) based on rare earth (RE) and cadmium are typically accessed by solution growth experiments, which operate in very narrow composition and temperature ...