Congruent Melting Research Articles

Petrographic and geochemical characterization of the granitic rocks of the Araguainha impact crater, Brazil

AbstractPetrographic and geochemical data obtained on the Araguainha impact crater (Goiás/Mato Grosso States, Brazil) indicate the existence of several molten products that originated during impact‐induced congruent melting of an alkali‐granite exposed in the inner part of the central uplift of the structure. Although previous studies have described these melts to some extent, there is no detailed discussion on the petrographic and geochemical variability in the granite and its impactogenic derivatives, and therefore, little is known about the geochemical behavior and mobility of trace elements during its fusion in the central part of the Araguainha crater. This paper demonstrates that the preserved granitoid exposed in the core of the structure is a magnesium‐rich granite, similar to postcollisional, A‐type granites, also found in terrains outside the Araguainha crater, in the Brasília orogenic belt. The molten products are texturally distinct and different from the original rock, but have very similar geochemical composition, making it difficult to separate these lithotypes based on concentrations of major and minor elements. This also applies for trace and rare earth elements (REE), thus indicating a high degree of homogenization during impact‐induced congruent melting under high pressure and postshock temperature conditions. Petrographic observations, along with geochemical data, indicate that melting occurs selectively, where some of the elements are transported with the melt. Simultaneously, there is an effective dissolution of the rock (granite), which leads to entrainment of the most resistant solid phases (intact or partially molten minerals) into the melt. Minerals more resistant to melting, such as quartz and oxides, contribute substantially to a chemical balance between the preserved granite and the fusion products generated during the meteoritic impact.

Ionic liquid, glass or crystalline solid? Structures and thermal behaviour of (C4mim)2CuCl3.

The ionic liquid (C4mim)2CuCl3 was synthesised from a mixture of copper(i) chloride and 1-butyl-3-methylimidazolium chloride (C4mimCl) and investigated using crystallographic and thermoanalytical methods. In the crystalline state, the compound consists of C4mim(+) cations and triangular [CuCl3](2-) anions and forms three different modifications, which are connected through phase transitions at 227 and 203 K. The high and intermediate temperature phases crystallise in the space group C2, whereas the low temperature phase exhibits the space group P21. The three crystal structures are related through an isomorphic and a klassengleiche symmetry transition, respectively. The solid undergoes congruent melting at 320 K. The enthalpy of fusion was determined to be 25.7 kJ mol(-1). The melting process is irreversible and the ionic liquid can be supercooled to its glass transition at 221 K.

Optical nonlinearities of small polarons in lithium niobate

An overview of optical nonlinearities of small bound polarons is given, which can occur in the congruently melting composition of LiNbO3. Such polarons decisively influence the linear and nonlinear optical performance of this material that is important for the field of optics and photonics. On the basis of an elementary phenomenological approach, the localization of carriers in a periodic lattice with intrinsic defects is introduced. It is applied to describe the binding energies of four electron and hole small polarons in LiNbO3: small free NbNb4+ polarons, small bound NbLi4+ polarons, small bound NbLi4+:NbNb4+ bipolarons, and small bound O− hole polarons. For the understanding of their linear interaction with light, an optically induced transfer between nearest-neighboring polaronic sites is assumed. It reveals spectrally well separated optical absorption features in the visible and near-infrared spectral range, their small polaron peak energies and lineshapes. Nonlinear interaction of light is assigned to the optical formation of short-lived small polarons as a result of carrier excitation by means of band-to-band transitions. It is accompanied by the appearance of a transient absorption being spectrally constituted by the individual fingerprints of the small polarons involved. The relaxation dynamics of the transients is thermally activated and characterized phenomenologically by a stretched exponential behavior, according to incoherent 3D small polaron hopping between regular and defect sites of the crystal lattice. It is shown that the analysis of the dynamics is a useful tool for revealing the recombination processes between small polarons of different charge. Nonlinear interaction of small polarons with light furthermore results in changes of the index of refraction. Besides its causal relation to the transients via Kramers-Kronig relation, pronounced index changes may occur due to optically generated electric fields modulating the index of refraction via the linear electro-optic effect, also. Based on a microscopic picture and by considering the local structural environment of bound polarons, the appearance of photovoltaic currents is explained straightforwardly as a result of the optically induced carrier transfer. Both transient absorption and index changes are spatially confined to the intensity profile of the interacting light allowing for the recording of efficient mixed absorption and phase volume holograms. By means of holographic spectroscopy, these small-polaron based optical nonlinearities are verified either without or with the action of the linear electro-optic effect; their prominent features are highlighted by appropriate experimental studies wherin the ultrafast response on the picosecond time scale is the most recognized one. Based on these findings, the consequences for applications of LiNbO3 in the field of nonlinear optics and photonics are presented. Besides visionary examples like real-time, 3D holographic displays, the impact of optical nonlinearities of small polarons for present applications are discussed with frequency conversion and respective limiting effects, such as green-induced infrared absorption and optical damage, as important example.

P89] Lanthanide(III)-Alkali Metal halide Systems: Characterization and Prediction of Phase Diagram Topology

The constitution of the ternary system Co–Si–Ti was investigated using electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and differential thermal analysis. Eleven ternary phases were identified and their homogeneity ranges characterized. The equilibria between these phases at 1000 °C are presented in an isothermal section. A reaction scheme linking this isothermal section with the liquidus surface is derived. It contains three ternary eutectics at 1195 °C, 1148 °C and 988 °C in the Si-rich, Co-rich and Ti-rich corners, respectively. The liquidus surface projection proposed shows large regions of primary crystallization for the congruently melting ternary phases τ1-CoSiTi and τ2-Co4Si7Ti4, the incongruently melting Laves phase (bundle) τ6, as well as the binary phases CoSi, CoTi, and Ti5Si3.

Nitrate (chloride) melts as media for crystal growth of complex phosphates of alkali and trivalent metals

The interaction in the molten systems MIPO3-MIII2O3-MINO3 (MICl) (MI – Na, K; MIII – Al, Fe, Y, Bi) was investigated at molar ratios P/MIII=1 or 3 at the temperatures 400°C (for MINO3) or 810°C (for MICl). Formation conditions of complex phosphates MI3MIII2(PO4)3 and MI3MIII(PO4)2 (MI – Na, K; MIII – Al, Fe, Bi) were established. It was shown that the crystal size of obtained phosphates can be controlled by using different salt melts. The synthesized compounds were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, Optical microscopy and Scanning electron microscopy with Energy-dispersive X-ray spectroscopy. Differential thermal data for Na3Bi(PO4)2 and Na3Fe(PO4)2 showed congruent and incongruent melting, respectively.

Investigation of residual anode material after electrorefining uranium in molten chloride salt

A buildup of material at uranium anodes during uranium electrorefining in molten chloride salts has been observed. Potentiodynamic testing has been conducted using a three electrode cell, with a uranium working electrode in both LiCl/KCl eutectic and LiCl each containing ∼5 mol% UCl3. The anodic current response was observed at 50° intervals between 450 °C and 650 °C in the eutectic salt. These tests revealed a buildup of material at the anode in LiCl/KCl salt, which was sampled at room temperature, and analyzed using ICP-MS, XRD and SEM techniques. Examination of the analytical data, current response curves and published phase diagrams has established that as the uranium anode dissolves, the U3+ ion concentration in the diffusion layer surrounding the electrode rises precipitously to levels, which may at low temperatures exceed the solubility limit for UCl3 or in the case of the eutectic salt for K2UCl5. The reduction in current response observed at low temperature in eutectic salt is eliminated at 650 °C, where K2UCl5 is absent due to its congruent melting and only simple concentration polarization effects are seen. In LiCl similar concentration effects are seen though significantly longer time at applied potential is required to effect a reduction in the current response as compared to the eutectic salt.

Cation ordered structure and F-ionic conductivity of Er0.7Ca0.3F2.7 tysonite-type crystals

Cation ordering in the Er0.7Ca0.3F2.7 monoclinic phase with the tysonite-type (LaF3) structure, which was formed in Er1−yCayF3−y samples of the 65–72.5mol% ErF3 composition range at solid state synthesis (905°C, 230h), has been studied in a transmission electron microscope. It is found that the three space groups C2, Cm and C2/m obey the reflection conditions, which were recognized through observation of supercell spots in electron diffraction patterns obtained by studying seven samples. Separate occupation of 20 available cation positions in the Er14Ca6F54 supercell by erbium and calcium ions can be only realized in the C2 space group. A structure model of the supercell has been proposed by fitting simulated electron diffraction patterns to experimental ones. A link between cation ordering and suppression of F-ionic conductivity of the Er0.7Ca0.3F2.7 phase, which belongs to the least conducting congruent melting phase R1−yCayF3−y with end elements of the rare-earth element family, has been suggested.

Electrical and thermal conductivities of congruently melting single crystals of isovalent M 1 − x M′xF2 solid solutions (M, M′ = Ca, Sr, Cd, Pb) in relation to their defect fluorite structure

The electrical and thermal conductive properties of two-component single crystals of Pb0.67Cd0.33F2, Ca0.59Sr0.41F2, and Cd0.77Sr0.23F2 solid solutions with fluorite-type structure (CaF2), characterized by congruent melting (presence of minima in melting curves) and uniform distribution of components in the crystal bulk. Pb0.67Cd0.33F2 crystals, in contrast to isostructural Ca0.59Sr0.41F2 and Cd0.77Sr0.23F2 crystals, are characterized by high fluorine-ion electrical conductivity (σ = 0.02 S/m at 293 K); low ion-transport activation enthalpy (ΔH ≈ 0.4 eV); low thermal conductivity (k = 1.1 W/mK at 300 K); and glassy behavior of heat transfer, which is atypical for crystalline state. This anomalous behavior of the electrical and thermal conductivities of Pb0.67Cd0.33F2 crystals is due to the strong structural disordering of the anionic subsystem (which is retained at room temperature) as a result of isovalent replacements of Pb2+ cations with Cd2+ cations.

Crystal structure and thermal stability of new iron phosphates KMFe(PO4)2 (M = Ni, Mg, and Co)

Three isostructural iron monophosphates KNiFe(PO4)2 (KNi), KMgFe(PO4)2 (KMg-LT, where LT means “low-temperature stable phase”), and KCoFe(PO4)2 (KCo-LT) are synthesized and structurally characterized from X-ray diffraction data. They crystallize in the monoclinic system with the space group P21/c. Their structures have in common a three-dimensional framework, built up by infinite zigzag chains of edge-sharing MO6 (M = Ni, Mg or Co) octahedra, linked by FeO5 and PO4 polyhedra via vertices and edges to form a rigid skeleton. The K+ ions are located in formed tunnels. DTA showed that KNi has a congruent melting at 941°C, whereas KMg-LT and KCo-LT undergo irreversible phase transitions from P21/c to different high-temperature structures with the C 2/c symmetry. IR absorption bands are assigned to different vibrations of the PO4 tetrahedron.

Constitution of the systems {V,Nb,Ta}-Sb and physical properties of di-antimonides {V,Nb,Ta}Sb2

The binary phase diagrams {V,Nb,Ta}-Sb below 1450 °C were studied by means of XRPD, EPMA, and DTA measurements. In the V-Sb system, five stable binary phases were observed in this investigation: V3+xSb1−x, ℓT-V3Sb2, hT-V2−xSb, V7.46Sb9, V1−xSb2. The V-Sb phase diagram is characterized by two degenerate eutectic reactions: L↔V3+xSb1−x+(V) (T > 1450 °C at 18.1 at.% Sb) and L↔V1−xSb2+(Sb) (T=(621 ± 5)°C at ∼99 at.% Sb), three peritectic reactions: L + V3+xSb1−x↔hT-V2−xSb (T=(1230 ± 10)°C at ∼42 at.% Sb), L + hT-V2−xSb↔V7.46Sb9 (T=(920 ± 10)°C at ∼87 at.% Sb), and L + V7.46Sb9↔V1−xSb2 (T=(869 ± 5)°C at ∼88 at.% Sb), a peritectoid reaction: V3+xSb1−x + hT-V2−xSb↔ℓT-V3Sb2 at (875 ± 25)°C, a eutectoid reaction: hT-V2−xSb↔ℓT-V3Sb2+V7.46Sb9 at (815 ± 15)°C and congruent melting of V3+xSb1−x (T > 1450 °C). An X-ray single crystal study of V5Sb4C1−x proved the existence of interstitial elements in the octahedral voids of a partially filled Ti5Te4-type structure (x∼0.5; RF2 = 0.0101), therefore this phase (earlier labeled “V5Sb4”) was excluded from the binary equilibrium phase diagram. V5Sb4C1−x is the first representative of a filled Ti5Te4-type structure.A re-investigation of the Nb-Sb system removed the contradiction between the hitherto reported phase diagrams and confirmed the version derived by Melnyk et al. (see ref. [1]).Three binary phases exist in the Ta-Sb system: Ta3+xSb1−x, Ta5Sb4, TaSb2. Due to instrumental limits (≤1450 °C), only the peritectic reaction of TaSb2: L + Ta5Sb4 ↔ TaSb2 ((1080 ± 10)°C at ∼92 at.% Sb) and a degenerate Sb-rich eutectic reaction (L↔TaSb2+(Sb); (622 ± 5)°C; ∼99 at.% Sb) have been determined.Physical properties (mechanical and transport properties) of binary di-antimonides were investigated with respect to a potential use of these metals either as diffusion barriers or electrodes for thermoelectric devices based on skutterudites. All group-V metal di-antimonides have low metallic-type resistivity and relatively high thermal conductivity. Magnetic field has little influence on the resistivity of V1−xSb2 at low temperature, while on {Nb,Ta}Sb2 it increases the resistivity, especially on NbSb2. The coefficient of thermal expansion (CTE) decreases from V1−xSb2 to TaSb2, particularly the CTE value of NbSb2 is in the range of average n-type filled skutterudites. In contrast to the CTE value, elastic moduli increase from V1−xSb2 to TaSb2. The value for V1−xSb2 is in the range of Sb-based skutterudites, whereas the values for {Nb,Ta}Sb2 are significantly higher.

Experimental Investigation of the Concentration Dependent Maximum Storage Capacity of two Inorganic Phase Change Materials

Abstract In large latent heat storages with the phase change material (PCM) being a salt hydrate, it is difficult to assure the stoichiometrically correct hydrate concentration of the salt hydrate. In this study, the influence of the composition of CaBr 2 + H 2 O around the congruent melting CaBr 2 ·6H 2 O and CaCl 2 + H 2 O around the semi-congruent melting CaCl 2 ·6H 2 O on the maximum storage capacity is investigated via differential scanning calorimetry (DSC). For a CaBr 2 concentration around 0.8 wt% lower than the concentration of CaBr 2 ·6H 2 O, a decrease of over 17% is found for the maximum storage capacity. For a CaCl 2 concentration around 0.7 wt% lower than the concentration of CaCl 2 ·6H 2 O, a decrease of over 11% is found for the maximum storage capacity. While reproducible results for the maximum storage capacity for samples of the same concentration of CaBr 2 + H 2 O are obtained via DSC, this is not the case for the CaCl 2 + H 2 O samples. Thus, the difficulty to measure representative enthalpy curves of non-congruent melting salt hydrates via DSC is shown.

Solidification and thermodynamic parameters of binary faceted organic alloys: Picric acid–Resorcinol system

With increasing interest in low power high speed microelectronic devices, organic based neutron detectors to replace helium and design of low power controlled explosives, thermodynamic and crystal growth parameters of single and binary organic materials have attracted attention significantly. We have studied Solid–liquid phase equilibrium for Picric acid–Resorcinol system, undercooling, crystallization velocity as function of undercooling, and thermodynamic parameters. The phase diagram shows 1:1 congruent melting compound melting at 374.9K along with two eutectics which melt at 360.4 and 369.3K. The linear velocity of crystallizations at different undercoolings followed the v=k (ΔT)n equation, where v is the crystallization velocity, ΔT, is the undercooling, k and n are constant. To understand the nature of molten liquid, excess Gibbs free energy, excess entropy, and excess enthalpy have been calculated from the measured values of heat of fusion and specific heat. FT-IR spectral studies indicated the formation of H-bond in the eutectic mixtures. The eutectics and congruent melting compound were investigated by X-ray diffraction technique and scanning electron microscopy. Microstructural studies were made in the presence and absence of impurities.

Calorimetric and theoretical determination of the concentration dependent enthalpy change around CaBr2·6H2O

In large latent heat storages based with the phase change material (PCM) being a salt hydrate, it is difficult to assure the stoichiometrically correct hydrate concentration of the salt hydrate. In this study the impact of the concentration of CaBr2+H2O in a concentration range of about 2.6wt% around the congruent melting CaBr2·6H2O on the melting enthalpy and the maximum storage capacity is exemplary investigated via differential scanning calorimetry (DSC) and via a model. The melting enthalpy of CaBr2·6H2O is found to be 142.1Jg−1, which is significantly larger than the value indicated in literature (115.5Jg−1). For a CaBr2 concentration around 0.8wt% lower than the concentration of CaBr2·6H2O, a decrease of over 17% is found for both the melting enthalpy and the maximum storage capacity. A good agreement is found for the maximum storage capacity between the experimentally determined values and the values determined by the model.

Growth, Structural Considerations, and Characterization of Ce-Doped (La,Gd)2Si2O7 Scintillating Crystals

Ce-doped lantanium-gadolinium pyrosilicate (La,Ce,Gd)2Si2O7 (Ce:La-GPS), crystals with various content of rare-earth elements were produced from the melt, and their optimal La/Gd ratio was examined. It was found that Ce:La-GPS single crystals of acceptable optical quality can be produced from the melts ranging from La0.5Gd1.5Si2O7 to La1.0Gd1.0Si2O7 and containing about 1 atom % Ce with respect to the host rare-earths of La and Gd. The crystal growth was performed by the micro-pulling-down and Czochralski methods. The crystals were chemically uniform along the growth axis, and their composition was equal to that of the melt, thus corresponding to vicinity of congruent melting composition. Spatial distribution of Ce in La-GPS was also inspected, and no variation of Ce content was detected as a result of its similarity to one of the host cations (La) regarding the size. Basic optical and scintillation properties of the Ce:La-GPS crystals are also reported, and it is demonstrated that partial substitution of...

ChemInform Abstract: Synthesis and Characterization of Cd4YbO(BO3)3 — A Congruent Melting Cadmium—Ytterbium Oxyborate with Large Nonlinear Optical Properties.

AbstractSingle crystals of the title compound are grown by solid state reaction of CdCO3, H3BO3, and Yb2O3 in a molar ratio of 8:6:1 (Pt crucible, 1200 °C).

Growth and characterization of potassium strontium iodide: A new high light yield scintillator with 2.4% energy resolution

A new ternary metal halide scintillator, potassium strontium iodide, activated with divalent europium (KSr2I5:Eu) has been discovered. This material has a monoclinic crystal structure with a density of 4.39g/cm3. Differential scanning calorimetry indicates a congruent melting point of 470°C and suggests that this compound has no solid–solid phase transitions. As is the case with most metal halides, the material is hygroscopic, and it has some internal radioactivity due to the presence of 40K. Single crystals of KSr2I5 doped with 4% Eu2+ were grown in evacuated quartz ampoules via the Bridgman technique. The X-ray excited emission spectrum consisted of a single peak at ~445nm due to the 5d–4f transition in Eu2+. The measured light yield is ~94,000photons/MeV with an energy resolution of 2.4% at 662keV. The crystal has an excellent proportionality response over a wide range of energies from 14keV to 1275keV.

Superior intrinsic thermoelectric performance with zT of 1.8 in single-crystal and melt-quenched highly dense Cu(2-x)Se bulks.

Practical applications of the high temperature thermoelectric materials developed so far are partially obstructed by the costly and complicated fabrication process. In this work, we put forward two additional important properties for thermoelectric materials, high crystal symmetry and congruent melting. We propose that the recently discovered thermoelectric material Cu2-xSe, with figure of merit, zT, over 1.5 at T of ~ 1000 K, should meet these requirements, based on our analysis of its crystal structure and the Cu-Se binary phase diagram. We found that its excellent thermoelectric performance is intrinsic, and less dependent on grain size, while highly dense samples can be easily fabricated by a melt-quenching approach. Our results reveal that the melt-quenched samples and single crystals exhibit almost the same superior thermoelectric performance, with zT as high as 1.7–1.8 at T of ~973 K. Our findings not only provide a cheap and fast fabrication method for highly dense Cu2-xSe bulks with superior thermoelectric performance, paving the way for possible commercialization of Cu2-xSe as an outstanding component in practical thermoelectric modules, but also provide guidance in searching for new classes of thermoelectric systems with high crystal symmetry or further improving the cost performance of other existing congruent-melting thermoelectric materials.

Phase Diagram Study of Succinonitrile-Vanillin Organic Alloy System

Phase diagram studies of succinonitrile-vanillin system show the formation of 2:1 congruent melting type compound. Crystallization velocities of pure components, succinonitrile-vanillin complex, and two eutectics have been determined at different undercoolings. On the basis of heat of fusion measurements, excess thermodynamic functions have been calculated. Microstructural studies revealed that impurities modify the morphology. FTIR spectral studies and computer simulation have shown the existence of hydrogen bonding in the eutectics and the congruent melting compound. On the basis of experimental results, the mechanism of formation of eutectics and its solidification behavior are discussed.

Magnetic and transport properties in the Heusler series Ni2−xMn1+xSn affected by chemical disorder

Crystal structure, magnetic and transport characteristics of Ni2−x Mn1+x Sn Heusler series have been studied with the emphasis on chemical disorder effects. It is shown that the structure and the disorder character in these series can be predicted by using simple rules. Ni2 MnSn is a ferromagnetic, congruent melting phase, which crystallizes cubic in the L21 structure type. By increasing x, Ni and Mn atoms randomly mix and occupy the heterocubic sites of the regular Heusler structure, and the magnetic structure becomes ferrimagnetic. The total magnetic moment msat decreases linearly in the range 0.2 ≤ x ≤ 1, while the Curie temperature TC increases. At low Mn content (x < 0.2), the unit cell volume shows anomalous behavior, characterized by constant msat and TC. Electrical resistivity, Seebeck coefficient, and thermal conductivity strongly depend on the amount of disorder, which increases with the Mn content. Results of first-principle calculations based on the coherent potential approximation (CPA) alloy theory for the magnetic and electrical properties are in reasonable agreement with the simple rules and all experimental data.

Gold-copper nano-alloy, "Tumbaga", in the era of nano: phase diagram and segregation.

Gold–copper (Au–Cu) phases were employed already by pre-Columbian civilizations, essentially in decorative arts, whereas nowadays, they emerge in nanotechnology as an important catalyst. The knowledge of the phase diagram is critical to understanding the performance of a material. However, experimental determination of nanophase diagrams is rare because calorimetry remains quite challenging at the nanoscale; theoretical investigations, therefore, are welcomed. Using nanothermodynamics, this paper presents the phase diagrams of various polyhedral nanoparticles (tetrahedron, cube, octahedron, decahedron, dodecahedron, rhombic dodecahedron, truncated octahedron, cuboctahedron, and icosahedron) at sizes 4 and 10 nm. One finds, for all the shapes investigated, that the congruent melting point of these nanoparticles is shifted with respect to both size and composition (copper enrichment). Segregation reveals a gold enrichment at the surface, leading to a kind of core–shell structure, reminiscent of the historical artifacts. Finally, the most stable structures were determined to be the dodecahedron, truncated octahedron, and icosahedron with a Cu-rich core/Au-rich surface. The results of the thermodynamic approach are compared and supported by molecular-dynamics simulations and by electron-microscopy (EDX) observations.