Early Stages Of Crystallization Research Articles

Djerfisherite in monticellite rocks of the Krestovskaya Intrusion (Polar Siberia)

Djerfisherite in the monticellite rocks of the Krestovskaya Intrusion is found in primary melt inclusions, mono- and polysulfide globules, and in the djerfisherite–hydrogarnet segregations. Melt inclusions are represented by three types. Type I is observed in the cores of perovskite phenocrysts and monticellite grains and corresponds to one of the early crystallization stages of the parental larnite-normative alkali ultrabasic magma enriched in water and other volatiles. Daughter phases of the inclusions are clinopyroxene, serpentine, phlogopite, apatite, nepheline, hydrogarnet, magnetite, djerfisherite, pectolite, and calcite. In some type I inclusions, melt at 1230–1250°C was immiscibly split into two fractions: alkali silicate fraction and highly fluidized water-bearing low-silica fraction enriched in alkali, sulfur, and CO2. The types II and III inclusions in perovskite, monticellite, Ti-garnet, and melilite were formed through the spatial separation of immiscible phases. This follows from the similarity of the modal composition of types II and III melt inclusions to the normative composition of immiscible fractions of type I inclusions. Type II inclusions contain mainly water-bearing silicate daughter phases (hydrogarnet, serpentine, phlogopite, and pectolite), as well as djerfisherite, calcite, and magnetite, Type III inclusions contain clinopyroxene, nepheline, apatite, magnetite, djerfisherite, calcite, and pectolite. The djerfisherite–hydrogarnet segregations are confined to the Ti-magnetite and perovskite phenocrysts and fractures radiating from them in monticellite. The mineral composition of the djerfisherite–hydrogarnet segregations together with their surrounding is similar to the composition of type II inclusions containing similar water-bearing silicates, djerfisherite, calcite, and magnetite.
 Such similarity gives grounds to relate the formation of the djerfisherite–hydrogarnet segregations, as type II inclusions, with the spatial separation and crystallization of highly fluidized low-silica melt enriched in water, alkalis, sulfur, and CO2. According to the homogenization experiment, the crystallization of highly fluidized melt at 990–1090°C was accompanied by silicate–sulfide immiscibility and the formation of globular, emulsion-like, and myrmekite structures in the djerfisherite–hydrogarnet segregations, as well as mono- and polysulfide globules with djerfisherite in the hydrogarnet–calcite–serpentine substrate. The formation of ferrobrucite–carbonate–hydrogarnet globules in the djerfisherite–hydrogarnet segregations was also related to melt liquation, which again confirms the magmatic origin of the latter. Sometimes, djerfisherite in the djerfisherite–hydrogarnet segregations becomes coarser and forms rims, bands, and veinlets, which is likely explained by the high mobility and low viscosity of sulfide melt. Scarce grains of heazlewoodite, godlevskite, and pentlandite hosted in the djerfisherite–hydrogarnet segregations frequently have the same shape as djerfisherite, which indirectly suggests their simultaneous crystallization from the same melt. The chemical composition of the djerfisherite from mono- and polysulfide globules, djerfisherite–hydrogarnet segregations, and type I inclusions, as most Yakutian kimberlites, is characterized by the high (12.1–16.7 wt %) Ni and low (0.1–0.9 wt %) Cu contents. The composition of the djerfisherite from types II and III inclusions differs in the lowered (3.3–1.6 wt %) Ni and elevated (40.9–53.2 wt %) Fe contents; type III inclusions have high Cu content: from 7.6 to 10.6 wt %.

A Strategy for Probing the Evolution of Crystallization Processes by Low-Temperature Solid-State NMR and Dynamic Nuclear Polarization.

Crystallization plays an important role in many areas, and to derive a fundamental understanding of crystallization processes, it is essential to understand the sequence of solid phases produced as a function of time. Here, we introduce a new NMR strategy for studying the time evolution of crystallization processes, in which the crystallizing system is quenched rapidly to low temperature at specific time points during crystallization. The crystallized phase present within the resultant "frozen solution" may be investigated in detail using a range of sophisticated NMR techniques. The low temperatures involved allow dynamic nuclear polarization (DNP) to be exploited to enhance the signal intensity in the solid-state NMR measurements, which is advantageous for detection and structural characterization of transient forms that are present only in small quantities. This work opens up the prospect of studying the very early stages of crystallization, at which the amount of solid phase present is intrinsically low.

Structural characteristics of lysozyme Langmuir layers grown on a liquid surface from an oligomeric mixture formed during the early stages of lysozyme crystallization

An approach for forming Langmuir monolayers of proteins is described, with lysozyme serving as an example. The essence of this approach is the deposition of a lysozyme solution containing a precipitant, KCl, onto the water surface in a Langmuir trough. The results of small-angle X-ray scattering indicate that the precipitant in the protein solution causes a significant fraction (>10%) of the protein molecules to assemble into dimers and octamers. Studying the formation of these monolayers by grazing-incidence X-ray standing waves (or X-ray standing waves under total external reflection conditions) showed that the thickness of the resulting protein layer was twice the diameter of an individual lysozyme molecule and matched the diameter of the octamer. Thin layers of precipitant ions (K and Cl) formed directly under the protein monolayer. Our results indicate that adding precipitant to the solution caused the formation of octamers with a retained structure that participated in Langmuir monolayer formation when the solution was applied to the water-subphase surface. Thus, the precipitant ions interacted with the protein monolayer. The proposed approach could facilitate the formation of ordered protein films in hybrid system design and in developing transition methods for nature-like technologies.

Revealing the Cluster-Cloud and Its Role in Nanocrystallization.

Elucidating the early stages of crystallization from supersaturated solutions is of critical importance, but remains a great challenge. An in situ liquid cell transmission electron microscopy study reveals an intermediate state of condensed atomic clusters during Pd and Au crystallizations, which is named a "cluster-cloud." It is found that nucleation is initiated by the collapse of a cluster-cloud, first forming a nanoparticle. The subsequent particle maturation proceeds via multiple out-and-in relaxations of the cluster-cloud to improve crystallinity: from a poorly crystallized phase, the particle evolves into a well-defined single-crystal phase. Both experimental investigations and atomistic simulations suggest that the cluster-cloud-mediated nanocrystallization involves an order-disorder phase separation and reconstruction, which is energetically favored compared to local rearrangements within the particle. This finding grants new insights into nanocrystallization mechanisms, and provides useful information for the improvement of synthesis pathways of nanocrystals.

Crystallization Mechanisms Applied to Understand the Crystal Formation of Rotaxanes

The present study discusses the crystalline packing formation of several [2]rotaxanes with Leigh‐type tetralactam macrocycle bearing different threads. The presence of solvent molecules in some structures are also addressed to shed some light on this matter. Additionally, the degree of similarity between supramolecular structures of rotaxanes was discussed using similarity indices. For this, new descriptors and crystallization mechanisms, which were proposed in terms of contact area and stabilization energy, were carried out to evaluate the rotaxane molecules. It was possible to observe similar general stages of crystallization dominated by the formation of 1D‐blocks and, in fewer cases, by dimers in the first stage of nucleation. The preference for the formation of 1D nuclei resides in the large contact area and complementarity involved in the large set of interactions between the rotaxanes at the earliest stages of crystallization. In this context, it was possible to propose when solvent molecules are trapped between the rotaxanes during crystal formation. Therefore, a unique example of a rotaxane whose topology favored the entrapment of water molecules between rotaxanes during the first stage of the crystallization process is presented. Crystallization mechanisms showed to be a valuable asset in the supramolecular investigation of rotaxanes in the crystalline state.

Magma chambers versus mush zones: constraining the architecture of sub-volcanic plumbing systems from microstructural analysis of crystalline enclaves.

There are clear microstructural differences between mafic plutonic rocks that formed in a dynamic liquid-rich environment, in which crystals can be moved and re-arranged by magmatic currents, and those in which crystal nucleation and growth are essentially in situ and static. Crystalline enclaves, derived from deep crustal mushy zones and erupted in many volcanic settings, afford a unique opportunity to use the understanding of microstructural development, established from the study of intrusive plutons, to place constraints on the architecture of sub-volcanic systems. Here, we review the relevant microstructural literature, before applying these techniques to interrogate the crystallization environments of enclaves from the Kameni Islands of Santorini and Rábida Volcano in the Galápagos. Crystals in samples of deep-sourced material from both case studies preserve evidence of at least some time spent in a liquid-rich environment. The Kameni enclaves appear to record an early stage of crystallization during which crystals were free to move, with the bulk of crystallization occurring in a static, mushy environment. By contrast, the Rábida enclaves were sourced from an environment in which hydrodynamic sorting and re-arrangement by magmatic currents were common, consistent with a liquid-rich magma chamber. While presently active volcanoes are thought to be underlain by extensive regions rich in crystal mush, these examples preserve robust evidence for the presence of liquid-rich magma chambers in the geological record. This article is part of the Theo Murphy meeting issue 'Magma reservoir architecture and dynamics'.

Identification and tracking of different types of crystalline nucleiduring isothermal crystallization of amorphous Ag

The isothermal crystallization of amorphous Ag is investigated by a molecular dynamics (MD) simulation, and the heredity and evolution of different types of crystalline clusters aretracked and analyzed by a reverse tracking method of atom trajectories with the help of cluster-type index method (CTIM) based on Honeycutt-Anderson (H-A) bond-type index. According to the difference in the type of crystalline cluster and the linkage mode, i.e., vertex-sharing (VS), edge-sharing (ES), face-sharing (FS) and intercross-sharing (IS), a cluster analysis method which can efficiently characterize fcc single-crystal, fcc poly-crystal and fcc hydrid-crystal, is proposed. That is, the IS-linkage of fcc basic clusters, i.e., a fcc medium range order, is defined as a fcc single-crystal cluster. The extended cluster of fccbasic clusterslinked by ISand FS modes is named fcc poly-crystal clusters. In the case of IS-linkages, if the majority of core atoms arefcc atoms, the extended cluster composed of fcc, hcp and bcc basic clusters will be regarded as a fcc hydrid-crystal cluster. Moreover, a structural analysis method of critical nuclei distinguishing embryosis also developed in terms of the hereditary characteristics of various crystalline clusters. In this scheme, the extended cluster which has only transient heredity and no continuous heredity is defined as an embryo, while it will be named nuclei if part of core atoms in extended clusters can keep cluster type of atoms unchanged and be continuously passed down in the early stage of crystallization. Thus, corresponding to the onset time/temperature of continuous heredity, the critical nuclei of fcc singe-crystals, fcc poly-crystals and fcc hybrid-crystals can be identified and characterized. It is found that the nuclei of fcc crystalsemerge after the steep drop of total energy of system and before the abrupt increase of sizesof tracked clusters. And regardless of critical sizes or geometric configurations, an evident difference exists among fcc singe-crystal, hybrid-crystal clusters and fcc poly-crystal clusters, of which the fcc single-crystal nucleus is the smallest (~1.6 nm ×1.0 nm × 1.1 nm), followed by poly-crystal nucleus (~1.7 nm × 1.0 nm × 1.6 nm) and hydrid-crystal nucleus (~2.3 nm × 2.0 nm × 2.4 nm) in sequence. There are a few hcp and bcc atoms at surfaces, i.e. shells, of single-crystal and poly-crystal nucleus, but neither hcp nor bcc atom can be detected at the shell of fcc hydrid-crystal nucleus. And theconfiguration of fcc single-crystal, poly-crystal and hydrid-crystal critical nuclei are all non-spherical.

Pseudo-equilibrium equation of calcium phosphate precipitation from aqueous solution.

An X-ray amorphous phase is frequently present at the early stage of calcium phosphate crystallization, and the relevant solution chemistry is essential for understanding the mechanism of reaction. Here, we report a quantitative study of a series of reaction systems at pseudo-equilibrium states. We determined the composition of solutions and the quantities of the precipitate samples, and characterized the long- and short-range order of the precipitate using X-ray diffraction and synchrotron X-ray absorption near-edge structure spectroscopy, respectively. We found that, in a particle with multiple structural units, only a fraction of the units was able to reach pseudo-equilibrium with the solution composition, which represents the average number of surficial clusters per unit. These findings enabled us to propose a general form of the equilibrium constant equation. The equation fits the pseudo-equilibrium data well, and it converts to the "solubility product (Ksp)" and the conventional "reaction quotient" in two limit cases, respectively. Further, using a cube model, we derived a "particle equation" that reveals the connection between the particle structure and the form of equilibrium constant equation. The dependency of the form of pseudo-equilibrium equation on the structure and size of the precipitate reveals a fundamental relation in chemistry, and its applicability remains to be examined in other reaction systems, such as those involving nanocrystals and porous materials.

Crystallization of Ge2Sb2Te5 and nitrogren-doped Ge2Sb2Te5 phase-change-materials thin films studied by in situ combined X-ray scattering techniques

The phase change from the amorphous to crystalline state which occurs upon thermal annealing in prototypical Ge2Sb2Te5 and nitrogen-doped Ge2Sb2Te5 phase-change-materials (PCM) thin films is studied by concomitant, complementary and combined in situ and ex situ X-ray diffraction (XRD) and X-ray reflectivity (XRR) techniques. It is demonstrated that combined in situ X-ray scattering techniques allow accurate investigation and clarification of the structural, morphological and mechanical variations occurring in the films upon crystallization. The crystallization process is correlated with volume shrinkage (densification and thickness reduction) and with structural change with a tensile strain build-up. The comparison of Ge2Sb2Te5 and nitrogen-doped Ge2Sb2Te5 reveals a significant slowdown of the crystallization process, induced by the incorporation of nitrogen. However, the mechanisms involved in the phase change are not strongly modified by the incorporation; rather, the crystallization process is inhibited because of the presence of nitrogen. In this way, different stages of the crystallization process can be observed. The combined XRD/XRR analysis gives new insights on the stress components built up in phase-change materials. First, at the early stage of crystallization, a large hydrostatic tensile stress builds up in the PCM thin film. Afterwards, concomitant grain growth, viscous flow, densification and thickness accommodation are observed, which lead to a partial stress relaxation in the PCM films. This combined characterization technique offers a new approach that may further our understanding of the phase change involved.

The first record of ultramafic cumulates from the Mt. Kalnik ophiolite mélange in the SW part of the Zagorje-Mid-Transdanubian Zone (NW Croatia): mineralogy, petrology, geochemistry and tectono-magmatic affinity

Ultramafic cumulate rocks represent the rarest allochthonous fragments of the Mesozoic oceanic lithosphere observed today in the Upper Jurassic to Lower Cretaceous melange of Mt. Kalnik, located in the SW part of the Zagorje‒Mid-Transdanubian Zone (ZMTDZ). Poikilitic heteroadcumulate ultramafic rocks of Mt. Kalnik are represented by amphibole lherzolites/ harzburgite sand plagioclase lherzolites. Both were formed by in-situ processes within a magma chamber following the general crystallization sequence of: Al-chromite → Mg-rich olivine → enstatite ± augite→ Ca-amphibole (pargasite ± edenite ± magnesiohornblende) → Ca-plagioclase (An82.6-87.4). Cumulate minerals are spinel and olivine as well as orthopyroxene and clinopyroxene which areusually enclosed in intercumulate phases such as amphibole and/or plagioclase that render aninterstitial mesostasis. Rocks’ textural characteristics, mineral crystallization order and their phase chemistry are all suggestive of low-pressure sub-solidus crystallization in an open system. The low Ti content in augite and scant HFSE abundances suggest the studied rocks may have formed from a depleted mantle source. In addition to the medium to high degree of partial melting of the source, the parental process that gave rise to the Mt. Kalnik ultramafic cumulates also included a low degree of fractional crystallization. The segregation of oxidized Al-chromite and oikocrysts of pargasite and edenite in an early crystallization stage illustrates the formation of a cumulate sequence from volatile-rich magmas. These magmas usually have a high oxidation potential and are exclusively found in intra-oceanic subduction zones, predominantly in island arcs. The overall whole-rock geochemistry [e.g. (Nb/La)n = 0.25-0.34; (Ti/Gd)n = 0.49-0.89;(Th/Nb)n = 5.29-8.63; (La/Lu)cn = 0.57-0.68] together with a record of Ca-rich plagioclase (up toAn87.4) and low Ti clinopyroxene (≤0.54 wt%) corroborate the supra-subduction tholeiitic nature of the magma source. Ultramafic cumulates from the ophiolitic melange of Mts. Kalnik and Medvednica show common genetic features and geotectonic provenance. Comparison with analogous ultramafic lithotypes of the north-eastern segment of the ZMTDZ (the Szarvasko Complex,Hungary), the ultramafic cumulates of Mts. Kalnik and Medvednica portray some subtle differences that may indicate their distinctive geotectonic provenance. Mts. Kalnik and Medvednica ultramafic cumulates represent the vestiges of a single Upper Jurassic intra-oceanic arc system formed in the western branch of the Meliata-Maliak segment of the Neotethyan oceanic realm.

Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the α-Phase (Part II).

The early-stage crystallization behavior in a triacylglycerol mixture has been investigated on the nanoscale with a novel global small-angle X-ray scattering analysis technique. This method has been tailored for the determination of the electron density profiles (EDPs) replicating both (i) the nanostructural texture of molten triacylglycerols (TAGs) (refer to "Global Small-Angle X-ray Scattering Data Analysis of Triacylglycerols in the Molten State (Part I)" of this publication series) and (ii) the lamellar structure of the metastable α-polymorph. In a first stage, the α-phase scattering contribution alone was examined by classical Fourier analysis as well as by globally fitting the data, leading to practically identical EDPs. On the basis of these findings, we extended our analysis to the entire X-ray scattering contribution arising from molten TAGs and the solid α-phase fraction. Remarkably, the experimental and theoretical data agree very well, providing for the first time a detailed nanostructural understanding about the coexisting molecular assemblies. This, in turn, also allowed us to quantitatively determine the solid fat content (SFC) with X-ray scattering data. Our new theoretical approach for measurement of SFC is based on the global analysis of small-angle scattering/diffraction patterns, and the SFC results are in good agreement with values obtained from other techniques such as NMR spectroscopy.

Early stages of drug crystallization from amorphous solid dispersion via fractal analysis based on chemical imaging

Early stages of crystallization from amorphous solid dispersion (ASD) are typically not detected by means of standard methods like powder X-ray diffraction (XRPD). The aim of this study is therefore to evaluate if fractal analysis based on energy dispersive X-ray imaging can provide the means to identify early signs of physical instability. ASDs of the poorly water-soluble compound, felodipine (FEL) were prepared by solvent evaporation using different grades of HPMCAS, at 50 wt% drug loading. Samples were stored at accelerated conditions of 40 °C. Scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDS) was used for elemental mapping of tablet surfaces. Comparative data were generated with a standard XRPD and with more sensitive methods for detection of early instability, i.e. laser scanning confocal microscopy (LSM) and atomic force microscopy (AFM). The SEM-EDS identified changes of drug-rich domains that were confirmed by LSM and AFM. Early changes in drug clusters were also revealed by a multifractal analysis that indicated a beginning phase separation and drug crystallization. Therefore, the presented fractal cluster analysis based on chemical imaging bears much promise as a new method to detect early signs of physical instability in ASD, which is of great relevance for pharmaceutical development.

Early Stages of Crystallization of Lanthanum-Borogermanate Glass by a Femtosecond Laser Beam

Regions in the bulk of lanthanum borogermanate glass modified by a femtosecond laser beam were studied by means of optical microscopy and confocal Raman scattering (RS) spectroscopy. The obtained data show that, at the stages preceding the formation of an LaBGeO5 microcrystal, upon irradiation by a femtosecond beam in a certain interval of laser pulse energy germanium nanocrystals precipitate in the zone of local heating. The correlation between the conditions of laser irradiation leading to the appearance of germanium nanocrystals and the conditions ensuring with high probability the crystallization of phases of the low-temperature modification of lanthanum borate and stillwellite-like lanthanum borogermanate suggest that germanium nanocrystals can serve as nuclei for heterogeneous crystallization of LaBO3 and LaBGeO3.

Nanometer scale thermal response of polymers to fast thermal perturbations.

Nanometer scale thermal response of polymers to fast thermal perturbations is described by linear integro-differential equations with dynamic heat capacity. The exact analytical solution for the non-equilibrium thermal response of polymers in plane and spherical geometry is obtained in the absence of numerical (finite element) calculations. The solution is different from the iterative method presented in a previous publication. The solution provides analytical relationships for fast thermal response of polymers even at the limit t → 0, when the application of the iterative process is very problematic. However, both methods give the same result. It was found that even fast (ca. 1 ns) components of dynamic heat capacity greatly enhance the thermal response to local thermal perturbations. Non-equilibrium and non-linear thermal response of typical polymers under pulse heating with relaxation parameters corresponding to polystyrene and poly(methyl methacrylate) is determined. The obtained results can be used to analyze the heat transfer process at the early stages of crystallization with fast formation of nanometer scale crystals.

Geochemical evidence for the fractionation of iridium group elements at the early stages of crystallization of the Dovyren magmas (northern Baikal area, Russia)

We have first generalized geochemical and mineralogical data indicating the important role of crystallization of Os-Ir-Ru phases and fractionation of refractory iridium subgroup of PGE (IPGE) at the early stages of the evolution of parental magmas and primitive cumulates from the Yoko-Dovyren layered massif (northern Baikal area, Russia). The object of study was two types of plagioclase peridotites from the lower part of the intrusion, differing in the porosity of primary olivine cumulates: less melanocratic (but more primitive) type I and more melanocratic type II. Inclusions of refractory IPGE (Os, Ir, and Ru) discovered during LA-ICP-MS studies of aluminochromite from type I rocks are the first evidence for the presence of Os-Ir-Ru phases. Subsequent electron microscopy examinations revealed more than 25 grains of laurite and Ir-containing osmium in aluminochromite from plagioperidotites of both types. Attention is focused on the importance of the Ru/Cr2O3 and Ir/Cr2O3 ratios in rocks for the separation of IPGE at early and late fractionation stages. The conclusion is drawn that the higher Ru/Cr2O3 and Ir/Cr2O3 ratios in type I plagioperidotites indicate higher enrichment of aluminochromite in inclusions of refractory IPGE minerals. This is consistent with the fact that these rocks are assigned to the most primitive high-temperature ultramafites genetically related to the parental magma, which was in equilibrium with olivine Fo88 at ~1290 °C. We have established that the parental Dovyren magma was already depleted in IPGE and rhodium before its entrance into a chamber. No signs of early sulfide-silicate immiscibility have been detected. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Computing Crystal Size Distribution by Focused‐Beam Reflectance Measurement when Aspect Ratio Varies

AbstractChord length distribution (CLD) can be determined by an in‐line measuring system with focused‐beam reflectance measurement, but it can differ from crystal size distribution (CSD). However, expected values of CLD can be calculated from CSD by statistical methods and vice versa. In this study, a correlation equation between crystal size and aspect ratio during cooling crystallization was obtained and a mapping matrix was calculated based on the correlation equation. Then, the suspension obtained in cooling crystallization was sampled and CSDs were measured by microscopy at the same time that CLDs were measured with FBRM. As a result of error evaluation, transformation of CLD into CSD reduced the errors between CLDs and CSDs except in the early stage of crystallization.

The barrier to ice nucleation in monatomic water.

Crystallization from a supercooled liquid initially proceeds via the formation of a small solid embryo (nucleus), which requires surmounting an activation barrier. This phenomenon is most easily studied by numerical simulation, using specialized biased-sampling techniques to overcome the limitations imposed by the rarity of nucleation events. Here, I focus on the barrier to homogeneous ice nucleation in supercooled water, as represented by the monatomic-water model, which in the bulk exhibits a complex interplay between different ice structures. I consider various protocols to identify solidlike particles on a computer, which perform well enough for the Lennard-Jones model, and compare their respective impact on the shape and height of the nucleation barrier. It turns out that the effect is stronger on the nucleus size than on the barrier height. As a by-product of the analysis, I determine the structure of the nucleation cluster, finding that the relative amount of ice phases in the cluster heavily depends on the method used for classifying solidlike particles. Moreover, the phase which is most favored during the earlier stages of crystallization may happen, depending on the nucleation coordinate adopted, to be different from the stable polymorph. Therefore, the quality of a reaction coordinate cannot be assessed simply on the basis of the barrier height obtained. I explain how this outcome is possible and why it just points out the shortcoming of collective variables appropriate to simple fluids in providing a robust method of particle classification for monatomic water.

The Sierra de Cacheuta Vein-Type Se Mineralization, Mendoza Province, Argentina

The Sierra de Cacheuta vein-type Se mineralization in the Mendoza Province predominantly consists of clausthalite, klockmannite, eskebornite, eucairite, and naumannite. These primary selenides formed in a fault zone, cutting through fine-grained trachytic host rock. Cross-sections perpendicular to the veinlets, polarized light microscopy, and scanning-electron microscopy, combined with electron-microprobe analysis, provide a record of the relationship between different crystallization and deformation events. Mineralization encompasses four episodes of fault formation (d1–d4): early zonal selenide crystallization (stage (I)); ductile deformation of the selenides (stage (II)); fault re-opening, fluid-mediated metal mobilization, metalliferous-fluid infiltration, and mineral precipitation (stage (III)); and subsequent alteration (stage (IV)). The Se vein originated from multiple injections of highly oxidized, metal-rich fluids. These low-T solutions (estimated max. temperature 100 °C, max. pressure 1 bar) possessed high to exceptionally high Se fugacities (log fSe2 between −14.5 and −11.2) that prevailed for most of the evolution of the deposit. The source of the Se and the accompanying metals (Cu, Ag, Pb, and Fe) is probably the neighboring bituminous shale. The deposition of Se minerals occurred when the oxidized metal-bearing solutions came in contact with a reductant, which caused the reduction of mobile selenate to immobile selenide or elemental Se. We identified several features that permit us to safely distinguish samples from Cacheuta from Argentinian Se deposits in the Province of La Rioja: (I) trachytic host rock fragments containing bitumen and TiO2 pseudomorphs after titanomagnetite; (II) early Co-rich and Ni-poor krut’aite (Co < 6.7 wt %, Ni < 1.2 wt %) partly replaced by clausthalite, umangite, klockmannite, eskebornite, Ni-poor tyrrellite (Ni < 2.7 wt %), Ni-poor trogtalite (Ni < 1.2 wt %), and end-member krut’aite and petříčekite; (III) lack of calcite gangue; and (VI) Se-bearing alteration minerals comprising chalcomenite, molybdomenite, cobaltomenite, an unnamed Cu selenide (for which the ideal formula may be either Cu2Se3 or Cu5Se8), and possibly mandarinoite, mereheadite, orlandiite, and scotlandite as new species for this occurrence.

Evidence of epitaxial growth of high-quartz solid solution on ZrTiO4 nuclei in a Li2O-Al2O3-SiO2 glass

The early stage of crystallization of a glass with the composition 7.6 Li2O – 0.2 Na2O – 0.1 K2O – 1.9 MgO – 0.3 BaO – 1.2 ZnO – 12.7 Al2O3 – 69.6 SiO2 – 4.2 TiO2 – 1.8 ZrO2 – 0.4 Sb2O3 (mol %), suitable for the production of zero thermal expansion glass-ceramics is reported. Thermal treatment at 740 °C for 24 h resulted in the formation of Zr1-xTi1+xO4 crystals and close to them, high-quartz solid solution crystals (lithium aluminosilicate solid solution of high-quartz structure) were formed. TEM studies showed tetragonal Zr1-xTi1+xO4 crystals with a puck-like shape, and on their flat sides, high-quartz solid solution crystals were precipitated, squeezing the “Zr1-xTi1+xO4 patty” in-between two halves of the “lithium-alumosilicate bun”. Selected area electron diffraction showed a distinct crystallographic relationship between these two crystal lattices. High resolution TEM micrographs indicate that the lattice planes observed in the Zr1-xTi1+xO4 crystal continue into the high-quartz solid solution crystal. This is evidence for epitaxial growth of the lithium-alumosilicate with high-quartz structure on the Zr1-xTi1+xO4 crystal. Epitaxial growth within glass-ceramics has hardly been shown up to now.

Rapid and partial crystallization to design ductile CuZr-based bulk metallic glass composites

Transformation-induced plasticity in CuZr-based bulk metallic glass (BMG) composites opens up a new perspective for the design of ductile BMG composites. In this work, rapid and partial crystallization of BMGs is proposed to tailor microstructures of ductile BMG composites. During the early crystallization stage, the precipitation of B2 CuZr crystals in the Cu42Zr42Al10Co6 BMGs is growth-controlled at low or high heating rates after having passed through a nucleation-dominated temperature region. Abundant nucleation is beneficial for the uniform precipitation of B2 crystals in the glassy matrix. Compared with annealing processes at slow heating, the degree of the free volume annihilation could be reduced to some content by employing a high heating rate. The microstructures of CuZr-based BMG composites can be effectively tuned by changing rapid annealing parameters, which enhances the ductility of the resulting BMG composites. This approach proves to be efficient for the development of ductile metastable alloys and composites.