Precursor Phase Research Articles

Técnicas para desarrollar aplicaciones web a través de Blockchain

This research proposes to identify techniques, tools, models and programming languages appropriate for the design and development of a secure application using Blockchain, since this technology is not only for cryptocurrencies, it can also develop applications for different sectors such as: health, insurance, stock exchange, real estate, value chains, financial, among others. Within its applicability are smart contracts, which became a very relevant topic when implementing disruptive technologies, however, currently it is still in a precursor phase that starts with some ideas, which foresees many challenges for researchers, engineers, technical and administrative staff of organizations. The development methodology takes as a reference UWE, web-oriented engineering, platforms for Blockchain environments, programming languages, tools for the development of smart contracts, the results obtained determine the existence of several platforms, programming languages and other tools that allow establishing the architecture of information systems that adapt this disruptive technology that provides many advantages to the user as long as the proper use is given, since it allows its applicability to different areas for the benefit of society in general.

GaAs to Si Direct Wafer Bonding at T ≤ 220 °C in Ambient Air Via Nano-Bonding™ and Surface Energy Engineering (SEE)

When different semiconductors are integrated into hetero-junctions, native oxides generate interfacial defects and cause electronic recombination. Two state-of-the-art integration methods, hetero-epitaxy and Direct Wafer Bonding (DWB), require temperatures, T > 400 °C to reduce native oxides. However, T > 400 °C leads to defects due to lattice and thermal expansion mismatches. In this work, DWB temperatures are lowered via Nano-Bonding™ (NB) at T ≤ 220 °C and P ≤ 60 kPa (9 psi). NB uses Surface Energy Engineering (SEE) at 300 K to modify surface energies (γT) to far-from-equilibrium states, so cross-bonding occurs with little thermal activation and compression. SEE modifies γT and hydro-affinity (HA) via chemical etching, planarization, and termination that are optimized to yield 2-D Precursor Phases (2D-PP) metastable in ambient air and highly planar at the nano- and micro- scales. Complementary 2D-PPs nano-contact via carrier exchange from donor 2D-PP surfaces to acceptor ones. Here, NB models and SEE are applied to the DWB of GaAs to Si for photovoltaics. SEE modifies (1) the initial γT0 and HA0 measured via Three Liquid Contact Angle Analysis, (2) the oxygen coverage measured via High Resolution Ion Beam Analysis, and (3) the oxidation states measured via X-Ray Photoelectron Spectroscopy. SEE etches hydrophobic GaAs oxides with γT = 33.4 ± 1 mJ/m2, and terminates GaAs (100) with H+, rendering GaAs hydrophilic with γT = 60 ± 2 mJ/m2. Similarly, hydrophilic Si native oxides are etched into hydrophobic SiO4H2. H+- GaAs nano-bonds reproducibly to Si, as measured via Surface Acoustic Wave Microscopy, validating the NB model and SEE design.

Multi-instrument Comparative Study of Temperature, Number Density, and Emission Measure during the Precursor Phase of a Solar Flare

We present a multi-instrument study of the two precursor brightenings prior to the M6.5 flare (SOL2015-06-22T18:23) in the NOAA Active Region 12371, with a focus on the temperature (T), electron number density (n), and emission measure (EM). The data used in this study were obtained from four instruments with a variety of wavelengths, i.e., the Solar Dynamics Observatory’s Atmospheric Imaging Assembly (AIA), in six extreme ultraviolet (EUV) passbands; the Expanded Owens Valley Solar Array (EOVSA) in microwave (MW); the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) in hard X-rays (HXR); and the Geostationary Operational Environmental Satellite (GOES) in soft X-rays (SXR). We compare the temporal variations of T, n, and EM derived from the different data sets. Here are the key results. (1) GOES SXR and AIA EUV have almost identical EM variations (1.5–3 × 1048 cm−3) and very similar T variations, from 8 to 15 million Kelvin (MK). (2) Listed from highest to lowest, EOVSA MW provides the highest temperature variations (15–60 MK), followed by RHESSI HXR (10–24 MK), then GOES SXR and AIA EUV (8–15 MK). (3) The EM variation from the RHESSI HXR measurements is always less than the values from AIA EUV and GOES SXR by at most 20 times. The number density variation from EOVSA MW is greater than the value from AIA EUV by at most 100 times. The results quantitatively describe the differences in the thermal parameters at the precursor phase, as measured by different instruments operating at different wavelength regimes and for different emission mechanisms.

Kinetics and energetics\xa0of metal halide perovskite conversion reactions at the nanoscale

Understanding the kinetics and energetics of metal halide perovskite formation, particularly from the structural point of view at the nanoscale, is important for the advancement of perovskite devices. In particular, insight is needed regarding the mechanisms by which perovskite conversion reactions occur, and their kinetics. Here, we examine the structural evolution of precursor and perovskite phases using in situ synchrotron x-ray scattering. This approach mitigates issues associated with illumination and electron beam-based techniques and allows conclusions to be drawn regarding the kinetics of these reactions. We find that kinetics and grain orientation strongly depend on both the lead halide framework and the nature of the A-cation, with fastest kinetics for MAPbI3, followed by FAPbI3, and slowest for MAPbBr3. Molecular dynamics simulations and density functional theory calculations further reveal that these reactions are diffusion-controlled with a hopping time of 5-400 s, corroborating experimental findings.

Mineral paragenesis in Paleozoic manganese ore deposits: Depositional versus post-depositional formation processes

Unlike modern Mn(IV)-dominated manganese nodules, ancient manganese deposits primarily contain Mn(II) (manganous) mineral phases. The general assumption is that these manganous minerals formed post-depositionally from a Mn(IV) precursor phase during diagenesis and metamorphism. However, recent studies have shown that aqueous Mn(II) may combine with either CO32–(aq) or H4SiO4(aq) to nucleate and precipitate as primary manganous phases within anoxic waters. These findings thus make it difficult to assess what comprised the primary mineral assemblage of ancient Mn deposits, which in turn, has implications for understanding the redox fabric of the past marine water column. Here, we investigate the paragenesis and oxidation state of various Mn minerals (oxides, carbonates, and silicates) from the late Devonian Xialei and middle to late Permian Zunyi manganese deposits in South China. Through characterization of the micro-scale distribution, composition, and speciation of different Mn-bearing mineral phases, we provide evidence to support an oxidative mechanism during Mn cycling at the time of deposition. We document the presence of a residual oxide phase (hausmannite; Mn3O4) that represents a primary to early formed Mn(III)-bearing oxide preserved in Mn(II)-carbonate nodules. Additionally, we observe spherulitic textures comprised of mixed-valence Mn(II,III,IV)-silicates enclosed in diagenetic Mn(II)-carbonate laminations. Our results allow for the construction of a paragenetic model for these deposits beginning with the reduction of a primary Mn(IV) phase and the subsequent precipitation of intermediate Mn(III)-oxide or -silicate mineral phases. Following continued exposure to reducing conditions during early diagenesis, Mn(III)-oxides were then replaced by Mn(II)-carbonates. Similarly, Mn(III)-silicates were transformed into various Mn(II)-silicates during late-stage diagenesis and metamorphism. This model suggests that the accumulation of various divalent Mn mineral phases in ancient sediments may, therefore, be indicative of deposition under a water column with a sufficient oxidizing potential to induce Mn(II) oxidation.

Insights of precursor phase transition of (Cu-Zn-Al)/γ-Al2O3 hybrid catalyst for one step dimethyl ether synthesis from syngas

The concerns on environmental pollution and climate change, along with ever-growing energy demands, have driven interest in dimethyl ether (DME) as a clean fuel alternative and a versatile chemical intermediate. Due to the advantages of single-step synthesis of DME, we investigated the influence of precursor phase transition of methanol synthesis catalyst from hydrotalcite to zincian malachite on the hybrid catalyst’s activity for direct syngas to DME process by varying its Cu/Al content. A series of Cu-Zn hybrid catalysts were prepared via a kneading extrusion process by physical mixing of methanol synthesis catalyst (CuO:ZnO:Al2O3) prepared via facile forward precipitation route with CuO/Al2O3 ratios 1.5–6 and the dehydration component boehmite (γ-AlO(OH)). The physicochemical aspects of prepared hybrid catalysts were studied in detail by BET, XRD, N2O chemisorption, H2-TPR, NH3-TPD, SEM, and TEM. The activity studies revealed that the catalyst with a lower CuO/Al2O3 (1.5) ratio derived from the phase pure hydrotalcite precursor showed enhanced catalytic activity with a high CO conversion 60.5% and DME selectivity 71.5%. Whereas the catalyst with a high CuO/Al2O3 (6) ratio showed relatively lower DME selectivity, although it was derived from the phase-rich zincian malachite, which is a preferred active phase for methanol synthesis. The higher yield of DME with hydrotalcite-derived hybrid catalyst was most likely attributed to the well dispersed nanostructured active Cu sites and the higher number of weak and medium strength acidic sites. Moreover, the phase transition of dehydration component boehmite to γ-Al2O3 helps in methanol dehydration with its characteristic Lewis acidity.

Capture Phosphates via Peptide Self‐assembly to Construct Templates Assisting Mineralization

AbstractThe development of synthetic scaffolds for template‐guided mineralization of calcium phosphates (CaP) is an ongoing challenge in biomimetic material design for bone graft substitute. To mimic the extracellular matrix (ECM)‐organized biomineralization, polymer‐induced liquid precursor (PILP) phase has been widely applied in the construction of biomineralized tissues. We proposed here a peptide self‐assembled scaffold as an easier fabricated alternative of charged polymers for PILP template. An arginine enriched pentapeptide was synthesized to serve as the basic building block for the construction of positively charged nanofibrils at physiological condition. By binding with multiple arginine residues via electrostatic interactions, phosphates cross‐link nanofibrils forming phosphate enriched scaffold to assist the mineralization of CaP during the calcium ion infiltration. The obtained CaP mineralized scaffold exhibited competent properties to polymer‐based biominerals with enhanced mechanical properties and reversible deformations, as well as good biocompatibility, promising great potentials as mimetic bone matrix.

Mass transport in binary TiO2:SiO2 and GeO2:SiO2 direct ink write glasses

AbstractThe mass transport mechanisms of Ti in TiO2:SiO2 and Ge in GeO2:SiO2 direct ink write, additively manufactured glasses were studied. Due to the low solubility of Ti in SiO2 and high melting point of TiO2 relative to SiO2, Ti transport was found to occur via solid state interdiffusion between adjoining SiO2 and TiO2 precursor particles. The diffusivity of titanium in SiO2 measured over typical sintering temperatures (1000–1300°C) using Rutherford backscattering spectrometry was . This provides an estimate of ∼30 nm for the diffusion length under typical sintering conditions (2 h at 1200°C). Although Ti and Ge have similar diffusivities in SiO2 glass at low concentrations, GeO2 was found to be much more mobile during the sintering of printed GeO2:SiO2 green bodies. This was evident in glasses with phase separated GeO2 regions over length scales of ∼10 µm and in experiments involving binary xerogel films in which GeO2 migrated over ∼10 µm through cracked, porous SiO2 layers. Large phase separated regions and long transport lengths in GeO2:SiO2 suggest that the transport of GeO2 occurs prior to the densification of the SiO2 matrix via an alternative mechanism such as capillary flow. These results inform important considerations in the design of index modifying inks for the direct ink write process, namely initial precursor phase, mutual solubility with the base SiO2 glass, and mass transport throughout the sintering process.

Massive transformation in FeNi nanopowders with nanotwin-assisted nitridation

L10-ordered FeNi alloy (tetrataenite), a promising candidate for rare-earth-free and low-cost permanent magnet applications, is attracting increasing attention from academic and industrial communities. Highly ordered single-phase L10-FeNi is difficult to synthesis efficiently because of its low chemical order–disorder transition temperature (200–320 °C). A non-equilibrium synthetic route utilizing a nitrogen topotactic reaction has been considered a valid approach, although the phase transformation mechanism is currently unknown. Herein, we investigated the basis of this reaction, namely the formation mechanism of the tetragonal FeNiN precursor phase during the nitridation of FeNi nanopowders. Detailed microstructure analysis revealed that the FeNiN precursor phase could preferentially nucleate at the nanotwinned region during nitridation and subsequently grow following a massive transformation, with high-index irrational orientation relationships and ledgewise growth motion detected at the migrating phase interface. This is the first report of a massive phase transformation detected in an Fe–Ni–N system and provides new insights into the phase transformation during the nitriding process. This work is expected to promote the synthetic optimization of fully ordered FeNi alloys for various magnetic applications.

Nucleation of glucose isomerase protein crystals in a nonclassical disguise: The role of crystalline precursors

Protein crystallization is an astounding feat of nature. Even though proteins are large, anisotropic molecules with complex, heterogeneous surfaces, they can spontaneously group into two- and three-dimensional arrays with high precision. And yet, the biggest hurdle in this assembly process, the formation of a nucleus, is still poorly understood. In recent years, the two-step nucleation model has emerged as the consensus on the subject, but it still awaits extensive experimental verification. Here, we set out to reconstruct the nucleation pathway of the candidate protein glucose isomerase (GI), for which there have been indications that it may follow a two-step nucleation pathway under certain conditions. We find that the precursor phase present during the early stages of the reaction process is nanoscopic crystallites that have lattice symmetry equivalent to the mature crystals found at the end of a crystallization experiment. Our observations underscore the need for experimental data at a lattice-resolving resolution on other proteins so that a general picture of protein crystal nucleation can be formed.

Faster Crystallization during Coral Skeleton Formation Correlates with Resilience to Ocean Acidification.

The mature skeletons of hard corals, termed stony or scleractinian corals, are made of aragonite (CaCO3). During their formation, particles attaching to the skeleton’s growing surface are calcium carbonate, transiently amorphous. Here we show that amorphous particles are observed frequently and reproducibly just outside the skeleton, where a calicoblastic cell layer envelops and deposits the forming skeleton. The observation of particles in these locations, therefore, is consistent with nucleation and growth of particles in intracellular vesicles. The observed extraskeletal particles range in size between 0.2 and 1.0 μm and contain more of the amorphous precursor phases than the skeleton surface or bulk, where they gradually crystallize to aragonite. This observation was repeated in three diverse genera of corals, Acropora sp., Stylophora pistillata—differently sensitive to ocean acidification (OA)—and Turbinaria peltata, demonstrating that intracellular particles are a major source of material during the additive manufacturing of coral skeletons. Thus, particles are formed away from seawater, in a presumed intracellular calcifying fluid (ICF) in closed vesicles and not, as previously assumed, in the extracellular calcifying fluid (ECF), which, unlike ICF, is partly open to seawater. After particle attachment, the growing skeleton surface remains exposed to ECF, and, remarkably, its crystallization rate varies significantly across genera. The skeleton surface layers containing amorphous pixels vary in thickness across genera: ∼2.1 μm in Acropora, 1.1 μm in Stylophora, and 0.9 μm in Turbinaria. Thus, the slow-crystallizing Acropora skeleton surface remains amorphous and soluble longer, including overnight, when the pH in the ECF drops. Increased skeleton surface solubility is consistent with Acropora’s vulnerability to OA, whereas the Stylophora skeleton surface layer crystallizes faster, consistent with Stylophora’s resilience to OA. Turbinaria, whose response to OA has not yet been tested, is expected to be even more resilient than Stylophora, based on the present data.

The Precursor Phase of an X-class Flare: Magnetic Reconnection, Powering and Non-thermal Electrons

In this paper, we report three interesting phenomena that occurred during the precursor phase of the X1.6 class flare on 2014 September 10. (1) The magnetic reconnection initiating the flare occurs between one of the two J-shaped magnetic flux ropes that constitute a sigmoidal structure and the overlying sheared magnetic arcade that runs across the sigmoid over its middle part. The reconnection formed an erupting structure that ultimately leads to flare onset. Another J-shaped magnetic flux rope remains unaffected during the whole eruption. The phenomenon is revealed by the observation made by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory (SDO) at 94 and 131 Å. (2) Being simultaneously with starting time of the precursor, photospheric vertical electric current (VEC) around the footpoint region of the overlying magnetic arcade underwent an obvious increase, as observed by the Helioseismic and Magnetic Imager (HMI) on board SDO. By only taking into account the VEC with current density over 3σ value (1σ: 10 mA m−2), we are able to pick out precursor-associated VEC increase starting from nearly the level of zero. We regard it as a kind of powering process for the magnetic reconnection between the two magnetic loops. (3) With high-resolution narrow-band Helium 10830 Å images taken by Goode Solar Telescope at Big Bear Solar Observatory (BBSO), we observe a narrow absorption (dark) front that runs along the erupting magnetic structure (or the erupting hot channel) and moves in the direction of the eruption during the precursor phase. Assuming the excitation mechanism of Helium atoms along the absorption front by non-thermal electrons, the phenomenon shows that the interaction between the erupted hot channel and the overlying (or surrounding) magnetic field has yielded electron acceleration.

From Subduction to LLSVP: The Core‐Mantle Boundary Heterogeneities Across North Atlantic

AbstractThe distribution of Ultra‐low Velocity Zones (ULVZs) is generally associated with the Large Low Shear Velocity Zones (LLSVPs). However, subducted slabs may be important for the characteristics of the ULVZs as well. Here we use ScS precursor (SdS) and postcursor (ScscS) phases, as well as Scd phases recorded by USArray to investigate the lowermost mantle structure across the north Atlantic, which spans the African LLSVP and the subducted Farallon slab. Our results show a ULVZ located near the edge of the African LLSVP, with thicknesses ranging from 11–16 km and S wave velocity reductions of 12%–24%. At the same time, a thin high‐velocity layer (HVL) with thicknesses of 20–30 km, Vs increases of 3%–4%, is also detected outside the LLSVP in the northwest region. Further west there is a clear D" layer at 250 km above the core mantle boundary (CMB), overlaid by a low velocity layer with Vs reduction of 3%. This transition profile from D" to HVL to ULVZ provides an excellent opportunity for us to understand the heterogeneities near the CMB region. We propose that interactions between the subducted Farallon slab with ambient mantle and LLSVP material, together with thermal effects, may result in this transition between different seismic structures along the CMB.

Effect of zirconium on precursor chemistry, phase stability, and oxidation of polyvinylsilazane-derived SiCN ceramics

Effect of zirconium on precursor chemistry, phase stability, and oxidation of polyvinylsilazane-derived SiCN ceramics

Multistage nanostructures induced by precursor phase spontaneous partitioning lead to an excellent thermoelectric performance in Cu1.8S0.8Se0.2

Multiscale nanostructures and nano-defects significantly increase the ZT of Cu1.8S0.8Se0.2 thermoelectric material.

Atomic structure and evolution of a precursor phase of Ω precipitate in an Al-Cu-Mg-Ag alloy

Precipitates in an aged Al-Cu-Mg-Ag alloy have been characterised using atomic-resolution energy-dispersive X-ray spectroscopy (EDXS) scanning transmission electron microscopy (STEM) and high-angle annular dark-field (HAADF) STEM. A metastable precursor phase, designated Ω′, which forms as thin plates on {111}α planes of the α-Al matrix phase, is found for Ω precipitate which is the key strengthening constituent in the Al-Cu-Mg-Ag alloy. The Ω′ phase has a hexagonal structure that is distinguishably different from that of the Ω precipitate, and this hexagonal structure is isomorphous to that of the single unit-cell thick T1 precipitate plates in Al-Cu-Li alloys. Our proposed hexagonal structure is also supported by density functional theory (DFT) calculations. One interesting feature of Ω′ phase is that its thickness is invariably one unit-cell height, ∼0.915 nm thick. In contrast to the commonly accepted view that shear is not involved in diffusional phase transformations, the formation of Ω′ phase involves an appreciably large shear component, which is equivalent to two 30° Shockley partial dislocations, and the magnitude of this shear component is significantly larger than the dilatational strain associated with the α-Al → Ω′ structural transformation. With continued ageing, the metastable Ω′ phase transforms in-situ into the Ω phase. Compared to the direct α-Al → Ω structural transformation, the existence of Ω′ considerably lowers the energy barrier to the nucleation of Ω via the reduction of the shear strain.

Coarse-Grained Model for the Hydrothermal Synthesis of Zeolites

Zeolites are the most used solid catalysts in the chemical industry. The hydrothermal synthesis of these porous aluminosilicate crystals is a multistep process that involves the polymerization of silica from solution to form amorphous aggregates, their crystallization, growth by oriented attachment, and eventually dehydration by heating. The molecular pathways by which zeolites are formed from the precursor solution are not yet fully understood. Molecular simulations can play an important role in elucidating these microscopic processes but are limited by the lack of models able to represent both the polymerization of silica and its crystallization with feasible computational costs. Here, we present a simple, computationally efficient coarse-grained model for the hydrothermal synthesis of zeolites from aqueous solutions. Our TS + W model has three components: silica, a structure-directing agent, and water, each represented by a single particle with short-range interactions. The model quantitatively reproduces the experimental evolution of silica species during the polymerization from solution, yielding amorphous nanoparticles with shape, composition, and silica speciation in agreement with the amorphous precursors of zeolites in experiments. Importantly, the TS + W model spontaneously nucleates and grows zeolites from the amorphous precursor phase and reproduces the temperature required for their dehydration. Our simulations indicate that the preferential formation of zeolites at the amorphous–water interface does not arise from an ability of that surface to heterogeneously nucleate the zeolite. The simplicity and computational efficiency of the TS + W model make it ideal to investigate the interplay between polymerization and crystallization in zeolite synthesis.

Impairment of human dopaminergic neurons at different developmental stages by perfluoro-octanoic acid (PFOA) and differential human brain areas accumulation of perfluoroalkyl chemicals

Perfluoroalkyl substances (PFASs) are synthetic chemicals widely used in industrial and consumer products. The environmental spreading of PFASs raises concerns for their impact on human health. In particular, the bioaccumulation in humans due to environmental exposure has been reported also in total brain samples and PFAS exposure has been associated with neurodevelopmental disorders. In this study we aimed to investigate the specific PFAS bioaccumulation in different brain areas. Our data reported major accumulation in the brainstem region, which is richly populated by dopaminergic neurons (DNs), in brain autopsy samples from people resident in a PFAS-polluted area of Italy.Since DNs are the main source of dopamine (DA) in the mammalian central nervous system (CNS), we evaluated the possible functional consequences of perfluoro-octanoic acid (PFOA) exposure in a human model of DNs obtained by differentiation of human induced pluripotent stem cells (hiPSCs). Particularly, we analyzed the specific effect of the exposure to PFOA for 24 h, at the concentration of 10 ng/ml, at 3 different steps of dopaminergic differentiation: the neuronal commitment phase (DP1), the neuronal precursor phase (DP2) and the mature dopaminergic differentiation phase (DP3). Interestingly, compared to untreated cells, exposure to PFOA was associated with a reduced expression of Tyrosine Hydroxylase (TH) and Neurofilament Heavy (NFH), both markers of dopaminergic maturation at DP2 phase. In addition, cells at DP3 phase exposed to PFOA showed a severe reduction in the expression of the Dopamine Transporter (DAT), functionally involved in pre-synaptic dopamine reuptake.In this proof-of-concept study we show a significant impact of PFOA exposure, mainly on the most sensitive stage of neural dopaminergic differentiation, prompting the way for further investigations more directly relevant to risk assessment of these chemicals.

New insights in the mechanisms of the reaction 3.65 Å phase = clinoenstatite + water down to nanoscales

Abstract. The reaction of 3.65 Å phase <=> clinoenstatite + water was investigated in five experiments at 10 GPa, 470–600 ∘C, using a rotating multi-anvil press. Under these P/T conditions, clinoenstatite exists in its high-pressure modification, which, however, is not quenchable to ambient conditions but transforms back to low-pressure clinoenstatite. The quenched run products were characterized by electron microprobe analyses (EMPA), powder X-ray diffraction (XRD), Raman spectroscopy and by high-resolution transmission electron microscopy (HRTEM) on focused ion beam (FIB)-cut foils. We bracketed the reaction in the T range 470 to 510 ∘C (at 10 GPa). The hydration of clinoenstatite to the 3.65 Å phase at 470 ∘C was very sluggish and incomplete even after 96 h. Clinoenstatites range in size from less than 1 to up to 50 µm. Usually clinoenstatite has a very small grain size and shows many cracks. In sub-micron-sized broken clinoenstatite, an amorphous phase (0.91Mg:1.04Si, with about 20 wt % H2O) was observed, which further transformed with increasing reaction time into the 3.65 Å phase (1Mg:1Si, with 34 wt % H2O). Thus, the sub-micron-sized fractured clinoenstatite transformed via an amorphous water-bearing precursor phase to the 3.65 Å phase. The dehydration to clinoenstatite was faster but still incomplete after 72 h at 600 ∘C. From the backscattered electron images of the recovered sample of the dehydration experiment, it is obvious that there is a high porosity due to dehydration of the 3.65 Å phase. Again, the grain size of clinoenstatite ranges from less than 1 up to 50 µm. There are still some clinoenstatite crystals from the starting material present, which can clearly be distinguished from newly formed sub-micron-sized clinoenstatite. Additionally, we observe a water-rich crystalline phase, which does not represent the 3.65 Å phase. Its Raman spectra show the double peaks around 700 and 1000 cm−1 characteristic for enstatite and strong water bands at 3700 and 3680 cm−1. The Mg:Si ratio of 0.90:1.04 was determined by EMPA, totalling to 81 wt %, in accordance with its high water content. Diffraction patterns from high-resolution images (fast Fourier transform – FFT) are in agreement with an orthoenstatite crystal structure (Pbca). The surprising observation of this study is that, in both directions of the investigated simple reaction, additional metastable phases occur which are amorphous in the hydration and crystalline in the dehydration reaction. Both additional phases are water rich and slightly deviate in composition from the stable products 3.65 Å phase and clinoenstatite, respectively. Thus, as a general remark, conventional investigations on reaction progress should be complemented by nanoscale investigations of the experimental products because these might reveal unpredicted findings relevant for the understanding of mantle processes. The extreme reduction in grain size observed in the dehydration experiments due to the formation of nanocrystalline clinoenstatite rather than the slowly released fluids might cause mechanical instabilities in the Earth's mantle and, finally, induce earthquakes.

Jadeite and related species in shocked meteorites: Limitations on inference of shock conditions

Abstract Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Some-times, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)M2(Al)M1(Si2)TO6–(Ca)M2(Al)M1(AlSi) TO6–(☐)M2(Si)M1(Si2)TO6 with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields (if any) and synthesis pathways, considered together with textural constraints, have different implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences casts a new light on many previous conclusions about the shock histories preserved in particular meteorites.