Composition Of Solid Solution Research Articles

Nonstoichiometry, thermal expansion and conductivity of Ba1-xPrxFe1-yCoyO3-δ solid solutions

Solid solutions Ba1-xPrxFe1-yCoyO3-δ (x = 0.3, y = 0.1-0.6 and x = 0.1-0.6, y = 0.2) with cubic structure were synthesized through a glycerol-nitrate technique. The oxygen content, thermal expansion, electrical conductivity and the Seebeck coefficient in the Ba1-xPrxFe1-yCoyO3-δ oxides were measured versus temperature in air. The oxygen content increases with increasing iron and praseodymium concentrations in Ba1-xPrxFe1-yCoyO3-δ. The value of the thermal expansion coefficient weakly depends on the composition of solid solutions. The conductivity of Ba1-xPrxFe1-yCoyO3-δ is practically independent of the concentration of 3d metals and increases significantly with increasing praseodymium content. The maximum conductivity value of 210 S/cm is obtained for Ba0.4Pr0.6Fe0.8Co0.2O3-δ at 450 °C in air. A positive value of the Seebeck coefficient indicates the predominant p-type conductivity in Ba1-xPrxFe1-yCoyO3-δ.

Local structure and phase composition of Neodymium-Zircon solid solution (NdxZr1-xSiO4-x/2)

To address the structural stability of host materials for immobilizing radioactive actinides in nuclear waste management applications, the present study is focused on the effect of various concentrations of Nd substitution on structural properties of synthetic zircon (NdxZr1-xSiO4-x/2). To achieve this, both pure and Nd-substituted zircon powders were prepared using the solid-state synthesis route. Rietveld refinement of X-ray Diffraction (XRD) data was employed to investigate the impact of various Nd substitutions on the phase composition of the zircon (ZrSiO4) crystal structure. This refined data was then utilized as input for the analysis of X-ray absorption spectroscopy (XAS) data. The results were further supported by observations from Raman spectroscopy, which indicated the substitution of Zr by Nd. In this work, we present an analysis of both regimes of XAS i.e. X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. Qualitative analysis of XANES data suggests that disorder in the samples increases with higher levels of Nd doping. Additionally, EXAFS analysis around Zr absorption edge also confirms an increased disorder in the system with higher Nd doping levels. However, EXAFS fitting around Nd edge indicated that disorder induced changes are more prominent and Nd–O bond is elongated as compared to Zr–O bond. This disorder in the system escalates at a Nd concentration of 10 atomic % (at %). An important finding of this study is the phase composition analysis using Rietveld refinement of XRD data. While XAS provided an insight into the changes in the local structure, the overall crystal structure remained unaffected even at a high doping of 10 at %. This work provides a comprehensive local structure analysis on this system. Such analysis would help in understanding the structural stability of the system and to determining the maximum loading of actinides in the host zircon for potential nuclear waste management applications.

Dual plate-like grains of (Ti, Zr)B2 and W2B5 toughened solid solution composites fabricated via in-situ reaction spark plasma sintering of (Ti, W)C and ZrB2 powders

Novel dual plate-like grains of (Ti, Zr)B2 and W2B5 toughened solid solution composites were fabricated by the in-situ reaction spark plasma sintering at 1800 °C using (Ti, W)C and ZrB2 powders. The composites were predominated and composed of the (Zr, Ti, W)C solid solutions and plate-like (Ti, Zr)B2. In the (Ti, W)C-ZrB2 reaction system, W promotes the anisotropic growth of (Ti, Zr)B2 grains, while Ti makes the formation reactions of WxBy thermodynamically feasible. When the addition of ZrB2 exceeds 40 mol%, W begins to be boronized into WxBy which is mainly composed of plate-like W2B5. The (Ti, W)C-50 mol% ZrB2 composite with dual plate-like grains of (Ti, Zr)B2 and W2B5 exhibited the best comprehensive mechanical properties of hardness of 26.5 GPa, flexural strength of 620 MPa, and fracture toughness of 6.6 MPa·m1/2, which provide a new approach for the enhanced toughness without the introducing of metal impurities.

Optical transition tuning of Er3+ in continuous tungsto-molybdate solid solution NaY(MoxW1-xO4)2 phosphors

Nowadays, the application scenarios of rare earth doped luminescent materials tend to be refined and complicated. The optical properties of rare earth doped materials are difficult to precisely control via the traditional design and synthesis methods, namely, changing doping concentration or preparative conditions. The aim of this study is to tune the optical transition properties of Er3+ in tungsto-molybdate NaY(MoxW1-xO4)2 (x = 0, 0.01, 0.1, 0.3, 0.5, 0.7, 0.9, 0.99 and 1.0) phosphors by changing the host matrix. The Er3+ doped continuous tungsto-molybdate solid solution NaY(MoxW1-xO4)2 phosphors were prepared via a solid state reaction technique at optimized calcination temperatures. The refractive indexes of the obtained solid solution samples were confirmed according to different models and compared. Subsequently, the optical transition intensity parameters, radiative transition rates and intrinsic radiative lifetimes of Er3+ in these solid solution phosphors were calculated in the framework of Judd-Ofelt theory. It was confirmed that the optical transition properties of Er3+ can be greatly tuned by the solid solution composition, and the tuning effects for different transitions are different. To validate the reliability of the Judd-Ofelt calculations, the temperature-dependent emission spectra of two green emissions of Er3+ for different solid solution samples were studied. It was found that the radiative transition rate ratios between two green emissions derived from theoretical calculations and experimental measurements are in reasonable agreement, thus proving that the optical transition calculations are reliable and the optical transition properties of Er3+ in the tungsto-molybdates can be tuned in a large range. This work reminds us of a new route for developing novel luminescence materials based on practical demands.

RESEARCH OF INFLUENCE OF MOLAR COMPOSITION ON ELECTRON MOBILITY IN ALUMINUM-GALLIUM ARSENIDE

Improvement in the technology of growing multicomponent semiconductors and the study of their potential applications contribute to the development of semiconductor devices with improved characteristics. Aluminum gallium arsenide is a promising three-component semiconductor in terms of crystal lattice matching, which caused a comprehensive study of the material in order to create high-performance electronic and optoelectronic devices on its basis. Predicting the prospects for creating devices based on certain materials requires a thorough knowledge, first of all, of their electrical properties.It should be noted that the possibilities of modeling the mobility of electrons in aluminum-gallium arsenide are not sufficiently disclosed in the scientific and technical literature. The aim of this work is to simulate the dependence of the electron mobility of the AlxGa1-xAs solid solution on the molar composition x.The simulation was carried out by the method of relaxation equations; based on the three-valley model of the conduction band. A technique is presented and a numerical experiment is carried out to determine the dependence of the mobility of charge carriers on the molar composition x of the solid solution. Attention is drawn to the peculiarity of modeling the processes of intervalley nonequivalent scattering, which corresponds to a significant convergence ofenergy valleys to each other. A model dependence of the Hall electron mobility in AlxGa1-xAs is obtained in the full range of molar composition values and compared with experimental results. Additional simulation results are presented that contribute to the understanding of the processes leading to the appearance of a specific feature of the dependence of the electron mobility on the molar composition of AlxGa1-xAs.A set of initial modeling parameters is determined, which provides good agreement with the experimental results considered in the work. The obtained results of numerical simulation open up opportunities for additional studies of the properties of aluminum-gallium arsenide. A technique for modeling the dependence of charge carrier mobility on the molar composition for three-component solid solutions is proposed.

Extending the solid solution range of sodium ferric pyrophosphate: Off‐stoichiometric Na3Fe2.5(P2O7)2 as a novel cathode for sodium‐ion batteries

AbstractIron‐based pyrophosphates are attractive cathodes for sodium‐ion batteries due to their large framework, cost‐effectiveness, and high energy density. However, the understanding of the crystal structure is scarce and only a limited candidates have been reported so far. In this work, we found for the first time that a continuous solid solution, Na4−αFe2+α/2(P2O7)2 (0 ≤ α ≤ 1, could be obtained by mutual substitution of cations at center‐symmetric Na3 and Na4 sites while keeping the crystal building blocks of anionic P2O7 unchanged. In particular, a novel off‐stoichiometric Na3Fe2.5(P2O7)2 is thus proposed, and its structure, energy storage mechanism, and electrochemical performance are extensively investigated to unveil the structure–function relationship. The as‐prepared off‐stoichiometric electrode delivers appealing performance with a reversible discharge capacity of 83 mAh g−1, a working voltage of 2.9 V (vs. Na+/Na), the retention of 89.2% of the initial capacity after 500 cycles, and enhanced rate capability of 51 mAh g−1 at a current density of 1600 mA g−1. This research shows that sodium ferric pyrophosphate could form extended solid solution composition and promising phase is concealed in the range of Na4−αFe2+α/2(P2O7)2, offering more chances for exploration of new cathode materials for the construction of high‐performance SIBs.

Synthesis and characterization of a new (Ti1-yCuy)2(Al1-xCux)C MAX phase solid solution

New [Ti(1-y)Cuy]2[Al(1-x)Cux]C solid solutions have been synthesized by solid-state reaction performed at 760 and 800 °C on compacted Ti2AlC-40 vol % Cu composite particles produced by mechanical milling. Using XRD and EDXS, it is demonstrated that Cu atoms can enter the crystallographic structure of the Ti2AlC MAX phase, whereas a Cu(Al) solid solution is formed during thermal treatment. A selective chemical etching of the Cu(Al) matrix is performed to determine the composition of the MAX phase solid solution by analyzing the filtrate and the solid phase using ICP-OES end EDXS methods respectively. (Ti0.85Cu0.15)2(Al0.75Cu0.25)C and (Ti0.85Cu0.15)2(Al0.58Cu0.42)C solid solutions are formed after thermal treatment at 760 and 800 °C, respectively. The substitution rate on the A site of the MAX phase thus increases with temperature.

Кераміка ZrB2 з добавками MoSi2, SiC і B4C: кінетика ущільнення, фазоутворення та опір повзучості

A study was carried out of the processes of compaction, structure formation and mechanical properties of ceramics based on zirconium boride with sintering-activating additives of boron, silicon and chromium carbides, as well as molybdenum silicide, obtained under hot pressing conditions in a CO atmosphere. In ZrB2—18% (vol.) B4C ceramics, the use of the B4C additive reduces the optimal hot pressing temperature to 1940 °C and accelerates the compaction process of the ceramics. The influence of the sample preparation background on high-temperature creep has been established, as a result of which either plastic flow of the material occurs over a wide temperature range, or a high temperature threshold for yield and brittle fracture. In ZrB2—SiC ceramics, during high-temperature plastic deformation both during sintering and in creep tests, a bidisperse structure with a submicrograined component is formed, which is responsible for high creep rates. In ZrB2—B4C ceramics there is no submicrograin component, which provides high creep resistance up to 2000 °C. The phase composition of ZrB2—MoSi2 ceramics changes dramatically during hot pressing; it is represented by a composition of a ZrB2 solid solution with the second phases of SiC and B4C, and in terms of creep resistance it occupies an intermediate position between two other ceramics. Keywords: ultra-high temperature ceramics, zirconium diboride, silicon, boron and chromium carbides, hot pressing in a CO atmosphere, compaction kinetics, structure, creep resistance.

Morphology and Phase Compositions of FePt and CoPt Nanoparticles Enriched with Noble Metal

The article reveals for the first time the features of nanoparticle morphology, phase compositions, and their changes when heating FePt and CoPt nanoalloys. Nanoparticles were obtained by co-reduction of precursor solution mixtures with hydrazine hydrate. The features were found by a complex of methods of X-ray diffraction (in situ XRD and X-ray scattering), TEM HR, and cyclic voltammetry. In addition, adsorbometry results were obtained, and the stability of different nanocluster structures was calculated by the molecular dynamics method. There were only FCC solid solutions in the X-ray patterns of the FePt and CoPt nanoalloys. According to XRD, in the case of nanoparticle synthesis with Fe and Co content less than 10 at. %, the composition of solid solutions was close to or practically equal to the composition of the as-synthesized nanoparticles quantified by inductively coupled plasma optical emission spectrometry. For systems synthesis with Fe and Co content greater than the above, the solubility limits (SLs) of Fe and Co in Pt were set 11.4 ± 0.7 at. % and 17.5 ± 0.6 at. %, respectively. Therefore, there were non-registered XRD extra-phases (XRNDPh-1) in the systems when CFe,Co ≥ SL. This statement was supported by the results of TEM HR and X-ray scattering: the smallest nanocrystals (1–2 nm) and amorphous particles were found, which qualitatively agreed with the sorbometry and SAXS results. Molecular dynamics calculations of stability for FePt and CoPt alloys claimed the structures of the most stable phase corresponded to phase diagrams (A1 and L12). Specific peculiarities of the morphology and compositions of the solid solutions of nanoalloys were established: structural blockiness (domain) and composition heterogeneity, namely, platinum enrichment of internal (deep) layers and homogenization of the nanoalloy compositions at relatively low temperatures (130–200 °C). The suggested model of the formation of nanoalloys during the synthesis, qualitatively, was compliant with the results of electrochemical deposition of FePt films on the surface of various electrodes. When nanocrystals of solid solutions (C(Fe, Co) < SL) were heated above specific temperatures, there were phase transformations with the formation of two-phase regions, with solid solutions enriched with platinum or iron (non-registered XRD phase XRNDPh-2). The newly formed phase was most likely intermetallic compounds, FePt3, CoPt3. As a result of the study, the model was developed, taking into account the nanoscale of the particles: XRDPh (A1, FeaPt1−a) → XRDPh (A1, Fem×a−xPtm−m×a+x) + XRNDPh-2 (Fen×a+yPtn−n×a−y) (here, m + n = 1, m ≤ 1, n ≤ 1).

High-pressure Raman spectroscopy study of α-quartz-like Si1-xGexO2 solid solution

Spontaneous α-Si1-xGexO2 single crystals were synthesized using the set of crystal growth techniques: hydrothermal (XGe = 0.09, 0.20), flux (XGe = 0.45, 0.70) and recycling (XGe = 0.96). The XRD and spectroscopic studies with non-negative matrix factorization show linear dependences of structural parameters and Raman shift on germanium content and confirmed the existence of a complete series of α-Si1-xGexO2 solid solution. The synthesized samples of the solid solution were studied by Raman spectroscopy at the ambient conditions and for the first time at high pressures up to ∼30 GPa. The obtained results suggest a phase transition “α-quartz → post-quartz” for Si1-xGexO2 in the examined pressure range. The formation of the possible intermediate phase (quartz-II) was detected for Si1-xGexO2 with XGe = 0.09, 0.20 and 0.45 at 11, 10 and 7.5 GPa, respectively. The linear dependences of the pressure value of phase transitions on germanium content were observed. At decompression, the post-quartz phase remained stable that was determined by Raman spectra for all compositions of solid solution. Obtained experimental results revealed the correlation of the chemical composition, spectroscopic characteristics, and structural deformations at ambient conditions and at high pressures.

Analysis of heat conductivity mechanisms in PbSnTe solid solutions

In the paper, a theoretical calculation of the coefficient of thermal conductivity of solid solutions of PbSnTe was carried out. The contribution of phonon scattering on substitution atoms to the effect of reducing thermal conductivity has been established. The composition of the PbSnTe solid solution, characterized by the lowest values of the lattice component of the thermal conductivity coefficient klat, was determined. The concentration of intrinsic charge carriers in solid solutions is calculated and their influence on the thermoelectric parameters of the material is shown.

High strain rate response and mechanical performance of tantalum carbide–hafnium carbide solid solution

Ultra-high temperature ceramics (UHTCs) based on the solid solution TaxHf1-xC have shown great promise as materials for extreme environments (>2500 °C) due to their improved thermo-mechanical properties. However, their dynamic response under high-impact loading remains unknown. In this study, we investigate the dynamic impact behavior and fracturing evolution of TaxHf1-xC samples (with x = 0, 0.2, 0.5, 0.8, and 1) at a strain rate > 103 s-1 using the Split Hopkinson Pressure Bar (SHPB) test. Among the different compositions, Ta0.5Hf0.5C exhibits the highest compressive strength of 1870 MPa, representing a 36% improvement over TaC and 54% over HfC. High frame rate videos and deformation analysis reveal that Ta0.5Hf0.5C, characterized by extensive Ta–Hf bonding, significantly reduces the crack propagation rate by approximately 1435% compared to TaC and 4050% compared to HfC. This effect is attributed to the dislocation pile-ups, nano-twin formation, inter grain twisting exhibited mostly along {111} plane as Hf substitutes Ta in TaxHf1-xC samples. Further, the surface energy is least for {111} plane eliciting the higher probability for bypassing crack propagation along this plane in TaxHf1-xC. The exceptional damage tolerance and improved mechanical properties of Ta0.5Hf0.5C, compared to other solid-solution TaxHf1-xC compositions, make it an extraordinary structural material for hypersonic applications. These findings provide valuable insights into the dynamic behavior of UHTCs and highlight the potential of Ta0.5Hf0.5C as a superior material for extreme environments requiring high-impact resistance.

Advances in hydration and thermodynamics of cementitious systems

Optimising the hydration of cementitious materials is crucial to leverage their full potential and avoid wasting resources, embodied energy and CO2. Understanding the fundamental mechanisms is key to reach these objectives. In this paper, we review progress in understanding hydration kinetics. We highlight how our practical understanding of cementitious materials is linked to the more fundamental field of aqueous solution thermodynamics. We concentrate on the knowledge gaps related to the aqueous speciation, the composition and structure of complex solid solutions (C-A-S-H, AFm, AFt), the solubility of anhydrous species and hydrates, and the water activities. We illustrate how these challenges are related to the development of meaningful models of early- and late-age hydration.

Modeling structure–properties relations in compositionally disordered relaxor dielectrics at the nanoscale

The solid solution Ba1−xSrxTiO3 (BSTO) displays dielectric response that is highly tunable, while also exhibiting low losses in a broad frequency regime, including the microwave band. Therefore, there is a need for a better understanding of the influence of the BSTO microstructure on its relaxor properties and performance in a variety of technological applications. Since the local polarization in BSTO is strongly dependent on composition, so is its response to an applied AC field. In this work, we have adopted a phase field method to study the frequency-dependent dielectric response of this system while accounting for the local fluctuations in the solid-solution composition. By utilizing a thermodynamic potential that includes spatial dependence on the averaged Sr content, we connected relaxor-like features in the dielectric dispersion to local spatial inhomogeneities, such as average size of Sr- or Ba-rich regions, across a wide range of temperatures. These results show that the adopted simple coarse-grained approach to the relaxor problem is sensitive enough to reveal correlations between the frequency and temperature dependence of the dielectric response and modulations in the material morphology and microstructure.

The prediction of alkali-silica reaction based on the alkali-Al ratio of pore solution using thermodynamic modeling

With the aim to predict ASR based on the Alkali-Al ratio of pore solution, blends consisting of Portland cement and various SCMs, including MK, FA, GGBS, SF, and GP, were formulated using thermodynamic modeling. The solid phase assemblages and pore solution compositions were measured by means of XRD, TGA, and ICP-OES. The wrapped AMBT was carried out to confirm the ASR prediction performance. Results showed that ASR expansion increases with the Alkali-Al ratio of pore solution and the reactivity of the used aggregate. The feasibility of predicting ASR based on Alkali-Al ratios using thermodynamic modeling was verified by comparing the prediction effects and the experimental results. In addition, a ternary diagram for predicting the ASR risk when using PC-SF/MK/FA/GGBS-GP blends was proposed, through which the efficacy of various SCMs on mitigating ASR can also be evaluated.

Structure and Physical Properties of Ceramic Materials Based on ZrO2-Sc2O3 for SOFC Electrolytic Membranes Obtained from Powders of Melted Solid Solutions with a Similar Composition.

This paper presents the results of studying the phase composition, luminescent characteristics, and ionic conductivity of ceramic scandium-stabilized solid solutions of zirconium dioxide containing 9 and 10 mol% Sc2O3. Ceramic samples were prepared by sintering powders obtained by grinding melted solid solutions of the same composition. A comparative analysis of the obtained data with similar characteristics of single crystals has been carried out. Differences in the phase composition of ceramics and initial single crystals were found. The effect of the structure and properties of grain boundaries on the ionic conductivity of ceramic samples is discussed. It is shown that the differences in the ionic conductivity of ceramic samples and crystals are mainly due to changes in the structure and phase composition.

The effect of Si addition in NbTiZr coatings

Nb based alloys are considered the most appropriate to replace Ni alloys for new generation aircrafts, since Ni alloys can no longer meet the extreme environmental requirements. Processing Nb based alloys as coatings might bring a wider use of alloys depending on the available understanding of their processability. This investigation takes an important step to process Niobium alloys containing high hardness low toughness silicide compounds as multilayer coatings, taking advantage of in-situ synthesis of the alloy during the deposition of powder mixtures. Procedures started by preparing elemental powder mixtures adding Si to a NbTiZr solid solution composition with good processability. In-situ synthesis of silicides occurs during the deposition of (Nb24Ti18Si + 1Zr) (at.%) powder mixtures by Plasma Transferred arc hardfacing (PTA). Si accounts for the hardness increase of the deposited coatings and their reduced mass gain. The addition of Si into the powder mixtures induced the formation of primary Nb5Si3 that competes with the primary Nb(Ti,Si,Zr)ss. Three solidification paths are identified to be competing as the PTA torch moves and the melt pool solidifies. The thermal cycles of multilayer coating processing favour the epitaxial growth of Nb5Si3 at the remelted interface between layer and induce a coarsening of the silicides in the microstructure. Phase distribution in coatings, with the more ductile and toughness phases surrounding the silicides, contributes for the confinement of cracks within the larger silicides formed after the deposition of multilayer coatings.

Experimental Modeling of Transport of Ore-Forming Components by Water-Salt Fluids at Elevated P–T Parameters

Abstract —The modeling experiments were conducted to study transport of ore-forming components in the lithosphere, taking into account the possibility of ore matter remobilization under endogenous conditions. The experiments, which included temperature gradient-based ones, were conducted at T = 500–680 °C and P = 1.5–5.0 kbar on high gas pressure devices (HGPD) in highly concentrated water-salt solutions of alkaline specifics. The experiments consisted of two stages. During the first stage, we tested the possibility of recrystallization of the ore matter of “black smokers” in the presence of basalt at 500 ℃ and 5 kbar and water-salt fluids at a concentration of up to 5 wt.%. At the second stage, mechanisms of ore-forming components transport (P–T parameters: 450–650 ℃ and up to 5 kbar) were studied under conditions of a temperature gradient (0.3–0.4 °C/mm). The duration of the experiments was 14 days. The test products were: oceanic basalts, granite model mixtures (Fsp + Qz), as well as various sulfide minerals, oxides and noble metals (Au, Pt). It has been shown that at T 680–650 °C, intensive recrystallization and deposition of sulfide minerals (sphalerite, galena, chalcopyrite, pyrite, cooperite, etc.) along with feldspars, micas and quartz, takes place. Intensive transport of both the main petrogenic (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K) and ore-forming elements (Ni, Cu, Zn, As, Pb, Cd, Pt, Au, Hg, Bi), and a joint transport of silicate and ore matter is established. Some ore elements are either included into compositions of solid solutions or present as impurities in ore-forming minerals: Fe, Ni, Cu → pyrite, pyrrhotite; Pb, Au, As, Bi, Zn → galena; Zn, Cd, Fe, Mn, Cu → sphalerite; As → galena, orpiment, realgar, gold; Hg → gold. The obtained data attest to the possibility of modeling ore mineralization mechanisms. The experimental results apply to explain the genesis of the Zun-Kholba gold–quartz–sulfide deposit and describe the processes of epigenetic transformations of primary ores in polymetallic deposits, on the example of the Ozernoe Pb–Zn deposit. The discussed mechanisms can be extended to explain the genesis of other ore deposits occurring in the zones of tectonic-magmatic activation.

Late beryllium enrichment during dynamic growth of vesuvianite and scapolite from the Cuonadong Sn-W-Be skarn, Tibet

The genesis of beryllium (Be) mineralization associated with granitic tin (Sn)- tungsten (W) deposit has received little attention, especially the fluid Be concentration variation along with the developing of skarn. For revealing the less-known skarn Be enrichment characteristics, in-situ electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) along with element mapping were performed on the Be-bearing vesuvianite and scapolite grains from the Cuonadong Sn-W-Be skarn. As the main Be-bearing calc-silicate minerals, the vesuvianite (X19Y13Z18T0-5O68W10) and scapolite (M4T12O24A) incorporate Be element via occupying normally vacant T site and the Al-2(SiBe) substitution, respectively, and show outward increased Be content related to the varying solid-solution composition arising from the dynamic evolution of skarn. The homogeneous core enveloped by oscillatory mantle and rim under BSE or CL image and the increased liquid inclusion size towards the rim reflect both mineral’s staged growth under an elevated water–rock ratio. The increased Ca activity caused by enhanced interaction between fluid and Mn-containing carbonate may drive scapolite constituent change through (NaSi)-1(CaAl) substitution, creating more tetrahedral Al sites suitable for Be occupation and resulting in the increased Ca, CO32–, Be content and decreased Na content from core to rim. Precipitation of fluorite will lead to a reduce in hydrothermal Be solubility associated with a decreased fluorine activity, and favor Be to occupy the vacant T site by losing more hydrogen from the anion W site and finally form the Be-rich, Ca- and F-low vesuvianite rim. Significantly high Be, Sn, Mn and low Sr, LREE, U content at vesuvianite rim along with hydration alteration and mineralization suggest the onset of retrograde stage. Overall, the dynamic growth and epitaxially rising Be concentration of vesuvianite (∼97–1032 ppm) and scapolite (∼902–2928 ppm) recorded that the later pulsed fluid enriched Be as skarn developed, implying high grade Be mineralization tends to occur in the late magmatic-hydrothermal stage for F-rich peraluminous magmatic system.

Characterization of MoAlB ceramics synthesized via spark plasma sintering with Si addition and SiC reinforcement

The MoAlB phase with high purity and density from elemental precursors was successfully synthesized with SPS (Spark Plasma Sintering) at 1200 °C. Then, MoAlB-Si solid solution and MoAlB-SiC (5% SiC by volume) composite were fabricated to improve the mechanical properties and oxidation behavior of the MoAlB further. XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and EDS (Energy Dispersive X-Ray Spectroscopy) investigated the composition and microstructure of the MoAlB ceramics. The hardness was measured by the Vickers indentation test, and fracture toughness was calculated by radial cracks formed during the indentation test. The hardness and fracture toughness of pure MoAlB was 10.30 GPa and 6.73 MPa.m1/2. With the Si solid solution, the hardness increased to 11.93 GPa, while the fracture toughness decreased to 5.49 MPa.m1/2. The highest hardness and fracture toughness were obtained in the MoAlB-SiC composite, 12.39 GPa, and 7.38 MPa.m1/2, respectively. The oxidation tests of the samples were characterized in the air at 1200 ℃ for 12 h. A dense and continuous oxide layer was formed in all samples after 12 h at 1200 °C. While both Si solid solution and SiC reinforcement increase the oxidation resistance, the best results were obtained in the MoAlB-Si-SiC composite. The effect of Si addition and SiC reinforcement on electrical and thermal conductivity was measured from room temperature to 1000 ⁰C. The electrical conductivity of all samples decreased exponentially with the increase in temperature. The electrical conductivity of pure MoAlB was 2.82 S⋅m−1 at room temperature and decreased with the Si addition (2.49 S⋅m−1) or SiC reinforcement (2.67 S⋅m−1). On the other hand, thermal conductivity tends to decrease between room temperature to 400 °C but showed an increasing trend above 400 °C. In conclusion, the mechanical properties and oxidation resistance of MoAlB ceramics were improved with Si addition and SiC reinforcement.