Search Results (3,477)

The eddy covariance (EC) technique is a key tool in environmental monitoring, enabling continuous and non-invasive measurement of carbon dioxide (CO₂) fluxes at the ecosystem–atmosphere interface. In environments characterized by high levels of airborne particulates, such as volcanic regions, the reliability of enclosed-path EC measurements can be compromised by frequent filter clogging, potentially affecting data continuity, and increasing maintenance requirements. This study investigates whether the chemical and mineralogical signatures of particulate matter accumulated on clogged Swagelok pre-Licor filters can be used to identify dominant particle sources and provide insights into filter clogging processes. A multi-analytical workflow combining scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), portable Raman spectroscopy, and hyperspectral imaging (HSI) was applied to recovered filter residues. The combined approach provided complementary chemical, mineralogical, and morphological information, allowing discrimination among volcanogenic material (e.g., glass shards, crystals, and lithic fragments), aeolian lithogenic dust, including Saharan inputs, and biogenic particles such as plant fibers. The results revealed two dominant particulate groups, volcanogenic mineral phases and biogenic material, with a minor contribution from wind-transported lithogenic dust. Volcanogenic phases, enriched in Si, Al, and Fe, dominated the inorganic fraction, whereas O-, C-, and N-rich particles were mainly associated with local biogenic sources. No clear evidence of significant anthropogenic contributions was identified. These findings demonstrate that multi-analytical characterization of particles accumulated on EC pre-filters can provide qualitative source attribution and valuable information on the processes responsible for filter loading and clogging. By linking particle characteristics with meteorological and environmental conditions, this approach has the potential to support site-specific, predictive, and event-driven maintenance strategies, contributing to improved EC data quality and more efficient long-term monitoring in high-aerosol environments. Full article

The Fe–6.5 wt.% Si alloy is a promising soft magnetic material for electric motor applications owing to its high electrical resistivity and low core loss. However, the intrinsic brittleness of this alloy precludes fabrication of thin laminates using conventional rolling processes. Laser Powder Bed Fusion (LPBF) has therefore been considered as an alternative manufacturing route, offering both geometric flexibility and the inherent advantages of additive manufacturing. Nevertheless, successful LPBF processing of Fe–6.5 wt.% Si has remained challenging due to its high-silicon content. In this study, the Fe–6.5 wt.% Si alloy was modified by introducing 1 wt.% Cr, and LPBF process variables were optimized to yield defect-free parts. The effect of Cr addition on suppressing the disorder–order phase transformation during solidification was investigated through Thermo-Calc^® thermodynamic simulations and quantified via X-ray diffraction phase analysis. Crack morphology analysis from optical micrographs revealed a marked reduction in both solidification and liquation cracks, attributed to the role of Cr in mitigating silicon segregation and consequently lowering the fraction of ordered phases. Preheating the build plate to 200 °C was found to effectively eliminate vertical cracks by reducing thermal stresses within the parts; however, a limited number of horizontal cracks initiated at the sample edges and propagated inward, likely due to elevated thermal gradients at the perimeter. To address this issue, sacrificial walls were introduced at distances of 1.0 mm and 0.2 mm from the cube edges, locally reducing the cooling rates and effectively increasing the primary dendrite arm spacing (PDAS). The reduced cooling rate also led to lower lattice misorientation, confirmed by electron backscatter diffraction (EBSD), and a significant decrease in the crack length from ~2 mm to ~0.7 mm. Full article

This work is devoted to the investigation of rare-metal granites associated with anorthosite–rapakivi granite rock complexes. This article evaluates the physicochemical conditions that governed the formation of a rare-metal granite dike. It also explores assumptions regarding the geological characteristics of the magmatic chamber, describes evidence for liquid immiscibility, and addresses the post-entrapment evolution of hydrosilicate liquids. In addition, new mineralogical data are presented. The methods employed include optical and electron microscopy, Raman spectroscopy, secondary ion mass spectrometry, laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS), melt inclusion homogenisation experiments, and fluid inclusion study. The investigated granitic dike formed under low pressure (60–110 MPa) and temperatures of about 580–600 °C, from a specific volatile-saturated magma rich in H₂O (up to 16.76 wt% in quenched hydrosilicate liquid products) and in F (up to 4.16 wt%) and Li (up to 3804 ppm), as indicated by homogenised melt inclusions. At the time of emplacement, a silicate melt, a probable Ca-fluoride melt, an Mg-Fe Al-Si-rich hydrosilicate liquid (either mutually soluble with or mixed with the inferred Ca-fluoride melt), and an essentially aqueous fluid coexisted. Depolymerisation of the silicate melt and the presence of complex ions probably promoted the dissolution and transport of high field strength elements (HFSE) and large ion lithophile elements (LILE) elements by the Mg-Fe Al-Si-rich hydrosilicate liquid. During the final stage of evolution of the granitic magmatic system, Mg behaved incompatibly because of its negligible partitioning into mica; rather than accumulating in the silicate melt, it entered the hydrosilicate liquid as a major component. The residual silicate melt consequently attained even lower Zr/Hf, Nb/Ta, and Y/Ho ratios than the studied rock. Full article

Water retention on the lunar surface is governed by water–mineral interactions, yet the atomic-scale transition from isolated adsorption to high-coverage water accumulation remains insufficiently understood. We perform spin-polarized first-principles calculations to investigate single- and multi-water adsorption on representative surfaces of four major lunar regolith minerals: CaAl₂Si₂O₈, MgFeSi₂O₆, FeTiO₃, and Mg₃FeSi₂O₈. Single-water adsorption reveals that H₂O preferentially anchors at exposed metal sites via O-M coordination, with Ti and Fe sites exhibiting stronger initial binding than Mg, Ca, or Al sites. The Hard–Soft Acid–Base (HSAB) principle provides a qualitative framework for this low-coverage site preference based on Lewis acidity. Specifically, the accessible d-orbitals and localized states of Ti/Fe centers introduce substantial covalent orbital coupling and interfacial polarization, which effectively reinforce the binding with the hard O-donor of water. However, as water coverage increases, the stabilization mechanism undergoes a fundamental transition. At low coverage, adsorption is localized and site-specific, governed by cation acidity. At high coverage, the formation of laterally connected hydrogen-bonded networks becomes the dominant stabilizing factor, and the overall adsorption behavior is increasingly dictated by surface topology and geometric compatibility for hydrogen-bond connectivity rather than by isolated cation acidity. This coverage-dependent evolution from electronic-driven anchoring to topology-driven network formation establishes a dual-stage cooperative mechanism for water accumulation on lunar mineral surfaces. Our findings suggest that models for volatile retention on airless bodies must account for both the electronic activity of surface cations and the structural topology of mineral surfaces. Full article

The emplacement of mafic dikes into carbonate-bearing sedimentary successions commonly produces localized mineralogical and geochemical variations in adjacent country rocks. However, the spatial distribution of these variations remains poorly documented in the Permian sedimentary successions of Thailand. The study investigates spatial mineralogical and geochemical variations across intrusive rocks and adjacent sedimentary rocks in the Permian Nam Duk Formation, Phetchabun Province, Thailand. Petrographic observations and whole-rock geochemical analyses (XRF and ICP-MS), supported by qualitative XRD phase identification, were integrated to characterize mineral assemblages and whole-rock geochemistry. The intrusive rocks display porphyritic textures dominated by plagioclase and hornblende, whereas the adjacent country rocks are characterized by quartz, calcite, feldspar, clay minerals, and secondary alteration phases. Spatial variations in mineral assemblages are accompanied by changes in contents of some major oxides (SiO₂, Al₂O₃, Fe₂O₃, MgO, and CaO) and selected trace and rare earth elements. The sedimentary country rocks generally contain higher total REE concentrations, particularly La and Ce, whereas the contact-proximal sample shows values closer to the mafic dike. Site A shows the clearest spatial variations across the exposed mafic dike–country rock contact, whereas site B exhibits compositional variability associated with strongly altered porphyritic andesite and heterogeneous sedimentary rocks. The integrated results document localized mineralogical and geochemical variations across the investigated intrusive–sedimentary rock systems, although primary lithological heterogeneity and secondary alteration may also contribute to these patterns. Full article

Magnesium potassium phosphate cement (MKPC) exhibits rapid setting and high early strength, but its long-term performance is limited by microstructural heterogeneity and pore structure defects. These microstructural defects can increase pore connectivity and facilitate the ingress of aggressive agents, thereby limiting the long-term durability and service reliability of MKPC-based repair and protective materials. Nanomaterials have been applied to improve MKPC performance; however, the differences between conventional nano-SiO₂ (NS) and nano-Fe₂O₃ (NF), particularly their effects on hydration regulation and microstructure evolution, remain insufficiently understood. In this study, the effects of NF and NS incorporation on the hydration behavior, phase evolution, pore structure, and mechanical properties of MKPC were comparatively investigated. Orthogonal experiments, mechanical testing, calorimetry, XRD, FTIR, Raman mapping, SEM/EDS, MIP, and nanoindentation were employed to establish the relationship between nano-modification, microstructural evolution, and mechanical performance. The results provide a basis for selecting suitable nanomodifiers for MKPC-based materials used in rapid repair, protective applications, and other construction scenarios requiring rapid strength development and improved microstructural compactness. Compared with pure MKPC and previously reported NS-MKPC results, NF-MKPC showed higher strength development, refined pore structure, and improved micromechanical uniformity. The observed performance enhancement of NF-MKPC is consistent with accelerated early hydration, possible heterogeneous nucleation, pore refinement, and matrix densification. In comparison, NS-MKPC exhibited a different hydration and pore-evolution behavior under the investigated conditions. These findings indicate that NF and NS may regulate hydration and microstructure development differently in MKPC and provide guidance for selecting suitable nano-modifiers for high-performance phosphate cement materials. Under the investigated conditions, NF modification shows potential for MKPC applications requiring rapid strength development and improved microstructural compactness, such as rapid pavement repair, concrete surface repair, and protective coating applications. Full article

Antimony (Sb) nanopowder was synthesized using fine Sn powder as a reducing agent. The Sn powder was first produced by the chemical reduction of SnCl₂·2H₂O using commercial Al foil in acidic medium, yielding approximately 89% of the theoretical Sn yield. The resulting Sn powder exhibited a mean particle size of approximately 93 nm and a mean crystallite size of 57 nm, which promoted rapid reduction during Sb synthesis. Prior to synthesis, the composition of the Al foil was examined using SEM/EDS, confirming an Al-rich matrix containing minor Fe and Si impurities. High-purity Sb nanopowder was synthesized by reducing SbCl₃ in acetone at 50 °C under magnetic stirring and ultrasonic agitation, using the produced fine Sn powder as a reducing agent, achieving approximately 97% of the theoretical yield. SEM analysis revealed nearly spherical particles of black Sb nanoscale powder with the most frequent size falling within the 20–40 nm range and a mean particle size of approximately 32 nm. XRD analysis confirmed a trigonal Sb structure with a mean crystallite size of around 23 nm. For comparison, pellets prepared from synthesized Sb nanopowder and commercial Sb powder were compacted and sintered under identical conditions. Vickers microhardness measurements showed that the hardness of the sintered Sb nanopowder pellet was approximately 62% higher than that of the commercial Sb pellet. In addition, UV-Vis-NIR reflectance measurements (240–840 nm) demonstrated that the reflectance of the Sb nanopowder pellet was approximately three times higher than that of the commercial Sb pellet. These results demonstrate that fine Sn powder can serve as an efficient reducing agent for the synthesis of high-purity Sb nanopowder with enhanced mechanical and optical properties. Full article

Quasi in situ observations of the early stage of secondary recrystallization in Fe-3.25 wt.% Si high-permeability grain-oriented silicon steel indicate that large matrix grains locally impede the migration of secondary recrystallized grain boundaries. A critical grain-size criterion for identifying potential pinning grains is proposed, and a kinetic model incorporating the matrix grain-size distribution is developed. For the abnormal grain tracked at 1000 °C, the measured grain-size increment over 100 s was approximately 60 μm; the proposed pinning model predicted 47 μm, whereas the weighted-average model predicted 171 μm. Model calculations further suggest that matrix grain-size dispersion, pinning force, grain size, and relative grain-boundary energy jointly affect the early-stage growth of Goss grains. These results provide a framework for interpreting early secondary-recrystallization kinetics, while broader experimental validation is still required before the predicted parameter combinations can be used for process control. Full article

The accumulation of dissolved species during the in situ leaching (ISL) of uranium can lead to ore-layer blockage and reduced production capacity. Clay minerals, including montmorillonite, chlorite, kaolinite, and illite, are the primary cementing and filling materials in sandstone-hosted uranium deposits in China. However, previous studies have predominantly focused on the leaching behavior of uranium minerals, while systematic investigations into the dissolution mechanism of clay minerals under CO₂+O₂ conditions remain scarce. In this study, laboratory dissolution experiments, scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS), computed tomography (CT) scanning, and field verification were conducted to systematically investigate the dissolution behavior of major clay minerals and their contribution to ore-layer blockage under CO₂+O₂ leaching conditions. The results indicate the following: (1) Montmorillonite exhibited the most significant dissolution, with granular deposits rich in Ca and Si formed on its surface, which were inferred to be Ca-Si-rich precipitates. (2) Obvious changes in both microstructure and macroscopic physical properties of clay minerals were observed before and after leaching, with porosity decreasing by approximately 12.96% and permeability decreasing by approximately 10.16%. (3) Field verification revealed that the scale in the ore layer, filter cloth blockage, and resin surface caking were primarily composed of silica gel and hydroxide/carbonate precipitates of Al, Ca, and Fe, which are closely related to the dissolution and leaching of clay minerals. This study confirms that montmorillonite is the main source of clogging substances, and long-term closed circulation of injection and extraction leads to the accumulation of precipitates, exerting a significant impact on the uranium-leaching system. The findings provide a theoretical basis for anti-clogging and permeability enhancement in CO₂+O₂ ISL operations. Full article

Biomass, particularly agricultural waste, has emerged as a highly attractive alternative fuel source for domestic and industrial applications. This study investigates the suitability and potential of plantain peel biomass (PPB) as a viable feedstock for bioenergy production. The PPB was comprehensively characterized using proximate and ultimate analyses, thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Experimental results indicate that the weight ratio of plantain peel (skin) to unpeeled plantains ranges from 27% to 47%. Proximate analysis of the PPB yielded volatile matter (VM) of 65.8% and fixed carbon (FC) of 14.5%, suggesting substantial energy potential. The ultimate analysis results, conducted on a dry, ash-free basis, were used to determine the biomass higher heating value (HHV), which ranged from 13.93 to 16.35 MJ/kg. TGA showed that the thermal decomposition of PPB is typical of lignocellulosic biomass, occurring in three distinct stages over a temperature range of 25 to 1000 °C. FTIR spectroscopy identified O-H and C-H as key functional groups present in the PPB, further supporting its viability for biofuel production. Furthermore, SEM micrographs revealed a porous surface texture with heterogeneous particle sizes and shapes. At the same time, EDS confirmed carbon (C), potassium (K), and oxygen (O) as the dominant elements, alongside trace amounts of magnesium (Mg), silicon (Si), phosphorus (P), chlorine (Cl), and iron (Fe). In conclusion, PPB represents a promising and sustainable feedstock for biofuel production in both domestic and industrial sectors. Full article

Nickel coatings were deposited onto the surfaces of red mud, Al₂O₃, and Fe₂O₃ particles via an electroless plating technique. The nickel-coated particles (1.5 wt.%) were subsequently incorporated into a ZL109 aluminum alloy matrix to fabricate three types of composites using a stir-casting process, followed by a T6 heat treatment consisting of solution treatment at 515 °C for 8 h, water-bath quenching at 90–100 °C, and artificial aging at 175 °C for 12 h. The microstructural morphology and phase identification were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Furthermore, the high-temperature tensile properties of the fabricated alloys were evaluated at 350 °C and 400 °C. The results showed that the addition of 1.5 wt.% nickel-coated red mud led to a more uniform distribution of eutectic silicon and an increase in the content of the Al₅Cu₂Mg₈Si₆, Al₇Cu₄Ni, and Al₂Cu strengthening phases. These microstructural changes significantly enhanced the high-temperature tensile performance of the alloy. At 350 °C and 400 °C, the alloy reinforced with 1.5 wt.% nickel-coated red mud achieved tensile strengths of 97.8 MPa and 86.2 MPa, respectively. The combination of an appropriate amount of nickel-coated red mud and a suitable heat treatment process effectively improves the high-temperature stability and tensile properties of the ZL109 aluminum alloy, which could be attributed to the synergistic strengthening effect arising from the precipitation of high-temperature stable phases and the Orowan mechanism. Full article

Dephosphorisation in oxygen steelmaking depends on more than the equilibrium phosphorus partition ratio. It also depends on where gas, slag, metal and injected lime powder coexist while the bath is stirred. We develop a gas–slag–metal–particle reaction model for bottom-blown oxygen–CaO powder injection by coupling Euler–Euler transport of liquid steel, mixed slag, and gas with a discrete phase model (DPM) for CaO particles. The local source terms include oxygen dissolution, FeO/Fe₂O₃ conversion, CO/CO₂ buffering, competitive C/Si/P oxidation, ${\mathrm{P}}_2{\mathrm{O}}_5$ formation, $C_{2}S$–$C_{3}P$ fixation, reaction heat, and phase-wise mass conservation. Bubble swarms, dispersed slag, and emulsified metal–slag contact are represented through mean-field interfacial area densities tied to local phase fractions and mixing. Two simulated composition states have the same initial phosphorus content but different C, Si, and dissolved O levels; they are therefore compared as Case H and Case L rather than as a carbon-only test. Under the selected closures, Case H shows stronger decarburisation and CO-supported plume motion, whereas Case L retains more ${\mathrm{FeO}}_x$ and dissolved oxygen near the slag–metal interface. In both states, calculated P removal is confined mainly to locations where ${\mathrm{FeO}}_x$ supply, CaO availability, $P_2{O}_5$ generation, and $C_{2}S$–$C_{3}P$ fixation overlap. These observations are conditional on the reported parameters, a production mesh accompanied only by a two-grid qualitative sensitivity check, one time step, and the early transient considered here. Quantitative validation, systematic grid/time-step studies, closure-sensitivity tests, and controlled-composition simulations are required before the framework is used for process prediction. Full article

La_0.8Ce_0.2Fe_9.2Co_0.6Si_1.2/Fe bulk composites were fabricated via spark plasma sintering (SPS), and the effects of Fe powder content on the phase composition, microstructure, magnetic properties, mechanical properties, and thermal conductivity of the composites were investigated. The Fe powder content alters the α-Fe phase content in the composites. During SPS, atomic diffusion occurs between the Fe powder and the La_0.8Ce_0.2Fe_9.2Co_0.6Si_1.2 matrix, which reduces the compositional homogeneity of the desired 1:13 phase and induces the formation of thermal decomposition (TD) structures in particles adjacent to the Fe powder. As Fe powder content increases from 0 wt% to 15 wt%, the maximum magnetic entropy change ((−ΔS_M)^max) of the composites decreases from 8.11 to 5.78 J∙kg⁻¹∙K⁻¹ under 2 T. Interestingly, the α-Fe phase significantly enhances the mechanical strength and thermal conductivity (λ) of the composites. The composite with 15 wt% Fe (S15) forms a continuous α-Fe network structure and possesses the best mechanical and thermal properties: the (σ_bc)^max reaches 1463 MPa, and the λ at 300 K is 20 W·m⁻¹·K⁻¹. Owing to their balanced magnetic, mechanical, and thermal performances, the La_0.8Ce_0.2Fe_9.2Co_0.6Si_1.2/Fe composites exhibit distinctive and balanced properties, making them promising candidates for near-room-temperature magnetic refrigeration applications. Full article

In this work, a Fe-based amorphous coating (Fe₄₄Cr₁₈Mo₇Ni₄Cu₂B₂₀Si₃C₂) was fabricated via high-velocity oxygen fuel (HVOF) spraying, and the effect of annealing temperature on its microstructure, phase composition, and corrosion resistance in 3.5 wt.% NaCl solution was investigated. The as-sprayed (AS) coating exhibits an amorphous content of 85.71% and a porosity of 1.37%. Annealing at 540 °C (H540) reduces porosity to 0.98% without significant crystallization, whereas annealing at 640 °C (H640) and 740 °C (H740) triggers extensive crystallization (amorphous content drops to 24.18% and 19.20%), and porosity increases to 1.82% and 2.17%. Electrochemical tests show that corrosion resistance deteriorates progressively with increasing temperature. i_corr increases from 3.56 μA/cm² (AS) to 50.0 μA/cm² (H740), while R_p decreases from 8472 to 669 Ω·cm². EIS reveals that the AS coating is dominated by the inner barrier layer (R_b >> R_t), whereas annealing causes a drastic collapse of R_b (from 8.374 × 10⁴ to 5.011 Ω·cm²). This degradation is attributed to crystallization-induced grain boundaries and reduced effective Cr content, which impair passive film integrity and accelerate corrosion. Full article

Olivine, as (Mg, Fe)₂SiO₄ solid solution, governs the plastic flow of the Earth’s upper mantle. While extensive studies exist on natural olivine-rich rocks, the rheology of its Mg-end member, forsterite (Fo), remains less constrained, particularly for diffusion creep. Here we synthesize high-purity (≥98 vol.%), iron-free forsterite aggregates via pressureless sintering and perform axial compression experiments in a high-stress-precision Paterson gas-medium apparatus at 300 MPa, temperatures of 1423–1523 K, and differential stresses of 50–380 MPa. Our results reveal a stress exponent n = 1.0 ± 0.09, an activation energy Q = 365 ± 22.7 kJ/mol, and a grain size exponent p = 2.9 ± 0.23, demonstrating that forsterite deforms by diffusion creep under these conditions. The grain size exponent, close to the theoretical value of 3 for Coble creep, indicates that grain boundary diffusion is the rate-controlling mechanism. Compared to previous studies on forsterite and natural olivine, our flow law shows good agreement with the activation energy for olivine diffusion creep but provides a refined estimate grain size exponent. Critically, because our samples are chemically synthesized and iron-free, and lack the trace impurities that facilitate defect generation in natural olivine, they exhibit higher strength than natural Fe-bearing olivine. Our flow law therefore defines the Mg-end member for the olivine solid solution system and represents the viscosity upper bound for olivine-dominated mantle rocks deformed dominantly by diffusion creep. These findings not only fill a critical gap in the rheological data for the olivine solid solution end-members but also provide a robust basis for modeling viscosity variations in the upper mantle as functions of grain size, temperature, and iron content. Full article