Surface Chemical Composition Research Articles

Catalytic and Tribological Performances of a Novel Bi-Functional Ionic Liquid in Lubricating Ester Oil

To address the detrimental effects of the residue of catalysts on the tribological performances of ester lubricants, a novel and efficient bi-functional ionic liquid 1-(3,5-di-tert-butyl-4-hydroxybenzyl)-3-methylimidazole di(2-ethylhexyl) phosphate ([(BHT-1)MIM][DEHP]) was prepared. The catalyst not only facilitates the synthesis of pentaerythritol tetra-hexanoate (PETH) through the catalytic esterification reaction—achieving up to 96% conversion with a 94% yield—but also enhances the tribological performance of ester oil PETH when used as a lubricant additive. The tribological property has been improved remarkably: the mean friction coefficient for PETH + [(BHT-1)MIM][DEHP] is notably lower, at 0.110, compared to the PETH, which has a coefficient of 0.180. Meanwhile, the wear scar diameter of the steel ball, when lubricated with PETH + [(BHT-1)MIM][DEHP], is notably smaller than that of a steel ball lubricated solely with PETH. Especially, the reduction in the wear volume at 100 °C is up to 81.46% compared with the base oil PETH. [(BHT-1)MIM][DEHP], PETH + [(BHT-1)MIM][DEHP], and the worn track of the upper running ball and lower disc were systematically characterized by using Nuclear Magnetic Resonance (NMR) spectra, a Fourier Transform Infrared Spectrometer (FT-IR), a field emission scanning electron microscope (FESEM), Thermal gravity analysis (TG), X-ray photoelectron spectroscopy (XPS), and an optical microscope (OM). The wear mechanism of the tailored lubricant oil was discussed in terms of the chemical composition of the worn surface.

Effect of doping Mn ion on the crystal structure and cation distribution in Co1-xMnxFe2O4 compounds

In this study, we investigated the effect of Mn doping on the crystal structure and the distribution of cations at tetrahedral and octahedral sites in Co1-xMnxFe2O4 compounds (0 ≤ x ≤ 0.4), synthesized utilizing a solid phase reaction method, utilizing X-ray diffraction (XRD) and Raman spectroscopy measurements. The surface morphology and chemical composition of the compounds were studied using scanning electron microscope and X-ray energy dispersive spectroscopy. The Rietveld refinement of XRD data using the Fullprof package demonstrate that all studied samples are single phase spinels with no other detectable phases and have a cubic structure with the space group of Fd-3 m. The lattice constant and unit-cell volume increased with increased Mn doping concentration, which are attributed to the larger ionic radius of Mn in comparison with Co. Both the X-ray diffraction and Raman spectroscopy results demonstrated that doping Mn at the Co-site leads to the movement of Fe cations from the tetrahedral sites to the octahedral ones.

Characteristics of Ra-226 particles from legacy contamination and implications for radiological protection.

Radioactive particles are physically discrete sources of radioactivity that have been released into the environment as result of past accidents, incidents, and practices, and can present a hazard to members of the public. The historical use of radium in the luminising of aircraft components, and the subsequent decommissioning of those aircraft and associated waste disposal practices, has left a legacy of contamination, such as the radioactive particles containing Ra-226 at Dalgety Bay, Scotland. The aim of this research was to physically, chemically, and radiologically characterise Ra-226 particles from Dalgety Bay and consider the implications for radiological protection of the public. Physical characterisation measured particle size and shape using optical macroscopy with image analysis, measured particle mass, and calculated particle density, as well as general observations on their physical appearance. Chemical characterisation used scanning electron microscopy with energy dispersive X-ray spectroscopy to measure surface elemental composition, and gamma spectrometry was used to measure the activities of Ra-226 and its gamma-emitting daughter radionuclides. Qualitative observations on visual appearance indicated there were five distinct subpopulations, and measurements of size, shape and density varied widely. A wide range of surface chemical compositions were observed, and evidence of their estuarine origin was visible in the form of sand grains and salt deposits. Ra-226, Pb-214, Bi-214 and Pb-210 were detected in all samples with activities over several orders of magnitude and varying degrees of secular equilibrium. Two original aircraft artefacts were also included in the investigation, comparison with which showed the particles and artefacts differed in their characteristics, indicating that the source material has undergone alteration. The diversity of particle characteristics has implications for the radiological protection of the public from Ra-226 particles including pathways of exposure, assessment of radiation dose, and longevity in the environment.

Assessment of the chemical solubility of experimental and commercial lithium silicate glass-ceramics.

This study aimed to evaluate the chemical solubility (CS) and conduct a comprehensive physicochemical characterization of several experimental and commercial lithium silicate-based glass-ceramics towards an understanding of the chemical processes governing dissolution in these glass-ceramics. Glass-ceramic (GC) samples were categorized into two groups: experimental materials featuring lithium metasilicate crystals (GCE1 and GCE2); and five commercial brands relying mostly on lithium disilicate (Celtra®Duo, IPS e.max®CAD, Straumann®n!ce®, CEREC Tessera™, and VITA Suprinity®). CS was assessed by submerging samples in a 4 % acetic acid solution following ISO 6872 standards. High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) was employed to evaluate ion leaching from the residual acetic acid solution. Surface roughness and chemical composition were scrutinized using Atomic Force Microscopy (AFM) and X-Ray Photoelectron Spectroscopy (XPS), respectively. All groups met the CS standards. Kruskal-Wallis with the Dunn post-hoc test was used for CS, two-way ANOVA for roughness, and three-way ANOVA for XPS, each followed by Tukey's post-hoc test (α=0.05). AFM revealed no significant alteration in surface roughness post-immersion for the majority of the groups, except for IPS e.max®CAD (p < 0.001). XPS detected compositional changes in all GCs following CS testing. HR-ICP-MS indicated a higher leaching of Li+ ions (as expected) across all groups. This study supports the understanding of the chemical processes that govern the dissolution of glass-ceramics and evaluate how different formulations influenced the CS and elemental composition. In this sense, the GCE2 group exhibited the most favorable properties for dental applications, mirroring the performance of the main commercial materials.

Photocatalytic degradation of tetracycline antibiotics and elimination of N-nitrosodimethylamine formation potential by BiOCl/ZnIn2S4 heterostructure under visible-light irradiation.

Photocatalysis is an effective method for removing tetracycline antibiotics, which are important precursors to the potential carcinogen N-nitrosodimethylamine (NDMA). Herein, a BiOCl/ZnIn2S4 heterojunction was successfully synthesized using a simple hydrothermal method. This heterojunction was applied for the first time to degrade various tetracycline antibiotics and reduce NDMA formation potential (NDMA-FP) under visible-light irradiation. Characterization of surface morphology, crystal structure, chemical composition and photoelectrochemical properties revealed that the BiOCl/ZnIn2S4 heterojunction significantly improved light absorption, charge transport and carrier separation efficiency, thereby enhancing photocatalytic performance. The BiOCl/ZnIn2S4 catalyst achieved high degradation efficiencies of 88.0%, 90.7%, 88.7% and 91.7% for tetracycline, minocycline, chlortetracycline and doxycycline, respectively, within 60min of visible-light irradiation. Additionally, it exhibited the lowest NDMA-FP values of 1.5%, 3%, 0.9% and 1.4%, respectively. Radical trapping studies and EPR experiments identified •O2- and •OH radicals as the primary reactive species involved in the photocatalytic process. Analysis of the degradation intermediates and structure-activity relationships indicated that the variations in NDMA-FP were closely associated with the number of dimethylamine groups in the antibiotics and the stability of the resulting carbocations. Notably, the BiOCl/ZnIn2S4 catalyst presented satisfactory stability and positive tetracycline degradation in real antibiotic wastewater. Incorporating BiOCl/ZnIn2S4-loaded nonwoven fabric into a continuous-flow reactor efficiently degraded tetracycline in real wastewater under visible light. This work provides new insights on developing Z-scheme photocatalysts for the simultaneous degradation of various antibiotics and highlights their potential as commercially viable photocatalytic system.

Experimental and ANN based process optimization for bioremediation of Cr6+ and Cd2+ by green adsorbent prepared from Artocarpus Heterophyllus leaves

The effective removal of toxic pollutants from water and waste water, is a challenging issue for environmental protection. In the present work, the performance of Artocarpus Heterophyllus (jackfruit) leaves have been examined for reduction of toxic Cr (VI) and Cd (II) from synthetic wastewater. Characterization of the adsorbent was made to evaluate the surface morphology and chemical composition, by Scanning Electron Micrograph (SEM) and Energy Dispersive Spectroscopy (EDS). Characteristic surface groups [Fourier Transform Infra-Red (FTIR)], surface area and surface structure [Brunauer–Emmett–Teller, (BET)] were also determined. The influences of various factors which control the removal process were studied experimentally in batch method and optimized. High removal efficiency was obtained at pH ≤ 2 for Cr (VI); and for Cd (II) it was ≥ 6. The experimental data were tested using different kinetic and isotherm models. Artocarpus Heterophyllus leaf was found suitable to remove 99.7 % Cr (VI) and 98.4 % Cd (II) from a strength of 20 mg L-1 solution at 0.5 g L-1 adsorbent concentration, at their respective favorable pHs. The reaction followed pseudo second order kinetic model for both the cases. The calculated sorption energy of 16.16 and 12.68 kJ mol-1, suggested chemical nature for both the cases. Desorption studies showed the effective reuse of Artocarpus Heterophyllus leaf for three times. The relatively high equilibrium adsorption capacity of 32.29 and 20.37 mg g-1 for Cr (VI) and Cd (II) respectively, suggested use of Artocarpus Heterophyllus leaf as a reasonably good green bio-adsorbent. The modeling of the complex adsorption process based on artificial neural network approach exhibited reliability and high degree of proficiency (R values of 0.999) in the model’s prediction and experimental data indicated its applicability in forecasting removal efficiency for both the metal ions.

Deep eutectic solvent-assisted carbon quantum dots from biomass Triticum aestivum: A fluorescent sensor for nanomolar detection of dual analytes mercury (Ⅱ) and glutathione.

Deep eutectic solvents (DESs) have attracted significant attention in recent years due to its environment friendly characteristics and its participation in the multi-heteroatom doping of carbon quantum dots (CQDs). In this work, we present a simple, fast, and environment-friendly microwave synthesis approach for the synthesis of DES-assisted nitrogen and chloride co-doped CQDs (N,Cl-CQDs) using a choline chloride-urea based DES. A biomass-based precursor, i.e., wheatgrass (Triticum aestivum), has been used as a carbon source. Transmission electron microscopy (TEM) showed the spherical shape with average 1.75nm particle diameter of prepared CQDs. The surface functionality and chemical composition of prepared N,Cl-CQDs were determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopic techniques. The N,Cl-CQDs obtained a high quantum yield (QY), i.e., 36%, compared to undoped CQDs, which were synthesized in an aqueous medium (QY=15%). The prepared N,Cl-CQDs showed significant properties such as excellent photostability, favorable water solubility, and high optical stability. N,Cl-CQDs were used as sensing platform for the detection of Hg2+ ions and GSH with LOD value of 39nM and 43nM, respectively. The fluorescence quenching mechanism was confirmed by several photophysical parameters, such as average lifetime values, radiative rate constant (k r ), non-radiative rate constant (knr) and others. Furthermore, the current sensing system's viability is also tested in a river water sample for the detection of Hg2+. The N,Cl-CQDs prepared in this study exhibited a reduced detection limit and a broad linear range by an easy, environmentally friendly, and rapid method for detecting GSH and Hg2+ ions.

Morphological and surface chemical composition disorder induced efficient oxygen evolution and supercapacitor processes into Co3O4 nanostructures

Morphological and surface chemical composition disorder induced efficient oxygen evolution and supercapacitor processes into Co3O4 nanostructures

Moringa oleifera leaves extract-mediated synthesis of ZnO nanostructures for the enhanced photocatalytic oxidation of erythrosine.

This study was focused on the development of ZnO nanostructures for the efficient oxidation of erythrosine dye and for studying the antibacterial activity of ZnO. It was observed that the phytochemicals from Moringa oleifera leaves modified the size, shape, crystalline properties and surface chemical composition of the ZnO nanostructures. ZnO nanostructures synthesized with 15 mL Moringa oleifera leaves extract (S-15) demonstrated highly efficient oxidation of erythrosine dye under the illumination of natural sunlight. Various photocatalyst evaluation parameters, such as initial dye concentration, pH of the dye solution, catalyst dose and cycling stability, were studied. The S-15 sample of ZnO exhibited almost 100% dye removal in an alkaline pH of 12 and a low concentration of 4.54 × 10-5 M. Furthermore, improved antibacterial activity was also observed against E. coli and Bacillus subtilis bacteria strains. The use of Moringa oleifera leaves extract could be considered a low-cost, facile and ecofriendly green synthesis protocol for replacing the use of toxic chemicals and for eliminating the risk of releasing of toxic chemicals into the environment during the synthesis of high-performance nanostructured materials.

Atmospheric pressure plasma jet deposition of TiO2 layer on alumina/epoxy to improve electrical properties

In gas-insulated lines, basin-insulators can accumulate charge under non-uniform electric fields, distorting the field distribution and potentially causing surface flashover, which threatens the stability of power systems. In this study, Atmospheric Pressure Plasma Jet (APPJ) technology was used to deposit TiO2 on the surface of alumina/epoxy (Al2O3/EP) composites. The impact of deposition of TiO2 layer on the surface morphology and chemical composition of Al2O3/EP was studied using testing methods such as Scanning Electron Microscope, X-ray photoelectron spectroscopy, Fourier Transform Infrared Spectrometer, and Energy Dispersive Spectrometer. It was found that APPJ creates a dense, rough Ti-O layer on the Al2O3/EP surface, which bonds tightly with the substrate. The efficacy of APPJ was found to depend on processing time, with optimal results observed at 3 min, DC and AC flashover voltages increased by 29.6% and 15.7%, respectively. TiO2 layer enhances the conductivity of the resin and shallows trap levels. Through the synergistic effects of various factors, surface charges are efficiently dissipated and evenly distributed. This study not only reveals the physicochemical process of TiO2 deposition via APPJ but also integrates surface characteristics with electrical performance. The findings offer a new strategy to enhance surface flashover voltage and ensure equipment safety.

Surface Hydrophilic Modification of Polypropylene by Nanosecond Pulsed Ar/O2 Dielectric Barrier Discharge.

Polypropylene (PP) membranes have found diverse applications, such as in wastewater treatment, lithium-ion batteries, and pharmaceuticals, due to their low cost, excellent mechanical properties, thermal stability, and chemical resistance. However, the intrinsic hydrophobicity of PP materials leads to membrane fouling and filtration flux reduction, which greatly hinders the applications of PP membranes. Dielectric barrier discharge (DBD) is an effective technique for surface modification of materials because it generates a large area of low-temperature plasma at atmospheric pressure. In this study, O2 was added to nanosecond pulsed Ar DBD to increase its reactivity. Electrical and optical diagnostic techniques were used to study the discharge characteristics of the DBD at varying O2 contents. The uniformity of the discharge was quantitatively analyzed using the observed discharge images. Water contact angle measurements were used to assess the surface hydrophilicity of polypropylene. The surface morphology and chemical composition of the PP materials before and after treatment were analyzed using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results show that the moderate addition of O2 enhances surface hydrophilicity and the uniformity of the modification. By increasing the O2 addition from 0% to 0.1%, the average power increased from 4.19 W to 5.79 W, and the energy efficiency increased from 17.78% to 21.51%. The water contact angle of the DBD-treated PP showed a tendency to decrease and then increase with increasing O2 content, with the optimum O2 addition determined to be 0.1%. Under this condition, the water contact angle of the PP surface decreased by 31.88°, which is 52.31% lower than the untreated surface. O2 increases the number of oxygen-containing polar groups (-OH, C=O, and O-C=O) on the surface of the material, and deepens and densifies the grooves on the surface of the PP material, resulting in an increase in the hydrophilicity of the PP surface.

Ultrathin ALD Coatings of Zr and V Oxides on Anodic TiO2 Nanotube Layers: Comparison of the Osteoblast Cell Growth.

The current study investigates and compares the biological effects of ultrathin conformal coatings of zirconium dioxide (ZrO2) and vanadium pentoxide (V2O5) on osteoblastic MG-63 cells grown on TiO2 nanotube layers (TNTs). Coatings were achieved by the atomic layer deposition (ALD) technique. TNTs with average tube diameters of 15, 30, and 100 nm were fabricated on Ti substrates (via electrochemical anodization) and were used as primary substrates for the study. The MG-63 cell growth and proliferation after 48 h of incubation on hybrid TNTs/ZrO2 and TNTs/V2O5 surfaces was evaluated in comparison to the uncoated TNTs of each diameter. The density of viable MG-63 cells was assessed for all the TNT surfaces, along with the cell morphology and the spreading behavior (i.e., the cell length). The ultrathin coatings retained the original morphology of the TNTs but changed the surface chemical composition, wettability, and cell behavior, whose interplay is the subject of the present investigation. These findings offer interesting views on the influence of the composition of biomedical implant surfaces, triggered by ALD ultrathin coatings on them. The outcomes of this work shed light on the assessment of the biocompatibility of the two different ALD coatings.

THE IMPACT OF VARIOUS WHITENING AGENTS ON THE TRACE ELEMENT COMPOSITION OF DENTAL HARD TISSUES

Intorduction. Discoloration of teeth is a common aesthetic concern affecting various segments of the population and individuals of all ages. According to current literature, 74% of respondents believe that an unattractive smile negatively impacts their career, while 92% think it influences success in their personal lives. Modern dentistry offers numerous whitening methods to address tooth discoloration, with professional clinical bleaching being one of the most commonly performed procedures. Despite the variety of available techniques and the continuous emergence of new advancements in recent years, the issue of selecting the most effective and safe whitening agents remains a pressing concern. The purpose of this study was to clinically and experimentally substantiate the selection of optimal teeth whitening methods and to assess their effectiveness. This evaluation was based on experimental analyses of the chemical composition of dental hard tissues, as well as clinical and laboratory research methodologies. To achieve this purpose, the study outlined the following objectives: Identify changes in the chemical composition of tooth enamel in experimental settings after the application of various professional whitening systems and protocols. Evaluate the long-term effects of whitening agents on the chemical composition and structural integrity of dental hard tissues. Methods. Experimental and statistical research methods were utilized to achieve these objectives, including microscopic analysis of the morphological and chemical composition of enamel using a high-resolution Mira LM electron microscope. For the experimental groups, bleaching systems containing 35% hydrogen peroxide and 44% carbamide peroxide were used to analyze their effects on enamel composition. Results and Conclusions. The study compared the chemical composition of enamel surfaces following professional hygiene procedures and the use of carbamide peroxide and hydrogen peroxide as active components in clinical teeth whitening systems. The findings demonstrated that changes in enamel composition significantly influence various oral parameters, including the composition of the oral fluid, the activity of salivary glands, and the functional and structural resilience of dental hard tissues. Experimental results revealed notable deviations in the basic elements of enamel. These findings underscore the importance of selecting whitening agents based on clinical and laboratory tests. Moreover, the use of remineralizing agents with specific chemical formulations tailored to the chosen whitening components is essential to mitigate potential adverse effects and preserve enamel integrity.

Prediction of Olivine Composition Under Limited Calibration Inputs: Comparative Study of Mid-Infrared Reflection, Raman Scattering, and Laser-Induced Plasma Spectroscopies.

In situ optical analytical spectroscopies offer great geochemical insights due to their capability to resolve the chemical composition of regolith surfaces of rocky celestial bodies. The use of suitable calibration targets improves the precision of mineral determination, which is of critical importance for short-living, low-mobility landers, and enables, in special cases, determination of elemental composition. We investigate the capabilities of three space-relevant optical analytical techniques used for in situ mineralogical analysis, i.e., mid-infrared reflection, Raman light scattering, and laser-induced plasma spectroscopies, to predict the chemical composition of olivine under a limited calibration input, namely using two bulk samples of natural olivine, chemically close to the end-members of the mineral group. We determine the accuracy of the forsterite numbers obtained with each technique and discuss the choice of calibration methods applicable to limited in situ calibration input, which are summarized in recommendations for space instrumentation.

Discolouration and Chemical Changes of Beech Wood After CO2 Laser Engraving

This study evaluated the influence of infrared laser radiation produced by a CO2 laser, performing under different engraving parameters, on the colour changes and chemical composition of a beech wood surface. The results showed that the lightness clearly decreased with increasing laser power and density. At the highest laser power and the highest raster density, the ΔL* value was 51.3. The values of coordinates a* and b* moderately increased up to a raster density of 5 mm−1; then, with a subsequent raster density increase, the values of these coordinates decreased again. However, the coordinate values were positive in all cases. Even the lowest laser power and raster density resulted in conspicuous discolouration or even a completely new colour compared to the original (ΔE = 10) of the beech wood surface. Further increases in the laser power and raster density resulted in progressively pronounced colour differences and a darker brown colour of the surface. The ATR-FTIR chemical analysis of the beech wood surface revealed that discolouration was mainly caused by heat-induced processes associated with the degradation of carbonyl groups (C=O) in lignin and hemicelluloses. The splitting of C=O bonds induced changes in the content of chromophores responsible for the natural wood colour and for the engraving-related discolouration. The study demonstrates that the amount of energy supplied onto the wood surface by a laser beam using diverse combinations of radiation parameters can be represented by a single variable: the total irradiation dose. The functional relation detected between this variable and the colour differences may serve as a basis for using a controlled laser beam for targeted wood surface discolouration to improve the quality of patterns transferred onto a wood surface. Knowledge of this relation will enable the targeted setting of the laser parameters during engraving so that the laser beam can be used as a tool for transferring high-quality patterns onto wood surfaces.

Corrosion Rate of ASTM A53 Steel in Seawater Influenced by Variation in Concentration of Mangifera Indica L. Peel Extract

This study investigates the effectiveness of mango peel extract as a corrosion inhibitor for ASTM A53 steel, which is widely used in the oil and gas industry. The research aims to evaluate how different concentrations of mango peel extract can mitigate corrosion in seawater from Pangandaran, thereby extending the lifespan of steel components in marine environments. Corrosion tests were conducted through immersion experiments over durations of 1, 4, 9, 16, and 25 days with mango peel extract concentrations of 0 ppm, 20 ppm, 40 ppm, 60 ppm, and 80 ppm. Analytical methods including X-ray diffraction (XRD), Optical Microscopy (OM), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM) were used to examine the steel's surface morphology and chemical composition. The results demonstrate that mango peel extract significantly reduces the corrosion rate of ASTM A53 steel, with the highest efficiency achieved at 40 ppm (58.15%) and a notable reduction at 60 ppm (56.4%). The inhibition is attributed to chemical absorption, which lowers the steel's corrosion potential. These findings suggest that mango peel extract is an effective, eco-friendly corrosion inhibitor, offering practical and theoretical benefits for corrosion management. This research supports the use of bio-based inhibitors and may inform future industrial corrosion protection strategies.

Assessing the processes behind planet engulfment and its imprints

Newly formed stars are surrounded by a protoplanetary disc composed of gas and dust, part of which ends up forming planets. During the system's evolution, some of the planetary material may end up falling into the host star and being engulfed by it, leading to potential variation in the stellar composition. The present study explores how planet engulfment may impact the chemical composition of the stellar surface and discusses what the rate of events with an observable imprint would be for Sun-like stars. We used data on the formation and evolution of 1000 planetary systems from the New Generation Planetary Population Synthesis (NGPPS) calculations by the Generation III Bern model to analyse the conditions under which planet engulfment may occur. Additionally, we used stellar models computed with Cesam2k20 (Code d’Evolution Stellaire Adaptatif et Modulaire) to account for how the stellar internal structure and its processes may affect the dilution of the signal caused by planet engulfment. Our results show that there are three different phases associated with different mechanisms under which engulfment events may happen. Moreover, systems that undergo planet engulfment are more likely to come from protoplanetary discs that are more massive and more metal-rich than non-engulfing systems. Engulfment events leading to an observable signal happen after the dissipation of the protoplanetary disc when the convective envelope of the stars becomes thinner. With the stellar convective layer shrinking as the star evolves in the main sequence, they display a higher variation of chemical composition. This variation also correlates with the amount of engulfed material. By accounting for the physical processes happening in the stellar interior and in the optimistic case of being able to detect variations above 0.02 dex in the stellar composition, we find an engulfment rate no higher than $20&lt;!PCT!&gt;$ for Sun-like stars that may reveal detectable traces of planet engulfment. Engulfment events that lead to observable variation in the stellar composition are rare due to the specific conditions required to result in such signatures.

Nanoindentation behavior of the laser-repaired CoCrFeNiV high-entropy alloy

High-entropy alloys (HEAs) are solid-solution alloys composed of multiple elements, exhibiting excellent mechanical properties. The unique plastic deformation mechanism induced by their specific solid solution structures has attracted considerable attention but remains incompletely understood, particularly at the micro-scale. In this study, the surface morphology, chemical composition, and microstructures of CoCrFeNiV HEA before and after laser remelting repair were investigated. Nanoindentation testing was employed to characterize the surface hardness and creep behavior of the repaired surface. The distribution of surface hardness before and after laser remelting, as well as the indentation creep behavior under different loads, were studied. The mechanism of indentation creep on the repaired surface was discussed and analyzed. The effect of microstructures of HEAs, including precipitated phases and sub-grain boundaries, on dislocation-dominated micro-scale plastic deformation was elucidated by the transmission electron microscope (TEM). This study contributes to an in-depth understanding of the creep behavior and micro-scale deformation mechanisms in HEAs.

Effect of vacuum heat treatment temperature on anti-corrosion and conductivity properties of C/TiC nanocomposite coated titanium foil for PEMFC bipolar plates

In this work, a C/TiC nanocomposite coating was prepared on titanium foil using a combination of magnetron sputtering and heat treatment technology to improve the corrosion resistance and conductivity of bipolar plates. The effect of heat treatment temperature on surface morphology, chemical composition, mechanical property, hydrophobicity, corrosion resistance and conductivity of coated samples was investigated. The results indicate that the roughness of the coating increase with heat-treated temperature and the corrosion current density (icorr) firstly decreases and then increases in 0.5 M H2SO4 solution containing 5 ppm HF at 80 ℃, reducing its smallest value at 700 ℃ (1.28 μA cm−2), which is declined by 3 orders of magnitude compared to the substrate (562.90 μA cm−2). After potentiostatic polarization experiment (PP) for 12 h, the polarization current density (ipp) of the coatings firstly reduces and then increases, with values of 1.48, 0.70, 0.36, 0.41, 1.32 and 1.35 μA cm−2 corresponding to the substrate and coated samples, respectively. Furthermore, the interface contact resistance (ICR) of coated samples firstly decreases and then increase with temperature rising, which are less than 10 mΩ cm2. After 12 h PP tests, the ICR increase, with values of 18.42, 26.28, 13.64, 10.26 and 11.56 mΩ cm2 corresponding to RT, 600 700 800 and 900 ℃, respectively. The water contact angle of the coated sample for 600 and 700 ℃ are higher than that of other samples and they reached 87.6°and 85.3°, exhibiting a good hydrophobicity.

Autonomous Detection of Mineral Phases in a Rock Sample Using a Space-prototype LIMS Instrument and Unsupervised Machine Learning

In situ mineralogical and chemical analyses of rock samples using a space-prototype laser ablation ionization mass spectrometer along with unsupervised machine learning are powerful tools for the study of surface samples on planetary bodies. This potential is demonstrated through the examination of a thin section of a terrestrial rock sample in the laboratory. Autonomous isolation of mineral phases within the acquired mass spectrometric data is achieved with two dimensionality reduction techniques: uniform manifold approximation and projection (UMAP) and density-preserving variation of UMAP (densMAP), and the density-based clustering algorithm Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN). Both densMAP and UMAP yield comparable outcomes, successfully isolating the major mineral phases fluorapatite, calcite, and forsterite in the studied rock sample. Notably, densMAP reveals additional insights into the composition of the sample through outlier detection, uncovering signals from the trace minerals pyrite, rutile, baddeleyite, and uranothorianite. Through a grid search, the stability of the methods over a broad model parameter space is confirmed, revealing a correlation between the level of data preprocessing and the resulting clustering quality. Consequently, these methods represent effective strategies for data reduction, highlighting their potential application on board spacecraft to obtain direct and quantitative information on the chemical composition and mineralogy of planetary surfaces and to optimize mission returns through the unsupervised selection of valuable data.