Amorphous Phase Research Articles

Mix and measure II: joint high-energy laboratory powder diffraction and microtomography for cement hydration studies.

Portland cements (PCs) and cement blends are multiphase materials of different fineness, and quantitatively analysing their hydration pathways is very challenging. The dissolution (hydration) of the initial crystalline and amorphous phases must be determined, as well as the formation of labile (such as ettringite), reactive (such as portlandite) and amorphous (such as calcium silicate hydrate gel) components. The microstructural changes with hydration time must also be mapped out. To address this robustly and accurately, an innovative approach is being developed based on in situ measurements of pastes without any sample conditioning. Data are sequentially acquired by Mo Kα1 laboratory X-ray powder diffraction (LXRPD) and microtomography (µCT), where the same volume is scanned with time to reduce variability. Wide capillaries (2 mm in diameter) are key to avoid artefacts, e.g. self-desiccation, and to have excellent particle averaging. This methodology is tested in three cement paste samples: (i) a commercial PC 52.5 R, (ii) a blend of 80 wt% of this PC and 20 wt% quartz, to simulate an addition of supplementary cementitious materials, and (iii) a blend of 80 wt% PC and 20 wt% limestone, to simulate a limestone Portland cement. LXRPD data are acquired at 3 h and 1, 3, 7 and 28 days, and µCT data are collected at 12 h and 1, 3, 7 and 28 days. Later age data can also be easily acquired. In this methodology, the amounts of the crystalline phases are directly obtained from Rietveld analysis and the amorphous phase contents are obtained from mass-balance calculations. From the µCT study, and within the attained spatial resolution, three components (porosity, hydrated products and unhydrated cement particles) are determined. The analyses quantitatively demonstrate the filler effect of quartz and limestone in the hydration of alite and the calcium aluminate phases. Further hydration details are discussed.

Simultaneous determination of the phase boundary thermal resistance and thermal conductivity in phase-separated TiO2 thin films

Phase boundaries, most often between crystalline and amorphous phases of a material, are ubiquitous lattice imperfections in thin films, particularly deposited by low temperature processes such as atomic layer deposition (ALD). Thermal resistances from these boundaries may impede phonon transport and reduce thermal conductivity. However, to date, there have been no reports on the direct measurement of the phase boundary thermal resistance, due in part to challenges associated with fabricating an atomically flat yet geometrically planar interface between different phases within a film. Here, we present a systematic study to simultaneously determine the phase boundary thermal resistance and thermal conductivity in a series of phase-separated titanium oxide (TiO2) thin films prepared via plasma-enhanced ALD (PEALD). A precise implementation of per-cycle plasma treatment enables extremely localized crystallization—i.e., plasma-assisted atomic layer annealing (ALA)—and the fabrication of crystalline/amorphous layered structures with their respective thicknesses systematically varied. Frequency-domain thermoreflectance measures the effective thermal conductivity of each film and its top and bottom interfaces, confirmed independently using time-domain thermoreflectance. We simultaneously solve a system of linear equations generated by applying a series resistor model to each film, yielding the phase boundary thermal resistance of 5.1 m2 K GW–1 between crystalline and amorphous TiO2, as well as the thermal conductivities of 5.1 and 2.1 W m–1 K–1 for crystalline and amorphous TiO2, respectively. The results suggest that the crystalline/amorphous phase boundary acts like a layer of crystalline (amorphous) TiO2 with equivalent thickness ∼26 (∼11) nm.

Capacitive attribute of vanadium-oxide embedded activated charcoal composite

This paper reports the study of hydrothermally synthesized coconut charcoal (EDL material) and vanadium-oxide (pseudocapacitive material) based composite material. SEM and TEM studies reveal the formation of embedded V2O5 nanorods (NRs) in the presence of activated charcoal (AC). Whereas, the formation of nanosheet (NSs) morphology of V2O5 was explained based on Ostwald ripening. Embedded V2O5 nanorods (NRs) in AC could be revealed in the form of the blurred dotted electron diffraction pattern of CS-AC/V2O5 NRs, indicating the presence of crystalline and amorphous phases at a point simultaneously in the composite. The VO, O–V‒O signatures observed in RAMAN and FTIR studies indicate the presence of the α phase of V2O5 NSs and NRs. An enhanced diffusion coefficient for CS-AC/V2O5 NRs compared to V2O5 NSs was observed; a decreased total resistance for CS-AC/V2O5 NRs compared to CS-AC was also noted. A characteristic of stable specific capacitance was observed at various current levels of this composite compared to the specific capacitances of coconut shell-based charcoal and vanadium oxide.

Influence of Mn precursor on pre-pyrolysis modification of sugarcane bagasse biochar for enhanced removal of 2,4-dichlorophenoxyacetic acid from aqueous solutions: Experimental and theoretical insights

Biochars impregnated with Mn oxides were produced using sugarcane bagasse (SB) modified with MnCl2 (Mn(II)-BC) or KMnO4 (Mn(VII)-BC) for the removal of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) through adsorption. The composites were structurally and functionally characterized by various techniques, revealing an irregular surface with oxide microspheres. Elemental analyses showed the presence of manganese and oxygen in distinct proportions. X-ray diffraction identified crystalline planes of MnO and Mn3O4, as well as the amorphous carbon phase. Infrared spectroscopy confirmed Mn bonded to oxygen, and its influence on BC graphitization was corroborated by Raman spectroscopy. Thermogravimetry highlighted the oxides' influence on thermal stability, while the total number of acidic and basic functions revealed notable differences in surface chemistry. Adsorptive removal of 2,4-D was optimized under conditions of pH 2.00, dosage of 2 g L−1, and particle size smaller than 100 mesh. Adsorption equilibrium was attained after 24 and 12 hours for Mn(II)-BC and Mn(VII)-BC, respectively, with experimental maximum capacities of 36.78 and 57.19 mg g−1. Freundlich and Sips isotherms fit better for Mn(II)-BC and Mn(VII)-BC, respectively, while Elovich and pseudo-second-order kinetic models were suitable. Density Functional Theory (DFT) calculations confirm that, with decreasing pH, hydrogen bonding takes place. At higher pH,binding with Mn3O4 suggests efficacy in Mn(II)-BC composite adsorption, not observed in Mn(VII)-BC due to an additional oxide, differentiating available sites. Despite Mn leaching challenges, post-acid exposure reuse showed favorable removal percentages, indicating potential for reutilization. These findings confirm the suitability of the synthesized composites as adsorbents for the remediation of water contaminated with 2,4-D.

Evaluation of in-plane and out-of-plane crystallinities with residual amorphous phases for MgB2 superconductor

We focus on in-plane and out-of-plane crystallinities of the MgB2 superconductor. These two structural properties were evaluated in terms of peak broadening at lower angles in the X-ray diffraction. The angular behavior of the in-plane and out-of-plane peaks was used to compare it with the corresponding behavior estimated in the case of several crystallite sizes (that affect the in-field superconductivity of MgB2). We propose that this comparison allows a simple evaluation to provide insight into the individual influences of in-plane and out-of-plane crystallinities on the in-field critical current density (without needing to calculate numerical values of crystallite sizes and lattice strains of fabricated MgB2 materials). For this study, we used MgB2 samples sintered at different temperatures. The sintering conditions affected not only the crystallinities but also the phase compositions. The behavior of the compositions, including amorphous phases, was also evaluated by using a quantitative analysis for X-ray diffraction results.

What kind of corrosion products are “black spots”? —Effects of reduced sulfur compounds on corrosion of bronze artefacts

While deterioration due to the generation of “black spots” is reported, consensus on the specific corrosion products comprising black spots and underlying deterioration mechanisms is lacking. This study investigated the deterioration of copper objects by analysing the black spots that appeared on them and proposes environmental conditions to suppress the appearance of black spots. Bronze artefacts excavated from a marine archaeological site, on which black spots were generated, were closely observed, and investigated. First, X-ray fluorescence and micro-X-ray diffraction analyses were performed on a bronze artefact, from which the black spots were removed, to determine the composition of the artefact. Second, to investigate the composition of the black spots, fine structure analysis of the black spots on the fine fragments of the bronze artefacts was conducted using scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy, and electron diffraction (ED) analysis. The results indicate that the black spots were partially composed of metallic copper and a fine particle mixture of Cu2S and CuSO4. These results imply that the transformation of copper sulfide to metallic copper may have played an important role in the initiation and propagation of black spots. In this study, ED analysis was performed on the microscopic area of the black spots; no amorphous phases were detected, and all observed phases were identified as crystalline materials. To determine the sources of gas-phase sulfur compounds that cause black spots, H2S and carbonyl sulfide (COS) emissions from a spherical clay artefact (a cannon ball with gunpowder excavated from an underwater archaeological site) which was exhibited in the same showcase with the bronze artefacts were analysed via gas chromatography. The concentrations of H2S and COS were 0.462 and 8.636 ppb, respectively; these are significantly higher than those in the lower troposphere. These results indicate that deterioration by black spots occurred because of H2S and COS, which were emitted from the spherical clay artefact excavated from an underwater archaeological site in the exhibition case. In addition, it was confirmed that the inclusion of deoxygenating and dehumidifying agents (RP-AN) in the plastic bag in which the spherical clay artefact was inserted resulted in a significant decrease in the concentration of H2S and COS.

Determination of Reflectance Spectra and Colorimetry of Titanium and Tungsten Oxides Obtained by Microwave-assisted Hydrothermal Synthesis

Sustainability has driven the use of heterogeneous photocatalysis as one of the primary methods for environmental decontamination, reduction, degradation, remediation, or transformation of polluting chemical residues and purification treatment of effluents and wastewater. TiO<sub>2</sub> is the most commonly used semiconductor in heterogeneous photocatalysis. It acquires relevance, as it has favorable properties, such as non-toxicity, stability in a wide range of pH, economic viability, etc., which encourage its application as a semiconductor in photocatalytic processes. However, the photocatalytic capabilities of TiO<sub>2</sub> are only active in 3% of the solar spectrum, which limits its range of use. For this reason, some semiconductor metal oxides were incorporated into TiO<sub>2</sub> to increase its activation range in the UV-visible spectrum. Within this context, WO<sub>3</sub> is a metallic oxide widely used in mixtures with TiO<sub>2</sub>, aiming to improve its photocatalytic properties. Thus, this work synthesized TiO<sub>2</sub> and TiO<sub>2</sub> nanostructures mixed with two tungsten precursors (H<sub>2</sub>WO<sub>4</sub> and Na<sub>2</sub>WO<sub>4</sub>.2H<sub>2</sub>O) using a microwave-assisted hydrothermal route at 200°C for 120 minutes. The samples obtained were characterized by mL of a 20 ppm solution of methyl orange dye. The results show that it was possible to successfully produce TiO<sub>2</sub> and TiO<sub>2</sub> nanostructures containing tungsten precursors via a microwave-assisted hydrothermal route. This can be attributed to the fact that the energy associated with this temperature was sufficient to convert most of the precursors into crystalline products and little amorphous phase is present.

Polyamorphism gets a magnetic boost

Four decades since the concept of polyamorphism was introduced by [L. S. Palatnik (1909–1994), Fiz. Nizk. Temp. 25, 400 (1909)], numerous investigations proved its presence in a broad variety of nonmagnetic short-range ordered materials, like structural, metallic, a-metallic, inorganic molecule, orientational, electron glasses, water, ice, carbons, and others. It was manifested by phase transitions between amorphous states as a function of the quench condition and under compression, mediated by long-wave fluctuations of an order parameter. There has been much recent discussion given to the phenomenon of polyamorphism where distinct, different states of amorphous liquids and solids are observed as a function of density. The outstanding contribution of the recently late [A. Sella, et al. (1956–2022), Nat. Mater. 21, 490 (2022)],2 in the field should be recognized here. Underlying this phenomenon is the possibility of a first-order liquid-liquid phase transition driven by the density and entropy differences between the two amorphous phases. Magnetic boost of multilayer graphene under pressure was also recently discovered. Their famous spin counterparts, such as spin liquid, spin ice, and spin glass have been less studied at this end despite numerous similarities, registered so far. Taking that in mind, for further polyamorphism platform development, we demonstrate the signatures of phase transition in spin glass, driven by a magnetic field, and eventually, a novel type of polyamorphism, the spin-glass one.

Flexible CNT-based composite films with amorphous SiBCN-inhibited ultrafine SiC grains for high-temperature electromagnetic shielding

Lightweight, flexible and highly conductive electromagnetic interference (EMI) shielding materials are of great importance for protecting flexible electronics and telecommunication devices under extremely high temperature conditions. A potential solution is to incorporate ceramic phases with highly conductive flexible carbon nanotube films to improve their thermal stability. However, the grain size of the ceramic phase generally increased significantly as the temperature increased which led to brittleness. In this work, a highly flexible carbon nanotube (CNT) film with controllable ceramic nanocrystals was prepared by precursor infiltration and pyrolysis. The silicon carbide (SiC) grain size in the nanocomposites was inhibited by the spatial confinement effects of CNT networks and a second amorphous SiBCN phase. The SiC grain size in the composite film decreased with the increase of the SiBCN content and the elongation at break of the nanocomposites improved significantly by 45 %. Moreover, the initial thermogravimetric temperature of the prepared films has been significantly improved to exceed 600 °C compared to the raw CNT film. Importantly, the nanocomposite film exhibited an average EMI shielding effectiveness of ∼40 dB from 8.2 to 12.4 GHz. Benefiting from the ultrafine grain size, the nanocomposite films could be folded and extended without micro-cracks over 1000 times. Combining the performance and mechanical properties of the nanocomposite film, this approach provides important guidance for designing high-performance CNT-based electromagnetic shielding materials with superior flexibility at elevated temperatures.

Enhanced tribological behavior and corrosion resistance in AlSiC-based coatings through varied carbon content

A series of AlSiC-based nanocomposite coatings with varying carbon concentrations were fabricated by filtered cathodic vacuum arc (FCVA) technology. These coatings featured an amorphous matrix with embedded Al4Si3C6 nanocrystals. With the increase in carbon content, the proportion of amorphous structure within the structure grew, which was accompanied by a rise in sp3 hybridized carbon bonds. This compositional change led to a significant enhancement in hardness and toughness. Notably, the AlSiC coating deposited at a flow rate of 50 sccm displayed exceptional mechanical properties, including a high hardness of approximately 23.2 GPa, toughness indices of H/E = 0.096 and H3/E2 = 0.216 GPa, a low friction coefficient around 0.18, a wear rate as low as ∼1.09 × 10−5 mm3 N−1 m−1, and a corrosion current density of approximately 1.08 × 10−9 A/cm2. The coating's superior tribological characteristics and corrosion resistance can be attributed to two main factors. The enhanced hardness and toughness indices (H/E and H3/E2) contributed to its improved deformability, which is essential for wear resistance. Secondly, the presence of a graphite layer formed during friction provided self-lubrication, further reducing wear. Additionally, the chemical inertness of both the amorphous SiC and the amorphous carbon phases within the nanocomposite structure significantly bolstered the coating's resistance to corrosion. The AlSiC nanocomposite coatings deposited by FCVA exhibit outstanding mechanical properties, tribological performance, and corrosion resistance, making them highly suitable for applications in environments where wear and corrosion are significant concerns.

Gamma irradiated Er3+ ions doped Li2O–BaO–B2O3–P2O5 glasses: Structural, optical, and thermoluminescence glow curve analysis

Lithium barium borophosphate glasses doped with Er3+ rare earth ions are reported in terms of their physical, optical, structural, and thermoluminescence (TL) properties in this study. The melt quenching method was used to synthesize the glasses with varying concentration of the dopant (0.0, 0.2, 0.4 0.6, 0.8 and 1.0 mol%). A thorough analysis of physical characteristics, including their variation with erbium oxide, has been conducted. The amorphous phase of the as-quenched samples has been validated through X-ray diffraction patterns, while Fourier transform infrared spectroscopy confirmed the existence of different structural groups. UV–Vis–NIR spectroscopy at wavelengths ranging from 200 to 1100 nm has been utilized to investigate various optical properties. In the gamma dose range of 50 Gy to 10 kGy, the glass sample with 0.6 mol% of erbium concentration (LBPEr0.6) showed the maximum integrated TL intensity with an optimized heating rate of 5 °C/s and annealing temperature of 400 °C. The deconvolution of TL glow curves was done using the R-package “tgcd: Thermoluminescence Glow Curve Deconvolution" by employing the Kitis general order kinetics model. Chen's peak shape approach has been used to calculate the trapping parameters, including order of kinetics (b), shape factor (μg), frequency factor (s), and activation energy (E). The ideal thermoluminescence dosimeter characteristics showed that LBPEr0.6 glass has outstanding linearity, excellent sensitivity, minimal fading and good reproducibility over six cycles.

The study of interaction of the high energetic plasma and electron pulses with multicomponent alloy surface

This paper investigates the impact of high-energy sources, namely, high-energy plasma pulses and high-energy electron beam pulses, on materials in the form of layer through separate and combined exposures. Experimental setups utilizing a Rod Plasma Injector (RPI) and an electron gun were employed for irradiation tests. The studies involved pre- and post-treatment analysis of morphology, chemical, and phase composition using scanning electron microscopy and x-ray diffraction measurements. Surface modifications under different exposure conditions were characterized, revealing that both sources induced significant alterations in surface composition and crystal structure. These interactions result in a more uniform chemical composition, reduced surface roughness, and a shift from an amorphous phase to a nanocrystalline or amorphous-nanocrystalline state. The results underscore the potential of high-energy sources for efficient surface engineering, offering opportunities for customized material surface modifications through meticulous adjustment of these generation parameters.

Interactions of polychlorinated cyclodiene pesticides with model fungal membranes – Langmuir monolayer and liposome studies

Polychlorinated cyclodiene pesticides (CP) are persistent organic pollutants causing widespread soil contamination. CPs-contaminated soils could be purified by mycoremediation, i.e. the introduction of CP-degrading fungal strains into the soils. However, not all mycoremediation attempts are effective, and the microbial cells introduced into the soil die. CP molecules are highly hydrophobic, therefore, their toxicity may largely result from membrane activity, i.e. from the incorporation of CP molecules into membranes disturbing their functions. To test this hypothesis and shed light on the interactions of CPs with plasma membranes, we used lipid Langmuir monolayers and unilamellar liposomes as models of fungal membranes. In our research, we included the four most common CPs polluting soils: aldrin, endrin, endosulfan, and chlordecone. Our studies have shown that CPs can be incorporated into the membranes up to the molar ratio of approximately 0.15. In the case of Langmuir monolayers, greater effects were observed for the model composed of saturated lipids. For this model, however, X-ray diffraction studies have shown that CPs are incorporated into the ergosterol-enriched amorphous phase without disturbing the formation of crystalline phospholipid nanodomains. Langmuir monolayer studies showed that chlordecone disturbs the physical properties of the model membrane to the greatest extent. However, liposome studies have shown that the effect of all CPs is similar – their presence increases the fluidity of the bilayer. Our studies confirmed CPs’ membrane activity, however, also showed that the presence of CP molecules in lipid membranes does not cause drastic changes in their physical properties.

Preparation and characterization of Ti5Al16O34 PEO ceramic coatings deposited on CP-Ti in mixed aluminate-phosphate electrolytes

Oxide ceramic layers of Ti5Al16O34 were fabricated on commercially pure titanium grade 2 substrates by plasma electrolytic oxidation in aqueous electrolyte media at a fixed 10 g/L concentration of trisodium phosphate and 25 g/L sodium aluminate. Lowering the sodium aluminate concentration to 15 g/L and 20 g/L, β-TiAl2O5 and Ti2Al6O13 components were produced under similar PEO processing conditions. The composition and structure of the PEO coatings were studied using XPS, XRD, SEM, EDS, mechanical (hardness, adhesion, and tribology), electrochemical impedance spectroscopy, and potentiodynamic polarization tests. The layers possess a polycrystalline character with minor amorphous phases, while their thicknesses varied slightly between samples with similar treatment times. The PEO coatings consist of a compact inner layer with an enriched phosphorus content of about 5–10 wt% and a porous outer layer in which phosphorus is found in less than 1 wt%. Ti5Al16O34 coatings showed better mechanical performance regarding microhardness and corrosion resistance compared to β-TiAl2O5 and Ti2Al6O13. At a longer applied PEO process duration of 10 min, Ti5Al16O34 layer thickness, microhardness, and corrosion current densities of 40.2 μm, 9.37 GPa, and 2.8 nA/cm2 were measured.

In-situ TEM investigation of dislocation healing and recrystallization in nanoscratched silicon at elevated temperatures up to 800 °C

Nanoscratching introduces detrimental surface and subsurface defects like amorphous regions, dislocations, and stacking faults in monocrystalline silicon, hindering its application in microelectronics and high-performance optics. This study leverages in-situ transmission electron microscopy to unveil the thermal evolution of these defects in atomic scale. A key finding is the amorphous phase recrystallization starting at ∼500 °C. Epitaxial growth from the crystalline-amorphous boundary, guided by adjacent crystal planes, restores the original diamond structure phase. By 700–800 °C, almost complete recrystallization occurs, maintaining similar interplanar spacing despite residual crystal distortions and dislocations. Notably, heating above 600 °C results in the gradual vanishing of stacking faults, suggesting a dynamic thermal evolution of the crystal defects induced by surface nanoscratching. This work demonstrates thermal annealing as a promising strategy to mitigate nanoscratch-induced defects, paving the way for defect-free-surface of silicon components in ultra-precision machining processes. It offers valuable insights into the interplay between nanoscratching, temperature, and defect evolution, laying the groundwork for surface and subsurface defects elimination in silicon under thermal fields.

Fabrication of high speed steel electrodes with MoSi2–MoB–HfB2 ceramic additives for electrospark deposition on die steel

The electrodes for electrospark deposition (ESD) were fabricated from hot-pressed blanks composed of a mechanically alloyed powder mixture of R6M5K5 high speed steel. This mixture was enriched with a 40 % addition of heat-resistant MoSi2–MoB–HfB2 ceramics, produces through the self-propagating high-temperature synthesis method (resulting in the R6M5K5-K electrode), as well as variant without any ceramic addition (resulting in the R6M5K5 electrode). We examined both the composition and structure of the electrode materials and the coatings derived from them, identifying the characteristics of mass transfer from hot-pressed electrodes to substrates of 5KhNM die steel under various frequencies and energy conditions during processing. The R6M5K5 electrode consists of an α-Fe-based matrix incorporating dissolved alloying elements and contains discrete particles of ferrovanadium, tungsten carbide, and molybdenum. The R6M5K5-K electrode, in addition to the α-Fe-based matrix, includes borides and carbides, as well as hafnium oxide. The use of the R6M5K5 electrode resulted in a consistent weight increase in the cathode throughout the entire 10-minute processing period. In contrast, the application of the ceramicenhanced electrode led to weight gain only during the initial 3 min of processing. Subsequently, ESD produced coatings of 22 and 50 μm thickness on the surface of 5KhNM steel using R6M5K5 and R6M5K5-K electrodes, respectively. The introduction of SHS ceramics escalated the roughness (Ra) of the surface layers from 6 to 13 μm and the hardness from 9.1 to 15.8 GPa. The coating from the R6M5K5 electrode was composed of austenite (γ-Fe) and exhibited high uniformity. Conversely, the coating from the R6M5K5-K electrode consisted of a diverse matrix with both crystalline and amorphous iron, an amorphous phase rooted in the Fe–B alloy, and scattered phases of HfO2, HfSiO4, Fe3Si, and Fe3B. High-temperature tribological testing at 500 °C in an air atmosphere showed that the coatings possess a friction coefficient of 0.55–0.57 when coupled with a counterbody of AISI 440C steel. The integration of heat-resistant ceramics notably enhanced the coating's wear resistance, increasing it by a factor of 13.5.

Trace Iron-Doped Nickel-Cobalt selenide with rich heterointerfaces for efficient overall water splitting at high current densities

Developing bifunctional electrocatalysts based on non-precious metals for overall water splitting, while maintaining high catalytic activity and stability under high current densities, remains challenging. Herein, we successfully constructred trace iron-doped nickel–cobalt selenide with abundant CoSe2 (210)-Ni3Se4 (202) heterointerfaces via a simple one-step selenization reaction. The synthesized Fe-NiCoSex/NCFF (NCFF stands for nickel–cobalt-iron foam) exhibits outstanding hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity with low overpotentials of 328 mV for HER and 345 mV for OER at a high current density of 1000 mA cm−2, while maintaining stability for over 20 h. Additionally, the Fe-NiCoSex/NCFF exhibits the lowest Tafel slope values for both HER (33.7 mV dec-1) and OER (55.92 mV dec-1), indicating the fastest kinetics on its surface. The Fe-NiCoSex/NCFF features uniformly distributed micrometer-sized selenide particles with dense nanowires on their surface, providing a large reactive surface area and abundant active sites. Moreover, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses reveal that the catalyst is composed of nickel, cobalt, and iron, forming micrometer-sized particles with both crystalline and amorphous phases, thereby enhancing HER and OER performance under high current density. Density functional theory (DFT) calculations demonstrate that the heterostructure CoSe2 (210)-Ni3Se4 (202), with high electron density and suitable adsorption capacity for reaction intermediates, and low energy barriers for HER (−0.384 eV) and OER (ΔG1st: 0.243 eV, ΔG2nd: 0.376 eV), serves as an active center for both HER and OER.

Щодо взаємодії і захоплення металевих крапель доменним шлаком

The mechanism of capture of metal drops by the slag melt was investigated using blast furnace slag as an example. The role of the viscosity of the blast furnace slag in reducing iron loss at the output from the blast furnace is shown. Reducing the viscosity of slags contributes to the rapid settling of small drops of cast iron in the slag volume. It is noted that the CaO/SiO2 ratio is an important parameter that changes the viscosity of blast furnace slag. To ensure the minimum viscosity of blast furnace slag, it is necessary to establish the optimal chemical composition of the slag, in particular the CaO/SiO2 ratio. A study of the temperature dependence of the viscosity of blast furnace slag melts was carried out using the method of estimating the content of the solid phase in the melt during its cooling. Calculations of the volume fraction of the solid phase for blast furnace slags were performed. An increase in the CaO/SiO2 ratio in slags leads to an increase in their crystallization ability. The microstructure and chemical composition of individual phases of a blast furnace slag sample were studied using scanning electron microscopy (SEM). It was established that the experimental slag contained at least three phases. The main (matrix) phase was an amorphous phase, which contained mainly SiO2 and Al2O3. The volume of the matrix phase contained interspersions of the crystalline phase of different sizes, which mainly included CaO and SiO2. In the volume of the crystalline phase, a metallic phase was found, which consisted mainly of Fe and Mn and had a regular rounded shape. The mechanism of capture of a metal droplet by slag is described. The metal drop serves as a frame (center) for the nucleation of the crystalline phase in the slag volume, as its surface energy decreases at the "metal drop - slag" interface. An increase in the mass of the crystalline phase around the metal drop leads to an increase in its lifting force and capture of the metal drop. Keywords: blast furnace slag, viscosity, metal loss, crystallization, scanning electron microscopy.

Physico-mechanical and microstructural evolution of sintered pressed geopolymer: Dual effects of aging period and sintering temperature

Ceramics are highly valued for their exceptional thermal resistance and ability to withstand high temperatures. This study investigated the production of ceramic-like pressed geopolymer, focusing on the effects of aging period and sintering temperature. The results showed that the 7-day pressed geopolymer achieved the highest compressive (134.7 MPa) and flexural (34.9 MPa) strengths after sintering at 1000°C, with a density retention of 93.7 %, a mass loss of 7.9 %, and a thermal shrinkage of 1.4 %. Microstructural analysis at 1000°C showed a dense ceramic-like structure with nepheline formation. Phase analysis of the 7-day pressed geopolymer revealed a decrease in the amorphous phase as temperature increased, with nepheline formed at 800°C (26.0 %) and maximized at 1000°C (61.0 %). This work offers an optimal aging period and sintering temperature to maximize the mechanical strength and nepheline crystal formation, making them perfect for fire-resistant panels and precast construction products.

Molecular dynamics of monocrystal copper nano-scratched with tungsten tip

The utilization of ultra-sharp tungsten tips for nano-scratching has been employed in the fabrication of copper micro/nanostructures. Understanding the material removal mechanisms and the evolution of subsurface defects during this process is crucial for optimizing manufacturing processes. Nevertheless, the mechanisms of material removal and subsurface defect evolution of ultra-sharp tungsten tips nano-scratching monocrystal copper remain elusive. This study utilizes molecular dynamics simulation to investigate the material removal mechanism, subsurface defect, and dislocation evolution of monocrystal copper nano-scratched with tungsten tip. Furthermore, the formation mechanism of stress-induced stacking faults is revealed through spatially distributed hydrostatic pressure analysis. Finally, the effect of scratching parameters on subsurface damage and workpiece machinability is explored. The results indicate that plastic deformation mechanisms of nano-scratching monocrystal copper include amorphization, dislocation slip, and atomic phase transition. During the nano-scratching process, V-shaped dislocation loops and prismatic dislocation loops are formed in the shearing-plowing region, and atomic clusters and stacked fault tetrahedrons are generated in the subsurface region. Scratching along the [100] crystal orientation, coupled with relatively increased scratching distance, velocity, and appropriate depth facilitates the attainment of shallow subsurface deformed layer and excellent machinability.