Search Results (74)

The formation and evolution of ice in the Yellow River represent complex dynamic processes. To elucidate the structural characteristics of ice crystals and their governing mechanisms in the Inner Mongolia reach, this investigation utilized high-resolution Sentinel-2 satellite imagery to systematically monitor spatiotemporal variations in open-water formations across diverse channel morphologies throughout the ice regime period. Systematic ice sampling was conducted across diverse channel morphologies of the Yellow River to quantify critical parameters, including crystalline structure characteristics, equivalent diameter distributions, density variations, and sediment content profiles. The results indicate the transformation of open water resulting from various river configurations during the freezing season exhibits distinct characteristics, which are significantly influenced by temperature variations. Ice crystal characterization exhibits that the crystalline structure predominantly manifests as two primary forms: columnar and granular ice formations, with their distribution varying systematically across different channel configurations. Ice crystal morphology exhibits heterogeneity in both form and dimensional characteristics. Columnar ice consistently exhibits larger equivalent diameters compared to granular ice formations. A progressive enhancement in the equivalent diameter of crystals is observed along the vertical axis corresponding to the thickness of the ice during the growth process. The ranges of variation in ice crystal size, ice density, and mud content within ice exhibit differences contingent upon the specific crystal structures present. Observational studies and comparative analyses of ice samples from the Inner Mongolia reach of the Yellow River reveal that channel morphology, ambient thermal conditions, and hydrodynamic parameters are the primary determinants governing the variability in ice microstructure and its associated physical characteristics. This investigation provides fundamental scientific insights and quantitative data that advance our understanding of river ice microstructural characteristics. Full article

Determination of nozzle quality ratings based on macroscopic and microscopic parameters generally requires the use of separate measurement methods in research. The guiding idea determining the direction of the conducted research was to use a 2D (two-dimensional) laser analyzer LDA/PDA (laser Doppler anemometry/phase Doppler anemometry) to evaluate the values of selected micro and macro parameters (microstructure characterization with simultaneous evaluation of lateral distribution) of the spray. The research was conducted for variable measurement times. The main issue of the research was an attempt to reduce the measurement cycle time, important in the case of point tests performed with an analyzer. The scope of the conducted research covered three areas. In the first stage of the research, the variability of the coefficients characterizing the spray spectrum as a function of variable measurement time was analyzed. In the next, the value of the coefficient of transverse volume distribution (for a single sprayer) was determined. The results were determined on the basis of the volume diameters obtained from measuring the droplets with a 2D LDA/PDA analyzer. In the third stage, an attempt was made to combine the volume distribution results obtained for single nozzles on the boom. The results obtained were compared with those determined using a groove table. Both measurement methods used a different representativeness in volume measurement (sampling method and significantly different amounts of liquid analyzed); nevertheless, the results of the transverse volume distribution were found to be consistent. Full article

Fly ash and slag powder, as two of the most widely utilized industrial solid waste-based mineral admixtures, have demonstrated through extensive validation that their combined incorporation technology effectively enhances the mechanical properties and microstructural characteristics of concrete. Systematic investigations remain imperative regarding material response mechanisms under dynamic loading conditions. This study conducted microstructural analysis, static compression tests, and dynamic Split Hopkinson Pressure Bar (SHPB) impact compression tests on concrete specimens, complemented by dynamic impact simulations employing an established three-dimensional mesoscale concrete aggregate model. Through integrated analysis of macroscopic mechanical test results, mesoscale numerical simulations, and microstructural characterization data, the research systematically elucidated the influence mechanisms of different mineral admixture combinations on concrete’s dynamic mechanical behavior, energy dissipation characteristics, and fracture mechanisms. The results showed that all specimens exhibited strain rate enhancement characteristics as the strain rate increased. As the admixture approach transitioned from non-admixture to single admixture and subsequently to binary admixture, the dynamic strength, elastic modulus, and DIF of concrete increased progressively. Both the energy dissipation capacity and its proportion relative to total energy absorption showed continuous enhancement. The simulated stress–strain curves, failure modes, and fracture processes show good agreement with experimental results, this effectively verifies both the scientific validity of the mesoscale concrete model’s multiscale modeling approach and the reliability of the numerical simulations. Compared to FHC1, FMHC1’s mesoscale structure can more effectively convert externally applied energy into stored internal energy, thereby achieving superior dynamic compressive energy dissipation capacity. Full article

Significant improvements in the tribological performance of graphene-doped additively manufactured structures are reported, with absolute values of friction coefficients reaching 0.09 corresponding to ca. 70% decreases from plain/un-doped samples. The findings highlight an impressive potential of the nanocarbon variant, to endow superior tribological performance to polymers, bringing them a step closer to the ideal superlubric regime. Such structures of intrinsic superlubric performance are envisioned as viable candidates for the containment of great amounts of energy, currently wasted as friction in a plethora of applications, hence also promoting an ecologically sustainable development. Indications that superlubricity is greatly promoted by nanocarbons, especially by the two-dimensional variant of graphene with excellent response in shear action, are investigated in combination with the effect of surface topography, for the investigation of the tribological performance of three-dimensional structures with geometric surface patterning, additively manufactured from graphene-doped polymers. Spectroscopic, mechanical, and microstructural characterization of plain polymer-based samples and their graphene-enhanced nanocomposite counterparts was followed by tribometric measurements for the establishment of the evolution of the friction coefficient on a certified commercial tribometer operating under the ball-on-disk configuration as well as on a conceptual purpose-built setup. The individual and combined effects of nanomaterial presence and patterning are reported, and the influence of manufacturing-prone micropatterning is examined. Full article

Using reduced-dimensional halide perovskites is emerging as a promising strategy for enhancing the stability of optoelectronic devices such as solar cells, even if their performances remain a step below those of the 3D halide perovskites. Two-dimensional Ruddlesden–Popper (2D-RP) structures are characterized by the n parameter that represents the number of PbI₆ layers in the spacer-separated perovskite slabs. The present study focuses on formamidinium (FA)-based 2D-RP type perovskites denoted as PMA₂FA_n−1Pb_nI_3n+1 (PMA = Phenylmethylammonium or benzylammonium). We investigate the effect of n on the one step growth mechanism and the film morphology, microstructure, phase purity, and optoelectronic properties. Our findings demonstrate that the average n is not only determined by the initial spacer content in the precursor solution but also by the thermal annealing process that leads to a partial spacer loss. Depending on n, perovskite solar cells achieving a power conversion efficiency up to 21%, coupled with enhanced film stability compared to 3D perovskites have been prepared. By using MACl additive and an excess of PbI₂ in the perovskite precursor solution, we have been able to achieve high efficiency and to stabilize the n = 5 perovskite solar cells. This research represents a significant stride in comprehending the formation of FA-based layered perovskites through one-step sequential deposition, enabling control over their phase distribution, composition, and orientation. Full article

Granite is widely regarded as an ideal material for the construction of underground liquefied natural gas (LNG) storage reservoirs due to its high mechanical strength and broad geological availability. However, the ultra-low storage temperature of LNG (−162 °C) poses potential risks in altering the permeability of granite, which may compromise the long-term safety and integrity of the reservoir. To investigate the permeability characteristics and microstructural degradation of granite under low-temperature conditions, both coarse-grained and fine-grained granite samples were subjected to a series of experiments, including one-dimensional (1D) gas permeability tests (conducted before and after freeze–thaw cycles ranging from −20 °C to −120 °C), nuclear magnetic resonance (NMR) tests, and two-dimensional (2D) gas permeability tests performed under real-time low-temperature conditions. Experimental results indicated that the gas permeability of granite under real-time low-temperature conditions exhibited a linear increase as the temperature decreased. In contrast, the gas permeability after freeze–thaw cycling followed a nonlinear trend: it increased initially, plateaued, and then increased again as the freezing temperature continued to drop. A further analysis of pore structure evolution and permeability changes revealed distinct degradation mechanisms depending on grain size. In coarse-grained granite, freeze–thaw damage was primarily characterized by the initiation and propagation of new microcracks, which originated as micropores and expanded into mesopores. In fine-grained granite, the damage primarily resulted from the progressive widening of existing fissures, with micropores gradually evolving into mesopores over successive cycles. The study’s findings provide a useful theoretical foundation for the secure subterranean storage of LNG. Full article

Precision micromilling is currently widely used for the fabrication of injection mold inserts for the mass production of microfluidic devices. However, for complex devices with micrometer-scale and high density of structures, micromilling results in high production times and costs for production runs of hundreds or thousands of units. Femtosecond laser (fs-laser) technology has emerged as a promising solution for high-precision micromachining. This study analyzes the potential of fs-laser micromachining for the fabrication of injection mold inserts for the large-scale production of thermoplastic microfluidic devices. For the evaluation of technology, a reference design was defined. The parameters of the fs-laser process were optimized to achieve high resolution of the structures and optimal surface quality, aiming to minimize production times and costs while ensuring the quality of the final part. The microstructures were replicated in two different grades of COC (Cyclic Olefin Copolymer) by injection molding. The dimensional tolerance of the structures and the surface finish achieved both in the insert and the polymer parts were characterized by scanning electron microscopy (SEM) and confocal microscopy. The surface quality of the final parts and its suitability for microfluidic fabrication were also assessed performing chemical bonding tests. The fs-laser machining process has shown great potential for the mass production of microfluidic devices. The developed process has enabled for a reduction of up to 90% in the fabrication times of the insert compared to micromilling. The parts exhibited very smooth surfaces, with roughness values (Sa) of 64.6 nm for the metallic insert and 71.8 nm and 72.9 nm for the COC E-140 and 8007S-04 replicas, respectively. The dimensional tolerance and the surface quality need to be improved to be competitive with the finishes achieved with precision micromilling. Nonetheless, there is still room for improvement considering the significant reduction in the production times through new laser processing strategies. Full article

Restoring components in the hot gas path of turbine engines after service-induced degradation is crucial for economic efficiency. This study investigates the printability of Rene 65 powder on a degraded first-stage turbine blade using two additive manufacturing techniques: Laser Powder Bed Fusion (L-PBF) and Laser Powder Directed Energy Deposition (L-DED). Deposited material was evaluated using optical microscopy (OM), scanning electron microscopy (SEM), and Electron Backscatter Diffraction (EBSD) to characterize its crystallographic texture, while microhardness testing provided insight into its mechanical properties. Our results show that L-PBF excels at replicating intricate features, such as small cooling holes, and produces a highly texturized microstructure oriented parallel to <001> under optimal parameters (80 W, 400 mm/s, unidirectional scanning), although at a slower pace. In contrast, L-DED offers a versatile, rapid, and cost-effective method for repairing medium to large parts, yielding an equiaxed microstructure and higher as-printed hardness—approaching GTD 111 values due to an aging effect from high heat input. Both processes effectively restored the dimensional integrity of degraded blade tips, paving the way for more sustainable and economical maintenance strategies in the aerospace industry. Full article

This study systematically investigates the rheological modification mechanism of steel slag powder (SSP) as an alternative filler in asphalt mastics, with comparative analysis against conventional limestone powder (LP). Four filler-to-asphalt (F/A) ratios (0.6–1.2) were employed to prepare modified mastics. Comprehensive characterization through laser diffraction analysis, BET nitrogen adsorption, and scanning electron microscopy (SEM) revealed SSP’s significant microstructural advantages: a 29.2% smaller median particle size (D50) and 7.06% larger specific surface area compared to LP, accompanied by enhanced interparticle connectivity and morphological complexity. Rheological evaluation via dynamic shear rheology (DSR) demonstrated SSP’s superior performance enhancement—particularly at elevated F/A ratios (1.0–1.2), where multiple stress creep recovery (MSCR) tests showed a 6.9–46.06% improvement in non-recoverable creep compliance (J_nr) over LP-modified counterparts. The temperature sweep analysis indicated SSP’s effectiveness in reducing the temperature susceptibility index by 9.37–18.06% relative to LP. Fourier-transform infrared spectroscopy (FTIR) combined with two-dimensional correlation analysis (2D-COS) confirmed the dominance of physical interactions over chemical bonding in the SSP–asphalt interface. The results establish SSP’s dual functionality as both a rheological modifier and sustainable construction material, providing mechanistic insights for optimizing steel slag utilization in pavement engineering. Full article

Lattice materials are renowned for their exceptional mechanical performance and transformative potential for aerospace and structural engineering applications. However, current research primarily focuses on the effective elastic properties of lattice microstructures, whereas there are few studies on the prediction of their effective nonlinear properties, thus limiting the practical application of lattice materials. In addition, the characterization of complex micro structured lattice materials often requires the generation of many elements and performing nonlinear finite element analysis, which involves high computational costs. To address these challenges and enable the efficient prediction of the nonlinear effective properties of complex lattice microstructures in heterogeneous materials, the FEM-Cluster-based Analysis (FCA) approach is proposed. In the offline phase, a reduced-order model and offline database are established. In the online phase, the principle of the cluster minimum complementary energy incremental algorithm is used to rapidly predict the nonlinear effective properties of heterogeneous materials. This method is applied to conduct extensive comparisons with direct numerical simulation across two-dimensional and three-dimensional lattice materials to demonstrate that FCA can achieve similar accuracy while significantly enhancing computational efficiency, thereby offering promising potential for optimizing lattice material design in structural applications. Full article

Hardness and wear resistance are the requirements of nickel-based superalloys used in gas turbine blades. This study uses laser cladding technology to develop three types of wear-resistant coatings—NiCr-2%hBN, NiCr-12%cBN, and NiCr-2%hBN-12%cBN—on GTD-111 superalloy. The above coatings’ microstructure, microhardness, and tribological behavior were systematically characterized by scanning electron microscope, hardness tester, pin-on-disc wear device, and three-dimensional profiles. The hardness test results showed that the hBN coating has the lowest hardness (692 HV) due to its layered structure, and the hBN-cBN coating has the highest hardness (992 HV) due to its complex structure and the creation of inhomogeneous nucleation centers in the coating. The wear test results showed that the hBN coating has a lower coefficient of friction (COF) (0.49) than the hard cBN coating (0.53) due to its lubricating properties. Meanwhile, the wear rate of the hBN coating is lower than the wear rate of the hard cBN due to the weak forces of one in the B-N bond. However, the wear test results of hBN-cBN coating showed that the effects of hBN and the high hardness of cBN cause the formation of a coating with the lowest wear rate (0.22 × 10⁻⁶ mm³/N·m), COF (0.41), fluctuation, wear depth (17.2 µm), and wear volume loss (0.32 × 10⁵ µ³) compared to the other two coatings. In addition, in the hBN-cBN coating, due to the greater driving force for the inhomogeneous nucleation of the melt, a larger area of equiaxed grains was formed, which in turn had a significant effect on increasing the wear resistance. Full article

On the Loess Plateau of China, the number of projects involving the excavation of mountains and the filling of valleys to create new land is rising. The loess excavated from the mountain is directly used as building material. After being filled into the valley and remolded, it serves as the foundation for overlying structures. However, significant differences in mechanical behavior exist between intact and remolded loess, leading to various issues such as differential settlement. Understanding the microstructure of loess is essential for improving our comprehension of its macro-level hydrological and mechanical behavior. Due to the inherent limitation of the conventional methods (e.g., scanning electron microscopy and mercury intrusion porosimetry) for microstructure investigation, an in-depth understanding of the three-dimensional (3D) microstructural differences between intact and remolded loess remains elusive. To address this gap, this study employs advanced X-ray micro-computed tomography (micro-CT) to investigate the 3D microstructure of both intact and remolded loess from two typical man-made new land creation projects. The three-dimensional microstructures are segmented into a series of cubes of varying dimensions to identify the structure’s representative volume element (RVE) and assess the uniformity of both loess types. The pore network of the RVE is quantitatively analyzed to characterize the microstructure. The results reveal significant disparities between the microstructure of intact and remolded loess, particularly in terms of uniformity, pore size distribution, and pore connectivity. Remolded loess exhibits a denser structure with poorer pore connectivity and greater heterogeneity compared to intact loess. These microstructural differences are attributed to the distinct formation processes of the two types of loess. Full article

Flexible polymer-based piezoelectric nanogenerators (PENGs) have gained significant interest due to their ability to deliver clean and sustainable energy for self-powered electronics and wearable devices. Recently, the incorporation of fillers into the ferroelectric polymer matrix has been used to improve the relatively low piezoelectric properties of polymer-based PENGs. In this study, we investigated the effect of various nanofillers such as titania (TiO₂), zinc oxide (ZnO), reduced graphene oxide (rGO), and lead zirconate titanate (PZT) on the PENG performance of the nanocomposite thin films containing the nanofillers in poly(vinylidene fluoride-co-trifluoro ethylene) (P(VDF-TrFE)) matrix. The nanocomposite films were prepared by depositing molecularly thin films of P(VDF-TrFE) and nanofiller nanoparticles (NPs) spread at the air/water interface onto the indium tin oxide-coated polyethylene terephthalate (ITO-PET) substrate, and they were characterized by measuring their microstructures, crystallinity, β-phase contents, and piezoelectric coefficients (d₃₃) using SEM, FT-IR, XRD, and quasi-static meter, respectively. Multiple PENGs incorporating various nanofillers within the polymer matrix were developed by assembling thin film-coated substrates into a sandwich-like structure. Their piezoelectric properties, such as open-circuit output voltage (V_OC) and short-circuit current (I_SC), were analyzed. As a result, the PENG containing 4 wt% PZT, which was named P-PZT-4, showed the best performance of V_OC of 68.5 V with the d₃₃ value of 78.2 pC/N and β-phase content of 97%. The order of the maximum V_OC values for the PENGs of nanocomposite thin films containing various nanofillers was PZT (68.5 V) > rGO (64.0 V) > ZnO (50.9 V) > TiO₂ (48.1 V). When the best optimum PENG was integrated into a simple circuit comprising rectifiers and a capacitor, it demonstrated an excellent two-dimensional power density of 20.6 μW/cm² and an energy storage capacity of 531.4 μJ within 3 min. This piezoelectric performance of PENG with the optimized nanofiller type and content was found to be superior when it was compared with those in the literature. This PENG comprising nanocomposite thin film with optimized nanofiller type and content shows a potential application for a power source for low-powered electronics such as wearable devices. Full article

The large-scale and engineering preparation of NiPd powder with an excellent structure is crucial for promoting the development of catalytic applications and the utilization of hydrogen energy. In this study, micro-nano dual-size NiPd alloy with a flake-like microstructure was synthesized using a simple and efficient high-energy ball milling method. Micro-structural analysis was performed on samples at various stages of ball milling to investigate the atomic migration and refinement mechanisms during the process. The microstructure and elemental distribution at different stages of particle refinement were examined, and the particle size distribution of NiPd alloy at varying ball milling times was statistically analyzed. The NiPd alloy produced using this method exhibits two distinct structural features: a flake-like polycrystalline structure and a dual-size nanocrystalline structure. A flake-like polycrystalline powder was achieved using relatively short ball milling durations and characterized by a polygonal two-dimensional structure with a single particle aspect ratio of 24. After 60 h of ball milling, the NiPd alloy developed a dual-size nanocrystalline structure. Under a high ball-to-powder ratio, the average particle size of the alloy decreased to 3.6 μm, more than tenfold smaller than the initial size. The alloy particles transformed from their original elemental metals into alloy phases, with nanoscale alloy particles (approximately 158 nm) adhering to micrometer-sized alloy particles. Additionally, the influence of the ball-to-powder ratio on the refinement process and outcomes was investigated, indicating that a higher ball-to-powder ratio can effectively improve preparation efficiency by accelerating the ball milling process and reducing the final particle size of the NiPd alloy at each milling stage. Full article

The aim of this work is to compare the traditional uniaxial pressing with an innovative shaping technique, Digital Light Processing (DLP), in the preparation of porous mullite (3Al₂O₃·2SiO₂) supports to be functionalized with an active coating for CO₂ capture. Indeed, the fabrication of complex geometries with 3D-printing technologies allows the production of application-targeted solid sorbents with increased potentialities. Therefore, this research focused on the effect of the purity of the selected raw materials and of the microstructural porosity of 3D-printed ceramic substrates on the Metal Organic Frameworks (MOFs) coating efficiency. Two commercial mullite powders (Mc and Mf) differing in particle size distribution (D₅₀ of 9.19 µm and 4.38 µm, respectively) and iron oxide content (0.67% and 0.38%) were characterized and used to produce the substrates, after ball-milling and calcination. Mc and Mf slurries were prepared with 69 wt% of solid loading and 5 wt% of dispersant: both show rheological behavior suitable for DLP and good printability. DLP 3D-printed and pressed pellets were sintered at three different temperatures: 1350 °C, 1400 °C and 1450 °C. Mf 3D-printed samples show slightly lower geometrical and Archimedes densities, compared to Mc pellets, probably due to the presence of lower Fe₂O₃ amounts and its effect as sintering aid. Mullite substrates were then successfully functionalized with HKUST-1 crystals by a two-step solvothermal synthesis process. Ceramic substrate porosity, depending on the shaping technique and opportunely tuned controlling the sintering temperature, was correlated with the functionalization efficiency in terms of MOFs deposition. Three-dimensional-printed substrates exhibit a higher and more homogeneous HKUST-1 uptake compared to the pressed pellets as DLP introduces desirable porosities able to enhance the functionalization. Therefore, this work provides preliminary guidelines to improve MOFs coating on mullite surfaces for CO₂ capture applications, by opportunely tuning the substrate porosity. Full article