Fragmentation Of Particles Research Articles

Microstructure and tribological behaviour of CoCrCuFeTi high entropy alloy reinforced SS304 through friction stir processing

Surface modification by suitable technique aids in improving the characteristics of material to resist severe wear in demanding environments and challenging applications. The present study aims to analyse the tribological performance of Stainless Steel (SS304) reinforced with CoCrCuFeTi High Entropy Alloy (HEA) through friction stir processing and compares the results with annealed specimens. The CoCrCuFeTi HEA was ball milled and revealed irregular fragment particles with Body Centred Cubic (BCC) phase. The processed samples exhibited excellent refinement in grains with uniform HEA reinforcement distribution. The grains were observed to be in nano level post-annealing promoting exceptional microhardness. The pin-on-disc wear test was conducted by varying load (10-40N), sliding velocity (0.5–3.5 m/s) and sliding distance (500–2000 m) and the respective worn surface was analysed. The processed sample with HEA after annealing offered 29.8%, 57.4% and 58.49% improved wear resistance at the minimum level of load, sliding velocity and sliding distance than the processed base samples. The worn morphology revealed delamination, abrasion, adhesion and oxide layer formation to be the predominant wear mechanisms.

Investigation of renal calculi fragmented tracer particles in lithotripsy model by laser speckle technique

We have developed a laser sheet method to evaluate micro-sized fragmented calcium oxalate granular particles created kidney stones suspended in a Newtonian fluid in an in vitro model. These tracer particles are examined by laser optical techniques. An optical setup is configured with a laser sheet to conduct image velocimetry on these calcium oxalate seed particles in the urine environment. The experimental setup involves the application of ultrasonic waves to fragment the calcium oxalate tiny stones of varying sizes and disperse them in random directions in the fluid. The data acquisition process employs double frame-single exposure imaging, which captures images at specified time intervals using a high-resolution CCD camera. This provides information regarding particle displacement and track the flow path within the Newtonian fluid. In addition, the bigger fragmented particles are identified, and their sizes are also measured.

Aggregation and breakage dynamics of alumina particles under shear by coupled Computational Fluid Dynamics – Discrete Element Method

HypothesisShear affects simultaneous aggregation and fragmentation of fine particles. Understanding the effect of shear on the dynamics of particle aggregation and break-up is important to predict aggregate size and structure. It is hypothesized that there is a transition from pure breakage of large aggregates to regimes where restructuring and aggregation also play a role as aggregates become smaller. SimulationsHere, aggregation and fragmentation dynamics of alumina particles are investigated under laminar shear flow using Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD). The effect of the shear rate on the aggregation and breakage rates is quantified accounting for particle–particle and particle–fluid interactions. FindingsHigh shear rates promote the formation of small, compact aggregates. The collision efficiency decreases with increasing shear rate following a power law for shear rates higher than 1250 s−1. The transition from the pure breakage limit to the region dominated by breakage and restructuring has been observed for the first time. The breakage rate decreases significantly as the transition occurs upon decreasing aggregate size. CFD-DEM-derived collision efficiency and breakage rate equations are proposed that can be readily employed in detailed population balance equation models for industrial particle process design.

Mechanical Activation of CaSO4 Enriched Petroleum Coke Fly Ash for Development of Green Pellets

Mechanical Activation of calcium sulphate enriched petroleum coke fly ash (PCFA) generated from circulation fluidized bed combustion (CFBC) boiler was investigated to improve the surface reactivity of PCFA. The physico- chemical, mineralogical (XRD), morphological (SEM) characteristics of PCFA, activated PCFA and developed green pellets were studied in detail. It was found that the milling time of 45 minutes is efficient for the activation of PCFA and results in fragmentation of coarse particle into fine porous particles. Mechanical activation results in enhancing physical properties and reactivity of PCFA without any further chemical treatment. The mean particle size of activated PCFA with 45 min milling time was 12.51-12.60µm and the porous morphology were seen through SEM. The hydration phases like ettringite, portlandite and calcium silicate hydrate mainly contribute to the development of mechanical strength in activated PCFA pellets which were also confirmed through morphology of needle-shaped crystallites. The study recommends that mechanically activated PCFA could be used as an adsorbent material for heavy metals removal from waste waters.

Pulsed Laser Ultrasonic Vibration-Assisted Cutting of SiCp/Al Composites through Finite Element Simulation and Experimental Research

Silicon carbide particle-reinforced aluminum matrix composites (SiCp/Al) find diverse applications in engineering. Nevertheless, SiCp/Al exhibit limited machinability due to their special structure. A pulsed laser ultrasonic vibration assisted cutting (PLUVAC) method was proposed to enhance the machining characteristics of SiCp/Al and decrease surface defects. The finite element model was constructed, considering both the thermal effect of the pulsed laser and the location distribution of SiC particles. The model has been developed to analyze the damage forms of SiC particles and the formation mechanisms for the surface morphology. The influence of pulsed laser power on average cutting forces has also been analyzed. Research results indicate that PLUVAC accelerates the transition from the brittleness to the plastic of SiC particles, which helps to reduce surface scratching caused by fragmented SiC particles. Furthermore, the enhancement of surface quality is attributed to the decrease in surface cracks and the beneficial coating effect of the Al matrix. The accuracy of the simulation is verified by experiments, and the feasibility of PLUVAC method to enhance the surface quality of SiCp/Al is confirmed.

Double-differential cross sections for charged particle emissions from α particle impinging on Al at 230 MeV/u

ABSTRACT Charged particle production from α particle fragmentation reactions was investigated experimentally by measurement of 230-MeV/u α particles bombarding an aluminum target. Double differential cross sections were measured for each ejectile of p, d, t, 3He, and 4He using counter telescopes composed of Si surface barrier detectors and crystal scintillators, which were located at laboratory angles between 15° and 60°. The obtained data were analyzed for comparison with data observed at lower incident energies. The results found the following common characteristics: (1) spectra of proton- and neutron-emission are similar in high energy region at forward angle, (2) triton-to-3He ratio of α-breakup yield is 1:2, which is similar to lower incident energy experiment, and (3) the shape of broad peak formed by 3He and α particles could be explained by the process with collision between induced α particle and target nucleus.

A threshold model of plastic waste fragmentation: New insights into the distribution of microplastics in the ocean and its evolution over time

Plastic pollution in the aquatic environment has been assessed for many years by ocean waste collection expeditions around the globe or by river sampling. While the total amount of plastic produced worldwide is well documented, the amount of plastic found in the ocean, the distribution of particles on its surface and its evolution over time are still the subject of much debate. In this article, we propose a general fragmentation model, postulating the existence of a critical size below which particle fragmentation becomes extremely unlikely. In the frame of this model, an abundance peak appears for sizes around 1 mm, in agreement with real environmental data. Using, in addition, a realistic exponential waste feed to the ocean, we discuss the relative impact of fragmentation and feed rates, and the temporal evolution of microplastics (MP) distribution. New conclusions on the temporal trend of MP pollution are drawn.

Self-weighting of the overlying soil horizon catalyzed by freeze–thaw cycles leads to silt particle enrichment in the soil profile

Freeze–thaw cycles, as a strong weathering effect, can cause changes in the soil particle size and content, which can affect changes in the geological environment of the soil. A zone of silt enrichment was found at certain depths in the soil profile of the study regions. To understand and analyze the causes of this substratum phenomenon, a unidirectional freeze–thaw test on soil under static loading was designed and simulated in the laboratory in accordance with actual field conditions to investigate the process of changes in the physical index parameters after freeze–thaw cycles when the soil is under pressure. The changes in the parameters in the upper, middle and lower parts of the test soil column after 6, 10, 20, 40 and 50 freeze–thaw cycles were measured for the three regions. The test results show that the mechanical composition of the soil changes significantly after freeze–thaw cycles, the sand content decreases significantly, the clay and silt contents increase, and the particle frequency curve moves in the direction of particle size reduction. The freeze–thaw process is always accompanied by the fragmentation and aggregation of soil particles, and the fractal dimension is used to describe the distribution width of the soil particle population and to compare the clay content. The larger the fractal dimension is, the higher the clay content in the sample. Kvar(Coefficient of granulometric variation) decreases as the number of freeze–thaw cycles increases, the soil particles change from high-intensity to low-intensity variation, and the soil particles gradually transition to silt particles. The occurrence of silt-rich zones is the result of a combination of freeze–thaw action and static loading. This study can provide a new reference and vision for the freeze–thaw evolution process and tectonic development of soil in middle- and high-latitude cold regions.

Microstructure and corrosion behavior of thermo-mechanically processed rare earth Mg alloy: Effect of friction stir processing

This study focuses on the application of friction stir processing (FSP) on a rare earth based WE43 magnesium alloy aiming to improve microstructure and corrosion resistance. Ultra-refined microstructure with an average grain size of 4 um was obtained due to plastic deformation in the FSPed specimen. Corrosion rate determined from Tafel extrapolation results for WE43 base alloy and FSPed samples are 2.31 mmpy and 0.938 mmpy respectively. The FSPed specimen showed improvement in corrosion behavior with increased uniformity in the protective passive layer and decreased occurrence of micro-galvanic coupling (pitting corrosion), which can be ascribed to the redistribution and fragmentation of second-phase particles.

Study on the morphology, nanostructure and fragmentation properties of diesel and diesel-DMM soot particles oxidized in the air/air-NO environment

As an alternative fuel for diesel engines, dimethoxymethane (DMM) has attracted wide attention in recent years, but its impact on the post-treatment process of diesel exhaust particles has been rarely studied. To get a better understanding of the oxidation kinetics of soot in diesel particulate filters (DPFs), the oxidation process of soot emitted from a modern compression ignition (CI) fueled by diesel (D100) and its blend with 11 vol% dimethoxymethane (DMM11) at the same working conditions were investigated by a thermogravimetric analyzer in the air and air-NO atmospheres in this study, respectively. Soot samples at different oxidation degrees (0 %, 20 %, 50 % and 80 % mass loss) were tested by a high-resolution transmission microscopy to characterize the variations of physical properties (morphology, fractal dimension, primary particle diameter and nanostructure) and oxidation-induced fragmentation properties over the oxidation process. The results showed that DMM11 soot had higher oxidation reactivity than D100 soot, and the oxidation reactivity of soot was enhanced by NO involved in the air atmosphere. During the oxidation process, the fractal dimension of D100 and DMM11 soot aggregates gradually increased, and the number and diameter of the primary particles in an aggregate became smaller. This variation trends became more obvious with the presence of NO in the air environment. The nanostructures of D100 and DMM11 soot particles gradually become ordered (characterized by longer fringe length, narrower separation distance and less tortuosity) as the oxidation proceeds. While, when NO added in the air atmosphere the possibility of microcrystals oxidation inside the particles decrease to slow down the getting-ordered rate of soot. Moreover, the fragmentation probability of D100 and DMM11 soot aggregates decreases gradually as oxidation proceeds. During the oxidation process, the probability of primary particle fragmentation for D100 soot increases continuously, while the probability of DMM11 primary soot particles fragmentation showed an increase-then-decrease trend. Compare with D100 soot, DMM11 soot are more likely to occur the fragmentation behavior over the oxidation process. It is worth noting that the addition of NO to the air atmosphere increases the possibility of aggregate fragmentation, while it decreases the possibility of primary particle fragmentation. This work can provide theoretical basis for the development of high efficiency purification technology for diesel exhaust particles.

DETERMINING ROCK FRAGMENT SIZE DISTRIBUTION USING A CONVOLUTIONAL NEURAL NETWORK

Fast and relatively accurate determination of the fragment size distribution of a muck-pile is still a challenge in mining operations and the existing measurement methods are inefficient. In this research, a new algorithm to determine fragment size distribution due to blasting was presented, using the image processing technique. In the newly proposed approach, delineating of the fragmented rock particles, as the main core of processing, was carried out, using a convolutional neural network. Two networks were defined and trained by 150 laboratory and 150 field data images. Also, 30 laboratory and 30 field data images were applied to carry out the validation visually, and by using F1-scores. For the two laboratory and field networks and results obtained by Split-Desktop software automatic edge detection on the same images, the F1-scores are equal to (0.98, 0.74) and (0.99, 0.85) respectively. Also, for determination of fragment size distribution by laboratory data network and Split-Desktop software automatic edge detection on the same images, the Root Mean Square Error (RMSE) for F30 and F80 are equal to (0.36, 1.20) and (0.31, 1.24) respectively. These indicate better performance of the proposed approach for both rock edge detection and fragment size distribution over Split-Desktop software automatic edge detection.

Thermophysical properties of suspensions with [NI₃(μ₃-PPZA)₄CL₂] metal string complex microparticles

The study investigated the thermophysical properties of suspensions containing Ni₃(μ₃-ppza)4Cl₂ metal string complex (MSC) microparticles in aqueous glycerol solutions. The results showed that the use of microparticles of monocrystalline metal string complexes Ni₃(μ₃-ppza)4Cl₂ and Ni₅(μ₅-pppmda)4Cl₂ leds to the highest thermal conductivity enhancements and a decrease in freezing point. A comparative analysis of thermal conductivity enhancements of suspensions with micro- and nanoparticles was also conducted. Compared to the base fluid, at 5% volume fraction Ni₃-water-glycerol showed a 72% increase in thermal conductivity, while Cu-water-glycerol and Ni5-water-glycerol showed enhancements of 53% and 47%, respectively. The study suggests that the higher stability of suspensions with MSC microparticles, due to the formation of hydrogen bonds between the organic fragments of particles and water molecules, thier lower density and the formation of particle assemblies, is responsible for the significant thermal conductivity enhancement compared to nanofluids. The colloidal structure of suspensions with MSC microparticles greatly affects their thermophysical properties. Keywords: nanofluid, microfluid, metal string complex, thermal conductivity, suspension.

Optimizing Si-Dominant Anodes in High-Energy Li-Ion Batteries with a Binary Binder System: Exploring Impacts on Adhesion, Cohesion, and Electrochemical Performance

Silicon anode stands out as a promising game-changer for Li-ion batteries (LIBs) due to its remarkable gravimetric and volumetric capacities, boasting 4200 mAh/g1 and 2200 mAh/cm3, respectively. In addition, its operating voltage of 0.4 V vs Li/Li+, abundant availability, and environmental friendliness make Si a strong candidate to revolutionize energy densities in the next-generation high-performance LIBs. However, challenges arise during lithiation as silicon undergoes an expansion of ~300% of its initial volume, leading to a cascade of detrimental effects on the electrode.1 The micron-sized silicon particles tend to pulverize, and resulting in fragmented silicon particles that become electrically isolated. Such volume variations compromise the adhesion of the Si electrode to the current collector. Furthermore, the repetitive expansion and shrinkage cycles contribute to cohesive failure within the electrode. Collectively, these factors considerably diminish the electrochemical performance and lifespan of Si anodes. Consequently, these challenges have placed major constraints on the utilization of silicon, making it currently viable only at levels below 10 wt% in LIB anodes, thereby impacting the commercial feasibility of Si-dominant anodes in high-energy LIBs.Such challenges in Si anodes impose strict demands on the binder, requiring it to maintain intimate contact between electrode components and to the current collector and preserve the integrity of ion and electron transport channels during frequent volume changes upon cycling. Obviously, the traditional binders like PVDF or carboxymethylcellulose (CMC)/Styrene-butadiene rubber (SBR) are not suitable options for addressing these specific challenges.Many approaches have been explored to address such requirements including increased crosslinking, different binding functionalities, adhesion promoters, etc.2 In this study, we investigate a binder system comprising two key components: (i) an acrylic acid-based polymer enriched with a high concentration of carboxyl groups. This component not only forms effective bonds with the silicon surface but also fosters interactions with other polar species, facilitating the self-healing properties. (ii) Incorporating a styrene-butadiene-based polymer, renowned for its exceptional flexibility, improves adhesion and enhances the tensile properties of the electrode, particularly in response to volume expansion challenges. We evaluated the characteristics of the binders and electrode properties, including adhesion to the current collector, cohesion within the electrode, and binder distribution. These properties were subsequently correlated with the initial columbic efficiencies (IEC) and electrode cycle life in Si-dominant/NMC811 cells. We show that there is an optimal binder ratio that achieves the desired adhesion and significantly enhances cohesive strength, leading to improved cycling stability compared to a single binder system.

Studying Degradation of Micro- and Nano-Scale Silicon in Si/ Rgo-Anode Materials for Lithium-Ion Batteries – Towards a Fair Comparison

An attractive approach to increase the Li+-storage capacity of anode materials in Lithium-ion batteries (LiBs), is to replace or combine the routinely-applied graphite (372 mAh g-1) with higher-capacity materials. Among others, silicon (Si) with a theoretical capacity of 3579 mAh g-1 is a promising candidate [1]. Silicon is not yet been used as an anode material in its pure form, due to its low conductivity and volume increase of up to 300 % during lithiation. This two-step expansion (1st: Si + 2 Li+ + 2 e- → SiLi2.0; 2nd: SiLi2.0 + 1.5 Li+ + 1.5 e- → SiLi3.5) is a source of mechanical stress that can ultimately lead to battery failure. Furthermore, the initial lithiation of crystalline silicon (c-Si + 3.5 Li+ + 3.5 e- → SiLi3.5) causes an amorphization of the pristine crystalline lattice. This structural change causes further degradation of the material, which can hardly be avoided [2].The main degradation mechanisms resulting from expansion and amorphization are I) The uncontrolled formation of a passivation layer due to the cyclic volume change taking place during (de-)lithiation, which leads to a continuous break-up and reformation of the solid electrolyte interphase (SEI). II) The pulverization of particles resulting in mechanical stress and the electrical isolation of particles or particle fragments delaminating from the electrode [3]. The first mechanism discussed is more dominant for nanometer scaled particles (nm-Si), while the second mechanism occurs mostly for particles in the micrometer range (µm-Si).Our approach combines, nm- or µm-sized Si particles with different matrix materials. By incorporating the particles into an either graphitic or soft carbon-like support, we aim to increase the conductivity of the electrode material and gain additional buffer space thereby reducing interparticle mechanical stress [4]. On the one hand, the systems of carbon-based anode materials are already well understood in terms of electrode composition, processing parameters, electrolyte compatibility, formation of a stable SEI and the resulting high cycling stability. On the other hand, the observed degradation mechanisms will occur with different predominance in different Si/C composites depending on the Si particle size and the chosen carbon matrix. However, the latter is not completely understood. We will address these issues by comparing different Si/C-composites consisting of nm-Si-particles or µm-Si particles in a reduced graphite oxide (rGO) matrix and in a graphite-matrix.Electrochemical methods, such as galvanostatic cycling, impedance spectroscopy and dq/dU-analysis in 2- and 3-electrode setups, were coupled with optical and spectroscopical techniques (e.g. XRD, FTIR, SEM) to trace back the electrochemically measurable degradation of the electrode to structural changes during formation and cycling. Particular attention was paid to the localization and analysis of defect areas with increased degradation by correlating the optical and spectroscopical results data with the lithiation and delithiation processes. Considering the different SoC levels, we can identify the ongoing aging of the different electrode materials. Based on this, we propose the use of soft carbon-like structures such as rGO as a matrix material for Si/C composites due to its higher cycling stability under the investigated conditions.

Disintegration behavior and its grading entropy characterization of polyurea modified graded carbonaceous mudstone under loading and drying-wetting cycles

To study the disintegration behavior and characterization indexes of Modified Graded Carbonaceous Mudstone (MGCM), soaking disintegration tests of MGCM under vertical loading and cyclic drying-wetting were carried out with a disintegration test instrument which self-designed by our team. The grain size distribution of MGCM during drying-wetting cycles was analysed. Standard basal entropy, as an important parameter of grading entropy that quantitatively characterizes distribution curves, was introduced to characterize the disintegration behavior of MGCM and correlated with the comprehensive evaluation index, namely, disintegration ratio. The results show that as the number of drying-wetting cycles increases, the Graded Carbonaceous Mudstone (GCM) blocks disintegrate rapidly and the fine-grain content increases. With an increase in vertical load, the particles disintegrate more completely. The contents of each particle group in the GCM test groups stabilize after 9, 7, and 4 drying-wetting cycles under vertical loads of 0, 100, and 200 kPa, respectively. Under the same vertical load of 200 kPa, the contents of each particle group in MGCM test groups with Polyurea (PU) content 0, 5, and 10 wt% stabilize after 4, 6, and 8 drying-wetting cycles, respectively. The inclusion of PU can effectively retard the disintegration of GCM, and the effect is more pronounced with 5 wt% PU content compared to 10 wt%. However, it is also susceptible to the deterioration of PU layer caused by mechanical screen. The grading entropy model of MGCM under loading and cyclic drying-wetting is established. There is a significant positive, linear correlation between the standard basal entropy and the disintegration ratio. A smaller standard basal entropy to a smaller disintegration ratio, indicating a greater degree of particle disintegration and fragmentation. The standard basal entropy can characterize the disintegrated particles of MGCM with different PU content under vertical loading and drying-wetting cycles. The standard basal entropy of GCM decreases rapidly initially and then stabilizes as the number of drying-wetting cycles increases. The standard basal entropy decreases exponentially as the vertical load increases. The results provide a new quantitative index for analyzing the grading characteristics of MGCM following disintegration, which are valuable for engineering construction and disaster prevention in carbonaceous mudstone areas.

Effective reinforcement on the structural stability and electrochemical performances of ultra-high nickel cobalt free cathode material by co-doping

Ultra-high nickel ternary cathode material with high energy density is a very important material to meet the long driving range of new energy vehicles. However, cobalt has high toxicity, high price and supply chain risks, so the material is being developed in the direction of low cobalt or no cobalt. For ultra-high nickel cobalt free cathode material with high theoretical capacity (LiNi0.9Mn0.1O2, NM90), the lattice collapse and particle fragmentation caused by microcracks during long cycle will lead to inferior rate performance and cycle life. At present, the effect of different cobalt content on structure and electrochemical properties of cobalt-free cathode material is rarely reported. Therefore, based on cobalt-free precursors, the effects of proper Co doping on structure and electrochemical properties of NM90 material are studied in depth. It showed that proper Co doping can effectively reduce cationic mixing and improve Li+ diffusion rate of NM90 material. The NM90–1.5%Co material exhibits discharge specific capacity of 167.1 mA h g−1 after 100 cycles at 1C and 121.2 mA h g−1 after 200 cycles at 5C, respectively. Furthermore, NM90–1.5%Co material shows an initial discharge specific capacity of 144.1 mA h g−1 at 10C. Therefore, Co doping provides a feasible way to improve the structural stability and electrochemical performances of ultra-high nickel cobalt free cathode material.

Experimental study on the fragmentation behavior of coal particles during gasification process in drop-tube furnace

Studying the fragmentation characteristics of coal particles is important for enhancing furnace gasification efficiency. Based on the processing method of visualization imaging technology, this study investigated the proportion of particle fragmentation, fragmentation mode, surface temperature, and other characteristics of the Fuhua Indonesian Coal (FIC) gasification process at different temperatures and oxygen concentrations in a drop-tube furnace. The results show that the proportion of fragmentation at the center was higher than the proportion of fragmentation at the outer zone under experimental conditions. The most significant difference between the two phenomena was the length of the fragmentation period and the overall structural changes. The proportion of fragmentation at the center positively correlated with an increase in temperature and negatively correlated with an increase in oxygen concentration. Under high-temperature and low-oxygen concentration conditions, FIC tends to be in the high fragmentation mode. The temperature at the time of FIC fragmentation increased with increasing particle size. Compared with the temperature, the change in oxygen concentration had a more remarkable effect on the fragmentation temperature, specifically in the outer zone. Elevating the oxygen concentration and temperature both promoted particle fragmentation. Temperature had a greater effect on fragmentation in the outer zone, while fragmentation at the center was more sensitive to changes in oxygen concentration.

Fifty-year pollution history of microplastics and influencing factors in offshore sediments: A case study of Ningbo, China

Sediment cores are optimal mediums for investigating the historical presence of offshore microplastics (MPs). In this study, two sediment cores were collected at varying water depths, i.e., XS2 (10 m) and XS3 (20 m), from the Xiangshan offshore (XSO) in Ningbo. We focused on the spatiotemporal distribution characteristics of MPs within two sediment cores and explored the response differences of MPs abundance to natural factors and human activities. The results showed that the MPs abundance in sediments has gradually increased since the late 1960s, but with interannual fluctuations. MPs abundance in XS2 and XS3 were 1133–8700 and 633–11433 items/kg dry weight, respectively. The predominant polymers were PA, PU, PET and ACR, with fragmented particles being the most prevalent shape of MPs. The MPs abundance in XS2 and XS3 had a similar response to natural factors, mainly including (i) MPs abundance significantly correlated with the sediment load of the Qiantang River (p < 0.01), indicating that sediment load might be an important factor affecting the MPs abundance and that MPs transported by rivers had characteristics of near-source sedimentation; (ii) typhoons had the effect of weakening the MPs abundance; and (iii) geological activities might be potential contributing factors to variations in MPs’ abundance in deep sediments. Correlation analyses demonstrated that MPs in XSO was the result of multiple sources, stemming from plastic production, sewage discharge, marine fisheries and shipping activities. Notably, XS3 exhibited higher sensitivity to human activities compared to XS2, owing to differences in sampling locations. This study underscores the significance of employing two sediment cores, rather than a single core, as it provides a more comprehensive insight into the overarching trends and disparities in the historical pollution of MPs. Our findings contribute to a deeper understanding of the history of offshore MPs pollution, shedding new light on this critical environmental issue.

Effects of friction stir processing and nano-hydroxyapatite on the microstructure, hardness, degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications

Nowadays, magnesium alloys are emerging in biomedical implants for their similar properties to natural bones. However, the rapid degradation of magnesium alloys in biological media hinders successful implantation. Refinement of microstructure, as well as reinforcement particles can significantly improve the degradation rate. In this work, multi-pass friction stir processing (FSP) was proposed to synthesize WE43/nano-hydroxyapatite (nHA) surface composite, the microstructure, reinforced particle distribution, micro-hardness, corrosion behavior and in-vitro bioactivity were studied. The subsequent FSP passes of WE43 alloy and WE43/nHA composite refined the grain size which was reduced by 94.29% and 95.92% (2.63 and 1.88 µm, respectively) compared to base metal after three passes. This resulted in increasing the microhardness by 120% (90.86 HV0.1) and 135% (105.59 HV0.1) for the WE43 and WE43-nHA, respectively. It is found that increasing FSP passes improved the uniform distribution of nHA particles within the composite matrix which led to improved corrosion resistance and less degradation rate. The corrosion rate of the FSPed WE43/nHA composite after three passes was reduced by 38.2% (4.13 mm/year) and the degradation rate was reduced by 69.7% (2.87 mm/y). This is attributed to secondary phase (Mg24Y5 and Mg41Nd5) particle fragmentation and redistribution, as well as a homogeneous distribution of nHA. Additionally, the growing Ca-P and Mg(OH)2 layer formed on the surface represented a protective layer that reduced the degradation rate. The wettability test revealed a relatively hydrophilic surface with water contact angle of 49.1 ± 2.2° compared to 71.2 ± 2.1° for base metal. Also, biomineralization test showed that apatite layer grew after immersion 7d in simulated body fluid with atomic ratio of Ca/P 1.60 approaching the stoichiometric ratio (1.67) indicating superior bioactivity of FSPed WE43/nHA composite after three passes. These results raise that the grain refinement by FSP and introduction of nHA particles significantly improved the degradation rate and in-vitro bioactivity of WE43 alloy for biomedical applications.

Analysis of microscopic deformation mechanism of SiCp/Al composites induced by ultrasonic vibration nanoindentation

Ultrasonic vibration machining technology affords environmentally friendly dry cutting without employing a cutting fluid and has been applied to the macro-scale dry cutting precision machining of SiCp/Al composites. However, the high-frequency vibration on the atomic-scale deformation mechanism of such materials remains unclear. Hence, this paper combines the molecular dynamics simulations (MD) with ultrasonic vibration indentation tests to investigate the effect of ultrasonic vibration on the multiscale deformation of SiCp/Al composites. The results demonstrate that the vibration amplitude exceeding the lattice constant (4.05 Å) of Al induces the plastic flow of Al atoms after breaking through the interatomic force. On the one hand, the ultrasonic high-frequency vibration energy accelerates the interfacial failure and the SiC particle fragmentation and promotes the dislocation movement to form the dislocation loop. On the other hand, compared with conventional indentation, ultrasonic vibration energy reduces the FCC phase transition rate by up to 40.8% and improves the toughness of the composites. Meanwhile, the high-frequency impact energy promotes the material to produce lattice distortion and subgranular grains, where grain slippage and lamination faults occur at the grain boundaries. Besides, the maximum depth of the material impact layer is about 1.45 times that of a conventional indentation, which contributes to the material being removed efficiently. The results of this research provide potential insights into ultrasonic vibration-assisted micro and nano removal processing of SiCp/Al composites, which could help to expand the efficient and precise clean processing of this type of material.