•Ni@CF is proven to enhance the stability of solder joints during multiple reflows.•Grain structure evolution of interfacial IMC was studied during multiple reflows.•The shift of the shear fracture ...path was attributed to reinforced interface.•The strengthening mechanism of carbon fiber was related to the inclination angle.
Today’s 3D electronic packaging is characterized by smaller size and higher functional density, which generally require multiple reflow cycles. However, due to the Ostwald ripening process of the interfacial intermetallic compound (IMC), the solder joint’s strength would decrease as the number of reflow cycles increases. To address this, we developed a novel composite solder by incorporating nickel-coated carbon fiber (Ni@CF) into the Sn–3.0Ag–0.5Cu (SAC305) solder connection. The study showed that Ni@CF effectively enhanced the stability and reliability of solder joints during multiple reflow processes. Compared with Ni@CF-free equivalents, Ni@CFs promoted the nucleation of interfacial IMC during the solid–liquid reaction and inhibited Ostwald ripening, leading to a refinement of the interfacial IMC grains. As a result, the interface was strengthened, and the shift of shear fracture to the brittle interface seen in the SAC305 solder joint with multiple reflows did not occur in the composite solder joint. Furthermore, carbon fiber strengthened the solder matrix through the load transfer and shear-off mechanisms, depending on its inclination angle with the shear plane. Consequently, the Ni@CFs-reinforced solder joints maintained a shear strength of over 42 MPa throughout ten reflow cycles, while the pristine SAC305 solder joint exhibited decreased shear strength to 33 MPa. This study provides new insights into composite solder joints’ stability and reinforcement characteristics when subjected to multiple reflows.
•Expanded PS granules with 100 μm diameter begin to sink after 2 weeks of biofouling.•The sinking onset of PE and PP granules are similar and earlier than EPS granules.•Smaller MPs sinking faster is ...applicable for granules of same polymer as small as 100 μm.•Film, fiber and granular MPs with contrasting surface area to volume ratios sink at similar rates.
Sinking of microplastics (MPs) after biofouling is considered an important mechanisms responsible for the downward transport/sedimentation of MPs in the ocean and freshwaters. Previous studies demonstrated MP sinking caused by an increase in the composite density of MPs after biofouling, while MPs with smaller size or shapes with higher surface area to volume ratios (SA:V), such as films, are speculated to sink faster. In this study, we designed an in situ microcosm to simulate the ambient environmental conditions experienced by floating MPs to elucidate the biofouling and sinking of polyethylene (PE), polypropylene (PP), and expanded-polystyrene (EPS) MPs of various sizes and shapes. Our results showed smaller PE and PP MP granules sank faster than large ones. Even EPS granules of 100 μm diameter, having a much lower density (0.02 mg/mm3) than water, started to sink after 2 weeks of biofouling. Moreover, PE film and fiber MPs with higher SA:V did not sink faster than PE MP granules of the same mass, implying that mechanisms other than SA:V, such as fouling contact area and drag coefficient, play a role in the regulation of biofouling and sinking of MPs.
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Minerals are ubiquitous in the natural environment and have close contact with microorganisms. In various scenarios, microorganisms that harbor extracellular electron transfer (EET) capabilities have ...evolved a series of beneficial strategies through the mutual exchange of electrons with extracellular minerals to enhance survival and metabolism. These electron exchange interactions are highly relevant to the cycling of elements in the epigeosphere and have a profound significance in bioelectrochemical engineering applications. In this review, we summarize recent advances related to the effects of different minerals that facilitate the EET process and discuss the underlying mechanisms and outlooks for future applications. The promotional effects of minerals arise from their redox-active ability, electrical conductivity and photocatalytic capability. In mineral-promoted EET processes, various responses have concurrently arisen in microorganisms, such as stretching of electrically conductive pili (e-pili), upregulated expression of outer-membrane cytochromes (Cyts) and production of specific enzymes, and secretion of extracellular polymeric substances (EPSs). This review synthesizes the understanding of electron exchange mechanisms between microorganisms and minerals and highlights potential applications in development of renewable energy production and pollutant remediation, which are topics of particular significance to future exploitation of biotechnology.
•Redox-active minerals can serve as a temporary mediator for electron storage.•(Semi)conductive minerals ameliorate electrical conductivities in the attached interface.•Magnetite assists bioelectrocatalytic performance.•Semi-conductive minerals drive intimately coupled photoelectrochemical-microbial reduction process.
Microplastics are an emerging and persistent pollutant due to their threat to global ecological systems and human health. Recent studies showed that microplastics have infiltrated the remote Third ...Pole – the Tibetan Plateau. Here, we summarize the current evidence for microplastic pollution in the different environments (rivers/lakes, sediment, soil, ice/snow and atmosphere) of the Tibetan Plateau. We assess the spatial distribution, source, fate, and potential ecological effects of microplastics in this broad plateau. The integrated results show that microplastics were pervasive in biotic and abiotic components of the Tibetan Plateau, even at the global highest-altitude, Mt. Everest. Although the concentration of microplastics in the Tibetan Plateau was far below that found in the densely populated lowlands, it showed a higher concentration than that in the ocean system. Tourist populations are identified as a substantial source of anthropogenic plastic input rather than local residents due to the rapid development of the tourism industry. In the sparsely inhabited remote area of the Tibetan Plateau, long-range atmospheric transport facilitates allochthonous microplastic diffusion. Robust solar radiation in the Tibetan Plateau might enhanced production of secondary microplastics by weathering (UV-photooxidation) of abandoned plastic waste. A rough estimation showed that the microplastic export flux from melting glaciers was higher than that measured in most of the world's largest rivers, which affects local and downstream areas. Since the Tibetan Plateau is vital for Asian water supply and numerous endangered wildlife, the potential human and ecological risk of microplastics to these fragile ecosystems needs to be fully evaluated within the context of climate-change impacts.
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•Microplastics are ubiquitous in all the environmental media of the Tibetan Plateau.•The contribution of plastic waste from tourists is higher than local residents.•Robust weathering condition enhanced the production of secondary microplastics.•Atmospheric transport facilitates long range diffusion of microplastics in this area.•Ecological risk assessment on microplastics in this fragile ecosystem is urgently needed.
The inherent ductile-to-brittle transition (DBT) of body-centered tetragonal Sn at cryogenic temperatures restricts the use of Sn-based solders in the interconnection of cryogenic electronics, but ...little is known about the deformation behaviors accompanying with the transition and the underlying transition mechanism. In this work, the deformation features before cryogenic brittle fracture and the DBT mechanism in polycrystalline Sn were studied through uniaxial tensile experiments at different temperatures. Compared to the softening process stimulated by dynamic recovery and dynamic recrystallization before ductile fracture at room temperature (~293 K), a high strain hardening rate (~5% of the shear modulus) is maintained during the linear hardening period preceding brittle fracture at the liquid nitrogen temperature (~77 K) due to the pronounced intersecting of {301} deformation twins. But the irreconcilable velocity difference between dislocation glide (~3 µm/s) and twin thickening (~10 µm/s) at 77 K leads to a premature brittle fracture in the midst of the linear hardening, and indeed the DBT. The suggested specific DBT mechanism is substantiated by the fact that a significant increase in the velocity (~1500 µm/s) with the increasing temperature (123 K) allows the dislocation slip to readily accommodate the shear strains due to {301} twin thickening at the grain boundaries, thereby resulting in ductile fracture rather than brittle fracture. This deep understanding about the DBT in polycrystalline Sn may help forge a new path to design ductile and strong Sn-based solders and solder joints for cryogenic electronics by deformation twinning.
•As the temperature declines from 293 K to 77 K, the plastic deformation mechanism of polycrystalline Sn transforms from dislocation-mediated to deformation twinning-dominated.•The irreconcile velocity difference between dislocation glide (~3 µm/s) and twin thickening (~10 µm/s) leads to the brittle failure at 77 K, terminating the linear strain hardening.•Ductile-to-brittle transition will occur when the dislocation slip velocity cannot keep up with the thickening rate of deformation twins with the declining temperature.
A protocol was described for obtaining a variety of substituted thiophenes with functional potential via metal-free dehydration and sulfur cyclization of alkynols with elemental sulfur (S8) or ...EtOCS2K in moderate-to-good yields. The method provides the base-free generation of a trisulfur radical anion (S3 •–) and its addition to alkynes as an initiator. This research broadens the applications of S3 •– in the synthesis of sulfur-containing heterocycles.
Intimate coupling of microbial extracellular electron transfer (EET) and photoelectrochemical processes is an emerging research area with great potential to circumvent many disadvantages associated ...with traditional techniques that depend on independent microbial or photocatalysis treatment. Microbial EET processes involve microorganism oxidation of extracellular electron donors for respiration and synchronous reduction of extracellular electron acceptors to form an integrated respiratory chain. Coupled microbial EET-photoelectrochemical technologies greatly improve energy conversion efficiency providing both economic and environmental benefits. Among substitutes for semiconductor photocatalysts, cadmium sulfide nanoparticles (CdS NPs) possess several attractive properties. Specifically, CdS NPs have suitable electrical conductivity, large specific surface area, visible light-driven photocatalysis capability and robust biocompatibility, enabling them to promote hybrid microbial-photoelectrochemical processes. This review highlights recent advances in intimately coupled CdS NPs-microbial extracellular electron transfer systems and examines the mechanistic pathways involved in photoelectrochemical transformations. Finally, the prospects for emerging applications utilizing hybrid CdS NPs-based microbial-photoelectrochemical technologies are assessed. As such, this review provides a rigorous fundamental analysis of electron transport dynamics for hybrid CdS NPs-microbial photoelectrochemical processes and explores the applicability of engineered CdS NPs-biohybrids for future applications, such as in environmental remediation and clean-energy production.
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•CdS NPs assists hybrid microbial-photoelectrochemical processes.•CdS NPs display desirable biocompatibility with microorganisms.•CdS NPs-immobilized biohybrids display a potential for environmental application.
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•NIR provides a comprehensive method for quality evaluation of Dendrobium officinale.•Rapid content determination and origin identification was performed.•CARS algorithm was ...outstanding in model optimization.•SVC model obtained satisfactory discrimination results.
Dendrobium officinale, often used as a kind of tea for daily drinks, has drawn increasing attention for its beneficial effects. Quality evaluation of D. officinale is of great significance to ensure its health care value and safeguard consumers’ interest. Given that traditional analytical methods for assessing D. officinale quality are generally time-consuming and laborious, this study developed a comprehensive strategy, with the advantages of being rapid and efficient, enabling the quality evaluation of D. officinale from different geographical origins using near-infrared (NIR) spectroscopy and chemometrics. As the quality indicators, polysaccharides, polyphenols, total flavonoids, and total alkaloids were quantified. Three types of wavelength selection methods were used for model optimization and these were synergy interval (SI), genetic algorithm (GA), and competitive adaptive reweighted sampling (CARS). From the qualitative perspective, the geographical origins of D. officinale were differentiated by NIR spectroscopy combined with partial least squares-discriminant analysis (PLS-DA) and support vector classification (SVC). The PLS models constructed based on the wavelengths selected by CARS yielded the best performance for prediction of the contents of quality indicators in D. officinale. The root mean square error (RMSEP) and coefficient of determination (Rp2) in the independent test sets were 12.7768 g kg−1 and 0.9586, 1.1346 g kg−1 and 0.9670, 0.3938 g kg−1 and 0.8803, 0.0825 and 0.7031 and for polysaccharides, polyphenols, total flavonoids, and total alkaloids, respectively. As for the origin identification, the nonlinear SVC was superior to the linear PLS-DA, with the correct recognition rates in calibration and prediction sets up to 100% and 100%, respectively. The overall results demonstrated the potential of NIR spectroscopy and chemometrics in the rapid determination of quality parameters and geographical origin. This study could provide a valuable reference for quality evaluation of D. officinale in a more rapid and comprehensive manner.
We reported a phenomenon and mechanism of recrystallization evolution in solder joint under thermo-mechanical stress. Ball Grid Array samples fabricated by Sn3.0Ag0.5Cu solder were placed into the ...thermal cycling test chamber with a temperature range of −55 °C to 125 °C. Characterized using electron backscattered diffraction technique, three stages of recrystallization occurring in the solder joint were found to co-exist in one joint after 2500 thermal cycles. To better understand the formation of recrystallized grains during thermal cycling, especially dislocation substructures at the early stage, thin foils corresponding to different stages of the recrystallization were extracted by focus ion beam from the solder joint and analyzed by high-resolution transmission electron microscope. We summarize the recrystallization process including the annihilation of dislocation dipoles contributes to the evolution of sub-grain boundaries, and then the recrystallized grains are generated by sub-grain rotation mechanism. In addition, the recrystallized grains proceed to the subsequent same cycle until the failure of solder joint. The study provides the theoretical basis and technical support for further improving the thermo-mechanical reliability of Sn-based lead-free solder joints.
•Three stages of recrystallization were found to co-exist in one solder joint after 2500 thermal cycles.•The early stage of recrystallization in solder joint was proposed to explain the formation of sub-grains.•The recrystallized grains proceed to the subsequent same cycle until the failure of solder joint.
A protocol was described to access diverse isothiazoles with functionalization potential via transition metal‐free three‐component annulation of alkynones, potassium ethylxanthate (EtOCS2K) and ...ammonium iodide (NH4I). A sequential regioselective hydroamination/thiocarbonylation/intramolecular cyclization cascade achieved the efficient formation of consecutive C−N, C−S and N−S bonds in a one‐pot process.
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