Microwave-assisted rapid preparation of hollow carbon nanospheres@TiN nanoparticles for lithium-sulfur batteries

Highly conductive titanium nitride (TiN) has a strong anchoring ability for lithium polysulfides (LiPSs). However, the complexity and high cost of fabrication limit their practical applications. Herein, a typical structure of hollow carbon nanospheres@TiN nanoparticles (HCNs@TiN) was designed and successfully synthesized via a microwave reduction method with the advantages of economy and efficiency. With unique structural and outstanding functional behavior, HCN@TiN-S hybrid electrodes display not only a high initial discharge capacity of 1097.8 mA h g−1 at 0.1C, but also excellent rate performance and cycling stability. After 200 cycles, a reversible capacity of 812.6 mA h g−1 is still retained, corresponding to 74% capacity retention of the original capacity and 0.13% decay rate per cycle, which are much better than those of HCNs-S electrodes

Facile synthesis of TiN nanocrystals/graphene hybrid to chemically suppress the shuttle effect for lithium-sulfur batteries

Herein, we present a microwave reduction strategy for the synthesis of reduced-graphene-oxide (rGO) supported TiN nanoparticle hybrid (TiN/rGO) under N2 atmosphere. The method involves GO reduction, metal oxide reduction and nitridation reaction in one single step. Due to TiN high conductivity and good interfacial affinity between it and lithium polysulfides (LiPSs), the prepared TiN/rGO-Sulfur (TiN/rGO-S) cathodes demonstrate rapid charge transfer, lower polarization, faster surface redox reaction kinetic and enhanced stability cycling performance than rGO-Sulfur (rGO-S) and TiO2/rGO-Sulfur (TiO2/rGO-S) cathodes. The initial capacity reaches 1197.6 mA h g−1 with a reversible capacity of 888.7 mA h g−1 being retained after 150 cycles at 0.1 C

Al-based MOF derived self-assembled carbon nanosheets as innovative anodes for Li-and Na-ion batteries

Functional modification and structural design of carbon electrode materials are considered as a cost-effective method to improve their electrochemical performance. In this study, a solvothermal method is applied to realize self-assembly of the metal-organic framework. After simple carbonization and acid treatment, carbon nanosheets with 2D adjustable defective sub-units are successfully prepared for the first time. It is found that carbonization temperature has a significant effect on the carbon skeleton structure. The optimal nanostructures with large specific surface area and appropriate pore size distribution make self-assembled carbon nanosheets having excellent Li/Na- ion storage properties. In addition, the adjustable carbon skeleton structure can effectively avoid irreversible damage when charge-discharge cycles. For Li-ion batteries, a specific capacity of 825 mAh g−1 is achieved after 100 cycles at 0.1 C, while for Na-ion batteries a specific capacity of 193 mAh g−1 is observed after 100 cycles at 0.5 C. Moreover, for Na-ion batteries, even at a high rate of 5 C the material delivers a specific capacity of 109.5 mAh g−1 after 3500 cycles

Exploring the prevalence and chest CT predictors of Long COVID in children: a comprehensive study from Shanghai and Linyi

IntroductionCOVID-19 constitutes a pandemic of significant detriment to human health. This study aimed to investigate the prevalence of Long COVID following SARS-CoV-2 infection, analyze the potential predictors of chest CT for the development of Long COVID in children.MethodsA cohort of children who visited the respiratory outpatient clinics at Shanghai Children's Medical Center or Linyi Maternal and Child Health Care Hospital from December 2022 to February 2023 and underwent chest CT scans within 1 week was followed up. Data on clinical characteristics, Long COVID symptoms, and chest CT manifestations were collected and analyzed. Multivariate logistic regression models and decision tree models were employed to identify factors associated with Long COVID.ResultsA total of 416 children were included in the study. Among 277 children who completed the follow-up, the prevalence of Long COVID was 23.1%. Chronic cough, fatigue, brain fog, and post-exertional malaise were the most commonly reported symptoms. In the decision tree model for Long COVID, the presence of increased vascular markings, the absence of normal CT findings, and younger age were identified as predictors associated with a higher likelihood of developing Long COVID in children. However, no significant correlation was found between chest CT abnormality and the occurrence of Long COVID.DiscussionLong COVID in children presents a complex challenge with a significant prevalence rate of 23.1%. Chest CT scans of children post-SARS-CoV-2 infection, identified as abnormal with increased vascular markings, indicate a higher risk of developing Long COVID

Long-term ageing effect on mechanical properties of polyamide 12 printed by multi-jet-fusion

Multi-Jet-Fusion (MJF) is a relatively new powder-based face-sintering additive manufacturing technique that exhibits great potential in high-volume manufacturing due to its rapid printing speed. Extensive research has been conducted on the mechanical properties of MJF-printed polyamide 12 (MJF PA12) by investigating the powder characteristics and build orientations. However, no work has been conducted to study the effect of humidity and physical ageing on the mechanical performance of MJF PA12 specimens. Here, the physical and mechanical properties of MJF PA12 specimens that were printed in different build orientations and stored under ambient and dryer conditions for 474 days were investigated. It was found that specimens stored under ambient conditions exhibited a drop in glass transition temperature due to moisture absorption followed by an increase, which could indicate that ageing of the specimens occurred. The moisture absorption was also found to have an insignificant effect on the crystallinity and crystallite size of the specimens. The change in mechanical properties, such as the tensile modulus and ultimate tensile strength, was more significant for specimens stored in ambient conditions than those in dryer conditions. It was also found that the build orientation does not have a significant impact on the moisture absorption rate, glass transition temperature, and the change in the trend of mechanical properties. In addition, an artificial neural network was adopted to predict the mechanical properties of the MJF PA12 specimens under the influence of physical ageing, humidity, and build orientations. The neural network adopted in this work can predict the change in the mechanical properties of differently-orientated MJF PA12 with different moisture content over time. The neural network prediction could be useful in providing guidance on the structure and risk assessment of the parts before print.Nanyang Technological UniversityNational Research Foundation (NRF)Part of this research was conducted in collaboration with HP Inc. and supported by Nanyang Technological University and the Singapore Government through the Industry Alignment Fund-Industry Collaboration Projects Grant (I1801E0028). The research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Medium-Sized Centre funding scheme

In-situ TiC particle reinforced TiCuZrNi brazing alloy for joining C/C composites to Ti6Al4V

Chromium carbide modified C/C and Ti6Al4V were successfully joined using a TiCuZrNi brazing alloy in powder form. The braze/composite interface and the mechanical strength of C/C-Ti6Al4V joints were evaluated. The apparent shear strength of chromium carbide modified C/C joined to Ti6Al4V, measured by single lap test in compression, was 52 ± 6 MPa, which was highest among that without chromium carbide modification (15 ± 2 MPa) and the intrinsic C/C shear strength. The fractography of joints without chromium carbide modification indicated that failure mainly occurred at the TiC layer formed at the composite/ braze interface while the joints with chromium carbide modification failed within the C/C

Crystallisation behaviour of polyamide-12 during additive manufacturing process

Polyamide 12 (PA12) is a semi-crystalline polymer as its crystallisation behaviour varies due to manufacturing conditions. In this work, the crystallisation behaviour of PA12 was observed through experiments conducted at a constant cooling rate from different maximum heated temperatures. From the differential scanning calorimetry (DSC) experiment, PA12 exposed at a higher temperature crystallised at a lower temperature. The crystallisation shrinkage observed from thermomechanical analysis (TMA) was lower after PA12 was exposed at a higher temperature. Judging from the crystal growth process of PA12 from in-situ optical microscope and phase field modelling, the crystals of PA12 exposed at a higher temperature were found to be smaller and more compact. The exposure to a high temperature allows PA12 to have lower melt viscosity, ensuring the material to sinter evenly, and this enhances better molecular interactions from polymer chains for the formation of crystals.Nanyang Technological UniversityThis research work is conducted in collaboration with HP Inc. and supported by Nanyang Technological University and the Singapore Government through the Industry Alignment Fund – Industry Collaboration Projects Grant (I1801E0028)

Microstructure and mechanical properties of C/C composite/Ti6Al4V joints with aCu/TiCuZrNi composite brazing alloy

C/C compositesandTi6Al4V sheetswerejoinedusinganovelCu/TiCuZrNicompositebrazeandtheeffectofCufoilthicknessonthe microstructure andmechanicalpropertiesofthejointswereinvestigated.Acompositejoiningmaterial,consistingofaTiCparticlereinforced brazing alloyformedinsituduringthebrazingprocesswasobtained.Beforethejoiningprocess,theC/Ccompositesurfacewasmodified by solid statereactionwithchromiumtoformachromiumcarbidecoating.ThiscarbidereactionlayercanreactwiththeTi-basedbrazingalloyand form evenlydistributedTiCparticles.Themaximumapparentshearstrengthofas-receivedjointwas3978.5 MPaobtainedbyusinga40 μm thick CufoiltogetherwiththeTiCuZrNialloy;thisvaluewas70%higherthanthemechanicalstrengthobtainedforjointsbrazedwiththe TiCuZrNi alloyonly