Experimental study on the propagation characteristics of hydrogen/methane/air premixed flames in a narrow channel

This work is focused on the explosion characteristics of premixed gas containing different volume fractions of hydrogen in a narrow channel (1000 mm × 50 mm × 10 mm) under the circumstance of stoichiometric ratio. The ignition positions were set in the closed end and the middle of the pipeline respectively. The results showed that when the gas was ignited at the pipeline closed end, the propagating flame was tulip structure for different premixed gas. When the hydrogen volume fraction was less than 40%, the flame propagation speed increased significantly with the rise of hydrogen volume fraction, and the overpressure peak also appeared obviously in advance. However, when the volume fraction of hydrogen was more than 40%, the increase of flame propagation speed and the overpressure peak occurrence time varied slightly. Furthermore, when the ignition position was placed in the middle of the pipeline, the flame propagation speed propagating to the opening end was much faster than that propagating to the closing end, and there was no tulip shape when the flame propagates to the opening end. The flame propagating to the closed end appeared tulip shape under the influence of airflow, and high-frequency flame oscillation occurred during the propagation. This work shows that the hydrogen volume fraction and ignition position significantly affected the flame structure, flame front speed, and explosion overpressure.     

Anisotropy Effects in the Shape-Memory Performance of Polymer Foams

Isotropic and anisotropic shape-memory polymer foams are prepared by supercritical carbon dioxide foaming from a multiblock copolymer (PDLCL) consisting of poly(ω-pentadecalactone) and poly(ε-caprolactone) segments. Analysis by micro-computed tomography reveals for the anisotropic PDLCL foam cells a high shape anisotropy ratio of R = 1.72 ± 0.62 with a corresponding Young's compression moduli ratio between longitudinal and transversal direction of 4.3. The experimental compression data in the linear elastic range can be well described by the anisotropic open foam model of Gibson and Ashby. A micro-morphological analysis for single pores using scanning electron microscopy images permits the correlation between the macroscopic stress-compression behavior and microscale structural changes.     

Harvesting Air and Light Energy via “All-in-One” Polymer Cathodes for High-Capacity,Self-Chargeable,and Multimode-Switching Zinc Batteries

Aqueous rechargeable Zinc (Zn)–polymer batteries are promising alternatives to prevalent Li-ion cells in terms of cost, safety, and rate capability but they suffer from limited specific capacity in addition to poor environmental adaptability. Herein, air and light are successfully utilized from external environments in single near-neutral two-electrode Zn batteries to enable remarkably improved electrochemical performance, fast self-charging, and switchable multimode-operation from Zn–polymer to Zn–air cells. This system is enabled by a well-designed polyaniline-nanorod-array based “all-in-one” cathode combining reversible redox capability, oxygen reduction activity, and photothermal-responsiveness. The initiative design allows perfect integration of multiple energy harvesting from ambient “air” and light, energy conversion, and storage in one single cathode. Thus, it can act as an efficient light-assisted electrically-rechargeable Zn–polymer cell featuring the highest specific capacity of 430.0 mAh g⁻¹ among all existing polymer cathodes. Without external power sources, it can be self-charged to deliver a high discharging capacity of 363.1 mAh g⁻¹ by concurrently harvesting chemical energy from air and light energy for only 20 min. It can also switch to a light-responsive Zn–air battery mode to surmount the output capacity limit of Zn–polymer battery mode for continued electricity supply.     

3D-printing of polymer‐derived SiCN ceramic matrix composites by digital light processing

In this study, we present a DLP 3D-printing strategy for the fabrication of SiCN ceramic matrix composites (CMCs). The polysilazane-based preceramic polymer containing inert fillers was UV-cured into a green body and then converted to SiCN CMCs after pyrolysis. The introduced fillers (Si₃N₄ particles and Si₃N₄ whiskers) as reinforcements are well dispersed in the matrix, which can not only effectively reduce the linear shrinkage and weight loss, but also greatly improve the mechanical properties of the SiCN CMCs. The bending strength of the SiCN CMCs reinforced with 10 wt% Si₃N₄ whiskers (without surface polished) reached 180.7 ± 15.6 MPa. Furthermore, the effect of fillers content on microstructure and porosity of the SiCN CMCs are discussed, and it was found that the excessive fillers led to increased pore defects and decreased continuity of the matrix, thereby reducing the mechanical properties of the SiCN CMCs. This strategy provides a promising ceramic manufacturing technique to fabricate polymer‐derived CMCs with complex-shaped and high-performance for potential demanding applications.     

Predetermination of potential plastic hinges on reinforced concrete frames using GFRP reinforcement

In the past, glass fiber-reinforced polymer (GFRP)-reinforcement has been successfully applied in reinforced concrete (RC) structures where corrosion resistance, electromagnetic neutrality, or cuttability were required. Previous investigations suggest that the application of GFRP in RC structures could be advantageous in areas with seismic activity due to their high deformability and strength. However, especially the low modulus of elasticity of GFRP limited its wide application as GFRP-reinforced members usually exhibit considerably larger deformations under service loads than comparable steel-reinforced elements. To overcome the aforementioned issues, the combination of steel and GFRP reinforcement in hybrid RC sections has been investigated in the past. Based on this idea, this paper presents a novel concept for the predetermination of potential plastic hinges in RC frames using GFRP reinforcement. To analyze the efficiency of the concept, nonlinear finite element simulations were performed. The results underscore the high efficiency of hybrid steel-GFRP RC sections for predetermining potential plastic hinges on RC frames. The results also indicate that the overall seismic behavior of RC structures could be improved by means of GFRP as both the column base shear force during the seismic activity as well as the plastic deformations after the earthquake were considerably less pronounced than in the steel-reinforced reference structure.     

Synthesis and characterization of a long side-chain double-cation crosslinked anion-exchange membrane based on poly(styrene-b-(ethylene-co-butylene)-b-styrene)

By choosing a triple block polymer, poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS), as the backbone and adopting a long side-chain double-cation crosslinking strategy, a series of SEBS-based anion-exchange membranes (AEMs) was successively synthesized by chloromethylation, quaternization, crosslinking, solution casting, and alkalization. The 70C16-SEBS-TMHDA membrane showed high OH⁻ conductivity (72.13 mS/cm at 80 °C) and excellent alkali stability (only 10.86% degradation in OH⁻ conductivity after soaking in 4-M NaOH for 1700 h at 80 °C). Furthermore, the SR was only 9.3% at 80 °C and the peak power density of the H₂/O₂ single cell was up to 189 mW/cm² at a current density of 350 mA/cm² at 80 °C. By introducing long flexible side chains into a polymer SEBS backbone, the structure of the hydrophilic–hydrophobic microphase separation in the membrane was constructed to improve the ionic conductivity. Additionally, network crosslinked structure improved dimensional stability and mechanical properties.     

Deep eutectic solvent-based supramolecular gel polymer electrolytes for high-performance electrochemical double layer capacitors

Gel polymer electrolytes (GPEs) can avoid the electrolyte leakage risk of electrochemical double layer capacitors (EDLCs). But aqueous GPEs often suffer from narrow electrochemical windows. Herein, a series of deep eutectic solvent (DES)-based supramolecular GPEs are firstly developed for carbon-based EDLCs with wide voltage windows. The as-fabricated DES-based GPE shows an ionic conductivity of ~58 mS cm^?1, which makes the stable voltage window of a carbon-based EDLC reach 2.4 V. The carbon-based EDLC exhibits a specific capacitance of 32.1 F g^?1, an energy density of 24.6 Wh kg^?1 and a capacitance retention of ~90% after 15,000 charge-discharge cycles. Moreover, when quinhydrone is added into the DES-based GPE, the specific capacitance and energy density of the corresponding EDLC can be further expanded to 60 F g^?1 and 43.6 Wh kg^?1, respectively. Therefore, our work may present a universal strategy to prepare novel supramolecular GPEs for high-performance EDLCs with wide voltage windows.     

Chemical exposures from upholstered furniture with various flame retardant technologies

Upholstered furniture is often manufactured with polyurethane foam (PUF) containing flame retardants (FRs) to prevent the risk of a fire and/or to meet flammability regulations, however, exposure to certain FRs and other chemicals have been linked to adverse health effects. This study developed a new methodology for evaluating volatile organic compound (VOC) and FR exposures to users of upholstered furniture by simulating use of a chair in a controlled exposure chamber and assessing the health significance of measured chemical exposure. Chairs with different fire-resistant technologies were evaluated for VOC and FR exposures via inhalation, ingestion, and dermal contact exposure routes. Data show that VOC exposure levels are lower than threshold levels defined by the US and global indoor air criteria. Brominated FRs were not detected from the studied chairs. The organophosphate FRs added to PUF were released into the surrounding air (0.4 ng/m³) and as dust (16 ng/m²). Exposure modeling showed that adults are exposed to FRs released from upholstered furniture mostly by dermal contact and children are exposed via dermal and ingestion exposure. Children are most susceptible to FR exposure/dose (2 times higher average daily dose than adults) due to their frequent hand to mouth contact.     

Flame characteristics of premixed H2-air mixtures explosion venting in a spherical container through a duct

The explosion venting duct can effectively reduce the hazard degree of a gas explosion and conduct the venting energy to the safe area. To investigate the flame quantitative propagation law of explosion venting with a duct, the effects of hydrogen fraction and explosion venting duct length on jet flame propagation characteristics of premixed H₂-air mixtures were analyzed through experiment and simulation. The experiment results under initial conditions of room temperature and 1 atm show that when hydrogen fraction was high enough, part of the unburned hydrogen was mixed with air again to reach an ignitable concentration, resulting in the secondary combustion was easier produced and the duration of the secondary flame increased. With the increase of venting duct length, the flame front distance and propagation velocity increased. Meanwhile, the spatial distribution of pressure field and temperature field, and the propagation process and mechanism of the flame venting with a duct were analyzed using FLUENT software. The variation of the pressure wave and the pressure reflection oscillation law in the explosion venting duct was captured. Therefore, in the industrial explosion venting design with a duct, the hazard caused by the coupling of venting pressure and venting flame under different fractions should be considered comprehensively.     

基于柠檬酸-铕纳米配位聚合物构建荧光探针快速检测汤煲中5’-肌苷酸含量

基于柠檬酸-铕金属有机纳米配体聚合物（citrate/europium lanthanide coordination polymer nanoparticles，Cit/Eu LCP NPs）构建快速检测肉品汤煲中5’-肌苷酸（inosine-5’-monophosphate，5’-IMP）的荧光探针。研究结果表明，5’-IMP对Cit/Eu?LCP?NPs有良好的荧光猝灭作用。在最佳条件下，该荧光探针在5’-IMP?2.5～200?μg/mL的质量浓度范围内呈现出良好的线性关系，检出限为0.17?μg/mL，且具备良好的抗干扰、稳定性和重复性。为了验证方法可行性，将该方法应用于实际鸡汤样品中的5’-IMP检测，测得加标回收率为97.85%～103.95%，可为快速检测肉品汤煲中5’-IMP提供新的思路和方法。