Spark plasma sintering of UO2 nanopowders: Pressure,heating rate and current effects

We analysed with different methods the densification of UO₂ nanopowders in SPS under constant heating rate (CHR) and isothermal sintering conditions. The apparent activation energy of densification in SPS (75 kJ/mol with CHR method) is significantly smaller than in conventional sintering. It is shown that this is likely not an effect of the applied current. We also observed a threshold stress at 64 MPa for the transition from pressure-insensitive sintering (stress exponent n≈0) to pressure-assisted sintering, suggesting that the contribution of the capillary stresses in such nanopowders is comparable with the typical stress applied in SPS.     

石油降解菌ZS1对典型抗生素毒害作用的应激响应机制

为了解抗生素对石油降解菌的生态效应及微生物对典型抗生素毒害作用的应激响应机制，通过开展不同浓度典型抗生素对高效石油降解菌铜绿假单胞菌（ZS1）的毒性试验，研究了菌体细胞在3种不同种类抗生素（土霉素、红霉素、磺胺嘧啶）作用下的生长及毒理指标。结果表明，3种抗生素对ZS1有不同的抑菌效果，其中土霉素对ZS1活性的抑制程度最强，抑制率随着土霉素浓度的增大而明显上升，有显著的浓度-效应关系。研究了ZS1抗氧化酶（过氧化氢酶、过氧化物酶、超氧化物歧化酶）对抗生素的响应机制，结果表明ZS1受到污染时会通过产生抗氧化酶抵抗外界污染并维持细胞功能。     

Local scour at offshore windfarm monopile foundations: A review

In this article, current research findings of local scour at offshore windfarm monopile foundations are presented. The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized, including the current-only condition, wave-only condition, combined wave-current condition, and complex dynamic condition. Furthermore, this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific conditions. The weakness of existing researches and future prospects are also discussed. It is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex loadings. The computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.     

Braking behaviours of C/C–SiC mated with iron/copper-based PM in dry,wet and salt fog conditions

C/C–SiC composites have enormous potential as a new generation of brake materials. It is worth studying the friction and wear behaviours of these materials in special environments to ensure the safe and effective braking of trains in practical applications. In this study, the braking behaviours and wear mechanisms of C/C–SiC mating with iron/copper-based PM in dry, wet and salt fog conditions are compared in detail. The results show that the coefficient of friction (COF) in the wet condition is reduced by 14.13% compared with that under the dry condition. The COF value of the first braking under salt fog condition is increased by 12.27% and 30.75% compared to the dry and wet conditions, respectively. Additionally, the tail warping phenomenon of the braking curve disappears in wet condition, which is attributed to the weak adhesion of friction interfaces and the lubrication of the water film. The main wear mechanisms of C/C–SiC mating with iron/copper-based PM under dry condition are adhesive, fatigue and oxidation wear. However, the dominant wear in wet condition is abrasive wear. The cooling and lubrication of water reduce the tendency of thermal stress, and weaken adhesive and fatigue wear. Furthermore, salt fog can accelerate the corrosion of alloy friction film, leading to the damage of friction film. Meanwhile, the third body particles formed in salt fog condition participate in the braking process. The wear mechanisms in salt fog condition are dominated by abrasive and delamination wear.     

In-situ elongated aluminium borate grains toughening WC- 1.87 wt % Al2O3- 4.13 wt % ZrO2 composite via spark plasma sintering

In this work, a novel way was developed to facilitate the sintering of a binderless cemented carbide with Al₂O₃ contain while improving its toughness. WC- 1.87 wt % Al₂O₃- 4.13 wt %ZrO₂ cemented carbides with 1 wt % B₂O₃ as additives were consolidated by high energy ball-milling and spark plasma sintering the as-milled composite powders. The effects of 1 wt % B₂O₃ content on the sintering behaviour, microstructure and mechanical properties of the obtained cemented carbides were investigated. The presence of B₂O₃ significantly lowers the sintering temperature by forming liquid phase and react with Al₂O₃ which contributed to obtaining fully dense specimens at 1350 °C and maintains fine grain sizes of WC until the temperature exceeding 1450 °C. The sintering temperature of the specimens with optimum mechanical properties has been also reduced comparing that of the original WC- 1.87 wt % Al₂O₃- 4.13 wt %ZrO₂ cemented carbides. Furthermore, the addition of B₂O₃ triggered the reaction between B₂O₃ and Al₂O₃ resulting in forming in-situ elongated aluminium borate grains (A₄B₂O₉ and A₁₈B₄O₃₃ whiskers), which promoted the toughness. The specimens sintered at 1450 °C exhibited optimal mechanical properties: the Vickers hardness and fracture toughness were 19.26 GPa and 11.49 MPa m^1/2, respectively.     

Foam-based cleaning of surfaces contaminated with mixtures of oil and soot

Liquid foams of intermediate stability have been shown to be very efficient in the cleaning of sensitive surfaces because of the synergy between imbibition and foam decay. While we quantified these mechanisms for contaminations with liquid oils in our previous work, we show here their extension to oils containing soot particles in an effort to simulate increasingly realistic contaminations. Using foams with a wide range of liquid fractions and with different stabilities, we show that the main cleaning mechanisms remain very similar, with the oil entraining the soot particles. However, we find much less efficient soot removal when the liquid channels of the foams are small enough to hinder efficient transport of the soot particles.     

High-entropy ferroelastic rare-earth tantalite ceramic: (Y0.2Ce0.2Sm0.2Gd0.2Dy0.2)TaO4

In this study, high-entropy rare-earth tantalate ceramics (Y_0.2Ce_0.2Sm_0.2Gd_0.2Dy_0.2)TaO₄ ((5RE_0.2)TaO₄) have been successfully fabricated. The possibility of formation of (5RE_0.2)TaO₄ was verified via first-principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE_0.2)TaO₄ ceramics have lower phonon thermal conductivity (1.2–2.6 W·m^–1·K^–1) in the entire temperature range than that of RETaO₄ and YSZ. (5RE_0.2)TaO₄ has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE_0.2)TaO₄ are as high as 10.3 × 10^-6 K^–1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE_0.2)TaO₄ possesses great potential for application in thermal barrier coatings (TBCs).     

Microstructure,mechanical properties,and fracture behaviour of Ti(C,N)-based cermets with a composite structure

Ti(C,N)-based cermets with a composite structure were designed to maintain the balance between strength and toughness. The cermets with the composite structure comprised coarse particles and the matrix, and the coarse particles included fine hard phases compounded in the matrix. A new hard phase grain with a four-layered structure was found. The composite structure of the cermet can contribute to high toughness, and the grain with the four-layered structure in the composite structure imparts high strength and toughness. As the granule size increases, the fracture toughness of the cermets increased, but the hardness and transverse rupture strength (TRS) showed the opposite trend. The toughening mechanisms of the cermet were crack branching, crack bridging, crack deflection, and formation of tear ridges.     

超高效液相色谱-串联质谱法测定化妆品中同分异构体构型糖皮质激素

目的 建立超高效液相色谱-串联质谱法(ultra performance liquid chromatography-tandem mass spectrometry, UPLC-MS/MS)测定化妆品中同分异构体构型糖皮质激素(glucocorticoids, GCs)的分析方法。方法样品经饱和氯化钠分散、乙腈提取,亚铁氰化钾-醋酸锌沉淀大分子基质后,通过分散固相萃取技术(QuEChERS)净化。以0.1%甲酸水溶液和乙腈作为流动相迚行梯度洗脱,采用多反应监测模式(multiple reaction monitoring, MRM)对美白祛斑类化妆品中同分异构体构型糖皮质激素迚行定量和定性检测。结果 本方法完成了对糖皮质激素中最难以分离的差向同分异构体倍他米松、地塞米松以及它们的衍生物倍他米松醋酸酯、地塞米松醋酸酯的分离检测。在5.0、10和20μg/kg添加水平时的回收率为78.6%～102.7%,相对标准偏差小于10.60%(n=6),方法定量限为6.0μg/kg。结论 该方法快速、稳定、灵敏度高、选择性好,适合分析检测化妆品中非法添加的GCs类化合物。