Effect of nitrogen on deflagration characteristics of hydrogen / methane mixture

In order to study the influence of nitrogen on the deflagration characteristics of premixed hydrogen/methane, the explosion parameters of premixed hydrogen/methane within various volume ratios and different dilution ratios were studied by using a spherical flame method at room temperature and pressure. The results are as follows: The addition of nitrogen makes the upper limit of explosion of hydrogen/methane premixed gas drop, and the lower limit rises. For explosion hazard (F-number), hydrogen/methane premixed fuel with a hydrogen addition ratio of 10% has the lowest risk, and nitrogen has a greater impact on the dangerous degree of hydrogen and methane premixed gas whose hydrogen addition ratio does not exceed 30%. In terms of flame structure, the spherical flame was affected by buoyancy instability as the percentage of nitrogen dilution increased, but the buoyancy instability gradually decreased as the percentage of hydrogen addition increased. The addition of diluent gas reduces the spreading speed of the stretching flame and reduces the stretching rate in the initial stage of flame development. The laminar flame propagation velocity calculated by the experiment in this paper is consistent with the laminar flow velocity of the hydrogen/methane premixed gas calculated by GRI Mech 3.0. Considering the explosion parameters such as flammability limit, laminar combustion rate and deflagration index, when hydrogen is added to 70%, it is the turning point of hydrogen/methane premixed fuel.     

Effect of SnO–P2O5–MgO glass addition on the ionic conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

NASICON-type structured compounds Li_1+xM_xTi_2-x(PO₄)₃ (M = Al, Fe, Y, etc.) have captured much attention due to their air stability, wide electrochemical window and high lithium ion conductivity. Especially, Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) is a potential solid electrolyte due to its high ionic conductivity. However, its actual density usually has a certain gap with the theoretical density, leading the poor ionic conductivity of LATP. Herein, LATP solid electrolyte with series of SnO–P₂O₅–MgO (SPM, 0.4 wt%, 0.7 wt%, 1.0 wt%, 1.3 wt%) glass addition was successfully synthesized to improve the density and ionic conductivity. The SPM addition change Al/Ti–O bond and P–O bond distances, leading to gradual shrinkage of octahedral AlO₆ and tetrahedral PO₄. The bulk conductivity of the samples increases gradually with SPM glass addition from 0.4 wt% to 1.3 wt%. Both SPM and the second-phase LiTiPO₅, caused by glass addition, are conducive to the improvement of compactness. The relative density of LATP samples increases first from 0 wt% to 0.7 wt%, and then decreases from 0.7 wt% to 1.3 wt% with SPM glass addition. The grain boundary conductivity also changes accordingly. Especially, the highest ionic conductivity of 2.45 × 10^?4 S cm^?1, and a relative density of 96.72% with a low activation energy of 0.34 eV is obtained in LATP with 0.7 wt% SPM. Increasing the density of LATP solid electrolyte is crucial to improve the ionic conductivity of electrolytes and SPM glass addition can promote the development of dense oxide ceramic electrolytes.     

Novel hydrophilic N-halamine polymer with enhanced antibacterial activity synthesized by inverse emulsion polymerization

N-halamine-based antibacterial agents have high efficiency and rechargeable antibacterial properties. However, their applications are limited due to their complex synthetic process and fuzzy antibacterial mechanism. In this study, a novel N-halamine antibacterial polymer was synthesized by inverse emulsion polymerization and characterized by Fourier transform infrared, nuclear magnetic resonance, scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Due to the difficulty of purification, most of the subjects studied previously were hydrophobic polymers, while little research on hydrophilic polymers. In this experiment, this difficulty was overcome by controlling the dosage of sodium hypochlorite and methods of dialysis. Because of the complex cell structure of Gram-negative bacteria, it is difficult for N-halamines to release the oxidizing chlorine into the cell. However, the hydrophilic N-halamines can solve this problem, which showed a stronger antibacterial effect on Gram-negative Escherichia coli synthesized in this study. In addition, the particle size and hydrophilic property of the polymer were changed by changing the amount of initiator, and the differences in their antibacterial properties were studied. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47419.     

基体稀释或基体匹配石墨炉原子吸收光谱法测定土壤样品中铅和镉

用石墨炉原子吸收光谱法测定土壤样品中Pb和Cd时,有时候直接按照方法标准GB/T 17141—1997操作,测定结果不能满足质控要求。研究结果表明,目标元素系列标准溶液中,分别含和不含土壤基体元素Na、Mg、Al、Si、Fe、Ca等元素混合成分时,校准曲线斜率明显不同。为减小基体效应的影响,基于文献调研和实验结果,对上述方法标准实验步骤进行了下列改进:(1)取相同体积实际样品消解液混合后,定量加入到用于建立校准曲线的系列标准溶液中,用于基体匹配;(2)对消解液进行适度稀释,仍采用标准溶液建立校准曲线。用4个土壤标样和土壤样品加标测定结果对改进后的方法进行了验证,结果表明,基体稀释法测定Pb的回收率范围分别为90.4%~114%;测定低含量Cd时,回收率范围为84.1%~125%。基体匹配法测定Pb和Cd的回收率范围分别为93.0%~105%和102%~119%,基本满足土壤样品中重金属回收率为80%~120%的质控要求。样品中痕量镉在测定下限附近时,应严格控制稀释倍数,或采用基体匹配法测定。改进后的操作步骤适合日常检测工作中大批量土壤样品中Pb和Cd的准确测定。     

优化气相色谱法测定生活饮用水中六六六和滴滴涕

目的优化GB/T 5750.9-2006《生活饮用水标准检验方法农药指标》中的气相色谱法测定生活饮用水中六六六(α-666、β-666、γ-666、δ-666)和滴滴涕(ρ,ρ'-DDE、ο,ρ'-DDT、ρ,ρ'-DDD、ρ,ρ'-DDT)含量。方法样品经石油醚萃取浓缩后,经由电子捕获检测器-气相色谱测定α-666、β-666、γ-666、δ-666、ρ,ρ'-DDE、ο,ρ'-DDT、ρ,ρ'-DDD、ρ,ρ'-DDT的含量。结果 8种组分在8 min内全部出峰,各物质在5～100.0μg/L浓度范围内线性关系良好,相关系数均大于0.999,检出限为0.007～0.010μg/L,回收率为85.10%～105.85%,相对标准偏差为0.43%～2.68%。结论该方法分离效果高,灵敏度高,重复性好,准确度高,可以满足实验室条件下水样中六六六和滴滴涕的测定。     

超高效液相色谱-四极杆飞行时间质谱法快速测定混合型饲料添加剂中14种化学药物

目的 建立超高效液相色谱-四极杆飞行时间质谱法快速测定混合型饲料添加剂中培氟沙星、氯霉素、沙丁胺醇、盐酸克伦特罗、氧氟沙星、恩诺沙星、诺氟沙星、氟苯尼考、磺胺嘧啶、磺胺甲噁唑、磺胺间甲氧嘧啶、甲硝唑、多西环素、金刚烷胺共14种化学药物的分析方法。方法 样品经乙腈-水(8:2, V:V)提取, 上清液离心后上样, 以0.1%(V:V)甲酸甲醇溶液和0.1%(V:V)甲酸水溶液为流动相进行梯度洗脱(负离子模式流动相为乙腈-水), C18色谱柱(50 mm×2.1 mm, 1.7 μm)分离。分别采用正/负离子模式检测分析。结果 14种药物的质量数误差绝对值小于5 mDa, 在2.0~100.0 μg/L范围内线性关系良好, 相关系数大于0.99。4个浓度水平的平均回收率为70.6%~119.80%, 相对标准偏差1.0%~12.4%。结论 该方法操作简便、结果准确, 适用于混合型饲料添加剂中非法添加药物的快速筛查分析。     

Effects of Al addition on the phase transformation and interfacial evolution in multilayer Ti-B4C composite

The fully-dense multilayer Ti-B₄C composite doped with 6 wt% Al was fabricated via tape-casting and hot-pressing sintering at 1800 °C and under a uniaxial pressure of 30 MPa for 60 min. The effects of Al addition on the phase composition, interfacial microstructure and fracture toughness of the laminate composite were investigated. Based on the results of WDS and EDS, Al addition was proved to be effective on accelerating atom diffusion between Ti and B₄C due to the melting pool around interface where liquid Al enriched, besides, it helps to transform the interfacial bonding method of physical to metallurgical. Finally, the improvement on toughness of Al doped composite can be attributed to the strong metallurgical bonding and hybrid fracture mode of interface. Our study may provide a potential method for producing high strength and toughness multilayer metal/ceramic composites.     

Numerical investigation on the effects of load conditions and hydrogen-air ratio on the combustion processes of a HSDI engine

Owing to high specific energy and low emissions production, hydrogen is a desirable alternative fuel. The combustion and emission performance can be improved by hydrogen addition injected in-cylinder, intake manifold and aspirated with air. However, engine loads and hydrogen-air ration have a significant effect on the performance, combustion and emission of the diesel-hydrogen (high speed direct injection) HSDI engine. In this paper, the CFD method is used to calculate the combustion process of a diesel-hydrogen dual HSDI engine working at constant speed of 4000 rpm, at different hydrogen added from intake port (hydrogen volume fraction of 0%–10%) and five engine loads (equivalent to 20%, 40%, 60%, 80% and 100% of its maximum output power), respectively. The modelling results showed that the in-cylinder pressure and temperature under low engine load were more affected by hydrogen addition. With increasing hydrogen volume fraction, the indicated expansion work and in-cylinder peak pressure increased, and combustion duration decreased due to faster fuel-air mixing and spray flame speed.     

Influence of trace Ca addition on texture and stretch formability of AM50 magnesium alloy sheet

The AM50, AM50–0.1Ca, AM50–0.3Ca and AM50–0.5Ca (wt.%) alloys were hot-rolled and their mechanical properties were determined for the purpose of investigating the effect of trace Ca addition on the texture and stretch formability of AM50 alloy. The results show that the addition of trace Ca can effectively modify the basal texture, which is characterized by the split of basal poles deviated from the normal direction (ND) after the hot rolling, while a broad spread of the basal planes toward the transverse direction (TD) after the annealing. Such change of the basal texture is related to the prior formation of massive compression twins and the decrease of the c/a ratio. Erichsen value increases from 2.25 to 4.21 mm with the increase of Ca content. The enhancement of stretch formability is ascribed to the weakened basal texture, which results in the increase of n-value and the decrease of r-value.