Dielectric relaxation and conduction mechanism in Aurivillius ceramic Bi5Ti3FeO15

For this study, we synthesized Aurivillius Bi5Ti3FeO15 ceramic using the generic solid-state reaction route and then performed room-temperature X-ray diffraction to confirm that the compound had a single phase with no impurities. The surface morphology of the prepared sample was observed to contain microstructural grains approximately 0.2–2 μm in size. The dielectric properties of the sample were determ-ined as a function of frequency in a range of approximately 100 Hz to 1 MHz at various temperatures (303 K ≤ T ≤ 773 K). Nyquist plots of the impedance data were found to exhibit a semi-circular arc in the high-temperature region, which is explained by the equivalent electrical circuit (R1C1)(R2QC2), where R1 and R2 represent the resistances associated with the grains and grain boundaries, respectively, C1 and C2 are the re-spective capacitances, and Q is the constant phase element (CPE), which accounts for non-Debye type of behavior. Our results indicate that both the resistance and capacitance of the grain boundaries are more prominent than those of the grains. The alternating current (ac) conductiv-ity data were analyzed based on the Jonscher universal power law, which indicated that the conduction process is dominated by the hopping mechanism. The calculated activation energies of the relaxation and conduction processes were very similar (0.32 to 0.53 eV), from which we conclude that the same type of charge carriers are involved in both processes.     

钒酸铋光电催化分解水的研究进展

光电化学(photoelectrochemical, PEC)催化分解水制氢被认为是生态友好、规模化和可持续性地转化与储存太阳能的理想途径之一,但光阳极较低的工作效率限制了PEC分解水的发展.近年来,钒酸铋光阳极因具有较高的理论光电流密度受到科学界的广泛关注.大量的工作聚焦在如何将钒酸铋光阳极所具有的理论潜力尽可能地发挥并应用至PEC分解水制氢.本文通过回顾和分析钒酸铋光阳极的吸光效率、光生载流子分离效率与表面催化产氧效率3个方面的研究进展,对高性能钒酸铋光阳极的设计思路与合成方法进行评述、总结与展望,为进一步挖掘钒酸铋光电极的潜力与开发下一代光电极提供参考和思路.     

Effect of Co substitution on the structural,dielectric and optical properties of KBiFe2O5

Cobalt (Co)-modified brownmillerite KBiFe2O5 (KBFO; [KBiFe2(1?x)Co2xO5 (x = 0, 0.05)]) polycrystalline is synthesized following the solid-state reaction route. Rietveld refinement of X-ray diffraction data confirmed the phase purity of KBFO and KBiFe1.9Co0.1O5 (KBFCO). The optical bandgap energy (Eg) of KBFO decreased from 1.59 to 1.51 eV because of Co substitution. The decrease in bandgap can be attributed to the tilting of the Fe–O tetrahedral structure of KBFCO. The observed room-temperature Raman peaks of KBFCO shifted by 3 cm?1 toward a lower wavenumber than that of KBFO. The shift in Raman active modes can be attributed to the change in the bond angles and bond lengths of the Fe–O tetrahedral structure and modification in response to oxygen deficiency in KBFO because of Co doping. Compared with that of KBFO, the frequency-dependent dielectric constant and dielectric loss of KBFCO decrease at room temperature, which is a con-sequence of the reduction in oxygen migration and modification in response to vibrational modes present in the sample.     

Corrosion behavior of cold-rolled and post heat-treated 316L stainless steel in 0.9wt%NaCl solution

The effect of cold rolling and post-rolling heat treatment on the microstructural and electrochemical properties of the 316L stainless steel was investigated.Two-pass and four-pass cold-rolled stainless steel specimens were heat-treated by annealing at 900℃followed by quenching in water.During the cold rolling,the microstructure of the as-received specimen transformed from austenite to strain-inducedα′-martensite due to significant plastic deformation that also resulted in significant grain elongation(i.e.,~33%and 223%increases in the grain elongation after two and four rolling passes,respectively).The hardness of the heat-treated as-received specimen decreased from HV 190 to 146 due to the recovery and recrystallization of the austenite grain structure.The cyclic polarization scans of the as-rolled and heat-treated specimens were obtained in 0.9wt%NaCl solution.The pitting potential of the four-pass rolled specimen was significantly increased from 322.3 to 930.5 mV after post-rolling heat treatment.The beneficial effect of the heat treatment process was evident from~10-times-lower corrosion current density and two-orders-of-magnitude-lower passive current density of the heat-treated specimens compared with those of the as-rolled specimens.Similarly,appreciably lower corrosion rate(3.302×10^?4mm/a)and higher pitting resistance(1115.5 mV)were exhibited by the postrolled heat-treated specimens compared with the as-rolled 316L stainless steel specimens.     

基于GC-MS对牛奶菜治疗蛇伤作用机制的初步研究

【目的】初步考察牛奶菜(Marsdenia sinensis)治疗蛇伤作用机制。【方法】采用乙醇回流提取法和水回流提取法制备牛奶菜提取物,再采用石油醚、三氯甲烷、乙酸乙酯、正丁醇对水提物依次萃取,对各萃取物进行气相色谱-质谱联用法(GC-MS)分析。【结果】从牛奶菜中共检测出77种组分,其中含有大量具有抑制蛇毒活性的组分,包括十四烷酸、十六烷酸、十六烷酸衍生物、十八烷酸衍生物、十八烯酸及它的衍生物、2,4-二叔丁基苯酚、谷甾醇、豆甾醇等。【结论】牛奶菜主要通过抑制蛇毒氧化损伤以及抑制蛇毒神经毒素发挥治疗功效。     

转子流道倾斜式的外驱旋转压能交换器性能研究

为提高外驱式旋转压能交换器性能，设计了转子流道倾斜式的外驱式旋转压能交换器，以能量回收效率和体积混合率为性能指标，利用商业CFD软件Fluent对模型求解计算，并与直流道外驱式旋转压能交换器模拟数据对比分析。结果表明，处理量相等的情况下，能量回收效率和体积混合率均随转子转速的升高而降低；同一转速下，转子倾斜角度改变，能量回收效率变化不超过0.04%，而对体积混合率有明显影响。研究结果对于提高外驱式旋转压能交换器设备性能具有一定指导意义。     

大物质分选机在餐厨垃圾预处理中的应用

餐厨垃圾预处理阶段物质分选对整体处理工艺影响较大，如果分选不到位，浆料中杂物多，会导致管道磨损严重、设备故障率高等问题。通过调节进料频率及大物质分选机的运行频率，探究大物质分选机较优的运行参数范围，使分选工作更加有效。试验结果表明：大物质分选机运行频率为70 Hz，进料频率小于17 Hz为较优运行参数，此时设备电流值较低且波动曲线较为平稳，分选料中有机质质量占比在33%~37%，与其他工况相比，有机质质量占比至少低了3%；运行工况的变化不会对浆料的组成成分造成影响，其中剩余物、果皮和骨头质量占比较大，三者占比总和在98%以上，其他杂物质量占比不超过2%。     

第三届“中国科普月”活动全面启动

 3月22日，科普中国、新浪新闻联合打造的第三届“中国科普月”活动在科普中国官方微博平台开启。     

AR技术在科普教育活动中的研究应用

正0引言增强现实(augmented reality,AR)技术在各行各业的应用已如火如荼,在医疗、教育、建筑、军事、娱乐等行业,均可见AR技术的身影。但国内在AR教学应用方面例子尚少,国内教育主管部门也提出必要时可向国外借鉴。2016年广东科学中心利用中央引导地方科技发展专项资金建设了AR实验室,创新了STEAM(科学、技术、工程、艺术、数学)教