Co?N graphene encapsulated cobalt catalyst for H2O2 decomposition under acidic conditions

Hydrogen peroxide (H₂O₂) has been listed as one of the 100 most important chemicals in the world. However, huge amount of residual H₂O₂ is hard to timely decomposed into O₂ and H₂O under acidic condition, easily resulting in explosion hazard. Here, we reported a core–shell structure catalyst, that is graphene with Co N structure encapsulated Co nanoparticles. Co N graphene shell serves as the active site for the H₂O₂ decomposition, and Co core further enhance this decomposition. Benefiting from it, the H₂O₂ decomposition were close to 100% after 6 cycles without pH adjustment, which increased 6 orders of magnitude compared with no catalyst. At the same time, the O₂ generation reached 99.67% in 2 h with little metal leaching, and ·OH has been greatly inhibited to only 0.08%. This work can cleanly remove H₂O₂ with little deep oxidation and protect the process of H₂O₂ utilization to achieve a safer world.     

Good dielectric performance and broadband dielectric polarization in Ag,Nb co-doped TiO2

Due to the demand of miniaturization and integration for ceramic capacitors in electronic components market, TiO₂-based ceramics with colossal permittivity has become a research hotspot in recent years. In this work, we report that Ag⁺/Nb⁵⁺ co-doped (Ag_1/4Nb_3/4)_xTi_1−xO₂ (ANTOx) ceramics with colossal permittivity over a wide frequency and temperature range were successfully prepared by a traditional solid–state method. Notably, compositions of ANTO0.005 and ANTO0.01 respectively exhibit both low dielectric loss (0.040 and 0.050 at 1 kHz), high dielectric permittivity (9.2 × 10³ and 1.6 × 10⁴ at 1 kHz), and good thermal stability, which satisfy the requirements for the temperature range of application of X9R and X8R ceramic capacitors, respectively. The origin of the dielectric behavior was attributed to five dielectric relaxation phenomena, i.e., localized carriers' hopping, electron–pinned defect–dipoles, interfacial polarization, and oxygen vacancies ionization and diffusion, as suggested by dielectric temperature spectra and valence state analysis via XPS; wherein, electron-pinned defect–dipoles and internal barrier layer capacitance are believed to be the main causes for the giant dielectric permittivity in ANTOx ceramics.     

Synthesis and performance evaluation of a new drag reducer based on acrylamide/12-allyloxydodecyl acid sodium

Hydraulic fracturing with slickwater is a field-proven stimulation technology used in tight reservoirs. Because of the high pumping rate associated with slickwater fracturing, drag reduction (DR) is critical in minimizing pressure drop and the success of oilfield operations. In this paper, a new type of drag reducer (SPR) was synthesized with acrylamide and 12-allyloxydodecyl acid sodium, and its drag reduction performance was evaluated. The results showed that the new drag reducer features low molecular weight, fast-dissolving rate and low interfacial tension. The algorithm of estimating the drag reduction rate of non-Newtonian fluid SPR was proposed and validated. Empirical or semianalytical models for estimating the friction ratio (σ) or friction factor (λ or f) were used to simulate the turbulence behavior of the SPR drag reducer under different Reynolds numbers (Re). The modified Virk's correlation could accurately model the turbulent behavior of the SPR drag reducer. A unified calculation formula was established in this study for different pipe diameters.     

等通道挤压纯铝的冷轧织构与组织演变

研究了冷轧形变量对等通道挤压纯铝的形变织构与显微组织的影响。结果表明：当形变量较小时，冷轧使挤压高纯铝的显微组织分布更加均匀。然而，随着形变量的增加，晶粒由等轴向纤维状转变。织构的演变规律为旋转立方织构和{111}<110>向冷轧织构（铜织构、黄铜织构和S织构）转变，同时出现了R织构。由此可见，等通道挤压变形对高纯铝的冷轧组织和织构存在一定的影响。     

计及RSC控制的DFIG短路电流直流分量解析表达

现有文献针对计及转子变流器(RSC)控制的双馈感应风电机组(DFIG)定子短路电流解析表达,将定子磁链当作一阶直流衰减分量或忽略功率外环控制。基于DFIG电压、磁链和RSC控制方程,得到定子电流关于定子电压和定子功率的传递函数,提出定子电流的精确解析表达式。基于RSC内、外环PI参数关系,推导直流分量衰减时间常数和角频率关于PI参数的表达式。分析了RSC内外环PI参数对定子电流直流衰减分量的影响。仿真结果验证了解析表达式的准确性,为PI参数选取和保护装置测量、整定提供依据。     

页岩气地质评价关键实验技术的进展与展望

页岩气地质评价实验结果为页岩气地质"甜点"评价、地质选区、储量计算、水平井压裂层段优选及开发方案确定等提供了重要的数据基础与科学依据。近年来,随着我国页岩气勘探开发工作的不断深入,相关地质评价实验技术也取得了较大的进展。特别是在页岩微观孔隙结构、含气性和物性这3个方面,通过引进先进技术与自主设备研发相结合,建立了适用于我国海相页岩的分析测试技术和标准,对于推动我国页岩气的勘探开发进程发挥了重要的作用。为了给我国页岩气基础地质研究、实验室建设及相关标准制定提供参考和指导,归纳总结了国内外在上述3项页岩气地质评价关键实验技术方面所取得的进展,并对相关技术未来的发展趋势进行了展望。研究结果表明:①对于页岩微观孔隙结构测试,目前已经形成了多种手段相结合的定性观测和定量表征测试方法,实现了由静态表征向动态表征的转化,未来需要在页岩孔隙结构的原位表征和孔内流体赋存特征直接观测等方面做进一步的研究;②对于页岩含气性测试,目前已经建立了现场与室内相结合的含气性定量表征系列技术,实现了对页岩吸附气和游离气赋存特征的定量评价,未来需要在深层页岩损失气量计算、页岩气吸附机理及模型等方面做进一步的研究;③对于页岩物性测试,目前已经建立了多种方法相结合的孔隙度和渗透率测试技术,实现了对页岩孔隙有效性的定量评价,未来需要在孔隙度测试条件和方法等方面进行对比研究并统一标准。结论认为,只有不断地改进和优化页岩气地质评价实验技术,才能够满足科研与生产的需求。     

Vertically aligned reduced graphene oxide/Ti3C2Tx MXene hybrid hydrogel for highly efficient solar steam generation

Effective utilization of abundant solar energy for desalination of seawater and purification of wastewater is one of sustainable techniques for production of clean water, helping relieve global water resource shortage. Herein, we fabricate a vertically aligned reduced graphene oxide/Ti₃C₂T_x MXene (A-RGO/MX) hybrid hydrogel with aligned channels as an independent solar steam generation device for highly efficient solar steam generation. The vertically aligned channels, generated by a liquid nitrogen-assisted directional-freezing process, not only rapidly transport water upward to the evaporation surface for efficient solar steam generation, but also facilitate multiple reflections of solar light inside the channels for efficient solar light absorption. The deliberate slight reduction endows the RGO with plenty of polar groups, decreasing the water vaporization enthalpy effectively and hence accelerating water evaporation efficiently. The MXene sheets, infiltrated inside the A-RGO hydrogel on the basis of Marangoni effect, enhance light absorption capacity and photothermal conversion performance. As a result, the A-RGO/MX hybrid hydrogel achieves a water evaporation rate of 2.09 kg·m⁻²·h⁻¹ with a high conversion efficiency of 93.5% under 1-sun irradiation. Additionally, this photothermal conversion hydrogel rapidly desalinates seawater and purifies wastewater to generate clean water with outstanding ion rejection rates of above 99% for most ions.

     

Electron beam processed surface textures on titanium alloys for fluid-drag reduction

Ti-6Al-4V and Ti-4Al-1.5Mn alloys were employed for electron beam processing with the aim to produce surface textures efficient for fluid-drag reduction. The as-resulted surface textures were examined by using advanced optical microscopy for surface morphology analysis, optical microscopy and scanning electron microscopy for near-surface microstructure observation. The titanium model with electron beam processed surface textures was tested in wind tunnel to evaluate their fluid-drag reduction efficiency. It showed that the as-resulted non-smooth surface was characterized by parallel ridges and grooves, with height and spacing able to be customized by adjusting processing parametres. The ridges displayed continuous scales while the valley of grooves presented V-shaped ripples. Their dimensions were also related to and could be controlled by processing parametres. Further, the near-surface region was occupied by fusion zone, heat-affected zone and base metal from the outermost surface to the underlying bulk alloy. The microstructure of fusion zone was characterized by martensite phase. A heat-affected zone was sandwiched between fusion zone and the underlying base metal, with different microstructural features compared to both fusion zone and the base metal. With respect to fluid-drag reduction efficiency, titanium model with electron beam processed surface textures exhibits a reducing efficiency over 15% at attack angles of 0° and ±1°, with an air flow velocity at 24 m/s.     

稀土La2O3改性脲醛树脂的黏度特性研究

脲醛树脂(UF树脂)胶黏剂具有胶合强度高、制作简单、成本低廉、原料来源丰富等一系列特点,成为我国人造板生产的主要胶种,是市场上需求量最大的胶黏剂之一。但由于在固化时会放出刺激性的甲醛,游离甲醛高,在使用时严重危害人的健康。近年来,随着人们环保意识的提高,生产和使用低毒UF树脂胶势在必行。本文介绍了稀土氧化镧对脲醛树脂的改性过程并对改性后脲醛树脂胶的各项性能进行了测试。本实验通过在不同反应阶段加入稀土氧化镧,分别探讨它们对脲醛树脂胶黏剂性能影响。实验表明:在脲醛树脂胶中加入稀土氧化镧可以增加黏度、固化时间、固含量,并可以减少游离甲醛释放量。