Effect of Ni/tubular g-C3N4 on hydrogen storage properties of MgH2

Additive doping is one of the effective methods to overcome the shortcomings of MgH₂ on the aspect of relatively high operating temperatures and slow desorption kinetics. In this paper, hollow g-C₃N₄ (TCN) tubes with a diameter of 2 μm are synthesized through the hydrothermal and high-temperature pyrolysis methods, and then nickel is chemically reduced onto TCN to form Ni/TCN composite at 278 K. Ni/TCN is then introduced into the MgH₂/Mg system by means of hydriding combustion and ball milling. The MgH₂–Ni/TCN composite starts to release hydrogen at 535 K, which is 116 K lower than the as-milled MgH₂ (651 K). The MgH₂–Ni/TCN composite absorbs 5.24 wt% H₂ within 3500 s at 423 K, and takes up 3.56 wt% H₂ within 3500 s, even at a temperature as low as 373 K. The apparent activation energy (E_a) of the MgH₂ decreases from 161.1 to 82.6 kJ/mol by the addition of Ni/TCN. Moreover, the MgH₂–Ni/TCN sample shows excellent cycle stability, with a dehydrogenation capacity retention rate of 98.0% after 10 cycles. The carbon material enhances sorption kinetics by dispersing and stabilizating MgH₂. Otherwise, the phase transformation between Mg₂NiH₄ and Mg₂NiH_0.3 accelerates the re/dehydrogenation reaction of the composite.     

Effect of stoichiometry and Cu-substitution on the phase structure and hydrogen storage properties of Ml-Mg-Ni-based alloys

To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ...     

Hydrogel photocatalysts for efficient energy conversion and environmental treatment

Photocatalysts have attracted great research interest owing to their excellent properties and potential for simultaneously addressing challenges related to energy needs and environmental pollution. Photocatalytic particles need to be in contact with their respective media to exhibit efficient photocatalytic performances. However, it is difficult to separate nanometer-sized photocatalytic materials from reaction media later, which may lead to secondary pollution and a poor recycling performance. Hydrogel photocatalysts with a three-dimensional (3D) network structures are promising support materials for photocatalysts based on features such as high specific surface areas and adsorption capacities and good environmental compatibility. In this review, hydrogel photocatalysts are classified into two different categories depending on their elemental composition and recent progresses in the methods for preparing hydrogel photocatalysts are summarized. Moreover, current applications of hydrogel photocatalysts in energy conversion and environmental remediation are reviewed. Furthermore, a comprehensive outlook and highlight future challenges in the development of hydrogel photocatalysts are presented.     

A study on tribological behaviour of transfer films of PTFE/bronze composites

Transfer films of PTFE/bronze composites with 5–30% volume content of bronze were prepared using a RFT friction and wear tester on surface of AISI-1045 steel bar by different sliding time (5–60 min). Tribological properties of these transfer films were studied using a DFPM reciprocating tribometer in a point contacting configuration under normal loads of 0.5, 1.0, 2.0 and 3.0 N. Thickness and surface morphology of the transfer films were investigated. It was found thickness of the transfer films slightly increased along with the increase of bronze content of corresponding composites. Increased sliding time of transfer film preparation is helpful to form transfer film with better ductibility and continuity, but sliding time almost has no effect on tribological properties of the transfer film. Higher bronze content in the composite improved tribological properties of the corresponding transfer film, i.e., reduced friction coefficient and prolonged wear life. All these transfer films are sensitive to load change. Their wear life becomes shorter along with the increase of load. SEM image of the worn surface show fatigue wear and adhesion wear have happened on the transfer film during the friction process. The author believe bronze in the transfer film effectively partaked in shear force applied on the transfer film and its good ductibility helped to improve tribological properties of the transfer films.     

Effect of Nb on Mechanical Properties of HAZ for High-Nb X80 Pipeline Steels

The mechanical properties of heat affected zone (HAZ) of two commercial high-Nb X80 grade pipeline steels with different alloy elements were investigated using thermal simulation performed on a Gleeble-3500 thermal simulator. The results showed that the high-Nb steels have excellent weldability. Embrittlement regions appear in coarse grain heat affected zone (CGHAZ) and intercritically heat affected zone (ICHAZ); Softening region appears in fine-grain heat affected zone (FGHAZ), and the strength here was even lower than 555 MPa as required in the standard. Meanwhile, with the increase of heat input, the strength and the toughness of HAZ of steel with high Nb, C and lower alloy decrease notably. Therefore, take into account the welding procedure during manufacture of weld pipe, suitable amount of alloy elements, such as Cr, Ni, Cu, Mo and so on, is necessary for high Nb X80 heavy-thick steel plate.     

Superior electrochemical performances of LaMgNi alloys with A2B7/A5B19 double phase

Here, phase transformation and electrochemical characteristics of non-stoichiometry La₄MgNi_x (x = 16, 17 and 18) hydrogen storage alloys were studied. It is found that after annealed at 1223 K for 24 h, the minor AB₃ and AB₅ phases in La₄MgNi₁₆ alloy transform into A₂B₇ phase by a peritectic reaction and the La₄MgNi₁₆ alloy shows a A₂B₇ single phase structure. Double phase structures of A₂B₇/A₅B₁₉ are obtained in La₄MgNi₁₇ and La₄MgNi₁₈ alloys after annealed at the same condition. The abundance of A₅B₁₉ phase increases as x increases, indicating the increasing x value contributes to the formation of A₅B₁₉ phases. Electrochemical studies show that the maximum discharge capacity and capacity retention at the 100^th charge/discharge cycles (S₁₀₀) of A₂B₇ single phase La₄MgNi₁₆ alloy is 373 mAh g⁻¹ and 78.4%, respectively. The appearance of A₅B₁₉ (minor) phase in the La₄MgNi₁₇ alloy makes a remarkable improvement in the discharge capacity from 373 mAh g⁻¹ to 388.8 mAh g⁻¹, as well as the S₁₀₀ from 78.4% to 90.1%. It is believed that the LaMgNi-based alloy with the A₂B₇(main)/A₅B₁₉(minor) phase structure possesses the good overall electrochemical properties and is applicable to the high-power and long-cycle life negative electrode material for nickel metal hydride batteries.     

Electrochemical hydrogen storage properties of MgAlMnNi quaternary alloys

Al was partially substituted by Mn in Mg₃AlNi₂ to improve the discharge capacity and electrochemical kinetic properties of Mg₃AlNi₂ alloy electrode. By means of pretreatment of ultrasonic dispersion, followed by mechanical milling and combustion synthesis, a series of quaternary alloys, namely Mg₃Al_1-xMn_xNi₂ (x = 0, 0.2, 0.4, 0.6, 0.8) were synthesized. X-ray diffraction analysis shows that partial substitution of Mn for Al can cause lattice expansion of Mg₃AlNi₂ and the samples all appear similar multiphase structures. The introduction of Mn enhances obviously the maximum discharge capacity of Mg₃AlNi₂ alloy electrode. The high rate dischargeability of the alloys can also be remarkably enhanced by substitution of Mn for Al. The exchange current density (I₀) and charge transfer resistance (R_ct) of the alloy electrode increase and decrease continuously with increasing the Mn substitution content, respectively, indicating the improvement of electrochemical kinetics properties. Combining with the potentiostatic discharge test, it is concluded that in the MgAlMnNi quaternary alloys, the kinetic properties are mainly controlled by charge transfer reaction on the electrode surface.     

Wear behavior of bainitic steels

A systematic study of the wear properties of a series of 0.5 wt.% Mo, 0.003 wt.% B bainitic steels has been made under dry sliding conditions. In contrast to most of the established wear models and experimental data, it was found that, for eight of the nine materials, the wear rate is not a linear function of load.The wear rate data have been analyzed with respect to chemical composition, hardness, monotonic-cyclic stress strain parameters, fatigue properties, Charpy impact data and microstructure. It is shown that the chromium content has the most significant influence on wear rate. Since these bainitic steels have inherently high impact resistance, which is improved with chromium additions, it is possible to achieve an attractive combination of properties with a steel containing 0.2 wt.% C, 2.0 wt.% Cr and 1.5 wt.% Mn.The wear resistance of the bainitic steels is compared with previous work on pearlitic steels tested under the same conditions. While the best pearlitic steels stand apart, it is seen that the best bainitic steel tested to date is better than some fully eutectoid steels containing 0.7 wt.% C.     

MWCNTs-GONRs/Co3O4 electrode with needle-like arrays for outstanding supercapacitors

Multiwalled carbon nanotubes-graphene oxide nanoribbons (MWCNTs-GONRs) exhibit high specific surface area and good electroconductivity because of their unique three-dimensional cross-linking structure with the properties of both CNTs and GONRs. In this study, a hydrothermal method was employed to anchor MWCNTs–GONRs onto a Ni foam (NF) to obtain a precursor substrate. Subsequently, Co₃O₄ arrays were grown on the NF substrate to synthesize a MWCNTs–GONR/Co₃O₄ electrode. The electrode showed a capacitance of 846.2 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 90.1% after 3000 cycles. Furthermore, MWCNTs–GONRs/Co₃O₄ and active carbon (AC) were used as the positive and negative electrodes, respectively, to assemble a supercapacitor, which delivered a maximum energy density of 38.23 W h kg⁻¹ and a high power density of 6.80 kW kg⁻¹. In addition, the specific capacitance of the device reached a maximum of 91.5% after 9000 cycles. Thus, the MWCNTs–GONRs/Co₃O₄ electrode showed huge potential for supercapacitor applications.     

承压管道磁记忆检测缺陷信号量化数值研究

利用Ansys数值模拟软件,对含埋藏缺陷的承压管道进行磁记忆检测有限元模拟,分析磁记忆信号值在不同缺陷参数、不同应力状态下的变化规律.结果表明,磁记忆信号可以对管道埋藏型裂纹及气孔产生的应力集中进行表征,随着缺陷埋深的减小与内压载荷的增加,磁记忆信号变化幅度增大,法向梯度极值增加.通过法向和切向信号协同分析,可以实现对...