天然气水合物储层泥质细粉砂挡砂介质堵塞规律与微观挡砂机制

中国南海海域部分天然气水合物储层中地层砂为高泥质含量细粉砂，开采防控砂难度较大。针对高泥质细粉砂挡砂机制问题，使用粒度中值为10.13 μm的泥质细粉砂样品，模拟单向气液携砂流动条件，使用绕丝筛板、金属烧结网、金属纤维、预充填陶粒4类挡砂介质在20~80 μm挡砂精度下进行挡砂模拟实验，采用显微成像系统观察挡砂介质内部及表面砂粒沉积与堵塞动态，分析介质流通性能和挡砂性能变化，总结堵塞规律、微观挡砂机制与形态及其控制因素。研究结果表明，不同类型和精度的挡砂介质对泥质细粉砂的堵塞总体呈现堵塞开始、堵塞加剧和堵塞平衡3个阶段。随着驱替进行，挡砂介质渗透率逐渐降低，幅度会高达90%以上；同时过砂速度减缓，最终过砂率为5%~10%。根据堵塞规律和微观图像分析，提出了粗组分分选桥架、局部砂团适度挡砂、整体砂桥阻挡等挡砂介质对泥质细粉砂的3种微观挡砂机制。以粗组分分选桥架挡砂机制为主的挡砂工况下，挡砂介质堵塞渗透率较高，但过砂率超过15%，挡砂效果较差；以整体砂桥挡砂机制为主时，过砂率在10%以下，挡砂性能较好，但各类挡砂介质的堵塞渗透率不足1 D，流通性能较差。局部砂团适度挡砂机制为主时介质挡砂性能及流通性能介于两者之间。挡砂介质对天然气水合物储层泥质细粉砂的微观挡砂机制和形态受挡砂介质类型、精度、地层砂特征以及流动条件等因素控制，其规律对于水合物泥质细粉砂防控砂优化有指导意义。     

Recent advances in carbon nanotubes-based microwave absorbing composites

With the blossom of information industry, electromagnetic wave technology shows increasingly potential in many fields. Nevertheless, the trouble caused by electromagnetic waves has also drawn extensive attention. For instance, electromagnetic pollution can threaten information safety in vital fields and the normal function of delicate electronic devices. Consequently, electromagnetic pollution and interference become an urgent issue that needs to be addressed. Carbon nanotubes (CNTs) have become a potential candidate to deal with these problems due to many advantages, such as high dielectric loss, remarkable thermodynamic stability, and low density. With the appearance of climbing demands, however, the carbon nanotubes combining various composites have shown greater prospects than the single CNTs in microwave absorbing materials. In this short review, recent advances in CNTs-based microwave absorbing materials were comprehensively discussed. Typically, we introduced the electromagnetic wave absorption mechanism of CNTs-based microwave absorbing materials and generalized the development of CNTs-based microwave absorbers, including CNTs-based magnetic metal composites, CNTs-based ferrite composites, and CNTs-based polymer composites. Ultimately, the growing trend and bottleneck of CNTs-based composites for microwave absorption were analyzed to provide some available ideas to more scientific workers.     

Surface modification mechanism of SiC particles using KH5X0 (X=5,6,7,8,9) silane coupling agents: First principle study

Silicon carbide surface modification is still a challenging task. Its modification mechanism is also still unclear. This paper provides a study of the surface modification mechanism of KH5X0 (X = 5, 6, 7, 8, 9) on the silicon carbide (111) using density functional theory. The electronic structures and densities of states of KH5X0 (X = 5, 6, 7, 8, 9) on SiC surfaces indicates that the surface modification mechanism is attributed to the electronic effects of the functional groups of KH5X0 (X = 5, 6, 7, 8, 9). From the results the easier it is for a functional group to obtain electrons, the better the modifying performance of silane coupling agent will be. Furthermore, the interface energy results showed that silicon carbide (111) modification performance by KH580 silane and KH590 silane is better than KH550, KH560, and KH570. The present work provides theoretical guidance for the fabrication of SiC heat sink products.     

Ablation behavior and mechanism of bulk MoAlB ceramic at ∼1670–2550 °C in air plasma flame

In this work, MoAlB samples for plasma exposure test were condensed by spark plasma sintering at 1200 °C for 10 min. Ablation resistance of MoAlB ceramic was investigated in a plasma torch facility for about 30 s at high temperature range of ～1670?2550 °C, which provided a quasi-real hypersonic service environment. The results showed that the linear ablation rate was increased from 0 μm/s at ～1670 °C to 86.4 μm/s at ～2550 °C. At ～1670 °C, the ablated surface of MoAlB ceramic was covered by Al₂O₃ layer, presenting excellent ablation resistance. At ～2220 °C, the macroscopic cracks were induced by thermal stress, which opened up channels for the inward diffusion of oxygen and deteriorated the ablation resistance of the substrate. Above ～2400 °C, the volatile MoO₃ and B₂O₃ and the erosion of viscous oxides by the high shearing force of plasma stream were the main ablation mechanisms.     

木质纤维与水泥共同改良软土的力学性能与微观机制分析

通过压实试验、无侧限抗压强度试验和劈裂试验,分析不同木质纤维含量、水泥含量和固化时间对软土力学性能的影响规律,探讨木质纤维、水泥改良软土的微观机制。结果表明,木质纤维的加入对水泥改良软土的击实特性有显著的影响;木质纤维与水泥可有效改善土体的抗压和劈裂抗拉强度,随着木质纤维含量的增加,改良土的抗压和劈裂抗拉强度呈现出明显的“驼峰”现象,并在木质纤维含量为0.25%时最大;木质纤维与水化产物、软土颗粒形成互锁效应,增大了改良土的摩擦力,同时木质纤维还承担一定的拉伸强度,使改良土的劈裂强度增加。     

Nickel/Cobalt nanoparticles for electrochemical production of hydrogen

The electrolytic production of hydrogen (POH) from alkaline water electrolysis is at the forefront of technology for alternative energy sources of the future. The present work evaluates the improvement of electro-catalytic activity (ECA) on Ni electrodes for the POH by electrodeposition of cobalt (Co). Tests were conducted in alkaline solution and the ECA of Ni and Ni–Co electrodes for the POH were compared using alternative and direct current techniques. Tafel polarization tests exemplified a significant improvement in the ECA of the bimetallic electrode (Ni–Co) compared with the Ni-electrode. Besides, the bimetallic electrode required less input overpotential energy (η) for the given POH rate under constant current density. Electrochemical impedance spectroscopy (EIS) revealed a significant increase in the number of electrochemical active sites and changed the surface morphology following the electrodeposition of Co over Ni electrodes.     

Combustion enhancement and inhibition of hydrogen-doped methane flame by HFC-227ea

Hydrogen enriched with compressed natural gas is an efficient and environment-friendly gaseous fuel. However, the safety issues of mixture and the method to control or weaken their combustion are highly concerned. To explore the inhibition effect of halogenated fire suppressants on the mixture, the effect of HFC-227ea on the laminar premixed methane/air flames, with different fractions of H₂, have been studied. Burning velocities have been measured with constant-volume combustion chamber and kinetically modelled a recently assembled kinetic mechanism. The fractions of H₂ influence the enhancement and inhibition effect of HFC-227ea, and it is less effective with the lean mixture. In stoichiometric condition, HFC-227ea showed good inhibition effect on the mixture flames. The HFC-227ea increased the burning velocities of CH₄-0% H₂-air and CH₄-10% H₂-air flames at leanest condition, whereas the increased burning velocity arising from HFC-227ea not occurred as the addition of H₂ above 20%. Experimental results coincided well with numerical results, however the agreement was poor for the leanest flames at low agent loading. Lastly, kinetic mechanism analysis was used to interpret the combustion enhancement and inhibition effect of hydrogen-doped methane flame by HFC-227ea.     

Microencapsulation of camellia oil to maintain thermal and oxidative stability with focus on protective mechanism

Camellia oil (CO) microcapsules were developed using chitosan–soybean protein isolate (CS-SPI) complexes as wall materials and transglutaminase (TGase) as the cross-linking agent. Results indicated that CO/SPI under the ratio of 1:2 exhibited the highest microencapsulation efficiency and yield, possessing the best encapsulation effect. Morphology observation showed that CO microcapsules were intact, compact and nearly spherical. The microencapsulated CO exhibited the improved thermal resistance and significantly lower peroxide values after 3 days storage, demonstrating that the produced microcapsule was a promising way to maintain the thermal and oxidative stability of camellia oil. It could be found evidence from FTIR, which indicated that covalent cross-linking and hydrogen bonding might be involved among wall materials, and physical interactions between the core and wall materials. Therefore, the produced CO microcapsules could be an effective way to protect camellia oil, which was helpful for improving the processing and storage qualities of camellia oil.     

Mechanisms of synthesis gas production via thermochemical cycles over La0·3Sr0·7Co0·7Fe0·3O3

La_0·3Sr_0·7Co_0·7Fe_0·3O₃ (LSCF3773) was chosen as an oxygen carrier material for synthesis gas production and synthesized using ethylene-diamine-tetra-acetic acid (EDTA) citrate-complexing method. LSCF exhibited a pure cubic structure where 110 and 100 plane diffractions were active for CO₂ splitting, while 111 was more favored by H₂O splitting. Overall oxygen storage capacity (OSC) of LSCF was 4072 μmol/g_cat. During the reduction process, regular cations (Co⁴⁺, Fe⁴⁺), polaron cations (Co³⁺, Fe³⁺) and localized cations (Co²⁺, Fe²⁺) were achieved when the LSCF was reduced at 500, 700 and 900 °C, respectively. The strength of the active sites depended on reduction temperatures. An increase in oxidation temperature enhanced H₂ production at temperature ranging from 500 °C to 700 °C while effected CO production at 900 °C. H₂O and CO₂ was competitively split during the oxidation step, especially at 700 °C. The activation energy of each reaction was ordered as; CO₂ splitting > H₂O splitting > CO₂ adsorption, supporting the above evidence where H₂ and CO production were found to increase when the operating temperature was increased.