Stabilization of natural gas foams using different surfactants at high pressure and high temperature conditions

Natural gas foam can be used for mobility control and channel blocking during natural gas injection for enhanced oil recovery, in which stable foams need to be used at high reservoir temperature, high pressure and high water salinity conditions in field applications. In this study, the performance of methane (CH₄) foams stabilized by different types of surfactants was tested using a high pressure and high temperature foam meter for surfactant screening and selection, including anionic surfactant (sodium dodecyl sulfate), non-anionic surfactant (alkyl polyglycoside), zwitterionic surfactant (dodecyl dimethyl betaine) and cationic surfactant (dodecyl trimethyl ammonium chloride), and the results show that CH₄-SDS foam has much better performance than that of the other three surfactants. The influences of gas types (CH₄, N₂, and CO₂), surfactant concentration, temperature (up to 110°C), pressure (up to 12.0 MPa), and the presence of polymers as foam stabilizer on foam performance was also evaluated using SDS surfactant. The experimental results show that the stability of CH₄ foam is better than that of CO₂ foam, while N₂ foam is the most stable, and CO₂ foam has the largest foam volume, which can be attributed to the strong interactions between CO₂ molecules with H₂O. The foaming ability and foam stability increase with the increase of the SDS concentration up to 1.0 wt% (0.035 mol/L), but a further increase of the surfactant concentration has a negative effect. The high temperature can greatly reduce the stability of CH₄-SDS foam, while the foaming ability and foam stability can be significantly enhanced at high pressure. The addition of a small amount of polyacrylamide as a foam stabilizer can significantly increase the viscosity of the bulk solution and improve the foam stability, and the higher the molecular weight of the polymer, the higher viscosity of the foam liquid film, the better foam performance.     

Facile synthesis of Ni doped CoWO4 nanoarrays grown on nickel foam substrates for efficient urea oxidation

Urea electrolysis is a promising technology for hydrogen production, which can alleviate environmental pollution of urea-rich wastewater. It's worth noting that electrochemistry activity can be significantly improved by reasonably regulating the electron configuration around the active site for the doped materials. In this work, a series of well-tuned Ni doped CoWO₄ nanoarrays on Ni foam supports have been prepared through a typical hydrothermal approach for the first time. Moreover, the resulting Ni–CoWO₄-2 material significantly promotes urea oxidation performance with an applied potential of 1.35 V at 50 mA cm^?2, which is lower than that of water oxidation reaction (1.60 V). Density functional theory results suggest that the Ni doped CoWO₄ has larger urea adsorption energy compared with CoWO₄ and the CO(NH₂)₂ molecule is strongly adsorbed on surface of Ni doped CoWO₄, which is beneficial to accelerate the kinetics of the reaction and improve the electrocatalytic activity of the urea electrolysis.     

Iron-doped cobalt nitride nanoparticles (Fe–Co3N): An efficient electrocatalyst for water oxidation

The exploration of efficient, low-cost and earth-abundant oxygen-evolution reaction (OER) electrocatalysts and the understanding of the intrinsic mechanism are important to advance the clean energy conversion technique based on electrochemical water oxidation. In this work, Fe-doping Co₃N catalysts were successfully synthesized by a simple nitridation reaction of the Co_3-xFe_xO₄ precursor. This material exhibited a low overpotential of 294 mV at a current density of 10 mA cm^?2, and a small Tafel slope of 49 mV dec^?1 in 1 M KOH solution, superior to the performance of Co₃N and IrO₂. As revealed by the spectroscopic and electrochemical analyses, the enhanced OER performance mainly originates from the electronic modulation induced by the incorporation of Fe into Co₃N, benefitting the formation of CoOOH as active surface species and thus facilitating the OER process. These findings also demonstrate the introduction of heterogeneous element is a simple and effective strategy to regulate the OER property of the cobalt nitrides (Co₃N) catalysts.     

未开发历史保护街区更新提升设计环境行为研究——以哈尔滨花园街为例

花园街目前最无法解决的问题就是确定历史保护和改造的重点方向.研究使用者在旧街道空间中的行为以及与现有物理环境的互动,可作为未来改造和发展道路空间的一项参考.根据行为环境和空间关系学,采用行为映射法和视觉观察法、主成分分析和聚类法等,对街道使用者的行为和空间物理特征进行收集和处理.分析表明共三组行为,包括:(1)各种行为频繁发生路段;(2)各种行为较低频发生路段;(3)以通行和停滞为主的交叉口.对每类模式分别提出改善建议,并对花园街未来保护和发展提出相关策略.     

Transparent niobate glass-ceramics for optical limiting

The construction of nonlinear optical materials featuring asymmetric transmission of light is of great technological importance for various applications, including optical switching and optical power limiting. A significant challenge is the scalable fabrication of material candidates with good photochemical stability, high optical transmittance, and excellent optical limiting performance. Here, we present a nanocrystallization avenue for constructing hybrid optical limiting materials that exhibit ultrafast and robust optical limiting performance. The experimental results show that the controllable relaxation of a niobate glass may lead to the clustering of Nb-O units and contracting of the bandgap. It results in the notable improvement in nonlinear optical properties, including the enhanced saturation irradiance (380 GW/cm²), doubly increased nonlinear coefficient, and decreased limiting threshold (200 GW/cm²). Our results suggest a promising material that exhibits promising applications for protecting eyes and sensitive components from laser-induced damage.     

Interactions between dislocations and twins in deformed titanium aluminide crystals

Using scanning, transmission electron microscopy and aberration-corrected scanning transmission electron microscopy, we have studied the interactions between dislocations and twins in impact deformed polysynthetic twinned TiAl crystal. The 1/3?<?1$\overline{1}\overline{1}$] and 1/6?<?211] step dislocations on coherent twin boundaries reveal the interactions of glissile 1/2?<?101> dislocations with the coherent twin boundaries. An abnormal stacking fault was found adjacent to the coherent twin boundary. It has the same stacking sequence but different atom species in the [$\overline{1}$10] direction with an additional displacement of 1/4[$\overline{1}$10] in two neighboring {111} layers, and is likely induced by the slip of a 1/12[112] (i.e. 1/4[$\overline{1}$10] + 1/6[2$\overline{1}$1]) dislocation.     

Tuning effect of silicon substitution on magnetic and high frequency electromagnetic properties of R2Fe17 and their composites

In this work, we report the tuning effect of the Si substitution on the magnetic and high frequency electromagnetic properties of R₂Fe₁₇ compounds and their paraffin composites. It is found that the introduction of Si can remarkably improve the magnetic and electromagnetic properties of the R₂Fe₁₇ compounds, making the R₂Fe_17–xSi_x-paraffin composites excellent microwave absorption materials (MAMs). By introducing the Si element, their saturation magnetizations decrease slightly, while much higher Curie temperatures are obtained. Furthermore, better impedance match is reached due to the decrease of the high-frequency permittivity ε′ by about 40%–50%, which finally enhances the performance of the microwave absorption. The peak frequency (f_RL) of the reflection loss (RL) curve moves toward high frequency domain and the qualified bandwidth (QB, RL ≤ ?10 dB) increases remarkably. The maximum QB of 3.3 GHz (12.0–15.3 GHz) is obtained for the Sm_1.5Y_0.5Fe₁₅Si₂-paraffin composite (d = 1.0 mm) and the maximum RL of ?53.6 dB is achieved for Nd₂Fe₁₅Si₂-paraffin composite (d = 2.2 mm), both surpassing most of the reported MAMs. Additionally, a distinguished dielectric microwave absorption peak is observed, which further increases the QB in these composites.     

Grain growth kinetics and growth mechanism of columnar Al2O3 crystals in xNb2O5–7.5La2O3-Al2O3 ceramic composites

xNb₂O₅–7.5La₂O₃-Al₂O₃ ceramic composites with in-situ-grown columnar Al₂O₃ crystals were successfully prepared by microwave sintering at 1450–1525?°C using α-Al₂O₃, Nb₂O₅, and La₂O₃ powders as raw materials. X-ray diffraction results indicated that the main phases were Al₂O₃, LaNbO₄, and Nb₂O₅ in the prepared samples. A field emission scanning electron microscope (FESEM) showed that the Al₂O₃ crystals appeared as columnar in the structure. Moreover, the grain size of the columnar Al₂O₃ crystals increased with the Nb₂O₅ content. The ratio of the major axis to the minor axis of the crystals was largest when the Nb₂O₅ content was 15?vol%. Furthermore, the grain-growth kinetics index (n), growth activation energy (Q), and growth mechanism of the columnar Al₂O₃ crystals were studied. The results indicated that the Nb₂O₅ addition could promote formation and growth of columnar Al₂O₃ crystals, and the grain-growth activation energy indicated that the dissolution process controls the crystal growth. The growth mechanism of the columnar Al₂O₃ crystals was also studied. The present work demonstrated that Nb₂O₅ is a good additive for the preparation of Nb₂O₅–7.5La₂O₃-Al₂O₃ composite ceramics with columnar Al₂O₃ crystals.     

Tunable microwave absorption properties of nickel-carbon nanofibers prepared by electrospinning

The nickel-carbon nanofibers (Ni-C NFs) were fabricated by the electrospinning of poly(vinyl alcohol) (PVA) and nickel acetate tetrahydrate (NiAc) solution precursor with succedent PVA pyrolyzation and calcination process. The microwave absorption performance and electromagnetic (EM) parameters of the NFs were researched over the frequency range of 2.0–18.0?GHz. Both the impedance matching and EM wave absorption properties of the Ni-C NFs were improved by changing the carbonization temperature. The effect of graphitization degree on reflection loss (RL) and the possible loss mechanisms were directly displayed in the comparative study of each sample. The optimal RL value of ??44.9?dB and an effective frequency bandwidth of 3.0?GHz under a thickness of 3.0?mm can be reached by a sample calcined at 650?°C. These lightweight Ni-C NFs composites can be promising candidates for EM wave absorbers due to the combination of multiple loss mechanisms, nano-size effect and good impedance matching between Ni nanoparticles and CNFs.