Interfacial phenomena of aqueous systems in dense carbon dioxide

The interfacial tensions of initially pure liquids (water, ethanol and corn germ oil) and water–ethanol mixtures against dense carbon dioxide as well as against dense carbon dioxide mixtures with water and ethanol at 313 K and at pressures up to 27 MPa are measured. The wettabilities of ethanol and water on PTFE, glass and steel surrounded by pressurized carbon dioxide are also included in this paper. The interfacial tension results reported are the static values as well as the values which are measured during mass transfer.Generally, it is known that the interfacial tension depends on the composition of the coexisting phases. However, up to now, it is not clear whether only the composition of the interface does have an influence on the interfacial tension or if the composition of the bulk phase also affects this property. The detail discussion on this issue can be found in this paper. In this regard, the estimated pressure difference over the meniscus of a water drop with a diameter of 5 mm is reported.During mass transfer some interesting but scarcely reported drop phenomena such as drop kicking, upwards motion of the continuous phase around the drop, rising bubbles and intense mixing in the drop phase are observed. They are closely related to the interfacial turbulence, free convection, diffusion and stranding of the carbon dioxide molecules.The contact angle of ethanol and water drop over a pressure range of 27 MPa on PTFE, stainless steel and glass surfaces in the presence of dense carbon dioxide are included.     

Adhesion aspects of levulinic-acid-modified furan polymers to crystalline zinc phosphate metal surfaces

The nature of the interfacial interactions between functional levulinic-acid-modified furan resin coatings and crystalline zinc phosphate hydrate films deposited on carbon steel surfaces has been systematically investigated. The typical surface topography of the highly crystallized zinc phosphate films was found to be characterized by the presence of a dendritic microstructure array of interlocking triclinic crystals. This structure acts significantly to develop mechanical interlocking bonds with the functional blend polymer which penetrates into the open surface structure of the films. Both the thickness of deposition film and the polar H₂O molecules of hydrate at the outermost film surface sites play essential roles in wetting by the functional liquid resin. When the polarized furan polymers spread on the oxide film surfaces, the carboxylate groups derived from the levulinic ester and acid molecules react to form strong hydrogen bonds with the crystallized H₂O molecules on the hopeite film. This formation of hydrogen bonding was shown to be a major factor affecting the chemical intermolecular attractions. A formulation consisting of 95 parts furan to 5 parts levulinic acid was found to yield the optimum protective coating. More than 5 parts levulinic acid resulted in the transformation of the characteristics of the polymer film from hydrophobic to hydrophilic.     

PTFE／GF透波复合材料成型工艺与性能研究

为制备高性能聚四氟乙烯(PTFE)基透波复合材料,对玻璃布(GF)增强PTFE的成型工艺进行了研究。通过差示扫描量热法确定了PTFE/GF复合材料的烧结温度,考察了烧结时间、冷却速率、压制压力及组分配比等因素对复合材料性能的影响。结果表明,当GF质量含量为40%、压制压力为45MPa时,PTFE/GF复合材料的拉伸强度最大,可达81.2MPa,介电性能也满足透波复合材料的要求。     

Effect of synthesized silver nanoparticles in promoting methane hydrate formation at 4.7 MPa and 5.7 MPa

Using gas hydrates as materials for storage and transportation of natural gas have attracted much attention in recent years. However, there are two barriers in industrializing this new method. Firstly, methane hydrate induction time is relatively high. On the other hand the amount of gas trapped in methane hydrate crystals is too low. In this survey, silver nanoparticles were synthesized using a chemical reduction method and introduced to the hydrate reactor. Experiments were conducted at initial reactor pressures of 4.7 MPa and 5.7 MPa. At each pressure three independent experiments were performed. According to the results, in the presence of silver nanoparticles, methane hydrate induction time decreased by 85% and 73.9%, and the amount of methane trapped in hydrate crystals increased by 33.7% and 7.4% at the pressures of 4.7 MPa and 5.7 MPa respectively.     

Rhombohedral Twinning in Alumina

Alumina single crystals were deformed in compression along the c axes at T= 625 to 1373 K. Large-scale deformation by rhombohedral twinning was observed at a constant resolved shear stress of only 12.6 MPa between ∼900 and 1373 K. Below 900 K, the twinning stress for specimens with ground surfaces rose rapidly to 227 MPa at 625 K. A model for twin growth in the absence of dislocation slip is proposed.     

Accelerated methane storage in clathrate hydrates using surfactantstabilized suspension with graphite nanoparticles

In this study, enhanced kinetics of methane hydrate formation in the sodium dodecyl sulfate(SDS) solution with different concentrations of suspended graphite nanoparticles(GNPs) were investigated at 6.1–9.0 MPa and 274.15 K. The GNPs with rough surfaces and excellent thermal conductivity not only provided a considerable number of microsites for hydrate nucleation but also facilitated the fast hydrate heat transfer in the suspension system. At a relatively low pressure of 6.1 MPa, the suspension with 0.4 wt% of GNPs exhibited the minimum induction time of 22 min and maximum methane uptake of 126.1 cm~3·cm~(-3). However, the methane storage performances of the suspensions with higher and lower concentrations of GNPs were not satisfactory. At the applied pressure, the temperature increase arising from the hydrate heat in the suspension system with the optimized concentration(0.4 wt%) of GNPs was more significant than that in the traditional SDS solution. Furthermore,compared with those of the system without GNPs, enhanced hydration rate and storage capacity were achieved in the suspensions with GNPs, and the storage capacities were increased by 3.9%–17.0%. The promotion effect of GNPs on gas hydrate formation at low pressure is much more obvious than that at high pressure.     

Unusual kinetic inhibitor effects on gas hydrate formation

Gas hydrate formation experiments were conducted with a methane-ethane mixture at 273.7 or 273.9 K and 5100 kPa and using water droplets or water contained in cylindrical glass columns. The effect of kinetic inhibitors and the water/solid interface on the induction time for hydrate crystallization and on the hydrate growth and decomposition characteristics was studied. It was found that inhibitors GHI 101 and Luvicap EG delayed the onset of hydrate nucleation. While this inhibition effects has been reported previously some unusual behaviour was observed and reported for the first time. In particular, the water droplet containing GHI 101 or Luvicap EG was found to collapse prior to nucleation and spread out on the Teflon surface. Subsequently, hydrate was formed as a layer on the surface. Catastrophic growth and spreading of the hydrate crystals was also observed during hydrate formation in the glass columns in the presence of the kinetic inhibitor. Finally, when polyethylene oxide (PEO) was added into the kinetic inhibitor solution the memory effect on the induction time decreased dramatically.     

Ageing of plasma-treated poly(tetrafluoroethylene) surfaces

Highly hydrophobic poly(tetrafluoroethylene) (PTFE) surfaces were modified with an air glow discharge plasma to improve their wettability. However, the hydrophilic character obtained diminishes with time, due to molecular movement in the polymer. We have determined that the ageing process is strongly affected by the environment and temperature in which the surfaces are stored. A hydrophobic environment and high temperatures promote faster recovery of the original properties of PTFE than low temperatures. Nonetheless, a hydrophilic environment, even at high temperatures, prevents the surface from losing the polar character obtained from the plasma treatment, stopping the ageing process. Moreover, this process is reversible since the character of the treated surface changes when the environment changes (i.e. from water to air). The hydrophilicity of the surfaces was evaluated by contact angle measurements of a droplet of water.     

Effect of surface curvature and wettability on nucleation of methane hydrate

Natural gas hydrate nucleation is a complex physical and chemical process that is not well understood presently. In this article, an improved thermodynamic model is proposed to analyze the effects of surface curvature and wettability on methane hydrate nucleation for the first time. The results indicate that methane hydrate nucleation is more difficult on hydrophilic curvature surfaces under the same conditions, with a larger critical nucleation radius and required energy barrier than on hydrophobic surfaces. Furthermore, a convex surface is more favorable for forming methane hydrate under the same conditions than a concave surface. The model's results are critical in elucidating the microscopic mechanism of methane hydrate nucleation and providing a theoretical foundation for developing technologies for strengthening and inhibiting hydrate formation.     

Study of the Kinetics and Morphology of Gas Hydrate Formation

The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270–280 K, over a pressure range of 8.83–16.67 bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas‐water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110–190 rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis‐like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton‐like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate.     

Bioinspired steel surfaces with extreme wettability contrast

The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on alloy steels by both nano-flake or needle patterns and tuning of the surface energy. Steels were provided with hierarchical micro/nanostructures of Fe oxides by fluorination and by a subsequent catalytic reaction of fluorine ions on the steel surfaces in water. A hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.     

甲烷水合物在纯水中的生成动力学

引言一些低分子量气体,如石油和天然气中C_1～C_4轻烃、氮气、硫化氢、二氧化碳和惰性气体等,在一定压力和温度的条件下可与水形成一类笼形结构的冰状晶体,即所谓的气体水合物．气体水合物是一类较为特殊的包络化合物：主体水分子通过氢键相互结合形成一种内含空隙的笼形框架,客体分子则被笼罩于这些空隙中．主、客体分子之间的作用力为vanderWaals力．水合物晶体最为常见的两种结构分别称为结构I（体心立方构型）和结构Ⅱ（金刚石构型）．甲烷和水形成结构I水合物．文献阐述了开展水合物生成动力学研究的重要意义．但由于水合物生成…     

甲烷水合物在纯水中的生成动力学

The kinetic behavior of methane hydrate formation in pure water was investigated.12 sets of experimental data on methane hydrate formation were determined at temperatures ranging from 273.65 to 276.15K and pressures ranging from 4.47 to 8.47MPa.The duration of three stages in methane hydrate formation,known as the dissolution,nucleation and growth periods,that are lacking in open literature,was obtained.The effect of pressure and temperature on the kinetics of methane hydrate formation was also studied.     

甲烷+氨水体系水合物生成条件实验测定及计算

甲烷在氨水体系中生成水合物的实验数据对于开发水合法回收合成氨驰放气工艺以及操作条件的确定具有重要意义。本文测定了氨摩尔分数为1.018、3.171、5.278氨水溶液中甲烷气体水合物的生成条件。结果表明：氨的加入对甲烷水合物的生成起着明显抑制作用,而且随着氨浓度的增加,生成压力越高。采用Chen-Guo模型对甲烷在氨水中生成水合物的数据进行了计算,得到了较为满意的计算结果,平均误差为2.71%,说明Chen-Guo模型能够较好地预测该类体系的水合物的生成条件。     

Ultra-stability of gas hydrates at 1 atm and 268.2 K

This paper details creation of methane sI hydrates that are much more stable at 1 atm and 268.2 K than any previously reported. Extraordinarily stable natural gas sII hydrates at 1 atm and 268.2-270.2 K are reported for the first time. Test innovations that achieved ultra-stabilities give insight into hydrate self-preservation mechanisms. Water-surfactant liquid solutions were used to nucleate hydrate crystals that adsorbed as extremely small particles on surfaces of high thermal conductivity. The small hydrate particles packed and consolidated symmetrically upon Al or Cu cylindrical surfaces, minimizing internal void spaces and fractures in the accumulated 250-400 g hydrate mass. Resulting hydrate stability window is 268.2-270.2 K at 1 atm. Methane sI, as well as natural gas sII, hydrates exhibit only minimal decomposition upon reducing confining system pressure to 1 atm in the 268.2-270.2 K stability window. Total gas that evolved after 24 h at 1 atm in the stability window typically amounted to less than 0.5% of originally stored gas, and this ultra-stability was shown to persist when the test was allowed to run 256 h before terminating. The entire methane sI or natural gas sII hydrate mass remains stable during pressure reduction to 1 atm, whereas previous reports defined hydrate anomalous stability for only about 50% of fractional hydrate remnants.     

基于紫外光辐照改性自组装单层膜图案化表面的铁酸铋薄膜制备与表征

采用自组装单层膜(self-assembled monolayers,SAMs)技术在玻璃基板表面制备了十八烷基三氯硅烷(octadecyltrichlorosilane,OTS)-SAMs,将OTS-SAMs基体在光掩膜覆盖下用紫外光进行刻蚀,得到含有亲水性和疏水性区域的模板,利用液相沉积法在OTS-SAMs模板表面制备了铁酸铋(BiFeO3)图案化薄膜。通过接触角仪、原子力显微镜、X射线衍射、扫描电镜、X射线能谱仪等测试手段对OTS膜和BiFeO3薄膜进行表征。结果表明:以OTS为模板利用液相沉积法制备出边缘轮廓清晰、粗糙度较小,与基板结合力较强,条纹宽度为10～20μm的BiFeO3图案化薄膜。     

13X分子筛耦合四丁基溴化铵促进剂作用下CO2/H2水合物形成动力学

水合物法捕集CO₂技术因其清洁环保、工艺简单等优点成为研究热点。但气液传热传质速度慢导致的形成速率慢、储气能力低等关键问题亟待解决。利用13X分子筛耦合四丁基溴化铵（TBAB）促进剂在279.15～280.65K、3.0～6.0MPa研究了CO₂/H₂（39.8% CO₂/60.2% H₂）水合物的形成过程的压降曲线和气体消耗量,并对比分析了TBAB浓度、压力对其促进效果的影响。实验结果表明,与采用搅拌方式的TBAB/CO₂/H₂水合物形成过程相比,13X分子筛可显著提高TBAB/CO₂/H₂水合物的压降速率和气体消耗量。在279.15K、3.0MPa,随着TBAB溶液浓度增大,CO₂/H₂水合物形成过程的气体消耗量先增大后减小;而当温压条件为280.65K、3.0MPa时,气体消耗量随耦合促进剂中TBAB浓度变化仍遵循类似规律。此外,13X分子筛耦合TBAB促进剂对CO₂/H₂水合物压降速率和气体消耗量的影响随着实验压力升高而升高。     

TBAB水合物晶体生长过程的实验研究

通过对常压下9%(w) TBAB溶液降温生成水合物晶体的过程进行观察,以过冷度作为生长驱动力,研究了TBAB水合物晶体的生长特性. TBAB水合物刚形成时,晶体呈高透光度及规则柱体外形,随晶体继续生长逐渐变得不规则,透光度下降. 当恒温浴的过冷度分别为6.0, 8.1和9.6 K时,水合物晶体长度/宽度方向生长时间依次为183 min/140 min, 85 min/65 min, 70 min/37 min,同时反应前的等待时间即生成时间分别为83, 53和55 min. 生长时间和生成时间随过冷度增加逐渐降低,幅度逐渐减小,表明过冷度增加能有效减少水合反应时间,促进水合物的快速生成. 过冷度增加会增加TBAB水合物晶体成核数量,因此晶体与溶液的总体接触面积增加,有利于水合物的快速形成.     

Experimental study of CO2 hydrate formation in porous media with different particle sizes

To investigate the effect of the particle size of porous media on CO₂ hydrate formation, the formation experiments of CO₂ hydrate in porous media with three particle sizes were performed. Three kinds of porous media with mean particle diameters of 2.30 μm (clay level), 5.54 μm (silty sand level), and 229.90 μm (fine sand level) were used in the experiments. In the experiments, the formation temperature range was 277.15–281.15 K and the initial formation pressure range was 3.4–4.8 MPa. The final gas consumption increases with the increase in the initial pressure and the decrease in the formation temperature. The hydrate formation at the initial formation pressure of 4.8 MPa in 229.90 μm porous media is much slower than that at the lower formation pressure and displays multistage. In the experiments with different formation temperatures, the gas consumption rate at the temperature of 279.15 K is the lowest. In 2.30 and 5.54 μm porous media, the hydrate formation rates are similar and faster than those in 229.90 μm porous media. The particle size of the porous media does not affect the final gas consumption. The gas consumption rate per mol of water and the final water conversion increase with the decrease in the water content. The induction time in 5.54 μm porous media is longer than that in 2.30 and 229.90 μm porous media, and the presence of NaCl significantly increases the induction time and decreases the final conversion of water to hydrate.     

天然气水合物生成条件的测定和计算

利用全透明蓝宝石水合物静力学实验装置,测定了4种塔里木油田天然气在纯水中的水合物生成条件.将Chen-Guo 水合物模型应用于天然气水合物生成条件的计算,实验测定的4种天然气水合物生成条件的计算结果和实验结果符合得很好.