PDMS-b-PPO非对称渗透汽化膜对乙醇/水的分离性能

以聚二甲基硅氧烷聚苯醚(PDMS-PPO)嵌段共聚物为膜材料,正丁醇为添加剂,氯仿为溶剂,采用凝胶溶胶法制备非对称渗透汽化膜,利用扫描电镜和能谱仪对膜进行形貌表征及元素分析.研究了铸膜液浓度、膜后侧压力、进料液流速对乙醇/水混合物渗透汽化分离性能的影响.结果表明,随着铸膜液中嵌段共聚物质量分数的增大,非对称膜的分离因子和渗透通量呈先上升后下降的趋势;随着膜后侧压力的增加,分离因子呈上升趋势,而渗透通量下降较快;随着料液流速的提高,分离因子先上升后下降,而渗透通量呈减小的趋势.以嵌段共聚物质量分数为11%制备的非对称膜,在进料液乙醇含量(质量分数)5%、温度60℃、膜后侧压力10kPa、料液流速0.267L/min时,膜的渗透通量为850.7g/(m2.h),分离因子为8.78.实验表明,PDMS-b-PPO非对称膜对乙醇具有优先选择性,并有较高的渗透通量.     

壳聚糖／羧甲基纤维素聚电解质络合物膜的乙醇／水渗透汽化性能研究

采用壳聚糖和羧甲基纤维素进行聚离子反应．制备聚电解质络合物膜。该膜用于乙醇／水的渗透汽化分离，显示具有优先透水性，在乙醇浓度90％，温度60℃下，渗透通量和分离系数分别达197g／m2·h，1588。随料液乙醇浓度的增加，膜渗透通量下降，而分离系数增加，分离系数在乙醇浓度90％左右有一极大值。随温度升高，膜渗透通量和分离系数同步上升，渗透通量随温度的关系符合Arrhe－nius方程，渗透汽化表现活化能为34kJ／mol。     

聚二甲基硅氧烷膜蒸汽渗透分离低浓度乙醇/水溶液的研究

对聚二甲基硅氧烷(PDMS)膜蒸汽渗透分离低浓度乙醇/水溶液的性能进行了研究,考察了料液浓度、膜器温度、循环气体流量、真空度等因素对PDMS膜蒸汽渗透性能的影响.结果表明,渗透通量和渗透侧乙醇浓度随着料液中乙醇浓度的增大而增大,但分离因子有所降低;随着膜器温度的升高,渗透通量增加,渗透侧乙醇浓度下降,影响显著;随着循环气体流量的增大,渗透通量和渗透侧乙醇浓度均有较大幅度的提升,有利于蒸汽渗透过程的进行;随着真空度的增大,渗透通量上升,渗透侧乙醇浓度下降.     

VTES交联PDMS渗透汽化膜分离水中乙醇性能的研究

以乙烯基三乙氧基硅烷(VTES)为交联剂对端羟基聚二甲基硅氧烷(H-PDMS)进行交联制备了疏水性更强的渗透汽化膜.通过考察交联温度、交联剂用量及料液温度等对该PDMS膜渗透汽化性能的影响发现:对乙醇浓度为6%的体系,交联温度为80℃,质量比m(H-PDMS)∶m(VTES)∶m(DBTDL)(二丁基二月桂酸锡)=1∶0.2∶0.02,原料液温度为40℃时,分离因子和渗透通量分别达到15.5和421.67 g/(m2.h),表明该VTES交联的PDMS膜具有良好的优先透醇性.     

碳黑填充PDMS渗透蒸发优先脱醇膜的制备研究

通过碳黑填充有机硅膜的方法,制备了一种新型聚二甲基硅氧烷(PDMS)优先脱醇渗透蒸发分离膜,考察了铸膜液制备、溶剂、碳黑粒径及处理方法和进料温度与膜的渗透蒸发性能之间的关系.结果表明,采用超声分散碳黑和正癸烷溶剂可以制得性能良好的膜.利用热处理过的N110碳黑填充PDMS膜,可以在保持分离因子不变的前提下,使总渗透通量提高到空白膜的两倍以上.碳黑填充PDMS膜总通量随进料温度升高而增加,选择性基本保持不变.     

聚二甲基硅氧烷膜分离甲醇/碳酸二甲酯混合物的渗透汽化研究

制备了一系列聚二甲基硅氧烷(PDMS)均质膜,用于渗透汽化法分离甲醇/碳酸二甲酯混合物,此系列PDMS均质膜优先脱除碳酸二甲酯.考查了PDMS均质膜在甲醇和碳酸二甲酯液体中的溶胀性能,并研究了PDMS预聚体的黏度、交联剂浓度、操作温度及料液浓度对渗透汽化分离性能的影响.结果表明,对于不同黏度的PDMS预聚体均表现出随交联剂浓度增加分离因子先增加后减小,而渗透通量则逐渐减小;随操作温度增加分离因子减小而渗透通量增大;随料液中碳酸二甲酯浓度增加分离因子先增加后减小,而渗透通量则逐渐增大.对于碳酸二甲酯浓度为30%的甲醇/碳酸二甲酯混合物,40℃时渗透侧碳酸二甲酯浓度为59.7%,分离因子为3.46,渗透通量为1.41 kg/(m2·h).     

炭黑填充PDMS复合膜的渗透蒸发性能

通过炭黑填充改性的方法,制备了一种新型聚二甲基硅氧烷(PDM S)优先脱醇渗透蒸发复合分离膜,考察了炭黑含量和料液浓度与分离膜分离性能之间的关系。结果表明,利用该复合膜可以有效分离乙醇/水混合物中的乙醇,在料液浓度为13.73%时,复合膜的选择性与空白膜相当,而渗透通量可由空白膜的70.74 g/m2.h提高到127.32 g/m2.h。     

分离润滑油中脱蜡溶剂的有机硅膜的制备

以聚二甲基硅烷为分离膜材料,正庚烷为溶剂,正硅酸乙酯为交联剂,二桂酸二丁基锡为催化剂,聚四氟乙烯膜为基膜,制得聚二甲基硅氧烷/聚四氟乙烯复合膜,用于脱蜡润滑油与溶剂(甲苯和丁酮)的分离.研究了溶液配方、硫化温度、硫化时间等因素对膜性能的影响.在操作压力2.0MPa,溶液温度20℃,进料溶剂质量分数85%条件下,膜对油的截留率为84%,通量为4.8kg/(m2·h).     

高通量ZSM-5填充硅橡胶复合膜渗透汽化性能研究

以硅铝比为360的ZSM-5型沸石对聚二甲基硅氧烷(PDMS)进行填充,以聚偏氟乙烯(PVSF)为支撑层,制备了ZSM-5填充PDMS/PVDF复合膜,用于渗透汽化乙醇/水混合物的分离.研究了沸石填充量、操作温度、进料液浓度对乙醇/水的渗透汽化分离性能的影响,发现该复合膜较文献报道中的沸石填充膜,其渗透通量有了明显的提高,在50℃沸石填充量为40%时,对乙醇的分离因子为11.7,其渗透通量达到749.8 g/(m2·h).随着操作温度的升高或料液中乙醇浓度升高,渗透通量增大,分离因子下降.     

聚酯(PET)硅橡胶复合膜制备与渗透汽化分离性能的研究

讨论了以聚酯(PET)为支撑层,以聚二甲基硅氧烷(PDMS107)为皮层的硅橡胶复合膜的制备工艺,并以乙醇水物系为料液,分析了硅橡胶、交联剂正硅酸乙酯(TAOS)、催化剂(二月桂酸二丁基锡)对分离系数及渗透通量的影响,并考察了膜下侧渗透压、料液浓度对膜分离性能的影响.     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.     

Degradation behaviour of sputtered Co–Al coatings on superalloy

Degradation behaviour of sputtered Co–Al coatings on Superni-718 substrate has been investigated. Cyclic high temperature oxidation tests were conducted on uncoated and coated samples at peak temperatures of 900 °C for up to 100 thermal cycles between the peak and room temperatures. The results showed that a dense scale formed on the coated samples during thermal cycling at the peak temperature of 900 °C. The external scale exhibited good spallation resistance during cyclic oxidation testing at both temperatures. The improvement in oxide scale spallation resistance is believed to be related to the fine-grained structure of the coating. Nanostructured Co–Al coatings on Superni-718 substrate were deposited by DC/RF magnetron sputtering. FE-SEM/EDS, AFM, and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. The Co–Al coating on superalloy substrate showed better performance of cyclic high temperature oxidation resistance due to its possession of β-CoAl phase as Al reservoir and the formation of Al₂O₃ and spinel phases such as CoCr₂O₄ and CoAl₂O₄ in scale. The oxidation results confirmed an improved oxidation resistance of the Co–Al coating on superalloy as compare to bare substrate in air at 900 °C temperature up to 100 cycles.     

Capacitance based mass metering for cryogenic fluids

This paper describes a method for measuring the mass of cryogenic fluids in on-board rocket propellant tanks or ground storage tanks. Linear approximations to the Clausius-Mossotti relationship serve as the foundation for a capacitance based mass sensor, regardless of fluid density stratification or tank shape. Sensor design considerations are presented along with the experimental results for a capacitance based mass gage tested in liquid nitrogen. This test data is shown to be consistent with theory resulting in a demonstrated mass measurement accuracy of ±0.75% and a deviation from linearity of less than ±0.30% of full scale mass. Theoretical accuracies are also shown to be ±0.73% for hydrogen and ±1.39% for oxygen for a select range of pressures and temperatures.     

Equipment using a “static-analytic” method for solubility measurements in potentially hazardous binary mixtures under cryogenic temperatures

A new apparatus designed to study, at cryogenic temperatures, thermodynamic equilibria of potentially explosive binary systems such as hydrocarbon-oxygen mixtures is described herein. This equipment has an equilibrium cell which was especially designed to minimize hazards while allowing accurate phase equilibrium measurements. Reliability of results, obtained with this equipment has been verified by working on the nitrogen-propane system, for which data are already available in literature, over a large range of compositions and at various temperatures. Four isothermal curves describing liquid phase compositions at 109.98, 113.77, 119.75 and 125.63 K have been determined. Our experimental data are represented within 2% in compositions and in pressures through the Peng-Robinson equation of state implying Mathias-Copeman alpha function and Huron-Vidal mixing rule. Comparisons to literature allow pointing out: good agreement is observed with Kremer and Knapp data (1983) while the three sets of Poon and Lu data (1974) presenting systematic positive deviation are consequently judged as suspicious.     

Thermal Stability of Amorphous Hydride Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45)

The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre-sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction(XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were preparedby mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas-eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most oftheir hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. Thecrystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphousMg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep-tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on thecrystallization of amorphous alloys was discussed.     

长余辉材料Sr_4Al_(14)O_(25)∶Eu~(2+),Nd~(3+)的溶胶凝胶法制备及性能研究

首次研究了以Nd~(3+)离子为辅助激活剂,对Eu~(2+)掺杂的发光材料Sr_4Al_(14)O_(25):Eu~(2+)余辉性能的影响.用溶胶凝胶法合成了Eu~(2+), Nd~(3+)共掺杂的Sr_4Al_(14)O_(25):Eu~(2+),Nd~(3+)发光粉末,并用扫描电镜、X射线衍射计、荧光分光光度计、余辉亮度测试仪、热释光剂量计等手段对粉末样品进行了表征.结果表明,在1350℃得到了单一的Sr_4Al_(14)O_(25)相,粉末颗粒平均粒度在1μm左右.Eu~(2+), Nd~(3+)共掺杂的Sr_4Al_(14)O_(25):Eu~(2+),Nd~(3+)发光粉末有402和485nm两个发射峰,与Eu~(2+)单掺杂的Sr_4Al_(14)O_(25):Eu~(2+)相比,发射峰位置没有变化,但适量的掺杂可以大大提高余辉时间和余辉亮度,余辉时间可达18h以上.最后通过对热释光谱的分析解释了双掺杂发光粉余辉性能增强的原因,适宜深度的陷阱可以有效存储光能,增强余辉的时间和强度.     

链结构对偏氟乙烯铁电共聚物介电性质的影响

用改进的介电松弛谱仪(精度 2‰)测定了 VDF(52)/TrFE(48)和VDF(47.5)/TrFE(47.5)/HeFP(5)在-120—140℃,10~(-2)-10~4Hz 范围的复数介电常数。介电松弛研究结果显示5mol%的 HeFP 导致三元共聚物 T_c 下降(30℃),非晶松弛强度减弱,T_g 降低(3℃),并引起局域松弛活化能升高(10.1kJ/mol),松弛时间增长。     

Development of No-Vent™ liquid hydrogen storage system for space applications

A number of technological advances required to store and maintain normal-boiling-point and densified cryogenic liquids, including liquid hydrogen, under zero boil-off conditions in-space, for long periods of time, have been developed. These technologies include (1) thermally optimized compact cryogen storage systems that reduce environmental heat leak to the lowest-temperature cryogen, which minimizes cryocooler size and input power, and (2) actively-cooled shields that surround the storage systems and intercept heat leak. The processes and tools used to develop these technologies are discussed. A zero boil-off liquid hydrogen storage system technology demonstrator for validating the actively-cooled shield technology is presented.     

Gas gap thermal switches using neon or hydrogen and sorption pump

The very low pressure obtained thanks to adsorption phenomenon at low temperature can be used to build cryogenic heat switches, which offer the possibility to make or break thermal contact between two parts of a cryogenic system. The ON (conducting) and OFF (insulating) states of the switch are obtained by varying the gas pressure between two copper blocks separated by a gap of 100 μm. This pressure is controlled by acting upon the temperature of a small sorption pump (activated charcoal) connected to the gap space. For a “high” sorption pump temperature, the gas previously adsorbed in the sorption pump is released to the gap between the two blocks, allowing a good thermal conduction through the gas (ON state). On the opposite, cooling the sorption pump allows a very good vacuum between the copper blocks, which efficiently break the thermal contact (OFF state). Experimental thermal characteristics (Conductance in the ON and OFF state, ON-OFF switching temperature) of such a “Gas Gap Heat Switch” are described using hydrogen or neon as exchange gas and are compared with theoretical calculations.