基于SPOD方法的压气机转子叶顶区域非定常流动分析

为了研究叶顶区域非定常流动特性,对跨声速轴流压气机转子NASA Rotor37在多工况下进行了三维非定常数值模拟,采用谱本征正交分解（Spectral Proper Orthogonal Decomposition,SPOD）方法从叶顶区域流场中提取出时空耦合的单频相干结构进行分析。研究结果表明：相比于常规分析方法,SPOD方法能够高效地从非定常流场中识别出流动特征,有助于揭示叶顶区域流动规律;在“小流量”工况下叶顶区域流动呈现出强的非定常性,且随着质量流率的减小叶顶区域非定常流动增强、波动范围增加、波动频率呈现出“阶跃式”下降;造成叶顶区域流场非定常周期性波动的主要原因是叶顶间隙泄漏涡破碎区的扰动以及叶顶间隙泄漏涡破碎后与主流相互作用所形成的叶尖二次涡的波动。     

Covalently cross-linked sulfonated poly(ether ether ketone)/tungstophosphoric acid composite membranes for water electrolysis application

Composite polymer electrolyte membranes consisting of covalently cross-linked sulfonated polyether ether ketone (SPEEK) with tungstophosphoric acid (TPA) are prepared and their electrochemical and mechanical properties are investigated with regards to application in water electrolysis. Covalently cross-linked membranes (CL-SPEEK) comprised of sulfochlorinated SPEEK membranes and SPEEK partially lithiated by LiCl, are prepared by reaction with 1,4-diiodobutane, and blended with TPA to avoid excessive water swelling and to reinforce their mechanical properties. These ion-exchange membranes show good electrochemical properties, including proton conductivity, ion exchange capacity (IEC), thermal stability, anti-oxidative stability, and satisfactory mechanical characteristics, such as tensile strength and elongation. In particular, among the TPA-composite membranes, the CL-SPEEK/TPA30 (30 wt.% TPA) membrane displays higher proton conductivity (0.128 S cm⁻¹) and tensile strength (75.01 MPa) than Nafion^® 117 at 80 °C. The ion-exchange membranes are used to construct membrane electrode assemblies (MEAs) of use in polymer electrolyte membrane electrolysis (PEME). The MEA are prepared using a non-equilibrium impregnation–reduction (I–R) method. The electrochemical surface area (ESA) and roughness factor of the MEA prepared with CL-SPEEK/TPA30 electrolyte measured by cyclic voltammetry are 25.11 m² g⁻¹ and 321.4 cm² Pt cm⁻², respectively. The prepared MEAs are used in the water-electrolysis unit cells. The cell voltage is 1.78 V at 1 A cm⁻² and 80 °C, with a platinum loading of 1.28 mg cm⁻². The results of the present study suggest that the good conductivity and mechanical properties of covalently CL-SPEEK/TPA composite membranes make them well suited for use in PEME.     

Vicious cycle during chemical degradation of sulfonated aromatic proton exchange membranes in the fuel cell application

Weak phase separation and vulnerable linking groups between aromatic units are common setbacks of sulfonated aromatic proton exchange membranes (PEMs) from durability point of view. In this study, sulfonated poly(ether ether ketone) (SPEEK) membranes were exposed to Fenton's solution for a specific time, ranging from 10 to 60 minutes. Chemical structure and morphology evolution, decay in mechanical and thermal stability, and H₂ permeability of SPEEK membranes were evaluated during the chemical degradation. Less-entangled polymeric chains with lower average molecular weight of degraded SPEEK samples diminished mechanical rigidity. In addition, reduction of aromatic rings in each repeat unit led to higher thermal decomposition rate. Furthermore, randomly distributed micro-defects in the SPEEK morphology and an increase in water sorption can reduce the fatigue strength of membranes in the wet-dry cycles. Eventually, hydrogen cross-over rate was gradually increased, and henceforth, accelerated destructive radical formation and degradation can be predicted.     

Tungstophosphoric acid incorporated hierarchical HZSM-5 catalysts for direct synthesis of dimethyl ether

HZSM-5 zeolites are active materials in dimethyl ether (DME) production with high surface acidity. In this study, hierarchical HZSM-5 catalysts were synthesized with steam-assisted crystallization (SAC) method and then in order to increase its surface acidity, TPA was loaded into the HZSM-5 catalyst having various mass ratios (5, 10, 25%) by wet impregnation method. Synthesized catalysts were characterized by N₂ physisorption (BET analysis), X-Ray diffraction and pyridine adsorbed diffuse reflectance FTIR spectroscopy techniques. Characterization analysis of tungstophosphoric acid (TPA) impregnated catalysts indicated that hierarchical HZSM-5 possesses mesoporous structures. The average pore size distribution of TPA impregnated HZSM-5 catalysts were between 17 and 20 nm. TPA impregnation promoted Brønsted acid sites of the catalyst, which favors methanol dehydration reaction. Activity tests have been performed at reaction temperatures of 200–300 °C at 50 bar reaction pressure in the presence of admixed catalysts (physically mixed commercial HifuelR-120 and HZSM-5 based catalysts with a weight ratio of 1:1). Results revealed that the increase in the amount of heteropoly acid has enhanced DME selectivity and CO conversion. Maximum DME selectivity of 57% and CO conversion of 46% were achieved in the presence of the 25TPA@HZSM-5 catalyst at the optimum reaction temperature of 275 °C. TGA analysis result of spent catalysts presented the highest amount of coke over HZSM-5. TPA incorporation decreased coke formation due to suppression of the Lewis acid site, which is responsible for the coke formation.     

热老化对植物油中绝缘纸样频域介电谱的影响

为研究不同绝缘纸样在植物油中的老化行为,对FR3植物油与菱格点胶纸、DPE纸和Nomex纸构成的油纸绝缘组合,在130℃环境中开展人工加速热老化试验,测量绝缘纸在10-1~107 Hz范围内的频域介电谱(FDS),分析FR3植物油中绝缘纸样老化前后的tanδ、复介电常数实部ε′和虚部ε″,利用扫描电子显微镜观察绝缘纸的表面微观结构,并测试各纸样的拉伸强度。结果表明,三种纸样在低频下的介电谱随老化程度延长呈现降低趋势,下降幅度为点胶纸>DPE纸>Nomex纸;热老化破坏绝缘纸紧密的纤维排列结构,使其孔洞、裂纹增多;相同老化时间下DPE纸纤维结构比点胶纸纤维结构的劣化程度低;Nomex比点胶纸和DPE纸抗热老化能力更强,机械强度更稳定。     

Brønsted酸性离子液体合成及催化制备生物柴油

合成4种成功能化酸性离子液体,采用红外光谱、热重分析等分析法进行表征验证,并用其催化菜籽油酯交换制备生物柴油,考察醇/油物质的量之比、反应温度、反应时间、离子液体用量和水含量对转化率的影响。结果表明,4种离子液体都有较强酸性,与浓硫酸酸性相当;带—SO₃H基团的离子液体表现出更好的催化活性,且随着烷基链的增加,催化活性提高;在（n甲醇）∶n（菜籽油）=12∶1,反应温度130 ℃,反应时间3 h,离子液体（[BSO₃HMIM][HSO₄]）用量为菜籽油质量2%（质量分数）条件下,生物柴油转化率可达99%以上。在反应体系中,水会破坏离子液体的结构并导致其失活,而升高反应温度,可缓解水对离子液体的结构破坏,在130 ℃条件下,即使水分含量为5%时,生物柴油转化率仍可保持在约85%。     

Hydrogenation and annealing effect on electrical properties of nanostructured Mg/Mn bilayer thin films

Bilayer Mg/Mn thin films have prepared using thermal evaporation method at pressure 10⁻⁵ torr. Hydrogenation process has been done on pristine and annealed bilayer structure of films at different hydrogen pressure for half an hour. In case of annealed samples partially semiconductor nature is observed and conductivity of films found to decrease with hydrogen pressure and increased with annealing temperature. The XRD analysis shows microcrystalline nature of as-deposited films and after annealing it produce crystalline nature. After hydrogenation an additional peaks of magnesium hydride are also observed that suggesting the presence of hydrogen and hydrogen storage capacity of thin film bilayer structure. Optical band gap of annealed bilayer thin films found to increase with hydrogen pressure. It means hydrogenation process is capable to change bilayer structure from metallic to semi-conducting. The variation in relative resistivity is found nonlinear with time and increases with hydrogen pressure, due to the net effect of hydrogen absorption. Raman spectra show the decrease in intensity of peaks with hydrogen pressure that confirm the presence of hydrogen. Optical photographs are taken in reflection mode that shows a change of color from brown to dark black state with increasing hydrogen gas pressure. This dark black state may be used as solar thermal energy collector because black body is good absorber of heat.     

Characterization of Cu(InxGa1−x)2Se3.5 thin films prepared by rf sputtering

Cu(In_xGa_1−x)₂Se_3.5 thin films were fabricated by rf sputtering from CuIn_xGa_1−xSe₂ and Na mixture target by controlling the mixture ratio. X-ray diffraction analyses show that the structure of Cu(In_xGa_1−x)₂Se_3.5, thin films is different from chalcopyrite structure: especially, CuIn₂Se_3.5 thin films have a defect chalcopyrite structure. The lattice parameters for Cu(In_xGa_1−x)₂Se_3.5 thin film are slightly smaller than those for CuIn_xGa_1−xSe₂ thin film and linearly decreased with increasing Ga content. The optical absorption coefficients for Cu(In_xGa_1−x)₂Se_3.5, thin films exceed 2 × 10⁴ cm⁻¹ in energy region above the fundamental band edge. The band gap for Cu(In_xGa_1−x)₂Se_3.5 thin films is larger than that for CuIn.Ga_1−x2Se₂ with the same Ga content and increased with increasing Ga content.     

Effect of salt concentration on poly (vinyl chloride)/poly (acrylonitrile) based hybrid polymer electrolytes

Hybrid, solid polymer electrolyte films consisting of poly (vinyl chloride) (PVC), poly (acrylonitrile) (PAN) and, propylene carbonate (PC) with different concentrations of LiClO₄ are prepared by means of a using solvent-casting technique. The structure and complex formation are studied by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The temperature dependence of the ionic conductivities of the polymer films is explained in terms of a free volume model. The conductivities of PVC–PAN–LiClO₄–PC complexes are determined at different salt concentrations. The highest ionic conductivity (8.35 × 10⁻⁵ S cm⁻¹) is obtained for 8 wt.% LiClO₄ in the polymer complex at 304 K. The thermal stability of the electrolyte is examined by thermogravimetric/differential thermal analysis (TG/DTA).     

Thin film of CeO2-SiO2: a new ion storage layer for smart windows

Thin solid films of CeO₂-SiO₂, used as a counter-electrode layer in electrochromic devices, were prepared by the sol–gel dip coating, using an aqueous-based process. The influence of the SiO₂ addition on electrochemistry of the CeO₂ oxide coatings was determined by chronoamperometric measurements. The films exhibit a larger charge storage capacity, which was determined as a function of the coatings thickness. The peak occurrence in the chronoamperometric curve during the deintercalation of lithium ions in the cerium/silicon films is analyzed in terms of trapping energy levels for Li⁺ ions into the film.

In situ UV–Vis spectroelectrochemical measurements of the CeO₂-SiO₂ coatings indicated that the films remained transparent in the visible spectral range during the intercalation process. Powders were characterized by X-ray diffraction after the same thermal treatment of the films, indicating a decrease of crystallinity with the doping. The feasibility for use of these electrodes as ion storage for electrochromic devices was investigated.     

Poly(arylene ether)s with pendant sulfoalkoxy groups prepared by direct copolymerization method for proton exchange membranes

A novel sulfonated monomer sodium-3-(4-(2,6-difluorobenzoyl)phenoxy)propane-1-sulfonate was designed and synthesized. Based on above monomer, a series of sulfonated poly(arylene ether) copolymers containing aliphatic acid groups between aromatic backbones and sulfonic acid groups (PSOA-SPAE) were successfully prepared by direct copolymerization. Ion exchange capacity (IEC) of the copolymers could be mediated in the range of 1.07–1.61 meq g⁻¹ by the monomer ratios used in the copolymerization. These copolymers exhibited good oxidative and dimensional stability. The proton conductivities of copolymer films increased with the increase of IEC and temperature. The conductivity of PSOA-SPAE-80 was 4.94 × 10⁻² S cm⁻¹ at room temperature, and was up to 1.35 × 10⁻¹ S cm⁻¹ at 100 °C, which was close to that of Nafion 117. These copolymers may be promising proton exchange membranes (PEMs) due to their high proton conductivity and good oxidative and dimensional stability.     

Novel branched sulfonated poly(arylene ether)s based on carbazole derivative for proton exchange membrane

Proton exchange membrane (PEM) is a vital part of polymer electrolyte fuel cells (PEFCs). So it is of great importance to design the novel polymers for PEMs to improve the performance of PEFCs. Here two highly branched sulfonated copolymers (SBP-Cz-x) were synthesized based on a novel AB₂ monomer. For all we know, it is the first time that the 9H site of carbazole was used to prepare branched polymers. These copolymers given tough and transparent membranes by solvent casting method. SBP-Cz-x membranes exhibited excellent thermal stability and remarkable dimensional stability. Moreover, proton conductivity of SBP-Cz-x was very excellent. SBP-Cz-15 (IEC = 1.33 meq.g⁻¹) owned high proton conductivity of 42.1 mS cm⁻¹ at 80 °C. SBP-Cz-15 showed a pretty low swelling ratio of 12.7% with high water uptake (32.0%). SBP-Cz-x also owned remarkable oxidation stability. This study demonstrated that the strategy of fixing locally dense sulfonic acid groups on the branched points, which were surrounded by hydrophobic segment, could improve oxidative stability and dimensional stability efficiently.     

Defect reduction in electrochemically deposited CdS thin films by annealing in 02

Using the electrochemical deposition method, CdS thin films were deposited from acid solutions (pH = 2.5) containing CdS0₄ and Na₂S₂0₃ on indium-oxide coated glass substrates. These films were annealed in N₂, air, or O₂ atmosphere at 200–500°C for 30 min. Photoluminescence spectra were measured at 77 K. For the films annealed in N₂, the band edge emission became weaker and the luminescence due to defects shifted to longer wavelengths as the annealing temperature was raised above 300°C. However, for the films annealed in air or O₂, the band edge emission was observed strongly irrespective of the annealing temperature and the luminescence due to defects was weak. Thus the O₂ annealing is useful for the defects reduction.     

Effect of the heating rate on crystallization behavior of mechanically alloyed amorphous alloy

The mechanical alloying is the most convenient method to produce Mg–Ni alloys. In this study, the effect of ball-to-powder weight ratios and the mechanical alloying time on amorphization of Mg₅₀Ni₅₀ alloy and its thermal stabilities were investigated. Mg₅₀Ni₅₀ alloy has been produced by using Spex 8000 D mixer/mill with different ball-to-powder weight ratios (5:1, 10:1, 20:1). Amorphization times by XRD analysis are found to be 60 h for 5:1 ball-to-powder weight ratio, 10 h for 10:1 ball-to-powder weight ratio and 5 h for 20:1 ball-to-powder weight ratio. The thermal stabilities of amorphous Mg₅₀Ni₅₀ alloys, obtained by different ball-to-powder weight ratios, have been determined and the effect of heating rates on the crystallization temperatures have also been investigated by DSC. The heating rates employed were 5, 10, 15, 20 °C/min. During the first crystallization reaction, the amorphous and Mg₂Ni intermetallic phases occurred. DSC studies show that increase in heating rates increased the crystallization temperatures for all samples. The apparent activation energies were determined by means of the Kissinger method.     

High-chain fatty acid esters of myristyl alcohol with even carbon number: Novel organic phase change materials for thermal energy storage—1

High-chain fatty acid esters have not been investigated for their thermal properties as phase change materials (PCMs) in thermal energy storage. A series of high-chain fatty acid esters of myristyl alcohol (1-tetradecanol) were synthesized via esterification of lauric, myristic, palmitic, stearic and arachidic acids under vacuum and in the absence of any catalyst. The esterification reactions were studied by FT-IR spectroscopy. A differential scanning calorimeter (DSC) and a thermo-gravimetric analyzer (TGA) were intensively used to determine the thermal properties of the introduced thermal storage materials. The thermal properties were given in terms of phase change temperature, enthalpy, specific heat (C_p) and thermal decomposition temperature with related statistical data. The thermal reliability of the novel organic PCMs was investigated by thermal cycling with 1000 thermal cycles with respect to the thermal properties of the original synthesized PCMs. In addition to the synthesized esters, one commercial product was also investigated. The DSC analyses indicated that the melting points of the novel organic PCMs were between 38 and 53 °C with phase change enthalpy above 200 kJ/kg. The effect of chemical structure of the materials on thermal properties was also discussed. The results showed that these materials were favorable for low temperature heat transfer applications with superior thermal properties and reliability.     

Fast pyrolysis of cellulose in a single pulse shock tube

A shock tube technique was employed to study the thermal decomposition of cellulose in an inert argon gas under the conditions of high temperature, high heating rate, and short reaction times. The influence of temperature and reaction times on product yields and their distribution were investigated. A clean, tar and char free gas consisting mainly of CO, CO₂, C₂H₂, C₂H₄ and CH₄ were produced throughout the course of this investigation. A mass conversion of cellulose to gas exceeding 90 wt% has been realized between the temperatures 700 and 2200°C for the reaction times examined. Carbon monoxide is the major product and attains a yield in excess of 65 wt% for temperatures above 1300°C. Global kinetic parameters for the decomposition of cellulose and its principal gas products were obtained by fitting the experimental data to a single, first order kinetic model. The energy of activation for the decomposition of cellulose was found to be 130.5 kJ/mol. The material balances made for the total mass, carbon and oxygen are good.     

铝传感层蒸镀速率对飞秒激光抽运探测热反射方法测量热导率影响的研究

对飞秒激光抽运探测热反射实验中的一个关键因素传感层进行了研究,发现铝传感层的蒸镀速率对飞秒激光抽运实验有着很大的影响。分别在3种不同类型的硅片和玻璃片基底上用不同的蒸镀速率蒸镀了100nm的铝膜蒸镀速率控制在2×10-10到15×10-10 m/s。通过扫描电子显微镜(SEM)和X射线反射(XRR)研究了蒸镀铝膜表面的形貌及铝膜的厚度。基于飞秒激光抽运探测热反射方法对基底的热导率进行了测量,发现随着蒸镀速率的增大,不同基底测量得到的热导率呈现一致的规律。结果表明,蒸镀速率越大,铝传感层的晶粒越大,传感层的体积热容越小,当蒸镀速率大到一定程度时,由于晶粒的不规则度越来越大,反过来又影响体积热容的大小,从而影响了飞秒激光抽运探测热反射。     

Effect of citric acid on properties of CeO2 films for electrochromic windows

An alcohol based sol–gel process involving cerium chloride heptahydrate and citric acid in different mole ratios has been employed for the deposition of CeO₂ films. The structural, electrochemical, and optical properties of the films have been investigated using a wide range of techniques. Differential thermal analysis has shown the onset of crystallization of CeO₂ at 389 °C. The addition of an additive (citric acid) to the precursor sol has led to homogeneity and also a reduced ion storage capacity in the films. This observation emphasizes on the use of optimum content of the citric acid such that the films are suitable in terms of transparency as well as uniformity characteristics and also exhibit good electrochemical response. As is evidenced by the SEM study, the degree of polycrystalline grain formation in the citric acid derived films is observed to be less. The XPS results have confirmed the presence of Ce⁴⁺ state in the films. The optically passive behavior of the films is affirmed by their negligible transmission modulation upon Li ion insertion and extraction. A higher proportion of citric acid has also resulted in a reduced porosity and diminished crystallite size of the cerianite phase. The effect of the CeO₂ films on the switching kinetics of the tungsten oxide (WO₃) films has revealed an increase in the coloration time of the latter with the diminished crystallite size of CeO₂ nanograins in the former.     

磷酸催化热解木质素模化物的反应机理研究

采用密度泛函理论计算及快速热解-气相色谱/质谱联用(Py-GC/MS)实验相结合的方法,研究磷酸对β-O-4型木质素二聚体模型化合物苯乙基苯基醚(PPE)热解过程的影响。计算结果表明:磷酸以氢键方式与PPE结合形成复合物H3PO4-PPE,并影响PPE的热解反应。在非催化热解过程中,PPE主要发生Cβ-O键、Cα-Cβ键均裂反应和协同断裂反应(逆烯反应和Maccoll消除反应);在磷酸催化作用下,Cβ-O键、Cα-Cβ键均裂反应的能垒会升高,而上述2种协同断裂反应的能垒会降低,同时还会促进一种新协同断裂反应的发生,且其反应活性优于Cβ-O键、Cα-Cβ键均裂反应、逆烯反应和Maccoll消除反应。实验结果表明,磷酸可促进PPE协同断裂反应的发生,同时抑制均裂反应的发生,与计算结果相符。     

Catalytic decomposition of liquid hydrocarbons in an aerosol reactor: A potential solar route to hydrogen production

Catalytic decomposition of liquid fuels (n-octane, iso-octane, 1-octene, toluene and methylcyclohexane) is achieved in a continuous tubular aerosol reactor as a model for the solar initiated production of hydrogen, and easily separable CO free carbonaceous aerosol product. The effects of fuel molecular structure and catalyst concentration on the overall hydrogen yield were studied. Iron aerosol particles used as the catalysts, were produced on-the-fly by thermal decomposition of iron pentacarbonyl. The addition of iron catalyst significantly decreases the onset temperature of hydrogen generation as well as improves the reaction kinetics by lowering the reaction activation energy. The activation energy without and with iron addition was 260 and 100 kJ/mol, respectively representing a decrease of over 60%. We find that with the addition of iron, toluene exhibits the highest hydrogen yield enhancement at 900 °C, with a 6 times yield increase over thermal decomposition. The highest H₂ yield obtained was 81% of the theoretical possible, for n-octane at 1050 °C. The general trend in hydrogen yield enhancement is that the higher the non-catalytic thermal decomposition yield, the weaker the catalytic enhancement. The gaseous decomposition products were characterized using a mass spectrometer. An XRD analysis was conducted on the wall deposit to determine the product composition and samples for electron-microscopic analysis were collected exiting the furnace by electrostatically precipitating the aerosol onto a TEM grid.