On alloying and low-temperature stability of thin,supported PdAg membranes

Electroless plating is the technically most facile and most frequently studied method for preparation of PdAg/ceramic composite membranes. Limited high-temperature stability of such membranes requires alloying of sequentially deposited Pd and Ag layers far below their melting points, however. Here it is demonstrated that 600–800 h are needed for forming 2–4 μm thick, homogeneous alloy layers from Pd–Ag bilayers at 823 K under atmospheric H₂ pressure. This is also the time scale on which the activation energy for H₂ permeation becomes stable so that this characteristic can be employed for non-destructive, in-process monitoring of the alloying progress. High-temperature H₂ permeation rates are shown to be less well suited for this purpose because they are not sufficiently sensitive to the homogeneity of PdAg membranes. The activation energies for the well-alloyed membranes indicate that diffusion through the bulk of the PdAg layer limits H₂ permeation through these composite membranes. It is further shown that a fully alloyed Pd₇₅Ag₂₅ membrane tolerates temperature cycling under H₂ well down to 373 K while H₂/N₂ exchanges at that temperature trigger a rapid growth of the N₂ leak rate of that membrane. The defect formation is attributed to mechanical stress caused by the substantial expansion and shrinking of the alloy lattice during hydriding and dehydriding at low temperatures.     

Carbon dioxide reforming of methane in a SrCe0.7Zr0.2Eu0.1O3−δ proton conducting membrane reactor

Utilizing CO₂ for fuel production holds the promise for reduced carbon energy cycles. In this paper we demonstrate a membrane reactor, integrating catalytic CO₂ reforming of methane with in-situ H₂ separation, that results in increased CO₂ and CH₄ conversion and H₂ production compared to a Ni catalyst alone. The tubular proton-conducting SrCe_0.7Zr_0.2Eu_0.1O_3−δ membrane reactor demonstrates that the addition of the membrane improves CO₂ conversion, due to in-situ H₂ removal, by 10% and 30% at 900 °C for CH₄/CO₂ = 1/1 and CH₄/CO₂/H₂O = 2/1/1 feed ratios, respectively. It also improves total H₂ production at 900 °C by 15% and 18% for CH₄/CO₂ = 1/1 and CH₄/CO₂/H₂O = 2/1/1, respectively. Further, the H₂/CO in the reactor side effluent can be adjusted for subsequent desired Fischer-Tropsch products by combining CO₂ reforming and steam reforming of methane.     

臭氧降解制备低聚壳聚糖的研究

为制备分子量较低的可溶于水的低聚壳聚糖,研究了在乙酸均相体系中臭氧对壳聚糖的氧化降解过程,采用凝胶渗透色谱法(GPC)跟踪测定了壳聚糖氧化降解过程中分子量及其分布的变化,探索制备不同分子量低聚壳聚糖的适宜条件。结果表明,壳聚糖降解的最佳条件为氧气流量1.2L/min、处理时间20min、壳聚糖浓度2g/L,此条件下水溶性低聚壳聚糖得率为66.7%,其平均相对分子量为9500u。     

Chitosan Film Mechanical and Permeation Properties as Affected by Acid, Plasticizer, and Storage

The effects of acid (acetic, formic, lactic, propionic) concentrations, plasticizer concentrations, and storage time (up to 9 wk) on mechanical properties, water vapor permeability, and oxygen permeability of solution-cast chitosan films were determined. Measured water vapor permeability coefficients ranged from 5.35 to 13.20 × 10^?1 g/m·day·atm. Oxygen permeated coefficients ranged from 0.08 to 31.67 × 10^?3 cc O₂ m·day·atm. Neither property was affected by storage time. Tensile strength (6.85–31.88 Mpa) also was not time dependent, but elongation (14–70%) decreased with storage time. Lactic acid solutions produced the lowest oxygen permeability values, formic acid the highest. Films formed with 7.5% lactic acid solutions had uniquely high values for elongation at break.     

Complexes between linoleate and native or aggregated β-lactoglobulin: Interaction parameters and in vitro cytotoxic effect

The dairy protein β-lactoglobulin (βlg) is known to form a complex with fatty acids (FA). Due to industrial processing, βlg is often in its non-native form in food products, which can modify the FA/βlg complex properties. We investigated the interaction of bovine βlg, in selected structural forms (native βlg, a covalent dimer and as nanoparticles), with linoleate (C18:2). Using fluorescence and Isothermal Titration Calorimetry, linoleate was found to bind βlg at two different binding sites. Regardless of the structural state of βlg, association constants remained in the same order of magnitude. However, the stoichiometry increased up to 6-fold for nanoparticles, compared to that of native βlg. The impact of these structural changes on linoleate uptake in vitro was measured by cytotoxicity assays on Caco-2 cells. The order of cytotoxicity of linoleate was as follows: free > complexed to dimers > complexed to nanoparticles > complexed to native βlg. Therefore, the in vitro cytotoxicity of linoleate could be modulated by altering the state of βlg aggregation, which in turn affects its binding capacity to the FA.     

用表面渗透法检测高温工程陶瓷的热震性能

本文介绍依据热弹性理论,利用表面渗透法测量高温工程陶瓷材料的热震性能。对几种有代表性的高温工程陶瓷材料进行测试,并将结果与热震后测弯曲强度、依据热弹性理论计算的R、R′进行对比。本方法有简易、可靠、热震裂纹及分布可直接观察等特点。     

Al2O3微粒对Cd-Al2O3复合镀渗氢量的影响

利用电化学方法探讨了在电镀镉及加入Al2O3微粒过程中,A12O3微粒的加入量对其氢渗入量的影响。试验表明：在其过程中,夹杂Al2O3微粒可以减少氢的渗入量,且随着夹杂到镀层中Al2O3微粒的增加,渗入到基体金属的氢量减少;同时还发现,渗氢电流均是由突峰到稳定,一段时间后再以较快的速度上升,然后缓慢平稳。     

Hydrogen Trapping in Some Automotive Martensitic Advanced High‐Strength Steels

Hydrogen permeation experiments are used to investigate hydrogen trapping in commercial automotive martensitic advanced high‐strength steels. Hydrogen trapping increases with increasing mechanical strength, as indicated by (i) the decrease in the hydrogen diffusion coefficient, and (ii) the increase in reversible hydrogen trap density. The measured trap densities are in the order of ≈10¹⁷– ≈ 10¹⁸ cm^?3. The relationship between trapping characteristics and HE susceptibility of MS‐AHSS is discussed in terms of Hydrogen Enhanced Macroscopic Plasticity (HEMP) and Hydrogen Assisted Micro‐fracture (HAM).

     

非对称膜及其复合膜结构参数的确定

根据非对称膜及其复合膜与气体渗透之间关系的数学模型，建立了通过测定气体渗透率确定膜结构参数的计算方法，并建立了相应的电算软件。可确定的膜结构参数为涂层厚度、致密层厚度、底膜和复合膜的表面平均孔径及表面孔隙率。并利用此方法确定了两种气体分离复合膜的结构参数。     

不锈钢及其镀膜复合材料气相氢渗透研究

叙述了全金属超高真空气相氢渗透装置和HR－1超低碳不锈钢镀膜复合材料的研制，以及氢通过不锈钢基体及其镀膜复合材料的气相氢渗透实验．实验表明，镀膜复合材料的氢渗透率比基体材料降低二个量级以上。