Vanadium carbide coating as hydrogen permeation barrier: A DFT study

Density functional calculations are used to investigate hydrogen (H) behaviors in vanadium carbide (VC). Molecular H₂ dissociation, atomic H diffusion and penetration are analyzed using the transition state theory. H₂ prefers to be close to the surface as physical adsorption, providing an environment conducive for further dissociation, and dissociates into atomic H adsorbed at the top C atom sites with co-adsorption state. The dissociation rate on the surface is mainly limited by the temperature-controlled activation energy barrier. The adsorptivity of atomic H by the surface tends to decrease as increasing of H coverage. For atomic H penetration through the surface, a significantly endothermic energy barrier and the low diffusion prefactor suggest that the main resistant effect of H permeation takes place at the surface. Energetic, vibrational, electronic consequences, and quantum effects on the H behaviors are discussed thoroughly. Our theoretical investigation indicates VC is a promising hydrogen permeation barrier.     

Effects of rolling and annealing on hydrogen permeability and crystal orientation in Nb-TiNi two-phase alloys

The Nb₁₉Ti₄₀Ni₄₁ alloy has a lamellar structure with bcc-Nb and B2-TiNi phases. It is known that a granule Nb phase forms in the TiNi matrix after thermal annealing and that the hydrogen permeability of unrolled annealed alloy is higher than that of rolled annealed alloy, even though the two alloys have granule Nb phase. Although the “cube-on-cube” relationship of crystal orientation for these phases has been observed in unrolled annealed alloy, no specific crystal orientation relationship has been seen in rolled annealed alloy. This indicates that the crystal orientation between the two phases strongly affects hydrogen permeability in Nb-TiNi two-phase alloys.     

A rational asymmetric hollow fiber membrane for oxygen permeation

A typical oxygen permeation hollow fiber membrane fabricated by phase inversion-based extrusion process demonstrates heterogeneous porous microstructures, in which the surface layer with relatively low porosity is used as a separation layer after sintering. It is usually not convenient to control the thickness of separation layer. And a high sintering temperature is needed to densify the separation layer, which in turn could destroy the desired porous microstructures in other portion. This paper studies a novel process to fabricate multilayer asymmetric hollow fiber membrane with a rational design using 67 vol. % Gd_0.2Ce_0.8O_2−δ−33 vol. % La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (GDC-LSCF) as a model material system. The phase inversion-based extrusion process in open literature is employed to fabricate a hollow fiber substrate featuring radially well-aligned microchannels open at the inner surface. Built upon the hollow fiber substrate, a thin dense separation layer and porous surface catalyst layer at shell side are then fabricated through dip-coating and sintering process alternatively. The oxygen permeation flux of the fabricated hollow fiber membrane reaches 2.68 mL/cm²/min at 900°C under Ar/air gradient, the highest performance of the membranes with GDC-LSCF material system in open literature. The innovative fabrication process is able to readily control the thickness of functional layers while decreasing sintering temperatures.     

金属有机骨架膜的制备与应用进展

膜分离技术因其高效节能的特点,被认为是最有前景的分离技术之一。由于众多待分离的混合组分在物理性质（如尺寸）上极为接近,实现精确的膜分离仍具有极大的挑战。金属有机骨架材料具有孔径精确可调、孔隙率高等优点,使其有望实现对尺寸相近分子的精确筛分,因此可以作为理想的膜材料。本文对传统的多孔膜材料进行了比较,并对基于金属有机骨架材料的多孔膜进行了分类,包括支撑型金属有机骨架膜和混合基质膜。同时,系统地总结了两大类金属有机骨架膜的制备方法及其发展历程,对先进的膜制备技术进行了展望;总结了金属有机骨架膜在气体分离、纳滤及海水淡化、渗透汽化等方面的应用。最后,针对支撑型金属有机骨架膜提出了改善其透量和选择性的思路。     

Fabrication of lanthanum-based perovskites membranes on porous alumina hollow fibre (AHF) substrates for oxygen enrichment

In this work, two types of lanthanum-based MIEC perovskite oxides, namely La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) and La_0.6Sr_0.4Co_0.2Ni_0.8O_3-δ (LSCNi), were deposited onto porous alumina hollow fibre (AHF) substrates and used for oxygen enrichment. Such structure was developed to shorten oxygen ion diffusion distances in dense membranes and simultaneously leading to higher oxygen flux. The perovskite oxides were prepared using Pechini sol-gel method and deposited via a vacuum-assisted technique. The deposition of lanthanum-based membranes onto the outer and inner sides of the porous AHF has been facilitated through numerous microchannels in the AHF substrates. The effects of operating temperature and argon sweep gas flowrate on oxygen permeation flux of lanthanum-based AHF membrane were investigated. The results revealed that the oxygen permeation flux of LSCF-AHF and LSCNi-AHF increased with operating temperatures due to the improvement of bulk diffusion and surface exchange properties after the lanthanum-based perovskite deposition. Higher oxygen flux was observed for LSCNi-AHF as LSCNi possessed balanced oxygen ionic and electronic conductivities as compared to LSCF membranes. Benefitting from improved oxygen activation and vacancy generation properties after Ni substitution into the B-site ion of LSC perovskite, a dramatic increased oxygen fluxes up to 4.5 mL/min·cm² was observed at 950 °C. The present work demonstrated a feasible method for fabricating oxygen transport membrane (OTM) using porous AHF substrates     

凝胶渗透色谱净化-气相色谱-质谱法测定肉品中的甲氧滴滴涕

建立肉品中甲氧滴滴涕残留的气相色谱-质谱(GC-MS)分析方法。采用均质提取方法提取样品中的甲氧滴滴涕,经凝胶渗透色谱净化,浓缩定容后用GC-MS检测分析,外标法定量。样品添加水平为0.005、0.01、0.02mg/kg时,甲氧滴滴涕的回收率在82.8%～103.2%之间,方法检测限为0.001mg/kg。本方法操作简便、准确、灵敏度高,净化效果好,满足残留分析要求。     

无硫低糖莲藕脯制作工艺优化

采用单因素和L9(34)正交试验研究不同因素对无硫莲藕脯护色及微波渗糖效果的影响,通过测定处理后莲藕片的褐变度和含糖量的变化确定最佳护色和微波渗糖工艺条件。结果表明:L-半胱氨酸质量分数0.40%、EDTA-Na2质量分数0.15%、食盐质量分数0.20%组合成的复合护色剂对莲藕片护色效果最佳;糖液质量分数30%,40%(320W)微波火力渗糖20min,其效果最佳。     

Reasonable construction of proton conducting channel via biomimetic caterpillar-like alumina fiber to improve the properties of its composite proton exchange membrane

In this paper, we prepare a novel biomimetic caterpillar-like alumina fiber with the characteristic of continuous alumina backbone and fine needle whiskers spine. Then the high-performance caterpillar-like alumina fiber composite proton exchange membrane (CAPEM) is obtained by introducing the amino modified biomimetic caterpillar-like alumina fiber into sulfonated polysulfone (SPSF) matrix, which successfully reasonable construction of the proton conducting channels in both vertical and horizontal orientation. The properties of CAPEM, including proton conductivity, methanol permeability, etc. Are systematically studied. The results show that the proton conductivity of CAPEM increases with rising the temperature, which reaches the maximum of 0.263 S/cm at 80 °C and 100% RH, respectively. The excellent proton conductivity of CAPEM is attributed to the long-range continuous proton conducting channel formed by the horizontal continuous alumina skeleton in the in-plane direction and the vertical overlapped fine needle whiskers spine in the through-plane direction. In addition, the interfacial compatibility between amino modified caterpillar-like alumina fiber and SPSF matrix is enhanced through the reasonable construction of proton conducting channels, which effectively inhibits the methanol permeation of the composite membrane with 4.18 × 10^?7 cm² s^?1 and improves the comprehensive performance of the CAPEM.     

The effects of hydrogen-induced lattice distortion and Nb-D formation on its permeation through niobium

Abnormal permeation behavior of hydrogen through niobium has been investigated in this paper, i.e. the permeation flux saturated with long-term decrease after reaching a maximum. The diffusivity and permeability have been deduced from the decay edge of permeation transient. Three kinds of polycrystalline niobium foils with different annealing temperature have been compared, to verify the effect of defects and grain properties on the permeability and diffusivity. In the temperature range of (773–1023) K, the heat treatment along with the permeation cycles could either reduce or increase the permeability and diffusivity depending sensitively on temperature and showing a temperature threshold around 950 K. The permeation flux is proportional to square root of pressure, revealing that the abnormal permeation was still bulk diffusion-limited. The diffusivity gradually decreased with permeation cycles, and became more and more sensitive to pressure. The niobium foil expanded macroscopically along the gradient of hydrogen concentration, which reveals the strong and unrecoverable lattice distortion in this temperature and pressure range. The X-ray diffraction studies showed that splitting of all the Nb peaks and shifting of Nb-D peaks along with hydrogen loadings. The phase transition was expected to eliminate the lattice strain during hydrogen loading and which in turn acted as a diffusion barrier.     

Sorption kinetics in metal hydrides by leaky coating

The 3D geometry of a hydrogen absorbing metal grain (Pd) is mimicked by a membrane made of the metal with identical properties, which is sealed on one side with a hydrogen semi-impermeable surface (Cu). The hydrogen loss through the sealed membrane surface is negligible, i.e., the hydrogen uptake measurement is that of a bulk material (Sieverts measurement), but the surface desorbs sufficient hydrogen to be detected by a mass spectrometer. With this, two independent spatial and temporal kinetic properties are defined which allow the reconstruction of the time dependent hydrogen distribution inside the membrane. As proof of concept, the mechanism of hydride formation in Pd is analyzed, corroborating the formation and growth of incoherent interfaces during hydrogen sorption.