FBRM在线研究三水碳酸镁在电解质溶液中的二次过程

实验采用聚焦光束反射测量仪(FBRM)在线监测三水碳酸镁在电解质溶液中颗粒弦长和弦粒数变化趋势,结合扫描电镜(SEM)和粉末晶体衍射(XRD)表征形貌和晶型,考察了介质对三水碳酸镁二次过程的影响。实验结果表明:在NaCl和Na2CO3溶液中二次过程不显著,对三水碳酸镁形貌和尺寸无明显影响;在MgCl2溶液中三水碳酸镁尺寸增大。理论计算表明,对于三水碳酸镁的二次过程,Ostwald熟化可以忽略,结合MgCO3.3H2O特定晶体结构和产物形貌分析,表明MgCl2可以促进三水碳酸镁的聚结,使颗粒形成束状形貌;实验条件下颗粒弦长增长率达到20%以上,并且随氯化镁浓度的升高先增大后减小。三水碳酸镁聚结主要是弦长20μm以下颗粒的行为,聚结使得20μm以上颗粒数量和尺寸增加。     

Kinetics of Sorption Processes in the Course of Polymer Composite Formation

The important mechanism of interface layer formation in polymer composite materials is a sorption interaction between polymer fillers and binder components. The structure and properties of the interface layer will be dependent on the kinetics of the sorption. The kinetics of diffusion of some low molecular compounds including epoxies into aramide fibers are studied by the method of isothermic calorimetry. Discrepancy of the kinetics from Fickian was found. Theoretical consideration showed the cause of it could be the structural inhomogeneity of the sorbents. Experimental and theoretical data evidencing that the heterogeneous structure of the sorbent is the cause of the time dependence of the diffusion coefficient are presented in this paper.     

冷冻-解冻循环及气体吹扫对质子交换膜燃料电池的影响

1 INTRODUCTION Polymer electrolyte membrane fuel cell (PEMFC) is promising for its advantages of simple structure, relatively low operating temperature, high efficiency, convenient maintenance and rapid startup. PEMFCs can be used in many potential fields, especially as power sources for vehicles to replace normal combus- tion engine[1,2]. However, the availability of fuel cell vehicles is not quite close to us so far, although both concept design and demonstration have proved its feas…     

PIN/PAN聚合物基电解质膜的制备及性能

利用静电纺丝技术制备了聚吲哚/聚丙烯腈(PIN/PAN)聚合物基电解质膜,代替纸基铝空气电池中的纤维素纸(C-P),并应用于固态铝空气电池。探究了PIN含量对电解质膜离子电导率及吸液率的影响。采用SEM和FTIR对PIN/PAN聚合物基电解质膜表面形貌及化学组成进行分析。借助电化学工作站和电池测试系统,分析了电解质膜离子电导率及固态铝空气电池放电特性。结果表明,采用PIN/PAN聚合物基电解质膜可有效提升固态铝空气电池性能,在3 mA.cm_^-2、5 mA.cm_^-2、7 mA.cm_^-2电流密度下,放电时长比纸基铝空气电池分别提升了21%、27%、34%,且放电时长与电解质膜的吸液率及离子电导率相关。其中4%PIN/PAN聚合物基电解质膜离子电导率可达6.7×10_^-4 S.cm_^-1,同时对碱性溶液具有良好的吸附能力,吸液率最高可达496%,为纤维素纸的3.2倍。     

PVA基碱性聚合物电解质Ni(OH)2/AC超级电容器的电化学性能

Polyvinyl alcohol(PVA)-sodium polyacrylate(PAAS)-KOH-H₂O alkaline polymer electrolyte film with high ionic conductivity was prepared by a solution-casting method.Polymer Ni(OH)₂/activated carbon(AC) hybrid supercapacitors with different electrode active material mass ratios(positive to negative) were fabricated using this alkaline polymer electrolyte,nickel hydroxide positive electrodes,and AC negative electrodes.Galvanostatic charge/discharge and electrochemical impedance spectroscopy(EIS) methods were used to study the electrochemical performance of the capacitors,such as charge/discharge specific capacitance,rate charge/discharge ability,and charge/discharge cyclic stability.Experimental results showed that with the decreasing of active material mass ratio m(Ni(OH)₂)/m(AC),the charge/discharge specific capacitance increases,but the rate charge/discharge ability and the charge/discharge cyclic stability decrease.     

Effects of the Diffusion Layer Characteristics on the Performance of Polymer Electrolyte Fuel Cell Electrodes

Several carbon blacks and graphite were investigated as candidates for diffusion layer preparation in polymer electrolyte fuel cell electrodes (PEFC). Single cell electrochemical characterizations under different working cell conditions were carried out on the electrodes by varying the kind of carbon in the diffusion layer. An improvement in cell performance was found by using Shawinigan Acetylene Black (SAB) as carbon, resulting in a measured power density of about 360 mW cm^–2 in H₂/air operation at 70°C and 1/1 bar. Pore size distribution and scanning electron microscopy analyses were carried out to help the understanding of the different behaviour of the investigated carbon diffusion layers.     

In-Situ Measurement of Chloride Ion at the Coating/Metal Interface

One of the main reasons for the lack of a complete understanding of corrosion and adhesion failures of a coated metal is the lack of analytical instrumentation to probe the behaviors of corrosive agents at the coating/metal interface. We have developed a procedure based on microelectrodes for studying in situ the behavior of chloride ions at a coating/metal interface. The procedure requires an attachment of a double-barreled Cl^- ion-selective microelectrode at the coating/metal interface, thus allowing direct measurements of Cl^- concentration changes at localized areas under a coating. The procedure provided very useful information for mechanistic studies of corrosion under coatings, as well as for transport studies of Cl^- ions through a coating. The procedure should also be useful for studying the roles of Cl^- in localized corrosion.     

In-Situ Measurement of Chloride Ion at the Coating/Metal Interface

One of the main reasons for the lack of a complete understanding of corrosion and adhesion failures of a coated metal is the lack of analytical instrumentation to probe the behaviors of corrosive agents at the coating/metal interface. We have developed a procedure based on microelectrodes for studying in situ the behavior of chloride ions at a coating/metal interface. The procedure requires an attachment of a double-barreled Cl^? ion-selective microelectrode at the coating/metal interface, thus allowing direct measurements of Cl^? concentration changes at localized areas under a coating. The procedure provided very useful information for mechanistic studies of corrosion under coatings, as well as for transport studies of Cl^? ions through a coating. The procedure should also be useful for studying the roles of Cl^? in localized corrosion.     

Effect of Hydrogen Reduction of Silver Ions on the Performance and Structure of New Solid Polymer Electrolyte PEI/Pebax2533/AgBF4 Composite Membranes

In this paper, the effect of hydrogen reduction of silver ions on the performance and structure of new solid polymer electrolyte polyetherimide (PEI)/Pebax2533 (Polynylon12/tetramethylene oxide block copolymer, PA12-PTMO)/AgBF₄ composite membranes is investigated. For PEI/Pebax2533/AgBF₄ composite membranes prepared with different AgBF₄ concentration, the permeances of propylene and ethylene increase with the increase of AgBF₄ concentration due to the carrier-facilitated transport, resulting in a high selectivity. But for propylene/propane mixture, the mixed-gas selectivity is lower than its ideal selectivity. The hydrogen reduction strongly influences the membrane performance, which causes the decrease of propylene permeance and the increase of propane permeance. With the increase of hydrogen reduction time, the membranes show a clearly color change from white to brown, yielding a great selectivity loss. The data of X-ray diffraction and FT-IR prove that silver ions are reduced to Ag⁰ after hydrogen reduction, and aggregated on the surface of PEI/Pebax2533/AgBF₄ composite membranes.     

A Spectroscopic Technique for Studies of Water Transport Along the Interface and Hydrolytic Stability of Polymer/Substrate Systems

Information on water transport along the polymer/substrate interface is valuable for understanding the mechanisms and the controlling factors affecting the water-induced adhesion loss of polymer-coated metals, adhesive-bonded joints, and polymer/fiber composites subjected to aqueous environments. This paper presents data to demonstrate the capability of a technique, which combines a vertical cell with Fourier transform infrared spectroscopy in the multiple internal reflection mode, for studying water transport along the polymer/substrate interface and interfacial hydrolytic stability of polymeric composites and systems exposed to water and high relative humidities. The technique can distinguish water transport through the film from that along the interface; the latter transport is predominant for polymer/untreated substrate systems. Spectroscopic analyses of fractured surfaces of poor and well-bonded polymer/substrate systems after water exposure indicate that the technique is capable of discerning a hydrolytically-stable interface from a water-susceptible interface.     

Effects of Surface Modifications on the Peel Strength of Copper Based Polymer/Metal Interfaces with Characteristic Morphologies

This paper summarizes a study on the effect of changes in surface chemistry on the peel strength of copper/polymer interfaces. Two different surface topographics were created and evaluated, one produced by cleaning and etching in sodium persulfate, the other by etching then mechanically roughening using 180 grit sandpaper. Both surfaces were then oxidized in an alkaline/oxidizing treatment to form cupric oxide. Ion implantation and benzotriazole priming modified the surface chemistry of the cupric oxide samples. After lamination to form an epoxy/copper interface, peel strength measurements were taken. The results showed that ion implantation degraded the peel strength while priming with benzotriazole improved the peel strength compared with the unmodified cupric oxide. In a separate comparison study, peel strength measurements were taken on interfaces formed from copper oxides with the same oxide structure but with widely different gross morphologies, “As laminated” adhesive strength was virtually the same. The bonded interfaces were aged at elevated temperature and the peel strength obeyed first order degradation kinetics. Two terms can be determined from the degradation studies, the first is the long term peel strength, A(∞), and the other is Ω, the degradation rate with units of time^-1. A value of A(∞) was 3.0 lbs/in for etched copper interfaces while A(∞) was 0.5 lbs/in for the sanded interfaces.     

Preparation of conductive polylactic acid/high density polyethylene/carbon black composites with low percolation threshold by locating the carbon black at the Interface of co-continuous blends

In the current study, polylactic acid/high density polyethylene/carbon black (PLA/HDPE/CB) composites are prepared via a two-step method. A double percolation network with co-continuous structure and filler distribution at the interface is constructed to design conductive polymer composites with low percolation threshold. The controllable distribution of CB at the interface is achieved by appropriate processing procedures involved mixing sequence and mixing time by taking advantage of the migration of CB from the unfavorable PLA phase to the favorable HDPE phase. Morphology characterization reveals that when the mixing time of the added HDPE is 3 min, the formation of co-continuous structure of PLA/HDPE (60/40, w/w) is observed, and CB particles migrate to the co-continuous interface. The electrical conductivity measurement shows that such double percolation conductive network reduces the percolation threshold of PLA/HDPE/CB to 2.42 wt%. The rheological property proves the establishment of particle percolation network, and the rheological percolation threshold is determined as 1.20 wt%. The prepared PLA/HDPE/CB composite by the two-step method displays a notably low percolation threshold than that prepared by one-step simultaneous mixing. Moreover, this strategy presents a high potential application in the fabrication of conductive polymer composites involving other miscible multiphase systems.     

电纺EVOH磺酸锂/TiO_2聚合物电解质电性能的研究

将纳米二氧化钛加入到EVOH-SO3Li中制备纺丝液,利用高压静电纺丝法制备EVOH-SO3Li/TiO2复合膜。组装扣式电池,测试EVOH-SO3Li/TiO2聚合物电解质的电化学稳定窗口及离子电导率。结果表明:复合薄膜的电化学性能稳定,离子电导率达到0.96×10-3s/cm。     

New mechanism of gas transport at the interface solid/liquid

It was recently shown that an abnormally fast transport of CO molecules takes place at the electrode/electrolyte interface of Pt and PtRu electrodes in H₂SO₄ and HClO₄ solutions. In the present paper, this phenomenon is tested for other gases, such as hydrogen and oxygen. The fast transport is also observed at the solid/electrolyte solution interface of other electrode materials and at the glass/electrolyte interface. Several experiments are shown, demonstrating that mass transfer takes place at a velocity, which is more than one order of magnitude higher than expected for usual diffusion conditions.Assuming radial mass transfer at the interface of a Pt disc, the activation energy, E_a = 23 kJ mol⁻¹, was calculated from Arrhenius plots. The same value was measured in H₂SO₄ and HClO₄ as supporting electrolytes. The mass transport parameter, Y, at 298 K was 4.8 × 10⁻³ cm² s⁻¹ and 2.9 × 10⁻³ cm² s⁻¹ in 0.5 M H₂SO₄ and 1 M HClO₄ respectively.     

Evidence of Acid-Base Interfacial Adducts in Various Polymer/Metal Systems by IRAS: Improvement of Adhesion

The physical interactions of polymers with inorganic substrates are determined by two major contributions: Van der Waals forces and acid-base interactions, taken in the most general “Lewis” electron acceptor-donor sense. The present work shows that the work of adhesion can be very appreciably increased by the creation of interfacial acid-base interactions. Practically, polymers such as poly(ethylene-co-vinyl acetate) (EVA), terpene-phenol resins (TPR), and their blends, were solution cast on basic and acidic substrates. The nature of the interfacial bonds and the enthalpy of adduct formation through electron exchange are evidenced by Fourier transform infrared reflection-absorption spectroscopy (IRAS). Moreover, it is shown that, on the one hand, modification of the electron donor ability of the polymer functionalities reveals the amphoteric character of the substrate and, on the other hand, modification of the electron donor ability of the substrate changes the nature of the species involved in interfacial adduct formation. Then, practical adhesion tests were carried out in order to correlate the nature and strength of interfacial acid-base bonds with simultaneous increases in adhesive strengths. Thermodynamic considerations allowed us to propose estimated values of the acid-base work of adhesion, W^ab , and of the density of acid-base sites, n^ab .     

Evidence of Acid-Base Interfacial Adducts in Various Polymer/Metal Systems by IRAS: Improvement of Adhesion

The physical interactions of polymers with inorganic substrates are determined by two major contributions: Van der Waals forces and acid-base interactions, taken in the most general “Lewis” electron acceptor-donor sense. The present work shows that the work of adhesion can be very appreciably increased by the creation of interfacial acid-base interactions. Practically, polymers such as poly(ethylene-co-vinyl acetate) (EVA), terpene-phenol resins (TPR), and their blends, were solution cast on basic and acidic substrates. The nature of the interfacial bonds and the enthalpy of adduct formation through electron exchange are evidenced by Fourier transform infrared reflection-absorption spectroscopy (IRAS). Moreover, it is shown that, on the one hand, modification of the electron donor ability of the polymer functionalities reveals the amphoteric character of the substrate and, on the other hand, modification of the electron donor ability of the substrate changes the nature of the species involved in interfacial adduct formation. Then, practical adhesion tests were carried out in order to correlate the nature and strength of interfacial acid-base bonds with simultaneous increases in adhesive strengths. Thermodynamic considerations allowed us to propose estimated values of the acid-base work of adhesion, W^ab, and of the density of acid-base sites, n^ab.     

表面活性剂在固液界面吸附研究的某些新进展

本文综述了离子型表面活性剂以及阳离子与非离子型表达活性剂的混合体系在固液界面吸附情况。     

Influence of the Electronic Structure of the Metal at the Polymer/Metal Interface: A Tentative Interpretation on the Basis of Lewis Acid-Base Reactions

In the present paper, we examine the link between theoretical qualitative predictions made on the grounds of the Lewis acid-base concept and the actual interface built between polyamide-6,6 (PA-6,6) and copper, and PA-6,6 and platinum. By using a combination of very-surface-sensitive photoemission spectroscopies and model polymers, it becomes possible to obtain important information about the chemical nature of the polymer/metal interface. Our experiments show a complete dissociative chemisorption of the polymer on Pt, while PA-6,6 retains its chemical integrity on copper.     

Ge/Si异质键合界面纳米级氧化层对Ge/Si异质结光电特性调控机制

由于Ge/Si存在4.2%晶格失配,Si基外延Ge中的穿透位错密度(TDD)极高,导致器件暗电流偏大。低温Ge/Si异质键合可以通过抑制失配位错传播降低Ge薄膜中的TDD,在高质量大失配薄膜制备方面展现出巨大的潜力。然而,Ge/Si键合界面由于亲水反应形成的纳米级氧化层会对异质结性能产生影响。基于载流子基本方程,在键合界面构建载流子非局域量子隧穿模型,通过半经典近似解法研究Ge/Si异质键合界面氧化层厚度(dO)对异质结暗电流、总电流、光谱响应、带宽等性能的影响,并揭示异质结性能影响机制。研究表明:随着dO的增加,氧化层对载流子的阻挡效应增强,导致器件暗电流、总电流和光谱响应下降。由于氧化层的分压效应,dO的增加导致Ge层中电场下降,载流子速率降低,进而导致异质结高频特性变差。为确保键合Ge/Si异质结优异的光电特性,dO必须控制在0.50 nm以内。     

Interfacial Rheology of Mixed Surfactants at the Oil/Water Interface

The interfacial rheology of surfactant mixtures (SBT and Tween^® 80) at the oil/water interface is investigated using toluene as a model oil. The surfactant ratio in the mixed system has an important impact on the interfacial properties. After adding Tween^® 80, the interfacial tension and modulus of SBT show remarkable changes. Compared with the individual SBT or Tween^® 80 systems, the interfacial properties of the mixed surfactant system improve, especially at a 1:1 ratio. At the optimum ratio, synergistic adsorption takes place resulting in improved asphalt emulsion stability.