Development of function-graded proton exchange membrane for PEFC using heavy ion beam irradiation

The graded energy deposition of heavy ion beam irradiation to polymeric materials was utilized to synthesize a novel proton exchange membrane (PEM) with the graded density of sulfonic acid groups toward the thickness direction. Stacked Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) films were irradiated by Xe⁵⁴⁺ ion beam with the energy of 6 MeV/u under a vacuum condition. The induced trapped radicals by the irradiation were measured by electron spin resonance (ESR) spectroscopy. Irradiated films were grafted with styrene monomer and then sulfonated. X-ray photo-electron spectroscopy (XPS) spectra showed that the densities of sulfonic acid groups were controlled for injection “Surface” and transmit “Back” sides of the fabricated PEM. The membrane electrode assembly (MEA) fabricated by the function-graded PEM showed improved fuel cell performance in terms of voltage stability. It was expected that the function-graded PEM could control the graded concentration of sulfonic acid groups in PEM.     

Synthesis and characterization of PEFC membranes based on fluorinated-polymer-alloy using pre-soft-EB grafting method

Polymer electrolyte fuel cell (PEFC) membranes based on thin film of crosslinked perfluorinated polymer-alloys (RX-FA) have been fabricated by soft electron beam (soft-EB) grafting with styrene monomers using soft-EB irradiation under nitrogen atmosphere at room temperature (RT). The characteristic properties of styrene-grafted materials (GRX-FA) and sulfonated materials (SRX-FA) have been measured by differential scanning calorimetry (DSC) and FT-IR spectroscopy, ionic conductivity and so on. The glass transition temperatures (dry state) of all obtained SRX-FA were about 105 ± 1 °C, which are higher than Nafion^®. The ion exchange capacities of SRX-FA have been achieved about 3.3 meq/g (dry). The ionic conductivity of obtained SRX-FA has showed about 0.17 S/cm at 60 °C with relative humidity (RH) of ∼95%. The ionic conductivities of the obtained SRX-FA were higher than that of conventional perfluoro-sulfonic acid membranes (PFSA). Fabricated membrane electrode assemblies (MEAs) based on the obtained SRX-FA have shown encouraging performance in the PEFC, compared with the conventional PFSA. The power density of obtained MEAs based on the SRX-FA was about 330-340 mW/cm² under 500 mA/cm² at 60 °C operation. Moreover, the maximum power densities of obtained MEAs based on the SRX-FA shows about 630 mW/cm² at 60 °C. On the other hand, the power density at 500 mA/cm² and maximum power density of MEA based on Nafion^®112 were about 320 and 590 mW/cm² at 60 °C. Thus, the power density of the obtained SRX-FA was higher than that of conventional PFSA.     

辐射接枝高分子电解膜的制备、表征及其在燃料电池中的应用

高分子电解膜是高分子燃料电池的关键材料之一。担当着阴阳极反应原料的隔离及离子电导的功能,其性能决定着燃料电池的性能、成本及应用前景。辐射接枝电解膜由氟化的高分子骨架及磺化的接枝高分子链构成。前者赋予电解膜必要的强度、尺寸稳定性及低气体透过性,后者赋予其质子电导功能。综述了基材、单体及交联剂的筛选、合成工艺的调整等与辐射接枝电解膜的性能关系。     

Solid polymer electrolyte water electrolysis systems for hydrogen production based on our newly developed membranes, Part I: Analysis of voltage–current characteristics

A new solid polymer electrolyte water electrolysis system was constructed using an original proton exchange membrane (PEM). The highly proton-conductive PEM was prepared by the γ-ray-induced post-grafting of styrene into a crosslinked-polytetrafluoroethylene (PTFE) film and subsequent sulfonation. The water vapor to be electrolyzed was controlled at a constant relative humidity and introduced into the cell at different temperatures up to 80 °C. As the cell voltage was increased, the current became higher; the maximum current was 50 mA/cm² at 2.5 V at a temperature of 80 °C, corresponding to a hydrogen production rate of 0.38 mL/min cm² in the normal state (25 °C, 1 atm). The voltage–current characteristics were analyzed with a theoretical model based on Butler–Volmer kinetics for electrodes and transport resistance through the PEM. This analysis revealed that the anode exchange current density and interfacial resistance determined the electrolysis performance.     

过氟化聚合物的苯乙烯接枝研究--辐照条件与反应条件的影响

Fuel cell is in focus as a very low exhaust new dynamo system. Especially polymer electrolyte fuel cells (PEFC) using proton exchange membranes (PEM) have attracted much attention for the electrical vehicle and other mobile applications such as cellar phone and personal computer. Conventional perfluoro-sulfonic acid membranes such as Nation() (DuPont de Nemours LTD.) have been the popular PEM used in PFEC. However, there are still several problems such as insufficient gas barrier properties, low thermal resistance, and their high costs.In this study, hawse have studied the partially fluorinated PEM for PEFC by radiation grafting onto per-fluorinated polymers such as PFA, FEP and ETFE with reactive styrene monomers using pre-irradiation grafting method in gas and in liquid phase, respectively, and successive sulfonation. Characteristic properties of the grafted and sulfonated materials have been discussed and optimized fabricating conditions were determined.Characteristic properties of the obtained materials have been measured by differential scanning calorimetry,thermogravimetric analysis and FT-IR spectroscopy, etc.In the case of irradiation in air, glass transition temperatures (Tg) of the grafted materials depend on the yields of styrene grafting onto the materials. That is higher yields of grafting give lower thermal stability. On the other hand, when the peroxy radicals were converted trapped radicals by exposure in air after irradiation under oxygen-free atmosphere, Tg of the grafted materials hardly depends on the grafting yields.Moreover, the yields of grafting in gas phase were higher than that of liquid phase. However, the sample form of grafting in gas phase has been greatly changed, whereas the sample form of grafting in liquid phase has kept its original feature.Therefore, it is suggested that the fabricating conditions for PEFC membranes were preferred to irradiation under oxygen-free atmosphere and grafting in liquid phase.Ion exchange capacities of the sulfonated-materials could be 3.0meq/g. Other properties of the obtained membranes such as chemical structure were also discussed.     

Preparation and characterization of proton exchange membranes from polystyrene grafted poly（vinylidene fluoride） powder

Proton exchange membranes(PEMs) were prepared in three steps:graRing of polystyrene onto PVDF powder using pre-irradiation graft polymerization technique, processing the grafted PVDF powder into membranes of around 50-μm thickness, and sulfonating them with cholorosulfonic acid to form poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) membranes. Kinetics of the graft polymerization was studied. The existing of polystyrene side-chains in the grafted PVDF powders, and PSSA groups in PEMs, were proved by FT-IR. Properties of the PEMs, i.e. the ion exchange capacity, water uptake, proton conductivity, thermal property and oxidative stability,were characterized. Dependence of properties on the degree of grafting was investigated, too.     

Radiolytic preparation of poly(styrene sulfonic acid) - grafted poly(tetrafluoroethylene-co-perfluorovinyl vinyl ether) membranes with highly cross-linked networks

In this study, various amounts of a divinylbenzene (DVB) cross-linking agent (5∼30%) were introduced during a simultaneous irradiation grafting of styrene onto a PFA film of a 25 μm thickness in order to prepare a series of poly(styrene sulfonic acid)-grafted poly(tetrafluoroethylene-co-perfluorovinyl vinyl ether) (PFA) membranes with various degrees of cross-linking and grafting (29∼74%). The effects of the DVB cross-linking agent on the properties of the prepared membranes, such as water uptake, proton conductivity, methanol permeability, and chemical stability, were also investigated in this study. The results indicated that the ion exchange capacity (IEC) slightly decreased with increasing DVB content, whereas the water uptake, proton conductivity, and methanol permeability of the membrane greatly decreased. The chemical stability of the prepared membranes was found to be significantly improved with increasing DVB content. The results indicated that the cross-linked network membranes are promising for application in a direct methanol fuel cell.     

Studies on Ion-Exchange Equilibria for Cesium-Hydrogen System

Ion-exchange equilibrium between Cs and H on a sulfonated polystyrene resin of Dowex 50W with 8% crosslinking has been studied over a temperature range of 25°to 60°C, using 137Cs as radioactive tracer; the various experimental data related to the equilibrium experiments were examined in detail by several different methods; a new treatment to take into account the water uptake in the exchange system Cs-H was also applied with the aid of a radioactive tracer technique. The thermodynamic equilibrium constant K^cs _H determined by the present study compares well with the values calculated indirectly from experimental data found by other investigators. Data are also given for the heats, free energies and entropies of the exchange reaction involving Dowex 50W. Fairly good results have been obtained on the exchange of Cs and H.     

Durability of Irradiated Polymers in Solid-Polymer-Electrolyte Water Electrolyzer

The durability of irradiated organic polymers in solid-polymer-electrolyte water electrolyzer was investigated by gamma-ray irradiation tests around 500 kGy. Serious deteriorations for the tensile strength and ion exchange capacity of the ion exchange membrane (Nafion®) were not observed up to 850 kGy. No serious damage was also observed for tensile strength of the gasket materials (Aflas®) up to 500 kGy. The insulator materials (PFA and FEP) lost their tensile strength at 200 kGy and 300 kGy, respectively. From the above results, we can safely say that the electrolysis cell could be used up to around 500 kGy of irradiation conditions in the case where PFA and FEP are replaced by the polyimide resin which durability against the irradiation is well demonstrated. Two degrading mechanisms were supposed as the effect of irradiation. One is the direct degradation of the chain and branch by gamma-ray. The other is degradation by the attack of radicals. It was demonstrated that the effect of radicals on degradation of the membrane was not dominant. In addition, oxygen was observed to have a large influence on degradation. The quantity of dissolved fluorine in water that could be measured easily was found to correlate closely with tensile strength and ion exchange capacity. Hence, it is possible to evaluate the degradation of ion exchange membrane by monitoring the quantity of dissolved fluorine in water. Concerning the difference of degrading mechanism of the ion exchange membrane due to irradiation source, the combinations of tensile strength, ion exchange capacity and quantity of dissolved fluorine are proposed as deterioration indexes.     

Radiation synthesis and characteristics of PTFE-g-PSSA ion exchange membrane applied in vanadium redox battery

Radiation-induced grafting of styrene onto polytetrafluoroethylene （PTFE） membranes was studied by a simultaneous irradiation technique. Grafting was carded out using γ-radiation from a ^60Co source at room temperature. Effects of absorbed dose, atmosphere, dose rate, and the concentration of initial monomer on the degree of grafting （DOG） were investigated and the most appropriate grafting condition was obtained. Subsequently, sulphonation of the grafted PTFE membrane （PTFE-g-PS） was carded out and a series of ion exchange membranes （PTFE-g-PSSA） was prepared. Further characterizations of FTIR, TGA, and SEM testified that grafting and sulphonation of the membranes were successfully processed; moreover, grafting of styrene not only occurred in the surface of PTFE membrane, but also in the micropores of the membrane. Ion exchange capacity （IEC） and conductivity were found increase with the grafting yield. The results suggest that at a low dose, such as 17 kGy, the ion exchange membrane （IEM） which will be suitable for vanadium redox battery （VRB） use can be obtained.     

Fluorine analysis of human enamel around fluoride-containing materials under different pH-cycling by μ-PIGE/PIXE system

The caries preventive effect of fluoride-containing materials (FCMs) might depend on the caries risk of the individuals. Two pairs of demineralizing and remineralizing solutions of pH-cycling were prepared for simulating low and high caries risk. The purpose of this study was to determine fluorine (F) uptake into human enamel around FCMs under different pH-cycling using the in-air μ-PIGE/PIXE system. Fluoride-containing glass ionomer cement (Fuji IX_GP FAST CAPSULE (FN)), and composite resin (BEAUTIFIL II with FLUORO BOND SHAKE ONE (BS)) were used in this study. The pH-cycling (pH 6.8-4.5) was carried out for 5 weeks. After pH-cycling, the caries progression was analyzed using transverse micro-radiography (TMR). The fluorine and calcium distributions in the carious lesion in each specimen were evaluated using the PIGE/PIXE system. From TMR analysis, there was a difference in caries risk between the two kinds of pH-cycling. Although the caries preventive effect of BS and FN was confirmed at low risk, the effect at high risk was confirmed for FN only. From the analysis of the fluorine uptake in the outer 200 μm of the lesion we concluded that there was no significant difference between the pH-cycling solutions. However, we found different fluorine concentrations in the enamel for the two FCMs. The decreased caries progression under high risk for FN indicated that an adequate amount of fluorine supplied from the material is required at higher caries risk. It was confirmed that the caries preventive effect of FCM depends on the caries risk. The fluorine analysis of teeth under various pH-cycling conditions gives information to evaluate the caries preventive effect of fluoride-containing materials according to the caries risk.     

Examination of C/C flat tile mock-ups with hypervapotron cooling after high heat flux testing

Two C/C flat tile mock-ups with a hypervapotron cooling concept, have been successfully tested beyond ITER specification (3000 cycles at 15 MW/m², 300 cycles at 20 MW/m² and 800-1000 cycles at 25 MW/m²) in two electron beam testing facilities [F. Escourbiac, et al., Experimental simulation of cascade failure effect on tungsten and CFC flat tile armoured HHF components, Fusion Eng. Des., submitted for publication; F. Escourbiac, et al., A mature industrial solution for ITER divertor plasma facing components: hypervapotron cooling concept adapted to Tore Supra flat tile technology, Fusion Eng. Des. 75-79 (2005) 387-390]. Both mock-ups provide a SNECMA SEPCARB^® NS31 armour, which has been joined onto the CuCrZr heat sink by active metal casting (AMC) and electron beam welding (EBW). No tile detachment or sudden loss of single tiles has been observed; a cascade-like failure of flat tile armours was impossible to generate. At the maximum cyclic heat flux load of 25 MW/m² all tested tiles performed well except one, which revealed already a clear indication in the thermographic examination at the end of the manufacture. Visual examination and analysis of metallographic cuts of the remaining tiles demonstrated that the interface has not been altered. In addition, the shear strength of the C/C to copper joints measured after the high heat flux (HHF) test has been found to be still above the interlamellar shear strength of the used C/C material. The high resistance of the interface is explained by a modification of the C/C to copper joint interface due to silicon originating from the used C/C material.     

Fluorine uptake into human enamel around fluoride-containing dental materials during cariogenic pH cycling

Using PIGE (Proton Induced Gamma Emission) technique at TARRI (Takasaki Advanced Radiation Research Institute), Japan, we measured fluorine (F) uptake into the tooth enamel around two fluoride-containing materials during caries progression using pH cycling. Class V cavities in extracted human teeth were drilled and filled with fluoride-containing materials (i.e. “Fuji IX” (FN) and “UniFil flow with MEGA bond” (UF)) and a non-fluoride-containing material (i.e. “SOLARE with MEGA bond” (SO)). Three 120 μm longitudinal sections including the filling material were obtained from each tooth. In order to simulate daily acid attack occurring in the oral cavity, the pH cycling (pH 6.8–4.5) was carried out for 1, 3 and 5 weeks, separately. After pH cycling, the caries progression in all specimens was observed using transverse microradiography (TMR). The F and calcium distributions of the specimens were evaluated using PIGE and PIXE techniques. The F distribution of the specimens clearly showed the F uptake from FN into enamel adjacent to the filling material, while the F uptakes from UF and SO were not detected. For UF, the MEGA bond (non-fluoride-containing) between the tooth and UniFil flow interfered with the F absorption into the tooth. For FN, the amount of F uptake into the subsurface enamel increased during pH cycling. The amount of F uptake in 5-week pH cycling had significantly higher value compared to those in 1- and 3-week pH cycling. For UF and SO, there were no significant differences between the different durations of pH cycling.Among fluoride-containing materials, there were some differences in the F uptake with increased pH cycling, which could possibly lead to obtaining difference in clinical performance. The data obtained using PIGE and PIXE techniques were useful in understanding the benefit of fluorine by means of fluoride-containing material for preventing caries.     

内充气电离室相对测氡标准装置

本标准装置包括有效体积为１．９４Ｌ和１．５４Ｌ的电离室、可编程静电计、高压电源以及可进行数据获取及处理的微机系统。采用标准液体镭源进行刻度，通过一系列实验对各种因素的影响作了测量。测得的电离室刻度系数分别为２４．６２、２３．９０Ｂｑ／ｐＡ，电离室电离电流测量不确定度（２σ）＜２％。     

乳腺专用PET符合处理电子学系统的研制

中国科学院高能物理研究所研制了1台具有自主知识产权的乳腺专用正电子发射断层扫描仪。本工作从硬件架构和软件逻辑功能两方面对该样机的符合处理系统的研制进行介绍。在本设计中,符合处理系统采用FPGA高速数据接口和光纤互连技术获取前端连续采样板的预处理数据,然后采用符合时间窗的方法对挑选出的非零数据进行符合处理,最后通过千兆以太网将符合数据传给后端计算机进行重建。整个系统由局域控制总线进行控制。测试结果表明,符合处理系统的设计功能正确,性能优良。     

Study on the Pulsed Flashover Characteristics of Solid-Solid Interface in Electrical Devices Poured by Epoxy Resin

In electrical devices poured by epoxy resin, there are a lot of interfaces between epoxy resin and other solid dielectrics, i.e. solid-solid interfaces. Experiments were carried out to study the flashover characteristics of two typical solid-solid interfaces （epoxy-ceramic and epoxy~ PMMA） under steep high-voltage impulse for different electrode systems （coaxial electrodes and finger electrodes） and different types of epoxy resin （neat epoxy resin, polyether modified epoxy resin and polyurethane modified epoxy resin）. Results showed that, the flashover of solid-solid interface is similar to the breakdown of solid dielectric, and there are unrecoverable carbonated tracks after flashover. Under the same distance of electrodes, the electric stress of coaxial electrodes is lower than that of finger electrodes; and after the flashover, there are more severe breakdown and larger enhanced surface conductivity at interface for coaxial electrodes, as compared with the case of finger electrode. The dielectric properties are also discussed.     

Effects of Displaced Grids on the Fusion Reactivity of an Inertial Electrostatic Confinement Device

Inertial Electrostatic Confinement (IEC) devices consist of nearly transparent, concentric grid electrodes that accelerate ions radially using voltage differences of 10–100s of kV. This paper investigates the effect of offsetting the inner grid with respect to the outer grid. Offsetting the grids changes the electric fields set up between the two grids and hence affects the ion flow into the cathode. Raising the cathode from the mean position has relatively more deteriorating effect than lowering it. In general, displacing the grids from the mean (concentric) condition seems to deteriorate the fusion reactivity. However, fine adjustments can be done to fine tune the fusion reactivity. The microchannels that form in IEC devices move with the cathode grid orientation. The shape and especially the locations of the microchannels are determined by the grid wire spacing of the cathode. New microchannels are also formed when the grid is offset, the region of maximum E-field, which is the direction in which the grid is moved, favors such microchannel formation.     

Discharge Modes Suggested by Emission Spectra of Nitrogen Dielectric Barrier Discharge with Wire-Cylinder Electrodes

In this paper,nitrogen dielectric barrier discharge(DBD) plasma was generated in a quartz tube with coaxial wire-cylinder electrodes at atmospheric pressure.By varying the nitrogen gas flow(FN) in the range of 0-1 m3/h,the plasma optical emission spectra(OES) were measured and studied.The vibration(T_(vib)) and rotation temperature(T_(rot)) of nitrogen were obtained,by fitting the rovibronic bands of N_2(C~3∏_u-B~3∏_g,0-1),and by the Boltzmann plot method for purposes of comparison.T_(vib) increased up to 2481 K with increasing nitrogen flow till0.2 m3/h,and then decreased with further increasing FN,while Trot decreased monotonously and approached to-350 K for FN ≥ 0.6 m~3/h.The intensity of N_2(C~3∏_u-B~3∏_g,0-0,1-0,0-3) and N_2~+(B~2∑_u~+-X~2Σ_g~+,0-0) exhibited similar evolution with increasing FN to those of the T_(vib) and Trot,respectively.The discharge photos revealed that the discharge filaments gradually decreased with increasing FN,and eventually disappeared,which implied that a discharge mode transition emerged with increasing FN.The possible mechanism for the discharge mode transition is studied in detail according to the vibration(T_(vib)) and rotation temperature(T_(rot)) of nitrogen.     

Ion Exchange Separation for Decontamination of Centrifuge Enrichment Plant

Ion exchange separation of uranyl ion (UO²⁺ ₂) from metal cations has been carried out by the columnar operation using ion exchange resins in 0.1 mol/dm³ sulfuric acid medium. Uranyl ion was adsorbed in an anion exchange resin and the rest metal cations, Fe(III), Al(III), Cr(III), Ni(II) and Cu(II) ions, were adsorbed in a cation exchange resin in this system. Desorption of uranyl ion and metal cations adsorbed in the resins were tested by 2 mol/dm³ sulfuric acid solution. Desorbed elements were confirmed to be precipitated by appropriate alkaline solutions. On the basis of the results obtained, a concept was made on a decontamination system for uranium-contaminated waste solution from centrifuge enrichment plant.     

A self-standing two-fluid CFD model for vertical upward two-phase annular flow

In this paper, a new two-fluid CFD (computational fluid dynamics) model is proposed to simulate the vertical upward two-phase annular flow. This model solves the basic mass and momentum equations for the gas core region flow and the liquid film flow, where the basic governing equations are accounted for by the commercial CFD package Fluent6.3.26^®. The liquid droplet flow and the interfacial inter-phase effects are accounted for by the programmable interface of Fluent, UDF (user defined function). Unlike previous models, the present model includes the effect of liquid roll waves directly determined from the CFD code. It is able to provide more detailed and, the most important, self-standing information for both the gas core flow and the film flow as well as the inner tube wall situations.