用正电子湮没寿命谱法研究铝阳极氧化膜

退火纯铝(99.99%)在15%H_2SO_4中于不同电解条件下进行阳极氧化,然后测其正电子湮没寿命谱,寿命谱拟合为三个寿命成份,指认第二寿命成分为e~ 在氧化膜中的湮没。从I_2随电解条件的变化推知膜厚与槽压近似成正比,在恒温和固定槽压条件下,膜厚只能达到某极限值。根据τ_2的变化推断出,使用较高槽压或延长电解时间均使膜的结晶度提高,它诱发了裂缝或微洞的形成,导致膜体松散。根据上述结论进一步分析提高膜机械性能的可能途径。     

用正电子素探测叶绿素三线激发态浓度的变化

测量了在不同光强下叶绿素环已烷溶液(77 K)和酒精溶液(296 K)的正电子湮没寿命谱。提出正电子素光磁湮没模型以解释实验事实。在77 K固化的叶绿素环已烷溶液中, 正电子湮没寿命谱长寿命组分的湮没参数I_2和Λ_2随光强变化而呈现规律性变化, 表明可利用正电子素光磁猝灭效应来追踪光敏剂分子三线激发态浓度的变化。     

电催化氧化制备苯甲醛的研究

在超声波槽中电生成纳米金属氧化物,继而以MnO2/Mn2 或金属氧化物氧化还原电对作为媒介,电催化氧化合成苯甲醛.实验表明,电流效率和苯甲醛的产率在超声的参与下有明显的提高,优化了超声电解的条件.在较高温度下反应时,有利于提高生成苯甲醛的电流效率.反应选择性较高,苯甲醛产率可达88.9%.     

高活性Ti基纳米TiO_2膜催化电极的制备

采用“牺牲阳极法”恒槽压电解含有 0 .0 0 5mol·L- 1四乙基溴化铵的乙醇溶液 ,加入微量乙酰丙酮作稳定剂 ,电合成TiO2 前驱体钛酸乙酯Ti(EtO) 4 ,经水解、涂膜、煅烧制备Ti基纳米TiO2 膜电极 (Ti/nano_TiO2 ) .TEM、SEM、XRD测试表明 :TiO2 颗粒尺寸在 10～ 35nm ,膜厚达 0 .5μm ,主要为锐钛矿晶型 ,膜为多孔三维网状结构 .循环伏安法研究了纳米TiO2 膜电极对草酸还原为乙醛酸、硝基苯还原为对氨基苯酚反应的电催化活性 ,结果发现纳米膜中的Ti(Ⅳ ) /Ti(Ⅲ )氧化还原电对起一种中介作用 ,可使有机物如草酸和硝基苯间接电还原 ,且电极催化活性高 ,性能稳定     

钆铁磁——顺磁相变的正电子寿命研究

通过测量金属钆在居里点附近的正电子湮没寿命谱随温度变化的关系，发现钆的正电子湮没寿命在居里点近邻Ｔ〈ＴＣ－侧随温度有显著变化，而在此温区以外几乎不随温度变化。     

钆铁磁－顺磁相变的正电子寿命研究

通过测量金属钆在居里点附近的正电子湮没寿命谱随温度变化的关系，发现钆的正电子湮没寿命在居里点近邻Ｔ＜ＴＣ一侧随温度有显著变化，而在此温区以外几乎不随温度变化     

Y沸石中的正电子湮没

本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱,得到了四个寿命组份,并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化,而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响,但随着质子酸浓度增加,o-Ps在沸石内表面湮没的几率大于笼内,故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系,以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。     

在线超声成对电合成苯甲醛和丁二酸

将间接电合成苯甲醛与电还原马来酸制备丁二酸的过程有机结合, 构建了一个新的成对电解体系, 即在隔膜电解槽中, 以纯Pb为阴极, PbO₂/Pb为阳极, 硫酸溶液为介质, 在施加超声波的条件下, 阳极氧化Ce³⁺为Ce⁴⁺, 阴极还原马来酸生成丁二酸; 同时, 在槽外采用Ce⁴⁺氧化甲苯生成苯甲醛. 实验结果表明, 阴极和阳极电解的平均电流效率分别为92.71%和87.81%, 总的电流效率高达180.52%; 且Ce⁴⁺槽外氧化甲苯为苯甲醛的收率为95.78%, 马来酸电还原为丁二酸的转化率为92.09%; 电解的槽电压与单一电解氧化Ce³⁺相比降低了0.25 V.     

用正电子研究CuCl2在NaY上的扩散

用正电子湮没谱学研究了机械混合CuCl₂与NaY中CuCl₂在NaY沸石中的扩散.分别测量了不同质量比的CuCl₂-NaY(0～0.03)沸石分子筛经140℃烘烤1h;CuCl₂-NaY(0～0.05)经450℃烘烤4h;CuCl₂-NaY(0.01)经不同温度烘烤1h以及经300℃下烘烤烘不同时间后的正电子寿命谱.所有谱中都出现了5(或4)个寿命分量,其第3,4,5寿命分量分别与β笼、超笼及沸石微粒界面空间的大小和数量相关.实验表明,正电子湮没谱学可敏感地探测出少量CuCl₂在NaY沸石中的扩散变化.而对于只含少量氯化铜(0.01)的情况,虽经高温长时间烘烤,但仍有相当数量的氯化铜存在于NaY外表面.     

Y沸石中的正电子湮没

本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱, 得到了四个寿命组份, 并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化, 而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响, 但随着质子酸浓度增加, o-Ps在沸石内表面湮没的几率大于笼内, 故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系, 以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。     

Slow positron studies of anodized aluminium

Porous anodic layers were grown on aluminium alloys under different anodizing conditions. Positron annihilation energy spectra were measured as a function of the positron energy. Ortho-positronium formation in the porous layer was detected. The positron characteristics could be correlated to known parameters of the layers. This demonstrates that the positron annihilation method is a particularly useful technique to characterise the anodic layers.     

Study of multiblock polyamide-6/Poly-(isoprene) copolymers by positron annihilation spectroscopy

Positron annihilation lifetime spectroscopy (PALS) has been used to determine the free volume in multiblock polyamide-6/poly-(isoprene) copolymers (PA-6/PI), synthesized via activated anionic bulk copolymerization. The diisocyanate functionalized telechelic PI, blocked with caprolactam (CL) has been used as a commoner and an activator at the same time. The elastic PI block incorporated into the main chain of PA-6 affects the amorphous and crystal phase of the copolymer leading to changing in degree of crystallinity. The positron annihilation lifetime spectroscopy (PAL) and Doppler broadening of annihilation line (DBAL) technique in a set of pure PA-6 and PA-6/PI copolymers with two different compositions have been applied and evaluation of the size of free-volume holes (pores), localized mainly in the disordered regions of the PA-6/PI copolymer by measuring the o-Ps lifetime (τ₃) and o-Ps intensity (I₃) has been performed.      

Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external ²²Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled or β cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by ²²Na. These powders showed a long lifetime component of 7–8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200°C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from cages only. The beam experiments revealed a high fraction of 3-gamma annihilations in the pressed powder and thin film samples, indicating the annihilation of o-Ps and thereby the existence of large open volumes.     

Application of a pulsed slow-positron beam to polymers

Pulsed slow positrons were produced using a time-varying moderator bias with an interval of 82 ns; 97% of the positrons were compressed within 2 ns width at the target position. Both the positron annihilation lifetime and Doppler broadening of the positron annihilation radiation (DBPR) of polytetrafluoroethylene (PTFE) were measured as a function of the incident energy of slow positrons. It was shown that the lifetime and intensity of the long-lived component of positron annihilation are independent of the positron incident energy above 1.2 keV. However, the width of the Doppler-broadened annihilation γ-ray increased in the energy region below 1.2 keV.     

聚对苯二甲酸乙二酯中正电子湮没寿命参数温度效应的研究

对聚对苯二甲酸乙二酯的非晶、低温热处理(54℃)、高温热处理(180℃)以及双轴拉伸等四种不同试样,测量了室温到180℃范围内不同温度在的正电子湮没寿命谱.根据最小二乘曲线拟合解谱结果,可知最长寿命成份的湮没参数τ和I的温度曲线分别灵敏地反映了聚对苯二甲酸乙二酯的玻璃转变过程和结晶过程.据此讨论了正电子湮没寿命参数与PET转变的关联以及PET玻璃转变的有关性质.     

Characterization of multilayer nanofiltration membranes using positron annihilation spectroscopy

Positron annihilation spectroscopy (PAS) coupled with a slow positron beam was used to characterize in situ the layer structure and depth profile of the cavity size in thin film composite (TFC) polyamide nanofiltration (NF) membranes prepared by the interfacial polymerization method. Two techniques, using PAS coupled with a slow positron beam of Doppler broadening energy spectra (DBES) and positron annihilation lifetime spectroscopy (PALS) designed to reveal the layer structure and the cavity sizes contained in a multilayer thin film composite NF membrane, were assessed. To the best knowledge of the authors, a characterization of the depth profile of cavities in NF membranes using PAS coupled with a slow positron beam has never been reported. The membranes selected have a composite structure containing three layers: a selective polyamide layer, a transition layer, and a porous support prepared by the phase inversion technique. Furthermore, the cavity size distribution in the selective top layer plays an important role in determining the performance of the NF membranes.     

用正电子湮没寿命谱法研究电沉积镍结构缺陷

应用正电子湮没寿命谱研究了十二种典型镍镀层的结构缺陷。根据电沉积镍含有杂质的特点, 采用四态模型对寿命谱进行理论分析。利用寿命谱二组分拟合结果计算了未退火试样的类空位和类微洞的浓度。研究了第10号试样的退火行为, 根据有关的湮没参数与退火温度的关系曲线, 推断出镀层中的氢既以吸附态形式存在于微洞也以固溶态的形式存在于空位, 同时也观察到在退火过程中空位热迁移并入微洞和镀层杂质发生化学聚团作用的现象。     

Enrichment,incorporation and oxidation of copper during anodising of aluminium–copper alloys

Porous anodic oxides generated on copper‐containing aluminium alloys are less regular than anodic oxides generated on pure aluminium. Specifically, a porous oxide morphology comprising layers of embryo pores, generated by a cyclic process of oxide film growth and oxygen evolution, is generally observed. In this work, the relation between the oxidation behaviour of copper during anodising and the specific porous oxide film morphology was investigated by electrochemical techniques, transmission electron microscopy and Rutherford backscattering spectroscopy (RBS). It was found that the anodising potential determines the oxidation behaviour of copper, and the latter determines the porous oxide morphology. At low voltage, relatively straight pores with continuous cell walls were obtained on Al? Cu alloys, but selective oxidation of aluminium atoms resulted in the occlusion of copper‐containing metallic nanoparticles in the anodic film. At higher potentials, copper oxidation promoted oxygen evolution within the barrier layer, and generation of a less regular film morphology. RBS, performed on Al? Cu alloy specimens, revealed a high volume fraction of copper atoms in the anodic films generated at low potentials and a reduced amount of copper atoms in the anodic oxide films generated at high potentials. Copyright © 2009 John Wiley & Sons, Ltd.