共查询到19条相似文献,搜索用时 125 毫秒
1.
针对大面积功率器件软钎料的失效问题,运用扫描电子显微镜(SEM)分析了SnPb软钎料的微观结构并运用能谱仪对其进行成分分析,找出了失效的主要原因:对软钎料进行刚玉抛光后,未能将残留在软钎料内的Al2O3成分完全去除,以至于器件的可焊性变差.根据分析提出了改进意见,较好地解决了SnPb软钎料的失效问题. 相似文献
2.
镀液中Ce^3+离子对锡镀层结构缺陷和可焊性的影响 总被引:1,自引:0,他引:1
应用荧光分析法、X光电子能谱法(XPS)及正电子湮没寿命谱法(PALS)等研究了从含硫酸铈添加剂的酸性光亮锡镀液获得的锡镀层结构缺陷与可焊性的关系。结果表明,电镀时Ce与Sn不发生共沉积,Ce~(3+)的主要作用是阻化Sn~(2+)的水解和氧化使镀液稳定,因而使锡镀层纯度提高、结构致密、表层氧含量减少,有利于提高镀层的可焊性。当Ce~(3+)浓度控制在3.5g/L左右时,可使镀层结构缺陷较少,可焊性较佳,说明结构缺陷是影响锡镀层可焊性的直接原因。 相似文献
3.
本文用X射线光电子能谱(XPS)和俄歇电子能谱(AES)研究了Sn-Pb合金镀层的表面氧化物膜状态并用润湿称量法测定了可焊性。结果表明,Sn-Pb合金镀层表面生成的氧化物膜主要由四价锡的氧化物(SnO_2·XH_2O和SnO_2)组成,铅的氧化物只占很少部分。这说明Sn-Pb合金镀层中锡组分较铅容易氧化。 Sn-Pb合金镀层经155℃加热16小时后,表面氧化物膜的厚度增长很大,同时可焊性明显下降。当Sn-Pb合金镀层经过热熔后,表面变得致密光亮;经155℃加热16小时后生成氧化物膜的厚度较未经热熔的在相同条件下要薄。同时可焊性也较未热熔的好。这说明Sn-Pb合金表面生成氧化物膜的厚度是影响可焊性的重要因素,热熔使Sn-Pb镀层均匀的再结晶改变了镀层结构,使之成为致密的细晶结构,增加了镀层表面的抗氧化能力。故经热熔处理的Sn-Pb合金镀层具有较长的贮存期仍能保持良好的可焊性。 相似文献
4.
5.
采用改进的Hummers法制备氧化石墨烯(GO),首先,石墨与浓硫酸、过硫酸钾和五氧化二磷反应制得强氧化产物,随后将其与浓硫酸、硝酸钠、高锰酸钾反应,经双氧水发泡、酸洗、超声等合成氧化石墨烯水溶液,再通过金属箔还原和基底转移过程制备GO-氧化铟锡(ITO)复合电极材料.通过金属箔还原和基底转移过程制备GO-氧化铟锡(ITO)复合电极材料.利用电化学聚合法在GO-ITO复合电极上制备聚苯胺(PANI)薄膜,并对其形貌结构、电化学及电致变色性质进行表征.结果表明,与ITO电极相比,采用GO-ITO复合电极制备的PANI的成膜性得到明显改善,复合电极具有更加均匀细致的颗粒表面,增大了聚合物与电解液之间的接触面积,为电致变色过程中平衡离子的注入/脱出提供了更多的通道,因而PANI薄膜在700nm处的光学对比度提高了约13%,响应速度缩短了约2.6 s,着色效率高达169.6 cm2/C.GO的引入保持了PANI良好的电化学稳定性.GO-ITO复合电极有效改善了聚合物的综合性能,对于聚合物电致变色材料及器件的开发具有潜在的应用前景. 相似文献
6.
生物医学工程、微电子加工技术和神经科学的进展推动了用于神经电刺激的新型和先进的生物医学器件的问世,使各类患者的某些感官功能得以恢复,并改善了患者的生活质量.在这些生物医学器件中,人工耳蜗植入器件、人工视觉植入器件、深层脑部刺激器件和脊髓刺激器件都取得了很大进展.刺激电极是生物医学植入器件中的关键部件之一.当刺激电极与活体组织相接触时,形成了电子器件和生物体组织间的接触界面.本文首先以耳蜗植入器件和视觉植入器件为例,简要介绍了生物医学植入器件的工作原理和现状.在此基础上,着重对神经电刺激器件所涉及的电化学概念、测试方法及其进展进行了评述.介绍了电刺激和电极/活体组织界面上电荷注入的基本原理和机制.也对常用的电极材料和微电极加工技术进行了评介.讨论了植入式器件研发过程中所遇到的与电化学相关的挑战,诸如电极反应、电极阻抗、电荷注入容量、微电极阵列、电极腐蚀以及生物兼容性等.此外,也讨论了微型传感器和微型生物传感器在植入式器件中的应用前景.刺激电极长期处于活体组织内的苛刻条件下会渐渐失效,腐蚀、氧化和脱壳等情况的出现都会降低器件的使用寿命,甚至危及机体.本文也对此进行了讨论.对设计和加工所面临挑战的清醒认识促使包括电化学家在内的多学科专家和工程技术人员共同努力,以推进神经刺激生物医学植入器件的长足进展和实际应用,使感官功能失效的患者得以受惠. 相似文献
7.
锡钴合金电沉积层的结构与锂离子嵌脱行为 总被引:4,自引:0,他引:4
应用电沉积方法制备Sn-Co合金镀层.X-射线衍射和扫描电子显微镜分析表明,该Sn-Co合金镀层为六方固溶体结构,含Co量为20%的Sn-Co合金,其沉积层呈现(110)择优取向.表面微孔随沉积层Co含量的增加而增多.以Sn-Co合金镀层作锂离子电极材料,电化学性能测试表明,其首次充电曲线表现出锡钴合金、锡及锡氧化物与锂合金化的多个反应综合特征,随后的充电曲线趋于稳定,呈现L i-Sn-Co合金化反应特征;具有择优取向和多孔结构的Sn-Co合金电极材料的充放电性能较好,首次库仑效率为63.9%,经过20次充放电循环后,其充电容量为461mAg/h,库仑效率为99%. 相似文献
8.
9.
锂离子电池的合金电极材料的失效研究 总被引:1,自引:0,他引:1
采用电镀技术在铜箔上电镀金属锡, 并对其充放电过程中的厚度和结构的变化进行了观察和分析. 锡电极经过热处理后, 活性物质锡与基体铜相互扩散生成中间合金Cu6Sn5. 在合金电极嵌锂过程中, 由于有机电解液的分解, 形成了大量的锂氧化物, 这是合金电极体积膨胀的最主要的原因之一. 锂脱嵌后, 部分锂以Li2SnCu的形态保留在合金中, 造成了合金电极首次充放电的不可逆容量损失. 一些新型电解质的应用可能有助于降低合金电极材料体积的膨胀并提高其循环寿命. 相似文献
10.
采用恒电流电沉积法在铜箔基底上获得镍锡合金镀层电极. 电子能谱(EDS)、X射线衍射(XRD)以及高分辨透射电镜(HRTEM)分析表明, 随着锡含量的增加, 镀层由镍晶胚与非晶镍锡构成的非晶态结构转变为Ni3Sn4与Ni3Sn2的混晶结构. 扫描电镜(SEM)分析发现, 非晶结构镍锡合金电极表面粒子分布均匀且粒径细小, Ni3Sn4与Ni3Sn2混晶结构的镍锡合金电极表面粗糙且断面呈分层自组装结构. 在25℃, 1 mol·L-1 NaOH溶液中的稳态极化曲线表明非晶结构的镍锡合金电极具有良好的催化活性, 其析氢过电位仅为85 mV. 交流阻抗测试表明, 非晶以及混晶结构的镍锡合金在析氢电催化反应过程中由电化学吸附(Volmer)以及电化学脱附(Heyrovsky) 两个电荷转移过程控制, 且非晶结构电极相比于Ni3Sn4与Ni3Sn2混晶结构电极的高活性源于其活性氢具有更快的电化学吸附以及脱附速度. 相似文献
11.
The occurrence of tin in plants, animals and humans is discussed in relation to its abundance in the lithosphere and hydrosphere and the range of different tin(II) and tin(IV) complexes formed. A reasoned consideration of the essentiality or otherwise of tin for living species is given and it is concluded that tin is beneficial even if not yet proved to be an essential element. After reference to the chemistry of tin compounds, there is a detailed discussion of their toxicity in animals and humans. Feasible routes for tin intake and uptake into humans are described. The use of tin pharmaceuticals in previous and current times is reviewed and areas for which they are currently permitted for use in man as dentifrices and mouth washes, as radiopharmaceuticals and for the treatment of jaundiced newborns are described. A detailed review of tin-coating antitumour agents as representative tin pharmaceuticals is given. Finally, a range of tin compounds having other specific pharmaceutical applications and which are currently being investigated are listed. 相似文献
12.
13.
The problem of the reliability of measurements of impurity diffusion coefficients has been investigated using the sandwich technique in combination with EPMA. To get reliable results it is necessary to measure at least 4 profiles paying attention to irregularities at the welding plane as well as to a careful determination of the end of the profiles and the boundary conditions. 相似文献
14.
The airship structures made of multi-layer composite fabrics or membranes can offer the platform for earth observations, wireless communications and space research due to light weight and good mechanical performance. The structural safety and serviceability strongly depend on material properties and working conditions. Available studies are limited within service stress limits or are lack of suitable biaxial tensile constitutive models for understanding structural behavior. This paper thus focuses on a refined numerical model for determining inflation-burst behavior of composite airship structures considering new biaxial constitutive equations, novel failure criteria and manufacture factors.The differences between ideal and real forms of airship structures, e.g. volume difference, demonstrate the necessity for incorporating cutting-pattern effects in the initial numerical model. For structural analysis, stress distributions on real structural forms are different from those on ideal forms because of welding parts that can enhance local stiffness. The ultimate pressures are 56.7 kPa and 59.5 kPa for ideal and real structural forms. Structural breaking initiated at the maximum diameter of ideal structural forms propagates fast while welding parts can prevent breaking propagation for real structural forms. Therefore, the refined numerical model can reveal basic structural behavior and safety performance of airship structures in the inflation-burst processes. 相似文献
15.
A Universal Reduced Rupture Creep Approach for Prediction of Long Term Failure Behavior of Aged Glass Polymers from the Short Term Test of Rupture Creep Compliance by the Unified Master Curved Extrapolation 下载免费PDF全文
The prediction of long term failure behaviors and lifetime of aged glass polymers from the short term tests of reduced rupture creep compliance (or strain) is one of difficult problems in polymer science and engineering. A new “universal reduced rupture creep approach” with exact theoretical analysis and computations is proposed in this work. Failure by creep for polymeric material is an important problem to be addressed in the engineering. A universal equation on reduced extensional failure creep compliance for PMMA has been derived. It is successful in relating the reduced extensional failure creep compliance with aging time, temperature, levels of stress, the average growth dimensional number and the parameter in K-W-W function. Based on the universal equation, a method for the prediction of failure behavior, failure strain criterion, failure time of PMMA has been developed which is named as a universal “reduced rupture creep approach”. The results show that the predicted failure strain and failure time of PMMA at di?erent aging times for different levels of stress are all in agreement with those obtained directly from experiments, and the proposed method is reliable and practical. The dependences of reduced extensional failure creep compliance on the conditions of aging time, failure creep stress, the structure of fluidized-domain constituent chains are discussed. The shifting factor, exponent for time-stress superposition at differentlevels of stress and the shifting factor, exponent for time-time aging superposition at different aging time are theoretically defined respectively. 相似文献
16.
17.
BorECO®™ BA212E is a polypropylene block co-polymer which has become a common material in the manufacturing of large diameter non-pressurized gravity offshore intake pipelines. These lines are used for transportation of sea water for cooling of petrochemical process plants. The pipe sections are joined by butt heat fusion welding to create the pipeline. Recently a few premature failures of such pipelines have been reported in the field. Hence, there is a need to characterize the constitutive behavior of the pipe and weld material in order to properly design these pipes. The aim of this work is to determine the material constitutive behaviors of the pipe material and the welded joint material. Uniaxial tensile tests of both the pipe and weld joint material are conducted at various strain rates. Both the pipe and weld material show a rather high strain rate dependency, with the weld material having about half the yield strength than that of the pipe material. An analytical constitutive material model is developed for both the pipe and weld material, incorporating the effect of strain rate. The failure locus, expressed in terms of the equivalent plastic strain at failure vs. the stress triaxiality, for both materials is also determined as part of the constitutive model using notched dumbbell specimens. The constitutive model and failure loci for the pipe and weld material are implemented in a finite element model (FEM) and are validated by conducting a series of independent four-point bend experiments on both material types. The validation is carried out by comparing the FEM results of the four-point bend model with the experimental results, which show a rather good agreement. 相似文献
18.
The particulate emission caused by welding of steel plates covered with 29 diversified shop primers has been investigated. The investigation includes the determination of particle mass, particle size distribution, and of the contents of heavy metals such as lead and cadmium. The results show that all investigated primers except those with high concentration of zinc pigment produce mass emissions which are very low in comparison to manual arc welding with covered electrode and CO2-welding on uncoated steel. The emitted particles of the primers are smaller than 1 μm particle diameter and therefore respirable. Lead and cadmium was found in particles emitted during the welding process of all investigated primers. The highest amount was found in particles of primers with high contents of zinc and ferric oxide. 相似文献
19.