【作者】 贺庆；

【导师】 杨辉；

【作者基本信息】 浙江大学 ， 材料物理与化学， 2014， 博士

【摘要】 电接触材料及元件作为电器工业的核心基础,担负着接通与分断电流的任务,其性能直接关系到整机设备的通断容量、使用寿命和运行可靠性。Ag/CdO电接触材料因其接触电阻低、抗熔焊、耐电弧侵蚀等优良性能曾经得到广泛应用,享有“万能触点”的美誉。近年来,Cd对人体和环境的危害引起人们的重视,环保型替代材料的开发受到学术界与产业界普遍关注,其中Ag/导电陶瓷复合材料体系已成为环保型电接触材料研究的一个重要方向。本研究分别采用固相法和溶胶凝胶法制备了La0.5Sr0.5Co03-δ (LSCO)微米、纳米颗粒,并比较分析了LSCO纳米颗粒作为电接触材料增强相的潜在优势；分别采用水热法和静电纺丝法制备了LSCO微球及LSCO纤维。为进一步改善LSCO与Ag之间的界面性能,采用机械球磨技术、水热法及静电纺丝法分别对上述制备的三种不同形貌的LSCO粉体进行表面载银改性。在此基础上,将获得的LSCO粉体应用于Ag/LSCO电接触材料制备,考察了不同形貌的LSCO增强相及其载银方法对Ag/LSCO电接触材料性能的影响。最后,对Ag/LSCO电接触材料的电弧侵蚀行为及机理进行了研究。全文主要研究内容和结论如下：(一)分别采用固相法、溶胶凝胶法、水热法和静电纺丝法制备LSCO陶瓷粉体,系统考察络合剂种类、用量、pH值、前驱体浓度、反应时间、反应温度、热处理工艺等因素对LSCO陶瓷粉体结构形貌的影响,以实现对不同形貌LSCO陶瓷粉体的可控制备。研究结果表明：(1)在LSCO颗粒的制备过程中,固相法和溶胶-凝胶法都适用于制备La1-xSrxCoO3-δ(x=0.1-0.7)颗粒。与固相法相比,溶胶-凝胶法可制备出平均粒径在50nm左右的LSCO纳米颗粒(LSCOP),并且在700～950℃温度(接近Ag熔点960℃)范围内会发生分解,释放02,更适宜作为银基电接触材料的增强相。(2)在水热法制备LSCO微球(LSCOS)的过程中,当柠檬酸与金属离子总量的摩尔比为2：1,反应温度为180℃,反应时间为30h时,可获得平均粒径为5～10μm、纯度较高、分散性较好的LSCO微球。(3)在静电纺丝法制备LSCO纤维(LSCOf)的过程中,采用平均分子量为1300000的PVP配置纺丝成型剂,前驱体纺丝液中PVP的加入量为3.5wt%,金属离子浓度为0.125mol/L时,纺丝效率最高,能达到9ml/h。获得的LSCO前驱体纤维在800℃热处理下能够获得平均直径为0.5～2μm的LSCO陶瓷纤维。(二)开展不同形貌LSCO粉体的表面载银改性研究。采用机械球磨技术制备载银LSCO复合颗粒(LSCOmp),采用水热法制备载银LSCO微球(LSCOms),采用静电纺丝法制备载银LSCO纤维(LSCOmf).研究结果表明：(1)在机械球磨法制备LSCOmP的过程中,Ag与LSCO的质量比为80：20,PEG6000含量3wt%,空气环境中球磨40h,可获得LSCOp充分嵌入银颗粒的麻球状LSCOmp。(2)以葡萄糖作还原剂,采用水热法制备的LSCOms纯度较高。水热前驱体微球在800℃的高温处理下发生烧结晶化,但银粒子仍能完整包覆在LSCO微球表面。(3)在静电纺丝法制备LSCO纤维的工艺中引入银镜反应,合成的LSCOmf前驱体表面粗糙,有小颗粒附着,热处理后发现LSCOmf表面银包覆均匀,直径为0.5～2μm。(三)采用粉末冶金法结合复压复烧工艺制备Ag/LSCO电接触材料,开展不同LSCO增强相形貌、载银改性等因素对Ag/LSCO电接触材料性能的影响研究。研究结果表明：(1)在粉末冶金法制备Ag/LSCO电接触材料的过程中,采用600MPa初压、880℃初烧,再以800MPa复压、880℃复烧退火的工艺条件可使材料获得最高的致密度、硬度和最低的电阻率。(2)三种不同形貌的LSCO增强相制备的Ag/LSCO电接触材料性能各有优势。LSCOp增强相在改善材料的燃弧时间、燃弧能量、弹跳次数和材料损失方面具有优势,其不足之处在于材料电阻率和接触电阻较高,抗熔焊性能较差。LSCOS增强相制备的电接触材料具有良好的抗熔焊性能,并在降低材料本身的电阻率和接触电阻方面,介于其它两种形貌的增强相之间。其劣势在于制备材料的燃弧时间长,燃弧能量大,弹跳次数较多,材料转移损失严重。LSCOf增强相在提高材料物理性能、降低接触电阻方面优势明显,制备的材料抗熔焊性能良好,且燃弧时间、燃弧能量、弹跳次数和材料转移损失情况介于其它两种形貌的增强相之间。(3)在物理性能上,由LSCOmp增强的银基电接触材料(Ag/LSCOmp)的密度从9.57g/cm3提高到9.72g/cm3,维氏硬度从80.07提高到102.53,电阻率从3.73μΩ·cm降低到3.10μΩ·cm;由LSCOms增强的银基电接触材料(Ag/LSCOms)的密度从9.51g/cm3提高到9.75g/cm3,维氏硬度从85.65提高到94.97,电阻率从2.96μΩ·cm降低到2.17μΩ·cm;由LSCOmf增强的银基电接触材料(Ag/LSCOmf)的密度从9.72g/cm3提高到9.78g/cm3,维氏硬度从88.09提高到102.70,电阻率从2.81μΩ·cm。降低到2.03μΩ·cm。(4)在电接触性能上,Ag/LSCOmp材料的平均接触电阻从9.31mΩ降到6.29mΩ,燃弧时间从6.74ms降到5.61ms,燃弧能量从557.40mJ降到439.96mJ,平均弹跳次数从1.18降到1.12次,材料转移损失从7.63%降到0.07%,抗熔焊性能明显改善；Ag/LSCOms材料的平均接触电阻从5.52mΩ降到5.42mΩ,燃弧时间从18.22ms降到14.78ms,燃弧能量从3021.80mJ降到2045.46mJ,平均弹跳次数从1.97降到1.75次,材料转移损失从13.27%降到0.77%,抗熔焊性能保持良好,材料的综合性能得到提高；Ag/LSCOmf材料的平均接触电阻从4.41mΩ降到4.27mΩ,燃弧时间从15.39ms降到14.01ms,燃弧能量从2511.85mJ降到2369.02mJ,平均弹跳次数从1.80降到1.60次,材料转移损失从12.42%降到1.05%,抗熔焊性能保持良好,材料的综合性能得到提高。(5) Ag/LSCOmp的接触电阻较高但其它性能均超过同等条件下制备的Ag/CdO和Ag/SnO2,有望在接触电阻要求不高的领域替代Ag/CdO;Ag/LSCOms的接触电阻较高,燃弧时间和弹跳次数优于Ag/CdO而略逊于Ag/SnO2,其它性能均超过Ag/CdO和Ag/SnO2,有望在接触电阻要求不高的领域替代Ag/CdO;Ag/LSCOmf的综合性能均超过同等条件下制备的Ag/SnO2;除材料转移和电寿命方面略逊与Ag/CdO外,其它性能均超过Ag/CdO,有望在电寿命要求不高的领域替代Ag/CdO。(四)开展了载银改性前后LSCOp增强Ag基电接触材料的电弧侵蚀行为研究。研究结果表明：(1) Ag/LSCOp电触头在电弧侵蚀下呈现凸丘、球状结构、骨架结构、气孔、裂纹等5种特征侵蚀形貌,这归因于LSCO增强相与Ag基体之间的界面结合不足、受电弧作用后的成分偏析,一旦出现上述特征侵蚀形貌后,材料的性能将急剧下降。(2) Ag/LSCOmp电触头在电弧侵蚀下呈现海绵状结构和波纹状结构这2种特征形貌,可能是由于LSCO与Ag基体之间的界面结合增强,均匀度增加,电弧发生过程中复合熔体的粘度增加。这表明Ag/LSCOmp抗电弧侵蚀性能高、工作性能稳定,具有较长的电寿命。(3) Ag/LSCO电接触材料的电弧侵蚀特性与材料的制备工艺及其组织结构有关,通过机械球磨技术进行载银改性可改善增强相与银基体之间的界面性能,有效提高电接触材料的抗电弧侵蚀性能。更多还原

【Abstract】 As core foundation of electrical industry, electrical contact materials and components are responsible for making and breaking a current, and thus their performance directly determine switching capacity, service life and reliability of equipment. Ag/CdO electrical contact material is known as a "universal contact" and has been widely used due to its excellent performance such as low contact resistance, welding resistance, arc erosion resistance, etc. In recent years, people more and more pay attention to the harm of Cd element to human body as well as environment, so the development of environmentally friendly replacement materials attract wildly attentions from academia and industries. To date, Ag/conductive ceramic composite material system has become an important research direction of the environmental friendly electrical contact materials.In this thesis, La0.5Sr0.5CoO3-δ (LSCO) micronparticles and nanoparticles were prepared by solid-phase method and the sol-gel method respectively, and the potential advantages of LSCO nanoparticles used as a reinforcement of electrical contact material were also comparatively analysed. LSCO microspheres and fibers were prepared by hydrothermal method and electrospinning method respectively. In order to further improve the interfacial bonding between LSCO and Ag, the above LSCO powders with different morphologies were modified by silver loading through mechanical milling technology, hydrothermal method and electrospinning method, respectively. On this basis, the obtained LSCO powders were applied as reinforced phases to prepare Ag/LSCO electrical contact materials, and the influence of different morphologies of LSCO reinforced phase and silver-loading modification on the properties of Ag/LSCO electrical contact material were investigated. Finally, the arcing erosive behaviors and corresponding mechanisms of Ag/LSCO electrical contact material erosion were studied. The main contents and conclusions are as follows:(1) LSCO ceramic powders were prepared by solid-phase method, sol-gel method, hydrothermal method and electrostatic spinning method, respectively. In order to realize the controllable preparation of LSCO ceramic powders with different morphologies, the influences of varieties and amount of the complexing agent, pH value, concentration of precursor, reaction time, reaction temperature and heat treatment process on the structure and morphology of LSCO ceramic powders were investigated. The results show that:(i) For the preparation of LSCO particles, the solid phase method and sol-gel method can be used to prepare La1-xSrxCoO3_s (x=0.1-0.7) particles. Compared with solid-phase method, the average size of LSCO particles prepared by sol-gel method is about50nm. The LSCO nanoparticles prepared by sol-gel method can decompose and release O2at the temperature ranged from700℃to950℃(close to the melting point of silver of960℃). This feature makes the LSCO nanoparticles more suitable for being used as a reinforced phase of electrical contact material.(ii) For the preparation of LSCO microspheres by hydrothermal method, the high-purity and well-dispersed LSCO microspheres with average particle diameter of5-10μm can be prepared under the conditions that the molar ratio of citric acid to the total amount of metal ions is2:1, the reaction temperature is180℃and the reaction time is30h.(iii) For the preparation of LSCO fibers by electrostatic spinning method, the optimum preparation conditions are that the spinning forming agent is prepared by3.5wt%PVP with the average molecular weight of1300000, and the concentration of metal ions is0.125mol/L. The spinning speed can reach9ml/h under these conditions. After treating the LSCO precursor fiber at800℃, the LSCO ceramic fibers with diameters ranged from0.5μm to2μm can be prepared.(2) Silver-loading modification of LSCO powders with different morphologies is carried out. Silver-loaded LSCO composite particles (LSCOmp), silver-loaded LSCO microspheres (LSCOms) and silver-loaded LSCO fibers (LSCOmf) were prepared by mechanical milling technology, hydrothermal method and electrospinning method, respectively. The results show that:(i) For the preparation of LSCOmp by mechanical milling technology, the optimum conditions are that the mass ratio of Ag powder and LSCO ceramic is80:20, the content of PEG6000is3wt%, and the powders are milled for40h in the air. Under these conditions, LSCOp can be well inserted into silver, leading to the formation of globular LSCOmp.(ii) For the preparation of LSCOms by hydrothermal method, the purity of LSCOms can reach a high level when using glucose as a reducing agent. Although precursor microspheres experiences LSCO ceramic crystallization sinter at800℃, the silver particles can still fully loaded on the surface of LSCO microsphere.(iii) For the preparation of LSCOmf by electrospinning method, silver mirror reaction is introduced in the electrospinning process. The surface of obtained precursor fibers is rough and coated with small particles. After thermal treatment, LSCOmf with the diameter of0.5-2μm can be obtained and are loaded by silver uniformly.(3) Ag/LSCO electrical contact materials were prepared by powder metallurgy method combined with repressing and resintering process, and the influence of LSCO morphology and silver-loading modification on their properties. The results show that:(i) For the preparation of Ag/LSCO electrical contact materials by powder metallurgy method, the optimum repressing and resintering process is that the powders are first suppressed at600MPa and sintered at880℃, and then suppressed at800MPa and sintered at880℃. Under these conditions, the highest density, hardness and minimum resistivity can be achieved in Ag/LSCOmp electrical contact materials.(ii) The performances of Ag/LSCO electrical contact materials prepared by LSCO reinforced phase with three different morphologies have their own advantages each other. The electrical contact material prepared with LSCOP reinforced phase has advantages in improving the arcing time, arcing energy, bouncing times and material loss, but leads to a higher resistivity, a higher contact resistance and a poor welding resistance performance. For the LSCOS reinforced phase, the ability of lowering resistivity and the contact resistance is between that of the two other reinforced phases. Electrical contact materials prepared with LSCOs reinforced phase have a good welding resistance performance, but leads to a longer arcing time, a higher arcing energy, a more bouncing time and a worse lost of materials. LSCOf reinforced phase has advantages in improving the physical performance and contact resistant of the materials. Electrical contact materials prepared with LSCOf reinforced phase have a good welding resistance.(iii) From the aspects of physical properties, for Ag/LSCOmp electrical contact materials, the density is increased from9.57g/cm3to9.72g/cm3, the Vickers hardness is increased from80.07to102.53, the resistivity is reduced from3.73μΩ·cm cm to3.10μΩ·cm; For Ag/LSCOms electrical contact materials, the density is increased from9.51g/cm3to9.75g/cm3, the Vickers hardness is increased from85.65to94.97, the resistivity is reduced from2.96μΩ·cm to2.17μΩ·cm; For Ag/LSCOmf electrical contact materials, the density is increased from9.72g/cm3to9.78g/cm3, the Vickers hardness is increased from88.09to102.70, the resistivity is reduced from2.81μΩ·cm to2.03μΩ·cm;(iv) From the aspects of electrical properties, for Ag/LSCOmp electrical contact materials, the average contact resistant is reduced from9.31mΩ to6.29mΩ, the arcing time is reduced from6.74ms to5.61ms, the arcing energy is reduced from557.40mJ to439.96mJ, the average bouncing time is reduced from1.18to1.12, the lost percent of material transfer is reduced from7.63%to0.07%, the welding resistance is improved; For Ag/LSCOms electrical contact materials, the average contact resistant is reduced from5.52mQ to5.42mQ, the arcing time is reduced from18.22ms to14.78ms, the arcing energy is reduced from3021.80mJ to2045.46mJ, the average bouncing time is reduced from1.97to1.75, the lost percent of material transfer is reduced from13.27%to0.77%, the welding resistance performance maintains well, the combination property is improved; For Ag/LSCOmf electrical contact materials, the average contact resistant is reduced from4.41mQ to4.27mΩ, the arcing time is reduced from15.39ms to14.01ms, the arcing energy is reduced from2511.85mJ to2369.02mJ, the average bouncing time is reduced from1.80to1.60, the lost percent of material transfer is reduced from12.42%to1.05%, the welding resistance maintains well, the combination property was improved.(V) Ag/LSCOmp electrical contact materials have a high contact resistant, whereas other properties are better than that of Ag/CdO and Ag/SnO2prepared at the same conditions. Ag/LSCOmp is therefore expected to replace Ag/CdO in the contact resistance of less demanding areas. Ag/LSCOms electrical contact materials have a high contact resistant and its arcing time as well as bouncing time is superior to Ag/CdO and inferior to Ag/SnO2, Whereas other properties are better than that of Ag/CdO and Ag/SnO2. Ag/LSCOms is expected to replace Ag/CdO in the contact resistance of less demanding areas. The combination property of Ag/LSCOmf is better than Ag/SnO2prepared at the same condition. Though the material transfer and electrical life are inferior to Ag/CdO, its other properties are superior to Ag/CdO. Ag/LSCOmf electrical contact materials are expected to replace Ag/CdO in the electrical life of less demanding areas.(4) The arcing erosive behaviors of Ag-based electrical contact materials reinforced by LSCOP powders before and after Ag-loading modification. The results shows that:(i) There are five kinds of arcing erosive morphologies on the Ag/LSCOp electrical contact after arc erosion, such as undulating hill structure, globular structure, skeletal structure, pore or hole, and crack. These characteristic morphologies might be associated with a weak binding force between LSCO reinforced phase and silver, and the composition segregation after arc erosion. Once these erosion morphologies appear, the performance of the material will decline sharply.(ii) There are two kinds of arcing erosive morphologies on the Ag/LSCOmp electrical contact, such as spongeous structure and corrugate structure. These characteristic morphologies might be associated with the strong binding force between LSCO reinforced phase and silver matrix, improved wettability, increased uniformity and the improved recombination viscosity during arcing erode. These indicate that Ag/LSCOmp have high arc erosion resistant capacity, stable performance, and long electrical life.(iii) The arc erosion behaviors of Ag/LSCO electrical contact material are related to their structure and preparation process. By means of mechanical milling technology, the Ag-loading modification of LSCO can efficiently improve interfacial bonding between LSCO and silver matrix, thereby increasing the arc erosion resistance property of Ag/LSCO electrical contact material.更多还原