1、此文档收集于网络,如有侵权请联系网站删除摘要基于纳米材料诱人的特性和应用前景,本论文首次将纳米技术应用在AgC 触头材料的制备中,研制出性能优异的新型AgC触头,并对其机械物理性能和 耐电弧磨损性能进行了系统研究。为整体改善传统机械混粉AgC触头的机械物理性能和耐电弧磨损性能,首 先从粉体制备上入手,引入化学包覆工艺改善其成分偏聚和组织不均匀性,采用 高能球磨获得纳米级石墨作为后续银原子非均质形核核心,结合还原剂液相喷雾技术制备出纳米晶AgC包覆粉,利用该粉体良好的烧结致密性能实现了块体 触头性能的全面改善。以纯度为C995、粒度为200目的石墨粉为原料,通过QM1SP型行星 式球磨机,经过最
2、佳球磨时间10h高能球磨后,制备出一维纳米级石墨,平均厚度5060nm。对球磨包覆Ag5C粉的x衍射测试表明,制备的包覆粉中Ag的 平均晶粒尺寸约为50nm。论文研究了制备出的纳米晶AgC包覆粉体的烧结性能及其块体触头材料的 机械物理性能,研究了球磨时间对触头性能及组织的影响以及烧结温度对其性能 的影响,对AgC体系三种不同的粉体制备工艺触头材料进行了组织和机械物理性能对比分析并建立了简要的机理模型分析,研究了纳米晶包覆粉的配比添加对常规机械混粉触头性能的影响。研究结果表明,随着球磨时间的增加,AgC块体触头出现了石墨定向组织。 电导率均匀组织时最高,出现石墨定向组织时降低,又随定向组织的增多
3、而回升, 但材料的硬度和致密性下降。随着烧结温度的升高触头的致密度增加,硬度上 升,电导率明显提高。在840。C左右,材料性能最佳。与机械混粉和滴加包覆工 艺相比,球磨石墨喷雾一包覆工艺制备的Ag一5C材料具有极好的机械物理性能 和更加均匀的组织。新工艺中采用还原剂液相喷雾技术,大大增加了还原剂与反 应溶液单位时间接触面积,提高了分散在反应溶液中的c粉充当Ag原子非均质 形核核心的几率;同时大大降低了还原剂在反应溶液中的局域浓度,有效抑制了 Ag原子长大速率。两方面作用下该技术实现了细化包覆粉体及其晶粒度的作用 并改善了其包覆效果,更好地消除了c在Ag基体中的成分偏聚。利用球磨包 覆工艺制备的
4、纳米晶Ag一5C包覆粉,混合在传统的Ag5C机械混粉中,实现了通过利用纳米晶粉的晶粒长大填补机械混粉材料中的微小孔隙,从而达到了改善机械物理性能的目的。A此文档仅供学习和交流将制备出的新型Agc触头与传统粗石墨机械混粉工艺触头安装在ASTM机 械式低频断开触头材料寿命试验机上进行了不间断电弧磨损对比分断试验,同时 结合4组混合配粉触头进行了分阶段电弧磨损对比分断试验,测试并研究了该新 型触头材料的耐电弧磨损性能和特性及其电弧腐蚀特征,并对其耐电弧磨损性能 提高的机理进行了分析与探讨。研究结果表明。不间断电弧磨损试验中球磨包覆工艺制备的新型AgC触头 平均分断电弧质量损失远低于粗石墨机械混粉触头
5、,抗电弧腐蚀性能提高了40 以上并具有更好的抗熔焊性能。分阶段电弧磨损试验中各组样品在最初阶段损耗量相差不大,随着分断次数的增加,相较于常规机械混粉工艺触头,球磨包覆 Ag5C触头每一阶段均表现出少得多的电弧损耗量。Ag5C机械混粉触头随分断次数电弧磨损量呈指数大于1的指数函数规律上升,即到分断后期,由于表面坑洼程度加剧导致电涡流磨损现象的存在,电弧对触头的腐蚀加重,触头性能 急剧劣化甚至失效。而球磨包覆Ag5C触头随分断次数电弧磨损量呈近线性 规律变化,在分断各阶段电弧腐蚀对材料的损耗比较稳定,不会出现分断后期性 能和损耗急剧劣化的情况。AgC体系触头材料经电弧侵蚀后其工作面上形成的 形貌特
6、征包括结构松散区、富银区、C沉积区、电弧冲击坑、气孔和孔洞以及裂 纹,在电弧冲击作用下新工艺触头表现出了比传统粗石墨机械混粉触头更好的阻 止熔融Ag珠喷溅损失脱离基体和阻碍表面裂纹生成扩展的能力。将研制的新型AgC触头材料应用在上海施耐德低压终端电器有限公司及北 京ABB低压电器有限公司生产的小型断路器上,分别通过了国家低压电器质量 监督检验中心的运行短路能力试验测试。该新型材料已经小批量供应上海施奈德 和北京ABB等生产企业,并取得了良好的经济收益。采用将高能球磨、化学包覆和粉末冶金工艺相结合配以适量碳纳米管作为纤 维增强体的思路,制各出一种新型的碳纳米管增强AgC电接触材料并申请了国 家发
7、明专利。试验采用的碳纳米管直观团聚体尺寸数十微米,由网状碳纳米管纠 结构成,构成的碳纳米管丝平均尺寸3060rim,制备出的碳纳米管增强Ag5C 包覆粉中银的平均晶粒尺寸约为50nm。包覆粉中微米尺寸的Ag颗粒呈絮凝状 结构包覆在石墨片及碳纳米管的外面,这种絮凝体内部孔洞尺寸细小且分布均 匀,有助于后续烧结过程的进一步致密化。相较于传统机械混粉Ag5C触头, 球磨一包覆工艺和碳纳米管增强球磨包覆工艺Ag5C触头均表现出了极佳的机 械物理性能,主要性能指标大幅提高:同为球磨包覆工艺,碳纳米管增强Ag-5C 触头硬度进一步提升。尽管在电弧磨损最初阶段材料损耗量相差不大,随着分断次数的增加相较 于传
8、统机械混粉触头,球磨一包覆工艺和碳纳米管增强球磨一包覆工艺Ag一5C触B头每一阶段的材料损耗量都少得多,表现出了优异的耐电弧磨损性能。同为球磨包覆工艺,碳纳米管增强Ag一5C触头耐电弧磨损性能各分断阶段均显示了轻 微程度的劣化。尽管如此,碳纳米管增强球磨包覆Ag5C触头随分断次数电 弧磨损量呈指数小于l的指数函数规律变化,即到分断后期其材料损耗量趋于稳定,材料损耗速率下降,有效地抑制了电涡流磨损现象,这种优异的电弧磨损特 性对于提高其工作寿命具有重要意义。在触头分断后期,碳纳米管的存在及其强 化基体骨架作用,有效地阻止了触头工作面的大量剥离,减轻了工作面坑洼度, 抑制了电涡流磨损现象,是碳纳米
9、管增强Ag5C触头具有优异的电弧磨损特性的机理之所在。关键词:触头,AgC纳米技术,球磨,还原剂液相喷雾化学包覆,电弧磨 损,碳纳米管CAbstractIn view of the distinguished feature and application prospect of nanomaterials, the nanotechnology WaS first applied in the fabrication of silvergraphite electrical contact materials,and newly developed Age electrical contac
10、ts were prepared in the thesisAnd also,their physical and mechanical properties and arc erosion resistance were systematically researchedTo improve the properties oftraditional blending AgC electrical contact material, electroless plating technique was employed in powder preparation to improve their
11、 component segregation and microstructure nonuniformityNanocrystalline AgC coating powders were then prepared under the combination of the reducer liquid sprayingelectroless plating method and nanosized graphite,which carne from the high-energy milling and worked as the heterogeneous cores of Ag ato
12、ms nucleatingBecause of its well sintering densification,the properties of block contacts were totally improvedThe graphite powders with over 995content of C and 200 mesh granularity were used as raw material and milled for the best ten hours on the QM-1SP planetary mill and one-dimension nanosized
13、graphite was then fabricated,with the average thickness of 5060nmThe X-ray diffraction test showed that the average grain size of Ag in the as-prepared electroless plating Ag-5C powders was about 50nmIn the thesis,the sintering properties of fabricated nanocrystalline AgC electroless plating powders
14、 and the physical and mechanical properties of their block contacts were researched,along with the influence of milling time on their properties and microstructure and the sintering time on the propertiesAt the same time,the AgC contacts fabricated by three different techniques were compared on thei
15、rmicrostructure and properties and accordingly a brief mechanism model WaS establishedAt last,the influence of nanocrystalline electroless plating powders on the properties ofconventional blendingAge contacts was researchedThe research showed that with milling time going,graphite orientation structu
16、re appeared in the AgC block contactsAt that time,the electrical conductivity went lower,which was highest when uniformly microstructured,but it rose again as the orientation structure growing,with the decline of its hardness and density ratio at theDSalTIe timeWhile with the sintering temperature g
17、rowing,the density ratio,hardness and electrical conductivity of the contacts increased and arrived their highlight at about 840CThe Ag一5C material fabricated by milled graphite sprayingelectroless plating technique had superior physical and mechanical properties and uniform microstructure to those
18、made by blending and dropping-electroless plating techniques With the reducer liquid sprayingelectroless plating method,the contact area between reaction solution and reducer in unit time and the ratio of graphite powders separated in the reaction solution working as heterogeneous cores of Ag atoms
19、nucleating were greatly increasedAt the sarne time,the local concentration of reducer in reactiOnsolution was largely reduced,and then the growth of Ag atoms was suppressed,Because ofthe factors mentioned above,the refinement ofelectroless plming powders and their grmns and the improvement of electr
20、oless plating effect were achieved,and the component segregation of graphite in the Ag matrix was well eliminatedMixed with various content of the asprepared nanocrystalline electroless plating powders, the micropores in blending AgC material were filled by the growth of nanocrystallinegrainsAs a re
21、sult,the mechanical and physical properties of the fabricated contactswere improvedThe uninterrupted experiment for erosion behavior ofthe prepared new type AgC contact and its traditional blending counterpart by breaking arcs were done by using an ASTM Contact Material Automatic Measuring DeviceIn
22、the meantime,the experiment for erosion behavior of 6 group contacts,the two contacts mentioned and four blending contacts mixed with nanocrystalline electroless plating powders,by breaking arcs were doneThe arC erosion resistance properties and characteristics ofthe asprepared new type AgC contact
23、material were tested and studied,and also the improvement mechanism ofthe former was analyzed and discussedAs was shown in the uninterrupted experiment for erosion behavior,compared with coarse graphite blending material,the uew type AgC electrical contact had less average weight loss of breaking ar
24、cs and 40higher arc erosion resistance and better resistance against weldingIn the experiment for erosion behavior by stages,the samples had similar weight loss at the beginning,but with breaking time growing,the fabricated new type AgC contact showed better arc erosion resistance at every stage tha
25、n blending contacts,For blending materials,the relationship between their loss and breaking times took the shape of an exponent function curvewhose exponent waslarger than 1That meant in the anaphase of breaking,the arc erosion got aggravatedEand the properties of contacts got worse and even noneffe
26、ctive because of the existence of electric vortex erosion,which was caused by tlle aggravation of the potholes of contact surfaceAnd for millingelectroless plating Ag一5C contact,the relationship between its loss and breaking times presented the shape like a linearity function Curve,which meant the w
27、eight loss tended to be stable at every stage and the situation mentioned above wont happenAfter arc erosion,such morphology characteristics were formed on me contact surface ofAge materials as loose structure Ag enrichment structure,graphite sediment structure,arc impact crater structure,gaspore an
28、d hole structure and crack structureUnder the impact of arcs,the new typeelectrical contact were superior to its traditional blending counterpart to prevent the melted Ag beads to spray and get away from the matrix and keep up the formation and development of surface cracksThe new type AgC contact m
29、aterial,employed on the miniature circuit breakersfrom Schneider Shanghai low voltage terminal Apparatus Co,Ltdand ABB Beijinglow voltage Apparatus Co,Lid,had respectively passed the short circuit circulation test by China National Centre for Quality Supervision and Test of Low Voltage ApparatusIt h
30、ad been supplied to several manufacturing corporations like SSLVTA and ABB Beijing by small batch and good economic income had been achievedPrepared by the combination of highenergy milling,electroless plating and powder metallurgy technique、析th carbon nanotubes as the fiber reinforcer,the new type
31、carbon nanotubes-reinforced AgC electrical contact material was fabricated and its National Invention Patent Was appliedThe carbon nanotubes aggregate employedhad the size of tens of microns,which WaS comprised of carbon nanotubes sized 30-60nmAnd the average grain size of Ag in the as-prepared carb
32、on nanotubesreinforced Ag一5C electtoless plating powders was about 50nmInelectroless plating powdersgraphite and carbon nanotubes were coated by microsizedAg granules with flocculent structure and the floccules had small and uniform intemal micropores,which was helpful to the further densification i
33、n sintering,Thus,the prepared carbon nanotubesreinforced Ag5C contact showed better phy7sical andmechanical properties compared with blending contacts and better hardness even withother millingelectroless plating contactAlthough they had similar weight loss at the original stages,the new Ag-5C elect
34、rical contact prepared by millingelectroless plating technique and nanotubes-reinforced milling-electroless plating technique showed better arc erosionFresistance than traditional blending contact at the after stagesEven all prepared by milling-electrolessplatingtechnique,thearcerosionresistanceof n
35、anotubes-reinforced Ag一5C contact displayed slight worsening at every stage,and the relationship between its loss and breaking times ofthe former took the shape ofanexponent function curve,with exponent less than 1That meant in the anaphase ofbreaking,the arc erosion tended to be stable,the material
36、 wastage was decreased and the electric vortex erosion was effectively controlled,which WaS important to prolong its working life-spanIn the anaphase of breaking,because of the existence of carbon nanotubes and its role to reinforce the matrix,the peel-off of the contact surfacematerial was efficien
37、tly prevented,the potholes of contact surface were lightened and the arc erosion of current vortex was effectively controlled,which were the mechanism why the carbon nanotubesreinforced Ag5C electrical contact hadexcellent arc erosion characteristicKeywords:electrical contact,silvergraphite,nanotech
38、nology,milling,reducerliquid sprayingelectroless plating,arc erosion,carbon nanotuhesG原创性声明本人声明:所呈交的论文是本人在导师指导下进行的研究工作。 除了文中特别加以标注和致谢的地方外,论文中不包含其他人已发表 或撰写过的研究成果。参与同一工作的其他同志对本研究所做的任何 贡献均已在论文中作了明确的说明并表示了谢意。签名:主兰叁矗日期丝!:2:本论文使用授权说明本人完全了解上海大学有关保留、使用学位论文的规定,即:学 校有权保留论文及送交论文复印件,允许论文被查阅和借阅;学校可 以公布论文的全部或部分内容
39、。(保密的论文在解密后应遵守此规定)签名:潋导师签名:呈乙出期:兰竺!:上滴-夫掌博士掌位论文第一章电接触材料研究进展触头是电器开关、仪器仪表等的接触元件。主要承担接通、断开电路及负 载电流的作用。因此它的性能直接影响着开关电器的可靠运行与寿命。而电接 触材料则是开关电器中的关键材料,开关电器的主要性能以及寿命的长短,在 很大程度上决定于其触头材料的好坏。触头在实际使用过程中的情况非常复杂, 除了机械力和磨擦作用外,还有焦耳热、电弧的灼烧,以及因电流极性而产生 的材料转移等,这些都会对材料产生影响,并且,对不同的材料来说,影响也 不尽相同。由于使用场合的不同,对触头材料的要求也是多方面的【lj
40、,通常要 求它具有良好的导电性和导热性、低而稳定的接触电阻、高的耐磨损性(电弧 磨损和机械磨损)、抗熔焊性、良好的化学稳定性和一定的机械强度,对于真空 触头材料还要求截断电流小、含气量低、耐电压能力强、热电子发射能力低等等。目前,应用于弱电领域中的触头材料大多采用金和铂族金属及其合金(高 的化学稳定性)。在强电领域中主要有银基触头材料(主要用于低压电器、家用 电器等)、铜基触头材料(主要用于真空断路器等)和钨基触头材料(用于高压 油路断路器、SF6断路器、复合开关等)21。用于生产制造的触头材料品种很多, 二元或多元复合触头材料共计有数百种,广泛应用的触头材料只不过几十种。 在二元或多元体系中
41、,大部分触头材料形成的是“假合金”,其制造工艺主要是 粉末冶金法与熔炼法两大类,可以根据不同的成分和性能要求,选用不同的制 造工艺。随着强电触头材料向着高电压、大电流、大容量的方向发展以及i电 触头材料小型化、高寿命和高灵敏度的发展趋势,对触头材料的要求越来越高。 近年来,随着冶金技术的不断发展,国内外在触头材料的制造技术方面有了很 大的发展,新工艺、新技术得到了广泛应用,如采用纤维强化冶金工艺制备出 的钨纤维、镍纤维等纤维强化触头材料具有优良的电性能;德国发展了生产银 石墨间接重复挤压工艺,得到了密度高、延伸性好的产品;此外,烧结挤压工 艺、等静压技术、超声波场中压制成形技术以及机械合金化、
42、离子注入等技术 已经应用在触头材料的制备中,触头材料的性能得到了很大的提高。1。1电接触材料简介电接触材料是开关电器中的核心部件,担负着接通、承载和分断电流的任上海大学博士学位论文务。由于触头在电器开关中的作用和功能,加之电器种类的多样化,决定了针 对不同的开关电器和使用条件,选用不同的触头材料,因而促使触头材料多样 化和制备工艺的不断提高和发展。现代化的大型复电气系统,如大型电力系统、 自动控制系统、通讯系统等,其中包含的电接触数目常在数十万以上,如果其 中的一个或几个工作失效,则将导致整个系统工作紊乱,甚至全部瘫痪,它所 造成的后果将是无法估量的,因此触头材料既是电子、电讯、电器等产品的关
43、 键和核心,又是它们的致命弱点,已成为电子技术中不可缺少的重要材料。世 界各先进工业国家如美、俄、德、日、法、英和东欧等都十分重视电接触材料的研究31。我国从1956年开始生产触头,四十多年来已形成一定的生产能力41。111开关电器对触头材料的基本要求触头材料在开关电器中的功能是在电路中接通和断开电流,触头在开闭过 程中产生的现象极其复杂,影响因素较多,因此为了满足各类实际应用,开关 电器对触头材料的要求,最重要的是以下几方面【5】:一良好的导电性和导热性。由于开关电器中触头和支座的热容量不大,并且 散热所需的面积或体积也有限,因此所用的触头材料应该具有良好的导电 性和导热性,使得因电流通过而
44、产生的焦耳热不会使温升超过规定值。抗熔焊性。触头闭合状态时,因线路故障通过大电流造成所谓静熔焊。触 头在闭合前的瞬间或闭合后的弹跳时,会因电弧使材料熔化而造成所谓动 熔焊。触头间微弱的熔焊(熔粘、粘接),是接触点的温度达到材料软化点 而发生的,牢固的熔焊(焊接、焊住),则是因为达到了熔化温度。触头间 发生熔焊,特别是牢固熔焊时,便会因线路不能开断而发生很大的事故。 触头材料具有高的熔点、高的软化温度,以及低的电阻率,都对抗熔焊性 有好处。有些材料本身的可焊性差,或者表面熔化之后生成脆性的或疏松 的膜,即使发生了熔焊,但焊接力很小,这样也提高了抗熔焊性。耐电弧磨损性。是决定开关电器通断能力和电寿
45、命的重要性能。电弧磨损 也称为电弧烧损或电弧腐蚀,在强电情况下,电弧造成的金属汽化是损耗 的主要形式,金属因电弧造成猛烈蒸发而产生的蒸汽,会吹走触头上的金 属液滴而造成剧烈的烧损。触头材料的耐电弧磨损性与热导率、熔点、熔 化潜热、蒸发潜热、材料中组元的分解温度和分解热,以及材料的组织结 构等,有着密切的关系。通常经受电弧的触头采用复合物材料,但当电流 达100kA的数量级时,目前所有的触头材料的烧损相同,因此没有选择余 地。2上浔大掌得_士掌位论文分断大电流时不易发生电弧重燃。在一些灭弧方式简单而又需要分断大电 流的开关电器中,往往因灭弧能力不够,在分断交流电流时发生多次电弧 重燃,严重时会因
46、持续燃弧而把电器烧毁。开关电器分断后发生电弧重燃 与否,决定于触头之间的气隙介质强度与系统的恢复电压之争。如果气隙 介质强度恢复得比系统恢复电压快,电弧便能保持熄灭,也就是说这个开 关成功地分断了交流电流,介质强度恢复得快慢决定于开关的设计、试验 参数以及绝缘材料和触头材料的物理性能。对于触头材料来说,含有热离 子发射型元素和低电离电势元素的材料。容易使电弧重燃。还有触头材料 的热学性能以及组织结构和表面状态,对电弧的重燃都起着重要作用,良 好的热学性能可以帮助冷却电弧,而结构和形貌则影响电弧的运动。材料 的组织结构和表面状态与制造方法也有关系。低的截流水平。这对真空开关电器是非常重要的,在真
47、空开关的分断过程 中,触头间隙内的介质强度迅速恢复,使电弧很快地熄灭。这种情况下, 触头只受到最多半个周波的电弧烧灼,烧损量很小,所以真空开关的电寿 命很长。但是,由于电弧的很快熄灭,使电流立刻降至零,也即所谓“截 止了电流”,这种截流是有害的,将会因线路中感生的高电压而把设备的绝 缘击穿。在真空开关电器中,介质强度的迅速恢复,是因为电流变零时金 属蒸汽凝结到电极和屏蔽罩上,而使触头间隙迅速地被抽空的缘故。因此, 当触头材料中含有蒸汽压高的元素时,可以降低截流水平。_低的气体含量。真空开关电器要求触头材料含有极少的气体,因为真空开 关的灭弧室内任何时候都要使压力保持在10。4mbar以下,在使用过程中, 触头材料内的气体在电弧的作用下会释放出来,如果材料所含的气体太多, 释放出来的气体便会破坏真空,严重时会把开关毁坏掉。因此,一般地说, 作为真空开关的触头材料,其含气量只能是几