Metal oxide varistor (MOV), or ZnO varistor, is a kind of polycrystallinesemiconductor ceramics composed of multiple metal oxides and sinteredby conventional ceramic technology. ZnO varistors have good nonlinearvolt-ampere characteristics and excellent impulse energy-absorbing capacities.These advantages make them widely used in transient overvoltage protectionsfor electrical/electronic systems. Now, varistors have been widely used asguardianstoprotectcircuitsoveraverywiderangeofvoltages,fromafewvoltsin semiconductor circuits to 1000kV AC and ± 1100kV DC in electrical power transmission and distribution networks. Correspondingly, they can also handlean enormous range of energies from a few joules to many megajoules. Remarkably,theyarealsoveryfast,switchinginnanosecondsfromtheirhigh-resistancestate to highly conducting state and then restores to a normal high-impedanceoperatingconditions. Abulkvaristorisacomplexmultijunctiondevicecomposedoflargenumbersofbothohmicandnonlinearelementsconnectedinarandomnetwork.Thefeatures ofbulkvaristorsarein?uencedbythegeometryandthetopologyofthegranularmicrostructure,aswellasthepropertiesandthedistributionofelectricalcharacteristicsofgrainboundaries.ThisbooktriestobridgetheMacro-Characteristics with the properties in microstructures of ZnO varistors to provide insights into someoftheaspectsinthemicrostructuresofZnOvaristors,whichin?uencethefeatures of the bulk varistors and further the science and the understanding onmicrostructuresofZnOvaristorsandthoseparametersthata?ectthee?ciencyduringthemanufacturingprocess. The book includes 12 chapters, which mainly focuses on ZnO varistors.Chapter 1 introduces and highlights the fundamental knowledge and applications of ZnO varistors. Chapter 2 introduces the conduction mechanism of theZnO varistor, among the numerous conduction models, the one presented by G.E. Pike and further developed by G. Blatter and F. Greuter has been widelyrecognized and may meet most of the experimental phenomena. Various additives to improve the electrical characteristics were discovered and the synthesisconditionswereoptimized,whichwillbeintroducedinChapter3.TheelectricalpropertiesofeachindividualgrainboundarywillcontributetotheglobalelectricalcharacteristicsofZnOvaristors,Chapter4characterizesthemicrostructuralelectrical properties of ZnO varistors. The simulation is helpful to reveal theconnection between the microstructure and the macroscopic characteristics of varistor ceramics, the details on how to simulate varistor ceramics will be presented in Chapter 5. The breakdown of ZnO varistors is an originalphenomenonduringtheirapplications,andthefailuremodelsresultindi?erentenergy handling capabilities, which will be introduced in Chapter 6. ZnO varistors can be electrically, chemically, and thermally degraded during use, leadingto the reduction of barrier voltage height and, consequently, to the increaseof leakage current, which could be catastrophic for ZnO varistors, Chapter 7discusses the electrical degradation of ZnO varistors. Chapter 8 introducesother ZnO varistorsystemsinsteadofbismuth, suchaspraseodymium,barium,andvanadium,forovercomingtheshortcomingsofBi2O3-basedZnOvaristors. The applications in electronic systems require the miniaturized varistors andlow-voltage varistors. Chemical processing, such as sol–gel, solution, precipitation, microemulsion techniques, etc., facilitates a homogeneous doping at themolecular level to obtain a miniature device with a higher breakdown voltage,which will be introduced in Chapter 9. Interestingly, the ceramic–polymercomposite varistor is a composite one, incorporating varistor particles orsemiconducting particles, and its ?eld-dependent property varies with the ?llerconcentration. The composite varistor, with a lower breakdown voltage, can bea suitable substitute for ZnO-based varistors for the purpose of protection forlow-voltagesystems,whichwillbeintroducedinChapter1. Besides works on improving the performance of the ZnO varistor material,othernewmaterialshavealsobeensearchedinordertoachieveabetterstabilityand be used for new applications. The titanium-based capacitor–varistor dual-function varistor ceramics, such as TiO2,SrTiO3 CaCu3Ti4O12 (CCTO), and BaTiO3 varistor ceramics, have realized the goal to achieve component miniaturization and provide a superior high-frequency and high-amplitude transientvoltage protection, which will be introduced in Chapter 10. Di?erent fromthe multiphase structure of the ZnO-based varistor, the SnO2-based varistor has a simple microstructure, good stability, and better thermal conductivity,which makes the SnO2-based varistor one of the most promising candidates tocommercially compete with the ZnO-based varistor. The SnO2-based varistors will be introduced in Chapter 11. The WO3-based varistor ceramic is another kind of low-voltage varistor with a low threshold electric ?eld of 5–10Vmm?1 and a high dielectric constant, which enables it to act as a varistor in parallelwithacapacitor,whichwillbeintroducedinChapter12. Thisbookcoversmainaspectsofmetaloxidevaristors,whichintroducefundamentalandadvancedtheoriesandtechnologiesrelatedtometaloxide varistors, research achievements in the this ?eld, and has re?ected the recent research works of the authors and their students and colleagues in Tsinghua University,especiallythePh.D. dissertationsofDr. ChenQingheng,Dr. HuJun,Dr. LiuJun, Dr. LongWangcheng,Dr. ZhaoHongfeng,Dr.XieJingcheng,Dr.ChengChenlu, andMScthesisofMs. WeiQiaoyuan.Theauthortriedtocoveralltheaspectsofmetaloxidevaristors,butitishardtoavoidtenthousandmayhavebeenleftout. ProfessorJinliangHe TsinghuaUniversityBeijingChina Acknowledgments My research works on metal oxide varistors in Tsinghua University weresupported by the National Natural Science Foundations of China under Grants59907001, 50425721, 50677029, and 50737001, and was supported in part bythe 11th Five-Year Science and Technology Support Plan of China, and by theNational Basic Research Program of China under grant 2014CB239504. Enormous references hadbeencited inourbook,all hadbeenlistedineverychapter, but it is hard to avoid careless omission, in this case, I beg your pardon.I am so sorry,some formulas areunable to ?ndthe originalreferences wheretheycame from. I have had a long-term cooperation in the research of metal oxide varistorswith Prof. Nan Cewen of Tsinghua University, who is an Academician of ChineseAcademy of Sciences, and Prof. Lin Yuanhua, who is the Dean of the School ofMaterialsScience andTechnology in TsinghuaUniversity,I havelearnta lotfromthem, and many cooperation results have been collected in the book. I would like to extend my sincere thanks to them. Special thanks go to Dr. Han-Goo Cho and Dr. Se-Won Han, from KoreaElectrotechnology Research Institute (KERI), for providing me the chance to doresearch works in the ?eld of metal oxide varistors during 1997–1998. KERI iswhereIstartedmyresearchinthis?eld. Special thanks also go to my students, including Dr. Long Wangcheng, Dr. LuoFengchao, Dr. Xie Jingcheng, Ms. Wei Qiaoyuan, and Mr. Meng Pengfei, for theirassistance on preparing the draft of the book and to my colleagues for their generous help in many ways so as to allow me to allocate time working on the book.GreatgratitudeisgiventoProf.HuJunforpreparingthemanuscriptofChapter5,Dr.ChengChenluforpreparingpartmanuscriptsofChapters2and7,andDr.LiuJun for preparing the part manuscript of Chapter 7. Gratitude is extended to Mr. Lesley Jebaraj, Project Editor at Wiley, for hiseditorial and technical reviews on this book. His professionalism and experiencehave greatly enhanced the quality and value of this book. Lastly, but not least, my most special gratitude goes to my supporting andunderstanding family, my mother, Yang Ruiru, who taught me working hard andenjoying the wonderful life; my wife, Prof. Tu Youping, who had done and hasbeen still doing a great job on supporting the family. Most of all, I am indebted tomy son, Ziyu, I have not spent much time to enjoying his grow-up process, but itis gratifying that he is working hard to become a scientist in the ?eld of statisticsand machine learning. Jinliang He

• 暂无课件
• 样章下载
• 暂无网络资源

扫描二维码
下载APP了解更多

版权图片链接