Completely uptodate, this is the first comprehensive monograph on metal oxide varistors with a focus on microstructure, conduction mechanisms, device failures, ageing, additive impacts and future varistor systems. Electrical properties of zno varistors prepared by direct mixing of constituent phases m. Unpublished msc thesis, school of materials engineering, northern malaysia. Zinc oxide zno varistor, which is a kind of polycrystalline semiconductor ceramic composed of multiple. Changes in grain size, compact density, additives distribution, and voltagecurrent capacitancevoltage relations were investigated for the characterization of the samples sintered at temperatures from 1473 to 1573 k without calcination or with.
The optimizations of undoped zno thin film growth using molecularbeam epitaxy mbe are. Pdf zno varistors with high voltage gradient and low leakage. Technical information physical properties of zinc oxide varistors. Pdf on sep 6, 2011, mohammad reza meshkatoddini and others published metal oxide zno based varistor ceramics find, read and cite all the research you need on researchgate. Low temperature dielectric relaxations in zno varistor. The zinc oxide nanoparticles find application in varistors and other functional. The dlts signals, correlated to the doping of mn and co. Sw molecular orbital calculations using simplified cluster models. Nanoscale characterisation of barriers to electron conduction in zno varistor materials. Submitted to university of baghdad college of education for pure. Zn 3 vo 4 2 has been determined to be monoclinic with space group p2 1 and lattice parameters of a 9. Jianlin liu, chairperson doping in zinc oxide zno thin films is discussed in this dissertation. Investigation of electrical properties of field grading materials based zno microvaristors a thesis submitted to cardiff university in the candidature for the degree of doctor of philosophy by hafisoh ahmad, b. Interface states in zno varistor with mn, co, and cu.
Zno varistors have been widely applied for the protection of electronic and electrical equipment from lightning 1,2. Mechanical properties and microstructure of zinc oxide. A thesis submitted in partial fulfilment of the requirements of the. Zinc oxide varistors are strongly nonlinear resistors that have been used to regulate transient voltage surges of unwanted magnitude for high voltage and powerrelated applications, such as surge arresters in power transmission and distribution for the protection of electronic devices. Stability of zinc oxide varistors a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical sciences 2014 poonsuk poosimma school of materials.
The filler is made of commercially available doped zno varistor powder. Comprehensive summaries of uppsala dissertations from the faculty of science and technology 686. This thesis has never previously been submitted for a degree or any other quali cation at. In this study, in order to explore the failure mode of zno varistors under multiple lightning strokes, a fivepulse 820. Metal oxide zno based varistor ceramics 331 conductors.
Modeling of electrical transport in zinc oxide varistors. Synthesis and characterization of solgel derived zno thin. Synthesis and characterization of zno nanoparticles. Several studies demonstrated that electrical stresses on varistors cause a deformation of their. Zno based varistors are widely used for overvoltage protection in many electrical and electronic circuits, at voltages ranging from a few to over a million volts. Home key engineering materials electroceramics in japan iii electric characteristics of znovaristors sintered. Thermoionic emission and tunneling are acknowledged to be the major transport mechanisms. The effects of zinc oxide microstructure on the electrical characteristics of lowvoltage ceramic varistors kesan mikrostruktur zink oksida terhadap ciriciri elektrik varistor seramik voltan rendah by shahrom mahmud thesis submitted in fulfillment of the requirements for the degree of master of science january 2004. Effect of compaction parameters and sintering configurations on the performance of zno varistor a thesis submitted in fulfilment of the requirements for the degree of doctor of philosophy to dublin city university by a n mustafizul karim, b. Cobalt, praseodymiumadded zinc oxide varistor was prepared through a wet chemical method followed by sintering with or without calcination. The presented varistor composite materials show very low values for the breakdown field strength down to 200 v mm. Stability of zinc oxide varistors a thesis submitted to the university of manchester for the degree of doctor of philosophy in the faculty of engineering and physical.
The zno varistor is a mutiphase polycrystalline ceramic made by. In carefully prepared aifree compositions the microstructure shows more globular grains. Comparative study of metal oxide varistors movs for. Nanoscale characterisation of barriers to electron. R jandrell a thesis submitted in ful lment of the requirements for the degree doctor of philosophy in electrical engineering may 2016. Stability of zinc oxide varistors research explorer. Convergentbeam electron diffraction has been used to determine the space groups of. Under extreme electrical stresses the nonlinear characteristics of a varistor. Various types of zinc oxide varistors under different processing conditions were sintered using microwave heating. The polycrystalline filler particles act as varistors due to their typical grainboundary structure. Requirements for the degree of doctor of philosophy. Both bi 2o 3rich and zn 7sb 2o 12 spinel phases are also usually present at the grain boundaries of the zno, but the presence of a bi 3zn 2sb3o14 phase is possible as well.
Degradation analysis of metal oxide varistors under. Stability of zinc oxide varistors manchester escholar. The failure processes of zno varistors caused by multiple. Electron holography study of active interfaces in zinc oxide varistor materials. I, pitshou bokoro, declare that this thesis titled, degradation analysis of metal oxide varistors under harmonic distortion conditions and the work presented in it are my own. The interface states in zno with impurities of transitionmetals, mn, co, and cu, were investigated by the dlts deeplevel transient spectroscopy measurements in zno prcoo x zno junctions as model systems of zno ceramic varistors and by the scfx. Zno needles of aidoped lowvoltage varistor ceramics often exhibit a. It was preserved for the fabrication of varistor discs. Electronic transitions in semiconductors between localised energy levels in the forbidden gap or between localised energy levels and the free bands are in totally. The interface traps situated between zno zno grain boundaries and the bulk traps due to donorlike traps in the bulk of zno grains.
Pdf metal oxide znobased varistor ceramics researchgate. These electronic devices, often referred to as movs, or metal oxide varistors, find. Synthesis of zno based nanopowders via a nonhydrolytic. Novel zno based ternary oxides for optoelectronic applications mareike trunk thesis submitted in partial ful.
The varistors consist of a disc of low e zno ceramic material with two solid copper leads s20 types only or copper clad steel wire. Pdf the surge arrester of kv gasinsulated substation gis needs. Olsson, interfacial microstructure in zno varistor materials, ph. Evidence for depletion layers in the varistor is shown in. They exhibit a highly nonlinear currentvoltage relation with a 5%. A model of znozno grain boundaries in a zinc oxide varistor. They are coated with ul 94 v0 approved ocher colored halogen free epoxy, which provides electrical, mechanical and climatic protection.
Advances in the synthesis of zno nanomaterials for. Zn 3 vo 4 2 particles in vanadium oxidedoped zinc oxide varistors. Varistor ceramics are composed of a large number of zno grains of different shape, size and orientation. Zinc oxide varistors are electronic ceramic materials whose electrical behavior is dominated by grainboundary interface states. Improvement of the vi characteristic of zinc oxide zno based metal oxide varistors movs using silicon telluride site2 and lanthanum hexaboride lab6 materials miidzo hove a thesis submitted to the faculty of engineering and the built environment, university of witwatersrand, johannesburg, in fulfilment of the requirements for. The emphasis is given to the fabrication of dense, uniform and defect free zno layers for the memristive application by. Synthesis of zno nanoparticles for varistor application using zn. After milling the powders, disc shaped samples were pressed and sintered for 2 hours at temperatures in the range 950c to 1250c. Of zno based varistor ceramics doped with rare earth. Declaration of authorship i, pitshou bokoro, declare that this thesis titled, degradation analysis of metal. Powder processing parameters and their influence on the electrical performance of zno varistor a thesis submitted to dublin city university in fulfilment of the requirements for the degree of doctor of philosophy by shahida begum, bsc eng name of supervisors prof m s j hashmi dr ramon puyane collaborating establishment harris corporation. Restart of the chemical preparation process for the. National institute of technology, rourkela certificate this is to certify that the thesis entitled synthesis and characterization of zno nanoparticles is submitted by mr. The work presented in this thesis is concerned with the microstructure of.
Scanning electron microscopy sem and xray diffractometry xrd were used to analyze the microstructure of the material. Varistors under harmonic distortion conditions author. The varistors consist of a disc of low zno ceramic material with two solid copper leads s20 types only or copper clad steel wire. Sintering of nanocrystalline multicomponent zinc oxide. Thesis submitted to the school of graduate studies, universiti putra malaysia, in fulfillment of the. An experimental study of the failure mode of zno varistors. They are coated with ul 94 v0 approved ocher colored halogen free epoxy, which provides electrical. Zinc oxide zno has been used in a wide range of products for many years, including, among others, varistors, surface acoustic wave. Additives distribution and electrical properties in zinc. University of california riverside doping in zinc oxide. We investigate the physical bases of the degradation processes observed in the ac tests. New varistor type polymer composites for lowvoltage application have been developed. Zno semiconductor ceramics inner electrode palladium sn plating ni plating ag termination.
Insitu quantitative measurement of electric fields in zinc oxide thin films using electrostatic force microscopy jan harloff. A surge in excess of the specified withstanding surge current may cause short circuits or package rupture with expulsion of material. Pdf advances in the synthesis of zno nanomaterials for. The single crystal microtube of zno has a band gap of 3. Mohd sabri bin mohd ghazali universiti putra malaysia. Brankovic center for multidisciplinary studies, university of belgrade, kneza viseslava 1, 1 belgrade, serbia abstract. When rareearth oxide additives are added into zno varistors, the.
An impulse test is the most direct means to study the performance of zno varistors. Mechanism and development of tio2doped zno bi2o3based varistors 81 layer in the grain on both sides of the interface. Manufacturing of zinc oxide varistors zinc oxide varistors are ceramic. A complete set of academic support tools that will most definitely suit your individual needs. School of mechanical and manufacturing engineering dublin city university. Physically, a zno varistor contains numerous pieces of zinc oxide grains of. Novel znobased ternary oxides for optoelectronic applications. Electrical properties of zno varistors prepared by direct. Powder processing parameters and their influence on the.
Products were characterised in terms of phase development and microstructure by xray diffraction and scanning electron microscopy. Electric characteristics of znovaristors sintered at low. By careful control of the microstructure, through nanostructuring by chemical routes, it should be possible to produce varistors with high breakd. The work presented in this thesis is concerned with the microstructure of zinc oxide varistor materials. The obtained breakdown fields are 1588 and 2584 v cm1 for er2o3 free and 0. Ceramic varistors based on zno, bi2o3, sb2o3, mno and co3o4 were prepared by the mixed oxide route. Chapter vi, which is the core part of this thesis work, is mainly devoted to the characterization study of zno based building blocks. Nonlinear iv characteristics of a zinc oxide varistor 10 2.
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