Revisão: efeito dos metais doadores nas propriedades elétricas e microestruturais dos varistores cerâmicos à base de SnO2

Oliveira, Marcelo Moizinho; Rangel, J. H. G.; Sousa, Vânia Caldas de; Longo, Elson; Filho, R. N. R.

doi:10.1590/s0366-69132008000300005

Cited by 4 publications

(3 citation statements)

References 39 publications

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“…Os estudos em sistemas a base de WO 3 realizados por Zang et al [16] [27,28] como pode ser observado pela equação geral (3).…”

Section: Resultsunclassified

Varistores à base de WO3 - revisão

Oliveira¹,

Pessoa²,

Brito³

et al. 2016

Matéria (Rio J.)

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RESUMOVaristores são elementos que fazem parte do sistema de transmissão e distribuição de energia elétrica ou de instalações elétricas especiais. Estes dispositivos são amplamente produzidos variando a escala, dependendo de sua aplicação, como dispositivos de baixa voltagem, com poucos grãos, exibindo ruptura de alguns volts, a vários kilovolts como usado em para-raios em rede de distribuição de energia. A física de operação dos varistores tem sido amplamente estudada e tem elementos comuns como barreiras Schottky formado na junção metal/semicondutor. Vários estudos têm sido desenvolvidos a fim de obter cerâmicas varistoras para aplicação em alta e baixa tensão. Dentre esses estudos encontram-se os varistores a base de ZnO, SnO 2 , TiO 2 e mais recentemente os de WO 3 . Diferente das três composições citadas, os a base de WO 3 apresentam comportamento varistor intrínseco devido a presença das fases monoclínica e triclínica. A adição de dopantes doadores e aceitadores de elétrons e o tratamento térmico em diferentes atmosferas também alteram as propiedades não lineares desses sistemas, uma vez que influencia na formação da barreira Schottky. Neste estudo foi realizada uma revisão sobre trabalhos relacionados a nova composição de cerâmica varistora a base de óxido de tungstênio (WO 3 ). Palavras-chave: propriedades elétricas, WO 3 , varistores. _______________________________________________________________________________________ ABSTRACTVaristors are elements that are part of electric power transmission and distribution systems or of special electrical installations. Varistors are manufactured in a wide variety of types, depending on their application, such as low-voltage devices with a layer of a few grains of thickness and low breakdown voltage, to varistors with a breakdown voltage of several kilovolts, such as those used in the lightning arresters of electric power distribution networks. Varistors, whose physical operation has been extensively studied, share common elements such as metal-semiconductor Schottky barrier junctions. Several studies have focused on the development of varistor ceramics for high and low voltage applications, including ZnO, SnO 2 , TiO 2 , and more recently, WO 3 -based ceramics. Unlike the first three compositions, WO 3 -based ceramics present an intrinsic varistor behavior because they contain monoclinic and triclinic phases. The addition of electron donor and acceptor dopants and heat treatments in different atmospheres also alter the non-linear properties of these systems, since they affect the formation of the Schottky barrier. This paper offers a review of the literature on the new varistor ceramic composition based on tungsten oxide (WO 3 ). Keywords: electrical properties, WO 3 , varistors. _______________________________________________________________________________________ INTRODUÇÃOVaristores, resistores não ôhmicos ou ainda resistores variáveis, são elementos que fazem parte do sistema de transmissão e distribuição de energia elétrica ou de instalações elétricas espec...

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“…Os estudos em sistemas a base de WO 3 realizados por Zang et al [16] [27,28] como pode ser observado pela equação geral (3).…”

Section: Resultsunclassified

Varistores à base de WO3 - revisão

Oliveira¹,

Pessoa²,

Brito³

et al. 2016

Matéria (Rio J.)

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“…A review of the effect of donor metals on the electrical and microstructural properties of SnO 2 -based ceramic varistors was done and it was found that some of these oxides, such as Cr 2 O 3 and La 2 O 3 , significantly improve the electrical properties of varistors while others, such as Bi 2 O 3 and Er 2 O 3 , for instance, do not have this effect [5]. The evolution of the varistor performance has also been attributed to oxygen species produced by the reaction with these dopants.…”

Section: Introductionmentioning

confidence: 99%

Electrical and microstructural properties of microwave sintered SnO2-based varistors

et al. 2012

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An investigation was made of the microstructural and electrical properties of SnO 2 -based varistors microwave sintered at 1200 ºC, applying a heating rate of 120 ºC/min and treatment times of 10, 20, 30, 40, 50 and 60 min. The system used in this study was (98.95-X)%SnO 2 .1.0%CoO.0.05%Cr 2 O 3 .X%Ta 2 O 5 , where X corresponds to 0.05 and 0.065 mol%. Sintering was carried out in a domestic microwave oven (2.45 GHz) fitted for lab use. Silicon carbide was placed in a refractory vessel to form a heating chamber surrounding the sample holder. The pellets were examined by scanning electron microscopy, X-ray diffractometry, direct current measurements and impedance spectroscopy. The parameters of density, medium grain size, coefficient of nonlinearity, breakdown electrical field, leakage current, and height and width of the potential barrier were analyzed.

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“…Oliveira et al [11] found out that the antimony oxide acts as an electron donor, increasing the conductivity of the SnO 2 -based ceramics. Although this oxide is trivalent and contains fewer valence electrons than tin, studies on SnO 2 -based varistors indicate the coexistence of Sb 5+ and Sb 3+ and that the ratio between them depends on both the temperature as well as the oxygen concentration in the environment [12].…”

Section: Introductionmentioning

confidence: 99%

SnO<sub>2</sub> Dense Ceramic Microwave Sintered with Low Resistivity

Perazolli¹,

Gasparotto²,

Jaomaci³

et al. 2012

MSA

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The Hall-Héroult process is used for alumina reduction by the use of graphite anodes even though it involves a high emission of carbon dioxide (CO 2 ) and several other organic compounds. Proposals have been made aiming at substituting graphite for a single-phase SnO 2 -based ceramic with low resistivity and chemical resistance to cryolite, which is characterized as an inconsumable anode, reducing pollutant emissions. To this end, a wide range of studies were carried out on SnO 2 -based ceramics modified with ZnO as a densification aid doped with the promoters of electrical conductivity such as Nb 2 O 5 , Al 2 O 3 and Sb 2 O 3 through a mixture of oxides and hybrid sintering in a microwave oven. The pressed pellets were sintered in a microwave oven up to 1050˚C under a constant heating rate of 10˚C/min. After sintering, the density was determined by the Archimedes method, the phases were then characterized by X-ray diffraction, the microstructure and chemical composition resulting from the sintered SnO 2 -based ceramics were also investigated by field emission scanning electron microscopy (FE-SEM) coupled with an energy-dispersive X-ray spectroscopy (EDS) and the electrical properties were determined by the measurements of the electric field × current density. A single-phase ceramic was obtained with a relative density of above 90% and electrical resistivity of 6.1 Ω·cm at room temperature. The ceramics obtained in this study could be a potential candidate as an inconsumable anode to replace the current fused coke used in the reduction of alumina.

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Revisão: efeito dos metais doadores nas propriedades elétricas e microestruturais dos varistores cerâmicos à base de SnO2

Abstract: resumoO estudo da adição de dopantes trivalentes é uma das principais pesquisas na área de varistores. Vários autores têm buscado entender os efeitos destes dopantes nas propriedades elétricas e microestruturais destas cerâmicas eletrônicas.

Cited by 4 publications

References 39 publications

Varistores à base de WO3 - revisão

Varistores à base de WO3 - revisão

Electrical and microstructural properties of microwave sintered SnO2-based varistors

SnO<sub>2</sub> Dense Ceramic Microwave Sintered with Low Resistivity

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Revisão: efeito dos metais doadores nas propriedades elétricas e microestruturais dos varistores cerâmicos à base de SnO2

Abstract: resumoO estudo da adição de dopantes trivalentes é uma das principais pesquisas na área de varistores. Vários autores têm buscado entender os efeitos destes dopantes nas propriedades elétricas e microestruturais destas cerâmicas eletrônicas.

Cited by 4 publications

References 39 publications

Varistores à base de WO3 - revisão

Varistores à base de WO3 - revisão

Electrical and microstructural properties of microwave sintered SnO2-based varistors

SnO&lt;sub&gt;2&lt;/sub&gt; Dense Ceramic Microwave Sintered with Low Resistivity

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Product

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About

SnO<sub>2</sub> Dense Ceramic Microwave Sintered with Low Resistivity