Final-stage sintering behavior of Fe-doped CeO2

Zhang, T.S.; Ma, Jun; Kong, Ling Bing; Zeng, Zhiqiang; Hing, Peter; Kilner, John A.

doi:10.1016/s0921-5107(03)00198-3

Cited by 55 publications

(45 citation statements)

References 18 publications

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“…However, the need to produce such cells economically at low temperature remains an issue and has prompted studies into the use of dopants and nano-sized powders to reduce the 1200C traditionally required to densify CGO electrolytes [4,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

Section: Objectives and Experimentsmentioning

confidence: 99%

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Nicholas

2007

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Cerium gadolinium oxide (CGO) has been identified as an acceptable solid oxide fuel cell (SOFC) electrolyte at temperatures (500-700°C) where cheap, rigid, stainless steel interconnect substrates can be used. Unfortunately, both the high sintering temperature of pure CGO, >1200°C, and the fact that constraint during sintering often results in cracked, low density ceramic films, have complicated development of metal supported CGO SOFCs.The aim of this work was to find new sintering aids for Ce 0.9 Gd 0.1 O 1.95 , and to evaluate whether they could be used to produce dense, constrained Ce 0.9 Gd 0.1 O 1.95 films at temperatures below 1000°C. To find the optimal sintering aid, Ce 0.9 Gd 0.1 O 1.95 was doped with a variety of elements, of which lithium was found to be the most effective.Dilatometric studies indicated that by doping CGO with 3mol% lithium nitrate, it was possible to sinter pellets to a relative density of 98.5% at 800C-a full one hundred degrees below the previous low temperature sintering record for CGO. Further, it was also 2 found that a sintering aid's effectiveness could be explained in terms of its size, charge and high temperature mobility.A closer examination of lithium doped Ce 0.9 Gd 0.1 O 1.95 indicated that lithium affects sintering by producing a Li 2 O-Gd 2 O 3 -CeO 2 liquid at the CGO grain boundaries. Due to this liquid phase sintering, it was possible to produce dense, crack-free constrained films of CGO at the record low temperature of 950C using cheap, colloidal spray deposition processes. This is the first time dense constrained CGO films have been produced below 1000C and could help commercialise metal supported ceria based solid oxide fuel cells. Thesis Motivation, Background and Overview MotivationMore efficient technologies are needed if the world is to meet the doubling of energy demand that is projected to occur in the next 25 years. Given the large natural reserves of hydrocarbons and the existing infrastructure, it seems likely that traditional fuels (such as gasoline and liquefied natural gas) will retain their importance, even as alternatives such as bio-fuels enter the marketplace. Thankfully, the efficiency increases possible by electrochemically reacting these fuels inside a fuel cell instead of combusting them are considerable, making it possible to lower the environmental costs associated with their continued use. For instance, solid oxide fuel cells (SOFCs) are expected to achieve first law efficiencies of 80-85% when used with cogeneration [1]; whereas, the mostefficient combustion systems used today only achieve efficiencies of 50% [2]. Fuel Cell BasicsA fuel cell utilizing an oxygen-conducting electrolyte, such as a solid oxide fuel cell, is schematically illustrated in Figure 1. Here an oxidant (usually atmospheric O 2 ) is added to the cathode chamber of the fuel cell where it takes on electrons and destroys oxygen ion vacancies within the electrolyte by filling them with oxygen. At the same time, fuel, such as H 2 , is added to the anode chamber where i...

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Section: Objectives and Experimentsmentioning

confidence: 99%

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Nicholas

2007

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“…A literatura apresenta resultados que mostram que esses metais atuam como aditivo de sinterização da céria-ítria. Um tipo de mecanismo responsável por essa densificação foi observado por Zhang et al [14] 2 [ 15] Microestruturas da composição CY sinterizadas a 1400 e 1600 ºC e das composições CYLSM e CYLSCF sinterizadas a 1400 ºC. A barra de aumento vale para todas as micrografias.…”

Section: Análise Das Microestruturasunclassified

“…A Figura 7 mostra as curvas obtidas comparadas com o da amostra CY1600. Contrariamente ao esperado, as amostras dopadas apresentaram comportamento semelhante à amostra CY não dopada sinterizada a 1600 ºC, isto é, para PO 2 < 10 -15 ocorre incremento da condutividade devido ao surgimento de condução eletrônica como conseqüência da redução Ce ) / (po2 = 0, 14) ], onde é a condutividade elétrica total medida na respectiva pressão parcial de oxigênio (índice correspondente). Considerando a situação ideal, isto é, aquela na qual não ocorre redução, r seria igual a 1.…”

Section: Espectroscopia De Impedânciaunclassified

Efeito de íons aliovalentes nas propriedades elétricas de céria dopada com ítria

Godoi

Souza

2008

Matéria (Rio J.)

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A alta temperatura de operação da PaCOS pode causar a formação de fases resistivas isolantes na interface eletrólito-catodo o que contribui para a perda de eficiência da pilha, podendo-se citar como exemplo a formação de zirconatos na interface manganita de lantânio dopada com estrôncio (LSM) -zircônia estabilizada com ítria (ZEI). Outro aspecto importante em PaCOS é o uso de material de eletrólito com uma condutividade iônica maior do que a da zircônia em temperaturas mais baixas. Essa característica é importante para a redução da temperatura de operação da PaCOS minimizando os problemas relacionados com a alta temperatura de operação, sendo Céria dopada com ítria (CY) um exemplo desse tipo de material. Por isso, para o uso de CY como eletrólito em PaCOS é importante avaliar a possibilidade de formação de fase isolante envolvendo esse material e o material do catodo, como perovskitas de lantânio. Para avaliar possíveis reações entre céria dopada com ítria e dois tipos de perovskitas usadas como catodo, LSM and LSCF, foi realizado, neste trabalho, a dopagem de CY com dois conjuntos de íons: La, Sr, Mn e La, Sr, Fe, Co. A dopagem provocou aumento da condutividade elétrica do grão enquanto que a condutividade efetiva do contorno de grão decresceu. Contudo a condutividade total não foi comprometida com a dopagem. A dopagem com La, Mn e Sr forneceu amostra de Céria dopada com Itria mais estáveis em alta temperatura e atmosfera redutora.Palavras-chaves: céria dopada com ítria, perovskita de lantânio, propriedades elétricas, microestrutura. Effect of aliovalent ions on the electrical properties of Yttria doped Ceria ABSTRACTThe high operating temperature of SOFCs can produces the formation of insulating interphases in the electrolyte-cathode interface contributing for the efficiency loss. As an example, there is the formation of zirconates in the interface strontium doped lanthanum manganite (LSM) -yttria stabilized zirconia (YSZ). Another important aspect in SOFCs concerns to the use of an electrolyte material with a higher ionic conductivity at lower temperatures than that of YSZ. Yttria doped ceria (CY) is an example of this kind of material. This feature is important to reduce the operating temperature of SOFC minimizing the problems related to their high operating temperature. Therefore, if one intends to use CY as an electrolyte in SOFC it is important to evaluate the possibility of any insulating phase formation involving this material and the cathode material, as doped lanthanum perovskites. To verify possible deleterious reactions between yttria doped ceria and two kinds of perovskites cathode, LSM and LSCF, in this work CY composition was doped with two set of ions: La, Sr, Mn and La, Sr, Fe, Co. The doping increased the grain electrical conductivity while the effective grain boundary conductivity decreased, for both set of dopant. Although, the total electrical conductivity stayed almost constant. The La, Mn, Sr doped sample was more stable at high temperature compared with the undoped CY composition.

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“…CeO 2 nanocrystals and their solid solutions that are substituted with Fe 3+ ions have been prepared by various methods such as sol-gel [4], hydrothermal synthesis [5], conventional mixed-oxide method [6] and ball--milling process [7]. It was found that ferromagnetic and photocatalytic properties as well as grain growth stabilization at higher temperatures can be significantly improved by doping CeO 2 nanocrystals with transition metal elements such as Fe [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

“…It was found that ferromagnetic and photocatalytic properties as well as grain growth stabilization at higher temperatures can be significantly improved by doping CeO 2 nanocrystals with transition metal elements such as Fe [7][8][9]. But still one of the major challenges for the preparation techniques remains the precise control of particle size.…”

Section: Introductionmentioning

confidence: 99%

Hydrothermal Synthesis of CeO₂and Ce_0.9Fe_0.1O₂Nanocrystals

Radović¹,

Dohčević‐Mitrović²,

Golubović³

et al. 2009

Acta Phys. Pol. A

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Pure and 10 mol% Fe 3+ doped CeO2 nanocrystals were synthesized by hydrothermal method using two different basic solutions (NH4OH and NaOH). All the samples were calcinated at 140• C and 200• C. The characterization of crystalline structure, vibrational and optical properties was performed using X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. The obtained results showed that the Fe-doped samples are solid solutions with different size of nanocrystals, very dependent on the synthesis temperature and type of basic solution. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas doping provokes a small decrease of optical absorption edge in comparison with pure ceria.

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Final-stage sintering behavior of Fe-doped CeO2

Cited by 55 publications

References 18 publications

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Efeito de íons aliovalentes nas propriedades elétricas de céria dopada com ítria

Hydrothermal Synthesis of CeO₂and Ce_0.9Fe_0.1O₂Nanocrystals

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Final-stage sintering behavior of Fe-doped CeO2

Cited by 55 publications

References 18 publications

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Low Temperature Constrained Sintering of Cerium Gadolinium OxideFilms for Solid Oxide Fuel Cell Applications

Efeito de íons aliovalentes nas propriedades elétricas de céria dopada com ítria

Hydrothermal Synthesis of CeO2and Ce0.9Fe0.1O2Nanocrystals

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Hydrothermal Synthesis of CeO₂and Ce_0.9Fe_0.1O₂Nanocrystals