Sintering Analysis of Undoped and Cobalt Oxide Doped Ceria Solid Solutions

Jud, Eva; Huwiler, Christoph; Gauckler, Ludwig J.

doi:10.1111/j.1551-2916.2005.00567.x

Cited by 103 publications

(66 citation statements)

References 39 publications

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“…TEM and/or dilatometry results on Fe [47], Mn [16], and Co doped CGO [4,41] suggest that, at least during the initial stages of sintering, a liquid-like intergranular film forms which helps densify the ceramic. For Fe doped CGO, the liquid-like intergranular film allows the constrained film to sinter at temperatures as low as 1000C [5].…”

Section: The Reason This Third Option Work Is Because As Originallymentioning

confidence: 99%

“…Using this Vegard's Slope analysis, lithium was predicted to be a good CGO sintering aid and experiments revealed that despite the fact that pure nano-sized CGO requires 1200C to reach full density, nanosized CGO doped with as little as 3mol% lithium nitrate could be sintered to 98.5% density at the record low temperature of 800C. In the literature there is currently a debate over whether CGO sintering aids act by increasing mass transport in the grain boundary cores through the formation of liquids/sub-eutectic intergranular films [4,41], or whether they act in the space charge layers within the grains through an alteration of the grain boundary oxygen vacancy concentration [16,20]. This chapter presents data indicating that a liquid phase sintering mechanism is active in lithium nitrate doped CGO.…”

Section: Introductionmentioning

confidence: 99%

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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: The Reason This Third Option Work Is Because As Originallymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Nicholas

2007

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“…This results in lower sintering temperatures and consequently in a fine-grained microstructure. 15 Transition metal oxides, such as cobalt oxide as additives, seem not only to promote densification, but also to enhance grain growth. The comparison of cobalt oxide doped CeO 2 to undoped CeO 2 reveals larger grain sizes at all dwell temperatures upon doping.…”

Section: -6mentioning

confidence: 99%

Grain Growth of Micron-Sized Grains in Undoped and Cobalt Oxide Doped Ceria Solid Solutions

Jud

Huwiler

Gauckler

2006

J. Ceram. Soc. Japan

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Isothermal grain growth experiments have been conducted for undoped as well as cobalt oxide doped CeO 2 and Ce 0.8 Gd 0.2 O 1.9 CGO20 . Due to the solute drag effect of the dissolved gadolinium ions, the grain boundary mobility of CGO20 was significantly lower than that one of CeO 2 . The addition of cobalt oxide increases the grain boundary mobility of CGO20. This increase is assigned to the formation of a characteristic cobalt oxide rich grain boundary film. In undoped and cobalt oxide doped CGO20, a transition from regular grain growth at high temperature in micron-sized grains to self-limited grain growth at low temperature in nanometer-sized grains occurs. As a consequence, highly stable microstructures result at lower temperatures. It is suggested that strain in amorphous grain boundary films becomes important for the self limited grain growth for very small grains at low temperatures.

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“…Complexions V and VI are often structurally disordered, in which case they can be broadly grouped by the term "disordered intergranular films." These interfacial films are thought to be responsible for activated sintering in ceramics [3][4][5] and refractory metals [6,7]. Similarly, the change of grain boundary mobility resulting from transitions between different complexion types can be used to understand abnormal grain growth in some materials [2,[8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Effect of grain boundary character on segregation-induced structural transitions

Pan

Rupert

2016

Phys. Rev. B

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Segregation-induced structural transitions in metallic grain boundaries are studied with hybrid atomistic Monte Carlo/molecular dynamics simulations using Cu-Zr as a model system, with a specific emphasis on understanding the effect of grain boundary character. With increasing global composition, the six grain boundary types chosen for this study first form ordered complexions, with the local segregation pattern depending on the grain boundary core structure, then transform into disordered complexions when the grain boundary composition reaches a critical value that is temperature dependent. The tendency for this transition to a disordered interfacial structure consistently depends on the relative solute excess, instead of the grain boundary energy or misorientation angle. Grain boundaries with high relative solute excess go through gradual disordering transitions, whereas those with low relative solute excess remain ordered until high global Zr concentrations but then abruptly transform into thick disordered films.The results presented here provide a clear picture of the effect of interface character on both dopant segregation patterns and disordered intergranular film formation, showing that all grain boundaries are not equal when discussing complexion transitions.2

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Sintering Analysis of Undoped and Cobalt Oxide Doped Ceria Solid Solutions

Cited by 103 publications

References 39 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

Grain Growth of Micron-Sized Grains in Undoped and Cobalt Oxide Doped Ceria Solid Solutions

Effect of grain boundary character on segregation-induced structural transitions

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