Enhanced sinterability of mechanical alloyed La9.33Si2Ge4O26 oxyapatite powders for IT-SOFC electrolytes

Serra, R.; Alves, C.F. Almeida; Oliveira, Fernando A. Costa; Marcelo, Teresa; Mascarenhas, João; Trindade, B.

doi:10.1016/j.ceramint.2012.03.042

Cited by 17 publications

(7 citation statements)

References 26 publications

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“…The substitution of Si ions by Ge ions has been found to decrease sintering temperatures and improve electrical conductivities. 19), 20) As reported in the literature, 19), 20) the electrical conductivities of La 10 …”

Section: Introductionsupporting

confidence: 50%

Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

Wang

Chen

Hsu

et al. 2015

J. Ceram. Soc. Japan

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In this study, the effects of various amounts of Ga 3+ dopants on the densification, phase structure, microstructure and electrical conductivity of La 9.5 Ge 6.0 O 26.25 ceramics are examined. The incorporation of Ga 3+ ions into the La 9.5 Ge 6.0 O 26.25 lattices leads to the retardation of the densification and an increase in the triclinic structure, caused by the evaporation of GeO 2 and the largeness of the size difference between the Ga 3+ ions and Ge 4+ ions. Of the compositions studied, the La 9.5 Ge 5.7 Ga 0.3 O 26.1 ceramic sintered at 1450°C shows an electrical conductivity of 4.02 © 10 ¹2 Scm ¹1 at 800°C, which is higher than that of an 8YSZ ceramic. The

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Section: Introductionsupporting

confidence: 50%

Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

Wang

Chen

Hsu

et al. 2015

J. Ceram. Soc. Japan

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“…The electrical conductivity of La 9.33 Ge 6 O 26 ceramic at 800°C was reported to be 0.01 S/cm, which is much higher than that of La 9.33 Si 6 O 26 (2.02 × 10 −3 S/cm) . However, lanthanum germanate apatites often encounter the downside of GeO 2 volatilization at high temperatures, leading to the formation of another conducting phase, La 2 GeO 5 . It has been reported in the literature that a triclinic apatite phase exists in the La‐Ge‐O phase diagram .…”

Section: Introductionmentioning

confidence: 99%

“…An approach to resolve the barrier is to utilize the germanium‐containing apatites, such as La 10− y Ge 6 O 26±δ, instead of silicon‐based apatites, to reduce the sintering temperature . The replacement of Si ions by Ge ions was found not only to decrease their sintering temperatures, but also to improve their electrical conductivities . The electrical conductivity of La 9.33 Ge 6 O 26 ceramic at 800°C was reported to be 0.01 S/cm, which is much higher than that of La 9.33 Si 6 O 26 (2.02 × 10 −3 S/cm) .…”

Section: Introductionmentioning

confidence: 99%

Effects of La content on the densification, microstructure, and conductivity of doped La_10−xGe₆O_26±δ electrolytes

Wang

Liu

Hsu

et al. 2016

Int J Applied Ceramic Tech

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In this study, the influence of La content on the characteristics of Nb‐, Mo‐, and W‐doped LaxGe6O26±δ electrolytes was investigated through sintering study, X‐ray diffraction, scanning electron microscopy, and conductivity measurement. The densification of LaxGe5.5Nb0.5O26±δ and LaxGe5.5W0.5O26±δ was retarded as the x reached 9.75, while that of LaxGe5.5Mo0.5O26±δ improved with increasing La content. The average grain size slightly increased and weight loss due to evaporation of GeO2 significantly reduced with increasing La content, ranging from 1.39% to 0.26%. Among the systems studied, La9.33Ge5.5Nb0.5O26.245, La9.33Ge5.5Mo0.5O26.045, and La9.50Ge5.5W0.5O26.75 electrolytes revealed great potential for use in SOFC applications.

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“…However, traces of a second phase (La 4 GeO 8 ) were detected after sintering. This phase was already referred in previous work [3]. Figure 1 shows the morphology of the two samples obtained by SEM and AFM as well as the corresponding particles size distributions.…”

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confidence: 98%

Effect of the sintering conditions on the morphology of La_9.33Si₂Ge₄O₂₆ oxyapatite for SOFCs electrolytes

et al. 2013

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Solid oxide fuel cells (SOFCs) are devices that allow direct conversion of chemical to electrical energy through an electrochemical reaction in a cleaner and more efficient way than conventional processes (eg. gas turbines) [1]. They are characterized by the use of a solid oxide material as the electrolyte. Yttria-stabilised zirconia (YSZ) has traditionally been used in SOFCs electrolytes at temperatures in the range of 850-1000 °C. Recent research is being focused on the development of new materials with increased ionic conductivity at intermediate temperatures (500-800ºC) as alternative materials to YSZ. Rare earth silicates with an apatite-type structure, such as doped lanthanum oxides of general formula La ( 10 MO 4 ) 6 O 2 , where M = Ge, Co, Si, Al, or P, are among these materials [2]. The major limitation associated with the manufacture of these materials is their poor sinterability, which requires high sintering temperatures (1600ºC).The present work concerns the production of La 9.33 Si 2 Ge 4 O 26 dense materials from La 2 O 3 (99.9%), SiO 2 (99.4%) and GeO 2 (99.9%) powders by mechanical alloying (MA) followed by conventional and microwave hybrid sintering at 1350ºC. Dry mechanical milling was carried out in protective atmosphere (argon at 200 kPa) by using a rotating speed of 350 rpm for 15h. Prior to the synthesis of the La 9.33 Si 2 Ge 4 O 26 mixture, the starting materials were milled separately at 350 rpm in argon at 50 kPa in order to achieve low particle size distributions with a greater ability for sintering. The MA mixture was compacted by uniaxial pressing at 390 MPa followed by sintering for 1 h at 1350 °C. Density of the La 9.33 Si 2 Ge 4 O 26 pellets was determined by the boiling test method. SEM/EDS, XRD and atomic force microscopy (AFM) were used for samples characterization.The bulk densities and the open porosities of the pellets (EF and MW for conventional and microwave hybrid sintering, respectively) are presented in Table 1. Dense pellets were obtained in both cases. However, sample MW showed higher density and, consequently, lower porosity than sample EF. Both mechanically alloyed samples are formed by an apatite phase. This phase remains stable during sintering. However, traces of a second phase (La 4 GeO 8 ) were detected after sintering. This phase was already referred in previous work [3]. Figure 1 shows the morphology of the two samples obtained by SEM and AFM as well as the corresponding particles size distributions. The sintered samples were as-polished and thermal etched in air at 1300 ºC, for 10 min., for detailed microstructural observation. SEM images at low amplification confirm that sample EF is more porous than sample MW (Figure 1 (a) and (b), respectively). Although the same sintering temperature was used in both sintering processes, sample MW has a coarser grain size (Figure 1 (c) to (f)). This feature was already been reported in previous work [4]. Mean values of 0.9 and 1.9 μm were determined for samples EF and MW, respectively.As conclusion, one may say that mic...

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Enhanced sinterability of mechanical alloyed La9.33Si2Ge4O26 oxyapatite powders for IT-SOFC electrolytes

Cited by 17 publications

References 26 publications

Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

Effects of La content on the densification, microstructure, and conductivity of doped La_10−xGe₆O_26±δ electrolytes

Effect of the sintering conditions on the morphology of La_9.33Si₂Ge₄O₂₆ oxyapatite for SOFCs electrolytes

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Enhanced sinterability of mechanical alloyed La9.33Si2Ge4O26 oxyapatite powders for IT-SOFC electrolytes

Cited by 17 publications

References 26 publications

Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

Gallium-doped lanthanum germanates as electrolyte material of solid oxide fuel cells

Effects of La content on the densification, microstructure, and conductivity of doped La10−xGe6O26±δ electrolytes

Effect of the sintering conditions on the morphology of La9.33Si2Ge4O26 oxyapatite for SOFCs electrolytes

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Effects of La content on the densification, microstructure, and conductivity of doped La_10−xGe₆O_26±δ electrolytes

Effect of the sintering conditions on the morphology of La_9.33Si₂Ge₄O₂₆ oxyapatite for SOFCs electrolytes