Direct measurement of interface energies of magnesium aluminate spinel and a brief sintering analysis

Pereira, Gilberto José; Bolis, Karen; Muche, Dereck N.F.; Gouvêa, Douglas; Castro, Ricardo H. R.

doi:10.1016/j.jeurceramsoc.2017.05.035

Cited by 15 publications

(17 citation statements)

References 44 publications

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“…As indicated by the calculations of Cai et al, the proportion of MgO surface termination significantly increases the surface energy, which can explain the higher surface energy observed by Mordekovitz and Hayun, because their measurements indicated the median energies. Both results are in accordance with our previous observations of the surface energy and the surface lixiviation in this study . However, interestingly, Al excess reduces the MgAl 2 O 4 surface energy and can promote preferential formation of Al 2 O 3 termination or the auto‐segregation of Al ions on MgAl 2 O 4 .…”

Section: Resultssupporting

confidence: 93%

“…Both results are in accordance with our previous observations of the surface energy and the surface lixiviation in this study. 25 However, interestingly, Al excess reduces the MgAl 2 O 4 surface energy 34 and can promote preferential formation of Al 2 O 3 termination or the auto-segregation of Al ions on MgAl 2 O 4 . The argument agrees with the results presented in Table 3 that shows a very low lithium or magnesium oxides occupancy and demonstrating that surfaces are dominated by 111_O 2 (Al) termination.…”

Section: Surface Excess Characterizationmentioning

confidence: 99%

“…However, the separation of the kinetic and thermodynamic contributions is difficult with the addition of additives to the material, which are usually seen as physical barriers reducing the GB mobility and are mostly studied as kinetic phenomena. With the advancements of calorimetric techniques for the measurement of the interface energy of nanoparticles, it is possible to show that the surface energy does not remain constant with an increase in the doping content; thus, the nanostability is partially attributed to thermodynamic effects …”

Section: Introductionmentioning

confidence: 99%

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Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

et al. 2019

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Manufacturing nanoceramics is challenging owing to the instability of the grain size resulting from the high driving force toward growth associated with the interfaces. Nanometric ceramics of some oxides have exceptional mechanical and optical properties, eg, magnesium aluminate spinel (MgAl 2 O 4 ). The production of these fully conformed ceramics requires a precursor powder, which generally contains sintering-promoting additives. Li salts are typically used as sintering promoters for MgAl 2 O 4 , but the interface stability associated with the segregation of the additive is poorly understood. In this study, MgAl 2 O 4 samples containing 0-2.86 mol% Li ions were synthesized via a simultaneous-precipitation method in an ethylic medium and subsequently calcined at 800°C in air. The nanopowders exhibited only the MgAl 2 O 4 phase, and the crystallite size was determined by the Li 2 O concentration. The crystallite size was changed via the chemical modification of the interfaces by the segregation of Li ions. The solubility in the bulk material was very low at the fabrication temperature, and small amounts of Li ions saturated the bulk material and segregated to the grain boundaries (GBs), significantly stabilizing the grain-grain interface compared with the surface. The resulting powder was then aggregated further owing to the initial stage of sintering. The surface excess obtained via the selective lixiviation method confirmed that the segregation to the GBs was greater than that to the surface. Energetics calculations confirmed these results, indicating a high enthalpy of segregation at the GBs (ΔH segr GB = −52.0 kJ∕mol) compared with that at the surfaces (ΔH segr s = −31.5 kJ/mol). The enthalpy of segregation together with theinterface excess allowed us to estimate the reduction in the interface energy with Li + segregation of 0.8% to the surface and 11.2% to the GBs. The Li + segregation to the surfaces started by Al 3+ substitution, and for powders with ≥1.8 mol% Li ions, Mg +2 was preferentially substituted at the surfaces.

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Section: Resultssupporting

confidence: 93%

Section: Surface Excess Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

et al. 2019

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“…The presence of GBFs (or more general-GB complexions) strongly influences the grain growth as well as GB character distribution in oxides and metallic alloys [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130][151][152][153][154][155][156][157][158][159][160]. It has been known for a long time that impurities can shift the borders between GBs with special and general structure and properties [142,143,220,221].…”

Section: Discussionmentioning

confidence: 99%

“…As a result, one can measure the thermal effect of GB phase transitions with the aid of a DSC [114,[148][149][150]. DSC also permits to observe the indications of GB phase transformations in nanocrystalline ceramics [151][152][153][154][155][156][157][158][159][160]. The GB phase transformations can also lead to abnormal grain growth and radical changes in the GB character distribution [54,[56][57][58][59]63,75,76,79,80,83,106,[123][124][125][126][127][128][129][130]151,[154][155][156][157][158][159].…”

Section: Introductionmentioning

confidence: 99%

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

Kogtenkova

Straumal

Korneva

et al. 2018

Metals

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High-pressure torsion has been used to obtain the ultra-fine grained (UFG) state with a high specific area of grain boundaries (GBs) in Al-Zn, Al-Mg, Cu-Ag, Cu-Co, and Cu-Ni solid solutions with face-centered cubic (fcc) lattices. The UFG samples were heated in a differential scanning calorimeter (DSC). Small endothermic peaks in the DSC curves were observed in the one-phase solid-solution area of the respective phase diagrams, i.e., far away from the bulk solidus and solvus lines. A possible explanation of these endothermic peaks is based on the hypothesis of phase transformations between GB complexions. This hypothesis has been supported by observations with transmission electron microscopy and electron backscattering diffraction. The new lines of GB phase transformations have been constructed in the Al-Zn, Al-Mg, Cu-Ag, Cu-Co, and Cu-Ni bulk phase diagrams.

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Two‐Photon Polymerization of Nanocomposites for Additive Manufacturing of Transparent Magnesium Aluminate Spinel Ceramics

Prediger,

Sriyotha,

Schell

et al. 2024

Advanced Science

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Transparent polycrystalline magnesium aluminate (MAS) spinel ceramics are of great interest for industry and academia due to their excellent optical and mechanical properties. However, shaping of MAS is notoriously challenging especially on the microscale requiring hazardous etching methods. Therefore, a photochemically curable nanocomposite is demonstrated that can be structured using high‐resolution two‐photon lithography. The printed nanocomposites are converted intro transparent MAS by subsequent debinding, sintering, and hot isostatic pressing. The resulting transparent spinel ceramics exhibit a surface roughness Sq of only 10 nm and can be shaped with minimum feature sizes of down to 13 µm. This technology will be important for the production of microstructured ceramics used for optics, photonics, or photocatalysis.

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Direct measurement of interface energies of magnesium aluminate spinel and a brief sintering analysis

Cited by 15 publications

References 44 publications

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

Two‐Photon Polymerization of Nanocomposites for Additive Manufacturing of Transparent Magnesium Aluminate Spinel Ceramics

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Direct measurement of interface energies of magnesium aluminate spinel and a brief sintering analysis

Cited by 15 publications

References 44 publications

Li2O‐doped MgAl2O4 nanopowders: Energetics of interface segregation

Li2O‐doped MgAl2O4 nanopowders: Energetics of interface segregation

Grain Boundary Complexions and Phase Transformations in Al- and Cu-Based Alloys

Two‐Photon Polymerization of Nanocomposites for Additive Manufacturing of Transparent Magnesium Aluminate Spinel Ceramics

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Product

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Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation

Li₂O‐doped MgAl₂O₄ nanopowders: Energetics of interface segregation