Synthesis of nanostructured materials in supercritical ammonia: nitrides, metals and oxides

Desmoulins-Krawiec, Sophie; Aymonier, Cyril; Loppinet-Serani, Anne; Weill, François; Gorsse, Stéphane; Étourneau, J.; Cansell, François

doi:10.1039/b310806f

Cited by 78 publications

(38 citation statements)

References 24 publications

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“…We assume that the crystal structure varies upon the replacement of O atoms by N atoms, leading to the expansion in the mesostructural domain size. Several kinds of cobalt nitrides have been reported (CoN, [4,7,34] Co 2 N, [4,7,35] Co 3 N, [4,6,7,9] Co 4 N, [4,6,8] and Co 3 N 2 [36] ), but only CoN is recorded in our ammonia nitridation process. In general, CoN has two kinds of crystal forms, namely zinc blende (ZB) structure with the F43m symmetry and rock salt (RS) structure with Fm3m space group.…”

Section: Mesoporous Con Materialsmentioning

confidence: 99%

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

Shi

Wan

Zhang

et al. 2008

Adv Funct Materials

102

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Herein, we demonstrate an ammonia nitridation approach to synthesize self‐supported ordered mesoporous metal nitrides (CoN and CrN) from mesostructured metal oxide replicas (Co3O4 and Cr2O3), which were nanocastly prepared by using mesoporous silica SBA‐15 as a hard template. Two synthetic routes are adopted. One route is the direct nitridation of mesoporous metal oxide nanowire replicas templated from SBA‐15 to metal nitrides. By this method, highly ordered mesoporous cobalt nitrides (CoN) can be obtained by the transformation of Co3O4 nanowire replica under ammonia atmosphere from 275 to 350 °C, without a distinct lose of the mesostructural regularity. Treating the samples above 375 °C leads to the formation of metallic cobalt and the collapse of the mesostructure due to large volume shrinkage. The other route is to transform mesostructured metal oxides/silica composites to nitrides/silica composites at 750–1000 °C under ammonia. Ordered mesoporous CrN nanowire arrays can be obtained after the silica template removal by NaOH erosion. A slowly temperature‐program‐decrease process can reduce the influence of silica nitridation and improve the purity of final CrN product. Small‐angle XRD patterns and TEM images showed the 2‐D ordered hexagonal structure of the obtained mesoporous CoN and CrN nanowires. Wide‐angle XRD patterns, HRTEM images, and SAED patterns revealed the formation of crystallized metal nitrides. Nitrogen sorption analyses showed that the obtained materials possessed high surface areas (70–90 m2 g−1) and large pore volumes (about 0.2 cm3 g−1).

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Section: Mesoporous Con Materialsmentioning

confidence: 99%

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

Shi

Wan

Zhang

et al. 2008

Adv Funct Materials

102

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“…Not only water, but solvent mixtures like ammonia/methanol, H 2 O/ethanol, or ethanol/CO 2 have also been used. [23][24][25][26] A common feature of these boehmite studies is the determination of the size and morphology by ex situ characterization of the final product, mainly by transmission electron microscopy (TEM) sometimes supplemented by powder X-ray diffraction (PXRD) for phase determination. Furthermore, the variation in particle morphology with synthesis conditions has been explained by thermodynamic calculations.…”

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confidence: 99%

In Situ High‐Energy Synchrotron Radiation Study of Boehmite Formation, Growth, and Phase Transformation to Alumina in Sub‐ and Supercritical Water

Lock¹,

Bremholm²,

Christensen³

et al. 2009

Chemistry A European J

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Boehmite (AlOOH) nanoparticles have been synthesized in subcritical (300 bar, 350 degrees C) and supercritical (300 bar, 400 degrees C) water. The formation and growth of AlOOH nanoparticles were studied in situ by small- and wide-angle X-ray scattering (SAXS and WAXS) using 80 keV synchrotron radiation. The SAXS/WAXS data were measured simultaneously with a time resolution greater than 10 s and revealed the initial nucleation of amorphous particles takes place within 10 s with subsequent crystallization after 30 s. No diffraction signals were observed from Al(OH)(3) within the time resolution of the experiment, which shows that the dehydration step of the reaction is fast and the hydrolysis step rate-determining. The sizes of the crystalline particles were determined as a function of time. The overall size evolution patterns are similar in sub- and supercritical water, but the growth is faster and the final particle size larger under supercritical conditions. After approximately 5 min, the rate of particle growth decreases in both sub- and supercritical water. Heating of the boehmite nanoparticle suspension allowed an in situ X-ray investigation of the phase transformation of boehmite to aluminium oxide. Under the wet conditions used in this work, the transition starts at 530 degrees C and gives a two-phase product of hydrated and non-hydrated aluminium oxide.

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“…The growth of Ga 2 O 3 may not be preferential in a-Ti alloy because of the Ga concentration at the interface; the Gibbs free energies of oxide formation according to Ellingham diagrams are À530 kJ/mol for Ga 2 O 3 , À660 kJ/mol for TiO 2 , and À830 kJ/mol for Al 2 O 3 at 1000 K (727°C). [40] The pure components of Al 2 O 3 and Ga 2 O 3 are stable phases in air from their melting points to room temperature. [41] In addition, according to the phase relationship in the Ga 2 O 3 -Al 2 O 3 -TiO 2 system at 1673 K (1400°C), a continuous solid solution exists between Ga 2 TiO 5 and Al 2 TiO 5 .…”

Section: Resultsmentioning

confidence: 99%

Effects of Ga and Sn Additions on the Creep Strength and Oxidation Resistance of Near-α Ti Alloys

Kitashima

Yamabe‐Mitarai

Iwasaki

et al. 2016

Metall Mater Trans A

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The effects of Ga and Sn additions, with an almost constant value regarding Al equivalence, on the creep properties and oxidation resistance of the near-a Ti alloy Ti-5Al-4Zr-1Mo were investigated. The creep strain rate increased due to the replacement of Sn with Ga, which was accompanied by an increase in the volume fraction of primary equiaxed a phase. In addition, the replacement of Sn with Ga decreased the activation energy of the steady-state creep rate for the similar volume fraction of the equiaxed a phase. Ga addition improved the oxidation resistance without Ga segregation at the TiO 2 /substrate interface, whereas Sn promoted oxide spallation with metallic Sn segregation at the interface. Ga uniformly dissolved into the internal TiO 2 and into the external Al 2 O 3 as a result of solid solution formation between Ga 2 O 3 and the aforementioned oxides, which suppressed oxide growth. The formation of (GaAl) 2 TiO 5 in TiO 2 and Al 2 O 3 was also discussed on the basis of the phase relationships in the TiO 2 -Al 2 O 3 -Ga 2 O 3 system.

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Synthesis of nanostructured materials in supercritical ammonia: nitrides, metals and oxides

Cited by 78 publications

References 24 publications

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

In Situ High‐Energy Synchrotron Radiation Study of Boehmite Formation, Growth, and Phase Transformation to Alumina in Sub‐ and Supercritical Water

Effects of Ga and Sn Additions on the Creep Strength and Oxidation Resistance of Near-α Ti Alloys

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