Study of the behavior in oxidation at high temperature of Ni, Co and Fe-base alloys containing very high fractions of carbides

International audienceNine cast alloys reinforced by very high fractions of carbides, Ni-30Cr-xC, Co-30Cr-xC and Fe-30Cr-xC with x varying from 1.2 to 2.0, were tested in oxidation at high temperature between 1,000 and 1,200°C in air for 50 hours. After oxidation, their surfaces and sub-surfaces were characterized. Even for very high carbon contents, the chromia-forming behaviour of the nickel alloys is kept. The oxidation modes of the cobalt alloys and iron alloys are not changed compared to low carbon alloys of these families. The differences of diffusion easiness of chromium in matrix, between nickel alloys, cobalt alloys and iron alloys are the same as for alloys with lower carbon contents, as suggested by the lower chromium gradients in the nickel alloys compared to the two other alloy types. Sub-surface microstructure transformations due to oxidation were observed in some cases (coarsening of carbides due to an inwards diffusion of carbon, change of the sharing between BCC-FCC of iron matrix due to outwards diffusion of chromium). Catastrophic oxidation never occurred for these alloys during the 50 hours of exposition to air at high temperature

High temperature microstructures of ternary Co-30wt.% Cr - based alloys over the [0 to 2.0wt.%] carbon range

International audienceThe Co-30wt.%-xC system was experimentally explored from x=0 to 2wt.%, by considering the stable microstructures at 1,000, 1,100 and 1,200°C, and the intervals of fusion. The strengthening potential and the refractoriness of several alloys belonging to this family were specified. Such simple alloys are able to display simultaneously a high amount of chromium for limiting hot corrosion, solidus temperatures as high as 1,300 °C and refractory carbides fractions that can reach 20 % in volume. Natures and fractions of carbides, and solidus temperatures were in good agreements with thermodynamic calculations. Inversely the measured liquidus temperatures were significantly higher than the calculated ones. In addition, thermodynamic modeling allowed to better interpret the disappearance of carbides due to oxidation at high temperature

Supramolecular Anchoring of Octahedral Molybdenum Clusters onto Graphene and Their Synergies in Photocatalytic Water Reduction

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/10.1021/acs.inorgchem.9b02529"[EN] Dihydrogen (H-2) production from sunlight should become one of the most important energy production means in the future. To reach this goal, low-cost and efficient photocatalysts still need to be discovered. Here we show that red near-IR luminescent metal cluster anions, once combined with pyrene-containing cations, are able to photocatalytically produce molecular hydrogen from water. The pyrene moieties act simultaneously as energy transmitters and as supramolecular linkers between the cluster anions and graphene. This association results in a hybrid material combining the emission abilities of pyrene and cluster moieties with the electronic conduction efficiency of graphene. Hydrogen evolution reaction (HER) studies show that this association induces a significant increase of H 2 production compared to that produced separately by clusters or graphene. Considering the versatility of the strategy described to design this photocatalytic hybrid material, transition-metal clusters are promising candidates to develop new, environmentally friendly, and low-cost photocatalysts for HER.The Severo Ochoa Program (SEV-2016-0683), Ministerio de Ciencia, Innovation y Universidades (PGC2018-099744), Consejo Superior de Investigaciones Cientificas (I-Link1063), and University of Rennes are thanked for financial support. We thank Dr. Marta Puche for her technical assistance with the preparation of dispersed graphene solutions at the ITQ.Feliz Rodriguez, M.; Atienzar Corvillo, PE.; Amela-Cortes, M.; Dumait, N.; Lemoine, P.; Molard, Y.; Cordier, S. (2019). Supramolecular Anchoring of Octahedral Molybdenum Clusters onto Graphene and Their Synergies in Photocatalytic Water Reduction. Inorganic Chemistry. 58(22):15443-15454. https://doi.org/10.1021/acs.inorgchem.9b02529S1544315454582

Contribution à l'étude des propriétés structurales et magnétiques de composés intermétalliques isotypes de CeScSi et Th6Mn23

The structural and electronic properties study of the RMgSn and RMgPb (R = rare-earth) series allowed to show that the great stability of the CeScSi-type is related to strong T X and R-X bonds and to good structure adaptation to the size of the element R. These series represent the first two examples of CeScSi-type compounds with antiferromagnetic behaviors characterized by complex modulated magnetic structures. The new RTiGeBx (R = Y, Gd-Tm, Lu) compounds crystallize in the YTiGeCx-type structure, a partially carbon filled CeScSi-type. They exhibit ferromagnetic ordering at high temperature locally perturbed by the boron atoms. For the first time, neutron diffraction experiments evidenced an antiferromagnetic order of the chromium sublattice in the ThCr2Si2 compound, while UCr2Si2 exhibits only an antiferromagnetic ordering of the uranium sublattice. The new UCr2Si2C compound crystallizes in the CeCr2Si2C-type and presents, on the contrary of the other RCr2Si2C, an antiferromagnetic order of the chromium sublattice. The new RCr3Si2C (R = Y, Gd-Tm, Lu, U) compounds crystallize in the new YCr3Si2C-type structure with the space group P6/mmm and cell parameters a ~ 9 Å et c ~ 4 Å. Electronic structure calculations allowed to explain the structural stability. In the field of the magnetic refrigeration, the study of the R6Mn23 (R = Gd-Tm) compounds has been undertaken. These materials exhibit a moderate magnetocaloric effect over a broad temperature range. Many substitutions showed that these characteristics can be easily adjusted.L'étude des propriétés structurales et électroniques des séries RMgSn et RMgPb (R = terre rare) a montré que la grande stabilité du type CeScSi est liée aux liaisons fortes T-X et R-X et à une bonne adaptation de la structure à la taille de l'élément R. Ces séries sont les premières isotypes de CeScSi à comportements antiferromagnétiques caractérisés par des structures complexes modulées en amplitude. Les nouveaux composés RTiGeBx (R = Y, Gd-Tm, Lu) cristallisent dans la structure YTiGeCx, une variante partiellement carburée de la structure CeScSi, et présentent une mise en ordre ferromagnétique à haute température localement perturbée par les atomes de bore. Par diffraction neutronique, la mise en ordre antiferromagnétique du sous-réseau de chrome dans le composé type ThCr2Si2 a été observée pour la première fois. UCr2Si2 ne présente quant à lui qu'une mise en ordre antiferromagnétique du sous-réseau d'uranium. Le nouveau carbure UCr2Si2C cristallise dans la structure CeCr2Si2C et présente, à l'inverse des autres RCr2Si2C, un ordre antiferromagnétique du sous-réseau de chrome. Les nouveaux composés RCr3Si2C (R = Y, Gd-Tm, Lu, U) cristallisent dans une nouvelle structure-type de groupe d'espace P6/mmm et de paramètres a ~ 9 Å et c ~ 4 Å. Des calculs de structures électroniques ont permis d'expliquer la stabilité de cette structure. Dans le contexte de la recherche sur la magnétoréfrigération, l'étude des composés R6Mn23 (R = Gd-Tm) a été entreprise. Ils présentent un effet magnétocalorique d'intensité modérée mais s'étendant sur un très large intervalle en température. De nombreuses substitutions montrent que ces caractéristiques peuvent être facilement ajustées

Contribution to the study of structural and magnetic properties of intermetallic compounds isotypes with CeScSi and Th6Mn23

L'étude des propriétés structurales et électroniques des séries RMgSn et RMgPb (R = terre rare) a montré que la grande stabilité du type CeScSi est liée aux liaisons fortes T-X et R-X et à une bonne adaptation de la structure à la taille de l'élément R. Ces séries sont les premières isotypes de CeScSi à comportements antiferromagnétiques caractérisés par des structures complexes modulées en amplitude. Les nouveaux composés RTiGeBx (R = Y, Gd-Tm, Lu) cristallisent dans la structure YTiGeCx, une variante partiellement carburée de la structure CeScSi, et présentent une mise en ordre ferromagnétique à haute température localement perturbée par les atomes de bore. Par diffraction neutronique, la mise en ordre antiferromagnétique du sous-réseau de chrome dans le composé type ThCr2Si2 a été observée pour la première fois. UCr2Si2 ne présente quant à lui qu'une mise en ordre antiferromagnétique du sous-réseau d'uranium. Le nouveau carbure UCr2Si2C cristallise dans la structure CeCr2Si2C et présente, à l'inverse des autres RCr2Si2C, un ordre antiferromagnétique du sous-réseau de chrome. Les nouveaux composés RCr3Si2C (R = Y, Gd-Tm, Lu, U) cristallisent dans une nouvelle structure-type de groupe d'espace P6/mmm et de paramètres a ~ 9 Å et c ~ 4 Å. Des calculs de structures électroniques ont permis d'expliquer la stabilité de cette structure. Dans le contexte de la recherche sur la magnétoréfrigération, l'étude des composés R6Mn23 (R = Gd-Tm) a été entreprise. Ils présentent un effet magnétocalorique d'intensité modérée mais s'étendant sur un très large intervalle en température. De nombreuses substitutions montrent que ces caractéristiques peuvent être facilement ajustées.The structural and electronic properties study of the RMgSn and RMgPb (R = rare-earth) series allowed to show that the great stability of the CeScSi-type is related to strong T X and R-X bonds and to good structure adaptation to the size of the element R. These series represent the first two examples of CeScSi-type compounds with antiferromagnetic behaviors characterized by complex modulated magnetic structures. The new RTiGeBx (R = Y, Gd-Tm, Lu) compounds crystallize in the YTiGeCx-type structure, a partially carbon filled CeScSi-type. They exhibit ferromagnetic ordering at high temperature locally perturbed by the boron atoms. For the first time, neutron diffraction experiments evidenced an antiferromagnetic order of the chromium sublattice in the ThCr2Si2 compound, while UCr2Si2 exhibits only an antiferromagnetic ordering of the uranium sublattice. The new UCr2Si2C compound crystallizes in the CeCr2Si2C-type and presents, on the contrary of the other RCr2Si2C, an antiferromagnetic order of the chromium sublattice. The new RCr3Si2C (R = Y, Gd-Tm, Lu, U) compounds crystallize in the new YCr3Si2C-type structure with the space group P6/mmm and cell parameters a ~ 9 Å et c ~ 4 Å. Electronic structure calculations allowed to explain the structural stability. In the field of the magnetic refrigeration, the study of the R6Mn23 (R = Gd-Tm) compounds has been undertaken. These materials exhibit a moderate magnetocaloric effect over a broad temperature range. Many substitutions showed that these characteristics can be easily adjusted

Contribution à l'étude des propriétés structurales et magnétiques de composés intermétalliques isotypes de CeScSi et Th6Mn23

L'étude des propriétés structurales et électroniques des séries RMgSn et RMgPb (R = terre rare) a montré que la grande stabilité du type CeScSi est liée aux liaisons fortes T-X et R-X et à une bonne adaptation de la structure à la taille de l'élément R. Ces séries sont les premières isotypes de CeScSi à comportements antiferromagnétiques caractérisés par des structures complexes modulées en amplitude. Les nouveaux composés RTiGeBx (R = Y, Gd-Tm, Lu) cristallisent dans la structure YTiGeCx, une variante partiellement carburée de la structure CeScSi, et présentent une mise en ordre ferromagnétique à haute température localement perturbée par les atomes de bore. Par diffraction neutronique, la mise en ordre antiferromagnétique du sous-réseau de chrome dans le composé type ThCr2Si2 a été observée pour la première fois. UCr2Si2 ne présente quant à lui qu'une mise en ordre antiferromagnétique du sous-réseau d'uranium. Le nouveau carbure UCr2Si2C cristallise dans la structure CeCr2Si2C et présente, à l'inverse des autres RCr2Si2C, un ordre antiferromagnétique du sous-réseau de chrome. Les nouveaux composés RCr3Si2C (R = Y, Gd-Tm, Lu, U) cristallisent dans une nouvelle structure-type de groupe d'espace P6/mmm et de paramètres a ~ 9 Å et c ~ 4 Å. Des calculs de structures électroniques ont permis d'expliquer la stabilité de cette structure. Dans le contexte de la recherche sur la magnétoréfrigération, l'étude des composés R6Mn23 (R = Gd-Tm) a été entreprise. Ils présentent un effet magnétocalorique d'intensité modérée mais s'étendant sur un très large intervalle en température. De nombreuses substitutions montrent que ces caractéristiques peuvent être facilement ajustées.The structural and electronic properties study of the RMgSn and RMgPb (R = rare-earth) series allowed to show that the great stability of the CeScSi-type is related to strong T X and R-X bonds and to good structure adaptation to the size of the element R. These series represent the first two examples of CeScSi-type compounds with antiferromagnetic behaviors characterized by complex modulated magnetic structures. The new RTiGeBx (R = Y, Gd-Tm, Lu) compounds crystallize in the YTiGeCx-type structure, a partially carbon filled CeScSi-type. They exhibit ferromagnetic ordering at high temperature locally perturbed by the boron atoms. For the first time, neutron diffraction experiments evidenced an antiferromagnetic order of the chromium sublattice in the ThCr2Si2 compound, while UCr2Si2 exhibits only an antiferromagnetic ordering of the uranium sublattice. The new UCr2Si2C compound crystallizes in the CeCr2Si2C-type and presents, on the contrary of the other RCr2Si2C, an antiferromagnetic order of the chromium sublattice. The new RCr3Si2C (R = Y, Gd-Tm, Lu, U) compounds crystallize in the new YCr3Si2C-type structure with the space group P6/mmm and cell parameters a ~ 9 Å et c ~ 4 Å. Electronic structure calculations allowed to explain the structural stability. In the field of the magnetic refrigeration, the study of the R6Mn23 (R = Gd-Tm) compounds has been undertaken. These materials exhibit a moderate magnetocaloric effect over a broad temperature range. Many substitutions showed that these characteristics can be easily adjusted.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

INFLUENCE DES CARBURES DE CHROME SUR LE COMPORTEMENT THERMODILATOMETRIQUE D'ALLIAGES TERNAIRES BASE NICKEL, BASE COBALT ET BASE FER A HAUTE TENEUR EN CARBONE

International audienceNine ternary alloys, based on Ni, Co or Fe, with 30wt.% Cr and three different carbon contents (1.2, 1.6 and 2.0wt.%C), were synthesized by foundry and their dilatometric behaviours were studied. All of them contain high carbides fractions (often more than 30%). The Ni alloys, the matrixes of which do not know changes, lead to expansion curves which are almost linear, except near 1200°C where the carbide network begins to stress the matrix in compression since thermal expansion is lower for carbides than for matrix. The matrix of the Co alloys resist more to this action of the carbides but the HCP → FCC matrix change may modify the thermal expansion behaviour. The BCC → FCC change induces a contraction in two of the Fe alloys, followed by a faster expansion and sometimes followed by a contraction near 1200°C. The microstructure anisotropy may also influence thermal expansion in some cases.Neuf alliages ternaires, basés sur le nickel, le cobalt ou le fer, contenant 30% de chrome et trois teneurs en carbone, 1,2%, 1,6% et 2% (en masse), ont été élaborés par fonderie et testés en dilatation thermique jusqu’à 1200°C. Ces alliages contiennent de fortes fractions de carbures, pouvant excéder 30% en masse. Les alliages base Ni, sans transformation de la matrice, se dilatent linéairement jusque vers 1200°C, température à laquelle le réseau de carbures, dont la dilatation thermique est moins grande, commence à comprimer la matrice. Les alliages base Co sont moins sensibles à cette action des carbures à l’approche de 1200°C, mais le changement de matrice HC CFC induit des modifications de comportement vers 900°C pour l’alliage à 1,2%C. Les alliages base Fe, très chargés en carbures (M23C6), ont leur comportement dilatométrique influencé par le changement de matrice CC CFC (contraction transitoire vers 900°C, suivi par une dilatation plus rapide). L’anisotropie microstructurale peut aussi induire une anisotropie pour le comportement dilatométrique

Microstructures at high temperature of Fe-30 wt.% Cr- x C Alloys with x varying from 0 to 2 wt.%

International audienc

On the Crystal Structures of the Polymorphs of Manganese(II) Chloride Tetrahydrate: alpha-MnCl2 center dot 4H(2)O and beta-MnCl2 center dot 4H(2)O

International audienceThe manganese(II) chloride tetrahydrate MnCl2 center dot 4H(2)O (alpha-form) crystallizes in the space group P2(1)/n with a = 6.1918(4) angstrom,b = 9.5230(6) angstrom,c = 11.1918(6) angstrom, beta = 99.757(3)degrees, and V = 650.37(7) angstrom(3)(Z = 4). A second polymorph of MnCl2 center dot 4H(2)O (beta-form) is mentioned in the literature to be isomorphous with FeCl2 center dot 4H(2)O but its crystal structure was never confirmed. In this study, we report for the first time on the crystal structure of this second polymorph of manganese(II) chloride tetrahydrate, beta-MnCl2 center dot 4H(2)O, using room temperature single-crystal X-ray diffraction. The beta-form crystallizes in space group P2(1)/c with a = 5.9893(5) angstrom,b = 7.2877(6) angstrom,c = 8.5838(7) angstrom, beta = 110.952(4)degrees, and V = 349.89(5) angstrom(3)(Z = 2), confirming that beta-MnCl2 center dot 4H(2)O is isotype to Fe(II)Cl-2 center dot 4H(2)O. To the best of our knowledge this is the first compound reported to crystallize in both MnCl2 center dot 4H(2)O-type (alpha-form) and FeCl2 center dot 4H(2)O-type (beta-form) structures. The crystal structure of both alpha-form and beta-form of MnCl2 center dot 4H(2)O consists of discrete octahedra complexes [MnCl2(H2O)(4)] linked by O-H center dot center dot center dot Cl- hydrogen bonds. However, chlorine atoms are intrans-configuration in the beta-form (trans-[MnCl2(H2O)(4)] complexes) and incis-configuration in the alpha-form (cis-[MnCl2(H2O)(4)] complexes). Moreover, the coordination polyhedra of the manganese(II) atoms are less distorted in the beta-form. This leads to two different hydrogen bond networks and to a slightly more compact [MnCl2(H2O)(4)] complexes arrangement in the alpha-form [GRAPHICS]

On the Crystal Structures of the Polymorphs of Manganese(II) Chloride Tetrahydrate: alpha-MnCl2 center dot 4H(2)O and beta-MnCl2 center dot 4H(2)O

International audienceThe manganese(II) chloride tetrahydrate MnCl2 center dot 4H(2)O (alpha-form) crystallizes in the space group P2(1)/n with a = 6.1918(4) angstrom,b = 9.5230(6) angstrom,c = 11.1918(6) angstrom, beta = 99.757(3)degrees, and V = 650.37(7) angstrom(3)(Z = 4). A second polymorph of MnCl2 center dot 4H(2)O (beta-form) is mentioned in the literature to be isomorphous with FeCl2 center dot 4H(2)O but its crystal structure was never confirmed. In this study, we report for the first time on the crystal structure of this second polymorph of manganese(II) chloride tetrahydrate, beta-MnCl2 center dot 4H(2)O, using room temperature single-crystal X-ray diffraction. The beta-form crystallizes in space group P2(1)/c with a = 5.9893(5) angstrom,b = 7.2877(6) angstrom,c = 8.5838(7) angstrom, beta = 110.952(4)degrees, and V = 349.89(5) angstrom(3)(Z = 2), confirming that beta-MnCl2 center dot 4H(2)O is isotype to Fe(II)Cl-2 center dot 4H(2)O. To the best of our knowledge this is the first compound reported to crystallize in both MnCl2 center dot 4H(2)O-type (alpha-form) and FeCl2 center dot 4H(2)O-type (beta-form) structures. The crystal structure of both alpha-form and beta-form of MnCl2 center dot 4H(2)O consists of discrete octahedra complexes [MnCl2(H2O)(4)] linked by O-H center dot center dot center dot Cl- hydrogen bonds. However, chlorine atoms are intrans-configuration in the beta-form (trans-[MnCl2(H2O)(4)] complexes) and incis-configuration in the alpha-form (cis-[MnCl2(H2O)(4)] complexes). Moreover, the coordination polyhedra of the manganese(II) atoms are less distorted in the beta-form. This leads to two different hydrogen bond networks and to a slightly more compact [MnCl2(H2O)(4)] complexes arrangement in the alpha-form [GRAPHICS]