Synthesis and characterization of Fe/Co/Ni alloys-MgO nanocomposite powders

A mixed oxalate β-Mg 0.896 Fe 0.047 Co 0.034 Ni 0.023 C 2 O 4 ·2H 2 O of well controlled size and morphology was prepared by coprecipitation. The corresponding quaternary solid solution between MgO, FeO, CoO and NiO was prepared by thermal decomposition and calcination in a H 2 /H 2 O/N 2 atmosphere. The selective reduction of the solid solution in an H 2 atmosphere was studied by a combination of X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and associated analysis. This work has brought to light the very high stability of Fe 2+ , Co 2+ and notably Ni 2+ when substituted for Mg 2+ in the MgO rocksalt lattice. It is necessary to perform the reduction at 1300 °C fully to reduce the transition metal ions. The alloy particles are either distributed as relatively large particles (tens to hundreds of nanometers) at the surface of the MgO grains or as much smaller particles (≤20 nm) probably located inside the matrix grains and epitaxial with it. The composition distribution of the large surface particles is fairly broad when the reduction was performed at 1100 and 1300 °C. In contrast, it is much narrower in the powder prepared by reduction at 1200 °C, although the particles are still low in Ni compared to the target composition

Elaboration, microstructure and oxidation behavior of metal-alumina and metal-chromia nanocomposite powders.

Metal-Al203 and metal-Cr203 nanocomposite powders have been prepared by selective reduction in hydrogen of oxide solid solutions. The metallic phase (either Cr or an (Fe, Cr) alloy) is present in the form of nanometric particles inside and/or at the surface of the oxide matrix grains. The microstructure of the different composites has been compared and their air oxidation behavior has been investigated. The metal particles located in the open porosity of the matrix are totally oxidized at temperatures lower than 600°C, whereas those intragranularly located are stable up to 800°C. The oxidation behavior is generally complex and explanations in relation to the powder microstructure are proposed

Synthesis, microstructure and oxidation of Co-MgAl2O4 and Ni-MgAl2O4 nanocomposite powders

MgAl2O4-CoAl2O4 and MgAl2O4-NiAl2O4 solid solutions are synthesized by combustion in urea of the appropriate metal nitrates. The selective reduction in hydrogen of these oxides gives rise to a dispersion of nanometric Co or Ni particles in the spinel matrix. The reduction of the Co2+ and Ni2+ ions is complete at 900 and 1000 °C respectively. Owing to the homogeneity of the starting oxide solid solution, the size distribution of the metal particles is narrow and their average size is about 10 nm. During a thermal treatment in air, the nanometric metal particles located in the open porosity of the matrix are totally oxidized at temperatures lower than 700 °C, whereas those dispersed inside the matrix grains are stable up to 900 °C. These latter particles account for more than half of the total metal content

Iron-alumina interface in ceramic matrix nanocomposites

The composite powders investigated in the present study consisted of nanometric iron particles dispersed in an alumina matrix. According to the temperature of formation, iron particles are either directly epitaxied in the alumina matrix or separated from the alumina by a thin layer of iron aluminate spinel. This layer disappears after annealing under hydrogen. Transmission electron micrographic and electron microdiffraction pattern analyses led to a general epitaxial relationship between iron nanoparticles and alumina, which holds whatever the elaboration process. A mechanism for the crystallographical reorientation of the iron particles, when the spinel phase is reduced, is proposed

Epidemiological investigation for grouped cases of Trichosporon asahii using whole genome and IGS1 sequencing

International audienc

Relationship between serotypes, disease characteristics and 30-day mortality in adults with invasive pneumococcal disease

International audienc