Spark plasma sintering of cobalt ferrite nanopowders prepared by coprecipitation and hydrothermal synthesis.

International audience; Cobalt ferrite exhibits a high coercivity at room temperature and a strong magnetic anisotropy compared to the other spinel ferrites and, consequently appears as an interesting material for permanent magnets and high-density recording. The magnetic properties depend also on the crystallite size. In order to keep the powder properties in a bulk material, dense nanostructured cobalt ferrite has to be sintered. A field activated sintering process like spark plasma sintering (SPS) may be promising for such challenge. The present paper deals with: (i) the preparation of cobalt ferrite by two methods: coprecipitation and hydrothermal synthesis in supercritical water; (ii) …

Raw materials dossier

Nano-SiC/CNT composites sintered by SPS: CNT amount effect on mechanical, thermal and electrical properties.

International audience

Dense Mosi2 produced by reactive flash sintering: Control of Mo/Si agglomerates prepared by high-energy ball milling

The objective of this work is to determine the influence of the agglomeration state of the MA mixture on the microstructure and the chemical composition of SPS end-products. In order to produce MoSi2 with a microstructure and a density perfectly controlled via reactive sintering implying an SHS reaction, the characteristics of Mo/Si mechanically activated (MA) powder mixtures were investigated. Indeed, the MA powders have been characterized in terms of their surface specific area, size, phase composition and microstructure. The high-energy milling allows the formation of agglomerates (0.8 to 800 μm) composed of nanometric crystallites of molybdenum and silicon, as a consequence of a continu…

Spark Plasma Sintering tool design for preparing alumina-based Functionally Graded Materials

Abstract A way to produce Functionally Graded Materials (FGM) is by means of Spark Plasma Sintering (SPS) and specifically designated tools. These new tools permit a current density modulation and therefore a temperature variation along the z-axis. The key feature relies on a varying die section. FEM modelling has given the suitable range of die dimensions between the top and the bottom to obtain a given temperature gradient (around 300 °C) out of roughly a 15 mm height. Experiments conducted in different configurations (with or without samples) and the measurement of the associated thermal gradient led to improvements of the mould (in particular the introduction of a counter-piston). By th…

Inelastic Light Scattering Contribution to the Study of the Onset of Sintering of a Nanopowder

International audience; The onset of the sintering of 5 nm ZrO2 and TiO2 nanoparticles is investigated by various methods including inelastic light scattering. A special attention is paid to low-frequency Raman spectra where scattering from confined acoustic vibrations and quasielastic scattering manifest. Significant changes are observed between samples sintered at different temperatures or applied forces. A detailed analysis of the spectra enables to follow the variation of the size of the nanoparticles, the surface area, and the formation of internanoparticles necks in the sintered materials. Finally, low-frequency scattering is shown to be more sensitive to the onset of sintering than m…

MoSi2 Formation Mechanisms during a Spark Plasma Synthesis from Mechanically Activated Powder Mixture

Mechanical, thermal and electrical properties of nanostructured CNTs/SiC composites

International audience; Dense SiC-based nanostructured composites reinforced by well-distributed carbon nanotubes (CNTs) were elaborated for the first time by spark plasma sintering (SPS) without sintering additive. Microstructures of materials containing different amounts of CNTs – up to 8.0 vol% – were correlated with their mechanical, electrical and thermal properties. A continuous decrease of the SiC grain size was observed when the amount of CNT was increased, while the evolution of density showed a different behavior that could be explained by the particular combination of SPS technique with the electrical resistivity evolution of the green bodies. Optimal effect of CNTs addition on h…