Nanostructured cobalt powders synthesised by polyol process and consolidated by Spark Plasma Sintering: Microstructure and mechanical properties

Fellah, F.; Schoenstein, Frédéric; Dakhlaoui-Omrani, Amel; Chérif, S. M.; Dirras, G.; Jouini, N.

doi:10.1016/j.matchar.2012.03.017

Cited by 25 publications

(11 citation statements)

References 45 publications

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“…It is interesting to note that XRD measurements showed that the sample consolidated by HIP presents a more or less noticeable amount of cobalt oxide CoO (6%), whereas those consolidated by SPS are pure cobalt phases. This can be due to the difference in the elaboration protocol 21. However, no significant variation of the fitted magnetic parameters was noticed in the case of the HIP240 sample.…”

Section: Resultsmentioning

confidence: 82%

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Magnetic properties of ultrafine‐grained cobalt samples obtained from consolidated nanopowders

Fellah

Chérif

Bouziane

et al. 2011

Physica Status Solidi (a)

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Co powders having nominal average particle size of 50 and 240 nm were synthesized using a polyol method and then consolidated by hot isostatic pressing (HIP) or the emerging spark plasma sintering (SPS) compaction processes. Bulk polycrystalline aggregates were obtained, having average grain sizes of about 200 and 300 nm, respectively. It is found that both nanoparticles and consolidated samples exhibit a soft ferromagnetic behavior. The magnetization reversal likely occurs by nucleation/propagation process. However, a curling process can be involved in the magnetization reversal for the smaller particles. The dynamic measurements provide for the consolidated samples magnetic parameters corresponding to bulk cobalt with vanishing anisotropy. The contribution of the intergranular region is found to be negligible. We can infer that the used consolidation routes insure a good magnetic interfacial contact between the particles.

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Section: Resultsmentioning

confidence: 82%

“…The elaboration processes, the structural and morphological properties are briefly presented and commented on. Details are presented elsewhere 20, 21. The hysteresis loops for the Co nanoparticles were obtained using a magnetic balance of the Faraday type.…”

Section: Introductionmentioning

confidence: 99%

Magnetic properties of ultrafine‐grained cobalt samples obtained from consolidated nanopowders

Fellah

Chérif

Bouziane

et al. 2011

Physica Status Solidi (a)

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“…This polycrystalline characteristic is due to the well-known stacking faults defect occurring along the c axis of the Co hcp structure. This results from the breakdown in the hcp "ABABAB.." packing sequence into the fcc "ABCABCABC.." one over few atomic planes [15]. It is interesting to note that the stacking faults density calculated according to [16,17] decreases from 5.21% to 2.96% when the NR length increases from 256 to 538 nm.…”

Section: Shape and Structure Characterizationsmentioning

confidence: 98%

Enhanced Magnetic Behavior of Cobalt Nano-Rods Elaborated by the Polyol Process Assisted with an External Magnetic Field

et al. 2020

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Cobalt nano-rods with the hexagonal close-packed (hcp) structure were prepared by reduction of the long-chain carboxylate Co (II) precursor in polyol. The application of an external magnetic field (µ0H = 1.25 T) during the nucleation and growth steps resulted in a noticeable modification of the mean aspect ratio (length/diameter) of the particles. The particle morphology was also modified as the nano-rods did not exhibit conical heads at their extremities anymore, which are observed for particles prepared without application of an external magnetic field. Besides, the stacking faults density along the c axis of the hcp structure in the cobalt nano-rods has been found to decrease with the increase in the applied magnetic field. The coercive field of randomly oriented nano-rods increased with the aspect ratio, showing the highest value (i.e., 5.8 kOe at 300 K) for the cobalt nano-rods obtained under the highest applied magnetic field. For partially oriented Co nano-rods in toluene solution, the magnetic properties were significantly enhanced with a coercive field of 7.2 kOe at 140 K, while the magnetization saturation reached 92% of the bulk. The MR/MS value was about 0.8, indicating a good orientation of the anisotropic particles relative to each other, making them suitable for the preparation of permanent magnets via a bottom-up approach.

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“…Extensive efforts have been devoted to the making of nanostructured Co by either a top-down or bottom-up strategy [12]; the factors governing the grain-refining process are related to the synthesis method. In this respect, various methods have been reported for the production of UFG and NC materials ( [13] and references therein).…”

Section: Introductionmentioning

confidence: 99%

Nanostructured Cobalt Obtained by Combining Bottom-Up and Top-Down Approach

Cabibbo

2018

Metals

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Nanostructured metallic materials can be obtained by two major processing strategies: a bottom-up approach that starts with powdered metals to be mechanically and chemically compacted via different compaction methodologies, and a top-down approach that starts with bulk conventional metallic materials that are induced to a sometimes-extraordinary grain size reduction via different severe plastic deformation (SPD) methods. In the present study, a dual strategy was followed to obtain a sound and stable nanostructured commercially pure cobalt. Powdered cobalt of 2 μm was compacted by ball-milling (BM) followed by spark-plasma sintering (SPS) to obtain a bulk metallic material whose relative mass density reached a value of 95.8%. This process constituted a bottom-up strategy to obtain ultrafine submicrometer-grained bulk cobalt, and a top-down strategy of subjecting the BM + SPS submicrometer-grained cobalt to a specific SPD technique, namely equal-channel angular pressing (ECAP). The latter was carried out in one to four passes following so-called route BC, reaching 98.4% density and a nanometric-grained microstructure. The material was microstructurally and mechanically characterized by TEM (transmission electron microscope) and nanoindentation. The obtained results are a representative solid example for obtaining nanostructured metallic materials using both grain-refining strategies, bottom-up and top-down.

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Nanostructured cobalt powders synthesised by polyol process and consolidated by Spark Plasma Sintering: Microstructure and mechanical properties

Cited by 25 publications

References 45 publications

Magnetic properties of ultrafine‐grained cobalt samples obtained from consolidated nanopowders

Magnetic properties of ultrafine‐grained cobalt samples obtained from consolidated nanopowders

Enhanced Magnetic Behavior of Cobalt Nano-Rods Elaborated by the Polyol Process Assisted with an External Magnetic Field

Nanostructured Cobalt Obtained by Combining Bottom-Up and Top-Down Approach

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