Cobalt-based anisotropic particles prepared by the polyol process

Abstract

Cobalt and Co 80 Ni 20 metal particles were prepared by reduction of acetate salts in a liquid polyol. The relative amount of the hcp phase and the probability of stacking faults in this phase vary with the experimental conditions of synthesis. The formation of either isotropic or anisotropic particles appears to be closely related to the stacking faults. Several kinds of anisotropic particles were detected by TEM: platelets, rods or diabolo-like particles. For isolated diabolos and rods, HRTEM and electron diffraction showed that the crystallographic c axis is parallel to the rotation axis of the particles. Magnetic property measurements showed high values of coercivity and remanence for the anisotropic particles. The anisotropic shapes differ markedly from those previously observed for cobalt-based particles prepared by the polyol process. A mechanism that involves a solid intermediate phase as either precursor or template is proposed.

Dynamic and rate-dependent yielding behavior of Co0.9Ni0.1 microcluster based magnetorheological fluids

“…The selected area diffraction (SAED) pattern for the material indicates polycrystalline nature of sample ( Magnetic saturation for Co 0.9 Ni 0.1 was lower than that of bulk Co or Co 80 Ni 20 alloy [12]. As reported earlier, M s values for nanoparticles are considerably smaller than that of bulk alloys with same compositions, possibly due to the presence of passive dead layer of metal oxides [12][13]. The ratio of M r to M s at room temperature was 0.17 which is considerably lower than 0.35, indicating randomly oriented, blocking type nanoparticles [15].…”

“…The nanoparticles in polyol can either follow stepwise addition of metal atoms to form seed and subsequent coalescence of seed into nanoparticles, or primary nanoparticles aggregate to form larger nanoclusters. It was seen that in this case, the latter arrangement takes place [11][12][13][14]. The selected area diffraction (SAED) pattern for the material indicates polycrystalline nature of sample ( Magnetic saturation for Co 0.9 Ni 0.1 was lower than that of bulk Co or Co 80 Ni 20 alloy [12].…”

Ferromagnetic Cobalt Nanodots, Nanorices, Nanowires and Nanoflowers by Polyol Process

“…1,2 To fabricate monodispersed Co nanoparticles, several processes and related chemicals have been proposed during the last decade. [1][2][3][4][5][6][7][8][9][10][11][12][13] The rapid thermal decomposition process, which consists of rapid injection of organometallic precursor into high-temperature solvent with surfactant, is widely used to fabricate Co nanoparticles. 1,3 Relatively little attention is paid to slow processes, which take more time for nucleation and growth of nanoparticles than rapid process does due to slow reaction rate and low monomer concentration.…”

Mechanism for controlling the shape of Cu nanocrystals prepared by the polyol process

“…[1][2][3][4][5][6] Rapid thermal decomposition can produce nanocrystals with a uniform size distribution and an average size below 10 nm by separating the nucleation and growth mechanisms. 1,3 However, the control of nanocrystal shape during rapid thermal decomposition is relatively difficult.…”

“…Moreover, nanocrystals of various shapes can be fabricated using the polyol process, including cubes, spheres, rods, and wires. 2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17] The process parameters such as temperature, reaction time, and type of surfactant can influence the shape of nanocrystals. 2,[4][5][6][7][8][9][10][11][12][13][14][15][16][17] However, the mechanism for controlling the shape of nanocrystals is not fully understood.…”