Papers by Keyword: Amorphous Particles

Abstract: Soft magnetic Fe-B-P ultrafine particles with amorphous structure were prepared by aqueous reduction method with variable pH values. The microstructure, compositions and the soft magnetic properties of Fe-B-P submicron particles were investigated by using field emission scanning electron microscope (FE-SEM), X-Ray Diffraction (XRD), mössbauer spectrum (MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), vibrating sample magnetometer (VSM). The results showed that a series of Fe-B-P amorphous particles with the average particle size of 0.26~0.42 μm were obtained depending on the pH value of solution. As pH value increased, the contents of B and P increased, and the specific saturation magnetization of the Fe-B-P submicron particles decreased. Some electrons, transferred from p-shell of B atoms and P atoms to 3d-shell of Fe atom, resulted in the decrease of the number of unpaired electron, which in turn led to reduction of the average hyperfine magnetic field of the Fe-B-P particles and the decrease of the magnetic torque of Fe atoms. The relation between hyperfine magnetic field (H_hf) and the specific saturation magnetization was in accord with the Marshall’s equation. At the same time, the enhancement of the shielding effect on 4s electron orbital, i.e., the density of 4s electron reduced, leading to the increase of Isomer Shift.

Abstract: In this paper both electric discharge assisted milling [1, 2] and conventional mechanosynthesis techniques were applied to investigate the effects of milling conditions on the fracture and agglomeration of amorphous CoSiB ribbons produced by planar flow casting. The effect of spark energy on particle shape and size produced by discharge milling was studied. Conventional milling in inert atmosphere for extended periods generally leads to the formation of porous powder particle aggregates, each particle comprised of small amorphous or, after extended milling times, nanocrystalline elements. The mechanism of agglomeration was believed to originate from repeated fracture, deformation and cold welding of individual ribbon elements. In contrast to conventional milling, spark discharge milling was found to induce the formation of predominantly sub-micron single particles of amorphous powder. The morphology of individual particles varied from sub-micron irregular shaped particles to remelted particles, depending on selection of vibrational amplitude during discharge. For high vibrational amplitudes and high energy input a wider range of particles as produced. These included sub-micron particles, remelted particles and welded agglomerates, and nano-sized particles produced as a fume and collected during discharge milling under flowing argon. These results combined with observations that most re-melted particles produced by discharge milling were also amorphous confirmed that extremely high heating and cooling rates are associated with discharge milling of metals. They also confirm the potential of electrical discharge milling as a new route for the synthesis of ultrafine and nanosized powder particles from amorphous ribbon, for possible processing into 3-D shapes.