Fabrication of spherical particles with mixed amorphous / crystalline nanostructured cores and insulating oxide shells
By spark-eroding Fe75Si15B10 in water/ethanol mixtures, spherical particles with nanostructured cores consisting of mixed amorphous and crystalline phases were produced. The relative volume fractions of the amorphous and crystalline phases were dependent on the water/ethanol ratio. In the same process, continuous oxide layers were formed on the particle surfaces. The basic mechanisms responsible for the formation of the surface oxide layers and the core nanostructures were modeled. At frequencies ranging from 1 to 100 MHz, the combination of the core nanostructures and the insulating oxide shells yielded exceptionally low-loss magnetic behavior.
Spark erosion: A method for producing rapidly quenched fine powders
Spark erosion is a method for producing fine powders of metals, alloys, semiconductors, and compounds. The technique involves maintaining repetitive spark discharges among chunks of material immersed in a dielectric liquid. As a result of the spark discharge there is highly localized melting or vaporization of the material. The powders are produced by the freezing of the molten droplets or the condensation and freezing of the vapor in the dielectric liquid. Since the powders are quenched in situ , they may be extremely rapidly cooled. Particles can be produced in sizes ranging from 5 nm to 75 μm. The average powder size and production rate depend on the power parameters, material used, and the dielectric liquid.
Energy absorption in Ni-Mn-Ga/ polymer composites
Martensitic Ni-Mn-Ga single crystals are easily twinned and the twin boundaries can be displaced by applying a mechanical stress or magnetic field. Twin boundary motion is a highly dissipative process. Composites of aligned Ni-Mn-Ga particles in a polymer matrix show evidence of stress-induced twin boundary motion that results in stress-strain curves with significantly greater hysteresis than for Fe-polymer composites or polymer samples.