Reactive High-energy Ball Milling Research Articles

Zinc Ferrite Powder Synthesized by High Energy Reactive Ball Milling

The nanocrystalline zinc ferrite (ZnFe2O4) powder was synthesized by high energy reactive ball milling (RM) in a planetary mill. As starting materials a mixture of commercial zinc oxide (ZnO) powder and iron oxide (Fe2O3) powder was used. The starting mixture was milled for different periods of time, up to 30 h. The milled powders were annealed for 4 h at 350 oC in order to eliminate the internal stress and to finish the solid state reaction of ferrite formation. Zinc ferrite formation was investigated by X-ray diffraction. The obtained powder has a mean crystallite size of 12 nm after 20 h of milling. Using scanning electron microscopy (SEM) the particle morphology was studied. Particles size range of the powders was also determined using a laser particle size analyser.

Nickel Ferrite Powder Obtained by High Energy Reactive Ball Milling

Nanocrystalline nickel ferrite powder was obtained using high energy reactive ball milling technique. Nickel oxide (NiO) and iron oxide (Fe2O3) powders were used as starting material. Milling was performed in air atmosphere using a planetary ball mill. Milling time was up to 30 hours. The product of milling was annealed at 350 oC for 4 hours in order to eliminate the internal stresses and finish the solid state reaction. X-ray diffraction analysis was used to study the nickel ferrite formation. A nanocrystallite mean size of 10 nm was found after 24 hours of milling. Using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDX) the particle morphology and the chemical homogeneity were studied. It was found that the obtained product has particle size in range of micron and submicron.

Preparation of WC/MgO composite nanopowders by high-energy reactive ball milling and their plasma-activated sintering

Nanosized WC/MgO powders are synthesized by high-energy ball milling the mixture of WO 3 , C, and Mg elements in an atomic ratio of 1:1:3 under argon gas atmosphere at room temperature, and the composite is made by plasma-activated sintering. The microstructure of the mixture powders produced by ball milling and the sample consolidated by plasma-activated sintering is investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is indicated that self-propagating reduction reactions occur between the mixed element powders during high-energy ball milling, leading to the formation of nanosized WC/MgO crystalline particles with an average size of 35 nm after ball milling for 5h. The obtained nanosized WC/MgO powders are consolidated by plasma-activated sintering at 1473K under the pressure in a range of 5 to 7.5 kN for 1.05 ksec, and then WC/MgO composite with nanomicrostructure and full density can be obtained. The WC/MgO composite exhibits high hardness and high fracture toughness in comparison with commercial WC/Co composites.

Are carbon nanostructures an efficient hydrogen storage medium?

Literature data on the storage capacities of hydrogen in carbon nanostructures show a scatter over several orders of magnitude which cannot be solely explained by the limited quantity or purity of these novel nanoscale materials. With this in mind, this article revisits important experiments. Thermal desorption spectroscopy as a quantitative tool to measure the hydrogen storage capacity needs an appropriate calibration using a suitable hydride. Single-walled carbon nanotubes that have been treated by ultra-sonication show hydrogen uptake at room temperature. However, this storage can be assigned to metal particles incorporated during the sonication treatment. Reactive high-energy ball milling of graphite leads to a high hydrogen loading, however the temperatures for hydrogen release are far too high for application. In view of today’s knowledge, which is mainly based on experiments with small quantities and poorly characterised samples, carbon nanostructures at around room temperature cannot store the amount of hydrogen required for automotive applications.

X-ray investigations of high energy ball milled transition metal carbides

Nanostructured NbC ZrC TiC and VC were obtained by reactive high energy ball milling of the elemental powders. A milling rate of 250 r.p.m. leads to carbides after 4 to 12 hrs in correlation with the formation enthalpy of the compounds. Between 11 and 36 hrs the nanocrystalline state (≤10 nm) is reached and the final value of crystallite size for all carbides is (7 ± 1) nm. The nanocrystals possess a high degree of lattice strains, from about 0.5 to 1 %. High temperature treatment of the nanostructured carbides leads to the increase of the grain size and continuous reduction of lattice defects. The reduction of lattice strains is caused by the recrystallization process.

Structure and stability of nanocrystalline TiC-powders obtained by reactive high energy milling

Nanostructured TiC can be obtained by reactive high energy ball milling of titanium and carbon powders. Milling rates of 250 or 320 r.p.m. lead to TiC grains with 0.1–2 μm diameter. The TiC grains consist of a nanosubstructure with the extent of 7 nm. The nanocrystals possess a high degree of lattice strains (0.8%). Neighboring nanocrystals in one grain are similar in their crystallographic orientation and are distinguished by small angle boundaries. High temperature treatment of the nanostructured TiC lead to continuous reduction of the lattice defects with increasing temperature. The nanocrystals starts to grow at about 600°C.