Microstructure of NiCoAlFeCuCr multi-component systems synthesized by mechanical alloying

The present study uses the mechanical alloying method to produce series of binary to senary alloys based on Ni, Co, Al, Fe, Cu, Cr. Milling times are 0, 10, 20 and 30 h and experiments are performed in a high energy ball mill. The results of this investigation show that an FCC solid solution is formed in all the studied systems, but a different phase formation response is presented in each system. A mixture of FCC and BCC solid solutions in quaternary to senary systems, is formed for short milling times. Apparently, the dissolution rate of Fe and Cr into the FCC solid solution, is low. Moreover, it is observed that additions of these elements promote the formation of BCC solid solution, which is stable at temperatures up to ?1273 K. Finally, it is observed that the heat treated products present a mixture of FCC and BCC solid solutions with lattice parameters close to those found in the milled products.     

Enhanced mechanical properties and corrosion behavior of polypropylene/multi-walled carbon nanotubes/carbon nanofibers nanocomposites for application in bipolar plates of proton exchange membrane fuel cells

Polypropylene (PP) nanocomposites with multi-walled carbon nanotubes (MWCNT) alone or combined with carbon nanofibers (CNF) at different loadings have been fabricated by melt mixing with a focus on their mechanical properties and corrosion resistance for bipolar plates applications in proton exchange membrane fuel cells (PEMFCs). The incorporation of up to 20 wt% MWCNT in the PP matrix produces enhancements of 71, 47, 56, and 30% in microhardness, elastic modulus, and tensile and flexural strength, respectively. Combined additions of MWCNT and CNF allow producing hybrid nanocomposites with increased strength than when neat MWCNT as reinforcement, preserving their processability even at a total filler content of up to 30 wt%. The measured values of i_corr in both PP/MWCNT and PP/MWCNT/CNF suggest a slow degradation rate in the PEMFC environment. Based on the US Department of Energy (DOE) targets, PP/20MWCNT, PP/21.5MWCNT, and PP/15MWCNT/15CNF nanocomposites are good candidates to produce bipolar plates for PEMFCs.     

Co(3)O(4) nanoparticles produced by mechanochemical reactions

Co(3)O(4) nanoparticles have been produced by mechanochemical reactions involving cobalt carbonate, sodium oxide and sodium carbonate. The mechanochemical reactions are carried out during milling at room temperature and the nanoparticles have been obtained without the need for any thermal treatment after the milling operation. The CoO phase is produced in the first 30?min of the mechanochemical process, followed by a second stage of oxidation to Co(3)O(4) which lasts for several hours. Under proper milling conditions the final products were soft agglomerates of ultrafine particles with average sizes between 15 and 20?nm.     

TiO2 anatase thin films deposited by spray pyrolysis of an aerosol of titanium diisopropoxide

Titanium dioxide thin films were deposited on crystalline silicon (100) and fused quartz substrates by spray pyrolysis (SP) of an aerosol, generated ultrasonically, of titanium diisopropoxide. The evolution of the crystallization, studied by X-ray diffraction (XRD), atomic force (AFM) and scanning electron microscopy (SEM), reflection and transmission spectroscopies, shows that the deposition process is nearly close to the classical chemical vapor deposition (CVD) technique, producing films with smooth surface and good crystalline properties. At deposition temperatures below 400 °C, the films grow in amorphous phase with a flat surface (roughness∼0.5 nm); while for equal or higher values to this temperature, the films develop a crystalline phase corresponding to the TiO₂ anatase phase and the surface roughness is increased. After annealing at 750 °C, the samples deposited on Si show a transition to the rutile phase oriented in (111) direction, while for those films deposited on fused quartz no phase transition is observed.     

Production and Characterization of (Al, Fe)-C (Graphite or Fullerene) Composites Prepared by Mechanical Alloying

(Al, Fe)-C_graphite and (Al, Fe)-C_fullerene composites have been prepared by mechanical alloying using ball milling of powders. Consolidation has been achieved by a spark plasma sintering technique (SPS). Results of XRD and TEM indicate that pure fullerene withstands milling. SEM results show homogeneous powders after milling but with different morphologies depending on the specific system. Milling produces a fine mixture of Al or Fe and graphite or fullerene. SPS produces a dense material with a nanocrystalline structure. The sintered samples have a metallic matrix (Al or Fe) with a fine dispersion of AI₄C₃ in the case of Al-C_{( graphiteorfullerene)}, Fe₃,C in the case of Fe-C_(graphite), and fullerene in the case of Fe-C _(fullerene), Hardness measurements show that higher values are obtained in the Al-C_(fullerene), and Fe-C_{(graphite )} specimens.     

Mechanically alloyed Ni50Ti50 and its transformation by thermal treatments

Amorphous powders have been obtained by mechanical alloying (MA) equiatomic powder mixtures of nickel and titanium. The amorphous phase thus formed decomposes upon heating first into the cubic B2 NiTi intermetallic compound; however, further heating promotes the precipitation of the intermetallics Ni₃Ti and NiTi₂. These transformations are shown to occur also in mechanically ground (MG) NiTi wire, but not in this same material exempted from ball-milling processing. It is suggested that this unique behaviour is brought about by the particular structural features of the MA or MG powders, which promote the otherwise sluggish decomposition of B2 NiTi.     

The synthesis of Ni-activated carbon nanocomposites via electroless deposition without a surface pretreatment as potential hydrogen storage materials

This work presents the deposition of Ni nanoparticles on a potassium hydroxide (KOH) activated carbon (AC) support by an electroless deposition (ED) technique without using sensitization and activation surface pretreatments. The hydrogen storage properties of Ni-activated carbon nanocomposites (Ni/AC) were investigated at room temperature and under moderate pressure. The chemical composition, morphology and textural parameters are characterized using an inductively coupled plasma spectrometer (ICP), scanning and transmission electron microscopy (SEM and TEM) and N₂ adsorption isotherms. Fine and well-dispersed Ni nanoparticles were obtained by ED that had spherical shape with an average size of 5 nm. The hydrogen storage capacity of the AC can be improved through Ni loading; which results in a hydrogen storage enhancement factor of two compared with the Ni-free AC. This enhancement factor is due to the greater interactions between the Ni and the AC, which facilitate the hydrogen spillover mechanism.