Journal of Nano Research Vol. 29

Abstract: Graphene aerogel-poly (vinylidene fluoride) (GA-PVDF) nanoporous composites with different concentrations of PVDF are fabricated. Scanning electron microscopy reveals that PVDF films with a typical thickness below 100 nm are coated at the graphene sheets in the nanoporous composites. The GA-PVDF composites show excellent compressibility, ductility and mechanical strength, as well as better sensitivity of stress-dependent electrical resistance compared with those of GAs. The improved mechanical and electro-mechanical behaviours of nanoporous composites are ascribed to the PVDF which possesses piezoelectricity. The structural properties of the graphene-PVDF nanosized hybrid scaffolds are analyzed by dynamical mechanical relaxation. The results demonstrate that the nanoporous composites could be used as high-performance sensors, actuators and kinetic energy harvesters.

Abstract: Pure potassium sulfate single crystals are transparent in a wide spectral range up to 155 nm and do not show fluorescence and absorption over a wide spectral range of 200-800 nm before and after X-ray irradiation of the samples. The centers of luminescence in thallium-doped potassium sulfate crystals showed a maximum absorption 216 nm and emission 285 nm at room temperature. These centers are singly charged thallium ions. It is interesting to research the optical properties with decreasing size of crystals (size effects). For this, we used a supersaturated aqueous solution of potassium sulfate, in which the crystallization begins. The results of computer simulations using Scigress quantum chemistry package show that the occurrence of macromolecules in a cooled supersaturated solution should result in an increased absorption. In supercooled saturated aqueous solutions of ionic crystals nucleation occurs. A decrease of transparency of saturated solutions with decreasing temperature is clearly seen. This is due to absorption and scattering in the medium with the growing small crystals in the solution.

Abstract: Nanomaterial Cr₇₅Ni₂₅ alloy with a mean crystallite size of 8.3 nm and microstrain of 1.23% after 48h of milling was synthesized by mechanical alloying using a high energy planetary ball milling. The morphological changes and particles size were investigated by scanning electron microscopy and laser diffraction. Magnetic results were measured by Foucault currants, coercive field and residual magnetisation. Structural change during ball milling was evaluated by X-ray diffraction. It was found that the paramagnetic Cr_0.8Ni_0.2 phase with bcc structure appears for 12 h of milling.

Abstract: Nanocrystalline powders of iron aluminum alloy of the Fe82Al18 nominal composition were prepared under air, hydrogen and nitrogen atmospheres from the Fe and Al elemental powders by mechanical alloying and also from the conventionally cast Fe82Al18 alloy by the high-energy ball milling. The intensive plastic deformation during high-energy mechanical treatment has introduced high concentrations of open volume defects and contributed to a rapid decrease in the crystallite size down to a nanoscopic range.The hydrogen atmosphere was found to be the most efficient for the Fe-Al mechanical alloying since it has resulted into the fully alloyed Fe82Al18 after 30 h of milling. On the other hand, the nitrogen and air atmosphere have slightly prevented mechanical alloying and after the same milling time the pure iron particles were still detected in the powder mixtures. This partial suppression of the mechanical alloying process is explained by a formation of thin iron nitride and/or oxide layers on the surface of Fe particles preventing mutual inter-diffusion of Fe and Al atoms.

Abstract: We analyze graphene obtained by electrochemical exfoliation. This showed an interesting process for obtaining fast and low cost exfoliated graphene. Within a few minutes a large amount exfoliated graphite oxide was produced. Analysis by Raman spectroscopy of the exfoliated graphene showed the effectiveness of the process and the factors that may intensify the disorder of graphene obtained.

Abstract: NiTe nanocrystals were prepared through facile and fast solid state reaction (mechanical alloying) of pure elemental tellurium and nickel powders in an argon atmosphere. The samples processed for 3 h, 5 h and 10 h were characterized by X-ray diffraction, transmission electron microscopy, magnetization and Raman spectroscopy. Hexagonal NiTe crystals with an average size of 30 nm can be obtained after only 3 h of processing time. Transmission electron microscopy images showed a broad crystalline size distribution in the agglomerated particles and selected area electron diffraction revealed its crystalline character. NiTe ferromagnetic behavior was confirmed and magnetic parameters were dependent on processing time. Raman spectra showed no unreacted Te or tellurium oxides, but it also showed that laser induced phases transitions (including Te re-crystallization) can be observed for modest laser power (<3 mW).

Abstract: Polymeric nanocomposites are hybrid materials, where inorganic nanoscale dimensions substances are dispersed in a polymeric matrix. The fillers have a high surface area, promoting better dispersion in the polymeric matrix and therefore an improvement in physical properties of the composite depending on the homogeneity of the material. The preparation of nanocomposites polymer matrix allows in many cases to find a relationship between low cost due to the use of a lower amount of charge, and a high level of performance. In the present work, nanocomposites of polypropylene with different concentrations of pseudoboehmite obtained by a sol-gel process, and treated with octadecylamine were prepared. After preparation, the samples were irradiated with a 0, 50, 100, 200 e 300kGy radiation dose in an electron accelerator. The pseudoboehmite nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, differential thermal analysis and thermogravimetric analysis. The nanocomposites were characterized by thermal and mechanical tests. The addition of pseudoboehmite promoted a reduction of the melting flow during the production of the composites evidencing the interaction of pseudoboehmite with the polymeric matrix. Because the polypropylene is a semicrystalline polymer, when exposed to the irradiation process, their morphology was modified due to scission mechanisms of the polymer chains.

Abstract: The work we have undertaken consists of preparing nanocrystalline Fe₄₀Co₆₀ powders by the Mechanical Alloying (MA) route. Characterization of obtained powders was applied on two steps. First, structural properties were investigated. X-ray Diffraction (XRD) was used to identify the formation of a disordered α (Fe₄₀Co₆₀) solid solution with a bcc lattice after 60h milling. By the Halder-Wagner approach lattice size, average grain size and residual strain were fixed. The morphology of milled powders was investigated by Scanning Electron Microscopy (SEM). Then bulk specimens were prepared by cold compaction for microwave measurements. Microwave dielectric permittivity and conductivity were determined using cavity perturbation technique. Microwave absorbing characteristic was measured according to line transmission method. Results obtained confirm that the developed structure after milling is the main factor that influences the microwave properties of nanocrystalline Fe₄₀Co₆₀ powders compared to elemental Fe.

Abstract: the porous carbon solid (mean pore size 0.1μm ; porosity 32%) was prepared by pyrolysis of composite paste of phenolic resin/AC with a mass ratio (1/1) and a mean grain size of AC of 2.28 μm. The porous agent (starch and PVB) is then added to the paste at 5% and 9% respectively to maintain a pore size of 0.1 microns and maximum porosity. A layer of pure zeolite Na-A is deposited on the carbon support after an oxidation by nitric acid and a seeding of the surface with pre-synthesized Na-A zeolite crystals.