M. Nakhl

Hydrogen absorption properties of CeNiAl: influence on its crystal structure and magnetic behaviour

CeNiAl absorbs up to 1.93(5) hydrogen per formula unit at room temperature and at a pressure of 1 MPa. This hydride is stable in air. Hydrogenation induces both: (i) a structural transition hexagonal ZrNiAl-type→hexagonal AlB 2 -type; (ii) a valence transition for cerium. At low temperature for T<7 K. the hydride CeNiAlH 1.93 shows a spin fluctuation behaviour.

Influence of the mechanical grinding on the magnetic properties of GdMn2

Abstract The cubic C15 phase GdMn2 was submitted to high-energy ball milling. The resulting products were investigated by X-ray powder diffraction, scanning electron microscopy, ac-magnetic susceptibility and dc-magnetization measurements. With increasing speed of the milling treatment, amorphization of the sample appears, as shown by X-ray diffraction analysis. Furthermore, this treatment induces a magnetic transition from antiferromagnetism (unmilled sample) to ferromagnetism below TC≅105(5) K (milled sample at high speed). This effect is compared with that of the application of hydrostatic pressure on GdMn2.

Structural and hydriding properties of the intermetallic Y1−xNi2 synthesized by mechanical alloying or submitted to mechanical grinding

Abstract The sample ‘YNi 2 ’ and the powder mixture (Y+2 Ni) were submitted to a milling process under an argon atmosphere. X-ray powder diffraction and microprobe analysis revealed the formation of the phase Y 0.97 Ni 2 by mechanical alloying (MA). This compound, after a heat treatment at 823 K, decomposes into two phases having the following formula composition: Y 0.92 Ni 2 and YNi 1.84 . The hydriding properties were studied at T =373 K and P H 2 =1.1 MPa; it absorbs≅3 H mol −1 and decomposes into four phases: yttrium hydrides YH 2 and YH 3 , Ni metal and an amorphous phase. The hydriding properties of the ground sample ‘YNi 2 ’ were also studied. Its hydrogen absorption capacity has increased at 373 K but only for mechanical grinding (MG) performed for 3 h. X-ray diffraction did not reveal in this case any amorphization after hydrogenation at 373 K.

Effect of the Ball Milling Conditions, under Air, on the Preliminary Hydriding Properties of the Mixtures Mg-x Wt% Graphite. Role of Solvent

The effect of wet milling on the hydriding properties of magnesium based mixture has been investigated. To prepare these mixtures, magnesium was ball milled with different weight percent of graphite (5, 10 and 25), at 300 rpm under air, for various duration using a ball miller apparatus Retsch S100 (R=12). Different solvents have been used such as benzene, heptane, styrene, DMSO. The hydriding properties were studied using a manual Sievert-type apparatus, at different temperatures (25°C, 100°C, 150°C and 200°C). The mixture Mg + 5wt% graphite milled during 6 hours in presence of 5mL heptane has shown the best hydriding properties at 150°C. The improvement of these properties has been related to the dielectric constant of the solvent and to the small size of the particles. The different mixtures have been analysed by means of scanning electron microscopy and laser granulometry.

Interplay of negative pressure and hydrogen chemical effects in CeRhSn from first principles

Abstract.Investigations within the local spin density functional theory (LSDF) of the intermetallic hydride system CeRhSnHx were carried out for discrete model compositions in the range 0.33 ≤xH ≤ 1.33 with the purpose of assessing the change of the cerium valence state in the neighborhood of the experimental hydride composition, CeRhSnH0.8. In agreement with experiment, the analyses of the electronic and magnetic structures and of the chemical bonding properties point to trivalent cerium for 1 ≤xH ≤ 1.33. In contrast, for lower hydrogen amounts the hydride system stays in an intermediate-valent state for cerium, like in CeRhSn. The influence of the insertion of hydrogen is addressed from both the volume expansion and chemical bonding effects. The latter are found to have the main influence on the change of Ce valence character. Spin polarized calculations point to a finite magnetic moment carried by the Ce 4f states; its magnitude increases with xH in the range 1 ≤xH ≤ 1.33.

Preliminary characterization of the intermetallic 'YNi' obtained by both mechanical grinding and alloying

Abstract The intermetallic compound YNi and the (Y+Ni) mixture were submitted to a high-energy milling process under argon atmosphere. X-ray powder diffraction and microprobe analysis revealed in both cases the formation of a new phase ‘YNi’. Its structural properties were different from those of the YNi as-cast sample (orthorhombic FeB type) and presented some similarities with GdNi (orthorhombic CrB type) milled under the same conditions. The application of isostatic pressure on the YNi as-cast sample gives a comparable result. This non-equilibrium material ‘YNi’ still exists even after annealing treatments performed up to 873 K. The presence of air during milling leads to the formation of a mixture of (oxy)nitride Y(O,N) and Ni metal and the new phase ‘YNi’ is not synthesized under such conditions. Also, the influence of the milling process on the magnetic properties of similar compounds such as GdNi and ErNi is discussed.

Two superstructures of Ce3Rh4Ge4

Abstract Two different samples of Ce3Rh4Ge4 were synthesized from different starting compositions by melting of the elements in an arc-melting furnace followed by annealing sequences in a sealed tantalum ampoule in a muffle furnace. The structures of two different stacking variants were refined on the basis of temperature dependent single-crystal X-ray diffractometer data. At high temperature Ce3Rh4Ge4 adopts the U3Ni4Si4 type structure with strongly enhanced anisotropic displacement parameters for the Rh1 atoms. For the two different crystals, additional reflections start to appear at different temperatures. The first crystal showed additional reflections already at room temperature (stacking variant I) and the second one showed additional reflections emerging below 270 K (stacking variant II). Stacking variant I could be described with the (3+1)D superspace group I2/m(α0γ)00; α=1/2a*, γ=1/2c*; (Z=2), 1252 F2 values, 48 variables, wR=0.0306 for the main and wR=0.0527 for 440 1st order satellite reflections, similar to Pr3Rh4Ge4. For stacking variant II the (3+1)D superspace group is Immm(α00)00s; α=1/2a*; (Z=2). The structure could be refined with 1261 F2 values, 53 variables and residuals of wR=0.0331 for the main reflections and wR=0.1755 (R1obs=0.0788) for the 1st order satellite reflections, [a=406.2(1), b=423.7(1) and c=2497.1(1) pm]. The commensurate description could be transformed to a three-dimensional (3D) supercell with space group Pnma and Z=4: a=812.5(1), b=423.7(1), c=2497.1(2) pm, 1261 F2 values, 69 variables and wR=0.0525. The relation of the U3Ni4Si4 type structure, the (3+1)D modulated and the 3D supercells are discussed on the basis of group-subgroup schemes. Ab initio electronic structure calculations are in line with the diffraction experiments, revealing the lowest total energy for the Pnma phase.

Assessment of Charged AuNPs: From Synthesis to Innate Immune Recognition

Gold nanoparticle (AuNP) physicochemical characteristics, mainly size and charge, modulate their biodistribution, cytotoxicity, and immunorecognition as reported from in vitro and in vivo studies. While data from in vitro studies could be biased by several factors including activation of cells upon isolation and lack of sera proteins in the microenvironment of primary generated cell lines, in vivo studies are costly and time-consuming and require ethics consideration. In this study, we developed a simple and novel in vivo-like method to test for NP immunorecognition from freshly withdrawn human blood samples. AuNPs with a size range of 30 ± 5 nm coated with cationic poly(L-lysine) (PLL) dendrigraft and slightly negative poly(vinyl alcohol) (PVA) were synthesized in water. PLL-capped AuNPs were further coated with poly(ethylene glycol) (PEG) to obtain nearly neutrally charged PEG-AuNPs. Physicochemical properties were determined using zeta potential measurements, UV-Vis spectroscopy, dynamic light scattering (DLS), and scanning electron microscopy (SEM). Gel electrophoretic separation, zeta potential, and DLS were also used to characterize our NPs after human blood plasma treatment. PLL-AuNPs showed similar variation in charge and binding affinity to plasma proteins in comparison with PVA-AuNPs. However, PLL-AuNPs.protein complexes revealed a drastic change in size compared to the other tested particles. Results obtained from the neutrophil function test and pyridine formazan extraction revealed the highest activation level of neutrophils (~70%) by 50 μg/mL of PLL-AuNPs compared to a null induction by PEG- and PVA-AuNPs. This observation was further verified by flow cytometry analysis of polymorphonuclear cell size variation in the presence of coated AuNPs. Overall, our in vivo-like method, to test for NP immunorecognition, proved to be reliable and effective. Finally, our data supports the use of PEG-AuNPs as promising vehicles for drug delivery, as they exhibit minimal protein adsorption affinity and insignificant charge and size variation once introduced in whole blood.

Fabrication of biomimetic titanium laminated material using flakes powder metallurgy

Inspired from the microstructure of natural biological materials, a laminated titanium material was successfully elaborated using a novel approach of “flakes powder metallurgy.” Ti flakes powders, used as building blocks of the layers microstructure, were prepared by ball milling. They were then assembled into fully dense laminated materials using the spark plasma sintering technique. The results show (1) an anisotropy microstructure of the sintered material prepared from the flakes powder, (2) 15% of contribution of the lamellar architecture to the strength (hardness) of the material, and (3) faster densification of the flakes powder compared to unmilled powder.

Carbon-modified MgH2: Experimental and ab-initio Investigations

The results of experimental and theoretical investigations of carbon-modified MgH2 for improving its sorption performances in hydrogen storage devices are reported. Large changes on its absorption/desorption capacities have been found. The following aspects are considered: size effects where finer particles obtained by energetic ball milling enable easier penetration, catalytic effects of carbon at the surface, and entrance of small quantities of C interstitially into the MgH2 structure. The energies and charge densities as studied by DFT suggest the activation of MgH2 through a decrease of the cohesive energy of the pristine hydride and a reduced ionic charge on hydrogen. Graphical Abstract Carbon-modified MgH2: Experimental and ab-initio Investigations