Nanoparticles alloying in liquids: Laser-ablation-generated Ag or Pd nanoparticles and laser irradiation-induced AgPd nanoparticle alloying

International audienceLaser irradiation of a mixture of single element micro/nanomaterials may lead to their alloying and fabrication of multielement structures. In addition to the laser induced alloying of particulates in the form of micro/nanopowders in ambient atmosphere which forms the basis of the field of additive manufacturing technology another interesting problem is the laser induced alloying of a mixture of single element nanoparticles in liquids since this process may lead to the direct fabrication of alloyed nanoparticles colloidal solutions. In this work Ag and Pd bare, surface ligand-free nanoparticles in solution were prepared by laser ablation of the corresponding bulk target materials separately in water, the two solutions were mixed and the mixed solution was laser irradiated for different time durations in order to investigate the laser induced nanoparticles alloying in liquid. Nanoparticles alloying and formation of AgPd alloyed nanoparticles takes place with the decrease of the intensity of the surface plasmon resonance peak of the Ag nanoparticles (at ~405 nm) with the irradiation time while the low wavelength interband absorption peaks of either Ag or Pd nanoparticles remain unaffected by the irradiation for times even as long as 30 mins. The alloyed nanoparticles have lattice constants with values between those of the pure metals which indicates that they consist of Ag and Pd in approximately 1:1 ratio similar to the atomic composition of the starting mixed nanoparticles solution. Formation of nanoparticle networks consisting of bimetallic alloyed nanoparticles and nanoparticles which remain as single elements even after the end of the irradiation, joining together, are also formed. The binding energies of the 3d core electrons of both Ag and Pd nanoparticles shift to lower energies with the irradiation time also a typical characteristic of AgPd alloyed nanoparticles

Structural and hydrogenation study on the ball milled TiH2eMgeNi

International audienceWith the aim of further understanding for TieNieMg alloys and their hydrogenation behavior, powders of TiH2, Mg and Ni with the molar ratio of 3:1:2 have been mechanically milled for 10 h, 20 h, 30 h, 40 h according to the stoichiometry (TiH2)1.5Mg0.5Ni. Microstructures of the milled sample were analyzed and their hydrogenation properties as negative electrodes for Ni-MH batteries were studied. Phase change with milling time revealed the fast formation of the Ti-Mg-H FCC phase. The alloying priority among Ti, Mg and Ni was demonstrated by comparing phase compositions in different milling time. Hydrogen capacities evaluated by both solidegas reaction and electrochemical cycling under galvanostatic conditions show that overall capacities increase with milling time. Except for the sample milled 10 h, which hardly delivers any reversible hydrogen capacity, all samples exhibit excellent cycling stability after capacity drop in the first few cycles. The best discharge capacity 100 mAh/g is observed for the sample milled 40 h. The PCI (Pressure-Composition-Isotherms) and GITT (Galvanostatic Intermittent Titration Technique) curves indicate that all samples absorb hydrogen in solid solution. The measured capacities are concluded to be contributed by the TieMgeH phase and the TiNi phase, while only the latter can provide reversible capacity

Effect of Reaction Parameters on Composition and Morphology of Titanate Nanomaterials

International audienceIn the present article, we report the synthesis of titanate nanotubes and nanoribbons with controlled morphology, structure, and chemical composition depending on the main parameters of the synthesis. Hydrothermal processing time, grain size of the precursor, type of agitation, and acid treatment were investigated, and the principal controversies mentioned in the literature such as nanotube crystallographic structure, their chemical composition, and acid treatment impact are discussed. These controversies may be due to the heterogeneities present in all the samples and are rarely considered in the literature. These nanostructures were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy. A careful desummation of the first XRD peaks revealed the presence of both nanosheets and nanotubes and allowed an estimation of their proportions. In addition, the titanate nanotube section is observed to be not perfectly circular but rather elliptic. Moreover, the first acid treatment effect is shown to remove any trace of sodium and structural water. The second effect of acid washing is a morphological evolution

Nature and origin of natural Zn clay minerals from the Bou Arhous Zn ore deposit: Evidence from electron microscopy (SEM-TEM) and stable isotope compositions (H and O)

International audienceZn-clay minerals have been found in the non-sulfide deposit of Bou Arhous (High Atlas, Morocco). They occur as white or ochre clays embedding willemite (Zn2SiO4) and are commonly associated to red detrital clays in karstic cavities. Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) with Energy Dispersive X-ray (EDX) analyses were combined in order to characterize the clay minerals and to determine the mechanism of their formation. XRD patterns on oriented and powdered clays and Fourier Transform Infrared (FTIR) spectroscopic analyses suggest that fraipontite is the major Zn clay phase (with some smectite interstratifications). SEM observation (back-scattered electron mode) shows that Zn clays are closely associated to willemite; euhedral willemite crystals show partial dissolution that preferably affects edges adjacent to newly formed fraipontite. Zn clays are also present as aggregates of about 50 μm filling the porosity or pervading the detrital clays. Intimate mixtures of Zn clays with detrital micas can also be observed. TEM-EDX analyses were carried out on clay separates but also on TEM foils prepared by Focused Ion Beam (FIB) milling directly on the thin section. Low- and high-resolution transmission electron microscopy images were acquired on selected areas preserving the texture of the sample. Two types of textural sites were selected: the Zn clay aggregates filling the porosity and the detrital clays partially replaced by Zn clay minerals. STEM-EDX map and point analyses confirm the occurrence of fraipontite. Individual particles of clay minerals with about 10% of Zn were analyzed. Structural formulae support the presence of a trioctahedral TO clay mineral like fraipontite. In the analyzed aggregates, the clays are composed of crystals of about 0.5–1 μm in diameter and 10 to 100 nm in thickness. At high magnification, the 0.7 nm layer periodicity was clearly imaged. Double layer periodicity is also common. In some fraipontite crystals, some intercalations with 1 nm layer were imaged. Stable isotope measurements suggest that this Zn clay mineral formed by direct precipitation of fluids which could be meteoritic and/or hydrotherma

Effect of Ni content on the structure and hydrogenation property of mechanically alloyed TiMgNix ternary alloys

International audienceIn this study, TiMgNix samples (x ¼ 0.2, 0.4, 0.6, 0.8, 1) have been prepared by mechanicalalloying using a planetary high-energy ball mill. The structural transformations werecharacterized by XRD and indicated that all the as-milled TiMgNix alloys consist of mixturesof crystalline Mg and amorphous Ti-Ni-(Mg) phase. TEM analyses also show thatnanocrystallites and amorphous phases coexist in the as-milled TiMgNi alloy. Electrochemicaltest shows that the TiMgNi composition yields the highest discharge capacity.The discharge capacities and activation properties of TiMgNix alloys linearly increase withincreasing Ni content. The MgTiNi0.8 composition boasts the best cycling property which isconsistent with its XRD pattern after the electrochemical test. No decomposition norcrystallization are found after 21 consecutive charge/discharge cycles which implies thatthe as-milled TiMgNix alloys possess a good corrosion resistance in alkaline electrolytes.PCI measurements were carried out at 598 K and 648 K on the TiMgNi composition. Thepressure plateau during hydrogen absorption is raised by two steps and its level increaseswith increasing temperature. The hydrogen absorption capacity of TiMgNi is around 1.3weight %. XRD analyses show that the dehydrogenated TiMgNi sample consists of TiH2,Mg, Mg2Ni and TiNi3, in which Mg and Mg2Ni are identified as the hydrogen absorptionphases

Microstructure impact on high temperature corrosion behavior of AISI 316L stainless steel additively manufactured by Selective Laser Melting (AM-SLM)

International audienceAdditive Manufacturing by Selective Laser Melting (AM-SLM) is a near-net shape method producing dense and geometrically complex materials from micrometric powders. This process involves complete melting and very high cooling rates who induce a refinement of microstructure, improving the mechanical properties of the material [1,2]. However, the impact of these new microstructures on real functioning properties, like for instance the high temperature durability, needs to be studied. In this purpose, AISI 316L is considered in this work. Samples elaborated by AM-SLM and by conventional metallurgy were oxidized under laboratory air at 900°C for periods up to 3000h. The results highlight better behaviour for AM samples, which present a very good corrosion resistance throughout the 3000 hours. The conventional samples show a good resistance only during the first 1000 hours. These differences were related to the different composition of the oxide layers growing on the surface of the samples during the high temperature ageing: protective chromia for AM-SLM and non-protective iron oxides for conventional samples. To explain these differences of reactivity, several hypotheses were considered. XRD, SEM-EBSD and TEM studies were performed on initial samples in order to evaluate their microstructure, surface mechanical state and crystallographic orientation. The most promising hypothesis seems to be related to the microstructure (probably at nanoscale) of the samples. For AM-SLM coupons, a typical cellular structure was identified by TEM, with a size between 0.2 and 1 µm, corresponding to a very dense network of dislocations, which accumulate forming cell walls. Dislocation might act during the high temperature exposure as short-circuit paths for Cr diffusion from the bulk to the surface allowing the growth of protective scales for long ageing times. Moreover, AM-SLM samples found to contain large quantity of nano-inclusion that might equally influence corrosion behaviour

Improving structural stability of water-dispersed MCM-41 silica nanoparticles through post-synthesis pH aging process

The colloidal and structural stabilities of MCM-41 mesoporous silica nanoparticles (MSNs) are of great importance in order to prepare optimal nanovectors. In this paper, MSNs (approximatively 160 nm in diameter) were synthesized using n-cetyltrimethylammonium bromide as a template and tetraethyl orthosilicate as a silica source under high N2 flow (MSN/N2) to obtain stable dispersions in water. The degradation of the porous nanoparticles was investigated by immersion in water. The morphology and the porous structure were studied by TEM, XRD, N2 sorption, and 29Si MAS NMR and were compared to that of MSNs prepared in ambient air (MSN/air). The volumetric properties of the MSN/N2 after 1 day in water were drastically more decreased than MSN/air (a pore volume decrease of 85 % for MSN/N2 and 59 % for MSN/air) and the 2D-hexagonal porous structure was totally lost. Furthermore, synthesizing MSNs under a high N2 flow leads to a decrease in the synthesis yield (45 % MSN/N2 and 75 % for MSN/air). The lower structural stability of the MSN/N2 is explained by the lower polycondensation degree of the MSN/N2 observed by 29Si MAS NMR (Q4/Q3 = 0.86 for MSN/N2 and 1.61 for MSN/air) and the lower silica molar ratio in the nanomaterials (SiO2/CTA = 3.9 for MSN/N2 7.1 for MSN/air). This allows for enhanced solubilization of silica in water. Four strategies were hence evaluated in order to reinforce the porous structure of the MSNs. Among them, the most efficient route was based on a pH adjustment of the colloidal suspension (pH 7.5) after 2 h of synthesis without any purification and while keeping a N2 static atmosphere (called MSN/N2/7.5). After 1 day in water, the volumetric and structural properties of MSN/N2/7.5 were similar to that obtained for MSN/air. The improvement of the stability arose as a result of the increase in the silica condensation (Q4/Q3 = 1.58) and silica molar ratio in the nanomaterials (SiO2/CTA = 6.8). After the post-treatment, the silica framework condensation is improved while keeping the colloidal stability, thus allowing further functionalization and/or drug loading. Cytotoxicity assays using SW480 cancer cells show a greater improvement in the cell viability

Nanoparticles alloying in liquids: Laser-ablation-generated Ag or Pd nanoparticles and laser irradiation-induced AgPd nanoparticle alloying

International audienceLaser irradiation of a mixture of single-element micro/nanomaterials may lead to their alloying and fabrication of multi-element structures. In addition to the laser induced alloying of particulates in the form of micro/nanopowders in ambient atmosphere (which forms the basis of the field of additive manufacturing technology), another interesting problem is the laser-induced alloying of a mixture of single-element nanoparticles in liquids since this process may lead to the direct fabrication of alloyed-nanoparticle colloidal solutions. In this work, bare-surface ligand-free Ag and Pd nanoparticles in solution were prepared by laser ablation of the corresponding bulk target materials, separately in water. The two solutions were mixed and the mixed solution was laser irradiated for different time durations in order to investigate the laser-induced nanoparticles alloying in liquid. Nanoparticles alloying and the formation of AgPd alloyed nanoparticles takes place with a decrease of the intensity of the surface-plasmon resonance peak of the Ag nanoparticles (at ~405 nm) with the irradiation time while the low wavelength interband absorption peaks of either Ag or Pd nanoparticles remain unaffected by the irradiation for a time duration even as long as 30 min. The nanoalloys have lattice constants with values between those of the pure metals, which indicates that they consist of Ag and Pd in an approximately 1:1 ratio similar to the atomic composition of the starting mixed-nanoparticle solution. Formation of nanoparticle networks consisting of bimetallic alloyed nanoparticles and nanoparticles that remain as single elements (even after the end of the irradiation), joining together, are also formed. The binding energies of the 3d core electrons of both Ag and Pd nanoparticles shift to lower energies with the irradiation time, which is also a typical characteristic of AgPd alloyed nanoparticles. The mechanisms of nanoparticles alloying and network formation are also discussed

Hot Carriers-Induced Nonlinear Photoluminescence in Thin Indium Tin Oxide Layer Patterned by Ga Ion Beam Milling

26 p.This paper explores the nonlinear photoluminescence emitted by Indium Tin Oxide (ITO) thin layers patterned by focused gallium ion beam milling. Using tightly focused near-infrared femtosecond pulsed laser excitation, a broad up-converted luminescence spanning the visible spectrum is detected. The intensity of the luminescence follows a non-monotonous relationship with milling doses and can be related to the modification of the ITO electronic band structure by the implantation of Ga ions. The shape and the power dependence of the spectrum share strong similarities with nonlinear photoluminescence arising from metals. The results are consistent with a nonlinear luminescence process originating from the radiative decay of photo-generated hot carriers. The ther-1 mal coefficient relating the hot carrier temperature to the laser intensity is determined as a function of milling dose

Hot Carriers-Induced Nonlinear Photoluminescence in Thin Indium Tin Oxide Layer Patterned by Ga Ion Beam Milling

26 p.This paper explores the nonlinear photoluminescence emitted by Indium Tin Oxide (ITO) thin layers patterned by focused gallium ion beam milling. Using tightly focused near-infrared femtosecond pulsed laser excitation, a broad up-converted luminescence spanning the visible spectrum is detected. The intensity of the luminescence follows a non-monotonous relationship with milling doses and can be related to the modification of the ITO electronic band structure by the implantation of Ga ions. The shape and the power dependence of the spectrum share strong similarities with nonlinear photoluminescence arising from metals. The results are consistent with a nonlinear luminescence process originating from the radiative decay of photo-generated hot carriers. The ther-1 mal coefficient relating the hot carrier temperature to the laser intensity is determined as a function of milling dose