Electro-precipitation of magnetite nanoparticles: an electrochemical study

Nanoparticles of magnetites (Fe3O4) are synthesized with a new process based on electro-precipitation in ethanol medium. A mechanism pathway is proposed consisting of a Fe(OH)3 precipitation followed by the reduction of iron hydroxide to magnetite in the presence of hydroxyl ions which are enerated at the cathode

Fluidized bed chemical vapor deposition of copper nanoparticles on multiwalled carbon nanotubes

Multi-walled carbon nanotubes tangled in easy-to-fluidize porous balls have been decorated by pure copper nanoparticles using a pre-industrial fluidized bed chemical vapor deposition process. Copper (II) acetylacetonate Cu(acac)2 was used as precursor. The low precursor volatility led to low deposition rates, responsible for a nonuniformity of the deposit both on the MWCNT balls and from the outer part to the center of the balls. An oxidative pre-treatment of the MWCNTs allowed to increase slightly the deposit weight and uniformity, by creating new nucleation sites on the nanotube surface. It also allowed decreasing the size of Cu nanoparticles by a factor of ten. A decrease of the deposition temperature increased more markedly the deposit weight, by probably favoring the formation of gaseous reactive intermediate species more reactive on the oxidized nanotube surface. A more efficient precursor delivery system would allow reaching higher deposition rates and much more uniform deposits, making possible an industrial production of metallized carbon nanotube

X-ray diffraction as a tool for the determination of the structure of double-walled carbon nanotube batches

The average structure of double-walled carbon nanotube DWCNT samples can be determined by x-ray diffraction XRD. We present a formalism that allows XRD patterns of DWCNTs to be simulated and we give researchers the tools needed to perform these calculations themselves. Simulations of XRD patterns within this formalism are compared to experimental data obtained on two different DWCNT samples, produced by chemical vapor deposition or by peapod conversion i.e., high-temperature peapod annealing. For each sample, we are able to determine structural aspects such as the number of walls, the diameter distribution of inner and outer tubes, the intertube spacing, and the bundled structure

Iron deposition on multi-walled carbon nanotubes by fluidized bed MOCVD for aeronautic applications

The fluidized bed MOCVD process has been studied in order to uniformly deposit iron nanoparticles on the outer surface of multi‐walled carbon nanotubes (MWCNTs) tangled in balls of 388 µm in diameter. Using ferrocene as organometallic precursor at atmospheric pressure, various reactive atmospheres of deposition (under N2, air and H2) and an ozone O3 surface pre‐treatment of MWCNTs were tested. Around 10 g Fe/100 g MWNCTs were deposited during each run. Under N2 at 650 °C on the raw MWCNTs, nanoparticles formed of Fe and Fe3C were deposited which have catalyzed the formation of carbon nanofibers (CNFs). 20 h of ozone (O3) pre‐treatment improved the number and distribution of iron nanoparticles but without increasing the surface coverage of nanotubes. A more intense amorphous carbon deposit also appeared. Under H2 at 550 °C, the amorphous carbon was partly eliminated but fewer iron nanoparticles were present. Under air at 450 °C, a part of the MWCNTs was lost and a Fe2O3 shell covered each remaining MWCNTs ball. New works are in progress to increase more markedly the surface reactivity of MWCNTs and to deposit pure iron. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

Decoration of carbon nanotubes by semiconducting or metallic nanoparticles using fluidized bed chemical vapour deposition

Multi-Walled Carbon Nanotubes (MWCNTs) have promising properties that make them potentially useful in a wide variety of applications. The decoration of MWCNTs by metallic or semiconducting nanoparticles aims to intensify some of their properties, in particular thermal and electrical conductivity. Fluidized Bed Chemical Vapour Deposition (FBCVD) is an efficient process to uniformly coat powders by various materials. The coating by SnO2, Fe and Si nanoparticles of MWCNTs (Graphistrength®) tangled in balls of 360 microns in mean diameter using the FBCVD process has been studied. The influence of some deposition parameters with and without oxidative pre-treatment is analysed on the nucleation and growth of nanoparticles. The various results obtained indicate that the intrinsic surface reactivity of MWCNTs is high enough for CVD precursors involving the formation of highly reactive unsaturated species such as silylene SiH2 formed from silane SiH4 pyrolysis in the case of Si deposition. But it must be enhanced for less reactive CVD precursors such as tin tetrachloride SnCl4 which needs the presence of oxygen-containing groups at the nanotube surface to allow Sn nucleation. So, provided the reactivity of the powder surface and that of the CVD precursors are well tuned, the FBCVD process can uniformly coat the outer surface of MWCNTs by metallic or semiconducting nanoparticles

Large-Scale Oxidation of Multi-Walled Carbon Nanotubes in Fluidized Bed from Ozone-Containing Gas Mixtures

100 g of multi-walled carbon nanotubes (MWCNTs) tangled in balls of 388 microns in Sauter diameter were treated per run in a pre-industrial scale fluidized bed reactor, using ozone-based gaseous mixtures at ambient temperature. The influence of ozone concentration and of the addition of water vapour was studied, for treatment durations between 1 h and 20 h. The process behavior was analyzed in terms of fluidized bed pressure drop and temperature profile. The nature and amount of the grafted oxygen based functions were analyzed, as the structural modifications created. An oxidation mechanism in two steps was evidenced, showing the grafting of hydroxyl, phenol and ether functions in a first step and then of lactone, quinone, carbonyl and carboxylic groups. A moderate etching of the MWCNT outer walls was observed. The amount of grafted functions and of structural defects increased with treatment duration and was highly exalted by the presence of water vapour. All the results obtained showed that the oxidation was uniform on the whole powder of the bed and from the outer part to the center of the balls, probably thanks to the high fluidization quality maintained all along the ozone treatment

Metal nanoparticles in contemporary potters’ master pieces: Lustre and red “pigeon blood” potteries as models to understand the ancient pottery

International audienceReduction of metal precursors within the molten glaze is a rather complex route to obtain coloured glaze. " Sang de boeuf " , " pigeon blood " or " flammé" first discovered glazes by the Chinese potters of the Song Dynasty (10 th c.) are produced by atmosphere controlled firing of copper-containing glaze on porcelain and stoneware body. Lustre pottery, an Abbasid potters' innovation (9 th c.), offers to the eyes of the connoisseur an iridescent reflection, which is only visible at specular position. For centuries connoisseurs' interest in these objects has been continuous and the development of transmission electronic microscopy (TEM) associated with energy-dispersive X-ray spectroscopy (TEM-EDX) allows us an in depth study of the micro and nano-structure of these objects. A porcelain with red " pigeon blood " decor made by the late famous French-American potter Fance Franck, and lustre stonewares made by the French potter Eva Haudum, have been investigated by TEM-EDX and nanochemical analysis in order to better understand the key parameters controlling the microstructure and the colour of glazes. Although some authors assigned the red colour of pigeon-blood to Cu 2 O, our results clearly demonstrate that the colour only arises from Cu° nanoparticles. Phase separation of the glassy phase was observed close to the surface. Concerning the lustrewares, analysis confirmed that the alternating reducing and oxidizing conditions during the firing lead well to the formation of metal-free/metal-rich alternate layers in the lustre decor

Decorated carbon nanotubes by silicon deposition in fluidized bed for Li-ion battery anodes

Multi-walled carbon nanotubes Graphistrength® were decorated with silicon by Fluidized Bed Chemical Vapor Deposition. The ability to fluidize of these nanotubes forming ball-shaped jumbles with diameters in the range of several hundreds of microns was first studied. Coating experiments from silane SiH4 were performed, in the 30-60wt. % range of silicon deposited. SEM and TEM imaging reveals that the nanotubes are coated by silicon nanoparticles uniformly distributed from the periphery to the center of the balls for the whole conditions tested. On-line acquisition of key process parameters evolution shows that the material remains fluidizable, even for large proportions of silicon deposited. The density of balls increases with the percentage of silicon deposited whereas their specific surface area decreases. This composite material is a promising candidate as anode material to replace graphite in lithium-ion batteries

Deposition of copper nanoparticles on ozone pre-treated MWCNTs in fluidized-bed CVD

In the field of aeronautics, the mass reduction of the on-board electronic equipment packaging is of major importance to make planes greener. To produce lighter packaging while keeping their electrical and thermal evacuation capacities and mechanical properties, a new composite material combining carbon nanotubes (CNTs) and polymer matrix represents a promising alternative to aluminium. The aim of this work is to improve the electrical and thermal conductivities of Multi-Walled CNTs, and consequently those of the final composite material, by depositing homogeneously dispersed nanoparticles (NPs) of copper on the MWCNT surface. Prior to copper deposition, Graphistrength®C100 MWCNTs tangled in porous balls of ca. 400 micrometres were oxidised in fluidized bed using a gaseous mixture of ozone, water vapor, and oxygen in order to increase their surface reactivity by grafting oxygen-containing groups and creating moderate structural defects uniformly on the MWCNT surface. 100 g of MWCNTs were treated for each experiment in a fluidization reactor at ambient temperature and atmospheric pressure. The same reactor was used to deposit copper NPs from Cu(acac)2 between 250°C and 280°C at atmospheric pressure, on both raw and pre-treated MWCNTs. On the raw MWCNTs, polycrystalline Cu NPs of several hundreds of nanometres are only present at the MWCNT ball surface over ~40 micrometre depth. With pre-treatment, the deposition of (much smaller, 20-50 nm) polycrystalline Cu nanoparticles occurs more uniformly both over the MWCNT surface and deeper inside the balls. The work demonstrates the upscalability of the process as a reasonably green and low cost technology

Fluidized Bed Chemical Vapor Deposition of Silicon on Carbon Nanotubes for Li-Ion Batteries

Silicon was deposited on balls of entangled multi-walled carbon nanotubes (CNT) with a mean diameter of several hundred microns, by Fluidized Bed Chemical Vapor Deposition from silane (SiH4). The weight total percentage of deposited silicon was between 30 and 70%, to test their efficacy in Li-ion battery anodes. TEM and SEM imaging revealed that silicon deposits were of the form of nanoparticles uniformly dispersed on the whole CNT surface. The diameter of these nanoparticles increases with the deposited silicon percentage from 18 to 36 nm whereas their density remains constant at 5 1022 nanoparticles/g of CNT. This indicates a low affinity of chemical species born from silane pyrolysis with the CNT surface for nucleation. The increase of the silicon nanoparticles diameter leads to the decrease of the specific surface area and the porous volume of the balls, probably due to the filling of the pores of the CNT network by silicon. A slight increase of the mean diameter of the balls was observed for the two highest silicon percentages, certainly due to the ability of the CNT network to be deformed under the mechanical stress induced by the silicon nanoparticles growth