High resolution electron energy loss spectroscopy of manganese oxides: application to Mn3O4 nanoparticles

Manganese oxides particularly Mn3O4 Hausmannite are currently used in many industrial applications such as catalysis, magnetism, electrochemistry or air contamination. The downsizing of the particle size of such material permits an improvement of its intrinsic properties and a consequent increase in its performances compared to a classical micron-sized material. Here, we report a novel synthesis of hydrophilic nano-sized Mn3O4, a bivalent oxide, for which a precise characterization is necessary and for which the determination of the valency proves to be essential. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and particularly High Resolution Electron Energy Loss Spectroscopy (HREELS) allow us to perform these measurements on the nanometer scale. Well crystallized 10–20 nm sized Mn3O4 particles with sphere-shaped morphology were thus successfully synthesized. Meticulous EELS investigations allowed the determination of a Mn3+/Mn2+ ratio of 1.5, i.e. slightly lower than the theoretical value of 2 for the bulk Hausmannite manganese oxide. This result emphasizes the presence of vacancies on the tetrahedral sites in the structure of the as-synthesized nanomaterial

Optical properties of metallic nanowires by valence electron energy loss spectroscopy

The determination of intrinsic conductivity of nanowires (NWs) is essential to understand the charge transport behaviour involved in hybrid nanocomposites. These high conductive metallic fillers are good candidate to improve electrical properties of composites in aeronautic industry. The main difficulty is often to achieve the combination of both high spatial resolution and information on the physical properties as electrical conductivity. One of the suitable methods to give the desired information is electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM) mode, especially in the low-loss region. This is demonstrated by studying the nickel and gold nanowire

Eco-Efficient Synthesis of LiFePO4 with Different Morphologies for Li-Ion Batteries

LiFePO4 is presently the most studied electrode material for battery applications. It can be prepared via solution, although it requires well-controlled pH conditions to master the iron valence state in the newly created material. Here we report its synthesis via the use of "latent bases" capable of releasing a nitrogen base upon heating. This way of controlling the reaction pH enables, in the absence of excess Li, the preparation of Fe+3-free LiFePO4 powders having various morphologies and showing good electrochemical performance. This approach is shown to offer great opportunities for the low-temperature synthesis of various electrode materials

Effect of surface preparation on the corrosion of austenitic stainless steel 304L in high temperature steam and simulated PWR primary water

The corrosion behavior of 304L grade stainless steel (SS) in high-temperature steam and in a simulated Pressurized Water Reactor (PWR) is studied. The goal was to characterize the nature of the oxide coating generated during 500 h exposure of samples in a 400 °C steam (200 bar) or a 340 °C simulated PWR. Accelerating the effect of the steam environment as well as the influence of surface preparation have been studied. Two initial sample surfaces were used: mechanical polishing and finishing grinding. Oxide coatings were investigated using TEM imaging coupled with EELS spectroscopy and R – SIMS (Secondary Ion Mass Spectroscopy)

Structural and electrical properties of gold nanowires/P(VDF-TrFE) nanocomposites

High aspect ratio gold nanowires were uniformly dispersed into a poly(vinylidene difluoride–trifluoroethylene) [P(VDF-TrFE)] matrix. The nanowires were synthesized by electrodeposition using nanoporous anodic alumina oxide templates. The intrinsic optical conductivity of the gold nanowires was determined by valence electron energy loss spectroscopy. The effect of increasing volume fraction of Au nanowires on the morphology and crystallization of P(VDF-TrFE) matrix was investigated by differential scanning calorimetry. The crystallinity of P(VDF-TrFE) is strongly depressed by the randomly dispersed nanowires. Above 30 vol% the crystallization of P(VDF-TrFE) is suppressed. The bulk electrical conductivity of nanocomposite films, at room temperature, obeys a percolation behaviour at a low threshold of 2.2 vol% and this was confirmed using the surface resistivity value. An electrical conductivity of 100 S m−1 is achieved for a 3 vol% filler content

Influence of secondary phases during annealing on re-crystallization of CuInSe2 electrodeposited films

Electrodeposited CuInSe2 thin films are of potential importance, as light absorber material, in the next generation of photovoltaic cells as long as we can optimize their annealing process to obtain dense and highly crystalline films. The intent of this study was to gain a basic understanding of the key experimental parameters governing the structural–textural-composition evolution of thin films as function of the annealing temperature via X-ray diffraction, scanning/transmission electron microscopy and thermal analysis measurements. The crystallization of the electrodeposited CuInSe2 films, with the presence of Se and orthorhombic Cu2−xSe (o-Cu2−xSe) phases, occurs over two distinct temperature ranges, between 220 °C and 250 °C and beyond 520 °C. Such domains of temperature are consistent with the melting of elemental Se and the binary CuSe phase, respectively. The CuSe phase forming during annealing results from the reaction between the two secondary species o-Cu2−xSe and Se (o-Cu2−xSe+Se→2 CuSe) but can be decomposed into the cubic β-Cu2−xSe phase by slowing down the heating rate. Formation of liquid CuSe beyond 520°C seems to govern both the grain size of the films and the porosity of the substrate–CuInSe2 film interface. A simple model explaining the competitive interplay between the film crystallinity and the interface porosity is proposed, aiming at an improved protocol based on temperature range, which will enable to enhance the film crystalline nature while limiting the interface porosity

Piezoelectric properties of polyamide 11/NaNbO3nanowire composites

Polyamide 11(PA 11)/sodium niobate nanowire (NW) 0–3 composites with different volume fractions of NWs were synthesized. The electric polarization (P) was measured as a function of the applied electric field (E). The P–E hysteresis loop was used to work out the remanent polarization Pr of these materials. The dielectric permittivity and the piezoelectric strain constant were determined. Good impedance matching between inorganic and organic phases leads to higher electroactivity than conventional lead-free 0–3 composites. The piezoelectric voltage of the PA 11/NaNbO3 NW composites is of the same order as those obtained for fluorinated piezoelectric polymers. These composites could have some applications in flexible, low-cost, environmentally friendly piezoelectric sensors and actuators

Structure of graphite precipitates in cast iron

This study presents microstructural investigations of graphite precipitates found in cast irons. Binary Fe eC, FeeCeSb and FeeCeCe alloys containing different graphite morphologies (flake and spheroidal) were produced and compared to commercial irons in an attempt to rationalize the effect of Sb and Ce on graphite growth. The extensive use of transmission electron microscopy (mainly electron diffraction and high resolution lattice fringe imaging) enabled further understanding of graphite growth mechanisms. It was found that the inner structure of graphite precipitates consists of growth blocks stacked upon each other, for all investigated morphologies. This suggests that graphite crystals develop mainly by a 2D nucleation and growth mechanism, and that the final shape of the precipitates is associated to the occurrence of crystallographic defects in the graphite lattice (such as twins, misorientations and rotations) during growth

Nanotexture influence of BaTiO3 particles on piezoelectric behaviour of PA 11/BaTiO3 nanocomposites

The piezoelectric activity of a hybrid ferroelectric nanocomposite, i.e. polyamide 11/barium titanate (BT), has been investigated for different loadings of BT particles. The BT volume fraction (/) was ranging from 0.024 to 0.4 with a particle size of 50, 100, 300 and 700 nm. The influence of polarization mode on the piezoelectric behaviour has been studied. The magnitude of the poling field used in this study is in the same order of magnitude of the one used for bulk BT i.e. significantly lower than for piezoelectric polymers. The optimum piezoelectric coefficient is reached when the amorphous phase of the polymeric matrix is in the liquid state i.e. for a polarization temperature higher than the glass transition and for time constant allowing macromolecular mobility. The composite piezoelectric activity decreases for particles size lower than 300 nm due to the loss of the tetragonal phase. The nanotexture of these particles has been investigated by transmission electron microscopy (TEM) and high-resolution TEM. A core shell structure has been observed. An increase of the longitudinal piezoelectric strain coefficient d33 with the raising of BT volume fraction was shown. Contrary to inorganic piezoelectric ceramics, the dielectric permittivity of hybrid composites remains moderate; therefore it allows the piezoelectric voltage coefficient of composites to be higher than ceramics

Structural characterization of the scale formed on a Ti–46Al–8Nb alloy oxidised in air at 700 C

The structures of the oxide scale formed on a lamellar (gþ a2) Ti46Al8Nb alloy after heat-treatment in air at 700 C for 50 and 1000 h have been compared. Though the outer scale is thicker after 1000 h, both oxide scales are similarly layered with an outer aluminium-rich layer. The main difference is that the aluminium-rich oxide is amorphous after 50 h while it becomes cubic gamma alumina after 1000 h. After 50 h, the presence of TiN was detected at the interface between the scale and the base metal. After 1000 h of oxidation, the subscale region is divided into two clearly separated zones differing by their composition, with a thick TiN layer close to the oxide scale. From these observations, it appears that the development of the oxide scale at 700 C is similar to the scheme proposed in the literature for short times at higher temperatures, with the initial formation of a transient aluminium-rich oxide layer, which here is amorphous, and precipitates of TiN at the scale/metal interface that oxidise afterwards to rutil