A multimaterial based on metallic copper and spinel oxide made by powder bed laser fusion: A new nanostructured material for inert anode dedicated to aluminum electrolysis

Coherent 3D parts of cermets, made of spinel ferrite and metallic copper, are prepared in a nitrogen atmosphere by powder bed additive manufacturing of a mixture of oxide and metallic powders. The cermets obtained are constituted by the association of blocks of about 500 μm, which create between them, a relatively large porosity (# 35%). Each block is subdivided into intimately nested zones that are either predominantly metallic or predominantly oxide type. In the metal parts, a dispersion of oxide crystals is observed, whose size varies from ten nanometers to a few micrometers. A similar distribution of metal particles in the oxide zones is also demonstrated. The chemical compositions of metallic and oxide phases are slightly different from those in the initial powders. Due to the high energy density of the laser, the melting temperature of the metal and oxides could be reached and therefore this could explain the chemical composition variations in the phases and the shape of oxide and metallic nanometric grains. The process used can therefore be described as powder bed fusion. These nanostructured cermets have been used as "inert" anodes for the electrolysis of aluminum in molten cryolite. Although penalized by a high porosity, 5 mm in diameter anodes allowed to carry out an electrolysis for 4 h. Since Spark Plasma Sintering can greatly reduce their porosity, while retaining their specific microstructure, the implementation of additive manufacturing for producing "inert" anodes is therefore of real interest

Composition and porosity graded La2−xNiO4+δ (x≥0) interlayers for SOFC: Control of the microstructure via a sol–gel process

We have developed composition and porosity graded La2−xNiO4+δ (x≥0) cathode interlayers for low-temperature solid oxide fuel cell that exhibit good adhesion with the electrolyte, controlled porosity and grain size and good electrochemical behaviour. La2−xNiO4+δ (x≥0) monolayers are elaborated from a derived sol–gel method using nitrate salts, acetylacetone and hexamethylenetetramine in acetic acid. As a function of the organic concentration and the molar ratio of lanthanum to nickel, these layers present platelets or spherical shape grains with a size distribution ranging from 50 to 200 nm, as verified by SEM-FEG. On the basis of this processing protocol, we prepared porosity and composition graded lanthanum nickelates interlayers with effective control of the pore distribution, the nanocrystalline phase, the thickness and the subsequent electrochemical properties

Synthesis of La2NiO4+d oxides by sol–gel process: Structural and microstructural evolution from amorphous to nanocrystallized powders

In this paper, the structural and microstructural transition from amorphous to La2NiO4+d nanocrystallized oxides synthesized by a polymeric route based on Pechini’s work has been studied by several experimental techniques including infrared spectroscopy and wide angle X-ray scattering. The synthesis parameters which govern this transition have been identified in order to synthesize La2NiO4+d oxides with various mean crystallite sizes and non stoichiometry levels. Therefore, it has been demonstrated that the control of the nature and the content of organic compounds in the polymeric sols allows the preparation of La2NiO4+d metastable phases with a mean crystallite size ranging from 100 to 220 nm and a non stoichiometry level ranging from 0.15 to 0.22 at 25 8C. As the cathodic performance strongly depends on the physical characteristics of the oxides, this study shows that our versatile process may be suitable to elaborate electrodes with different electrochemical behaviours

GNSS transpolar earth reflectometry exploriNg system (G-TERN): Mission concept

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA's Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a "dynamic mapper" of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025-2030 or optimally 2025-2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance

Mixed-Valence Defect Ferrites : a New Family of Fine Powders and Thin Films of Spinel Ferrites

When highly divided spinel ferrites become reactive enough with oxygen, to allow the oxidation of the Fe2+ ions at low temperature and of substitute cations too, when these cations are capable of different valence states. We prepared fine particles of spinel ferrites substituted by Mn, Mo, Cu, by "chimie douce", especially from oxalate precursors and used them to reveal and to study the oxido-reduction phenomena occurring in these finely divided materials. It was shown that the oxidation created a new family of spinel ferrites : the mixed-valence defect ferrites, having specific characteristics and properties. The ferrites of this type can be fine powders prepared at low temperature, or ground ferrites obtained at high temperature, or thin films

Thin Films and Fine Powders of Ferrites : Materials for Magneto-Optical Recording Media

In the near future, the magneto-optical (MO) recording will require materials having high MO effects at short wavelengths (400-500 nm). Ferrites, especially garnets, but also spinel ferrites have highly advantageous MO properties in this spectrum and also have very stable structural and chemical properties. The present paper evaluates their used as MO media, in comparison with the rare-earth transition metals alloys and the metallic multilayers

Fine Powders of Co-Mn Cation Deficient Spinel Ferrites for Magneto-Optical Pigments

Very small particles of Co-Mn defect spinel ferrites with acicular and spherical shape were prepared. Their magnetic and magneto-optical properties were measured in function of their oxidation state and their size. It was shown that the coercivity of acicular (AP) and spherical (SP) particles with a mean crystallite size close to 20 nm, reached 3800 and 2950 Oe respectively. The SP coercivity decreases when the grains sizes become lower than 20 nm, but remains higher than 1000 Oe for particles having crystallites close to 10-15 nm. The Curie temperature decreases also sligthly when the grains are smaller than 20 nm, while the remanent Faraday rotation falls from 0.6 to 0 deg/µm when the crystallite size is reduced from 40 to 7-8 nm. The Co-Mn ferrite particles studied have interesting properties, even they have not, for now, all the required properties to be high performance pigments for magneto-optical recording

Optical and Magnetooptical Properties of Copper and Cobalt-Manganese Ferrite Thin Films

Optical absorption and Faraday rotation of copper and cobalt-manganese ferrite thin films, prepared by sputtering, were measured in the visible and near infrared spectral regions. Main magneto-optical features can be explained by the respective transitions of CU2+ and Co2+ ions tetrahedrally and octahedrally coordinated. Annealings at 450 and 665°C cause migration of these ions into tetrahedral positions and, consequently, increase corresponding peaks in the figure of merit. Therefore, these films range among the promissing materials for the magneto-optical recording

Microstructural characterization of CoMnFeO

CoMnFeO4 thin films are stable materials useful to study the influence of radio-frequency sputtering experimental conditions, on the microstructure of oxide films. From various techniques of electronic microscopy, gas adsorption techniques and ellipsometry measurements, it was shown that such oxides films prepared with 0.5 Pa sputtering argon pressure and 5 cm target–substrate distance are very dense. On the other hand, the samples obtained under higher pressure and/or longer distance, are microporous. This porosity is mainly due to shadowing and energetic effects of sputtered particles. According to different characterization techniques, a simple model is proposed to describe the microstructure of the films studied