Copper Nanoparticles Prepared fromOxalic Precursors

The synthesis of nanoparticles of copper metal via a soft chemistry route is presented in this paper. The method is based on the thermal decomposition under nitrogen or hydrogen of oxalic precursors with a well-controlled morphology and particle size. The precipitation of the copper oxalates in a water-alcohol medium allows the submicron size of the precursor grains to be controlled and, consequently, the nanometric size of the metallic copper particles to be determined, as required, between 3.5 and 40 nm. The majority of the final particles are made of pure copper metal although some present a superficial layer of cuprous oxide (Cu2O)

Preparation and electrical properties of dense micro-cermets made of nickel ferrite and metallic copper

Dense micro-cermets made of nickel ferrites and copper micrometric particles were obtained from partial reduction under hydrogenated atmosphere at 350 C of mixed copper nickel ferrites, and sintering in nitrogen at 980 C. The small copper particles are homogeneous in size and well dispersed in the spinel oxide matrix. No exudation of copper metal was observed after sintering. The micro-cermets prepared are semi-conducting materials with electrical conductivity lying from 44 to 130 S/cm at 980 C. Their overall characteristics make them interesting for inert anodes dedicated to aluminium electrolysis in melted cryolite

Correlation between the morphology of cobalt oxalate precursors and the microstructure of metal cobalt powders and compacts

Metal cobalt powders of well-controlled size and morphology were synthesized by thermal decomposition under hydrogen of precipitated cobalt oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strength of the metal compacts was measured. A precipitation from ammonium oxalate and oxalic acid gives rise to the formation of β-CoC2O4·2H2O particles of parallelepipedic and acicular morphology, respectively. An increase in the length to diameter ratio of the precursor particles favours an entanglement of the elementary grains during the thermal decomposition. Therefore, irregular and rough metal particles have been obtained. This specific morphology favours a mechanical interlocking of the particles during the compaction, leading to high values of green density and green strength of the metal compacts

Synthesis and characterization of Fe/Co/Ni alloys-MgO nanocomposite powders

A mixed oxalate β-Mg 0.896 Fe 0.047 Co 0.034 Ni 0.023 C 2 O 4 ·2H 2 O of well controlled size and morphology was prepared by coprecipitation. The corresponding quaternary solid solution between MgO, FeO, CoO and NiO was prepared by thermal decomposition and calcination in a H 2 /H 2 O/N 2 atmosphere. The selective reduction of the solid solution in an H 2 atmosphere was studied by a combination of X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and associated analysis. This work has brought to light the very high stability of Fe 2+ , Co 2+ and notably Ni 2+ when substituted for Mg 2+ in the MgO rocksalt lattice. It is necessary to perform the reduction at 1300 °C fully to reduce the transition metal ions. The alloy particles are either distributed as relatively large particles (tens to hundreds of nanometers) at the surface of the MgO grains or as much smaller particles (≤20 nm) probably located inside the matrix grains and epitaxial with it. The composition distribution of the large surface particles is fairly broad when the reduction was performed at 1100 and 1300 °C. In contrast, it is much narrower in the powder prepared by reduction at 1200 °C, although the particles are still low in Ni compared to the target composition

Elaboration of metallic compacts with high porosity for mechanical supports of SOFC

The development of third generation Solid Oxide Fuel Cells (SOFC) with metallic mechanical supports presents several advantages over that of ceramic stacks by offering a lower cost and longer lifetime of the stacks. As a consequence, it is necessary to prepare metallic porous compacts that remain stable at the operating temperature of the SOFC (700–800 C) under reductive atmosphere. This paper presents an innovative process to elaborate iron, nickel and cobalt porous compacts. The process is based on the thermal decomposition of metal oxalate precursors with controlled morphology into metallic powders with coralline shape. Uniaxial compaction of such powders (without binder addition to the powders) under low uniaxial pressures (rising from 20 to 100 MPa) gave rise to green compacts with high porosity and good mechanical properties. After annealing at 800 C under H2 atmosphere, the compacts still present interconnected porosity high enough to allow sufficient gas flow to feed a SOFC single cell in hydrogen: the porosity rises from 25 to 50% for iron compacts, from 20 to 50% for cobalt compacts, and is higher than 40% for nickel compacts. Results from physicochemical characterization (XRD, SEM, gas permeation, Hg porosimetry) corroborated the process for SOFC application

Developing new joining materials for low-temperature electronics assembly

International audienceThe present work focuses on a new kind of lead-free joining method for surface-mount technology based on precursor chemistry. The interest of metal oxalates as new soldering materials for die attachment (1st level packaging) was previously demonstrated with silver oxalate. The thermal decomposition of metal oxalates under controlled atmosphere can be used to produce small metal particles below their melting point. These particles are found to be in a highly active particulate form. First experimental studies are focusing on several metal oxalates (tin oxalate and bismuth oxalate) to assess their suitability for low-temperature metal particle production. The main work is dealing with controlled chemical precipitation synthesis and characterization of the compounds as well as study of the properties of decomposition solid products (powder X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and thermal analyses under different atmospheres)

Silver oxalate-based solders: New materials for high thermal conductivity microjoining

Micrometric oxalate powders can be decomposed starting from temperatures as low as 90°C, leading to the formation of temporary nanometric grains of metallic silver with a high propensity for sintering. The decomposition being highly exothermic, this additional energy favours the sintering, i.e. the soldering, process. Solders processed at 300°C and very low pressure (<0.5 MPa) displayed a thermal conductivity close to 100 W m-1 K-1, making silver oxalate very promising for safe, moderate temperature and very low pressure bonding

Study on the effect of cuprite content on the electrical and CO2 sensing properties of cuprite-copper ferrite nanopowder composites

The paper reports the synthesis and characterization of cuprite/copper ferrite nanopowder composites. The composites were synthesized using co-precipitation with oxalates precursor route. The phase and microstructure of the powder samples were characterized using X-ray diffraction, BET surface area analyzer and scanning electron microscopy. The powders were fabricated to device using a simple and efficient shaping technique. These devices were used further to carry out electrical property measurements in various atmospheres. The type of charge carriers were found by noting the sense of change in resistance when the air atmosphere on the sample was replaced with argon. CO2 responses were reported for the whole series of composites. The effect of cuprite concentration on the CO2 sensing performance was found to be independent of cuprite concentration up to certain limits (70%at)

Matériaux innovants sans plomb pour l'assemblage de composants électroniques à basse température

Dans le cadre du développement de nouveaux matériaux d’assemblage sans plomb, les premiers résultats de synthèse et de caractérisations physicochimiques d’oxalate de bismuth sont présentés. Par une méthode de décomposition thermique de précurseurs métal-organiques, la possibilité de produire des particules métalliques en dessous de la température de fusion du bismuth massif (271°C) est discutée ici. L’étude du comportement en température de l’oxalate de bismuth montre l’influence de l’atmosphère (air ou azote) sur la nature des produits de décomposition (oxyde ou métal). Sous une atmosphère inerte contrôlée, les échantillons d’oxalate préparés se décomposent en bismuth métallique entre 210 et 250°C

Inkjet printing of ceramic colloidal suspensions: Filament growth and breakup

Filament growth and breakup are investigated in the context of ceramic inkjet printing. Several inks were formulated and ejected on a printer dedicated to ceramic materials. They consisted of six colloidal inks, four simple fluids and two graphic inks. For each, stroboscopic snapshots were acquired and the filament shape was extracted and analysed, for different nozzle actuation pulses. The filament length and the thread minimum radius were measured during the ejection process. A scaling of the breakup time with the Rayleigh number was obtained, as well as a general behaviour for the filament growth rate during the ejection process