Formation of controlled alumina films using Supercritical Fluids Chemical Deposition for electronic and telecommunicatio
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Formation of controlled alumina films using Supercritical Fluids Chemical Deposition for electronic and telecommunication devices C. Aymonier1,2*, M. Lamirand-Majimel1,2, C. Bousquet1, C. Moncade1, F.Cansell1,2, M. Maglione1, C. Ellisalde1, J.-M. Heintz1,2, J.-F. Silvain1 1
Institut de Chimie de la Matière Condensée de Bordeaux / Centre National de la Recherche Scientifique, Université Bordeaux 1, 87 Avenue du Dr Albert Schweitzer, 33608 Pessac Cedex, FRANCE 2 Ecole Nationale Supérieure de Chimie et de Physique de Bordeaux, 16 avenue Pey Berland, 33607 Pessac Cedex, FRANCE * [email protected] ABSTRACT Alumina is one of the most widely used oxide ceramic material. It exists in many metastable forms, among which is the thermodynamically stable α phase, obtained upon severe thermal treatment. Sintering of alumina is generally performed in several stages: first, phase transitions towards the stable α phase followed by its densification. The first step is strongly dependent on the crystallinity of initial powders. By controlling this parameter, it is possible to optimize the sintering properties, in particular by decreasing the phase transition temperature. This effect has been studied for alumina elaborated in sub- and supercritical fluid media. This work highlights the possibilities to obtain, according to the nature of the fluid, different kinds of transition alumina: boehmite AlO(OH) or amorphous Al2O3. The sintering processes of these powders all lead to α-alumina, however, different microstructures and densities can be obtained. A significant shift towards lower γ/α phase transition temperature is also observed when amorphous alumina is considered, compared to boehmite. The transfer of this know-how to the design of core-shell nanoparticles and film deposition onto copper heat sinks is investigated to develop nanostructured ceramics for telecommunications and electronics. INTRODUCTION Alumina is the most widely used oxide ceramic material for many applications in electronics, aeronautics, high temperature metallurgy or biomedicine, thanks to its interesting mechanical, thermal, electrical and chemical properties. It exists in many stable and metastable forms (γ, α, δ, θ, κ, ε, η, χ), α− and γ-alumina being considered the most interesting ones. [1] The α phase is used in a wide range of ceramic and refractory applications, whereas γ-alumina is used as a substrate for catalysis processes. [2,3] Although this system is well known, the production of alumina by conventional processes is still challenging for it presents several shortcomings such as long reaction times and high calcination temperatures, which are required to obtain dense alumina-based ceramics. A key parameter for cost reduction is to soften sintering conditions of alumina. Additionally, nanostructured alumina-based ceramics have to be synthesized for further developments of catalysis applications.
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Several chemical and physical methods have been studied to produce alumina nanopowders (solid state, sol-gel, co-precipitatio
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