Assembly of nano-domain buildings blocks of copper oxalate with a cubic morphology
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Assembly of nano-domain buildings blocks of copper oxalate with a cubic morphology L. C. Soare, P. Bowen, J. Lemaître, H. Hofmann Powder Technology Laboratory, Institute of Materials, Swiss Federal Institute of Technology, EPFL, CH1015 Lausanne, Switzerland.
M. Pijolat, F. Valdivieso, École Nationale Supérieure des Mines de Saint-Étienne 158, cours Fauriel F-42023 Saint-Étienne cedex 2 E-mail : [email protected]
Abstract Metallic copper nanostructured particles were synthesised by thermal decomposition of a CuC2O4 precursor obtained via the precipitation reaction between Cu(NO3)2·6H2O and Na2C2O4 in the present of hydroxyl propyl methyl cellulose (HPMC). X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM) and thermogravimetric analysis (TG) were used to characterise the particles and their evolution during the transformation to metallic copper. We highlight the nanostructured nature of the oxalate precursor, which is made up of anisotropic nanosized buildings blocks (25nm by 40nm). These produce an anisotropy in the oxalate particle and influence the decomposition pathway. The results show the evolution of the nanostructure as a function of degree of reaction and a possible kinetic model is discussed.
Introduction The quest for high purity materials for the electronics industry had led to the widespread use of sol-gel and co-precipitation techniques with the goal of producing and controlling materials at the nanoscale. The electrical, optical, transport and magnetic properties of the materials depend not only on the characteristics of individual nanocrystallites, but also on the coupling and interaction among the nanocrystals. These may be arranged with or without long- range order with respect to translation and orientation. In precipitation techniques the metal ions are simultaneously precipitated in the desired stoichiometric proportion and in several cases a singlephase solid solution precipitation is achieved assuring homogeneity at a molecular level. Granular magnetic systems, consisting of nanometer-sized particles of a magnetic material (Co) dispersed in non-magnetic matrix (Cu) are expected to exhibit giant magneto-resistance behaviour. Oxalate coprecipitation, followed by the appropriate thermal treatment, is a possible route for the preparation of such nanocomposite particles. A good understanding of the transformation from an oxalate into the metal is needed to be able to produce these magnetic composites. As a first step we have focussed on thermal and kinetic transformation of each simple oxalate. It is important to follow the evolution of the nanostructure as a function of reaction yield; as well as understanding the structure evolution at an atomic scale. Previous work has shown that nanostructured copper oxalate precipitates can be produced and the shape and the size of the particles and nanodomains modified with an organic additive (hydroxyl propyl methyl cellulose (HPMC)(6). The copper oxalate precipitates show a strong anisotropy at the molecular, nanometre
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