Fe-Ni Alloy Synthesis Based on Nitrates Thermal Decomposition Followed by H 2 Reduction
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IN general, many material properties are dependent on the particle size and, therefore, can be enhanced through its reduction to the nanometer range. Magnetic properties, for example, are positively affected by a size reduction,[1] as nanostructured particles are known to behave superparamagnetically.[2] In fact, this means that almost no hysteresis can be detected during the inversion of the applied field. As a result, the fast changing of the magnetic dipole orientations so as to get aligned with the external field can be explored for the construction of electronic devices, such as those based on magnetic random access memory technology.[3] This characteristic is potentially present in all materials, which contain magnetic elements, for example, Fe-Ni alloys, which are attractive, not only because of the associated low thermal expansion coefficient, but also for the construction of soft magnet devices.[4,5]
ORFELINDA AVALO CORTEZ, Professor, is with the Facultad de Ingenierı´ a Geolo´gica, Minera y Metalu´rgica - Escuela de Metalurgia (FIGMM), Universidad Nacional de Ingenieria, Av. Tu´pac Amaru, 210, Rimac District, Lima 25, Lima, Lima Province, Peru. FRANCISCO JOSE´ MOURA, ROGE´RIO NAVARRO CORREIA DE SIQUEIRA, and EDUARDO DE ALBUQUERQUE BROCCHI, Professors, and RODRIGO FERNANDES MAGALHA˜ES DE SOUZA, DSc Student, are with the Department of Materials Engineering, Pontifical Catholic University of Rio de Janeiro (DEMa/ PUC-Rio), Rua Marqueˆs de Sa˜o Vicente, 225, Ga´vea, 22453-900 Rio de Janeiro, Rio de Janeiro, Brazil. Manuscript submitted February 4, 2014. Article published online October 30, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
This particular scenario has encouraged further investigations on alternative nanostructured alloys synthesis methods. With time, chemical methods,[5–9] in comparison to the ones based on the physical mixture of pure metals followed by sintering,[10–12] achieved considerable importance, as they can easily lead to the formation of alloys of considerable nanostructured content. In relation to the physical routes, the production of pure metal nanostructured particles through milling is extensively energy dependent, and also involves significant concerns regarding the homogeneity of the samples. Recently, our research group has worked on a twostep synthesis method based on the nitrates solution thermal decomposition followed by hydrogen reduction of the co-formed oxides,[13–15] which can easily result in nanostructured crystals of varying nature—alloys, CERMET composites, and spinels. This process has been employed in the present article for the synthesis of Fe-Ni alloys with distinct iron mole fractions. All materials, including the obtained alloys, have been characterized through quantitative X-ray diffraction analysis (XRD). Moreover, specific magnetization measurements under varying external field have been conducted for the alloy samples at 298 K (25 °C) so as to investigate the amount of magnetic hysteresis present.
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THERMODYNAMIC BACKGROUND
The following section focuses
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