Thermal and Structural Characterization of Nanocomposite Iron Nitride - Alumina and Iron Nitride - Silica Particles
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Thermal and Structural Characterization of Nanocomposite Iron Nitride - Alumina and Iron Nitride - Silica Particles Ann M. Viano1 and Sanjay R. Mishra2 Department of Physics, Rhodes College, 2000 North Parkway Memphis, TN 38112, U.S.A. 2 Department of Physics, The University of Memphis, Memphis, TN 38152, U.S.A. 1
ABSTRACT Nanocomposite iron nitride based powders are known to have enhanced magnetic and other physical properties. To further explore their potential for application in various fields, we have performed a systematic study of the iron nitride - alumina and iron nitride - silica systems. Iron nitride powder of composition FexN (2 < x < 4), containing both Fe3N and Fe4N phases, was mechanically milled with Al2O3 or SiO2 powder for 4, 8, 16, 32, and 64 hours at the following compositions; (FexN)0.2(Al2O3)0.8, (FexN)0.6(Al2O3)0.4, (FexN)0.2(SiO2)0.8, and (FexN)0.6(SiO2)0.4. Differential thermal analysis and X-ray diffraction were performed to investigate thermal and structural transitions as a function of milling time. As the milling time is increased, the thermal peak corresponding to Fe4N is diminished, while the one corresponding to Fe3N is enhanced. These transitions are correlated with X-ray diffraction patterns. All XRD peaks broaden as a function of milling time, corresponding to smaller particle size. Transmission electron microscopy also reveals a decrease in particle size as the milling time in increased.
INTRODUCTION Small magnetic particles are important in many practical applications for their superior magnetic properties such as high saturation magnetization and high coercive field. Improvements in these properties have been obtained through sputtering [1,2] and mechanical alloying [3] of iron particles with alumina or silica, an improvement which has been correlated with a reduction in particle size. Metal-metalloids, such as FexN, have these desirable magnetic properties, but conventional techniques used to produce small particles often lead to oxidation and the formation of an iron oxynitride surface layer, which is ferromagnetically coupled to the core of a particle. Surface oxidation may be avoidable by embedding single domain FexN particles in an insulating matrix such as Al2O3 or SiO2. In fact, iron particles dispersed in such an insulating matrix have shown enhanced magnetic and mechanical properties [3-5]. In this work, small FexN particles are embedded in an insulating matrix through mechanical ballmilling. The resulting particles should have the advantageous properties of both small particle size and metal-metalloid composition. To fully understand the mechanisms producing these particles, structural and thermal studies are performed in this study to evaluate the phase formation as a function of milling time.
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EXPERIMENTAL DETAILS Samples of iron nitride - alumina or iron nitride - silica were formed by mechanically milling powder of FexN (2
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