The Effect of Alkali Concentration on the Structural and Magnetic Properties of Mn-Ferrite Nanoparticles Prepared via th
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TRODUCTION
NANO-SIZED ferrites have been under intense research for their use in a large number of applications such as loading coils, magnetic storage, and biomedical applications.[1–4] There are many methods for preparing nanoparticles.[4–7] Chemistry plays an important role in the development of novel nanostructured materials, and a simple control of solution chemistry can lead to specific changes in crystallite properties.[8–11] One of the most common chemical techniques in the synthesis of nanoparticles is coprecipitation. The advantages of using this method are that the mean size of nanoparticles can be varied by controlling the alkali concentration, reaction temperature, molar ratio of salts, ionic strength of aqueous medium, and reaction time. However, the disadvantage is the lack of control over size, shape, and stability of the produced nanoparticles.[12–14] Recently, two published articles reported the effect of alkali concentration on particle size, structure, and consequently the magnetic properties of two different spinel ferrite nanoparticles.[15,16] In this work, the influence of NaOH concentration on phase formation and magnetic properties (in particular, the Curie temperature and magnetization) of Mn-Ferrite nanoparticles was investigated from a chemical point of view. II.
EXPERIMENTAL PROCEDURE
Manganese ferrite (MnFe2O4) nanoparticles were synthesized by the coprecipitation method and subsequent aging procedure as follows. Appropriate amounts of SOMAYEH POURBAFARANI, Teacher, is with the Department of Physics, Faculty of science, University of Isfahan, Isfahan, Iran. Contact e-mail: [email protected] Manuscript submitted September 7, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A
MnCl2 4H2O and FeCl3 6H2O were dissolved in distilled and deionized water at concentrations of 0.25 M and 0.50 M, respectively, under the condition of [Fe3+]/ [Mn2+] = 2:1, at room temperature.[17] These solutions were mixed and then the new solution was quickly poured into 250 mL of 1.5 M stirred NaOH solution at 355 K (82 °C). The aging procedure was performed at 355 K (82 °C) for 60 minutes. In order to study the effect of alkali concentration, these procedures were repeated, except that the solution of sodium hydroxide with the molarity of 1.5 was replaced with the solution of 6 M. After aging, the obtained precipitates were washed with double distilled water to reach a pH of 7 and dried at 333 K ± 10 K (60 °C ± 10 °C). The structural properties of the samples evaluated by X-ray diffraction (XRD) pattern were recorded on a diffractor model X Pert Pro MPD (Panalytical, The Netherlands) using Cu Ka (k = 1.54060 A˚) radiation with a 2h step size of 0.0390 and a step time of 118.3200 seconds. The morphological evaluations of two samples were performed with an scanning electron microscope (SEM, Philips XL-30, Holland). To obtain a SEM image, each of the fine powder samples was sprinkled onto a carbon tape of the SEM stub surface, and the excess was blown away. Then the sample was coated with a 20 nm thick Au layer. In
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