RUSSIAN JOURNAL OF EARTH SCIENCES VOL. 7, ES4003, doi:10.2205/2005ES000177, 2005

Preparation of Samples and the Methods of Their Study

[5]  The polymer nanocomposites examined in this study had been synthesized at the Chemical Faculty of the Moscow State University in Petri dishes in the ambient laboratory magnetic field, disregarding its direction. The synthesis was made using a 4% PVA water solution with the addition of a mixture of FeCl2cdot 4H2O and FeCl3cdot 6H2O (with a molar ratio Fe2+/Fe3+ =0.5) dissolved in water. As a result of this reaction and after the addition of a six-percent NaOH solution and a gel-forming agent, Fe3O4 nanoparticles were formed. The resulting gel varied in color during 5-10 minutes from reddish brown to black, depending on the concentration of iron oxide in the samples. This proved the in situ formation of not only magnetite particles but also of maghemite and partially oxidized magnetite particles. After the 24-hour storage of the gel in a closed Petri dish, the gel was washed with water for a long time and then dried in air at room temperature for 3-5 days. This resulted in the formation of polymer films, 200  m m thick, with iron oxide nanoparticles distributed over their volumes. In the course of the drying of the films the latter changed in color, this potentially being caused by the air access. To sum up, the real composition of the nanoparticles in the synthesized polymer films could be determined only in further studies. Conventionally, the particles were identified as magnetite, and their calculated volumetric ( Cv ) and weight ( Cp ) concentrations were referred to Fe3O4. Several syntheses of this kind were performed. As a result we got nanocomposite samples with different volumetric concentrations of Fe3O4 nanoparticles (from Cv = 0.6% to Cv = 43%), this corresponding to the Cp values varying from 2.4% to 75.4%. The total number of samples examined in this work was ten samples with different concentrations obtained from three syntheses. The composition and size of the crystalline grains, the homogeneity of the distribution of particles in the film sequences, and the magnetic state of the nanoparticles were determined using X-ray diffraction, a number of methods used to study rock magnetism, and transmission and depth-selective Mössbauer spectroscopy.

[6]  The macroscopic magnetic characteristics of the films, such as saturation magnetization ( Js ), remanent saturation magnetization ( Jrs ), natural remanent magnetization ( Jn ), as well as their temperature dependence Js(T) and Jrs(T), were carried out in the Geomagnetic Laboratory of the Institute of Physics of the Earth, Russian Academy of Science, using a JR-4 magnetometer (AGIKO), a vibromagnetometer (VSM), and a two-component laboratory thermomagnetometer (Orion Company, Borok). The magnetic field used to produce Js and Jrs was equal to 450 mT. The coercive force ( Hc ) and the remanent coercive force ( Hcr ) were measured using a coercimeter in the maximum magnetic field of 1.7T (Orion Company, Borok). In this case Jn denotes the magnetization acquired by the films during the laboratory synthesis in the ambient geomagnetic field. Conventionally, we will refer to this magnetization as laboratory synthesis magnetization (LSM). In order to obtain the LSM vector and Jrs characteristics and study the anisotropy of these types of magnetization we measured the films in a cubic nonmagnetic organic glass container in three orthogonal directions X, Y, and Z. The Z axis was taken to be perpendicular to the film, the X and Y axes residing in the film plane. Since this synthesis was carried out without fixing the direction of the Earth magnetic field, the direction of the maximum values of the LSM and J rs vectors in the film plane was chosen after the measurements to be the X-axis.

[7]  The Mössbauer transmission spectra were obtained in the laboratory of the Solid State Physics Department, Moscow State University, using a spectrometer of constant acceleration. The radioactive source was Co57(Rh), the velocity scale of the spectrometer was calibrated using a standard a -Fe absorber. All experimental spectra were subject to compute fitting using a special program based on the Lorentz form of spectra lines. To check the homogeneity of the particle distributions of over the thickness of the film, Mössbauer spectra were obtained for different thicknesses below the surfaces of the study samples. Depth selective Mössbauer spectroscopy was performed in the geometry of back scattering with registration of two types of secondary radiation: conversion electrons (information from the subsurface layer ~0.3  m m) and conversion X-ray (information from the subsurface lay ~20  m m) [Kuprin and Novakova, 1992].


RJES

Citation: Gendler, T. S., A. A. Novakova, and E. V. Smirnov (2005), Specific magnetic structure forming in polymer nanocomposites containing magnetite nanoparticles, Russ. J. Earth Sci., 7, ES4003, doi:10.2205/2005ES000177.

Copyright 2005 by the Russian Journal of Earth Sciences

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