Carbonization behavior of polyimide film containing iron complex in relation to magnetic properties
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M. Inagaki Faculty of Engineering, Aichi Institute of Technology, Yakusa, Toyota 470-0392, Japan
A ferromagnetic film composed of carbon matrix and dispersed fine iron particles was prepared by heating a polyimide film containing iron complex at temperatures up to 1000 °C. The particles were formed and distributed homogeneously on the film surfaces by heat treatments at 600 °C and above, and inside the films at 700 °C and above. The particles were ␣–Fe, ␥–Fe (or austenite), and Fe3C with fractions of about 7:2:1 in the films heated at 800 °C and above. The mean crystallite sizes of ␣–Fe and ␥–Fe (or austenite) particles were evaluated to be 19 and 15 nm in the film heated at 800 °C, and 32 and 30 nm at 1000 °C, respectively. The films heated at 600 °C and below were superparamagnetic, while those at 700 °C and above were ferromagnetic, but both components existed in all films. The iron particles promoted the growth of carbon crystallites in the films; i.e., the interlayer spacing was about 0.341–0.343 nm and mean crystallite size 4.0–6.5 nm for the films heated in the range of 700 to 1000 °C. Pores were observed on the surfaces and cross sections of the carbonized films, and they seemed to be loopholes of the clusters. Iron oxides were scarcely formed in the films, even after being kept for a long duration at room temperature in atmosphere. I. INTRODUCTION
Carbon materials containing transition metals have interesting properties and commercially valuable applications as catalysts,1 electronic components,2 and many other functions, depending on the metals. Carbon clusters in the spherical or tubular form encapsulating transition metals have been synthesized by arc plasma between graphite cathodes and anodes containing transition metals.3–6 Iron implantation into graphite by physical means has been carried out.7,8 Clusters of transition metals dispersed in a graphite matrix have also been obtained as reduction products from graphite intercalation compounds of metal chlorides such as FeCl3.9–11 On the other hand, organic precursors containing metal ions were proposed for preparation of metal–carbon composite materials, since carbonization and reduction to metal take place simultaneously by heat treatment of the precursors in an inert atmosphere.12,13 Simple processes for the preparation of polyimide films and their carbonization also suggest their application to doping of transition metals into carbon.14 –18 However, preparation of polyimide films containing transition metals from mix-
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J. Mater. Res., Vol. 16, No. 2, Feb 2001 Downloaded: 12 Mar 2015
tures of polyamic acid and metallic compounds in solution and following carbonization have not been made extensively.19,20 Hatori et al. investigated the carbonization behavior of polyimide films containing nickel, paying attention to the catalytic effect of nickel on carbonization.19 We incorporated iron particles into carbon films by mixing an
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