Microstructural evolution of nanocrystalline magnetite synthesized by electrocoagulation
- PDF / 1,214,482 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 180 Views
I.A. Rusakova and Andrei Baikalov Texas Center for Superconductivity and Advanced Materials, University of Houston, Houston, Texas 77204-5932
J.W. Chen Department of Physics, National Taiwan University, Taipei 106, Taiwan, Republic of China
Nae-Lih Wua) Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan, Republic of China (Received 28 April 2004; accepted 21 September 2004)
Nanocrystalline magnetite powders were synthesized by an electrocoagulation technique, in which an electric current was passed across two plate electrodes of carbon steel immersed in NaCl(aq) electrolyte, and the microstructure of the oxide powder was found to evolve in roughly three stages. The first stage involves formation and growth of severely defective colloidal crystallites. This is followed by agglomeration among the oxide crystallites to form mesoporous agglomerates containing predominantly inter-crystallite pores, and the average crystallite size was found to reach a plateau. Finally, coarsening of the crystallites within the agglomerates leads to another rapid increase in crystallite size and reduction in pore opening. The synthesized powders typically showed a saturation magnetization of ∼75 emu/g and a coercivity Hc of ∼118 Oe. A mechanism involving competition between nucleation and growth of free colloids and coarsening of the skeletal framework was proposed to explain the temporary level-off in crystallite size during the synthesis.
I. INTRODUCTION
Magnetite (Fe3O4) has long been a material of both industrial and scientific interests. It has been used, for instance, as a black pigment,1 a recording media,2 a magnetic component in magnetic fluids,3 and a magnetic carrier for bioseparation and drug delivery.4,5 Photocatalystcoated magnetite has also been suggested for decomposition of organics in wastewater treatment.6 Different applications may prefer different microstructural properties, in addition to the magnetic ones. For instance, the magnetic fluid and recording applications favor nonporous nanocrystalline particles, while catalysis and biological and medical applications prefer large surface area and mesoporosity. As a result, many synthesis methods, such as precipitation,7 microemulsion,8 hydrothermal,9,10 solventothermal,11,12 and microwave hydrothermal,13,14
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0003 J. Mater. Res., Vol. 20, No. 1, Jan 2005
have been developed to give magnetite powders of particular microstructures to meet the application requirements. Tsouris et al.15–17 recently reported an electrocoagulation (EC) method for producing nanocrystalline magnetite powder, where Fe ions are produced at the anode through electrochemical oxidation and then react with water to form the oxide. The oxide particles are then coagulated due to adsorption of ions on particle surface to neutralize the charge of the particles. Compared with other solution synthesis methods,7–14 the EC method has the advantages of low-cost, continuous-proces
Data Loading...
