Journal of Sol-Gel Science and Technology 19, 631–635, 2000 c  2000 Kluwer Academic Publishers. Manufactured in The Netherlands. SiO 2 -Iron Oxide Composites Obtained by Sol-Gel Method MARIA ZAHARESCU ∗ , MARIA CRISAN, A. JITIANU AND D. CRISAN Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, Bucharest, Romania AURELIA MEGHEA AND ILEANA RAU POLITEHNICA University of Bucharest, Romania, Faculty of Industrial Chemistry, Department of Applied Physical Chemistry and Electrochemistry, Polizu Street 1, 78126 Bucharest, Romania Abstract. Composite SiO 2 -iron oxide materials were prepared by three experimental procedures. In the first case (1), the iron oxides were precipitated during the sol-gel process. In the second case (2), the SiO 2 matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe 2+ salt in the previously processed matrix. In the third method (3), ferrite powders, prepared by wet chemical method, were embedded into a SiO 2 based sol-gel matrix. Two type of precursors (tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS) were used as SiO 2 sources. Various properties versus both type of precursor and on the method of preparation were noticed. Materials with high porosity and nano-sized iron oxide content could be prepared using the mentioned above methods. Keywords: SiO 2 -iron oxide system, sol-gel method, nanocomposite materials 1. Introduction Sol-gel oxide materials prepared in the SiO 2 -Fe 2 O 3 system may display specific magnetic, electrical as well as catalytic properties, both in bulk and in the film form. Compositions containing 10–40% Fe 2 O 3 were prepared as amorphous magnetic materials [1]. If the Fe 2 O 3 is reduced to Fe, the resulting two phases nanoscale Fe-SiO 2 composites show catalytic action [2, 3]. Fe-SiO 2 cermet films of 0.5 μm thickens, deposited on glass substrates by following the reduction of the sol-gel derived SiO 2 -Fe 2 O 3 coatings are electrically ac- tive [4]. The micro- and nano-structure of SiO 2 -Fe 2 O 3 sol-gel derived thick films was studied by Mezinskis et al. [5]. Studies related to the structure evolution by heating and the thermal stability of the SiO 2 -Fe 2 O 3 gels were realised by Lopez et al. [6, 7]. Nanocomposites Fe 2 O 3 /SiO 2 with magnetic properties have been syn- thesised using sol-gel method, by Niznansky et al. [8]. ESR study of the iron state in the initial and thermally treated gels were done by Tanaka et al. [9]. ∗ To whom all correspondence should be addressed. Despite the rather large work accomplished on the materials belonging to the SiO 2 -Fe 2 O 3 system many supplementary informations could be still ob- tained concerning their structure and their field of application. As resulted from literature data, no substituted Si- alkoxides were tested as precursor for obtaining the SiO 2 matrix of the SiO 2 -iron oxide nanocomposites. The dense texture of the gels obtained with substituted Si-alkoxides could influence the iron oxides crystallite size development. In the present work some results concerning prepa- ration and characterisation of sol-gel nanocomposite materials in the SiO 2 -Fe 2 O 3 system using TEOS and MTEOS as SiO 2 sources are presented. 2. Experimental Gel Preparation For the composite SiO 2 -iron oxide materials prepara- tion, three different sol-gel methods were used: