Microwave-assisted synthesis of spherical monodispersed magnesium fluoride Mariusz Pietrowski * , Maria Wojciechowska Adam Mickiewicz University, Faculty of Chemistry, 60-780 Poznan ´, Grunwaldzka 6, Poland Received 13 September 2006; received in revised form 7 December 2006; accepted 15 December 2006 Available online 20 December 2006 Abstract Spherical monodispersed magnesium fluoride has been obtained using the microwave-assisted precipitation technique from magnesium nitrate and ammonium fluoride solutions. Studies aimed at optimizing synthesis conditions from the point of view of preparing spherical MgF 2 particles of possibly high monodispersity were performed. Spherical MgF 2 particles of 0.25–0.36 mm in diameter have been obtained with relative standard deviation from the average value ranging from 7 to 15%. It has been established that a certain optimal range of Mg(NO 3 ) 2 and NH 4 F concentrations exists that enables a highly monodispersed MgF 2 to be prepared. The range is narrow (0.01–0.03 mol dm 3 ) for both precursors. Spherical MgF 2 particles have been characterized by SEM, XRD, DTG/DTA and FTIR techniques. # 2007 Elsevier B.V. All rights reserved. Keywords: Monodispersed magnesium fluoride; Spherical magnesium fluoride; Microwave-assisted synthesis; MgF 2 1. Introduction The fascination with monodispersed colloids began from experiments carried out almost one and a half centuries ago by Faraday, who prepared gold sols and described their glistening colours that were particle-size dependent [1]. At first homogeneously dispersed matter attracted the attention of academic circles only and concerned studies of its physical and chemical properties as well as their relation with size and shape of particles. Now it is possible to prepare monodispersed materials from a few nanometers to a few micrometers in diameter. Many compounds, for example SiO 2 [2,3], TiO 2 [4– 7], ZrO 2 [8,9], sulfides [10–12], carbonates [13–15] and halides [16,17] have been synthesized in the form of monodispersed particles. Such materials have found application in ceramics, manufacture of pigments, manufacture of electronic data carriers, medical diagnostics and catalysis. One of the halides, for which attempts have been made to obtain it in the form of spherical particles, is magnesium fluoride. It crystallizes in the rutile structure. The coordination surrounding of magnesium ions has a distorted octahedral shape, where the Mg–F distances are 1.94 A ˚ for four fluorine ions and 1.99 A ˚ for the other two [18]. MgF 2 shows good thermal stability and significant hardness. It is an insulator with a broad band gap. Magnesium fluoride is used extensively in optical thin films [19–23], for example, as anti-reflective coatings on glasses and as rutile seed for pigment applications [24] and for composite optical filters with titania [25]. It was also reported that magnesium fluoride, which played the role of a support for a number of oxide [26,27], metallic [28] and sulfide [29] phases, enabled syntheses of catalysts active for such reactions as decomposition and reduction of nitrogen oxides [30], hydrodechlorination of chlorofluorocarbons (CFC) [31] and hydrodesulfurization of thiophene [32,33]. In conventional thermal processing, energy is transferred to the material through convection, conduction, and radiation of heat from the surfaces of the material which results in temperature gradient formation. In contrast, microwave heating leads to the direct interaction between microwaves and materials and this fact enables an uniform and fast heating of a sample. This difference can result in many potential advantages for microwaves in processing of materials. Therefore microwave- assisted synthesis has been applied widely in various fields such as molecular sieve preparation, the preparation of inorganic complexes and oxides, organic reactions, plasma chemistry, analytical chemistry and catalysis [34,35]. www.elsevier.com/locate/fluor Journal of Fluorine Chemistry 128 (2007) 219–223 * Corresponding author. Tel.: +48 61 8291470; fax: +48 61 8658008. E-mail address: mariop@amu.edu.pl (M. Pietrowski). 0022-1139/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jfluchem.2006.12.009