Journal of Alloys and Compounds 476 (2009) 373–378 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Synthesis and magnetic properties of strontium hexaferrite from celestite ore M.M. Hessien ∗ , M.M. Rashad, M.S. Hassan, K. El-Barawy Central Metallurgical Research and Development Institute (CMRDI), P.O. Box 87 Helwan, Cairo, Egypt article info Article history: Received 13 July 2008 Received in revised form 13 August 2008 Accepted 24 August 2008 Available online 17 October 2008 Keywords: Sr-M-type ferrite Celestite ore Reduction Co-precipitation synthesis Hard magnets Nanoparticles Magnetic properties abstract Nanocrystalline strontium hexaferrite (SrFe 12 O 19 ) powders have been synthesized from Egyptian celestite ore (SrSO 4 ), as a source of strontium, via co-precipitation route. The raw celestite ore was first dissolved in hydrochloric acid to remove about 10% CaO and the acid soluble impurities associated with the ore. Then, the treated celestite was washed and dried followed by a reduction with carbon to give acid–water sol- uble strontium sulfide SrS. The ferrite precursors were obtained from a precipitation of the produced SrS dissolved in dil. HCl and pure ferric chloride at pH 10 using 5 M sodium hydroxide. These precursors were annealed at 1000 ◦ C for constant time 2 h in open atmosphere. The effect of Fe 3+ /Sr 2+ mole ratio on the for- mation, crystallite size, morphology and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and VSM, respectively. The results obtained showed that the single phase SrFe 12 O 19 powders was achieved at the Fe 3+ /Sr 2+ mole ratios 8.57 and 8.00 at annealing temperature 1000 ◦ C for 2 h. The maximum saturation magnetization (74.15 emu/g) was achieved at the Fe 3+ /Sr 2+ mole ratio to 8.57 and annealing temperature 1000 ◦ C due to the formation of a uniform-like hexagonal shape structure. Moreover, wide coercivities can be obtained at different synthesis conditions (2011–3504Oe). © 2008 Elsevier B.V. All rights reserved. 1. Introduction The hexagonal M-type hard hexaferrites have attracted much attention as the most widely used permanent magnets, which account for about 90% of the annual production of permanent magnets due to good combination of high magnetic properties, chemical stability and low cost. Moreover, M-type hexaferrites have widely used in telecommunication, magnetic recording media, magneto-optics and microwave devices [1–4]. Strontium hexa- ferrite SrFe 12 O 19 is a hard magnetic material due to their high coercivities (6.64 kOe) which originates from its high magnetocrys- talline anisotropy and it is strongly dependent on the size and the shape of the particles. Moreover, the Curie temperature of SrFe 12 O 19 is around 470 ◦ C and the saturation magnetization between 74.3 and 92.6 emu/g [5–10]. For the preparation of hexaferrite, the solid state reaction method is commonly employed that involves firing of a stoichiometric mixture of strontium carbonate and iron oxide at high temperature (∼1200 ◦ C) but the obtaining fine, high chem- ical homogeneity and monodispersed particles may not be easy. In order to improve the properties of strontium hexaferrite, sev- eral low temperature methods, namely sol–gel [5], hydrothermal [6], microemulsion [7], sonochemical [1], mechanical alloying [8] glass crystallization [9] and microwave synthesis [10,11] techniques have also suggested. However, some of these methods are complex ∗ Corresponding author. Tel.: +20 2 25588292; fax: +20 2 25010642. E-mail address: hessienmahmoud@yahoo.com (M.M. Hessien). and require expensive equipment. The chemical co-precipitation [3,12–15] is a simple technique, low cost, good for mass produc- tion and ensures proper distribution of various metal ions resulting into stoichiometric and smaller particles size product compared to some of the others. On the other hand, celestite ore SrSO 4 is present in Egypt mainly in two localities [16,17] namely Wadi Essel with reverses 2.3 million tons and Abu-Gharbon with reverses 0.5 million tons. Celestite occurred as fine and coarse-grained irreg- ular crystals varying in diameter between 0.07 and 0.18mm [16]. The celestite ore can be promising as a source of strontium in the synthesis of strontium hexaferrite. Celestite ore is the main source for the production of most of the strontium compounds. Over 95% of the world production is con- sumed by the chemical industry for conversion to various strontium compounds. From which other strontium chemicals are obtained, e.g., strontium carbonate SrCO 3 , strontium nitrate Sr(NO 3 ) 2 , stron- tium chloride SrCl 2 , strontium hydroxide Sr(OH) 2 and strontium oxide SrO. The most common commercial process for produc- ing strontium compounds from celestite ore is the “black ash” process in which the celestite ore is calcined at elevated tem- perature at about 1000–1100 ◦ C with finely ground carbon in the presence of nitrogen gas to produce strontium sulfide (SrS). The produced strontium sulfide is leached with hot water and then with hydrochloric acid to separate the solid impurities by filtration. The produced strontium chloride solution can be mixed with differ- ent molar ratios of pure anhydrous iron chloride and the formed solution is precipitated using sodium hydroxide to form stron- tium ferrite precursors. The formed precursors is washed, filtered, 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.08.076