CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 40 (2014) 10223–10229 Fine tuning of CoFe 2 O 4 properties prepared by solution combustion synthesis Robert Ianoş n , Marian Bosca, Radu Lazău “Politehnica” University of Timişoara, Faculty of Industrial Chemistry and Environmental Engineering, Piaţa Victoriei No. 2, Timişoara 300006, Romania Received 24 January 2014; received in revised form 24 February 2014; accepted 25 February 2014 Available online 6 March 2014 Abstract Single phase CoFe 2 O 4 powders were prepared by solution combustion synthesis using β-alanine as fuel. By adding to the reaction mixture various amounts of oxalic acid, which act as a retarding agent and pore generator, properties of CoFe 2 O 4 powders can be properly adjusted. Depending on the amount of oxalic acid, the average crystallite size of CoFe 2 O 4 ranges between 13 and 41 nm, whilst the specific surface area varies between 1.8 and 34.4 m 2 /g. The combustion synthesized CoFe 2 O 4 powders exhibit a hard ferimagnetic behavior. The CoFe 2 O 4 coercivity varies between 71.8 and 126.0 kA/m and the saturation magnetization ranges between 53.0 and 70.6 emu/g. After uniaxial pressing and sintering at 1400 1C for 4 h, the pellets reached relative densities up to 90% of the CoFe 2 O 4 theoretical density. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Powders: chemical preparation; A. Sintering; C. Magnetic properties; D. Ferrites; Combustion synthesis 1. Introduction Cobalt ferrite, CoFe 2 O 4 , has an inverse spinel structure and it is an important material that has exceptional magnetic, optical and electrical properties, exploited in various applica- tions, such as catalysis [1–3], adsorption and separation [1], microwave absorbers [2,4], photonic and electronic devices [3–5], ferrofluid technology [3,6–8], magnetocaloric refrigera- tion [6,7], medical diagnosis [6–9], drug delivery [7–9], magnetocytolysis [8,9], magnetic cell sorting schemes, hyperthermia [3], permanent magnets [2], and sensors [2]. Generally, the magnetic properties of cobalt ferrite namely coercivity, anisotropy and saturation magnetization, are highly dependent on several parameters, amongst which the preparation method is probably the most important. Therefore, by properly selecting the synthesis route one can obtain CoFe 2 O 4 powders with high/moderate coercivity and high/moderate saturation magnetization, according to the desired applications [1,2,5,6,10]. Alongside the co-precipitation method [2,11] many other preparation routes have been reported for CoFe 2 O 4 preparation: hydrothermal and solvothermal method [3,4], microemulsion technique [7,12], reverse micelles [9], Massart [13], sonochemical method [14], sol–gel [15], organic precursors [16] etc. Although it has been reported that combustion synthesis has a great potential in the preparation of metal oxide nanopowders, little attention has been paid to the preparation of CoFe 2 O 4 . In a recent review on combustion synthesis of spinel-type ferrite nanomaterials, Sutka and Mezinskis [17] reported that the most popular fuels tested for combustion synthesis of CoFe 2 O 4 are urea [5], glycine [6,18] and citric acid [10,19,20]. In this paper we investigated the solution combustion synthesis of CoFe 2 O 4 using an alternative fuel (β-alanine) alongside with various amounts of oxalic acid. Properties of the resulting powders were investigated and explained in relation with the synthesis conditions. 2. Experimental 2.1. Powder preparation Based on combustion reaction (1) stoichiometric amounts of Co(NO 3 ) 2  6H 2 O (Fluka, 98%), Fe(NO 3 ) 3  9H 2 O (Roth, 96%) and C 3 H 7 NO 2 (β-alanine, Fluka, 99%) were dissolved in www.elsevier.com/locate/ceramint http://dx.doi.org/10.1016/j.ceramint.2014.02.110 0272-8842 & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. n Corresponding author. Tel.: þ40 256 404167. E-mail address: robert_ianos@yahoo.com (R. Ianoş).