Bulk synthesis of monodisperse Fe nanoparticles by electromagnetic levitational gas condensation method A. Kermanpur ⁎, B. Nekooei Rizi, M. Vaghayenegar, H. Ghasemi Yazdabadi Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran abstract article info Article history: Received 5 November 2008 Accepted 25 November 2008 Available online 3 December 2008 Keywords: Nanomaterials Electron microscopy Levitation melting Fe A one-step bulk synthesis method for monodisperse Fe nanoparticles was developed by electromagnetic levitational gas condensation (ELGC) process. The Fe vapours ascending from the high temperature levitated droplet was condensed by cryogenic He–Ar gas mixture under atmospheric pressure. The spherical Fe nanoparticles with particle size of 72.1±19.5 nm and a narrow size distribution were prepared using the He– 20%Ar gas mixture with the flow rate of 20 l/min. The production rate of the one-step ELGC process was estimated as high as 10 g/h. The nanoparticles were passivated by the formation of a thin layer of Fe oxides with the thickness of 3 nm. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Currently, pure Fe nanoparticles (NPs) have been successfully studied for a wide range of applications such as magnetic recording media [1], environmental remediation [2], rocket solid fuels [3] and biomedical fields [4]. Several synthesis approaches, including inert gas evaporation [5], chemical vapor condensation [6], sol–gel [7], sonochemical [8], wet chemical [9], and laser-driven thermal methods [10] are applied for the fabrication of Fe NPs. However, production rate for almost all these approaches is low (e.g. 100 mg/h for laser-driven decomposition of iron pentacarbonyl (Fe(CO) 5 ) vapour [10]). Recently, a gram-scale method for the synthesis of Fe NPs has been developed by injection of iron carbonyl into kerosene in one pot [11]. In addition, the product in some processes may contain certain impurities and texture such as ball-milling [12]. In the present work, we have developed a one-step method for the synthesis of monodisperse Fe NPs with the production rate of about 10 g/h in a continuous manner, by using electromagnetic levitational gas condensation (ELGC) method. This method is based on the levitation melting technology [13]. Although the first successful experimental work for the levitation melting was performed by Okress et al. [14] in 1952, the electromagnetic levitation melting technology has been recently used for the synthesis of NPs of some metals and alloys [15–22]. The first attempt was reported by Bigot and Champion for the synthesis of Fe and several other NPs using liquid N 2 /Ar as the cryogenic media with the consumption rate of 1 lit/min [15,16]. Recently, Rhee et al. have used this method for the synthesis of Fe NPs and other metals and oxides NPs [17,18]. They used Ar gas under the pressure of 18 kPa for condensation of metallic atoms. Due to the difficulty in the levitation melting of alloys, no extensive works have been reported so far for the synthesis of different nanomaterials and there are still many unknown aspects of the process need to be investigated. The novelty of the present work lies in two aspects compared with the previous works. Firstly, no reduced atmosphere was used; the process was carried out at about atmospheric pressure. Secondly, the He gas cooled by liquid N 2 was used for condensing the metal vapours; therefore it has the advantages of not using vacuum facilities, and more safety in spite of direct using of liquid N 2 in the process. 2. Experimental procedure Experimental set-up of the present ELGC rig is explained else- where [19]. The levitation of Fe is a difficult task, especially in the molten state. The suitable coil was therefore designed by computer simulation of the electromagnetic field [20]. Effects of inert gas type, Materials Letters 63 (2009) 575–577 ⁎ Corresponding author. Tel.: +98 311 3915738; fax: +98 311 3912752. E-mail address: ahmad_k@cc.iut.ac.ir (A. Kermanpur). Table 1 The experimental conditions of the present work Experiment number Gas type Gas flow rate [lit/min] Gas temperature [K] Temperature of levitated Fe droplet, [K] 1 Ar 10 298 2550 2 Ar 20 298 2523 3 Ar 30 298 2498 4 He–20%Ar 20 298 2406 5 He–20%Ar 20 248⁎ 2406 ⁎The gas mixture was cooled by passing through the liquid N 2 . 0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2008.11.047 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/matlet