Journal of Magnetism and Magnetic Materials 257 (2003) 119–125 On the mechanisms of iron microspheres formation in argon plasma jet Ioan Bica Department of Physics, Faculty of Physics, West University of Timioara, Bd. V.Prvan. nr.4, 1900 Timioara, Romania Received 4 January 2002 Abstract The paper presents the conditions of iron microspheres formation in argon plasma jet. We developed a set of equations for computing the inner and outer microsphere radii, and for describing their dependence on technological process parameters. r 2002 Elsevier Science B.V. All rights reserved. Keywords: Microspheres; Iron; Plasma jet; Internal radius; Liquid membrane 1. Introduction Hollow particles with dimensions ranging be- tween 1 and 100 mm are usually known as micro- spheres. They are interesting from the scientific point of view and also as regards their application. The scientific interest is related to the mechanism of their formation, and the applicative interest is connected with punctual applications. Thus, the microsphere filled in with cytostatics are injected in a diseased organ and are kept there by an external magnetic field [1]. Through oxidation reactions, the microsphere is transformed into iron ions [2], the cytostatics being thus released. The iron ions contribute to the biomedical equilibrium of the body [3], and the cytostatics improve the status of the diseased organ [4]. The iron microspheres can be used for the preparation of magnetorheological fluids [5] consisting of micrometer-sized iron particles dispersed in liquid matrices (siliconic oil, mineral oil, etc.). There are various procedures for production of microspheres: the sol–gel method described in Ref. [6], the rotating electric arc described in Refs. [7,8], and plasma jet method presented in Ref. [9]. In all cases, it is important to know the condition for microspheres formation and the dependence of their dimensions (the internal radius and the wall thickness) on the vapors quantity. The knowledge of all these aspects offers the possibility of adjusting the technological para- meters (the power in the plasma jet, the plasma jet speed, the geometry of the plasma generator nozzle and the speed of the electrode iron wire) for obtaining iron microspheres with pre-estab- lished dimensions. 0304-8853/03/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0304-8853(02)00480-8