J. Ind. Eng. Chem., Vol. 12, No. 5, (2006) 806-810 SHORT COMMUNICATION Electrical Conductivit y of Ma gnetorheological Suspensions Based on Iron Microparticles and Mineral Oil in Alternative Magnetic Field Ioan Bica † Department of Physics, West University of Timisoara, Bd. V. Parvan, no. 4, 300223, Timisoara, Romania Received March 30, 2006; Accepted July 3, 2006 Abstract: A magnetorheological suspension (MRS) obtained by thermal decomposition of Fe 2 (CO) 9 in mineral oil with stearic acid was prepared. The mean diameter of the microparticles was 2.10 µm at a standard deviation of 0.40 µm. For volume fractions of 0.06 and 0.30, the MRS is conductive only for alternative magnetic fields with a minimal effective intensity of 60 kA/m. The experimental results are discussed. Keywords: magnetoresistance, magnetorheological suspension, magnetic field, iron microparticles, electrical conductivity, alternative current Introduction 1) Magnetorheological suspensions (MRSs) are known under the generic name of intelligent fluids [1,2]. They are obtained from mixtures consisting of a liquid phase media (e.g., mineral oil, silicon oil), tensioactive sub- stances, and ferro- or ferrimagnetic microparticles [3-15]. When mixed with graphite microparticles [16,17], MRSs become electroconductive under the action of an external magnetic field, similar to the behavior of electrocon- ductive polymers subjected to an electric field [18]. Recent research [19] has shown that the MRSs obtained through thermal decomposition of Fe 2 (CO) 9 in mineral oil with stearic acid become electroconductive in a time- constant magnetic field. The electrical conductivity of an MRS depends on the intensity and direction of the external magnetic field [17]. In this paper, we show that the MRSs obtained by the procedure described in Ref. [5] are conductive in an alternative magnetic field. The electrical conductivity characterizing MRS magne- toresistances occurs in narrow stripes [20]. In addition, we are in the position to prepare sensors for the detection of fringe fields in magnetic heads [21] as well as warfare agents [22]. † To whom all correspondence should be addressed. (e-mail: ibica2@yahoo.com) Sample Preparation A mixture consisting of 0.082 kg ±5 % Fe 2 (CO) 9 powder with granulation ranging between 4.5 and 5.2 µm, 0.025 kg ± 5 % mineral oil (Aneron/Merck type), and 0.002 kg ± 2 % stearic acid was treated thermally [5] for 1.800 s at the temperature of 510 K ±10 %. An MRS was obtained, having iron microparticles dispersed in mineral oil (Figure 1). The possible losses of mineral oil with stearic acid can be compensated using the supplier, as described in Ref. [5]. Experimental Device The experimental device used for the study of the electrical conductivity of MRSs in an alternative magnetic field is described in Ref. [17]. The overall configuration of the device is shown in Figure 2. The device consists of a coil 1, placed on a core 2. Between the polar parts 3 and 4 there is a magne- toresistance (electric resistance with MRS). The mag- netoresistance is built by means of the glass tube 5 and the electrodes 6. Between the electrodes there is the MRS (position 7 in Figure 2). The body, consisting of the MRS, has its length and diameter equal to 0.005 m± 10 %. The electrodes of the magnetoresistance are provided