Influence of the magnetic field on the electric conductivity of magnetorheological elastomers Ioan Bica West University of Timis ¸ oara, Faculty of Physics, Bd. V. Pa ˆrvan, No. 4, 300223 Timis ¸ oara, Romania 1. Introduction The product formed following polymerization of silicone rubber, in the presence of iron microparticles and of other additives, is called magnetorheological elastomers (MREs) [1– 5a]. Like magnetorheological suspensions, with and whitout additives [5b–7], the magnetizable particles follow the direction of the magnetic field lines. Interactions of magnetic type set in [5a– v] both between the particles in the chain and between the chains of particles. Accounting for these interactions, the rheological properties and, implicitly, the material characteristics of MREs are drastically modified [8–11], a property which is used in several applications [5a,12–15,17,18]. By introduction of additives in the form of graphite micro- particles (electroconductive materials) into the elastic matrix, MREs become electroconductive [16,17]. This property of MREs can be used for achieving magnetoresistors, magnetic field sensors, transductors of mechanical distorsions, strains, etc. Because of this, some mechanisms are presented below, regarding the electrical conductivity of MREs based on silicone rubber, iron microparticles and graphite powders in transverse magnetic field. 2. Electroconductive MRE: magnetoresistor Electroconductive MRE is achieved based on the procedure described in Ref. [16] and it contains (in vol.%): silicone rubber RTV 3325-Bluestar Silicones SAS (40%), silicone oil with viscosity of 200 mPa s at 295 K, Merck type (15%), iron microparticles with diameters ranging between 0.1 mm and 0.6 mm (20%), graphite powder (20%) with granulation ranging between 30 mm and 45 mm-obtained by grinding Kahler/Bratislava graphite electrodes and Rho ˆne–Poulenc catalyst (5%). The iron microparticles are obtained by thermal decomposi- tion of iron carbonyl (Merck type, with granulation ranging between 4.5 mm and 5.4 mm, min. 97% Fe) with silicone oil (Merck type), according to the procedure described in Ref. [5b]. The mean diameter of the iron microparticles is of 0.27 mm. The mixture, formed of silicone rubber, iron microparticles, graphite powder, silicone oil and catalyst, is poured into a parallelipipedic chamber, of the shape and dimensions shown in Fig. 1. The chamber is made of dielectric materials and is provided, at its ends, with two copper electrodes. Following polymerization of silicone rubber, electroconductive MRE is obtained, in the shape of a parallelipipedic body, which adheres well to the walls of the chamber and to the electrodes. The aggregate consisting of MRE and the two copper electrodes at the ends is called magnetoresistor. 3. Experimental results and discussion The overall configuration of the device used for the study, in magnetic field, of the electrical conductivity of MRE based on silicone rubber, iron microparticles and graphite powder, is shown in Fig. 2. Journal of Industrial and Engineering Chemistry 16 (2010) 359–363 ARTICLE INFO Article history: Received 31 August 2009 Accepted 19 November 2009 Keywords: Magnetorheological elastomer (MRE) Magnetoresistor Graphite powder Transverse magnetic field Iron microparticles ABSTRACT In this paper one shows that magnetoresistors can be manufactured by processing silicone rubber, iron microparticles and graphite powders. The magnetic field dependence of the current flowing through the magnetoresistor, say I = I(H) U , is measured for constant voltages. Functions established in this manner have been discussed both during and after polymerization. ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. E-mail address: ibica2@yahoo.com. Contents lists available at ScienceDirect Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec 1226-086X/$ – see front matter ß 2010 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2010.01.034