Materials Science and Engineering B77 (2000) 210 – 212 Letter Formation of glass microspheres with rotating electrical arc Ioan Bica West Uniersity of Timisoara, Bd. V. Paran no. 4, 1900 Timisoara, Romania Received 5 April 2000; accepted 16 May 2000 Abstract The paper presents the experimental device for obtaining glass microspheres in rotating electrical arc. With this device, for arc power values of 5 ×10 3 W and for frequency of  =850 s -1 , the glass powder with arbitrary shaped particles was transformed in microsphere with diameters between 2 and 24 m and the wall thickness between 0.4 and 1.6 m. The particles in the powder were up to 30 m in diameters, have a flow rate of 2 g·min -1 and were transported in argon (5 Nl min -1 ). The mean diameter is d  =5.62 m. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Rotating electric arc; Glass powder; Microspheres www.elsevier.com/locate/mseb 1. Introduction Glass microspheres are made of sputtered materials (known in general). The raw material used is specific to commercial glass or to special behaviour glass. By melting with flame or/and vaporization in plasma, in certain conditions, microspheres of glass are obtained. They are used for obtaining reflecting paints, reflect- ing layers and for dielectric materials with a certain dielectric permittivity [1]. Recently, glass microspheres have been in magneto-fluidic composites applied in selective absorbants of mechanical shocks [2,3] and earthquake waves [3,4] and in sensors, respectively [5]. Inner and outer diameters of microsphere are sup- posed to have pre-established values. Chemical compo- sition and surface conditions should be such that the elasticity coefficients have values suitable for applica- tions and small meeting energy respectively. Consequently, flexible methods for obtaining glass microspheres for several applications are of interest. Such a method is presented below. 2. Experimental device The experimental device, designed for obtaining the microspheres in rotating electrical arc plasma is pre- sented in Fig. 1. The electrical arc between electrodes 1 and 2 is supplied by the current source 3, at a value I of electrical discharge current. Coils 4 and 5 produce a magnetic field so that the induction B is perpendicular to the density of electrical discharge current vector j. The interaction between the magnetic field and the current results in the effect of Lorentz force F =j ×B, i.e. the rotation of the electric arc. The frequency is measured by the device 6. By means of the device 7, under the gas pressure, the glass particles, with pre-es- tablished flow rate, are carried in the thermal ionized gas. 3. Results and discussions Particles obtained from glass mechanical processing have the shape and dimensions as shown in Fig. 2. After sieving, samples of particles with dimensions up to 30 m were obtained. Parameters of the rotating electrical arc are those used for making spherical parti- cles made up of chamote rod [6] i.e.: electrical discharge current intensity, I =100 A d.c. ; arc electrical voltage, U =50 V d.c. ; total magnetic field induction, B =26 mT; rotating frequency of the electrical arc,  =850 s -1 ; plasmagen gas flow rate (Ar), D =7.5 Nl min -1 ; carrier gas flow rate (Ar), D c =5 Nl min -1 . 0921-5107/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5107(00)00483-9