We have developed an original method for indium purification. Our approach is based on the directional transfer of impurities by applying crossed electric and magnetic fields to the melting volume. The method reduced the concentration of nickel and tin by a factor of 10 while copper was reduced by a factor of 3. A simple hydrodynamic mass transport model describing the process was also derived. Ó 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.Keywords: Impurity migration; Indium; Inductively coupled plasma-optical emission spectroscopy (ICP-OES); Purification Since the late 1980s the demand for, and the price of, indium has increased due to the constant growth of its market [1,2]. High-purity indium is mainly used in the making of indium tin oxide (ITO) thin films for liquid crystal displays (about 65% of the total industrial consumption) and for the production of semiconductor compounds. The required level of the purity here is more than 99.9999 wt.% (6 N quality), i.e. the total concentration of the impurities should be less than 1 part per million (ppm). 6 N indium is produced by a fine purification of primary 4 N metal using different physical and physical-chemical methods (for a review, see Refs. [2,3] and references cited therein) but only physical methods can guarantee minimum contamination by any foreign chemicals or purification plant materials. Traditional crystallization methods such as zone melting and Czochralski crystal growth [4] are also used to achieve a high purification. However, these crystallization methods cannot remove from the solid phase impurities with a unit segregation coefficient, whereas most elements in the concentration range of 10 À5 % to 10 À6 % and lower possess such a segregation.In the present paper, we propose an original approach for a fine purification of indium and other low-melting-point metals. Our method is based on the directional transfer of impurities by applying crossed electric and magnetic fields [5,6]. We report the construction of our experimental set-up and present the results of the trace element analysis with inductively coupled plasma-optical emission spectroscopy (ICP-OES).The schematic configuration of our experimental setup is shown in Figure 1. Liquid indium is moved by the magnetohydrodynamic pump MHDP placed in the pumping zone Z1 via 1.5 mm diameter pipes toward the purification zone Z2, where it passes through the crossed magnetic and electric fields. The static magnetic fields with induction B of 0.6 and 0.5 T in zones Z1 and Z2, respectively, are produced by a set of samarium-cobalt block magnets [7]. The electric currents are provided by 30 A DC power supplies U1, U2 assembled in our laboratory. The electrical connectors k1, k2 equipped with 1.8 mm diameter pure tungsten rods are used to supply power to the liquid metal. All the reservoirs, pipes, pumps and connectors are made of pure Teflon Ò to avoid contamination of the liquid metal. The length of the circuit is 1.5 m, while the length of the purification zone alone i...

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We focus on the origin and sources of surface contamination and defects causing the failure of MEMS electrostatic switches. The morphology, and elemental and chemical compositions of the contacting surfaces, conducting paths, and other parts of switches have been characterized by means of SEM, EDXA, and XPS in order to understand the difference between the data collected for the devices that had passed the electrical conductivity test and those found to be defective. C, O, Al, Ca, Ti, Cu, and some other impurities were detected on the details of defective switches. Contrariwise, the working switches were found to be clean, at least on the level of EDXA and XPS sensitivity. The main sources of surface contamination and defects were incompletely deleted sacrificial layers, substrate materials, and electrolytes employed for Rh plating of the contacts. The negative influence of foreign microparticles, especially alumina and copper oxides, on the conductivity and porosity of contacts was highlighted.