Purification of liquid indium by electric current-induced impurity migration in a static transverse magnetic field

Abstract

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...

Separation of particles from suspensions using transverse force field: a mass transport analysis

“…Further we assume that the particles hitting the duct wall stick on it and disappear without modifying the domain contour. Such conditions are in agreement with what previously found in [1,2,4]. Under these conditions the motion of the aggregates is purely hydrodynamic and in the case of the separation generated by the presence of the transverse force, the drift velocity of the aggregates is inversely proportional to viscous drag.…”

“…The purpose of our investigation is the determination of the purification efficiency for a variety of processes based on the directional transfer of impurities originated by the application of magnetic field and crossed [1][2][3]. The application of these techniques to the purification of liquid indium has been recently reported [1,4]. The purification effect has been interpreted in [4] in terms of the existence of small aggregates of contaminants, insoluble in the melt, in the nanometre range.…”

“…The application of these techniques to the purification of liquid indium has been recently reported [1,4]. The purification effect has been interpreted in [4] in terms of the existence of small aggregates of contaminants, insoluble in the melt, in the nanometre range. Such heterogeneities, show lower electrical conductivity compared to the bulk of the melt.…”

“…The application of a magnetic field orthogonal to current flowing in the duct hence produce an apparent Lorentz force capable of moving the aggregates. It has been proved [4] that the particles hitting the wall, stick on it, reducing the contaminants concentration in the liquid. The calculation does not require any hypothesis on the nature of the driving force, hence the derived equations show general validity.…”

Electrochemical growth of platinum nanostructures for enhanced ethanol oxidation

“…The need for high Pt loadings poses severe limitations, as the scarcity of platinum resources limits its use to applications where it is absolutely unavoidable. Recently the European Union has classified platinum among the so-called "critical raw materials", stressing both on its technological relevance and rarity [23,24]. The US Department of Energy periodically publishes reports on future technology targets [25].…”