In-Situ Observation of the Behavior of Liquid Oxides during the Application of an Electric Potential: Precipitation of P
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In this work, a study of the effect and impact of applying external electric fields on liquid lime-aluminasilica oxides was initiated to clarify the role of an applied potential on the crystallization of liquid oxides. Few studies, from the perspective of the in-situ observation, have been carried out in this field,[1] while many electrochemical measurements have been reported.[2,3] Consequently, a new experimental apparatus, which has the ability of in-situ observation under the application of an electric potential was developed based on the double hot thermocouple technique. First, the validity of the new system was demonstrated; then, careful comparative reviews between the visual observations and the results of the electrochemical measurements were conducted. The basic experimental apparatus that was used in this study was the conventional double hot thermocouple equipment (DHTT), which was developed by Kashiwaya.[4] The DHTT allows high-temperature in-situ observation under conditions of atmospheric control and high heating and high cooling rates. Though the hot thermocouple technique itself was developed in the1950s,[5,6] this combination of two hot thermocouples extended its application to new regions of research.[7,8] The DHTT was subsequently modified by Nakata[9] to allow the application of a potential across the thermocouples. This technique, the modified–double hot thermocouple technique (M-DHTT), allowed the influence of an electrical potential to be observed in liquid oxides. This led to the discovery that normally transparent liquid oxides became translucent and finally became opaque under the application of an electrical potential and that noble metal dissolution in liquid oxides is promoted and metal dispersed ceramics can be produced by this technique. M. NAKATA, Manager–Technology, is with the Nippon Steel Corporation, 6-3, Otemachi 2-chome, Chiyoda-ku, Tokyo 100-8071, Japan. A.W. CRAMB, Dean of Engineering, is with Rensselaer Polytechnic Institute, Troy, NY 12180-3590. Contact e-mail: cramb@ rpi.edu Manuscript submitted February 23, 2007. Article published online July 26, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
In the M-DHTT, a melted oxide sample, approximately 2.5 mg, was held between two thermocouples, and the temperature was controlled by a computer-controlled device that independently controlled the current flowing through the thermocouple wires and thus the temperature of the wires. The sample was located in an atmosphere-controlled chamber, and ultra-high-purity argon was then used to purge the chamber. The system was monitored and recorded through a camcorder positioned above the chamber. Figure 1 shows the setup of the experimental apparatus. In the M-DHTT, an additional electric circuit was introduced. A schematic of the electric circuit diagram is shown in Figure 2. The function of this circuit is to apply an electric potential difference between the two thermocouples. While the thermocouple in the conventional DHTT operates as a heater and a temperature measurement sensor, the thermo
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