Oxygen Potential in Molten Tin and Gibbs Energy of Formation of SnO 2 Employing an Oxygen Sensor
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On-line monitoring of the dissolved impurities in molten metals is important for better process control during alloying and metal refining operations. Disposable-type oxygen sensors are commercially available and are used in the iron and steel industry worldwide. However, there is a need for developing low-cost, reliable, long-life oxygen sensors for continuous monitoring of dissolved oxygen in molten metals. In this paper we present the results of the physical and electrical characterization of the solid electrolyte material ZrO2 (8 mol%Y2O3). The experimental results of the application of long-life solid-state electrochemical sensors designed using yttria-stabilized zirconia solid electrolyte for the measurement of oxygen potential in molten tin between 823 to 1273 K and standard Gibbs energy of formation of SnO2 from its elements are also reported.
I. INTRODUCTION
In the production of the high-grade metals and alloys, the control of dissolved metallic and nonmetallic impurities is vital. In view of the present demand for highpurity metals and the process involved in their production, on-line electrochemical sensors for in situ analysis are preferred. In most of the metal-refining processes the analysis of dissolved impurity is carried out discretely by sampling the liquid metal or alloy and analyzing the impurity content by chemical analysis or spark-emission analysis method of cast samples. Metal refining constitutes one of the important steps in the production of high-quality metals and alloys. The advantages of on-line sensors over traditional sampling and chemical analysis includes in situ analysis, energy conservation, instant response, easy handling, and computercontrolled process monitoring. This also helps in controlling the extent of the critical impurities to the required level during the metal-refining process. Therefore, the development of a long-life, on-line, reliable, and robust sensor for the molten metals is very important. Kale and Kurchania1 have recently published a detailed review of the electrochemical sensors for use in moltenmetal-refining process. In view of this technological need for improved process control, present research work was carried out to design and develop the long-life electrochemical sensor for molten metals. An oxygen sensor was designed and
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J. Mater. Res., Vol. 15, No. 7, Jul 2000 Downloaded: 16 Mar 2015
tested in the laboratory in molten tin between 823 to 1273 K. 8 mol% yttria-stabilized zirconia (YSZ) has been used as a solid electrolyte because of its superior oxygen ion conducting characteristics.2,3 The sintering temperature range was selected to obtain the cubic phase.4 YSZ is one of the most widely used materials for the fabrication of oxygen-ion-conducting solid electrolyte tubes. The amount of Y2O3 required to fully stabilize the cubic structure is 8 to 9 mol%.5 Solid solution of zirconia with a sufficient amount of aliovalent metal oxide such as Y2O3, CaO, and MgO not onl
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