The measurement of hydrogen activities in molten copper using an oxide protonic conductor
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I.
INTRODUCTION
AT the last stage of fire refining of molten copper, called the poling process, a large amount of hydrogen dissolves in molten copper from reductants and/or the atmosphere as the oxygen content in molten copper decreases. During the casting process, hydrogen combines with the remaining oxygen to generate water vapor. The water vapor bubbles, which separate from the molten copper, cause some mass defects such as voids and cavities. Therefore, monitoring of the hydrogen content in molten copper is necessary to optimize the poling process. However, the only method of analyzing the hydrogen content in molten copper is sampling the melt and subsequent analysis by the vacuum collection method.[1,2,3] This method cannot avoid errors in the data owing to the sampling procedure and cannot be used as a continuous monitoring tool. In 1980, some proton-conducting solid electrolytes of perovskite-type oxides were developed by Takahashi and Iwahara.[4] Later, many oxide systems were examined. Recently, the same group[5,6] developed a CaZrO3-based solid electrolyte which is chemically more stable and mechanically stronger than most others. One type of this electrolyte, 10 mol pct In-doped CaZrO3 (represented as CaZr0.9In0.1O32d hereafter) has already been utilized as the electrolyte material in a hydrogen sensor for molten aluminum.[7] NORIAKI KURITA, Research Associate, NORIHIKO FUKATSU, Associate Professor, and TERUO OHASHI, Professor, are with the Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466, Japan. SATOSHI MIYAMOTO and FUMIAKI SATO, formerly Undergraduate Students, Department of Materials Science and Engineering, Nagoya Institute of Technology, are with Toyota Auto Body Co. Ltd., Kariya, 448 Japan. HIROYUKI NAKAI, formerly Undergraduate Student, Department of Materials Science and Engineering, Nagoya Institute of Technology, is with Sanyo Special Steel Co. Ltd., Himeji, 672 Japan. KAZUHIKO IRIE, formerly Undergraduate Student, Department of Materials Science and Engineering, Nagoya Institute of Technology, is with Tokai Business Communication Headquarters, Nippon Telegraph and Telephone Corporation, Nagoya 460, Japan. Manuscript submitted August 18, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS B
We have been examining the fundamental properties[8] and applications[9,10] of this electrolyte. In this work, we have developed a hydrogen sensor for molten copper based on the hydrogen concentration cell in which CaZr0.9In0.1O32d has been used as the solid electrolyte. The calculation method of the electromotive force (emf) of the concentration cell, when two movable ions exist in the electrolyte, has also been discussed. II.
EXPERIMENTAL PRINCIPLE
Consider the following hydrogen concentration cell using the proton conducting oxide CaZr0.9In0.1O32d as the electrolyte: (ref.,2)Pt, (p'H2, p'O2)/CaZr0.9In0.1O3-d /(p"H2, p"O2), Pt(1,meas.) [I]
where pH2 and pO2 are the hydrogen and oxygen activities on both electrodes, respectively, and ‘‘ref.’’ and ‘‘meas.’’ in pare
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