Activity of boron in Ni-B-C melts saturated with carbon
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{Fe-Si}/{CaO-SiO2} ( 1 ) / ( M g O or C ) / {CaO-SiO2} (2)/{Fe-Si} by considering the presence of silicate anions, such as SiO44- , Si2076- , e t c . On the other hand, nickel is inert to oxygen under the carbon-saturation condition. Consequently, the measured e m f is exclusively related to the difference in the boron activities. Thus, the activity of boron in the {Ni-B-C} melt, aB, was calculated by E -
RT
aB In - -
3F
was
(C)/{Ni-B-C
the difference in activities of boron in the two alloy electrodes by considering the presence of borate anions, such as BO33-, B 2 0 5 4 - , etc., in the electrolyte in an analogous manner to that discussed by Goto and Pluschkell t3] in the case of the e m f measurement of the following double cell:
[ref J}/ {B203-A1203-CaO}/ {Ni-B-C} / (C)
where the angular brackets ( ) and the braces { } refer to solid and liquid states, respectively, and the [ref] denotes the reference electrode. A graphite crucible was used to hold the B203-A120 3CaO oxide electrolyte of which composition was chosen as 27 wt pct B203, 33 wt pct A1203, and 40 wt pct CaO so that it might melt at 1150 ~ and be nearly saturated with alumina to avoid reaction with alumina tubes. Sanbongi and Omori C21have shown that there is no substantial difference between a graphite container and a magnesia container for molten CaO-SiO2-A1203 electrolyte in their measurement of alumina activity. Since boron has similar affinity for oxygen to that of silicon, the presence of graphite in the cell of this study would not affect the e m f measurement through reaction with B 2 0 3. As molybdenum, tungsten, and platinum lead wires are soluble in molten Ni-B-C alloy, a graphite rod was placed between the molten alloy and a molybdenum lead wire as an interlinking conductor. Due to the presence of the graphite crucible and the graphite rod in the Ni-B-C electrodes, all of the melts in this study were saturated with carbon. It has been concluded by Goto and Pluschkell t3] that the ionic transference numbers in the silicate, borate, and aluminate melts of alkali and alkali earth metal oxides are all unity, provided that the FexO content is smaller than several weight percent. In the e m f measurement of the above cell, the e m f actually measured is caused by the difference in oxygen partial pressures at the two interfaces between the Ni-B-C electrodes and the molten oxide electrolyte. But the e m f can readily be related to M. YUKINOBU, formerly Graduate Student, Department of Metallurgy, The University of Tokyo, is Chief Researcher with Sumitomo Metal Mining Co., Ltd., Niihama Research Laboratories, Nishibara, Niihama 792, Japan. O. OGAWA, Associate Professor, is with the Department of Metallurgy, The University of Tokyo, Tokyo 113, Japan. S. GOTO, Professor, formerly with the Department of Metallurgy, The University of Tokyo, is with the Department of Metallurgy, Chiba Institute of Technology, Narashino, Chiba 275, Japan. Manuscript submitted December 27, 1989. METALLURGICALTRANSACTIONS B
[1]
aa[ref]
where aB~:f] is the activit
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