Activities of boron in the binary Ni-B and the ternary Co-Fe-B melts
- PDF / 481,878 Bytes
- 6 Pages / 603.28 x 783.28 pts Page_size
- 11 Downloads / 233 Views
I.
INTRODUCTION
A S a continuation of previous studies and measurements of the activities of boron in the binary Fe-B, Co-B, and Cu-B melts m and in the ternary Ni-B-C melts saturated with carbon, tEl activities of boron in the binary Ni-B and the ternary Co-Fe-B melts were measured by the electromotive force (emf) method in a temperature range of 1127 ~ to 1236 ~ for the former and at 1300 ~ for the latter. The ternary system has been selected because there are several kinds of high magnetic permeability amorphous alloys which contain both cobalt and iron together with boron and because a phase diagram is available for the system, t3~ II.
EXPERIMENTAL
The cell construction mainly used in this study was
Mo / (B )/ {B203-AI203-CaO} / {Ni-B } or
{Co-Fe-B}/{Pb}/Mo
where the angular brackets, ( }, and the braces, { }, refer to solid and liquid states, respectively. Figure 1 is a schematic of the cell assembly. The construction was similar to that used in previous work, m except that a boron crystal directly immersed in the {BzO3-A1203-CaO} electrolyte was used as a reference electrode instead of a boron-saturated Cu-B melt in which a boron crystal was immersed, tl] The direct immersion of the boron crystal for several hours in the electrolyte became possible by increasing the alumina content of alumina cement for the reference electrode and by improving the drying procedure of the cement. The standard drying procedure consisted of drying at room temperature for 24 hours, at 100 ~ for 3 hours, and then at 500 ~ in an argon atmosphere for 5 hours. It has been shown I21that the ionic transference number in the electrolyte is unity and that the measured emf can
R. USHIO, formerly Graduate Student, Department of Metallurgy, The University of Tokyo, is Researcher, Sumitomo Metal Mining Company, Ltd., CentralResearch Laboratories, Nakakokubun,Ichikawa 272, Japan. O. OGAWA, Associate Professor, is with the Department of Metallurgy, The University of Tokyo, Bunkyo-Ku, Tokyo 113, Japan. Manuscript submitted June 21, 1990. METALLURGICALTRANSACTIONSB
be exclusively related to the difference in the boron activities of the reference and the working electrodes. Due to the use of a boron crystal as the reference electrode, the activity of boron referred to pure solid boron was unity, and the activity of boron in the Co-Fe-B melt was calculated by RT E = - - - In aB 3F
[1]
Since molybdenum is soluble in Ni-B and Co-Fe-B melts, molten lead was placed, as in the previous work, m between a molybdenum lead wire and an alloy as an interlinking conductor (Figure 1). It was considered that the mutual solubilities between the molten lead and a molten alloy might change the composition of the latter during emf measurements. From phase diagrams, t41 lead is almost immiscible in iron and cobalt at 1300 ~ but dissolves in nickel to about 2 at. pct at 1200 ~ However, average Pb contents of Ni-B and Co-Fe-B alloys after emf measurements were 0.18 and 0.07 at. pct, respectively, and were considered to be sufficiently small not to affect th
Data Loading...
