Effect of arsenic on the activity of oxygen dissolved in dilute liquid copper solutions
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INTRODUCTION
A study of the arsenic-oxygen interactions in liquid copper is interesting in view of the position of arsenic in the periodic table. In group V, arsenic lies between phosphorus and antimony, the former having a strong negative effect on the activity of oxygen in liquid copper l'z while the latter has been shown 3 8 to have very little effect. The interaction parameter of arsenic with respect to oxygen in liquid copper has earlier been reported by Taskinen 9 to be 4.0 at 1423 K. In the present work, arsenic-oxygen interactions in dilute liquid copper solutions have been studied in the temperature range 1373 to 1473 K at very low levels of oxygen in the molten metal. The measurements of the oxygen activities have been carried out by means of the galvanic cell ( - ) Pt, W/O~c,-O-A~>IIZrOz-CaO IINiO, Ni/Pt (+) Cells of this type have been used in similar measurements earlier. JO,ll
II.
EXPERIMENTAL
Electrolytic copper (99.99 pct) and pure arsenic (spectroscopic grade) were supplied by Boliden Company, Sweden. The copper metal was deoxidized in H2 atmosphere at 900 ~ overnight before being used in the experiments. Arsenic was added to liquid copper in the form of Cu-As master alloy. This alloy was prepared by adding Cu3As to molten copper kept in a graphite crucible in argon atmosphere at 1473 K. For the preparation of Cu3As itself, a method similar to that used by Azakami and Yazawa ~2was adopted. The master-alloy samples were subsequently heat treated in hydrogen atmosphere at 600 ~ for 10 hours. A number of samples were analyzed for arsenic by the atomic absorption method and the average arsenic content was found to be 4.30 _+ 0.02 wt pct. Partially stabilized ZrO~ tubes (with 3.5 wt pct CaO) from Zircoa Corporation, USA, were used as solid electrolytes in the present work. The experimental arrangement and the procedure adopted are similar to those described elsewhere. 11 H. WALQUI, formerly on leave at the Department of Theoretical Metallurgy, The Royal Insutute of Technology, Ls now the Manager, U. P Refinena de Cobre de ILO, Pampa de Cahche KM.9, Casdla 117ILO, Peru. S SEETHARAMAN, Docent, and L.-I STAFFANSSON, Professor, are w~th the Department of Theoretical Metallurgy, The Ro t al Insutute of Technology, 100 44 Stockholm, Sweden Manuscript submttted March 22, 1984. METALLURGICAL TRANSACTIONS B
Extensive studies of the activity of oxygen in the Cu-O binary system were also made to check the experimental set-up. In these cases, due to higher oxygen contents in the melt, a cermet electrode was used instead of tungsten, After each emf measurement a sample of the melt was withdrawn and analyzed for oxygen. The measurements of the oxygen activity in the ternary melts were carried out at 1373, 1423, and 1473 K. The oxygen activity, ao could be calculated from the emf value E, obtained after each arsenic addition, using the relationship E -
RT ao 2F In 1--; Po~
[1]
where R is the gas constant, T the temperature of the cell, F the Faraday constant, and Po, the partial pressure of oxygen in equil
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