Activities of phosphorous in liquid Ni + P alloys saturated with solid nickel
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Pr'2 =
-5.6 - 9700/(T/K)
at temperatures between 1477 and 1612 K, and 2 log ae ~ log PP2 = -22.0 + 17000/(T/K) at temperatures between 1612 and 1663 K.
I.
INTRODUCTION
BY using an electrochemical technique incorporating magnesia-stabilized zirconia, the activities of phosphorus in liquid Cu and {Cu + Ni} alloys at dilute concentrations (< 1 wt pct) were determined by the present authors, tl.21The work has now been extended to {Ni + P} liquid alloys saturated with solid nickel. In this study, mixtures of Ni (s) + {Ni + P} liquid alloys were brought into equilibrium with A1203 and A1PO4 in alumina crucibles at temperatures between 1477 and 1663 K, and the equilibrium oxygen partial pressures were measured by means of solid-oxide galvanic cell: Mo / Mo + MoO2 / ZrO2 (MgO) / Ni (s) + {Ni + P} (1) + A1203 + A1PO4 / N i II.
EXPERIMENTAL ASPECTS
Aluminum phosphate (A1PO4) was prepared by mixing alumina and diammonium hydrogen phosphate ((NI-I4)2HPO4) to yield a mole ratio of AI203/P20s = 1/I. The mixture was heated very slowly to 1473 K in an alumina crucible at ambient atmosphere; heating was continued until the product became constant in weight. The aluminum phosphate thus obtained was then mixed with pure alumina at a mole ratio of A12OJA1PO4 = 1:4, pressed into a steel die to form a pellet of 20-ram diameter and 10- to 17-mm thickness, fired at 1473 K for 24 hours, and cooled eventually in air. X-ray diffraction analysis for the resulting pellets revealed the expected phases only. With respect to the thermodynamic stability of A1PO4, the following is pertinent. The phase diagram of the binary system A1203 + PzO5 is from Tananaev et al.t31 Following these authors, A13POs rather than AIPO4 coexists with A1203. Their study is based on the measurements of liquidus
R. KAWABATA, Graduate Student, and M. IWASE, Associate Professor, are with the Department of Energy Science and Engineering, Kyoto University, Kyoto 606-01, Japan. E. ICHISE, formerly with Kyoto University, is retired. Manuscript submitted March 9, 1994. METALLURGICALAND MATERIALS TRANSACTIONS B
temperatures between 2073 and 2373 K by visual observations. It was mentioned that the existence of the intermediate compound A13PO8 was confirmed by X-ray diffraction, although the pattern was not given in their article. Contrarily, in the phase diagram studies of the ternary systems A1203 + P205 + MgO t41 and A1203 + P2Os + CaO,tS] A13PO8 was not detected. In addition, following Miyamoto and Iwase,t6] a mixture of A1203 + A1PO4 at a mole ratio of A1203:P205 = 3:1, fired 48 hours at temperatures between 1473 and 1723 K, did not form A13PO8. It is concluded that at the experimental temperatures of this study, A13PO8 does not exist. The experimental apparatus used in this study is shown schematically in Figure 1. A SiC resistance furnace was equipped with a mullite reaction tube of 70-mm o.d., 60mm i.d. and 1000 mm in length. The electrochemical half cell, Mo/Mo + M o O 2 / Z r O 2 (MgO), shown in Figure 1, consisted of a zirconia tube and a two-phase mixture of
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