PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
INSTITUTE named after S. M. KIROV

Vol. 174                  1971

STUDY OF INTERMETALLIC COMPOUNDS OF ANTIMONY WITH SOME ELEMENTS BY THE METHOD OF AMALGAM POLAROGRAPHY WITH ACCUMULATION

L. F. ZAICHKO, M. S. ZAKHAROV

(Submitted by the scientific-methodological seminar of the problem laboratory of microimpurities)

Metals in mercury often form intermetallic compounds with one another, which interferes with the performance of analyses, the proper conduct of amalgam metallurgy processes, etc. There are various methods for detecting and studying intermetallic compounds (potentiometric, amalgam polarography with a dropping electrode, the method of amalgam polarography with accumulation, and others). Previously we [1] studied the possibility of formation of intermetallic compounds of antimony with gold and nickel and determined the composition and solubility product of the intermetallic compounds formed by the method of A. G. Stromberg and V. E. Gorodovykh [2], based on the assumption that intermetallic compounds are sparingly soluble compounds in mercury.

However, the question of the phase nature of intermetallic compounds in liquid amalgam has still not been resolved. In works [3, 4, 5] an interesting method is proposed for establishing the phase nature of intermetallic compounds, based on consideration of the dependence of the height of the anodic waves of the elements forming the indicated compounds on the time of preliminary accumulation in the method of amalgam polarography with accumulation. The authors also propose, for the case when both elements form anodic waves, formulas for determining the composition of intermetallic compounds and for calculating the solubility product or dissociation constant characterizing the equilibrium state in complex amalgams. Irrespective of the assumption about the nature of the intermetallic compounds, its composition can be calculated by the formula

\[ n=\frac{I_2^0-I_2}{I_1^0-I_1}\cdot\frac{a_1}{a_2}, \tag{1} \]

where

\[ a=Fw\cdot v\frac{z_i}{\delta_i} \tag{2} \]

\(w\) is the rate of change of potential, volts/sec; \(v\) is the volume of the electrode amalgam, cm³; \(F\) is the Faraday number; \(z_i\) is the number of electrons participating in the anodic process per atom of the element; \(\delta\) is the width of the anodic half-wave of the \(i\)-th component, volts; \(I_1\) and \(I_2\) are the heights of the anodic waves of the components when they are jointly present in the amalgam; \(I_1^0\) and \(I_2^0\) are the heights of the anodic peaks of the same components in experiments with separate metals at the same initial concentration of the amalgam.

The cited authors also examined in detail the case in which only one of the elements under study gives an anodic peak.

The present work is devoted to a study, by the method of amalgam polarography with accumulation, of the phase nature of intermetallic compounds of antimony with certain elements in mercury.

Experimental Part

All investigations were carried out on a polarograph of the 7-77-4B type with an electrolytic cell with insert cups [6]. A saturated calomel electrode served as the reference electrode; the indicator electrode was a stationary mercury drop 0.08 cm in diameter, obtained electrolytically on a platinum contact. In studies of the mutual influence of antimony and gold in mercury, \(2N\) KOH was used as the background; in studying the interaction of antimony with nickel and copper, \(2N\) KOH \(+\) 0.5 e.d.a. was used. The content of heavy-metal impurities in the polarographed solutions was less than \(5 \cdot 10^{-8} M\). Polarographic waves of Sb, Au, and Ni were first obtained on the corresponding backgrounds, and an electrolysis potential of \(-1.65\) V was selected. Three series of experiments were carried out: in the first series, the dependence \(I-\tau\) for Sb in the absence of Au and Ni was recorded (Fig. 1). A direct proportional relationship (curve 1) between the oxidation current of the antimony amalgam and the time of pre-electrolysis is observed under the experimental conditions up to 15 min of electrolysis, which is associated with attainment of the solubility of antimony in mercury. The solubility determined from the \(I-\tau\) curve coincides with the solubility determined earlier on a \(1N\) HCl background [9]. The second series of experiments was carried out with solutions in which antimony and gold ions, taken in equivalent amounts, were simultaneously present. The results of the investigations are represented by curve 2 (Fig. 1). The appearance of the \(I-\tau\) curve for this case makes it possible to conclude (in accordance with the propositions of [4]) that the intermetallic compound of antimony with gold is present in mercury in solid form and has the composition SbAu.

Fig. 1. Curves: 1—dependence \(I-\tau\) for antimony \((C = 6 \cdot 10^{-6}\) g-ion/l); 2—\(I-\tau\) curve for antimony in the presence of an equivalent amount of gold; 3—\(I-\tau\) curve for antimony in the presence of nickel \((C = 6 \cdot 10^{-6}\) g-ion/l); \(W = 5.3 \cdot 10^{-3}\) V/sec.

A similar regularity is also observed for the case of Sb and Ni (Fig. 1, curve 3), taken in equivalent amounts, which makes it possible to characterize the state of equilibrium in the complex amalgam by the value of the solubility product. The composition and solubility product for these compounds were determined in [1].

In the case of formation of an intermetallic-compound precipitate, it is necessary to take into account the possibility of slow establishment of equilibrium. Therefore, after completion of the electrolysis, before recording the anodic polarogram, the system was allowed to stand for 1.5, 5, and 15 min. The depths of the anodic peaks obtained were identical, which may be regarded as an indication that equilibrium in the system is established immediately after electrolysis.

We also studied the interaction of antimony and copper in amalgam from the \(I-\tau\) curves. According to the theoretical considerations developed in [7], antimony and copper can form intermetallic compounds with one another in mercury. The curves for the individual elements (Cu and Sb) and in their joint presence in mercury are presented in Fig. 2. \(n\), calculated by formula (1), is equal to 1.1. Consequently, under the experimental conditions the intermetallic compound of antimony with copper has the composition CuSb. From the character of the \(I-\tau\) curves it follows that CuSb is present in mercury in the form of a sparingly soluble precipitate. The solubility product of CuSb was calculated by formula (16) of [4]

\[ L_p=\frac{I_1^*}{a_1}\left(\frac{I_2^*}{a_2}\right)^n, \]

and was found to be \(3.2\cdot 10^{-7}\). The results of the calculations of \(n\) and \(L_p\) from data obtained at different rates of change of potential coincided, which indicates the absence of displacement of the phase equilibrium during recording of the polarograms. In mercury-free alloys, antimony forms intermetallic compounds with Au, Ni, Cu [8].

Fig. 2. Experimental dependence of the depths of the anodic waves of copper and antimony on the electrolysis time, taken separately and in their joint presence in solution: \(\circ\)—experimental points for antimony, \(\times\)—experimental points for copper.

Conclusions

By the method of amalgam polarography with accumulation it was found that antimony with gold, nickel, and copper forms sparingly soluble intermetallic compounds in mercury.

LITERATURE

1. L. F. Zaichko, M. S. Zakharov. Izv. Tomskogo politekhnicheskogo instituta, vol. 164, 183, 1967.

2. A. G. Stromberg, V. E. Gorodovykh. Zh. neorgan. khimii, 8, 2355 (1963).

3. M. S. Zakharov, A. G. Stromberg, N. A. Mesyats. Izv. Tomskogo politekhnicheskogo instituta, vol. 164, 163, 1967.

4. A. G. Stromberg, M. S. Zakharov, N. A. Mesyats. Izv. TPI, vol. 164, 1967, p. 165.

5. M. S. Zakharov, A. G. Stromberg, N. A. Mesyats. Izvestiya Tomskogo politekhnicheskogo in-ta, vol. 164, 171, 1967.

6. V. I. Kuleshov, A. G. Stromberg. Metody analiza khim. reaktivov i preparatov, issue 5–6, IREA, 1963, p. 37.

7. M. S. Zakharov, N. A. Mesyats, L. F. Zaichko, L. G. Baletskaya. Izv. VUZ, khimiya i khimicheskaya tekhnologiya, vol. 9, 355 (1966).

8. M. Hansen, K. Anderko. Structures of Binary Alloys, vol. 1, II, Moscow, 1962, p. 252.

9. L. F. Zaichko, M. S. Zakharov. Zhurn. analit. khimii, No. 1, 65, 1966.