STUDY OF INTERMETALLIC COMPOUNDS OF ANTIMONY WITH GOLD AND NICKEL BY AMALGAM POLAROGRAPHY WITH ACCUMULATION

M. S. ZAKHAROV, L. F. ZAICHKO

(Presented by the scientific-methodological seminar of the KhTF)

Recently, for the determination of trace amounts of a number of elements, the method of amalgam polarography with accumulation on a stationary mercury electrode has been finding ever broader application. Quite often, metals in mercury form intermetallic compounds with one another, which interferes with carrying out analyses, the proper conduct of processes in amalgam metallurgy, etc.

It is of interest to study intermetallic compounds of antimony with a number of elements by the method of amalgam polarography with accumulation [1, 2].

According to the theoretical considerations developed in [3], stable intermetallic compounds in mercury are formed between metals if the atom of one of them has an unfilled outer $d$- or $s$-shell. Of the elements considered, the gold atom has an unfilled $s$-shell, and the nickel atom a $d$-shell. Therefore, proceeding from theoretical considerations, one may expect the formation of intermetallic compounds of antimony with gold and nickel.

Methods for determining the composition of intermetallic compounds by the indicated method are set forth in works [1, 4]. According to Kemula [4], determination of the composition of intermetallic compounds is carried out from the ratios of the concentrations of elements in solution at which complete disappearance of the anodic waves is observed. It should be noted that, in order to determine the composition of an intermetallic compound by this method, it is necessary to take into account the ratio of the diffusion coefficients of the ions in solution. This is due to the fact that, other electrolysis conditions being equal, the amount of substance deposited on the electrode will be directly proportional to $D^m$ ($D$ is the diffusion coefficient of the ions in solution; $m$ is the exponent and is the same for all ions).

Determination of the composition of the intermetallic compound $AB_n$ according to [1] is carried out by the formula:

\[ \frac{n+1}{n}=\lg \frac{x_m''}{x_m'} \lg \frac{C_1'}{C_1''}, \]

where $n$ is the number of atoms of the added element in the intermetallic compound (Au, Ni); $C_1$, $C_1'$ are the concentrations of metal ions in solution (Sb) for two series of experiments. The values $x_m''$ and $x_m'$ are found from the gra-

... graph for two series of experiments in the coordinates \(\lg y\) \(\left(y=\dfrac{I}{I^\circ}\right)\) and \(\lg x\) \(\left(x=\dfrac{C_2}{C_1}\right)\).

The values \(I^\circ\), \(I\), \(C_2\), and \(C_1\) are easily determined from experiment.

At \(\lg y_m = 0\), the values \(\lg x_m'\) and \(\lg x_m''\) are found from the graph, and \(n\) is determined from the equation.

Experimental Part

All investigations were carried out on a 7-77-4B-type polarograph with an electrochemical cell equipped with insert cups [5]. A saturated calomel electrode served as the reference electrode. A stationary mercury drop 0.04 cm in diameter served as the indicator electrode. In studying the interaction of antimony and gold in mercury, 2N KOH was used as the supporting electrolyte; in studying the interaction of antimony with nickel, 2N KOH + 0.5 M EDTA was used. The content of heavy-metal impurities was less than \(5 \cdot 10^{-8}\) M.

Table 1

Results of studies on the interaction of antimony with gold and nickel in mercury

Discussion of Results

It is seen from Table 1 that the anodic notches of antimony disappear completely at concentration ratios \([\mathrm{Au}]:[\mathrm{Sb}] = 1\) and \([\mathrm{Ni}]:[\mathrm{Sb}] = 1\). The ratios of the diffusion coefficients for each of the ion pairs studied are approximately equal to unity (the diffusion coefficients were determined from the Ilkovič equation). The values of \(n\), calculated by the method [1], are respectively \(\sim 1\) and \(\sim 1\). Standard solutions of antimony and gold were prepared from the metals, and that of nickel from the salt \(\mathrm{NiSO}_4\).

Two series of experiments were carried out: in the first series, when studying the interaction of Sb and Au, the Sb concentration was \(2{,}6 \cdot 10^{-5}\) M/l; in the second, \(2 \cdot 10^{-5}\) M/l. When studying the interaction of Sb and Ni, the antimony concentrations in solution were \(1{,}2 \cdot 10^{-5}\) M/l and \(1 \cdot 10^{-5}\) M/l for the 1st and 2nd series, respectively. Solutions of gold and nickel were add-

were added to the electrolyzer during the investigation until the antimony waves had completely disappeared. To obtain reproducible results, stirring of the solution, freed from oxygen with nitrogen, was kept the same. Electrolytic accumulation was carried out for 5 minutes, after which, 1 minute after the nitrogen was turned off, the anodic polarogram was recorded.

The electrolysis potential during accumulation of Sb, Au, and Ni was \(-1.65\) V (sat. cal. el.). At this potential, for all the indicated elements, a diffusion current is reached. The background volume was 5 ml. The results of the investigations are presented in Tables 1 and 2 and in the figure.

Fig. 1. Plot of \(\lg y\)—\(\lg x\)
\(1,2\)—\(\mathrm{Au}_n\mathrm{Sb}\)  \(C_{\mathrm{Sb}}\cdot 10^5\ \mathrm{mol/l}:\) \(1\)—2.6; \(2\)—2.
\(3,4\)—\(\mathrm{SbNi}_n\)  \(C_{\mathrm{Sb}}\cdot 10^5\ \mathrm{mol/l}:\) \(3\)—1.2; \(4\)—1.

Table 2

Calculated data for determining the composition of intermetallic compounds by the method of Stromberg and Gorodovykh

Consequently, the intermetallic compounds have the composition AuSb and NiSb. In alloys without mercury these metals form the intermetallic compounds AuSb and NiSb [6].

For the intermetallic compounds AuSb and NiSb, the solubility product \(L_p\) was calculated from equation (16) of work [1].

\[ \lg L_p = n\lg x_m + (n+1)\lg C_1^\circ - n\lg K', \]

\(\lg x_m\) is obtained from the graph in the coordinates \(\lg x - \lg y\); \(C_1^\circ\) is the concentration of antimony atoms in the amalgam in the absence of gold and nickel and is calculated from the equation:

\[ C_1^\circ=\frac{q}{zFV_k}, \]

where \(q\) is the area under the anodic wave, in coulombs; \(K'\) was calculated from the ratio of the diffusion-current constants of the elements in the electrolytes studied.

For the Ni—Sb system, \(K'=\dfrac{K_D^{\mathrm{Ni}}}{K_D^{\mathrm{Sb}}}=0.5\), and for the Au—Sb system \(K'=1\).

The solubility products were calculated for two series of experiments. For the compound AuSb, at antimony concentrations in solution of \(2.6\cdot10^{-5}\) M and \(2\cdot10^{-5}\) M, the solubility product is, respectively, \(2.8\cdot10^{-9}\) and \(2.1\cdot10^{-9}\ \text{g-at}^2/\text{l}^2\). For the compound NiSb, at antimony concentrations of \(1.2\cdot10^{-5}\) M and \(1\cdot10^{-5}\) M, the solubility product is \(1.9\cdot10^{-8}\) and \(1.5\cdot10^{-8}\ \text{g-at}^2/\text{l}^2\). Thus, with a change in the concentration of antimony in solution, and consequently also in the amalgam, \(L_p\) changes. Apparently, the representation of equilibrium in the Au—Sb and Ni—Sb systems in mercury in the form of a solubility product must be treated with caution.

Conclusions

By the method of amalgam polarography with accumulation, the composition of the intermetallic compounds of nickel and gold with antimony has been determined.

REFERENCES

1. A. G. Stromberg, V. E. Gorodovykh. Zh. neorganicheskoi khimii, 8, 2355, 1963.

2. O. S. Stepanova, M. S. Zakharov, L. F. Trushina, V. I. Aparina. Izv. vuzov. Khimiya i khimich. tekhnologiya, 7, 184, 1964.

3. M. S. Zakharov, L. F. Zaichko, N. A. Mesyats, L. G. Baletskaya. Izv. vysshikh uchebnykh zavedenii, khimiya i khim. tekhnologiya, in press.

4. W. Kemula, Z. Galus. Physical chemistry 7, 553 (1959).

5. V. I. Kuleshov, A. G. Stromberg. In: Methods of Analysis of Chemical Reagents and Preparations, issue 5–6, p. 37, IREA, Moscow, 1963.

6. M. Hansen, K. Anderko. Structures of Binary Alloys, vols. I, II, p. 251. Metallurgizdat, Moscow, 1962.