Determination of Antimony in Gallium Arsenide by Amalgam Polarography

E. A. Zakharova, Z. G. Kilina

(Presented by the Scientific-Methodological Seminar of the Chemical-Technological Faculty)

The literature contains data on the polarographic behavior of Sb(+5) in hydrochloric acid media [1, 2], and the behavior of Sb(+3) in hydrochloric acid media has also been studied by the method of amalgam polarography [3, 4], but the literature contains no data on obtaining an anodic peak of Sb(+5) in these media.

In the course of analysis of GaAs, a weighed portion of GaAs is decomposed in a mixture of HNO₃ + HCl, with Sb and As being oxidized to the pentavalent state. To simplify the course of the analysis, the main components Ga(+3) and As(+5) were not removed, and Sb(+5) was not reduced to Sb(+3). In this connection, we investigated the amalgam-polarographic behavior of Sb(+5) in hydrochloric acid media of various concentrations, and also proposed a method for determining Sb(+5) in GaAs without separating the matrix, using a mercury drop.

All determinations were carried out on an OH-101 polarograph; the rate of potential change was 333 mV/min. An electrolyzer with insert beakers was used in the work. The stationary electrode was a mercury drop obtained by deposition of mercury released during electrolysis from a solution of mercurous nitrate for 60 sec at a current of 30 mA. The reference electrode was a saturated calomel electrode, relative to which all potential values are given.

To prepare a standard solution of Sb(+5), 0.1 g of metallic antimony was heated in a fluoroplastic dish with 2 ml of H₂SO₄ ($d = 1.84$) until it dissolved; 10 ml of HCl (6 N) was added, and then H₂O₂ (5 ml) was added dropwise. To decompose the H₂O₂, the solution was heated for one hour at $t = 60^\circ$, adding 6 N HCl; the contents of the dish were transferred to a 100 ml volumetric flask and brought to the mark with 6 N HCl. The standard is stable for several months.

Solutions of lower concentration were prepared by successive dilution of the stock standard.

The working solutions, $8 \cdot 10^{-6}$ M and $8 \cdot 10^{-7}$ M, were prepared every 3–4 days.

For the preparation of standard solutions, tridistillate was used; sulfuric acid of chemically pure grade was used; hydrochloric acid (6–9 N) was purified by a known method; hydrogen peroxide was of especially pure grade.

The results of several studies on the amalgam-polarographic behavior of Sb(+5) in hydrochloric acid media of various concentrations are presented in Table 1.

The observed decrease in the peak in 2 and 3 \(N\) HCl is apparently explained by the tendency of Sb \((+5)\) to hydrolyze. A 4 \(N\) HCl supporting electrolyte was selected for the work.

The effect of the electrolysis potential on the anodic peak of Sb \((+5)\) was studied in the interval \(-0.3 \div 0.9\) V. As can be seen from Fig. 1, beginning at a potential of \(-0.5\) V, the anodic peak of Sb \((+5)\) remains constant (see Fig. 1). Accumulation of Sb \((+5)\) was carried out at a potential of \(-0.6\) V.

The calibration graph for Sb \((+5)\) in the concentration range \(2.5 \cdot 10^{-8}\) g-ion/l—

Table 1

Amalgam-polarographic behavior of Sb \((+5)\) in hydrochloric-acid supporting electrolytes

Experimental conditions: \(C_{\mathrm{Sb}} = 4 \cdot 10^{-7}\) g-ion/l, \(\tau = 5\) min,
\(i^* = 1 \cdot 10^{-8}\) A/mm

Fig. 1. Effect of the electrolysis potential on the height of the anodic peak of Sb \((+5)\) in 4 \(N\) HCl supporting electrolyte. Experimental conditions: \(C_{\mathrm{Sb}}(+5) = 4 \cdot 10^{-7}\) g-ion/l; \(\tau = 5\) min, \(i^* = 2 \cdot 10^{-9}\) A/mm, \(V = 5\) ml.

Fig. 2. Calibration graph for Sb \((+5)\) in 4 \(N\) HCl supporting electrolyte (curve 1) and in the presence of As \((+5)\) and Ga \((+3)\) (curve 2). Experimental conditions: \(i^* = 2 \cdot 10^{-9}\) A/mm; \(\tau = 10\) min; \(V = 5\) ml; \(r = 0.04\) cm.

\(-2 \cdot 10^{-7}\) g-ion/l in pure 4 \(N\) HCl supporting electrolyte and in the presence of As \((+5)\) and Ga \((+3)\), in the concentration range \(2 \cdot 10^{-7}\) g-ion/l—\(8 \cdot 10^{-7}\) g-ion/l, is presented in Fig. 2.

Anodic notches of Sb (+5) against the background of As (+5) and Ga (+3) + 4 N HCl are shown in Fig. 3.

Determination of Sb (+5) on a mercury drop under the conditions of the analysis is not hindered by a threefold excess of Cu, if the Cu and Sb (+5) notches are recorded with stopping of the potential after obtaining the anodic peaks. The potentials of the anodic peaks against the background of 4 N HCl for Sb (+5) and Cu are, respectively, -0.25 V and -0.35 V.

On the basis of the investigations carried out, the following procedure was developed for determining microconcentrations of Sb (+5) in GaAs.

A weighed portion of ground GaAs, 0.2 g, is dissolved in a quartz beaker in 1 ml of HNO3 in the presence of 0.5 ml of 9 N HCl at \(t = 70^\circ\)–\(80^\circ\) for 30 minutes and evaporated to dryness over 3 hours. Then 3 ml of 4 N HCl is added.

The beaker is placed in the electrolyzer, hydrogen purified of oxygen with an alkaline pyrogallol solution is passed through the solution under study, and electrolytic accumulation is carried out for

Fig. 3. Anodic notches of Sb (+5) against the background of As (+5) + Ga (+3) + 4 N HCl; curve 1—background, 2—\(2 \cdot 10^{-7}\) g-ion/l, 3—\(4 \cdot 10^{-7}\) g-ion/l, 4—\(6 \cdot 10^{-7}\) g-ion/l, 5—\(8 \cdot 10^{-7}\) g-ion/l. Experimental conditions: \(\tau = 5\) min; \(V = 5\) ml; \(\varphi_{\mathrm{el}} = -0.6\) V; \(i^* = 2 \cdot 10^{-9}\) A/mm. During formation of the notches, the change in potential was stopped.

Table 2

Determination of Sb (+5) in GaAs without removal of the base against the background of 4 N HCl

10 minutes while stirring the solution with a magnetic stirrer and at a potential of -0.6 V.

In the GaAs samples studied, Sb (+5) was not detected; therefore Sb (+5) was introduced into separate GaAs weighed portions before decomposition and then analyzed as described above. The results of the experiments are presented in Table 2.

The maximum sensitivity of the procedure is \(4 \cdot 10^{-6}\%\), with a GaAs weighed portion of 0.2 g, a solution volume of 3 ml, and an electrolysis time of 10 minutes.

Conclusions

1. The amalgam-polarographic behavior of antimony (+5) on hydrochloric-acid backgrounds of different concentration has been studied.

2. A procedure has been developed for determining Sb (+5) in GaAs with a sensitivity of \(4 \cdot 10^{-6}\%\).

Literature

1. I. Kolthoff, R. Probst. Anal. Chem., 21, 753, 1949.

2. J. Lingane. J. Am. Chem. Soc., 69, 530, 1947.

3. L. F. Zanchko, V. F. Yankauskas, M. S. Zakharov. Zavodskaya laboratoriya, 265, 1965.

4. L. F. Zanchko, M. S. Zakharov. In: Methods for the Analysis of Chemical Reagents and Preparations, IREA, issue 5–6, p. 79, 1963.