References

1. I. A. Makarov. Synthesis of corundum ceramics with specified electrical properties. Author’s abstract of dissertation, Moscow, 1969.

2. A. Yu. Borisova et al. Steatite electrotechnical ceramic materials. Department of VNIISM for Scientific and Technical Information, Standardization, and Normalization in Electrical Engineering. Moscow, 1968.

3. V. I. Levitov. Electric machines with a solid rotor, Part I, II. Moscow, 1963, 1965.

4. Kh. S. Valeev. Electrical properties of steatite materials at elevated temperatures. “Elektrichestvo,” 4, 1955.

5. B. M. Tareev. Physics of dielectric materials. Energiya Publishing House, Moscow, 1973.

6. W. Eitel. Physical Chemistry of Silicates. Foreign Literature Publishing House, Moscow, 1962.

AMALGAM-POLAROGRAPHIC DETERMINATION OF IMPURITIES OF

Zn, Cd, Pb, Cu, AND Bi IN NIOBATES AND TANTALATES OF ALKALI

METALS AND IN NIOBIUM AND TANTALUM PENTOXIDES

Z. S. Mikhailova, P. F. Zayachko, A. A. Kaplin

Niobium, tantalum, and their compounds are among the most complex analytical objects, especially in the determination of small quantities of impurities in them. The sensitivity of spectral and chemical-spectral methods known in the literature for determining heavy metals in niobium, tantalum, and their compounds is \(1 \cdot 10^{-4}\)–\(5 \cdot 10^{-5}\%\). In work /1/, for the first time, for the determination of lead, antimony, and bismuth in \(Nb_2O_5\) with a sensitivity of \(5 \cdot 10^{-5}\)–\(5 \cdot 10^{-4}\%\), the method of amalgam polarography with accumulation (APN) was applied. The aim of the present work was to expand the number of elements (\(Zn\), \(Cd\), \(Cu\)) determined in niobium, tantalum, and their compounds by the APN method and to increase the sensitivity of determination of these elements.

In the work a polarograph OH-102 was used, with a cell containing inserted quartz cups; the indicator electrode was a mercury-film electrode, and the reference electrode was a saturated calomel electrode. As solvents, on the basis of literature /1,2/ and our own data, mixtures of acids were used: \((HF + H_2SO_4)\) or \((HF + HNO_3)\). Increasing the sensitivity of determination of the elements without separating the principal component /1/ is not possible because of the exceptional

the tendency of niobium and tantalum compounds to undergo hydrolysis in aqueous solutions, even in the presence of a complexing agent, for example tartaric acid.

We have established that the determination of cadmium and bismuth at concentrations of \(10^{-5} \div 10^{-6}\%\) in the presence of 0.035 g of the analyzed sample is difficult. The anodic peak of cadmium is not recorded because of the large residual current at a potential of \((-0.7)\) V against the background \((0.1\,\mathrm{N}\ \mathrm{C}_4\mathrm{H}_6\mathrm{O}_6 + 0.2\,\mathrm{N}\ \mathrm{HCl})\). Apparently this is due to partial reduction of niobium /4/. The anodic peak of bismuth is indistinct because of overlap with the anodic current of mercury dissolution. The peaks of copper and lead do not decrease even in gel-like solutions; evidently these elements are not sorbed on the hydroxides of niobium and tantalum. The anodic peak of antimony at a concentration of \(5 \cdot 10^{-4}\%\) decreases with time, and the determination of antimony under the conditions of our experiments is practically impossible. The determination of traces of zinc in niobium and tantalum compounds is impossible without separating the principal components because of the large residual current, since strong mineral acids are their solvents. Thus, for the determination of \(Zn, Cd, Bi\) (as well as \(Pb\) and \(Cu\)), niobium and tantalum must first be separated. For separating impurities from macrocomponents we used an extraction method. Studies were carried out on the possibility of separating the indicated elements by extraction with sodium diethyldithiocarbamate (\(NaDDC\)) /3/ in chloroform from a tartaric-acid medium. To isolate the elements from the organic phase, it was proposed to use \((8–9)\,\mathrm{N}\ \mathrm{HCl}\) as the re-extractant. Conditions for extraction and re-extraction were selected. It was established that, under the conditions of our experiments, \(Cd, Pb, Cu\), and \(Bi\) are re-extracted practically completely by twofold re-extraction, and \(Zn\) by threefold re-extraction; the time of a single re-extraction is 1 min.

The completeness of determination of the analyzed impurities was evaluated. For this purpose, standard solutions of \(Zn, Cd, Pb\), and \(Cu\) were introduced into a Teflon beaker, before decomposition, together with weighed portions of \(Nb_2O_5\) and \(Ta_2O_5\), and then the total content of each of the elements was evaluated. In parallel, the same sample was analyzed without introducing the standard solution at the initial stage.

The data are given in Table I.

Table I

Completeness of determination of \(Zn\), \(Cd\), \(Pb\), \(Cu\), and \(Bi\)
in \(Ta_2O_5\), \(Nb_2O_5\)

Conditions: \(\tau_{\mathrm{e}} = 5\); \(S = 1 \cdot 10^{-8}\ \mathrm{A/mm}\); \(\varphi_{\mathrm{e}} = -1.6\ \mathrm{V}\);
\(K_{\mathrm{e}} = 2 \cdot 10^{2}\ \mathrm{A \cdot s/g\text{-}ion}\); \(K_{\mathrm{a}} = 5 \cdot 10^{-4}\ \mathrm{cm^2\,(g\text{-}atom)^{-1}}\); \(\chi = 2.5 \cdot 10^{-3}\).

* Average data from three determinations.

From these data it follows that there are no losses of the elements being determined during the analytical operations.

As a supporting electrolyte for the simultaneous determination of \(Cu\), \(Pb\), \(Cd\), and \(Zn\), \(0.1\ \mathrm{N}\ NH_4F\) was chosen; the amalgam-polarographic determination of \(Bi\) was carried out in a hydrochloric-acid medium. It was established that antimony, under the conditions of the experiments and at its content in the sample of \(1 \cdot 10^{-6}\)–\(1 \cdot 10^{-5}\%\), is extracted by 10–15% and, consequently, does not hinder the determination of bismuth in a hydrochloric-acid medium.

The following procedure is proposed for the determination of \(Bi\), \(Cu\), \(Pb\), \(Cd\), and \(Zn\) in tantalates and niobates of alkali metals and in pentoxides of \(Nb\) and \(Ta\).

A 0.1-g portion of the sample being analyzed is placed in a Teflon beaker and dissolved in a mixture of acids \((0.1\ \mathrm{ml}\ 20\ \mathrm{N}\ H_2SO_4 + 3\ \mathrm{ml}\) conc. \(HF)\) with heating to \(90^\circ\mathrm{C}\); the resulting solution is then evaporated until sulfuric acid vapors are evolved. To the beaker are added \(10\ \mathrm{ml}\) of \(0.1\ \mathrm{N}\) tartaric acid solution and \(1\ \mathrm{ml}\) of \(8\ \mathrm{N}\) hydrochloric acid. The resulting solution is transferred to a separatory funnel; \(3\ \mathrm{ml}\) of \(0.1\ \mathrm{N}\) sodium diethyldithiocarbamate and \(5\)–\(6\ \mathrm{ml}\) of chloroform are added, and extraction is carried out three times for two minutes each. After separation of the layers, the organic phases are combined in another separatory funnel and washed with \(3\)–\(4\ \mathrm{ml}\) of bidistillate to remove mechanically entrained niobium or tantalum extracted during the extraction. Then, from this phase, the impurities \(Zn\), \(Cd\), \(Pb\), \(Cu\), and \(Bi\) are reextracted three times, for one minute each, with \(8\)–\(9\ \mathrm{N}\ HCl\) solution. The aqueous phase is dra—

poured into a beaker, evaporated to a volume of 4–5 ml, and the amalgam-polarographic determination of bismuth is carried out from a hydrochloric acid solution. The aqueous phase is evaporated, the residue is dissolved in 5 ml of 0.1 N \(NH_4F\), electrolytic accumulation of the impurities is carried out at \((-1.6\ \mathrm{V})\) for 5–10 min, and the anodic polarogram of \(Zn\), \(Cd\), \(Pb\), and \(Cu\) is recorded.

To check the purity of the reagents used and of the cell, a “blank” experiment is carried out under the analytical conditions.

The concentration of impurities is estimated by the method of additions and calculated by the formula

\[ C\%=\frac{h_{\mathrm{pr}}\cdot V\cdot C\cdot 10^{-4}}{h_g\cdot m}. \]

where \(h_{\mathrm{pr}}\) is the height of the anodic peak of the impurity in the sample, mm; \(h_g\) is the height of the anodic peak from the addition of the standard solution, mm; \(C\) is the concentration of the standard solution, g/ml; \(m\) is the sample weight, g; \(V\) is the volume of the addition of the standard solution, ml.

Analyses of a number of samples were carried out by the proposed procedure. The results of the analysis are given in Table 2.

Table 2

Statistical processing of the results of analysis of several objects for the content of impurities \(Zn\), \(Cd\), \(Pb\), \(Cu\), \(Bi\). Background 0.1 N \(NH_4F\); \(\varphi_\mathrm{e}=-1.6\ \mathrm{V}\) (sat. cal. el.); \(\alpha=0.95\).

The analysis time for two parallel samples and one blank sample is 5–6 hours. The limiting sensitivity of determination of the analyzed elements is \(n\cdot10^{-6}\%\).

Literature

1. A. I. Kamenev, V. N. Vinogradova. Zav. lab., 33, 929–931, 1967.
2. E. N. Vinogradova, A. I. Kamenev. ZhAKh, 20, 183, 1965.

1. I. M. Gibalo. Analytical Chemistry of Niobium and Tantalum. Moscow, 1967.
2. I. K. Stepanova, S. I. Sinyakova. Zav. lab., vol. 33, 931, 1967.

FORMATION OF THE STRUCTURE OF PEAT COKE IN THE PRESENCE OF IRON OXIDES

N. G. Aktonov, S. I. Smolyaninov, V. P. Zarylo, G. L. Marzelova

The properties of solid residues from peat pyrolysis depend to a considerable extent on their structure.

The present work gives data from a study of the porous structure of peat and peat-ore materials and of the regions of coherent scattering of X-rays by the carbon of coke.

Peat moldings prepared from high-moor peat (degree of decomposition 20–25%, moisture content 88.2%, ash content 4.9%) and peat-ore moldings with an addition of iron oxide of 24.84% on a dry-substance basis were coked in a laboratory shaft furnace at a heating rate of \(5^\circ/\mathrm{min}\) and with a one-hour hold at the end of the coking interval. The porous structure was studied by Plachenov’s method /1/ on a mercury porosimetric apparatus. The range of pores studied had an effective radius from 60 to 360000 Å.

To investigate the regions of coherent scattering of X-rays, the samples were deashed according to the method of /2/. X-ray diffraction patterns were recorded on a DRON-1 unit, with a copper anode, anode voltage 30 kV, anode current 20 mA. Determination of the crystal size and half-widths of the interference maxima was carried out according to /3/. Crystals of calcined chemically pure sodium chloride were used as the standard for determining the instrumental half-width of the interference peaks.

The mercury porosimetry data showed that the peat and peat-ore material is characterized by a polydisperse porous structure. The introduction of iron oxides into peat promotes an increase in the number of pores in the interval studied, compared with peat without additives. The introduction of fine particles of iron oxide into pores larger than 360000 Å partially fills them; “fragmentation” of large pores into smaller ones occurs, as a result of which the porosity in the range of pores with radii of 360000–60 Å increases, and the number of porosity maxima also increases. Thus, if in the initial-