Capacitance of the Electrical Double Layer on Liquid Hg–Ga Alloy in Aqueous Solutions

Differential capacitance curves on an Hg–Ga electrode are obtained in aqueous solutions of various composition. An Hg–Ga electrode containing 2.1 at. % Hg to a high accuracy models electrochemical properties of a liquid Hg electrode at negative charges. This result can justify the approach according to which studying liquid In–Ga, Tl–Ga, Cd–Ga, and Pb–Ga alloys permit qualitative characterization of lyophilic properties of corresponding solid alloys.     

Electrical Double Layer Structure in Surface-Inactive Electrolytes on a Liquid Cd–Ga Electrode in Methanol and Propylene Carbonate

Differential capacitance curves and potentials of zero charge are obtained for liquid Cd–Ga electrodes in methanol and propylene carbonate solutions of a surface-inactive electrolyte. It is found that double-layer characteristics of the Cd–Ga electrode differ from those of a Ga electrode both in nonaqueous solutions and in water. The lyophilic nature of the Cd–Ga electrode, relative to methanol and propylene carbonate, is shown to approach that of the In–Ga electrode. In the absence of a metal–solvent chemisorption interaction, the difference between reciprocal metallic capacitances for Cd–Ga and Hg electrodes is independent of the solvent nature. The chemisorption interaction between the solvents and Cd–Ga, Ga, and In–Ga electrodes increases with the solvents' donor number.     

Electrical Double Layer on Liquid Sn–Ga Alloy in Aqueous Solutions

Double-layer parameters of a liquid Sn–Ga electrode in aqueous electrolyte solutions are studied. It is shown that Sn in the alloy with Ga is a surface-active component and is forced out onto a surface layer of the electrode. The double-layer parameters of an Sn–Ga electrode (8 at. % Sn), which are measured in the experimentally accessible range of charges, differ radically from the parameters of Ga electrodes and are close to those of Sn electrode. Hence, an Sn–Ga electrode containing 8 at. % Sn simulates electrochemical properties of a liquid Sn electrode. The difference between reciprocal electronic capacitances of Hg and Sn and a corrected electrochemical work function of Sn are determined. It is shown that the chemisorption interaction of an Sn–Ga electrode with water molecules is virtually absent at charges more negative than –7 C/cm². A potential drop on uncharged Sn, which is associated with water chemisorption, is –20 mV. Thus, the hydrophilicity of Sn is slightly higher than that of Hg, Bi–Ga, Pb–Ga, and Tl–Ga and significantly lower than that of In–Ga, Cd–Ga, and Ga.     

Structure of Electrical Double Layer on Liquid Pb–Ga Alloy in Aqueous Electrolytes

A new electrode, which is a liquid Pb–Ga alloy (0.06 at. % Pb), is developed and studied. It is shown that the alloy's double-layer characteristics dramatically differ from characteristics of a Ga electrode and are practically identical to characteristics of a Pb electrode. Hence, the Pb–Ga electrode in fact models electrochemical properties of a liquid Pb electrode. It is established that the metallic capacitance of the Pb–Ga electrode occupies an intermediate position between values of metallic capacitance of Ga and Hg electrodes, provided the metal–water chemisorption interaction is absent and the electrode charge is fixed. Hydrophilicity of the Pb–Ga electrode is substantially lower than hydrophilicity of a Ga electrode and coincides with hydrophilicity of an Hg electrode. It is shown that In–Ga, Cd–Ga, and Pb–Ga electrodes have close values of the electrochemical work function, and the chemisorption potential drop of the solvent in them increases in the series Pb–Ga < In–Ga < Cd–Ga with decreasing distance of closest approach of water molecules to the ionic core of the metal. The absorbability of anions at the Pb–Ga electrode increases in the series BF^– ₄= SO^2– ₄< Cl^–< Br^–< I^–.     

Adsorption of n-Butanol on Pb–Ga in Aqueous Solutions: Effect of Metal on the Adsorption of Organic Compounds in the Absence of Metal–Water Chemisorption Interaction

The potential dependence of the differential capacitance is measured by an ac bridge at 420 Hz and 32°C at Pb–Ga/H₂O interface in 0.05 M Na₂SO₄ solutions containing n-butanol in different concentrations. Adsorption parameters for n-butanol are determined using a regression analysis and compared with those for Hg, Tl–Ga, and Bi–Ga. As follows from this comparison, though there is no chemisorption interaction between these metals and water, the energy of n-butanol adsorption at these metals depends on the metal nature. The Pb–Ga data fit a common correlation dependence of the electronic capacitance of different electrodes (C _m ^–1)_phys on the energy of the n-butanol molecules adsorption thereon in the absence of a metal–water chemisorption interaction. This finding evidences that the dependence of the energy parameters for the adsorption of organic compounds on the metals' electronic properties, when characterized by (C _m ^–1)_phys, is of general nature.     

Revelation of Nonideal Properties of the Diffuse Layer Near the Surface of a Charged Electrode

It is shown that the charge dependence of the difference between reciprocal differential capacitances for two La₂(SO₄)₃concentrations at the same charge qreliably reveals that properties of the diffuse layer at |q| of 1 to 2 C/cm²are not ideal. Experimental values of the capacitance of Hg, Tl–Ga, and Cd–Ga electrodes in La₂(SO₄)₃aqueous solutions suggest that this phenomenon is adequately described by the Gonzalez–Sanz theory, which links activity coefficients of ions in the diffuse layer with the average stoichiometric activity coefficient in the electrolyte and the electrode charge.     

Electrical Double Layer at a Liquid Pb–Ga Electrode in Propylene Carbonate Solutions

Differential-capacitance curves and potentials of zero charge are obtained for a liquid Pb–Ga electrode in propylene carbonate (PC) solutions of surface-inactive electrolyte LiBF₄and 0.1 M solutions of LiBr and LiI. In PC and water, double-layer parameters of Pb–Ga differ from those of Ga. The lyophilicity of Pb–Ga in respect to PC is lower than that of Ga and coincides with that of Hg.     

Can a radioactive implant induced X-ray emission (RIXE) technique be used to in vivo measurement of heavy elements?

A radioactive implant induced X-ray emission (RIXE) technique was examined for the in vivo determination of heavy elements. By the use of⁶⁷Ga,^99mTc,¹²³I,¹²³Xe and²⁰¹Tl implant excitation sources, the excitation efficiency and X-ray attenuation were measured to reveal the potential pairs of source-heavy element of interest for in vivo elemental analysis by the RIXE technique. Detection limits for the RIXE in vivo analysis were evaluated according to Currie's criterion. Four pairs,^99mTc–Pb,²⁰¹Tl–I,¹³³Xe–Cd and¹²³I–Cd are potential.     

Nonlinear Impedance of Liquid In–Ga Electrode in Aqueous Solutions of a Symmetrical Surface-Inactive Electrolyte

Experimental data related to the potential dependence of nonlinear characteristics of the electrical double layer at a liquid In–Ga electrode in aqueous solutions of a symmetrical surface-inactive electrolyte are obtained for the first time. It is shown that, as opposed to polycrystalline Cd and Pb electrodes, on a liquid (atomically smooth) In–Ga electrode, as on Hg, there is a clear intersection of the potential dependences of a nonlinear signal for different concentrations of a 1–1-valence surface-inactive electrolyte at one point. The intersection point exactly corresponds to the potential of zero charge of an electrode undistorted by specific adsorption of ions. It is established that, when estimating hydrophilicity of metals by a nonlinear impedance method, most information is provided by the region of average negative charges, rather than by the region near zero charge. It is shown that, as opposed to a linear impedance method, the nonlinear impedance method makes it possible to determine, directly from experiment, quantities that directly characterize the metal–solvent chemisorption interaction in a pure form; at the same time, these quantities are criteria of lyophilic nature of metals. Quantities that characterize the metal–solvent chemisorption interaction, obtained by the linear and nonlinear impedance methods are in good agreement, which confirms the validity of the approach we proposed earlier for separating the difference between reciprocal capacitances of the inner part of the electrical double layer on Hg and metal M, ^Hg _M C ^-1 _i= 1/C ^Hg _i– 1/C ^M _iinto physical (^Hg _M C ^–1)_physand chemical constituents. This coincidence also confirms correctness of numerical values obtained earlier for quantities (^Hg _M C ^–1)_phys.     

On the determination of trace impurities in carbon concentrates used in the spectrochemical analysis of extra-pure substances

The effects of concentration of NaCl, employed as the carrier substance in a carbon collector, on line excitation conditions for trace impurities and on other factors which determine detection limita in spectrochemical analysis with a d.c. arc have been studied. It was shown that over the range 4–0.5 per cent NaCl the change in excitation conditions has but a slight effect on the intensity of spectral lines. The major role in the marked lowering of detection limits for trace impurities (Ag, Be, Bi, Cd, Cu, Ga, Ge, In, Mn, Zn, down to n × 10⁻¹⁰ g; Au, Ba, Co, Cr, Ni, Pb, Sb, Sn, Tl—to n × 10⁻⁹ g and for As, B, Pt, Te—n × 10⁻⁸ g) is played by a decline in background intensity and a better coefficient of vapour utilization. For some trace impurities this limit may be improved still further by re-shaping the upper electrode.     

Thallium determination in reference materials by Isotope Dilution Mass Spectrometry (IDMS) using thermal ionization

Summary Using Isotope Dilution Mass Spectrometry (IDMS) with thermal ionization, thallium concentrations were determined in reference materials from NIST and BCR, from other sources, and reference materials from the German Environmental Specimen Bank. ²⁰³Tl spike solution is applied for the isotope dilution technique. Thallium concentrations in the investigated materials range from 2.67 g Tl·kg^–1 to 963 g Tl·kg^–1 with a relative standard deviation from 0.14 to 10%. The detection limit was 0.1 ng thallium for this work.     

Surface Activity of sp-Metals in Molten Intermetallic Compounds

The dependence of the surface-layer composition of a molten binary intermetallic compound (IMC) on factors determining electrochemical properties of liquid electrodes in indifferent electrolytes is studied. The segregation of the binary melt components at the interface with vacuum is considered in terms of physical materials technology. The interface state of the molten IMC is described by the Landau–Ginzburg functional for a surface excess of the Gibbs free energy. An examination of the functional shows that a minimum energy at a given temperature and system volume is reached by depositing the component with the lowest surface tension at the plain component's mp on the melt surface. The deposit has the character of a mesophase; therefore, it remains liquid at temperatures much lower than the plain component's mp in the bulk phase. The dilation interactions between atoms near the interface, caused by different atomic volumes of components, favor the deposition of the metal with a higher atomic volume. The calculated change of the surface tension of Ga–Tl IMC as related to plain Ga is close to relevant experimental value obtained on neutral Ga and Ga–Tl electrodes in an indifferent electrolyte.     

Extraction–Photometric Determination of Thallium in High-TcSuperconducting Materials Using Toluylene Blue

A procedure has been developed for the extraction–photometric determination of thallium as an ion-pair complex with bromide ions and toluylene blue. The procedure allows thallium to be determined in Tl–Cu-containing high-T _csuperconducting materials based on Cu, Ca, Ba, Sr, La, Pb, In, and Hg immediately after sample dissolution without separating Tl from its concomitants.     

New spectrometric method for the determination of trace elements in petroleum by double plasma arc source in a graphite tube

Summary A method is described for the determination of trace elements (V, Mo, Ni, Co, Mn, Ag, Be, Sn, Ga, In, Cr) in petroleum, using a double plasma arc source in a graphite tube. The sample is mixed with graphite powder in the ratio 14, heated to 220° C, mixed with 6% NaCl and loaded into graphite electrodes. Petroleum of different origin was successfully analysed (standard deviation 7–11%; limit of detection 0.003 –0.1 ppm).

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Neues Verfahren zur spektrometrischen Bestimmung von Spurenelementen in Erdöl mit Hilfe eines doppelten Plasmabogens im Graphitrohr

Zusammenfassung Bei dem Verfahren wird die Probe im Verhältnis 14 mit Graphit vermischt, auf 220° C erhitzt, mit 6% NaCl versetzt und in Graphitelektroden gegeben. Erdöl verschiedenen Ursprungs wurde mit dem Verfahren analysiert (Standardabweichung 7–11%; Nachweisgrenze 0,003–0,1 ppm). Folgende Spurenelemente wurden erfaßt: V, Mo, Ni, Co, Mn, Ag, Be, Sn, Ga, In, Cr.

     

Electrical Double Layer on Liquid Bi–Ga Alloys in Aqueous Solutions

Double-layer characteristics of a liquid bismuth–gallium electrode are studied in aqueous electrolyte solutions. Based on the results obtained it is shown that Bi in an alloy with Ga is a surface-active component and forced out to the electrode surface layer. For electrode charges q –5 C/cm², the double layer characteristics of Bi–Ga electrodes approach those of a bismuth electrode. Thus, with respect to its electrochemical properties, a Bi–Ga electrode containing 0.25 at. % Bi simulates a liquid bismuth electrode. The corrected electrochemical work function is determined for bismuth. The close values of the difference of zero-charge potentials on mercury and bismuth in water and the difference of corrected electrochemical work functions for these metals points to the very low hydrophilicity of the Bi–Ga electrode, which approaches the value for mercury at negative electrode potentials. Taking into account that the Bi–Ga electrode displays no semimetallic properties, the similarity of the electric double layer (EDL) parameters for the Bi–Ga alloy and solid pure Bi indicates that the semimetallic properties of bismuth make no contribution to the EDL characteristics of the alloy in the studied range of negative charges q –5 C/cm².     

Adsorption of n-Butanol from Aqueous Solutions on a Bi–Ga Electrode

Curves of the differential capacitance at the Bi–Ga/H₂O interface in 0.05 M Na₂SO₄ solutions with different concentrations of n-C₄H₉OH are obtained by a bridge method at 420 Hz and 32°C. Adsorption parameters of n-C₄H₉OH, determined by a regression analysis of these curves, are compared with relevant data for mercury and partially fused polycrystalline bismuth (pBi). That the adsorption behavior of organic molecules at Hg differs from that at pBi and Bi–Ga is due not to their different hydrophilicity but to a different physical interaction water–electrode. The reason for this phenomenon can be an unequal spread of electron density beyond the ionic cores of Hg and Bi. These notions are corroborated by the fact that the Bi–Ga data fit overall correlation dependence between the electronic capacitance of different electrodes in the absence of a chemisorption interaction metal–water and the adsorbability of the n-C₄H₉OH molecules on them.     

The effect of the nature of a modifying additive (Pt,Zn, Ga) on the activity of oxide and zeolite catalysts in ethane dehydrogenation and aromatization

The catalytic properties of Pt, Zn, and Ga deposited on supports of various natures (Al₂O₃, SiO₂, NaZSM, and HZSM) in the dehydrogenation and aromatization of ethane were investigated. Pt-containing catalysts are the most active in the conversion of ethane: the selectivity with respect to ethylene is 25–87 % depending on the nature of the support. In the presence of Zn- and Ga-containing catalysts the yield of ethylene is 2–3 times lower than with Pt-catalysts. With HZSM modified by Pt, Zn, or Ga aromatic hydrocarbons (ArH) and methane are the main products of ethane transformation. Ga/HZSM is the most efficient catalyst of the aromatization of ethane under the conditions studied (550 °C, 120 h^–1).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 606–609, April, 1994.     

Photoelectrochemistry of indium hexacyanoferrate–titania composite films

The voltammetric and electrochromic behavior of two types of indium(III) hexacyanoferrate(II/III) (InHCF) films, potentiodynamically grown either on polycrystalline Au or on tin-doped indium oxide (ITO) support electrodes, are described. A new spectral feature was seen at ca. 475 nm for the InHCF films grown on Au under extended potential window (EPW) conditions, in addition to the dominant 420 nm feature described by previous authors. The 420 nm band is the sole electrochromic feature in films grown under restricted potential window (RPW) conditions. The InHCF films were also grown in the presence of TiO₂ particles in the deposition bath. The resultant InHCF–TiO₂ composite films showed distinctly different photoelectrochemical responses for the EPW and the RPW counterparts. X-ray phoelectron spectroscopy data showed a higher TiO₂ particle uptake for the EPW films relative to their RPW counterparts, under otherwise identical growth conditions. A second film configuration built up by InHCF derivatization of a pre-formed In–TiO₂ film, yielded decidedly inferior photoresponses. Mechanistic reasons for this are presented as is evidence for the dominance of two distinct forms of InHCF under the EPW growth conditions.     

Determination of iron in high purity gallium arsenide, gallium and arsenic as the bathophenanthroline complex

Summary A spectrophotometric method is described for the determination of iron in high purity GaAs and As or Ga, having a limit of detection of 3.5×10^–5% and 7×10^–5% Fe, resp. After sample dissolution and pre-reduction of Fe³⁺ to the bivalent state with hydroxylammonium chloride the red iron(II)-bathophenanthroline complex is formed in the presence of sodium citrate, ascorbic acid and perchlorate. It is extracted into chloroform and optical density of the resulting extract is measured at 533 nm. The effect of copper is discussed. The procedure is stated to be rapid and applicable not only to Ga, As and GaAs, but also to other materials.

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Zusammenfassung Es wird eine spektralphotometrische Methode zur Eisenbestimmung in Ga oder As und GaAs mit Nachweisgrenzen von 3,5 · 10^–5% bzw. 7,0 · 10^–5% Fe beschrieben. Nach Lösung der Probe und Vorreduktion des Eisens mit Hydroxylammoniumchlorid wird in Anwesenheit von Natriumcitrat, Ascorbinsäure und Perchlorat ein roter Komplex von Eisen(II)-bathophenanthrolin gebildet, der mit Chloroform extrahiert wird und dessen optische Dichte bei 533 nm gemessen wird. Der Einfluß des Kupfers wird diskutiert. Die vorgeschlagene Methode ist schnell durchfÜhrbar und kann nicht nur fÜr Ga, As und GaAs, sondern auch fÜr andere Materialien angewendet werden.

     

Electrolytic Iron Sulfide Products in Lithium Batteries

A technology for electrolytic production of iron sulfide compounds applicable in thin-layer lithium batteries is developed. Physicochemical and structural properties and the surface morphology of compounds are studied by x-ray diffraction and thermal analyses, absorption IR spectroscopy, and atomic force microscopy. Specific discharge characteristics of compounds in thin-layer compact nonballast and paste electrodes of model lithium power sources are determined. The discharge capacity of compounds in thin layers weighing 1.0–7.5 mg cm^–2 galvanostatically cycled in electrolyte PC, DME, 1 M LiClO₄ at room temperature stays at 200–320 mA h g^–1 for 40–50 cycles.