Kinetics of Gold Electrodeposition from Cyanide Electrolytes at a Monitored Surface Coverage by Thallium Atoms

A procedure for measuring kinetic parameters of gold electrodeposition in the presence of catalytically active thallium(I) ions while monitoring the coverage of the gold surface by thallium adatoms, , is described. The procedure accounts for the duration of contact between a freshly renewed surface of gold and a thallium-containing solution and assumes that the incorporation rate of thallium adatoms is proportional to and the current density of gold electrodeposition. At = const, kinetic dependences correspond to the Tafel equation. Values of and i ₀ increase with . At = 0.3, 0.6 and i ₀ 3 × 10^–4 A cm^–2, which conforms to values calculated from anodic curves obtained in similar conditions.     

Effects of adsorbed bismuth on Si(001) surface electronic states

It is shown that depositing Bi on an Si(001) surface fills the free broken-bond surface states, whose concentration decreases linearly as the bismuth coating 8 increases up to _st, = 0.6 monolayer. The bismuth desorption activation energy is constant < _st, (E_d = 2.77 ± 0.1 eV) and decreases for > _st.Taras Shevachenko Kiev National University, ul. Vladimirskaya 64, 252601 Kiev-17, Ukraine. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 3, pp. 168–171, May–June, 1996. Original article submitted September 19, 1995.     

Analysis of the Probability of the Mössbauer Effect in Iron(III) β-Diketonates

The probability of the Mössbauer effect f has been evaluated and the Debye temperatures of intermolecular vibrations _M at 295 and 78 K have been determined for ten Fe(III) -diketonates, which are complexes of molecular type. Variation of _M with temperature and molecular mass M has been found; in the latter case, _M decreases as M increases. As a result of this antibatic change in _M and M, the effect of a decreased energy of intermolecular interaction dominates the effect of increased molecular mass, and f decreases in conformity with the prediction provided by the molecular crystal model.     

Activity coefficients for ternary systems: VI. The system HCl + MgCl2 + H2O at different temperatures; application of Pitzer's equations

Electromotive-force measurements have been made on HCl–MgCl₂–H₂O mixtures at 5, 15, 25, 35 and 45°C at eleven different ionic strengths from 0.1–5.0 mol-kg ^–1 . The results are interpreted in terms of the simple Harned's equations, as well as the more complicated Pitzer ion-component treatment of multicomponent electrolyte mixtures. Activity coefficients for HCl in the salt mixtures obey Harned's rule up to and including I=5.0. For the salt in the acid mixtures, Harned's rule holds true up to and including I=0.5. The contribution of higher-order electrostatic terms (E and E') in the Pitzer equations is important for accurate evaluations of unlike cation-cation interactions (_H,Mg), and cation-anion-cation interactions (_H,Mg,Cl). The values of^S_H,Mg and _H,Mg,Cl (determined with E and E'), _H,Mg and _H,Mg,Cl (determined without E and E'), as well as the trace activity coefficients of HCl, _tr ^A , in solutions of MgCl₂ (where ionic strength fraction of the salt,y _B = 1) at all the experimental temperatures and ionic strengths, are reported. Results of this study are compared with those for similar systems. At I=0.1 and 25°C, the results of the Brönsted-Guggenheim specific interaction theory are discussed briefly.     

Epitaxially Grown LaSrCoO3 Thin Films on Various Substrates by the Sol-Gel Method

LaSrCoO₃ thin films have been prepared on various substrates by the sol-gel method using inorganic salts as starting materials. The crystallinity and in-plane alignment of the films were analyzed by X-ray diffraction -2 scans and scans (pole-figure analysis), respectively. Highly (h00)/(00l)-oriented LaSrCoO₃ films with crack-free surfaces were obtained by annealing at 800°C on SrTiO₃(100), while films grown on MgO(100) and Si(100) exhibited poor crystallinity. According to the X-ray diffraction -2 scan, crystallinity of the product films was found to depend on lattice-misfit values between the films and the substrates used. On the contrary, the lattice-misfit values were less effective to the epitaxy of the LSCO film. Epitaxial film grown on SrTiO₃ annealed at 800°C was found by reciprocal-space mapping (-2 scan) analysis to consist of the pseudocubic phase.     

Ferromagnetism of Two-Bridge Clusters

A generalized model of angular overlapping was used to analyze the magnetic properties of polynuclear complexes. The structural elements of these complexes contain planar binuclear fragments of the M(LR)₂M type. The maximum ferromagnetism for the monoatomic bridges corresponds to = MLM, which is about 100°. Weak planar interactions between L and R displace the ferromagnetism maximum towards lower , while interactions shift it towards higher . In almost all cases, strong planar interactions (LLR 180°) are responsible for strong antiferromagnetism.     

A calorimetric investigation into copper–arginine and copper–alanine solid state interactions

Complexes of formula CuCl₂ · 2arg and CuCl₂ · 4ala (arg = arginine; ala = alanine) were prepared at room temperature by a solid state route. The metal–amino acid solid state interactions were studied by i.r. spectroscopy and solution calorimetry. For both complexes, participation of the carboxylate group as well as nitrogen in coordination are inferred, based on the i.r. data. For the copper–arginine compound, the calculated thermochemical parameters are: _rH_m = –114.9 ± 1.42 and _fH_m = –1608.3 ± 11.6 kJ mol^–1. For copper–alanine compound, a complete set of thermochemical parameters were calculated: _rH_m = –18.0 ± 0.9; _fH_m = –2490.4 ± 4.3; _DH_m = 597.2 ± 17.7; _MH_m = 771.9 ± 18.7; _gH_m = 627.1 ± 22.3 and D (Cu–L) = 156.8 ± 5.7 kJ mol^–1. Based on _rH_m and dissolution enthalpy values, a stronger intermolecular solid state interaction can be inferred for the arginine complex, than for the alanine one complex, probably due to the formation of intermolecular hydrogen bonds in the former.     

Evaluation of energy distribution on a heterogeneous surface from heat of adsorption and its application to the ammonia/Na-Y zeolite system

The— function (energy level function) which represents surface heterogeneity was derived from theq— function (experimental heat function) in the case of reversible adsorption. The Langmuir equation was extended and applied to the procedure of calculations. An iterative calculation led to the most probable— function by setting theq— function and adsorption temperature. As an example for actual cases, the— function of Na-Y zeolite was calculated from theq— function obtained by the measurement of heats of adsorption of ammonia at 373 K. The— function thus derived seemed to be consistent with the positional distribution of sodium ions.     

Übergangsmetall-Chalkogensysteme, 3. Mitt.: Das System Nickel-Tellur

Zusammenfassung Auf Grund thermischer und röntgenographischer Unter-suchungen wurde das vollständige Phasendiagramm Ni–Te aufgestellt. Die Anlage für die thermische Analyse wurde teilweise automatisiert, so daß ausgewählte Temperaturintervalle mit einstellbaren Heiz- udn Kühlgeschwindigkeiten periodisch durchlaufen werden konnten. Zwischen Ni und der kub. f. z. Hochtemperaturphase ₁ (Ni_3±x Te₂) liegt ein Eutektikum bei 34 At% Te und 1004,5°C. ₁ schmilzt kongruent bei 38 At% Te und 1021,5°C und hat eine maximale Phasenbreite von 37 At% Te (1004,5°C) bis 43,5 At% Te (880°C). Nickelreiches ₁ wandelt sich zwischen 796 und 789°C in eine Ordnungsphase ₁ um, die bei 37,7 At% Te und 731°C eutektoidisch in Ni und ₂ zerfällt. ₁ und ₁ wandeln sich unterhalb bei 790°C in die tetragonale ₂-Phase um, deren maximaler Homogenitätsbereich von 38,8 At% Te (731°C) bis 41 At% Te (775°C) reicht. Bei 42,5 At% Te und 775°C zerfällt ₁ eutektoidisch in ₂ und ₂. Die ₂-Phase (NiTe_0,85) bildet sich peritektisch bei 880°C und zerfällt bei 690°C nach _{2 1} + . Orthorhombisches ₁ disproportioniert sich peritektoidisch bei 742,5°C in ₂ und ₂. ₂ bildet bei 873°C und 49,5 At% Te ein Eutektikum mit der -Phase vom NiAs-Typ. hat einen kongruenten Schmelzpunkt von 900,5°C bei 56 At% Te und eine maximale Phasenbreite von 52 At% Te (690°C) bis 66,6 At% Te (448,5°C). Mit Te bildet die -Phase ein entartetes Eutektikum bei 448,5°C. Die Phasen ₂, ₁ und wurden röntgenographisch verifiziert und die Abhängigkeit der Gitterparameter der -Phase von der Konzentration vermessen.

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Transition metal-chalcogene systems, III: The system Ni–Te

Based on thermal and X-ray measurements the complete Ni–Te phase diagram was constructed. The equipment for thermal analysis was partially automated so that selected temperature intervals could be periodically scanned by programmed heating and cooling rates. Between Ni and thefcc high temperature phase ₁ (Ni_3±x Te₂) a eutectic exists at 34 at% Te and 1004.5°C. ₁ melts congruently at 38 at% Te and 1004.5°C, and has a maximum phase width from 37 at% Te (1004.5°C) to 43.5 at% Te (880°C). Nickel-rich ₁ transforms between 796 and 789°C into an ordered phase ₁ which decomposes eutectoidally into Ni and ₂ at 37.7 at% Te and 731°C. ₁ and ₁ transform at temperatures below 790°C into the tetragonal ₂-phase which has a maximum range of homogeneity from 38.8 at% Te (731°C) to 41 at% Te (775°C). At 42.5 at% Te and 775°C ₁ decomposes eutectoidally into ₂ and ₂. The ₂-phase (NiTe_0.85) is formed by the peritectic reactionL + _{1 2} at 880°C and decomposes at 690°C according to _{2 1} + . Orthorhombic ₁ disproportionates peritectoidally at 742.5°C into ₂ and ₂. ₂ forms at 873°C and 49.5 at% Te a eutectic with the -phase of the NiAs-type. has a congruent melting point of 900.5°C at 56 at% Te and a maximum phase width from 52 at% Te (690°C) to 66.6 at% Te (448.5°C). Te and the -phase form a degenerate eutectic at 448.5°C. The phases ₂, ₁, and were verified by X-ray diffraction and the lattice parameters of the -phase were determined as a function of concentration.

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Mit 2 Abbildungen     

Interelectronic angle densities of atoms in momentum space

For the 102 atoms from He to Lr in their ground states, the Hartree–Fock interelectronic angle densities,¯A(¯₁₂), in momentum space are reported, where ¯₁₂ is the angle between the momentum vectorsp₁ and p₂ of two electrons. In the first three atoms, He–Be, ¯A(¯₁₂) is found to be uniform independent of ¯₁₂, while in the remaining 99 atoms,¯A(¯₁₂) is larger for a large ¯₁₂ than for a small ¯₁₂. Accordingly, the average interelectronic angles in momentum space are 90° precisely for the three atoms and greater than 90° for the 99 atoms.     

Preparation and Characterization of Thin Optically Transparent Alumina and Ce-doped Alumina

Transparent and porous boehmite, -Al₂O₃ (500°C) and -Al₂O₃ (900° and 1000°C) thin sheets (50–100 m) have been prepared from boehmite sols. -Al₂O₃ shows about 48% porosity and 292 m²/g surface area. On transformation from -Al₂O₃ (500°C) to -Al₂O₃ (900°C), the porosity still remains high, i.e. 45%; however, the surface area becomes 138 m²/g. The porosity and surface area of -Al₂O₃ become about 41% and 97 m²/g respectively on further heating to 1000°C. A gradual increase of average pore radius during this thermal treatment suggests that coarsening of the pore occurred during the densification process. Both -Al₂O₃ and -Al₂O₃ show high degree of transmission from UV to NIR wavelength region. Cerium exists in +4 oxidation state in the boehmite as well as in the - and -Al₂O₃. The ultraviolet absorption edge of the alumina was tailored by varying the concentration of cerium.     

Eigenvalues of large even annulenes in terms ofK 3,S 4 andS 5

Squares of the adjacency matrices of bipartite cycles (C_v) can be block-factored into matrices which correspond to vertex-weighted complete graphs forv = 6, vertex-weighted strongly regular graphs forv = 8 and 10, and vertex-weighted metrically regular graphs forv > 10. Using this fact and some properties of strongly and metrically regular graphs, it is shown that eigenvalues of large bipartite C _v graphs (i.e. large even annulenes) can be expressed by the general formula ± (2 ± (2 ± (... ± (2 +r _p)) ...), wherev = 2 ⁿ ×p,n is the number of surd () signs required andp = 3, 4 and 5. Here,r ₃,r ₄, andr ₅, are the eigenvalues of the complete graphK ₃ and the strongly regular graphsS ₄ andS ₅ respectively. The procedure does not require construction of characteristic polynomials for the determination of eigenvalues, and brings out a common topological origin for the two-fold degeneracies observed in the eigenvalue spectra of all even cycles and many odd cycles.     

Some Anomalies in Coadsorption of Two Organic Substances Due to Differences in Molecular Interaction of Species Undergoing Coadsorption

Effect of molecular interaction between species undergoing coadsorption on the potential dependences of coverages ₁and ₂, surface tension, and equilibrium and nonequilibrium differential capacitances is analyzed on the basis of a set of isotherms for coadsorption of components 1 and 2 within a common monolayer when the EDL inner part obeys a model of three parallel capacitors. It is shown that, in a certain potential interval, at a certain ratio between adsorption parameters, the set of isotherms may have solutions that correspond to a minimum in a free energy surface, which is a function of ₁and ₂.     

Effect of Lead Ions on the Kinetics of Gold Deposition from Cyanide Electrolytes

The depolarization of the gold electrodeposition in the presence of lead ions depends on their concentration and the duration of electrode contact with solution preceding a potential scan in an extremum fashion. At constant coverages of the gold surface by lead adatoms , the process rate depends on the overvoltage in accord with the Tafel equation. Effective values of the exchange current i ₀ and transfer coefficient increase with from i ₀ 3 × 10^–5 A cm^–2 and = 0.23 in pure solutions to 3 × 10^–4 A cm^–2 and 0.53 at 0.4. The reaction order by cyanide ions is independent of and equals nearly –0.9. Effects of lead adatoms on the kinetics of cathodic and anodic processes are compared and the obtained data may be brought to conformance given that their mechanisms in pure solutions differ and converge in the presence of lead adatoms.     

Bounds for reactivity indices

Lower and upper bounds are derived for bond number, localization energy and atom self-polarizability of alternant hydrocarbons. It is proved that in acyclic polyenes the maximal bond number is 1, 2 and 3, respectively for primary, secondary and tertiary carbon atoms.     

Temperature effects in capillary electrophoresis 2: Some theoretical calculations and predictions

Summary The dependence of the temperature excess, , in the capillary bore on the applied power, EI, is considered for both natural and forced convective cooling, using classical heat equations. The dependence of on EI is found to be linear for forced convection but not for natural convection. Use of forced convective cooling and capillaries of large outer diameter reduces . Direct comparison of the performance of different systems can be achieved by consideration of . Column performance is ultimately limited by thermal gradients across the capillary bore.     

Deposition of Langmuir-Blodgett layers

The behavior of a liquid being pulled out along a vertical plate is discussed, assuming that, in equilibrium, the liquid has a finite contact angle _e . Using a simplified form of the Huh-Scriven analysis for viscous friction, we show that a steady state solution (with a dynamic contact angle< _e ) exists provided that the velocity of pull-outU is below a certain thresholdU _m(_e). These considerations can be transposed (with a modification in numerical coefficients) to the case where the liquid is covered with a surfactant monolayer, to be transferred towards the solid in theY mode. SinceU _m is predicted in terms of interfacial tensions, this may provide a general scheme of interpretation for reactive deposition.     

Effect of substituents at silicon on the oxidative addition of trisubstituted silanes to [RhCl(cod)PPh3]

Summary Trisubstituted silanes, HSiR_3–n X _n (R = Me, Et, Pr or Bu; X = Cl, OEt or Ph; and n = 0–3) readily undergo oxidative addition to complex [RhCl(cod)PPh₃] (where cod = cycloocta-1,5-diene).The quantitative correlation between rate constants, k ₁, of the reaction, followed spectrophotometrically at 20 °C in benzene solutions, and the structure of tri-substituted silanes represented by stereoelectronic parameters , and E of the substituents, was established: logk ₁ = a + b + c + dE. The reaction rate is accelerated by electron-withdrawing substituents at silicon and retarded by the bulk and pd donation of nonalkyl substituents.Author to whom all correspondence should be directed.     

A systematic treatment of three-dimensional quantum mechanical reaction coordinates

Summary The rigorous, collinear, canonical point transformation method with hyper-hyperbolic coordinates is extended to the infinite central mass problem in three dimensions. The initial transformation performed is (x_A, y _A, z _A, x _C, y _C, z _C) (, , , r, R, ), where (, , ) are the Euler angles; r and R are the AB and BC interatomic distances, respectively, and is the angle between r and R. A second transformation is then performed to (, , , , , ), where is the reaction coordinate mimicking the reaction path, and is the vibrational coordinate of the diatom. The transformed spaces are all one-to-one mappings from the original spaces, and thus do not have any three-to-one regions. The transformed momenta and Hamiltonians are derived, and are Hermitian in their respective transformed spaces.     

The application of the ion-interaction model to multicomponent 1-1 type electrolytes in mixed solvents

The ion-interaction model has been applied to published measurements for the multicomponent electrolytes HCl+MCl (M means Na or K) in mixed solvents (urea + water or methanol + water). The Pitzer parameters _HCl ⁽⁰⁾ , _HCl ⁽¹⁾ , C _HCl , ( _NaCl ⁽⁰⁾ + _NaH), _NaCl ⁽¹⁾ , _NaHCl in the HCl+NaCl + urea + water system were obtained by the method of least squares. A temperature and molality dependent equation for _HCl in this system was obtained. In the HCl+MCl + methanol + water system, the mixing parameter _HCl was obtained in terms of the Harned Rule. The relationship between Pitzer parameters and the composition of the mixed solvent was discussed.on leave from Department of Chemistry, Liaoning University Shenyang, China.