Characterization of CuO phase in SnO<Subscript>2</Subscript>–CuO prepared by the modified Pechini method

The modified Pechini method has been applied to the preparation of nano-structured SnO₂ and SnO₂:CuO. The sample characterization was carried out by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), infrared spectroscopy (IR) and nitrogen adsorption isotherms (BET). The CuO phase in SnO₂:CuO samples was successfully characterized by XRD, XPS and IR. The highest degree of crystallinity and subsequently the maximum intensity and area of CuO (002) diffraction peaks were observed for the samples prepared with templates. The morphology and microstructure of the hybrid were studied using SEM. The core level binding energies of Cu 2p, Sn 3d, and O 1s were measured in these samples. The appearance of a satellite peak in the Cu 2p spectra provided definitive evidence for the presence of Cu²⁺ ions in these samples. The influence of synthesis conditions such as solvent, precursor type, calcinations temperature and time on the detectability of CuO and the morphology and microstructure of the hybrid were also studied. The calcinations conditions had a significant effect on the appearance and intensity of CuO diffraction peaks.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Phases of the NiAs family in Cu-Pd-Sn and Au-Pd-Sn systems

Phases with with a NiAs-based structure have been studied in Au-Pd-Sn and Cu-Pd-Sn systems at 500°C using powder X-ray diffraction, X-ray structure analysis, and energy-dispersive X-ray microanalysis. In the Cu-Pd-Sn system, binary phases γ-Pd₂Sn and Cu6Sn5 both having the Ni2In structure form a phase region (Pd,Cu)_{2 − x} Sn, which preserves the Ni₂In structure and is confined at 500°C by an L + (Pd,Cu)_{2 − x} Sn + ɛ-Cu₃Sn three-phase region. In the Au-Pd-Sn system, the δ-AuSn phase with the NiAs structure and γ-Pd₂Sn with the Ni₂In structure form a single phase region (Pd,Au)_{2 − x} Sn, which is bounded at 500°C by an L + (Pd,Au)_{2 − x} Sn two-phase region; the structure of the ternary phase changes from Ni2In with incompletely filled trigonal-prismatic interstices to NiAs. The Pd₂₀Sn₁₃ phase, which crystallizes in the GaGe₂Ni₄ type structure, penetrates into both ternary systems up to ∼5 at % of the third component. The solubilities of copper and gold in PdSn and Pd₂Sn phases, which have structures based on orthorhombically distorted NiAs and Ni₂In lattices, respectively, do not exceed 2 at %.     

Metal Emulsion-Based Synthesis,Characterization, and Properties of Sn-Based Microsphere Phase Change Materials

A comparative study of the metal emulsion-based synthesis of Sn-based materials in two different types of molten salts (namely LiCl–KCl–CsCl and LiNO₃-NaNO₃-KNO₃ eutectics) is presented, and the properties of Sn, Sn-Cu and Sn-Cu-Zn microsphere phase change materials prepared in chloride salts are evaluated by differential scanning calorimetry (DSC) to understand the effect of element doping. Despite a high ultrasonic power (e.g., 600 W or above) being required for dispersing liquid Sn in the chloride system, well-shaped Sn microspheres with a relatively narrow size range, e.g., about 1 to 15 µm or several micrometers to around 30 µm, can be prepared by adjusting the ultrasonic power (840–1080 W), sonication time (5–10 min) and the volume ratio of salts to metal (25:1–200:1). Such a method can be extended to the synthesis of Sn-based alloy microspheres, e.g., Sn-Cu and Sn-Cu-Zn microspheres. In the nitrate system, however, a very low ultrasonic power (e.g., 12 W) can be used to disperse liquid Sn, and the particles obtained are much smaller. At low ultrasonic power (e.g., 12 W), the particle size is generally less than 10 or 4 µm when the sonication time reaches 2 or 5 min, and at high ultrasonic power, it is typically in the range of hundreds of nanometers to 2 µm, regardless of the change in ultrasonic power (480–1080 W), irradiation time (5–10 min), or volume ratio of salts to metal (25:1–1000:1). In addition, the appearance of a SnO phase in the products prepared under different conditions hints at the occurrence of a reaction between Sn droplets and O₂ in situ generated by the ultrasound-induced decomposition of nitrates, and such an interfacial reaction is believed to be responsible for these differences observed in two different molten salt systems. A DSC study of Sn, Sn-Cu, and Sn-Cu-Zn microspheres encapsulated in SiO₂ reveals that Cu (0.3–0.9 wt.%) or Cu-Zn (0.9 wt.% Cu and 0.6% Zn) doping can raise the onset freezing temperature and thus suppress the undercooling of Sn, but a broad freezing peak observed in these doped microspheres, along with a still much higher undercooling compared to those of reported Sn-Cu or Sn-Cu-Zn solders, suggests the existence of a size effect, and that a low temperature is still needed for totally releasing latent heat. Since the chloride salts can be recycled by means of the evaporation of water and are stable at high temperature, our results indicate that the LiCl–KCl–CsCl salt-based metal emulsion method might also serve as an environmentally friendly method for the synthesis of other metals and their alloy microspheres.     

Elementary steps and mechanism of electrodeposition of Al from complex hydride ions in tetrahydrofuran baths

Electrocrystallization of Al cannot be achieved from aqueous media, but is possible from low melting-point organic salts, and from aromatic and etheric solutions. In the present paper studies are reported on the kinetics and mechanisms of electrodeposition of Al from plating baths of varying ratios of AlCl₃ and LiAlH₄ dissolved in tetrahydrofuran (THF). A complementary paper, which follows, deals with the topic of nucleation and growth processes involved in Al phase electrocrystallization and provides experimental results on that process. Steady-state cathodic and anodic Tafel polarization relations are determined, complemented by ac impedance studies. Back-reaction corrected Tafel plots enable anodic and cathodic transfer coefficients (α) to be evaluated together with corresponding stoichiometric numbers (ν). Critical evaluation both of the present α and ν results, and previous α values in the literature, enables a mechanism of elementary steps in Al deposition from the hydrido-chloride baths to be proposed.     

Cyclic voltammetry of copper in sodium hydroxide solutions

The cyclic voltammograms of the Cu electrode were, obtained in NaOH solution as a function of the voltage scanning rate, electrolyte concentration and voltage range. A correlation was made between three well-defined anodic peaks and their corresponding cathodic ones. The anodic peaks were found to correspond successively to the formation of a monolayer of Cu₂O, formation of a thick multilayer film of CuO and finally Cu₂O₃ upon which O₂ is evolved. It is suggested that CuO is formed from the oxidation of Cu₂O and/or direct oxidation of metallic copper.Below 0.1 M NaOH the ratio of anodic to cathodic charges was found to be about unity, indicating the quantitative reduction of solid oxidation products, while at higher alkali concentrations higher charge ratios were obtained due to increasing proportions of soluble reaction products.The behaviour of the copper electrode in NaOH was found to be quite complicated. Thus, no simple relations were found between the voltage scanning rate and both the peak current and peak potential or between the peak current and the alkali, concentration. Further work is needed to obtain a definitive explanation of this behaviour.     

FTIR spectroscopy study of the electrochemical reduction of CO2 on various metal electrodes in methanol

The electrochemical reduction of CO₂ on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO₂ increases the cathodic current at potentials below −1.3 V vs. Ag|0.01 M Ag⁺ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO₂ on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO²⁻₃, is formed by reaction of CO₂ with hydroxyl anions produced in the electroreduction of residual water.In order to identify the electroreduction products of CO₂ it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO₂-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.     

Blue TiO2 nanotube arrays as semimetallic materials with enhanced photoelectrochemical activity towards water splitting

In the past years there has been a great interest in self-doped TiO₂ nanotubes (blue TiO₂ nanotubes) compared to undoped ones owing to their high carrier density and conductivity. In this study, blue TiO₂ nanotubes are investigated as photoanode materials for photoelectrochemical water splitting. Blue TiO₂ nanotubes were fabricated with enhanced photoresponse behavior through electrochemical cathodic polarization on undoped and annealed TiO₂ nanotubes. The annealing temperature of undoped TiO₂ nanotubes was tuned before cathodic polarization, revealing that annealing at 500 °C improved the photoresponse of the nanotubes significantly. Further optimization of the blue TiO₂ nanotubes was achieved by adjusting the cathodic polarization parameters. Blue TiO₂ nanotubes obtained at the potential of –1.4 V (vs. SCE) with a duration of 10 min exhibited twice more photocurrent response (0.39 mA cm^-2) compared to the undoped TiO₂ nanotube arrays (0.19 mA cm^-2). Oxygen vacancies formed through the cathodic polarization decreased charge recombination and enhanced charge transfer rate; therefore, a high photoelectrochemical activity under visible light irradiation could be achieved.     

浓碱溶液中铜阳极产物的阴极还原行为研究I: Cu(I)产物的阴极还原

采用特定的电势扫描程序测出了浓碱溶液中Cu(I)阳极产物的多重还原电流峰。根据各峰之间转化或竞争的关系, 提出了亚铜氧化物的吸附成相和溶解沉淀两种途径共存的形成机理。为确定各阴极峰的归属, 本文采用了将阴极电流峰与XRD和XPS特征峰进行半定量对比的方法。     

Initial 119Sn Mössbauer Spectroscopy and X-ray Diffractometry Investigations of Electrodeposited Tin-Chromium and Tin-Zinc-Chromium Alloys

¹¹⁹Sn conversion electron Mössbauer spectroscopy, X-ray diffractometry and energy dispersive X-ray analysis (EDAX) were employed to investigate microstructure, composition and phases present in as-electroplated Sn-Cr and Sn-Cr-Zn alloys deposited on copper substrates. In the Sn-Cr deposits Cu, -Sn, Cr-Sn phases can be identified by X-ray diffractometry. The phase composition is significantly different between the samples prepared with relatively higher and lower current densities. In the diffractograms of Sn-Cr-Zn deposits Cu, -Sn, Zn phases can be well identified. A small intensity amorphous peak is also present, which can perhaps be associated with the presence of some amorphous Zn and Sn alloy. ¹¹⁹Sn Mössbauer spectra of Sn-Cr deposits exhibit an asymmetric broad main line centered near the isomer shift characteristic of -Sn as well as they contain a small component near the zero velocity which can be attributed to a SnO₂ phase based upon its characteristic. ¹¹⁹Sn Mössbauer spectra of Sn-Cr-Zn deposits are roughly similar to those of Sn-Cr deposits although the Mössbauer parameters of the third phase are different and vary with the Zn content. The presence of SnO₂ on the surface mainly in the Sn-Cr samples can be attributed to the corrosion process in the air.     

Codeposition of copper and tin from acidic sulfate solutions containing polyethylene glycols. Effect of length of the hydrocarbon chain

Voltammetry and electrochemical impedance spectroscopy technique were applied to study the effect of polyethylene glycols (PEG) with different molecular mass on Cu(II) and Sn(II) reduction kinetics in acidic sulfate solutions. Tetraethylene glycol was found to be the surface-active oligomer on both Cu and Sn substrates that holds the shortest (–CH₂–CH₂–O–)_m chain. The exchange current density of the rate-limiting step Cu²⁺ + e → Cu⁺ falls drastically with an increase in the molecular mass of PEG. An addition of PEG into halide-free Sn(II) solutions results in the significant inhibition of Sn(II) reduction in the entire range of cathodic polarizations including the region of limiting current. Inhibition degree also increases with PEG molecular mass. In contrast with Cu|Cu(II) system, formation of adsorption layers on Sn electrodes proceeds significantly slower. Underpotential deposition of Sn(II) is observed in the region of Cu(II)-limiting current. The characteristic current minimum arises in the region where free Sn phase is thermodynamically stable. It deepens with the length of the hydrocarbon chain of PEG. The fall of current density seems to arise from the inhibitive PEG adsorption on tin atoms that are still not incorporated into general Cu–Sn lattice.     

Mössbauer studes of electrocodeposited cobalt—Tin alloys

Cobalt—tin alloys electrocodeposited from a mildly alkaline sulfate bath were studied using¹¹⁹Sn absorption and⁵⁷Co Emission Mössbauer Spectroscopy. The Results reveal that dissolved tin and cubic CoSn (not appearing in the phase diagram) are the components obtained from fresh plating solutions. Upon exhaustion, the formation of Co₃Sn₂ is favoured, with the eventual deposition of cobalt particles as a separated phase. A precipitate is formed during bath operation which is richer in Sn(II), contrasting to the mother solution which is richer in Sn(IV).     

Synthesis of Cu3Sn Alloy Nanocrystals through Sequential Reduction Induced by Gradual Increase of the Reaction Temperature

Cu₃Sn alloy nanocrystals are synthesized by sequential reduction of Cu and Sn precursors through a gradual increase of the reaction temperature. By transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDS), UV/Vis spectroscopy, and X‐ray diffraction (XRD) analyses, the alloy formation mechanism of Cu₃Sn nanocrystals has been studied. The incremental increase of the reaction temperature sequentially induces the reduction of Sn, the diffusion of Sn into the preformed Cu nanocrystals, resulting in the intermediate phase of Cu–Sn alloy nanocrystals, and then the formation of Cu₃Sn alloy nanocrystals. We anticipate that the synthesis of Cu₃Sn alloy nanocrystals encourages studies toward the synthesis of various alloy nanomaterials.     

Effect of the Electrode Potential on the Oxygen Reaction Rate in the Electrode System O2, Au/La0.88Sr0.12Ga0.82Mg0.18O2.85

The polarization dependences of a porous gold electrode in contact with a solid electrolyte of the composition La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 are studied at 600–800°C and oxygen pressures of 2 × 10⁻²-1 atm. It is shown that the rate of cathodic reduction of oxygen out of the gas phase depends on the preliminary treatment of the sample. The activation energy is equal to 110–135 kJ mol⁻¹ at a low polarization. After increasing the polarization, the activation energy for the cathodic reduction of oxygen equals 75–85 kJ mol⁻¹ and depends on the oxygen pressure as a power function with a power index of 1/4. The rate of the anodic evolution of oxygen is dependent neither on the preliminary treatment of the sample nor on the oxygen pressure in the gas phase and the polarization curve has a characteristic segment, which corresponds to a limiting overvoltage.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 954–962.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Beresnev.     

Sol-Gel Synthesis of Metal Nanoclusters-Silica Composite Films

In a program on the development of metal nanoclusters in sol-gel derived thin films, attempts were made to synthesize pure and mixed metal clusters, control the cluster size and increase the volume fract f the clusters. Thus, Ag, Cu and Ag-Cu nanoclusters were prepared in silica films using dip- and spin-coating techniques. The annealing of Ag/SiO₂ films in different atmospheres (air, argon and 5% H₂-95% N₂ gas) caused modifications of Ag nanoclusters resulting in changes in their surface plasmon resonance (SPR) peak positions. The Cu and Ag-Cu codoped films were annealed in reducing atmosphere (5% H₂-95% N₂ gas). In order to prepare Cu nanoclusters of different sizes, the concentrations of Cu in Cu/SiO₂ composite films were varied from 8 to 30 mol% and annealed at 800°C for different times for growth. The size of the Cu nanoclusters was measured from the half band width of Cu SPR peak (appearing within 570–557 nm range) and X-ray diffraction. In this way Cu-nanoclusters of size ranges from about 3.5 to 10 nm (average diameters) were prepared . The Ag-Cu nanocluster-containing silica films show the existence of both Ag and Cu SPR peaks with some blue shifting in comparison with to their pure analogues depending on the Ag:Cu ratio.     

The electrochemical interface between copper(111) and aqueous electrolytes

The electrochemical double layer between Cu(111) electrodes and aqueous electrolytes (F⁻ and SO²⁻₄ at various pH values) was studied by means of linear scan voltammetry and ac impedance measurements. It is found that electrochemisorption of oxygen species proceeds on the Cu(111) surface in the potential regions more negative than the electrodissolution potential of copper. The adsorption-desorption kinetics are analysed; the anodic and cathodic symmetry coefficients are found to be equal (α = β = 0.3), and the standard rate constant is k° = 4 × 10⁻¹⁰cm s⁻¹.     

Solid state phase transitions characterized by ESR and XAS

Measurements of the relaxation time, τ of electron systems to a disturbance, by two different spectroscopic methods are examined in detail, with the purpose to establish how the presence of fluctuations near a solid state phase transition are made evident in insulators, conductors and superconductors. The absolute temperature and the relaxation time determine the thermodynamic stability of the electronic system near a phase transition by the Uncertainty Principle. At a given temperature T, Landau and Lifshitz obtain the stability from the lower limit of the uncertainty in entropy in units of the Boltzmann constant, ΔS/k_B<<1 when T τ>>3.82 K ps. Magnetic resonance can measure τ>>10⁻¹⁰ s, when v=9 GHz. X-ray spectroscopy can measure τ<10⁻¹⁶s for hv>5 keV. The results extract information about phenomena that occur at the phase transition by following the evolution of spectral features versus T and crystal orientation. Electron spin resonance identifies the phase transition by the evolution of doublet, triplet and antiferromagnetic resonance, and energy loss. Analysis of the X-ray absorption near an element edge determines one, the relative valence: V(Cu in chains)−V(Cu in planes) ≈1 in YBa₂Cu₃O_7−δ, two, the appearance of allowed Cu K pre-edge quadrupole transitions at T_c, three, the enhancement of Ba L3,2 edge transitions by an order of magnitude, just above T_c, at a crystal orientation of the c-axis to the X-ray polarization vector of 8 π/18, and four, difference X-ray absorption spectra, relative to the transition temperature, identify the bonds as well as the atoms involved in the transition. The figure abstract shows the changes in electron density obtained by temperature difference X-ray absorption near the Y K-edge in YBa₂Cu₃O_7−δ below T_c.     

Syntheses,molecular structure,and electrochemical investigations of cobalt(II), copper(II), palladium(II), and zinc(II) complexes with 3-methylpyrazole

Mononuclear complexes of 3-methylpyrazole with general formulas (3-Mepz)₄CuCl₂ (1), (3-Mepz)₄CoCl₂ (2), (3-Mepz)₂PdCl₂ (3), and (3-Mepz)₂ZnCl₂ (4) were prepared by reaction of the corresponding MCl₂ salt (M?=?Cu, Co, Pd, and Zn) with 3-methylpyrazole in appropriate amounts using acetonitrile as solvent at ambient temperature. The X-ray crystal structure determination reveals that 1 and 2 possess octahedral geometry, while 3 and 4 are square planar and tetrahedral, respectively. All the synthesized compounds have the MCl₂ fragment, thus making the synthesized compounds attractive synthons for further transformation. The cyclic voltammograms of the synthesized complexes were obtained and the voltammetric signatures of 1, 2, and 4 showed a single irreversible pH-dependent cathodic peak, while 3 has two reversible cathodic peaks. Involvement of protons accompanying the electron transfer processes was ascertained from differential pulse voltammetric results, indicating peak potential shift as a function of pH.     

Effect of polarization on the electrode behavior and microstructure of (La,Sr)MnO<Subscript>3</Subscript> electrodes of solid oxide fuel cells

The electrode behavior and microstructure of freshly prepared (La_0.8Sr_0.2)_0.9MnO₃ (LSM) electrodes were investigated under various polarization conditions. The original, large agglomerates in freshly prepared LSM electrodes were broken down into sphere-shaped grains when exposed to cathodic or anodic current passage of 200 mA cm^–2 at 800 °C in air for 3 h. Microstructural changes under cathodic polarization could be related to the pronounced diffusion and migration of oxygen vacancies and Mn ions on the LSM surface and lattice expansion, while lattice shrinkage under oxidation conditions most likely contributes to the structural changes under anodic polarization. Such morphological changes were irreversible and were found to be beneficial to the performance of freshly prepared LSM electrodes. Freshly prepared LSM electrodes behaved very differently with respect to the cathodic and anodic current passage treatment.     

High-Tc superconductors studied by57Co,57Fe,119Sn,and151Eu mössbauer spectroscopy

¹⁵¹Eu,¹¹⁹Sn,⁵⁷Fe, and⁵⁷Co Mössbauer spectroscopy was used to study YBa₂Cu₃O_7– high-T_c superconductors in which sites were replaced by various Mössbauer nuclides in order to get information about site preference and structural changes. By decomposition of the Mössbauer spectra, the Y site substituted by Eu and the Cu sites occupied by Sn, Fe, and Co substituents were identified. It was found that Fe and Co prefer the Cu(1) site while Sn prefers the Cu(2) site in the orthorhombic perovskite lattice of these superconductors. The site preference is enhanced in the presence of additional substituents. A sequence of thermal heat treatments permits reversible cycling of⁵⁷Co between the two copper sites in the YBa₂[Cu(⁵⁷Co)]₃O_7– perovskite. In all cases Eu(III) and Sn(IV) states are determined, but the valence state of Fe and Co can be both three and four. BelowT _c, low-temperature phase transformation and phonon softening were shown from the anomalous temperature dependence of isomer shifts and the area fractions of¹⁵¹Eu and¹¹⁹Sn Mössbauer spectra of EuBa₂(Cu_1-xSn_x)₃O_7- cuprates.