Electrocatalytic Oxidation of Hydrogen Peroxide by Poly(NiIIteta) modified Electrodes§

[Ni^II(teta)]²⁺ (teta=C-meso-(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) was electropolymerized on glassy carbon (GC) and Nafion^® coated GC electrodes (GC/Nf). These poly(Ni^IIteta) modified electrodes showed 70 mV shift per pH unit and electrocatalysed the oxidation of H₂O₂. The thickness of the Nafion^® film was found to influence the rate of the electrocatalytic reaction. A rate constant of 1.77 × 10³ dm³ mol^–1 s^–1 was observed at 1.0 × 10^–5 cm thick Nafion^® film, whereas a rate constant of 0.08 × 10³ dm³ mol^–1 s^–1 was observed at 3.6 × 10^–5 cm thick film. At a plain GC electrode, a rate constant of 1.29 × 10³ dm³ mol^–1 s^–1 was observed. The poly(Ni^IIteta) is stabilized in the Nafion^® film when compared to the poly(Ni^IIteta) coated on plain electrode.     

Electrochemical formation of Ni-Y intermetallic compound layer in molten chloride

The reduction of Y(III) ions in molten chloride is known to be a one-step three electron reaction [1, 2, 3], but a voltammogram of YCl₃ in molten LiCl-KCI-NaCl at a nickel electrode shows at least two reduction peaks of Y(III) ions, indicating the possibility of formation of Ni-Y intermetallic compounds. Using a galvanostatic electrolysis method, samples were prepared at several current densities at 450, 500, 600 and 700°C, respectively, and were identified with X-ray diffraction (XRD) and electron probe microanalysis (EPMA) methods. The results show that Ni₂Y, Ni₂Y₃ and NiY can be produced by electrolysis and Ni₂Y is found to be the predominant Ni-Y intermetallic compound under the experimental conditions. Nickel appears to diffuse in Ni₂Y faster than yttrium, and the diffusion process is the rate determining step during Ni₂Y formation.     

Preparation and properties of raney nickel electrodes on Ni-Zn base for H2 and O2 evolution from alkaline solutions Part I: electrodeposition of Ni-Zn alloys from chloride solutions

Experimental results for the electrodeposition of Ni-Zn alloys from chloride solutions, with addition of H₃BO₃ and without other additives, in a laboratory cell with a perforated nickel sheet cathode and with recirculating electrolyte are presented. The dependence of the zinc content in the alloy on the following operating conditions was investigated: cathodic current density, 1.0–20.0 A dm^–2; temperature, 35–65°C; pH 1.5–5.5; total molarity,M _tot=M _Ni ²⁺ +M _Zn ²⁺ =1.1–2.8 M; and, molar ratio,P=M _Ni ²⁺ /M _Zn ²⁺ =1.0–15. Depending on the operating conditions the Zn content in the alloy varied over the range 22–88 mol%. In separate experiments galvanostatic polarization curves were measured in the direction of increasing and then decreasing cathodic current density in the range 0.1–20.0 A dm^–2 with all other operating conditions as used for electroplating experiments. In all cases significant hysteresis effects were observed. It was found that the current efficiency for the electrodeposition of Ni-Zn alloys from chloride solutions as a function of the zinc content in the alloy showed a sharp minimum of about 55% atX _Zn=55 mol % irrespective of other operating conditions.     

A peculiar heterotrimetallic Mn–Co–Ni complex: Synthesis, crystal structure and magnetic properties

The first complex [Mn(H₂O)₆][NiCo(TTHA)(H₂O)₂] · 4H₂O 1 (TTHA⁶⁻ = triethylenetetraminehexaacetate) containing Mn^II–Co^II–Ni^II three different 3d metal ions is synthesized and magnetic measurement suggests that ferromagnetic interactions occur between Ni²⁺ ions and rarely found low-spin Co²⁺ ions.     

Interaction between the components of the powders of the Nb-Y2O3 system

Conclusions In the particulate Nb-Y₂O₃ system subjected to heating in the 25–2000°C range, interaction of the unit cells of niobium and yttrium oxide was evaluated on the basis of the variation of the lattice parameters. It was established that oxidation of niobium starts at 800°C and that niobium oxides of different compositions form at temperatures exceeding 800°C.The transformation of yttrium oxide into a disordered phase occurs in the 500–1000°C range. The lattice parameter of the disordered phase of yttrium oxide varies in the 1100–1300°C range and remains unaltered in the 1300–1500°C range. In the same temperature range, niobium oxides dissolved in the lattice of yttrium oxide to form a substitutional solid solution. The concentration of niobium present in the lattice of yttrium oxide as a solute amounts to 3.7%.Translated from Ogneupory, No. 6, pp. 7–9, June, 1992.     

Investigation of electroless plating of Ni–W–P alloy films

The electroless deposition of Ni–W–P alloy coatings onto metal substrates using H₂PO₂ ^– as reducing agent from solutions containing nickel sulfate, sodium tungstate, sodium citrate, ammonium sulfate and other additives was studied. At most temperatures (60–80 °C) and pHs (7–11) investigated, bright and coherent coatings uniform in appearance were produced. Phosphorous and tungsten contents ranging from 3.5 to 8 wt % and 0.5 to 6 wt %, respectively, were obtained depending upon solution temperature and pH. Trends such as the effects of pH and temperature on average metal deposition rate and the P content in the alloy are similar to that reported previously for the Ni–P system. Correlation of open-circuit potentials with events occurring at the electrode surface in different solutions and polarization curves provide strong evidence that Ni²⁺ ions participate in W and P deposition, H₂ evolution and H₂PO₂ ^– oxidation and that H₂PO₂ ^– ions participate in cathodic reduction. This indicates that the partial reactions for the Ni–W–P system do not occur independently of one another.     

Properties and structure of periclase — Yttrium materials

Conclusions An analysis was carried out of the properties of a ceramic material in the system MgO-Y₂O₃ containing 5–64.8% yttrium oxide.The vaporization of a periclase-yttrium ceramic is attributable to its large surface area and to the state of the material (monocrystalline grains and a fine-ground component). The addition of yttrium oxide to the periclase material results in a lower weight loss in a vacuum of 1.5·10^–5 mm Hg at 1700°C, more especially in the case of a mix produced from chemically pure materials. The weight loss was lowest for a composition designed as a chemical compound, viz., 1.1% after holding for 20 h.Granular mixes (2-0, 1-0 mm) are more stable to vacuum than a fine-grain material. An analysis of the structure of the cylindrical surface of the specimens showed that the vaporization rate is greater for the fine-ground component.Translated from Ogneupory, No. 1, pp. 50–54, January, 1976.     

Space — charge — limited conduction in NiCl2 — doped PMMA films

Summary The effect of weight fraction (1–4%) of NiCl₂ dopant on some parameters characterising the space charge limited conduction (SCLC) in polymethylmethacrylate (PMMA) composites was investigated. The studied parameters are the concentrations of traps, trapped and free charge carriers. It was implied that NiCl₂ acts as an efficient electron acceptor and this was attributed to the formation of Ni₁₁CL₄ ^2–.     

Dimethyl ether synthesis via methanol and syngas over rare earth metals modified zeolite Y and dual Cu–Mn–Zn catalysts

A series of zeolite Y modified with La, Ce, Pr, Nd, Sm and Eu were prepared via ion-exchange, and characterized by XRD, FT-IR and NH₃-TPD. It was found that these rare earth metals were encapsulated in the supercage of zeolite Y and resulted in its enhanced acidity. Among them, La-, Ce-, Pr- and Nd-modified zeolite Y exhibited higher activity and stability (than pure HY) for methanol dehydration to dimethyl ether (DME). For DME synthesis directly from CO hydrogenation using the dual Cu–Mn–Zn/modified-Y catalysts, it was found that Cu–Mn–Zn/La–Y and Cu–Mn–Zn/Ce–Y were more active than Cu–Mn–Zn/pure-HY. The conversion of CO on Cu–Mn–Zn/Ce–HY achieved 77.1% in an isothermal fixed bed reactor at 245 °C, 2.0 MPa, H₂/CO = 3/2 and 1500 h⁻¹.     

The effect of long-term firing at 2100–2200°C on the concentration and microstructure of solid solutions in the systems ZrO2-Y2O3-CaO and ZrO2-Y2O3-MgO

Conclusions Solid solutions in the system ZrO₂-MgO fired at a high temperature (above 2000°C) in vacuo (5 · 10^–4mm Hg) for 5 h decompose as a result of the complete vaporization of the MgO. Solid solutions of ZrO₂-CaO undergo partial decomposition when fired in these conditions. The addition of 2 mole % or more yttrium oxide to the solid solutions ZrO₂-CaO and ZrO₂-MgO results in significantly lower CaO and MgO vaporization.The long-term exposure of solid solutions in the system ZrO₂-CaO and ZrO₂-MgO to 2200°C in a helium atmosphere results in the formation of an intercrystalline layer in which not only the stabilizing oxide but also the impurities are concentrated.In three-component solid solutions which contain yttrium oxide the degree of vaporization is lower and the intergranular secondary phase less developed so that the degree of collective recrystallization is lower.Translated from Ogneupory, No. 8, pp. 44–48, August, 1976.     

An investigation of the adsorption of aromatic hydrocarbons in zeolite Na–Y by solid-state NMR spectroscopy

The adsorption of toluene inside zeolite Na–Y was investigated by solid-state NMR spectroscopy. The environment of Na⁺ ions at different sites in Na–Y before and after adsorption was characterized by ²³Na magic-angle spinning (MAS) NMR. The information on the dynamic behavior of guest molecules inside the supercage of Na–Y was obtained by analyzing wideline ²H NMR spectra. The effect of loading level and temperature on molecular dynamics was also examined. The cation–sorbate interactions were directly probed by ²³Na{¹H} rotational-echo double-resonance (REDOR) experiments at different temperatures. Molecular Monte Carlo simulations were also performed to assist in the interpretation of the NMR data. ²³Na MAS and ²³Na{¹H} REDOR results show that each toluene molecule is facially coordinated to a Na⁺ ion at the SII site in the supercage, forming a π-complex. The adsorption also causes the Na⁺ ions initially located at the SI′ site to slightly shift to a new position within the sodalite cage, but has little effect on the Na⁺ at the SI site. The ²H NMR results indicate that the toluene molecules undergo a 2-site flip around the molecular long axis in addition to the methyl group rotation about its C₃ axis. ²³Na MAS spectra suggest that the adsorptive behavior of benzene and p-xylene in Na–Y is similar to that of toluene/Na–Y. ²³Na{¹H} REDOR results further indicate that inside the supercage, the degree of molecular motion follows the order of benzene > toluene > p-xylene.     

Synthesis and electrochemical properties of layered LiNi<Subscript>1/2</Subscript>Mn<Subscript>1/2</Subscript>O<Subscript>2</Subscript>prepared by coprecipitation

Spherical LiNi_1/2Mn_1/2O ₂ powders were synthesized from LiOH . H₂O and coprecipitated metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The average particle size of the powders was about 10 m and the size distribution was quite narrow due to the homogeneity of the metal hydroxide, (Ni_1/2Mn_1/2)(OH)₂. The tap-density of the LiNi_1/2Mn_1/2O₂ powders was approximately 2.2 g cm_–3, which is comparable to the tap-density of commercial LiCoO₂. The LiNi_1/2Mn_1/2 O₂electrode delivered a discharge capacity of 152, 163, 183, and 189 mA h g^–1 in the voltage ranges of 2.8–4.3, 2.8–4.4, 2.8–4.5, and 2.8–4.6 V, respectively, with good cyclability. Furthermore, Al(OH)₃-coated LiNi_1/2Mn_1/2O₂exhibited excellent cycling behavior and rate capability compared to the pristine electrode.     

Ring-opening polymerization of ϵ-caprolactone initiated by rare earth complex catalysts

The polymerization of caprolactone (ϵ-CL) was initiated by yttrium triisopropoxide {Y(OPⁱ_r)₃}, bimetallic isopropoxide of yttrium and aluminum {Y[Al(OPⁱ_s)₄]₃}, yttrium and tin(II) {Y[Sn(OPⁱ_r)₃]₃}, and tin(II) and yttrium {Sn[Y(OPⁱ_r)₄]₂}, respectively. The polymerization was carried out through coordinative insertion of a monomer into the free metal-oxygen bond. The molecular weight and yield of poly(ϵ-caprolactone) (PCL) were affected drastically by the mol % of the initiator to the monomer (C_o/M_o). The results showed that Y(OPⁱ_r)₃ and Sn[Y(OPⁱ_r)₄]₂ were more effective than were {Y[Al(OPⁱ_r)₄]₃} and {Y[Sn(OPⁱ_r)₃]₃} for the polymerization of ϵ-CL. When polymerization was conducted at 5°C using Y(OPⁱ_r)₃ as the initiator or at 10°C using Sn[Y(OPⁱ_r)₄]₄ as the initiator, polymers with a molecular weight of 45.9 × 10³ or 54.0 × 10³ and high yield resulted in 30 or 5 min, respectively. The polymer was characterized by FTIR, H-NMR, and GPC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1295–1299, 1997     

Dissolution kinetics of dehydroxylated nickeliferous goethite from limonitic lateritic nickel ore

The dissolution kinetics in 2 M H₂SO₄ of variously dehydroxylated nickeliferous goethites was investigated for five oxide-type lateritic nickel deposits. Goethite was the main constituent with minor amounts of quartz, talc, kaolinite and Mn oxides. Dissolution of Fe from heated materials followed the Kabai equation. There was a 9–34-fold increase in the Kabai dissolution rate constant (k) for samples heated at 340–400 °C due to both the increased surface area (1.5–2.6 fold) and higher density of structural defects (5–10 fold) in the variously dehydroxylated products. The presence of structural Al and Cr in goethite appears to reduce dissolution rate possibly through the greater M³⁺–OH, O bond strength relative to Fe³⁺, Ni²⁺–OH, O. Nickel showed congruent dissolution with Fe indicating that Ni was uniformly incorporated in the goethite structure. Pre-heating goethite to 600–800 °C for 30 min resulted in incongruent dissolution of Fe and Ni. It is postulated that some Ni is ejected from the neo-formed hematite structure and resides on the crystal surface or in voids. These results may contribute to the development of more efficient procedures for Ni extraction including heap leaching of lateritic nickel ores.     

Subsolidus Structure of the NiO – MgO – Al2O3 – SiO2 System

The subsolidus structure of a four-component oxide system MgO – NiO – Al₂O₃ – SiO₂ is considered using thermodynamic data of solid-phase reactions in the system and results of its geometric-topological analysis. Specific features of the subsolidus structure at different temperatures are discussed with allowance for the reversibility of individual solid-phase reactions. Technological implications in the prediction of the phase composition of materials in the NiO – Ni₂SiO₄ – MgAl₂O₄ – Mg₂SiO₄ concentration region are discussed.     

Corrosion of nickel in sodium sulphate-sodium chloride melts. Part I

The corrosion behaviour of Ni in molten Na₂SO₄, NaCl, and in mixtures of these two salts, at 900° C, in laboratory air and under O₂+SO₂/SO₃ atmospheres has been examined by electrochemical curves and topochemical analysis of corrosion products.Ni passivity in pure Na₂SO₄ was observed under potentiodynamic and potentiometric conditions, the passive film corresponding to NiO. Passivity was not so easy to achieve in chloride melts as in sulphate alone, but once a thick oxide film forms on the specimen, the Cl^– addition is accompanied by an increase in the film stability. The inhibiting role of NaCl on Ni in the passive-transpassive area was also evidenced. In opposition, halide additions (especially those up to 25%) increased the dissolution current densities of Ni in the active region. These higher dissolution rates are represented by the equation Ni₃S₂+4NaCl+1/2 O₂ = 2NiCl₂+2Na₂S + NiO which is also suggested as a critical factor in the Ni passivation.The passive capability found for Ni in Na₂SO₄/NaCl melts, in air, is destroyed by SO₃ atmospheres. This corrosion-stimulation is due to the SO₃ role in promoting reactions such as NiS + 3O^2– = Ni²⁺+SO₃+8e which would be potential-determining at the Ni surface until Ni²⁺ precipitates or the conjugate oxygen cathodic reduction process takes place. Microprobe analysis also evidenced S penetration which might be the reason for the Ni embrittlement.The polarization curves for Ni in pure NaCl showed the lack of a passive region; occurrence of extensive intergranular attack was also indicated by metallographic observation. The observed dissolution must occur at the expense of the Ni interactions with the species which intervene in the reaction equilibrium between O₂ and molten NaCl (O₂, Cl^–, Cl₂ and O^2–) as well as with the Na⁺ cations, as has been discussed elsewhere. Its self-sustaining nature is enhanced by the continuous reduction of the nickel ion content of the melt by NiCl₂ evaporation.     

Bimetallic nickel complexes of trimethyl phenyl linked salicylaldimine ligands: Synthesis, structure and their ethylene polymerization behaviors

Bimetallic salicylaldimine-nickel complexes, 2,4,6-Me₃-1,3-{[NCH–(3′-R-5′-Y-2′-O–C₆H₃)-κ²-N,O]Ni(Ph) (PPh₃)}₂ [R = tert-Bu, Y = Me, 1b; R = Ph, Y = H, 2b] were prepared and their catalytic behaviors of ethylene polymerization were investigated. The bimetallic complex 2b shows higher activities (2.9 × 10⁵ g PE mol⁻¹ Ni h⁻¹) for ethylene polymerization and affords polymer with high molecular weight (M_w = 1.41 × 10⁵) and broad molecular weight distribution (M_w/M_n = 6.1) than its mononuclear matrix, {[(2,6-Me₂C₆H₃)–NCH–(3′-Ph-2′-O–C₆H₃)-κ²-N,O]Ni(Ph)(PPh₃)} (3) (Activity = 5.5 × 10⁴ g PE mol⁻¹ Ni h⁻¹; M_w = 1.86 × 10⁴; M_w/M_n = 2.8).     

Electrodeposition of cobalt–yttrium hydroxide/oxide nanocomposite films from particle-free aqueous baths containing chloride salts

The feasibility of growing nanostructured films composed of cobalt and yttrium hydroxide/oxide phases by electrodeposition is demonstrated. Particle-free aqueous solutions containing YCl₃ and CoCl₂ salts and glycine were used. The incorporation of yttrium compounds into the cobalt deposit was achieved using pulse deposition (t_on = 0.1 ms, t_off = 0.9 ms) and for cathodic pulses higher than −500 mA cm⁻². Deposits obtained were crack-free, typically with 1–5 wt% yttrium, and exhibited morphologies markedly different from the ones shown by pure cobalt deposits. Moreover, yttrium-rich films (up to 30 wt% Y) could be deposited under certain conditions, though incipient cracking developed in this case. X-ray photoelectron spectroscopy analyses revealed that Y(OH)₃/Y₂O₃ compounds were present in the films. From the structural viewpoint, the composites exhibited a partially amorphous/nanocrystalline character, with the crystalline fractions originating from the hexagonal-close packed structure of α-Co. A refinement of the α-Co crystallite size was observed in deposits containing higher weight percentage of yttrium compounds. Nanoindentation tests revealed that hardness increased with the yttrium content. This result can be explained by taking into account both the presence of intrinsically hard oxide phases and the effects promoted by incorporation of yttrium hydroxides/oxides on the α-Co matrix (namely, grain-refining and higher concentration of stacking faults).     

Role of chromate, molybdate and tungstate anions on the inhibition of aluminiumin chloride solutions

The effect of CrO₄ ^2–, MoO₄ ^2– and WO₄ ^2– anions on the inhibition of aluminium corrosion in 0.5 M NaCl solution was investigated. The study comprised potentiodynamic polarization, potentiostatic current–time measurements complemented by SEM–EDAX and XPS investigations. It was found that, the pitting potential of an Al electrode in 0.5 M NaCl solution shifts in the positive direction by addition of CrO₄ ^2–, MoO₄ ^2– and WO₄ ^2– anions, and the shift in potential increases with increase in concentration. A pronounced inhibiting influence was achieved on addition of CrO₄ ^2–, MoO₄ ^2– and WO₄ ^2– anions to the electrolyte during potentiostatic current–time measurements. Chromate anions exhibit a great passivating influence during I/t measurements. This can be explained by the fact that the chromate anion, as a powerful oxidizing agent, is capable of oxidizing the corrosion sites to give a stable Al₂O₃ film. The inhibition observed on addition of molybdate anions is attributed to the adsorption and reaction of MoO₄ ^2– anions on the electrode surface forming a molybdate layer which selectively impedes the ingress of Cl^– ions and hence inhibits the pitting attack. The adsorption of WO₄ ^2– anions at flawed areas and developing pits was found to be the main factor for the observed inhibition.     

Electrochemical properties of layered Li[Ni1/2Mn1/2]O2 cathode material synthesised by ultrasonic spray pyrolysis

Layered Li[Ni_1/2Mn_1/2]O₂ was synthesized by an ultrasonic spray pyrolysis method. The Li[Ni_1/2Mn_1/2]O₂ powder was characterized by means of X-ray diffraction, charge/discharge test, and cyclic voltammetry. The discharge capacity increases linearly with increase of the upper cut-off voltage limit and attains a high discharge capacity of 187 mA h g^–1 between 2.8 and 4.6 V with excellent cyclability. A cyclic voltammetric study of the Li[Ni_1/2Mn_1/2]O₂ electrode showed only one redox peak implying no structural phase change during cycling.