Sintering diagrams for cobalt,nickel and iron

Sintering diagrams were calculated for cobalt, nickel and iron powders. Using parameters such as shrinkage, electrical conductivity or elastic modulus, it was possible to determine the activation energies and confirm the predominant sintering mechanisms predicted by the maps.     

Gas permeability of graphite foil modified with iron,cobalt, and nickel oxides

Graphite foils containing iron(III), cobalt(II), and nickel(II) oxides have been prepared via the impregnation of oxidized graphite in aqueous FeCl₃, Co(NO₃)₂, and Ni(NO₃)₂ solutions, followed by exfoliation via thermal shock and pressing of the resultant exfoliated graphite. The materials thus prepared have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. We have studied the gas transport properties of the modified graphite foil samples and observed a considerable increase in the nitrogen and hydrogen permeabilities of the metal oxide-modified graphite foils relative to the unmodified graphite foil. The thermal properties of the samples have been studied by thermogravimetry and differential scanning calorimetry. The results demonstrate that their oxidation onset temperature reaches 570°C.     

Corrosion of nickel,iron, cobalt and their alloys in molten salt electrolytes

The processes of high-temperature corrosion, anodic dissolution and passivation of nickel, iron, cobalt and their alloys are reviewed to reveal the progress in understanding the reaction mechanisms defined in the last two decades. In the first part, the procedures of thermodynamical analysis of corrosion processes by potential — pO^2– diagrams are outlined. The second part is devoted to the electrochemical corrosion, anodic dissolution and passivation of the metals studied, the reaction mechanisms and composition of the corrosion layers formed. The effect of the alloying elements on the corrosion resistance and anodic behaviour of the base metal is treated in the third part. A brief summary of the kinetics of the so-called hot corrosion of the studied metals and their alloys in contact with thin molten salt films and aggressive atmospheres is then given. Finally, some conclusions are drawn and some future trends of investigation are indicated.     

In situ high-temperature electron microscopy of 3DOM cobalt,iron oxide,and nickel

High-temperature electron microscopy was used to follow how the structure of two specimens of three-dimensionally ordered macroporous (3DOM) materials, also known as inverse opals, and one specimen of a precursor to a 3DOM material changed with temperature. The change in grain size with temperature of 3DOM cobalt and 3DOM iron oxide (as magnetite) was monitored in situ in the TEM by heating in stages to 900 and 1,000 °C, respectively. The two materials studied by TEM showed contrasting grain growth behavior. For 3DOM cobalt, carbon surrounding the nanometer-size grains led to slower grain growth in thinner sample areas than in areas in closer contact with other grains; a bimodal grain-size distribution was observed after heating above 700 °C for 90 min. The grains of the 3DOM iron oxide had no carbon coating and coarsened more evenly to give a unimodal size distribution. Line scans from selected-area diffraction (SAD) patterns were used for phase analysis and showed that traces of cobalt oxide present in the 3DOM cobalt sample at room temperature disappeared when the sample was heated above 500 °C. The transformation of a 3DOM precursor material, nickel(II) oxalate–polystyrene (PS) latex composites, was followed in situ by variable-temperature environmental scanning electron microscopy (ESEM) from room temperature to ca. 700 °C in 0.5–0.7 kPa O₂. The ESEM examination of the 3DOM precursors permitted real-time observation of the polymer template decomposition and the shrinkage that occurs upon calcination of these precursor materials.     

Synthesis of SiC from rice husks catalysed by iron,cobalt or nickel

The synthesis of SiC (both powder and whiskers) was carried out from rice husks with and without the use of catalysts (iron, cobalt and nickel). The introduction of the catalyst increased the reaction rate, the yield becoming up to three times that for the uncatalysed reaction, and increased the proportion of -phase from 95% to 99%. The general behaviour of the three catalysts was very similar, although nickel was the most effective from the point of view of reaction rate, and cobalt in producing larger crystal size. Analysis of the evolution of reaction rate, morphology of the whisker formed, evolution of gases during reaction, crystal size and intermetallic phases, led to a reaction mechanism based on the formation of an M-Si-C liquid phase which is essential for the nucleation and growth of the SiC whiskers.     

Influence of nickel and cobalt on microstructure of silicon solution strengthened ductile iron

‘Second Generation’ ductile iron with a silicon content of up to 4.3 wt-% exhibits a fully ferritic matrix, which is solution strengthened by silicon. Outstanding advantages of these ductile iron grades result in their strongly increasing demand. However, due to a presumed formation of a silicon long range order, the maximum strength is limited to 600 MPa at 4.3 wt-% silicon. At higher silicon content, the mechanical properties dramatically decrease. In order to increase the maximum achievable strength, the potential of additional solution strengthening elements is subject of present research. Initially, the effects of cobalt and nickel on matrix, graphite shape and nodule count are investigated. Cobalt and nickel are identified as promising candidates for further solid solution hardening.     

A x-ray photoelectron spectroscopy study of the diffusion of iron,nickel and cobalt through gold films

X-ray photoelectron spectroscopy was employed to study the thermal diffusion of iron, nickel and cobalt through gold in bilayer thin film structures under an oxidizing environment. The data suggest that the driving force for the diffusion is the oxidation of the transition metal at the surface. The activation energies are consistent with a grain boundary diffusion mechanism.     

Compatibility studies of carbon fibres with nickel and cobalt

Techniques have been evolved to study the compatibility of single carbon fibres coated with nickel or cobalt, and the results have been shown to be applicable to bulk composites. Carbon fibres undergo structural recrystallisation in contact with the nickel or cobalt matrix by a dissolution/diffusion/reprecipitation mechanism. The effective activation energy for this recrystallisation process approximates that for carbon diffusion in nickel or cobalt.     

Carbothermic reduction of copper,nickel, and cobalt oxides and molybdates

The carbothermic reduction of NiO, CoO, CuO, MoO₃, and the MMoO₄ (M = Ni, Co, Cu) molybdates has been studied by thermogravimetry. The results demonstrate that the reactivity of the molybdates with solid carbon, the sequence of reduction reactions, and the composition of reaction intermediates are determined by the reactivity of the constituent oxides, which decreases in the order CuO > MoO₃ > NiO > CoO. The reaction intermediates in the reduction of CuMoO₄ are Cu₆Mo₅O₁₈ and Cu₂Mo₃O₁₀, and those in the reduction of CoMoO₄ are Co₂Mo₃O₈ and CoMoO₃. NiMoO₄ is reduced without oxide intermediates. The reactions of CuMoO₄ and NiMoO₄ with solid carbon lead to selective reduction of the molybdates to metals (Cu or Ni) and molybdenum oxides (MoO₂ and MoO_{3 ? x} ). In the reactions of NiMoO₄ and CoMoO₄ with CO gas, the metals are formed at comparable rates, which favors the formation of metal solid solutions, intermetallic phases, and mixed carbides.     

Voltammetric reduction of nickel and cobalt dimethylglyoximate

The determination of cobalt and nickel in aqueous solutions by stripping voltammetry after adsorptive preconcentration is an established procedure. The method is highly sensitive, but there is some controversy concerning the reasons for the excellent sensitivity. Using a variety of voltammetric techniques, we have determined that the reduction of nickel dimethylglyoximate in an ammonia buffer is consistent with an overall process involving 16 or possibly 18 electrons. This hypothesis is confirmed by independently measuring the total quantity of metal adsorptively deposited on the mercury electrode and comparing the amount with the quantity of electricity required for its reduction.     

Carbothermic reduction of cobalt and nickel tungstates

Data are presented on the formation sequence of metallic, carbide, and intermediate oxide phases in the carbon reduction of CoWO₄ and NiWO₄. The surface reaction between CoWO₄ particles and solid carbon yields the mixed carbide Co₆W₆C, while the reaction with the CO originating from carbon vaporization yields the intermetallic phase Co₇W₆. The initial stage of the solid-state and gas-phase reduction of NiWO₄ yields a solid solution of tungsten in nickel (～10 at % W), Ni₄W, and, presumably, the NiWO₄-WO₃ eutectic. The solid solution reacts with carbon to form Ni₂W₄C and with CO to form filamentary tungsten crystals.     

Preparation,sintering and electrical behaviour of cobalt,nickel and zinc germanate

Cobalt, nickel and zinc germanate were prepared by solid state reactions between the relevant oxides in air. Ceramics with monophase structures could be obtained by adopting the optimum temperature and time. The as-fired ceramics exhibited insulating properties; however, by an additional heat treatment under reducing conditions, variable electrical conductivity could be induced in the ceramic bodies. Temperature/resistivity characteristics of these materials showed typical semiconducting behaviour. X-ray studies showed that despite the changes in electrical behaviour, and apparent changes in colour after annealing, the structures remained unaltered. Microstructural studies using scanning electron microscopy also showed that there were no substantial changes due to the reductive annealing processes.     

Development of a selective and sensitive flotation method for determination of trace amounts of cobalt, nickel, copper and iron in environmental samples

A simple, selective and rapid flotation method for the separation-preconcentration of trace amounts of cobalt, nickel, iron and copper ions using phenyl 2-pyridyl ketone oxime (PPKO) has been developed prior to their flame atomic absorption spectrometric determinations. The influence of pH, amount of PPKO as collector, type and amount of eluting agent, type and amount of surfactant as floating agent and ionic strength was evaluated on the recoveries of analytes. The influences of the concomitant ions on the recoveries of the analyte ions were also examined. The enrichment factor was 93. The detection limits based on 3 sigma for Cu, Ni, Co and Fe were 0.7, 0.7, 0.8, and 0.7 ng mL(-1), respectively. The method has been successfully applied for determination of trace amounts of ions in various real samples.