High Cobalt Content Research Articles

Structure and Constitution of Zinc-Cobalt Electrodeposits

SUMMARYThe purpose of alloying zinc with more noble metals is to improve its corrosion resistance properties, which depend on micro-structure and constitution. The co-deposited zinc-cobalt alloy structure and constitution have been investigated by means of X-ray Diffraction (XRD), Extended X-ray Absorption Fine Structure (EXAFS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The constitution of the deposit changes with cobalt content. Whilst low cobalt content coatings are single phase solid solutions (η phase), the high cobalt content presents an extra intermetallic phase (Co5Zn21) in addition to the η phase. The structure of the solid solution was found to be hexagonal following the two metal constituents. Morphological differences were also related to cobalt content in the alloy. The deposit changed from dendritic to nodular with decreasing grain size as the cobalt content increased. During in-situ heat treatment the formation of precipitates was observed.

Improvement in capacity of cobalt-free Mm-based hydrogen storage alloys with good cycling stability

Abstract A multi-phase and multi-component cobalt-free Mm-based hydrogen storage alloy was examined. The phase composition, alloy microstructure, P – C – T and electrochemical properties were investigated. The physical and electrochemical properties of the cobalt-free alloy were compared with a typical AB 5 alloy containing higher cobalt content and with a low-cobalt Mm-based alloy. The results showed that the cobalt-free alloy had a flatter discharge plateau with electrochemical capacity of 302 mAh/g at 0.2 C rate and good rate capability. The hydrogen storage capacity of the cobalt-free alloy was significantly improved as compared with that of the low-cobalt Mm-based alloy (273 mAh/g). The cobalt-free Mm-based hydrogen storage alloy is a promising candidate for development of low-cost NiMH batteries with high capacity, good rate capability and cycling stability.

Thermal behavior and cation distribution in nanosized Mo-Co ferrite spinels Mo 0.5Co yFe 2.5− yO 4 (0 ≤ y ≤ 1) studied by DTG, FT–IR and DC conductivity

a cobalt content varying in a large domain of composition (0 ≤ y ≤ 1) has been studied by X-ray diffraction, infrared spectroscopy, thermal analyses (DTG and DSC) and electrical conductivity. Because of their small crystallite size (about 40 nm), these ferrites can be oxidized between 100 and 500°C while retaining the spinel structure. Based essentially on a quantitative determination of the cation distribution on the octahedral (B) and tetrahedral (A) sites by derivative thermogravimetry (DTG), it has been found that Fe 2+ B, Mo 3+ B, Mo 4+ B and Fe 2+ A are successively oxidized into Fe 3+ and Mo 6+ ions. Moreover, for high cobalt content, stoichiometric spinels have a low proportion of these ions in valency state 3+. FT–IR spectroscopy indicated, as a result of the oxidation in cation-deficient spinels, the change in the coordination around Mo 6+ ions from A to B-sites with cobalt substitution. The conductivity evolution during oxidation has also been related to the change in the cation distribution occurring for high cobalt content causing the hopping mechanism to be destroyed.

Spanende Bearbeitung von Hartlegierungen - Drehen und Schleifen. Teil II: Drehen von Hartlegierungen

Turning tests were carried out on selected hard alloys on iron (FeCr12C2.1, FeCr13Nb9MoTiC2.3, FeCr14Mo5WVC4.2) and cobalt basis (CoCr29W5C1.3) in a cutting speed range of between v c = m/min and 180 m/min. Polycrystalline cubic boron nitride (PCBN) turned out to be a suitable tool material. Subsequent examinations focused on evaluating the mechanisms of chip formation, cutting tool wear and surface integrity of the workpiece. During turning of hard alloys the formation of chips is primarily influenced by the ductility and fracture toughness of the work material. While a ductile matrix enables the formation of highly deformable chips, the chips stemming from martensitically hardened alloys show low deformation. As the cutting depth increases shear and segmented chips are chiefly produced. Type and arrangement of the hard phases play a significant role. Adhesion is the main wear mechanism impacting the cutting face of the tool. Particularly, strong adhesion effects will arise during the machining of the work hardening alloy on cobalt basis. A high cobalt content of the metallic bonding phase of the PCBN cutting tool appears to be a disadvantage with this type of work material. When machining alloys on iron basis adhesion is promoted by the mechanical linking of alloy-specific hard phases to the cutting material binder. Abrasion primarily acts on the flank. The hard carbides of the work material produce typical grooves in the cutting edge zone of the tool. The flank wear increases as the carbide content goes up. As the cutting speed rises the tool wear ascertained passes through a minimum. Whereas the formation of built-up cutting edges predominates at lower speeds, a thermal softening of the PCBN binder takes place and is dominating at high cutting speeds. The location of the wear minimum depends not only on the cutting temperature but also on the strain hardening capability of the metal matrix. Raising the cutting speed will cause the cutting force to continuously reduce. The highest cutting forces are found for the Co-based alloy. The passive forces develop in line with cutting tool wear and vary with content and hardness of the hard phases involved. The selected process parameters also affect the surface near zone. With low cutting speeds and process temperatures the surface is mainly stressed mechanically. Carbides break or detach from the surrounding matrix. If the cutting speed and process temperature are increased the eutectic carbides (M 7 C 3 ) are deformed together with the metal matrix. Microhardness profiles are indicative of near-surface strain-hardened zones after cutting of the Co-based alloy. Fe-based matrices do not show hardness changes worth mentioning. Although there are no new hardened zones noticeable even at maximum cutting speed, the matrix is nevertheless influenced thermally so that residual stresses will develop in the machined surface layer. In the lower cutting speed range the surface quality is characterized by flakes and material squeezing (Co-based alloy) and by spalling (Fe-based alloy). Only if the cutting speed is raised, a minor roughness is detected due to a potential deformation of eutectic hard phases.

Determination of cobalt species in niobia supported catalysts

Niobia-supported cobalt catalysts were prepared by incipient wetness impregnation and were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed reductioon (TPR) and magnetic measurements. At least two different types of cobalt species were present on the calcined catalysts: Co3O4 particles and Co2+ surface species. At high cobalt content, Co3O4 particles are the main species whereas the percentage of Co2+ species linked to the support increases as the cobalt loading is decreased. XPS results revealed that the Co2+ species could be better represented by a mixture of Co2Nb5O14 and CoNb2O6. TPR analyses allowed one to quantify the percentage of Co3O4 particles on the niobia-supported Co catalyst. However, due to partial reduction of niobia, TPR alone did not permit the quantification of the reduction degree of cobalt in these catalysts. Magnetic measurements linked to a TPR technique is a possible way to measure the reduction degree of cobalt in Co/Nb2O5 catalysts. After reduction at high temperature, the mixture of cobalt niobates was reduced and NbO2 produced led to the strong metal-support interaction (SMSI) effect.

Physico-chemical Properties of Zn-Co Alloy Deposits from an Alkaline Sulphate Bath Containing Triethanolamine and Gelatin

SUMMARYComposition, properties and morphology of Zn-Co alloy deposited from an alkaline sulphate bath have been investigated. A bath containing higher cobalt content produced an alloy with low cobalt content. The percentage of Co in the alloy decreased with increase in current density. Higher cobalt content in the alloy increased the hardness of the alloy. The morphology of alloy deposits depended on the amount of cobalt in the alloy deposit.

Crystallisation kinetics of amorphous W–Co–C sputtered films

The transformation kinetics from the amorphous to crystalline state in W–Co–C samples with different cobalt contents is investigated by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results show that cobalt influences the crystallisation process of the amorphous (W–C)-based system. The higher the cobalt content, the lower the crystallisation temperature. The transformation kinetics were analysed from the Kissinger equation. It was found that the crystallisation process occurs by steps and is mainly characterised by the formation of the carbide phase M 2C, controlled by diffusion. The activation energy, E, as calculated varies between 1.8 and 4.3 eV, depending on the chemical composition of the sample. With respect to the determination of the temperature vs. time transformation (TTT) diagrams, the results obtained reveal that the sample with higher content of cobalt is that which has a lower incubation time.

Synthesis and Characterization of a New Cobalt Aluminophosphate with an Open-Framework Structure

A new cobalt aluminophosphate, CoxAl1-xPO4[(NH4)x(NH3)0.5-x], with relatively high cobalt content (x ≤ 0.4) has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and infrared and visible light spectroscopies. The structure of the compound is a new zeolite-like open framework (monoclinic, C2/c, Z = 4, a = 13.312(3), b = 13.160(3), c = 8.914(2) Å, β = 100.94(3)° for x = 0.38). It contains channels of eight-membered rings of alternating tetrahedra of (Co,Al)O4 and PO4. The templates of NH4+ and NH3 reside in the channels and are surrounded by oxygen atoms with N−O distances of 3.0 Å and above.

Élaboration et caractérisation physico-chimique de nouveaux ferrites mixtes Mo-Co

New Mo x Co y Fe 3 − x − y O 4 ferrites have been prepared from hydroxide precursors leading to fine spherical particles. The so-obtained products have quite high substitution rates (x ≈ 0.5 and 0 ⩽ y ⩽ 1), higher than those ever reported for Mo-Co ferrites. The substitution of Fe 2+ ions by Co 2+ ions, which have a stronger magnetocrystalline anisotropy, and the directional order phenomenon both involve an enhancement in coercivity. Nevertheless, because of differences in composition, in cationic distribution and in particle morphology, the Mo-Co ferrites synthesized according to our process show a coercive force lower than that observed by other workers. The cobalt element stabilizes the spinel structure of the ferrites by decreasing their reactivity towards oxygen. Besides, for high cobalt content, a proportion of these ions has the valency state + III.

Preparation, identification and thermal investigation of solid solutions of cobalt-copper oxalates

The solid-solution oxalates of the series CoxCu1 − xC2O4·nH2O were prepared by coprecipitation from nitrate solutions. The characterization of the coprecipitates was carried out using X-ray powder diffraction (XRD), scanning electron microscopy and thermal analysis (TG/DTA) experiments in nitrogen. The results reveal the formation of a solid-solution with high cobalt content (x = 0.7) whereas other compositions with x = 0.3 or 0.5 did not form. The final solid products of the thermal treatment of the investigated oxalates are characterized by the formation of oxygen-deficient non-stoichiometric oxides. The thermal decomposition of the solid-solution and its mechanical mixture with the same mole ratio are very different. The first gave mixed lattice oxides in tri- and divalent states, whilst the latter gave separate oxides in the divalent state.

Genesis of cobalt oxide-induced surface structure in [formula omitted] catalysts

Molecular approach to surface structure of the PtCo x Al 2O 3 (x = 0–0.67) samples prepared by co-impregnation with aqueous solution of H 2[PtCl 6] and Co(NO 3) 2 as precursors, has been investigated by means of X-ray photoelectron spectroscopy during the drying-calcination-reduction sequence of preparation. Ion exchange between the chloride ligands and oxygen ions during calcination in oxygen of the samples containing constant loading of Pt and increasing amount of Co, was induced by cobalt oxide at high cobalt content. Simultaneously, CoO was anchored to alumina surface, whereby, after subsequent reduction, a novel CoO-modified-support interface was developed and metallic platinum and intermetallic PtCo species were formed. As a result, the estimated dispersion of Pt, D Pt passed through a shallow minimum over the various composition. Similar trend was observed for the reaction rate in the CO hydrogenation suggesting that the catalytic activity of the PtCo x Al 2O 3 samples is related to platinum, while product selectivity is primarily controlled in a complex manner by the platinum particles on the CoO-modified support. The present work represented how molecular approach in the genesis of a bimetallic catalyst helps in understanding the mechanism of the catalytic reaction.

A comparative study of the crystallization of CoSiB metallic glasses

The crystallization of CoSiB metallic glasses was studied by X-ray, neutron diffraction, resistivity and calorimetry. With high cobalt and boron contents two steps and a decrease of resistivity is found upon crystallization. With low cobalt and high silicon content a single step and a tendency for the resistivity to increase are found. There is an anomalously large increase in resistivity for Co 70Si 9B 21.

Fabrication and magnetic properties of metal/cobalt ferrite composite thin films

To improve the saturation magnetization (Ms) of cobalt ferrite thin films, metal/cobalt ferrite composite thin films were prepared by controlling the sputtering conditions such as oxygen concentration in sputtering gas, substrate temperature, composition of the thin films. With decreasing the oxygen ratio from 50% to 5% in sputtering gas and increasing the substrate temperature from room temperature to 400 °C, the Ms of the thin films was increased and the coercivity (Hc) decreased. The result was attributed to deposition of the metal/cobalt ferrite thin films. With increasing the metal ratio in the thin films, preferred orientation of (111) of cobalt ferrite was worsened in the thin films. The metal deposited in the thin films was identified as cobalt with (002) preferred orientation. In higher cobalt content than the stoichiometric composition of CoFe2O4, the thin films with high Ms and Hc could be deposited in the wide substrate temperature range of 200–400 °C. We can prepare the metal/cobalt ferrite composite thin films with Ms about 580 emu/cm3 and Hc 1700 Oe by controlled the sputtering conditions. The thin films are thought to be applicable to the magnetic recording media with high recording density.

EQUILBRIUM MODELING OF TRACE METAL TRANSPORT FROM DULUTH COMPLEX ROCKPILE

Geochemical modeling was used to predict weathering processes and the formation of trace metal-adsorbing secondary phases in a waste rock stockpile containing Cu-Ni ore mined from the Duluth Complex, MN. Amorphous ferric hydroxide was identified as a secondary phase within the pile, from observation and geochemical modeling of the weathering process. Due to the high content of cobalt, copper, nickel, and zinc in the primary minerals of the waste rock and in the effluent, it was hypothesized that the predicted and observed precipitant ferric hydroxide would adsorb small quantities of these trace metals. This was verified using sequential extractions and simulated using adsorption geochemical modeling. It was concluded that the trace metals were adsorbed in small quantities, and adsorption onto the amorphous ferric hydroxide was in decreasing order of Cu > Ni > Zn > Co. The low degree of adsorption was due to low pH water and competition for adsorption sites with other ions in solution.

液相法による酸化亜鉛バリスタ材料の調製とその電気的特性

In attempt to obtain chemically pure and homogenous product, a wet chem ical method has been applied to synthesize zinc oxide varistor, which is marketed by sintering after mixing of powders by a ball mill.Efficient yield was attained for precursors by a precipitation method using zinc acetate and zinc acetyl ace tonate as starting materials with praseodymium oxide and cobalt chloride as additives.Calcination process, crystalline size of zinc oxide, additives distri bution and voltage-current curve were characterized by thermogravimetric analyzer, reflected right microscope, SEM-EPMA and varistor tester.The samples sintering over 1200°C showed a decreasing tendency of the grain size of zinc oxide with the increase of praseodymium content.Uniform distribution of praseodymi um was observed for the samples obtained by the wet chemical method, especially for the samples with calcination before sintering, rather than the samples ob tained from zinc oxide and praseodymium oxide powders by using a ball mill.Non-linearity of voltage-current curve was observed for the both samples of ZnO-PrO2 obtained by a wet chemical and a conventional ball-mill methods. The non-linearity, however, was not observed for a cobalt-added sample except for a sample containing high cobalt content obtained by a wet chemical method.

An ac magnetic susceptibility study of Er(Fe1−Co )3

Abstract AC magnetic susceptibility measurements have been performed on the Er(Fe 1− x Co x ) 3 compounds with x = 0.0, 0.24, 0.44, 0.61 and 1.0. This system shows a competition between the different anisotropies of Fe and Co and the two crystallographically different Er sites. The magnetic phase diagram, previously proposed down to 10 K based on magnetization and neutron diffraction measurements, has been confirmed by magnetic susceptibility experiments. At lower temperatures our results suggest the possible existence of a new spin reorientation (SR) transition at high cobalt content.

Effects of cobalt on plants

Effects of cobalt on plants

Hyperfine interaction and crystalline environment in NdTi(Fe 1− xCo x) 11 compounds by 57Fe Mössbauer study

In this paper, the Mössbauer spectra for NdTi(Fe 1− x Co x ) 11 compounds have been investigated. The hyperfine interaction has been studied with respect to the crystalline environment. The results show that cobalt atom prefers to occupy the 8f site in the range of high iron content and iron atom prefers to occupy the 8j site in the range of high cobalt content. The variations of the magnetic moments for each iron site 8i, 8j and 8f are very small with increasing cobalt content in compounds. At the step of the initial replacement of the iron atom by cobalt, the quadrupole splittings QS and isomer shift IS for the 8f site increase and for 8i decrease corresponding to the occupation preference on the iron site for cobalt atoms. Similar composition dependences of QS and IS implies that there exists a shielding effect or coupling of s-d electrons in the compounds.

Mechanochemical decomposition of copper cobaltite

Phase segregation of copper cobaltite to copper oxide and a cobaltite of higher cobalt content proceeds by a mechanochemical reaction. The grinding almost doubles the specific surface area. The composition of the surface was determined by ESCA. The Cu:Co ratio on the surface of the initial sample was twice the ratio determined by chemical analysis, and reached a value close to the average for the sample only after 10 h of treatment. In addition, Cu+ species were detected in the X-ray photoelectron spectrum (XPS) of the mechano-chemically treated copper cobaltite. Simultaneously with the beginning of the phase-segregation process homogenization of the sample is attained.

Magnetic and structural properties of TbFe 10.8-xCo xW 1.2 alloys

A series of new alloys of composition TbFe 10.5Co ξW 1.2(0⩽ x ⩽10.8) has been synthesized and studied for their hard magnetic properties over the temperature range 4.2–1200 K. It is found that all compounds with x ⩽ 5 crystallize in a tetragonal structure of the ThMn 19 type. At higher cobalt content, i.e. x ⩽ 5, a considerable amount of an extraneous phase of the rhombohedral Th 2Zn 27 structure is observed. These compounds exhibit planar anisotropy for ξ ⩽ 5 at room temperature. Above room temperature the plane-tocone-type spin reorientation is found for this system. The Curie temperature T c of these materials is considerably enhanced by cobalt substitution and ranges from 560 K (TbFe 0.8W 1.2) to 1003 K (TbFe 5.8Co 5W 1.2). The effect of cobalt substitution on the anisotropic behaviour in the Tb (Fe, Co) 10.8W 1.2system is analysed.