Partial Substitution Of Cobalt Research Articles

Wear Resistance of Experimental Hard Alloys Grades with Co-Mo-Ti Binders upon Conditions of Friction without Lubricant on Stainless Steel

The results of studies of wear resistance and tribological properties of experimental single carbide hard alloys grades with modified Co-Mo-Ti binders upon conditions of friction without lubricant on stainless steel are presented. All the data obtained were compared with similar parameters for the basic alloy VK8 (Co-Mo), on the basis of which the experimental grades were developed. Tribological tests were performed on tribometer which implemented a scheme of friction "pin on disk" at constant sliding speed and normal load values with artificially heated tribo contact zone. Studies have found that partial substitution of cobalt in a binder by Mo and Ti has led to a decrease in average friction rates. It was established that the greatest wear resistance and the best tribological characteristics were obtained for specimens of experimental grade 2.22 (5,65%Co+1,8%Mo+0,6%Ti). The process of friction for this pin material was characterized by the formation of secondary structures with high shielding properties, reducing of the adhesive interaction of materials, low volume wear intensity, minimal friction coefficient, as well as the least roughness of friction tracks on the counter body (disk). An increase in the proportion of molybdenum in the binder of more than 5% reduced the wear resistance of the experimental grades in comparison with the basic alloy VK8.

Microstructural evolution and its outcome on the photo induced micro actuation effect and mechanical properties of copper doped Co-Ni-Al FSMA

In this work, we studied the effect of doping with copper to seek improvement in mechanical and photo induced micro actuation (PIMA) properties of a Co-Ni-Al ferromagnetic shape memory alloy (FSMA). Unique and unexplored PIMA property of FSMA system has opened up the scope of various laser controlled micro-mechanical engineering applications in miniature scale. Transmission Electron Microscopy and X-ray diffraction technique were used to characterize and correlate the evolved microstructure with the corresponding changes in the PIMA and mechanical properties. Magnetic properties of these samples were studied by performing hysteresis experiments at room temperature. It was found that partial substitution of cobalt with copper resulted in samples with lower magnetic and PIMA properties but better mechanical property, however, in case of substituting aluminum, it resulted in improvement of the ferromagnetic property but destroyed the PIMA effect altogether. In order to understand these properties changes, the electron density of each of the samples was calculated and compared. These studies should help in deciding on use of new alloys with optimization of PIMA and mechanical property for desired and customized engineering applications.

Effect of Transitional Metals (Mn and Ni) Substitution in LiCoPO4 Olivines.

Transition metal substitution is a key strategy to optimize the functional properties of advanced crystalline materials used as positive electrodes in secondary lithium batteries (LIBs). Here we investigate the structural alterations in the olivine lattice of Mn and Ni substituted LiCoPO4 phase and the impact on performance in LIBs. X-ray diffraction (XRD) and extended X-ray absorption experiments have been carried out in order to highlight the structural alterations induced by partial substitution of cobalt by manganese and nickel. XRD analysis suggests that substitution induces an expansion of the lattices and an increase of the antisite disorder between lithium and transition metal ions in the structure. XAS data highlight negligible electronic disorder but a relevant modulation in the local coordination around the different metal ions. Moreover, galvanostatic tests showed poor reversibility of the redox reaction compared to the pure LCP sample, and this failure is discussed in detail in view of the observed remarkable structural changes.

Partial substitution of cobalt by rare-earths (Gd or Sm) in cobalt ferrite: Effect on its microstructure and magnetic properties

Microstructure and magnetic properties of partially substituted cobalt ferrite, with small amounts of gadolinium or samarium, were investigated. Co1-xGdxFe2O4+δ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, and 0.15) and Co1-xSmxFe2O4+δ (x = 0.04, and 0.08) were obtained through the citrate precursors route. X-ray powder diffraction patterns, of samples treated at temperatures between 400 and 1000 °C, are consistent with a cubic spinel-type structure. Substituted ferrites, with x = 0.04 and 0.08 (600 °C/2 h), show the combination of maximum enhancement of crystallinity and minimum change of the lattice parameters. At this temperature and composition range the crystallite size decreases up to a 41%. Rietveld analyses of Co1-x(Gd/Sm)xFe2O4+δ (x = 0, 0.04, and 0.08), carried out considering that Gd3+ (or Sm3+) occupies Co2+ positions, give rise to a good quality of refinement and cell parameters which are slightly smaller than those provided in the crystallographic database of CoFe2O4. Raman spectra of Gd3+ or Sm3+ substituted ferrites show the characteristic Raman modes expected in inverse spinel ferrites without additional signals. TEM micrographs reveal the presence of small agglomerates of nanoparticles. SAED patterns and HRTEM micrographs, are characteristic of polycrystalline powders while the interplanar distances well correspond to those of CoFe2O4. EDS analyses confirm the presence of Gd or Sm in substituted ferrites. Magnetic hysteresis loops of samples suggest a ferrimagnetic behavior and their squareness ratio values decrease up to 36% in Co1-xSmxFe2O4+δ (x = 0.04). Mössbauer studies reveal the presence of only Fe3+ ions, distributed in a proportion of 60 and 40% through octahedral and tetrahedral sites, respectively and a canted ferrimagnetic structure. Although the formation of the mixed spinel, rather than different substances (Sm or Gd oxide), fall in the sensitivity limits of the XRD technique all the results demonstrate that the replacement of Co2+ by Gd3+ or Sm3+ ions, in CoFe2O4, can tailor the crystal structure, microstructure, and magnetic properties of cobalt ferrite.

Materials design for ceramic oxygen permeation membranes: Single perovskite vs. single/double perovskite composite, a case study of tungsten-doped barium strontium cobalt ferrite

Pure oxygen is an important raw material with many important applications. The production of oxygen via a conducting ceramic membrane is a new, cost-effective and advanced technology with the advantage of continuous oxygen production. The perovskite-type mixed-conducting oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) exhibits superb oxygen permeability, yet it suffers from poor phase stability. In this study, we aim to improve the operational stability of the BSCF membrane by introducing a high-valence W6+ ion as a B-site dopant. Its effect on the phase composition, structure, structural stability, electrical conductivity, oxygen transfer rate and oxygen permeability as a membrane is systematically investigated. Upon the partial substitution of cobalt and iron in the W6+-doped BSCF, single/double perovskite composites are formed instead of single perovskite composites. Remarkably, the formation of the single/double perovskite composites enhances the oxygen permeation stability without obviously compromising the oxygen permeability. Among the various materials, the composite with the nominal composition of Ba0.5Sr0.5Co0.8Fe0.1W0.1O3-δ shows the best performance in terms of stability and oxygen permeability. These findings thus introduce a new way to design conducting ceramic membranes for oxygen separation at high temperatures.

Synthesis and Characterization of Ba0.5Sr0.5NixCo0.8‐xFe0.2O3‐δ (x=0 and 0.2) Perovskites as Electro‐catalysts for Methanol Oxidation in Alkaline Media

AbstractIn this study, the perovskite‐type oxides Ba0.5Sr0.5Ni0.2Co0.6Fe0.2O3‐δ (BSNCF) with different B‐site transition metal elements were investigated as a new catalyst for methanol oxidation. They were prepared by the partial substitution of cobalt by nickel in Ba0.5Sr0.5Co0.8Fe0.2O3‐δ (BSCF) sample. Both materials prepared using a combined citrate/EDTA complexing method and their catalytic activitiesfor methanol oxidation were comparativelystudied using cyclic‐voltammetry (CV) and chronoamperometry (CA) in alkaline media at room temperature. Structural, textural, morphological and redox properties of the synthesized solids were investigated by several physicochemical methods such as XRD, FTIR, LRS, SEM‐EDX, BET and H2‐TPR. The as‐prepared materials were obtained with high purity and high crystallinity. The partial substitution of cobalt by nickel in BSCF perovskite changes the structure of the solid which pass from cubic structure to a mixture of cubic and hexagonal forms. This change is accompanied by an increase in BET surface area and a decrease in crystalline size. For the electro‐catalysis measurements, results demonstrated that partially substituting of Co by Ni in BSCF structure enhance the electro‐catalytical activity towards the oxidation of methanol under alkaline conditions, making it an electro‐catalyst candidate for practical utilization in DMFCs.

High-pressure high-temperature decomposition of CeCoGa to the Laves phases CeCo0.58Ga1.42, CeCo0.72Ga1.28, and CeCo2

Abstract The monoclinic intermediate-valent gallide CeCoGa decomposes under high-pressure (HP) (9.5 GPa) high-temperature (HT) (1470 K) conditions into the Laves phases CeCo0.58Ga1.42 (MgCu2 type), CeCo0.72Ga1.28 (MgZn2 type; major product phase), and CeCo2 (MgCu2 type). The structures of the ternary Laves phases were refined from single crystal X-ray diffractometer data: Fd3̅m, a=778.3(1) pm, wR2=0.0310, 63 F 2 values, five variables for CeCo0.58(3)Ga1.42(3) and P63/mmc, a=547.24(5), c=858.76(7) pm, wR2=0.1009, 195 F 2 values, 13 variables for CeCo0.72(1)Ga1.28(1). Partial substitution of cobalt by gallium leads to a significant increase of the distances within the tetrahedral network: 253 pm Co–Co in CeCo2 as compared to 275 pm in CeCo0.58(3)Ga1.42(3) and 265–277 pm in CeCo0.72(1)Ga1.28(1). The crystal chemical consequences are briefly discussed.

Modification of mixed conducting Ba0.5Sr0.5Co0.8Fe0.2O3–δ by partial substitution of cobalt with tungsten

The Ba0.5Sr0.5Co0.8–xWxFe0.2O3–δ (х = 0–0.1) materials prepaMIECred by partial substitution of cobalt in BSCF with tungsten were studied. The tungsten solubility limit in the structure of cubic perovskite BSCF was shown to be ~2%. The doping with the highly charged W6+ (2%) cation improved the functional properties of BSCF: it increased the oxygen permeability and membrane stability in the CO2-containing atmosphere and suppressed the cubic–hexagonal perovskite polymorphic transition. This stabilizes high oxygen fluxes during long-term stability tests.

Improvement of Ba0.5Sr0.5Co0.8Fe0.2O3−δ functional properties by partial substitution of cobalt with tungsten

The work deals with the studies of Ba0.5Sr0.5Co0.8−xWxFe0.2O3−δ (х=0–0.1) materials obtained by the partial substitution of cobalt in Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) by tungsten. It is shown by means of XRD that the solubility limit of tungsten in the structure of cubic perovskite BSCF is about 2%<x<3%. Continuous equilibrium «3−δ−lgpO2−T» diagrams obtained by oxygen release technique are presented for the compositions BSCF and Ba0.5Sr0.5Co0.78W0.02Fe0.2O3−δ (BSCFW2) for the first time. The diagrams allowed us to detect the new phase transition P1 (low temperature phase, Pm3¯m) – P2 (high-temperature phase, Fm3¯c). It is demonstrated that Co substitution by highly charged cation W+6 (2%) improves the functional properties of BSCF; increases the oxygen permeability, suppresses phase transition «cubic–hexagonal» perovskite, enhances the stability of membrane material in the atmosphere of CO2, which provides the long-term stability of oxygen fluxes. The dependence of oxygen fluxes on membrane thickness provides evidence that for L≥1.60mm oxygen permeability is limited by the bulk diffusion of oxygen ions.

Hydrides Formed in ZrCo2 – Based Intermetallic Compounds Under High Hydrogen Pressure / Wodorki Wytwarzane Pod Wysokimi Cisnieniami Wodoru Ze Zwiazków Miedzymetalicznych Na Osnowie ZrCo2

The hydrides of zirconium based pseudobinary alloys Zr(Co1-xTx)2, (T = Fe, V or Cr) and Zr1-xRxCo2 (R = Y, La, Pr) were synthesized under 1.2 GPa of hydrogen pressure. It was revealed that partial substitution of cobalt by V, Cr or Fe increases hydrogen absorption capacity and stability of derived hydrides. Especially, it was found that ZrCo1:8V0:2 alloy exposed to high hydrogen pressure can absorb 50% more hydrogen than pure ZrCo2 and the hydride ZrCo1:8V0:2Hy has surprisingly high stability. Substitution of zirconium by Y, La or Pr in ZrCo2 alloys improved hydrogen absorption but hydrides derived from La and Pr substituted alloys were less stable than ZrCo2H2. Only for Zr0:7Y0:3Co0:2Hy the hydrogen absorption was higher and desorption rate markedly smaller comparing ZrCo2H2.

Lithium Storage Mechanisms and Effect of Partial Cobalt Substitution in Manganese Carbonate Electrodes

A promising group of inorganic salts recently emerged for the negative electrode of advanced lithium-ion batteries. Manganese carbonate combines low weight and significant lithium storage properties. Electron paramagnetic resonance (EPR) and magnetic measurements are used to study the environment of manganese ions during cycling in lithium test cells. To observe reversible lithium storage into manganese carbonate, preparation by a reverse micelles method is used. The resulting nanostructuration favors a capacitive lithium storage mechanism in manganese carbonate with good rate performance. Partial substitution of cobalt by manganese improves cycling efficiency at high rates.

Synthesis, structure and properties of LnBa(Co,Me)2O5+δ (Ln = Nd, Sm, Ho and Y; Me = Fe, Ni, Cu) as potential cathodes for SOFCs

ABSTRACTLayered LnBa(Co,Me)2O5+δ (Ln = Nd, Sm, Ho and Y; Me = Fe, Ni, Cu) with double perovskite structure were synthesized by the solid-state reaction and glycerin-nitrate technique and characterized by X-ray diffraction, thermogravimetric analysis, iodometric titration and dilatometry. Homogeneity ranges for the solid solutions were determined. The oxygen content in LnBa(Co,Me)2O5+δ decreases with decreasing rare-earth cation size. Partial substitution of cobalt by iron increases oxygen content while introduction of copper decrease it. The average thermal expansion coefficients were calculated. Chemical compatibility of studied perovskites with Ce0.8Sm0.2O2 and Zr0.85Y0.15O2 solid electrolytes has been studied.

Insights on the role of Ru substitution in the properties of LaCoO3-based oxides as catalysts precursors for the oxidative reforming of diesel fuel

The partial substitution of Co by Ru in lanthanum cobaltite perovskites (LaCo1−xRuxO3, x=0.05 and 0.2) and its influence on the reducibility and structural modifications in the perovskite lattice have been evaluated by N2 adsorption isotherms, in situ X-ray diffraction (XRD), temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). Characterization of LaCo1−xRuxO3 perovskite precursors reveals that Ru is incorporated into the perovskite lattice, producing a distortion of the original rhombohedral structure, a decrease in mean crystallite size and some increase in the surface area. The structural evolution of the LaCo1−xRuxO3 precursors under a reductive treatment indicates that Ru promotes the reducibility of the perovskite leading to a greater reduction degree of cobalt species. Moreover, the smaller perovskite crystallites obtained with the partial substitution of cobalt by ruthenium evolve to smaller crystal domains of both Co0 and La2O3 after reduction. The catalysts formed after the reduction of perovskite precursors present very high catalytic efficiency to extract hydrogen from diesel molecules by oxidative reforming. However, those catalysts derived from Ru-substituted perovskites show better catalytic performance associated with the higher development of active metallic phases achieved on the surface of these catalysts. Additionally, Ru promotes the catalytic activity and stability for this reaction increasing the reduction degree of cobalt and decreasing coke formation and sulfur poisoning through the formation of smaller cobalt crystallites.

Effect of Substitution of Cobalt for Iron in Sr4Fe6O13−( on the Catalytic Activity for Methane Combustion

AbstractA series of mixed oxides Sr4Fe6−xCoxO13−δ (x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr4Fe5CoO13−δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr4Fe5CoO13−δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr4Fe6O13, which was confirmed by TGA and XPS.

Improvement of electrochemical performance of tin dioxide negative electrode materials upon cobalt substitution

The cobalt-substituted tin dioxide nanocrystals were synthesized by the one-pot hydrothermal method. According to the powder X-ray diffraction and elemental analyses, the cobalt ions were successfully substituted into the rutile lattice of the SnO 2 phase, which consequently resulted in an increase in the volume of the unit cell. Electron microscopy revealed that with an increase in the content of the substituted cobalt ions, the particle size of the SnO 2 nanocrystals becomes smaller. In addition, the X-ray absorption spectroscopy clearly demonstrated that the substituent cobalt ions were stabilized in a divalent oxidation state in a distorted octahedral symmetry, while the tin ions were in a tetravalent oxidation state. The electrochemical measurements revealed that the substitution of Sn with Co significantly enhanced the negative electrode performance of tin dioxide nanocrystals at optimal Co content. The present study clearly demonstrated that a partial substitution of cobalt in the SnO 2 phase can provide an effective way of optimizing the electrochemical properties of the tin dioxide nanocrystals.

Electrochemical hydrogenation and corrosion behaviour of LaCo4.8M0.2 alloys

AbstractHydrogen absorption properties and the corrosion characteristics of three LaCo4.8M0.2 alloys (where M ≡ antimony, magnesium or bismuth) have been investigated using electrochemical techniques. Absorption of hydrogen and corrosion behaviour of LaCo4.8M0.2 alloys have been compared with LaCo5 intermetallic compound. Typical potentiokinetic polarisation curves in 6 M potassium hydroxide solution showed that modification of LaCo5 by partial substitution of antimony, magnesium or bismuth for cobalt resulted in lower anodic currents in the passive range. The substitution does not significantly affect the shape of potentiokinetic polarisation curves in 0.5 M sulphate solutions for pH 2 and 7. Partial substitution of cobalt with bismuth in LaCo5 alloy increases the effectiveness of absorption of cathodically evolved hydrogen in strong alkaline solutions.

La(1−)Sr Co1−Fe O3 perovskites prepared by sol–gel method: Characterization and relationships with catalytic properties for total oxidation of toluene

La(1-x)SrxCo(1-y)FeyO3 samples have been prepared by sol-gel method using EDTA and citric acid as complexing agents. For the first time, Raman mappings were achieved on this type of samples especially to look for traces of Co3O4 that can be present as additional phase and not detect by XRD. The prepared samples were pure perovskites with good structural homogeneity. All these perovskites were very active for total oxidation of toluene above 200 degrees C. The ageing procedure used indicated good thermal stability of the samples. A strong improvement of catalytic properties was obtained substituting 30% of La3+ by Sr2+ cations and a slight additional improvement was observed substituting 20% of cobalt by iron. Hence, the optimized composition was La0.7Sr0.3Co0.8Fe0.2O3. The samples were also characterized by BET measurements, SEM and XRD techniques. Iron oxidation states were determined by Mossbauer spectroscopy. Cobalt oxidation states and the amount of O- electrophilic species were analyzed from XPS achieved after treatment without re-exposition to ambient air. Textural characterization revealed a strong increase in the specific surface area and a complete change of the shape of primary particles substituting La3+ by Sr2+. The strong lowering of the temperature at conversion 20% for the La0.7Sr0.3Co(1-y)FeyO3 samples can be explained by these changes. X photoelectron spectra obtained with our procedure evidenced very high amount of O- electrophilic species for the La0.7Sr0.3Co(1-y)FeyO3 samples. These species able to activate hydrocarbons could be the active sites. The partial substitution of cobalt by iron has only a limited effect on the textural properties and the amount of O- species. However, Raman spectroscopy revealed a strong dynamic structural distortion by Jahn-Teller effect and Mossbauer spectroscopy evidenced the presence of Fe4+ cations in the iron containing samples. These structural modifications could improve the reactivity of the active sites explaining the better specific activity rate of the La0.7Sr0.3Co0.8Fe0.2O3 sample. Finally, an additional improvement of catalytic properties was obtained by the addition of 5% of cobalt cations in the solution of preparation. As evidenced by Raman mappings and TEM images, this method of preparation allowed to well-dispersed small Co3O4 particles that are very efficient for total oxidation of toluene with good thermal stability contrary to bulk Co3O4. (C) 2008 Elsevier B.V. All rights reserved.

Effect of Si Substitution and Annealing on Magnetocaloric Properties in TbCo2

We report on magnetocaloric properties of the as-cast and annealed TbCo2 with partial substitution of cobalt by silicon. The samples were characterized by powder X-ray diffraction and investigated by heat capacity measurements (8–300 K, in fields 0 T and 1 T). TbCo2 undergoes a second-order type phase transition at TC = 240 K, from paramagnetic to ferrimagnetic state; similar behavior was revealed in the Si-doped compounds. The temperature dependence of magnetic entropy and the corresponding magnetocaloric effect were derived for all studied samples. The influence of the heat treatment and Si doping on magnetocaloric properties will be discussed in context of the analogue case Er(Co1−xSix)2.

Alloy design of WC-10Co hard metals with modifications in carbide and binder phases

In the present study a detailed investigation of modification of both carbide and binder phases in WC-1OCo (16·5% vol.) has been carried out in order to develop equivalent steel cutting grade hard metals. The hard phase, WC, was partially replaced by TiC and the binder phase, Co, by Ni and Mo. The volume percentage of hard phases WC and TiC were kept in all alloys as 63% and 20% respectively. Sintering studies were made in both a hydrogen atmosphere and a vacuum at different temperatures in the range 1450–1500°C. The partial substitution of cobalt in WC-8 TiC-12Co hard metal by nickel necessitated addition of molybdenum either in elemental or carbide form, the latter being a better proposition. The hard metal shows equivalent properties with those prepared using (W,Ti)C solid solution.

Effect of TiN addition on sintering behaviour and mechanical properties of WC-10Co hard metals containing Mo2C and Ni

The aim of the present work was to substitute a portion of WC in WC-10 wt% Co hard metal by TiN by modification of the binder phase, and to produce an equivalent grade of hard metal. Sintering studies were carried out in both H2 and H2-N2 (50∶50) mixture. Introduction of TiN into WC-10Co hard metal resulted in a high sintered porosity, and as a consequence the mechanical properties deteriorated. Partial substitution of cobalt in WC-8.7TiN-12Co by nickel further increased the sintered porosity and led to a non-uniform microstructure. Incorporation of Mo2C along with cobalt-nickel binder promoted a fine-grained structure, which resulted in better sintered properties than those of WC-8.7TiN-6Co-6Ni hard metal. However, hot isostatic pressing (HIP) treatment of the liquid-phase sintered alloys was effective in eliminating the large pores and thus greatly enhanced the mechanical properties. HIPed hard metal of WC-8.7TiNS-12Co composition showed properties almost equivalent to those of WC-10Co hard metal.