Cobalt Powder Research Articles

Powder roll-compaction process for controlling grain orientation texture and size in spark plasma sintered carbides

The objective of this work is to develop and evaluate a powder roll-compaction procedure for fabricating cemented carbides that enables control over its surface/sub-surface grain orientation texture and grain size. The primary motivation for this work is to gain the ability to impart spatial material (property) gradients in bulk hard materials and composites for the realization of bio-inspired designs of material-systems. For this study, measured mixtures of tungsten carbide (WC) and cobalt (Co) powders were subjected to pressurized roll-compaction operations to create (malleable) thin sheets, which were then stacked and spark plasma sintered to obtain bulk cemented WC-Co specimens. When using this procedure, it was observed through XRD results that the basal plane orientation texture was increased by about 21%, and that transitions in layer-by-layer carbide grain sizes could be reliably achieved.

Sintered FeCuRe Alloys Produced from Commercially Available Powders

Abstract This paper discusses the mechanical properties of materials fabricated from commercially available powders designed for use as a metal matrix of diamond-impregnated composites. The powders with the catalogue numbers CSA and CSA800 produced in China were tested under laboratory conditions. The specimens were fabricated in a graphite mould using hot pressing. The materials were analysed for density, porosity, hardness and static tensile strength. A scanning electron microscope (SEM) was employed to observe the microstructure and fracture surfaces of the specimens. The experimental data was used to determine how the chemical composition of the powders and the process parameters affected the microstructure and properties of the materials. The properties of the sintered materials produced from the Chinese powders were compared with the properties reported for specimens fabricated from cobalt powder (Co SMS). Even though the hot pressed CSA and CSA800 powders had inferior mechanical properties to their cobalt analogue, they seem well-suited for general-purpose diamond-impregnated tools with less demanding applications.

Electrochemical preparation of tungsten and cobalt from cemented carbide scrap in NaF–KF molten salts

In this study, WC-10Co was used as a consumable anode for the direct preparation of cobalt and tungsten from NaF–KF molten salt at 1023K. Electrochemical analysis was performed via cyclic and square wave voltammetry. Results showed that cobalt and tungsten ions possess different precipitation potentials in the molten salt, thus theoretically proving the feasibility of preparing separating metallic cobalt and tungsten respectively. Tungsten and cobalt ions exist as W2 + and Co2+, and the reaction is reversible and controlled by diffusion. The effects of electrolytic current, duration, and temperature on anodic dissolution mass, dissolution rate, and cathode composition and morphology were studied via electrochemical analysis. The cathode product was analyzed by XRD and SEM. The results further showed that cobalt powder can be obtained when the electrolytic current was 12mA for a short period of time. Tungsten powder can be obtained by increasing electrolytic current and duration. Furthermore, tungsten powder with a particle diameter of less than 1μm can be obtained under the following electrolysis conditions: current of 88mA, duration of 7h, and temperature of 1023K.

"Effect of Substitution of Positive Ion (M+2) on the Physical Properties of M-Fe2O4 "

"Cobalt, Manganese and Magnesium ferrites powders have been synthesized using chemical mixing method. Calcination and sintering temperatures were 800oC respectively. The characteristics of spinal ferrite have been investigated by XRD technique while the magnetic characterization samples have been done using vibrating sample magnetometer (V.S.M). The magnetic properties such as initial magnetic permeability, quality factor, inductor factor and power loss density are studied under variation of frequency using L.C.R meter as well. Saturation magnetization, coercive field and remanent agnetization are determined from hysteresis loops for all prepared sample.

Preparation process and mechanism of ultra-fine spherical cobalt powders by hydrogen reduction of calcium cobaltite

For the improvement of the properties of cemented carbides, ultra-fine spherical cobalt powders as binder were prepared using calcium cobaltite. The effects of the ratio of CaO to CoO, the calcination temperature and the reduction temperature on particle size and morphology of cobalt powders were studied. The results show that the average particle size of cobalt powders decreases with increasing the weight ratio of CaO to CoO, but increases with the calcination temperature and reduction temperature. The spherical cobalt powders with the mean particle size of 84 nm are obtained when the weight ratio of CaO to CoO is 7:4 and the calcination temperature and reduction temperature are 1000 °C and 700 °C, respectively. In addition, CaO regarded as the blocking agent can refine cobalt powders during the hydrogen reduction process.

In-situ synthesis of WC–X% Co composite in the WO3–Co3O4–C system by carbothermal reduction method

The main aim of this study is to show the fabrication of WC–Co composite with different content of cobalt (13–33% wt) from WO3 and Co3O4 by in-situ carbothermic reduction method while using activated carbon as a reducing agent. Cobalt and tungsten oxide powders with different ratio and 17% carbon (30% more than stoichiometric value) were mixed by ball milling under atmosphere of argon for 20 h. The homogenized powder mixture followed the process of pressing and heat treatment (carbothermic reduction + sintering) under different protective layer or atmosphere at 1500 °C for 2 h. To evaluate the appropriate temperature for carbothermic reduction, the differential thermal analyses (DTA) were conducted on mixture sample of WO3, Co3O4, and C. Hardness (Vickers), toughness (Vickers indentation and crack length measurement), density (Archimedes), phase composition (XRD), and micro structure (scanning electron and optical microscopic) of sintered sample were evaluated. DTA results show the complete reduction of oxides at 1050 °C and the formation of tungsten carbide and the metallic phase of cobalt. The XRD results showed that in the milling stage even up to 20 h no reduction reaction occurred and only powder activation took place; therefore, the reduced compacted samples show the presence of unreduced oxides and extra phases protective foil of steel in comparison with alumina and carbon mixture as a layer protective. From investigated composites, the composites with 25% cobalt showed the highest density and strength while the composite with 36 and 14% cobalt showed the highest toughness and hardness, respectively.

Effect of WC and Co on the Microstructure and Properties of TiC Steel-Bonded Carbide

TiC base high manganese steel-bonded carbide was manufactured with conventional powder metallurgy method to service in wear and impact resistant condition. WC was added in the alloy in the form of (W,Ti)C carbides to improve the impact toughness and expand the applications of alloy, meanwhile, cobalt powder was also used to enhance the wettability of the metallic binder on the ceramic phase. Results showed that the impact toughness of the alloy was increased remarkably with the increase of WC content. The impact toughness reached 10.6 J/cm2 when WC content was 10.5 wt.%, while the hardness of the alloy did not decrease. It was indicated that the appropriate content of WC and cobalt can improve impact toughness and wear resistance of the alloy greatly with little increase in the production cost.

Size-controlled synthesis, growth mechanism and magnetic properties of cobalt microspheres

Monodispersed cobalt microspheres with remarkably uniform morphology and tunable size have been successfully synthesized via a facile and effective solvothermal route. It is found that sodium hydroxide has a great influence on the size and shape of the resulting cobalt powders. Through adjusting the molar ratio of NaOH to Co2+, the size of cobalt microspheres can be precisely manipulated. In addition, the magnetic properties of the as-synthesized samples demonstrate that cobalt microspheres exhibit ferromagnetic property related to their sizes. More importantly, this study not only provides a facile and effective strategy to prepare the cobalt microspheres with tunable sizes, but also gives a reference for the synthesis of other magnetic functional materials.

Electrolytic separation of cobalt and tungsten from cemented carbide scrap and the electrochemical behavior of metal ions

Molten salt electrolysis is used to separate and recycling of elemental tungsten and cobalt from cemented carbides. WC–6wt% Co scrap and NaCl–KCl molten salt was used as a sacrificial anode and electrolyte, respectively. The range of preparation parameters and the electrochemical behavior of tungsten and cobalt ions were investigated through electrochemical techniques, such as cyclic voltammetry (CV) and square wave voltammetry (SWV). Results showed that the dissolution potential of cobalt and WC were 0V and 0.6V (vs. Ag/AgCl), and the reduction potentials of Co (II)+2e− ↔ Co (0) and W(II)+2e− ↔ W (0) were −0.2 and 0.2V (vs. Ag/AgCl), respectively. The reduction processes of Co(II) to Co and W(II) to W were both reversible reactions controlled by ion diffusion. The average diffusion coefficients of Co(II) and W(II) were determined by CP to be 5.62×10−5and 3.94×10−5cm2s−1, respectively. Furthermore, the products at cathodes Nos. 1 and 2 were characterized by scanning electron microscopy, X-ray fluorescence and X-ray diffraction analyses. Results showed that pure cobalt and WC powder with a diameter of <100nm was obtained at cathode No. 1 and cathode No. 2. And the result of XRF shows that the purity of the products both Co and WC were higher than 90%. This study reveals that cobalt and tungsten can be separated from WC–6wt% Co scrap by controlling process parameters during electrolysis.

Life time of cemented carbide inserts with Ni-Fe binder in steel turning

Health concerns associated with cobalt powder are a strong motivator for conducting research on alternative binders for cemented carbides. It has previously been shown possible to make cemented carbides with alternative binders, which offer good hardness and toughness. However, it is not fully known if these cemented carbides can be successfully used as metal cutting tools. In this study we have tested turning inserts from cemented carbide with a nickel-iron binder and compared these with cobalt based reference inserts in dry face turning of steel in a pairwise comparison. To facilitate relevant comparisons, both the alternative binder and the reference cemented carbide are gradient sintered and coated in the same way as commercial turning grades. It is found that the life time in this dry face turning test is only approximately 15% shorter with the nickel-iron binder than with the cobalt reference, which motivates further studies with this alternative binder. Flaking of the coating and thus less coating adhesion was identified as one reason for the shorter life time.

Peroxidase-like activity of nanocrystalline cobalt selenide and its application for uric acid detection.

Dendrite-like cobalt selenide nanostructures were synthesized from cobalt and selenium powder precursors by a solvothermal method in anhydrous ethylenediamine. The as-prepared nanocrystalline cobalt selenide was found to possess peroxidase-like activity that could catalyze the reaction of peroxidase substrates in the presence of H2O2. A spectrophotometric method for uric acid (UA) determination was developed based on the nanocrystalline cobalt selenide-catalyzed coupling reaction between N-ethyl-N-(3-sulfopropyl)-3-methylaniline sodium salt and 4-aminoantipyrine (4-AAP) in the presence of H2O2. Under optimum conditions, the absorbance was proportional to the concentration of UA over the range of 2.0–40 μM with a detection limit of 0.5 μM. The applicability of the proposed method has been validated by determination of UA in human serum samples with satisfactory results.

Development of La(CrCoFeNi)O3 system perovskites as interconnect and cathode materials for solid oxide fuel cells

The purpose of this research is to develop interconnect and cathode materials for use in solid oxide fuel cells (SOFCs) which demonstrate desired properties of outstanding sintering properties, high electrical conductivity, and excellent chemical stability at high temperatures. Five different perovskite oxides of lanthanum in combination with chromium, iron, cobalt and nickel oxides powders, i.e. LaCr0.7Co0.1Fe0.1Ni0.1O3(LCr7CFN), LaCo0.7Cr0.1Fe0.1 Ni0.1O3(LCo7CFN), LaFe0.7Cr0.1Co0.1Ni0.1O3(LFe7CCN), LaNi0.7Cr0.1Co0.1Fe0.1O3(LNi7CCF), and LaCr0.25Co0.25Fe0.25Ni0.25O3(LCCFN), were synthesized through the Pechini method. XRD results show that all materials are in single phase, either rhombohedral or orthorhombic crystal structure. The resulting powders were able to be sintered to a high relative density at a temperature of 1400°C for 2h in air. The electrical conductivity of the sintered sample was measured and evaluated from 300°C to 800°C. The LCCFN sample appears to have the best combination of sintering property (approximate 94% relative density) and electrical conductivity (88.13Scm−1 at 800°C).

An Analysis of the Retention of a Diamond Particle in a Metallic Matrix after Hot Pressing

Abstract This paper deals with computer modelling of the retention of a synthetic diamond particle in a metallic matrix produced by powder metallurgy. The analyzed sintered powders can be used as matrices for diamond impregnated tools. First, the behaviour of sintered cobalt powder was analyzed. The model of a diamond particle embedded in a metallic matrix was created using Abaqus software. The preliminary analysis was performed to determine the mechanical parameters that are independent of the shape of the crystal. The calculation results were compared with the experimental data. Next, sintered specimens obtained from two commercially available powder mixtures were studied. The aim of the investigations was to determine the influence of the mechanical and thermal parameters of the matrix materials on their retentive properties. The analysis indicated the mechanical parameters that are responsible for the retention of diamond particles in a matrix. These mechanical variables have been: the elastic energy of particle, the elastic energy of matrix and the radius of plastic zone around particle.

Mechanochemically synthesized cobalt monoselenide: structural characterization and optical properties

Chalcogenide semiconductor cobalt monoselenide, CoSe, was prepared from metallic cobalt and selenium powders in stoichiometric ratio by simple and fast mechanochemical synthesis after 120 min of milling in a planetary ball mill Pulverisette 6 (Fritsch, Germany) in an argon atmosphere. Crystal structure and morphology of the product were characterized by X-ray diffraction, specific surface area measurements, and transmission electron microscopy. X-ray diffraction analysis confirmed the hexagonal crystal structure of the product-CoSe (freboldite) with the average size of the crystallites 26 nm. Transmission electron microscopy analysis has revealed that CoSe nanostructures are composed of agglomerated and randomly oriented nanoparticles. The optical properties were studied using UV–Vis and photoluminescence spectroscopy. Mechanochemically synthesized CoSe nanostructures showed higher absorption in whole UV–Vis optical region and the determined band-gap energy 1.70 eV is blue-shifted relative to the bulk CoSe. Both UV–Vis and photoluminescence spectra indicate quantum size effect of CoSe nanocrystals.

CARBON NANOTUBES FUNCTIONALIZED WITH METAL NANOPARTICLES ON THE SURFACE FOR DIRECTIONAL ARRANGEMENT

In order to arrange directionally, multi-wall carbon nanotubes (MWCNTs) are functionalized with ferromagnetic cobalt on the surface via the electroless plating method. The uniform and continuous cobalt coating was received in pH [Formula: see text] 9 at 45[Formula: see text]C for 30[Formula: see text]min. It is found that the hydroxyl and carbonyl groups could be successfully introduced on the surface of raw MWCNTs after treated in boiling nitric acid that would provide the active points for cobalt deposition. The diameters of the cobalt (Co)-coated MWCNTs increase to 20–50[Formula: see text]nm from 8–15[Formula: see text]nm of purified ones. As a result of nanoscale cobalt coating, MWCNTs show strong ferromagnetism at room temperature. The Co-coated MWCNT respond to magnetic field susceptibly in the distilled water and arrange themselves in the direction of the applied magnetic field up to 1[Formula: see text]T. The hysteresis curve results show that the coercivity of Co-MWCNTs is 1285.2 Oe, which is about four times that of cobalt powder itself.

A Porous Material Based on Cobalt and Nickel Powders

A Porous Material Based on Cobalt and Nickel Powders

Fabrication of nanosized cobalt powder from Cobalt(II) hydroxide of spent lithium ion battery

This study was investigated to fabricate nanosized cobalt (Co) powder from cobalt hydroxide Co(OH)2 recovered from spent lithium ion battery. Direct process newly proposed was attempted to transform phases as follow: Co(OH)2→Co3O4→Co. The variation of weight with time of the sample was measured using thermogravimetric analysis (TGA) and it was found that weight loss was observed over 500°C. Thermal treatment was conducted to determine proper operating time for phase transformation of Co3O4 at 500°C. Subsequently, hydrogen reduction was carried out on the effect of temperature, reaction time and flowrate. In the long run, nanosized cobalt powder was successfully fabricated with a mean particle size of 100–500nm as well as purity of 99.21wt.%.

Properties of Nanosized Ferrite Powders and Sintered Materials Prepared by the Co-Precipitation Technology, Combined with the Spray-Drying Method

Cobalt and nickel ferrites powders are synthesized by the co-precipitation technology, combined with the spray-drying method. The crystallite size, specific surface area (SSA), magnetic properties of synthesized products are investigated. All the synthesized ferrites are nanocrystalline single phase materials with crystallite size of 5-6 nm, the SSA of 80-85 m2/g and the calculated particle size of 13-15 nm. After spray-drying granules of the size up to 10 μm are obtained. After thermal treatment at 550 and 950 °C SSA decreases to 40-50 m2/g and 20-22 m2/g, respectively. The saturation magnetization at these temperatures increase from 17 to 40 emu/g for NiFe2O4 and from 51 to 77 emu/g for CoFe2O4. By the pressure-less sintering method the dense material forms at 1100 °C for CoFe2O4 and 1200-1300 °C for NiFe2O4.

Properties of Sinters Produced from Commercially Available Powder Mixtures

Abstract This paper discusses the mechanical properties of a material fabricated from commercially available metal powder mixtures designed for use as a metal matrix of diamond impregnated composites. The mixtures with the catalogue numbers CSA and CSA800 provided by a Chinese producer are suitable for experimental laboratory testing. The specimens were fabricated in a graphite mould using hot pressing. The material was tested for density, porosity, hardness, and tensile strength under static loading. A scanning electron microscope (SEM) was used to analyze the microstructure and cleavage fracture of broken specimens. It was essential to determine how the chemical composition and the fabrication process affected the microstructure and properties of the material. The properties of the sinters were compared with those of hot pressed specimens fabricated from sub-micron size cobalt powder (Cobalt SMS). Although the as-consolidated material is inferior to cobalt, it displays a favourable combination of hardness, yield strength and ductility, and seems to have a great potential for moderate and general purpose applications.

Direct Electrochemical Preparation of Cobalt, Tungsten, and Tungsten Carbide from Cemented Carbide Scrap

A novel process of preparing cobalt, tungsten, and tungsten carbide powders from cemented carbide scrap by molten salt electrolysis has been investigated in this paper. In this experiment, WC-6Co and NaCl–KCl salt were used as sacrificial anode and electrolyte, respectively. The dissolution potential of cobalt and WC was determined by linear sweep voltammetry to be 0 and 0.6 V (vs Ag/AgCl), respectively. Furthermore, the electrochemical behavior of cobalt and tungsten ions was investigated by a variety of electrochemical techniques. Results of cyclic voltammetry (CV) and square-wave voltammetry show that the cobalt and tungsten ions existed as Co2+ and W2+ on melts, respectively. The effect of applied voltage, electrolysis current, and electrolysis times on the composition of the product was studied. Results showed that pure cobalt powder can be obtained when the electrolysis potential is lower than 0.6 V or during low current and short times. Double-cathode and two-stage electrolysis was utilized for the preparation of cobalt, tungsten carbide, and tungsten powders. Additionally, X-ray diffraction results confirm that the product collected at cathodes 1 and 2 is pure Co and WC, respectively. Pure tungsten powder was obtained after electrolysis of the second part. Scanning electron microscope results show that the diameters of tungsten, tungsten carbide, and cobalt powder are smaller than 100, 200, and 200 nm, respectively.