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Showing 12 results for Cobalt

M. Nusheh*, H. Yoozbashizadeh,
Volume 7, Issue 2 (6-2010)
Abstract

Abstract:

the competition between the precipitation of cobalt ions and evolution of hydrogen gas on the cathode surface during

the reduction process in a sulfate bath, investigation on the mechanism of metal precipitation is of great importance.

In the present work, study on the kinetics of cobalt electrowinning and the mechanism of the involved reactions have

been carried out. The obtained results, confirm the mechanism of cobalt precipitation by depletion of hydroxides. The

effects of temperature and scan rate parameters were studied on electrowinning of cobalt by cyclic voltammetry

technique. The diffusion coefficient and rate constant of the reactions were measured and calculated by performed

experiments.

Nowadays cobalt is mostly produced through the electrowinning process of sulfate solutions. Regarding to

A. A. Hosseini, A. Sadigzadeh, S. Mohammadi,
Volume 8, Issue 3 (9-2011)
Abstract

Abstract: In this study, carbon nanotubes (CNTs) were grown directly in the pores of micro porous pyrex membranes
and consequently ceramic membranes with very fine pores and high porosity were achieved. Our experiment was done
in two stages. Initially cobalt powder with different percent was homogeneously mixed with pyrex powder. In order to
produce row membranes, each of these mixtures were compacted in the form of tablet by use of a uniaxial cold press
and in a stainless steel mould, and then the tablets were sintered at different temperature in an electric furnace. In
second stage chemical vapor deposition (CVD) method was used to grow CNTs within the pores of the membranes.
Argon and ammonia were used as carrier and reactive gas respectively and acetylene was used as the carbon
feedstock. Morphology of the membranes before and after CVD process was studied by scanning electron microscopy
(SEM). After CVD process CNTs were grown in the pores of membranes and the pores size was decreased but total
porosity of the membrane was not changed considerably. In this way membranes with high porosity and fine pores were
fabricated.
Mr. Hossein Minouei, Dr. Mohammadhossein Fathi, Dr. Mahmood Meratian, Mr. Hossein Ghazvinizadeh,
Volume 9, Issue 3 (9-2012)
Abstract

ASTM F-75 Cobalt-base alloy castings are widely used for manufacturing orthopedic implants. This alloy needs both homogenization and solutionizing heat treatment after casting, as well as bioactivation of the surface to increase the ability of tissue bonding. In this study, ASTM F-75 Cobalt-base substrate was heat treated at 1220°C for 1 hour in contact with Hydroxyapatite-Bioglass powder in order to solutionize and homogenize the microstructure and promote surface bioactivation. For bioactivity evaluation, heat treated specimens were immersed in Simulated Body Fluid (SBF). Surface of specimens before and after the immersion was analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDX) and X-Ray Diffraction (XRD). Results showed an appropriate microstructure with bioactive layer on the surface of specimens after heat treatment. In vitro result and formation of bone-like apatite layer on specimens indicated that heat treated samples were potentially suitable for bone replacement and tissue regeneration under highly loaded conditions.
Z. Shahri, S.r. Allahkaram,
Volume 9, Issue 4 (12-2012)
Abstract

Metal matrix composite coatings reinforced with nano-particles have attracted scientific and technological interest due to the enhanced properties exhibited by these coatings. Cobalt/hexagonal boron nitride nano-composite coatings were prepared by means of the pulse current electroplating from a chloride electrolyte on copper substrates and a comparison was made with the pure cobalt in terms of structure and tribological properties. Effects of particles concentration (5-20 gL-1) and current density (50-200 mA cm-2) on the characterization of electroplated coatings were investigated via X-ray diffraction analysis, energy dispersive spectroscopy and Vickers micro-hardness. Moreover, the tribological behavior was studied using pin-on-disc method. The results showed that cobalt/hexagonal boron nitride nano-composite coatings have higher hardness, wear resistance and lower friction coefficient than pure cobalt and the plating parameters strongly affect the coating’s properties
Z. Shahri, S. R. Allahkaram,
Volume 10, Issue 4 (12-2013)
Abstract

Metal matrix nano composite coatings possess enhanced properties such as corrosion and wear resistance. This paper aims to study the corrosion behavior of pure Co and Co-BN nano composite coatings deposited with different particles concentration (5-20 g L-1) on copper substrates using electroplating technique. Morphology and elemental compositions of the coatings were investigated by means of scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS). The corrosion behavior was analyzed in a 3.5 wt% NaCl via polarization and impedance techniques. The results obtained in this study indicate that the co-deposition of BN nano particles improved corrosion resistance of electrodeposited cobalt coatings.
M. Ahangarkani, K. Zangeneh-Madar, H. Abbaszadeh, A. A. Rahmani , S. Borgi,
Volume 11, Issue 3 (9-2014)
Abstract

In the present paper, the influence of cobalt additive on the sintering/infiltration behavior of W-Cu composite was studied. For this purpose, the mixed powders of tungsten and cobalt were compacted by CIP method and then sintered at 1450, 1550 and 1600 °C in a hydrogen atmosphere. The sintered specimens at 1550 °C were subsequently infiltrated with liquid copper at 1250 °C for 10, 60 and 120 min. The microstructure and composition of samples were evaluated using SEM, EDS as well as XRD techniques. The density of the sintered samples was measured by Archimedes method. Vickers indentation test was used to measurement hardness. It was found that sintering mechanism of tungsten powder depends on temperature and cobalt additive content. Also, the best infiltration behavior was observed in the samples with optimum cobalt value. In addition, it was found that the W-W contiguity as well as dihedral angle decreases as cobalt increases. Density and hardness of infiltrated specimens are attained 16.28-16.79 g.cm-3 and 220-251 VHN, respectively.
N Parvin, R Derakhshandeh Haghighi, M Naeimi, R Parastar Namin, M. M. Hadavi,
Volume 11, Issue 4 (12-2014)
Abstract

In this research, infiltration behavior of W-Ag composite compacts with Nickel and Cobalt as additives has been investigated. Nickel and Cobalt were added to Tungsten powder by two distinct methods: mixing elementally and reduction of salt solution. The coated Tungsten powders were compacted under controlled pressures to make porous skeleton with 32-37 vol. % porosity. Infiltration process was carried out at 1100 ̊C under a reducing atmosphere for 1h. The effect of additives on infiltration of Ag and density were evaluated by SEM and Archimedes methods. Properties of the specimens were compared following two distinct processes namely: I) sintering simultaneously with infiltration process and II) sintering prior to infiltration (pre-sintering process). It was found that specimens which were pre-sintered and then infiltrated with molten silver represent higher hardness and finer microstructure than the specimens infiltrated simultaneously with sintering.
M. Siadat-Cheraghi, S. R. Allahkaram, Z. Shahri,
Volume 12, Issue 1 (3-2015)
Abstract

Pure cobalt coatings were electrodeposited on copper substrate by means of direct electric current in a chloride solution at different current densities in the range of 10-70 mA cm -2 . The surface morphology and microstructure were investigated via X-ray diffraction analysis and scanning electron microscopy. Corrosion behavior of cobalt coatings was also studied in a 3.5 wt% NaCl solution using potentiodynamic polarization and impedance spectroscopy techniques. The results showed that corrosion resistance of deposits was strongly influenced by the coating’s morphology. Co deposit obtained in lower current densities exhibited the highest corrosion resistance, due to their lower grain boundaries and so the least density of active sites for preferential corrosion attacks
G. Chandraprabha, T. Sankarappa, T. Sujatha,
Volume 15, Issue 4 (12-2018)
Abstract

Polythiophene (PTh) and cobalt nanoparticles (Co-nps) were prepared by chemical oxidation and modified polyol processes respectively. Composites were made by mixing them in the proportions, PTh1-xCox; x = 0.1, 0.2, 0.3, 0.4, 0.5.  Morphology of the samples has been studied by SEM technique. Dielectric properties with temperature and frequency as variables were investigated. Dielectric constant and loss factor decreased with frequency and increased with temperature. AC conductivity was estimated from the dielectric data. Ac conductivity decreased with increase of Co-nps in the composites which indicates that electrically insulating effect has been induced by Co-nps. Small polaron hopping mechanism is found to be the conduction mechanism operated. Activation energy for ac conduction decreased with increase of frequency and weight percent of Co-nps in the composites.  Electric modulus was determined and its analysis leads to the estimation of dielectric relaxation time. Relaxation time decreased with increase of temperature for all the five composites. For the first time PTh-Co nanocomposites have been reported for dielectric properties and ac conductivity as a function of frequency and temperature.
N. Yazdani, J. Javadpour, B. Eftekhari Yekta, M. Hamrang,
Volume 16, Issue 1 (3-2019)
Abstract

This study focuses on the physical, magnetic, biological and antibacterial behaviour of cobalt-doped HAp powder samples. Pure and Cobalt- doped HAp nanoparticles were synthesized by hydrothermal method. Calcium nitrate, di- ammonium hydrogen phosphate and cobalt nitrate were used as precursor materials.  The synthesized powders were characterized using x-ray diffraction pattern (XRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), Raman spectroscopy as well as MTT assay and cell adhesion test. Disc diffusion method was used to investigate antibacterial activity of the samples. The results confirmed the substitution of Ca by Co ions in the HAp lattice. In addition, this substitution induced size reduction and morphology change in HAp particles. All cobalt substituted HAp powder samples displayed paramagnetic properties, as opposed to the diamagnetic behaviour observed in the pure HAp samples. In addition, these nanoparticles exhibited cell adhesion, biocompatibility and antibacterial activity against S.aureus bacteria.
This study focuses on the physical, magnetic, biological and antibacterial behaviour of cobalt-doped HAp powder samples. Pure and Cobalt- doped HAp nanoparticles were synthesized by hydrothermal method. Calcium nitrate, di- ammonium hydrogen phosphate and cobalt nitrate were used as precursor materials.  The synthesized powders were characterized using x-ray diffraction pattern (XRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), Raman spectroscopy as well as MTT assay and cell adhesion test. Disc diffusion method was used to investigate antibacterial activity of the samples. The results confirmed the substitution of Ca by Co ions in the HAp lattice. In addition, this substitution induced size reduction and morphology change in HAp particles. All cobalt substituted HAp powder samples displayed paramagnetic properties, as opposed to the diamagnetic behaviour observed in the pure HAp samples. In addition, these nanoparticles exhibited cell adhesion, biocompatibility and antibacterial activity against S.aureus bacteria.
V. Dave, R. Kotian, P. Madhyastha, K. Boaz, P. Rao, B.p. Charitha,
Volume 16, Issue 4 (12-2019)
Abstract

The aim of the present study is to assess the hardness, corrosion, and cytotoxicity of a commercially available cobalt-chromium (Co-Cr) alloy before and after simulated heat treatments at porcelain firing temperature. Five Co-Cr samples were fabricated using lost wax casting procedure. Heat treatments were carried out at 650°C, 750°C, 850°C, and 950°C. Vickers hardness was measured for as-cast and heat treated samples. The corrosion test was carried out separately in 0.1 N NaCl, 1% citric acid and artificial saliva at room temperature using potentiodynamic polarization technique. Gingival tissue biopsy of patients was taken and cultured to measure the cell viability by MTT colorimetric assay. Lowest hardness was observed at 650°C. 0.1 N NaCl and 1% citric acid corrosion medium showed a similar trend of corrosion rate. The least corrosion rate was found in artificial saliva. Firing temperature has an impact on the physical, chemical and biological properties of Co-Cr alloy in long-term clinical use.
A. Hasanvand, M. Pourabdoli, A. Ghaderi,
Volume 17, Issue 1 (3-2020)
Abstract

The main problem of cobalt oxide as a thermochemical heat storage material is its slow re-oxidation kinetics. In addition, redox (reduction and oxidation) behavior of as-received Co3O4 is degraded with increasing the number of redox cycles. To overcome this drawback, Al2O3 and Y2O3 were added to Co3O4 and  effect of mechanical activation time (2, 4, 8, and 16 h) on the redox behavior (weight change value/rate, redox reversibility, reduction and re-oxidation values, and particle morphologies) of Co3O4-5 wt.% Al2O3 and Co3O4-5 wt. % Y2O3 composites was investigated using thermogravimetry method. The composites were studied by SEM, EDS, and X-ray map analyses before and after redox reactions. Results showed that increasing the mechanical activation time improves the redox kinetics of Co3O4-5wt. % Al2O3 in comparison with as-received Co3O4. Although, the alumina-containing samples, activated in short time showed the better redox kinetics than samples activated in long time. It was found that increasing the activation time to more than 8 h for alumina-containing samples reduces the redox kinetics due to decreasing the positive effect of Al2O3 in controlling the particle size growth and sintering. In the case of Co3O4-5wt. % Y2O3, an increase in activation time generally reduced the redox kinetics. As a result, redox reactions in a 16 h-activated Co3O4-5wt.% Y2O3 composite was completely stopped. In addition, results showed that weak performance of Co3O4-5 wt. % Y2O3 is related to intensive sintering and growth of cobalt oxide particles during redox reactions


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