Cobalt

About: Cobalt is a research topic. Over the lifetime, 69899 publications have been published within this topic receiving 1242058 citations. The topic is also known as: Co & Element 27.

Synthesis, Characterization and Catalytic Oxidation of Carbon Monoxide over Cobalt Oxide

Abstract: A mix-valenced cobalt oxide, CoOx, was prepared from cobalt nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoOx by temperature-programmed reduction (TPR) at 170, 230 and 300 °C (labeled as R-170, R-230 and R-300, respectively). They were characterized by X-ray (XRD), infrared (IR), thermogravimetry (TG) and TPR. The major composition of CoOx is CoO(OH), with a small amount of Co4+ species; R-170 is CoO(OH) with a hexagonal structure; R-230 is Co3O4 with a spinel structure and R-300 is CoO with a cubic structure. Their catalytic activities toward the CO oxidation were further studied in a continuous flow microreactor. The results indicated that the relative activity decreased significantly with the oxidation state of cobalt, i.e., CoO(+2)≳Co3O4(+8/3)≫CoO(OH)( +3)≳CoOx(>+3).

Corrosion of metals and alloys in mixed gas environments at elevated temperatures

Abstract: The attack of nickel, cobalt, iron, and alloys of these metals containing chromium and aluminum, by gases containing sulfur-oxygen, carbon-oxygen, and nitrogen-oxygen has been studied at temperatures of 600 and 900°C. The degradation of these metals and alloys was characterized by using standard analytical techniques with emphasis on optical metallography. Three types of accelerated degradation were identified for the attack of alloys by gases containing another oxidant in addition to oxygen. One type of degradation occurred because of the formation of reaction products composed of mixtures of phases involving both of the oxidants. Another type resulted from the reaction of second oxidant phases with oxygen. The third form of degradation involved the development of less protective phases due to thermodynamic instabilities. Thermodynamic stability diagrams are used to help account for the effects produced by different elements in the alloys.

First Row Transition Metal Ion-Assisted Ammonia−Borane Hydrolysis for Hydrogen Generation

Abstract: Ammonia-borane (AB) hydrolysis for the generation of hydrogen has been studied using first row transition metal ions, such as $Co^{2+}$, $Ni^{2+}$, and $Cu^{2+}$. In the cases of cobalt- and nickel-assisted AB hydrolysis, amorphous powders are formed that are highly catalytically active for hydrogen generation. Annealing of these amorphous powders followed by powder X-ray diffraction measurements revealed the presence of Co(O) and $Co_2B$ and Ni(O) and $Ni_3B$, respectively. On the other hand, copper-assisted AB hydrolysis was catalyzed by in situ generated $H^+$ and Cu(0) nanoparticles. The reduction ability of AB for the realization of coinage metal nanoparticles from the respective metal salts has also been studied. These reduction reactions were found to be facile, affording colloids of pure metal nanoparticles. Nanoparticles prepared in this manner were characterized by UV-visible spectroscopy and high-resolution electron microscopy.

Change in the magnetostructural properties of rare earth doped cobalt ferrites relative to the magnetic anisotropy

Abstract: The superparamagnetic properties of the doped cobalt ferrite nanocrystals have been demonstrated. The significance of the sol–gel autocombustion method in yielding the as obtained doped cobalt ferrite oxide powder in the nano-range has been very well complemented with structural, dimensional and morphological analytical techniques such as X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), particle size analysis and Scanning Electron Microscopy (SEM). The lattice strain and lattice parameters have been calculated by making use of the Williamson–Hall extrapolation. The valence states of the metal ions and single phase formation of the polycrystalline oxides have been confirmed with the help of X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The magnetic measurements M–H and M–T have been carried out demonstrating a change in the magnetic moment and a superparamagnetic–ferrimagnetic transition in the ferrite system. The influence of the distribution of the metal ions in the crystal lattice and the dimensions of the ferrite oxides on the resultant magnetic properties has been demonstrated. The contribution of the spin–orbit coupling generating from the Co2+ ions in the octahedral lattice towards higher magnetic anisotropy and hence the magnetic properties is investigated. The results provide an insight into the inter-relationship of the particle dimension, the spin–orbit coupling and the resulting superparamagnetic property.