Showing papers on "Cobalt published in 2003"
TL;DR: There is a marked resemblance in superconducting properties between the present material and high-Tc copper oxides, suggesting that the two systems have similar underlying physics.
Abstract: Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that Na(x)CoO2*yH2O (x approximately 0.35, y approximately 1.3) is a superconductor with a T(c) of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-T(c) copper oxides, suggesting that the two systems have similar underlying physics.
1,495 citations
TL;DR: Recent advances in the synthesis of various magnetic nanoparticles using colloidal chemical approaches are reviewed and ferrite nanoparticles have been synthesized by the thermal decomposition of organometallic precursors followed by oxidation or by low-temperature reactions inside reverse micelles.
1,433 citations
TL;DR: The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling.
Abstract: A highly efficient advanced oxidation process for the destruction of organic contaminants in water is reported. The technology is based on the cobalt-mediated decomposition of peroxymonosulfate that leads to the formation of very strong oxidizing species (sulfate radicals) in the aqueous phase. The system is a modification of the Fenton Reagent, since an oxidant is coupled with a transition metal in a similar manner. Sulfate radicals were identified with quenching studies using specific alcohols. The study was primarily focused on comparing the cobalt/peroxymonosulfate (Co/PMS) reagent with the traditional Fenton Reagent [Fe(II)/H2O2] in the dark, at the pH range 2.0-9.0 with and without the presence of buffers such as phosphate and carbonate. Three model contaminants that show diversity in structure were tested: 2,4-dichlorophenol, atrazine, and naphthalene. Cobalt/peroxymonosulfate was consistently proven to be more efficient than the Fenton Reagent for the degradation of 2,4-dichlorophenol and atrazine, at all the conditions tested. At high pH values, where the efficiency of the Fenton Reagent was diminished, the reactivity of the Co/PMS system was sustained at high values. When naphthalene was treated with the two oxidizing systems in comparison, the Fenton Reagent demonstrated higher degradation efficiencies than cobalt/peroxymonosulfate at acidic pH, but, at higher pH (neutral), the latter was proven much more effective. The extent of mineralization, as total organic carbon removed,was also monitored, and again the Co/PMS reagent demonstrated higher efficiencies than the Fenton Reagent. Cobalt showed true catalytic activity in the overall process, since extremely low concentrations (in the range of microg/L) were sufficient for the decomposition of the oxidant and thus the radical generation. The advantage of Co/PMS compared to the traditional Fenton Reagent is attributed primarily to the oxidizing strength of the radicals formed, since sulfate radicals are stronger oxidants than hydroxyl and the thermodynamics of the transition-metal-oxidant coupling.
1,390 citations
TL;DR: The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface and the results confirm theoretical predictions and are of fundamental value to understanding how magnetic an isotropy develops in finite-sized magnetic particles.
Abstract: The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.
887 citations
TL;DR: In this paper, the removal of heavy metals such as Mn, Co, Ni, and Cu from aqueous solution is studied using a raw kaolinite. And the results show that heavy metal removal is an endothermic process and the process of adsorption is favored at high temperatures.
707 citations
TL;DR: The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide, and it is proposed that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals.
Abstract: Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable.
680 citations
TL;DR: These findings show that cobalt mimics hypoxia, at least in part, by occupying the VHL-binding domain of HIF-α and thereby preventing the degradation of Hif-α.
548 citations
TL;DR: The thermodynamic data indicate that Co(II) adsorption onto sepiolite is entropically driven and characterized by physical adsOrption.
445 citations
TL;DR: The influence of cobalt loading (10 −40 wt% Co), cobalt precursor, and promoters (Re, Mn) on the physico-chemical and catalytic properties of mesoporous Co/SBA-15 catalysts for the Fischer-Tropsch Synthesis (FTS) reaction (T=493 K, P=20 bar, H2/CO=2) has been investigated as discussed by the authors.
434 citations
TL;DR: It is demonstrated that the central channel of the tobacco mosaic virus can be used as a template to synthesize nickel and cobalt nanowires only a few atoms in diameter, with lengths up to the micrometer range.
Abstract: Large biomolecules are attractive templates for the synthesis of metal1-7 and inorganic8-10 compound nanostructures. The well-defined chemical and structural heterogeneity of the biotemplates can be exploited for the precise control of the size and shape of the formed nanostructures. Here, we demonstrate that the central channel of the tobacco mosaic virus (TMV) can be used as a template to synthesize nickel and cobalt nanowires only a few atoms in diameter, with lengths up to the micrometer range.
379 citations
TL;DR: This finding prompted us to look carefully at 1D systems containing anisotropic elements, such as cobalt and low-spin iron centers that the authors synthesized recently, and opened the perspective of a potential use of 1D magnetic molecular nanowires for information storage.
Abstract: and opened the perspective of a potential useof 1D magnetic molecular nanowires for information storage.Even though 1D magnetism is a very active area of research,such dynamic behavior was never detected before since it isnot clear how to fulfill experimentally the requirements of aperfect 1D Ising-type chain. This finding prompted us to lookcarefully at 1D systems containing anisotropic elements,suchas cobalt(ii) and low-spin iron(iii) centers that we synthesizedrecently,
TL;DR: In this article, a self-assembly of latex particles on water surface was used to produce a large-scale, 2D arrays of perfectly ordered magnetic nanoparticles using nanosphere lithography.
TL;DR: In this article, strong magnetoelectric coupling was observed in zinc-substituted layered composites of ferrites and lead zirconate titanate (PZT).
Abstract: The observation of strong magnetoelectric (ME) coupling is reported in zinc-substituted layered composites of ferrites and lead zirconate titanate (PZT). Multilayer samples contained cobalt zinc ferrite ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ (CZFO) $(x=0--0.6)$ or nickel zinc ferrite ${\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ (NZFO) $(x=0--0.5)$ and were prepared by laminating and sintering ferrite and PZT thick films obtained by tape casting. The ME voltage coefficient ${\ensuremath{\alpha}}_{E}$ was measured for transverse and longitudinal field orientations for frequencies 10--1000 Hz. A substantial enhancement in ${\ensuremath{\alpha}}_{E}$ is observed with the substitution of Zn. The largest increase, by about 500%, is observed in CZFO-PZT and the smallest increase of 60% is measured for NZFO-PZT. As the Zn concentration is increased, ${\ensuremath{\alpha}}_{E}$ increases and shows a maximum for $x=0.2--0.4,$ depending on the ferrite. The data is analyzed based on a theoretical model for a ferrite-PZT bilayer, taking into consideration less than ideal coupling at the interface. The interface coupling parameter k is quite small for CZFO-PZT; it increases from 0 to 0.6 as Zn concentration is increased from 0% to 40%. Composites of NZFO-PZT, however, have a near perfect interface coupling. The Zn-assisted enhancement in the ME coefficient is discussed in terms of joule magnetostriction, initial permeability, and magnetomechanical coupling for the ferrites.
TL;DR: A review of mixed oxide supported Mo and W catalysts for ultradeep desulfurization can be found in this paper, where an overview of the available literature with emphasis on research carried out in our laboratory is provided.
TL;DR: In this paper, the CoOx/CeO2 composite catalysts of different cobalt/ceria ratios have been prepared and tested for carbon monoxide oxidation in mixtures of carbon dioxide and oxygen, showing markedly enhanced catalytic activities due to the combined effect of cobalt oxide and ceria.
Abstract: CoOx/CeO2 composite catalysts of different cobalt/ceria ratios have been prepared and tested for carbon monoxide oxidation in mixtures of carbon monoxide and oxygen. The small activity decay observed for them is due to carbon dioxide retention. The CoOx/CeO2 composite catalyst showed good resistance to water vapor poisoning. The catalysts were investigated by X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO-TPD and XPS. The CoOx/CeO2 composite catalysts exhibit high catalytic activity in carbon monoxide oxidation, showing markedly enhanced catalytic activities due to the combined effect of cobalt oxide and ceria. Combining the results of XRD, TPR and XPS, we propose that the finely dispersed and higher valence state CoOx species mainly contribute to the catalytic activity.
TL;DR: In this paper, the tensile properties of fully dense nanocrystalline cobalt electrodeposits with an average grain size of 12 nm were studied at different strain rates.
TL;DR: The N2 complexes of iron that are described are the first thoroughly characterized examples to exhibit a 4-coordinate geometry.
Abstract: The chemistry of low-valent iron and cobalt has been slow to develop, due
largely in part to a lack of ligand scaffolds that can stabilize these species.
Using the anionic tris(phosphino)borate ligand, [PhB(CH_2PiPr_2)_3]-, we have
stabilized reactive complexes of the type [P_3M-L] where L can be varied from
weakly-donating π-acidic ligands (e.g. N_2), to strongly π-basic ligands where
multiple bonding occurs between the metal and L (e.g. NR ^2-). In addition to
stabilizing a broad range of ligand types in a variety of oxidation states, the
[P_3M] template has been shown to mediate the coordination and activation of
dinitrogen on both iron and cobalt. The reaction chemistry of the [P_3M-L]
scaffolds will be presented in addition to synthetic strategies targeting high-valent
species (M^(IV), L=N ^3-).
TL;DR: In this paper, the synthesis of monodispersed, amorphous cobalt nanoparticles coated with silica in aqueous/ethanolic solution is described, and the transformation of the cobalt cores into crystalline, metallic cobalt upon annealing in air is demonstrated through X-ray diffraction data.
Abstract: The synthesis of monodispersed, amorphous cobalt nanoparticles coated with silica in aqueous/ethanolic solution is described. Both the core size and the silica shell thickness can be controlled through the synthetic conditions. Furthermore, the transformation of the cobalt cores into crystalline, metallic cobalt upon annealing in air is demonstrated through X-ray diffraction data. Both the initial, amorphous nanoparticles and their crystalline counterpart are magnetic, which promises important applications for ferrofluid preparation and for magnetic recording media.
TL;DR: The hazard due to cobalt exposure seems to be underestimated, especially when individuals are co-exposed to cadmium or lead, and the existence of more than multiplicative effects for co-exposures of Cadmium, cobalt and lead is found.
Abstract: Co-exposure to cadmium, cobalt, lead and other heavy metals occurs in many occupational settings, such as pigment and batteries production, galvanization and recycling of electric tools. However, little is known about interactions between several heavy metals. In the present study we determined DNA single strand break (DNA-SSB) induction and repair capacity for 8-oxoguanine in mononuclear blood cells of 78 individuals co-exposed to cadmium (range of concentrations in air: 0.05-138.00 micro g/m(3)), cobalt (range: 0-10 micro g/m(3)) and lead (range: 0-125 micro g/m(3)). Exposure to heavy metals was determined in air, blood and urine. Non-parametric correlation analysis showed a correlation between cadmium concentrations in air with DNA-SSB (P = 0.001, R = 0.371). Surprisingly, cobalt air concentrations correlated even better (P < 0.001, R = 0.401), whereas lead did not correlate with DNA-SSB. Logistic regression analysis including 11 possible parameters of influence resulted in a model showing that cobalt in air, cadmium in air, cadmium in blood and lead in blood influence the level of DNA-SSB. The positive result with cobalt was surprising, since exposure levels were much lower compared with the TRK-value of 100 micro g/m(3). To examine, whether the positive result with cobalt is stable, we applied several logistic regression models with two blocks, where all factors except cobalt were considered preferentially. All strategies resulted in the model described above. Logistic regression analysis considering also all possible interactions between the relevant parameters of influence finally resulted in the following model: Odds ratio = 1.286(Co in air) x 1.040(Cd in air) x 3.111(Cd in blood) x 0.861(Pb in air) x 1.023(Co in air x Pb in air). This model correctly predicts an increased level of DNA-SSB in 91% of the subjects in our study. One conclusion from this model is the existence of more than multiplicative effects for co-exposures of cadmium, cobalt and lead. For instance increasing lead air concentrations from 1.6 to 50 micro g/m(3) in the presence of constant exposures to cobalt and cadmium (8 micro g/m(3) and 3.8 micro g/m(3)) leads to an almost 5-fold increase in the odds ratio, although lead alone does not increase DNA-SSB. The mechanism behind these interactions might be repair inhibition of oxidative DNA damage, since a decrease in repair capacity will increase susceptibility to reactive oxygen species generated by cadmium or cobalt. Indeed, repair of 8-oxoguanine decreased with increasing exposures and inversely correlated with the level of DNA-SSB (P = 0.001, R = -0.427). Protein expression patterns of individuals exposed to cobalt concentrations of approximately 10 micro g/m(3) were compared with those of unexposed individuals using two-dimensional gel electrophoresis. Qualitative and apparent quantitative alterations in protein expression were selective and certainly occurred in <0.1% of all proteins. In conclusion, the hazard due to cobalt exposure - that has been classified only as IIB by the IARC - seems to be underestimated, especially when individuals are co-exposed to cadmium or lead. Co-exposure may cause genotoxic effects, even if the concentrations of individual heavy metals do not exceed TRK-values.
TL;DR: The new synthetic strategy affords four polymorphous frameworks of cobalt(II) imidazolates of crystalline substances, of which the compound 4 is an isomorphous compound of [Zn(im)(2)]( infinity ), which was also synthesized in a gas-phase reaction in 1980.
Abstract: Five polymorphous frameworks of cobalt(II) imidazolates (1-5) have been prepared by solvatothermal syntheses. Of these, compound 3 has already been synthesized in a gas-phase reaction by Seel et al. in 1969 and structurally characterized by Sturm et al. in 1975. The new synthetic strategy affords four polymorphous frameworks of cobalt(II) imidazolates (1, 2, 4, 5) of crystalline substances, of which the compound 4 (a = b = 23.450(3), c = 12.460(3) A, tetragonal, I4(1)cd, Z = 16) is an isomorphous compound of [Zn(im)(2)]( infinity ), which was also synthesized in a gas-phase reaction in 1980. The frameworks of compounds 1 and 2 are porous and isostructural; they have the same framework topology that represents a novel uninodal (6,4)-net: 1: a = 18.513(4), b = 24.368(5), c = 9.2940(19) A, orthorhombic, Fdd2, Z = 16; 2: a = 17.635(4), b = 27.706(6), c = 9.0810(18) A, orthorhombic, Fdd2, Z = 16. The framework of compound 5 exhibits a topology of zeolitic structure with the unit-cell parameters: a = 24.3406(8), b = 9.4526(3), c = 24.8470(8) A, beta = 91.977(1) degrees, monoclinic, P2(1)/n, Z = 4. All polymorphous frameworks of cobalt(II) imidazolates reflect the structural features of silica (SiO(2)) and also exhibit different magnetic behaviors, although the imidazolates transmit the antiferromagnetic coupling between the cobalt(II) ions in all cases. However, the uncompensated antiferromagnetic couplings arise from spin-canting are sensitive to the structures: compound 1 is an antiferromagnet with T(N) = 13.11 K; compounds 2-4 are weak ferromagnets (canted antiferromagnets): 2 shows a very weak ferromagnetism below 15 K, 3 exhibits a relatively strong ferromagnetism below 11.5 K and a coercive field (H(C)) of 1800 Oe at 1.8 K, and 4 displays the strongest ferromagnetism of the three cobalt imidazolates and demonstrates a T(C) of 15.5 K with a coercive field, H(C), of 7300 Oe at 1.8 K. However, compound 5 seems to be a hidden canted antiferromagnet with a magnetic ordering temperature of 10.6 K.
TL;DR: Forty-one percent of patients receiving metal-on-metal articulations had increasing metal ion levels at the latest followup, and there were no differences in radiographic outcomes or outcome measurement tools between patients.
Abstract: A prospective, randomized, blinded clinical trial was done to evaluate polyethylene versus metal bearing surfaces in total hip replacement. Forty-one patients were randomized to receive either a metal (23 patients) or a polyethylene (18 patients) insert. The femoral and acetabular components were identical with the acetabular insert the only variable. Patients were assessed preoperatively and postoperatively using radiographs, multiple outcome measures (Western Ontario MacMaster University Score, Harris hip score, Short Form-12), erythrocyte metal ion analysis (cobalt, chromium, titanium), and urine metal ion analysis (cobalt, chromium, titanium). Patients were followed up for a minimum of 2 years (mean 3.2 years; range, 2.2-3.9 years). There were no differences in radiographic outcomes or outcome measurement tools between patients. Patients receiving a metal-on-metal articulation had significantly elevated erythrocyte and urine metal ions compared with patients receiving a polyethylene insert. Patients who had metal-on-metal inserts had on average a 7.9-fold increase in erythrocyte cobalt, a 2.3-fold increase in erythrocyte chromium, a 1.7-fold increase in erythrocyte titanium, a 35.1-fold increase in urine cobalt, a 17.4-fold increase in urine chromium, and a 2.6-fold increase in urine titanium at 2 years followup. Patients receiving a polyethylene insert had no change in erythrocyte titanium, urine cobalt, or urine chromium and a 1.5-fold increase in erythrocyte cobalt, a 2.2-fold increase in erythrocyte chromium, and a 4.2-fold increase in urine titanium. Forty-one percent of patients receiving metal-on-metal articulations had increasing metal ion levels at the latest followup.
TL;DR: Structurally characterised cobalt(II) complexes containing pyridazine, triazole or triazolate ligands are the subject of a review as discussed by the authors, focusing on macrocyclic complexes.
TL;DR: It is known that metal‐on‐metal total hip prostheses will produce a certain amount of wear debris, which results in increased whole‐blood metal levels, which may cause adverse effects.
TL;DR: In this article, the ethanol steam-reforming reaction was studied over ZnO-supported cobalt catalysts (10.5% Co), which were prepared by impregnation of nitrate and carbonyl cobalt precursors.
Abstract: The ethanol steam-reforming reaction was studied over ZnO-supported cobalt catalysts (10 wt.% Co). Catalysts were prepared by impregnation of nitrate and carbonyl cobalt precursors. Characterization was accomplished by transmission electron microscopy (TEM), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), and in situ techniques: magnetic measurements, and diffuse reflectance infrared spectroscopy (DRIFT) coupled to mass spectrometry. The use of Co 2 (CO) 8 as precursor produced a catalyst that was highly stable and selective for the production of CO-free hydrogen at reaction temperature as low as 623 K. The only by-product was methane and selectivity of 73% to H 2 and 25% to CO 2 was obtained. Under reaction conditions, the catalyst showed 92% of reduced cobalt, mainly as small particles.
TL;DR: In this paper, the authors characterized the catalysts for carbon nanotube growth in chemical vapor deposition (CVD) by using electron microscopy, and showed that the nanoparticles of iron and cobalt exhibit a melting point that is similar to the melting point of graphite.
Abstract: We characterize the iron and cobalt catalysts for carbon nanotube growth in chemical vapor deposition (CVD) by using electron microscopy. Nanoparticles of iron and cobalt exhibit a melting point dr...
TL;DR: In this paper, the microstructure and magnetic properties of cobalt substituted ZnO thin films deposited on sapphire (0001) substrates by pulsed laser deposition were investigated.
Abstract: We have investigated the microstructure and the magnetic properties of cobalt substituted ZnO thin films deposited on sapphire (0001) substrates by pulsed laser deposition. We have optimized the growth condition using in situ monitoring by reflection high-energy electron diffraction. We found that ferromagnetic films need to be grown at low oxygen partial pressure (<10−6 Torr). Films with 25% of Co are ferromagnetic at room temperature with clear out-of-plane anisotropy. We have looked for spurious origins of the ferromagnetic signal and found none.
TL;DR: In this paper, the effect of support mesoporous structure and cobalt content on reducibility was studied using two series of Fischer-Tropsch (FT) silica supported cobalt catalysts.
Abstract: The effect of support mesoporous structure and cobalt content on cobalt dispersion and reducibility was studied using two series of Fischer–Tropsch (FT) silica supported cobalt catalysts. The first series of the catalysts was supported by an SBA-15 periodic mesoporous silica with narrow pore size distribution, the second series was supported by a commercial mesoporous silica with broader pore size distribution. It was shown that in a wide range of cobalt surface densities (0–50 Co/nm 2 ), cobalt dispersion in silica supported catalysts was largely influenced by support texture. Cobalt dispersion was higher in Co catalysts supported by the SBA-15 silica with a pore diameter of 9.1 nm than in the commercial mesoporous silica with an average pore diameter of 33 nm. A more than 10-fold increase in cobalt surface density did not result in any noticeable sintering of Co 3 O 4 particles in SBA-15 periodic mesoporous silicas; the cobalt dispersion seems to be maintained by catalyst mesoporous structure. The effect of support pore diameter on cobalt dispersion was less significant for the catalysts supported by commercial silicas with broader pore size distribution. At the range of cobalt surface densities from 5 to 15 Co/nm 2 , higher Fischer–Tropsch reaction rates were observed over cobalt catalysts supported by the SBA-15 periodic mesoporous silica. This effect was attributed to higher cobalt dispersion in these catalysts. An increase in cobalt surface densities did lead to any significant changes in hydrocarbon selectivities and in chain growth probabilities for both series of supported catalysts.