Cobalt Transport Research Articles

Bulk versus surface transport of nickel and cobalt on silicon.

We compare directly the rates of bulk versus surface transport for Ni in and on Si(111) by depositing a laterally confined dot of Ni on one side of a double-polished and UHV cleaned Si wafer and then measuring the lateral Auger profile on the reverse side following annealing and quenching. Ni reaches the far side of the wafer at temperatures as low as 550\ifmmode^\circ\else\textdegree\fi{}C via bulk diffusion with no measurable contribution from surface paths, which are short circuited by numerous, fast bulk paths. Similar results are found for Ni and Co on Si(111) and Si(100). Implications for silicide reactions in general are described.

Transport and separation of cobalt, nickel and copper ions with alamine liquid membranes

AbstractThe transfer and separation of Co(II), Ni(II) and Cu(II) ions across a flat‐sheet supported liquid membrane containing Alamine 336 as the mobile carrier dissolved in kerosene solvent has been investigated. Both the Alamine composition in the organic solution and the hydrochloric acid concentration in the feed solution have a marked effect on Co(II) and Cu(II) transport. A maximum flow of these ions at 50% of Alamine in the diluent was obtained. Ni(II) ion was not transported in the whole range of experimental conditions studied and good separation from Co(II) and Cu(II) could thus be performed. With decreasing hydrochloric acid concentration in the feed solution the separation factor of Cu(II) from Co(II) increases thus decreasing the Cu(II) recuperation factor.

On the mechanism of metal-ions facilitated transport through pseudo-liquid membranes

On the basis of FT-IR spectroscopy investigation and the data on the membrane extraction the new “flow-type” mechanism of the facilitated transport of cobalt through a pseudo-liquid membrane — the tri- n-octylamine (TOA) in n-decane solution, immobilised in porous polymeric nitrocellulose microfilter Synpor, has been suggested. The specific channels of metal ions conductivity seem to be formed when the organic phase reaches a definite stoichiometrical composition of ingredients including the metal ions. The swift current of protons takes with it negatively charged metal ions and transports them through the membrane against the metal concentration gradient. The empirical relationship between the TOA concentration by the maximum cobalt transport and its initial concentration has been found: C max(TOA) = 0.33 lg{ C in(Co) } + 3.30. This relationship describes the experimental data quite well and allows the calculation (by the same condition) of the concentration of TOA providing more effective transfer of cobalt. It is shown that the nature of the porous surface of a microfilter practically does not influence the mechanism of the cobalt ion transport.

Cloning, sequencing, and expression of the uroporphyrinogen III methyltransferase cobA gene of Propionibacterium freudenreichii (shermanii)

We cloned, sequenced, and overexpressed cobA, the gene encoding uroporphyrinogen III methyltransferase in Propionibacterium freudenreichii, and examined the catalytic properties of the enzyme. The methyltransferase is similar in mass (27 kDa) and homologous to the one isolated from Pseudomonas denitrificans. In contrast to the much larger isoenzyme encoded by the cysG gene of Escherichia coli (52 kDa), the P. freudenreichii enzyme does not contain the additional 22-kDa peptide moiety at its N-terminal end bearing the oxidase-ferrochelatase activity responsible for the conversion of dihydrosirohydrochlorin (precorrin-2) to siroheme. Since it does not contain this moiety, it is not a likely candidate for synthesis of a cobalt-containing early intermediate that has been proposed for the vitamin B12 biosynthetic pathway in P. freudenreichii. Uroporphyrinogen III methyltransferase of P. freudenreichii not only catalyzes the addition of two methyl groups to uroporphyrinogen III to afford the early vitamin B12 intermediate, precorrin-2, but also has an overmethylation property that catalyzes the synthesis of several tri- and tetra-methylated compounds that are not part of the vitamin B12 pathway. The enzyme catalyzes the addition of three methyl groups to uroporphyrinogen I to form trimethylpyrrocorphin, the intermediate necessary for biosynthesis of the natural products, factors S1 and S3, previously isolated from this organism. A second gene found upstream from the cobA gene encodes a protein homologous to CbiO of Salmonella typhimurium, a membrane-bound, ATP-dependent transport protein thought to be part of the cobalt transport system involved in vitamin B12 synthesis. These two genes do not appear to constitute part of an extensive cobalamin operon.

Observation of long localization length along b-axis PrBa 2Cu 3O 7 in a-axis YBa 2Cu 3O 7/a, b-axis PrBa 2Cu 3O 7 superlattices

We have studied resistive transitions of a-axis YBa 2Cu 3O 7/a, b-axis superlattices in a magnetic field to investigate the correlation length of vortices along the a-axis direction of YBa 2Cu 3O 7 across an a, b-axis oriented PrBa 2Cu 3O 7 barrier. The correlation of vortices across up to 480Å of a, b-axis PrBa 2Cu 3O 7 is evidence consistent with long proximity coupling coherence lengths in PrBa 2Cu 3O 7 found in sandwich type YBa 2Cu 3O 7 PrBa 2Cu 3O 7/YBa 2Cu 3O 7 Josephson junctions. Investigation of a&.sbnd;b plane and b-axis transport of undoped and cobalt doped PrBa 2Cu 3O 7 films suggests that a long localization length along the b-axis of PrBa 2Cu 3O 7 is the origin of this long range proximity coupling, consistent with our vortex coupling experiments and recent theoretical and experimental work based on the electronic structure of PrBa 2Cu 3O 7.

Selective Transport of Copper(I, II), Cadmium(II), and Zinc(II) Ions through a Supported Liquid Membrane Containing Bathocuproine, Neocuproine, or Bathophenanthroline

Abstract Some selective transport systems for heavy metallic ions through a supported liquid membrane (SLM) containing a 2,2′-dipyridyl derivative ligand, 4,7-diphenyl-2,9-dimethyl-1,10-phenanthroline (bathocuproine), 2,9-dimethyl-1,10-phenanthro-line (neocuproine), or 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline), were investigated. The transport of copper(I, II), cadmium(II), zinc(II), lead(II), and cobalt(II) ions was accomplished with a halogen ion such as chloride, bromide, or iodide ion as a pairing ion species for any SLM. The ranking of the permeability of the metallic ions was Cu+,2+, Zn2+, Cd2+ ≫ Pb2+, Co2+. When the oxidation-reduction potential gradient was used as a driving force for metallic ions, the transport of Cu+ ion was higher than those of Cd2+ and Zn2+ ions for any SLM containing bathocuproine, neocuproine, or bathophenanthroline. On the other hand, in the transport system which used the concentration gradient of pairing ion species, the permeability of the Cu2+ ion decrease...

Effect of Al on high-temperature corrosion of Co-15a/oNb alloys in H2-H2O-H2S environments

Co−15 at.% Nb alloys containing up to 15 at.% Al were corroded in gaseous H2−H2O−H2S mixtures over the temperature range of 600–900°C. The corrosion kinetics followed the parabolic rate law at all temperatures. Corrosion resistance improved with increasing Al content except at 900°C. Duplex scales formed on alloys consisting of an outer layer of cobalt sulfide and a heterophasic inner layer. A small amount of Al2O3 was found only on Co−15Nb−15Al. Contrary to what formed in Co−Nb binary alloys, neither NbS2 nor NbO2 were found in the inner layer of all alloys, but Nb3S4 did form. The absence of NbS2 and NbO2 is due to the formation of stable Al2O3 and Al2S3 that effectively blocked the inward diffusion of oxygen and sulfur, respectively, and to the reduction of activity of Nb by Al additions in the alloys. Intercalation of ions in the empty hexagonal channels of Nb3S4 is associated with the blockage of the transport of cobalt. An unknown phase (possibly Al0.5NbS2) was detected. Alloys corroded at 900°C were abnormally fast and formed a scale containing CoNb3S6 and Co. Pt markers were found at the interface between the inner and outer layers.

Rate-Controlling Mechanism of Cobalt Transport through Supported Liquid Membranes Containing Di(2-ethylhexyl)phosphoric Acid

Abstract In this paper the permeation process of trace cobalt(II) through supported liquid membranes using di(2-ethylhexyl)phosphoric acid as a mobile carrier was modeled and the rate-controlling mechanism was examined. The permeation rate equations were derived considering diffusion of metal ions across the aqueous stagnant layers toward the membrane, chemical reaction at the feed-membrane interface, and diffusion of extractant and its metal complex in the membrane phase. The application of the measured permeation rates for determining the kinetic parameters of the solvent extraction reaction was also investigated. It was found that the calculated rates were in good agreement with the measured ones (average standard error, 12%).

Transport of cobalt(2+) in a physically and chemically heterogeneous porous medium

The fate of radionuclides in the subsurface is of critical importance to the planning, siting, and evaluation of repositories for radioactive wastes. Mathematical models are an integral component of this process. An accurate understanding of radionuclide transport is required to successfully formulate and use these models. It is wellknown that the subsurface is both physically and chemically heterogeneous. Recent research has shown that the resultant spatial variability of hydraulic conductivity and of sorption capacity can significantly affect solute transport in the subsurface. The impact of hydraulic conductivity variability and sorption capacity variability on the transport of radionuclides is, therefore, of great interest. Very few well-controlled, experimentally based laboratory investigations of the transport of radionuclides in physically and chemically heterogeneous porous media have been reported in the literature. The purpose of this paper is to report the preliminary results of such an investigation. We present results obtained for transport of Co2+ in a column packed with two media of differing hydraulic conductivities and sorption capacities. In addition to being influenced by these heterogeneities, transport of the Co2+ is also influenced by rate-limited diffusive mass transfer and nonequilibrium sorption.

FT-IR-Spectroscopic investigation of the mechanism of membrane extraction of cobalt(II) from HCl solutions by solutions of tri-n-octylamine inn-decane

The extraction of cobalt(II) from aqueous HCl by tri-n-octylamine (TOA) inn-decane is investigated by means of FT-IR spectroscopy. The sharp increase in cobalt(II) transport during its membrane extraction from a HCl solution by solutions of TOA in a narrow interval of extradant-carrier concentrations is explained by a change in the transport mechanism which seems to differ from the diffusion and “relay” mechanisms.

Characterization of the cobalamin (vitamin B12) biosynthetic genes of Salmonella typhimurium

Salmonella typhimurium synthesizes cobalamin (vitamin B12) de novo under anaerobic conditions. Of the 30 cobalamin synthetic genes, 25 are clustered in one operon, cob, and are arranged in three groups, each group encoding enzymes for a biochemically distinct portion of the biosynthetic pathway. We have determined the DNA sequence for the promoter region and the proximal 17.1 kb of the cob operon. This sequence includes 20 translationally coupled genes that encode the enzymes involved in parts I and III of the cobalamin biosynthetic pathway. A comparison of these genes with the cobalamin synthetic genes from Pseudomonas denitrificans allows assignment of likely functions to 12 of the 20 sequenced Salmonella genes. Three additional Salmonella genes encode proteins likely to be involved in the transport of cobalt, a component of vitamin B12. However, not all Salmonella and Pseudomonas cobalamin synthetic genes have apparent homologs in the other species. These differences suggest that the cobalamin biosynthetic pathways differ between the two organisms. The evolution of these genes and their chromosomal positions is discussed.

The COT2 gene is required for glucose-dependent divalent cation transport in Saccharomyces cerevisiae.

Eleven cobalt-tolerant mutants were found to belong to a single complementation group, cot2. In addition to cobalt, the cot2 mutants were found to tolerate increased levels of the divalent cations Zn2+, Mn2+, and Ni2+ as well. All of the cot2 mutants exhibited a wiener-shaped cellular morphology that was exacerbated by the carbon and nitrogen source but was unaffected by metals. The rate of glucose-dependent transport of cobalt into cells was reduced in strains that carry mutations in the COT2 gene. COT2 is not essential for growth. Strains that carry a COT2 allele conferring complete loss of function are viable and exhibit phenotypes similar to those of spontaneous cot2 mutations. The sequence of the COT2 gene shows that it is identical to GRR1, which encodes a protein required for glucose repression. The glucose dependence of the transport defect implies that cot2 mutations affect the link between glucose metabolism and divalent cation active transport.

The COT2 gene is required for glucose-dependent divalent cation transport in Saccharomyces cerevisiae.

Eleven cobalt-tolerant mutants were found to belong to a single complementation group, cot2. In addition to cobalt, the cot2 mutants were found to tolerate increased levels of the divalent cations Zn2+, Mn2+, and Ni2+ as well. All of the cot2 mutants exhibited a wiener-shaped cellular morphology that was exacerbated by the carbon and nitrogen source but was unaffected by metals. The rate of glucose-dependent transport of cobalt into cells was reduced in strains that carry mutations in the COT2 gene. COT2 is not essential for growth. Strains that carry a COT2 allele conferring complete loss of function are viable and exhibit phenotypes similar to those of spontaneous cot2 mutations. The sequence of the COT2 gene shows that it is identical to GRR1, which encodes a protein required for glucose repression. The glucose dependence of the transport defect implies that cot2 mutations affect the link between glucose metabolism and divalent cation active transport.

Mechanistic study of cobalt, nickel and copper transfer across a supported liquid membrane

AbstractThe mechanism of cobalt, copper and nickel transport through supported liquid membranes containing di(2‐ethylhexyl)phosphoric acid as a mobile carrier has been studied. An equation describing the permeation rate has been derived, taking into account stagnant layer aqueous diffusion, interfacial resistance due to solvatation reaction and liquid membrane diffusion as simultaneous controlling factors. The validity of this model is evaluated with experimental data of mass transfer coefficient measured employing a permeation cell. For these ions it was found that at low stirring conditions the stagnant layer resistance mainly controlled the processes, but it is controlled by diffusion of the ion complex through the supported liquid membrane when the stagnant layer resistance is negligible.

COT1, a Gene Involved in Cobalt Accumulation in Saccharomyces cerevisiae

The COT1 gene of Saccharomyces cerevisiae has been isolated as a dosage-dependent suppressor of cobalt toxicity. Overexpression of the COT1 gene confers increased tolerance to cobalt and rhodium ions but not other divalent cations. Strains containing null alleles of COT1 are viable yet more sensitive to cobalt than are wild-type strains. Transcription of COT1 responds minimally to the extracellular cobalt concentration. Addition of cobalt ions to growth media results in a twofold increase in COT1 mRNA abundance. The gene encodes a 48-kDa protein which is found in mitochondrial membrane fractions of cells. The protein contains six possible membrane-spanning domains and several potential metal-binding amino acid residues. The COT1 protein shares 60% identity with the ZRC1 gene product, which confers resistance to zinc and cadmium ions. Cobalt transport studies indicate that the COT1 product is involved in the uptake of cobalt ions yet is not solely responsible for it. The increased tolerance of strains containing multiple copies of the COT1 gene is probably due to increased compartmentalization or sequestration of the ion within mitochondria.

COT1, a gene involved in cobalt accumulation in Saccharomyces cerevisiae.

The COT1 gene of Saccharomyces cerevisiae has been isolated as a dosage-dependent suppressor of cobalt toxicity. Overexpression of the COT1 gene confers increased tolerance to cobalt and rhodium ions but not other divalent cations. Strains containing null alleles of COT1 are viable yet more sensitive to cobalt than are wild-type strains. Transcription of COT1 responds minimally to the extracellular cobalt concentration. Addition of cobalt ions to growth media results in a twofold increase in COT1 mRNA abundance. The gene encodes a 48-kDa protein which is found in mitochondrial membrane fractions of cells. The protein contains six possible membrane-spanning domains and several potential metal-binding amino acid residues. The COT1 protein shares 60% identity with the ZRC1 gene product, which confers resistance to zinc and cadmium ions. Cobalt transport studies indicate that the COT1 product is involved in the uptake of cobalt ions yet is not solely responsible for it. The increased tolerance of strains containing multiple copies of the COT1 gene is probably due to increased compartmentalization or sequestration of the ion within mitochondria.

Impurity transport during the H-mode in DIII-D

In H-mode plasmas in DIII-D, large modulations in spectroscopically measured impurity densities have been observed during shots with giant edge localized modes (ELMs). These spectral modulations have been analysed with the MIST impurity transport code. This analysis indicates that impurities are alternately flowing towards the plasma centre and then away from it. This alternating flow is correlated with ELM produced changes in the electron density. The electron density oscillations are extreme, causing the density profile to switch from hollow (just before an ELM) to centrally peaked (just after an ELM). Neoclassical convection, dependent on ion density gradients, causes impurities to concentrate most heavily where the electron density is largest and can explain the modulating impurity behaviour. Anomalous diffusion, D ≃ 1.0 × 104 cm2/s, reduces the degree of impurity peaking. As the plasma current increases, the increase in hollowness of electron density profiles can account for the observed decrease in central impurity accumulation. Transport of cobalt, injected by laser ablation, has also been studied; cobalt transport variations are consistent with the ELM induced changes seen in intrinsic impurity transport. The transport results may be consistent with neoclassical impurity convective fluxes and suggest that impurity accumulation in tokamaks will occur unless the electron density profile is flat or particle confinement is low.

Mass transport of cobalt and nickel in Incoloy-800

Lattice diffusion of cobalt and nickel in Incoloy-800 has been studied in the temperature range 1070 to 1500K by serial sectioning and residual activity techniques using radioactive tracers60Co and63Ni. The lattice diffusion coefficient can be expressed by the relation: $$\begin{gathered} D_{Co/Incoloy - 800} = 2.54 x 10^{ - 5} exp \left( { - \frac{{249.5kJ mol^{ - 1} }}{{RT}}} \right)m^{^2 } sec^{ - 1} \hfill \\ D_{Ni/Incoloy - 800} = 8.62 x 10^{ - 5} exp \left( { - \frac{{255.9kJ mol^{ - 1} }}{{RT}}} \right)m^2 sec^{ - 1} \hfill \\ \end{gathered} $$ Segregation and mass transport studies of these tracers along the grain boundary in Incoloy-800 have also been carried out in the temperature range 750 to 1080 K. The grain boundary diffusion coefficients are evaluated by Whipple and Suzuoka methods and are found to be in good agreement. Grain boundary diffusivityD gb can be expressed by the equation $$\begin{gathered} D_{gb Co/Incoloy - 800} = 1.06 x 10^{ - 5} exp \left( { - \frac{{152.72kJ mol^{ - 1} }}{{RT}}} \right)m^2 sec^{ - 1} \hfill \\ D_{gb Ni/Incoloy - 800} = 3.82 x 10^{ - 5} exp \left( { - \frac{{156.40kJ mol^{ - 1} }}{{RT}}} \right)m^2 sec^{ - 1} \hfill \\ \end{gathered} $$ Segregation of these tracers along the grain boundary in Incoloy-800 has been studied by autoradiographic technique. The results have been discussed and presented in this paper.

Microemulsion liquid membranes. I. Cobalt transport in a surfactant-dodecane system

Cobalt transport across supported microemulsion liquid membranes containing reversed micelles of dinonylnaphthalenesulfonic acid (HDNNS) was measured as a function of organic phase composition, aqueous phase composition, stirring rate and temperature. A microporous polypropylene film served as the membrane support. The membrane phase was characterized by interfacial tension and viscosity measurements. Stirring speed and temperature effects suggest that diffusion processes play a major role in the transfer of cobalt across the membrane. The experimental results at relatively low carrier concentration are explained by a membrane transport model involving counter-diffusion of HDNNS reversed micelles and metal-reversed micelle complexes.

Application of the pH-Stat Technique in Donnan Dialysis Effect of Anion Invasion in the CoSO4/NAFION 117/H2SO4 System

Abstract Cobalt transport during Donnan dialysis in the CoSO4 Nafion 117/H2SO4 system was measured with a pH-stat technique, (i.e., the pH in the feed compartment was maintained constant). During the transfer process, Co2+ ions moved from the cobalt reservoir to the sink compartment, while hydrogen ions moved in the opposite direction. A standardized NaOH solution was used to neutralize the H+ ions entering the reservoir compartment, and in the absence of anion invasion, the cobalt flux was determined as