Authors:G. Shengli, J. Mian, C. Sanping, H. Rongzu, and S. Qizhen
The enthalpy change of formation reaction of cobalt(II) histidine (His) complex in water has been determined by a microcalorimeter,
using cobalt chloride with L-α-histidinein the temperature range of 25~50C. On the basis of experimental and calculated results, three thermodynamics
parameters (the activation enthalpies, the activation entropies, the activation free energies), the rate constant, three kinetic
parameters (the activation energies, the pre-exponential constant and the reaction order) are obtained. The results show that
the titled reaction easily took place in the studied temperature.
The thermal evolution of a very fine-grained hydrated cobalt molybdate, CoMoO4 · · 0.9H2O, has been studied by dilatometry, DTA, X-ray crystallography and scanning electron microscopy. Four principal stages have been detected between 25 and 1000°: dehydration, polymorphism (or precipitation), recrystallization, and high-temperature phase change. Such phenomena also occurred with some other hydrated molybdates (Ni, Mn).
Radiolysis of aqueous solutions of di- and trivalent cobalt with 2,2-bis/aminoethyl/ether-tetraacetic acid /BAETA/ was investigated, both in absence and in presence of oxygen. A radiolytic mechanism has been proposed where it has been shown that the degradation of the chelation is due to OH only.
Authors:E. Hernández-Barrales and F. Granados-Correa
The ability of a natural Mexican clinoptilolite to sorb radioactive cobalt from aqueous solution was studied. The zeolite
was stabilized partially with sodium and the content of Na+ in the samples was determined by neutron activation analysis. Ion exchange experiments were performed with solution labeled
with radioactive60Co at pH 6.5. XRD patterns were used to verify if the crystallinity of the aluminosilicate was affected by ionic exchange.
A fast sorption uptake was observed and it was found that 0.408 meq/g of zeolite of Na+ ions were replaced by cobalt ions, followed by a desorption process where the uptake decrease to 0.314 meq/g of zeolite.
This behavior is a consequence of the partial dehydration of the zeolite.
Equilibrium distribution coefficients have been determined for the extraction of cobalt(II) with 8-mercaptoquinoline as a function of pH and reagent concentraton at ambient temperature. The extractable complex is a diadduct, i. e. two molecules of the reagent are coordinated to the cobalt(II) chelate. The adduct formation constant in chloroform and the overall formation constant in the aqueous phase have been determined. Pyridine and its methyl derivatives were found to enhance the extraction of Co(II) into chloroform in the presence of 8-mercaptoquinoline. From the extraction equilibrium data, the adduct formation constants of 12 chelate to nitrogen base adducts were evaluated. The special role of steric factors is discussed.
Authors:K. Shang, Y. Yang, J. Guo, W. Lu, F. Liu, and W. Wang
The extraction of cobalt by Winsor II microemulsion system was studied. In the bis (2-ethylhexyl) sulfosuccinate sodium salt
(AOT)/n-pentanol/n-heptane/NaCl system, AOT was used as a anionic surfactant to form microemulsion in n-heptane, n-pentanol was injected in the microemulsion as a cosurfactant. Co(II) was found to be extracted into the microemulsion phase
due to ion pair formation such as Co2+(R–SO3−)Cl. The influence of different parameters such as the volume ratio of aqueous phase to microemulsion, surfactant concentration,
pH of the feed solutions, cosurfactant concentration as well as temperature on the extraction yield (E%) were investigated. The results showed that it was possible to extract 95% of cobalt by the AOT Winsor II microemulsion.
The concentration dependence of experimental diffusion coefficients of cobalt ions in presence of some alkali metal chlorides is examined in the light of the Onsager theory. The diffusion coefficients are measured in 1% agar gel using the zone-diffusion technique. The positive and negative deviations observed at higher and lower concentrations, respectively, are explained in terms of relative contributions of various types of effects occurring in the diffusion medium.
Authors:G. A. El-Shobaky, A. S. Ahmad, A. N. Al-Noaimi, and H. G. El-Shobaky
Basic cobalt and copper carbonates were prepared by precipitation from solutions of their nitrates using KHCO3 at room temperature in CO2 atmosphere. The thermal decomposition of the prepared basic carbonates was studied by means of TG and DTA techniques and the phases produced were identified by XRD measurements. The products obtained at 400‡C were subjected to different doses of gamma-rays (40–160 M rad) and the thermal stabilities of these solids were investigated.
Authors:Asuka Kurokawa, Masahiro Tsuchiya, and Mari Onodera
A series of coordination polymers, cobalt(II)–[dipicolylamide-propyl poly(dimethylsiloxane)]s (Co-DPPDMS), was prepared and
studied by thermogravimetry (TG) and double-shot pyrolysis-gas chromatograph-mass spectrometry (Pyro-GC-MS). The TG curves
of the Co-DPPDMSs exhibited two events for the mass loss, and the Pyro-GC-MS results suggested that the decomposition reaction
of the PDMS chains in the ligand polymer occurred at the second event. The activation energy Ea and the reaction order n of each event were estimated by curve fitting based on the order rate equation, and the results were compared with those
obtained using the Kissinger method for non-isothermal degradation.
The non-isothermal decomposition of cobalt acetate tetrahydrate was studied up to 500°C by means of TG, DTG, DTA and DSC techniques
in different atmospheres of N2, H2 and in air. The complete course of the decomposition is described on the basis of six thermal events. Two intermediate compounds
(i.e. acetyl cobalt acetate and cobalt acetate hydroxide) were found to participate in the decomposition reaction.
IR spectroscopy, mass spectrometry and X-ray diffraction analysis were used to identify the solid products of calcination
at different temperatures and in different atmospheres. CoO was identified as the final solid product in N2, and Co3O4 was produced in air. A hydrogen atmosphere, on the other hand, produces cobalt metal. Scanning electron microscopy was used
to investigate the solid decomposition products at different stages of the reaction. Identification of the volatile gaseous
products (in nitrogen and in oxygen) was performed using gas chromatography. The main products were: acetone, acetic acid,
CO2 and acetaldehyde. The proportions of these products varied with the decomposition temperature and the prevailing atmosphere.
Kinetic parameters (e.g.E and lnA) together with thermodynamic functions (e.g. °H, Cp and °S) were calculated for the different decomposition steps.