A refined chemical procedure for speciation studies of sediments has been thoroughly examined. The suggested method, although only tested on210Pb (210Po), could be applied to other chemical species, especially heavy metals and radioactive nuclides. Successive dissolutions using dilute HC1 (1–2.5%) and NaOH (0.5–1%) proved that the geochemistry of fulvic, humic, and mineral compounds plays an important role in the mobility, transport, and accumulation of210Pb in various aquatic systems. This work demonstrates that210Pb, as well as analogous isotopes and metals-based dating and tracing applications, could be further improved and extended using proper speciation techniques. The procedure given here allows not only evaluation of supported and unsupported210Pb but also the resolution of anomalies in modelling biogeochemical cycles.
Authors:G. Manjón, F. El-Daoushy, and R. García-Tenorio
For a better understanding of the behaviour of90Sr in aquatic systems, this -emitter has been determined in the different layers of a lake sediment core which has been previously dated using the well established210Pb dating method. For this, a radiochemical technique has been developed for the isolation of strontium from the sediment samples and for its activity measurement with a low-level gas-flow proportional counter. A conservative behaviour of90Sr in the water column remaining dissolved in the water body, can be inferred from the data obtained. Consequently, a possible90Sr transport pathway through the outflowing waters of the lake can be deduced.
Authors:F. Arellano, I. García-Sosa, and M. Solache-Ríos
The sorption behavior of cobalt and cadmium by zeolite Y has been investigated. Cobalt and cadmium solutions were exchanged with the zeolite at different pH's. Cobalt, cadmium and sodium in the samples were determined by neutron activation analysis. The sorption of cadmium was higher than that of cobalt, however, the selectivity for both cations by the zeolite was low.
Authors:V. Braga, F. Garcia, J. Dias, and Sílvia Dias
Nb2O5 supported on SiO2-Al2O3 were prepared with a wide loading range (2, 5, 10, 15, 20 and 25 mass%) and analyzed by simultaneous thermogravimetric (TG)
and differential thermal analysis (DTA). The materials presented a phase transition close to 1364°C. This phase transition
was studied by XRD, FTIR and Raman spectroscopy. Amixture of orthorhombic (T) andmonoclinic (H andM) crystalline phases was
evidenced in the supported samples, which is coverage dependent, in contrast to the formation of only the monoclinic phase
(H and M) when pure Nb2O5 is heated under the same conditions. These results indicate the stabilization of Nb2O5 on silica-alumina surface.
Authors:M. Alonso, M. Oliet, J. García, F. Rodríguez, and J. Echeverría
Kinetics of thermosetting polymers curing is difficult to study by isothermal
methods based on the differential scanning calorimetry (DSC) technique. The
difficulty is due to the low sensitivity of the equipment for total reaction
heat measurements during high temperature process. The aim of this paper is
to display the equivalence between a dynamic model, the Ozawa method, and
an isothermal isoconversional fit, which allows predicting the isothermal
behavior of the resol resins cure through dynamic runs by DSC. In this work,
lignin–phenol–formaldehyde and commercial phenol–formaldehyde
resol resins were employed. In addition, the isothermal kinetic parameters
for both resins were performed by means of transformation of the data obtained
from the dynamic Ozawa method.
Authors:F. Chitry, R. Garcia, L. Nicod, J. Gass, C. Madic, and M. Lemaire
A new method is proposed for the separation of gadolinium(III) and lanthanum(III) in aqueous medium by nanofiltration combined
with a complexation step. First DTPA was chosen as ligand for a selective Gd(III)/La(III) complexation. Having investigated
the influence of three factors (pH, temperature and amount of ligand) for the selective complexation of DTPA towards Gd(III)
and La(III), the system is then combined with a nanofiltration separation process to remove 92% of initial Gd(III) and only
12% of initial La.
Authors:D. Tenorio, M. G. Almazán-Torres, F. Monroy-Guzmán, N. L. Rodrígiez-García, and Luis C. Longoria
Ceramic samples found in San Miguel Ixtapan, Mexico State, Mexico, were analyzed by means of NAA, PIXE, SEM and XRD. Statistical
treatments such as bivariate cluster and principal-components analysis were applied to the data set. The origins of these
ceramic samples were classified as local, regional and foreign.
Authors:Irina Catta Preta, Solange Sakata, G. Garcia, J. Zimmermann, F. Galembeck, and Claudia Giovedi
(PAN) polymers are used as precursors for carbon fiber production. This process
requires an oxidative stabilization step, which can be studied by differential
scanning calorimetry (DSC). In this sense, thermal behavior of PAN based terpolymers
by different polymerization processes, compositions and itaconic acid concentrations
in the reaction media were investigated. The obtained results showed that
the addition of itaconic acid and methyl acrylate as comonomers resulted a
lower heat flow during the process comparing to the PAN homopolymer. It suggested
that these comonomers aid the oxidative stabilization stage for all studied
process. The redox system polymerization at 40C resulted in a lower heat
flow. Itaconic acid decreases slightly initial and peak temperatures of the
terpolymer and heat flow until concentration of 3y. The cyclization temperature
decreases when MAis incorporated into the terpolymer compared to the MMA terpolymer
and increases when MAA is the acidic monomer. Among terpolymers the AN/MA/AA
polymer showed the best thermal behavior for carbon fiber producing.