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  • Author or Editor: A.M. Garcia x
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Abstract  

U, Th and Ra isotopic activities have been measured in water and sediment samples collected over three years from the Guadalquivir river channel (South of Spain). The study of the radioactivity levels and activity ratios evolution in space and time has provided information on the behavior of the radionuclides mentioned above in the estuarine and non-estuarine zones of the river.

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Abstract  

The occurrence of anomalous enhancements of U-isotope activities in the surrounding environment of a phosphate fertilizer factory complex at the southwest of Spain has been established. It seems that significant amounts of U, released by such industries, are being accumulated in the environment, which may substantially contribute to the collective radiation dose received by the local population.

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Abstract  

To combust coal together with a small percentage (<10%) of sewage sludge may be an option for the management of these wastes. Combustion of two different sewage sludge, one semianthracite coal and several sludges-coal blends (containing different dried mass% of each of the two sewage sludges) were studied by simultaneous TG/MS dynamic runs carried out at 5C min–1 in the temperature range 100–800C. No interactions have been observed between coal and sludge during the blends combustion. Neither the combustion process, neither the studied emissions have changed appreciably for the mass% of sludge in the blends considered in this work.

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Abstract  

Sewage sludge disposal is a difficult task owing to increasingly restrictive re-use policies. Its final destination will obviously depend on its nature and composition but the generation of energy is a significant option. The thermochemical conversion requires exhaustive gas emission controls. In this regard, this paper offers the results of the use of mass spectrometry together with a thermogravimetric analysis system used to study the thermal conversion processes of two kinds of sewage sludge under different atmospheres simulating pyrolysis, gasification and combustion. This TG-MS combination indicates that gasification is the best process for one kind of sludge while a co-combustion process is more suitable for the other.

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Abstract  

An extensive study on the distribution of natural radionuclides in an estuarine ecosystem located in Southwestern Spain is presented. This environment is highly affected by the wastes released by a phosphoric acid industry which uses phosphate rocks as raw material for fertilizer production. This rock has generally high concentrations of U and its daughters. The estuary is formed by two rivers, Odiel and Tinto, which have a common mouth into the Atlanic Ocean and a salt marsh (Odiel marsh) affected by the income of Odiel riverwaters. This river receives directly the liquid and part of the solid (gypsum) wastes released from the industries. Besides that, most of the phosphogypsum wastes are stored in uncovered piles at the right margin of the Tinto river. The study has concluded that the wastes from such industries are the cause of the enhanced concentrations found at the bed of both river channels as well as the enhancement found in surface soils in certain zones of the Odiel wet marshland. Indeed, the Northern marsh and the Mojarrera channel at the Odiel marsh seem to be the main sinks of the contaminant released by the phosphoric acid industry.

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Abstract  

Concentrations of U- and Ra-isotopes in rainwater samples taken in the South Spanish atmospheric environment during the years 1986, 1987 and 1988 are presented. Such data have been obtained by applying a simple method for the simultaneous determination of such radionuclides from the same rainwater sample. Ra is firstly coprecipitated as Ba–Ra sulfate. Then two alternatives can be used for U analysis: a coprecipitation of U with Fe, followed by a selective redissolution of the precipitate with ammonium carbonate, or a solvent extraction technique by using tributyl phosphate. Levels of 0.99 to 1.81 g/l, 3.4 to 17.9 mBq/l and 0.5 to 5.5 mBq/l, respectively for U,226Ra and224Ra are found during the studied time period. The dependence of such concentration variability on meteorological parameters is discussed.

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Starting from some satisfactory preliminary studies, the possibility of identifying single cations in solution has been investigated, by means of ionic exchange with a highly acidic resin (Dowex 50W) and a subsequent study by differential thermal analysis of the same resin. A catalogue of DTA curves has been prepared with 19 ionic forms of the said resin, and it has been found that the DTA curves are sufficiently distinguishable and reproducible to suggest an eventual analytical use in more complex cases of solutions containing more than one cationic species.

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The parasitization behaviour of Chelonus oculator (F.), egg-larval parasitoid of noctuid lepidopteran species, has been studied under laboratory conditions, using Ephestia kuehniella Zeller as host, at four different temperature levels (10,20, 30 and 40±1 °C) and five densities of host eggs (50,100,150, 200 and 250). A significant effect of temperature and parasitism density was observed. At 10 °C, there was no parasitism, whilst at 40 °C it was very low; presenting adequate values at the two other temperatures (20 and 30 °C). With regard to these facts, the functional responses of this parasitoid species were adjusted and we noted that they display Holling type III. Estimating the handling times from the respective mathematical expressions, we obtained 10.944 and 15.250 min, at 20 and 30°C, respectively. These values are considerably higher than the respective times obtained by direct observation, 0.597 and 0.560 min for these temperatures (this difference is due to the fact that in the first case, unlike the second one, the time used for the search of the host is also included). The results obtained from the parasitization behaviour of Ch. oculator are discussed, also considering it as a candidate biological control agent against Spdoptera exigua (Hübner), beet armyworm, with a view to its possible use in greenhouse crops in Spain.

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Journal of Thermal Analysis and Calorimetry
Authors: R. Artiaga, A. Garcia, L. Garcia, A. Varela, J. Mier, S. Naya, and M. Grana

Abstract  

The nickel-titanium alloys are usually known as Shape Memory alloys because of their ability to return to some previously defined shape or size when subjected to the appropriate thermal procedure. Mechanical properties of a nickel titanium wire were investigated by DMTA using cylindrical tension mode. The Young"s modulus, the maximum strain and residual deformation have been calculated. Recovery of previously deformed samples was observed in constant stress temperature ramp tests. Relaxation stress behaviour at temperatures above the austenitic transformation has been studied. The strain and frequency ranges of linear response have been determined by dynamic experiments. Strain amplitude of 0.1% and frequency of 1 Hz have been chosen for the temperature ramp dynamic experiments. A big change between 65 and 95C is observed in the storage modulus. The values of E' at temperatures below and above the transition are essentially constant. Finally, the effects of the frequency at different temperatures have been examined.

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Thermal studies on metal complexes of 5-nitrosopyrimidine derivatives IV

Complexes of Fe(II), Co(II), Ni(II) and Cu(II) with 6-amino-5-nitrosouracil

Journal of Thermal Analysis and Calorimetry
Authors: J. M. Salas-Peregrin, M. A. Romero-Molina, M. A. Ferro-Garcia, and M. N. Moreno-Carretero

The thermal decomposition processes of the complexes of 6-amino-5-nitrosouracil with Fe(II), Co(II), Ni(II) and Cu(II) have been studied using TG and DSC techniques. Dehydration energies have been calculated from the DSC curves.

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