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  • Author or Editor: C. Garcia x
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A critical assessment of the so-called “peak temperature methods” (originally proposed by Kissinger) is presented. The two ingredients of peak temperature methods, namely, Kissinger's assumption and transformation equations, are considered. First it is argued that Kissinger's assumption although not being valid for DTA holds for DSC. Then it is shown that the only way to use kinetic parameters obtained from non-isothermal experimental data to describe both iso- and anisothermal kinetics is to take the same reaction rate equation for the two kinetics, as previously done by Henderson.

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Abstract  

We describe the procedure developed for the electrolytic concentration of3H in water, together with systematically applied checks to guarantee the reproducibility of the process and to minimize the variability between water samples concentrated simultaneously in the different electrolytic cells. Starting from initial volume of 250 ml water, we obtained enrichment parameters normally greater than 70%, with a dispersion always less than 5%. Measuring the concentrated and the unelectrolyzed samples under the same conditions, we found that the lowest detectable activities had been improved from around 1.5 to 0.3 Bq/l. This allowed us to quantify the3H activity levels of 100% of the rainwater samples collected in Cáceres from 1994 to 1996. The resulting average value for this period was (0.79±0.38) Bq/l.

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The analysis of99Tc was carried out in filter, peat and rainwater samples. A solvent extraction technique was used to separate Tc from them, where tributylphosphate was the extracting agent. Radiochemical yield was obtained by using99mTc as an internal tracer. A typical value of 60% was found for it. However, problems encountered in its determination are discussed in the text. Additionally, rainwater samples were analyzed for137Cs. This was adsorbed in ammonium phosphomolibdate. Radiochemical yield was obtained by using134Cs as an internal tracer.

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The thermal behaviour of [CoCO3(NH3)4]2SO4 · 3H2O was studied using X-ray diffraction diagrams, DTA, TG and heating at constant temperatures for different periods of time. The X-ray study was made in order to characterize with the powder diagrams the phases obtained and to follow the reactions of the complex when heated in air up to 800‡. A parallel infrared spectral study was also made. The results obtained by the various experimental methods were compared with the theoretical weight losses.

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Abstract  

From 1994 to 1996 we have studied a number of radioactive (total b and residual b-activity levels and 3H activity) and physico-chemical (pH, conductivity, and natural potassium content) parameters in the water of two Alcántara and Guadiloba reservoirs, which are artificially connected by interbasin transfers. The analysis of the results showed the existence of major correlations between the two systems for tritium activity, conductivity, and stable potassium content. A model based on the water balance in the Guadiloba reservoir was also elaborated which allowed us to forecast its effective surface area monthly, which varied extraordinarily between 0.405 and 135 km2.

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Thermogravimetry technique is useful to determine the thermal stability of vegetable oils. In this paper some vegetable oils obtained from brazilian Cerrado native plants were studied based on their high oleic acid content. Amburana, baru and pequi pulp oils presented higher yield of extraction compared to soybean oil. The thermal stability of oils in nitrogen was very close hence their fatty acid composition was very similar. Amburana and baru oils have major amount of unsaturated fatty acids, especially linoleic acid and pequi pulp oil has the highest short chain fatty acid content which can explain its lowest thermal stability in synthetic air.

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A discussion on the influence of grafted polar groups (succinic anhydride and succinil-fluorescein) in glass transition behaviour of atactic polypropylene is shown in this work, on the basis of the reaction conditions used to obtain the modified polymers, kind and amount of grafted groups, and the degradation processes which may take place. The Box-Wilson experimental design methodology for two independent variables (reactant concentration to obtain the modified polymer) has been used to follow variations in glass transition temperatures. The existence of undesired degradation processes is considered as independent of the grafting reactions, and the model predictions seem to agree with this latter.

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The gasification in air and in steam of a bituminous coal from Belmez (Cordoba, Spain) (SAO) and of samples resulting either from acid treatment (HCl, SAH; HNO3 SAN and HF, SAF) or from thermal treatment (SAOC) has been studied under dynamic conditions.

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Summary  

The feasibility of measuring picogram levels of actinides in a urine matrix using ion chromatography coupled on-line to an inductively coupled plasma quadrupole mass spectrometer (IC-Q-ICPMS) was investigated. A chelation column for separation of matrix ions and preconcentration of the actinides was combined with a cation-exchange column for separation of the actinides. Sample preparation required simple addition of ammonium acetate to adjust the pH of the urine matrix. Spike solutions containing 232 Th, 237Np, 238U, 239Pu, and 241Am were added to undiluted urine, diluted urine (1 : 9) and water. Results showed that this approach enhanced the signal sensitivities of all the tested actinides over two orders of magnitude in the water matrix, while certain elements (especially Am) can still be effectively concentrated in undiluted urine.

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