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  • Author or Editor: Y. Kawano x
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Abstract  

The thermal behavior of Nafion-117 membranes was investigated by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG measurements revealed that the mechanism of thermal degradation of a Nafion membrane in the acid form is different from that of Nafion in the sodium form. The DSC curves for the first heating, for both acid and salt forms, display two endothermic peaks, near 120 and 230°C. The high-temperature peak was assigned to the crystalline domains melting in Nafion, and the low-temperature peak was attributed to a transition into ionic clusters, since this transition exhibits significant changes depending on the nature of the counterion and the degree of hydration.

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Abstract  

The thermal behavior of perfluorosulfonated membranes of three equivalent mass (EW=910, 1000 and 1100 g eq−1) has been studied for membranes in acid form and in the alkali metal countercations substituted samples. The water contents of the membranes decrease progressively with increasing EW and the countercations charge density. The monovalent cations substitutions increase the membranes thermal stability. DSC curves show a single endothermic peak around 120�C that give low peak temperature for low EW and high peak temperature for large cations size. The membrane mechanical properties changed for different EW and temperatures of membranes. Stress-strain analysis showed that K+ substituted membranes at both temperatures present a highest YM compared to the other alkali cation substitutions. The thermal properties of perfluorosulfonated membranes depend on the water contents, cation size, temperature and also on EW value.

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Abstract  

The thermal decomposition of Nafion has been studied by means of high-resolution and constant heating rate thermogravimetry (TG), under nitrogen and synthetic air atmospheres. Nafion membranes have been studied in acid and salt (alkali chlorides) forms. The TG curves of Nafion with alkali countercations show similar profiles, whichever the atmosphere employed. The kinetics of thermal decomposition of the Nafion-Cs+ has also been studied. The method employed to calculate the kinetic parameters and to estimate the polymer lifetime from the data was based on Kissinger's method.

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Abstract  

We determined 137Cs concentrations in deep water samples of the subtropical gyre in the South Pacific collected during the BEAGLE2003 cruise. This was done at an underground facility to achieve extremely low background γ-spectrometry, and we, therefore, obtained reliable values of 137Cs activity in the deeper layers. 137Cs activity in the layers between 2000 and 4500 m ranged from 7 ± 4 mBq m−3 to 25 ± 11 mBq m−3. The inventory of 137Cs in the water column from 2000 m to the sea bottom was estimated to be 20 ± 8 Bq m−2 to 94 ± 41 Bq m−2 in this region.

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