| Grant number: | 11/10564-3 |
| Support Opportunities: | Regular Research Grants |
| Start date: | April 01, 2012 |
| End date: | March 31, 2014 |
| Field of knowledge: | Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials |
| Principal Investigator: | Ana Candida Martins Rodrigues |
| Grantee: | Ana Candida Martins Rodrigues |
| Host Institution: | Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil |
Abstract
Ionic transport in glasses is very sensitive to their chemical composition. The control of this property is especially important for the development of highly conductive glasses to be applied in electrochemical energy storage or selective membranes. A spectacular enhancement of several orders of magnitude in ionic transport is obtained by dissolution of halogenated salts in a glass. However, the origin of this behavior remains unknown. For instance, glasses in the xAgI(1-x)AgPO3 series are well known as good silver ions conductors. Their ionic conductivity at room temperature as a function of AgI concentration (x) show an increase of several orders of magnitude when x varies from 0 to 0.5, though the total concentration of silver ions remains constant. This fact has been the subject of intense study in the 70's and 80's and, because of that, ionic conductivity data and structural studies on this glass system are largely available in literature. To investigate these large variations in conductivity, we propose a thermodynamic approach, similar to those used for liquid electrolytic solution of weak electrolytes. Basically, using dissociation equilibria, this approach allows to correlate ionic transport to the partial free energy (or thermodynamic activity) of the dissociating species. This approach, currently denominated "weak electrolyte theory", has been already successfully applied in the 70's to explain the variation in ionic transport in glasses with the concentration of network modifier. We propose, in the present project, to extend it to glasses containing halogenated salts. For this purpose, we suggest to assemble electrochemical cells whose electrolyte is the xAgI(1-x)AgPO3 glass, with different values of x. The EMF generated by these cells will provide the thermodynamic activity of AgI in the glass. These measured values will be then correlated with the ionic conductivity, for glasses with different concentrations of AgI. The hypothesis of the "weak electrolyte theory", eg., the existence, in the ionic vitreous system, of large variation of thermodynamic activity of the dissociating species that generates large differences in the number of effective charge carriers, will be then tested. (AU)
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