Evidence of fluoride oxidation for development of the electrochemically-induced crystallization observed in lead oxyfluoroborate glasses

Abstract

This work reports on a distinct experimental procedure conceived to closely approach the question of development of crystallization in lead oxyfluoroborate glasses in the presence of an electric field. After proposing earlier that this phenomenon should involve occurrence of redox-type electrochemical reactions occurring at the electrodes, it was in fact recently shown that a direct contact of the glasses with both the cathode and anode revealed essential, provided that crystallization did not develop when ions migration to these electrodes became frustrated. The present study demonstrates that, even in Pt,Ag/Glass/YSZ:PbF 2 /Ag,Pt-type electrochemical cells subjected to electric field action, where YSZ:PbF 2 represents composite-like mixtures (formed by Y 2 O 3 -doped ZrO 2 and PbF 2 ) placed between the glass and anode, crystallization was observable in given cases. In summary, supported by (micro)structural and electrical characterizations, clear evidence is provided here that, besides Pb 2+ reduction at the cathode, crystallization really involves simultaneous F − oxidation at the anode, completing thus the whole redox electrochemical reaction so far postulated. In these cases, F − migration to the anode was achievable following PbF 2 percolative-like paths through the YSZ:PbF 2 mixtures.

Sinterização de vidro soda-cal-sílica comercial assistida por campo elétrico

“…Os estudos que utilizam a aplicação de campo em vidros estão relacionados à utilização de peças maciças para diminuir a temperatura de cristalização [11,12], ou em vidros fundidos durante o resfriamento para orientar o crescimento de cristais [14][15][16]. O vidro também pode ser utilizado como aditivo para a sinterização por Flash de cerâmicas cristalinas isolantes elétricas [17,18].…”

“…A aplicação de campo elétrico em vidros vem sendo utilizada para diminuir as temperaturas de cristalização [11,12] e amolecimento (ou softening) [13], assim como orientar o crescimento de cristal [14][15][16]. Vidros também podem ser utilizados como aditivo auxiliar da sinterização com campo elétrico de cerâmicas cristalinas de baixa condutividade iônica [17,18], como a alumina, diminuindo a temperatura de sinterização.…”