Equilibrium of the protonic species in hydrates of some heteropolyacids at elevated temperatures

• Published in: Solid state ionics 1991-05, Vol.46 (1), p.103-109
• Main Authors: Mioč, U., Davidović, M., Tjapkin, N., Colomban, Ph, Novak, A.
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Diffusion in solids; Exact sciences and technology; Physics; Theory of diffusion and ionic conduction in solids; Transport properties of condensed matter (nonelectronic)
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/0167-2738(91)90136-Y

Hydrates of three heteropolyacids: 12-molybdophosphoric H 3PMo 12O 40· nH 2O (MoPA· nH 2O), 12-tungstophosphoric H 3PW 12O 40· nH 2O (WPA· nH 2O) and 12-tungstosilisilic acid H 4SiW 12O 40· nH 2O (WSiA· nH 2O) were examined by using thermal analysis, infrared spectroscopy and impedance measurements. These compounds are known as superionic proton conductors and their behaviour was examined as a function of temperature. At the TGA and DSC curves, in the 300–500 K temperature range, transformations were observed at several temperatures. These transformations are partially due to the dehydration process and partially to the change of equilibrium of protonic species (H 3O +, H 2O and OH - and their possible association: H 5O + 2, H 7O + 3, ...), as shown by thermal analysis and infrared spectroscopy.