Acid Ag salts of WPA obtained by neutralization of aqueous
solutions of WPA acid and evaporation of the obtained precipitate,
have a specific surface area and thermal stability close to that of
WPA. They are less hydrated than WPA and partly insoluble in
water. According the physicochemical properties these salts are
between soluble A group and insoluble B group of salts. All the
salts exhibited a cubic structure, with lattice parameter and the ratio
I[110]/I[222] that decreases with Ag mass%. The Raman spectra
have shown that although the Keggin structure of the obtained
salts remains unaltered, there is an interaction between the Ag cation
and tungstophosphate anion mainly through terminal oxygen.
The XRD patterns of the acid salts with number of replaced protons
less than two showed that these salts are two-phase mixtures consisting
of neutral Ag salt and parent acid, as in the case of insoluble
alkali salts of WPA