LAYERED ZIRCONIUM-TIN PHOSPHATES .1. CHEMICAL AND PHYSICAL CHARACTERIZATION

Crystalline zirconium-tin phosphates of formula Zr(x)Sn1-x(HPO4)2.H-2O (0 less-than-or-equal-to x less-than-or-equal-to 1) were synthesized and characterized in terms of their physical and chemical properties. From X-ray and thermal analysis it was found that solid solutions are formed for every composition. The tin content in mixed phases has a marked influence on thermal behaviour, speeding up the kinetics of transformation to layered pyrophosphates (L-Py). Mixed phosphates posses surface areas which are markedly higher than pure phosphates. The method of ammonia thermodesorption (TPD) was employed for the acidity measurements. This method has allowed the evaluation of the concentration and strength of surface acid sites present on the external surface of L-Py or mixed hydrogen-L-Py phases obtained after a variety of thermal treatments. The acid strength of L-Py phases increases with increasing tin content.