ON THE HIGH-TEMPERATURE PHASE-TRANSITION OF RBH2PO4 - A POLYMORPHIC TRANSITION

X-ray diffraction, thermogravimetric analysis (TGA) and differential s canning calorimetry (DSC) were used to study the dynamic process of de hydration and the high-temperature phase transition at T-p = 98.5 +/- 26.5 degrees C (often stated as 86 degrees C) in rubidium dihydrogen p hosphate (RDP). Our results indicate that the phase transition at T-p in RDP is not a bulk structural transition (tetragonal to monoclinic) but the onset temperature of the formation of the double salt 2RbH2PO4 . Rb2H2P2O7. Thus, our results support Lee's suggestion that the term high-temperature phase transition should be replaced by the term ''ons et of partial polymerization at reaction sites distributed on the surf ace''. (C) 1998 Elsevier Science Ltd. All rights reserved.