On the high-temperature phase transition of RbH2PO4 -: A polymorphic transition?

X-ray diffraction, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the dynamic process of dehydration and the high-temperature phase transition at T-p = 98.5 +/- 26.5 degrees C (often stated as 86 degrees C) in rubidium dihydrogen phosphate (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 ''onset of partial polymerization at reaction sites distributed on the surface". (C) 1998 Elsevier Science Ltd. All rights reserved.