Temperature dependence on addition of urea and its related compounds on formation of neodymium condensed phosphates

Urea (CO(NH2)(2)) and its related compounds (biuret: NH(CONH2)(2) and cyanuric acid: (CONH)(3)) were mixed with phosphoric acid (H3PO4) and neodymium oxide (Nd2O3). The thermal behavior of these dried mixtures was estimated by differential thermal analyses, X-ray diffraction, and Fourier-transform infrared spectroscopy. Furthermore, specific surface area of phosphates was calculated by BET method using nitrogen adsorption. The addition of urea prevented the crystal growth of Monazite-type NdPO4 in samples at P/Nd = 2 heated at 450 and 550 degrees C, and promoted the dehydration-condensation reaction of phosphate. Urea was considered to be decomposed at 400-450 degrees C in these systems. The decomposition of urea was considered to be related to the formation of neodymium dihydrogenphosphate and then this phosphate transformed to neodymium polyphosphate. The ratio of urea and phosphorus had influence on the promotion of the dehydration-condensation reaction. Thermal behavior of sample added with biuret or cyanuric acid was also investigated. (C) 2004 Elsevier Ltd. All rights reserved.