CONDITIONS OF THE FORMATION OF RARE EARTH PHOSPHATES AND THE COLORS OF THEIR POWDERS.

Abstract

Rare earth oxides, such as La//2O//3, Pr//6O//1//1, Nd//2O//3, and Sm//2O//3, can react with phosphoric acid to give four kinds of rare earth phosphates. While in the reaction of CeO//2 with phosphoric acid, there are formed five kinds of phosphates (orthophosphate CePO//4, pyrophosphate CeP//2O//7, two types of catena-polyphosphate Ce(PO//3)**3 and CE(PO//3)//4, and ultraphosphate CeP//5O//1//4). The formation of these products in the CeO//2-H//3PO//4 system are notably different from these in other systems, showing that cerium (III) phosphates as well as cerium (IV) phosphates can exist stably. It can be seen from the X-ray diffraction patterns that each corresponding phosphate (ortho, catena-poly, and ultraphosphates) of lanthanum, cerium (III), praseodymium, neodymium, and samarium is isomorphous.