Chemical preparation, thermal behavior, kinetic and IR studies are given for the cyclotriphosphate Mn3(P3O9)2.10H2O. Mn3(P3O9)2.10H2O, which has already been studied, is monoclinic P21/n with the following unit-cell dimensions : a = 9.631(5)Å,b = 18,173(7)Å, c = 7,976(4), = 109,438(4)° and Z = 2. The study of the structural modifications of cyclophosphates of manganese from Mn3(P3O9)2.10H2O to Mn2P4O12 during thermal behavior process by infrared spectroscopy has never been performed. It’s the first time where a cyclotriphosphate P3O9 is converted to a cyclotetraphosphate P4O12 by thermal dehydration. The thermal behavior of Mn3(P3O9)2.10H2O has been investigated and interpreted by comparison with IR absorption spectrometry, X-ray diffraction experiments, chemical analyses, thermal analyses (TGA-DTA) and differential scanning calorimetry (DSC). Mn3(P3O9)2.10H2O is stable, in the conditions of temperature and pressure of our laboratory, until 70°C. It is impossible to dehydrate Mn3(P3O9)2.10H2O without breaking its rings P3O93- and leading to amorphous compounds in X-ray diffraction and IR absorption spectrometry. The final product of the dehydration and calcination of Mn3(P3O9)2.10H2O cyclotriphosphate, under atmospheric pressure, is its cyclotetraphosphate Mn2P4O12. Mn2P4O12 is prepared otherwise by dry way.
