THERMAL-BEHAVIOR OF AMMONIUM POLYPHOSPHATE-INORGANIC COMPOUND MIXTURES .2. MANGANESE-DIOXIDE

The chemical interaction between ammonium polyphosphate (APP) and mang anese dioxide (MnO2) was studied by thermogravimetry with linear heati ng. The products of interaction were collected at successive steps of weight loss and analysed by X-ray diffraction (on crystalline products ) or by chemical analysis (on amorphous products). It was found that M nO, starts to interact with APP at the beginning of the thermal decomp osition of APP at 270-280 degrees C. At the onset of weight loss of th e APP/MnO2 mixtures, manganese(VI) is reduced to manganese(III) and (I I) producing MnNH4P2O7 and Mn(NH4)(2)(PO3)(4) respectively. Ammonia, w hich is partially reduced to nitrogen, is evolved from PP. The formati on of MnNH4P3O9 and then Mn2P4O12 is observed on further heating of th e mixtures to 560-570 degrees C. The content and ratio of the products of reaction depend on the temperature and the ratio of components in the initial APP/MnO2 mixtures. Assignment of the X-ray powder diffract ion peaks and an estimation of the lattice parameters have been made o n orthorhombic MnNH4P3O9 (n = 7.357(3), b = 12.186(8), c = 9.390(5)Ang strom, space group P-mcn).