ON THE THERMAL-DECOMPOSITION OF (NH4)2[FEF5(H2O)] ON QUASI-ISOBARIC CONDITIONS

The thermal decomposition of (NH4)2[FeF5(H2O)] was investigated by thermal and X-ray analysis. Quasi-isobaric conditions are realized by using a special crucible which guaranteed a pressure of the gaseous products of 70 kPa. In dependence on the partial pressure alpha- or beta-(NH4)2FeF5 were formed during dehydration. Further intermediate products are NH4FeF4, (NH4)1(-x)FeF4-y, and (NH4)(y)FeF3 with x = 0.15-0.20 and y = 0.12-0.15. Structural relations between these phases are discussed and comparable considerations to the Al system were made.