Kinetics of thermal dehydration and decomposition of hydrated chlorides of 3d transition metals (Mn-Cu series). Part-II. Dehydration of FeCl2.4H2O

Regional Research Laboratory, Bhubaneswar-751 013, India
Manuscript received 4 July 2003, revised 9 March 2004, accepted 10 March 2004

An attempt has been made to study the thermal dehydration of FeCI₂.4H₂O in static air as well as in flowing nitrogen atmosphere
using the simultaneous DTA/TG method. In static air or self-generated atmosphere, the salt dehydrates in three
steps losing about 2.0, 1.1 and 1.0 moles of H₂O, respectively which do not undergo any significant change with increase in
heating rate from 2^° to 10^°/min. In flowing nitrogen atmosphere dehydration also takes place in three steps. While the average
loss of 2.1 moles of H₂O in the first step does not show any variation with heating rate, loss in the second step tends to
increase with corresponding decrease in the third step with increase in heating rate. Consequently, the total loss of H₂O in
nitrogen atmosphere in about 0.5 moles higher than in the static air. While in static air nucleation and growth appears to
be the most appropriate mechanistic model, in flowing nitrogen only the first step obeys this model. The other two steps
obey the contracting phase boundary model. A comparison of the thermal dehydration characteristics between MnCl₂ and
FeCI₂ hydrates has been presented.