Irreversible thermal transformation kinetics of halloysite to metahalloysite using XRD analysis

Dehydration of halloysite (Hly) to metahalloysite (m-Hly) was examined by X-ray diffraction (XRD). The Hly samples heated in temperature range of 80-400 ?. The heating time (t) at each temperature was changed up to 420 min. The peak intensities (I) for the basal spacing (d(001)) of Hly (1.0 nm) and m-Hly (0.7 nm) were determined. The variation of the intensities with the heating time was evaluated for each temperature. The full heating time (t(f)) for each completed crystal transformation was determined graphically and used as kinetic variable. The rate constant (k) was evaluated as k=1/tf for the crystal transformation assumed from the zeroth order (n=0). It has been observed that the drawn lnk-1/T graph conforms to the Arrhenius equation in the form of lnk=-3247.2/T+3.4215. The activation energy was calculated as E-#=27 kJ mol(-1) from the slope of this line equation, and the frequency factor from its intercept was calculated as A=31 min(-1).