Akademik Veri Yönetim Sistemi
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, cilt.140, sa.6, ss.2667-2672, 2020 (SCI-Expanded)
A method was proposed to use XRD-data for thermal analyses of crystalline solids. Therefore, the XRD-pattern was recorded for natural and preheated sepiolite samples at the different temperatures in the interval of 25-800 degrees C for 4 h. The temperature-dependent intensity (I) of the most characteristic 001 reflection was used as a crystallite variable. The assumed parameters k=-( partial differential Iand K=mml:mfenced close=")" open="(1-x/x were calculated for each heating temperature, where I-0 is the intensity for the natural sample and x=I/I0is the relative crystallite of the heated ones, since the k and K supply Arrhenius equation and van't Hoff equation behave as reaction rate constant and equilibrium constant for a chemical reaction, respectively. Arrhenius plot showed that the degradation has three kinetic steps. Two of these are due to the stepwise (1, 2) dehydration and third (3) originated from dehydroxylation of sepiolite crystal. Three activation energies were obtained such as E1#=8.6 kJ mol(-1), E2#=28.5 kJ mol(-1), and E3#=124.8 kJ mol(-1) from the slope of three intersected straight lines which are plotted according to the Arrhenius equation. Otherwise, van't Hoff plot indicated that the degradation has two thermodynamic steps which are due to the dehydration (1, 2) and dehydroxylation (3). The basic thermodynamic relationship, Delta G0=Delta H0-T Delta S0, for these steps are Delta G1,20=46,933-65.7Tand Delta G30=143,491-177.1T respectively. Finally, the spontaneous tendency for the thermal degradation was discussed.