Investigation of effect of mechanical activation on decomposition kinetics of diaspore

Keywords: Diasporitic bauxite, mechanical activation, decomposition kinetics, non-isothermal kinetics. In this study, the effect of mechanical activation on decomposition kinetics of diasporic bauxite from Gaziantep – Islahiye region. Diasporic bauxite (α-AlOOH) was activated mechanically for 30 min by using planetary ball milling. Non-activated and activated diasporic bauxite were analyzed by thermogravimetri with different heating rates (5 – 10 – 15 – 20 °C/min). The decomposition of non-activated was taken place between 300°C and 600°C in one step. On the other hand, the decomposition of activated diasporic bauxite was started at about 150°C and the reaction was completed at 600°C owing to structural disordering during mechanical activation. Non – isothermal decomposition kinetics of non-activated and activated diasporic bauxite was performed by using KAS (Kissenger – Akahira – Sunrose) equation. This is a model – free method. Using thermogravimetric data at different heating rates (β), temperatures of decomposition for each decomposition ratio (α) was deduced and activation energies were calculated from the slopes from ln(β/T2) – 1/T diagram. According to the results obtained in this study, it was concluded that the activation energy for decomposition of non-activated diasporic bauxite is about 220 kJ/mol. This value was in the range of 80 – 140 kJ/mol for 0,1≤ α ≤0,5 because of structural disorderings and then increased to 230 kJ/mol because of the remainder of the undeformed structure.