KINETICS OF BORAX DEHYDRATION BY THERMAL ANALYSIS

Abstract

Anhydrous borax is an important industrial product obtained either from borax decahydrate or borax pentahydrate. The kinetics of dehydration of borax pentahydrate using TG and DTA techniques was studied. It was shown that 2.25 mole of the crystal water removes in the first step with zero order kinetics in the temperature range between 382 and 433 K. The removing of the remaining water was completed at 733 K with the second order reaction in the second steps. Arrhenius form of reaction rate constant for step 1 and 2 were also determined. They are: 5.37 10 exp( 16141.5 ) 15 k0    T and 1.4exp( 1575.6 ) k2   T respectively, where T is absolute temperature in K. The total activation energy calculated from Coats-Redfern method was found to be 147.3 kJ/mol. It was also found that this value is in a good agreement with those calculated from Kissinger and Doyle methods.