Synthesis, crystal structure and dehydration kinetics of NaB(OH)4•2H2O

Abstract

Sodium metaborate tetrahydrate (NaB(OH)(4)center dot 2H(2)O) was synthesized by reaction of anhydrous borax (Na2O center dot 2B(2)O(3)) with sodium hydroxide (NaOH) under conditions at 90 degrees C for 150 min. The structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM) and Thermogravimetric (TG) analyses. Moreover, dehydration kinetics of NaB(OH)(4)center dot 2H(2)O was carried out under non-isothermal conditions and the Coats-Redfem method was applied to analyze the TG data for calculation of activation energies (E-a) and pre-exponential factors (k(o)) for different heating rates. It was determined that dehydration of sodium metaborate tetrahydrate occurred in five steps. According to the Coats-Redfern non-isothermal model, E-a and k(o) were calculated as 50.89 kJ/mol and 26x10(4) min(-1) for region 1, 18.51 kJ/mol and 0.87x10(3) min(-1) for region II, 15.72 kJ/mol and 0.52x10(3) min(-1) for region III, 4.37 kJ/mol and 0.04x10(3) min(-1) for region IV and 37.42 kJ/mol and 8.56x10(3) min(-1) for region V, respectively.