Ultrasound assisted synthesis of zinc borate

With developing technology the interest in flame retardants is increasing. Zinc borate is one of the most preferred flame retardant with various production methods and it can be used together with other materials. In this study, zinc borate with commercial formula 2ZnO.3B2O3.3.5H2O was synthesized using ultrasound energy. For this purpose, zinc oxide (ZnO) and boric acid (H3BO3) in aqueous solutions were used. The effect of ultrasound parameters on reaction temperature, reaction time and H3BO3/ ZnO ratio was investigated. Also, the physical and chemical characterization of zinc borate synthesized using ultrasound energy were determined to characterize molecular formula, particle structure and thermal behavior. The experiments in stirred batch reactor have been performed with 19 mm ultrasonic probe and 50 W acoustic power at stirring rate of 400 rpm and at certain reaction temperatures. It was determined that the obtained samples have 44.7 % ZnO, 38.8 % B2O3 and 16.5 % H2O as a result of chemical analysis. When XRD and TGA results are analyzed; in the presence of ultrasonic energy obtained products were found to have higher amounts of zinc and water content. Also, it has the formula in the form of 3ZnO.3B2O3.5H2O and 3ZnO.3B2O3.3.5H2O. It has also been observed that the hydrate water amount decreases as the temperature increases. When examined SEM images, it was observed that the samples produced by ultrasound energy has smaller particle size than those obtained by conventional methods and morphological structures of samples changed from disk shape to uniform mixture of disk and rod shapes. According to the results, zinc borates obtained by using ultrasound energy, have higher amounts of hydration water content and smaller particle structure with uniformly distributed. It has more effective flame retardant and smoke suppressing properties than obtained by conventional (silent) methods. In addition, shorter reaction times are enough for satisfactory yields and this possesses significant advantage in terms of cost and time. It is concluded that the use of ultrasonic energy in the synthesis of zinc borate can be applied as a useful method. Keywords: Zinc borate, Ultrasound, Sonochemistry, Synthesis, Flame retardancy