Microwave intensified synthesis of regular shaped sodium bisulfate crystal

• Microwave-intensified crystallization of sodium bisulfate was investigated.
• Transformation of crystal phases was relevant to water content.
• The dehydrating efficiency was enhanced greatly by microwave heating.
• Regular shaped sodium bisulfate crystal could be obtained using microwave.
• The possible mechanisms of regular crystal growth were proposed.

Microwave was employed to prepare sodium bisulfate crystal using equimolar quantities of sulfuric acid and sodium sulfate. The effects of microwave on heating behavior and water content changes were studied by monitoring the temperature and weight. To embody the positive effect of microwave on dehydrating speed and crystal transformation, thermal conductive heating was compared. The phase transformation and micro morphology of the product were characterized by X-ray diffraction and scanning electron microscopy. It was observed that crystallization with lower water content obtained higher percentage of sodium bisulfate. Microwave can significantly speed up dehydration and the dehydrating efficiency increase over the output power. According to the phase transformation process, a possible mechanism for H+-dependent sodium bisulfate crystallization is proposed. Moreover, regular crystal with greater size was obtained under microwave irradiation. The specific phenomenon may be ascribed to the oriented attachment of hydrogen sulfate in alternating electromagnetic field.