Determination of metastable zone width of potassium sulfate in aqueous solution by ultrasonic sensor and FBRM

•Effects of cooling rate, stirring rate and impurities on MSZW are investigated.•Nývlt-like equation and 3D nucleation approach estimate MSZW of K2SO4 solution.•The accuracy and sensitivity of ultrasonic sensor are similar with FBRM on MSZW.

The metastable zone width (MSZW) and nucleation kinetics of potassium sulfate in the aqueous solution were investigated. MSZW was measured using both the ultrasonic velocity sensor and the focused beam reflectance measurement (FBRM) at different cooling rate, stirring rate and impurities concentration (aluminum ions and silicon ions), and the effects of these conditions on MSZW were discussed in details. In addition, the accuracy and sensitivity of detectors to measure the nucleation temperature of potassium sulfate in the aqueous solution were compared between the ultrasonic velocity sensor and FBRM over a wider range of operating conditions. Although two detectors measured MSZW with an acceptable accuracy, the ultrasonic velocity sensor had a higher sensitivity to the phase transition of potassium sulfate in solution since it directly detected the concentration change of potassium sulfate in solution. Furthermore, both self-consistent Nývlt-like equation method and classical 3D nucleation theory approach were applied to estimate MSZW of potassium sulfate in aqueous solution. According to these classical theories, the nucleation kinetics parameters were calculated based on the measured MSZW data for potassium sulfate aqueous solution with 40 °C, 50 °C and 60 °C saturation temperature, respectively. It was found two approaches could describe MSZW of potassium sulfate aqueous system very well.