Effects of Ultrasound and Its Amplitude on the Metastable Zone Width, Induction Time, and Nucleation Kinetics of Pyrazinamide in Acetone

A systematic investigation is carried out to analyze the effect of ultrasonic amplitudes (10, 30, and 50%) on the metastable zone width (MSZW) and induction time (t_ind) for unseeded batch cooling crystallization of pyrazinamide from its acetone solution. The MSZW is measured at five different saturation temperatures (293.15, 298.15, 303.15, 308.15, and 313.15 K) with different cooling rates. Five cooling rates (30, 24, 18, 12, and 6 K/h) were selected for the silent case, and three cooling rates (24, 18, and 6 K/h) were selected for sonicated cases with three different ultrasonic amplitudes (10, 30, and 50%). The induction time is measured at five different supersaturation ratios (1.05, 1.10, 1.15, 1.20, and 1.25) at three different saturation temperatures (293.15, 303.15, and 313.15 K) for both silent and sonicated cases. For the silent cases, at a given saturation temperature, the MSZW increases by 63–73% with increase in cooling rate from 6 to 30 K/h. Again, at a given cooling rate, the MSZW decreases by 19–40% with increase in saturation temperature from 293.15 to 313.15 K. For sonicated cases, at a given saturation temperature and cooling rate, the MSZW is decreased by almost half at a higher ultrasonic amplitude (50%). The MSZW data are analyzed using four different approaches (Nyvlt’s approach, Kubuto’s approach, Sangwal’s self-consistent Nyvlt-like equation approach, and Sangwal’s classical three-dimensional nucleation theory approach) to calculate various nucleation parameters. The application of ultrasound reduces the apparent nucleation order significantly, and the nucleation rate was increased by 2–3 times compared to the silent cases with increasing ultrasonic amplitude. The data obtained from the induction time are analyzed using classical nucleation theory to calculate important nucleation parameters such as interfacial energy (1.05–1.29 mJ/m²) and various nucleation parameters such as nucleation rate (5.23 × 10²²–7.28 × 10²⁵ #/m³ s), critical radius (0.34–1.91 Å), and critical free energy (0.05 × 10²⁰–1.91 × 10²⁰ J). Furthermore, the concept of nucleation potential is used to estimate MSZW from the measured induction time data. The estimated values are seen to be 80–85% accurate at low saturation temperatures and 66–72% accurate at higher saturation temperatures for the pyrazinamide–acetone solution.