Department of Chemical and Process Engineering, University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
Department of Chemical and Process Engineering, University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom.
Ultrason Sonochem. 2021 Nov;79:105763. doi: 10.1016/j.ultsonch.2021.105763. Epub 2021 Sep 22.
Ultrasound is known to promote crystal nucleation, but despite significant research there remains uncertainty about how the mechanisms are affected. Despite the proposal of various primary nucleation theories, most studies provide no way to quantify or observe the extent to which primary nucleation is taking place, leaving open the possibility that sonocrystallisation is occurring by a secondary nucleation-driven mechanism. By utilising the widely reported enantiomeric properties of sodium chlorate, the extent to which ultrasound can induce primary nucleation can clearly be observed. It was demonstrated during seeded cooling crystallisation that when stirring the seed similarity was 99.3% on average, indicating secondary nucleation had almost exclusively taken place. The application of ultrasound however, decreased the seed similarity to 85.8% and 92.4% when applying 98 kHz and 200 kHz ultrasound respectively, clearly showing that primary nucleation had been induced and indicating the frequency dependency of the induced primary nucleation. This frequency dependency suggests a link between crystal nucleation and high intensity cavitation collisions and collapses, and the potential existence of a collapse/collision intensity threshold required to induce primary nucleation. In addition, secondary nucleation rate was investigated using anti-solvent crystallisation and was observed to increase with the application of ultrasound, though it appeared frequency independent (between 98 kHz & 200 kHz), suggesting that higher energy cavitational events are less important in inducing secondary nucleation or that a lower cavitation intensity threshold exists compared to primary nucleation.
超声被认为可以促进晶体成核，但尽管进行了大量研究，其机制仍存在不确定性。尽管提出了各种初级成核理论，但大多数研究都无法定量或观察到初级成核的程度，因此超声成核可能是通过二次成核驱动机制发生的。利用广泛报道的氯酸钠对映体性质，可以清楚地观察到超声可以诱导初级成核的程度。在 seeded cooling 结晶中进行的实验表明，当搅拌晶种时，平均相似度为 99.3%，表明二次成核几乎完全发生。然而，当施加 98 kHz 和 200 kHz 超声时，超声的应用将晶种相似度分别降低到 85.8%和 92.4%，这清楚地表明已经诱导了初级成核，并表明了诱导初级成核的频率依赖性。这种频率依赖性表明晶体成核与高强度空化碰撞和崩溃之间存在联系，以及存在诱导初级成核所需的崩溃/碰撞强度阈值的可能性。此外，还使用反溶剂结晶法研究了二次成核速率，并观察到随着超声的施加而增加，但似乎与频率无关（在 98 kHz 和 200 kHz 之间），这表明更高能量的空化事件在诱导二次成核中不太重要，或者与初级成核相比存在更低的空化强度阈值。
