Nucleation

https://www.phase-trans.msm.cam.ac.uk/2025/PT-book.html An overview of the fundamental principles of nucleation, focusing on both homogeneous and heterogeneous mechanisms in phase transformations. The sources explain that nucleation involves the formation of a new phase through random thermal fluctuations that must overcome an activation energy barrier related to the interfacial energy. Crucially, heterogeneous nucleation, which occurs at defects or surfaces, is shown to have a significantly smaller activation energy than homogeneous nucleation, making it the dominant mechanism in most practical scenarios. Equations are provided to quantify the critical nucleus size and the activation energy in both homogeneous and heterogeneous contexts. Finally, the texts discuss practical applications, such as the use of nucleating agents (inoculants) to deliberately stimulate heterogeneous nucleation in processes like welding and steel production to achieve desired material microstructures.