Effect of interfacial energies on heterogeneous nucleation

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Abstract
From experimental evidence it has previously been shown that heterogeneous nucleation is non-reciprocal and therefore that the balance of interfacial energies is a controlling factor. If σNL > σNS + σSL the nucleus S can grow from the liquid L on the substrate N. When nucleation takes place the contact angle θ is small and there is epitaxy between the nucleant and the nucleus that reduces the σNS to very low values so that, as a first approximation, heterogeneous nucleation can be expected when σNL > σSL. Interfacial energies σSL are roughly proportional to the melting point, and high melting point phases usually nucleate lower melting phases. The contrary may happen if the low melting phase has a low symmetry crystal. Nucleation can take place on high index faces of this crystal because, although its average σNL is lower than the σSL of a higher melting point, high symmetry crystal, the σNL of its high index faces may be higher than the σSL. MST/845