Sunday, November 27, 2005

Another update: Melting mechanisms!

Do you rememeber the earlier post about melting mechanisms? Here is a very interesting letter by Wang et al published in the May 2005 issue of Philosophical Magazine Letters [vol. 85, no. 5, pp. 213-219(7)], in which they propose a vacancy decomposition induced lattice instability to explain melting. Here is the abstract:
Vacancy decomposition kinetics in crystals at elevated temperatures is analysed. It is found that lattice instability is induced by a significantly enhanced vacancy decomposition at a critical temperature ( T *). The critical temperature coincides with the kinetic instability limit (kinetic limit of superheating) of crystals in a variety of metals determined from the homogeneous nucleation catastrophe model.
While we are on the topic, there is also this paper by Mei et al published in the April 2005 issue of Philosophical Magazine Letters [vol. 85, no. 4, pp. 203-211(9)]; this one is about the kinetic limit of supercooling induced by semicoherent interfaces. Here is the abstract:
The superheating behaviour of embedded particles induced by semicoherent interfaces has been observed in many circumstances. In this paper, a phenomeno- logical model for melt nucleation on misfit dislocations at a semicoherent interface is proposed. A kinetic limit for semicoherent-interface-induced superheating, which is in good agreement with the results of experiments and computer simulations, is derived from this model. Calculations and analyses based on the model reveal that melting prefers to initiate at the semicoherent interface and that superheating of embedded particles is possible for a melt nucleation contact angle less than 90°. Among the matrix-dependent parameters, the contact angle and the shear modulus of the matrix are found to be dominant in determining the superheating of embedded particles.
Not surprisingly, both these papers originate from the same group in Shenyang, China, and both are worth taking a look at.

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