Molecular dynamics studies of the size and temperature dependence of the kinetics of freezing of Fe nanoparticles

• Solid state material synthesis.
• Material structure.
• Experimental study of nucleation in condensed materials.
• Computation study of nucleation in condensed materials.

Molecular dynamics (MD) computer simulations have been carried out and a novel modified technique of Voronoi polyhedra has been performed to identify solid-like particles in a molten nanoparticle. This technique works quite well in analyzing the effects of particle size on nucleation rates of iron nanoparticles in the temperature range of 750–1160 K. Nanoparticles with 1436 and 2133 Fe atoms have been examined and the results are compared with those obtained earlier with Fe331 nanoparticles. Nucleation rates for freezing obtained from MD simulations for Fe2133 vary from 8.8×1034 m3/s to 4.1×1035 m3/s at over a temperature range from 1160 K to 900 K, Rates for. Fe1436 and Fe331 are somewhat higher. Nucleation rates increase as supercooling deepens until the viscosity of the liquid increases sharply enough to slow down the rate. Bt applying classical nucleation theory, the interfacial free energy between solid and liquid cab be estimated From this and other thermodynamic information can be derived a theoretical expression for the size-dependence of the heat of fusion of nanoparticles. Results agreed quite well with those observed in our MD observations. An earlier expression in the literature for this size-dependence was shown to be incorrect. The size dependence of melting point is discussed.

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