ECE 350 Homework Set #7

Due Monday Sept. 28

1. The undercooling of iron has been reported to be 538°C . ¹ The melting temperature of iron is 1811 K. The surface tension of iron is given by the equation

Taking the temperature dependence of the surface energy into account modifies equation 4.2 of the text to the following:

Notice that you must convert the latent heat of melting from kJ/mol to kJ/m³ by dividing by the molar volume. The density of liquid iron at the melting point is 7.015 g/cm³.

a. Calculate the critical radius of an iron nucleus at the maximum observed undercooling.

b. Calculate the number of iron atoms in the critical nucleus. Assume the density of the solid iron is 7.02 g/cm³.

2. Calculate the radii of the tetragonal and octahedral interstitial voids in the BCC lattice of Fe (lattice parameter a = .286nm). Researcher's agree that the carbon atom occupies the octahedral type voids in the BCC lattice. Does this agree with your calculations?

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1. J. Schade, A. McLean, and W. A. Miller, "Surface Tension Measurements on Oscillating Droplets of Undercooled Liquid Metals and Alloys" Undercooled Alloy Phases, Proceedings of the 1986 Hume-Rothery Memorial Symposium, March 2-6, 1986, edited by E. W. Collings and C. C. Koch, The Metallurgical Society, pp. 233-248.