| Surface diffusion was studied by means of grain boundary grooving technique. The surface selfdiffusion coefficient of copper(D_s) has been measured between 847˚and 1,069℃ for six different orientations. These were the (111), (110), (100) and three higher index surfaces. The activation energy for D_s (designated Q_s) was found to be about 49 kcal per mole for all six surfaces, and Do about 2×10⁴sq cm per sec. At any temperature D_s varied by no more than a factor of three over these orientations. It is shown that, if the free energy of a surface atom is uniquely determined by its number of nearest neighbors, it follows from the principle of microscopic reversibility that Q_s should have the same value for all surface orientations, and D_s should vary little with orientation. This model also suggests that for clean fee metals Q_s=2/3 Hv(heat of vaporization). This is true for copper. These results will be supported by the results of radio isotope technique on copper surfaces performed by author at high temperatures. |
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