Volume diffusion in pure metals

The self-diffusion coefficients of metals, which describe die movement of atoms widiiti a pure metal, vary over a very wide range of values at any 

The total electrical resistance at room temperature includes tire contribution from scattering of conduction electrons by the vacancies as well as by ion-core and impurity scattering. If the experiment is repeated at a number of high temperarnre anneals, then the effects of temperarnre on tire vacancy conuibu-tion can be isolated, since the other two terms will be constant providing that 

Typical values of the energy to form vacancies are for silver, lOSkJmol and for aluminium, 65.5kJmol These values should be compared with the values for the activation enthalpy for diffusion which are given in Table 6.2. It can also be seen from the Table 6.2 that die activation enthalpy for selfdiffusion which is related to the energy to break metal-metal bonds and form a vacant site is related semi-quantitatively to the energy of sublimation of the metal, in which process all of the metal atom bonds are broken. 

At high temperatures there is experimental evidence tlrat the Anhenius plot for some metals is curved, indicating an increased rate of diffusion over tlrat obtained by linear exU apolation of tire lower temperature data. This effect is interpreted to indicate enhanced diffusion via divacancies, rather tlrair single vacaircy-atom exchange. The diffusion coefficient must now be represented by an Anheirius equation in the form 

Examples of this analysis are given in the data as follows  

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