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Many thermally excited reactions are described by | |||||||
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With Ea = activation energy (or enthalpy) of the process, and kT with its usual meaning. | |||||||
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This equation governs not only the equilibrium concentration of point defects, but also, for example, the emission of electrons from a hot wire or the growth of bacterial cultures. | |||||||
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An Arrhenius plot of this equation is simply a plot of log y (or ln y) over 1/T (or 1/kT). This produces a straight line: | |||||||
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The (extrapolated) cut with the ln y-axis gives directly the value of the pre-exponential factor y0, and the slope of the straight line gives the activation energy. | |||||||
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An Arrhenius plot is extremely useful if data are determined experimentally. It shows at a glance if the scatter of the data points is small or large, if we have an Arrhenius relation at all (i.e. a straight line), and if we have enough data points to get unambigous values for the activation energy and the pre-exponential factor. | |||||||
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In the following Java module, you can play a bit with the representations of the exponential law. | |||||||
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Shown is the function | |||||||
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in a direct plot and in an Arrhenius plot. You can change the values of the parameters and see what happens. | |||||||
2.1.1 Simple Vacancies and Interstitials
2.2.1 Extrinsic Point Defects and Agglomerates
Table of JAVA-Applets "Defects in Crystals"
© H. Föll (Defects - Script)