Diffusion coefficient copper oxide

A number of metals, such as copper, cobalt and h on, form a number of oxide layers during oxidation in air. Providing that interfacial thermodynamic equilibrium exists at the boundaries between the various oxide layers, the relative thicknesses of the oxides will depend on die relative diffusion coefficients of the mobile species as well as the oxygen potential gradients across each oxide layer. The flux of ions and electrons is given by Einstein s mobility equation for each diffusing species in each layer... 

If the range of homogeneity of the reaction product is sufficiently narrow, then the average diffusion coefficient as defined in eq. (8-9) can be calculated by means of defect thermodynamics, if it is assumed that the defects behave as the solute in ideally dilute solutions. In section 4.2 it was shown how the concentrations of the defect centers depend upon the component activities for a given type of disorder in binary ionic crystals. As an example, let us consider the formation of copper (I) oxide on copper sheet at 1000 °C in an oxidizing atmosphere whenis about 1 torr. The following defect equilibrium can be written ... 

Kingery et al. [10a] have collected the experimental results for cation and anion self-diffusion coefficients in various oxides. For instance, the rate of diffusion of copper in CU2O, a modifier, is six orders of magnitude larger than that of aluminum in AI2O3, a network former when the aluminum is four coordinate. This result is for a temperature of approximately 1500°C, but the relative relationship is expected to hold at room temperature. This finding also supports the postulate that network modifiers can recrystallize more easily than network formers. 

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