## 4 Discussion  
The criterion of thermodynamic probability of anodic processes in binary alloys is applicable for the process of dissolution of tungsten alloys with a more electronegative component (rhenium). The anode reaction involving a component with a more negative potential has the highest rate. For a tungsten-rhenium alloy, the process scheme is as follows:  
\[\mathrm{W(alloy\ W-Re)\ -\ ne^{-}=W^{n+}} \tag{1}\]  
\[\mathrm{Re(alloy\ W-Re)\ -\ ne^{-}=Re^{n+}} \tag{2}\]  
This process is accompanied by selective dissolution of rhenium from the surface layer of the alloy and the formation of a developed surface structure. The linear decrease in the \begin{table}
\begin{tabular}{c c c c c c} \hline
**Figure 5A** & **Component** & **Spectrum 1** & **Spectrum 2** & **Spectrum 3** & **Spectrum 4** \\ \hline  & W, wt.\% & 88.25 & 88.75 & 86.22 & 86.31 \\  & Re, wt.\% & 11.75 & 11.25 & 13.78 & 13.69 \\ \hline
**Figure 5B** & **Component** & **Spectrum 1** & **Spectrum 2** & **Spectrum 3** & **Spectrum 4** \\ \hline  & W, wt.\% & 90.66 & 90.73 & 88.63 & 88.36 \\  & Re, wt.\% & 9.34 & 9.27 & 11.37 & 11.64 \\ \hline \end{tabular}
\end{table} 
Table 2: EDS analysis of cross-section of the sample after dealloying. Figure 5: SEM images of cross-section of the sample after dealloying: (**A**) alloy after 3000 s; (**B**) alloy after 6000 s.  
thickness of the electrode and the difference in the partial diffusion coefficients of the alloy components were taken into account. Selective anodic dissolution of one of the alloy components is quantitatively characterized by the coefficient of selective dissolution. \[\mathrm{z_{A}}=\frac{(\mathrm{C_{W}}/\mathrm{C_{Re}})_{\mathrm{solution}}}{( \mathrm{C_{W}}/\mathrm{C_{Re}})_{\mathrm{alloy}}} \tag{3}\]  
A thermodynamic vacancy mechanism of this process has been developed for low-temperature electrolytes [33]. Based on the Darken dependence of the logarithm of the mutual diffusion coefficient from the inverse temperature, the value of the self-diffusion coefficient at 298K is estimated. \[\mathrm{D}=\mathrm{D_{0}}\cdot\mathrm{exp}\left(-\frac{\mathrm{E}}{\mathrm{ RT}}\right) \tag{4}\]  
The external flow is caused by two effects: a change in the concentration gradient \(\mathrm{C_{Re}}\) and a decrease in the thickness of the electrode, causing the dissolution of the electronegative component. The rate of dissolution of the alloy \(\mathrm{q_{Re}^{0}}\) (mol/cm\({}^{2}\)s) is given by the following equation:  
\[-\mathrm{q_{Re}^{0}}=-\mathrm{D}\frac{\mathrm{Q_{Re}}}{\mathrm{\partial x}}( 0,t)-\mathrm{C_{A}}(0,t)\mathrm{U_{L}}(t) \tag{5}\]  
where \(\mathrm{D}\) is the diffusion coefficient, \(x\) is the initial flat surface of the electrode, \(t\) is the time, and \(\mathrm{U_{L}}\) is the rate of linear loss of the alloy (cm/s). \[\mathrm{U_{L}}=\mathrm{q_{Re}}\mathrm{V_{alloy}} \tag{6}\]  
where \(\mathrm{V_{alloy}}\) is the molar volume of the alloy. The anodic dissolution of rhenium at the alloy-solution boundary, which is a powerful source of vacancies, where vacancies are absorbed by dislocations, and its diffusion from the depth of the alloy to the boundary cause the formation of vacancies in the alloy volume. There are two sources of vacancies with a total flow:  
\[\mathrm{J_{V}}=\mathrm{J_{V}^{\prime}}\uparrow\downarrow+\mathrm{J_{V}^{ \prime\prime}}\uparrow \tag{7}\]  
where \(\mathrm{J_{V}^{\prime}}\uparrow\downarrow\) is the flow of excess or lack of vacancies in comparison with the equilibrium concentration in the alloy volume, and \(\mathrm{J_{V}^{\prime\prime}}\uparrow\) is the flow of vacancies formed directly due to the process of selective dissolution of rhenium. The change in the total volume of the formed voids (negative crystals) as a result of selective dissolution can be calculated:  
\[\mathrm{\Delta V}=\mathrm{C^{-1}}\int_{0}^{t}\mathrm{J_{V}(t)dt} \tag{8}\]  
The excess of vacancies at the boundary causes the linear loss of the alloy and the decrease in the thickness of the electrode. Vacancies can both move to the border and merge into the pores.