## 3 Results  
Linear voltammetry was used to study the anodic process occurring on individual rhenium, tungsten, and tungsten-rhenium electrodes. Figure 1 shows that rhenium was dissolved in all solutions according to the mechanism of the delayed ionization. The active dissolution stage began at the potential of 600 mV relative to the silver chloride electrode. At current densities below 20 A/m\({}^{2}\), the addition of potassium chloride practically did not affect the course of the polarization curve. However, at high current densities above 2500 A/m\({}^{2}\), the addition of potassium chloride caused electrode salt passivation and the formation of potassium chlorrenate. The process taking place on the tungsten electrode was accompanied with significant polarization. The active stage began at the potential of 1100 mV (SCE) and was accompanied by abundant gas release. At the same time, there was no decrease in the mass of the electrode itself. Therefore, tungsten dissolution and the active release of gaseous oxygen were not observed. No pronounced processes were registered in solutions 1 and 2 for the tungsten-rhenium alloy. Pronounced peaks associated with the selective dissolution of rhenium were observed in solutions 3 and 4. The potential of rhenium release in hydrochloric acid solutions was determined on the basis of the obtained voltage dependences. The active dissolution stage of rhenium began at a potential of 600 mV (SCE) for both individual rhenium and the tungsten-rhenium alloy. The extraction of rhenium from a tungsten-rhenium alloy depending on the processing time was carried out using chronoamperometry at a constant potential (Figure 2). The samples of the tungsten-rhenium alloy after potentiostatic dealloying were subjected to X-ray phase analysis using a Rigaku D/MAX-2200 VL/PC X-ray diffractometer (Rigaku, Japan) (Figure 3). It was found that after dealloying, new phases (for example, an oxide film) were not formed on the surface of the samples. This indicates the absence of the process passivation and favorably affects the depth of extraction of rhenium from the alloy. Figure 1: The data of linear voltammetry in different solutions: (**a**) Solution 1; (**b**) Solution 2; (**c**) Solution 3; (**d**) Solution 4. Figure 2: Chronoamperogram of tungsten–rhenium alloy dissolution. To determine the change in the alloy composition, SEM studies of the samples' surfaces were carried out using energy-dispersive X-ray spectroscopy (EDS) with the TESCAN MIRA 3 LMU (Figure 4). Figure 4 shows that with the increase in the duration of the electrolysis, the sample surface dissolved selectively, forming a rough surface. The EDS spectra confirmed by linear voltammetry demonstrate that at a given potential, selective dissolution of rhenium occurs. In the first 3000 s, the process of active dissolution of rhenium proceeds and a strong change in the surface occurs. With the continuation of the electrolysis, the diffusion of rhenium ions from the electrode into the electrolyte bulk is hampered by the emerging bimodal structures, which leads to a slowdown but not to an interruption in the dealloying process. The EDS spectra of the sample after 6000 s exposure confirm this. To confirm the EDS data,  
Figure 4: Microstructure of initial alloy (**A**), alloy after 3000 s exposure in solution (**B**), and alloy after 6000 s exposure in the solution (**C**). Figure 3: Diffractograms of initial alloy, alloy after 3000 s exposure in the solution, and alloy after 6000 s exposure in the solution. the wavelengths of the samples were also analyzed using an XRF-1800 dispersive X-ray fluorescence spectrometer (Shimadzu, Japan). According to the results of the analysis, the concentration of rhenium in the alloy changed from 15 wt.% in the initial electrode up to 14 wt.% after 3000 s, to 12 wt.% after 6000 s, and to 6.8 wt.% after 30,000 s.  
The dealloying penetration depth was estimated by SEM images of the sample cross-section using EDS with the TSCAN MIRA 3 LMU (Figure 5 and Table 2).