## 3 Results
### The Influence of the Degree of Electrodes Asymmetry on the NP Synthesis with the ODP  
The characteristic side view of an electrode pair installed in the discharge chamber, with end faces located at the angle of 15\({}^{\circ}\) to each other, is shown in Figure 3 for the three cases of the ODP: the initial position before the SD process, during the SD process, and 6 h after the SD process. As it can be seen from Figure 3b, the SD is localized in the region of the shortest distance between the electrodes, which is characteristic of the electric breakdown of gas gaps. Figure 3c shows a significant wear of the beveled end faces of both electrodes during 6 h of processing: the ends were aligned during this time to a parallel state. Photos of the electrodes end faces, SEM images of their surface characteristic areas (types 1-3 in Figure 4a-c) and chemical composition of the obtained surfaces for the cases of electrodes parallel location and location at the angle of 15\({}^{\circ}\) are shown in Figure 4. Moreover, the surface characteristic areas of type 3 are similar to each other for the cases of parallel orientation (Figure 4b) and at an angle (Figure 4c). The SEM image of area 1 of Figure 4a shows a typical surface of the original polished electrode, characterized by an average roughness of Ra = 0.5 \(\upmu\)m. On the electrodes' end faces, initially located at the angle of 15\({}^{\circ}\) (Figure 4b), after processing with the SD, two typical areas marked in the Figure 4b with the numbers 2 and 3 are observed. As it can be seen from the SEM image of the area 2, the polished surface of the electrode is covered with a loose layer of dendrite-like NP agglomerates. Presumably, the main part of such agglomerates was formed with electrical erosion and transferred from the opposite electrode. Area 3 represents exactly the electrode surface treated with the SD, and as it can be seen from the SEM image, it consists of overlapping craters with dimensions of about 10 \(\upmu\)m. Each subsequent discharge, leading to the formation of a new crater, can occur in places of increased electric field density on microprotrusions formed over the previous crater edge as a result of spilling molten metal. The elemental composition of Ag electrode surfaces, according to the results of EDX (Figure 4g-i), dominantly consist of silver for all cases, presented in Figure 4a-c. In this case, the presence of carbon may be associated with the presence of carbon-containing compounds in the carrier gas and adsorbed substances in the gas discharge chamber and on the initial electrodes. Figure 3: Photos of the gap between the electrodes with end faces forming the angle of 15\({}^{\circ}\): (**a**) before the start of the SD process, (**b**) during the discharge process and (**c**) 6 h after the spark treatment by the ODP. For the three cases of the mutual arrangement of electrodes end faces (in parallel and at the angles of \(7^{\circ}\) and \(15^{\circ}\)), time dependences of modal distribution sizes of NP agglomerates and their concentrations, determined by electrical mobility during 6 h of NP synthesis, were studied (Figure 5). A characteristic of the measured dependences of agglomerates' modal dimensions from time is their asymptotic approximation to the average size of about 150 nm during 6 h of NP synthesis for each of the three cases of mutual arrangement of electrodes' end faces. Such an asymptotic behavior of the average agglomerate size-time-function indicates the stability of the SD process on asymmetrically installed electrodes, which leads to the formation of parallel end faces. The dependences comparison for the three cases shows that the average initial agglomerates' size and the average curvature of the function are higher with a greater degree of the electrodes' asymmetry. These features can be explained by a higher wear rate of electrodes with the end faces located at a large angle, due to their electrical erosion.