## 3 Results and Discussion
As a result of this heat treatment at 1000 \({}^{\circ}\)C for 6 s, the shape of aerosol particles was transformed from fractal-like agglomerates to spherical nanoparticles with a size of 20-50 nm, according to transmission electron microscopy, see Figure 7a-c. The transformation of the shape and size of aerosol nanoparticles using a tube furnace is described in detail in works [43]. After focused deposition and thermal sintering, the electrical resistivity, morphology, elemental composition and shrinkage of printed lines were also investigated. SEM images (Figure 7d) of lines from spherical nanoparticles sintered at \(T_{\text{sint}}=550\)\({}^{\circ}\)C show that they have a denser microstructure and fewer cracks, in contrast to lines from sintered agglomerates (Figure 5b). At the same time, the degree of shrinkage and the elemental composition of these lines were similar to structures of fractal-like agglomerates, see Tables 2 and 3. The aspects related to the influence of agglomeration on the sintering result have been previously investigated in various works [42; 44]. It is known that the agglomeration of nanoparticles, in general, reduces the density of the sintered microstructure [42]. Ag-glomeration refers to the assemblage of two or more primary nanoparticles held together by the van der Waals force [45]. The presence of bonds between nanoparticles prevents  
Figure 7: **(a,b)** TEM image of spherical nanoparticles obtained during heat treatment of agglomerates; and (c) corresponding electron diffraction pattern. (**d**) SEM images of printed lines of spherical nanoparticles on Al\({}_{2}\)O\({}_{3}\), BG, and Si substrates sintered in a reducing hydrogen atmosphere at \(T_{\text{sint}}=550\)\({}^{\circ}\)C.  
their displacement during the compaction process, and as a result, dense packing of the microstructure is not achieved. Moreover, the packing density decreases with decreasing nanoparticle size due to an increase in interparticle interaction [42]. It can be seen from the results of TEM images that the initial aerosol nanoparticles are highly agglomerated, since they consist of many primary nanoparticles (Figure 2a). At the same time, aerosol nanoparticles passed through the tube furnace are mainly single spherical nanoparticles (Figure 7a). According to the results of measurements on an aerosol spectrometer, it can be seen that the modal sizes of the initial agglomerates are larger than the sizes of nanoparticles that have passed through the tube furnace--98 \(\pm\) 9 nm and 62 \(\pm\) 7 nm, respectively (Figure A2, Appendix A). Based on early research [44], it is expected that sintered lines formed from non-agglomerated spherical nanoparticles will have lower porosity (high density), and low resistivity compared to structures formed from the initial agglomerates. This assumption is confirmed by the results of measurements of the surface morphology and electrical resistivity of the sintered lines. Figures 7d and 5c of the surfaces of sintered lines show qualitatively that lines from spherical nanoparticles have lower porosity than lines from initial agglomerates. Moreover, the resistivity of lines from spherical nanoparticles \(\sim\)5 \(\upmu\Omega\cdot\)cm (Table 3) is noticeably lower than the resistivity of lines from initial agglomerates 70-100 \(\upmu\Omega\cdot\)cm (Figure 4), sintered at 550 \({}^{\circ}\)C. High residual porosity and high electrical resistivity of printed lines from initial agglomerates are associated with their high degree of agglomeration. It is known that agglomeration is the cause of the appearance of a bimodal porous structure with large inter-agglomerate and small intra-agglomerate pores [46], respectively. During sintering, small intra-agglomerate pores shrink faster than larger ones due to the higher local curvature. Thus, large inter-agglomerate pores are more difficult to remove [46]. Consequently, agglomeration leads to residual voids and inhomogeneous microstructure during the sintering process.