Multiparametric diagnostic in the synthesis of carbon nanostructures via submerged arc discharge: Stability, nucleation and yield

Abstract

Submerged arc discharge (SAD) is a simple method to produce carbon nanostructures (CNSs). However, its potential cannot be fully exploited because it generates contaminants and unwanted by-products (CUBPs) that are difficult to eliminate. The formation mechanisms of CNSs and CUBPs were investigated by measuring the correlations between the SAD main parameters (current, voltage, power, anode displacement, and sound emission). It was demonstrated that the SAD takes place in a succession of stable and unstable zones that induce homogeneous and heterogeneous nucleation processes, respectively. In the stable zones, carbon vapor jets are generated and induce the appearance of vortices. Both processes stimulate nucleation. From the measurement of the sound emitted by the jets, the dimensions of the discharge channel were determined. These dimensions match the anode crater size measured by scanning electron microscopy. In the unstable zones, vibrations and thermal stress in the anode intensify. Graphite microparticles are released and act as nucleation centers that induce the formation of CUBPs. While most of the discharge elapses in stable zones, the highest fraction of anode erosion occurs in unstable zones. These results made evident that current theoretical models fail to explain the presence of observed impurities because they do not take into account the influence of vibrations and heterogeneous nucleation. The operation of the synthesis device was simulated, and the results obtained reinforce the aforementioned conclusions. The acoustic emission of the SAD allowed obtaining information on the installation operation for the optimization of its design. Based on this information, recommendations were made for the installation design.

Neutral red dye adsorption on carbon nano-onions: viability assay interference and adduct characterisation

“…As determined by prior studies through N 2 adsorption (Brunauer-Emmett-Teller) BET isotherms our CNOs rich SADW floating material exhibits no microporosity, an almost total absence of surface defects and a very modest specific surface area (SSA) of 14.7±0.3 m 2 g −1 [21]. A thorough characterisation of the SADW CNOs produced by our research group can be found in previously published articles [21,34,[41][42][43][44].…”

Detailed yield assessment of carbon nanostructures synthesized by submerged arc discharge in water

“…The functional groups present in these nanostructures ensure a high stability of this suspension. The precipitate has a more complex composition, being a mixture of nanostructures (MWCNTs, CNOs, and graphene) (1.4323 g, see figure 1(c)) and contaminants (amorphous carbon, nano, and micro graphite) [15]. Aggregates are also present in the precipitate [16] (see figure S4).…”

“…As analysed in [15], the SADW arc discharge process consists of a succession of slow-burning stable periods and high-erosion unstable periods called stable zones (SZ) and unstable zones (UZ), respectively. SZs were defined as periods where R 1 mg.s −1 , and UZs were defined as the periods where R > 1 mg.s −1 .…”

Stabilization Methods in the Submerged Arc Discharge Synthesis of Carbon Nanostructures

“…Ref. [29] reported on the relation between arc sound and other physical-chemical processes in SAD. The authors simultaneously recorded the arc current, voltage, and sound plus the anode displacement in a correlated manner.…”

“…Therefore, different values of flexural strength and thermal and electrical conductivities, among other parameters, can be observed in different electrode zones [28]. This factor is one of the causes that make the SAD technique unfree of contaminants [29].…”