Automated system for the synthesis of nanostructures via arc-discharge in liquids

Abstract

Submerged arc discharge in liquids has shown to be a promising method to synthesize a wide variety of nanomaterials. However, it requires an accurate arc current control to ensure the desired purity and structure of the products. A fluctuating arc current increases the dispersion in size distribution, as well as in the obtained nanoparticles structure pattern. Consequently, the arc current stability is essential to ensure the product homogeneity and quality. A system which ensures high stability of the arc discharge is presented. It has three basic elements: an electrode gap micropositioning system controlled by a feedback arc current measurement, a current’s stabilization element and a data acquisition system to record the magnitudes of the relevant physical parameters. The most suitable algorithm for micropositioning system was determined. The utilization of a step motor gave an additional advantage in measuring the anode displacement. The employed stabilization element improves the current and power stability by 4 and 2.7 times, respectively. The data acquisition system allows taking control and information about the relevant parameters of the process and the interaction between them. This system, based on direct arc current measurement, is superior in terms of achieving higher stability and current sensibility, to the ones based on arc voltage or arc light emission. It is also an adaptable tool to carry on further experiments.

Stabilization Methods in the Submerged Arc Discharge Synthesis of Carbon Nanostructures

“…Not considering these elements could lead to trying to stabilize the arc at a current where it is not appropriated and having a different arc power for the same arc current. An electric stabilization element like a ballast resistor significantly improves the current and the power stability [45].…”

“…In some studies, electrodes were forced to approach each other at a constant speed to try to stabilize the discharge [34,44]. Based on automatic welding machines that move the electrode at a constant speed to obtain a uniform welding cord, and supposing that such movement could lead to a constant arc power or gap between electrodes, a constant speed control algorithm was tested in [45]. For better stability, this method was combined with electrode rotation [34].…”

“…As mentioned before, the majority of the reported works on SAD did not use any stabilization technique. To evaluate the type of SAD, an experiment was performed using the installation described in [45]. The anode movement was, however, stopped once the discharge was initiated.…”

“…Optical Control. Arc discharge optical emission has been used to determine the carbon dimmers precursor concentrations and the different arc zone temperatures [31,41,[43][44][45][46][47][48]. However, it has been almost exclusively employed in controlling the arc discharges in gases and mainly in fullerene synthesis [49].…”

“…Ref. [45] reported that the use of a ballast resistor (0:7 Ω/4:2 kW) improves the current and the power stability by 4 and 2.7 times, respectively.…”