Carbon arc for nanoparticle production: Ablation rate calculation. Comparison to experiments

Abstract

A graphite anode ablates in an arc system producing nanoparticles. Experiments show that the ablation rate increases sharply when the current density at the anode exceeds some critical value, which separates the low ablation and high ablation modes. According to the existing hypotheses, the high ablation mode takes place when the anode voltage drop, which is negative in the low ablation mode, turns positive. Based on the work of Nemchinsky [J. Appl. Phys. 130, 103304 (2021)], where the anode voltage drop was evaluated, in this paper, the thermal regime of the anode is considered. It is shown that the main heating mechanism is electron condensation on the anode. The main cooling mechanism is radiation in the low ablation mode and cooling by sublimation in the high ablation mode. In the last case, the energy necessary to compensate for the strong cooling effect of sublimation is delivered by electrons accelerated at the positive anode drop inside the anode sheath. The proposed model allows one to find the ablation rate for a wide range of arc currents and anode diameters. Comparison to the available experimental data shows reasonable agreement. Based on analysis of the experiments and calculations, it was hypothesized that the ablation rate is not sensitive to the presence of a catalyst.