Juyong Jang

Visualization of arc and plasma flow patterns for advanced material processing

Results are presented for physical experiments that illustrate the possibilities and efficiency of visualization for studying the effect of operating conditions (backward-facing stepped forming nozzle, exit diameter of anode, mass flow, and composition of working gas) on plasma flows at low Reynolds numbers for advanced coating and powder processing. In particular, the shadow method, based on adaptive visualization transparency, is used for imaging electric arc and plasma jet flow patterns for different operating conditions. Because of visualization, the optimal geometrical characteristics of the backward-facing stepped forming nozzle, mass flow rate of the working gas, and its composition were found. These provide: (1) the absence of micro-shunting of the arc inside the backward-facing stepped nozzle for a transfer arc and twin arcs; and (2) compared to transient and turbulent jets, a higher density for the heat flux from a quasi-laminar flow to the surface of a flat substrate and the powder material to be treated, for nontransfer arc DC (direct current) torches and DC–RF (direct current and radio frequency) hybrid plasma flow system.Graphical Abstract

Preparation of Carbon-Doped TiO2 Nanopowder Synthesized by Droplet Injection of Solution Precursor in a DC-RF Hybrid Plasma Flow System

Carbon-doped titanium dioxide nanopowder has received much attention because of its higher photocatalytic performance, which is practically activated not only by UV, but also by visible light irradiation. In the present study, C-TiO2 nanopowder was synthesized by droplet injection of solution precursor in a DC-RF hybrid plasma flow system, resulting in higher photocatalytic performance even under visible light irradiation. In-flight C-TiO2 nanoparticles reacted with the high concentration of carbon in plasma flow and were then deposited on the surfaces of two quartz tubes in the upstream and downstream regions of this system. The collected C-TiO2 nanopowder contained anatase-rutile mixed-phase TiO2 and TiC, the contents of which depended on the location of the powder collection, the temperature, and the duration of plasma treatment. Highly functional C-TiO2 nanopowder collected in the downstream region exhibited a higher degradation rate of methylene blue than that of single-phase anatase TiO2, even under visible light irradiation, in spite of being TiC.

Evaluation of Highly Functional TiO2 Synthesized by Solution Precursor Spraying in a DC-RF Hybrid Plasma Flow System

Carbon doped TiO2 synthesized in a DC-RF hybrid plasma flow system by the solution precursor spraying method was evaluated. The effects of mass fraction of TTB in solution precursor on contents and photocatalytic activity of carbon doped TiO2 were investigated. Highly functional carbon doped TiO2 at 11 wt% TTB had higher UV-visible absorption characteristics, which showed higher degradation rate of methylene blue solution under visible light irradiation.

Discharge Study of Argon DC Arc Jet Assisted by DBD Plasma for Metal Surface Treatment

An argon dc arc jet assisted by dielectric barrier discharge (DBD) plasma was studied for discharge interaction between two plasmas and metal of plasma surface treatment at atmospheric pressure. While operating conditions of the dc arc jet were retained, DBD plasma was operated by changing the applied DBD voltage amplitudes (VDBD) between 6 and 12 kVpp to investigate the effect of DBD plasma addition to the dc arc jet on the changes of discharge structure and copper surface energy. By igniting the dc arc jet with DBD plasma, a glow plasma column is formed between the dc arc jet tail and the upper region of the DBD reactor, which transfers electrons and ions provided by the dc arc jet. From the correlation between maximum charge quantity (Qmax) and applied DBD voltage amplitude, the degree of activation of DBD plasma corresponding to the luminescent intensity is proportional to the Qmax. DBD plasma with the dc arc jet has the maximum of Qmax value at VDBD = 10 kVpp, then the dc arc jet assisted by DBD plasma becomes the most active. Based on the discharge property investigation, copper surface energy is effectively increased up to 127% at 10 kVpp using the dc arc jet assisted by DBD plasma, compared with using the dc arc jet alone.