Yusuke Ootani

A Study on Electrolytic Corrosion of Boron-Doped Diamond Electrodes when Decomposing Organic Compounds

Electrolytic corrosion of boron-doped diamond (BDD) electrodes after applying a high positive potential to decompose organic compounds in aqueous solution was studied. Scanning electron microscopy images, Raman spectra, and glow discharge optical emission spectroscopy revealed that relatively highly boron-doped domains were primarily corroded and relatively low boron-doped domains remained after electrolysis. The corrosion due to electrolysis was observed especially in aqueous solutions of acetic acid or propionic acid, while it was not observed in other organic compounds such as formic acid, glucose, and methanol. Electron spin resonance measurements after electrolysis in the acetic acid solution revealed the generation of methyl radicals on the BDD electrodes. Here, the possible mechanisms for the corrosion are discussed. Dangling bonds may be formed due to abstraction of OH groups from C-OH functional groups by methyl radicals generated on the surface of the BDD electrodes. As a result, the sp3 diamond structure would be converted to the sp2 carbon structure, which can be easily etched. Furthermore, to prevent electrolytic corrosion during electrolysis, both the current density and the pH condition in the aqueous solution were optimized. At low current densities or high pH, the BDD electrodes were stable without electrolytic corrosion even in the acetic acid aqueous solution.

Tight-Binding Quantum Chemical Molecular Dynamics Study on the Friction and Wear Processes of Diamond-Like Carbon Coatings: Effect of Tensile Stress

Diamond-like carbon (DLC) coatings have attracted much attention as an excellent solid lubricant due to their low-friction properties. However, wear is still a problem for the durability of DLC coatings. Tensile stress on the surface of DLC coatings has an important effect on the wear behavior during friction. To improve the tribological properties of DLC coatings, we investigate the friction process and wear mechanism under various tensile stresses by using our tight-binding quantum chemical molecular dynamics method. We observe the formation of C-C bonds between two DLC substrates under high tensile stress during friction, leading to a high friction coefficient. Furthermore, under high tensile stress, C-C bond dissociation in the DLC substrates is observed during friction, indicating the atomic-level wear. These dissociations of C-C bonds are caused by the transfer of surface hydrogen atoms during friction. This work provides atomic-scale insights into the friction process and the wear mechanism of DLC coatings during friction under tensile stress.