Research to apply boron, nitrogen, and phosphorus to P-type or N-type semiconductors during diamond deposition by CVD (chemical vapor deposition) is continuously being conducted. BDD (boron-doped diamond) with P-type semiconductor characteristics has a wide potential window of 2.8V and has excellent oxygen generation overvoltage, so it is a representative electrode used in advanced oxidation processes among electrochemical water treatment methods.

In this study, water-soluble waste cutting oil used in machining was treated with electrochemical water treatment. Since waste cutting fluid contains a large amount of difficult-to-decompose substances, special treatment is required as it can have a significant impact on the surrounding environment if it enters the water system without proper treatment. A BDD thin film was deposited on a Ti substrate using an HFCVD (hot filament chemical vapor deposition) apparatus and used as an electrode. Characteristics analysis by boron concentration of the deposited thin film evaluated the surface shape, growth rate, bonding structure and crystallinity of the diamond thin film through SEM, Raman spectroscopy, and X-ray diffraction analysis. And the electrochemical characteristics were analyzed through I/V curve, cyclic voltammetry, and Hall effects measurement. The ratio of boron to carbon atoms was defined as the B/C ratio. As the B/C ratio increased, the growth rate, crystal size, and crystallinity of the diamond thin film tended to decrease. Through I/V curve and cyclic voltammetry, the 2000ppm boron doping result showed the best electrical properties. In particular, in cyclic voltammetry analysis, it was found that the width of the potential window was 2.8 V, which showed oxygen overvoltage characteristics capable of reacting with strong oxidizing agents such as hydroxyl radicals and ozone. Electrochemical treatment experiments were conducted on waste coolant using BDD electrodes each doped with boron concentration of 0-8000 ppm. The BDD electrode used at this time was deposited on a Ti substrate to a thickness of 10 μm. The applied current density in the electrochemical treatment was 25mA/cm2 for 30 minutes, and as a result of the treatment, it was confirmed that the TOC (total organic carbon) content was reduced by 95% (9.6mg/l). On the other hand, when Ti was used as an electrode, the TOC removal rate was only 27%(129mg/l), indicating that the BDD electrode had excellent
characteristics in electrochemical waste cutting fluid treatment.