Anodic oxidation is a very attractive advanced oxidation process in wastewater treatment. Boron doped diamond (BDD) is a very active electrode for this process. BDD film grown on a titanium substrate (Ti/BDD) has shown certain stability with superior activity. Before the industrial application of Ti/BDD to wastewater treatment, the service life of the anode needs to be further increased....[ Read more ]

Anodic oxidation is a very attractive advanced oxidation process in wastewater treatment. Boron doped diamond (BDD) is a very active electrode for this process. BDD film grown on a titanium substrate (Ti/BDD) has shown certain stability with superior activity. Before the industrial application of Ti/BDD to wastewater treatment, the service life of the anode needs to be further increased.

Since the failure of the Ti/BDD results from the large residual thermal stress formed during cooling the substrate from 850°C to ambient temperature and the TiC layer corrosion between the BDD and substrate, the objective of this research is to prepare a more stable Ti/BDD anode at lower reaction temperatures and minimize or eliminate the Tic interlayer.

Specifically, Ti substrate was first pretreated by mirror polishing. An interlayer of silicon was then coated on the titanium surface before the deposition of diamond using hot filament chemical vapor deposition (HFCVD). The silicon layer was obtained by the evaporation method at 3300°C. The HFCVD conditions were: T_sub680-800°C, T_fil2000-2150°C, d_fil-sub5-8mm, t_dep 15 h.

The thickness of the silicone layer is 0.2-0.3 microns. The resistance of the layer is 12 ohm. The surface roughness is 1.4 nm. Ti/BDD electrode durability has been enhanced significantly by coating this Si on Ti substrate. Accelerate life time of up to 320 hours was obtained. Raman spectroscopy, XRD, and SEM examination demonstrated that TiC was reduced significantly and the quality of the diamond film improved. The films obtained have well-defined diamond features. The activity obtained on the Ti/Si/BDD electrode is the same as the Ti/BDD electrode in oxidizing acetic acid, maleic acid and phenol. The O₂-evolution over potential is 2.3 V vs. NHE.